Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

287 files changed, 71297 insertions, 0 deletions

diff --git a/third_party/rust/tokio/src/blocking.rs b/third_party/rust/tokio/src/blocking.rs
new file mode 100644
index 0000000000..f172399d5e
--- /dev/null
+++ b/third_party/rust/tokio/src/blocking.rs
@@ -0,0 +1,63 @@
+cfg_rt! {
+    pub(crate) use crate::runtime::spawn_blocking;
+
+    cfg_fs! {
+        #[allow(unused_imports)]
+        pub(crate) use crate::runtime::spawn_mandatory_blocking;
+    }
+
+    pub(crate) use crate::task::JoinHandle;
+}
+
+cfg_not_rt! {
+    use std::fmt;
+    use std::future::Future;
+    use std::pin::Pin;
+    use std::task::{Context, Poll};
+
+    pub(crate) fn spawn_blocking<F, R>(_f: F) -> JoinHandle<R>
+    where
+        F: FnOnce() -> R + Send + 'static,
+        R: Send + 'static,
+    {
+        assert_send_sync::<JoinHandle<std::cell::Cell<()>>>();
+        panic!("requires the `rt` Tokio feature flag")
+    }
+
+    cfg_fs! {
+        pub(crate) fn spawn_mandatory_blocking<F, R>(_f: F) -> Option<JoinHandle<R>>
+        where
+            F: FnOnce() -> R + Send + 'static,
+            R: Send + 'static,
+        {
+            panic!("requires the `rt` Tokio feature flag")
+        }
+    }
+
+    pub(crate) struct JoinHandle<R> {
+        _p: std::marker::PhantomData<R>,
+    }
+
+    unsafe impl<T: Send> Send for JoinHandle<T> {}
+    unsafe impl<T: Send> Sync for JoinHandle<T> {}
+
+    impl<R> Future for JoinHandle<R> {
+        type Output = Result<R, std::io::Error>;
+
+        fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Self::Output> {
+            unreachable!()
+        }
+    }
+
+    impl<T> fmt::Debug for JoinHandle<T>
+    where
+        T: fmt::Debug,
+    {
+        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+            fmt.debug_struct("JoinHandle").finish()
+        }
+    }
+
+    fn assert_send_sync<T: Send + Sync>() {
+    }
+}
diff --git a/third_party/rust/tokio/src/coop.rs b/third_party/rust/tokio/src/coop.rs
new file mode 100644
index 0000000000..96905319b6
--- /dev/null
+++ b/third_party/rust/tokio/src/coop.rs
@@ -0,0 +1,284 @@
+#![cfg_attr(not(feature = "full"), allow(dead_code))]
+
+//! Yield points for improved cooperative scheduling.
+//!
+//! Documentation for this can be found in the [`tokio::task`] module.
+//!
+//! [`tokio::task`]: crate::task.
+
+// ```ignore
+// # use tokio_stream::{Stream, StreamExt};
+// async fn drop_all<I: Stream + Unpin>(mut input: I) {
+//     while let Some(_) = input.next().await {
+//         tokio::coop::proceed().await;
+//     }
+// }
+// ```
+//
+// The `proceed` future will coordinate with the executor to make sure that
+// every so often control is yielded back to the executor so it can run other
+// tasks.
+//
+// # Placing yield points
+//
+// Voluntary yield points should be placed _after_ at least some work has been
+// done. If they are not, a future sufficiently deep in the task hierarchy may
+// end up _never_ getting to run because of the number of yield points that
+// inevitably appear before it is reached. In general, you will want yield
+// points to only appear in "leaf" futures -- those that do not themselves poll
+// other futures. By doing this, you avoid double-counting each iteration of
+// the outer future against the cooperating budget.
+
+use std::cell::Cell;
+
+thread_local! {
+    static CURRENT: Cell<Budget> = Cell::new(Budget::unconstrained());
+}
+
+/// Opaque type tracking the amount of "work" a task may still do before
+/// yielding back to the scheduler.
+#[derive(Debug, Copy, Clone)]
+pub(crate) struct Budget(Option<u8>);
+
+impl Budget {
+    /// Budget assigned to a task on each poll.
+    ///
+    /// The value itself is chosen somewhat arbitrarily. It needs to be high
+    /// enough to amortize wakeup and scheduling costs, but low enough that we
+    /// do not starve other tasks for too long. The value also needs to be high
+    /// enough that particularly deep tasks are able to do at least some useful
+    /// work at all.
+    ///
+    /// Note that as more yield points are added in the ecosystem, this value
+    /// will probably also have to be raised.
+    const fn initial() -> Budget {
+        Budget(Some(128))
+    }
+
+    /// Returns an unconstrained budget. Operations will not be limited.
+    const fn unconstrained() -> Budget {
+        Budget(None)
+    }
+
+    fn has_remaining(self) -> bool {
+        self.0.map(|budget| budget > 0).unwrap_or(true)
+    }
+}
+
+/// Runs the given closure with a cooperative task budget. When the function
+/// returns, the budget is reset to the value prior to calling the function.
+#[inline(always)]
+pub(crate) fn budget<R>(f: impl FnOnce() -> R) -> R {
+    with_budget(Budget::initial(), f)
+}
+
+/// Runs the given closure with an unconstrained task budget. When the function returns, the budget
+/// is reset to the value prior to calling the function.
+#[inline(always)]
+pub(crate) fn with_unconstrained<R>(f: impl FnOnce() -> R) -> R {
+    with_budget(Budget::unconstrained(), f)
+}
+
+#[inline(always)]
+fn with_budget<R>(budget: Budget, f: impl FnOnce() -> R) -> R {
+    struct ResetGuard<'a> {
+        cell: &'a Cell<Budget>,
+        prev: Budget,
+    }
+
+    impl<'a> Drop for ResetGuard<'a> {
+        fn drop(&mut self) {
+            self.cell.set(self.prev);
+        }
+    }
+
+    CURRENT.with(move |cell| {
+        let prev = cell.get();
+
+        cell.set(budget);
+
+        let _guard = ResetGuard { cell, prev };
+
+        f()
+    })
+}
+
+#[inline(always)]
+pub(crate) fn has_budget_remaining() -> bool {
+    CURRENT.with(|cell| cell.get().has_remaining())
+}
+
+cfg_rt_multi_thread! {
+    /// Sets the current task's budget.
+    pub(crate) fn set(budget: Budget) {
+        CURRENT.with(|cell| cell.set(budget))
+    }
+}
+
+cfg_rt! {
+    /// Forcibly removes the budgeting constraints early.
+    ///
+    /// Returns the remaining budget
+    pub(crate) fn stop() -> Budget {
+        CURRENT.with(|cell| {
+            let prev = cell.get();
+            cell.set(Budget::unconstrained());
+            prev
+        })
+    }
+}
+
+cfg_coop! {
+    use std::task::{Context, Poll};
+
+    #[must_use]
+    pub(crate) struct RestoreOnPending(Cell<Budget>);
+
+    impl RestoreOnPending {
+        pub(crate) fn made_progress(&self) {
+            self.0.set(Budget::unconstrained());
+        }
+    }
+
+    impl Drop for RestoreOnPending {
+        fn drop(&mut self) {
+            // Don't reset if budget was unconstrained or if we made progress.
+            // They are both represented as the remembered budget being unconstrained.
+            let budget = self.0.get();
+            if !budget.is_unconstrained() {
+                CURRENT.with(|cell| {
+                    cell.set(budget);
+                });
+            }
+        }
+    }
+
+    /// Returns `Poll::Pending` if the current task has exceeded its budget and should yield.
+    ///
+    /// When you call this method, the current budget is decremented. However, to ensure that
+    /// progress is made every time a task is polled, the budget is automatically restored to its
+    /// former value if the returned `RestoreOnPending` is dropped. It is the caller's
+    /// responsibility to call `RestoreOnPending::made_progress` if it made progress, to ensure
+    /// that the budget empties appropriately.
+    ///
+    /// Note that `RestoreOnPending` restores the budget **as it was before `poll_proceed`**.
+    /// Therefore, if the budget is _further_ adjusted between when `poll_proceed` returns and
+    /// `RestRestoreOnPending` is dropped, those adjustments are erased unless the caller indicates
+    /// that progress was made.
+    #[inline]
+    pub(crate) fn poll_proceed(cx: &mut Context<'_>) -> Poll<RestoreOnPending> {
+        CURRENT.with(|cell| {
+            let mut budget = cell.get();
+
+            if budget.decrement() {
+                let restore = RestoreOnPending(Cell::new(cell.get()));
+                cell.set(budget);
+                Poll::Ready(restore)
+            } else {
+                cx.waker().wake_by_ref();
+                Poll::Pending
+            }
+        })
+    }
+
+    impl Budget {
+        /// Decrements the budget. Returns `true` if successful. Decrementing fails
+        /// when there is not enough remaining budget.
+        fn decrement(&mut self) -> bool {
+            if let Some(num) = &mut self.0 {
+                if *num > 0 {
+                    *num -= 1;
+                    true
+                } else {
+                    false
+                }
+            } else {
+                true
+            }
+        }
+
+        fn is_unconstrained(self) -> bool {
+            self.0.is_none()
+        }
+    }
+}
+
+#[cfg(all(test, not(loom)))]
+mod test {
+    use super::*;
+
+    #[cfg(target_arch = "wasm32")]
+    use wasm_bindgen_test::wasm_bindgen_test as test;
+
+    fn get() -> Budget {
+        CURRENT.with(|cell| cell.get())
+    }
+
+    #[test]
+    fn bugeting() {
+        use futures::future::poll_fn;
+        use tokio_test::*;
+
+        assert!(get().0.is_none());
+
+        let coop = assert_ready!(task::spawn(()).enter(|cx, _| poll_proceed(cx)));
+
+        assert!(get().0.is_none());
+        drop(coop);
+        assert!(get().0.is_none());
+
+        budget(|| {
+            assert_eq!(get().0, Budget::initial().0);
+
+            let coop = assert_ready!(task::spawn(()).enter(|cx, _| poll_proceed(cx)));
+            assert_eq!(get().0.unwrap(), Budget::initial().0.unwrap() - 1);
+            drop(coop);
+            // we didn't make progress
+            assert_eq!(get().0, Budget::initial().0);
+
+            let coop = assert_ready!(task::spawn(()).enter(|cx, _| poll_proceed(cx)));
+            assert_eq!(get().0.unwrap(), Budget::initial().0.unwrap() - 1);
+            coop.made_progress();
+            drop(coop);
+            // we _did_ make progress
+            assert_eq!(get().0.unwrap(), Budget::initial().0.unwrap() - 1);
+
+            let coop = assert_ready!(task::spawn(()).enter(|cx, _| poll_proceed(cx)));
+            assert_eq!(get().0.unwrap(), Budget::initial().0.unwrap() - 2);
+            coop.made_progress();
+            drop(coop);
+            assert_eq!(get().0.unwrap(), Budget::initial().0.unwrap() - 2);
+
+            budget(|| {
+                assert_eq!(get().0, Budget::initial().0);
+
+                let coop = assert_ready!(task::spawn(()).enter(|cx, _| poll_proceed(cx)));
+                assert_eq!(get().0.unwrap(), Budget::initial().0.unwrap() - 1);
+                coop.made_progress();
+                drop(coop);
+                assert_eq!(get().0.unwrap(), Budget::initial().0.unwrap() - 1);
+            });
+
+            assert_eq!(get().0.unwrap(), Budget::initial().0.unwrap() - 2);
+        });
+
+        assert!(get().0.is_none());
+
+        budget(|| {
+            let n = get().0.unwrap();
+
+            for _ in 0..n {
+                let coop = assert_ready!(task::spawn(()).enter(|cx, _| poll_proceed(cx)));
+                coop.made_progress();
+            }
+
+            let mut task = task::spawn(poll_fn(|cx| {
+                let coop = ready!(poll_proceed(cx));
+                coop.made_progress();
+                Poll::Ready(())
+            }));
+
+            assert_pending!(task.poll());
+        });
+    }
+}
diff --git a/third_party/rust/tokio/src/doc/mod.rs b/third_party/rust/tokio/src/doc/mod.rs
new file mode 100644
index 0000000000..3a94934490
--- /dev/null
+++ b/third_party/rust/tokio/src/doc/mod.rs
@@ -0,0 +1,24 @@
+//! Types which are documented locally in the Tokio crate, but does not actually
+//! live here.
+//!
+//! **Note** this module is only visible on docs.rs, you cannot use it directly
+//! in your own code.
+
+/// The name of a type which is not defined here.
+///
+/// This is typically used as an alias for another type, like so:
+///
+/// ```rust,ignore
+/// /// See [some::other::location](https://example.com).
+/// type DEFINED_ELSEWHERE = crate::doc::NotDefinedHere;
+/// ```
+///
+/// This type is uninhabitable like the [`never` type] to ensure that no one
+/// will ever accidentally use it.
+///
+/// [`never` type]: https://doc.rust-lang.org/std/primitive.never.html
+#[derive(Debug)]
+pub enum NotDefinedHere {}
+
+pub mod os;
+pub mod winapi;
diff --git a/third_party/rust/tokio/src/doc/os.rs b/third_party/rust/tokio/src/doc/os.rs
new file mode 100644
index 0000000000..0ddf86959b
--- /dev/null
+++ b/third_party/rust/tokio/src/doc/os.rs
@@ -0,0 +1,26 @@
+//! See [std::os](https://doc.rust-lang.org/std/os/index.html).
+
+/// Platform-specific extensions to `std` for Windows.
+///
+/// See [std::os::windows](https://doc.rust-lang.org/std/os/windows/index.html).
+pub mod windows {
+    /// Windows-specific extensions to general I/O primitives.
+    ///
+    /// See [std::os::windows::io](https://doc.rust-lang.org/std/os/windows/io/index.html).
+    pub mod io {
+        /// See [std::os::windows::io::RawHandle](https://doc.rust-lang.org/std/os/windows/io/type.RawHandle.html)
+        pub type RawHandle = crate::doc::NotDefinedHere;
+
+        /// See [std::os::windows::io::AsRawHandle](https://doc.rust-lang.org/std/os/windows/io/trait.AsRawHandle.html)
+        pub trait AsRawHandle {
+            /// See [std::os::windows::io::FromRawHandle::from_raw_handle](https://doc.rust-lang.org/std/os/windows/io/trait.AsRawHandle.html#tymethod.as_raw_handle)
+            fn as_raw_handle(&self) -> RawHandle;
+        }
+
+        /// See [std::os::windows::io::FromRawHandle](https://doc.rust-lang.org/std/os/windows/io/trait.FromRawHandle.html)
+        pub trait FromRawHandle {
+            /// See [std::os::windows::io::FromRawHandle::from_raw_handle](https://doc.rust-lang.org/std/os/windows/io/trait.FromRawHandle.html#tymethod.from_raw_handle)
+            unsafe fn from_raw_handle(handle: RawHandle) -> Self;
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/doc/winapi.rs b/third_party/rust/tokio/src/doc/winapi.rs
new file mode 100644
index 0000000000..be68749e00
--- /dev/null
+++ b/third_party/rust/tokio/src/doc/winapi.rs
@@ -0,0 +1,66 @@
+//! See [winapi].
+//!
+//! [winapi]: https://docs.rs/winapi
+
+/// See [winapi::shared](https://docs.rs/winapi/*/winapi/shared/index.html).
+pub mod shared {
+    /// See [winapi::shared::winerror](https://docs.rs/winapi/*/winapi/shared/winerror/index.html).
+    #[allow(non_camel_case_types)]
+    pub mod winerror {
+        /// See [winapi::shared::winerror::ERROR_ACCESS_DENIED][winapi]
+        ///
+        /// [winapi]: https://docs.rs/winapi/*/winapi/shared/winerror/constant.ERROR_ACCESS_DENIED.html
+        pub type ERROR_ACCESS_DENIED = crate::doc::NotDefinedHere;
+
+        /// See [winapi::shared::winerror::ERROR_PIPE_BUSY][winapi]
+        ///
+        /// [winapi]: https://docs.rs/winapi/*/winapi/shared/winerror/constant.ERROR_PIPE_BUSY.html
+        pub type ERROR_PIPE_BUSY = crate::doc::NotDefinedHere;
+
+        /// See [winapi::shared::winerror::ERROR_MORE_DATA][winapi]
+        ///
+        /// [winapi]: https://docs.rs/winapi/*/winapi/shared/winerror/constant.ERROR_MORE_DATA.html
+        pub type ERROR_MORE_DATA = crate::doc::NotDefinedHere;
+    }
+}
+
+/// See [winapi::um](https://docs.rs/winapi/*/winapi/um/index.html).
+pub mod um {
+    /// See [winapi::um::winbase](https://docs.rs/winapi/*/winapi/um/winbase/index.html).
+    #[allow(non_camel_case_types)]
+    pub mod winbase {
+        /// See [winapi::um::winbase::PIPE_TYPE_MESSAGE][winapi]
+        ///
+        /// [winapi]: https://docs.rs/winapi/*/winapi/um/winbase/constant.PIPE_TYPE_MESSAGE.html
+        pub type PIPE_TYPE_MESSAGE = crate::doc::NotDefinedHere;
+
+        /// See [winapi::um::winbase::PIPE_TYPE_BYTE][winapi]
+        ///
+        /// [winapi]: https://docs.rs/winapi/*/winapi/um/winbase/constant.PIPE_TYPE_BYTE.html
+        pub type PIPE_TYPE_BYTE = crate::doc::NotDefinedHere;
+
+        /// See [winapi::um::winbase::PIPE_CLIENT_END][winapi]
+        ///
+        /// [winapi]: https://docs.rs/winapi/*/winapi/um/winbase/constant.PIPE_CLIENT_END.html
+        pub type PIPE_CLIENT_END = crate::doc::NotDefinedHere;
+
+        /// See [winapi::um::winbase::PIPE_SERVER_END][winapi]
+        ///
+        /// [winapi]: https://docs.rs/winapi/*/winapi/um/winbase/constant.PIPE_SERVER_END.html
+        pub type PIPE_SERVER_END = crate::doc::NotDefinedHere;
+
+        /// See [winapi::um::winbase::SECURITY_IDENTIFICATION][winapi]
+        ///
+        /// [winapi]: https://docs.rs/winapi/*/winapi/um/winbase/constant.SECURITY_IDENTIFICATION.html
+        pub type SECURITY_IDENTIFICATION = crate::doc::NotDefinedHere;
+    }
+
+    /// See [winapi::um::minwinbase](https://docs.rs/winapi/*/winapi/um/minwinbase/index.html).
+    #[allow(non_camel_case_types)]
+    pub mod minwinbase {
+        /// See [winapi::um::minwinbase::SECURITY_ATTRIBUTES][winapi]
+        ///
+        /// [winapi]: https://docs.rs/winapi/*/winapi/um/minwinbase/constant.SECURITY_ATTRIBUTES.html
+        pub type SECURITY_ATTRIBUTES = crate::doc::NotDefinedHere;
+    }
+}
diff --git a/third_party/rust/tokio/src/fs/canonicalize.rs b/third_party/rust/tokio/src/fs/canonicalize.rs
new file mode 100644
index 0000000000..403662685c
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/canonicalize.rs
@@ -0,0 +1,51 @@
+use crate::fs::asyncify;
+
+use std::io;
+use std::path::{Path, PathBuf};
+
+/// Returns the canonical, absolute form of a path with all intermediate
+/// components normalized and symbolic links resolved.
+///
+/// This is an async version of [`std::fs::canonicalize`][std]
+///
+/// [std]: std::fs::canonicalize
+///
+/// # Platform-specific behavior
+///
+/// This function currently corresponds to the `realpath` function on Unix
+/// and the `CreateFile` and `GetFinalPathNameByHandle` functions on Windows.
+/// Note that, this [may change in the future][changes].
+///
+/// On Windows, this converts the path to use [extended length path][path]
+/// syntax, which allows your program to use longer path names, but means you
+/// can only join backslash-delimited paths to it, and it may be incompatible
+/// with other applications (if passed to the application on the command-line,
+/// or written to a file another application may read).
+///
+/// [changes]: https://doc.rust-lang.org/std/io/index.html#platform-specific-behavior
+/// [path]: https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx#maxpath
+///
+/// # Errors
+///
+/// This function will return an error in the following situations, but is not
+/// limited to just these cases:
+///
+/// * `path` does not exist.
+/// * A non-final component in path is not a directory.
+///
+/// # Examples
+///
+/// ```no_run
+/// use tokio::fs;
+/// use std::io;
+///
+/// #[tokio::main]
+/// async fn main() -> io::Result<()> {
+///     let path = fs::canonicalize("../a/../foo.txt").await?;
+///     Ok(())
+/// }
+/// ```
+pub async fn canonicalize(path: impl AsRef<Path>) -> io::Result<PathBuf> {
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::canonicalize(path)).await
+}
diff --git a/third_party/rust/tokio/src/fs/copy.rs b/third_party/rust/tokio/src/fs/copy.rs
new file mode 100644
index 0000000000..b47f287285
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/copy.rs
@@ -0,0 +1,27 @@
+use crate::fs::asyncify;
+use std::path::Path;
+
+/// Copies the contents of one file to another. This function will also copy the permission bits
+/// of the original file to the destination file.
+/// This function will overwrite the contents of to.
+///
+/// This is the async equivalent of [`std::fs::copy`][std].
+///
+/// [std]: fn@std::fs::copy
+///
+/// # Examples
+///
+/// ```no_run
+/// use tokio::fs;
+///
+/// # async fn dox() -> std::io::Result<()> {
+/// fs::copy("foo.txt", "bar.txt").await?;
+/// # Ok(())
+/// # }
+/// ```
+
+pub async fn copy(from: impl AsRef<Path>, to: impl AsRef<Path>) -> Result<u64, std::io::Error> {
+    let from = from.as_ref().to_owned();
+    let to = to.as_ref().to_owned();
+    asyncify(|| std::fs::copy(from, to)).await
+}
diff --git a/third_party/rust/tokio/src/fs/create_dir.rs b/third_party/rust/tokio/src/fs/create_dir.rs
new file mode 100644
index 0000000000..411969500f
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/create_dir.rs
@@ -0,0 +1,52 @@
+use crate::fs::asyncify;
+
+use std::io;
+use std::path::Path;
+
+/// Creates a new, empty directory at the provided path.
+///
+/// This is an async version of [`std::fs::create_dir`][std]
+///
+/// [std]: std::fs::create_dir
+///
+/// # Platform-specific behavior
+///
+/// This function currently corresponds to the `mkdir` function on Unix
+/// and the `CreateDirectory` function on Windows.
+/// Note that, this [may change in the future][changes].
+///
+/// [changes]: https://doc.rust-lang.org/std/io/index.html#platform-specific-behavior
+///
+/// **NOTE**: If a parent of the given path doesn't exist, this function will
+/// return an error. To create a directory and all its missing parents at the
+/// same time, use the [`create_dir_all`] function.
+///
+/// # Errors
+///
+/// This function will return an error in the following situations, but is not
+/// limited to just these cases:
+///
+/// * User lacks permissions to create directory at `path`.
+/// * A parent of the given path doesn't exist. (To create a directory and all
+///   its missing parents at the same time, use the [`create_dir_all`]
+///   function.)
+/// * `path` already exists.
+///
+/// [`create_dir_all`]: super::create_dir_all()
+///
+/// # Examples
+///
+/// ```no_run
+/// use tokio::fs;
+/// use std::io;
+///
+/// #[tokio::main]
+/// async fn main() -> io::Result<()> {
+///     fs::create_dir("/some/dir").await?;
+///     Ok(())
+/// }
+/// ```
+pub async fn create_dir(path: impl AsRef<Path>) -> io::Result<()> {
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::create_dir(path)).await
+}
diff --git a/third_party/rust/tokio/src/fs/create_dir_all.rs b/third_party/rust/tokio/src/fs/create_dir_all.rs
new file mode 100644
index 0000000000..21f0c82d11
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/create_dir_all.rs
@@ -0,0 +1,53 @@
+use crate::fs::asyncify;
+
+use std::io;
+use std::path::Path;
+
+/// Recursively creates a directory and all of its parent components if they
+/// are missing.
+///
+/// This is an async version of [`std::fs::create_dir_all`][std]
+///
+/// [std]: std::fs::create_dir_all
+///
+/// # Platform-specific behavior
+///
+/// This function currently corresponds to the `mkdir` function on Unix
+/// and the `CreateDirectory` function on Windows.
+/// Note that, this [may change in the future][changes].
+///
+/// [changes]: https://doc.rust-lang.org/std/io/index.html#platform-specific-behavior
+///
+/// # Errors
+///
+/// This function will return an error in the following situations, but is not
+/// limited to just these cases:
+///
+/// * If any directory in the path specified by `path` does not already exist
+/// and it could not be created otherwise. The specific error conditions for
+/// when a directory is being created (after it is determined to not exist) are
+/// outlined by [`fs::create_dir`].
+///
+/// Notable exception is made for situations where any of the directories
+/// specified in the `path` could not be created as it was being created concurrently.
+/// Such cases are considered to be successful. That is, calling `create_dir_all`
+/// concurrently from multiple threads or processes is guaranteed not to fail
+/// due to a race condition with itself.
+///
+/// [`fs::create_dir`]: std::fs::create_dir
+///
+/// # Examples
+///
+/// ```no_run
+/// use tokio::fs;
+///
+/// #[tokio::main]
+/// async fn main() -> std::io::Result<()> {
+///     fs::create_dir_all("/some/dir").await?;
+///     Ok(())
+/// }
+/// ```
+pub async fn create_dir_all(path: impl AsRef<Path>) -> io::Result<()> {
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::create_dir_all(path)).await
+}
diff --git a/third_party/rust/tokio/src/fs/dir_builder.rs b/third_party/rust/tokio/src/fs/dir_builder.rs
new file mode 100644
index 0000000000..97168bff70
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/dir_builder.rs
@@ -0,0 +1,137 @@
+use crate::fs::asyncify;
+
+use std::io;
+use std::path::Path;
+
+/// A builder for creating directories in various manners.
+///
+/// This is a specialized version of [`std::fs::DirBuilder`] for usage on
+/// the Tokio runtime.
+///
+/// [std::fs::DirBuilder]: std::fs::DirBuilder
+#[derive(Debug, Default)]
+pub struct DirBuilder {
+    /// Indicates whether to create parent directories if they are missing.
+    recursive: bool,
+
+    /// Sets the Unix mode for newly created directories.
+    #[cfg(unix)]
+    pub(super) mode: Option<u32>,
+}
+
+impl DirBuilder {
+    /// Creates a new set of options with default mode/security settings for all
+    /// platforms and also non-recursive.
+    ///
+    /// This is an async version of [`std::fs::DirBuilder::new`][std]
+    ///
+    /// [std]: std::fs::DirBuilder::new
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::DirBuilder;
+    ///
+    /// let builder = DirBuilder::new();
+    /// ```
+    pub fn new() -> Self {
+        Default::default()
+    }
+
+    /// Indicates whether to create directories recursively (including all parent directories).
+    /// Parents that do not exist are created with the same security and permissions settings.
+    ///
+    /// This option defaults to `false`.
+    ///
+    /// This is an async version of [`std::fs::DirBuilder::recursive`][std]
+    ///
+    /// [std]: std::fs::DirBuilder::recursive
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::DirBuilder;
+    ///
+    /// let mut builder = DirBuilder::new();
+    /// builder.recursive(true);
+    /// ```
+    pub fn recursive(&mut self, recursive: bool) -> &mut Self {
+        self.recursive = recursive;
+        self
+    }
+
+    /// Creates the specified directory with the configured options.
+    ///
+    /// It is considered an error if the directory already exists unless
+    /// recursive mode is enabled.
+    ///
+    /// This is an async version of [`std::fs::DirBuilder::create`][std]
+    ///
+    /// [std]: std::fs::DirBuilder::create
+    ///
+    /// # Errors
+    ///
+    /// An error will be returned under the following circumstances:
+    ///
+    /// * Path already points to an existing file.
+    /// * Path already points to an existing directory and the mode is
+    ///   non-recursive.
+    /// * The calling process doesn't have permissions to create the directory
+    ///   or its missing parents.
+    /// * Other I/O error occurred.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::DirBuilder;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     DirBuilder::new()
+    ///         .recursive(true)
+    ///         .create("/tmp/foo/bar/baz")
+    ///         .await?;
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn create(&self, path: impl AsRef<Path>) -> io::Result<()> {
+        let path = path.as_ref().to_owned();
+        let mut builder = std::fs::DirBuilder::new();
+        builder.recursive(self.recursive);
+
+        #[cfg(unix)]
+        {
+            if let Some(mode) = self.mode {
+                std::os::unix::fs::DirBuilderExt::mode(&mut builder, mode);
+            }
+        }
+
+        asyncify(move || builder.create(path)).await
+    }
+}
+
+feature! {
+    #![unix]
+
+    impl DirBuilder {
+        /// Sets the mode to create new directories with.
+        ///
+        /// This option defaults to 0o777.
+        ///
+        /// # Examples
+        ///
+        ///
+        /// ```no_run
+        /// use tokio::fs::DirBuilder;
+        ///
+        /// let mut builder = DirBuilder::new();
+        /// builder.mode(0o775);
+        /// ```
+        pub fn mode(&mut self, mode: u32) -> &mut Self {
+            self.mode = Some(mode);
+            self
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/fs/file.rs b/third_party/rust/tokio/src/fs/file.rs
new file mode 100644
index 0000000000..2c38e8059f
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/file.rs
@@ -0,0 +1,779 @@
+//! Types for working with [`File`].
+//!
+//! [`File`]: File
+
+use self::State::*;
+use crate::fs::asyncify;
+use crate::io::blocking::Buf;
+use crate::io::{AsyncRead, AsyncSeek, AsyncWrite, ReadBuf};
+use crate::sync::Mutex;
+
+use std::fmt;
+use std::fs::{Metadata, Permissions};
+use std::future::Future;
+use std::io::{self, Seek, SeekFrom};
+use std::path::Path;
+use std::pin::Pin;
+use std::sync::Arc;
+use std::task::Context;
+use std::task::Poll;
+use std::task::Poll::*;
+
+#[cfg(test)]
+use super::mocks::JoinHandle;
+#[cfg(test)]
+use super::mocks::MockFile as StdFile;
+#[cfg(test)]
+use super::mocks::{spawn_blocking, spawn_mandatory_blocking};
+#[cfg(not(test))]
+use crate::blocking::JoinHandle;
+#[cfg(not(test))]
+use crate::blocking::{spawn_blocking, spawn_mandatory_blocking};
+#[cfg(not(test))]
+use std::fs::File as StdFile;
+
+/// A reference to an open file on the filesystem.
+///
+/// This is a specialized version of [`std::fs::File`][std] for usage from the
+/// Tokio runtime.
+///
+/// An instance of a `File` can be read and/or written depending on what options
+/// it was opened with. Files also implement [`AsyncSeek`] to alter the logical
+/// cursor that the file contains internally.
+///
+/// A file will not be closed immediately when it goes out of scope if there
+/// are any IO operations that have not yet completed. To ensure that a file is
+/// closed immediately when it is dropped, you should call [`flush`] before
+/// dropping it. Note that this does not ensure that the file has been fully
+/// written to disk; the operating system might keep the changes around in an
+/// in-memory buffer. See the [`sync_all`] method for telling the OS to write
+/// the data to disk.
+///
+/// Reading and writing to a `File` is usually done using the convenience
+/// methods found on the [`AsyncReadExt`] and [`AsyncWriteExt`] traits.
+///
+/// [std]: struct@std::fs::File
+/// [`AsyncSeek`]: trait@crate::io::AsyncSeek
+/// [`flush`]: fn@crate::io::AsyncWriteExt::flush
+/// [`sync_all`]: fn@crate::fs::File::sync_all
+/// [`AsyncReadExt`]: trait@crate::io::AsyncReadExt
+/// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+///
+/// # Examples
+///
+/// Create a new file and asynchronously write bytes to it:
+///
+/// ```no_run
+/// use tokio::fs::File;
+/// use tokio::io::AsyncWriteExt; // for write_all()
+///
+/// # async fn dox() -> std::io::Result<()> {
+/// let mut file = File::create("foo.txt").await?;
+/// file.write_all(b"hello, world!").await?;
+/// # Ok(())
+/// # }
+/// ```
+///
+/// Read the contents of a file into a buffer:
+///
+/// ```no_run
+/// use tokio::fs::File;
+/// use tokio::io::AsyncReadExt; // for read_to_end()
+///
+/// # async fn dox() -> std::io::Result<()> {
+/// let mut file = File::open("foo.txt").await?;
+///
+/// let mut contents = vec![];
+/// file.read_to_end(&mut contents).await?;
+///
+/// println!("len = {}", contents.len());
+/// # Ok(())
+/// # }
+/// ```
+pub struct File {
+    std: Arc<StdFile>,
+    inner: Mutex<Inner>,
+}
+
+struct Inner {
+    state: State,
+
+    /// Errors from writes/flushes are returned in write/flush calls. If a write
+    /// error is observed while performing a read, it is saved until the next
+    /// write / flush call.
+    last_write_err: Option<io::ErrorKind>,
+
+    pos: u64,
+}
+
+#[derive(Debug)]
+enum State {
+    Idle(Option<Buf>),
+    Busy(JoinHandle<(Operation, Buf)>),
+}
+
+#[derive(Debug)]
+enum Operation {
+    Read(io::Result<usize>),
+    Write(io::Result<()>),
+    Seek(io::Result<u64>),
+}
+
+impl File {
+    /// Attempts to open a file in read-only mode.
+    ///
+    /// See [`OpenOptions`] for more details.
+    ///
+    /// [`OpenOptions`]: super::OpenOptions
+    ///
+    /// # Errors
+    ///
+    /// This function will return an error if called from outside of the Tokio
+    /// runtime or if path does not already exist. Other errors may also be
+    /// returned according to OpenOptions::open.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    /// use tokio::io::AsyncReadExt;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let mut file = File::open("foo.txt").await?;
+    ///
+    /// let mut contents = vec![];
+    /// file.read_to_end(&mut contents).await?;
+    ///
+    /// println!("len = {}", contents.len());
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// The [`read_to_end`] method is defined on the [`AsyncReadExt`] trait.
+    ///
+    /// [`read_to_end`]: fn@crate::io::AsyncReadExt::read_to_end
+    /// [`AsyncReadExt`]: trait@crate::io::AsyncReadExt
+    pub async fn open(path: impl AsRef<Path>) -> io::Result<File> {
+        let path = path.as_ref().to_owned();
+        let std = asyncify(|| StdFile::open(path)).await?;
+
+        Ok(File::from_std(std))
+    }
+
+    /// Opens a file in write-only mode.
+    ///
+    /// This function will create a file if it does not exist, and will truncate
+    /// it if it does.
+    ///
+    /// See [`OpenOptions`] for more details.
+    ///
+    /// [`OpenOptions`]: super::OpenOptions
+    ///
+    /// # Errors
+    ///
+    /// Results in an error if called from outside of the Tokio runtime or if
+    /// the underlying [`create`] call results in an error.
+    ///
+    /// [`create`]: std::fs::File::create
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    /// use tokio::io::AsyncWriteExt;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let mut file = File::create("foo.txt").await?;
+    /// file.write_all(b"hello, world!").await?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// The [`write_all`] method is defined on the [`AsyncWriteExt`] trait.
+    ///
+    /// [`write_all`]: fn@crate::io::AsyncWriteExt::write_all
+    /// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+    pub async fn create(path: impl AsRef<Path>) -> io::Result<File> {
+        let path = path.as_ref().to_owned();
+        let std_file = asyncify(move || StdFile::create(path)).await?;
+        Ok(File::from_std(std_file))
+    }
+
+    /// Converts a [`std::fs::File`][std] to a [`tokio::fs::File`][file].
+    ///
+    /// [std]: std::fs::File
+    /// [file]: File
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// // This line could block. It is not recommended to do this on the Tokio
+    /// // runtime.
+    /// let std_file = std::fs::File::open("foo.txt").unwrap();
+    /// let file = tokio::fs::File::from_std(std_file);
+    /// ```
+    pub fn from_std(std: StdFile) -> File {
+        File {
+            std: Arc::new(std),
+            inner: Mutex::new(Inner {
+                state: State::Idle(Some(Buf::with_capacity(0))),
+                last_write_err: None,
+                pos: 0,
+            }),
+        }
+    }
+
+    /// Attempts to sync all OS-internal metadata to disk.
+    ///
+    /// This function will attempt to ensure that all in-core data reaches the
+    /// filesystem before returning.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    /// use tokio::io::AsyncWriteExt;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let mut file = File::create("foo.txt").await?;
+    /// file.write_all(b"hello, world!").await?;
+    /// file.sync_all().await?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// The [`write_all`] method is defined on the [`AsyncWriteExt`] trait.
+    ///
+    /// [`write_all`]: fn@crate::io::AsyncWriteExt::write_all
+    /// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+    pub async fn sync_all(&self) -> io::Result<()> {
+        let mut inner = self.inner.lock().await;
+        inner.complete_inflight().await;
+
+        let std = self.std.clone();
+        asyncify(move || std.sync_all()).await
+    }
+
+    /// This function is similar to `sync_all`, except that it may not
+    /// synchronize file metadata to the filesystem.
+    ///
+    /// This is intended for use cases that must synchronize content, but don't
+    /// need the metadata on disk. The goal of this method is to reduce disk
+    /// operations.
+    ///
+    /// Note that some platforms may simply implement this in terms of `sync_all`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    /// use tokio::io::AsyncWriteExt;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let mut file = File::create("foo.txt").await?;
+    /// file.write_all(b"hello, world!").await?;
+    /// file.sync_data().await?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// The [`write_all`] method is defined on the [`AsyncWriteExt`] trait.
+    ///
+    /// [`write_all`]: fn@crate::io::AsyncWriteExt::write_all
+    /// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+    pub async fn sync_data(&self) -> io::Result<()> {
+        let mut inner = self.inner.lock().await;
+        inner.complete_inflight().await;
+
+        let std = self.std.clone();
+        asyncify(move || std.sync_data()).await
+    }
+
+    /// Truncates or extends the underlying file, updating the size of this file to become size.
+    ///
+    /// If the size is less than the current file's size, then the file will be
+    /// shrunk. If it is greater than the current file's size, then the file
+    /// will be extended to size and have all of the intermediate data filled in
+    /// with 0s.
+    ///
+    /// # Errors
+    ///
+    /// This function will return an error if the file is not opened for
+    /// writing.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    /// use tokio::io::AsyncWriteExt;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let mut file = File::create("foo.txt").await?;
+    /// file.write_all(b"hello, world!").await?;
+    /// file.set_len(10).await?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// The [`write_all`] method is defined on the [`AsyncWriteExt`] trait.
+    ///
+    /// [`write_all`]: fn@crate::io::AsyncWriteExt::write_all
+    /// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+    pub async fn set_len(&self, size: u64) -> io::Result<()> {
+        let mut inner = self.inner.lock().await;
+        inner.complete_inflight().await;
+
+        let mut buf = match inner.state {
+            Idle(ref mut buf_cell) => buf_cell.take().unwrap(),
+            _ => unreachable!(),
+        };
+
+        let seek = if !buf.is_empty() {
+            Some(SeekFrom::Current(buf.discard_read()))
+        } else {
+            None
+        };
+
+        let std = self.std.clone();
+
+        inner.state = Busy(spawn_blocking(move || {
+            let res = if let Some(seek) = seek {
+                (&*std).seek(seek).and_then(|_| std.set_len(size))
+            } else {
+                std.set_len(size)
+            }
+            .map(|_| 0); // the value is discarded later
+
+            // Return the result as a seek
+            (Operation::Seek(res), buf)
+        }));
+
+        let (op, buf) = match inner.state {
+            Idle(_) => unreachable!(),
+            Busy(ref mut rx) => rx.await?,
+        };
+
+        inner.state = Idle(Some(buf));
+
+        match op {
+            Operation::Seek(res) => res.map(|pos| {
+                inner.pos = pos;
+            }),
+            _ => unreachable!(),
+        }
+    }
+
+    /// Queries metadata about the underlying file.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let file = File::open("foo.txt").await?;
+    /// let metadata = file.metadata().await?;
+    ///
+    /// println!("{:?}", metadata);
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn metadata(&self) -> io::Result<Metadata> {
+        let std = self.std.clone();
+        asyncify(move || std.metadata()).await
+    }
+
+    /// Creates a new `File` instance that shares the same underlying file handle
+    /// as the existing `File` instance. Reads, writes, and seeks will affect both
+    /// File instances simultaneously.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let file = File::open("foo.txt").await?;
+    /// let file_clone = file.try_clone().await?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn try_clone(&self) -> io::Result<File> {
+        let std = self.std.clone();
+        let std_file = asyncify(move || std.try_clone()).await?;
+        Ok(File::from_std(std_file))
+    }
+
+    /// Destructures `File` into a [`std::fs::File`][std]. This function is
+    /// async to allow any in-flight operations to complete.
+    ///
+    /// Use `File::try_into_std` to attempt conversion immediately.
+    ///
+    /// [std]: std::fs::File
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let tokio_file = File::open("foo.txt").await?;
+    /// let std_file = tokio_file.into_std().await;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn into_std(mut self) -> StdFile {
+        self.inner.get_mut().complete_inflight().await;
+        Arc::try_unwrap(self.std).expect("Arc::try_unwrap failed")
+    }
+
+    /// Tries to immediately destructure `File` into a [`std::fs::File`][std].
+    ///
+    /// [std]: std::fs::File
+    ///
+    /// # Errors
+    ///
+    /// This function will return an error containing the file if some
+    /// operation is in-flight.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let tokio_file = File::open("foo.txt").await?;
+    /// let std_file = tokio_file.try_into_std().unwrap();
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn try_into_std(mut self) -> Result<StdFile, Self> {
+        match Arc::try_unwrap(self.std) {
+            Ok(file) => Ok(file),
+            Err(std_file_arc) => {
+                self.std = std_file_arc;
+                Err(self)
+            }
+        }
+    }
+
+    /// Changes the permissions on the underlying file.
+    ///
+    /// # Platform-specific behavior
+    ///
+    /// This function currently corresponds to the `fchmod` function on Unix and
+    /// the `SetFileInformationByHandle` function on Windows. Note that, this
+    /// [may change in the future][changes].
+    ///
+    /// [changes]: https://doc.rust-lang.org/std/io/index.html#platform-specific-behavior
+    ///
+    /// # Errors
+    ///
+    /// This function will return an error if the user lacks permission change
+    /// attributes on the underlying file. It may also return an error in other
+    /// os-specific unspecified cases.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let file = File::open("foo.txt").await?;
+    /// let mut perms = file.metadata().await?.permissions();
+    /// perms.set_readonly(true);
+    /// file.set_permissions(perms).await?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn set_permissions(&self, perm: Permissions) -> io::Result<()> {
+        let std = self.std.clone();
+        asyncify(move || std.set_permissions(perm)).await
+    }
+}
+
+impl AsyncRead for File {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        dst: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        let me = self.get_mut();
+        let inner = me.inner.get_mut();
+
+        loop {
+            match inner.state {
+                Idle(ref mut buf_cell) => {
+                    let mut buf = buf_cell.take().unwrap();
+
+                    if !buf.is_empty() {
+                        buf.copy_to(dst);
+                        *buf_cell = Some(buf);
+                        return Ready(Ok(()));
+                    }
+
+                    buf.ensure_capacity_for(dst);
+                    let std = me.std.clone();
+
+                    inner.state = Busy(spawn_blocking(move || {
+                        let res = buf.read_from(&mut &*std);
+                        (Operation::Read(res), buf)
+                    }));
+                }
+                Busy(ref mut rx) => {
+                    let (op, mut buf) = ready!(Pin::new(rx).poll(cx))?;
+
+                    match op {
+                        Operation::Read(Ok(_)) => {
+                            buf.copy_to(dst);
+                            inner.state = Idle(Some(buf));
+                            return Ready(Ok(()));
+                        }
+                        Operation::Read(Err(e)) => {
+                            assert!(buf.is_empty());
+
+                            inner.state = Idle(Some(buf));
+                            return Ready(Err(e));
+                        }
+                        Operation::Write(Ok(_)) => {
+                            assert!(buf.is_empty());
+                            inner.state = Idle(Some(buf));
+                            continue;
+                        }
+                        Operation::Write(Err(e)) => {
+                            assert!(inner.last_write_err.is_none());
+                            inner.last_write_err = Some(e.kind());
+                            inner.state = Idle(Some(buf));
+                        }
+                        Operation::Seek(result) => {
+                            assert!(buf.is_empty());
+                            inner.state = Idle(Some(buf));
+                            if let Ok(pos) = result {
+                                inner.pos = pos;
+                            }
+                            continue;
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl AsyncSeek for File {
+    fn start_seek(self: Pin<&mut Self>, mut pos: SeekFrom) -> io::Result<()> {
+        let me = self.get_mut();
+        let inner = me.inner.get_mut();
+
+        loop {
+            match inner.state {
+                Busy(_) => panic!("must wait for poll_complete before calling start_seek"),
+                Idle(ref mut buf_cell) => {
+                    let mut buf = buf_cell.take().unwrap();
+
+                    // Factor in any unread data from the buf
+                    if !buf.is_empty() {
+                        let n = buf.discard_read();
+
+                        if let SeekFrom::Current(ref mut offset) = pos {
+                            *offset += n;
+                        }
+                    }
+
+                    let std = me.std.clone();
+
+                    inner.state = Busy(spawn_blocking(move || {
+                        let res = (&*std).seek(pos);
+                        (Operation::Seek(res), buf)
+                    }));
+                    return Ok(());
+                }
+            }
+        }
+    }
+
+    fn poll_complete(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
+        let inner = self.inner.get_mut();
+
+        loop {
+            match inner.state {
+                Idle(_) => return Poll::Ready(Ok(inner.pos)),
+                Busy(ref mut rx) => {
+                    let (op, buf) = ready!(Pin::new(rx).poll(cx))?;
+                    inner.state = Idle(Some(buf));
+
+                    match op {
+                        Operation::Read(_) => {}
+                        Operation::Write(Err(e)) => {
+                            assert!(inner.last_write_err.is_none());
+                            inner.last_write_err = Some(e.kind());
+                        }
+                        Operation::Write(_) => {}
+                        Operation::Seek(res) => {
+                            if let Ok(pos) = res {
+                                inner.pos = pos;
+                            }
+                            return Ready(res);
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl AsyncWrite for File {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        src: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        let me = self.get_mut();
+        let inner = me.inner.get_mut();
+
+        if let Some(e) = inner.last_write_err.take() {
+            return Ready(Err(e.into()));
+        }
+
+        loop {
+            match inner.state {
+                Idle(ref mut buf_cell) => {
+                    let mut buf = buf_cell.take().unwrap();
+
+                    let seek = if !buf.is_empty() {
+                        Some(SeekFrom::Current(buf.discard_read()))
+                    } else {
+                        None
+                    };
+
+                    let n = buf.copy_from(src);
+                    let std = me.std.clone();
+
+                    let blocking_task_join_handle = spawn_mandatory_blocking(move || {
+                        let res = if let Some(seek) = seek {
+                            (&*std).seek(seek).and_then(|_| buf.write_to(&mut &*std))
+                        } else {
+                            buf.write_to(&mut &*std)
+                        };
+
+                        (Operation::Write(res), buf)
+                    })
+                    .ok_or_else(|| {
+                        io::Error::new(io::ErrorKind::Other, "background task failed")
+                    })?;
+
+                    inner.state = Busy(blocking_task_join_handle);
+
+                    return Ready(Ok(n));
+                }
+                Busy(ref mut rx) => {
+                    let (op, buf) = ready!(Pin::new(rx).poll(cx))?;
+                    inner.state = Idle(Some(buf));
+
+                    match op {
+                        Operation::Read(_) => {
+                            // We don't care about the result here. The fact
+                            // that the cursor has advanced will be reflected in
+                            // the next iteration of the loop
+                            continue;
+                        }
+                        Operation::Write(res) => {
+                            // If the previous write was successful, continue.
+                            // Otherwise, error.
+                            res?;
+                            continue;
+                        }
+                        Operation::Seek(_) => {
+                            // Ignore the seek
+                            continue;
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        let inner = self.inner.get_mut();
+        inner.poll_flush(cx)
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        self.poll_flush(cx)
+    }
+}
+
+impl From<StdFile> for File {
+    fn from(std: StdFile) -> Self {
+        Self::from_std(std)
+    }
+}
+
+impl fmt::Debug for File {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("tokio::fs::File")
+            .field("std", &self.std)
+            .finish()
+    }
+}
+
+#[cfg(unix)]
+impl std::os::unix::io::AsRawFd for File {
+    fn as_raw_fd(&self) -> std::os::unix::io::RawFd {
+        self.std.as_raw_fd()
+    }
+}
+
+#[cfg(unix)]
+impl std::os::unix::io::FromRawFd for File {
+    unsafe fn from_raw_fd(fd: std::os::unix::io::RawFd) -> Self {
+        StdFile::from_raw_fd(fd).into()
+    }
+}
+
+#[cfg(windows)]
+impl std::os::windows::io::AsRawHandle for File {
+    fn as_raw_handle(&self) -> std::os::windows::io::RawHandle {
+        self.std.as_raw_handle()
+    }
+}
+
+#[cfg(windows)]
+impl std::os::windows::io::FromRawHandle for File {
+    unsafe fn from_raw_handle(handle: std::os::windows::io::RawHandle) -> Self {
+        StdFile::from_raw_handle(handle).into()
+    }
+}
+
+impl Inner {
+    async fn complete_inflight(&mut self) {
+        use crate::future::poll_fn;
+
+        if let Err(e) = poll_fn(|cx| Pin::new(&mut *self).poll_flush(cx)).await {
+            self.last_write_err = Some(e.kind());
+        }
+    }
+
+    fn poll_flush(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        if let Some(e) = self.last_write_err.take() {
+            return Ready(Err(e.into()));
+        }
+
+        let (op, buf) = match self.state {
+            Idle(_) => return Ready(Ok(())),
+            Busy(ref mut rx) => ready!(Pin::new(rx).poll(cx))?,
+        };
+
+        // The buffer is not used here
+        self.state = Idle(Some(buf));
+
+        match op {
+            Operation::Read(_) => Ready(Ok(())),
+            Operation::Write(res) => Ready(res),
+            Operation::Seek(_) => Ready(Ok(())),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests;
diff --git a/third_party/rust/tokio/src/fs/file/tests.rs b/third_party/rust/tokio/src/fs/file/tests.rs
new file mode 100644
index 0000000000..18a4c07859
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/file/tests.rs
@@ -0,0 +1,957 @@
+use super::*;
+use crate::{
+    fs::mocks::*,
+    io::{AsyncReadExt, AsyncSeekExt, AsyncWriteExt},
+};
+use mockall::{predicate::eq, Sequence};
+use tokio_test::{assert_pending, assert_ready_err, assert_ready_ok, task};
+
+const HELLO: &[u8] = b"hello world...";
+const FOO: &[u8] = b"foo bar baz...";
+
+#[test]
+fn open_read() {
+    let mut file = MockFile::default();
+    file.expect_inner_read().once().returning(|buf| {
+        buf[0..HELLO.len()].copy_from_slice(HELLO);
+        Ok(HELLO.len())
+    });
+    let mut file = File::from_std(file);
+
+    let mut buf = [0; 1024];
+    let mut t = task::spawn(file.read(&mut buf));
+
+    assert_eq!(0, pool::len());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+
+    pool::run_one();
+
+    assert!(t.is_woken());
+
+    let n = assert_ready_ok!(t.poll());
+    assert_eq!(n, HELLO.len());
+    assert_eq!(&buf[..n], HELLO);
+}
+
+#[test]
+fn read_twice_before_dispatch() {
+    let mut file = MockFile::default();
+    file.expect_inner_read().once().returning(|buf| {
+        buf[0..HELLO.len()].copy_from_slice(HELLO);
+        Ok(HELLO.len())
+    });
+    let mut file = File::from_std(file);
+
+    let mut buf = [0; 1024];
+    let mut t = task::spawn(file.read(&mut buf));
+
+    assert_pending!(t.poll());
+    assert_pending!(t.poll());
+
+    assert_eq!(pool::len(), 1);
+    pool::run_one();
+
+    assert!(t.is_woken());
+
+    let n = assert_ready_ok!(t.poll());
+    assert_eq!(&buf[..n], HELLO);
+}
+
+#[test]
+fn read_with_smaller_buf() {
+    let mut file = MockFile::default();
+    file.expect_inner_read().once().returning(|buf| {
+        buf[0..HELLO.len()].copy_from_slice(HELLO);
+        Ok(HELLO.len())
+    });
+
+    let mut file = File::from_std(file);
+
+    {
+        let mut buf = [0; 32];
+        let mut t = task::spawn(file.read(&mut buf));
+        assert_pending!(t.poll());
+    }
+
+    pool::run_one();
+
+    {
+        let mut buf = [0; 4];
+        let mut t = task::spawn(file.read(&mut buf));
+        let n = assert_ready_ok!(t.poll());
+        assert_eq!(n, 4);
+        assert_eq!(&buf[..], &HELLO[..n]);
+    }
+
+    // Calling again immediately succeeds with the rest of the buffer
+    let mut buf = [0; 32];
+    let mut t = task::spawn(file.read(&mut buf));
+    let n = assert_ready_ok!(t.poll());
+    assert_eq!(n, 10);
+    assert_eq!(&buf[..n], &HELLO[4..]);
+
+    assert_eq!(0, pool::len());
+}
+
+#[test]
+fn read_with_bigger_buf() {
+    let mut seq = Sequence::new();
+    let mut file = MockFile::default();
+    file.expect_inner_read()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(|buf| {
+            buf[0..4].copy_from_slice(&HELLO[..4]);
+            Ok(4)
+        });
+    file.expect_inner_read()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(|buf| {
+            buf[0..HELLO.len() - 4].copy_from_slice(&HELLO[4..]);
+            Ok(HELLO.len() - 4)
+        });
+
+    let mut file = File::from_std(file);
+
+    {
+        let mut buf = [0; 4];
+        let mut t = task::spawn(file.read(&mut buf));
+        assert_pending!(t.poll());
+    }
+
+    pool::run_one();
+
+    {
+        let mut buf = [0; 32];
+        let mut t = task::spawn(file.read(&mut buf));
+        let n = assert_ready_ok!(t.poll());
+        assert_eq!(n, 4);
+        assert_eq!(&buf[..n], &HELLO[..n]);
+    }
+
+    // Calling again immediately succeeds with the rest of the buffer
+    let mut buf = [0; 32];
+    let mut t = task::spawn(file.read(&mut buf));
+
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+
+    let n = assert_ready_ok!(t.poll());
+    assert_eq!(n, 10);
+    assert_eq!(&buf[..n], &HELLO[4..]);
+
+    assert_eq!(0, pool::len());
+}
+
+#[test]
+fn read_err_then_read_success() {
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_read()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(|_| Err(io::ErrorKind::Other.into()));
+    file.expect_inner_read()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(|buf| {
+            buf[0..HELLO.len()].copy_from_slice(HELLO);
+            Ok(HELLO.len())
+        });
+
+    let mut file = File::from_std(file);
+
+    {
+        let mut buf = [0; 32];
+        let mut t = task::spawn(file.read(&mut buf));
+        assert_pending!(t.poll());
+
+        pool::run_one();
+
+        assert_ready_err!(t.poll());
+    }
+
+    {
+        let mut buf = [0; 32];
+        let mut t = task::spawn(file.read(&mut buf));
+        assert_pending!(t.poll());
+
+        pool::run_one();
+
+        let n = assert_ready_ok!(t.poll());
+
+        assert_eq!(n, HELLO.len());
+        assert_eq!(&buf[..n], HELLO);
+    }
+}
+
+#[test]
+fn open_write() {
+    let mut file = MockFile::default();
+    file.expect_inner_write()
+        .once()
+        .with(eq(HELLO))
+        .returning(|buf| Ok(buf.len()));
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.write(HELLO));
+
+    assert_eq!(0, pool::len());
+    assert_ready_ok!(t.poll());
+
+    assert_eq!(1, pool::len());
+
+    pool::run_one();
+
+    assert!(!t.is_woken());
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn flush_while_idle() {
+    let file = MockFile::default();
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+#[cfg_attr(miri, ignore)] // takes a really long time with miri
+fn read_with_buffer_larger_than_max() {
+    // Chunks
+    let chunk_a = 16 * 1024;
+    let chunk_b = chunk_a * 2;
+    let chunk_c = chunk_a * 3;
+    let chunk_d = chunk_a * 4;
+
+    assert_eq!(chunk_d / 1024, 64);
+
+    let mut data = vec![];
+    for i in 0..(chunk_d - 1) {
+        data.push((i % 151) as u8);
+    }
+    let data = Arc::new(data);
+    let d0 = data.clone();
+    let d1 = data.clone();
+    let d2 = data.clone();
+    let d3 = data.clone();
+
+    let mut seq = Sequence::new();
+    let mut file = MockFile::default();
+    file.expect_inner_read()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(move |buf| {
+            buf[0..chunk_a].copy_from_slice(&d0[0..chunk_a]);
+            Ok(chunk_a)
+        });
+    file.expect_inner_read()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(move |buf| {
+            buf[..chunk_a].copy_from_slice(&d1[chunk_a..chunk_b]);
+            Ok(chunk_b - chunk_a)
+        });
+    file.expect_inner_read()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(move |buf| {
+            buf[..chunk_a].copy_from_slice(&d2[chunk_b..chunk_c]);
+            Ok(chunk_c - chunk_b)
+        });
+    file.expect_inner_read()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(move |buf| {
+            buf[..chunk_a - 1].copy_from_slice(&d3[chunk_c..]);
+            Ok(chunk_a - 1)
+        });
+    let mut file = File::from_std(file);
+
+    let mut actual = vec![0; chunk_d];
+    let mut pos = 0;
+
+    while pos < data.len() {
+        let mut t = task::spawn(file.read(&mut actual[pos..]));
+
+        assert_pending!(t.poll());
+        pool::run_one();
+        assert!(t.is_woken());
+
+        let n = assert_ready_ok!(t.poll());
+        assert!(n <= chunk_a);
+
+        pos += n;
+    }
+
+    assert_eq!(&data[..], &actual[..data.len()]);
+}
+
+#[test]
+#[cfg_attr(miri, ignore)] // takes a really long time with miri
+fn write_with_buffer_larger_than_max() {
+    // Chunks
+    let chunk_a = 16 * 1024;
+    let chunk_b = chunk_a * 2;
+    let chunk_c = chunk_a * 3;
+    let chunk_d = chunk_a * 4;
+
+    assert_eq!(chunk_d / 1024, 64);
+
+    let mut data = vec![];
+    for i in 0..(chunk_d - 1) {
+        data.push((i % 151) as u8);
+    }
+    let data = Arc::new(data);
+    let d0 = data.clone();
+    let d1 = data.clone();
+    let d2 = data.clone();
+    let d3 = data.clone();
+
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .withf(move |buf| buf == &d0[0..chunk_a])
+        .returning(|buf| Ok(buf.len()));
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .withf(move |buf| buf == &d1[chunk_a..chunk_b])
+        .returning(|buf| Ok(buf.len()));
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .withf(move |buf| buf == &d2[chunk_b..chunk_c])
+        .returning(|buf| Ok(buf.len()));
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .withf(move |buf| buf == &d3[chunk_c..chunk_d - 1])
+        .returning(|buf| Ok(buf.len()));
+
+    let mut file = File::from_std(file);
+
+    let mut rem = &data[..];
+
+    let mut first = true;
+
+    while !rem.is_empty() {
+        let mut task = task::spawn(file.write(rem));
+
+        if !first {
+            assert_pending!(task.poll());
+            pool::run_one();
+            assert!(task.is_woken());
+        }
+
+        first = false;
+
+        let n = assert_ready_ok!(task.poll());
+
+        rem = &rem[n..];
+    }
+
+    pool::run_one();
+}
+
+#[test]
+fn write_twice_before_dispatch() {
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .with(eq(HELLO))
+        .returning(|buf| Ok(buf.len()));
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .with(eq(FOO))
+        .returning(|buf| Ok(buf.len()));
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.write(FOO));
+    assert_pending!(t.poll());
+
+    assert_eq!(pool::len(), 1);
+    pool::run_one();
+
+    assert!(t.is_woken());
+
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.flush());
+    assert_pending!(t.poll());
+
+    assert_eq!(pool::len(), 1);
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn incomplete_read_followed_by_write() {
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_read()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(|buf| {
+            buf[0..HELLO.len()].copy_from_slice(HELLO);
+            Ok(HELLO.len())
+        });
+    file.expect_inner_seek()
+        .once()
+        .with(eq(SeekFrom::Current(-(HELLO.len() as i64))))
+        .in_sequence(&mut seq)
+        .returning(|_| Ok(0));
+    file.expect_inner_write()
+        .once()
+        .with(eq(FOO))
+        .returning(|_| Ok(FOO.len()));
+
+    let mut file = File::from_std(file);
+
+    let mut buf = [0; 32];
+
+    let mut t = task::spawn(file.read(&mut buf));
+    assert_pending!(t.poll());
+
+    pool::run_one();
+
+    let mut t = task::spawn(file.write(FOO));
+    assert_ready_ok!(t.poll());
+
+    assert_eq!(pool::len(), 1);
+    pool::run_one();
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn incomplete_partial_read_followed_by_write() {
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_read()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(|buf| {
+            buf[0..HELLO.len()].copy_from_slice(HELLO);
+            Ok(HELLO.len())
+        });
+    file.expect_inner_seek()
+        .once()
+        .in_sequence(&mut seq)
+        .with(eq(SeekFrom::Current(-10)))
+        .returning(|_| Ok(0));
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .with(eq(FOO))
+        .returning(|_| Ok(FOO.len()));
+
+    let mut file = File::from_std(file);
+
+    let mut buf = [0; 32];
+    let mut t = task::spawn(file.read(&mut buf));
+    assert_pending!(t.poll());
+
+    pool::run_one();
+
+    let mut buf = [0; 4];
+    let mut t = task::spawn(file.read(&mut buf));
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.write(FOO));
+    assert_ready_ok!(t.poll());
+
+    assert_eq!(pool::len(), 1);
+    pool::run_one();
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn incomplete_read_followed_by_flush() {
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_read()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(|buf| {
+            buf[0..HELLO.len()].copy_from_slice(HELLO);
+            Ok(HELLO.len())
+        });
+    file.expect_inner_seek()
+        .once()
+        .in_sequence(&mut seq)
+        .with(eq(SeekFrom::Current(-(HELLO.len() as i64))))
+        .returning(|_| Ok(0));
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .with(eq(FOO))
+        .returning(|_| Ok(FOO.len()));
+
+    let mut file = File::from_std(file);
+
+    let mut buf = [0; 32];
+
+    let mut t = task::spawn(file.read(&mut buf));
+    assert_pending!(t.poll());
+
+    pool::run_one();
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.write(FOO));
+    assert_ready_ok!(t.poll());
+
+    pool::run_one();
+}
+
+#[test]
+fn incomplete_flush_followed_by_write() {
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .with(eq(HELLO))
+        .returning(|_| Ok(HELLO.len()));
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .with(eq(FOO))
+        .returning(|_| Ok(FOO.len()));
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.write(HELLO));
+    let n = assert_ready_ok!(t.poll());
+    assert_eq!(n, HELLO.len());
+
+    let mut t = task::spawn(file.flush());
+    assert_pending!(t.poll());
+
+    // TODO: Move under write
+    pool::run_one();
+
+    let mut t = task::spawn(file.write(FOO));
+    assert_ready_ok!(t.poll());
+
+    pool::run_one();
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn read_err() {
+    let mut file = MockFile::default();
+    file.expect_inner_read()
+        .once()
+        .returning(|_| Err(io::ErrorKind::Other.into()));
+
+    let mut file = File::from_std(file);
+
+    let mut buf = [0; 1024];
+    let mut t = task::spawn(file.read(&mut buf));
+
+    assert_pending!(t.poll());
+
+    pool::run_one();
+    assert!(t.is_woken());
+
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn write_write_err() {
+    let mut file = MockFile::default();
+    file.expect_inner_write()
+        .once()
+        .returning(|_| Err(io::ErrorKind::Other.into()));
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    pool::run_one();
+
+    let mut t = task::spawn(file.write(FOO));
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn write_read_write_err() {
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(|_| Err(io::ErrorKind::Other.into()));
+    file.expect_inner_read()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(|buf| {
+            buf[0..HELLO.len()].copy_from_slice(HELLO);
+            Ok(HELLO.len())
+        });
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    pool::run_one();
+
+    let mut buf = [0; 1024];
+    let mut t = task::spawn(file.read(&mut buf));
+
+    assert_pending!(t.poll());
+
+    pool::run_one();
+
+    let mut t = task::spawn(file.write(FOO));
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn write_read_flush_err() {
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(|_| Err(io::ErrorKind::Other.into()));
+    file.expect_inner_read()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(|buf| {
+            buf[0..HELLO.len()].copy_from_slice(HELLO);
+            Ok(HELLO.len())
+        });
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    pool::run_one();
+
+    let mut buf = [0; 1024];
+    let mut t = task::spawn(file.read(&mut buf));
+
+    assert_pending!(t.poll());
+
+    pool::run_one();
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn write_seek_write_err() {
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(|_| Err(io::ErrorKind::Other.into()));
+    file.expect_inner_seek()
+        .once()
+        .with(eq(SeekFrom::Start(0)))
+        .in_sequence(&mut seq)
+        .returning(|_| Ok(0));
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    pool::run_one();
+
+    {
+        let mut t = task::spawn(file.seek(SeekFrom::Start(0)));
+        assert_pending!(t.poll());
+    }
+
+    pool::run_one();
+
+    let mut t = task::spawn(file.write(FOO));
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn write_seek_flush_err() {
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(|_| Err(io::ErrorKind::Other.into()));
+    file.expect_inner_seek()
+        .once()
+        .with(eq(SeekFrom::Start(0)))
+        .in_sequence(&mut seq)
+        .returning(|_| Ok(0));
+
+    let mut file = File::from_std(file);
+
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    pool::run_one();
+
+    {
+        let mut t = task::spawn(file.seek(SeekFrom::Start(0)));
+        assert_pending!(t.poll());
+    }
+
+    pool::run_one();
+
+    let mut t = task::spawn(file.flush());
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn sync_all_ordered_after_write() {
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .with(eq(HELLO))
+        .returning(|_| Ok(HELLO.len()));
+    file.expect_sync_all().once().returning(|| Ok(()));
+
+    let mut file = File::from_std(file);
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.sync_all());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn sync_all_err_ordered_after_write() {
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .with(eq(HELLO))
+        .returning(|_| Ok(HELLO.len()));
+    file.expect_sync_all()
+        .once()
+        .returning(|| Err(io::ErrorKind::Other.into()));
+
+    let mut file = File::from_std(file);
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.sync_all());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn sync_data_ordered_after_write() {
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .with(eq(HELLO))
+        .returning(|_| Ok(HELLO.len()));
+    file.expect_sync_data().once().returning(|| Ok(()));
+
+    let mut file = File::from_std(file);
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.sync_data());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn sync_data_err_ordered_after_write() {
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_write()
+        .once()
+        .in_sequence(&mut seq)
+        .with(eq(HELLO))
+        .returning(|_| Ok(HELLO.len()));
+    file.expect_sync_data()
+        .once()
+        .returning(|| Err(io::ErrorKind::Other.into()));
+
+    let mut file = File::from_std(file);
+    let mut t = task::spawn(file.write(HELLO));
+    assert_ready_ok!(t.poll());
+
+    let mut t = task::spawn(file.sync_data());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_pending!(t.poll());
+
+    assert_eq!(1, pool::len());
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn open_set_len_ok() {
+    let mut file = MockFile::default();
+    file.expect_set_len().with(eq(123)).returning(|_| Ok(()));
+
+    let file = File::from_std(file);
+    let mut t = task::spawn(file.set_len(123));
+
+    assert_pending!(t.poll());
+
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_ready_ok!(t.poll());
+}
+
+#[test]
+fn open_set_len_err() {
+    let mut file = MockFile::default();
+    file.expect_set_len()
+        .with(eq(123))
+        .returning(|_| Err(io::ErrorKind::Other.into()));
+
+    let file = File::from_std(file);
+    let mut t = task::spawn(file.set_len(123));
+
+    assert_pending!(t.poll());
+
+    pool::run_one();
+
+    assert!(t.is_woken());
+    assert_ready_err!(t.poll());
+}
+
+#[test]
+fn partial_read_set_len_ok() {
+    let mut file = MockFile::default();
+    let mut seq = Sequence::new();
+    file.expect_inner_read()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(|buf| {
+            buf[0..HELLO.len()].copy_from_slice(HELLO);
+            Ok(HELLO.len())
+        });
+    file.expect_inner_seek()
+        .once()
+        .with(eq(SeekFrom::Current(-(HELLO.len() as i64))))
+        .in_sequence(&mut seq)
+        .returning(|_| Ok(0));
+    file.expect_set_len()
+        .once()
+        .in_sequence(&mut seq)
+        .with(eq(123))
+        .returning(|_| Ok(()));
+    file.expect_inner_read()
+        .once()
+        .in_sequence(&mut seq)
+        .returning(|buf| {
+            buf[0..FOO.len()].copy_from_slice(FOO);
+            Ok(FOO.len())
+        });
+
+    let mut buf = [0; 32];
+    let mut file = File::from_std(file);
+
+    {
+        let mut t = task::spawn(file.read(&mut buf));
+        assert_pending!(t.poll());
+    }
+
+    pool::run_one();
+
+    {
+        let mut t = task::spawn(file.set_len(123));
+
+        assert_pending!(t.poll());
+        pool::run_one();
+        assert_ready_ok!(t.poll());
+    }
+
+    let mut t = task::spawn(file.read(&mut buf));
+    assert_pending!(t.poll());
+    pool::run_one();
+    let n = assert_ready_ok!(t.poll());
+
+    assert_eq!(n, FOO.len());
+    assert_eq!(&buf[..n], FOO);
+}
diff --git a/third_party/rust/tokio/src/fs/hard_link.rs b/third_party/rust/tokio/src/fs/hard_link.rs
new file mode 100644
index 0000000000..50cc17d286
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/hard_link.rs
@@ -0,0 +1,46 @@
+use crate::fs::asyncify;
+
+use std::io;
+use std::path::Path;
+
+/// Creates a new hard link on the filesystem.
+///
+/// This is an async version of [`std::fs::hard_link`][std]
+///
+/// [std]: std::fs::hard_link
+///
+/// The `dst` path will be a link pointing to the `src` path. Note that systems
+/// often require these two paths to both be located on the same filesystem.
+///
+/// # Platform-specific behavior
+///
+/// This function currently corresponds to the `link` function on Unix
+/// and the `CreateHardLink` function on Windows.
+/// Note that, this [may change in the future][changes].
+///
+/// [changes]: https://doc.rust-lang.org/std/io/index.html#platform-specific-behavior
+///
+/// # Errors
+///
+/// This function will return an error in the following situations, but is not
+/// limited to just these cases:
+///
+/// * The `src` path is not a file or doesn't exist.
+///
+/// # Examples
+///
+/// ```no_run
+/// use tokio::fs;
+///
+/// #[tokio::main]
+/// async fn main() -> std::io::Result<()> {
+///     fs::hard_link("a.txt", "b.txt").await?; // Hard link a.txt to b.txt
+///     Ok(())
+/// }
+/// ```
+pub async fn hard_link(src: impl AsRef<Path>, dst: impl AsRef<Path>) -> io::Result<()> {
+    let src = src.as_ref().to_owned();
+    let dst = dst.as_ref().to_owned();
+
+    asyncify(move || std::fs::hard_link(src, dst)).await
+}
diff --git a/third_party/rust/tokio/src/fs/metadata.rs b/third_party/rust/tokio/src/fs/metadata.rs
new file mode 100644
index 0000000000..ff9cded79a
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/metadata.rs
@@ -0,0 +1,47 @@
+use crate::fs::asyncify;
+
+use std::fs::Metadata;
+use std::io;
+use std::path::Path;
+
+/// Given a path, queries the file system to get information about a file,
+/// directory, etc.
+///
+/// This is an async version of [`std::fs::metadata`][std]
+///
+/// This function will traverse symbolic links to query information about the
+/// destination file.
+///
+/// # Platform-specific behavior
+///
+/// This function currently corresponds to the `stat` function on Unix and the
+/// `GetFileAttributesEx` function on Windows.  Note that, this [may change in
+/// the future][changes].
+///
+/// [std]: std::fs::metadata
+/// [changes]: https://doc.rust-lang.org/std/io/index.html#platform-specific-behavior
+///
+/// # Errors
+///
+/// This function will return an error in the following situations, but is not
+/// limited to just these cases:
+///
+/// * The user lacks permissions to perform `metadata` call on `path`.
+/// * `path` does not exist.
+///
+/// # Examples
+///
+/// ```rust,no_run
+/// use tokio::fs;
+///
+/// #[tokio::main]
+/// async fn main() -> std::io::Result<()> {
+///     let attr = fs::metadata("/some/file/path.txt").await?;
+///     // inspect attr ...
+///     Ok(())
+/// }
+/// ```
+pub async fn metadata(path: impl AsRef<Path>) -> io::Result<Metadata> {
+    let path = path.as_ref().to_owned();
+    asyncify(|| std::fs::metadata(path)).await
+}
diff --git a/third_party/rust/tokio/src/fs/mocks.rs b/third_party/rust/tokio/src/fs/mocks.rs
new file mode 100644
index 0000000000..b186172677
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/mocks.rs
@@ -0,0 +1,151 @@
+//! Mock version of std::fs::File;
+use mockall::mock;
+
+use crate::sync::oneshot;
+use std::{
+    cell::RefCell,
+    collections::VecDeque,
+    fs::{Metadata, Permissions},
+    future::Future,
+    io::{self, Read, Seek, SeekFrom, Write},
+    path::PathBuf,
+    pin::Pin,
+    task::{Context, Poll},
+};
+
+mock! {
+    #[derive(Debug)]
+    pub File {
+        pub fn create(pb: PathBuf) -> io::Result<Self>;
+        // These inner_ methods exist because std::fs::File has two
+        // implementations for each of these methods: one on "&mut self" and
+        // one on "&&self".  Defining both of those in terms of an inner_ method
+        // allows us to specify the expectation the same way, regardless of
+        // which method is used.
+        pub fn inner_flush(&self) -> io::Result<()>;
+        pub fn inner_read(&self, dst: &mut [u8]) -> io::Result<usize>;
+        pub fn inner_seek(&self, pos: SeekFrom) -> io::Result<u64>;
+        pub fn inner_write(&self, src: &[u8]) -> io::Result<usize>;
+        pub fn metadata(&self) -> io::Result<Metadata>;
+        pub fn open(pb: PathBuf) -> io::Result<Self>;
+        pub fn set_len(&self, size: u64) -> io::Result<()>;
+        pub fn set_permissions(&self, _perm: Permissions) -> io::Result<()>;
+        pub fn sync_all(&self) -> io::Result<()>;
+        pub fn sync_data(&self) -> io::Result<()>;
+        pub fn try_clone(&self) -> io::Result<Self>;
+    }
+    #[cfg(windows)]
+    impl std::os::windows::io::AsRawHandle for File {
+        fn as_raw_handle(&self) -> std::os::windows::io::RawHandle;
+    }
+    #[cfg(windows)]
+    impl std::os::windows::io::FromRawHandle for File {
+        unsafe fn from_raw_handle(h: std::os::windows::io::RawHandle) -> Self;
+    }
+    #[cfg(unix)]
+    impl std::os::unix::io::AsRawFd for File {
+        fn as_raw_fd(&self) -> std::os::unix::io::RawFd;
+    }
+
+    #[cfg(unix)]
+    impl std::os::unix::io::FromRawFd for File {
+        unsafe fn from_raw_fd(h: std::os::unix::io::RawFd) -> Self;
+    }
+}
+
+impl Read for MockFile {
+    fn read(&mut self, dst: &mut [u8]) -> io::Result<usize> {
+        self.inner_read(dst)
+    }
+}
+
+impl Read for &'_ MockFile {
+    fn read(&mut self, dst: &mut [u8]) -> io::Result<usize> {
+        self.inner_read(dst)
+    }
+}
+
+impl Seek for &'_ MockFile {
+    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
+        self.inner_seek(pos)
+    }
+}
+
+impl Write for &'_ MockFile {
+    fn write(&mut self, src: &[u8]) -> io::Result<usize> {
+        self.inner_write(src)
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        self.inner_flush()
+    }
+}
+
+thread_local! {
+    static QUEUE: RefCell<VecDeque<Box<dyn FnOnce() + Send>>> = RefCell::new(VecDeque::new())
+}
+
+#[derive(Debug)]
+pub(super) struct JoinHandle<T> {
+    rx: oneshot::Receiver<T>,
+}
+
+pub(super) fn spawn_blocking<F, R>(f: F) -> JoinHandle<R>
+where
+    F: FnOnce() -> R + Send + 'static,
+    R: Send + 'static,
+{
+    let (tx, rx) = oneshot::channel();
+    let task = Box::new(move || {
+        let _ = tx.send(f());
+    });
+
+    QUEUE.with(|cell| cell.borrow_mut().push_back(task));
+
+    JoinHandle { rx }
+}
+
+pub(super) fn spawn_mandatory_blocking<F, R>(f: F) -> Option<JoinHandle<R>>
+where
+    F: FnOnce() -> R + Send + 'static,
+    R: Send + 'static,
+{
+    let (tx, rx) = oneshot::channel();
+    let task = Box::new(move || {
+        let _ = tx.send(f());
+    });
+
+    QUEUE.with(|cell| cell.borrow_mut().push_back(task));
+
+    Some(JoinHandle { rx })
+}
+
+impl<T> Future for JoinHandle<T> {
+    type Output = Result<T, io::Error>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        use std::task::Poll::*;
+
+        match Pin::new(&mut self.rx).poll(cx) {
+            Ready(Ok(v)) => Ready(Ok(v)),
+            Ready(Err(e)) => panic!("error = {:?}", e),
+            Pending => Pending,
+        }
+    }
+}
+
+pub(super) mod pool {
+    use super::*;
+
+    pub(in super::super) fn len() -> usize {
+        QUEUE.with(|cell| cell.borrow().len())
+    }
+
+    pub(in super::super) fn run_one() {
+        let task = QUEUE
+            .with(|cell| cell.borrow_mut().pop_front())
+            .expect("expected task to run, but none ready");
+
+        task();
+    }
+}
diff --git a/third_party/rust/tokio/src/fs/mod.rs b/third_party/rust/tokio/src/fs/mod.rs
new file mode 100644
index 0000000000..ca0264b367
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/mod.rs
@@ -0,0 +1,126 @@
+#![cfg(not(loom))]
+
+//! Asynchronous file and standard stream adaptation.
+//!
+//! This module contains utility methods and adapter types for input/output to
+//! files or standard streams (`Stdin`, `Stdout`, `Stderr`), and
+//! filesystem manipulation, for use within (and only within) a Tokio runtime.
+//!
+//! Tasks run by *worker* threads should not block, as this could delay
+//! servicing reactor events. Portable filesystem operations are blocking,
+//! however. This module offers adapters which use a `blocking` annotation
+//! to inform the runtime that a blocking operation is required. When
+//! necessary, this allows the runtime to convert the current thread from a
+//! *worker* to a *backup* thread, where blocking is acceptable.
+//!
+//! ## Usage
+//!
+//! Where possible, users should prefer the provided asynchronous-specific
+//! traits such as [`AsyncRead`], or methods returning a `Future` or `Poll`
+//! type. Adaptions also extend to traits like `std::io::Read` where methods
+//! return `std::io::Result`. Be warned that these adapted methods may return
+//! `std::io::ErrorKind::WouldBlock` if a *worker* thread can not be converted
+//! to a *backup* thread immediately.
+//!
+//! [`AsyncRead`]: trait@crate::io::AsyncRead
+
+mod canonicalize;
+pub use self::canonicalize::canonicalize;
+
+mod create_dir;
+pub use self::create_dir::create_dir;
+
+mod create_dir_all;
+pub use self::create_dir_all::create_dir_all;
+
+mod dir_builder;
+pub use self::dir_builder::DirBuilder;
+
+mod file;
+pub use self::file::File;
+
+mod hard_link;
+pub use self::hard_link::hard_link;
+
+mod metadata;
+pub use self::metadata::metadata;
+
+mod open_options;
+pub use self::open_options::OpenOptions;
+
+mod read;
+pub use self::read::read;
+
+mod read_dir;
+pub use self::read_dir::{read_dir, DirEntry, ReadDir};
+
+mod read_link;
+pub use self::read_link::read_link;
+
+mod read_to_string;
+pub use self::read_to_string::read_to_string;
+
+mod remove_dir;
+pub use self::remove_dir::remove_dir;
+
+mod remove_dir_all;
+pub use self::remove_dir_all::remove_dir_all;
+
+mod remove_file;
+pub use self::remove_file::remove_file;
+
+mod rename;
+pub use self::rename::rename;
+
+mod set_permissions;
+pub use self::set_permissions::set_permissions;
+
+mod symlink_metadata;
+pub use self::symlink_metadata::symlink_metadata;
+
+mod write;
+pub use self::write::write;
+
+mod copy;
+pub use self::copy::copy;
+
+#[cfg(test)]
+mod mocks;
+
+feature! {
+    #![unix]
+
+    mod symlink;
+    pub use self::symlink::symlink;
+}
+
+feature! {
+    #![windows]
+
+    mod symlink_dir;
+    pub use self::symlink_dir::symlink_dir;
+
+    mod symlink_file;
+    pub use self::symlink_file::symlink_file;
+}
+
+use std::io;
+
+#[cfg(not(test))]
+use crate::blocking::spawn_blocking;
+#[cfg(test)]
+use mocks::spawn_blocking;
+
+pub(crate) async fn asyncify<F, T>(f: F) -> io::Result<T>
+where
+    F: FnOnce() -> io::Result<T> + Send + 'static,
+    T: Send + 'static,
+{
+    match spawn_blocking(f).await {
+        Ok(res) => res,
+        Err(_) => Err(io::Error::new(
+            io::ErrorKind::Other,
+            "background task failed",
+        )),
+    }
+}
diff --git a/third_party/rust/tokio/src/fs/open_options.rs b/third_party/rust/tokio/src/fs/open_options.rs
new file mode 100644
index 0000000000..f3b4654741
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/open_options.rs
@@ -0,0 +1,665 @@
+use crate::fs::{asyncify, File};
+
+use std::io;
+use std::path::Path;
+
+#[cfg(test)]
+mod mock_open_options;
+#[cfg(test)]
+use mock_open_options::MockOpenOptions as StdOpenOptions;
+#[cfg(not(test))]
+use std::fs::OpenOptions as StdOpenOptions;
+
+/// Options and flags which can be used to configure how a file is opened.
+///
+/// This builder exposes the ability to configure how a [`File`] is opened and
+/// what operations are permitted on the open file. The [`File::open`] and
+/// [`File::create`] methods are aliases for commonly used options using this
+/// builder.
+///
+/// Generally speaking, when using `OpenOptions`, you'll first call [`new`],
+/// then chain calls to methods to set each option, then call [`open`], passing
+/// the path of the file you're trying to open. This will give you a
+/// [`io::Result`][result] with a [`File`] inside that you can further operate
+/// on.
+///
+/// This is a specialized version of [`std::fs::OpenOptions`] for usage from
+/// the Tokio runtime.
+///
+/// `From<std::fs::OpenOptions>` is implemented for more advanced configuration
+/// than the methods provided here.
+///
+/// [`new`]: OpenOptions::new
+/// [`open`]: OpenOptions::open
+/// [result]: std::io::Result
+/// [`File`]: File
+/// [`File::open`]: File::open
+/// [`File::create`]: File::create
+/// [`std::fs::OpenOptions`]: std::fs::OpenOptions
+///
+/// # Examples
+///
+/// Opening a file to read:
+///
+/// ```no_run
+/// use tokio::fs::OpenOptions;
+/// use std::io;
+///
+/// #[tokio::main]
+/// async fn main() -> io::Result<()> {
+///     let file = OpenOptions::new()
+///         .read(true)
+///         .open("foo.txt")
+///         .await?;
+///
+///     Ok(())
+/// }
+/// ```
+///
+/// Opening a file for both reading and writing, as well as creating it if it
+/// doesn't exist:
+///
+/// ```no_run
+/// use tokio::fs::OpenOptions;
+/// use std::io;
+///
+/// #[tokio::main]
+/// async fn main() -> io::Result<()> {
+///     let file = OpenOptions::new()
+///         .read(true)
+///         .write(true)
+///         .create(true)
+///         .open("foo.txt")
+///         .await?;
+///
+///     Ok(())
+/// }
+/// ```
+#[derive(Clone, Debug)]
+pub struct OpenOptions(StdOpenOptions);
+
+impl OpenOptions {
+    /// Creates a blank new set of options ready for configuration.
+    ///
+    /// All options are initially set to `false`.
+    ///
+    /// This is an async version of [`std::fs::OpenOptions::new`][std]
+    ///
+    /// [std]: std::fs::OpenOptions::new
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::OpenOptions;
+    ///
+    /// let mut options = OpenOptions::new();
+    /// let future = options.read(true).open("foo.txt");
+    /// ```
+    pub fn new() -> OpenOptions {
+        OpenOptions(StdOpenOptions::new())
+    }
+
+    /// Sets the option for read access.
+    ///
+    /// This option, when true, will indicate that the file should be
+    /// `read`-able if opened.
+    ///
+    /// This is an async version of [`std::fs::OpenOptions::read`][std]
+    ///
+    /// [std]: std::fs::OpenOptions::read
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::OpenOptions;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let file = OpenOptions::new()
+    ///         .read(true)
+    ///         .open("foo.txt")
+    ///         .await?;
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn read(&mut self, read: bool) -> &mut OpenOptions {
+        self.0.read(read);
+        self
+    }
+
+    /// Sets the option for write access.
+    ///
+    /// This option, when true, will indicate that the file should be
+    /// `write`-able if opened.
+    ///
+    /// This is an async version of [`std::fs::OpenOptions::write`][std]
+    ///
+    /// [std]: std::fs::OpenOptions::write
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::OpenOptions;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let file = OpenOptions::new()
+    ///         .write(true)
+    ///         .open("foo.txt")
+    ///         .await?;
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn write(&mut self, write: bool) -> &mut OpenOptions {
+        self.0.write(write);
+        self
+    }
+
+    /// Sets the option for the append mode.
+    ///
+    /// This option, when true, means that writes will append to a file instead
+    /// of overwriting previous contents.  Note that setting
+    /// `.write(true).append(true)` has the same effect as setting only
+    /// `.append(true)`.
+    ///
+    /// For most filesystems, the operating system guarantees that all writes are
+    /// atomic: no writes get mangled because another process writes at the same
+    /// time.
+    ///
+    /// One maybe obvious note when using append-mode: make sure that all data
+    /// that belongs together is written to the file in one operation. This
+    /// can be done by concatenating strings before passing them to [`write()`],
+    /// or using a buffered writer (with a buffer of adequate size),
+    /// and calling [`flush()`] when the message is complete.
+    ///
+    /// If a file is opened with both read and append access, beware that after
+    /// opening, and after every write, the position for reading may be set at the
+    /// end of the file. So, before writing, save the current position (using
+    /// [`seek`]`(`[`SeekFrom`]`::`[`Current`]`(0))`), and restore it before the next read.
+    ///
+    /// This is an async version of [`std::fs::OpenOptions::append`][std]
+    ///
+    /// [std]: std::fs::OpenOptions::append
+    ///
+    /// ## Note
+    ///
+    /// This function doesn't create the file if it doesn't exist. Use the [`create`]
+    /// method to do so.
+    ///
+    /// [`write()`]: crate::io::AsyncWriteExt::write
+    /// [`flush()`]: crate::io::AsyncWriteExt::flush
+    /// [`seek`]: crate::io::AsyncSeekExt::seek
+    /// [`SeekFrom`]: std::io::SeekFrom
+    /// [`Current`]: std::io::SeekFrom::Current
+    /// [`create`]: OpenOptions::create
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::OpenOptions;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let file = OpenOptions::new()
+    ///         .append(true)
+    ///         .open("foo.txt")
+    ///         .await?;
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn append(&mut self, append: bool) -> &mut OpenOptions {
+        self.0.append(append);
+        self
+    }
+
+    /// Sets the option for truncating a previous file.
+    ///
+    /// If a file is successfully opened with this option set it will truncate
+    /// the file to 0 length if it already exists.
+    ///
+    /// The file must be opened with write access for truncate to work.
+    ///
+    /// This is an async version of [`std::fs::OpenOptions::truncate`][std]
+    ///
+    /// [std]: std::fs::OpenOptions::truncate
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::OpenOptions;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let file = OpenOptions::new()
+    ///         .write(true)
+    ///         .truncate(true)
+    ///         .open("foo.txt")
+    ///         .await?;
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn truncate(&mut self, truncate: bool) -> &mut OpenOptions {
+        self.0.truncate(truncate);
+        self
+    }
+
+    /// Sets the option for creating a new file.
+    ///
+    /// This option indicates whether a new file will be created if the file
+    /// does not yet already exist.
+    ///
+    /// In order for the file to be created, [`write`] or [`append`] access must
+    /// be used.
+    ///
+    /// This is an async version of [`std::fs::OpenOptions::create`][std]
+    ///
+    /// [std]: std::fs::OpenOptions::create
+    /// [`write`]: OpenOptions::write
+    /// [`append`]: OpenOptions::append
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::OpenOptions;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let file = OpenOptions::new()
+    ///         .write(true)
+    ///         .create(true)
+    ///         .open("foo.txt")
+    ///         .await?;
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn create(&mut self, create: bool) -> &mut OpenOptions {
+        self.0.create(create);
+        self
+    }
+
+    /// Sets the option to always create a new file.
+    ///
+    /// This option indicates whether a new file will be created.  No file is
+    /// allowed to exist at the target location, also no (dangling) symlink.
+    ///
+    /// This option is useful because it is atomic. Otherwise between checking
+    /// whether a file exists and creating a new one, the file may have been
+    /// created by another process (a TOCTOU race condition / attack).
+    ///
+    /// If `.create_new(true)` is set, [`.create()`] and [`.truncate()`] are
+    /// ignored.
+    ///
+    /// The file must be opened with write or append access in order to create a
+    /// new file.
+    ///
+    /// This is an async version of [`std::fs::OpenOptions::create_new`][std]
+    ///
+    /// [std]: std::fs::OpenOptions::create_new
+    /// [`.create()`]: OpenOptions::create
+    /// [`.truncate()`]: OpenOptions::truncate
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::OpenOptions;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let file = OpenOptions::new()
+    ///         .write(true)
+    ///         .create_new(true)
+    ///         .open("foo.txt")
+    ///         .await?;
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn create_new(&mut self, create_new: bool) -> &mut OpenOptions {
+        self.0.create_new(create_new);
+        self
+    }
+
+    /// Opens a file at `path` with the options specified by `self`.
+    ///
+    /// This is an async version of [`std::fs::OpenOptions::open`][std]
+    ///
+    /// [std]: std::fs::OpenOptions::open
+    ///
+    /// # Errors
+    ///
+    /// This function will return an error under a number of different
+    /// circumstances. Some of these error conditions are listed here, together
+    /// with their [`ErrorKind`]. The mapping to [`ErrorKind`]s is not part of
+    /// the compatibility contract of the function, especially the `Other` kind
+    /// might change to more specific kinds in the future.
+    ///
+    /// * [`NotFound`]: The specified file does not exist and neither `create`
+    ///   or `create_new` is set.
+    /// * [`NotFound`]: One of the directory components of the file path does
+    ///   not exist.
+    /// * [`PermissionDenied`]: The user lacks permission to get the specified
+    ///   access rights for the file.
+    /// * [`PermissionDenied`]: The user lacks permission to open one of the
+    ///   directory components of the specified path.
+    /// * [`AlreadyExists`]: `create_new` was specified and the file already
+    ///   exists.
+    /// * [`InvalidInput`]: Invalid combinations of open options (truncate
+    ///   without write access, no access mode set, etc.).
+    /// * [`Other`]: One of the directory components of the specified file path
+    ///   was not, in fact, a directory.
+    /// * [`Other`]: Filesystem-level errors: full disk, write permission
+    ///   requested on a read-only file system, exceeded disk quota, too many
+    ///   open files, too long filename, too many symbolic links in the
+    ///   specified path (Unix-like systems only), etc.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs::OpenOptions;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let file = OpenOptions::new().open("foo.txt").await?;
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// [`ErrorKind`]: std::io::ErrorKind
+    /// [`AlreadyExists`]: std::io::ErrorKind::AlreadyExists
+    /// [`InvalidInput`]: std::io::ErrorKind::InvalidInput
+    /// [`NotFound`]: std::io::ErrorKind::NotFound
+    /// [`Other`]: std::io::ErrorKind::Other
+    /// [`PermissionDenied`]: std::io::ErrorKind::PermissionDenied
+    pub async fn open(&self, path: impl AsRef<Path>) -> io::Result<File> {
+        let path = path.as_ref().to_owned();
+        let opts = self.0.clone();
+
+        let std = asyncify(move || opts.open(path)).await?;
+        Ok(File::from_std(std))
+    }
+
+    /// Returns a mutable reference to the underlying `std::fs::OpenOptions`
+    pub(super) fn as_inner_mut(&mut self) -> &mut StdOpenOptions {
+        &mut self.0
+    }
+}
+
+feature! {
+    #![unix]
+
+    use std::os::unix::fs::OpenOptionsExt;
+
+    impl OpenOptions {
+        /// Sets the mode bits that a new file will be created with.
+        ///
+        /// If a new file is created as part of an `OpenOptions::open` call then this
+        /// specified `mode` will be used as the permission bits for the new file.
+        /// If no `mode` is set, the default of `0o666` will be used.
+        /// The operating system masks out bits with the system's `umask`, to produce
+        /// the final permissions.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::fs::OpenOptions;
+        /// use std::io;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let mut options = OpenOptions::new();
+        ///     options.mode(0o644); // Give read/write for owner and read for others.
+        ///     let file = options.open("foo.txt").await?;
+        ///
+        ///     Ok(())
+        /// }
+        /// ```
+        pub fn mode(&mut self, mode: u32) -> &mut OpenOptions {
+            self.as_inner_mut().mode(mode);
+            self
+        }
+
+        /// Passes custom flags to the `flags` argument of `open`.
+        ///
+        /// The bits that define the access mode are masked out with `O_ACCMODE`, to
+        /// ensure they do not interfere with the access mode set by Rusts options.
+        ///
+        /// Custom flags can only set flags, not remove flags set by Rusts options.
+        /// This options overwrites any previously set custom flags.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use libc;
+        /// use tokio::fs::OpenOptions;
+        /// use std::io;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let mut options = OpenOptions::new();
+        ///     options.write(true);
+        ///     if cfg!(unix) {
+        ///         options.custom_flags(libc::O_NOFOLLOW);
+        ///     }
+        ///     let file = options.open("foo.txt").await?;
+        ///
+        ///     Ok(())
+        /// }
+        /// ```
+        pub fn custom_flags(&mut self, flags: i32) -> &mut OpenOptions {
+            self.as_inner_mut().custom_flags(flags);
+            self
+        }
+    }
+}
+
+feature! {
+    #![windows]
+
+    use std::os::windows::fs::OpenOptionsExt;
+
+    impl OpenOptions {
+        /// Overrides the `dwDesiredAccess` argument to the call to [`CreateFile`]
+        /// with the specified value.
+        ///
+        /// This will override the `read`, `write`, and `append` flags on the
+        /// `OpenOptions` structure. This method provides fine-grained control over
+        /// the permissions to read, write and append data, attributes (like hidden
+        /// and system), and extended attributes.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::fs::OpenOptions;
+        ///
+        /// # #[tokio::main]
+        /// # async fn main() -> std::io::Result<()> {
+        /// // Open without read and write permission, for example if you only need
+        /// // to call `stat` on the file
+        /// let file = OpenOptions::new().access_mode(0).open("foo.txt").await?;
+        /// # Ok(())
+        /// # }
+        /// ```
+        ///
+        /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea
+        pub fn access_mode(&mut self, access: u32) -> &mut OpenOptions {
+            self.as_inner_mut().access_mode(access);
+            self
+        }
+
+        /// Overrides the `dwShareMode` argument to the call to [`CreateFile`] with
+        /// the specified value.
+        ///
+        /// By default `share_mode` is set to
+        /// `FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE`. This allows
+        /// other processes to read, write, and delete/rename the same file
+        /// while it is open. Removing any of the flags will prevent other
+        /// processes from performing the corresponding operation until the file
+        /// handle is closed.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::fs::OpenOptions;
+        ///
+        /// # #[tokio::main]
+        /// # async fn main() -> std::io::Result<()> {
+        /// // Do not allow others to read or modify this file while we have it open
+        /// // for writing.
+        /// let file = OpenOptions::new()
+        ///     .write(true)
+        ///     .share_mode(0)
+        ///     .open("foo.txt").await?;
+        /// # Ok(())
+        /// # }
+        /// ```
+        ///
+        /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea
+        pub fn share_mode(&mut self, share: u32) -> &mut OpenOptions {
+            self.as_inner_mut().share_mode(share);
+            self
+        }
+
+        /// Sets extra flags for the `dwFileFlags` argument to the call to
+        /// [`CreateFile2`] to the specified value (or combines it with
+        /// `attributes` and `security_qos_flags` to set the `dwFlagsAndAttributes`
+        /// for [`CreateFile`]).
+        ///
+        /// Custom flags can only set flags, not remove flags set by Rust's options.
+        /// This option overwrites any previously set custom flags.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use winapi::um::winbase::FILE_FLAG_DELETE_ON_CLOSE;
+        /// use tokio::fs::OpenOptions;
+        ///
+        /// # #[tokio::main]
+        /// # async fn main() -> std::io::Result<()> {
+        /// let file = OpenOptions::new()
+        ///     .create(true)
+        ///     .write(true)
+        ///     .custom_flags(FILE_FLAG_DELETE_ON_CLOSE)
+        ///     .open("foo.txt").await?;
+        /// # Ok(())
+        /// # }
+        /// ```
+        ///
+        /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea
+        /// [`CreateFile2`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfile2
+        pub fn custom_flags(&mut self, flags: u32) -> &mut OpenOptions {
+            self.as_inner_mut().custom_flags(flags);
+            self
+        }
+
+        /// Sets the `dwFileAttributes` argument to the call to [`CreateFile2`] to
+        /// the specified value (or combines it with `custom_flags` and
+        /// `security_qos_flags` to set the `dwFlagsAndAttributes` for
+        /// [`CreateFile`]).
+        ///
+        /// If a _new_ file is created because it does not yet exist and
+        /// `.create(true)` or `.create_new(true)` are specified, the new file is
+        /// given the attributes declared with `.attributes()`.
+        ///
+        /// If an _existing_ file is opened with `.create(true).truncate(true)`, its
+        /// existing attributes are preserved and combined with the ones declared
+        /// with `.attributes()`.
+        ///
+        /// In all other cases the attributes get ignored.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use winapi::um::winnt::FILE_ATTRIBUTE_HIDDEN;
+        /// use tokio::fs::OpenOptions;
+        ///
+        /// # #[tokio::main]
+        /// # async fn main() -> std::io::Result<()> {
+        /// let file = OpenOptions::new()
+        ///     .write(true)
+        ///     .create(true)
+        ///     .attributes(FILE_ATTRIBUTE_HIDDEN)
+        ///     .open("foo.txt").await?;
+        /// # Ok(())
+        /// # }
+        /// ```
+        ///
+        /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea
+        /// [`CreateFile2`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfile2
+        pub fn attributes(&mut self, attributes: u32) -> &mut OpenOptions {
+            self.as_inner_mut().attributes(attributes);
+            self
+        }
+
+        /// Sets the `dwSecurityQosFlags` argument to the call to [`CreateFile2`] to
+        /// the specified value (or combines it with `custom_flags` and `attributes`
+        /// to set the `dwFlagsAndAttributes` for [`CreateFile`]).
+        ///
+        /// By default `security_qos_flags` is not set. It should be specified when
+        /// opening a named pipe, to control to which degree a server process can
+        /// act on behalf of a client process (security impersonation level).
+        ///
+        /// When `security_qos_flags` is not set, a malicious program can gain the
+        /// elevated privileges of a privileged Rust process when it allows opening
+        /// user-specified paths, by tricking it into opening a named pipe. So
+        /// arguably `security_qos_flags` should also be set when opening arbitrary
+        /// paths. However the bits can then conflict with other flags, specifically
+        /// `FILE_FLAG_OPEN_NO_RECALL`.
+        ///
+        /// For information about possible values, see [Impersonation Levels] on the
+        /// Windows Dev Center site. The `SECURITY_SQOS_PRESENT` flag is set
+        /// automatically when using this method.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use winapi::um::winbase::SECURITY_IDENTIFICATION;
+        /// use tokio::fs::OpenOptions;
+        ///
+        /// # #[tokio::main]
+        /// # async fn main() -> std::io::Result<()> {
+        /// let file = OpenOptions::new()
+        ///     .write(true)
+        ///     .create(true)
+        ///
+        ///     // Sets the flag value to `SecurityIdentification`.
+        ///     .security_qos_flags(SECURITY_IDENTIFICATION)
+        ///
+        ///     .open(r"\\.\pipe\MyPipe").await?;
+        /// # Ok(())
+        /// # }
+        /// ```
+        ///
+        /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea
+        /// [`CreateFile2`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfile2
+        /// [Impersonation Levels]:
+        ///     https://docs.microsoft.com/en-us/windows/win32/api/winnt/ne-winnt-security_impersonation_level
+        pub fn security_qos_flags(&mut self, flags: u32) -> &mut OpenOptions {
+            self.as_inner_mut().security_qos_flags(flags);
+            self
+        }
+    }
+}
+
+impl From<StdOpenOptions> for OpenOptions {
+    fn from(options: StdOpenOptions) -> OpenOptions {
+        OpenOptions(options)
+    }
+}
+
+impl Default for OpenOptions {
+    fn default() -> Self {
+        Self::new()
+    }
+}
diff --git a/third_party/rust/tokio/src/fs/open_options/mock_open_options.rs b/third_party/rust/tokio/src/fs/open_options/mock_open_options.rs
new file mode 100644
index 0000000000..cbbda0ec25
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/open_options/mock_open_options.rs
@@ -0,0 +1,38 @@
+//! Mock version of std::fs::OpenOptions;
+use mockall::mock;
+
+use crate::fs::mocks::MockFile;
+#[cfg(unix)]
+use std::os::unix::fs::OpenOptionsExt;
+#[cfg(windows)]
+use std::os::windows::fs::OpenOptionsExt;
+use std::{io, path::Path};
+
+mock! {
+    #[derive(Debug)]
+    pub OpenOptions {
+        pub fn append(&mut self, append: bool) -> &mut Self;
+        pub fn create(&mut self, create: bool) -> &mut Self;
+        pub fn create_new(&mut self, create_new: bool) -> &mut Self;
+        pub fn open<P: AsRef<Path> + 'static>(&self, path: P) -> io::Result<MockFile>;
+        pub fn read(&mut self, read: bool) -> &mut Self;
+        pub fn truncate(&mut self, truncate: bool) -> &mut Self;
+        pub fn write(&mut self, write: bool) -> &mut Self;
+    }
+    impl Clone for OpenOptions {
+        fn clone(&self) -> Self;
+    }
+    #[cfg(unix)]
+    impl OpenOptionsExt for OpenOptions {
+        fn custom_flags(&mut self, flags: i32) -> &mut Self;
+        fn mode(&mut self, mode: u32) -> &mut Self;
+    }
+    #[cfg(windows)]
+    impl OpenOptionsExt for OpenOptions {
+        fn access_mode(&mut self, access: u32) -> &mut Self;
+        fn share_mode(&mut self, val: u32) -> &mut Self;
+        fn custom_flags(&mut self, flags: u32) -> &mut Self;
+        fn attributes(&mut self, val: u32) -> &mut Self;
+        fn security_qos_flags(&mut self, flags: u32) -> &mut Self;
+    }
+}
diff --git a/third_party/rust/tokio/src/fs/read.rs b/third_party/rust/tokio/src/fs/read.rs
new file mode 100644
index 0000000000..ada5ba391b
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/read.rs
@@ -0,0 +1,51 @@
+use crate::fs::asyncify;
+
+use std::{io, path::Path};
+
+/// Reads the entire contents of a file into a bytes vector.
+///
+/// This is an async version of [`std::fs::read`][std]
+///
+/// [std]: std::fs::read
+///
+/// This is a convenience function for using [`File::open`] and [`read_to_end`]
+/// with fewer imports and without an intermediate variable. It pre-allocates a
+/// buffer based on the file size when available, so it is generally faster than
+/// reading into a vector created with `Vec::new()`.
+///
+/// This operation is implemented by running the equivalent blocking operation
+/// on a separate thread pool using [`spawn_blocking`].
+///
+/// [`File::open`]: super::File::open
+/// [`read_to_end`]: crate::io::AsyncReadExt::read_to_end
+/// [`spawn_blocking`]: crate::task::spawn_blocking
+///
+/// # Errors
+///
+/// This function will return an error if `path` does not already exist.
+/// Other errors may also be returned according to [`OpenOptions::open`].
+///
+/// [`OpenOptions::open`]: super::OpenOptions::open
+///
+/// It will also return an error if it encounters while reading an error
+/// of a kind other than [`ErrorKind::Interrupted`].
+///
+/// [`ErrorKind::Interrupted`]: std::io::ErrorKind::Interrupted
+///
+/// # Examples
+///
+/// ```no_run
+/// use tokio::fs;
+/// use std::net::SocketAddr;
+///
+/// #[tokio::main]
+/// async fn main() -> Result<(), Box<dyn std::error::Error + 'static>> {
+///     let contents = fs::read("address.txt").await?;
+///     let foo: SocketAddr = String::from_utf8_lossy(&contents).parse()?;
+///     Ok(())
+/// }
+/// ```
+pub async fn read(path: impl AsRef<Path>) -> io::Result<Vec<u8>> {
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::read(path)).await
+}
diff --git a/third_party/rust/tokio/src/fs/read_dir.rs b/third_party/rust/tokio/src/fs/read_dir.rs
new file mode 100644
index 0000000000..281ea4cd75
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/read_dir.rs
@@ -0,0 +1,295 @@
+use crate::fs::asyncify;
+
+use std::ffi::OsString;
+use std::fs::{FileType, Metadata};
+use std::future::Future;
+use std::io;
+use std::path::{Path, PathBuf};
+use std::pin::Pin;
+use std::sync::Arc;
+use std::task::Context;
+use std::task::Poll;
+
+#[cfg(test)]
+use super::mocks::spawn_blocking;
+#[cfg(test)]
+use super::mocks::JoinHandle;
+#[cfg(not(test))]
+use crate::blocking::spawn_blocking;
+#[cfg(not(test))]
+use crate::blocking::JoinHandle;
+
+/// Returns a stream over the entries within a directory.
+///
+/// This is an async version of [`std::fs::read_dir`](std::fs::read_dir)
+///
+/// This operation is implemented by running the equivalent blocking
+/// operation on a separate thread pool using [`spawn_blocking`].
+///
+/// [`spawn_blocking`]: crate::task::spawn_blocking
+pub async fn read_dir(path: impl AsRef<Path>) -> io::Result<ReadDir> {
+    let path = path.as_ref().to_owned();
+    let std = asyncify(|| std::fs::read_dir(path)).await?;
+
+    Ok(ReadDir(State::Idle(Some(std))))
+}
+
+/// Reads the the entries in a directory.
+///
+/// This struct is returned from the [`read_dir`] function of this module and
+/// will yield instances of [`DirEntry`]. Through a [`DirEntry`] information
+/// like the entry's path and possibly other metadata can be learned.
+///
+/// A `ReadDir` can be turned into a `Stream` with [`ReadDirStream`].
+///
+/// [`ReadDirStream`]: https://docs.rs/tokio-stream/0.1/tokio_stream/wrappers/struct.ReadDirStream.html
+///
+/// # Errors
+///
+/// This stream will return an [`Err`] if there's some sort of intermittent
+/// IO error during iteration.
+///
+/// [`read_dir`]: read_dir
+/// [`DirEntry`]: DirEntry
+/// [`Err`]: std::result::Result::Err
+#[derive(Debug)]
+#[must_use = "streams do nothing unless polled"]
+pub struct ReadDir(State);
+
+#[derive(Debug)]
+enum State {
+    Idle(Option<std::fs::ReadDir>),
+    Pending(JoinHandle<(Option<io::Result<std::fs::DirEntry>>, std::fs::ReadDir)>),
+}
+
+impl ReadDir {
+    /// Returns the next entry in the directory stream.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancellation safe.
+    pub async fn next_entry(&mut self) -> io::Result<Option<DirEntry>> {
+        use crate::future::poll_fn;
+        poll_fn(|cx| self.poll_next_entry(cx)).await
+    }
+
+    /// Polls for the next directory entry in the stream.
+    ///
+    /// This method returns:
+    ///
+    ///  * `Poll::Pending` if the next directory entry is not yet available.
+    ///  * `Poll::Ready(Ok(Some(entry)))` if the next directory entry is available.
+    ///  * `Poll::Ready(Ok(None))` if there are no more directory entries in this
+    ///    stream.
+    ///  * `Poll::Ready(Err(err))` if an IO error occurred while reading the next
+    ///    directory entry.
+    ///
+    /// When the method returns `Poll::Pending`, the `Waker` in the provided
+    /// `Context` is scheduled to receive a wakeup when the next directory entry
+    /// becomes available on the underlying IO resource.
+    ///
+    /// Note that on multiple calls to `poll_next_entry`, only the `Waker` from
+    /// the `Context` passed to the most recent call is scheduled to receive a
+    /// wakeup.
+    pub fn poll_next_entry(&mut self, cx: &mut Context<'_>) -> Poll<io::Result<Option<DirEntry>>> {
+        loop {
+            match self.0 {
+                State::Idle(ref mut std) => {
+                    let mut std = std.take().unwrap();
+
+                    self.0 = State::Pending(spawn_blocking(move || {
+                        let ret = std.next();
+                        (ret, std)
+                    }));
+                }
+                State::Pending(ref mut rx) => {
+                    let (ret, std) = ready!(Pin::new(rx).poll(cx))?;
+                    self.0 = State::Idle(Some(std));
+
+                    let ret = match ret {
+                        Some(Ok(std)) => Ok(Some(DirEntry(Arc::new(std)))),
+                        Some(Err(e)) => Err(e),
+                        None => Ok(None),
+                    };
+
+                    return Poll::Ready(ret);
+                }
+            }
+        }
+    }
+}
+
+feature! {
+    #![unix]
+
+    use std::os::unix::fs::DirEntryExt;
+
+    impl DirEntry {
+        /// Returns the underlying `d_ino` field in the contained `dirent`
+        /// structure.
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// use tokio::fs;
+        ///
+        /// # #[tokio::main]
+        /// # async fn main() -> std::io::Result<()> {
+        /// let mut entries = fs::read_dir(".").await?;
+        /// while let Some(entry) = entries.next_entry().await? {
+        ///     // Here, `entry` is a `DirEntry`.
+        ///     println!("{:?}: {}", entry.file_name(), entry.ino());
+        /// }
+        /// # Ok(())
+        /// # }
+        /// ```
+        pub fn ino(&self) -> u64 {
+            self.as_inner().ino()
+        }
+    }
+}
+
+/// Entries returned by the [`ReadDir`] stream.
+///
+/// [`ReadDir`]: struct@ReadDir
+///
+/// This is a specialized version of [`std::fs::DirEntry`] for usage from the
+/// Tokio runtime.
+///
+/// An instance of `DirEntry` represents an entry inside of a directory on the
+/// filesystem. Each entry can be inspected via methods to learn about the full
+/// path or possibly other metadata through per-platform extension traits.
+#[derive(Debug)]
+pub struct DirEntry(Arc<std::fs::DirEntry>);
+
+impl DirEntry {
+    /// Returns the full path to the file that this entry represents.
+    ///
+    /// The full path is created by joining the original path to `read_dir`
+    /// with the filename of this entry.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::fs;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let mut entries = fs::read_dir(".").await?;
+    ///
+    /// while let Some(entry) = entries.next_entry().await? {
+    ///     println!("{:?}", entry.path());
+    /// }
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// This prints output like:
+    ///
+    /// ```text
+    /// "./whatever.txt"
+    /// "./foo.html"
+    /// "./hello_world.rs"
+    /// ```
+    ///
+    /// The exact text, of course, depends on what files you have in `.`.
+    pub fn path(&self) -> PathBuf {
+        self.0.path()
+    }
+
+    /// Returns the bare file name of this directory entry without any other
+    /// leading path component.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::fs;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let mut entries = fs::read_dir(".").await?;
+    ///
+    /// while let Some(entry) = entries.next_entry().await? {
+    ///     println!("{:?}", entry.file_name());
+    /// }
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn file_name(&self) -> OsString {
+        self.0.file_name()
+    }
+
+    /// Returns the metadata for the file that this entry points at.
+    ///
+    /// This function will not traverse symlinks if this entry points at a
+    /// symlink.
+    ///
+    /// # Platform-specific behavior
+    ///
+    /// On Windows this function is cheap to call (no extra system calls
+    /// needed), but on Unix platforms this function is the equivalent of
+    /// calling `symlink_metadata` on the path.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::fs;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let mut entries = fs::read_dir(".").await?;
+    ///
+    /// while let Some(entry) = entries.next_entry().await? {
+    ///     if let Ok(metadata) = entry.metadata().await {
+    ///         // Now let's show our entry's permissions!
+    ///         println!("{:?}: {:?}", entry.path(), metadata.permissions());
+    ///     } else {
+    ///         println!("Couldn't get file type for {:?}", entry.path());
+    ///     }
+    /// }
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn metadata(&self) -> io::Result<Metadata> {
+        let std = self.0.clone();
+        asyncify(move || std.metadata()).await
+    }
+
+    /// Returns the file type for the file that this entry points at.
+    ///
+    /// This function will not traverse symlinks if this entry points at a
+    /// symlink.
+    ///
+    /// # Platform-specific behavior
+    ///
+    /// On Windows and most Unix platforms this function is free (no extra
+    /// system calls needed), but some Unix platforms may require the equivalent
+    /// call to `symlink_metadata` to learn about the target file type.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::fs;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let mut entries = fs::read_dir(".").await?;
+    ///
+    /// while let Some(entry) = entries.next_entry().await? {
+    ///     if let Ok(file_type) = entry.file_type().await {
+    ///         // Now let's show our entry's file type!
+    ///         println!("{:?}: {:?}", entry.path(), file_type);
+    ///     } else {
+    ///         println!("Couldn't get file type for {:?}", entry.path());
+    ///     }
+    /// }
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn file_type(&self) -> io::Result<FileType> {
+        let std = self.0.clone();
+        asyncify(move || std.file_type()).await
+    }
+
+    /// Returns a reference to the underlying `std::fs::DirEntry`.
+    #[cfg(unix)]
+    pub(super) fn as_inner(&self) -> &std::fs::DirEntry {
+        &self.0
+    }
+}
diff --git a/third_party/rust/tokio/src/fs/read_link.rs b/third_party/rust/tokio/src/fs/read_link.rs
new file mode 100644
index 0000000000..6c48c5e156
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/read_link.rs
@@ -0,0 +1,14 @@
+use crate::fs::asyncify;
+
+use std::io;
+use std::path::{Path, PathBuf};
+
+/// Reads a symbolic link, returning the file that the link points to.
+///
+/// This is an async version of [`std::fs::read_link`][std]
+///
+/// [std]: std::fs::read_link
+pub async fn read_link(path: impl AsRef<Path>) -> io::Result<PathBuf> {
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::read_link(path)).await
+}
diff --git a/third_party/rust/tokio/src/fs/read_to_string.rs b/third_party/rust/tokio/src/fs/read_to_string.rs
new file mode 100644
index 0000000000..26228d98c2
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/read_to_string.rs
@@ -0,0 +1,30 @@
+use crate::fs::asyncify;
+
+use std::{io, path::Path};
+
+/// Creates a future which will open a file for reading and read the entire
+/// contents into a string and return said string.
+///
+/// This is the async equivalent of [`std::fs::read_to_string`][std].
+///
+/// This operation is implemented by running the equivalent blocking operation
+/// on a separate thread pool using [`spawn_blocking`].
+///
+/// [`spawn_blocking`]: crate::task::spawn_blocking
+/// [std]: fn@std::fs::read_to_string
+///
+/// # Examples
+///
+/// ```no_run
+/// use tokio::fs;
+///
+/// # async fn dox() -> std::io::Result<()> {
+/// let contents = fs::read_to_string("foo.txt").await?;
+/// println!("foo.txt contains {} bytes", contents.len());
+/// # Ok(())
+/// # }
+/// ```
+pub async fn read_to_string(path: impl AsRef<Path>) -> io::Result<String> {
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::read_to_string(path)).await
+}
diff --git a/third_party/rust/tokio/src/fs/remove_dir.rs b/third_party/rust/tokio/src/fs/remove_dir.rs
new file mode 100644
index 0000000000..6e7cbd08f6
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/remove_dir.rs
@@ -0,0 +1,12 @@
+use crate::fs::asyncify;
+
+use std::io;
+use std::path::Path;
+
+/// Removes an existing, empty directory.
+///
+/// This is an async version of [`std::fs::remove_dir`](std::fs::remove_dir)
+pub async fn remove_dir(path: impl AsRef<Path>) -> io::Result<()> {
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::remove_dir(path)).await
+}
diff --git a/third_party/rust/tokio/src/fs/remove_dir_all.rs b/third_party/rust/tokio/src/fs/remove_dir_all.rs
new file mode 100644
index 0000000000..0a237550f9
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/remove_dir_all.rs
@@ -0,0 +1,14 @@
+use crate::fs::asyncify;
+
+use std::io;
+use std::path::Path;
+
+/// Removes a directory at this path, after removing all its contents. Use carefully!
+///
+/// This is an async version of [`std::fs::remove_dir_all`][std]
+///
+/// [std]: fn@std::fs::remove_dir_all
+pub async fn remove_dir_all(path: impl AsRef<Path>) -> io::Result<()> {
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::remove_dir_all(path)).await
+}
diff --git a/third_party/rust/tokio/src/fs/remove_file.rs b/third_party/rust/tokio/src/fs/remove_file.rs
new file mode 100644
index 0000000000..d22a5bfc88
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/remove_file.rs
@@ -0,0 +1,18 @@
+use crate::fs::asyncify;
+
+use std::io;
+use std::path::Path;
+
+/// Removes a file from the filesystem.
+///
+/// Note that there is no guarantee that the file is immediately deleted (e.g.
+/// depending on platform, other open file descriptors may prevent immediate
+/// removal).
+///
+/// This is an async version of [`std::fs::remove_file`][std]
+///
+/// [std]: std::fs::remove_file
+pub async fn remove_file(path: impl AsRef<Path>) -> io::Result<()> {
+    let path = path.as_ref().to_owned();
+    asyncify(move || std::fs::remove_file(path)).await
+}
diff --git a/third_party/rust/tokio/src/fs/rename.rs b/third_party/rust/tokio/src/fs/rename.rs
new file mode 100644
index 0000000000..4f980821d2
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/rename.rs
@@ -0,0 +1,17 @@
+use crate::fs::asyncify;
+
+use std::io;
+use std::path::Path;
+
+/// Renames a file or directory to a new name, replacing the original file if
+/// `to` already exists.
+///
+/// This will not work if the new name is on a different mount point.
+///
+/// This is an async version of [`std::fs::rename`](std::fs::rename)
+pub async fn rename(from: impl AsRef<Path>, to: impl AsRef<Path>) -> io::Result<()> {
+    let from = from.as_ref().to_owned();
+    let to = to.as_ref().to_owned();
+
+    asyncify(move || std::fs::rename(from, to)).await
+}
diff --git a/third_party/rust/tokio/src/fs/set_permissions.rs b/third_party/rust/tokio/src/fs/set_permissions.rs
new file mode 100644
index 0000000000..09be02ea01
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/set_permissions.rs
@@ -0,0 +1,15 @@
+use crate::fs::asyncify;
+
+use std::fs::Permissions;
+use std::io;
+use std::path::Path;
+
+/// Changes the permissions found on a file or a directory.
+///
+/// This is an async version of [`std::fs::set_permissions`][std]
+///
+/// [std]: fn@std::fs::set_permissions
+pub async fn set_permissions(path: impl AsRef<Path>, perm: Permissions) -> io::Result<()> {
+    let path = path.as_ref().to_owned();
+    asyncify(|| std::fs::set_permissions(path, perm)).await
+}
diff --git a/third_party/rust/tokio/src/fs/symlink.rs b/third_party/rust/tokio/src/fs/symlink.rs
new file mode 100644
index 0000000000..22ece7250f
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/symlink.rs
@@ -0,0 +1,18 @@
+use crate::fs::asyncify;
+
+use std::io;
+use std::path::Path;
+
+/// Creates a new symbolic link on the filesystem.
+///
+/// The `dst` path will be a symbolic link pointing to the `src` path.
+///
+/// This is an async version of [`std::os::unix::fs::symlink`][std]
+///
+/// [std]: std::os::unix::fs::symlink
+pub async fn symlink(src: impl AsRef<Path>, dst: impl AsRef<Path>) -> io::Result<()> {
+    let src = src.as_ref().to_owned();
+    let dst = dst.as_ref().to_owned();
+
+    asyncify(move || std::os::unix::fs::symlink(src, dst)).await
+}
diff --git a/third_party/rust/tokio/src/fs/symlink_dir.rs b/third_party/rust/tokio/src/fs/symlink_dir.rs
new file mode 100644
index 0000000000..736e762b48
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/symlink_dir.rs
@@ -0,0 +1,19 @@
+use crate::fs::asyncify;
+
+use std::io;
+use std::path::Path;
+
+/// Creates a new directory symlink on the filesystem.
+///
+/// The `dst` path will be a directory symbolic link pointing to the `src`
+/// path.
+///
+/// This is an async version of [`std::os::windows::fs::symlink_dir`][std]
+///
+/// [std]: std::os::windows::fs::symlink_dir
+pub async fn symlink_dir(src: impl AsRef<Path>, dst: impl AsRef<Path>) -> io::Result<()> {
+    let src = src.as_ref().to_owned();
+    let dst = dst.as_ref().to_owned();
+
+    asyncify(move || std::os::windows::fs::symlink_dir(src, dst)).await
+}
diff --git a/third_party/rust/tokio/src/fs/symlink_file.rs b/third_party/rust/tokio/src/fs/symlink_file.rs
new file mode 100644
index 0000000000..07d8e60419
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/symlink_file.rs
@@ -0,0 +1,19 @@
+use crate::fs::asyncify;
+
+use std::io;
+use std::path::Path;
+
+/// Creates a new file symbolic link on the filesystem.
+///
+/// The `dst` path will be a file symbolic link pointing to the `src`
+/// path.
+///
+/// This is an async version of [`std::os::windows::fs::symlink_file`][std]
+///
+/// [std]: std::os::windows::fs::symlink_file
+pub async fn symlink_file(src: impl AsRef<Path>, dst: impl AsRef<Path>) -> io::Result<()> {
+    let src = src.as_ref().to_owned();
+    let dst = dst.as_ref().to_owned();
+
+    asyncify(move || std::os::windows::fs::symlink_file(src, dst)).await
+}
diff --git a/third_party/rust/tokio/src/fs/symlink_metadata.rs b/third_party/rust/tokio/src/fs/symlink_metadata.rs
new file mode 100644
index 0000000000..1d0df12576
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/symlink_metadata.rs
@@ -0,0 +1,15 @@
+use crate::fs::asyncify;
+
+use std::fs::Metadata;
+use std::io;
+use std::path::Path;
+
+/// Queries the file system metadata for a path.
+///
+/// This is an async version of [`std::fs::symlink_metadata`][std]
+///
+/// [std]: fn@std::fs::symlink_metadata
+pub async fn symlink_metadata(path: impl AsRef<Path>) -> io::Result<Metadata> {
+    let path = path.as_ref().to_owned();
+    asyncify(|| std::fs::symlink_metadata(path)).await
+}
diff --git a/third_party/rust/tokio/src/fs/write.rs b/third_party/rust/tokio/src/fs/write.rs
new file mode 100644
index 0000000000..28606fb363
--- /dev/null
+++ b/third_party/rust/tokio/src/fs/write.rs
@@ -0,0 +1,31 @@
+use crate::fs::asyncify;
+
+use std::{io, path::Path};
+
+/// Creates a future that will open a file for writing and write the entire
+/// contents of `contents` to it.
+///
+/// This is the async equivalent of [`std::fs::write`][std].
+///
+/// This operation is implemented by running the equivalent blocking operation
+/// on a separate thread pool using [`spawn_blocking`].
+///
+/// [`spawn_blocking`]: crate::task::spawn_blocking
+/// [std]: fn@std::fs::write
+///
+/// # Examples
+///
+/// ```no_run
+/// use tokio::fs;
+///
+/// # async fn dox() -> std::io::Result<()> {
+/// fs::write("foo.txt", b"Hello world!").await?;
+/// # Ok(())
+/// # }
+/// ```
+pub async fn write(path: impl AsRef<Path>, contents: impl AsRef<[u8]>) -> io::Result<()> {
+    let path = path.as_ref().to_owned();
+    let contents = contents.as_ref().to_owned();
+
+    asyncify(move || std::fs::write(path, contents)).await
+}
diff --git a/third_party/rust/tokio/src/future/block_on.rs b/third_party/rust/tokio/src/future/block_on.rs
new file mode 100644
index 0000000000..91f9cc0055
--- /dev/null
+++ b/third_party/rust/tokio/src/future/block_on.rs
@@ -0,0 +1,15 @@
+use std::future::Future;
+
+cfg_rt! {
+    pub(crate) fn block_on<F: Future>(f: F) -> F::Output {
+        let mut e = crate::runtime::enter::enter(false);
+        e.block_on(f).unwrap()
+    }
+}
+
+cfg_not_rt! {
+    pub(crate) fn block_on<F: Future>(f: F) -> F::Output {
+        let mut park = crate::park::thread::CachedParkThread::new();
+        park.block_on(f).unwrap()
+    }
+}
diff --git a/third_party/rust/tokio/src/future/maybe_done.rs b/third_party/rust/tokio/src/future/maybe_done.rs
new file mode 100644
index 0000000000..486efbe01a
--- /dev/null
+++ b/third_party/rust/tokio/src/future/maybe_done.rs
@@ -0,0 +1,76 @@
+//! Definition of the MaybeDone combinator.
+
+use std::future::Future;
+use std::mem;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+/// A future that may have completed.
+#[derive(Debug)]
+pub enum MaybeDone<Fut: Future> {
+    /// A not-yet-completed future.
+    Future(Fut),
+    /// The output of the completed future.
+    Done(Fut::Output),
+    /// The empty variant after the result of a [`MaybeDone`] has been
+    /// taken using the [`take_output`](MaybeDone::take_output) method.
+    Gone,
+}
+
+// Safe because we never generate `Pin<&mut Fut::Output>`
+impl<Fut: Future + Unpin> Unpin for MaybeDone<Fut> {}
+
+/// Wraps a future into a `MaybeDone`.
+pub fn maybe_done<Fut: Future>(future: Fut) -> MaybeDone<Fut> {
+    MaybeDone::Future(future)
+}
+
+impl<Fut: Future> MaybeDone<Fut> {
+    /// Returns an [`Option`] containing a mutable reference to the output of the future.
+    /// The output of this method will be [`Some`] if and only if the inner
+    /// future has been completed and [`take_output`](MaybeDone::take_output)
+    /// has not yet been called.
+    pub fn output_mut(self: Pin<&mut Self>) -> Option<&mut Fut::Output> {
+        unsafe {
+            let this = self.get_unchecked_mut();
+            match this {
+                MaybeDone::Done(res) => Some(res),
+                _ => None,
+            }
+        }
+    }
+
+    /// Attempts to take the output of a `MaybeDone` without driving it
+    /// towards completion.
+    #[inline]
+    pub fn take_output(self: Pin<&mut Self>) -> Option<Fut::Output> {
+        unsafe {
+            let this = self.get_unchecked_mut();
+            match this {
+                MaybeDone::Done(_) => {}
+                MaybeDone::Future(_) | MaybeDone::Gone => return None,
+            };
+            if let MaybeDone::Done(output) = mem::replace(this, MaybeDone::Gone) {
+                Some(output)
+            } else {
+                unreachable!()
+            }
+        }
+    }
+}
+
+impl<Fut: Future> Future for MaybeDone<Fut> {
+    type Output = ();
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let res = unsafe {
+            match self.as_mut().get_unchecked_mut() {
+                MaybeDone::Future(a) => ready!(Pin::new_unchecked(a).poll(cx)),
+                MaybeDone::Done(_) => return Poll::Ready(()),
+                MaybeDone::Gone => panic!("MaybeDone polled after value taken"),
+            }
+        };
+        self.set(MaybeDone::Done(res));
+        Poll::Ready(())
+    }
+}
diff --git a/third_party/rust/tokio/src/future/mod.rs b/third_party/rust/tokio/src/future/mod.rs
new file mode 100644
index 0000000000..084ddc571f
--- /dev/null
+++ b/third_party/rust/tokio/src/future/mod.rs
@@ -0,0 +1,30 @@
+#![cfg_attr(not(feature = "macros"), allow(unreachable_pub))]
+
+//! Asynchronous values.
+
+#[cfg(any(feature = "macros", feature = "process"))]
+pub(crate) mod maybe_done;
+
+mod poll_fn;
+pub use poll_fn::poll_fn;
+
+cfg_process! {
+    mod try_join;
+    pub(crate) use try_join::try_join3;
+}
+
+cfg_sync! {
+    mod block_on;
+    pub(crate) use block_on::block_on;
+}
+
+cfg_trace! {
+    mod trace;
+    pub(crate) use trace::InstrumentedFuture as Future;
+}
+
+cfg_not_trace! {
+    cfg_rt! {
+        pub(crate) use std::future::Future;
+    }
+}
diff --git a/third_party/rust/tokio/src/future/poll_fn.rs b/third_party/rust/tokio/src/future/poll_fn.rs
new file mode 100644
index 0000000000..d82ce8961d
--- /dev/null
+++ b/third_party/rust/tokio/src/future/poll_fn.rs
@@ -0,0 +1,40 @@
+#![allow(dead_code)]
+
+//! Definition of the `PollFn` adapter combinator.
+
+use std::fmt;
+use std::future::Future;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+/// Future for the [`poll_fn`] function.
+pub struct PollFn<F> {
+    f: F,
+}
+
+impl<F> Unpin for PollFn<F> {}
+
+/// Creates a new future wrapping around a function returning [`Poll`].
+pub fn poll_fn<T, F>(f: F) -> PollFn<F>
+where
+    F: FnMut(&mut Context<'_>) -> Poll<T>,
+{
+    PollFn { f }
+}
+
+impl<F> fmt::Debug for PollFn<F> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("PollFn").finish()
+    }
+}
+
+impl<T, F> Future for PollFn<F>
+where
+    F: FnMut(&mut Context<'_>) -> Poll<T>,
+{
+    type Output = T;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
+        (&mut self.f)(cx)
+    }
+}
diff --git a/third_party/rust/tokio/src/future/trace.rs b/third_party/rust/tokio/src/future/trace.rs
new file mode 100644
index 0000000000..28789a604d
--- /dev/null
+++ b/third_party/rust/tokio/src/future/trace.rs
@@ -0,0 +1,11 @@
+use std::future::Future;
+
+pub(crate) trait InstrumentedFuture: Future {
+    fn id(&self) -> Option<tracing::Id>;
+}
+
+impl<F: Future> InstrumentedFuture for tracing::instrument::Instrumented<F> {
+    fn id(&self) -> Option<tracing::Id> {
+        self.span().id()
+    }
+}
diff --git a/third_party/rust/tokio/src/future/try_join.rs b/third_party/rust/tokio/src/future/try_join.rs
new file mode 100644
index 0000000000..8943f61a1e
--- /dev/null
+++ b/third_party/rust/tokio/src/future/try_join.rs
@@ -0,0 +1,82 @@
+use crate::future::maybe_done::{maybe_done, MaybeDone};
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pub(crate) fn try_join3<T1, F1, T2, F2, T3, F3, E>(
+    future1: F1,
+    future2: F2,
+    future3: F3,
+) -> TryJoin3<F1, F2, F3>
+where
+    F1: Future<Output = Result<T1, E>>,
+    F2: Future<Output = Result<T2, E>>,
+    F3: Future<Output = Result<T3, E>>,
+{
+    TryJoin3 {
+        future1: maybe_done(future1),
+        future2: maybe_done(future2),
+        future3: maybe_done(future3),
+    }
+}
+
+pin_project! {
+    pub(crate) struct TryJoin3<F1, F2, F3>
+    where
+        F1: Future,
+        F2: Future,
+        F3: Future,
+    {
+        #[pin]
+        future1: MaybeDone<F1>,
+        #[pin]
+        future2: MaybeDone<F2>,
+        #[pin]
+        future3: MaybeDone<F3>,
+    }
+}
+
+impl<T1, F1, T2, F2, T3, F3, E> Future for TryJoin3<F1, F2, F3>
+where
+    F1: Future<Output = Result<T1, E>>,
+    F2: Future<Output = Result<T2, E>>,
+    F3: Future<Output = Result<T3, E>>,
+{
+    type Output = Result<(T1, T2, T3), E>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut all_done = true;
+
+        let mut me = self.project();
+
+        if me.future1.as_mut().poll(cx).is_pending() {
+            all_done = false;
+        } else if me.future1.as_mut().output_mut().unwrap().is_err() {
+            return Poll::Ready(Err(me.future1.take_output().unwrap().err().unwrap()));
+        }
+
+        if me.future2.as_mut().poll(cx).is_pending() {
+            all_done = false;
+        } else if me.future2.as_mut().output_mut().unwrap().is_err() {
+            return Poll::Ready(Err(me.future2.take_output().unwrap().err().unwrap()));
+        }
+
+        if me.future3.as_mut().poll(cx).is_pending() {
+            all_done = false;
+        } else if me.future3.as_mut().output_mut().unwrap().is_err() {
+            return Poll::Ready(Err(me.future3.take_output().unwrap().err().unwrap()));
+        }
+
+        if all_done {
+            Poll::Ready(Ok((
+                me.future1.take_output().unwrap().ok().unwrap(),
+                me.future2.take_output().unwrap().ok().unwrap(),
+                me.future3.take_output().unwrap().ok().unwrap(),
+            )))
+        } else {
+            Poll::Pending
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/io/async_buf_read.rs b/third_party/rust/tokio/src/io/async_buf_read.rs
new file mode 100644
index 0000000000..ecaafba4c2
--- /dev/null
+++ b/third_party/rust/tokio/src/io/async_buf_read.rs
@@ -0,0 +1,117 @@
+use crate::io::AsyncRead;
+
+use std::io;
+use std::ops::DerefMut;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+/// Reads bytes asynchronously.
+///
+/// This trait is analogous to [`std::io::BufRead`], but integrates with
+/// the asynchronous task system. In particular, the [`poll_fill_buf`] method,
+/// unlike [`BufRead::fill_buf`], will automatically queue the current task for wakeup
+/// and return if data is not yet available, rather than blocking the calling
+/// thread.
+///
+/// Utilities for working with `AsyncBufRead` values are provided by
+/// [`AsyncBufReadExt`].
+///
+/// [`std::io::BufRead`]: std::io::BufRead
+/// [`poll_fill_buf`]: AsyncBufRead::poll_fill_buf
+/// [`BufRead::fill_buf`]: std::io::BufRead::fill_buf
+/// [`AsyncBufReadExt`]: crate::io::AsyncBufReadExt
+pub trait AsyncBufRead: AsyncRead {
+    /// Attempts to return the contents of the internal buffer, filling it with more data
+    /// from the inner reader if it is empty.
+    ///
+    /// On success, returns `Poll::Ready(Ok(buf))`.
+    ///
+    /// If no data is available for reading, the method returns
+    /// `Poll::Pending` and arranges for the current task (via
+    /// `cx.waker().wake_by_ref()`) to receive a notification when the object becomes
+    /// readable or is closed.
+    ///
+    /// This function is a lower-level call. It needs to be paired with the
+    /// [`consume`] method to function properly. When calling this
+    /// method, none of the contents will be "read" in the sense that later
+    /// calling [`poll_read`] may return the same contents. As such, [`consume`] must
+    /// be called with the number of bytes that are consumed from this buffer to
+    /// ensure that the bytes are never returned twice.
+    ///
+    /// An empty buffer returned indicates that the stream has reached EOF.
+    ///
+    /// [`poll_read`]: AsyncRead::poll_read
+    /// [`consume`]: AsyncBufRead::consume
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>>;
+
+    /// Tells this buffer that `amt` bytes have been consumed from the buffer,
+    /// so they should no longer be returned in calls to [`poll_read`].
+    ///
+    /// This function is a lower-level call. It needs to be paired with the
+    /// [`poll_fill_buf`] method to function properly. This function does
+    /// not perform any I/O, it simply informs this object that some amount of
+    /// its buffer, returned from [`poll_fill_buf`], has been consumed and should
+    /// no longer be returned. As such, this function may do odd things if
+    /// [`poll_fill_buf`] isn't called before calling it.
+    ///
+    /// The `amt` must be `<=` the number of bytes in the buffer returned by
+    /// [`poll_fill_buf`].
+    ///
+    /// [`poll_read`]: AsyncRead::poll_read
+    /// [`poll_fill_buf`]: AsyncBufRead::poll_fill_buf
+    fn consume(self: Pin<&mut Self>, amt: usize);
+}
+
+macro_rules! deref_async_buf_read {
+    () => {
+        fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+            Pin::new(&mut **self.get_mut()).poll_fill_buf(cx)
+        }
+
+        fn consume(mut self: Pin<&mut Self>, amt: usize) {
+            Pin::new(&mut **self).consume(amt)
+        }
+    };
+}
+
+impl<T: ?Sized + AsyncBufRead + Unpin> AsyncBufRead for Box<T> {
+    deref_async_buf_read!();
+}
+
+impl<T: ?Sized + AsyncBufRead + Unpin> AsyncBufRead for &mut T {
+    deref_async_buf_read!();
+}
+
+impl<P> AsyncBufRead for Pin<P>
+where
+    P: DerefMut + Unpin,
+    P::Target: AsyncBufRead,
+{
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        self.get_mut().as_mut().poll_fill_buf(cx)
+    }
+
+    fn consume(self: Pin<&mut Self>, amt: usize) {
+        self.get_mut().as_mut().consume(amt)
+    }
+}
+
+impl AsyncBufRead for &[u8] {
+    fn poll_fill_buf(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        Poll::Ready(Ok(*self))
+    }
+
+    fn consume(mut self: Pin<&mut Self>, amt: usize) {
+        *self = &self[amt..];
+    }
+}
+
+impl<T: AsRef<[u8]> + Unpin> AsyncBufRead for io::Cursor<T> {
+    fn poll_fill_buf(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        Poll::Ready(io::BufRead::fill_buf(self.get_mut()))
+    }
+
+    fn consume(self: Pin<&mut Self>, amt: usize) {
+        io::BufRead::consume(self.get_mut(), amt)
+    }
+}
diff --git a/third_party/rust/tokio/src/io/async_fd.rs b/third_party/rust/tokio/src/io/async_fd.rs
new file mode 100644
index 0000000000..93f9cb458a
--- /dev/null
+++ b/third_party/rust/tokio/src/io/async_fd.rs
@@ -0,0 +1,660 @@
+use crate::io::driver::{Handle, Interest, ReadyEvent, Registration};
+
+use mio::unix::SourceFd;
+use std::io;
+use std::os::unix::io::{AsRawFd, RawFd};
+use std::{task::Context, task::Poll};
+
+/// Associates an IO object backed by a Unix file descriptor with the tokio
+/// reactor, allowing for readiness to be polled. The file descriptor must be of
+/// a type that can be used with the OS polling facilities (ie, `poll`, `epoll`,
+/// `kqueue`, etc), such as a network socket or pipe, and the file descriptor
+/// must have the nonblocking mode set to true.
+///
+/// Creating an AsyncFd registers the file descriptor with the current tokio
+/// Reactor, allowing you to directly await the file descriptor being readable
+/// or writable. Once registered, the file descriptor remains registered until
+/// the AsyncFd is dropped.
+///
+/// The AsyncFd takes ownership of an arbitrary object to represent the IO
+/// object. It is intended that this object will handle closing the file
+/// descriptor when it is dropped, avoiding resource leaks and ensuring that the
+/// AsyncFd can clean up the registration before closing the file descriptor.
+/// The [`AsyncFd::into_inner`] function can be used to extract the inner object
+/// to retake control from the tokio IO reactor.
+///
+/// The inner object is required to implement [`AsRawFd`]. This file descriptor
+/// must not change while [`AsyncFd`] owns the inner object, i.e. the
+/// [`AsRawFd::as_raw_fd`] method on the inner type must always return the same
+/// file descriptor when called multiple times. Failure to uphold this results
+/// in unspecified behavior in the IO driver, which may include breaking
+/// notifications for other sockets/etc.
+///
+/// Polling for readiness is done by calling the async functions [`readable`]
+/// and [`writable`]. These functions complete when the associated readiness
+/// condition is observed. Any number of tasks can query the same `AsyncFd` in
+/// parallel, on the same or different conditions.
+///
+/// On some platforms, the readiness detecting mechanism relies on
+/// edge-triggered notifications. This means that the OS will only notify Tokio
+/// when the file descriptor transitions from not-ready to ready. For this to
+/// work you should first try to read or write and only poll for readiness
+/// if that fails with an error of [`std::io::ErrorKind::WouldBlock`].
+///
+/// Tokio internally tracks when it has received a ready notification, and when
+/// readiness checking functions like [`readable`] and [`writable`] are called,
+/// if the readiness flag is set, these async functions will complete
+/// immediately. This however does mean that it is critical to ensure that this
+/// ready flag is cleared when (and only when) the file descriptor ceases to be
+/// ready. The [`AsyncFdReadyGuard`] returned from readiness checking functions
+/// serves this function; after calling a readiness-checking async function,
+/// you must use this [`AsyncFdReadyGuard`] to signal to tokio whether the file
+/// descriptor is no longer in a ready state.
+///
+/// ## Use with to a poll-based API
+///
+/// In some cases it may be desirable to use `AsyncFd` from APIs similar to
+/// [`TcpStream::poll_read_ready`]. The [`AsyncFd::poll_read_ready`] and
+/// [`AsyncFd::poll_write_ready`] functions are provided for this purpose.
+/// Because these functions don't create a future to hold their state, they have
+/// the limitation that only one task can wait on each direction (read or write)
+/// at a time.
+///
+/// # Examples
+///
+/// This example shows how to turn [`std::net::TcpStream`] asynchronous using
+/// `AsyncFd`.  It implements `read` as an async fn, and `AsyncWrite` as a trait
+/// to show how to implement both approaches.
+///
+/// ```no_run
+/// use futures::ready;
+/// use std::io::{self, Read, Write};
+/// use std::net::TcpStream;
+/// use std::pin::Pin;
+/// use std::task::{Context, Poll};
+/// use tokio::io::AsyncWrite;
+/// use tokio::io::unix::AsyncFd;
+///
+/// pub struct AsyncTcpStream {
+///     inner: AsyncFd<TcpStream>,
+/// }
+///
+/// impl AsyncTcpStream {
+///     pub fn new(tcp: TcpStream) -> io::Result<Self> {
+///         tcp.set_nonblocking(true)?;
+///         Ok(Self {
+///             inner: AsyncFd::new(tcp)?,
+///         })
+///     }
+///
+///     pub async fn read(&self, out: &mut [u8]) -> io::Result<usize> {
+///         loop {
+///             let mut guard = self.inner.readable().await?;
+///
+///             match guard.try_io(|inner| inner.get_ref().read(out)) {
+///                 Ok(result) => return result,
+///                 Err(_would_block) => continue,
+///             }
+///         }
+///     }
+/// }
+///
+/// impl AsyncWrite for AsyncTcpStream {
+///     fn poll_write(
+///         self: Pin<&mut Self>,
+///         cx: &mut Context<'_>,
+///         buf: &[u8]
+///     ) -> Poll<io::Result<usize>> {
+///         loop {
+///             let mut guard = ready!(self.inner.poll_write_ready(cx))?;
+///
+///             match guard.try_io(|inner| inner.get_ref().write(buf)) {
+///                 Ok(result) => return Poll::Ready(result),
+///                 Err(_would_block) => continue,
+///             }
+///         }
+///     }
+///
+///     fn poll_flush(
+///         self: Pin<&mut Self>,
+///         cx: &mut Context<'_>,
+///     ) -> Poll<io::Result<()>> {
+///         // tcp flush is a no-op
+///         Poll::Ready(Ok(()))
+///     }
+///
+///     fn poll_shutdown(
+///         self: Pin<&mut Self>,
+///         cx: &mut Context<'_>,
+///     ) -> Poll<io::Result<()>> {
+///         self.inner.get_ref().shutdown(std::net::Shutdown::Write)?;
+///         Poll::Ready(Ok(()))
+///     }
+/// }
+/// ```
+///
+/// [`readable`]: method@Self::readable
+/// [`writable`]: method@Self::writable
+/// [`AsyncFdReadyGuard`]: struct@self::AsyncFdReadyGuard
+/// [`TcpStream::poll_read_ready`]: struct@crate::net::TcpStream
+pub struct AsyncFd<T: AsRawFd> {
+    registration: Registration,
+    inner: Option<T>,
+}
+
+/// Represents an IO-ready event detected on a particular file descriptor that
+/// has not yet been acknowledged. This is a `must_use` structure to help ensure
+/// that you do not forget to explicitly clear (or not clear) the event.
+///
+/// This type exposes an immutable reference to the underlying IO object.
+#[must_use = "You must explicitly choose whether to clear the readiness state by calling a method on ReadyGuard"]
+pub struct AsyncFdReadyGuard<'a, T: AsRawFd> {
+    async_fd: &'a AsyncFd<T>,
+    event: Option<ReadyEvent>,
+}
+
+/// Represents an IO-ready event detected on a particular file descriptor that
+/// has not yet been acknowledged. This is a `must_use` structure to help ensure
+/// that you do not forget to explicitly clear (or not clear) the event.
+///
+/// This type exposes a mutable reference to the underlying IO object.
+#[must_use = "You must explicitly choose whether to clear the readiness state by calling a method on ReadyGuard"]
+pub struct AsyncFdReadyMutGuard<'a, T: AsRawFd> {
+    async_fd: &'a mut AsyncFd<T>,
+    event: Option<ReadyEvent>,
+}
+
+const ALL_INTEREST: Interest = Interest::READABLE.add(Interest::WRITABLE);
+
+impl<T: AsRawFd> AsyncFd<T> {
+    #[inline]
+    /// Creates an AsyncFd backed by (and taking ownership of) an object
+    /// implementing [`AsRawFd`]. The backing file descriptor is cached at the
+    /// time of creation.
+    ///
+    /// This method must be called in the context of a tokio runtime.
+    pub fn new(inner: T) -> io::Result<Self>
+    where
+        T: AsRawFd,
+    {
+        Self::with_interest(inner, ALL_INTEREST)
+    }
+
+    #[inline]
+    /// Creates new instance as `new` with additional ability to customize interest,
+    /// allowing to specify whether file descriptor will be polled for read, write or both.
+    pub fn with_interest(inner: T, interest: Interest) -> io::Result<Self>
+    where
+        T: AsRawFd,
+    {
+        Self::new_with_handle_and_interest(inner, Handle::current(), interest)
+    }
+
+    pub(crate) fn new_with_handle_and_interest(
+        inner: T,
+        handle: Handle,
+        interest: Interest,
+    ) -> io::Result<Self> {
+        let fd = inner.as_raw_fd();
+
+        let registration =
+            Registration::new_with_interest_and_handle(&mut SourceFd(&fd), interest, handle)?;
+
+        Ok(AsyncFd {
+            registration,
+            inner: Some(inner),
+        })
+    }
+
+    /// Returns a shared reference to the backing object of this [`AsyncFd`].
+    #[inline]
+    pub fn get_ref(&self) -> &T {
+        self.inner.as_ref().unwrap()
+    }
+
+    /// Returns a mutable reference to the backing object of this [`AsyncFd`].
+    #[inline]
+    pub fn get_mut(&mut self) -> &mut T {
+        self.inner.as_mut().unwrap()
+    }
+
+    fn take_inner(&mut self) -> Option<T> {
+        let fd = self.inner.as_ref().map(AsRawFd::as_raw_fd);
+
+        if let Some(fd) = fd {
+            let _ = self.registration.deregister(&mut SourceFd(&fd));
+        }
+
+        self.inner.take()
+    }
+
+    /// Deregisters this file descriptor and returns ownership of the backing
+    /// object.
+    pub fn into_inner(mut self) -> T {
+        self.take_inner().unwrap()
+    }
+
+    /// Polls for read readiness.
+    ///
+    /// If the file descriptor is not currently ready for reading, this method
+    /// will store a clone of the [`Waker`] from the provided [`Context`]. When the
+    /// file descriptor becomes ready for reading, [`Waker::wake`] will be called.
+    ///
+    /// Note that on multiple calls to [`poll_read_ready`] or
+    /// [`poll_read_ready_mut`], only the `Waker` from the `Context` passed to the
+    /// most recent call is scheduled to receive a wakeup. (However,
+    /// [`poll_write_ready`] retains a second, independent waker).
+    ///
+    /// This method is intended for cases where creating and pinning a future
+    /// via [`readable`] is not feasible. Where possible, using [`readable`] is
+    /// preferred, as this supports polling from multiple tasks at once.
+    ///
+    /// This method takes `&self`, so it is possible to call this method
+    /// concurrently with other methods on this struct. This method only
+    /// provides shared access to the inner IO resource when handling the
+    /// [`AsyncFdReadyGuard`].
+    ///
+    /// [`poll_read_ready`]: method@Self::poll_read_ready
+    /// [`poll_read_ready_mut`]: method@Self::poll_read_ready_mut
+    /// [`poll_write_ready`]: method@Self::poll_write_ready
+    /// [`readable`]: method@Self::readable
+    /// [`Context`]: struct@std::task::Context
+    /// [`Waker`]: struct@std::task::Waker
+    /// [`Waker::wake`]: method@std::task::Waker::wake
+    pub fn poll_read_ready<'a>(
+        &'a self,
+        cx: &mut Context<'_>,
+    ) -> Poll<io::Result<AsyncFdReadyGuard<'a, T>>> {
+        let event = ready!(self.registration.poll_read_ready(cx))?;
+
+        Ok(AsyncFdReadyGuard {
+            async_fd: self,
+            event: Some(event),
+        })
+        .into()
+    }
+
+    /// Polls for read readiness.
+    ///
+    /// If the file descriptor is not currently ready for reading, this method
+    /// will store a clone of the [`Waker`] from the provided [`Context`]. When the
+    /// file descriptor becomes ready for reading, [`Waker::wake`] will be called.
+    ///
+    /// Note that on multiple calls to [`poll_read_ready`] or
+    /// [`poll_read_ready_mut`], only the `Waker` from the `Context` passed to the
+    /// most recent call is scheduled to receive a wakeup. (However,
+    /// [`poll_write_ready`] retains a second, independent waker).
+    ///
+    /// This method is intended for cases where creating and pinning a future
+    /// via [`readable`] is not feasible. Where possible, using [`readable`] is
+    /// preferred, as this supports polling from multiple tasks at once.
+    ///
+    /// This method takes `&mut self`, so it is possible to access the inner IO
+    /// resource mutably when handling the [`AsyncFdReadyMutGuard`].
+    ///
+    /// [`poll_read_ready`]: method@Self::poll_read_ready
+    /// [`poll_read_ready_mut`]: method@Self::poll_read_ready_mut
+    /// [`poll_write_ready`]: method@Self::poll_write_ready
+    /// [`readable`]: method@Self::readable
+    /// [`Context`]: struct@std::task::Context
+    /// [`Waker`]: struct@std::task::Waker
+    /// [`Waker::wake`]: method@std::task::Waker::wake
+    pub fn poll_read_ready_mut<'a>(
+        &'a mut self,
+        cx: &mut Context<'_>,
+    ) -> Poll<io::Result<AsyncFdReadyMutGuard<'a, T>>> {
+        let event = ready!(self.registration.poll_read_ready(cx))?;
+
+        Ok(AsyncFdReadyMutGuard {
+            async_fd: self,
+            event: Some(event),
+        })
+        .into()
+    }
+
+    /// Polls for write readiness.
+    ///
+    /// If the file descriptor is not currently ready for writing, this method
+    /// will store a clone of the [`Waker`] from the provided [`Context`]. When the
+    /// file descriptor becomes ready for writing, [`Waker::wake`] will be called.
+    ///
+    /// Note that on multiple calls to [`poll_write_ready`] or
+    /// [`poll_write_ready_mut`], only the `Waker` from the `Context` passed to the
+    /// most recent call is scheduled to receive a wakeup. (However,
+    /// [`poll_read_ready`] retains a second, independent waker).
+    ///
+    /// This method is intended for cases where creating and pinning a future
+    /// via [`writable`] is not feasible. Where possible, using [`writable`] is
+    /// preferred, as this supports polling from multiple tasks at once.
+    ///
+    /// This method takes `&self`, so it is possible to call this method
+    /// concurrently with other methods on this struct. This method only
+    /// provides shared access to the inner IO resource when handling the
+    /// [`AsyncFdReadyGuard`].
+    ///
+    /// [`poll_read_ready`]: method@Self::poll_read_ready
+    /// [`poll_write_ready`]: method@Self::poll_write_ready
+    /// [`poll_write_ready_mut`]: method@Self::poll_write_ready_mut
+    /// [`writable`]: method@Self::readable
+    /// [`Context`]: struct@std::task::Context
+    /// [`Waker`]: struct@std::task::Waker
+    /// [`Waker::wake`]: method@std::task::Waker::wake
+    pub fn poll_write_ready<'a>(
+        &'a self,
+        cx: &mut Context<'_>,
+    ) -> Poll<io::Result<AsyncFdReadyGuard<'a, T>>> {
+        let event = ready!(self.registration.poll_write_ready(cx))?;
+
+        Ok(AsyncFdReadyGuard {
+            async_fd: self,
+            event: Some(event),
+        })
+        .into()
+    }
+
+    /// Polls for write readiness.
+    ///
+    /// If the file descriptor is not currently ready for writing, this method
+    /// will store a clone of the [`Waker`] from the provided [`Context`]. When the
+    /// file descriptor becomes ready for writing, [`Waker::wake`] will be called.
+    ///
+    /// Note that on multiple calls to [`poll_write_ready`] or
+    /// [`poll_write_ready_mut`], only the `Waker` from the `Context` passed to the
+    /// most recent call is scheduled to receive a wakeup. (However,
+    /// [`poll_read_ready`] retains a second, independent waker).
+    ///
+    /// This method is intended for cases where creating and pinning a future
+    /// via [`writable`] is not feasible. Where possible, using [`writable`] is
+    /// preferred, as this supports polling from multiple tasks at once.
+    ///
+    /// This method takes `&mut self`, so it is possible to access the inner IO
+    /// resource mutably when handling the [`AsyncFdReadyMutGuard`].
+    ///
+    /// [`poll_read_ready`]: method@Self::poll_read_ready
+    /// [`poll_write_ready`]: method@Self::poll_write_ready
+    /// [`poll_write_ready_mut`]: method@Self::poll_write_ready_mut
+    /// [`writable`]: method@Self::readable
+    /// [`Context`]: struct@std::task::Context
+    /// [`Waker`]: struct@std::task::Waker
+    /// [`Waker::wake`]: method@std::task::Waker::wake
+    pub fn poll_write_ready_mut<'a>(
+        &'a mut self,
+        cx: &mut Context<'_>,
+    ) -> Poll<io::Result<AsyncFdReadyMutGuard<'a, T>>> {
+        let event = ready!(self.registration.poll_write_ready(cx))?;
+
+        Ok(AsyncFdReadyMutGuard {
+            async_fd: self,
+            event: Some(event),
+        })
+        .into()
+    }
+
+    async fn readiness(&self, interest: Interest) -> io::Result<AsyncFdReadyGuard<'_, T>> {
+        let event = self.registration.readiness(interest).await?;
+
+        Ok(AsyncFdReadyGuard {
+            async_fd: self,
+            event: Some(event),
+        })
+    }
+
+    async fn readiness_mut(
+        &mut self,
+        interest: Interest,
+    ) -> io::Result<AsyncFdReadyMutGuard<'_, T>> {
+        let event = self.registration.readiness(interest).await?;
+
+        Ok(AsyncFdReadyMutGuard {
+            async_fd: self,
+            event: Some(event),
+        })
+    }
+
+    /// Waits for the file descriptor to become readable, returning a
+    /// [`AsyncFdReadyGuard`] that must be dropped to resume read-readiness
+    /// polling.
+    ///
+    /// This method takes `&self`, so it is possible to call this method
+    /// concurrently with other methods on this struct. This method only
+    /// provides shared access to the inner IO resource when handling the
+    /// [`AsyncFdReadyGuard`].
+    #[allow(clippy::needless_lifetimes)] // The lifetime improves rustdoc rendering.
+    pub async fn readable<'a>(&'a self) -> io::Result<AsyncFdReadyGuard<'a, T>> {
+        self.readiness(Interest::READABLE).await
+    }
+
+    /// Waits for the file descriptor to become readable, returning a
+    /// [`AsyncFdReadyMutGuard`] that must be dropped to resume read-readiness
+    /// polling.
+    ///
+    /// This method takes `&mut self`, so it is possible to access the inner IO
+    /// resource mutably when handling the [`AsyncFdReadyMutGuard`].
+    #[allow(clippy::needless_lifetimes)] // The lifetime improves rustdoc rendering.
+    pub async fn readable_mut<'a>(&'a mut self) -> io::Result<AsyncFdReadyMutGuard<'a, T>> {
+        self.readiness_mut(Interest::READABLE).await
+    }
+
+    /// Waits for the file descriptor to become writable, returning a
+    /// [`AsyncFdReadyGuard`] that must be dropped to resume write-readiness
+    /// polling.
+    ///
+    /// This method takes `&self`, so it is possible to call this method
+    /// concurrently with other methods on this struct. This method only
+    /// provides shared access to the inner IO resource when handling the
+    /// [`AsyncFdReadyGuard`].
+    #[allow(clippy::needless_lifetimes)] // The lifetime improves rustdoc rendering.
+    pub async fn writable<'a>(&'a self) -> io::Result<AsyncFdReadyGuard<'a, T>> {
+        self.readiness(Interest::WRITABLE).await
+    }
+
+    /// Waits for the file descriptor to become writable, returning a
+    /// [`AsyncFdReadyMutGuard`] that must be dropped to resume write-readiness
+    /// polling.
+    ///
+    /// This method takes `&mut self`, so it is possible to access the inner IO
+    /// resource mutably when handling the [`AsyncFdReadyMutGuard`].
+    #[allow(clippy::needless_lifetimes)] // The lifetime improves rustdoc rendering.
+    pub async fn writable_mut<'a>(&'a mut self) -> io::Result<AsyncFdReadyMutGuard<'a, T>> {
+        self.readiness_mut(Interest::WRITABLE).await
+    }
+}
+
+impl<T: AsRawFd> AsRawFd for AsyncFd<T> {
+    fn as_raw_fd(&self) -> RawFd {
+        self.inner.as_ref().unwrap().as_raw_fd()
+    }
+}
+
+impl<T: std::fmt::Debug + AsRawFd> std::fmt::Debug for AsyncFd<T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("AsyncFd")
+            .field("inner", &self.inner)
+            .finish()
+    }
+}
+
+impl<T: AsRawFd> Drop for AsyncFd<T> {
+    fn drop(&mut self) {
+        let _ = self.take_inner();
+    }
+}
+
+impl<'a, Inner: AsRawFd> AsyncFdReadyGuard<'a, Inner> {
+    /// Indicates to tokio that the file descriptor is no longer ready. The
+    /// internal readiness flag will be cleared, and tokio will wait for the
+    /// next edge-triggered readiness notification from the OS.
+    ///
+    /// It is critical that this function not be called unless your code
+    /// _actually observes_ that the file descriptor is _not_ ready. Do not call
+    /// it simply because, for example, a read succeeded; it should be called
+    /// when a read is observed to block.
+    ///
+    /// [`drop`]: method@std::mem::drop
+    pub fn clear_ready(&mut self) {
+        if let Some(event) = self.event.take() {
+            self.async_fd.registration.clear_readiness(event);
+        }
+    }
+
+    /// This method should be invoked when you intentionally want to keep the
+    /// ready flag asserted.
+    ///
+    /// While this function is itself a no-op, it satisfies the `#[must_use]`
+    /// constraint on the [`AsyncFdReadyGuard`] type.
+    pub fn retain_ready(&mut self) {
+        // no-op
+    }
+
+    /// Performs the provided IO operation.
+    ///
+    /// If `f` returns a [`WouldBlock`] error, the readiness state associated
+    /// with this file descriptor is cleared, and the method returns
+    /// `Err(TryIoError::WouldBlock)`. You will typically need to poll the
+    /// `AsyncFd` again when this happens.
+    ///
+    /// This method helps ensure that the readiness state of the underlying file
+    /// descriptor remains in sync with the tokio-side readiness state, by
+    /// clearing the tokio-side state only when a [`WouldBlock`] condition
+    /// occurs. It is the responsibility of the caller to ensure that `f`
+    /// returns [`WouldBlock`] only if the file descriptor that originated this
+    /// `AsyncFdReadyGuard` no longer expresses the readiness state that was queried to
+    /// create this `AsyncFdReadyGuard`.
+    ///
+    /// [`WouldBlock`]: std::io::ErrorKind::WouldBlock
+    // Alias for old name in 0.x
+    #[cfg_attr(docsrs, doc(alias = "with_io"))]
+    pub fn try_io<R>(
+        &mut self,
+        f: impl FnOnce(&'a AsyncFd<Inner>) -> io::Result<R>,
+    ) -> Result<io::Result<R>, TryIoError> {
+        let result = f(self.async_fd);
+
+        if let Err(e) = result.as_ref() {
+            if e.kind() == io::ErrorKind::WouldBlock {
+                self.clear_ready();
+            }
+        }
+
+        match result {
+            Err(err) if err.kind() == io::ErrorKind::WouldBlock => Err(TryIoError(())),
+            result => Ok(result),
+        }
+    }
+
+    /// Returns a shared reference to the inner [`AsyncFd`].
+    pub fn get_ref(&self) -> &'a AsyncFd<Inner> {
+        self.async_fd
+    }
+
+    /// Returns a shared reference to the backing object of the inner [`AsyncFd`].
+    pub fn get_inner(&self) -> &'a Inner {
+        self.get_ref().get_ref()
+    }
+}
+
+impl<'a, Inner: AsRawFd> AsyncFdReadyMutGuard<'a, Inner> {
+    /// Indicates to tokio that the file descriptor is no longer ready. The
+    /// internal readiness flag will be cleared, and tokio will wait for the
+    /// next edge-triggered readiness notification from the OS.
+    ///
+    /// It is critical that this function not be called unless your code
+    /// _actually observes_ that the file descriptor is _not_ ready. Do not call
+    /// it simply because, for example, a read succeeded; it should be called
+    /// when a read is observed to block.
+    ///
+    /// [`drop`]: method@std::mem::drop
+    pub fn clear_ready(&mut self) {
+        if let Some(event) = self.event.take() {
+            self.async_fd.registration.clear_readiness(event);
+        }
+    }
+
+    /// This method should be invoked when you intentionally want to keep the
+    /// ready flag asserted.
+    ///
+    /// While this function is itself a no-op, it satisfies the `#[must_use]`
+    /// constraint on the [`AsyncFdReadyGuard`] type.
+    pub fn retain_ready(&mut self) {
+        // no-op
+    }
+
+    /// Performs the provided IO operation.
+    ///
+    /// If `f` returns a [`WouldBlock`] error, the readiness state associated
+    /// with this file descriptor is cleared, and the method returns
+    /// `Err(TryIoError::WouldBlock)`. You will typically need to poll the
+    /// `AsyncFd` again when this happens.
+    ///
+    /// This method helps ensure that the readiness state of the underlying file
+    /// descriptor remains in sync with the tokio-side readiness state, by
+    /// clearing the tokio-side state only when a [`WouldBlock`] condition
+    /// occurs. It is the responsibility of the caller to ensure that `f`
+    /// returns [`WouldBlock`] only if the file descriptor that originated this
+    /// `AsyncFdReadyGuard` no longer expresses the readiness state that was queried to
+    /// create this `AsyncFdReadyGuard`.
+    ///
+    /// [`WouldBlock`]: std::io::ErrorKind::WouldBlock
+    pub fn try_io<R>(
+        &mut self,
+        f: impl FnOnce(&mut AsyncFd<Inner>) -> io::Result<R>,
+    ) -> Result<io::Result<R>, TryIoError> {
+        let result = f(self.async_fd);
+
+        if let Err(e) = result.as_ref() {
+            if e.kind() == io::ErrorKind::WouldBlock {
+                self.clear_ready();
+            }
+        }
+
+        match result {
+            Err(err) if err.kind() == io::ErrorKind::WouldBlock => Err(TryIoError(())),
+            result => Ok(result),
+        }
+    }
+
+    /// Returns a shared reference to the inner [`AsyncFd`].
+    pub fn get_ref(&self) -> &AsyncFd<Inner> {
+        self.async_fd
+    }
+
+    /// Returns a mutable reference to the inner [`AsyncFd`].
+    pub fn get_mut(&mut self) -> &mut AsyncFd<Inner> {
+        self.async_fd
+    }
+
+    /// Returns a shared reference to the backing object of the inner [`AsyncFd`].
+    pub fn get_inner(&self) -> &Inner {
+        self.get_ref().get_ref()
+    }
+
+    /// Returns a mutable reference to the backing object of the inner [`AsyncFd`].
+    pub fn get_inner_mut(&mut self) -> &mut Inner {
+        self.get_mut().get_mut()
+    }
+}
+
+impl<'a, T: std::fmt::Debug + AsRawFd> std::fmt::Debug for AsyncFdReadyGuard<'a, T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("ReadyGuard")
+            .field("async_fd", &self.async_fd)
+            .finish()
+    }
+}
+
+impl<'a, T: std::fmt::Debug + AsRawFd> std::fmt::Debug for AsyncFdReadyMutGuard<'a, T> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("MutReadyGuard")
+            .field("async_fd", &self.async_fd)
+            .finish()
+    }
+}
+
+/// The error type returned by [`try_io`].
+///
+/// This error indicates that the IO resource returned a [`WouldBlock`] error.
+///
+/// [`WouldBlock`]: std::io::ErrorKind::WouldBlock
+/// [`try_io`]: method@AsyncFdReadyGuard::try_io
+#[derive(Debug)]
+pub struct TryIoError(());
diff --git a/third_party/rust/tokio/src/io/async_read.rs b/third_party/rust/tokio/src/io/async_read.rs
new file mode 100644
index 0000000000..93e5d3e66e
--- /dev/null
+++ b/third_party/rust/tokio/src/io/async_read.rs
@@ -0,0 +1,131 @@
+use super::ReadBuf;
+use std::io;
+use std::ops::DerefMut;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+/// Reads bytes from a source.
+///
+/// This trait is analogous to the [`std::io::Read`] trait, but integrates with
+/// the asynchronous task system. In particular, the [`poll_read`] method,
+/// unlike [`Read::read`], will automatically queue the current task for wakeup
+/// and return if data is not yet available, rather than blocking the calling
+/// thread.
+///
+/// Specifically, this means that the `poll_read` function will return one of
+/// the following:
+///
+/// * `Poll::Ready(Ok(()))` means that data was immediately read and placed into
+///   the output buffer. The amount of data read can be determined by the
+///   increase in the length of the slice returned by `ReadBuf::filled`. If the
+///   difference is 0, EOF has been reached.
+///
+/// * `Poll::Pending` means that no data was read into the buffer
+///   provided. The I/O object is not currently readable but may become readable
+///   in the future. Most importantly, **the current future's task is scheduled
+///   to get unparked when the object is readable**. This means that like
+///   `Future::poll` you'll receive a notification when the I/O object is
+///   readable again.
+///
+/// * `Poll::Ready(Err(e))` for other errors are standard I/O errors coming from the
+///   underlying object.
+///
+/// This trait importantly means that the `read` method only works in the
+/// context of a future's task. The object may panic if used outside of a task.
+///
+/// Utilities for working with `AsyncRead` values are provided by
+/// [`AsyncReadExt`].
+///
+/// [`poll_read`]: AsyncRead::poll_read
+/// [`std::io::Read`]: std::io::Read
+/// [`Read::read`]: std::io::Read::read
+/// [`AsyncReadExt`]: crate::io::AsyncReadExt
+pub trait AsyncRead {
+    /// Attempts to read from the `AsyncRead` into `buf`.
+    ///
+    /// On success, returns `Poll::Ready(Ok(()))` and places data in the
+    /// unfilled portion of `buf`. If no data was read (`buf.filled().len()` is
+    /// unchanged), it implies that EOF has been reached.
+    ///
+    /// If no data is available for reading, the method returns `Poll::Pending`
+    /// and arranges for the current task (via `cx.waker()`) to receive a
+    /// notification when the object becomes readable or is closed.
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>>;
+}
+
+macro_rules! deref_async_read {
+    () => {
+        fn poll_read(
+            mut self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            buf: &mut ReadBuf<'_>,
+        ) -> Poll<io::Result<()>> {
+            Pin::new(&mut **self).poll_read(cx, buf)
+        }
+    };
+}
+
+impl<T: ?Sized + AsyncRead + Unpin> AsyncRead for Box<T> {
+    deref_async_read!();
+}
+
+impl<T: ?Sized + AsyncRead + Unpin> AsyncRead for &mut T {
+    deref_async_read!();
+}
+
+impl<P> AsyncRead for Pin<P>
+where
+    P: DerefMut + Unpin,
+    P::Target: AsyncRead,
+{
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        self.get_mut().as_mut().poll_read(cx, buf)
+    }
+}
+
+impl AsyncRead for &[u8] {
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        _cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        let amt = std::cmp::min(self.len(), buf.remaining());
+        let (a, b) = self.split_at(amt);
+        buf.put_slice(a);
+        *self = b;
+        Poll::Ready(Ok(()))
+    }
+}
+
+impl<T: AsRef<[u8]> + Unpin> AsyncRead for io::Cursor<T> {
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        _cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        let pos = self.position();
+        let slice: &[u8] = (*self).get_ref().as_ref();
+
+        // The position could technically be out of bounds, so don't panic...
+        if pos > slice.len() as u64 {
+            return Poll::Ready(Ok(()));
+        }
+
+        let start = pos as usize;
+        let amt = std::cmp::min(slice.len() - start, buf.remaining());
+        // Add won't overflow because of pos check above.
+        let end = start + amt;
+        buf.put_slice(&slice[start..end]);
+        self.set_position(end as u64);
+
+        Poll::Ready(Ok(()))
+    }
+}
diff --git a/third_party/rust/tokio/src/io/async_seek.rs b/third_party/rust/tokio/src/io/async_seek.rs
new file mode 100644
index 0000000000..bd7a992e4d
--- /dev/null
+++ b/third_party/rust/tokio/src/io/async_seek.rs
@@ -0,0 +1,90 @@
+use std::io::{self, SeekFrom};
+use std::ops::DerefMut;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+/// Seek bytes asynchronously.
+///
+/// This trait is analogous to the [`std::io::Seek`] trait, but integrates
+/// with the asynchronous task system. In particular, the `start_seek`
+/// method, unlike [`Seek::seek`], will not block the calling thread.
+///
+/// Utilities for working with `AsyncSeek` values are provided by
+/// [`AsyncSeekExt`].
+///
+/// [`std::io::Seek`]: std::io::Seek
+/// [`Seek::seek`]: std::io::Seek::seek()
+/// [`AsyncSeekExt`]: crate::io::AsyncSeekExt
+pub trait AsyncSeek {
+    /// Attempts to seek to an offset, in bytes, in a stream.
+    ///
+    /// A seek beyond the end of a stream is allowed, but behavior is defined
+    /// by the implementation.
+    ///
+    /// If this function returns successfully, then the job has been submitted.
+    /// To find out when it completes, call `poll_complete`.
+    ///
+    /// # Errors
+    ///
+    /// This function can return [`io::ErrorKind::Other`] in case there is
+    /// another seek in progress. To avoid this, it is advisable that any call
+    /// to `start_seek` is preceded by a call to `poll_complete` to ensure all
+    /// pending seeks have completed.
+    fn start_seek(self: Pin<&mut Self>, position: SeekFrom) -> io::Result<()>;
+
+    /// Waits for a seek operation to complete.
+    ///
+    /// If the seek operation completed successfully,
+    /// this method returns the new position from the start of the stream.
+    /// That position can be used later with [`SeekFrom::Start`]. Repeatedly
+    /// calling this function without calling `start_seek` might return the
+    /// same result.
+    ///
+    /// # Errors
+    ///
+    /// Seeking to a negative offset is considered an error.
+    fn poll_complete(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>>;
+}
+
+macro_rules! deref_async_seek {
+    () => {
+        fn start_seek(mut self: Pin<&mut Self>, pos: SeekFrom) -> io::Result<()> {
+            Pin::new(&mut **self).start_seek(pos)
+        }
+
+        fn poll_complete(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
+            Pin::new(&mut **self).poll_complete(cx)
+        }
+    };
+}
+
+impl<T: ?Sized + AsyncSeek + Unpin> AsyncSeek for Box<T> {
+    deref_async_seek!();
+}
+
+impl<T: ?Sized + AsyncSeek + Unpin> AsyncSeek for &mut T {
+    deref_async_seek!();
+}
+
+impl<P> AsyncSeek for Pin<P>
+where
+    P: DerefMut + Unpin,
+    P::Target: AsyncSeek,
+{
+    fn start_seek(self: Pin<&mut Self>, pos: SeekFrom) -> io::Result<()> {
+        self.get_mut().as_mut().start_seek(pos)
+    }
+
+    fn poll_complete(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
+        self.get_mut().as_mut().poll_complete(cx)
+    }
+}
+
+impl<T: AsRef<[u8]> + Unpin> AsyncSeek for io::Cursor<T> {
+    fn start_seek(mut self: Pin<&mut Self>, pos: SeekFrom) -> io::Result<()> {
+        io::Seek::seek(&mut *self, pos).map(drop)
+    }
+    fn poll_complete(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<u64>> {
+        Poll::Ready(Ok(self.get_mut().position()))
+    }
+}
diff --git a/third_party/rust/tokio/src/io/async_write.rs b/third_party/rust/tokio/src/io/async_write.rs
new file mode 100644
index 0000000000..7ec1a302ef
--- /dev/null
+++ b/third_party/rust/tokio/src/io/async_write.rs
@@ -0,0 +1,408 @@
+use std::io::{self, IoSlice};
+use std::ops::DerefMut;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+/// Writes bytes asynchronously.
+///
+/// The trait inherits from [`std::io::Write`] and indicates that an I/O object is
+/// **nonblocking**. All non-blocking I/O objects must return an error when
+/// bytes cannot be written instead of blocking the current thread.
+///
+/// Specifically, this means that the [`poll_write`] function will return one of
+/// the following:
+///
+/// * `Poll::Ready(Ok(n))` means that `n` bytes of data was immediately
+///   written.
+///
+/// * `Poll::Pending` means that no data was written from the buffer
+///   provided. The I/O object is not currently writable but may become writable
+///   in the future. Most importantly, **the current future's task is scheduled
+///   to get unparked when the object is writable**. This means that like
+///   `Future::poll` you'll receive a notification when the I/O object is
+///   writable again.
+///
+/// * `Poll::Ready(Err(e))` for other errors are standard I/O errors coming from the
+///   underlying object.
+///
+/// This trait importantly means that the [`write`][stdwrite] method only works in
+/// the context of a future's task. The object may panic if used outside of a task.
+///
+/// Note that this trait also represents that the  [`Write::flush`][stdflush] method
+/// works very similarly to the `write` method, notably that `Ok(())` means that the
+/// writer has successfully been flushed, a "would block" error means that the
+/// current task is ready to receive a notification when flushing can make more
+/// progress, and otherwise normal errors can happen as well.
+///
+/// Utilities for working with `AsyncWrite` values are provided by
+/// [`AsyncWriteExt`].
+///
+/// [`std::io::Write`]: std::io::Write
+/// [`poll_write`]: AsyncWrite::poll_write()
+/// [stdwrite]: std::io::Write::write()
+/// [stdflush]: std::io::Write::flush()
+/// [`AsyncWriteExt`]: crate::io::AsyncWriteExt
+pub trait AsyncWrite {
+    /// Attempt to write bytes from `buf` into the object.
+    ///
+    /// On success, returns `Poll::Ready(Ok(num_bytes_written))`. If successful,
+    /// then it must be guaranteed that `n <= buf.len()`. A return value of `0`
+    /// typically means that the underlying object is no longer able to accept
+    /// bytes and will likely not be able to in the future as well, or that the
+    /// buffer provided is empty.
+    ///
+    /// If the object is not ready for writing, the method returns
+    /// `Poll::Pending` and arranges for the current task (via
+    /// `cx.waker()`) to receive a notification when the object becomes
+    /// writable or is closed.
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<Result<usize, io::Error>>;
+
+    /// Attempts to flush the object, ensuring that any buffered data reach
+    /// their destination.
+    ///
+    /// On success, returns `Poll::Ready(Ok(()))`.
+    ///
+    /// If flushing cannot immediately complete, this method returns
+    /// `Poll::Pending` and arranges for the current task (via
+    /// `cx.waker()`) to receive a notification when the object can make
+    /// progress towards flushing.
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>>;
+
+    /// Initiates or attempts to shut down this writer, returning success when
+    /// the I/O connection has completely shut down.
+    ///
+    /// This method is intended to be used for asynchronous shutdown of I/O
+    /// connections. For example this is suitable for implementing shutdown of a
+    /// TLS connection or calling `TcpStream::shutdown` on a proxied connection.
+    /// Protocols sometimes need to flush out final pieces of data or otherwise
+    /// perform a graceful shutdown handshake, reading/writing more data as
+    /// appropriate. This method is the hook for such protocols to implement the
+    /// graceful shutdown logic.
+    ///
+    /// This `shutdown` method is required by implementers of the
+    /// `AsyncWrite` trait. Wrappers typically just want to proxy this call
+    /// through to the wrapped type, and base types will typically implement
+    /// shutdown logic here or just return `Ok(().into())`. Note that if you're
+    /// wrapping an underlying `AsyncWrite` a call to `shutdown` implies that
+    /// transitively the entire stream has been shut down. After your wrapper's
+    /// shutdown logic has been executed you should shut down the underlying
+    /// stream.
+    ///
+    /// Invocation of a `shutdown` implies an invocation of `flush`. Once this
+    /// method returns `Ready` it implies that a flush successfully happened
+    /// before the shutdown happened. That is, callers don't need to call
+    /// `flush` before calling `shutdown`. They can rely that by calling
+    /// `shutdown` any pending buffered data will be written out.
+    ///
+    /// # Return value
+    ///
+    /// This function returns a `Poll<io::Result<()>>` classified as such:
+    ///
+    /// * `Poll::Ready(Ok(()))` - indicates that the connection was
+    ///   successfully shut down and is now safe to deallocate/drop/close
+    ///   resources associated with it. This method means that the current task
+    ///   will no longer receive any notifications due to this method and the
+    ///   I/O object itself is likely no longer usable.
+    ///
+    /// * `Poll::Pending` - indicates that shutdown is initiated but could
+    ///   not complete just yet. This may mean that more I/O needs to happen to
+    ///   continue this shutdown operation. The current task is scheduled to
+    ///   receive a notification when it's otherwise ready to continue the
+    ///   shutdown operation. When woken up this method should be called again.
+    ///
+    /// * `Poll::Ready(Err(e))` - indicates a fatal error has happened with shutdown,
+    ///   indicating that the shutdown operation did not complete successfully.
+    ///   This typically means that the I/O object is no longer usable.
+    ///
+    /// # Errors
+    ///
+    /// This function can return normal I/O errors through `Err`, described
+    /// above. Additionally this method may also render the underlying
+    /// `Write::write` method no longer usable (e.g. will return errors in the
+    /// future). It's recommended that once `shutdown` is called the
+    /// `write` method is no longer called.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if not called within the context of a future's
+    /// task.
+    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>>;
+
+    /// Like [`poll_write`], except that it writes from a slice of buffers.
+    ///
+    /// Data is copied from each buffer in order, with the final buffer
+    /// read from possibly being only partially consumed. This method must
+    /// behave as a call to [`write`] with the buffers concatenated would.
+    ///
+    /// The default implementation calls [`poll_write`] with either the first nonempty
+    /// buffer provided, or an empty one if none exists.
+    ///
+    /// On success, returns `Poll::Ready(Ok(num_bytes_written))`.
+    ///
+    /// If the object is not ready for writing, the method returns
+    /// `Poll::Pending` and arranges for the current task (via
+    /// `cx.waker()`) to receive a notification when the object becomes
+    /// writable or is closed.
+    ///
+    /// # Note
+    ///
+    /// This should be implemented as a single "atomic" write action. If any
+    /// data has been partially written, it is wrong to return an error or
+    /// pending.
+    ///
+    /// [`poll_write`]: AsyncWrite::poll_write
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[IoSlice<'_>],
+    ) -> Poll<Result<usize, io::Error>> {
+        let buf = bufs
+            .iter()
+            .find(|b| !b.is_empty())
+            .map_or(&[][..], |b| &**b);
+        self.poll_write(cx, buf)
+    }
+
+    /// Determines if this writer has an efficient [`poll_write_vectored`]
+    /// implementation.
+    ///
+    /// If a writer does not override the default [`poll_write_vectored`]
+    /// implementation, code using it may want to avoid the method all together
+    /// and coalesce writes into a single buffer for higher performance.
+    ///
+    /// The default implementation returns `false`.
+    ///
+    /// [`poll_write_vectored`]: AsyncWrite::poll_write_vectored
+    fn is_write_vectored(&self) -> bool {
+        false
+    }
+}
+
+macro_rules! deref_async_write {
+    () => {
+        fn poll_write(
+            mut self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            buf: &[u8],
+        ) -> Poll<io::Result<usize>> {
+            Pin::new(&mut **self).poll_write(cx, buf)
+        }
+
+        fn poll_write_vectored(
+            mut self: Pin<&mut Self>,
+            cx: &mut Context<'_>,
+            bufs: &[IoSlice<'_>],
+        ) -> Poll<io::Result<usize>> {
+            Pin::new(&mut **self).poll_write_vectored(cx, bufs)
+        }
+
+        fn is_write_vectored(&self) -> bool {
+            (**self).is_write_vectored()
+        }
+
+        fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            Pin::new(&mut **self).poll_flush(cx)
+        }
+
+        fn poll_shutdown(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+            Pin::new(&mut **self).poll_shutdown(cx)
+        }
+    };
+}
+
+impl<T: ?Sized + AsyncWrite + Unpin> AsyncWrite for Box<T> {
+    deref_async_write!();
+}
+
+impl<T: ?Sized + AsyncWrite + Unpin> AsyncWrite for &mut T {
+    deref_async_write!();
+}
+
+impl<P> AsyncWrite for Pin<P>
+where
+    P: DerefMut + Unpin,
+    P::Target: AsyncWrite,
+{
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.get_mut().as_mut().poll_write(cx, buf)
+    }
+
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.get_mut().as_mut().poll_write_vectored(cx, bufs)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        (**self).is_write_vectored()
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.get_mut().as_mut().poll_flush(cx)
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.get_mut().as_mut().poll_shutdown(cx)
+    }
+}
+
+impl AsyncWrite for Vec<u8> {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        _cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.get_mut().extend_from_slice(buf);
+        Poll::Ready(Ok(buf.len()))
+    }
+
+    fn poll_write_vectored(
+        mut self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        bufs: &[IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(io::Write::write_vectored(&mut *self, bufs))
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        true
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+}
+
+impl AsyncWrite for io::Cursor<&mut [u8]> {
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(io::Write::write(&mut *self, buf))
+    }
+
+    fn poll_write_vectored(
+        mut self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        bufs: &[IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(io::Write::write_vectored(&mut *self, bufs))
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        true
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(io::Write::flush(&mut *self))
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.poll_flush(cx)
+    }
+}
+
+impl AsyncWrite for io::Cursor<&mut Vec<u8>> {
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(io::Write::write(&mut *self, buf))
+    }
+
+    fn poll_write_vectored(
+        mut self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        bufs: &[IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(io::Write::write_vectored(&mut *self, bufs))
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        true
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(io::Write::flush(&mut *self))
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.poll_flush(cx)
+    }
+}
+
+impl AsyncWrite for io::Cursor<Vec<u8>> {
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(io::Write::write(&mut *self, buf))
+    }
+
+    fn poll_write_vectored(
+        mut self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        bufs: &[IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(io::Write::write_vectored(&mut *self, bufs))
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        true
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(io::Write::flush(&mut *self))
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.poll_flush(cx)
+    }
+}
+
+impl AsyncWrite for io::Cursor<Box<[u8]>> {
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(io::Write::write(&mut *self, buf))
+    }
+
+    fn poll_write_vectored(
+        mut self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        bufs: &[IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        Poll::Ready(io::Write::write_vectored(&mut *self, bufs))
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        true
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(io::Write::flush(&mut *self))
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.poll_flush(cx)
+    }
+}
diff --git a/third_party/rust/tokio/src/io/blocking.rs b/third_party/rust/tokio/src/io/blocking.rs
new file mode 100644
index 0000000000..1d79ee7a27
--- /dev/null
+++ b/third_party/rust/tokio/src/io/blocking.rs
@@ -0,0 +1,279 @@
+use crate::io::sys;
+use crate::io::{AsyncRead, AsyncWrite, ReadBuf};
+
+use std::cmp;
+use std::future::Future;
+use std::io;
+use std::io::prelude::*;
+use std::pin::Pin;
+use std::task::Poll::*;
+use std::task::{Context, Poll};
+
+use self::State::*;
+
+/// `T` should not implement _both_ Read and Write.
+#[derive(Debug)]
+pub(crate) struct Blocking<T> {
+    inner: Option<T>,
+    state: State<T>,
+    /// `true` if the lower IO layer needs flushing.
+    need_flush: bool,
+}
+
+#[derive(Debug)]
+pub(crate) struct Buf {
+    buf: Vec<u8>,
+    pos: usize,
+}
+
+pub(crate) const MAX_BUF: usize = 16 * 1024;
+
+#[derive(Debug)]
+enum State<T> {
+    Idle(Option<Buf>),
+    Busy(sys::Blocking<(io::Result<usize>, Buf, T)>),
+}
+
+cfg_io_std! {
+    impl<T> Blocking<T> {
+        pub(crate) fn new(inner: T) -> Blocking<T> {
+            Blocking {
+                inner: Some(inner),
+                state: State::Idle(Some(Buf::with_capacity(0))),
+                need_flush: false,
+            }
+        }
+    }
+}
+
+impl<T> AsyncRead for Blocking<T>
+where
+    T: Read + Unpin + Send + 'static,
+{
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        dst: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        loop {
+            match self.state {
+                Idle(ref mut buf_cell) => {
+                    let mut buf = buf_cell.take().unwrap();
+
+                    if !buf.is_empty() {
+                        buf.copy_to(dst);
+                        *buf_cell = Some(buf);
+                        return Ready(Ok(()));
+                    }
+
+                    buf.ensure_capacity_for(dst);
+                    let mut inner = self.inner.take().unwrap();
+
+                    self.state = Busy(sys::run(move || {
+                        let res = buf.read_from(&mut inner);
+                        (res, buf, inner)
+                    }));
+                }
+                Busy(ref mut rx) => {
+                    let (res, mut buf, inner) = ready!(Pin::new(rx).poll(cx))?;
+                    self.inner = Some(inner);
+
+                    match res {
+                        Ok(_) => {
+                            buf.copy_to(dst);
+                            self.state = Idle(Some(buf));
+                            return Ready(Ok(()));
+                        }
+                        Err(e) => {
+                            assert!(buf.is_empty());
+
+                            self.state = Idle(Some(buf));
+                            return Ready(Err(e));
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl<T> AsyncWrite for Blocking<T>
+where
+    T: Write + Unpin + Send + 'static,
+{
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        src: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        loop {
+            match self.state {
+                Idle(ref mut buf_cell) => {
+                    let mut buf = buf_cell.take().unwrap();
+
+                    assert!(buf.is_empty());
+
+                    let n = buf.copy_from(src);
+                    let mut inner = self.inner.take().unwrap();
+
+                    self.state = Busy(sys::run(move || {
+                        let n = buf.len();
+                        let res = buf.write_to(&mut inner).map(|_| n);
+
+                        (res, buf, inner)
+                    }));
+                    self.need_flush = true;
+
+                    return Ready(Ok(n));
+                }
+                Busy(ref mut rx) => {
+                    let (res, buf, inner) = ready!(Pin::new(rx).poll(cx))?;
+                    self.state = Idle(Some(buf));
+                    self.inner = Some(inner);
+
+                    // If error, return
+                    res?;
+                }
+            }
+        }
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        loop {
+            let need_flush = self.need_flush;
+            match self.state {
+                // The buffer is not used here
+                Idle(ref mut buf_cell) => {
+                    if need_flush {
+                        let buf = buf_cell.take().unwrap();
+                        let mut inner = self.inner.take().unwrap();
+
+                        self.state = Busy(sys::run(move || {
+                            let res = inner.flush().map(|_| 0);
+                            (res, buf, inner)
+                        }));
+
+                        self.need_flush = false;
+                    } else {
+                        return Ready(Ok(()));
+                    }
+                }
+                Busy(ref mut rx) => {
+                    let (res, buf, inner) = ready!(Pin::new(rx).poll(cx))?;
+                    self.state = Idle(Some(buf));
+                    self.inner = Some(inner);
+
+                    // If error, return
+                    res?;
+                }
+            }
+        }
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        Poll::Ready(Ok(()))
+    }
+}
+
+/// Repeats operations that are interrupted.
+macro_rules! uninterruptibly {
+    ($e:expr) => {{
+        loop {
+            match $e {
+                Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
+                res => break res,
+            }
+        }
+    }};
+}
+
+impl Buf {
+    pub(crate) fn with_capacity(n: usize) -> Buf {
+        Buf {
+            buf: Vec::with_capacity(n),
+            pos: 0,
+        }
+    }
+
+    pub(crate) fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    pub(crate) fn len(&self) -> usize {
+        self.buf.len() - self.pos
+    }
+
+    pub(crate) fn copy_to(&mut self, dst: &mut ReadBuf<'_>) -> usize {
+        let n = cmp::min(self.len(), dst.remaining());
+        dst.put_slice(&self.bytes()[..n]);
+        self.pos += n;
+
+        if self.pos == self.buf.len() {
+            self.buf.truncate(0);
+            self.pos = 0;
+        }
+
+        n
+    }
+
+    pub(crate) fn copy_from(&mut self, src: &[u8]) -> usize {
+        assert!(self.is_empty());
+
+        let n = cmp::min(src.len(), MAX_BUF);
+
+        self.buf.extend_from_slice(&src[..n]);
+        n
+    }
+
+    pub(crate) fn bytes(&self) -> &[u8] {
+        &self.buf[self.pos..]
+    }
+
+    pub(crate) fn ensure_capacity_for(&mut self, bytes: &ReadBuf<'_>) {
+        assert!(self.is_empty());
+
+        let len = cmp::min(bytes.remaining(), MAX_BUF);
+
+        if self.buf.len() < len {
+            self.buf.reserve(len - self.buf.len());
+        }
+
+        unsafe {
+            self.buf.set_len(len);
+        }
+    }
+
+    pub(crate) fn read_from<T: Read>(&mut self, rd: &mut T) -> io::Result<usize> {
+        let res = uninterruptibly!(rd.read(&mut self.buf));
+
+        if let Ok(n) = res {
+            self.buf.truncate(n);
+        } else {
+            self.buf.clear();
+        }
+
+        assert_eq!(self.pos, 0);
+
+        res
+    }
+
+    pub(crate) fn write_to<T: Write>(&mut self, wr: &mut T) -> io::Result<()> {
+        assert_eq!(self.pos, 0);
+
+        // `write_all` already ignores interrupts
+        let res = wr.write_all(&self.buf);
+        self.buf.clear();
+        res
+    }
+}
+
+cfg_fs! {
+    impl Buf {
+        pub(crate) fn discard_read(&mut self) -> i64 {
+            let ret = -(self.bytes().len() as i64);
+            self.pos = 0;
+            self.buf.truncate(0);
+            ret
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/io/bsd/poll_aio.rs b/third_party/rust/tokio/src/io/bsd/poll_aio.rs
new file mode 100644
index 0000000000..f1ac4b2d77
--- /dev/null
+++ b/third_party/rust/tokio/src/io/bsd/poll_aio.rs
@@ -0,0 +1,195 @@
+//! Use POSIX AIO futures with Tokio.
+
+use crate::io::driver::{Handle, Interest, ReadyEvent, Registration};
+use mio::event::Source;
+use mio::Registry;
+use mio::Token;
+use std::fmt;
+use std::io;
+use std::ops::{Deref, DerefMut};
+use std::os::unix::io::AsRawFd;
+use std::os::unix::prelude::RawFd;
+use std::task::{Context, Poll};
+
+/// Like [`mio::event::Source`], but for POSIX AIO only.
+///
+/// Tokio's consumer must pass an implementor of this trait to create a
+/// [`Aio`] object.
+pub trait AioSource {
+    /// Registers this AIO event source with Tokio's reactor.
+    fn register(&mut self, kq: RawFd, token: usize);
+
+    /// Deregisters this AIO event source with Tokio's reactor.
+    fn deregister(&mut self);
+}
+
+/// Wraps the user's AioSource in order to implement mio::event::Source, which
+/// is what the rest of the crate wants.
+struct MioSource<T>(T);
+
+impl<T: AioSource> Source for MioSource<T> {
+    fn register(
+        &mut self,
+        registry: &Registry,
+        token: Token,
+        interests: mio::Interest,
+    ) -> io::Result<()> {
+        assert!(interests.is_aio() || interests.is_lio());
+        self.0.register(registry.as_raw_fd(), usize::from(token));
+        Ok(())
+    }
+
+    fn deregister(&mut self, _registry: &Registry) -> io::Result<()> {
+        self.0.deregister();
+        Ok(())
+    }
+
+    fn reregister(
+        &mut self,
+        registry: &Registry,
+        token: Token,
+        interests: mio::Interest,
+    ) -> io::Result<()> {
+        assert!(interests.is_aio() || interests.is_lio());
+        self.0.register(registry.as_raw_fd(), usize::from(token));
+        Ok(())
+    }
+}
+
+/// Associates a POSIX AIO control block with the reactor that drives it.
+///
+/// `Aio`'s wrapped type must implement [`AioSource`] to be driven
+/// by the reactor.
+///
+/// The wrapped source may be accessed through the `Aio` via the `Deref` and
+/// `DerefMut` traits.
+///
+/// ## Clearing readiness
+///
+/// If [`Aio::poll_ready`] returns ready, but the consumer determines that the
+/// Source is not completely ready and must return to the Pending state,
+/// [`Aio::clear_ready`] may be used.  This can be useful with
+/// [`lio_listio`], which may generate a kevent when only a portion of the
+/// operations have completed.
+///
+/// ## Platforms
+///
+/// Only FreeBSD implements POSIX AIO with kqueue notification, so
+/// `Aio` is only available for that operating system.
+///
+/// [`lio_listio`]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/lio_listio.html
+// Note: Unlike every other kqueue event source, POSIX AIO registers events not
+// via kevent(2) but when the aiocb is submitted to the kernel via aio_read,
+// aio_write, etc.  It needs the kqueue's file descriptor to do that.  So
+// AsyncFd can't be used for POSIX AIO.
+//
+// Note that Aio doesn't implement Drop.  There's no need.  Unlike other
+// kqueue sources, simply dropping the object effectively deregisters it.
+pub struct Aio<E> {
+    io: MioSource<E>,
+    registration: Registration,
+}
+
+// ===== impl Aio =====
+
+impl<E: AioSource> Aio<E> {
+    /// Creates a new `Aio` suitable for use with POSIX AIO functions.
+    ///
+    /// It will be associated with the default reactor.  The runtime is usually
+    /// set implicitly when this function is called from a future driven by a
+    /// Tokio runtime, otherwise runtime can be set explicitly with
+    /// [`Runtime::enter`](crate::runtime::Runtime::enter) function.
+    pub fn new_for_aio(io: E) -> io::Result<Self> {
+        Self::new_with_interest(io, Interest::AIO)
+    }
+
+    /// Creates a new `Aio` suitable for use with [`lio_listio`].
+    ///
+    /// It will be associated with the default reactor.  The runtime is usually
+    /// set implicitly when this function is called from a future driven by a
+    /// Tokio runtime, otherwise runtime can be set explicitly with
+    /// [`Runtime::enter`](crate::runtime::Runtime::enter) function.
+    ///
+    /// [`lio_listio`]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/lio_listio.html
+    pub fn new_for_lio(io: E) -> io::Result<Self> {
+        Self::new_with_interest(io, Interest::LIO)
+    }
+
+    fn new_with_interest(io: E, interest: Interest) -> io::Result<Self> {
+        let mut io = MioSource(io);
+        let handle = Handle::current();
+        let registration = Registration::new_with_interest_and_handle(&mut io, interest, handle)?;
+        Ok(Self { io, registration })
+    }
+
+    /// Indicates to Tokio that the source is no longer ready.  The internal
+    /// readiness flag will be cleared, and tokio will wait for the next
+    /// edge-triggered readiness notification from the OS.
+    ///
+    /// It is critical that this method not be called unless your code
+    /// _actually observes_ that the source is _not_ ready.  The OS must
+    /// deliver a subsequent notification, or this source will block
+    /// forever.  It is equally critical that you `do` call this method if you
+    /// resubmit the same structure to the kernel and poll it again.
+    ///
+    /// This method is not very useful with AIO readiness, since each `aiocb`
+    /// structure is typically only used once.  It's main use with
+    /// [`lio_listio`], which will sometimes send notification when only a
+    /// portion of its elements are complete.  In that case, the caller must
+    /// call `clear_ready` before resubmitting it.
+    ///
+    /// [`lio_listio`]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/lio_listio.html
+    pub fn clear_ready(&self, ev: AioEvent) {
+        self.registration.clear_readiness(ev.0)
+    }
+
+    /// Destroy the [`Aio`] and return its inner source.
+    pub fn into_inner(self) -> E {
+        self.io.0
+    }
+
+    /// Polls for readiness.  Either AIO or LIO counts.
+    ///
+    /// This method returns:
+    ///  * `Poll::Pending` if the underlying operation is not complete, whether
+    ///     or not it completed successfully.  This will be true if the OS is
+    ///     still processing it, or if it has not yet been submitted to the OS.
+    ///  * `Poll::Ready(Ok(_))` if the underlying operation is complete.
+    ///  * `Poll::Ready(Err(_))` if the reactor has been shutdown.  This does
+    ///     _not_ indicate that the underlying operation encountered an error.
+    ///
+    /// When the method returns `Poll::Pending`, the `Waker` in the provided `Context`
+    /// is scheduled to receive a wakeup when the underlying operation
+    /// completes. Note that on multiple calls to `poll_ready`, only the `Waker` from the
+    /// `Context` passed to the most recent call is scheduled to receive a wakeup.
+    pub fn poll_ready<'a>(&'a self, cx: &mut Context<'_>) -> Poll<io::Result<AioEvent>> {
+        let ev = ready!(self.registration.poll_read_ready(cx))?;
+        Poll::Ready(Ok(AioEvent(ev)))
+    }
+}
+
+impl<E: AioSource> Deref for Aio<E> {
+    type Target = E;
+
+    fn deref(&self) -> &E {
+        &self.io.0
+    }
+}
+
+impl<E: AioSource> DerefMut for Aio<E> {
+    fn deref_mut(&mut self) -> &mut E {
+        &mut self.io.0
+    }
+}
+
+impl<E: AioSource + fmt::Debug> fmt::Debug for Aio<E> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Aio").field("io", &self.io.0).finish()
+    }
+}
+
+/// Opaque data returned by [`Aio::poll_ready`].
+///
+/// It can be fed back to [`Aio::clear_ready`].
+#[derive(Debug)]
+pub struct AioEvent(ReadyEvent);
diff --git a/third_party/rust/tokio/src/io/driver/interest.rs b/third_party/rust/tokio/src/io/driver/interest.rs
new file mode 100644
index 0000000000..d6b46dfb7c
--- /dev/null
+++ b/third_party/rust/tokio/src/io/driver/interest.rs
@@ -0,0 +1,132 @@
+#![cfg_attr(not(feature = "net"), allow(dead_code, unreachable_pub))]
+
+use crate::io::driver::Ready;
+
+use std::fmt;
+use std::ops;
+
+/// Readiness event interest.
+///
+/// Specifies the readiness events the caller is interested in when awaiting on
+/// I/O resource readiness states.
+#[cfg_attr(docsrs, doc(cfg(feature = "net")))]
+#[derive(Clone, Copy, Eq, PartialEq)]
+pub struct Interest(mio::Interest);
+
+impl Interest {
+    // The non-FreeBSD definitions in this block are active only when
+    // building documentation.
+    cfg_aio! {
+        /// Interest for POSIX AIO.
+        #[cfg(target_os = "freebsd")]
+        pub const AIO: Interest = Interest(mio::Interest::AIO);
+
+        /// Interest for POSIX AIO.
+        #[cfg(not(target_os = "freebsd"))]
+        pub const AIO: Interest = Interest(mio::Interest::READABLE);
+
+        /// Interest for POSIX AIO lio_listio events.
+        #[cfg(target_os = "freebsd")]
+        pub const LIO: Interest = Interest(mio::Interest::LIO);
+
+        /// Interest for POSIX AIO lio_listio events.
+        #[cfg(not(target_os = "freebsd"))]
+        pub const LIO: Interest = Interest(mio::Interest::READABLE);
+    }
+
+    /// Interest in all readable events.
+    ///
+    /// Readable interest includes read-closed events.
+    pub const READABLE: Interest = Interest(mio::Interest::READABLE);
+
+    /// Interest in all writable events.
+    ///
+    /// Writable interest includes write-closed events.
+    pub const WRITABLE: Interest = Interest(mio::Interest::WRITABLE);
+
+    /// Returns true if the value includes readable interest.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::io::Interest;
+    ///
+    /// assert!(Interest::READABLE.is_readable());
+    /// assert!(!Interest::WRITABLE.is_readable());
+    ///
+    /// let both = Interest::READABLE | Interest::WRITABLE;
+    /// assert!(both.is_readable());
+    /// ```
+    pub const fn is_readable(self) -> bool {
+        self.0.is_readable()
+    }
+
+    /// Returns true if the value includes writable interest.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::io::Interest;
+    ///
+    /// assert!(!Interest::READABLE.is_writable());
+    /// assert!(Interest::WRITABLE.is_writable());
+    ///
+    /// let both = Interest::READABLE | Interest::WRITABLE;
+    /// assert!(both.is_writable());
+    /// ```
+    pub const fn is_writable(self) -> bool {
+        self.0.is_writable()
+    }
+
+    /// Add together two `Interest` values.
+    ///
+    /// This function works from a `const` context.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::io::Interest;
+    ///
+    /// const BOTH: Interest = Interest::READABLE.add(Interest::WRITABLE);
+    ///
+    /// assert!(BOTH.is_readable());
+    /// assert!(BOTH.is_writable());
+    pub const fn add(self, other: Interest) -> Interest {
+        Interest(self.0.add(other.0))
+    }
+
+    // This function must be crate-private to avoid exposing a `mio` dependency.
+    pub(crate) const fn to_mio(self) -> mio::Interest {
+        self.0
+    }
+
+    pub(super) fn mask(self) -> Ready {
+        match self {
+            Interest::READABLE => Ready::READABLE | Ready::READ_CLOSED,
+            Interest::WRITABLE => Ready::WRITABLE | Ready::WRITE_CLOSED,
+            _ => Ready::EMPTY,
+        }
+    }
+}
+
+impl ops::BitOr for Interest {
+    type Output = Self;
+
+    #[inline]
+    fn bitor(self, other: Self) -> Self {
+        self.add(other)
+    }
+}
+
+impl ops::BitOrAssign for Interest {
+    #[inline]
+    fn bitor_assign(&mut self, other: Self) {
+        self.0 = (*self | other).0;
+    }
+}
+
+impl fmt::Debug for Interest {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.0.fmt(fmt)
+    }
+}
diff --git a/third_party/rust/tokio/src/io/driver/mod.rs b/third_party/rust/tokio/src/io/driver/mod.rs
new file mode 100644
index 0000000000..19f67a24e7
--- /dev/null
+++ b/third_party/rust/tokio/src/io/driver/mod.rs
@@ -0,0 +1,354 @@
+#![cfg_attr(not(feature = "rt"), allow(dead_code))]
+
+mod interest;
+#[allow(unreachable_pub)]
+pub use interest::Interest;
+
+mod ready;
+#[allow(unreachable_pub)]
+pub use ready::Ready;
+
+mod registration;
+pub(crate) use registration::Registration;
+
+mod scheduled_io;
+use scheduled_io::ScheduledIo;
+
+use crate::park::{Park, Unpark};
+use crate::util::slab::{self, Slab};
+use crate::{loom::sync::Mutex, util::bit};
+
+use std::fmt;
+use std::io;
+use std::sync::{Arc, Weak};
+use std::time::Duration;
+
+/// I/O driver, backed by Mio.
+pub(crate) struct Driver {
+    /// Tracks the number of times `turn` is called. It is safe for this to wrap
+    /// as it is mostly used to determine when to call `compact()`.
+    tick: u8,
+
+    /// Reuse the `mio::Events` value across calls to poll.
+    events: Option<mio::Events>,
+
+    /// Primary slab handle containing the state for each resource registered
+    /// with this driver. During Drop this is moved into the Inner structure, so
+    /// this is an Option to allow it to be vacated (until Drop this is always
+    /// Some).
+    resources: Option<Slab<ScheduledIo>>,
+
+    /// The system event queue.
+    poll: mio::Poll,
+
+    /// State shared between the reactor and the handles.
+    inner: Arc<Inner>,
+}
+
+/// A reference to an I/O driver.
+#[derive(Clone)]
+pub(crate) struct Handle {
+    inner: Weak<Inner>,
+}
+
+#[derive(Debug)]
+pub(crate) struct ReadyEvent {
+    tick: u8,
+    pub(crate) ready: Ready,
+}
+
+pub(super) struct Inner {
+    /// Primary slab handle containing the state for each resource registered
+    /// with this driver.
+    ///
+    /// The ownership of this slab is moved into this structure during
+    /// `Driver::drop`, so that `Inner::drop` can notify all outstanding handles
+    /// without risking new ones being registered in the meantime.
+    resources: Mutex<Option<Slab<ScheduledIo>>>,
+
+    /// Registers I/O resources.
+    registry: mio::Registry,
+
+    /// Allocates `ScheduledIo` handles when creating new resources.
+    pub(super) io_dispatch: slab::Allocator<ScheduledIo>,
+
+    /// Used to wake up the reactor from a call to `turn`.
+    waker: mio::Waker,
+}
+
+#[derive(Debug, Eq, PartialEq, Clone, Copy)]
+enum Direction {
+    Read,
+    Write,
+}
+
+enum Tick {
+    Set(u8),
+    Clear(u8),
+}
+
+// TODO: Don't use a fake token. Instead, reserve a slot entry for the wakeup
+// token.
+const TOKEN_WAKEUP: mio::Token = mio::Token(1 << 31);
+
+const ADDRESS: bit::Pack = bit::Pack::least_significant(24);
+
+// Packs the generation value in the `readiness` field.
+//
+// The generation prevents a race condition where a slab slot is reused for a
+// new socket while the I/O driver is about to apply a readiness event. The
+// generation value is checked when setting new readiness. If the generation do
+// not match, then the readiness event is discarded.
+const GENERATION: bit::Pack = ADDRESS.then(7);
+
+fn _assert_kinds() {
+    fn _assert<T: Send + Sync>() {}
+
+    _assert::<Handle>();
+}
+
+// ===== impl Driver =====
+
+impl Driver {
+    /// Creates a new event loop, returning any error that happened during the
+    /// creation.
+    pub(crate) fn new() -> io::Result<Driver> {
+        let poll = mio::Poll::new()?;
+        let waker = mio::Waker::new(poll.registry(), TOKEN_WAKEUP)?;
+        let registry = poll.registry().try_clone()?;
+
+        let slab = Slab::new();
+        let allocator = slab.allocator();
+
+        Ok(Driver {
+            tick: 0,
+            events: Some(mio::Events::with_capacity(1024)),
+            poll,
+            resources: Some(slab),
+            inner: Arc::new(Inner {
+                resources: Mutex::new(None),
+                registry,
+                io_dispatch: allocator,
+                waker,
+            }),
+        })
+    }
+
+    /// Returns a handle to this event loop which can be sent across threads
+    /// and can be used as a proxy to the event loop itself.
+    ///
+    /// Handles are cloneable and clones always refer to the same event loop.
+    /// This handle is typically passed into functions that create I/O objects
+    /// to bind them to this event loop.
+    pub(crate) fn handle(&self) -> Handle {
+        Handle {
+            inner: Arc::downgrade(&self.inner),
+        }
+    }
+
+    fn turn(&mut self, max_wait: Option<Duration>) -> io::Result<()> {
+        // How often to call `compact()` on the resource slab
+        const COMPACT_INTERVAL: u8 = 255;
+
+        self.tick = self.tick.wrapping_add(1);
+
+        if self.tick == COMPACT_INTERVAL {
+            self.resources.as_mut().unwrap().compact()
+        }
+
+        let mut events = self.events.take().expect("i/o driver event store missing");
+
+        // Block waiting for an event to happen, peeling out how many events
+        // happened.
+        match self.poll.poll(&mut events, max_wait) {
+            Ok(_) => {}
+            Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
+            Err(e) => return Err(e),
+        }
+
+        // Process all the events that came in, dispatching appropriately
+        for event in events.iter() {
+            let token = event.token();
+
+            if token != TOKEN_WAKEUP {
+                self.dispatch(token, Ready::from_mio(event));
+            }
+        }
+
+        self.events = Some(events);
+
+        Ok(())
+    }
+
+    fn dispatch(&mut self, token: mio::Token, ready: Ready) {
+        let addr = slab::Address::from_usize(ADDRESS.unpack(token.0));
+
+        let resources = self.resources.as_mut().unwrap();
+
+        let io = match resources.get(addr) {
+            Some(io) => io,
+            None => return,
+        };
+
+        let res = io.set_readiness(Some(token.0), Tick::Set(self.tick), |curr| curr | ready);
+
+        if res.is_err() {
+            // token no longer valid!
+            return;
+        }
+
+        io.wake(ready);
+    }
+}
+
+impl Drop for Driver {
+    fn drop(&mut self) {
+        (*self.inner.resources.lock()) = self.resources.take();
+    }
+}
+
+impl Drop for Inner {
+    fn drop(&mut self) {
+        let resources = self.resources.lock().take();
+
+        if let Some(mut slab) = resources {
+            slab.for_each(|io| {
+                // If a task is waiting on the I/O resource, notify it. The task
+                // will then attempt to use the I/O resource and fail due to the
+                // driver being shutdown.
+                io.shutdown();
+            });
+        }
+    }
+}
+
+impl Park for Driver {
+    type Unpark = Handle;
+    type Error = io::Error;
+
+    fn unpark(&self) -> Self::Unpark {
+        self.handle()
+    }
+
+    fn park(&mut self) -> io::Result<()> {
+        self.turn(None)?;
+        Ok(())
+    }
+
+    fn park_timeout(&mut self, duration: Duration) -> io::Result<()> {
+        self.turn(Some(duration))?;
+        Ok(())
+    }
+
+    fn shutdown(&mut self) {}
+}
+
+impl fmt::Debug for Driver {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Driver")
+    }
+}
+
+// ===== impl Handle =====
+
+cfg_rt! {
+    impl Handle {
+        /// Returns a handle to the current reactor.
+        ///
+        /// # Panics
+        ///
+        /// This function panics if there is no current reactor set and `rt` feature
+        /// flag is not enabled.
+        pub(super) fn current() -> Self {
+            crate::runtime::context::io_handle().expect("A Tokio 1.x context was found, but IO is disabled. Call `enable_io` on the runtime builder to enable IO.")
+        }
+    }
+}
+
+cfg_not_rt! {
+    impl Handle {
+        /// Returns a handle to the current reactor.
+        ///
+        /// # Panics
+        ///
+        /// This function panics if there is no current reactor set, or if the `rt`
+        /// feature flag is not enabled.
+        pub(super) fn current() -> Self {
+            panic!("{}", crate::util::error::CONTEXT_MISSING_ERROR)
+        }
+    }
+}
+
+impl Handle {
+    /// Forces a reactor blocked in a call to `turn` to wakeup, or otherwise
+    /// makes the next call to `turn` return immediately.
+    ///
+    /// This method is intended to be used in situations where a notification
+    /// needs to otherwise be sent to the main reactor. If the reactor is
+    /// currently blocked inside of `turn` then it will wake up and soon return
+    /// after this method has been called. If the reactor is not currently
+    /// blocked in `turn`, then the next call to `turn` will not block and
+    /// return immediately.
+    fn wakeup(&self) {
+        if let Some(inner) = self.inner() {
+            inner.waker.wake().expect("failed to wake I/O driver");
+        }
+    }
+
+    pub(super) fn inner(&self) -> Option<Arc<Inner>> {
+        self.inner.upgrade()
+    }
+}
+
+impl Unpark for Handle {
+    fn unpark(&self) {
+        self.wakeup();
+    }
+}
+
+impl fmt::Debug for Handle {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Handle")
+    }
+}
+
+// ===== impl Inner =====
+
+impl Inner {
+    /// Registers an I/O resource with the reactor for a given `mio::Ready` state.
+    ///
+    /// The registration token is returned.
+    pub(super) fn add_source(
+        &self,
+        source: &mut impl mio::event::Source,
+        interest: Interest,
+    ) -> io::Result<slab::Ref<ScheduledIo>> {
+        let (address, shared) = self.io_dispatch.allocate().ok_or_else(|| {
+            io::Error::new(
+                io::ErrorKind::Other,
+                "reactor at max registered I/O resources",
+            )
+        })?;
+
+        let token = GENERATION.pack(shared.generation(), ADDRESS.pack(address.as_usize(), 0));
+
+        self.registry
+            .register(source, mio::Token(token), interest.to_mio())?;
+
+        Ok(shared)
+    }
+
+    /// Deregisters an I/O resource from the reactor.
+    pub(super) fn deregister_source(&self, source: &mut impl mio::event::Source) -> io::Result<()> {
+        self.registry.deregister(source)
+    }
+}
+
+impl Direction {
+    pub(super) fn mask(self) -> Ready {
+        match self {
+            Direction::Read => Ready::READABLE | Ready::READ_CLOSED,
+            Direction::Write => Ready::WRITABLE | Ready::WRITE_CLOSED,
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/io/driver/platform.rs b/third_party/rust/tokio/src/io/driver/platform.rs
new file mode 100644
index 0000000000..6b27988ce6
--- /dev/null
+++ b/third_party/rust/tokio/src/io/driver/platform.rs
@@ -0,0 +1,44 @@
+pub(crate) use self::sys::*;
+
+#[cfg(unix)]
+mod sys {
+    use mio::unix::UnixReady;
+    use mio::Ready;
+
+    pub(crate) fn hup() -> Ready {
+        UnixReady::hup().into()
+    }
+
+    pub(crate) fn is_hup(ready: Ready) -> bool {
+        UnixReady::from(ready).is_hup()
+    }
+
+    pub(crate) fn error() -> Ready {
+        UnixReady::error().into()
+    }
+
+    pub(crate) fn is_error(ready: Ready) -> bool {
+        UnixReady::from(ready).is_error()
+    }
+}
+
+#[cfg(windows)]
+mod sys {
+    use mio::Ready;
+
+    pub(crate) fn hup() -> Ready {
+        Ready::empty()
+    }
+
+    pub(crate) fn is_hup(_: Ready) -> bool {
+        false
+    }
+
+    pub(crate) fn error() -> Ready {
+        Ready::empty()
+    }
+
+    pub(crate) fn is_error(_: Ready) -> bool {
+        false
+    }
+}
diff --git a/third_party/rust/tokio/src/io/driver/ready.rs b/third_party/rust/tokio/src/io/driver/ready.rs
new file mode 100644
index 0000000000..2430d3022f
--- /dev/null
+++ b/third_party/rust/tokio/src/io/driver/ready.rs
@@ -0,0 +1,250 @@
+#![cfg_attr(not(feature = "net"), allow(unreachable_pub))]
+
+use std::fmt;
+use std::ops;
+
+const READABLE: usize = 0b0_01;
+const WRITABLE: usize = 0b0_10;
+const READ_CLOSED: usize = 0b0_0100;
+const WRITE_CLOSED: usize = 0b0_1000;
+
+/// Describes the readiness state of an I/O resources.
+///
+/// `Ready` tracks which operation an I/O resource is ready to perform.
+#[cfg_attr(docsrs, doc(cfg(feature = "net")))]
+#[derive(Clone, Copy, PartialEq, PartialOrd)]
+pub struct Ready(usize);
+
+impl Ready {
+    /// Returns the empty `Ready` set.
+    pub const EMPTY: Ready = Ready(0);
+
+    /// Returns a `Ready` representing readable readiness.
+    pub const READABLE: Ready = Ready(READABLE);
+
+    /// Returns a `Ready` representing writable readiness.
+    pub const WRITABLE: Ready = Ready(WRITABLE);
+
+    /// Returns a `Ready` representing read closed readiness.
+    pub const READ_CLOSED: Ready = Ready(READ_CLOSED);
+
+    /// Returns a `Ready` representing write closed readiness.
+    pub const WRITE_CLOSED: Ready = Ready(WRITE_CLOSED);
+
+    /// Returns a `Ready` representing readiness for all operations.
+    pub const ALL: Ready = Ready(READABLE | WRITABLE | READ_CLOSED | WRITE_CLOSED);
+
+    // Must remain crate-private to avoid adding a public dependency on Mio.
+    pub(crate) fn from_mio(event: &mio::event::Event) -> Ready {
+        let mut ready = Ready::EMPTY;
+
+        #[cfg(all(target_os = "freebsd", feature = "net"))]
+        {
+            if event.is_aio() {
+                ready |= Ready::READABLE;
+            }
+
+            if event.is_lio() {
+                ready |= Ready::READABLE;
+            }
+        }
+
+        if event.is_readable() {
+            ready |= Ready::READABLE;
+        }
+
+        if event.is_writable() {
+            ready |= Ready::WRITABLE;
+        }
+
+        if event.is_read_closed() {
+            ready |= Ready::READ_CLOSED;
+        }
+
+        if event.is_write_closed() {
+            ready |= Ready::WRITE_CLOSED;
+        }
+
+        ready
+    }
+
+    /// Returns true if `Ready` is the empty set.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::io::Ready;
+    ///
+    /// assert!(Ready::EMPTY.is_empty());
+    /// assert!(!Ready::READABLE.is_empty());
+    /// ```
+    pub fn is_empty(self) -> bool {
+        self == Ready::EMPTY
+    }
+
+    /// Returns `true` if the value includes `readable`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::io::Ready;
+    ///
+    /// assert!(!Ready::EMPTY.is_readable());
+    /// assert!(Ready::READABLE.is_readable());
+    /// assert!(Ready::READ_CLOSED.is_readable());
+    /// assert!(!Ready::WRITABLE.is_readable());
+    /// ```
+    pub fn is_readable(self) -> bool {
+        self.contains(Ready::READABLE) || self.is_read_closed()
+    }
+
+    /// Returns `true` if the value includes writable `readiness`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::io::Ready;
+    ///
+    /// assert!(!Ready::EMPTY.is_writable());
+    /// assert!(!Ready::READABLE.is_writable());
+    /// assert!(Ready::WRITABLE.is_writable());
+    /// assert!(Ready::WRITE_CLOSED.is_writable());
+    /// ```
+    pub fn is_writable(self) -> bool {
+        self.contains(Ready::WRITABLE) || self.is_write_closed()
+    }
+
+    /// Returns `true` if the value includes read-closed `readiness`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::io::Ready;
+    ///
+    /// assert!(!Ready::EMPTY.is_read_closed());
+    /// assert!(!Ready::READABLE.is_read_closed());
+    /// assert!(Ready::READ_CLOSED.is_read_closed());
+    /// ```
+    pub fn is_read_closed(self) -> bool {
+        self.contains(Ready::READ_CLOSED)
+    }
+
+    /// Returns `true` if the value includes write-closed `readiness`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::io::Ready;
+    ///
+    /// assert!(!Ready::EMPTY.is_write_closed());
+    /// assert!(!Ready::WRITABLE.is_write_closed());
+    /// assert!(Ready::WRITE_CLOSED.is_write_closed());
+    /// ```
+    pub fn is_write_closed(self) -> bool {
+        self.contains(Ready::WRITE_CLOSED)
+    }
+
+    /// Returns true if `self` is a superset of `other`.
+    ///
+    /// `other` may represent more than one readiness operations, in which case
+    /// the function only returns true if `self` contains all readiness
+    /// specified in `other`.
+    pub(crate) fn contains<T: Into<Self>>(self, other: T) -> bool {
+        let other = other.into();
+        (self & other) == other
+    }
+
+    /// Creates a `Ready` instance using the given `usize` representation.
+    ///
+    /// The `usize` representation must have been obtained from a call to
+    /// `Readiness::as_usize`.
+    ///
+    /// This function is mainly provided to allow the caller to get a
+    /// readiness value from an `AtomicUsize`.
+    pub(crate) fn from_usize(val: usize) -> Ready {
+        Ready(val & Ready::ALL.as_usize())
+    }
+
+    /// Returns a `usize` representation of the `Ready` value.
+    ///
+    /// This function is mainly provided to allow the caller to store a
+    /// readiness value in an `AtomicUsize`.
+    pub(crate) fn as_usize(self) -> usize {
+        self.0
+    }
+}
+
+cfg_io_readiness! {
+    use crate::io::Interest;
+
+    impl Ready {
+        pub(crate) fn from_interest(interest: Interest) -> Ready {
+            let mut ready = Ready::EMPTY;
+
+            if interest.is_readable() {
+                ready |= Ready::READABLE;
+                ready |= Ready::READ_CLOSED;
+            }
+
+            if interest.is_writable() {
+                ready |= Ready::WRITABLE;
+                ready |= Ready::WRITE_CLOSED;
+            }
+
+            ready
+        }
+
+        pub(crate) fn intersection(self, interest: Interest) -> Ready {
+            Ready(self.0 & Ready::from_interest(interest).0)
+        }
+
+        pub(crate) fn satisfies(self, interest: Interest) -> bool {
+            self.0 & Ready::from_interest(interest).0 != 0
+        }
+    }
+}
+
+impl ops::BitOr<Ready> for Ready {
+    type Output = Ready;
+
+    #[inline]
+    fn bitor(self, other: Ready) -> Ready {
+        Ready(self.0 | other.0)
+    }
+}
+
+impl ops::BitOrAssign<Ready> for Ready {
+    #[inline]
+    fn bitor_assign(&mut self, other: Ready) {
+        self.0 |= other.0;
+    }
+}
+
+impl ops::BitAnd<Ready> for Ready {
+    type Output = Ready;
+
+    #[inline]
+    fn bitand(self, other: Ready) -> Ready {
+        Ready(self.0 & other.0)
+    }
+}
+
+impl ops::Sub<Ready> for Ready {
+    type Output = Ready;
+
+    #[inline]
+    fn sub(self, other: Ready) -> Ready {
+        Ready(self.0 & !other.0)
+    }
+}
+
+impl fmt::Debug for Ready {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Ready")
+            .field("is_readable", &self.is_readable())
+            .field("is_writable", &self.is_writable())
+            .field("is_read_closed", &self.is_read_closed())
+            .field("is_write_closed", &self.is_write_closed())
+            .finish()
+    }
+}
diff --git a/third_party/rust/tokio/src/io/driver/registration.rs b/third_party/rust/tokio/src/io/driver/registration.rs
new file mode 100644
index 0000000000..7350be6345
--- /dev/null
+++ b/third_party/rust/tokio/src/io/driver/registration.rs
@@ -0,0 +1,262 @@
+#![cfg_attr(not(feature = "net"), allow(dead_code))]
+
+use crate::io::driver::{Direction, Handle, Interest, ReadyEvent, ScheduledIo};
+use crate::util::slab;
+
+use mio::event::Source;
+use std::io;
+use std::task::{Context, Poll};
+
+cfg_io_driver! {
+    /// Associates an I/O resource with the reactor instance that drives it.
+    ///
+    /// A registration represents an I/O resource registered with a Reactor such
+    /// that it will receive task notifications on readiness. This is the lowest
+    /// level API for integrating with a reactor.
+    ///
+    /// The association between an I/O resource is made by calling
+    /// [`new_with_interest_and_handle`].
+    /// Once the association is established, it remains established until the
+    /// registration instance is dropped.
+    ///
+    /// A registration instance represents two separate readiness streams. One
+    /// for the read readiness and one for write readiness. These streams are
+    /// independent and can be consumed from separate tasks.
+    ///
+    /// **Note**: while `Registration` is `Sync`, the caller must ensure that
+    /// there are at most two tasks that use a registration instance
+    /// concurrently. One task for [`poll_read_ready`] and one task for
+    /// [`poll_write_ready`]. While violating this requirement is "safe" from a
+    /// Rust memory safety point of view, it will result in unexpected behavior
+    /// in the form of lost notifications and tasks hanging.
+    ///
+    /// ## Platform-specific events
+    ///
+    /// `Registration` also allows receiving platform-specific `mio::Ready`
+    /// events. These events are included as part of the read readiness event
+    /// stream. The write readiness event stream is only for `Ready::writable()`
+    /// events.
+    ///
+    /// [`new_with_interest_and_handle`]: method@Self::new_with_interest_and_handle
+    /// [`poll_read_ready`]: method@Self::poll_read_ready`
+    /// [`poll_write_ready`]: method@Self::poll_write_ready`
+    #[derive(Debug)]
+    pub(crate) struct Registration {
+        /// Handle to the associated driver.
+        handle: Handle,
+
+        /// Reference to state stored by the driver.
+        shared: slab::Ref<ScheduledIo>,
+    }
+}
+
+unsafe impl Send for Registration {}
+unsafe impl Sync for Registration {}
+
+// ===== impl Registration =====
+
+impl Registration {
+    /// Registers the I/O resource with the default reactor, for a specific
+    /// `Interest`. `new_with_interest` should be used over `new` when you need
+    /// control over the readiness state, such as when a file descriptor only
+    /// allows reads. This does not add `hup` or `error` so if you are
+    /// interested in those states, you will need to add them to the readiness
+    /// state passed to this function.
+    ///
+    /// # Return
+    ///
+    /// - `Ok` if the registration happened successfully
+    /// - `Err` if an error was encountered during registration
+    pub(crate) fn new_with_interest_and_handle(
+        io: &mut impl Source,
+        interest: Interest,
+        handle: Handle,
+    ) -> io::Result<Registration> {
+        let shared = if let Some(inner) = handle.inner() {
+            inner.add_source(io, interest)?
+        } else {
+            return Err(io::Error::new(
+                io::ErrorKind::Other,
+                "failed to find event loop",
+            ));
+        };
+
+        Ok(Registration { handle, shared })
+    }
+
+    /// Deregisters the I/O resource from the reactor it is associated with.
+    ///
+    /// This function must be called before the I/O resource associated with the
+    /// registration is dropped.
+    ///
+    /// Note that deregistering does not guarantee that the I/O resource can be
+    /// registered with a different reactor. Some I/O resource types can only be
+    /// associated with a single reactor instance for their lifetime.
+    ///
+    /// # Return
+    ///
+    /// If the deregistration was successful, `Ok` is returned. Any calls to
+    /// `Reactor::turn` that happen after a successful call to `deregister` will
+    /// no longer result in notifications getting sent for this registration.
+    ///
+    /// `Err` is returned if an error is encountered.
+    pub(crate) fn deregister(&mut self, io: &mut impl Source) -> io::Result<()> {
+        let inner = match self.handle.inner() {
+            Some(inner) => inner,
+            None => return Err(io::Error::new(io::ErrorKind::Other, "reactor gone")),
+        };
+        inner.deregister_source(io)
+    }
+
+    pub(crate) fn clear_readiness(&self, event: ReadyEvent) {
+        self.shared.clear_readiness(event);
+    }
+
+    // Uses the poll path, requiring the caller to ensure mutual exclusion for
+    // correctness. Only the last task to call this function is notified.
+    pub(crate) fn poll_read_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<ReadyEvent>> {
+        self.poll_ready(cx, Direction::Read)
+    }
+
+    // Uses the poll path, requiring the caller to ensure mutual exclusion for
+    // correctness. Only the last task to call this function is notified.
+    pub(crate) fn poll_write_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<ReadyEvent>> {
+        self.poll_ready(cx, Direction::Write)
+    }
+
+    // Uses the poll path, requiring the caller to ensure mutual exclusion for
+    // correctness. Only the last task to call this function is notified.
+    pub(crate) fn poll_read_io<R>(
+        &self,
+        cx: &mut Context<'_>,
+        f: impl FnMut() -> io::Result<R>,
+    ) -> Poll<io::Result<R>> {
+        self.poll_io(cx, Direction::Read, f)
+    }
+
+    // Uses the poll path, requiring the caller to ensure mutual exclusion for
+    // correctness. Only the last task to call this function is notified.
+    pub(crate) fn poll_write_io<R>(
+        &self,
+        cx: &mut Context<'_>,
+        f: impl FnMut() -> io::Result<R>,
+    ) -> Poll<io::Result<R>> {
+        self.poll_io(cx, Direction::Write, f)
+    }
+
+    /// Polls for events on the I/O resource's `direction` readiness stream.
+    ///
+    /// If called with a task context, notify the task when a new event is
+    /// received.
+    fn poll_ready(
+        &self,
+        cx: &mut Context<'_>,
+        direction: Direction,
+    ) -> Poll<io::Result<ReadyEvent>> {
+        // Keep track of task budget
+        let coop = ready!(crate::coop::poll_proceed(cx));
+        let ev = ready!(self.shared.poll_readiness(cx, direction));
+
+        if self.handle.inner().is_none() {
+            return Poll::Ready(Err(gone()));
+        }
+
+        coop.made_progress();
+        Poll::Ready(Ok(ev))
+    }
+
+    fn poll_io<R>(
+        &self,
+        cx: &mut Context<'_>,
+        direction: Direction,
+        mut f: impl FnMut() -> io::Result<R>,
+    ) -> Poll<io::Result<R>> {
+        loop {
+            let ev = ready!(self.poll_ready(cx, direction))?;
+
+            match f() {
+                Ok(ret) => {
+                    return Poll::Ready(Ok(ret));
+                }
+                Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+                    self.clear_readiness(ev);
+                }
+                Err(e) => return Poll::Ready(Err(e)),
+            }
+        }
+    }
+
+    pub(crate) fn try_io<R>(
+        &self,
+        interest: Interest,
+        f: impl FnOnce() -> io::Result<R>,
+    ) -> io::Result<R> {
+        let ev = self.shared.ready_event(interest);
+
+        // Don't attempt the operation if the resource is not ready.
+        if ev.ready.is_empty() {
+            return Err(io::ErrorKind::WouldBlock.into());
+        }
+
+        match f() {
+            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+                self.clear_readiness(ev);
+                Err(io::ErrorKind::WouldBlock.into())
+            }
+            res => res,
+        }
+    }
+}
+
+impl Drop for Registration {
+    fn drop(&mut self) {
+        // It is possible for a cycle to be created between wakers stored in
+        // `ScheduledIo` instances and `Arc<driver::Inner>`. To break this
+        // cycle, wakers are cleared. This is an imperfect solution as it is
+        // possible to store a `Registration` in a waker. In this case, the
+        // cycle would remain.
+        //
+        // See tokio-rs/tokio#3481 for more details.
+        self.shared.clear_wakers();
+    }
+}
+
+fn gone() -> io::Error {
+    io::Error::new(io::ErrorKind::Other, "IO driver has terminated")
+}
+
+cfg_io_readiness! {
+    impl Registration {
+        pub(crate) async fn readiness(&self, interest: Interest) -> io::Result<ReadyEvent> {
+            use std::future::Future;
+            use std::pin::Pin;
+
+            let fut = self.shared.readiness(interest);
+            pin!(fut);
+
+            crate::future::poll_fn(|cx| {
+                if self.handle.inner().is_none() {
+                    return Poll::Ready(Err(io::Error::new(
+                        io::ErrorKind::Other,
+                        crate::util::error::RUNTIME_SHUTTING_DOWN_ERROR
+                    )));
+                }
+
+                Pin::new(&mut fut).poll(cx).map(Ok)
+            }).await
+        }
+
+        pub(crate) async fn async_io<R>(&self, interest: Interest, mut f: impl FnMut() -> io::Result<R>) -> io::Result<R> {
+            loop {
+                let event = self.readiness(interest).await?;
+
+                match f() {
+                    Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+                        self.clear_readiness(event);
+                    }
+                    x => return x,
+                }
+            }
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/io/driver/scheduled_io.rs b/third_party/rust/tokio/src/io/driver/scheduled_io.rs
new file mode 100644
index 0000000000..76f93431ba
--- /dev/null
+++ b/third_party/rust/tokio/src/io/driver/scheduled_io.rs
@@ -0,0 +1,533 @@
+use super::{Interest, Ready, ReadyEvent, Tick};
+use crate::loom::sync::atomic::AtomicUsize;
+use crate::loom::sync::Mutex;
+use crate::util::bit;
+use crate::util::slab::Entry;
+use crate::util::WakeList;
+
+use std::sync::atomic::Ordering::{AcqRel, Acquire, Release};
+use std::task::{Context, Poll, Waker};
+
+use super::Direction;
+
+cfg_io_readiness! {
+    use crate::util::linked_list::{self, LinkedList};
+
+    use std::cell::UnsafeCell;
+    use std::future::Future;
+    use std::marker::PhantomPinned;
+    use std::pin::Pin;
+    use std::ptr::NonNull;
+}
+
+/// Stored in the I/O driver resource slab.
+#[derive(Debug)]
+pub(crate) struct ScheduledIo {
+    /// Packs the resource's readiness with the resource's generation.
+    readiness: AtomicUsize,
+
+    waiters: Mutex<Waiters>,
+}
+
+cfg_io_readiness! {
+    type WaitList = LinkedList<Waiter, <Waiter as linked_list::Link>::Target>;
+}
+
+#[derive(Debug, Default)]
+struct Waiters {
+    #[cfg(feature = "net")]
+    /// List of all current waiters.
+    list: WaitList,
+
+    /// Waker used for AsyncRead.
+    reader: Option<Waker>,
+
+    /// Waker used for AsyncWrite.
+    writer: Option<Waker>,
+
+    /// True if this ScheduledIo has been killed due to IO driver shutdown.
+    is_shutdown: bool,
+}
+
+cfg_io_readiness! {
+    #[derive(Debug)]
+    struct Waiter {
+        pointers: linked_list::Pointers<Waiter>,
+
+        /// The waker for this task.
+        waker: Option<Waker>,
+
+        /// The interest this waiter is waiting on.
+        interest: Interest,
+
+        is_ready: bool,
+
+        /// Should never be `!Unpin`.
+        _p: PhantomPinned,
+    }
+
+    /// Future returned by `readiness()`.
+    struct Readiness<'a> {
+        scheduled_io: &'a ScheduledIo,
+
+        state: State,
+
+        /// Entry in the waiter `LinkedList`.
+        waiter: UnsafeCell<Waiter>,
+    }
+
+    enum State {
+        Init,
+        Waiting,
+        Done,
+    }
+}
+
+// The `ScheduledIo::readiness` (`AtomicUsize`) is packed full of goodness.
+//
+// | reserved | generation |  driver tick | readiness |
+// |----------+------------+--------------+-----------|
+// |   1 bit  |   7 bits   +    8 bits    +   16 bits |
+
+const READINESS: bit::Pack = bit::Pack::least_significant(16);
+
+const TICK: bit::Pack = READINESS.then(8);
+
+const GENERATION: bit::Pack = TICK.then(7);
+
+#[test]
+fn test_generations_assert_same() {
+    assert_eq!(super::GENERATION, GENERATION);
+}
+
+// ===== impl ScheduledIo =====
+
+impl Entry for ScheduledIo {
+    fn reset(&self) {
+        let state = self.readiness.load(Acquire);
+
+        let generation = GENERATION.unpack(state);
+        let next = GENERATION.pack_lossy(generation + 1, 0);
+
+        self.readiness.store(next, Release);
+    }
+}
+
+impl Default for ScheduledIo {
+    fn default() -> ScheduledIo {
+        ScheduledIo {
+            readiness: AtomicUsize::new(0),
+            waiters: Mutex::new(Default::default()),
+        }
+    }
+}
+
+impl ScheduledIo {
+    pub(crate) fn generation(&self) -> usize {
+        GENERATION.unpack(self.readiness.load(Acquire))
+    }
+
+    /// Invoked when the IO driver is shut down; forces this ScheduledIo into a
+    /// permanently ready state.
+    pub(super) fn shutdown(&self) {
+        self.wake0(Ready::ALL, true)
+    }
+
+    /// Sets the readiness on this `ScheduledIo` by invoking the given closure on
+    /// the current value, returning the previous readiness value.
+    ///
+    /// # Arguments
+    /// - `token`: the token for this `ScheduledIo`.
+    /// - `tick`: whether setting the tick or trying to clear readiness for a
+    ///    specific tick.
+    /// - `f`: a closure returning a new readiness value given the previous
+    ///   readiness.
+    ///
+    /// # Returns
+    ///
+    /// If the given token's generation no longer matches the `ScheduledIo`'s
+    /// generation, then the corresponding IO resource has been removed and
+    /// replaced with a new resource. In that case, this method returns `Err`.
+    /// Otherwise, this returns the previous readiness.
+    pub(super) fn set_readiness(
+        &self,
+        token: Option<usize>,
+        tick: Tick,
+        f: impl Fn(Ready) -> Ready,
+    ) -> Result<(), ()> {
+        let mut current = self.readiness.load(Acquire);
+
+        loop {
+            let current_generation = GENERATION.unpack(current);
+
+            if let Some(token) = token {
+                // Check that the generation for this access is still the
+                // current one.
+                if GENERATION.unpack(token) != current_generation {
+                    return Err(());
+                }
+            }
+
+            // Mask out the tick/generation bits so that the modifying
+            // function doesn't see them.
+            let current_readiness = Ready::from_usize(current);
+            let new = f(current_readiness);
+
+            let packed = match tick {
+                Tick::Set(t) => TICK.pack(t as usize, new.as_usize()),
+                Tick::Clear(t) => {
+                    if TICK.unpack(current) as u8 != t {
+                        // Trying to clear readiness with an old event!
+                        return Err(());
+                    }
+
+                    TICK.pack(t as usize, new.as_usize())
+                }
+            };
+
+            let next = GENERATION.pack(current_generation, packed);
+
+            match self
+                .readiness
+                .compare_exchange(current, next, AcqRel, Acquire)
+            {
+                Ok(_) => return Ok(()),
+                // we lost the race, retry!
+                Err(actual) => current = actual,
+            }
+        }
+    }
+
+    /// Notifies all pending waiters that have registered interest in `ready`.
+    ///
+    /// There may be many waiters to notify. Waking the pending task **must** be
+    /// done from outside of the lock otherwise there is a potential for a
+    /// deadlock.
+    ///
+    /// A stack array of wakers is created and filled with wakers to notify, the
+    /// lock is released, and the wakers are notified. Because there may be more
+    /// than 32 wakers to notify, if the stack array fills up, the lock is
+    /// released, the array is cleared, and the iteration continues.
+    pub(super) fn wake(&self, ready: Ready) {
+        self.wake0(ready, false);
+    }
+
+    fn wake0(&self, ready: Ready, shutdown: bool) {
+        let mut wakers = WakeList::new();
+
+        let mut waiters = self.waiters.lock();
+
+        waiters.is_shutdown |= shutdown;
+
+        // check for AsyncRead slot
+        if ready.is_readable() {
+            if let Some(waker) = waiters.reader.take() {
+                wakers.push(waker);
+            }
+        }
+
+        // check for AsyncWrite slot
+        if ready.is_writable() {
+            if let Some(waker) = waiters.writer.take() {
+                wakers.push(waker);
+            }
+        }
+
+        #[cfg(feature = "net")]
+        'outer: loop {
+            let mut iter = waiters.list.drain_filter(|w| ready.satisfies(w.interest));
+
+            while wakers.can_push() {
+                match iter.next() {
+                    Some(waiter) => {
+                        let waiter = unsafe { &mut *waiter.as_ptr() };
+
+                        if let Some(waker) = waiter.waker.take() {
+                            waiter.is_ready = true;
+                            wakers.push(waker);
+                        }
+                    }
+                    None => {
+                        break 'outer;
+                    }
+                }
+            }
+
+            drop(waiters);
+
+            wakers.wake_all();
+
+            // Acquire the lock again.
+            waiters = self.waiters.lock();
+        }
+
+        // Release the lock before notifying
+        drop(waiters);
+
+        wakers.wake_all();
+    }
+
+    pub(super) fn ready_event(&self, interest: Interest) -> ReadyEvent {
+        let curr = self.readiness.load(Acquire);
+
+        ReadyEvent {
+            tick: TICK.unpack(curr) as u8,
+            ready: interest.mask() & Ready::from_usize(READINESS.unpack(curr)),
+        }
+    }
+
+    /// Polls for readiness events in a given direction.
+    ///
+    /// These are to support `AsyncRead` and `AsyncWrite` polling methods,
+    /// which cannot use the `async fn` version. This uses reserved reader
+    /// and writer slots.
+    pub(super) fn poll_readiness(
+        &self,
+        cx: &mut Context<'_>,
+        direction: Direction,
+    ) -> Poll<ReadyEvent> {
+        let curr = self.readiness.load(Acquire);
+
+        let ready = direction.mask() & Ready::from_usize(READINESS.unpack(curr));
+
+        if ready.is_empty() {
+            // Update the task info
+            let mut waiters = self.waiters.lock();
+            let slot = match direction {
+                Direction::Read => &mut waiters.reader,
+                Direction::Write => &mut waiters.writer,
+            };
+
+            // Avoid cloning the waker if one is already stored that matches the
+            // current task.
+            match slot {
+                Some(existing) => {
+                    if !existing.will_wake(cx.waker()) {
+                        *existing = cx.waker().clone();
+                    }
+                }
+                None => {
+                    *slot = Some(cx.waker().clone());
+                }
+            }
+
+            // Try again, in case the readiness was changed while we were
+            // taking the waiters lock
+            let curr = self.readiness.load(Acquire);
+            let ready = direction.mask() & Ready::from_usize(READINESS.unpack(curr));
+            if waiters.is_shutdown {
+                Poll::Ready(ReadyEvent {
+                    tick: TICK.unpack(curr) as u8,
+                    ready: direction.mask(),
+                })
+            } else if ready.is_empty() {
+                Poll::Pending
+            } else {
+                Poll::Ready(ReadyEvent {
+                    tick: TICK.unpack(curr) as u8,
+                    ready,
+                })
+            }
+        } else {
+            Poll::Ready(ReadyEvent {
+                tick: TICK.unpack(curr) as u8,
+                ready,
+            })
+        }
+    }
+
+    pub(crate) fn clear_readiness(&self, event: ReadyEvent) {
+        // This consumes the current readiness state **except** for closed
+        // states. Closed states are excluded because they are final states.
+        let mask_no_closed = event.ready - Ready::READ_CLOSED - Ready::WRITE_CLOSED;
+
+        // result isn't important
+        let _ = self.set_readiness(None, Tick::Clear(event.tick), |curr| curr - mask_no_closed);
+    }
+
+    pub(crate) fn clear_wakers(&self) {
+        let mut waiters = self.waiters.lock();
+        waiters.reader.take();
+        waiters.writer.take();
+    }
+}
+
+impl Drop for ScheduledIo {
+    fn drop(&mut self) {
+        self.wake(Ready::ALL);
+    }
+}
+
+unsafe impl Send for ScheduledIo {}
+unsafe impl Sync for ScheduledIo {}
+
+cfg_io_readiness! {
+    impl ScheduledIo {
+        /// An async version of `poll_readiness` which uses a linked list of wakers.
+        pub(crate) async fn readiness(&self, interest: Interest) -> ReadyEvent {
+            self.readiness_fut(interest).await
+        }
+
+        // This is in a separate function so that the borrow checker doesn't think
+        // we are borrowing the `UnsafeCell` possibly over await boundaries.
+        //
+        // Go figure.
+        fn readiness_fut(&self, interest: Interest) -> Readiness<'_> {
+            Readiness {
+                scheduled_io: self,
+                state: State::Init,
+                waiter: UnsafeCell::new(Waiter {
+                    pointers: linked_list::Pointers::new(),
+                    waker: None,
+                    is_ready: false,
+                    interest,
+                    _p: PhantomPinned,
+                }),
+            }
+        }
+    }
+
+    unsafe impl linked_list::Link for Waiter {
+        type Handle = NonNull<Waiter>;
+        type Target = Waiter;
+
+        fn as_raw(handle: &NonNull<Waiter>) -> NonNull<Waiter> {
+            *handle
+        }
+
+        unsafe fn from_raw(ptr: NonNull<Waiter>) -> NonNull<Waiter> {
+            ptr
+        }
+
+        unsafe fn pointers(mut target: NonNull<Waiter>) -> NonNull<linked_list::Pointers<Waiter>> {
+            NonNull::from(&mut target.as_mut().pointers)
+        }
+    }
+
+    // ===== impl Readiness =====
+
+    impl Future for Readiness<'_> {
+        type Output = ReadyEvent;
+
+        fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+            use std::sync::atomic::Ordering::SeqCst;
+
+            let (scheduled_io, state, waiter) = unsafe {
+                let me = self.get_unchecked_mut();
+                (&me.scheduled_io, &mut me.state, &me.waiter)
+            };
+
+            loop {
+                match *state {
+                    State::Init => {
+                        // Optimistically check existing readiness
+                        let curr = scheduled_io.readiness.load(SeqCst);
+                        let ready = Ready::from_usize(READINESS.unpack(curr));
+
+                        // Safety: `waiter.interest` never changes
+                        let interest = unsafe { (*waiter.get()).interest };
+                        let ready = ready.intersection(interest);
+
+                        if !ready.is_empty() {
+                            // Currently ready!
+                            let tick = TICK.unpack(curr) as u8;
+                            *state = State::Done;
+                            return Poll::Ready(ReadyEvent { tick, ready });
+                        }
+
+                        // Wasn't ready, take the lock (and check again while locked).
+                        let mut waiters = scheduled_io.waiters.lock();
+
+                        let curr = scheduled_io.readiness.load(SeqCst);
+                        let mut ready = Ready::from_usize(READINESS.unpack(curr));
+
+                        if waiters.is_shutdown {
+                            ready = Ready::ALL;
+                        }
+
+                        let ready = ready.intersection(interest);
+
+                        if !ready.is_empty() {
+                            // Currently ready!
+                            let tick = TICK.unpack(curr) as u8;
+                            *state = State::Done;
+                            return Poll::Ready(ReadyEvent { tick, ready });
+                        }
+
+                        // Not ready even after locked, insert into list...
+
+                        // Safety: called while locked
+                        unsafe {
+                            (*waiter.get()).waker = Some(cx.waker().clone());
+                        }
+
+                        // Insert the waiter into the linked list
+                        //
+                        // safety: pointers from `UnsafeCell` are never null.
+                        waiters
+                            .list
+                            .push_front(unsafe { NonNull::new_unchecked(waiter.get()) });
+                        *state = State::Waiting;
+                    }
+                    State::Waiting => {
+                        // Currently in the "Waiting" state, implying the caller has
+                        // a waiter stored in the waiter list (guarded by
+                        // `notify.waiters`). In order to access the waker fields,
+                        // we must hold the lock.
+
+                        let waiters = scheduled_io.waiters.lock();
+
+                        // Safety: called while locked
+                        let w = unsafe { &mut *waiter.get() };
+
+                        if w.is_ready {
+                            // Our waker has been notified.
+                            *state = State::Done;
+                        } else {
+                            // Update the waker, if necessary.
+                            if !w.waker.as_ref().unwrap().will_wake(cx.waker()) {
+                                w.waker = Some(cx.waker().clone());
+                            }
+
+                            return Poll::Pending;
+                        }
+
+                        // Explicit drop of the lock to indicate the scope that the
+                        // lock is held. Because holding the lock is required to
+                        // ensure safe access to fields not held within the lock, it
+                        // is helpful to visualize the scope of the critical
+                        // section.
+                        drop(waiters);
+                    }
+                    State::Done => {
+                        let tick = TICK.unpack(scheduled_io.readiness.load(Acquire)) as u8;
+
+                        // Safety: State::Done means it is no longer shared
+                        let w = unsafe { &mut *waiter.get() };
+
+                        return Poll::Ready(ReadyEvent {
+                            tick,
+                            ready: Ready::from_interest(w.interest),
+                        });
+                    }
+                }
+            }
+        }
+    }
+
+    impl Drop for Readiness<'_> {
+        fn drop(&mut self) {
+            let mut waiters = self.scheduled_io.waiters.lock();
+
+            // Safety: `waiter` is only ever stored in `waiters`
+            unsafe {
+                waiters
+                    .list
+                    .remove(NonNull::new_unchecked(self.waiter.get()))
+            };
+        }
+    }
+
+    unsafe impl Send for Readiness<'_> {}
+    unsafe impl Sync for Readiness<'_> {}
+}
diff --git a/third_party/rust/tokio/src/io/mod.rs b/third_party/rust/tokio/src/io/mod.rs
new file mode 100644
index 0000000000..cfdda61f69
--- /dev/null
+++ b/third_party/rust/tokio/src/io/mod.rs
@@ -0,0 +1,276 @@
+#![cfg_attr(loom, allow(dead_code, unreachable_pub))]
+
+//! Traits, helpers, and type definitions for asynchronous I/O functionality.
+//!
+//! This module is the asynchronous version of `std::io`. Primarily, it
+//! defines two traits, [`AsyncRead`] and [`AsyncWrite`], which are asynchronous
+//! versions of the [`Read`] and [`Write`] traits in the standard library.
+//!
+//! # AsyncRead and AsyncWrite
+//!
+//! Like the standard library's [`Read`] and [`Write`] traits, [`AsyncRead`] and
+//! [`AsyncWrite`] provide the most general interface for reading and writing
+//! input and output. Unlike the standard library's traits, however, they are
+//! _asynchronous_ &mdash; meaning that reading from or writing to a `tokio::io`
+//! type will _yield_ to the Tokio scheduler when IO is not ready, rather than
+//! blocking. This allows other tasks to run while waiting on IO.
+//!
+//! Another difference is that `AsyncRead` and `AsyncWrite` only contain
+//! core methods needed to provide asynchronous reading and writing
+//! functionality. Instead, utility methods are defined in the [`AsyncReadExt`]
+//! and [`AsyncWriteExt`] extension traits. These traits are automatically
+//! implemented for all values that implement `AsyncRead` and `AsyncWrite`
+//! respectively.
+//!
+//! End users will rarely interact directly with `AsyncRead` and
+//! `AsyncWrite`. Instead, they will use the async functions defined in the
+//! extension traits. Library authors are expected to implement `AsyncRead`
+//! and `AsyncWrite` in order to provide types that behave like byte streams.
+//!
+//! Even with these differences, Tokio's `AsyncRead` and `AsyncWrite` traits
+//! can be used in almost exactly the same manner as the standard library's
+//! `Read` and `Write`. Most types in the standard library that implement `Read`
+//! and `Write` have asynchronous equivalents in `tokio` that implement
+//! `AsyncRead` and `AsyncWrite`, such as [`File`] and [`TcpStream`].
+//!
+//! For example, the standard library documentation introduces `Read` by
+//! [demonstrating][std_example] reading some bytes from a [`std::fs::File`]. We
+//! can do the same with [`tokio::fs::File`][`File`]:
+//!
+//! ```no_run
+//! use tokio::io::{self, AsyncReadExt};
+//! use tokio::fs::File;
+//!
+//! #[tokio::main]
+//! async fn main() -> io::Result<()> {
+//!     let mut f = File::open("foo.txt").await?;
+//!     let mut buffer = [0; 10];
+//!
+//!     // read up to 10 bytes
+//!     let n = f.read(&mut buffer).await?;
+//!
+//!     println!("The bytes: {:?}", &buffer[..n]);
+//!     Ok(())
+//! }
+//! ```
+//!
+//! [`File`]: crate::fs::File
+//! [`TcpStream`]: crate::net::TcpStream
+//! [`std::fs::File`]: std::fs::File
+//! [std_example]: std::io#read-and-write
+//!
+//! ## Buffered Readers and Writers
+//!
+//! Byte-based interfaces are unwieldy and can be inefficient, as we'd need to be
+//! making near-constant calls to the operating system. To help with this,
+//! `std::io` comes with [support for _buffered_ readers and writers][stdbuf],
+//! and therefore, `tokio::io` does as well.
+//!
+//! Tokio provides an async version of the [`std::io::BufRead`] trait,
+//! [`AsyncBufRead`]; and async [`BufReader`] and [`BufWriter`] structs, which
+//! wrap readers and writers. These wrappers use a buffer, reducing the number
+//! of calls and providing nicer methods for accessing exactly what you want.
+//!
+//! For example, [`BufReader`] works with the [`AsyncBufRead`] trait to add
+//! extra methods to any async reader:
+//!
+//! ```no_run
+//! use tokio::io::{self, BufReader, AsyncBufReadExt};
+//! use tokio::fs::File;
+//!
+//! #[tokio::main]
+//! async fn main() -> io::Result<()> {
+//!     let f = File::open("foo.txt").await?;
+//!     let mut reader = BufReader::new(f);
+//!     let mut buffer = String::new();
+//!
+//!     // read a line into buffer
+//!     reader.read_line(&mut buffer).await?;
+//!
+//!     println!("{}", buffer);
+//!     Ok(())
+//! }
+//! ```
+//!
+//! [`BufWriter`] doesn't add any new ways of writing; it just buffers every call
+//! to [`write`](crate::io::AsyncWriteExt::write). However, you **must** flush
+//! [`BufWriter`] to ensure that any buffered data is written.
+//!
+//! ```no_run
+//! use tokio::io::{self, BufWriter, AsyncWriteExt};
+//! use tokio::fs::File;
+//!
+//! #[tokio::main]
+//! async fn main() -> io::Result<()> {
+//!     let f = File::create("foo.txt").await?;
+//!     {
+//!         let mut writer = BufWriter::new(f);
+//!
+//!         // Write a byte to the buffer.
+//!         writer.write(&[42u8]).await?;
+//!
+//!         // Flush the buffer before it goes out of scope.
+//!         writer.flush().await?;
+//!
+//!     } // Unless flushed or shut down, the contents of the buffer is discarded on drop.
+//!
+//!     Ok(())
+//! }
+//! ```
+//!
+//! [stdbuf]: std::io#bufreader-and-bufwriter
+//! [`std::io::BufRead`]: std::io::BufRead
+//! [`AsyncBufRead`]: crate::io::AsyncBufRead
+//! [`BufReader`]: crate::io::BufReader
+//! [`BufWriter`]: crate::io::BufWriter
+//!
+//! ## Implementing AsyncRead and AsyncWrite
+//!
+//! Because they are traits, we can implement [`AsyncRead`] and [`AsyncWrite`] for
+//! our own types, as well. Note that these traits must only be implemented for
+//! non-blocking I/O types that integrate with the futures type system. In
+//! other words, these types must never block the thread, and instead the
+//! current task is notified when the I/O resource is ready.
+//!
+//! ## Conversion to and from Sink/Stream
+//!
+//! It is often convenient to encapsulate the reading and writing of
+//! bytes and instead work with a [`Sink`] or [`Stream`] of some data
+//! type that is encoded as bytes and/or decoded from bytes. Tokio
+//! provides some utility traits in the [tokio-util] crate that
+//! abstract the asynchronous buffering that is required and allows
+//! you to write [`Encoder`] and [`Decoder`] functions working with a
+//! buffer of bytes, and then use that ["codec"] to transform anything
+//! that implements [`AsyncRead`] and [`AsyncWrite`] into a `Sink`/`Stream` of
+//! your structured data.
+//!
+//! [tokio-util]: https://docs.rs/tokio-util/0.6/tokio_util/codec/index.html
+//!
+//! # Standard input and output
+//!
+//! Tokio provides asynchronous APIs to standard [input], [output], and [error].
+//! These APIs are very similar to the ones provided by `std`, but they also
+//! implement [`AsyncRead`] and [`AsyncWrite`].
+//!
+//! Note that the standard input / output APIs  **must** be used from the
+//! context of the Tokio runtime, as they require Tokio-specific features to
+//! function. Calling these functions outside of a Tokio runtime will panic.
+//!
+//! [input]: fn@stdin
+//! [output]: fn@stdout
+//! [error]: fn@stderr
+//!
+//! # `std` re-exports
+//!
+//! Additionally, [`Error`], [`ErrorKind`], [`Result`], and [`SeekFrom`] are
+//! re-exported from `std::io` for ease of use.
+//!
+//! [`AsyncRead`]: trait@AsyncRead
+//! [`AsyncWrite`]: trait@AsyncWrite
+//! [`AsyncReadExt`]: trait@AsyncReadExt
+//! [`AsyncWriteExt`]: trait@AsyncWriteExt
+//! ["codec"]: https://docs.rs/tokio-util/0.6/tokio_util/codec/index.html
+//! [`Encoder`]: https://docs.rs/tokio-util/0.6/tokio_util/codec/trait.Encoder.html
+//! [`Decoder`]: https://docs.rs/tokio-util/0.6/tokio_util/codec/trait.Decoder.html
+//! [`Error`]: struct@Error
+//! [`ErrorKind`]: enum@ErrorKind
+//! [`Result`]: type@Result
+//! [`Read`]: std::io::Read
+//! [`SeekFrom`]: enum@SeekFrom
+//! [`Sink`]: https://docs.rs/futures/0.3/futures/sink/trait.Sink.html
+//! [`Stream`]: https://docs.rs/futures/0.3/futures/stream/trait.Stream.html
+//! [`Write`]: std::io::Write
+cfg_io_blocking! {
+    pub(crate) mod blocking;
+}
+
+mod async_buf_read;
+pub use self::async_buf_read::AsyncBufRead;
+
+mod async_read;
+pub use self::async_read::AsyncRead;
+
+mod async_seek;
+pub use self::async_seek::AsyncSeek;
+
+mod async_write;
+pub use self::async_write::AsyncWrite;
+
+mod read_buf;
+pub use self::read_buf::ReadBuf;
+
+// Re-export some types from `std::io` so that users don't have to deal
+// with conflicts when `use`ing `tokio::io` and `std::io`.
+#[doc(no_inline)]
+pub use std::io::{Error, ErrorKind, Result, SeekFrom};
+
+cfg_io_driver_impl! {
+    pub(crate) mod driver;
+
+    cfg_net! {
+        pub use driver::{Interest, Ready};
+    }
+
+    mod poll_evented;
+
+    #[cfg(not(loom))]
+    pub(crate) use poll_evented::PollEvented;
+}
+
+cfg_aio! {
+    /// BSD-specific I/O types.
+    pub mod bsd {
+        mod poll_aio;
+
+        pub use poll_aio::{Aio, AioEvent, AioSource};
+    }
+}
+
+cfg_net_unix! {
+    mod async_fd;
+
+    pub mod unix {
+        //! Asynchronous IO structures specific to Unix-like operating systems.
+        pub use super::async_fd::{AsyncFd, AsyncFdReadyGuard, AsyncFdReadyMutGuard, TryIoError};
+    }
+}
+
+cfg_io_std! {
+    mod stdio_common;
+
+    mod stderr;
+    pub use stderr::{stderr, Stderr};
+
+    mod stdin;
+    pub use stdin::{stdin, Stdin};
+
+    mod stdout;
+    pub use stdout::{stdout, Stdout};
+}
+
+cfg_io_util! {
+    mod split;
+    pub use split::{split, ReadHalf, WriteHalf};
+
+    pub(crate) mod seek;
+    pub(crate) mod util;
+    pub use util::{
+        copy, copy_bidirectional, copy_buf, duplex, empty, repeat, sink, AsyncBufReadExt, AsyncReadExt, AsyncSeekExt, AsyncWriteExt,
+        BufReader, BufStream, BufWriter, DuplexStream, Empty, Lines, Repeat, Sink, Split, Take,
+    };
+}
+
+cfg_not_io_util! {
+    cfg_process! {
+        pub(crate) mod util;
+    }
+}
+
+cfg_io_blocking! {
+    /// Types in this module can be mocked out in tests.
+    mod sys {
+        // TODO: don't rename
+        pub(crate) use crate::blocking::spawn_blocking as run;
+        pub(crate) use crate::blocking::JoinHandle as Blocking;
+    }
+}
diff --git a/third_party/rust/tokio/src/io/poll_evented.rs b/third_party/rust/tokio/src/io/poll_evented.rs
new file mode 100644
index 0000000000..ce4c1426ac
--- /dev/null
+++ b/third_party/rust/tokio/src/io/poll_evented.rs
@@ -0,0 +1,214 @@
+use crate::io::driver::{Handle, Interest, Registration};
+
+use mio::event::Source;
+use std::fmt;
+use std::io;
+use std::ops::Deref;
+use std::panic::{RefUnwindSafe, UnwindSafe};
+
+cfg_io_driver! {
+    /// Associates an I/O resource that implements the [`std::io::Read`] and/or
+    /// [`std::io::Write`] traits with the reactor that drives it.
+    ///
+    /// `PollEvented` uses [`Registration`] internally to take a type that
+    /// implements [`mio::event::Source`] as well as [`std::io::Read`] and or
+    /// [`std::io::Write`] and associate it with a reactor that will drive it.
+    ///
+    /// Once the [`mio::event::Source`] type is wrapped by `PollEvented`, it can be
+    /// used from within the future's execution model. As such, the
+    /// `PollEvented` type provides [`AsyncRead`] and [`AsyncWrite`]
+    /// implementations using the underlying I/O resource as well as readiness
+    /// events provided by the reactor.
+    ///
+    /// **Note**: While `PollEvented` is `Sync` (if the underlying I/O type is
+    /// `Sync`), the caller must ensure that there are at most two tasks that
+    /// use a `PollEvented` instance concurrently. One for reading and one for
+    /// writing. While violating this requirement is "safe" from a Rust memory
+    /// model point of view, it will result in unexpected behavior in the form
+    /// of lost notifications and tasks hanging.
+    ///
+    /// ## Readiness events
+    ///
+    /// Besides just providing [`AsyncRead`] and [`AsyncWrite`] implementations,
+    /// this type also supports access to the underlying readiness event stream.
+    /// While similar in function to what [`Registration`] provides, the
+    /// semantics are a bit different.
+    ///
+    /// Two functions are provided to access the readiness events:
+    /// [`poll_read_ready`] and [`poll_write_ready`]. These functions return the
+    /// current readiness state of the `PollEvented` instance. If
+    /// [`poll_read_ready`] indicates read readiness, immediately calling
+    /// [`poll_read_ready`] again will also indicate read readiness.
+    ///
+    /// When the operation is attempted and is unable to succeed due to the I/O
+    /// resource not being ready, the caller must call `clear_readiness`.
+    /// This clears the readiness state until a new readiness event is received.
+    ///
+    /// This allows the caller to implement additional functions. For example,
+    /// [`TcpListener`] implements poll_accept by using [`poll_read_ready`] and
+    /// `clear_read_ready`.
+    ///
+    /// ## Platform-specific events
+    ///
+    /// `PollEvented` also allows receiving platform-specific `mio::Ready` events.
+    /// These events are included as part of the read readiness event stream. The
+    /// write readiness event stream is only for `Ready::writable()` events.
+    ///
+    /// [`AsyncRead`]: crate::io::AsyncRead
+    /// [`AsyncWrite`]: crate::io::AsyncWrite
+    /// [`TcpListener`]: crate::net::TcpListener
+    /// [`poll_read_ready`]: Registration::poll_read_ready
+    /// [`poll_write_ready`]: Registration::poll_write_ready
+    pub(crate) struct PollEvented<E: Source> {
+        io: Option<E>,
+        registration: Registration,
+    }
+}
+
+// ===== impl PollEvented =====
+
+impl<E: Source> PollEvented<E> {
+    /// Creates a new `PollEvented` associated with the default reactor.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if thread-local runtime is not set.
+    ///
+    /// The runtime is usually set implicitly when this function is called
+    /// from a future driven by a tokio runtime, otherwise runtime can be set
+    /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter) function.
+    #[cfg_attr(feature = "signal", allow(unused))]
+    pub(crate) fn new(io: E) -> io::Result<Self> {
+        PollEvented::new_with_interest(io, Interest::READABLE | Interest::WRITABLE)
+    }
+
+    /// Creates a new `PollEvented` associated with the default reactor, for
+    /// specific `Interest` state. `new_with_interest` should be used over `new`
+    /// when you need control over the readiness state, such as when a file
+    /// descriptor only allows reads. This does not add `hup` or `error` so if
+    /// you are interested in those states, you will need to add them to the
+    /// readiness state passed to this function.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if thread-local runtime is not set.
+    ///
+    /// The runtime is usually set implicitly when this function is called from
+    /// a future driven by a tokio runtime, otherwise runtime can be set
+    /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter)
+    /// function.
+    #[cfg_attr(feature = "signal", allow(unused))]
+    pub(crate) fn new_with_interest(io: E, interest: Interest) -> io::Result<Self> {
+        Self::new_with_interest_and_handle(io, interest, Handle::current())
+    }
+
+    pub(crate) fn new_with_interest_and_handle(
+        mut io: E,
+        interest: Interest,
+        handle: Handle,
+    ) -> io::Result<Self> {
+        let registration = Registration::new_with_interest_and_handle(&mut io, interest, handle)?;
+        Ok(Self {
+            io: Some(io),
+            registration,
+        })
+    }
+
+    /// Returns a reference to the registration.
+    #[cfg(any(
+        feature = "net",
+        all(unix, feature = "process"),
+        all(unix, feature = "signal"),
+    ))]
+    pub(crate) fn registration(&self) -> &Registration {
+        &self.registration
+    }
+
+    /// Deregisters the inner io from the registration and returns a Result containing the inner io.
+    #[cfg(any(feature = "net", feature = "process"))]
+    pub(crate) fn into_inner(mut self) -> io::Result<E> {
+        let mut inner = self.io.take().unwrap(); // As io shouldn't ever be None, just unwrap here.
+        self.registration.deregister(&mut inner)?;
+        Ok(inner)
+    }
+}
+
+feature! {
+    #![any(feature = "net", feature = "process")]
+
+    use crate::io::ReadBuf;
+    use std::task::{Context, Poll};
+
+    impl<E: Source> PollEvented<E> {
+        // Safety: The caller must ensure that `E` can read into uninitialized memory
+        pub(crate) unsafe fn poll_read<'a>(
+            &'a self,
+            cx: &mut Context<'_>,
+            buf: &mut ReadBuf<'_>,
+        ) -> Poll<io::Result<()>>
+        where
+            &'a E: io::Read + 'a,
+        {
+            use std::io::Read;
+
+            let n = ready!(self.registration.poll_read_io(cx, || {
+                let b = &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]);
+                self.io.as_ref().unwrap().read(b)
+            }))?;
+
+            // Safety: We trust `TcpStream::read` to have filled up `n` bytes in the
+            // buffer.
+            buf.assume_init(n);
+            buf.advance(n);
+            Poll::Ready(Ok(()))
+        }
+
+        pub(crate) fn poll_write<'a>(&'a self, cx: &mut Context<'_>, buf: &[u8]) -> Poll<io::Result<usize>>
+        where
+            &'a E: io::Write + 'a,
+        {
+            use std::io::Write;
+            self.registration.poll_write_io(cx, || self.io.as_ref().unwrap().write(buf))
+        }
+
+        #[cfg(feature = "net")]
+        pub(crate) fn poll_write_vectored<'a>(
+            &'a self,
+            cx: &mut Context<'_>,
+            bufs: &[io::IoSlice<'_>],
+        ) -> Poll<io::Result<usize>>
+        where
+            &'a E: io::Write + 'a,
+        {
+            use std::io::Write;
+            self.registration.poll_write_io(cx, || self.io.as_ref().unwrap().write_vectored(bufs))
+        }
+    }
+}
+
+impl<E: Source> UnwindSafe for PollEvented<E> {}
+
+impl<E: Source> RefUnwindSafe for PollEvented<E> {}
+
+impl<E: Source> Deref for PollEvented<E> {
+    type Target = E;
+
+    fn deref(&self) -> &E {
+        self.io.as_ref().unwrap()
+    }
+}
+
+impl<E: Source + fmt::Debug> fmt::Debug for PollEvented<E> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("PollEvented").field("io", &self.io).finish()
+    }
+}
+
+impl<E: Source> Drop for PollEvented<E> {
+    fn drop(&mut self) {
+        if let Some(mut io) = self.io.take() {
+            // Ignore errors
+            let _ = self.registration.deregister(&mut io);
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/io/read_buf.rs b/third_party/rust/tokio/src/io/read_buf.rs
new file mode 100644
index 0000000000..8c34ae6c81
--- /dev/null
+++ b/third_party/rust/tokio/src/io/read_buf.rs
@@ -0,0 +1,291 @@
+use std::fmt;
+use std::mem::MaybeUninit;
+
+/// A wrapper around a byte buffer that is incrementally filled and initialized.
+///
+/// This type is a sort of "double cursor". It tracks three regions in the
+/// buffer: a region at the beginning of the buffer that has been logically
+/// filled with data, a region that has been initialized at some point but not
+/// yet logically filled, and a region at the end that may be uninitialized.
+/// The filled region is guaranteed to be a subset of the initialized region.
+///
+/// In summary, the contents of the buffer can be visualized as:
+///
+/// ```not_rust
+/// [             capacity              ]
+/// [ filled |         unfilled         ]
+/// [    initialized    | uninitialized ]
+/// ```
+///
+/// It is undefined behavior to de-initialize any bytes from the uninitialized
+/// region, since it is merely unknown whether this region is uninitialized or
+/// not, and if part of it turns out to be initialized, it must stay initialized.
+pub struct ReadBuf<'a> {
+    buf: &'a mut [MaybeUninit<u8>],
+    filled: usize,
+    initialized: usize,
+}
+
+impl<'a> ReadBuf<'a> {
+    /// Creates a new `ReadBuf` from a fully initialized buffer.
+    #[inline]
+    pub fn new(buf: &'a mut [u8]) -> ReadBuf<'a> {
+        let initialized = buf.len();
+        let buf = unsafe { slice_to_uninit_mut(buf) };
+        ReadBuf {
+            buf,
+            filled: 0,
+            initialized,
+        }
+    }
+
+    /// Creates a new `ReadBuf` from a fully uninitialized buffer.
+    ///
+    /// Use `assume_init` if part of the buffer is known to be already initialized.
+    #[inline]
+    pub fn uninit(buf: &'a mut [MaybeUninit<u8>]) -> ReadBuf<'a> {
+        ReadBuf {
+            buf,
+            filled: 0,
+            initialized: 0,
+        }
+    }
+
+    /// Returns the total capacity of the buffer.
+    #[inline]
+    pub fn capacity(&self) -> usize {
+        self.buf.len()
+    }
+
+    /// Returns a shared reference to the filled portion of the buffer.
+    #[inline]
+    pub fn filled(&self) -> &[u8] {
+        let slice = &self.buf[..self.filled];
+        // safety: filled describes how far into the buffer that the
+        // user has filled with bytes, so it's been initialized.
+        unsafe { slice_assume_init(slice) }
+    }
+
+    /// Returns a mutable reference to the filled portion of the buffer.
+    #[inline]
+    pub fn filled_mut(&mut self) -> &mut [u8] {
+        let slice = &mut self.buf[..self.filled];
+        // safety: filled describes how far into the buffer that the
+        // user has filled with bytes, so it's been initialized.
+        unsafe { slice_assume_init_mut(slice) }
+    }
+
+    /// Returns a new `ReadBuf` comprised of the unfilled section up to `n`.
+    #[inline]
+    pub fn take(&mut self, n: usize) -> ReadBuf<'_> {
+        let max = std::cmp::min(self.remaining(), n);
+        // Safety: We don't set any of the `unfilled_mut` with `MaybeUninit::uninit`.
+        unsafe { ReadBuf::uninit(&mut self.unfilled_mut()[..max]) }
+    }
+
+    /// Returns a shared reference to the initialized portion of the buffer.
+    ///
+    /// This includes the filled portion.
+    #[inline]
+    pub fn initialized(&self) -> &[u8] {
+        let slice = &self.buf[..self.initialized];
+        // safety: initialized describes how far into the buffer that the
+        // user has at some point initialized with bytes.
+        unsafe { slice_assume_init(slice) }
+    }
+
+    /// Returns a mutable reference to the initialized portion of the buffer.
+    ///
+    /// This includes the filled portion.
+    #[inline]
+    pub fn initialized_mut(&mut self) -> &mut [u8] {
+        let slice = &mut self.buf[..self.initialized];
+        // safety: initialized describes how far into the buffer that the
+        // user has at some point initialized with bytes.
+        unsafe { slice_assume_init_mut(slice) }
+    }
+
+    /// Returns a mutable reference to the entire buffer, without ensuring that it has been fully
+    /// initialized.
+    ///
+    /// The elements between 0 and `self.filled().len()` are filled, and those between 0 and
+    /// `self.initialized().len()` are initialized (and so can be converted to a `&mut [u8]`).
+    ///
+    /// The caller of this method must ensure that these invariants are upheld. For example, if the
+    /// caller initializes some of the uninitialized section of the buffer, it must call
+    /// [`assume_init`](Self::assume_init) with the number of bytes initialized.
+    ///
+    /// # Safety
+    ///
+    /// The caller must not de-initialize portions of the buffer that have already been initialized.
+    /// This includes any bytes in the region marked as uninitialized by `ReadBuf`.
+    #[inline]
+    pub unsafe fn inner_mut(&mut self) -> &mut [MaybeUninit<u8>] {
+        self.buf
+    }
+
+    /// Returns a mutable reference to the unfilled part of the buffer without ensuring that it has been fully
+    /// initialized.
+    ///
+    /// # Safety
+    ///
+    /// The caller must not de-initialize portions of the buffer that have already been initialized.
+    /// This includes any bytes in the region marked as uninitialized by `ReadBuf`.
+    #[inline]
+    pub unsafe fn unfilled_mut(&mut self) -> &mut [MaybeUninit<u8>] {
+        &mut self.buf[self.filled..]
+    }
+
+    /// Returns a mutable reference to the unfilled part of the buffer, ensuring it is fully initialized.
+    ///
+    /// Since `ReadBuf` tracks the region of the buffer that has been initialized, this is effectively "free" after
+    /// the first use.
+    #[inline]
+    pub fn initialize_unfilled(&mut self) -> &mut [u8] {
+        self.initialize_unfilled_to(self.remaining())
+    }
+
+    /// Returns a mutable reference to the first `n` bytes of the unfilled part of the buffer, ensuring it is
+    /// fully initialized.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `self.remaining()` is less than `n`.
+    #[inline]
+    pub fn initialize_unfilled_to(&mut self, n: usize) -> &mut [u8] {
+        assert!(self.remaining() >= n, "n overflows remaining");
+
+        // This can't overflow, otherwise the assert above would have failed.
+        let end = self.filled + n;
+
+        if self.initialized < end {
+            unsafe {
+                self.buf[self.initialized..end]
+                    .as_mut_ptr()
+                    .write_bytes(0, end - self.initialized);
+            }
+            self.initialized = end;
+        }
+
+        let slice = &mut self.buf[self.filled..end];
+        // safety: just above, we checked that the end of the buf has
+        // been initialized to some value.
+        unsafe { slice_assume_init_mut(slice) }
+    }
+
+    /// Returns the number of bytes at the end of the slice that have not yet been filled.
+    #[inline]
+    pub fn remaining(&self) -> usize {
+        self.capacity() - self.filled
+    }
+
+    /// Clears the buffer, resetting the filled region to empty.
+    ///
+    /// The number of initialized bytes is not changed, and the contents of the buffer are not modified.
+    #[inline]
+    pub fn clear(&mut self) {
+        self.filled = 0;
+    }
+
+    /// Advances the size of the filled region of the buffer.
+    ///
+    /// The number of initialized bytes is not changed.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the filled region of the buffer would become larger than the initialized region.
+    #[inline]
+    pub fn advance(&mut self, n: usize) {
+        let new = self.filled.checked_add(n).expect("filled overflow");
+        self.set_filled(new);
+    }
+
+    /// Sets the size of the filled region of the buffer.
+    ///
+    /// The number of initialized bytes is not changed.
+    ///
+    /// Note that this can be used to *shrink* the filled region of the buffer in addition to growing it (for
+    /// example, by a `AsyncRead` implementation that compresses data in-place).
+    ///
+    /// # Panics
+    ///
+    /// Panics if the filled region of the buffer would become larger than the initialized region.
+    #[inline]
+    pub fn set_filled(&mut self, n: usize) {
+        assert!(
+            n <= self.initialized,
+            "filled must not become larger than initialized"
+        );
+        self.filled = n;
+    }
+
+    /// Asserts that the first `n` unfilled bytes of the buffer are initialized.
+    ///
+    /// `ReadBuf` assumes that bytes are never de-initialized, so this method does nothing when called with fewer
+    /// bytes than are already known to be initialized.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure that `n` unfilled bytes of the buffer have already been initialized.
+    #[inline]
+    pub unsafe fn assume_init(&mut self, n: usize) {
+        let new = self.filled + n;
+        if new > self.initialized {
+            self.initialized = new;
+        }
+    }
+
+    /// Appends data to the buffer, advancing the written position and possibly also the initialized position.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `self.remaining()` is less than `buf.len()`.
+    #[inline]
+    pub fn put_slice(&mut self, buf: &[u8]) {
+        assert!(
+            self.remaining() >= buf.len(),
+            "buf.len() must fit in remaining()"
+        );
+
+        let amt = buf.len();
+        // Cannot overflow, asserted above
+        let end = self.filled + amt;
+
+        // Safety: the length is asserted above
+        unsafe {
+            self.buf[self.filled..end]
+                .as_mut_ptr()
+                .cast::<u8>()
+                .copy_from_nonoverlapping(buf.as_ptr(), amt);
+        }
+
+        if self.initialized < end {
+            self.initialized = end;
+        }
+        self.filled = end;
+    }
+}
+
+impl fmt::Debug for ReadBuf<'_> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("ReadBuf")
+            .field("filled", &self.filled)
+            .field("initialized", &self.initialized)
+            .field("capacity", &self.capacity())
+            .finish()
+    }
+}
+
+unsafe fn slice_to_uninit_mut(slice: &mut [u8]) -> &mut [MaybeUninit<u8>] {
+    &mut *(slice as *mut [u8] as *mut [MaybeUninit<u8>])
+}
+
+// TODO: This could use `MaybeUninit::slice_assume_init` when it is stable.
+unsafe fn slice_assume_init(slice: &[MaybeUninit<u8>]) -> &[u8] {
+    &*(slice as *const [MaybeUninit<u8>] as *const [u8])
+}
+
+// TODO: This could use `MaybeUninit::slice_assume_init_mut` when it is stable.
+unsafe fn slice_assume_init_mut(slice: &mut [MaybeUninit<u8>]) -> &mut [u8] {
+    &mut *(slice as *mut [MaybeUninit<u8>] as *mut [u8])
+}
diff --git a/third_party/rust/tokio/src/io/seek.rs b/third_party/rust/tokio/src/io/seek.rs
new file mode 100644
index 0000000000..e64205d9cf
--- /dev/null
+++ b/third_party/rust/tokio/src/io/seek.rs
@@ -0,0 +1,57 @@
+use crate::io::AsyncSeek;
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io::{self, SeekFrom};
+use std::marker::PhantomPinned;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// Future for the [`seek`](crate::io::AsyncSeekExt::seek) method.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct Seek<'a, S: ?Sized> {
+        seek: &'a mut S,
+        pos: Option<SeekFrom>,
+        // Make this future `!Unpin` for compatibility with async trait methods.
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+pub(crate) fn seek<S>(seek: &mut S, pos: SeekFrom) -> Seek<'_, S>
+where
+    S: AsyncSeek + ?Sized + Unpin,
+{
+    Seek {
+        seek,
+        pos: Some(pos),
+        _pin: PhantomPinned,
+    }
+}
+
+impl<S> Future for Seek<'_, S>
+where
+    S: AsyncSeek + ?Sized + Unpin,
+{
+    type Output = io::Result<u64>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let me = self.project();
+        match me.pos {
+            Some(pos) => {
+                // ensure no seek in progress
+                ready!(Pin::new(&mut *me.seek).poll_complete(cx))?;
+                match Pin::new(&mut *me.seek).start_seek(*pos) {
+                    Ok(()) => {
+                        *me.pos = None;
+                        Pin::new(&mut *me.seek).poll_complete(cx)
+                    }
+                    Err(e) => Poll::Ready(Err(e)),
+                }
+            }
+            None => Pin::new(&mut *me.seek).poll_complete(cx),
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/io/split.rs b/third_party/rust/tokio/src/io/split.rs
new file mode 100644
index 0000000000..8258a0f7a0
--- /dev/null
+++ b/third_party/rust/tokio/src/io/split.rs
@@ -0,0 +1,180 @@
+//! Split a single value implementing `AsyncRead + AsyncWrite` into separate
+//! `AsyncRead` and `AsyncWrite` handles.
+//!
+//! To restore this read/write object from its `split::ReadHalf` and
+//! `split::WriteHalf` use `unsplit`.
+
+use crate::io::{AsyncRead, AsyncWrite, ReadBuf};
+
+use std::cell::UnsafeCell;
+use std::fmt;
+use std::io;
+use std::pin::Pin;
+use std::sync::atomic::AtomicBool;
+use std::sync::atomic::Ordering::{Acquire, Release};
+use std::sync::Arc;
+use std::task::{Context, Poll};
+
+cfg_io_util! {
+    /// The readable half of a value returned from [`split`](split()).
+    pub struct ReadHalf<T> {
+        inner: Arc<Inner<T>>,
+    }
+
+    /// The writable half of a value returned from [`split`](split()).
+    pub struct WriteHalf<T> {
+        inner: Arc<Inner<T>>,
+    }
+
+    /// Splits a single value implementing `AsyncRead + AsyncWrite` into separate
+    /// `AsyncRead` and `AsyncWrite` handles.
+    ///
+    /// To restore this read/write object from its `ReadHalf` and
+    /// `WriteHalf` use [`unsplit`](ReadHalf::unsplit()).
+    pub fn split<T>(stream: T) -> (ReadHalf<T>, WriteHalf<T>)
+    where
+        T: AsyncRead + AsyncWrite,
+    {
+        let inner = Arc::new(Inner {
+            locked: AtomicBool::new(false),
+            stream: UnsafeCell::new(stream),
+        });
+
+        let rd = ReadHalf {
+            inner: inner.clone(),
+        };
+
+        let wr = WriteHalf { inner };
+
+        (rd, wr)
+    }
+}
+
+struct Inner<T> {
+    locked: AtomicBool,
+    stream: UnsafeCell<T>,
+}
+
+struct Guard<'a, T> {
+    inner: &'a Inner<T>,
+}
+
+impl<T> ReadHalf<T> {
+    /// Checks if this `ReadHalf` and some `WriteHalf` were split from the same
+    /// stream.
+    pub fn is_pair_of(&self, other: &WriteHalf<T>) -> bool {
+        other.is_pair_of(self)
+    }
+
+    /// Reunites with a previously split `WriteHalf`.
+    ///
+    /// # Panics
+    ///
+    /// If this `ReadHalf` and the given `WriteHalf` do not originate from the
+    /// same `split` operation this method will panic.
+    /// This can be checked ahead of time by comparing the stream ID
+    /// of the two halves.
+    pub fn unsplit(self, wr: WriteHalf<T>) -> T {
+        if self.is_pair_of(&wr) {
+            drop(wr);
+
+            let inner = Arc::try_unwrap(self.inner)
+                .ok()
+                .expect("`Arc::try_unwrap` failed");
+
+            inner.stream.into_inner()
+        } else {
+            panic!("Unrelated `split::Write` passed to `split::Read::unsplit`.")
+        }
+    }
+}
+
+impl<T> WriteHalf<T> {
+    /// Checks if this `WriteHalf` and some `ReadHalf` were split from the same
+    /// stream.
+    pub fn is_pair_of(&self, other: &ReadHalf<T>) -> bool {
+        Arc::ptr_eq(&self.inner, &other.inner)
+    }
+}
+
+impl<T: AsyncRead> AsyncRead for ReadHalf<T> {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        let mut inner = ready!(self.inner.poll_lock(cx));
+        inner.stream_pin().poll_read(cx, buf)
+    }
+}
+
+impl<T: AsyncWrite> AsyncWrite for WriteHalf<T> {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<Result<usize, io::Error>> {
+        let mut inner = ready!(self.inner.poll_lock(cx));
+        inner.stream_pin().poll_write(cx, buf)
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        let mut inner = ready!(self.inner.poll_lock(cx));
+        inner.stream_pin().poll_flush(cx)
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        let mut inner = ready!(self.inner.poll_lock(cx));
+        inner.stream_pin().poll_shutdown(cx)
+    }
+}
+
+impl<T> Inner<T> {
+    fn poll_lock(&self, cx: &mut Context<'_>) -> Poll<Guard<'_, T>> {
+        if self
+            .locked
+            .compare_exchange(false, true, Acquire, Acquire)
+            .is_ok()
+        {
+            Poll::Ready(Guard { inner: self })
+        } else {
+            // Spin... but investigate a better strategy
+
+            std::thread::yield_now();
+            cx.waker().wake_by_ref();
+
+            Poll::Pending
+        }
+    }
+}
+
+impl<T> Guard<'_, T> {
+    fn stream_pin(&mut self) -> Pin<&mut T> {
+        // safety: the stream is pinned in `Arc` and the `Guard` ensures mutual
+        // exclusion.
+        unsafe { Pin::new_unchecked(&mut *self.inner.stream.get()) }
+    }
+}
+
+impl<T> Drop for Guard<'_, T> {
+    fn drop(&mut self) {
+        self.inner.locked.store(false, Release);
+    }
+}
+
+unsafe impl<T: Send> Send for ReadHalf<T> {}
+unsafe impl<T: Send> Send for WriteHalf<T> {}
+unsafe impl<T: Sync> Sync for ReadHalf<T> {}
+unsafe impl<T: Sync> Sync for WriteHalf<T> {}
+
+impl<T: fmt::Debug> fmt::Debug for ReadHalf<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("split::ReadHalf").finish()
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for WriteHalf<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("split::WriteHalf").finish()
+    }
+}
diff --git a/third_party/rust/tokio/src/io/stderr.rs b/third_party/rust/tokio/src/io/stderr.rs
new file mode 100644
index 0000000000..2f624fba9d
--- /dev/null
+++ b/third_party/rust/tokio/src/io/stderr.rs
@@ -0,0 +1,109 @@
+use crate::io::blocking::Blocking;
+use crate::io::stdio_common::SplitByUtf8BoundaryIfWindows;
+use crate::io::AsyncWrite;
+
+use std::io;
+use std::pin::Pin;
+use std::task::Context;
+use std::task::Poll;
+
+cfg_io_std! {
+    /// A handle to the standard error stream of a process.
+    ///
+    /// Concurrent writes to stderr must be executed with care: Only individual
+    /// writes to this [`AsyncWrite`] are guaranteed to be intact. In particular
+    /// you should be aware that writes using [`write_all`] are not guaranteed
+    /// to occur as a single write, so multiple threads writing data with
+    /// [`write_all`] may result in interleaved output.
+    ///
+    /// Created by the [`stderr`] function.
+    ///
+    /// [`stderr`]: stderr()
+    /// [`AsyncWrite`]: AsyncWrite
+    /// [`write_all`]: crate::io::AsyncWriteExt::write_all()
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::io::{self, AsyncWriteExt};
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let mut stderr = io::stdout();
+    ///     stderr.write_all(b"Print some error here.").await?;
+    ///     Ok(())
+    /// }
+    /// ```
+    #[derive(Debug)]
+    pub struct Stderr {
+        std: SplitByUtf8BoundaryIfWindows<Blocking<std::io::Stderr>>,
+    }
+
+    /// Constructs a new handle to the standard error of the current process.
+    ///
+    /// The returned handle allows writing to standard error from the within the
+    /// Tokio runtime.
+    ///
+    /// Concurrent writes to stderr must be executed with care: Only individual
+    /// writes to this [`AsyncWrite`] are guaranteed to be intact. In particular
+    /// you should be aware that writes using [`write_all`] are not guaranteed
+    /// to occur as a single write, so multiple threads writing data with
+    /// [`write_all`] may result in interleaved output.
+    ///
+    /// [`AsyncWrite`]: AsyncWrite
+    /// [`write_all`]: crate::io::AsyncWriteExt::write_all()
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::io::{self, AsyncWriteExt};
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let mut stderr = io::stderr();
+    ///     stderr.write_all(b"Print some error here.").await?;
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn stderr() -> Stderr {
+        let std = io::stderr();
+        Stderr {
+            std: SplitByUtf8BoundaryIfWindows::new(Blocking::new(std)),
+        }
+    }
+}
+
+#[cfg(unix)]
+impl std::os::unix::io::AsRawFd for Stderr {
+    fn as_raw_fd(&self) -> std::os::unix::io::RawFd {
+        std::io::stderr().as_raw_fd()
+    }
+}
+
+#[cfg(windows)]
+impl std::os::windows::io::AsRawHandle for Stderr {
+    fn as_raw_handle(&self) -> std::os::windows::io::RawHandle {
+        std::io::stderr().as_raw_handle()
+    }
+}
+
+impl AsyncWrite for Stderr {
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        Pin::new(&mut self.std).poll_write(cx, buf)
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        Pin::new(&mut self.std).poll_flush(cx)
+    }
+
+    fn poll_shutdown(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), io::Error>> {
+        Pin::new(&mut self.std).poll_shutdown(cx)
+    }
+}
diff --git a/third_party/rust/tokio/src/io/stdin.rs b/third_party/rust/tokio/src/io/stdin.rs
new file mode 100644
index 0000000000..c9578f17b6
--- /dev/null
+++ b/third_party/rust/tokio/src/io/stdin.rs
@@ -0,0 +1,73 @@
+use crate::io::blocking::Blocking;
+use crate::io::{AsyncRead, ReadBuf};
+
+use std::io;
+use std::pin::Pin;
+use std::task::Context;
+use std::task::Poll;
+
+cfg_io_std! {
+    /// A handle to the standard input stream of a process.
+    ///
+    /// The handle implements the [`AsyncRead`] trait, but beware that concurrent
+    /// reads of `Stdin` must be executed with care.
+    ///
+    /// This handle is best used for non-interactive uses, such as when a file
+    /// is piped into the application. For technical reasons, `stdin` is
+    /// implemented by using an ordinary blocking read on a separate thread, and
+    /// it is impossible to cancel that read. This can make shutdown of the
+    /// runtime hang until the user presses enter.
+    ///
+    /// For interactive uses, it is recommended to spawn a thread dedicated to
+    /// user input and use blocking IO directly in that thread.
+    ///
+    /// Created by the [`stdin`] function.
+    ///
+    /// [`stdin`]: fn@stdin
+    /// [`AsyncRead`]: trait@AsyncRead
+    #[derive(Debug)]
+    pub struct Stdin {
+        std: Blocking<std::io::Stdin>,
+    }
+
+    /// Constructs a new handle to the standard input of the current process.
+    ///
+    /// This handle is best used for non-interactive uses, such as when a file
+    /// is piped into the application. For technical reasons, `stdin` is
+    /// implemented by using an ordinary blocking read on a separate thread, and
+    /// it is impossible to cancel that read. This can make shutdown of the
+    /// runtime hang until the user presses enter.
+    ///
+    /// For interactive uses, it is recommended to spawn a thread dedicated to
+    /// user input and use blocking IO directly in that thread.
+    pub fn stdin() -> Stdin {
+        let std = io::stdin();
+        Stdin {
+            std: Blocking::new(std),
+        }
+    }
+}
+
+#[cfg(unix)]
+impl std::os::unix::io::AsRawFd for Stdin {
+    fn as_raw_fd(&self) -> std::os::unix::io::RawFd {
+        std::io::stdin().as_raw_fd()
+    }
+}
+
+#[cfg(windows)]
+impl std::os::windows::io::AsRawHandle for Stdin {
+    fn as_raw_handle(&self) -> std::os::windows::io::RawHandle {
+        std::io::stdin().as_raw_handle()
+    }
+}
+
+impl AsyncRead for Stdin {
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        Pin::new(&mut self.std).poll_read(cx, buf)
+    }
+}
diff --git a/third_party/rust/tokio/src/io/stdio_common.rs b/third_party/rust/tokio/src/io/stdio_common.rs
new file mode 100644
index 0000000000..7e4a198a82
--- /dev/null
+++ b/third_party/rust/tokio/src/io/stdio_common.rs
@@ -0,0 +1,220 @@
+//! Contains utilities for stdout and stderr.
+use crate::io::AsyncWrite;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+/// # Windows
+/// AsyncWrite adapter that finds last char boundary in given buffer and does not write the rest,
+/// if buffer contents seems to be utf8. Otherwise it only trims buffer down to MAX_BUF.
+/// That's why, wrapped writer will always receive well-formed utf-8 bytes.
+/// # Other platforms
+/// Passes data to `inner` as is.
+#[derive(Debug)]
+pub(crate) struct SplitByUtf8BoundaryIfWindows<W> {
+    inner: W,
+}
+
+impl<W> SplitByUtf8BoundaryIfWindows<W> {
+    pub(crate) fn new(inner: W) -> Self {
+        Self { inner }
+    }
+}
+
+// this constant is defined by Unicode standard.
+const MAX_BYTES_PER_CHAR: usize = 4;
+
+// Subject for tweaking here
+const MAGIC_CONST: usize = 8;
+
+impl<W> crate::io::AsyncWrite for SplitByUtf8BoundaryIfWindows<W>
+where
+    W: AsyncWrite + Unpin,
+{
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        mut buf: &[u8],
+    ) -> Poll<Result<usize, std::io::Error>> {
+        // just a closure to avoid repetitive code
+        let mut call_inner = move |buf| Pin::new(&mut self.inner).poll_write(cx, buf);
+
+        // 1. Only windows stdio can suffer from non-utf8.
+        // We also check for `test` so that we can write some tests
+        // for further code. Since `AsyncWrite` can always shrink
+        // buffer at its discretion, excessive (i.e. in tests) shrinking
+        // does not break correctness.
+        // 2. If buffer is small, it will not be shrinked.
+        // That's why, it's "textness" will not change, so we don't have
+        // to fixup it.
+        if cfg!(not(any(target_os = "windows", test))) || buf.len() <= crate::io::blocking::MAX_BUF
+        {
+            return call_inner(buf);
+        }
+
+        buf = &buf[..crate::io::blocking::MAX_BUF];
+
+        // Now there are two possibilities.
+        // If caller gave is binary buffer, we **should not** shrink it
+        // anymore, because excessive shrinking hits performance.
+        // If caller gave as binary buffer, we  **must** additionally
+        // shrink it to strip incomplete char at the end of buffer.
+        // that's why check we will perform now is allowed to have
+        // false-positive.
+
+        // Now let's look at the first MAX_BYTES_PER_CHAR * MAGIC_CONST bytes.
+        // if they are (possibly incomplete) utf8, then we can be quite sure
+        // that input buffer was utf8.
+
+        let have_to_fix_up = match std::str::from_utf8(&buf[..MAX_BYTES_PER_CHAR * MAGIC_CONST]) {
+            Ok(_) => true,
+            Err(err) => {
+                let incomplete_bytes = MAX_BYTES_PER_CHAR * MAGIC_CONST - err.valid_up_to();
+                incomplete_bytes < MAX_BYTES_PER_CHAR
+            }
+        };
+
+        if have_to_fix_up {
+            // We must pop several bytes at the end which form incomplete
+            // character. To achieve it, we exploit UTF8 encoding:
+            // for any code point, all bytes except first start with 0b10 prefix.
+            // see https://en.wikipedia.org/wiki/UTF-8#Encoding for details
+            let trailing_incomplete_char_size = buf
+                .iter()
+                .rev()
+                .take(MAX_BYTES_PER_CHAR)
+                .position(|byte| *byte < 0b1000_0000 || *byte >= 0b1100_0000)
+                .unwrap_or(0)
+                + 1;
+            buf = &buf[..buf.len() - trailing_incomplete_char_size];
+        }
+
+        call_inner(buf)
+    }
+
+    fn poll_flush(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), std::io::Error>> {
+        Pin::new(&mut self.inner).poll_flush(cx)
+    }
+
+    fn poll_shutdown(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), std::io::Error>> {
+        Pin::new(&mut self.inner).poll_shutdown(cx)
+    }
+}
+
+#[cfg(test)]
+#[cfg(not(loom))]
+mod tests {
+    use crate::io::AsyncWriteExt;
+    use std::io;
+    use std::pin::Pin;
+    use std::task::Context;
+    use std::task::Poll;
+
+    const MAX_BUF: usize = 16 * 1024;
+
+    struct TextMockWriter;
+
+    impl crate::io::AsyncWrite for TextMockWriter {
+        fn poll_write(
+            self: Pin<&mut Self>,
+            _cx: &mut Context<'_>,
+            buf: &[u8],
+        ) -> Poll<Result<usize, io::Error>> {
+            assert!(buf.len() <= MAX_BUF);
+            assert!(std::str::from_utf8(buf).is_ok());
+            Poll::Ready(Ok(buf.len()))
+        }
+
+        fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+            Poll::Ready(Ok(()))
+        }
+
+        fn poll_shutdown(
+            self: Pin<&mut Self>,
+            _cx: &mut Context<'_>,
+        ) -> Poll<Result<(), io::Error>> {
+            Poll::Ready(Ok(()))
+        }
+    }
+
+    struct LoggingMockWriter {
+        write_history: Vec<usize>,
+    }
+
+    impl LoggingMockWriter {
+        fn new() -> Self {
+            LoggingMockWriter {
+                write_history: Vec::new(),
+            }
+        }
+    }
+
+    impl crate::io::AsyncWrite for LoggingMockWriter {
+        fn poll_write(
+            mut self: Pin<&mut Self>,
+            _cx: &mut Context<'_>,
+            buf: &[u8],
+        ) -> Poll<Result<usize, io::Error>> {
+            assert!(buf.len() <= MAX_BUF);
+            self.write_history.push(buf.len());
+            Poll::Ready(Ok(buf.len()))
+        }
+
+        fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+            Poll::Ready(Ok(()))
+        }
+
+        fn poll_shutdown(
+            self: Pin<&mut Self>,
+            _cx: &mut Context<'_>,
+        ) -> Poll<Result<(), io::Error>> {
+            Poll::Ready(Ok(()))
+        }
+    }
+
+    #[test]
+    fn test_splitter() {
+        let data = str::repeat("█", MAX_BUF);
+        let mut wr = super::SplitByUtf8BoundaryIfWindows::new(TextMockWriter);
+        let fut = async move {
+            wr.write_all(data.as_bytes()).await.unwrap();
+        };
+        crate::runtime::Builder::new_current_thread()
+            .build()
+            .unwrap()
+            .block_on(fut);
+    }
+
+    #[test]
+    fn test_pseudo_text() {
+        // In this test we write a piece of binary data, whose beginning is
+        // text though. We then validate that even in this corner case buffer
+        // was not shrinked too much.
+        let checked_count = super::MAGIC_CONST * super::MAX_BYTES_PER_CHAR;
+        let mut data: Vec<u8> = str::repeat("a", checked_count).into();
+        data.extend(std::iter::repeat(0b1010_1010).take(MAX_BUF - checked_count + 1));
+        let mut writer = LoggingMockWriter::new();
+        let mut splitter = super::SplitByUtf8BoundaryIfWindows::new(&mut writer);
+        crate::runtime::Builder::new_current_thread()
+            .build()
+            .unwrap()
+            .block_on(async {
+                splitter.write_all(&data).await.unwrap();
+            });
+        // Check that at most two writes were performed
+        assert!(writer.write_history.len() <= 2);
+        // Check that all has been written
+        assert_eq!(
+            writer.write_history.iter().copied().sum::<usize>(),
+            data.len()
+        );
+        // Check that at most MAX_BYTES_PER_CHAR + 1 (i.e. 5) bytes were shrinked
+        // from the buffer: one because it was outside of MAX_BUF boundary, and
+        // up to one "utf8 code point".
+        assert!(data.len() - writer.write_history[0] <= super::MAX_BYTES_PER_CHAR + 1);
+    }
+}
diff --git a/third_party/rust/tokio/src/io/stdout.rs b/third_party/rust/tokio/src/io/stdout.rs
new file mode 100644
index 0000000000..a08ed01eed
--- /dev/null
+++ b/third_party/rust/tokio/src/io/stdout.rs
@@ -0,0 +1,108 @@
+use crate::io::blocking::Blocking;
+use crate::io::stdio_common::SplitByUtf8BoundaryIfWindows;
+use crate::io::AsyncWrite;
+use std::io;
+use std::pin::Pin;
+use std::task::Context;
+use std::task::Poll;
+
+cfg_io_std! {
+    /// A handle to the standard output stream of a process.
+    ///
+    /// Concurrent writes to stdout must be executed with care: Only individual
+    /// writes to this [`AsyncWrite`] are guaranteed to be intact. In particular
+    /// you should be aware that writes using [`write_all`] are not guaranteed
+    /// to occur as a single write, so multiple threads writing data with
+    /// [`write_all`] may result in interleaved output.
+    ///
+    /// Created by the [`stdout`] function.
+    ///
+    /// [`stdout`]: stdout()
+    /// [`AsyncWrite`]: AsyncWrite
+    /// [`write_all`]: crate::io::AsyncWriteExt::write_all()
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::io::{self, AsyncWriteExt};
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let mut stdout = io::stdout();
+    ///     stdout.write_all(b"Hello world!").await?;
+    ///     Ok(())
+    /// }
+    /// ```
+    #[derive(Debug)]
+    pub struct Stdout {
+        std: SplitByUtf8BoundaryIfWindows<Blocking<std::io::Stdout>>,
+    }
+
+    /// Constructs a new handle to the standard output of the current process.
+    ///
+    /// The returned handle allows writing to standard out from the within the
+    /// Tokio runtime.
+    ///
+    /// Concurrent writes to stdout must be executed with care: Only individual
+    /// writes to this [`AsyncWrite`] are guaranteed to be intact. In particular
+    /// you should be aware that writes using [`write_all`] are not guaranteed
+    /// to occur as a single write, so multiple threads writing data with
+    /// [`write_all`] may result in interleaved output.
+    ///
+    /// [`AsyncWrite`]: AsyncWrite
+    /// [`write_all`]: crate::io::AsyncWriteExt::write_all()
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::io::{self, AsyncWriteExt};
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let mut stdout = io::stdout();
+    ///     stdout.write_all(b"Hello world!").await?;
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn stdout() -> Stdout {
+        let std = io::stdout();
+        Stdout {
+            std: SplitByUtf8BoundaryIfWindows::new(Blocking::new(std)),
+        }
+    }
+}
+
+#[cfg(unix)]
+impl std::os::unix::io::AsRawFd for Stdout {
+    fn as_raw_fd(&self) -> std::os::unix::io::RawFd {
+        std::io::stdout().as_raw_fd()
+    }
+}
+
+#[cfg(windows)]
+impl std::os::windows::io::AsRawHandle for Stdout {
+    fn as_raw_handle(&self) -> std::os::windows::io::RawHandle {
+        std::io::stdout().as_raw_handle()
+    }
+}
+
+impl AsyncWrite for Stdout {
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        Pin::new(&mut self.std).poll_write(cx, buf)
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        Pin::new(&mut self.std).poll_flush(cx)
+    }
+
+    fn poll_shutdown(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), io::Error>> {
+        Pin::new(&mut self.std).poll_shutdown(cx)
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/async_buf_read_ext.rs b/third_party/rust/tokio/src/io/util/async_buf_read_ext.rs
new file mode 100644
index 0000000000..b241e354ba
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/async_buf_read_ext.rs
@@ -0,0 +1,351 @@
+use crate::io::util::fill_buf::{fill_buf, FillBuf};
+use crate::io::util::lines::{lines, Lines};
+use crate::io::util::read_line::{read_line, ReadLine};
+use crate::io::util::read_until::{read_until, ReadUntil};
+use crate::io::util::split::{split, Split};
+use crate::io::AsyncBufRead;
+
+cfg_io_util! {
+    /// An extension trait which adds utility methods to [`AsyncBufRead`] types.
+    ///
+    /// [`AsyncBufRead`]: crate::io::AsyncBufRead
+    pub trait AsyncBufReadExt: AsyncBufRead {
+        /// Reads all bytes into `buf` until the delimiter `byte` or EOF is reached.
+        ///
+        /// Equivalent to:
+        ///
+        /// ```ignore
+        /// async fn read_until(&mut self, byte: u8, buf: &mut Vec<u8>) -> io::Result<usize>;
+        /// ```
+        ///
+        /// This function will read bytes from the underlying stream until the
+        /// delimiter or EOF is found. Once found, all bytes up to, and including,
+        /// the delimiter (if found) will be appended to `buf`.
+        ///
+        /// If successful, this function will return the total number of bytes read.
+        ///
+        /// If this function returns `Ok(0)`, the stream has reached EOF.
+        ///
+        /// # Errors
+        ///
+        /// This function will ignore all instances of [`ErrorKind::Interrupted`] and
+        /// will otherwise return any errors returned by [`fill_buf`].
+        ///
+        /// If an I/O error is encountered then all bytes read so far will be
+        /// present in `buf` and its length will have been adjusted appropriately.
+        ///
+        /// [`fill_buf`]: AsyncBufRead::poll_fill_buf
+        /// [`ErrorKind::Interrupted`]: std::io::ErrorKind::Interrupted
+        ///
+        /// # Cancel safety
+        ///
+        /// If the method is used as the event in a
+        /// [`tokio::select!`](crate::select) statement and some other branch
+        /// completes first, then some data may have been partially read. Any
+        /// partially read bytes are appended to `buf`, and the method can be
+        /// called again to continue reading until `byte`.
+        ///
+        /// This method returns the total number of bytes read. If you cancel
+        /// the call to `read_until` and then call it again to continue reading,
+        /// the counter is reset.
+        ///
+        /// # Examples
+        ///
+        /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
+        /// this example, we use [`Cursor`] to read all the bytes in a byte slice
+        /// in hyphen delimited segments:
+        ///
+        /// [`Cursor`]: std::io::Cursor
+        ///
+        /// ```
+        /// use tokio::io::AsyncBufReadExt;
+        ///
+        /// use std::io::Cursor;
+        ///
+        /// #[tokio::main]
+        /// async fn main() {
+        ///     let mut cursor = Cursor::new(b"lorem-ipsum");
+        ///     let mut buf = vec![];
+        ///
+        ///     // cursor is at 'l'
+        ///     let num_bytes = cursor.read_until(b'-', &mut buf)
+        ///         .await
+        ///         .expect("reading from cursor won't fail");
+        ///
+        ///     assert_eq!(num_bytes, 6);
+        ///     assert_eq!(buf, b"lorem-");
+        ///     buf.clear();
+        ///
+        ///     // cursor is at 'i'
+        ///     let num_bytes = cursor.read_until(b'-', &mut buf)
+        ///         .await
+        ///         .expect("reading from cursor won't fail");
+        ///
+        ///     assert_eq!(num_bytes, 5);
+        ///     assert_eq!(buf, b"ipsum");
+        ///     buf.clear();
+        ///
+        ///     // cursor is at EOF
+        ///     let num_bytes = cursor.read_until(b'-', &mut buf)
+        ///         .await
+        ///         .expect("reading from cursor won't fail");
+        ///     assert_eq!(num_bytes, 0);
+        ///     assert_eq!(buf, b"");
+        /// }
+        /// ```
+        fn read_until<'a>(&'a mut self, byte: u8, buf: &'a mut Vec<u8>) -> ReadUntil<'a, Self>
+        where
+            Self: Unpin,
+        {
+            read_until(self, byte, buf)
+        }
+
+        /// Reads all bytes until a newline (the 0xA byte) is reached, and append
+        /// them to the provided buffer.
+        ///
+        /// Equivalent to:
+        ///
+        /// ```ignore
+        /// async fn read_line(&mut self, buf: &mut String) -> io::Result<usize>;
+        /// ```
+        ///
+        /// This function will read bytes from the underlying stream until the
+        /// newline delimiter (the 0xA byte) or EOF is found. Once found, all bytes
+        /// up to, and including, the delimiter (if found) will be appended to
+        /// `buf`.
+        ///
+        /// If successful, this function will return the total number of bytes read.
+        ///
+        /// If this function returns `Ok(0)`, the stream has reached EOF.
+        ///
+        /// # Errors
+        ///
+        /// This function has the same error semantics as [`read_until`] and will
+        /// also return an error if the read bytes are not valid UTF-8. If an I/O
+        /// error is encountered then `buf` may contain some bytes already read in
+        /// the event that all data read so far was valid UTF-8.
+        ///
+        /// [`read_until`]: AsyncBufReadExt::read_until
+        ///
+        /// # Cancel safety
+        ///
+        /// This method is not cancellation safe. If the method is used as the
+        /// event in a [`tokio::select!`](crate::select) statement and some
+        /// other branch completes first, then some data may have been partially
+        /// read, and this data is lost. There are no guarantees regarding the
+        /// contents of `buf` when the call is cancelled. The current
+        /// implementation replaces `buf` with the empty string, but this may
+        /// change in the future.
+        ///
+        /// This function does not behave like [`read_until`] because of the
+        /// requirement that a string contains only valid utf-8. If you need a
+        /// cancellation safe `read_line`, there are three options:
+        ///
+        ///  * Call [`read_until`] with a newline character and manually perform the utf-8 check.
+        ///  * The stream returned by [`lines`] has a cancellation safe
+        ///    [`next_line`] method.
+        ///  * Use [`tokio_util::codec::LinesCodec`][LinesCodec].
+        ///
+        /// [LinesCodec]: https://docs.rs/tokio-util/0.6/tokio_util/codec/struct.LinesCodec.html
+        /// [`read_until`]: Self::read_until
+        /// [`lines`]: Self::lines
+        /// [`next_line`]: crate::io::Lines::next_line
+        ///
+        /// # Examples
+        ///
+        /// [`std::io::Cursor`][`Cursor`] is a type that implements
+        /// `AsyncBufRead`. In this example, we use [`Cursor`] to read all the
+        /// lines in a byte slice:
+        ///
+        /// [`Cursor`]: std::io::Cursor
+        ///
+        /// ```
+        /// use tokio::io::AsyncBufReadExt;
+        ///
+        /// use std::io::Cursor;
+        ///
+        /// #[tokio::main]
+        /// async fn main() {
+        ///     let mut cursor = Cursor::new(b"foo\nbar");
+        ///     let mut buf = String::new();
+        ///
+        ///     // cursor is at 'f'
+        ///     let num_bytes = cursor.read_line(&mut buf)
+        ///         .await
+        ///         .expect("reading from cursor won't fail");
+        ///
+        ///     assert_eq!(num_bytes, 4);
+        ///     assert_eq!(buf, "foo\n");
+        ///     buf.clear();
+        ///
+        ///     // cursor is at 'b'
+        ///     let num_bytes = cursor.read_line(&mut buf)
+        ///         .await
+        ///         .expect("reading from cursor won't fail");
+        ///
+        ///     assert_eq!(num_bytes, 3);
+        ///     assert_eq!(buf, "bar");
+        ///     buf.clear();
+        ///
+        ///     // cursor is at EOF
+        ///     let num_bytes = cursor.read_line(&mut buf)
+        ///         .await
+        ///         .expect("reading from cursor won't fail");
+        ///
+        ///     assert_eq!(num_bytes, 0);
+        ///     assert_eq!(buf, "");
+        /// }
+        /// ```
+        fn read_line<'a>(&'a mut self, buf: &'a mut String) -> ReadLine<'a, Self>
+        where
+            Self: Unpin,
+        {
+            read_line(self, buf)
+        }
+
+        /// Returns a stream of the contents of this reader split on the byte
+        /// `byte`.
+        ///
+        /// This method is the asynchronous equivalent to
+        /// [`BufRead::split`](std::io::BufRead::split).
+        ///
+        /// The stream returned from this function will yield instances of
+        /// [`io::Result`]`<`[`Option`]`<`[`Vec<u8>`]`>>`. Each vector returned will *not* have
+        /// the delimiter byte at the end.
+        ///
+        /// [`io::Result`]: std::io::Result
+        /// [`Option`]: core::option::Option
+        /// [`Vec<u8>`]: std::vec::Vec
+        ///
+        /// # Errors
+        ///
+        /// Each item of the stream has the same error semantics as
+        /// [`AsyncBufReadExt::read_until`](AsyncBufReadExt::read_until).
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// # use tokio::io::AsyncBufRead;
+        /// use tokio::io::AsyncBufReadExt;
+        ///
+        /// # async fn dox(my_buf_read: impl AsyncBufRead + Unpin) -> std::io::Result<()> {
+        /// let mut segments = my_buf_read.split(b'f');
+        ///
+        /// while let Some(segment) = segments.next_segment().await? {
+        ///     println!("length = {}", segment.len())
+        /// }
+        /// # Ok(())
+        /// # }
+        /// ```
+        fn split(self, byte: u8) -> Split<Self>
+        where
+            Self: Sized + Unpin,
+        {
+            split(self, byte)
+        }
+
+        /// Returns the contents of the internal buffer, filling it with more
+        /// data from the inner reader if it is empty.
+        ///
+        /// This function is a lower-level call. It needs to be paired with the
+        /// [`consume`] method to function properly. When calling this method,
+        /// none of the contents will be "read" in the sense that later calling
+        /// `read` may return the same contents. As such, [`consume`] must be
+        /// called with the number of bytes that are consumed from this buffer
+        /// to ensure that the bytes are never returned twice.
+        ///
+        /// An empty buffer returned indicates that the stream has reached EOF.
+        ///
+        /// Equivalent to:
+        ///
+        /// ```ignore
+        /// async fn fill_buf(&mut self) -> io::Result<&[u8]>;
+        /// ```
+        ///
+        /// # Errors
+        ///
+        /// This function will return an I/O error if the underlying reader was
+        /// read, but returned an error.
+        ///
+        /// [`consume`]: crate::io::AsyncBufReadExt::consume
+        fn fill_buf(&mut self) -> FillBuf<'_, Self>
+        where
+            Self: Unpin,
+        {
+            fill_buf(self)
+        }
+
+        /// Tells this buffer that `amt` bytes have been consumed from the
+        /// buffer, so they should no longer be returned in calls to [`read`].
+        ///
+        /// This function is a lower-level call. It needs to be paired with the
+        /// [`fill_buf`] method to function properly. This function does not
+        /// perform any I/O, it simply informs this object that some amount of
+        /// its buffer, returned from [`fill_buf`], has been consumed and should
+        /// no longer be returned. As such, this function may do odd things if
+        /// [`fill_buf`] isn't called before calling it.
+        ///
+        /// The `amt` must be less than the number of bytes in the buffer
+        /// returned by [`fill_buf`].
+        ///
+        /// [`read`]: crate::io::AsyncReadExt::read
+        /// [`fill_buf`]: crate::io::AsyncBufReadExt::fill_buf
+        fn consume(&mut self, amt: usize)
+        where
+            Self: Unpin,
+        {
+            std::pin::Pin::new(self).consume(amt)
+        }
+
+        /// Returns a stream over the lines of this reader.
+        /// This method is the async equivalent to [`BufRead::lines`](std::io::BufRead::lines).
+        ///
+        /// The stream returned from this function will yield instances of
+        /// [`io::Result`]`<`[`Option`]`<`[`String`]`>>`. Each string returned will *not* have a newline
+        /// byte (the 0xA byte) or CRLF (0xD, 0xA bytes) at the end.
+        ///
+        /// [`io::Result`]: std::io::Result
+        /// [`Option`]: core::option::Option
+        /// [`String`]: String
+        ///
+        /// # Errors
+        ///
+        /// Each line of the stream has the same error semantics as [`AsyncBufReadExt::read_line`].
+        ///
+        /// # Examples
+        ///
+        /// [`std::io::Cursor`][`Cursor`] is a type that implements `BufRead`. In
+        /// this example, we use [`Cursor`] to iterate over all the lines in a byte
+        /// slice.
+        ///
+        /// [`Cursor`]: std::io::Cursor
+        ///
+        /// ```
+        /// use tokio::io::AsyncBufReadExt;
+        ///
+        /// use std::io::Cursor;
+        ///
+        /// #[tokio::main]
+        /// async fn main() {
+        ///     let cursor = Cursor::new(b"lorem\nipsum\r\ndolor");
+        ///
+        ///     let mut lines = cursor.lines();
+        ///
+        ///     assert_eq!(lines.next_line().await.unwrap(), Some(String::from("lorem")));
+        ///     assert_eq!(lines.next_line().await.unwrap(), Some(String::from("ipsum")));
+        ///     assert_eq!(lines.next_line().await.unwrap(), Some(String::from("dolor")));
+        ///     assert_eq!(lines.next_line().await.unwrap(), None);
+        /// }
+        /// ```
+        ///
+        /// [`AsyncBufReadExt::read_line`]: AsyncBufReadExt::read_line
+        fn lines(self) -> Lines<Self>
+        where
+            Self: Sized,
+        {
+            lines(self)
+        }
+    }
+}
+
+impl<R: AsyncBufRead + ?Sized> AsyncBufReadExt for R {}
diff --git a/third_party/rust/tokio/src/io/util/async_read_ext.rs b/third_party/rust/tokio/src/io/util/async_read_ext.rs
new file mode 100644
index 0000000000..df5445c2c6
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/async_read_ext.rs
@@ -0,0 +1,1294 @@
+use crate::io::util::chain::{chain, Chain};
+use crate::io::util::read::{read, Read};
+use crate::io::util::read_buf::{read_buf, ReadBuf};
+use crate::io::util::read_exact::{read_exact, ReadExact};
+use crate::io::util::read_int::{ReadF32, ReadF32Le, ReadF64, ReadF64Le};
+use crate::io::util::read_int::{
+    ReadI128, ReadI128Le, ReadI16, ReadI16Le, ReadI32, ReadI32Le, ReadI64, ReadI64Le, ReadI8,
+};
+use crate::io::util::read_int::{
+    ReadU128, ReadU128Le, ReadU16, ReadU16Le, ReadU32, ReadU32Le, ReadU64, ReadU64Le, ReadU8,
+};
+use crate::io::util::read_to_end::{read_to_end, ReadToEnd};
+use crate::io::util::read_to_string::{read_to_string, ReadToString};
+use crate::io::util::take::{take, Take};
+use crate::io::AsyncRead;
+
+use bytes::BufMut;
+
+cfg_io_util! {
+    /// Defines numeric reader
+    macro_rules! read_impl {
+        (
+            $(
+                $(#[$outer:meta])*
+                fn $name:ident(&mut self) -> $($fut:ident)*;
+            )*
+        ) => {
+            $(
+                $(#[$outer])*
+                fn $name<'a>(&'a mut self) -> $($fut)*<&'a mut Self> where Self: Unpin {
+                    $($fut)*::new(self)
+                }
+            )*
+        }
+    }
+
+    /// Reads bytes from a source.
+    ///
+    /// Implemented as an extension trait, adding utility methods to all
+    /// [`AsyncRead`] types. Callers will tend to import this trait instead of
+    /// [`AsyncRead`].
+    ///
+    /// ```no_run
+    /// use tokio::fs::File;
+    /// use tokio::io::{self, AsyncReadExt};
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let mut f = File::open("foo.txt").await?;
+    ///     let mut buffer = [0; 10];
+    ///
+    ///     // The `read` method is defined by this trait.
+    ///     let n = f.read(&mut buffer[..]).await?;
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// See [module][crate::io] documentation for more details.
+    ///
+    /// [`AsyncRead`]: AsyncRead
+    pub trait AsyncReadExt: AsyncRead {
+        /// Creates a new `AsyncRead` instance that chains this stream with
+        /// `next`.
+        ///
+        /// The returned `AsyncRead` instance will first read all bytes from this object
+        /// until EOF is encountered. Afterwards the output is equivalent to the
+        /// output of `next`.
+        ///
+        /// # Examples
+        ///
+        /// [`File`][crate::fs::File]s implement `AsyncRead`:
+        ///
+        /// ```no_run
+        /// use tokio::fs::File;
+        /// use tokio::io::{self, AsyncReadExt};
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let f1 = File::open("foo.txt").await?;
+        ///     let f2 = File::open("bar.txt").await?;
+        ///
+        ///     let mut handle = f1.chain(f2);
+        ///     let mut buffer = String::new();
+        ///
+        ///     // read the value into a String. We could use any AsyncRead
+        ///     // method here, this is just one example.
+        ///     handle.read_to_string(&mut buffer).await?;
+        ///     Ok(())
+        /// }
+        /// ```
+        fn chain<R>(self, next: R) -> Chain<Self, R>
+        where
+            Self: Sized,
+            R: AsyncRead,
+        {
+            chain(self, next)
+        }
+
+        /// Pulls some bytes from this source into the specified buffer,
+        /// returning how many bytes were read.
+        ///
+        /// Equivalent to:
+        ///
+        /// ```ignore
+        /// async fn read(&mut self, buf: &mut [u8]) -> io::Result<usize>;
+        /// ```
+        ///
+        /// This method does not provide any guarantees about whether it
+        /// completes immediately or asynchronously.
+        ///
+        /// # Return
+        ///
+        /// If the return value of this method is `Ok(n)`, then it must be
+        /// guaranteed that `0 <= n <= buf.len()`. A nonzero `n` value indicates
+        /// that the buffer `buf` has been filled in with `n` bytes of data from
+        /// this source. If `n` is `0`, then it can indicate one of two
+        /// scenarios:
+        ///
+        /// 1. This reader has reached its "end of file" and will likely no longer
+        ///    be able to produce bytes. Note that this does not mean that the
+        ///    reader will *always* no longer be able to produce bytes.
+        /// 2. The buffer specified was 0 bytes in length.
+        ///
+        /// No guarantees are provided about the contents of `buf` when this
+        /// function is called, implementations cannot rely on any property of the
+        /// contents of `buf` being `true`. It is recommended that *implementations*
+        /// only write data to `buf` instead of reading its contents.
+        ///
+        /// Correspondingly, however, *callers* of this method may not assume
+        /// any guarantees about how the implementation uses `buf`. It is
+        /// possible that the code that's supposed to write to the buffer might
+        /// also read from it. It is your responsibility to make sure that `buf`
+        /// is initialized before calling `read`.
+        ///
+        /// # Errors
+        ///
+        /// If this function encounters any form of I/O or other error, an error
+        /// variant will be returned. If an error is returned then it must be
+        /// guaranteed that no bytes were read.
+        ///
+        /// # Cancel safety
+        ///
+        /// This method is cancel safe. If you use it as the event in a
+        /// [`tokio::select!`](crate::select) statement and some other branch
+        /// completes first, then it is guaranteed that no data was read.
+        ///
+        /// # Examples
+        ///
+        /// [`File`][crate::fs::File]s implement `Read`:
+        ///
+        /// ```no_run
+        /// use tokio::fs::File;
+        /// use tokio::io::{self, AsyncReadExt};
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let mut f = File::open("foo.txt").await?;
+        ///     let mut buffer = [0; 10];
+        ///
+        ///     // read up to 10 bytes
+        ///     let n = f.read(&mut buffer[..]).await?;
+        ///
+        ///     println!("The bytes: {:?}", &buffer[..n]);
+        ///     Ok(())
+        /// }
+        /// ```
+        fn read<'a>(&'a mut self, buf: &'a mut [u8]) -> Read<'a, Self>
+        where
+            Self: Unpin,
+        {
+            read(self, buf)
+        }
+
+        /// Pulls some bytes from this source into the specified buffer,
+        /// advancing the buffer's internal cursor.
+        ///
+        /// Equivalent to:
+        ///
+        /// ```ignore
+        /// async fn read_buf<B: BufMut>(&mut self, buf: &mut B) -> io::Result<usize>;
+        /// ```
+        ///
+        /// Usually, only a single `read` syscall is issued, even if there is
+        /// more space in the supplied buffer.
+        ///
+        /// This method does not provide any guarantees about whether it
+        /// completes immediately or asynchronously.
+        ///
+        /// # Return
+        ///
+        /// A nonzero `n` value indicates that the buffer `buf` has been filled
+        /// in with `n` bytes of data from this source. If `n` is `0`, then it
+        /// can indicate one of two scenarios:
+        ///
+        /// 1. This reader has reached its "end of file" and will likely no longer
+        ///    be able to produce bytes. Note that this does not mean that the
+        ///    reader will *always* no longer be able to produce bytes.
+        /// 2. The buffer specified had a remaining capacity of zero.
+        ///
+        /// # Errors
+        ///
+        /// If this function encounters any form of I/O or other error, an error
+        /// variant will be returned. If an error is returned then it must be
+        /// guaranteed that no bytes were read.
+        ///
+        /// # Cancel safety
+        ///
+        /// This method is cancel safe. If you use it as the event in a
+        /// [`tokio::select!`](crate::select) statement and some other branch
+        /// completes first, then it is guaranteed that no data was read.
+        ///
+        /// # Examples
+        ///
+        /// [`File`] implements `Read` and [`BytesMut`] implements [`BufMut`]:
+        ///
+        /// [`File`]: crate::fs::File
+        /// [`BytesMut`]: bytes::BytesMut
+        /// [`BufMut`]: bytes::BufMut
+        ///
+        /// ```no_run
+        /// use tokio::fs::File;
+        /// use tokio::io::{self, AsyncReadExt};
+        ///
+        /// use bytes::BytesMut;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let mut f = File::open("foo.txt").await?;
+        ///     let mut buffer = BytesMut::with_capacity(10);
+        ///
+        ///     assert!(buffer.is_empty());
+        ///
+        ///     // read up to 10 bytes, note that the return value is not needed
+        ///     // to access the data that was read as `buffer`'s internal
+        ///     // cursor is updated.
+        ///     f.read_buf(&mut buffer).await?;
+        ///
+        ///     println!("The bytes: {:?}", &buffer[..]);
+        ///     Ok(())
+        /// }
+        /// ```
+        fn read_buf<'a, B>(&'a mut self, buf: &'a mut B) -> ReadBuf<'a, Self, B>
+        where
+            Self: Sized + Unpin,
+            B: BufMut,
+        {
+            read_buf(self, buf)
+        }
+
+        /// Reads the exact number of bytes required to fill `buf`.
+        ///
+        /// Equivalent to:
+        ///
+        /// ```ignore
+        /// async fn read_exact(&mut self, buf: &mut [u8]) -> io::Result<usize>;
+        /// ```
+        ///
+        /// This function reads as many bytes as necessary to completely fill
+        /// the specified buffer `buf`.
+        ///
+        /// # Errors
+        ///
+        /// If the operation encounters an "end of file" before completely
+        /// filling the buffer, it returns an error of the kind
+        /// [`ErrorKind::UnexpectedEof`]. The contents of `buf` are unspecified
+        /// in this case.
+        ///
+        /// If any other read error is encountered then the operation
+        /// immediately returns. The contents of `buf` are unspecified in this
+        /// case.
+        ///
+        /// If this operation returns an error, it is unspecified how many bytes
+        /// it has read, but it will never read more than would be necessary to
+        /// completely fill the buffer.
+        ///
+        /// # Cancel safety
+        ///
+        /// This method is not cancellation safe. If the method is used as the
+        /// event in a [`tokio::select!`](crate::select) statement and some
+        /// other branch completes first, then some data may already have been
+        /// read into `buf`.
+        ///
+        /// # Examples
+        ///
+        /// [`File`][crate::fs::File]s implement `Read`:
+        ///
+        /// ```no_run
+        /// use tokio::fs::File;
+        /// use tokio::io::{self, AsyncReadExt};
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let mut f = File::open("foo.txt").await?;
+        ///     let mut buffer = [0; 10];
+        ///
+        ///     // read exactly 10 bytes
+        ///     f.read_exact(&mut buffer).await?;
+        ///     Ok(())
+        /// }
+        /// ```
+        ///
+        /// [`ErrorKind::UnexpectedEof`]: std::io::ErrorKind::UnexpectedEof
+        fn read_exact<'a>(&'a mut self, buf: &'a mut [u8]) -> ReadExact<'a, Self>
+        where
+            Self: Unpin,
+        {
+            read_exact(self, buf)
+        }
+
+        read_impl! {
+            /// Reads an unsigned 8 bit integer from the underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_u8(&mut self) -> io::Result<u8>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read unsigned 8 bit integers from an `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![2, 5]);
+            ///
+            ///     assert_eq!(2, reader.read_u8().await?);
+            ///     assert_eq!(5, reader.read_u8().await?);
+            ///
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_u8(&mut self) -> ReadU8;
+
+            /// Reads a signed 8 bit integer from the underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_i8(&mut self) -> io::Result<i8>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read unsigned 8 bit integers from an `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![0x02, 0xfb]);
+            ///
+            ///     assert_eq!(2, reader.read_i8().await?);
+            ///     assert_eq!(-5, reader.read_i8().await?);
+            ///
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_i8(&mut self) -> ReadI8;
+
+            /// Reads an unsigned 16-bit integer in big-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_u16(&mut self) -> io::Result<u16>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read unsigned 16 bit big-endian integers from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![2, 5, 3, 0]);
+            ///
+            ///     assert_eq!(517, reader.read_u16().await?);
+            ///     assert_eq!(768, reader.read_u16().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_u16(&mut self) -> ReadU16;
+
+            /// Reads a signed 16-bit integer in big-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_i16(&mut self) -> io::Result<i16>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read signed 16 bit big-endian integers from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![0x00, 0xc1, 0xff, 0x7c]);
+            ///
+            ///     assert_eq!(193, reader.read_i16().await?);
+            ///     assert_eq!(-132, reader.read_i16().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_i16(&mut self) -> ReadI16;
+
+            /// Reads an unsigned 32-bit integer in big-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_u32(&mut self) -> io::Result<u32>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read unsigned 32-bit big-endian integers from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![0x00, 0x00, 0x01, 0x0b]);
+            ///
+            ///     assert_eq!(267, reader.read_u32().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_u32(&mut self) -> ReadU32;
+
+            /// Reads a signed 32-bit integer in big-endian order from the
+            /// underlying reader.
+            ///
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_i32(&mut self) -> io::Result<i32>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read signed 32-bit big-endian integers from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![0xff, 0xff, 0x7a, 0x33]);
+            ///
+            ///     assert_eq!(-34253, reader.read_i32().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_i32(&mut self) -> ReadI32;
+
+            /// Reads an unsigned 64-bit integer in big-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_u64(&mut self) -> io::Result<u64>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read unsigned 64-bit big-endian integers from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![
+            ///         0x00, 0x03, 0x43, 0x95, 0x4d, 0x60, 0x86, 0x83
+            ///     ]);
+            ///
+            ///     assert_eq!(918733457491587, reader.read_u64().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_u64(&mut self) -> ReadU64;
+
+            /// Reads an signed 64-bit integer in big-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_i64(&mut self) -> io::Result<i64>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read signed 64-bit big-endian integers from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![0x80, 0, 0, 0, 0, 0, 0, 0]);
+            ///
+            ///     assert_eq!(i64::MIN, reader.read_i64().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_i64(&mut self) -> ReadI64;
+
+            /// Reads an unsigned 128-bit integer in big-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_u128(&mut self) -> io::Result<u128>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read unsigned 128-bit big-endian integers from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![
+            ///         0x00, 0x03, 0x43, 0x95, 0x4d, 0x60, 0x86, 0x83,
+            ///         0x00, 0x03, 0x43, 0x95, 0x4d, 0x60, 0x86, 0x83
+            ///     ]);
+            ///
+            ///     assert_eq!(16947640962301618749969007319746179, reader.read_u128().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_u128(&mut self) -> ReadU128;
+
+            /// Reads an signed 128-bit integer in big-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_i128(&mut self) -> io::Result<i128>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read signed 128-bit big-endian integers from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![
+            ///         0x80, 0, 0, 0, 0, 0, 0, 0,
+            ///         0, 0, 0, 0, 0, 0, 0, 0
+            ///     ]);
+            ///
+            ///     assert_eq!(i128::MIN, reader.read_i128().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_i128(&mut self) -> ReadI128;
+
+            /// Reads an 32-bit floating point type in big-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_f32(&mut self) -> io::Result<f32>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read 32-bit floating point type from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![0xff, 0x7f, 0xff, 0xff]);
+            ///
+            ///     assert_eq!(f32::MIN, reader.read_f32().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_f32(&mut self) -> ReadF32;
+
+            /// Reads an 64-bit floating point type in big-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_f64(&mut self) -> io::Result<f64>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read 64-bit floating point type from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![
+            ///         0xff, 0xef, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
+            ///     ]);
+            ///
+            ///     assert_eq!(f64::MIN, reader.read_f64().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_f64(&mut self) -> ReadF64;
+
+            /// Reads an unsigned 16-bit integer in little-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_u16_le(&mut self) -> io::Result<u16>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read unsigned 16 bit little-endian integers from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![2, 5, 3, 0]);
+            ///
+            ///     assert_eq!(1282, reader.read_u16_le().await?);
+            ///     assert_eq!(3, reader.read_u16_le().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_u16_le(&mut self) -> ReadU16Le;
+
+            /// Reads a signed 16-bit integer in little-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_i16_le(&mut self) -> io::Result<i16>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read signed 16 bit little-endian integers from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![0x00, 0xc1, 0xff, 0x7c]);
+            ///
+            ///     assert_eq!(-16128, reader.read_i16_le().await?);
+            ///     assert_eq!(31999, reader.read_i16_le().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_i16_le(&mut self) -> ReadI16Le;
+
+            /// Reads an unsigned 32-bit integer in little-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_u32_le(&mut self) -> io::Result<u32>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read unsigned 32-bit little-endian integers from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![0x00, 0x00, 0x01, 0x0b]);
+            ///
+            ///     assert_eq!(184614912, reader.read_u32_le().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_u32_le(&mut self) -> ReadU32Le;
+
+            /// Reads a signed 32-bit integer in little-endian order from the
+            /// underlying reader.
+            ///
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_i32_le(&mut self) -> io::Result<i32>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read signed 32-bit little-endian integers from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![0xff, 0xff, 0x7a, 0x33]);
+            ///
+            ///     assert_eq!(863698943, reader.read_i32_le().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_i32_le(&mut self) -> ReadI32Le;
+
+            /// Reads an unsigned 64-bit integer in little-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_u64_le(&mut self) -> io::Result<u64>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read unsigned 64-bit little-endian integers from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![
+            ///         0x00, 0x03, 0x43, 0x95, 0x4d, 0x60, 0x86, 0x83
+            ///     ]);
+            ///
+            ///     assert_eq!(9477368352180732672, reader.read_u64_le().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_u64_le(&mut self) -> ReadU64Le;
+
+            /// Reads an signed 64-bit integer in little-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_i64_le(&mut self) -> io::Result<i64>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read signed 64-bit little-endian integers from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![0x80, 0, 0, 0, 0, 0, 0, 0]);
+            ///
+            ///     assert_eq!(128, reader.read_i64_le().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_i64_le(&mut self) -> ReadI64Le;
+
+            /// Reads an unsigned 128-bit integer in little-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_u128_le(&mut self) -> io::Result<u128>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read unsigned 128-bit little-endian integers from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![
+            ///         0x00, 0x03, 0x43, 0x95, 0x4d, 0x60, 0x86, 0x83,
+            ///         0x00, 0x03, 0x43, 0x95, 0x4d, 0x60, 0x86, 0x83
+            ///     ]);
+            ///
+            ///     assert_eq!(174826588484952389081207917399662330624, reader.read_u128_le().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_u128_le(&mut self) -> ReadU128Le;
+
+            /// Reads an signed 128-bit integer in little-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_i128_le(&mut self) -> io::Result<i128>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read signed 128-bit little-endian integers from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![
+            ///         0x80, 0, 0, 0, 0, 0, 0, 0,
+            ///         0, 0, 0, 0, 0, 0, 0, 0
+            ///     ]);
+            ///
+            ///     assert_eq!(128, reader.read_i128_le().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_i128_le(&mut self) -> ReadI128Le;
+
+            /// Reads an 32-bit floating point type in little-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_f32_le(&mut self) -> io::Result<f32>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read 32-bit floating point type from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![0xff, 0xff, 0x7f, 0xff]);
+            ///
+            ///     assert_eq!(f32::MIN, reader.read_f32_le().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_f32_le(&mut self) -> ReadF32Le;
+
+            /// Reads an 64-bit floating point type in little-endian order from the
+            /// underlying reader.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn read_f64_le(&mut self) -> io::Result<f64>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered reader to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncReadExt::read_exact`].
+            ///
+            /// [`AsyncReadExt::read_exact`]: AsyncReadExt::read_exact
+            ///
+            /// # Examples
+            ///
+            /// Read 64-bit floating point type from a `AsyncRead`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncReadExt};
+            ///
+            /// use std::io::Cursor;
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut reader = Cursor::new(vec![
+            ///         0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xef, 0xff
+            ///     ]);
+            ///
+            ///     assert_eq!(f64::MIN, reader.read_f64_le().await?);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn read_f64_le(&mut self) -> ReadF64Le;
+        }
+
+        /// Reads all bytes until EOF in this source, placing them into `buf`.
+        ///
+        /// Equivalent to:
+        ///
+        /// ```ignore
+        /// async fn read_to_end(&mut self, buf: &mut Vec<u8>) -> io::Result<usize>;
+        /// ```
+        ///
+        /// All bytes read from this source will be appended to the specified
+        /// buffer `buf`. This function will continuously call [`read()`] to
+        /// append more data to `buf` until [`read()`] returns `Ok(0)`.
+        ///
+        /// If successful, the total number of bytes read is returned.
+        ///
+        /// [`read()`]: AsyncReadExt::read
+        ///
+        /// # Errors
+        ///
+        /// If a read error is encountered then the `read_to_end` operation
+        /// immediately completes. Any bytes which have already been read will
+        /// be appended to `buf`.
+        ///
+        /// # Examples
+        ///
+        /// [`File`][crate::fs::File]s implement `Read`:
+        ///
+        /// ```no_run
+        /// use tokio::io::{self, AsyncReadExt};
+        /// use tokio::fs::File;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let mut f = File::open("foo.txt").await?;
+        ///     let mut buffer = Vec::new();
+        ///
+        ///     // read the whole file
+        ///     f.read_to_end(&mut buffer).await?;
+        ///     Ok(())
+        /// }
+        /// ```
+        ///
+        /// (See also the [`tokio::fs::read`] convenience function for reading from a
+        /// file.)
+        ///
+        /// [`tokio::fs::read`]: fn@crate::fs::read
+        fn read_to_end<'a>(&'a mut self, buf: &'a mut Vec<u8>) -> ReadToEnd<'a, Self>
+        where
+            Self: Unpin,
+        {
+            read_to_end(self, buf)
+        }
+
+        /// Reads all bytes until EOF in this source, appending them to `buf`.
+        ///
+        /// Equivalent to:
+        ///
+        /// ```ignore
+        /// async fn read_to_string(&mut self, buf: &mut String) -> io::Result<usize>;
+        /// ```
+        ///
+        /// If successful, the number of bytes which were read and appended to
+        /// `buf` is returned.
+        ///
+        /// # Errors
+        ///
+        /// If the data in this stream is *not* valid UTF-8 then an error is
+        /// returned and `buf` is unchanged.
+        ///
+        /// See [`read_to_end`][AsyncReadExt::read_to_end] for other error semantics.
+        ///
+        /// # Examples
+        ///
+        /// [`File`][crate::fs::File]s implement `Read`:
+        ///
+        /// ```no_run
+        /// use tokio::io::{self, AsyncReadExt};
+        /// use tokio::fs::File;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let mut f = File::open("foo.txt").await?;
+        ///     let mut buffer = String::new();
+        ///
+        ///     f.read_to_string(&mut buffer).await?;
+        ///     Ok(())
+        /// }
+        /// ```
+        ///
+        /// (See also the [`crate::fs::read_to_string`] convenience function for
+        /// reading from a file.)
+        ///
+        /// [`crate::fs::read_to_string`]: fn@crate::fs::read_to_string
+        fn read_to_string<'a>(&'a mut self, dst: &'a mut String) -> ReadToString<'a, Self>
+        where
+            Self: Unpin,
+        {
+            read_to_string(self, dst)
+        }
+
+        /// Creates an adaptor which reads at most `limit` bytes from it.
+        ///
+        /// This function returns a new instance of `AsyncRead` which will read
+        /// at most `limit` bytes, after which it will always return EOF
+        /// (`Ok(0)`). Any read errors will not count towards the number of
+        /// bytes read and future calls to [`read()`] may succeed.
+        ///
+        /// [`read()`]: fn@crate::io::AsyncReadExt::read
+        ///
+        /// [read]: AsyncReadExt::read
+        ///
+        /// # Examples
+        ///
+        /// [`File`][crate::fs::File]s implement `Read`:
+        ///
+        /// ```no_run
+        /// use tokio::io::{self, AsyncReadExt};
+        /// use tokio::fs::File;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let f = File::open("foo.txt").await?;
+        ///     let mut buffer = [0; 5];
+        ///
+        ///     // read at most five bytes
+        ///     let mut handle = f.take(5);
+        ///
+        ///     handle.read(&mut buffer).await?;
+        ///     Ok(())
+        /// }
+        /// ```
+        fn take(self, limit: u64) -> Take<Self>
+        where
+            Self: Sized,
+        {
+            take(self, limit)
+        }
+    }
+}
+
+impl<R: AsyncRead + ?Sized> AsyncReadExt for R {}
diff --git a/third_party/rust/tokio/src/io/util/async_seek_ext.rs b/third_party/rust/tokio/src/io/util/async_seek_ext.rs
new file mode 100644
index 0000000000..46b3e6c0d3
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/async_seek_ext.rs
@@ -0,0 +1,93 @@
+use crate::io::seek::{seek, Seek};
+use crate::io::AsyncSeek;
+use std::io::SeekFrom;
+
+cfg_io_util! {
+    /// An extension trait that adds utility methods to [`AsyncSeek`] types.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::io::{self, Cursor, SeekFrom};
+    /// use tokio::io::{AsyncSeekExt, AsyncReadExt};
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let mut cursor = Cursor::new(b"abcdefg");
+    ///
+    ///     // the `seek` method is defined by this trait
+    ///     cursor.seek(SeekFrom::Start(3)).await?;
+    ///
+    ///     let mut buf = [0; 1];
+    ///     let n = cursor.read(&mut buf).await?;
+    ///     assert_eq!(n, 1);
+    ///     assert_eq!(buf, [b'd']);
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// See [module][crate::io] documentation for more details.
+    ///
+    /// [`AsyncSeek`]: AsyncSeek
+    pub trait AsyncSeekExt: AsyncSeek {
+        /// Creates a future which will seek an IO object, and then yield the
+        /// new position in the object and the object itself.
+        ///
+        /// Equivalent to:
+        ///
+        /// ```ignore
+        /// async fn seek(&mut self, pos: SeekFrom) -> io::Result<u64>;
+        /// ```
+        ///
+        /// In the case of an error the buffer and the object will be discarded, with
+        /// the error yielded.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::fs::File;
+        /// use tokio::io::{AsyncSeekExt, AsyncReadExt};
+        ///
+        /// use std::io::SeekFrom;
+        ///
+        /// # async fn dox() -> std::io::Result<()> {
+        /// let mut file = File::open("foo.txt").await?;
+        /// file.seek(SeekFrom::Start(6)).await?;
+        ///
+        /// let mut contents = vec![0u8; 10];
+        /// file.read_exact(&mut contents).await?;
+        /// # Ok(())
+        /// # }
+        /// ```
+        fn seek(&mut self, pos: SeekFrom) -> Seek<'_, Self>
+        where
+            Self: Unpin,
+        {
+            seek(self, pos)
+        }
+
+        /// Creates a future which will rewind to the beginning of the stream.
+        ///
+        /// This is convenience method, equivalent to to `self.seek(SeekFrom::Start(0))`.
+        fn rewind(&mut self) -> Seek<'_, Self>
+        where
+            Self: Unpin,
+        {
+            self.seek(SeekFrom::Start(0))
+        }
+
+        /// Creates a future which will return the current seek position from the
+        /// start of the stream.
+        ///
+        /// This is equivalent to `self.seek(SeekFrom::Current(0))`.
+        fn stream_position(&mut self) -> Seek<'_, Self>
+        where
+            Self: Unpin,
+        {
+            self.seek(SeekFrom::Current(0))
+        }
+    }
+}
+
+impl<S: AsyncSeek + ?Sized> AsyncSeekExt for S {}
diff --git a/third_party/rust/tokio/src/io/util/async_write_ext.rs b/third_party/rust/tokio/src/io/util/async_write_ext.rs
new file mode 100644
index 0000000000..93a318315e
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/async_write_ext.rs
@@ -0,0 +1,1293 @@
+use crate::io::util::flush::{flush, Flush};
+use crate::io::util::shutdown::{shutdown, Shutdown};
+use crate::io::util::write::{write, Write};
+use crate::io::util::write_all::{write_all, WriteAll};
+use crate::io::util::write_all_buf::{write_all_buf, WriteAllBuf};
+use crate::io::util::write_buf::{write_buf, WriteBuf};
+use crate::io::util::write_int::{WriteF32, WriteF32Le, WriteF64, WriteF64Le};
+use crate::io::util::write_int::{
+    WriteI128, WriteI128Le, WriteI16, WriteI16Le, WriteI32, WriteI32Le, WriteI64, WriteI64Le,
+    WriteI8,
+};
+use crate::io::util::write_int::{
+    WriteU128, WriteU128Le, WriteU16, WriteU16Le, WriteU32, WriteU32Le, WriteU64, WriteU64Le,
+    WriteU8,
+};
+use crate::io::util::write_vectored::{write_vectored, WriteVectored};
+use crate::io::AsyncWrite;
+use std::io::IoSlice;
+
+use bytes::Buf;
+
+cfg_io_util! {
+    /// Defines numeric writer.
+    macro_rules! write_impl {
+        (
+            $(
+                $(#[$outer:meta])*
+                fn $name:ident(&mut self, n: $ty:ty) -> $($fut:ident)*;
+            )*
+        ) => {
+            $(
+                $(#[$outer])*
+                fn $name<'a>(&'a mut self, n: $ty) -> $($fut)*<&'a mut Self> where Self: Unpin {
+                    $($fut)*::new(self, n)
+                }
+            )*
+        }
+    }
+
+    /// Writes bytes to a sink.
+    ///
+    /// Implemented as an extension trait, adding utility methods to all
+    /// [`AsyncWrite`] types. Callers will tend to import this trait instead of
+    /// [`AsyncWrite`].
+    ///
+    /// ```no_run
+    /// use tokio::io::{self, AsyncWriteExt};
+    /// use tokio::fs::File;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let data = b"some bytes";
+    ///
+    ///     let mut pos = 0;
+    ///     let mut buffer = File::create("foo.txt").await?;
+    ///
+    ///     while pos < data.len() {
+    ///         let bytes_written = buffer.write(&data[pos..]).await?;
+    ///         pos += bytes_written;
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// See [module][crate::io] documentation for more details.
+    ///
+    /// [`AsyncWrite`]: AsyncWrite
+    pub trait AsyncWriteExt: AsyncWrite {
+        /// Writes a buffer into this writer, returning how many bytes were
+        /// written.
+        ///
+        /// Equivalent to:
+        ///
+        /// ```ignore
+        /// async fn write(&mut self, buf: &[u8]) -> io::Result<usize>;
+        /// ```
+        ///
+        /// This function will attempt to write the entire contents of `buf`, but
+        /// the entire write may not succeed, or the write may also generate an
+        /// error. A call to `write` represents *at most one* attempt to write to
+        /// any wrapped object.
+        ///
+        /// # Return
+        ///
+        /// If the return value is `Ok(n)` then it must be guaranteed that `n <=
+        /// buf.len()`. A return value of `0` typically means that the
+        /// underlying object is no longer able to accept bytes and will likely
+        /// not be able to in the future as well, or that the buffer provided is
+        /// empty.
+        ///
+        /// # Errors
+        ///
+        /// Each call to `write` may generate an I/O error indicating that the
+        /// operation could not be completed. If an error is returned then no bytes
+        /// in the buffer were written to this writer.
+        ///
+        /// It is **not** considered an error if the entire buffer could not be
+        /// written to this writer.
+        ///
+        /// # Cancel safety
+        ///
+        /// This method is cancellation safe in the sense that if it is used as
+        /// the event in a [`tokio::select!`](crate::select) statement and some
+        /// other branch completes first, then it is guaranteed that no data was
+        /// written to this `AsyncWrite`.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::io::{self, AsyncWriteExt};
+        /// use tokio::fs::File;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let mut file = File::create("foo.txt").await?;
+        ///
+        ///     // Writes some prefix of the byte string, not necessarily all of it.
+        ///     file.write(b"some bytes").await?;
+        ///     Ok(())
+        /// }
+        /// ```
+        fn write<'a>(&'a mut self, src: &'a [u8]) -> Write<'a, Self>
+        where
+            Self: Unpin,
+        {
+            write(self, src)
+        }
+
+        /// Like [`write`], except that it writes from a slice of buffers.
+        ///
+        /// Equivalent to:
+        ///
+        /// ```ignore
+        /// async fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize>;
+        /// ```
+        ///
+        /// See [`AsyncWrite::poll_write_vectored`] for more details.
+        ///
+        /// # Cancel safety
+        ///
+        /// This method is cancellation safe in the sense that if it is used as
+        /// the event in a [`tokio::select!`](crate::select) statement and some
+        /// other branch completes first, then it is guaranteed that no data was
+        /// written to this `AsyncWrite`.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::io::{self, AsyncWriteExt};
+        /// use tokio::fs::File;
+        /// use std::io::IoSlice;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let mut file = File::create("foo.txt").await?;
+        ///
+        ///     let bufs: &[_] = &[
+        ///         IoSlice::new(b"hello"),
+        ///         IoSlice::new(b" "),
+        ///         IoSlice::new(b"world"),
+        ///     ];
+        ///
+        ///     file.write_vectored(&bufs).await?;
+        ///
+        ///     Ok(())
+        /// }
+        /// ```
+        ///
+        /// [`write`]: AsyncWriteExt::write
+        fn write_vectored<'a, 'b>(&'a mut self, bufs: &'a [IoSlice<'b>]) -> WriteVectored<'a, 'b, Self>
+        where
+            Self: Unpin,
+        {
+            write_vectored(self, bufs)
+        }
+
+        /// Writes a buffer into this writer, advancing the buffer's internal
+        /// cursor.
+        ///
+        /// Equivalent to:
+        ///
+        /// ```ignore
+        /// async fn write_buf<B: Buf>(&mut self, buf: &mut B) -> io::Result<usize>;
+        /// ```
+        ///
+        /// This function will attempt to write the entire contents of `buf`, but
+        /// the entire write may not succeed, or the write may also generate an
+        /// error. After the operation completes, the buffer's
+        /// internal cursor is advanced by the number of bytes written. A
+        /// subsequent call to `write_buf` using the **same** `buf` value will
+        /// resume from the point that the first call to `write_buf` completed.
+        /// A call to `write_buf` represents *at most one* attempt to write to any
+        /// wrapped object.
+        ///
+        /// # Return
+        ///
+        /// If the return value is `Ok(n)` then it must be guaranteed that `n <=
+        /// buf.len()`. A return value of `0` typically means that the
+        /// underlying object is no longer able to accept bytes and will likely
+        /// not be able to in the future as well, or that the buffer provided is
+        /// empty.
+        ///
+        /// # Errors
+        ///
+        /// Each call to `write` may generate an I/O error indicating that the
+        /// operation could not be completed. If an error is returned then no bytes
+        /// in the buffer were written to this writer.
+        ///
+        /// It is **not** considered an error if the entire buffer could not be
+        /// written to this writer.
+        ///
+        /// # Cancel safety
+        ///
+        /// This method is cancellation safe in the sense that if it is used as
+        /// the event in a [`tokio::select!`](crate::select) statement and some
+        /// other branch completes first, then it is guaranteed that no data was
+        /// written to this `AsyncWrite`.
+        ///
+        /// # Examples
+        ///
+        /// [`File`] implements [`AsyncWrite`] and [`Cursor`]`<&[u8]>` implements [`Buf`]:
+        ///
+        /// [`File`]: crate::fs::File
+        /// [`Buf`]: bytes::Buf
+        /// [`Cursor`]: std::io::Cursor
+        ///
+        /// ```no_run
+        /// use tokio::io::{self, AsyncWriteExt};
+        /// use tokio::fs::File;
+        ///
+        /// use bytes::Buf;
+        /// use std::io::Cursor;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let mut file = File::create("foo.txt").await?;
+        ///     let mut buffer = Cursor::new(b"data to write");
+        ///
+        ///     // Loop until the entire contents of the buffer are written to
+        ///     // the file.
+        ///     while buffer.has_remaining() {
+        ///         // Writes some prefix of the byte string, not necessarily
+        ///         // all of it.
+        ///         file.write_buf(&mut buffer).await?;
+        ///     }
+        ///
+        ///     Ok(())
+        /// }
+        /// ```
+        fn write_buf<'a, B>(&'a mut self, src: &'a mut B) -> WriteBuf<'a, Self, B>
+        where
+            Self: Sized + Unpin,
+            B: Buf,
+        {
+            write_buf(self, src)
+        }
+
+        /// Attempts to write an entire buffer into this writer.
+        ///
+        /// Equivalent to:
+        ///
+        /// ```ignore
+        /// async fn write_all_buf(&mut self, buf: impl Buf) -> Result<(), io::Error> {
+        ///     while buf.has_remaining() {
+        ///         self.write_buf(&mut buf).await?;
+        ///     }
+        ///     Ok(())
+        /// }
+        /// ```
+        ///
+        /// This method will continuously call [`write`] until
+        /// [`buf.has_remaining()`](bytes::Buf::has_remaining) returns false. This method will not
+        /// return until the entire buffer has been successfully written or an error occurs. The
+        /// first error generated will be returned.
+        ///
+        /// The buffer is advanced after each chunk is successfully written. After failure,
+        /// `src.chunk()` will return the chunk that failed to write.
+        ///
+        /// # Cancel safety
+        ///
+        /// If `write_all_buf` is used as the event in a
+        /// [`tokio::select!`](crate::select) statement and some other branch
+        /// completes first, then the data in the provided buffer may have been
+        /// partially written. However, it is guaranteed that the provided
+        /// buffer has been [advanced] by the amount of bytes that have been
+        /// partially written.
+        ///
+        /// # Examples
+        ///
+        /// [`File`] implements [`AsyncWrite`] and [`Cursor`]`<&[u8]>` implements [`Buf`]:
+        ///
+        /// [`File`]: crate::fs::File
+        /// [`Buf`]: bytes::Buf
+        /// [`Cursor`]: std::io::Cursor
+        /// [advanced]: bytes::Buf::advance
+        ///
+        /// ```no_run
+        /// use tokio::io::{self, AsyncWriteExt};
+        /// use tokio::fs::File;
+        ///
+        /// use std::io::Cursor;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let mut file = File::create("foo.txt").await?;
+        ///     let mut buffer = Cursor::new(b"data to write");
+        ///
+        ///     file.write_all_buf(&mut buffer).await?;
+        ///     Ok(())
+        /// }
+        /// ```
+        ///
+        /// [`write`]: AsyncWriteExt::write
+        fn write_all_buf<'a, B>(&'a mut self, src: &'a mut B) -> WriteAllBuf<'a, Self, B>
+        where
+            Self: Sized + Unpin,
+            B: Buf,
+        {
+            write_all_buf(self, src)
+        }
+
+        /// Attempts to write an entire buffer into this writer.
+        ///
+        /// Equivalent to:
+        ///
+        /// ```ignore
+        /// async fn write_all(&mut self, buf: &[u8]) -> io::Result<()>;
+        /// ```
+        ///
+        /// This method will continuously call [`write`] until there is no more data
+        /// to be written. This method will not return until the entire buffer
+        /// has been successfully written or such an error occurs. The first
+        /// error generated from this method will be returned.
+        ///
+        /// # Cancel safety
+        ///
+        /// This method is not cancellation safe. If it is used as the event
+        /// in a [`tokio::select!`](crate::select) statement and some other
+        /// branch completes first, then the provided buffer may have been
+        /// partially written, but future calls to `write_all` will start over
+        /// from the beginning of the buffer.
+        ///
+        /// # Errors
+        ///
+        /// This function will return the first error that [`write`] returns.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::io::{self, AsyncWriteExt};
+        /// use tokio::fs::File;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let mut file = File::create("foo.txt").await?;
+        ///
+        ///     file.write_all(b"some bytes").await?;
+        ///     Ok(())
+        /// }
+        /// ```
+        ///
+        /// [`write`]: AsyncWriteExt::write
+        fn write_all<'a>(&'a mut self, src: &'a [u8]) -> WriteAll<'a, Self>
+        where
+            Self: Unpin,
+        {
+            write_all(self, src)
+        }
+
+        write_impl! {
+            /// Writes an unsigned 8-bit integer to the underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_u8(&mut self, n: u8) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write unsigned 8 bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_u8(2).await?;
+            ///     writer.write_u8(5).await?;
+            ///
+            ///     assert_eq!(writer, b"\x02\x05");
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_u8(&mut self, n: u8) -> WriteU8;
+
+            /// Writes an unsigned 8-bit integer to the underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_i8(&mut self, n: i8) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write unsigned 8 bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_u8(2).await?;
+            ///     writer.write_u8(5).await?;
+            ///
+            ///     assert_eq!(writer, b"\x02\x05");
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_i8(&mut self, n: i8) -> WriteI8;
+
+            /// Writes an unsigned 16-bit integer in big-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_u16(&mut self, n: u16) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write unsigned 16-bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_u16(517).await?;
+            ///     writer.write_u16(768).await?;
+            ///
+            ///     assert_eq!(writer, b"\x02\x05\x03\x00");
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_u16(&mut self, n: u16) -> WriteU16;
+
+            /// Writes a signed 16-bit integer in big-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_i16(&mut self, n: i16) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write signed 16-bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_i16(193).await?;
+            ///     writer.write_i16(-132).await?;
+            ///
+            ///     assert_eq!(writer, b"\x00\xc1\xff\x7c");
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_i16(&mut self, n: i16) -> WriteI16;
+
+            /// Writes an unsigned 32-bit integer in big-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_u32(&mut self, n: u32) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write unsigned 32-bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_u32(267).await?;
+            ///     writer.write_u32(1205419366).await?;
+            ///
+            ///     assert_eq!(writer, b"\x00\x00\x01\x0b\x47\xd9\x3d\x66");
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_u32(&mut self, n: u32) -> WriteU32;
+
+            /// Writes a signed 32-bit integer in big-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_i32(&mut self, n: i32) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write signed 32-bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_i32(267).await?;
+            ///     writer.write_i32(1205419366).await?;
+            ///
+            ///     assert_eq!(writer, b"\x00\x00\x01\x0b\x47\xd9\x3d\x66");
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_i32(&mut self, n: i32) -> WriteI32;
+
+            /// Writes an unsigned 64-bit integer in big-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_u64(&mut self, n: u64) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write unsigned 64-bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_u64(918733457491587).await?;
+            ///     writer.write_u64(143).await?;
+            ///
+            ///     assert_eq!(writer, b"\x00\x03\x43\x95\x4d\x60\x86\x83\x00\x00\x00\x00\x00\x00\x00\x8f");
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_u64(&mut self, n: u64) -> WriteU64;
+
+            /// Writes an signed 64-bit integer in big-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_i64(&mut self, n: i64) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write signed 64-bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_i64(i64::MIN).await?;
+            ///     writer.write_i64(i64::MAX).await?;
+            ///
+            ///     assert_eq!(writer, b"\x80\x00\x00\x00\x00\x00\x00\x00\x7f\xff\xff\xff\xff\xff\xff\xff");
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_i64(&mut self, n: i64) -> WriteI64;
+
+            /// Writes an unsigned 128-bit integer in big-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_u128(&mut self, n: u128) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write unsigned 128-bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_u128(16947640962301618749969007319746179).await?;
+            ///
+            ///     assert_eq!(writer, vec![
+            ///         0x00, 0x03, 0x43, 0x95, 0x4d, 0x60, 0x86, 0x83,
+            ///         0x00, 0x03, 0x43, 0x95, 0x4d, 0x60, 0x86, 0x83
+            ///     ]);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_u128(&mut self, n: u128) -> WriteU128;
+
+            /// Writes an signed 128-bit integer in big-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_i128(&mut self, n: i128) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write signed 128-bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_i128(i128::MIN).await?;
+            ///
+            ///     assert_eq!(writer, vec![
+            ///         0x80, 0, 0, 0, 0, 0, 0, 0,
+            ///         0, 0, 0, 0, 0, 0, 0, 0
+            ///     ]);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_i128(&mut self, n: i128) -> WriteI128;
+
+            /// Writes an 32-bit floating point type in big-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_f32(&mut self, n: f32) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write 32-bit floating point type to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_f32(f32::MIN).await?;
+            ///
+            ///     assert_eq!(writer, vec![0xff, 0x7f, 0xff, 0xff]);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_f32(&mut self, n: f32) -> WriteF32;
+
+            /// Writes an 64-bit floating point type in big-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_f64(&mut self, n: f64) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write 64-bit floating point type to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_f64(f64::MIN).await?;
+            ///
+            ///     assert_eq!(writer, vec![
+            ///         0xff, 0xef, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
+            ///     ]);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_f64(&mut self, n: f64) -> WriteF64;
+
+            /// Writes an unsigned 16-bit integer in little-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_u16_le(&mut self, n: u16) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write unsigned 16-bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_u16_le(517).await?;
+            ///     writer.write_u16_le(768).await?;
+            ///
+            ///     assert_eq!(writer, b"\x05\x02\x00\x03");
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_u16_le(&mut self, n: u16) -> WriteU16Le;
+
+            /// Writes a signed 16-bit integer in little-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_i16_le(&mut self, n: i16) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write signed 16-bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_i16_le(193).await?;
+            ///     writer.write_i16_le(-132).await?;
+            ///
+            ///     assert_eq!(writer, b"\xc1\x00\x7c\xff");
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_i16_le(&mut self, n: i16) -> WriteI16Le;
+
+            /// Writes an unsigned 32-bit integer in little-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_u32_le(&mut self, n: u32) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write unsigned 32-bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_u32_le(267).await?;
+            ///     writer.write_u32_le(1205419366).await?;
+            ///
+            ///     assert_eq!(writer, b"\x0b\x01\x00\x00\x66\x3d\xd9\x47");
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_u32_le(&mut self, n: u32) -> WriteU32Le;
+
+            /// Writes a signed 32-bit integer in little-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_i32_le(&mut self, n: i32) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write signed 32-bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_i32_le(267).await?;
+            ///     writer.write_i32_le(1205419366).await?;
+            ///
+            ///     assert_eq!(writer, b"\x0b\x01\x00\x00\x66\x3d\xd9\x47");
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_i32_le(&mut self, n: i32) -> WriteI32Le;
+
+            /// Writes an unsigned 64-bit integer in little-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_u64_le(&mut self, n: u64) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write unsigned 64-bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_u64_le(918733457491587).await?;
+            ///     writer.write_u64_le(143).await?;
+            ///
+            ///     assert_eq!(writer, b"\x83\x86\x60\x4d\x95\x43\x03\x00\x8f\x00\x00\x00\x00\x00\x00\x00");
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_u64_le(&mut self, n: u64) -> WriteU64Le;
+
+            /// Writes an signed 64-bit integer in little-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_i64_le(&mut self, n: i64) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write signed 64-bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_i64_le(i64::MIN).await?;
+            ///     writer.write_i64_le(i64::MAX).await?;
+            ///
+            ///     assert_eq!(writer, b"\x00\x00\x00\x00\x00\x00\x00\x80\xff\xff\xff\xff\xff\xff\xff\x7f");
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_i64_le(&mut self, n: i64) -> WriteI64Le;
+
+            /// Writes an unsigned 128-bit integer in little-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_u128_le(&mut self, n: u128) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write unsigned 128-bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_u128_le(16947640962301618749969007319746179).await?;
+            ///
+            ///     assert_eq!(writer, vec![
+            ///         0x83, 0x86, 0x60, 0x4d, 0x95, 0x43, 0x03, 0x00,
+            ///         0x83, 0x86, 0x60, 0x4d, 0x95, 0x43, 0x03, 0x00,
+            ///     ]);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_u128_le(&mut self, n: u128) -> WriteU128Le;
+
+            /// Writes an signed 128-bit integer in little-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_i128_le(&mut self, n: i128) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write signed 128-bit integers to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_i128_le(i128::MIN).await?;
+            ///
+            ///     assert_eq!(writer, vec![
+            ///          0, 0, 0, 0, 0, 0, 0,
+            ///         0, 0, 0, 0, 0, 0, 0, 0, 0x80
+            ///     ]);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_i128_le(&mut self, n: i128) -> WriteI128Le;
+
+            /// Writes an 32-bit floating point type in little-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_f32_le(&mut self, n: f32) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write 32-bit floating point type to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_f32_le(f32::MIN).await?;
+            ///
+            ///     assert_eq!(writer, vec![0xff, 0xff, 0x7f, 0xff]);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_f32_le(&mut self, n: f32) -> WriteF32Le;
+
+            /// Writes an 64-bit floating point type in little-endian order to the
+            /// underlying writer.
+            ///
+            /// Equivalent to:
+            ///
+            /// ```ignore
+            /// async fn write_f64_le(&mut self, n: f64) -> io::Result<()>;
+            /// ```
+            ///
+            /// It is recommended to use a buffered writer to avoid excessive
+            /// syscalls.
+            ///
+            /// # Errors
+            ///
+            /// This method returns the same errors as [`AsyncWriteExt::write_all`].
+            ///
+            /// [`AsyncWriteExt::write_all`]: AsyncWriteExt::write_all
+            ///
+            /// # Examples
+            ///
+            /// Write 64-bit floating point type to a `AsyncWrite`:
+            ///
+            /// ```rust
+            /// use tokio::io::{self, AsyncWriteExt};
+            ///
+            /// #[tokio::main]
+            /// async fn main() -> io::Result<()> {
+            ///     let mut writer = Vec::new();
+            ///
+            ///     writer.write_f64_le(f64::MIN).await?;
+            ///
+            ///     assert_eq!(writer, vec![
+            ///         0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xef, 0xff
+            ///     ]);
+            ///     Ok(())
+            /// }
+            /// ```
+            fn write_f64_le(&mut self, n: f64) -> WriteF64Le;
+        }
+
+        /// Flushes this output stream, ensuring that all intermediately buffered
+        /// contents reach their destination.
+        ///
+        /// Equivalent to:
+        ///
+        /// ```ignore
+        /// async fn flush(&mut self) -> io::Result<()>;
+        /// ```
+        ///
+        /// # Errors
+        ///
+        /// It is considered an error if not all bytes could be written due to
+        /// I/O errors or EOF being reached.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::io::{self, BufWriter, AsyncWriteExt};
+        /// use tokio::fs::File;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let f = File::create("foo.txt").await?;
+        ///     let mut buffer = BufWriter::new(f);
+        ///
+        ///     buffer.write_all(b"some bytes").await?;
+        ///     buffer.flush().await?;
+        ///     Ok(())
+        /// }
+        /// ```
+        fn flush(&mut self) -> Flush<'_, Self>
+        where
+            Self: Unpin,
+        {
+            flush(self)
+        }
+
+        /// Shuts down the output stream, ensuring that the value can be dropped
+        /// cleanly.
+        ///
+        /// Equivalent to:
+        ///
+        /// ```ignore
+        /// async fn shutdown(&mut self) -> io::Result<()>;
+        /// ```
+        ///
+        /// Similar to [`flush`], all intermediately buffered is written to the
+        /// underlying stream. Once the operation completes, the caller should
+        /// no longer attempt to write to the stream. For example, the
+        /// `TcpStream` implementation will issue a `shutdown(Write)` sys call.
+        ///
+        /// [`flush`]: fn@crate::io::AsyncWriteExt::flush
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::io::{self, BufWriter, AsyncWriteExt};
+        /// use tokio::fs::File;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     let f = File::create("foo.txt").await?;
+        ///     let mut buffer = BufWriter::new(f);
+        ///
+        ///     buffer.write_all(b"some bytes").await?;
+        ///     buffer.shutdown().await?;
+        ///     Ok(())
+        /// }
+        /// ```
+        fn shutdown(&mut self) -> Shutdown<'_, Self>
+        where
+            Self: Unpin,
+        {
+            shutdown(self)
+        }
+    }
+}
+
+impl<W: AsyncWrite + ?Sized> AsyncWriteExt for W {}
diff --git a/third_party/rust/tokio/src/io/util/buf_reader.rs b/third_party/rust/tokio/src/io/util/buf_reader.rs
new file mode 100644
index 0000000000..60879c0fdc
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/buf_reader.rs
@@ -0,0 +1,311 @@
+use crate::io::util::DEFAULT_BUF_SIZE;
+use crate::io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, ReadBuf};
+
+use pin_project_lite::pin_project;
+use std::io::{self, IoSlice, SeekFrom};
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use std::{cmp, fmt, mem};
+
+pin_project! {
+    /// The `BufReader` struct adds buffering to any reader.
+    ///
+    /// It can be excessively inefficient to work directly with a [`AsyncRead`]
+    /// instance. A `BufReader` performs large, infrequent reads on the underlying
+    /// [`AsyncRead`] and maintains an in-memory buffer of the results.
+    ///
+    /// `BufReader` can improve the speed of programs that make *small* and
+    /// *repeated* read calls to the same file or network socket. It does not
+    /// help when reading very large amounts at once, or reading just one or a few
+    /// times. It also provides no advantage when reading from a source that is
+    /// already in memory, like a `Vec<u8>`.
+    ///
+    /// When the `BufReader` is dropped, the contents of its buffer will be
+    /// discarded. Creating multiple instances of a `BufReader` on the same
+    /// stream can cause data loss.
+    #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
+    pub struct BufReader<R> {
+        #[pin]
+        pub(super) inner: R,
+        pub(super) buf: Box<[u8]>,
+        pub(super) pos: usize,
+        pub(super) cap: usize,
+        pub(super) seek_state: SeekState,
+    }
+}
+
+impl<R: AsyncRead> BufReader<R> {
+    /// Creates a new `BufReader` with a default buffer capacity. The default is currently 8 KB,
+    /// but may change in the future.
+    pub fn new(inner: R) -> Self {
+        Self::with_capacity(DEFAULT_BUF_SIZE, inner)
+    }
+
+    /// Creates a new `BufReader` with the specified buffer capacity.
+    pub fn with_capacity(capacity: usize, inner: R) -> Self {
+        let buffer = vec![0; capacity];
+        Self {
+            inner,
+            buf: buffer.into_boxed_slice(),
+            pos: 0,
+            cap: 0,
+            seek_state: SeekState::Init,
+        }
+    }
+
+    /// Gets a reference to the underlying reader.
+    ///
+    /// It is inadvisable to directly read from the underlying reader.
+    pub fn get_ref(&self) -> &R {
+        &self.inner
+    }
+
+    /// Gets a mutable reference to the underlying reader.
+    ///
+    /// It is inadvisable to directly read from the underlying reader.
+    pub fn get_mut(&mut self) -> &mut R {
+        &mut self.inner
+    }
+
+    /// Gets a pinned mutable reference to the underlying reader.
+    ///
+    /// It is inadvisable to directly read from the underlying reader.
+    pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut R> {
+        self.project().inner
+    }
+
+    /// Consumes this `BufReader`, returning the underlying reader.
+    ///
+    /// Note that any leftover data in the internal buffer is lost.
+    pub fn into_inner(self) -> R {
+        self.inner
+    }
+
+    /// Returns a reference to the internally buffered data.
+    ///
+    /// Unlike `fill_buf`, this will not attempt to fill the buffer if it is empty.
+    pub fn buffer(&self) -> &[u8] {
+        &self.buf[self.pos..self.cap]
+    }
+
+    /// Invalidates all data in the internal buffer.
+    #[inline]
+    fn discard_buffer(self: Pin<&mut Self>) {
+        let me = self.project();
+        *me.pos = 0;
+        *me.cap = 0;
+    }
+}
+
+impl<R: AsyncRead> AsyncRead for BufReader<R> {
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        // If we don't have any buffered data and we're doing a massive read
+        // (larger than our internal buffer), bypass our internal buffer
+        // entirely.
+        if self.pos == self.cap && buf.remaining() >= self.buf.len() {
+            let res = ready!(self.as_mut().get_pin_mut().poll_read(cx, buf));
+            self.discard_buffer();
+            return Poll::Ready(res);
+        }
+        let rem = ready!(self.as_mut().poll_fill_buf(cx))?;
+        let amt = std::cmp::min(rem.len(), buf.remaining());
+        buf.put_slice(&rem[..amt]);
+        self.consume(amt);
+        Poll::Ready(Ok(()))
+    }
+}
+
+impl<R: AsyncRead> AsyncBufRead for BufReader<R> {
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        let me = self.project();
+
+        // If we've reached the end of our internal buffer then we need to fetch
+        // some more data from the underlying reader.
+        // Branch using `>=` instead of the more correct `==`
+        // to tell the compiler that the pos..cap slice is always valid.
+        if *me.pos >= *me.cap {
+            debug_assert!(*me.pos == *me.cap);
+            let mut buf = ReadBuf::new(me.buf);
+            ready!(me.inner.poll_read(cx, &mut buf))?;
+            *me.cap = buf.filled().len();
+            *me.pos = 0;
+        }
+        Poll::Ready(Ok(&me.buf[*me.pos..*me.cap]))
+    }
+
+    fn consume(self: Pin<&mut Self>, amt: usize) {
+        let me = self.project();
+        *me.pos = cmp::min(*me.pos + amt, *me.cap);
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub(super) enum SeekState {
+    /// start_seek has not been called.
+    Init,
+    /// start_seek has been called, but poll_complete has not yet been called.
+    Start(SeekFrom),
+    /// Waiting for completion of the first poll_complete in the `n.checked_sub(remainder).is_none()` branch.
+    PendingOverflowed(i64),
+    /// Waiting for completion of poll_complete.
+    Pending,
+}
+
+/// Seeks to an offset, in bytes, in the underlying reader.
+///
+/// The position used for seeking with `SeekFrom::Current(_)` is the
+/// position the underlying reader would be at if the `BufReader` had no
+/// internal buffer.
+///
+/// Seeking always discards the internal buffer, even if the seek position
+/// would otherwise fall within it. This guarantees that calling
+/// `.into_inner()` immediately after a seek yields the underlying reader
+/// at the same position.
+///
+/// See [`AsyncSeek`] for more details.
+///
+/// Note: In the edge case where you're seeking with `SeekFrom::Current(n)`
+/// where `n` minus the internal buffer length overflows an `i64`, two
+/// seeks will be performed instead of one. If the second seek returns
+/// `Err`, the underlying reader will be left at the same position it would
+/// have if you called `seek` with `SeekFrom::Current(0)`.
+impl<R: AsyncRead + AsyncSeek> AsyncSeek for BufReader<R> {
+    fn start_seek(self: Pin<&mut Self>, pos: SeekFrom) -> io::Result<()> {
+        // We needs to call seek operation multiple times.
+        // And we should always call both start_seek and poll_complete,
+        // as start_seek alone cannot guarantee that the operation will be completed.
+        // poll_complete receives a Context and returns a Poll, so it cannot be called
+        // inside start_seek.
+        *self.project().seek_state = SeekState::Start(pos);
+        Ok(())
+    }
+
+    fn poll_complete(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
+        let res = match mem::replace(self.as_mut().project().seek_state, SeekState::Init) {
+            SeekState::Init => {
+                // 1.x AsyncSeek recommends calling poll_complete before start_seek.
+                // We don't have to guarantee that the value returned by
+                // poll_complete called without start_seek is correct,
+                // so we'll return 0.
+                return Poll::Ready(Ok(0));
+            }
+            SeekState::Start(SeekFrom::Current(n)) => {
+                let remainder = (self.cap - self.pos) as i64;
+                // it should be safe to assume that remainder fits within an i64 as the alternative
+                // means we managed to allocate 8 exbibytes and that's absurd.
+                // But it's not out of the realm of possibility for some weird underlying reader to
+                // support seeking by i64::MIN so we need to handle underflow when subtracting
+                // remainder.
+                if let Some(offset) = n.checked_sub(remainder) {
+                    self.as_mut()
+                        .get_pin_mut()
+                        .start_seek(SeekFrom::Current(offset))?;
+                } else {
+                    // seek backwards by our remainder, and then by the offset
+                    self.as_mut()
+                        .get_pin_mut()
+                        .start_seek(SeekFrom::Current(-remainder))?;
+                    if self.as_mut().get_pin_mut().poll_complete(cx)?.is_pending() {
+                        *self.as_mut().project().seek_state = SeekState::PendingOverflowed(n);
+                        return Poll::Pending;
+                    }
+
+                    // https://github.com/rust-lang/rust/pull/61157#issuecomment-495932676
+                    self.as_mut().discard_buffer();
+
+                    self.as_mut()
+                        .get_pin_mut()
+                        .start_seek(SeekFrom::Current(n))?;
+                }
+                self.as_mut().get_pin_mut().poll_complete(cx)?
+            }
+            SeekState::PendingOverflowed(n) => {
+                if self.as_mut().get_pin_mut().poll_complete(cx)?.is_pending() {
+                    *self.as_mut().project().seek_state = SeekState::PendingOverflowed(n);
+                    return Poll::Pending;
+                }
+
+                // https://github.com/rust-lang/rust/pull/61157#issuecomment-495932676
+                self.as_mut().discard_buffer();
+
+                self.as_mut()
+                    .get_pin_mut()
+                    .start_seek(SeekFrom::Current(n))?;
+                self.as_mut().get_pin_mut().poll_complete(cx)?
+            }
+            SeekState::Start(pos) => {
+                // Seeking with Start/End doesn't care about our buffer length.
+                self.as_mut().get_pin_mut().start_seek(pos)?;
+                self.as_mut().get_pin_mut().poll_complete(cx)?
+            }
+            SeekState::Pending => self.as_mut().get_pin_mut().poll_complete(cx)?,
+        };
+
+        match res {
+            Poll::Ready(res) => {
+                self.discard_buffer();
+                Poll::Ready(Ok(res))
+            }
+            Poll::Pending => {
+                *self.as_mut().project().seek_state = SeekState::Pending;
+                Poll::Pending
+            }
+        }
+    }
+}
+
+impl<R: AsyncRead + AsyncWrite> AsyncWrite for BufReader<R> {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.get_pin_mut().poll_write(cx, buf)
+    }
+
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.get_pin_mut().poll_write_vectored(cx, bufs)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        self.get_ref().is_write_vectored()
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.get_pin_mut().poll_flush(cx)
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.get_pin_mut().poll_shutdown(cx)
+    }
+}
+
+impl<R: fmt::Debug> fmt::Debug for BufReader<R> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("BufReader")
+            .field("reader", &self.inner)
+            .field(
+                "buffer",
+                &format_args!("{}/{}", self.cap - self.pos, self.buf.len()),
+            )
+            .finish()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn assert_unpin() {
+        crate::is_unpin::<BufReader<()>>();
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/buf_stream.rs b/third_party/rust/tokio/src/io/util/buf_stream.rs
new file mode 100644
index 0000000000..595c142aca
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/buf_stream.rs
@@ -0,0 +1,207 @@
+use crate::io::util::{BufReader, BufWriter};
+use crate::io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, ReadBuf};
+
+use pin_project_lite::pin_project;
+use std::io::{self, IoSlice, SeekFrom};
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// Wraps a type that is [`AsyncWrite`] and [`AsyncRead`], and buffers its input and output.
+    ///
+    /// It can be excessively inefficient to work directly with something that implements [`AsyncWrite`]
+    /// and [`AsyncRead`]. For example, every `write`, however small, has to traverse the syscall
+    /// interface, and similarly, every read has to do the same. The [`BufWriter`] and [`BufReader`]
+    /// types aid with these problems respectively, but do so in only one direction. `BufStream` wraps
+    /// one in the other so that both directions are buffered. See their documentation for details.
+    #[derive(Debug)]
+    #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
+    pub struct BufStream<RW> {
+        #[pin]
+        inner: BufReader<BufWriter<RW>>,
+    }
+}
+
+impl<RW: AsyncRead + AsyncWrite> BufStream<RW> {
+    /// Wraps a type in both [`BufWriter`] and [`BufReader`].
+    ///
+    /// See the documentation for those types and [`BufStream`] for details.
+    pub fn new(stream: RW) -> BufStream<RW> {
+        BufStream {
+            inner: BufReader::new(BufWriter::new(stream)),
+        }
+    }
+
+    /// Creates a `BufStream` with the specified [`BufReader`] capacity and [`BufWriter`]
+    /// capacity.
+    ///
+    /// See the documentation for those types and [`BufStream`] for details.
+    pub fn with_capacity(
+        reader_capacity: usize,
+        writer_capacity: usize,
+        stream: RW,
+    ) -> BufStream<RW> {
+        BufStream {
+            inner: BufReader::with_capacity(
+                reader_capacity,
+                BufWriter::with_capacity(writer_capacity, stream),
+            ),
+        }
+    }
+
+    /// Gets a reference to the underlying I/O object.
+    ///
+    /// It is inadvisable to directly read from the underlying I/O object.
+    pub fn get_ref(&self) -> &RW {
+        self.inner.get_ref().get_ref()
+    }
+
+    /// Gets a mutable reference to the underlying I/O object.
+    ///
+    /// It is inadvisable to directly read from the underlying I/O object.
+    pub fn get_mut(&mut self) -> &mut RW {
+        self.inner.get_mut().get_mut()
+    }
+
+    /// Gets a pinned mutable reference to the underlying I/O object.
+    ///
+    /// It is inadvisable to directly read from the underlying I/O object.
+    pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut RW> {
+        self.project().inner.get_pin_mut().get_pin_mut()
+    }
+
+    /// Consumes this `BufStream`, returning the underlying I/O object.
+    ///
+    /// Note that any leftover data in the internal buffer is lost.
+    pub fn into_inner(self) -> RW {
+        self.inner.into_inner().into_inner()
+    }
+}
+
+impl<RW> From<BufReader<BufWriter<RW>>> for BufStream<RW> {
+    fn from(b: BufReader<BufWriter<RW>>) -> Self {
+        BufStream { inner: b }
+    }
+}
+
+impl<RW> From<BufWriter<BufReader<RW>>> for BufStream<RW> {
+    fn from(b: BufWriter<BufReader<RW>>) -> Self {
+        // we need to "invert" the reader and writer
+        let BufWriter {
+            inner:
+                BufReader {
+                    inner,
+                    buf: rbuf,
+                    pos,
+                    cap,
+                    seek_state: rseek_state,
+                },
+            buf: wbuf,
+            written,
+            seek_state: wseek_state,
+        } = b;
+
+        BufStream {
+            inner: BufReader {
+                inner: BufWriter {
+                    inner,
+                    buf: wbuf,
+                    written,
+                    seek_state: wseek_state,
+                },
+                buf: rbuf,
+                pos,
+                cap,
+                seek_state: rseek_state,
+            },
+        }
+    }
+}
+
+impl<RW: AsyncRead + AsyncWrite> AsyncWrite for BufStream<RW> {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.project().inner.poll_write(cx, buf)
+    }
+
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.project().inner.poll_write_vectored(cx, bufs)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        self.inner.is_write_vectored()
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.project().inner.poll_flush(cx)
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.project().inner.poll_shutdown(cx)
+    }
+}
+
+impl<RW: AsyncRead + AsyncWrite> AsyncRead for BufStream<RW> {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        self.project().inner.poll_read(cx, buf)
+    }
+}
+
+/// Seek to an offset, in bytes, in the underlying stream.
+///
+/// The position used for seeking with `SeekFrom::Current(_)` is the
+/// position the underlying stream would be at if the `BufStream` had no
+/// internal buffer.
+///
+/// Seeking always discards the internal buffer, even if the seek position
+/// would otherwise fall within it. This guarantees that calling
+/// `.into_inner()` immediately after a seek yields the underlying reader
+/// at the same position.
+///
+/// See [`AsyncSeek`] for more details.
+///
+/// Note: In the edge case where you're seeking with `SeekFrom::Current(n)`
+/// where `n` minus the internal buffer length overflows an `i64`, two
+/// seeks will be performed instead of one. If the second seek returns
+/// `Err`, the underlying reader will be left at the same position it would
+/// have if you called `seek` with `SeekFrom::Current(0)`.
+impl<RW: AsyncRead + AsyncWrite + AsyncSeek> AsyncSeek for BufStream<RW> {
+    fn start_seek(self: Pin<&mut Self>, position: SeekFrom) -> io::Result<()> {
+        self.project().inner.start_seek(position)
+    }
+
+    fn poll_complete(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
+        self.project().inner.poll_complete(cx)
+    }
+}
+
+impl<RW: AsyncRead + AsyncWrite> AsyncBufRead for BufStream<RW> {
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        self.project().inner.poll_fill_buf(cx)
+    }
+
+    fn consume(self: Pin<&mut Self>, amt: usize) {
+        self.project().inner.consume(amt)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn assert_unpin() {
+        crate::is_unpin::<BufStream<()>>();
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/buf_writer.rs b/third_party/rust/tokio/src/io/util/buf_writer.rs
new file mode 100644
index 0000000000..8dd1bba60a
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/buf_writer.rs
@@ -0,0 +1,310 @@
+use crate::io::util::DEFAULT_BUF_SIZE;
+use crate::io::{AsyncBufRead, AsyncRead, AsyncSeek, AsyncWrite, ReadBuf};
+
+use pin_project_lite::pin_project;
+use std::fmt;
+use std::io::{self, IoSlice, SeekFrom, Write};
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// Wraps a writer and buffers its output.
+    ///
+    /// It can be excessively inefficient to work directly with something that
+    /// implements [`AsyncWrite`]. A `BufWriter` keeps an in-memory buffer of data and
+    /// writes it to an underlying writer in large, infrequent batches.
+    ///
+    /// `BufWriter` can improve the speed of programs that make *small* and
+    /// *repeated* write calls to the same file or network socket. It does not
+    /// help when writing very large amounts at once, or writing just one or a few
+    /// times. It also provides no advantage when writing to a destination that is
+    /// in memory, like a `Vec<u8>`.
+    ///
+    /// When the `BufWriter` is dropped, the contents of its buffer will be
+    /// discarded. Creating multiple instances of a `BufWriter` on the same
+    /// stream can cause data loss. If you need to write out the contents of its
+    /// buffer, you must manually call flush before the writer is dropped.
+    ///
+    /// [`AsyncWrite`]: AsyncWrite
+    /// [`flush`]: super::AsyncWriteExt::flush
+    ///
+    #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
+    pub struct BufWriter<W> {
+        #[pin]
+        pub(super) inner: W,
+        pub(super) buf: Vec<u8>,
+        pub(super) written: usize,
+        pub(super) seek_state: SeekState,
+    }
+}
+
+impl<W: AsyncWrite> BufWriter<W> {
+    /// Creates a new `BufWriter` with a default buffer capacity. The default is currently 8 KB,
+    /// but may change in the future.
+    pub fn new(inner: W) -> Self {
+        Self::with_capacity(DEFAULT_BUF_SIZE, inner)
+    }
+
+    /// Creates a new `BufWriter` with the specified buffer capacity.
+    pub fn with_capacity(cap: usize, inner: W) -> Self {
+        Self {
+            inner,
+            buf: Vec::with_capacity(cap),
+            written: 0,
+            seek_state: SeekState::Init,
+        }
+    }
+
+    fn flush_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        let mut me = self.project();
+
+        let len = me.buf.len();
+        let mut ret = Ok(());
+        while *me.written < len {
+            match ready!(me.inner.as_mut().poll_write(cx, &me.buf[*me.written..])) {
+                Ok(0) => {
+                    ret = Err(io::Error::new(
+                        io::ErrorKind::WriteZero,
+                        "failed to write the buffered data",
+                    ));
+                    break;
+                }
+                Ok(n) => *me.written += n,
+                Err(e) => {
+                    ret = Err(e);
+                    break;
+                }
+            }
+        }
+        if *me.written > 0 {
+            me.buf.drain(..*me.written);
+        }
+        *me.written = 0;
+        Poll::Ready(ret)
+    }
+
+    /// Gets a reference to the underlying writer.
+    pub fn get_ref(&self) -> &W {
+        &self.inner
+    }
+
+    /// Gets a mutable reference to the underlying writer.
+    ///
+    /// It is inadvisable to directly write to the underlying writer.
+    pub fn get_mut(&mut self) -> &mut W {
+        &mut self.inner
+    }
+
+    /// Gets a pinned mutable reference to the underlying writer.
+    ///
+    /// It is inadvisable to directly write to the underlying writer.
+    pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut W> {
+        self.project().inner
+    }
+
+    /// Consumes this `BufWriter`, returning the underlying writer.
+    ///
+    /// Note that any leftover data in the internal buffer is lost.
+    pub fn into_inner(self) -> W {
+        self.inner
+    }
+
+    /// Returns a reference to the internally buffered data.
+    pub fn buffer(&self) -> &[u8] {
+        &self.buf
+    }
+}
+
+impl<W: AsyncWrite> AsyncWrite for BufWriter<W> {
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        if self.buf.len() + buf.len() > self.buf.capacity() {
+            ready!(self.as_mut().flush_buf(cx))?;
+        }
+
+        let me = self.project();
+        if buf.len() >= me.buf.capacity() {
+            me.inner.poll_write(cx, buf)
+        } else {
+            Poll::Ready(me.buf.write(buf))
+        }
+    }
+
+    fn poll_write_vectored(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        mut bufs: &[IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        if self.inner.is_write_vectored() {
+            let total_len = bufs
+                .iter()
+                .fold(0usize, |acc, b| acc.saturating_add(b.len()));
+            if total_len > self.buf.capacity() - self.buf.len() {
+                ready!(self.as_mut().flush_buf(cx))?;
+            }
+            let me = self.as_mut().project();
+            if total_len >= me.buf.capacity() {
+                // It's more efficient to pass the slices directly to the
+                // underlying writer than to buffer them.
+                // The case when the total_len calculation saturates at
+                // usize::MAX is also handled here.
+                me.inner.poll_write_vectored(cx, bufs)
+            } else {
+                bufs.iter().for_each(|b| me.buf.extend_from_slice(b));
+                Poll::Ready(Ok(total_len))
+            }
+        } else {
+            // Remove empty buffers at the beginning of bufs.
+            while bufs.first().map(|buf| buf.len()) == Some(0) {
+                bufs = &bufs[1..];
+            }
+            if bufs.is_empty() {
+                return Poll::Ready(Ok(0));
+            }
+            // Flush if the first buffer doesn't fit.
+            let first_len = bufs[0].len();
+            if first_len > self.buf.capacity() - self.buf.len() {
+                ready!(self.as_mut().flush_buf(cx))?;
+                debug_assert!(self.buf.is_empty());
+            }
+            let me = self.as_mut().project();
+            if first_len >= me.buf.capacity() {
+                // The slice is at least as large as the buffering capacity,
+                // so it's better to write it directly, bypassing the buffer.
+                debug_assert!(me.buf.is_empty());
+                return me.inner.poll_write(cx, &bufs[0]);
+            } else {
+                me.buf.extend_from_slice(&bufs[0]);
+                bufs = &bufs[1..];
+            }
+            let mut total_written = first_len;
+            debug_assert!(total_written != 0);
+            // Append the buffers that fit in the internal buffer.
+            for buf in bufs {
+                if buf.len() > me.buf.capacity() - me.buf.len() {
+                    break;
+                } else {
+                    me.buf.extend_from_slice(buf);
+                    total_written += buf.len();
+                }
+            }
+            Poll::Ready(Ok(total_written))
+        }
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        true
+    }
+
+    fn poll_flush(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        ready!(self.as_mut().flush_buf(cx))?;
+        self.get_pin_mut().poll_flush(cx)
+    }
+
+    fn poll_shutdown(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        ready!(self.as_mut().flush_buf(cx))?;
+        self.get_pin_mut().poll_shutdown(cx)
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub(super) enum SeekState {
+    /// start_seek has not been called.
+    Init,
+    /// start_seek has been called, but poll_complete has not yet been called.
+    Start(SeekFrom),
+    /// Waiting for completion of poll_complete.
+    Pending,
+}
+
+/// Seek to the offset, in bytes, in the underlying writer.
+///
+/// Seeking always writes out the internal buffer before seeking.
+impl<W: AsyncWrite + AsyncSeek> AsyncSeek for BufWriter<W> {
+    fn start_seek(self: Pin<&mut Self>, pos: SeekFrom) -> io::Result<()> {
+        // We need to flush the internal buffer before seeking.
+        // It receives a `Context` and returns a `Poll`, so it cannot be called
+        // inside `start_seek`.
+        *self.project().seek_state = SeekState::Start(pos);
+        Ok(())
+    }
+
+    fn poll_complete(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
+        let pos = match self.seek_state {
+            SeekState::Init => {
+                return self.project().inner.poll_complete(cx);
+            }
+            SeekState::Start(pos) => Some(pos),
+            SeekState::Pending => None,
+        };
+
+        // Flush the internal buffer before seeking.
+        ready!(self.as_mut().flush_buf(cx))?;
+
+        let mut me = self.project();
+        if let Some(pos) = pos {
+            // Ensure previous seeks have finished before starting a new one
+            ready!(me.inner.as_mut().poll_complete(cx))?;
+            if let Err(e) = me.inner.as_mut().start_seek(pos) {
+                *me.seek_state = SeekState::Init;
+                return Poll::Ready(Err(e));
+            }
+        }
+        match me.inner.poll_complete(cx) {
+            Poll::Ready(res) => {
+                *me.seek_state = SeekState::Init;
+                Poll::Ready(res)
+            }
+            Poll::Pending => {
+                *me.seek_state = SeekState::Pending;
+                Poll::Pending
+            }
+        }
+    }
+}
+
+impl<W: AsyncWrite + AsyncRead> AsyncRead for BufWriter<W> {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        self.get_pin_mut().poll_read(cx, buf)
+    }
+}
+
+impl<W: AsyncWrite + AsyncBufRead> AsyncBufRead for BufWriter<W> {
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        self.get_pin_mut().poll_fill_buf(cx)
+    }
+
+    fn consume(self: Pin<&mut Self>, amt: usize) {
+        self.get_pin_mut().consume(amt)
+    }
+}
+
+impl<W: fmt::Debug> fmt::Debug for BufWriter<W> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("BufWriter")
+            .field("writer", &self.inner)
+            .field(
+                "buffer",
+                &format_args!("{}/{}", self.buf.len(), self.buf.capacity()),
+            )
+            .field("written", &self.written)
+            .finish()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn assert_unpin() {
+        crate::is_unpin::<BufWriter<()>>();
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/chain.rs b/third_party/rust/tokio/src/io/util/chain.rs
new file mode 100644
index 0000000000..84f37fc7d4
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/chain.rs
@@ -0,0 +1,144 @@
+use crate::io::{AsyncBufRead, AsyncRead, ReadBuf};
+
+use pin_project_lite::pin_project;
+use std::fmt;
+use std::io;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// Stream for the [`chain`](super::AsyncReadExt::chain) method.
+    #[must_use = "streams do nothing unless polled"]
+    #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
+    pub struct Chain<T, U> {
+        #[pin]
+        first: T,
+        #[pin]
+        second: U,
+        done_first: bool,
+    }
+}
+
+pub(super) fn chain<T, U>(first: T, second: U) -> Chain<T, U>
+where
+    T: AsyncRead,
+    U: AsyncRead,
+{
+    Chain {
+        first,
+        second,
+        done_first: false,
+    }
+}
+
+impl<T, U> Chain<T, U>
+where
+    T: AsyncRead,
+    U: AsyncRead,
+{
+    /// Gets references to the underlying readers in this `Chain`.
+    pub fn get_ref(&self) -> (&T, &U) {
+        (&self.first, &self.second)
+    }
+
+    /// Gets mutable references to the underlying readers in this `Chain`.
+    ///
+    /// Care should be taken to avoid modifying the internal I/O state of the
+    /// underlying readers as doing so may corrupt the internal state of this
+    /// `Chain`.
+    pub fn get_mut(&mut self) -> (&mut T, &mut U) {
+        (&mut self.first, &mut self.second)
+    }
+
+    /// Gets pinned mutable references to the underlying readers in this `Chain`.
+    ///
+    /// Care should be taken to avoid modifying the internal I/O state of the
+    /// underlying readers as doing so may corrupt the internal state of this
+    /// `Chain`.
+    pub fn get_pin_mut(self: Pin<&mut Self>) -> (Pin<&mut T>, Pin<&mut U>) {
+        let me = self.project();
+        (me.first, me.second)
+    }
+
+    /// Consumes the `Chain`, returning the wrapped readers.
+    pub fn into_inner(self) -> (T, U) {
+        (self.first, self.second)
+    }
+}
+
+impl<T, U> fmt::Debug for Chain<T, U>
+where
+    T: fmt::Debug,
+    U: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Chain")
+            .field("t", &self.first)
+            .field("u", &self.second)
+            .finish()
+    }
+}
+
+impl<T, U> AsyncRead for Chain<T, U>
+where
+    T: AsyncRead,
+    U: AsyncRead,
+{
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        let me = self.project();
+
+        if !*me.done_first {
+            let rem = buf.remaining();
+            ready!(me.first.poll_read(cx, buf))?;
+            if buf.remaining() == rem {
+                *me.done_first = true;
+            } else {
+                return Poll::Ready(Ok(()));
+            }
+        }
+        me.second.poll_read(cx, buf)
+    }
+}
+
+impl<T, U> AsyncBufRead for Chain<T, U>
+where
+    T: AsyncBufRead,
+    U: AsyncBufRead,
+{
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        let me = self.project();
+
+        if !*me.done_first {
+            match ready!(me.first.poll_fill_buf(cx)?) {
+                buf if buf.is_empty() => {
+                    *me.done_first = true;
+                }
+                buf => return Poll::Ready(Ok(buf)),
+            }
+        }
+        me.second.poll_fill_buf(cx)
+    }
+
+    fn consume(self: Pin<&mut Self>, amt: usize) {
+        let me = self.project();
+        if !*me.done_first {
+            me.first.consume(amt)
+        } else {
+            me.second.consume(amt)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn assert_unpin() {
+        crate::is_unpin::<Chain<(), ()>>();
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/copy.rs b/third_party/rust/tokio/src/io/util/copy.rs
new file mode 100644
index 0000000000..d0ab7cb140
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/copy.rs
@@ -0,0 +1,175 @@
+use crate::io::{AsyncRead, AsyncWrite, ReadBuf};
+
+use std::future::Future;
+use std::io;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+#[derive(Debug)]
+pub(super) struct CopyBuffer {
+    read_done: bool,
+    need_flush: bool,
+    pos: usize,
+    cap: usize,
+    amt: u64,
+    buf: Box<[u8]>,
+}
+
+impl CopyBuffer {
+    pub(super) fn new() -> Self {
+        Self {
+            read_done: false,
+            need_flush: false,
+            pos: 0,
+            cap: 0,
+            amt: 0,
+            buf: vec![0; super::DEFAULT_BUF_SIZE].into_boxed_slice(),
+        }
+    }
+
+    pub(super) fn poll_copy<R, W>(
+        &mut self,
+        cx: &mut Context<'_>,
+        mut reader: Pin<&mut R>,
+        mut writer: Pin<&mut W>,
+    ) -> Poll<io::Result<u64>>
+    where
+        R: AsyncRead + ?Sized,
+        W: AsyncWrite + ?Sized,
+    {
+        loop {
+            // If our buffer is empty, then we need to read some data to
+            // continue.
+            if self.pos == self.cap && !self.read_done {
+                let me = &mut *self;
+                let mut buf = ReadBuf::new(&mut me.buf);
+
+                match reader.as_mut().poll_read(cx, &mut buf) {
+                    Poll::Ready(Ok(_)) => (),
+                    Poll::Ready(Err(err)) => return Poll::Ready(Err(err)),
+                    Poll::Pending => {
+                        // Try flushing when the reader has no progress to avoid deadlock
+                        // when the reader depends on buffered writer.
+                        if self.need_flush {
+                            ready!(writer.as_mut().poll_flush(cx))?;
+                            self.need_flush = false;
+                        }
+
+                        return Poll::Pending;
+                    }
+                }
+
+                let n = buf.filled().len();
+                if n == 0 {
+                    self.read_done = true;
+                } else {
+                    self.pos = 0;
+                    self.cap = n;
+                }
+            }
+
+            // If our buffer has some data, let's write it out!
+            while self.pos < self.cap {
+                let me = &mut *self;
+                let i = ready!(writer.as_mut().poll_write(cx, &me.buf[me.pos..me.cap]))?;
+                if i == 0 {
+                    return Poll::Ready(Err(io::Error::new(
+                        io::ErrorKind::WriteZero,
+                        "write zero byte into writer",
+                    )));
+                } else {
+                    self.pos += i;
+                    self.amt += i as u64;
+                    self.need_flush = true;
+                }
+            }
+
+            // If pos larger than cap, this loop will never stop.
+            // In particular, user's wrong poll_write implementation returning
+            // incorrect written length may lead to thread blocking.
+            debug_assert!(
+                self.pos <= self.cap,
+                "writer returned length larger than input slice"
+            );
+
+            // If we've written all the data and we've seen EOF, flush out the
+            // data and finish the transfer.
+            if self.pos == self.cap && self.read_done {
+                ready!(writer.as_mut().poll_flush(cx))?;
+                return Poll::Ready(Ok(self.amt));
+            }
+        }
+    }
+}
+
+/// A future that asynchronously copies the entire contents of a reader into a
+/// writer.
+#[derive(Debug)]
+#[must_use = "futures do nothing unless you `.await` or poll them"]
+struct Copy<'a, R: ?Sized, W: ?Sized> {
+    reader: &'a mut R,
+    writer: &'a mut W,
+    buf: CopyBuffer,
+}
+
+cfg_io_util! {
+    /// Asynchronously copies the entire contents of a reader into a writer.
+    ///
+    /// This function returns a future that will continuously read data from
+    /// `reader` and then write it into `writer` in a streaming fashion until
+    /// `reader` returns EOF.
+    ///
+    /// On success, the total number of bytes that were copied from `reader` to
+    /// `writer` is returned.
+    ///
+    /// This is an asynchronous version of [`std::io::copy`][std].
+    ///
+    /// [std]: std::io::copy
+    ///
+    /// # Errors
+    ///
+    /// The returned future will return an error immediately if any call to
+    /// `poll_read` or `poll_write` returns an error.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::io;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let mut reader: &[u8] = b"hello";
+    /// let mut writer: Vec<u8> = vec![];
+    ///
+    /// io::copy(&mut reader, &mut writer).await?;
+    ///
+    /// assert_eq!(&b"hello"[..], &writer[..]);
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn copy<'a, R, W>(reader: &'a mut R, writer: &'a mut W) -> io::Result<u64>
+    where
+        R: AsyncRead + Unpin + ?Sized,
+        W: AsyncWrite + Unpin + ?Sized,
+    {
+        Copy {
+            reader,
+            writer,
+            buf: CopyBuffer::new()
+        }.await
+    }
+}
+
+impl<R, W> Future for Copy<'_, R, W>
+where
+    R: AsyncRead + Unpin + ?Sized,
+    W: AsyncWrite + Unpin + ?Sized,
+{
+    type Output = io::Result<u64>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<u64>> {
+        let me = &mut *self;
+
+        me.buf
+            .poll_copy(cx, Pin::new(&mut *me.reader), Pin::new(&mut *me.writer))
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/copy_bidirectional.rs b/third_party/rust/tokio/src/io/util/copy_bidirectional.rs
new file mode 100644
index 0000000000..c93060b361
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/copy_bidirectional.rs
@@ -0,0 +1,120 @@
+use super::copy::CopyBuffer;
+
+use crate::io::{AsyncRead, AsyncWrite};
+
+use std::future::Future;
+use std::io;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+enum TransferState {
+    Running(CopyBuffer),
+    ShuttingDown(u64),
+    Done(u64),
+}
+
+struct CopyBidirectional<'a, A: ?Sized, B: ?Sized> {
+    a: &'a mut A,
+    b: &'a mut B,
+    a_to_b: TransferState,
+    b_to_a: TransferState,
+}
+
+fn transfer_one_direction<A, B>(
+    cx: &mut Context<'_>,
+    state: &mut TransferState,
+    r: &mut A,
+    w: &mut B,
+) -> Poll<io::Result<u64>>
+where
+    A: AsyncRead + AsyncWrite + Unpin + ?Sized,
+    B: AsyncRead + AsyncWrite + Unpin + ?Sized,
+{
+    let mut r = Pin::new(r);
+    let mut w = Pin::new(w);
+
+    loop {
+        match state {
+            TransferState::Running(buf) => {
+                let count = ready!(buf.poll_copy(cx, r.as_mut(), w.as_mut()))?;
+                *state = TransferState::ShuttingDown(count);
+            }
+            TransferState::ShuttingDown(count) => {
+                ready!(w.as_mut().poll_shutdown(cx))?;
+
+                *state = TransferState::Done(*count);
+            }
+            TransferState::Done(count) => return Poll::Ready(Ok(*count)),
+        }
+    }
+}
+
+impl<'a, A, B> Future for CopyBidirectional<'a, A, B>
+where
+    A: AsyncRead + AsyncWrite + Unpin + ?Sized,
+    B: AsyncRead + AsyncWrite + Unpin + ?Sized,
+{
+    type Output = io::Result<(u64, u64)>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        // Unpack self into mut refs to each field to avoid borrow check issues.
+        let CopyBidirectional {
+            a,
+            b,
+            a_to_b,
+            b_to_a,
+        } = &mut *self;
+
+        let a_to_b = transfer_one_direction(cx, a_to_b, &mut *a, &mut *b)?;
+        let b_to_a = transfer_one_direction(cx, b_to_a, &mut *b, &mut *a)?;
+
+        // It is not a problem if ready! returns early because transfer_one_direction for the
+        // other direction will keep returning TransferState::Done(count) in future calls to poll
+        let a_to_b = ready!(a_to_b);
+        let b_to_a = ready!(b_to_a);
+
+        Poll::Ready(Ok((a_to_b, b_to_a)))
+    }
+}
+
+/// Copies data in both directions between `a` and `b`.
+///
+/// This function returns a future that will read from both streams,
+/// writing any data read to the opposing stream.
+/// This happens in both directions concurrently.
+///
+/// If an EOF is observed on one stream, [`shutdown()`] will be invoked on
+/// the other, and reading from that stream will stop. Copying of data in
+/// the other direction will continue.
+///
+/// The future will complete successfully once both directions of communication has been shut down.
+/// A direction is shut down when the reader reports EOF,
+/// at which point [`shutdown()`] is called on the corresponding writer. When finished,
+/// it will return a tuple of the number of bytes copied from a to b
+/// and the number of bytes copied from b to a, in that order.
+///
+/// [`shutdown()`]: crate::io::AsyncWriteExt::shutdown
+///
+/// # Errors
+///
+/// The future will immediately return an error if any IO operation on `a`
+/// or `b` returns an error. Some data read from either stream may be lost (not
+/// written to the other stream) in this case.
+///
+/// # Return value
+///
+/// Returns a tuple of bytes copied `a` to `b` and bytes copied `b` to `a`.
+#[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
+pub async fn copy_bidirectional<A, B>(a: &mut A, b: &mut B) -> Result<(u64, u64), std::io::Error>
+where
+    A: AsyncRead + AsyncWrite + Unpin + ?Sized,
+    B: AsyncRead + AsyncWrite + Unpin + ?Sized,
+{
+    CopyBidirectional {
+        a,
+        b,
+        a_to_b: TransferState::Running(CopyBuffer::new()),
+        b_to_a: TransferState::Running(CopyBuffer::new()),
+    }
+    .await
+}
diff --git a/third_party/rust/tokio/src/io/util/copy_buf.rs b/third_party/rust/tokio/src/io/util/copy_buf.rs
new file mode 100644
index 0000000000..6831580b40
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/copy_buf.rs
@@ -0,0 +1,102 @@
+use crate::io::{AsyncBufRead, AsyncWrite};
+use std::future::Future;
+use std::io;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+cfg_io_util! {
+    /// A future that asynchronously copies the entire contents of a reader into a
+    /// writer.
+    ///
+    /// This struct is generally created by calling [`copy_buf`][copy_buf]. Please
+    /// see the documentation of `copy_buf()` for more details.
+    ///
+    /// [copy_buf]: copy_buf()
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    struct CopyBuf<'a, R: ?Sized, W: ?Sized> {
+        reader: &'a mut R,
+        writer: &'a mut W,
+        amt: u64,
+    }
+
+    /// Asynchronously copies the entire contents of a reader into a writer.
+    ///
+    /// This function returns a future that will continuously read data from
+    /// `reader` and then write it into `writer` in a streaming fashion until
+    /// `reader` returns EOF.
+    ///
+    /// On success, the total number of bytes that were copied from `reader` to
+    /// `writer` is returned.
+    ///
+    ///
+    /// # Errors
+    ///
+    /// The returned future will finish with an error will return an error
+    /// immediately if any call to `poll_fill_buf` or `poll_write` returns an
+    /// error.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::io;
+    ///
+    /// # async fn dox() -> std::io::Result<()> {
+    /// let mut reader: &[u8] = b"hello";
+    /// let mut writer: Vec<u8> = vec![];
+    ///
+    /// io::copy_buf(&mut reader, &mut writer).await?;
+    ///
+    /// assert_eq!(b"hello", &writer[..]);
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn copy_buf<'a, R, W>(reader: &'a mut R, writer: &'a mut W) -> io::Result<u64>
+    where
+        R: AsyncBufRead + Unpin + ?Sized,
+        W: AsyncWrite + Unpin + ?Sized,
+    {
+        CopyBuf {
+            reader,
+            writer,
+            amt: 0,
+        }.await
+    }
+}
+
+impl<R, W> Future for CopyBuf<'_, R, W>
+where
+    R: AsyncBufRead + Unpin + ?Sized,
+    W: AsyncWrite + Unpin + ?Sized,
+{
+    type Output = io::Result<u64>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        loop {
+            let me = &mut *self;
+            let buffer = ready!(Pin::new(&mut *me.reader).poll_fill_buf(cx))?;
+            if buffer.is_empty() {
+                ready!(Pin::new(&mut self.writer).poll_flush(cx))?;
+                return Poll::Ready(Ok(self.amt));
+            }
+
+            let i = ready!(Pin::new(&mut *me.writer).poll_write(cx, buffer))?;
+            if i == 0 {
+                return Poll::Ready(Err(std::io::ErrorKind::WriteZero.into()));
+            }
+            self.amt += i as u64;
+            Pin::new(&mut *self.reader).consume(i);
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn assert_unpin() {
+        use std::marker::PhantomPinned;
+        crate::is_unpin::<CopyBuf<'_, PhantomPinned, PhantomPinned>>();
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/empty.rs b/third_party/rust/tokio/src/io/util/empty.rs
new file mode 100644
index 0000000000..77db60e40b
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/empty.rs
@@ -0,0 +1,100 @@
+use crate::io::{AsyncBufRead, AsyncRead, ReadBuf};
+
+use std::fmt;
+use std::io;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+cfg_io_util! {
+    /// An async reader which is always at EOF.
+    ///
+    /// This struct is generally created by calling [`empty`]. Please see
+    /// the documentation of [`empty()`][`empty`] for more details.
+    ///
+    /// This is an asynchronous version of [`std::io::empty`][std].
+    ///
+    /// [`empty`]: fn@empty
+    /// [std]: std::io::empty
+    pub struct Empty {
+        _p: (),
+    }
+
+    /// Creates a new empty async reader.
+    ///
+    /// All reads from the returned reader will return `Poll::Ready(Ok(0))`.
+    ///
+    /// This is an asynchronous version of [`std::io::empty`][std].
+    ///
+    /// [std]: std::io::empty
+    ///
+    /// # Examples
+    ///
+    /// A slightly sad example of not reading anything into a buffer:
+    ///
+    /// ```
+    /// use tokio::io::{self, AsyncReadExt};
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let mut buffer = String::new();
+    ///     io::empty().read_to_string(&mut buffer).await.unwrap();
+    ///     assert!(buffer.is_empty());
+    /// }
+    /// ```
+    pub fn empty() -> Empty {
+        Empty { _p: () }
+    }
+}
+
+impl AsyncRead for Empty {
+    #[inline]
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        _: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        ready!(poll_proceed_and_make_progress(cx));
+        Poll::Ready(Ok(()))
+    }
+}
+
+impl AsyncBufRead for Empty {
+    #[inline]
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        ready!(poll_proceed_and_make_progress(cx));
+        Poll::Ready(Ok(&[]))
+    }
+
+    #[inline]
+    fn consume(self: Pin<&mut Self>, _: usize) {}
+}
+
+impl fmt::Debug for Empty {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad("Empty { .. }")
+    }
+}
+
+cfg_coop! {
+    fn poll_proceed_and_make_progress(cx: &mut Context<'_>) -> Poll<()> {
+        let coop = ready!(crate::coop::poll_proceed(cx));
+        coop.made_progress();
+        Poll::Ready(())
+    }
+}
+
+cfg_not_coop! {
+    fn poll_proceed_and_make_progress(_: &mut Context<'_>) -> Poll<()> {
+        Poll::Ready(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn assert_unpin() {
+        crate::is_unpin::<Empty>();
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/fill_buf.rs b/third_party/rust/tokio/src/io/util/fill_buf.rs
new file mode 100644
index 0000000000..bb07c766e2
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/fill_buf.rs
@@ -0,0 +1,59 @@
+use crate::io::AsyncBufRead;
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io;
+use std::marker::PhantomPinned;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// Future for the [`fill_buf`](crate::io::AsyncBufReadExt::fill_buf) method.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct FillBuf<'a, R: ?Sized> {
+        reader: Option<&'a mut R>,
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+pub(crate) fn fill_buf<R>(reader: &mut R) -> FillBuf<'_, R>
+where
+    R: AsyncBufRead + ?Sized + Unpin,
+{
+    FillBuf {
+        reader: Some(reader),
+        _pin: PhantomPinned,
+    }
+}
+
+impl<'a, R: AsyncBufRead + ?Sized + Unpin> Future for FillBuf<'a, R> {
+    type Output = io::Result<&'a [u8]>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let me = self.project();
+
+        let reader = me.reader.take().expect("Polled after completion.");
+        match Pin::new(&mut *reader).poll_fill_buf(cx) {
+            Poll::Ready(Ok(slice)) => unsafe {
+                // Safety: This is necessary only due to a limitation in the
+                // borrow checker. Once Rust starts using the polonius borrow
+                // checker, this can be simplified.
+                //
+                // The safety of this transmute relies on the fact that the
+                // value of `reader` is `None` when we return in this branch.
+                // Otherwise the caller could poll us again after
+                // completion, and access the mutable reference while the
+                // returned immutable reference still exists.
+                let slice = std::mem::transmute::<&[u8], &'a [u8]>(slice);
+                Poll::Ready(Ok(slice))
+            },
+            Poll::Ready(Err(err)) => Poll::Ready(Err(err)),
+            Poll::Pending => {
+                *me.reader = Some(reader);
+                Poll::Pending
+            }
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/flush.rs b/third_party/rust/tokio/src/io/util/flush.rs
new file mode 100644
index 0000000000..88d60b868d
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/flush.rs
@@ -0,0 +1,46 @@
+use crate::io::AsyncWrite;
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io;
+use std::marker::PhantomPinned;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// A future used to fully flush an I/O object.
+    ///
+    /// Created by the [`AsyncWriteExt::flush`][flush] function.
+    /// [flush]: crate::io::AsyncWriteExt::flush
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct Flush<'a, A: ?Sized> {
+        a: &'a mut A,
+        // Make this future `!Unpin` for compatibility with async trait methods.
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+/// Creates a future which will entirely flush an I/O object.
+pub(super) fn flush<A>(a: &mut A) -> Flush<'_, A>
+where
+    A: AsyncWrite + Unpin + ?Sized,
+{
+    Flush {
+        a,
+        _pin: PhantomPinned,
+    }
+}
+
+impl<A> Future for Flush<'_, A>
+where
+    A: AsyncWrite + Unpin + ?Sized,
+{
+    type Output = io::Result<()>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let me = self.project();
+        Pin::new(&mut *me.a).poll_flush(cx)
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/lines.rs b/third_party/rust/tokio/src/io/util/lines.rs
new file mode 100644
index 0000000000..717f633f95
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/lines.rs
@@ -0,0 +1,145 @@
+use crate::io::util::read_line::read_line_internal;
+use crate::io::AsyncBufRead;
+
+use pin_project_lite::pin_project;
+use std::io;
+use std::mem;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// Reads lines from an [`AsyncBufRead`].
+    ///
+    /// A `Lines` can be turned into a `Stream` with [`LinesStream`].
+    ///
+    /// This type is usually created using the [`lines`] method.
+    ///
+    /// [`AsyncBufRead`]: crate::io::AsyncBufRead
+    /// [`LinesStream`]: https://docs.rs/tokio-stream/0.1/tokio_stream/wrappers/struct.LinesStream.html
+    /// [`lines`]: crate::io::AsyncBufReadExt::lines
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
+    pub struct Lines<R> {
+        #[pin]
+        reader: R,
+        buf: String,
+        bytes: Vec<u8>,
+        read: usize,
+    }
+}
+
+pub(crate) fn lines<R>(reader: R) -> Lines<R>
+where
+    R: AsyncBufRead,
+{
+    Lines {
+        reader,
+        buf: String::new(),
+        bytes: Vec::new(),
+        read: 0,
+    }
+}
+
+impl<R> Lines<R>
+where
+    R: AsyncBufRead + Unpin,
+{
+    /// Returns the next line in the stream.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancellation safe.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use tokio::io::AsyncBufRead;
+    /// use tokio::io::AsyncBufReadExt;
+    ///
+    /// # async fn dox(my_buf_read: impl AsyncBufRead + Unpin) -> std::io::Result<()> {
+    /// let mut lines = my_buf_read.lines();
+    ///
+    /// while let Some(line) = lines.next_line().await? {
+    ///     println!("length = {}", line.len())
+    /// }
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn next_line(&mut self) -> io::Result<Option<String>> {
+        use crate::future::poll_fn;
+
+        poll_fn(|cx| Pin::new(&mut *self).poll_next_line(cx)).await
+    }
+
+    /// Obtains a mutable reference to the underlying reader.
+    pub fn get_mut(&mut self) -> &mut R {
+        &mut self.reader
+    }
+
+    /// Obtains a reference to the underlying reader.
+    pub fn get_ref(&mut self) -> &R {
+        &self.reader
+    }
+
+    /// Unwraps this `Lines<R>`, returning the underlying reader.
+    ///
+    /// Note that any leftover data in the internal buffer is lost.
+    /// Therefore, a following read from the underlying reader may lead to data loss.
+    pub fn into_inner(self) -> R {
+        self.reader
+    }
+}
+
+impl<R> Lines<R>
+where
+    R: AsyncBufRead,
+{
+    /// Polls for the next line in the stream.
+    ///
+    /// This method returns:
+    ///
+    ///  * `Poll::Pending` if the next line is not yet available.
+    ///  * `Poll::Ready(Ok(Some(line)))` if the next line is available.
+    ///  * `Poll::Ready(Ok(None))` if there are no more lines in this stream.
+    ///  * `Poll::Ready(Err(err))` if an IO error occurred while reading the next line.
+    ///
+    /// When the method returns `Poll::Pending`, the `Waker` in the provided
+    /// `Context` is scheduled to receive a wakeup when more bytes become
+    /// available on the underlying IO resource.  Note that on multiple calls to
+    /// `poll_next_line`, only the `Waker` from the `Context` passed to the most
+    /// recent call is scheduled to receive a wakeup.
+    pub fn poll_next_line(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<io::Result<Option<String>>> {
+        let me = self.project();
+
+        let n = ready!(read_line_internal(me.reader, cx, me.buf, me.bytes, me.read))?;
+        debug_assert_eq!(*me.read, 0);
+
+        if n == 0 && me.buf.is_empty() {
+            return Poll::Ready(Ok(None));
+        }
+
+        if me.buf.ends_with('\n') {
+            me.buf.pop();
+
+            if me.buf.ends_with('\r') {
+                me.buf.pop();
+            }
+        }
+
+        Poll::Ready(Ok(Some(mem::take(me.buf))))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn assert_unpin() {
+        crate::is_unpin::<Lines<()>>();
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/mem.rs b/third_party/rust/tokio/src/io/util/mem.rs
new file mode 100644
index 0000000000..4019db56ff
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/mem.rs
@@ -0,0 +1,295 @@
+//! In-process memory IO types.
+
+use crate::io::{AsyncRead, AsyncWrite, ReadBuf};
+use crate::loom::sync::Mutex;
+
+use bytes::{Buf, BytesMut};
+use std::{
+    pin::Pin,
+    sync::Arc,
+    task::{self, Poll, Waker},
+};
+
+/// A bidirectional pipe to read and write bytes in memory.
+///
+/// A pair of `DuplexStream`s are created together, and they act as a "channel"
+/// that can be used as in-memory IO types. Writing to one of the pairs will
+/// allow that data to be read from the other, and vice versa.
+///
+/// # Closing a `DuplexStream`
+///
+/// If one end of the `DuplexStream` channel is dropped, any pending reads on
+/// the other side will continue to read data until the buffer is drained, then
+/// they will signal EOF by returning 0 bytes. Any writes to the other side,
+/// including pending ones (that are waiting for free space in the buffer) will
+/// return `Err(BrokenPipe)` immediately.
+///
+/// # Example
+///
+/// ```
+/// # async fn ex() -> std::io::Result<()> {
+/// # use tokio::io::{AsyncReadExt, AsyncWriteExt};
+/// let (mut client, mut server) = tokio::io::duplex(64);
+///
+/// client.write_all(b"ping").await?;
+///
+/// let mut buf = [0u8; 4];
+/// server.read_exact(&mut buf).await?;
+/// assert_eq!(&buf, b"ping");
+///
+/// server.write_all(b"pong").await?;
+///
+/// client.read_exact(&mut buf).await?;
+/// assert_eq!(&buf, b"pong");
+/// # Ok(())
+/// # }
+/// ```
+#[derive(Debug)]
+#[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
+pub struct DuplexStream {
+    read: Arc<Mutex<Pipe>>,
+    write: Arc<Mutex<Pipe>>,
+}
+
+/// A unidirectional IO over a piece of memory.
+///
+/// Data can be written to the pipe, and reading will return that data.
+#[derive(Debug)]
+struct Pipe {
+    /// The buffer storing the bytes written, also read from.
+    ///
+    /// Using a `BytesMut` because it has efficient `Buf` and `BufMut`
+    /// functionality already. Additionally, it can try to copy data in the
+    /// same buffer if there read index has advanced far enough.
+    buffer: BytesMut,
+    /// Determines if the write side has been closed.
+    is_closed: bool,
+    /// The maximum amount of bytes that can be written before returning
+    /// `Poll::Pending`.
+    max_buf_size: usize,
+    /// If the `read` side has been polled and is pending, this is the waker
+    /// for that parked task.
+    read_waker: Option<Waker>,
+    /// If the `write` side has filled the `max_buf_size` and returned
+    /// `Poll::Pending`, this is the waker for that parked task.
+    write_waker: Option<Waker>,
+}
+
+// ===== impl DuplexStream =====
+
+/// Create a new pair of `DuplexStream`s that act like a pair of connected sockets.
+///
+/// The `max_buf_size` argument is the maximum amount of bytes that can be
+/// written to a side before the write returns `Poll::Pending`.
+#[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
+pub fn duplex(max_buf_size: usize) -> (DuplexStream, DuplexStream) {
+    let one = Arc::new(Mutex::new(Pipe::new(max_buf_size)));
+    let two = Arc::new(Mutex::new(Pipe::new(max_buf_size)));
+
+    (
+        DuplexStream {
+            read: one.clone(),
+            write: two.clone(),
+        },
+        DuplexStream {
+            read: two,
+            write: one,
+        },
+    )
+}
+
+impl AsyncRead for DuplexStream {
+    // Previous rustc required this `self` to be `mut`, even though newer
+    // versions recognize it isn't needed to call `lock()`. So for
+    // compatibility, we include the `mut` and `allow` the lint.
+    //
+    // See https://github.com/rust-lang/rust/issues/73592
+    #[allow(unused_mut)]
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut task::Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<std::io::Result<()>> {
+        Pin::new(&mut *self.read.lock()).poll_read(cx, buf)
+    }
+}
+
+impl AsyncWrite for DuplexStream {
+    #[allow(unused_mut)]
+    fn poll_write(
+        mut self: Pin<&mut Self>,
+        cx: &mut task::Context<'_>,
+        buf: &[u8],
+    ) -> Poll<std::io::Result<usize>> {
+        Pin::new(&mut *self.write.lock()).poll_write(cx, buf)
+    }
+
+    #[allow(unused_mut)]
+    fn poll_flush(
+        mut self: Pin<&mut Self>,
+        cx: &mut task::Context<'_>,
+    ) -> Poll<std::io::Result<()>> {
+        Pin::new(&mut *self.write.lock()).poll_flush(cx)
+    }
+
+    #[allow(unused_mut)]
+    fn poll_shutdown(
+        mut self: Pin<&mut Self>,
+        cx: &mut task::Context<'_>,
+    ) -> Poll<std::io::Result<()>> {
+        Pin::new(&mut *self.write.lock()).poll_shutdown(cx)
+    }
+}
+
+impl Drop for DuplexStream {
+    fn drop(&mut self) {
+        // notify the other side of the closure
+        self.write.lock().close_write();
+        self.read.lock().close_read();
+    }
+}
+
+// ===== impl Pipe =====
+
+impl Pipe {
+    fn new(max_buf_size: usize) -> Self {
+        Pipe {
+            buffer: BytesMut::new(),
+            is_closed: false,
+            max_buf_size,
+            read_waker: None,
+            write_waker: None,
+        }
+    }
+
+    fn close_write(&mut self) {
+        self.is_closed = true;
+        // needs to notify any readers that no more data will come
+        if let Some(waker) = self.read_waker.take() {
+            waker.wake();
+        }
+    }
+
+    fn close_read(&mut self) {
+        self.is_closed = true;
+        // needs to notify any writers that they have to abort
+        if let Some(waker) = self.write_waker.take() {
+            waker.wake();
+        }
+    }
+
+    fn poll_read_internal(
+        mut self: Pin<&mut Self>,
+        cx: &mut task::Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<std::io::Result<()>> {
+        if self.buffer.has_remaining() {
+            let max = self.buffer.remaining().min(buf.remaining());
+            buf.put_slice(&self.buffer[..max]);
+            self.buffer.advance(max);
+            if max > 0 {
+                // The passed `buf` might have been empty, don't wake up if
+                // no bytes have been moved.
+                if let Some(waker) = self.write_waker.take() {
+                    waker.wake();
+                }
+            }
+            Poll::Ready(Ok(()))
+        } else if self.is_closed {
+            Poll::Ready(Ok(()))
+        } else {
+            self.read_waker = Some(cx.waker().clone());
+            Poll::Pending
+        }
+    }
+
+    fn poll_write_internal(
+        mut self: Pin<&mut Self>,
+        cx: &mut task::Context<'_>,
+        buf: &[u8],
+    ) -> Poll<std::io::Result<usize>> {
+        if self.is_closed {
+            return Poll::Ready(Err(std::io::ErrorKind::BrokenPipe.into()));
+        }
+        let avail = self.max_buf_size - self.buffer.len();
+        if avail == 0 {
+            self.write_waker = Some(cx.waker().clone());
+            return Poll::Pending;
+        }
+
+        let len = buf.len().min(avail);
+        self.buffer.extend_from_slice(&buf[..len]);
+        if let Some(waker) = self.read_waker.take() {
+            waker.wake();
+        }
+        Poll::Ready(Ok(len))
+    }
+}
+
+impl AsyncRead for Pipe {
+    cfg_coop! {
+        fn poll_read(
+            self: Pin<&mut Self>,
+            cx: &mut task::Context<'_>,
+            buf: &mut ReadBuf<'_>,
+        ) -> Poll<std::io::Result<()>> {
+            let coop = ready!(crate::coop::poll_proceed(cx));
+
+            let ret = self.poll_read_internal(cx, buf);
+            if ret.is_ready() {
+                coop.made_progress();
+            }
+            ret
+        }
+    }
+
+    cfg_not_coop! {
+        fn poll_read(
+            self: Pin<&mut Self>,
+            cx: &mut task::Context<'_>,
+            buf: &mut ReadBuf<'_>,
+        ) -> Poll<std::io::Result<()>> {
+            self.poll_read_internal(cx, buf)
+        }
+    }
+}
+
+impl AsyncWrite for Pipe {
+    cfg_coop! {
+        fn poll_write(
+            self: Pin<&mut Self>,
+            cx: &mut task::Context<'_>,
+            buf: &[u8],
+        ) -> Poll<std::io::Result<usize>> {
+            let coop = ready!(crate::coop::poll_proceed(cx));
+
+            let ret = self.poll_write_internal(cx, buf);
+            if ret.is_ready() {
+                coop.made_progress();
+            }
+            ret
+        }
+    }
+
+    cfg_not_coop! {
+        fn poll_write(
+            self: Pin<&mut Self>,
+            cx: &mut task::Context<'_>,
+            buf: &[u8],
+        ) -> Poll<std::io::Result<usize>> {
+            self.poll_write_internal(cx, buf)
+        }
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, _: &mut task::Context<'_>) -> Poll<std::io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_shutdown(
+        mut self: Pin<&mut Self>,
+        _: &mut task::Context<'_>,
+    ) -> Poll<std::io::Result<()>> {
+        self.close_write();
+        Poll::Ready(Ok(()))
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/mod.rs b/third_party/rust/tokio/src/io/util/mod.rs
new file mode 100644
index 0000000000..21199d0be8
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/mod.rs
@@ -0,0 +1,97 @@
+#![allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+
+cfg_io_util! {
+    mod async_buf_read_ext;
+    pub use async_buf_read_ext::AsyncBufReadExt;
+
+    mod async_read_ext;
+    pub use async_read_ext::AsyncReadExt;
+
+    mod async_seek_ext;
+    pub use async_seek_ext::AsyncSeekExt;
+
+    mod async_write_ext;
+    pub use async_write_ext::AsyncWriteExt;
+
+    mod buf_reader;
+    pub use buf_reader::BufReader;
+
+    mod buf_stream;
+    pub use buf_stream::BufStream;
+
+    mod buf_writer;
+    pub use buf_writer::BufWriter;
+
+    mod chain;
+
+    mod copy;
+    pub use copy::copy;
+
+    mod copy_bidirectional;
+    pub use copy_bidirectional::copy_bidirectional;
+
+    mod copy_buf;
+    pub use copy_buf::copy_buf;
+
+    mod empty;
+    pub use empty::{empty, Empty};
+
+    mod flush;
+
+    mod lines;
+    pub use lines::Lines;
+
+    mod mem;
+    pub use mem::{duplex, DuplexStream};
+
+    mod read;
+    mod read_buf;
+    mod read_exact;
+    mod read_int;
+    mod read_line;
+    mod fill_buf;
+
+    mod read_to_end;
+    mod vec_with_initialized;
+    cfg_process! {
+        pub(crate) use read_to_end::read_to_end;
+    }
+
+    mod read_to_string;
+    mod read_until;
+
+    mod repeat;
+    pub use repeat::{repeat, Repeat};
+
+    mod shutdown;
+
+    mod sink;
+    pub use sink::{sink, Sink};
+
+    mod split;
+    pub use split::Split;
+
+    mod take;
+    pub use take::Take;
+
+    mod write;
+    mod write_vectored;
+    mod write_all;
+    mod write_buf;
+    mod write_all_buf;
+    mod write_int;
+
+
+    // used by `BufReader` and `BufWriter`
+    // https://github.com/rust-lang/rust/blob/master/library/std/src/sys_common/io.rs#L1
+    const DEFAULT_BUF_SIZE: usize = 8 * 1024;
+}
+
+cfg_not_io_util! {
+    cfg_process! {
+        mod vec_with_initialized;
+        mod read_to_end;
+        // Used by process
+        pub(crate) use read_to_end::read_to_end;
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/read.rs b/third_party/rust/tokio/src/io/util/read.rs
new file mode 100644
index 0000000000..edc9d5a9e6
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/read.rs
@@ -0,0 +1,55 @@
+use crate::io::{AsyncRead, ReadBuf};
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io;
+use std::marker::PhantomPinned;
+use std::marker::Unpin;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+/// Tries to read some bytes directly into the given `buf` in asynchronous
+/// manner, returning a future type.
+///
+/// The returned future will resolve to both the I/O stream and the buffer
+/// as well as the number of bytes read once the read operation is completed.
+pub(crate) fn read<'a, R>(reader: &'a mut R, buf: &'a mut [u8]) -> Read<'a, R>
+where
+    R: AsyncRead + Unpin + ?Sized,
+{
+    Read {
+        reader,
+        buf,
+        _pin: PhantomPinned,
+    }
+}
+
+pin_project! {
+    /// A future which can be used to easily read available number of bytes to fill
+    /// a buffer.
+    ///
+    /// Created by the [`read`] function.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct Read<'a, R: ?Sized> {
+        reader: &'a mut R,
+        buf: &'a mut [u8],
+        // Make this future `!Unpin` for compatibility with async trait methods.
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+impl<R> Future for Read<'_, R>
+where
+    R: AsyncRead + Unpin + ?Sized,
+{
+    type Output = io::Result<usize>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
+        let me = self.project();
+        let mut buf = ReadBuf::new(*me.buf);
+        ready!(Pin::new(me.reader).poll_read(cx, &mut buf))?;
+        Poll::Ready(Ok(buf.filled().len()))
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/read_buf.rs b/third_party/rust/tokio/src/io/util/read_buf.rs
new file mode 100644
index 0000000000..8ec57c0d6f
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/read_buf.rs
@@ -0,0 +1,72 @@
+use crate::io::AsyncRead;
+
+use bytes::BufMut;
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io;
+use std::marker::PhantomPinned;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pub(crate) fn read_buf<'a, R, B>(reader: &'a mut R, buf: &'a mut B) -> ReadBuf<'a, R, B>
+where
+    R: AsyncRead + Unpin,
+    B: BufMut,
+{
+    ReadBuf {
+        reader,
+        buf,
+        _pin: PhantomPinned,
+    }
+}
+
+pin_project! {
+    /// Future returned by [`read_buf`](crate::io::AsyncReadExt::read_buf).
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct ReadBuf<'a, R, B> {
+        reader: &'a mut R,
+        buf: &'a mut B,
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+impl<R, B> Future for ReadBuf<'_, R, B>
+where
+    R: AsyncRead + Unpin,
+    B: BufMut,
+{
+    type Output = io::Result<usize>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
+        use crate::io::ReadBuf;
+        use std::mem::MaybeUninit;
+
+        let me = self.project();
+
+        if !me.buf.has_remaining_mut() {
+            return Poll::Ready(Ok(0));
+        }
+
+        let n = {
+            let dst = me.buf.chunk_mut();
+            let dst = unsafe { &mut *(dst as *mut _ as *mut [MaybeUninit<u8>]) };
+            let mut buf = ReadBuf::uninit(dst);
+            let ptr = buf.filled().as_ptr();
+            ready!(Pin::new(me.reader).poll_read(cx, &mut buf)?);
+
+            // Ensure the pointer does not change from under us
+            assert_eq!(ptr, buf.filled().as_ptr());
+            buf.filled().len()
+        };
+
+        // Safety: This is guaranteed to be the number of initialized (and read)
+        // bytes due to the invariants provided by `ReadBuf::filled`.
+        unsafe {
+            me.buf.advance_mut(n);
+        }
+
+        Poll::Ready(Ok(n))
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/read_exact.rs b/third_party/rust/tokio/src/io/util/read_exact.rs
new file mode 100644
index 0000000000..dbdd58bae9
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/read_exact.rs
@@ -0,0 +1,69 @@
+use crate::io::{AsyncRead, ReadBuf};
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io;
+use std::marker::PhantomPinned;
+use std::marker::Unpin;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+/// A future which can be used to easily read exactly enough bytes to fill
+/// a buffer.
+///
+/// Created by the [`AsyncReadExt::read_exact`][read_exact].
+/// [read_exact]: [crate::io::AsyncReadExt::read_exact]
+pub(crate) fn read_exact<'a, A>(reader: &'a mut A, buf: &'a mut [u8]) -> ReadExact<'a, A>
+where
+    A: AsyncRead + Unpin + ?Sized,
+{
+    ReadExact {
+        reader,
+        buf: ReadBuf::new(buf),
+        _pin: PhantomPinned,
+    }
+}
+
+pin_project! {
+    /// Creates a future which will read exactly enough bytes to fill `buf`,
+    /// returning an error if EOF is hit sooner.
+    ///
+    /// On success the number of bytes is returned
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct ReadExact<'a, A: ?Sized> {
+        reader: &'a mut A,
+        buf: ReadBuf<'a>,
+        // Make this future `!Unpin` for compatibility with async trait methods.
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+fn eof() -> io::Error {
+    io::Error::new(io::ErrorKind::UnexpectedEof, "early eof")
+}
+
+impl<A> Future for ReadExact<'_, A>
+where
+    A: AsyncRead + Unpin + ?Sized,
+{
+    type Output = io::Result<usize>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
+        let me = self.project();
+
+        loop {
+            // if our buffer is empty, then we need to read some data to continue.
+            let rem = me.buf.remaining();
+            if rem != 0 {
+                ready!(Pin::new(&mut *me.reader).poll_read(cx, me.buf))?;
+                if me.buf.remaining() == rem {
+                    return Err(eof()).into();
+                }
+            } else {
+                return Poll::Ready(Ok(me.buf.capacity()));
+            }
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/read_int.rs b/third_party/rust/tokio/src/io/util/read_int.rs
new file mode 100644
index 0000000000..164dcf5963
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/read_int.rs
@@ -0,0 +1,159 @@
+use crate::io::{AsyncRead, ReadBuf};
+
+use bytes::Buf;
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io;
+use std::io::ErrorKind::UnexpectedEof;
+use std::marker::PhantomPinned;
+use std::mem::size_of;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+macro_rules! reader {
+    ($name:ident, $ty:ty, $reader:ident) => {
+        reader!($name, $ty, $reader, size_of::<$ty>());
+    };
+    ($name:ident, $ty:ty, $reader:ident, $bytes:expr) => {
+        pin_project! {
+            #[doc(hidden)]
+            #[must_use = "futures do nothing unless you `.await` or poll them"]
+            pub struct $name<R> {
+                #[pin]
+                src: R,
+                buf: [u8; $bytes],
+                read: u8,
+                // Make this future `!Unpin` for compatibility with async trait methods.
+                #[pin]
+                _pin: PhantomPinned,
+            }
+        }
+
+        impl<R> $name<R> {
+            pub(crate) fn new(src: R) -> Self {
+                $name {
+                    src,
+                    buf: [0; $bytes],
+                    read: 0,
+                    _pin: PhantomPinned,
+                }
+            }
+        }
+
+        impl<R> Future for $name<R>
+        where
+            R: AsyncRead,
+        {
+            type Output = io::Result<$ty>;
+
+            fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+                let mut me = self.project();
+
+                if *me.read == $bytes as u8 {
+                    return Poll::Ready(Ok(Buf::$reader(&mut &me.buf[..])));
+                }
+
+                while *me.read < $bytes as u8 {
+                    let mut buf = ReadBuf::new(&mut me.buf[*me.read as usize..]);
+
+                    *me.read += match me.src.as_mut().poll_read(cx, &mut buf) {
+                        Poll::Pending => return Poll::Pending,
+                        Poll::Ready(Err(e)) => return Poll::Ready(Err(e.into())),
+                        Poll::Ready(Ok(())) => {
+                            let n = buf.filled().len();
+                            if n == 0 {
+                                return Poll::Ready(Err(UnexpectedEof.into()));
+                            }
+
+                            n as u8
+                        }
+                    };
+                }
+
+                let num = Buf::$reader(&mut &me.buf[..]);
+
+                Poll::Ready(Ok(num))
+            }
+        }
+    };
+}
+
+macro_rules! reader8 {
+    ($name:ident, $ty:ty) => {
+        pin_project! {
+            /// Future returned from `read_u8`
+            #[doc(hidden)]
+            #[must_use = "futures do nothing unless you `.await` or poll them"]
+            pub struct $name<R> {
+                #[pin]
+                reader: R,
+                // Make this future `!Unpin` for compatibility with async trait methods.
+                #[pin]
+                _pin: PhantomPinned,
+            }
+        }
+
+        impl<R> $name<R> {
+            pub(crate) fn new(reader: R) -> $name<R> {
+                $name {
+                    reader,
+                    _pin: PhantomPinned,
+                }
+            }
+        }
+
+        impl<R> Future for $name<R>
+        where
+            R: AsyncRead,
+        {
+            type Output = io::Result<$ty>;
+
+            fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+                let me = self.project();
+
+                let mut buf = [0; 1];
+                let mut buf = ReadBuf::new(&mut buf);
+                match me.reader.poll_read(cx, &mut buf) {
+                    Poll::Pending => Poll::Pending,
+                    Poll::Ready(Err(e)) => Poll::Ready(Err(e.into())),
+                    Poll::Ready(Ok(())) => {
+                        if buf.filled().len() == 0 {
+                            return Poll::Ready(Err(UnexpectedEof.into()));
+                        }
+
+                        Poll::Ready(Ok(buf.filled()[0] as $ty))
+                    }
+                }
+            }
+        }
+    };
+}
+
+reader8!(ReadU8, u8);
+reader8!(ReadI8, i8);
+
+reader!(ReadU16, u16, get_u16);
+reader!(ReadU32, u32, get_u32);
+reader!(ReadU64, u64, get_u64);
+reader!(ReadU128, u128, get_u128);
+
+reader!(ReadI16, i16, get_i16);
+reader!(ReadI32, i32, get_i32);
+reader!(ReadI64, i64, get_i64);
+reader!(ReadI128, i128, get_i128);
+
+reader!(ReadF32, f32, get_f32);
+reader!(ReadF64, f64, get_f64);
+
+reader!(ReadU16Le, u16, get_u16_le);
+reader!(ReadU32Le, u32, get_u32_le);
+reader!(ReadU64Le, u64, get_u64_le);
+reader!(ReadU128Le, u128, get_u128_le);
+
+reader!(ReadI16Le, i16, get_i16_le);
+reader!(ReadI32Le, i32, get_i32_le);
+reader!(ReadI64Le, i64, get_i64_le);
+reader!(ReadI128Le, i128, get_i128_le);
+
+reader!(ReadF32Le, f32, get_f32_le);
+reader!(ReadF64Le, f64, get_f64_le);
diff --git a/third_party/rust/tokio/src/io/util/read_line.rs b/third_party/rust/tokio/src/io/util/read_line.rs
new file mode 100644
index 0000000000..e641f51532
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/read_line.rs
@@ -0,0 +1,119 @@
+use crate::io::util::read_until::read_until_internal;
+use crate::io::AsyncBufRead;
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io;
+use std::marker::PhantomPinned;
+use std::mem;
+use std::pin::Pin;
+use std::string::FromUtf8Error;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// Future for the [`read_line`](crate::io::AsyncBufReadExt::read_line) method.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct ReadLine<'a, R: ?Sized> {
+        reader: &'a mut R,
+        // This is the buffer we were provided. It will be replaced with an empty string
+        // while reading to postpone utf-8 handling until after reading.
+        output: &'a mut String,
+        // The actual allocation of the string is moved into this vector instead.
+        buf: Vec<u8>,
+        // The number of bytes appended to buf. This can be less than buf.len() if
+        // the buffer was not empty when the operation was started.
+        read: usize,
+        // Make this future `!Unpin` for compatibility with async trait methods.
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+pub(crate) fn read_line<'a, R>(reader: &'a mut R, string: &'a mut String) -> ReadLine<'a, R>
+where
+    R: AsyncBufRead + ?Sized + Unpin,
+{
+    ReadLine {
+        reader,
+        buf: mem::take(string).into_bytes(),
+        output: string,
+        read: 0,
+        _pin: PhantomPinned,
+    }
+}
+
+fn put_back_original_data(output: &mut String, mut vector: Vec<u8>, num_bytes_read: usize) {
+    let original_len = vector.len() - num_bytes_read;
+    vector.truncate(original_len);
+    *output = String::from_utf8(vector).expect("The original data must be valid utf-8.");
+}
+
+/// This handles the various failure cases and puts the string back into `output`.
+///
+/// The `truncate_on_io_error` bool is necessary because `read_to_string` and `read_line`
+/// disagree on what should happen when an IO error occurs.
+pub(super) fn finish_string_read(
+    io_res: io::Result<usize>,
+    utf8_res: Result<String, FromUtf8Error>,
+    read: usize,
+    output: &mut String,
+    truncate_on_io_error: bool,
+) -> Poll<io::Result<usize>> {
+    match (io_res, utf8_res) {
+        (Ok(num_bytes), Ok(string)) => {
+            debug_assert_eq!(read, 0);
+            *output = string;
+            Poll::Ready(Ok(num_bytes))
+        }
+        (Err(io_err), Ok(string)) => {
+            *output = string;
+            if truncate_on_io_error {
+                let original_len = output.len() - read;
+                output.truncate(original_len);
+            }
+            Poll::Ready(Err(io_err))
+        }
+        (Ok(num_bytes), Err(utf8_err)) => {
+            debug_assert_eq!(read, 0);
+            put_back_original_data(output, utf8_err.into_bytes(), num_bytes);
+
+            Poll::Ready(Err(io::Error::new(
+                io::ErrorKind::InvalidData,
+                "stream did not contain valid UTF-8",
+            )))
+        }
+        (Err(io_err), Err(utf8_err)) => {
+            put_back_original_data(output, utf8_err.into_bytes(), read);
+
+            Poll::Ready(Err(io_err))
+        }
+    }
+}
+
+pub(super) fn read_line_internal<R: AsyncBufRead + ?Sized>(
+    reader: Pin<&mut R>,
+    cx: &mut Context<'_>,
+    output: &mut String,
+    buf: &mut Vec<u8>,
+    read: &mut usize,
+) -> Poll<io::Result<usize>> {
+    let io_res = ready!(read_until_internal(reader, cx, b'\n', buf, read));
+    let utf8_res = String::from_utf8(mem::take(buf));
+
+    // At this point both buf and output are empty. The allocation is in utf8_res.
+
+    debug_assert!(buf.is_empty());
+    debug_assert!(output.is_empty());
+    finish_string_read(io_res, utf8_res, *read, output, false)
+}
+
+impl<R: AsyncBufRead + ?Sized + Unpin> Future for ReadLine<'_, R> {
+    type Output = io::Result<usize>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let me = self.project();
+
+        read_line_internal(Pin::new(*me.reader), cx, me.output, me.buf, me.read)
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/read_to_end.rs b/third_party/rust/tokio/src/io/util/read_to_end.rs
new file mode 100644
index 0000000000..f4a564d7dd
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/read_to_end.rs
@@ -0,0 +1,112 @@
+use crate::io::util::vec_with_initialized::{into_read_buf_parts, VecU8, VecWithInitialized};
+use crate::io::AsyncRead;
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io;
+use std::marker::PhantomPinned;
+use std::mem;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct ReadToEnd<'a, R: ?Sized> {
+        reader: &'a mut R,
+        buf: VecWithInitialized<&'a mut Vec<u8>>,
+        // The number of bytes appended to buf. This can be less than buf.len() if
+        // the buffer was not empty when the operation was started.
+        read: usize,
+        // Make this future `!Unpin` for compatibility with async trait methods.
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+pub(crate) fn read_to_end<'a, R>(reader: &'a mut R, buffer: &'a mut Vec<u8>) -> ReadToEnd<'a, R>
+where
+    R: AsyncRead + Unpin + ?Sized,
+{
+    ReadToEnd {
+        reader,
+        buf: VecWithInitialized::new(buffer),
+        read: 0,
+        _pin: PhantomPinned,
+    }
+}
+
+pub(super) fn read_to_end_internal<V: VecU8, R: AsyncRead + ?Sized>(
+    buf: &mut VecWithInitialized<V>,
+    mut reader: Pin<&mut R>,
+    num_read: &mut usize,
+    cx: &mut Context<'_>,
+) -> Poll<io::Result<usize>> {
+    loop {
+        let ret = ready!(poll_read_to_end(buf, reader.as_mut(), cx));
+        match ret {
+            Err(err) => return Poll::Ready(Err(err)),
+            Ok(0) => return Poll::Ready(Ok(mem::replace(num_read, 0))),
+            Ok(num) => {
+                *num_read += num;
+            }
+        }
+    }
+}
+
+/// Tries to read from the provided AsyncRead.
+///
+/// The length of the buffer is increased by the number of bytes read.
+fn poll_read_to_end<V: VecU8, R: AsyncRead + ?Sized>(
+    buf: &mut VecWithInitialized<V>,
+    read: Pin<&mut R>,
+    cx: &mut Context<'_>,
+) -> Poll<io::Result<usize>> {
+    // This uses an adaptive system to extend the vector when it fills. We want to
+    // avoid paying to allocate and zero a huge chunk of memory if the reader only
+    // has 4 bytes while still making large reads if the reader does have a ton
+    // of data to return. Simply tacking on an extra DEFAULT_BUF_SIZE space every
+    // time is 4,500 times (!) slower than this if the reader has a very small
+    // amount of data to return.
+    buf.reserve(32);
+
+    // Get a ReadBuf into the vector.
+    let mut read_buf = buf.get_read_buf();
+
+    let filled_before = read_buf.filled().len();
+    let poll_result = read.poll_read(cx, &mut read_buf);
+    let filled_after = read_buf.filled().len();
+    let n = filled_after - filled_before;
+
+    // Update the length of the vector using the result of poll_read.
+    let read_buf_parts = into_read_buf_parts(read_buf);
+    buf.apply_read_buf(read_buf_parts);
+
+    match poll_result {
+        Poll::Pending => {
+            // In this case, nothing should have been read. However we still
+            // update the vector in case the poll_read call initialized parts of
+            // the vector's unused capacity.
+            debug_assert_eq!(filled_before, filled_after);
+            Poll::Pending
+        }
+        Poll::Ready(Err(err)) => {
+            debug_assert_eq!(filled_before, filled_after);
+            Poll::Ready(Err(err))
+        }
+        Poll::Ready(Ok(())) => Poll::Ready(Ok(n)),
+    }
+}
+
+impl<A> Future for ReadToEnd<'_, A>
+where
+    A: AsyncRead + ?Sized + Unpin,
+{
+    type Output = io::Result<usize>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let me = self.project();
+
+        read_to_end_internal(me.buf, Pin::new(*me.reader), me.read, cx)
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/read_to_string.rs b/third_party/rust/tokio/src/io/util/read_to_string.rs
new file mode 100644
index 0000000000..b3d82a26ba
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/read_to_string.rs
@@ -0,0 +1,78 @@
+use crate::io::util::read_line::finish_string_read;
+use crate::io::util::read_to_end::read_to_end_internal;
+use crate::io::util::vec_with_initialized::VecWithInitialized;
+use crate::io::AsyncRead;
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::marker::PhantomPinned;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use std::{io, mem};
+
+pin_project! {
+    /// Future for the [`read_to_string`](super::AsyncReadExt::read_to_string) method.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct ReadToString<'a, R: ?Sized> {
+        reader: &'a mut R,
+        // This is the buffer we were provided. It will be replaced with an empty string
+        // while reading to postpone utf-8 handling until after reading.
+        output: &'a mut String,
+        // The actual allocation of the string is moved into this vector instead.
+        buf: VecWithInitialized<Vec<u8>>,
+        // The number of bytes appended to buf. This can be less than buf.len() if
+        // the buffer was not empty when the operation was started.
+        read: usize,
+        // Make this future `!Unpin` for compatibility with async trait methods.
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+pub(crate) fn read_to_string<'a, R>(
+    reader: &'a mut R,
+    string: &'a mut String,
+) -> ReadToString<'a, R>
+where
+    R: AsyncRead + ?Sized + Unpin,
+{
+    let buf = mem::take(string).into_bytes();
+    ReadToString {
+        reader,
+        buf: VecWithInitialized::new(buf),
+        output: string,
+        read: 0,
+        _pin: PhantomPinned,
+    }
+}
+
+fn read_to_string_internal<R: AsyncRead + ?Sized>(
+    reader: Pin<&mut R>,
+    output: &mut String,
+    buf: &mut VecWithInitialized<Vec<u8>>,
+    read: &mut usize,
+    cx: &mut Context<'_>,
+) -> Poll<io::Result<usize>> {
+    let io_res = ready!(read_to_end_internal(buf, reader, read, cx));
+    let utf8_res = String::from_utf8(buf.take());
+
+    // At this point both buf and output are empty. The allocation is in utf8_res.
+
+    debug_assert!(buf.is_empty());
+    debug_assert!(output.is_empty());
+    finish_string_read(io_res, utf8_res, *read, output, true)
+}
+
+impl<A> Future for ReadToString<'_, A>
+where
+    A: AsyncRead + ?Sized + Unpin,
+{
+    type Output = io::Result<usize>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let me = self.project();
+
+        read_to_string_internal(Pin::new(*me.reader), me.output, me.buf, me.read, cx)
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/read_until.rs b/third_party/rust/tokio/src/io/util/read_until.rs
new file mode 100644
index 0000000000..90a0e8a18d
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/read_until.rs
@@ -0,0 +1,79 @@
+use crate::io::AsyncBufRead;
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io;
+use std::marker::PhantomPinned;
+use std::mem;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// Future for the [`read_until`](crate::io::AsyncBufReadExt::read_until) method.
+    /// The delimiter is included in the resulting vector.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct ReadUntil<'a, R: ?Sized> {
+        reader: &'a mut R,
+        delimiter: u8,
+        buf: &'a mut Vec<u8>,
+        // The number of bytes appended to buf. This can be less than buf.len() if
+        // the buffer was not empty when the operation was started.
+        read: usize,
+        // Make this future `!Unpin` for compatibility with async trait methods.
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+pub(crate) fn read_until<'a, R>(
+    reader: &'a mut R,
+    delimiter: u8,
+    buf: &'a mut Vec<u8>,
+) -> ReadUntil<'a, R>
+where
+    R: AsyncBufRead + ?Sized + Unpin,
+{
+    ReadUntil {
+        reader,
+        delimiter,
+        buf,
+        read: 0,
+        _pin: PhantomPinned,
+    }
+}
+
+pub(super) fn read_until_internal<R: AsyncBufRead + ?Sized>(
+    mut reader: Pin<&mut R>,
+    cx: &mut Context<'_>,
+    delimiter: u8,
+    buf: &mut Vec<u8>,
+    read: &mut usize,
+) -> Poll<io::Result<usize>> {
+    loop {
+        let (done, used) = {
+            let available = ready!(reader.as_mut().poll_fill_buf(cx))?;
+            if let Some(i) = memchr::memchr(delimiter, available) {
+                buf.extend_from_slice(&available[..=i]);
+                (true, i + 1)
+            } else {
+                buf.extend_from_slice(available);
+                (false, available.len())
+            }
+        };
+        reader.as_mut().consume(used);
+        *read += used;
+        if done || used == 0 {
+            return Poll::Ready(Ok(mem::replace(read, 0)));
+        }
+    }
+}
+
+impl<R: AsyncBufRead + ?Sized + Unpin> Future for ReadUntil<'_, R> {
+    type Output = io::Result<usize>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let me = self.project();
+        read_until_internal(Pin::new(*me.reader), cx, *me.delimiter, me.buf, me.read)
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/repeat.rs b/third_party/rust/tokio/src/io/util/repeat.rs
new file mode 100644
index 0000000000..1142765df5
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/repeat.rs
@@ -0,0 +1,72 @@
+use crate::io::{AsyncRead, ReadBuf};
+
+use std::io;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+cfg_io_util! {
+    /// An async reader which yields one byte over and over and over and over and
+    /// over and...
+    ///
+    /// This struct is generally created by calling [`repeat`][repeat]. Please
+    /// see the documentation of `repeat()` for more details.
+    ///
+    /// This is an asynchronous version of [`std::io::Repeat`][std].
+    ///
+    /// [repeat]: fn@repeat
+    /// [std]: std::io::Repeat
+    #[derive(Debug)]
+    pub struct Repeat {
+        byte: u8,
+    }
+
+    /// Creates an instance of an async reader that infinitely repeats one byte.
+    ///
+    /// All reads from this reader will succeed by filling the specified buffer with
+    /// the given byte.
+    ///
+    /// This is an asynchronous version of [`std::io::repeat`][std].
+    ///
+    /// [std]: std::io::repeat
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::io::{self, AsyncReadExt};
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let mut buffer = [0; 3];
+    ///     io::repeat(0b101).read_exact(&mut buffer).await.unwrap();
+    ///     assert_eq!(buffer, [0b101, 0b101, 0b101]);
+    /// }
+    /// ```
+    pub fn repeat(byte: u8) -> Repeat {
+        Repeat { byte }
+    }
+}
+
+impl AsyncRead for Repeat {
+    #[inline]
+    fn poll_read(
+        self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        // TODO: could be faster, but should we unsafe it?
+        while buf.remaining() != 0 {
+            buf.put_slice(&[self.byte]);
+        }
+        Poll::Ready(Ok(()))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn assert_unpin() {
+        crate::is_unpin::<Repeat>();
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/shutdown.rs b/third_party/rust/tokio/src/io/util/shutdown.rs
new file mode 100644
index 0000000000..6d30b004b1
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/shutdown.rs
@@ -0,0 +1,46 @@
+use crate::io::AsyncWrite;
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io;
+use std::marker::PhantomPinned;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// A future used to shutdown an I/O object.
+    ///
+    /// Created by the [`AsyncWriteExt::shutdown`][shutdown] function.
+    /// [shutdown]: crate::io::AsyncWriteExt::shutdown
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    #[derive(Debug)]
+    pub struct Shutdown<'a, A: ?Sized> {
+        a: &'a mut A,
+        // Make this future `!Unpin` for compatibility with async trait methods.
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+/// Creates a future which will shutdown an I/O object.
+pub(super) fn shutdown<A>(a: &mut A) -> Shutdown<'_, A>
+where
+    A: AsyncWrite + Unpin + ?Sized,
+{
+    Shutdown {
+        a,
+        _pin: PhantomPinned,
+    }
+}
+
+impl<A> Future for Shutdown<'_, A>
+where
+    A: AsyncWrite + Unpin + ?Sized,
+{
+    type Output = io::Result<()>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let me = self.project();
+        Pin::new(me.a).poll_shutdown(cx)
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/sink.rs b/third_party/rust/tokio/src/io/util/sink.rs
new file mode 100644
index 0000000000..05ee773fa3
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/sink.rs
@@ -0,0 +1,87 @@
+use crate::io::AsyncWrite;
+
+use std::fmt;
+use std::io;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+cfg_io_util! {
+    /// An async writer which will move data into the void.
+    ///
+    /// This struct is generally created by calling [`sink`][sink]. Please
+    /// see the documentation of `sink()` for more details.
+    ///
+    /// This is an asynchronous version of [`std::io::Sink`][std].
+    ///
+    /// [sink]: sink()
+    /// [std]: std::io::Sink
+    pub struct Sink {
+        _p: (),
+    }
+
+    /// Creates an instance of an async writer which will successfully consume all
+    /// data.
+    ///
+    /// All calls to [`poll_write`] on the returned instance will return
+    /// `Poll::Ready(Ok(buf.len()))` and the contents of the buffer will not be
+    /// inspected.
+    ///
+    /// This is an asynchronous version of [`std::io::sink`][std].
+    ///
+    /// [`poll_write`]: crate::io::AsyncWrite::poll_write()
+    /// [std]: std::io::sink
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::io::{self, AsyncWriteExt};
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let buffer = vec![1, 2, 3, 5, 8];
+    ///     let num_bytes = io::sink().write(&buffer).await?;
+    ///     assert_eq!(num_bytes, 5);
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn sink() -> Sink {
+        Sink { _p: () }
+    }
+}
+
+impl AsyncWrite for Sink {
+    #[inline]
+    fn poll_write(
+        self: Pin<&mut Self>,
+        _: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<Result<usize, io::Error>> {
+        Poll::Ready(Ok(buf.len()))
+    }
+
+    #[inline]
+    fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    #[inline]
+    fn poll_shutdown(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
+        Poll::Ready(Ok(()))
+    }
+}
+
+impl fmt::Debug for Sink {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad("Sink { .. }")
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn assert_unpin() {
+        crate::is_unpin::<Sink>();
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/split.rs b/third_party/rust/tokio/src/io/util/split.rs
new file mode 100644
index 0000000000..7489c24281
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/split.rs
@@ -0,0 +1,121 @@
+use crate::io::util::read_until::read_until_internal;
+use crate::io::AsyncBufRead;
+
+use pin_project_lite::pin_project;
+use std::io;
+use std::mem;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// Splitter for the [`split`](crate::io::AsyncBufReadExt::split) method.
+    ///
+    /// A `Split` can be turned into a `Stream` with [`SplitStream`].
+    ///
+    /// [`SplitStream`]: https://docs.rs/tokio-stream/0.1/tokio_stream/wrappers/struct.SplitStream.html
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless polled"]
+    #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
+    pub struct Split<R> {
+        #[pin]
+        reader: R,
+        buf: Vec<u8>,
+        delim: u8,
+        read: usize,
+    }
+}
+
+pub(crate) fn split<R>(reader: R, delim: u8) -> Split<R>
+where
+    R: AsyncBufRead,
+{
+    Split {
+        reader,
+        buf: Vec::new(),
+        delim,
+        read: 0,
+    }
+}
+
+impl<R> Split<R>
+where
+    R: AsyncBufRead + Unpin,
+{
+    /// Returns the next segment in the stream.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use tokio::io::AsyncBufRead;
+    /// use tokio::io::AsyncBufReadExt;
+    ///
+    /// # async fn dox(my_buf_read: impl AsyncBufRead + Unpin) -> std::io::Result<()> {
+    /// let mut segments = my_buf_read.split(b'f');
+    ///
+    /// while let Some(segment) = segments.next_segment().await? {
+    ///     println!("length = {}", segment.len())
+    /// }
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn next_segment(&mut self) -> io::Result<Option<Vec<u8>>> {
+        use crate::future::poll_fn;
+
+        poll_fn(|cx| Pin::new(&mut *self).poll_next_segment(cx)).await
+    }
+}
+
+impl<R> Split<R>
+where
+    R: AsyncBufRead,
+{
+    /// Polls for the next segment in the stream.
+    ///
+    /// This method returns:
+    ///
+    ///  * `Poll::Pending` if the next segment is not yet available.
+    ///  * `Poll::Ready(Ok(Some(segment)))` if the next segment is available.
+    ///  * `Poll::Ready(Ok(None))` if there are no more segments in this stream.
+    ///  * `Poll::Ready(Err(err))` if an IO error occurred while reading the
+    ///    next segment.
+    ///
+    /// When the method returns `Poll::Pending`, the `Waker` in the provided
+    /// `Context` is scheduled to receive a wakeup when more bytes become
+    /// available on the underlying IO resource.
+    ///
+    /// Note that on multiple calls to `poll_next_segment`, only the `Waker`
+    /// from the `Context` passed to the most recent call is scheduled to
+    /// receive a wakeup.
+    pub fn poll_next_segment(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<io::Result<Option<Vec<u8>>>> {
+        let me = self.project();
+
+        let n = ready!(read_until_internal(
+            me.reader, cx, *me.delim, me.buf, me.read,
+        ))?;
+        // read_until_internal resets me.read to zero once it finds the delimiter
+        debug_assert_eq!(*me.read, 0);
+
+        if n == 0 && me.buf.is_empty() {
+            return Poll::Ready(Ok(None));
+        }
+
+        if me.buf.last() == Some(me.delim) {
+            me.buf.pop();
+        }
+
+        Poll::Ready(Ok(Some(mem::take(me.buf))))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn assert_unpin() {
+        crate::is_unpin::<Split<()>>();
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/take.rs b/third_party/rust/tokio/src/io/util/take.rs
new file mode 100644
index 0000000000..df2f61b9e6
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/take.rs
@@ -0,0 +1,137 @@
+use crate::io::{AsyncBufRead, AsyncRead, ReadBuf};
+
+use pin_project_lite::pin_project;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use std::{cmp, io};
+
+pin_project! {
+    /// Stream for the [`take`](super::AsyncReadExt::take) method.
+    #[derive(Debug)]
+    #[must_use = "streams do nothing unless you `.await` or poll them"]
+    #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
+    pub struct Take<R> {
+        #[pin]
+        inner: R,
+        // Add '_' to avoid conflicts with `limit` method.
+        limit_: u64,
+    }
+}
+
+pub(super) fn take<R: AsyncRead>(inner: R, limit: u64) -> Take<R> {
+    Take {
+        inner,
+        limit_: limit,
+    }
+}
+
+impl<R: AsyncRead> Take<R> {
+    /// Returns the remaining number of bytes that can be
+    /// read before this instance will return EOF.
+    ///
+    /// # Note
+    ///
+    /// This instance may reach `EOF` after reading fewer bytes than indicated by
+    /// this method if the underlying [`AsyncRead`] instance reaches EOF.
+    pub fn limit(&self) -> u64 {
+        self.limit_
+    }
+
+    /// Sets the number of bytes that can be read before this instance will
+    /// return EOF. This is the same as constructing a new `Take` instance, so
+    /// the amount of bytes read and the previous limit value don't matter when
+    /// calling this method.
+    pub fn set_limit(&mut self, limit: u64) {
+        self.limit_ = limit
+    }
+
+    /// Gets a reference to the underlying reader.
+    pub fn get_ref(&self) -> &R {
+        &self.inner
+    }
+
+    /// Gets a mutable reference to the underlying reader.
+    ///
+    /// Care should be taken to avoid modifying the internal I/O state of the
+    /// underlying reader as doing so may corrupt the internal limit of this
+    /// `Take`.
+    pub fn get_mut(&mut self) -> &mut R {
+        &mut self.inner
+    }
+
+    /// Gets a pinned mutable reference to the underlying reader.
+    ///
+    /// Care should be taken to avoid modifying the internal I/O state of the
+    /// underlying reader as doing so may corrupt the internal limit of this
+    /// `Take`.
+    pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut R> {
+        self.project().inner
+    }
+
+    /// Consumes the `Take`, returning the wrapped reader.
+    pub fn into_inner(self) -> R {
+        self.inner
+    }
+}
+
+impl<R: AsyncRead> AsyncRead for Take<R> {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<Result<(), io::Error>> {
+        if self.limit_ == 0 {
+            return Poll::Ready(Ok(()));
+        }
+
+        let me = self.project();
+        let mut b = buf.take(*me.limit_ as usize);
+
+        let buf_ptr = b.filled().as_ptr();
+        ready!(me.inner.poll_read(cx, &mut b))?;
+        assert_eq!(b.filled().as_ptr(), buf_ptr);
+
+        let n = b.filled().len();
+
+        // We need to update the original ReadBuf
+        unsafe {
+            buf.assume_init(n);
+        }
+        buf.advance(n);
+        *me.limit_ -= n as u64;
+        Poll::Ready(Ok(()))
+    }
+}
+
+impl<R: AsyncBufRead> AsyncBufRead for Take<R> {
+    fn poll_fill_buf(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<&[u8]>> {
+        let me = self.project();
+
+        // Don't call into inner reader at all at EOF because it may still block
+        if *me.limit_ == 0 {
+            return Poll::Ready(Ok(&[]));
+        }
+
+        let buf = ready!(me.inner.poll_fill_buf(cx)?);
+        let cap = cmp::min(buf.len() as u64, *me.limit_) as usize;
+        Poll::Ready(Ok(&buf[..cap]))
+    }
+
+    fn consume(self: Pin<&mut Self>, amt: usize) {
+        let me = self.project();
+        // Don't let callers reset the limit by passing an overlarge value
+        let amt = cmp::min(amt as u64, *me.limit_) as usize;
+        *me.limit_ -= amt as u64;
+        me.inner.consume(amt);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn assert_unpin() {
+        crate::is_unpin::<Take<()>>();
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/vec_with_initialized.rs b/third_party/rust/tokio/src/io/util/vec_with_initialized.rs
new file mode 100644
index 0000000000..208cc939c1
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/vec_with_initialized.rs
@@ -0,0 +1,132 @@
+use crate::io::ReadBuf;
+use std::mem::MaybeUninit;
+
+mod private {
+    pub trait Sealed {}
+
+    impl Sealed for Vec<u8> {}
+    impl Sealed for &mut Vec<u8> {}
+}
+
+/// A sealed trait that constrains the generic type parameter in `VecWithInitialized<V>`.  That struct's safety relies
+/// on certain invariants upheld by `Vec<u8>`.
+pub(crate) trait VecU8: AsMut<Vec<u8>> + private::Sealed {}
+
+impl VecU8 for Vec<u8> {}
+impl VecU8 for &mut Vec<u8> {}
+/// This struct wraps a `Vec<u8>` or `&mut Vec<u8>`, combining it with a
+/// `num_initialized`, which keeps track of the number of initialized bytes
+/// in the unused capacity.
+///
+/// The purpose of this struct is to remember how many bytes were initialized
+/// through a `ReadBuf` from call to call.
+///
+/// This struct has the safety invariant that the first `num_initialized` of the
+/// vector's allocation must be initialized at any time.
+#[derive(Debug)]
+pub(crate) struct VecWithInitialized<V> {
+    vec: V,
+    // The number of initialized bytes in the vector.
+    // Always between `vec.len()` and `vec.capacity()`.
+    num_initialized: usize,
+}
+
+impl VecWithInitialized<Vec<u8>> {
+    #[cfg(feature = "io-util")]
+    pub(crate) fn take(&mut self) -> Vec<u8> {
+        self.num_initialized = 0;
+        std::mem::take(&mut self.vec)
+    }
+}
+
+impl<V> VecWithInitialized<V>
+where
+    V: VecU8,
+{
+    pub(crate) fn new(mut vec: V) -> Self {
+        // SAFETY: The safety invariants of vector guarantee that the bytes up
+        // to its length are initialized.
+        Self {
+            num_initialized: vec.as_mut().len(),
+            vec,
+        }
+    }
+
+    pub(crate) fn reserve(&mut self, num_bytes: usize) {
+        let vec = self.vec.as_mut();
+        if vec.capacity() - vec.len() >= num_bytes {
+            return;
+        }
+        // SAFETY: Setting num_initialized to `vec.len()` is correct as
+        // `reserve` does not change the length of the vector.
+        self.num_initialized = vec.len();
+        vec.reserve(num_bytes);
+    }
+
+    #[cfg(feature = "io-util")]
+    pub(crate) fn is_empty(&mut self) -> bool {
+        self.vec.as_mut().is_empty()
+    }
+
+    pub(crate) fn get_read_buf<'a>(&'a mut self) -> ReadBuf<'a> {
+        let num_initialized = self.num_initialized;
+
+        // SAFETY: Creating the slice is safe because of the safety invariants
+        // on Vec<u8>. The safety invariants of `ReadBuf` will further guarantee
+        // that no bytes in the slice are de-initialized.
+        let vec = self.vec.as_mut();
+        let len = vec.len();
+        let cap = vec.capacity();
+        let ptr = vec.as_mut_ptr().cast::<MaybeUninit<u8>>();
+        let slice = unsafe { std::slice::from_raw_parts_mut::<'a, MaybeUninit<u8>>(ptr, cap) };
+
+        // SAFETY: This is safe because the safety invariants of
+        // VecWithInitialized say that the first num_initialized bytes must be
+        // initialized.
+        let mut read_buf = ReadBuf::uninit(slice);
+        unsafe {
+            read_buf.assume_init(num_initialized);
+        }
+        read_buf.set_filled(len);
+
+        read_buf
+    }
+
+    pub(crate) fn apply_read_buf(&mut self, parts: ReadBufParts) {
+        let vec = self.vec.as_mut();
+        assert_eq!(vec.as_ptr(), parts.ptr);
+
+        // SAFETY:
+        // The ReadBufParts really does point inside `self.vec` due to the above
+        // check, and the safety invariants of `ReadBuf` guarantee that the
+        // first `parts.initialized` bytes of `self.vec` really have been
+        // initialized. Additionally, `ReadBuf` guarantees that `parts.len` is
+        // at most `parts.initialized`, so the first `parts.len` bytes are also
+        // initialized.
+        //
+        // Note that this relies on the fact that `V` is either `Vec<u8>` or
+        // `&mut Vec<u8>`, so the vector returned by `self.vec.as_mut()` cannot
+        // change from call to call.
+        unsafe {
+            self.num_initialized = parts.initialized;
+            vec.set_len(parts.len);
+        }
+    }
+}
+
+pub(crate) struct ReadBufParts {
+    // Pointer is only used to check that the ReadBuf actually came from the
+    // right VecWithInitialized.
+    ptr: *const u8,
+    len: usize,
+    initialized: usize,
+}
+
+// This is needed to release the borrow on `VecWithInitialized<V>`.
+pub(crate) fn into_read_buf_parts(rb: ReadBuf<'_>) -> ReadBufParts {
+    ReadBufParts {
+        ptr: rb.filled().as_ptr(),
+        len: rb.filled().len(),
+        initialized: rb.initialized().len(),
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/write.rs b/third_party/rust/tokio/src/io/util/write.rs
new file mode 100644
index 0000000000..92169ebc1d
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/write.rs
@@ -0,0 +1,46 @@
+use crate::io::AsyncWrite;
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io;
+use std::marker::PhantomPinned;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// A future to write some of the buffer to an `AsyncWrite`.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct Write<'a, W: ?Sized> {
+        writer: &'a mut W,
+        buf: &'a [u8],
+        // Make this future `!Unpin` for compatibility with async trait methods.
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+/// Tries to write some bytes from the given `buf` to the writer in an
+/// asynchronous manner, returning a future.
+pub(crate) fn write<'a, W>(writer: &'a mut W, buf: &'a [u8]) -> Write<'a, W>
+where
+    W: AsyncWrite + Unpin + ?Sized,
+{
+    Write {
+        writer,
+        buf,
+        _pin: PhantomPinned,
+    }
+}
+
+impl<W> Future for Write<'_, W>
+where
+    W: AsyncWrite + Unpin + ?Sized,
+{
+    type Output = io::Result<usize>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
+        let me = self.project();
+        Pin::new(&mut *me.writer).poll_write(cx, me.buf)
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/write_all.rs b/third_party/rust/tokio/src/io/util/write_all.rs
new file mode 100644
index 0000000000..abd3e39d31
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/write_all.rs
@@ -0,0 +1,55 @@
+use crate::io::AsyncWrite;
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io;
+use std::marker::PhantomPinned;
+use std::mem;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct WriteAll<'a, W: ?Sized> {
+        writer: &'a mut W,
+        buf: &'a [u8],
+        // Make this future `!Unpin` for compatibility with async trait methods.
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+pub(crate) fn write_all<'a, W>(writer: &'a mut W, buf: &'a [u8]) -> WriteAll<'a, W>
+where
+    W: AsyncWrite + Unpin + ?Sized,
+{
+    WriteAll {
+        writer,
+        buf,
+        _pin: PhantomPinned,
+    }
+}
+
+impl<W> Future for WriteAll<'_, W>
+where
+    W: AsyncWrite + Unpin + ?Sized,
+{
+    type Output = io::Result<()>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        let me = self.project();
+        while !me.buf.is_empty() {
+            let n = ready!(Pin::new(&mut *me.writer).poll_write(cx, me.buf))?;
+            {
+                let (_, rest) = mem::take(&mut *me.buf).split_at(n);
+                *me.buf = rest;
+            }
+            if n == 0 {
+                return Poll::Ready(Err(io::ErrorKind::WriteZero.into()));
+            }
+        }
+
+        Poll::Ready(Ok(()))
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/write_all_buf.rs b/third_party/rust/tokio/src/io/util/write_all_buf.rs
new file mode 100644
index 0000000000..05af7fe99b
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/write_all_buf.rs
@@ -0,0 +1,56 @@
+use crate::io::AsyncWrite;
+
+use bytes::Buf;
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io;
+use std::marker::PhantomPinned;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// A future to write some of the buffer to an `AsyncWrite`.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct WriteAllBuf<'a, W, B> {
+        writer: &'a mut W,
+        buf: &'a mut B,
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+/// Tries to write some bytes from the given `buf` to the writer in an
+/// asynchronous manner, returning a future.
+pub(crate) fn write_all_buf<'a, W, B>(writer: &'a mut W, buf: &'a mut B) -> WriteAllBuf<'a, W, B>
+where
+    W: AsyncWrite + Unpin,
+    B: Buf,
+{
+    WriteAllBuf {
+        writer,
+        buf,
+        _pin: PhantomPinned,
+    }
+}
+
+impl<W, B> Future for WriteAllBuf<'_, W, B>
+where
+    W: AsyncWrite + Unpin,
+    B: Buf,
+{
+    type Output = io::Result<()>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        let me = self.project();
+        while me.buf.has_remaining() {
+            let n = ready!(Pin::new(&mut *me.writer).poll_write(cx, me.buf.chunk())?);
+            me.buf.advance(n);
+            if n == 0 {
+                return Poll::Ready(Err(io::ErrorKind::WriteZero.into()));
+            }
+        }
+
+        Poll::Ready(Ok(()))
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/write_buf.rs b/third_party/rust/tokio/src/io/util/write_buf.rs
new file mode 100644
index 0000000000..82fd7a759f
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/write_buf.rs
@@ -0,0 +1,55 @@
+use crate::io::AsyncWrite;
+
+use bytes::Buf;
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io;
+use std::marker::PhantomPinned;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// A future to write some of the buffer to an `AsyncWrite`.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct WriteBuf<'a, W, B> {
+        writer: &'a mut W,
+        buf: &'a mut B,
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+/// Tries to write some bytes from the given `buf` to the writer in an
+/// asynchronous manner, returning a future.
+pub(crate) fn write_buf<'a, W, B>(writer: &'a mut W, buf: &'a mut B) -> WriteBuf<'a, W, B>
+where
+    W: AsyncWrite + Unpin,
+    B: Buf,
+{
+    WriteBuf {
+        writer,
+        buf,
+        _pin: PhantomPinned,
+    }
+}
+
+impl<W, B> Future for WriteBuf<'_, W, B>
+where
+    W: AsyncWrite + Unpin,
+    B: Buf,
+{
+    type Output = io::Result<usize>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
+        let me = self.project();
+
+        if !me.buf.has_remaining() {
+            return Poll::Ready(Ok(0));
+        }
+
+        let n = ready!(Pin::new(me.writer).poll_write(cx, me.buf.chunk()))?;
+        me.buf.advance(n);
+        Poll::Ready(Ok(n))
+    }
+}
diff --git a/third_party/rust/tokio/src/io/util/write_int.rs b/third_party/rust/tokio/src/io/util/write_int.rs
new file mode 100644
index 0000000000..63cd49126f
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/write_int.rs
@@ -0,0 +1,152 @@
+use crate::io::AsyncWrite;
+
+use bytes::BufMut;
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::io;
+use std::marker::PhantomPinned;
+use std::mem::size_of;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+macro_rules! writer {
+    ($name:ident, $ty:ty, $writer:ident) => {
+        writer!($name, $ty, $writer, size_of::<$ty>());
+    };
+    ($name:ident, $ty:ty, $writer:ident, $bytes:expr) => {
+        pin_project! {
+            #[doc(hidden)]
+            #[must_use = "futures do nothing unless you `.await` or poll them"]
+            pub struct $name<W> {
+                #[pin]
+                dst: W,
+                buf: [u8; $bytes],
+                written: u8,
+                // Make this future `!Unpin` for compatibility with async trait methods.
+                #[pin]
+                _pin: PhantomPinned,
+            }
+        }
+
+        impl<W> $name<W> {
+            pub(crate) fn new(w: W, value: $ty) -> Self {
+                let mut writer = Self {
+                    buf: [0; $bytes],
+                    written: 0,
+                    dst: w,
+                    _pin: PhantomPinned,
+                };
+                BufMut::$writer(&mut &mut writer.buf[..], value);
+                writer
+            }
+        }
+
+        impl<W> Future for $name<W>
+        where
+            W: AsyncWrite,
+        {
+            type Output = io::Result<()>;
+
+            fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+                let mut me = self.project();
+
+                if *me.written == $bytes as u8 {
+                    return Poll::Ready(Ok(()));
+                }
+
+                while *me.written < $bytes as u8 {
+                    *me.written += match me
+                        .dst
+                        .as_mut()
+                        .poll_write(cx, &me.buf[*me.written as usize..])
+                    {
+                        Poll::Pending => return Poll::Pending,
+                        Poll::Ready(Err(e)) => return Poll::Ready(Err(e.into())),
+                        Poll::Ready(Ok(0)) => {
+                            return Poll::Ready(Err(io::ErrorKind::WriteZero.into()));
+                        }
+                        Poll::Ready(Ok(n)) => n as u8,
+                    };
+                }
+                Poll::Ready(Ok(()))
+            }
+        }
+    };
+}
+
+macro_rules! writer8 {
+    ($name:ident, $ty:ty) => {
+        pin_project! {
+            #[doc(hidden)]
+            #[must_use = "futures do nothing unless you `.await` or poll them"]
+            pub struct $name<W> {
+                #[pin]
+                dst: W,
+                byte: $ty,
+                // Make this future `!Unpin` for compatibility with async trait methods.
+                #[pin]
+                _pin: PhantomPinned,
+            }
+        }
+
+        impl<W> $name<W> {
+            pub(crate) fn new(dst: W, byte: $ty) -> Self {
+                Self {
+                    dst,
+                    byte,
+                    _pin: PhantomPinned,
+                }
+            }
+        }
+
+        impl<W> Future for $name<W>
+        where
+            W: AsyncWrite,
+        {
+            type Output = io::Result<()>;
+
+            fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+                let me = self.project();
+
+                let buf = [*me.byte as u8];
+
+                match me.dst.poll_write(cx, &buf[..]) {
+                    Poll::Pending => Poll::Pending,
+                    Poll::Ready(Err(e)) => Poll::Ready(Err(e.into())),
+                    Poll::Ready(Ok(0)) => Poll::Ready(Err(io::ErrorKind::WriteZero.into())),
+                    Poll::Ready(Ok(1)) => Poll::Ready(Ok(())),
+                    Poll::Ready(Ok(_)) => unreachable!(),
+                }
+            }
+        }
+    };
+}
+
+writer8!(WriteU8, u8);
+writer8!(WriteI8, i8);
+
+writer!(WriteU16, u16, put_u16);
+writer!(WriteU32, u32, put_u32);
+writer!(WriteU64, u64, put_u64);
+writer!(WriteU128, u128, put_u128);
+
+writer!(WriteI16, i16, put_i16);
+writer!(WriteI32, i32, put_i32);
+writer!(WriteI64, i64, put_i64);
+writer!(WriteI128, i128, put_i128);
+
+writer!(WriteF32, f32, put_f32);
+writer!(WriteF64, f64, put_f64);
+
+writer!(WriteU16Le, u16, put_u16_le);
+writer!(WriteU32Le, u32, put_u32_le);
+writer!(WriteU64Le, u64, put_u64_le);
+writer!(WriteU128Le, u128, put_u128_le);
+
+writer!(WriteI16Le, i16, put_i16_le);
+writer!(WriteI32Le, i32, put_i32_le);
+writer!(WriteI64Le, i64, put_i64_le);
+writer!(WriteI128Le, i128, put_i128_le);
+
+writer!(WriteF32Le, f32, put_f32_le);
+writer!(WriteF64Le, f64, put_f64_le);
diff --git a/third_party/rust/tokio/src/io/util/write_vectored.rs b/third_party/rust/tokio/src/io/util/write_vectored.rs
new file mode 100644
index 0000000000..be40322943
--- /dev/null
+++ b/third_party/rust/tokio/src/io/util/write_vectored.rs
@@ -0,0 +1,47 @@
+use crate::io::AsyncWrite;
+
+use pin_project_lite::pin_project;
+use std::io;
+use std::marker::PhantomPinned;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use std::{future::Future, io::IoSlice};
+
+pin_project! {
+    /// A future to write a slice of buffers to an `AsyncWrite`.
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct WriteVectored<'a, 'b, W: ?Sized> {
+        writer: &'a mut W,
+        bufs: &'a [IoSlice<'b>],
+        // Make this future `!Unpin` for compatibility with async trait methods.
+        #[pin]
+        _pin: PhantomPinned,
+    }
+}
+
+pub(crate) fn write_vectored<'a, 'b, W>(
+    writer: &'a mut W,
+    bufs: &'a [IoSlice<'b>],
+) -> WriteVectored<'a, 'b, W>
+where
+    W: AsyncWrite + Unpin + ?Sized,
+{
+    WriteVectored {
+        writer,
+        bufs,
+        _pin: PhantomPinned,
+    }
+}
+
+impl<W> Future for WriteVectored<'_, '_, W>
+where
+    W: AsyncWrite + Unpin + ?Sized,
+{
+    type Output = io::Result<usize>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<usize>> {
+        let me = self.project();
+        Pin::new(&mut *me.writer).poll_write_vectored(cx, me.bufs)
+    }
+}
diff --git a/third_party/rust/tokio/src/lib.rs b/third_party/rust/tokio/src/lib.rs
new file mode 100644
index 0000000000..35295d837a
--- /dev/null
+++ b/third_party/rust/tokio/src/lib.rs
@@ -0,0 +1,537 @@
+#![allow(
+    clippy::cognitive_complexity,
+    clippy::large_enum_variant,
+    clippy::needless_doctest_main
+)]
+#![warn(
+    missing_debug_implementations,
+    missing_docs,
+    rust_2018_idioms,
+    unreachable_pub
+)]
+#![deny(unused_must_use)]
+#![doc(test(
+    no_crate_inject,
+    attr(deny(warnings, rust_2018_idioms), allow(dead_code, unused_variables))
+))]
+#![cfg_attr(docsrs, feature(doc_cfg))]
+#![cfg_attr(docsrs, allow(unused_attributes))]
+
+//! A runtime for writing reliable network applications without compromising speed.
+//!
+//! Tokio is an event-driven, non-blocking I/O platform for writing asynchronous
+//! applications with the Rust programming language. At a high level, it
+//! provides a few major components:
+//!
+//! * Tools for [working with asynchronous tasks][tasks], including
+//!   [synchronization primitives and channels][sync] and [timeouts, sleeps, and
+//!   intervals][time].
+//! * APIs for [performing asynchronous I/O][io], including [TCP and UDP][net] sockets,
+//!   [filesystem][fs] operations, and [process] and [signal] management.
+//! * A [runtime] for executing asynchronous code, including a task scheduler,
+//!   an I/O driver backed by the operating system's event queue (epoll, kqueue,
+//!   IOCP, etc...), and a high performance timer.
+//!
+//! Guide level documentation is found on the [website].
+//!
+//! [tasks]: #working-with-tasks
+//! [sync]: crate::sync
+//! [time]: crate::time
+//! [io]: #asynchronous-io
+//! [net]: crate::net
+//! [fs]: crate::fs
+//! [process]: crate::process
+//! [signal]: crate::signal
+//! [fs]: crate::fs
+//! [runtime]: crate::runtime
+//! [website]: https://tokio.rs/tokio/tutorial
+//!
+//! # A Tour of Tokio
+//!
+//! Tokio consists of a number of modules that provide a range of functionality
+//! essential for implementing asynchronous applications in Rust. In this
+//! section, we will take a brief tour of Tokio, summarizing the major APIs and
+//! their uses.
+//!
+//! The easiest way to get started is to enable all features. Do this by
+//! enabling the `full` feature flag:
+//!
+//! ```toml
+//! tokio = { version = "1", features = ["full"] }
+//! ```
+//!
+//! ### Authoring applications
+//!
+//! Tokio is great for writing applications and most users in this case shouldn't
+//! worry too much about what features they should pick. If you're unsure, we suggest
+//! going with `full` to ensure that you don't run into any road blocks while you're
+//! building your application.
+//!
+//! #### Example
+//!
+//! This example shows the quickest way to get started with Tokio.
+//!
+//! ```toml
+//! tokio = { version = "1", features = ["full"] }
+//! ```
+//!
+//! ### Authoring libraries
+//!
+//! As a library author your goal should be to provide the lightest weight crate
+//! that is based on Tokio. To achieve this you should ensure that you only enable
+//! the features you need. This allows users to pick up your crate without having
+//! to enable unnecessary features.
+//!
+//! #### Example
+//!
+//! This example shows how you may want to import features for a library that just
+//! needs to `tokio::spawn` and use a `TcpStream`.
+//!
+//! ```toml
+//! tokio = { version = "1", features = ["rt", "net"] }
+//! ```
+//!
+//! ## Working With Tasks
+//!
+//! Asynchronous programs in Rust are based around lightweight, non-blocking
+//! units of execution called [_tasks_][tasks]. The [`tokio::task`] module provides
+//! important tools for working with tasks:
+//!
+//! * The [`spawn`] function and [`JoinHandle`] type, for scheduling a new task
+//!   on the Tokio runtime and awaiting the output of a spawned task, respectively,
+//! * Functions for [running blocking operations][blocking] in an asynchronous
+//!   task context.
+//!
+//! The [`tokio::task`] module is present only when the "rt" feature flag
+//! is enabled.
+//!
+//! [tasks]: task/index.html#what-are-tasks
+//! [`tokio::task`]: crate::task
+//! [`spawn`]: crate::task::spawn()
+//! [`JoinHandle`]: crate::task::JoinHandle
+//! [blocking]: task/index.html#blocking-and-yielding
+//!
+//! The [`tokio::sync`] module contains synchronization primitives to use when
+//! needing to communicate or share data. These include:
+//!
+//! * channels ([`oneshot`], [`mpsc`], and [`watch`]), for sending values
+//!   between tasks,
+//! * a non-blocking [`Mutex`], for controlling access to a shared, mutable
+//!   value,
+//! * an asynchronous [`Barrier`] type, for multiple tasks to synchronize before
+//!   beginning a computation.
+//!
+//! The `tokio::sync` module is present only when the "sync" feature flag is
+//! enabled.
+//!
+//! [`tokio::sync`]: crate::sync
+//! [`Mutex`]: crate::sync::Mutex
+//! [`Barrier`]: crate::sync::Barrier
+//! [`oneshot`]: crate::sync::oneshot
+//! [`mpsc`]: crate::sync::mpsc
+//! [`watch`]: crate::sync::watch
+//!
+//! The [`tokio::time`] module provides utilities for tracking time and
+//! scheduling work. This includes functions for setting [timeouts][timeout] for
+//! tasks, [sleeping][sleep] work to run in the future, or [repeating an operation at an
+//! interval][interval].
+//!
+//! In order to use `tokio::time`, the "time" feature flag must be enabled.
+//!
+//! [`tokio::time`]: crate::time
+//! [sleep]: crate::time::sleep()
+//! [interval]: crate::time::interval()
+//! [timeout]: crate::time::timeout()
+//!
+//! Finally, Tokio provides a _runtime_ for executing asynchronous tasks. Most
+//! applications can use the [`#[tokio::main]`][main] macro to run their code on the
+//! Tokio runtime. However, this macro provides only basic configuration options. As
+//! an alternative, the [`tokio::runtime`] module provides more powerful APIs for configuring
+//! and managing runtimes. You should use that module if the `#[tokio::main]` macro doesn't
+//! provide the functionality you need.
+//!
+//! Using the runtime requires the "rt" or "rt-multi-thread" feature flags, to
+//! enable the basic [single-threaded scheduler][rt] and the [thread-pool
+//! scheduler][rt-multi-thread], respectively. See the [`runtime` module
+//! documentation][rt-features] for details. In addition, the "macros" feature
+//! flag enables the `#[tokio::main]` and `#[tokio::test]` attributes.
+//!
+//! [main]: attr.main.html
+//! [`tokio::runtime`]: crate::runtime
+//! [`Builder`]: crate::runtime::Builder
+//! [`Runtime`]: crate::runtime::Runtime
+//! [rt]: runtime/index.html#current-thread-scheduler
+//! [rt-multi-thread]: runtime/index.html#multi-thread-scheduler
+//! [rt-features]: runtime/index.html#runtime-scheduler
+//!
+//! ## CPU-bound tasks and blocking code
+//!
+//! Tokio is able to concurrently run many tasks on a few threads by repeatedly
+//! swapping the currently running task on each thread. However, this kind of
+//! swapping can only happen at `.await` points, so code that spends a long time
+//! without reaching an `.await` will prevent other tasks from running. To
+//! combat this, Tokio provides two kinds of threads: Core threads and blocking
+//! threads. The core threads are where all asynchronous code runs, and Tokio
+//! will by default spawn one for each CPU core. The blocking threads are
+//! spawned on demand, can be used to run blocking code that would otherwise
+//! block other tasks from running and are kept alive when not used for a certain
+//! amount of time which can be configured with [`thread_keep_alive`].
+//! Since it is not possible for Tokio to swap out blocking tasks, like it
+//! can do with asynchronous code, the upper limit on the number of blocking
+//! threads is very large. These limits can be configured on the [`Builder`].
+//!
+//! To spawn a blocking task, you should use the [`spawn_blocking`] function.
+//!
+//! [`Builder`]: crate::runtime::Builder
+//! [`spawn_blocking`]: crate::task::spawn_blocking()
+//! [`thread_keep_alive`]: crate::runtime::Builder::thread_keep_alive()
+//!
+//! ```
+//! #[tokio::main]
+//! async fn main() {
+//!     // This is running on a core thread.
+//!
+//!     let blocking_task = tokio::task::spawn_blocking(|| {
+//!         // This is running on a blocking thread.
+//!         // Blocking here is ok.
+//!     });
+//!
+//!     // We can wait for the blocking task like this:
+//!     // If the blocking task panics, the unwrap below will propagate the
+//!     // panic.
+//!     blocking_task.await.unwrap();
+//! }
+//! ```
+//!
+//! If your code is CPU-bound and you wish to limit the number of threads used
+//! to run it, you should use a separate thread pool dedicated to CPU bound tasks.
+//! For example, you could consider using the [rayon] library for CPU-bound
+//! tasks. It is also possible to create an extra Tokio runtime dedicated to
+//! CPU-bound tasks, but if you do this, you should be careful that the extra
+//! runtime runs _only_ CPU-bound tasks, as IO-bound tasks on that runtime
+//! will behave poorly.
+//!
+//! Hint: If using rayon, you can use a [`oneshot`] channel to send the result back
+//! to Tokio when the rayon task finishes.
+//!
+//! [rayon]: https://docs.rs/rayon
+//! [`oneshot`]: crate::sync::oneshot
+//!
+//! ## Asynchronous IO
+//!
+//! As well as scheduling and running tasks, Tokio provides everything you need
+//! to perform input and output asynchronously.
+//!
+//! The [`tokio::io`] module provides Tokio's asynchronous core I/O primitives,
+//! the [`AsyncRead`], [`AsyncWrite`], and [`AsyncBufRead`] traits. In addition,
+//! when the "io-util" feature flag is enabled, it also provides combinators and
+//! functions for working with these traits, forming as an asynchronous
+//! counterpart to [`std::io`].
+//!
+//! Tokio also includes APIs for performing various kinds of I/O and interacting
+//! with the operating system asynchronously. These include:
+//!
+//! * [`tokio::net`], which contains non-blocking versions of [TCP], [UDP], and
+//!   [Unix Domain Sockets][UDS] (enabled by the "net" feature flag),
+//! * [`tokio::fs`], similar to [`std::fs`] but for performing filesystem I/O
+//!   asynchronously (enabled by the "fs" feature flag),
+//! * [`tokio::signal`], for asynchronously handling Unix and Windows OS signals
+//!   (enabled by the "signal" feature flag),
+//! * [`tokio::process`], for spawning and managing child processes (enabled by
+//!   the "process" feature flag).
+//!
+//! [`tokio::io`]: crate::io
+//! [`AsyncRead`]: crate::io::AsyncRead
+//! [`AsyncWrite`]: crate::io::AsyncWrite
+//! [`AsyncBufRead`]: crate::io::AsyncBufRead
+//! [`std::io`]: std::io
+//! [`tokio::net`]: crate::net
+//! [TCP]: crate::net::tcp
+//! [UDP]: crate::net::UdpSocket
+//! [UDS]: crate::net::unix
+//! [`tokio::fs`]: crate::fs
+//! [`std::fs`]: std::fs
+//! [`tokio::signal`]: crate::signal
+//! [`tokio::process`]: crate::process
+//!
+//! # Examples
+//!
+//! A simple TCP echo server:
+//!
+//! ```no_run
+//! use tokio::net::TcpListener;
+//! use tokio::io::{AsyncReadExt, AsyncWriteExt};
+//!
+//! #[tokio::main]
+//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
+//!     let listener = TcpListener::bind("127.0.0.1:8080").await?;
+//!
+//!     loop {
+//!         let (mut socket, _) = listener.accept().await?;
+//!
+//!         tokio::spawn(async move {
+//!             let mut buf = [0; 1024];
+//!
+//!             // In a loop, read data from the socket and write the data back.
+//!             loop {
+//!                 let n = match socket.read(&mut buf).await {
+//!                     // socket closed
+//!                     Ok(n) if n == 0 => return,
+//!                     Ok(n) => n,
+//!                     Err(e) => {
+//!                         eprintln!("failed to read from socket; err = {:?}", e);
+//!                         return;
+//!                     }
+//!                 };
+//!
+//!                 // Write the data back
+//!                 if let Err(e) = socket.write_all(&buf[0..n]).await {
+//!                     eprintln!("failed to write to socket; err = {:?}", e);
+//!                     return;
+//!                 }
+//!             }
+//!         });
+//!     }
+//! }
+//! ```
+//!
+//! ## Feature flags
+//!
+//! Tokio uses a set of [feature flags] to reduce the amount of compiled code. It
+//! is possible to just enable certain features over others. By default, Tokio
+//! does not enable any features but allows one to enable a subset for their use
+//! case. Below is a list of the available feature flags. You may also notice
+//! above each function, struct and trait there is listed one or more feature flags
+//! that are required for that item to be used. If you are new to Tokio it is
+//! recommended that you use the `full` feature flag which will enable all public APIs.
+//! Beware though that this will pull in many extra dependencies that you may not
+//! need.
+//!
+//! - `full`: Enables all features listed below except `test-util` and `tracing`.
+//! - `rt`: Enables `tokio::spawn`, the basic (current thread) scheduler,
+//!         and non-scheduler utilities.
+//! - `rt-multi-thread`: Enables the heavier, multi-threaded, work-stealing scheduler.
+//! - `io-util`: Enables the IO based `Ext` traits.
+//! - `io-std`: Enable `Stdout`, `Stdin` and `Stderr` types.
+//! - `net`: Enables `tokio::net` types such as `TcpStream`, `UnixStream` and
+//!          `UdpSocket`, as well as (on Unix-like systems) `AsyncFd` and (on
+//!          FreeBSD) `PollAio`.
+//! - `time`: Enables `tokio::time` types and allows the schedulers to enable
+//!           the built in timer.
+//! - `process`: Enables `tokio::process` types.
+//! - `macros`: Enables `#[tokio::main]` and `#[tokio::test]` macros.
+//! - `sync`: Enables all `tokio::sync` types.
+//! - `signal`: Enables all `tokio::signal` types.
+//! - `fs`: Enables `tokio::fs` types.
+//! - `test-util`: Enables testing based infrastructure for the Tokio runtime.
+//!
+//! _Note: `AsyncRead` and `AsyncWrite` traits do not require any features and are
+//! always available._
+//!
+//! ### Internal features
+//!
+//! These features do not expose any new API, but influence internal
+//! implementation aspects of Tokio, and can pull in additional
+//! dependencies.
+//!
+//! - `parking_lot`: As a potential optimization, use the _parking_lot_ crate's
+//! synchronization primitives internally. MSRV may increase according to the
+//! _parking_lot_ release in use.
+//!
+//! ### Unstable features
+//!
+//! These feature flags enable **unstable** features. The public API may break in 1.x
+//! releases. To enable these features, the `--cfg tokio_unstable` must be passed to
+//! `rustc` when compiling. This is easiest done using the `RUSTFLAGS` env variable:
+//! `RUSTFLAGS="--cfg tokio_unstable"`.
+//!
+//! - `tracing`: Enables tracing events.
+//!
+//! [feature flags]: https://doc.rust-lang.org/cargo/reference/manifest.html#the-features-section
+
+// Test that pointer width is compatible. This asserts that e.g. usize is at
+// least 32 bits, which a lot of components in Tokio currently assumes.
+//
+// TODO: improve once we have MSRV access to const eval to make more flexible.
+#[cfg(not(any(
+    target_pointer_width = "32",
+    target_pointer_width = "64",
+    target_pointer_width = "128"
+)))]
+compile_error! {
+    "Tokio requires the platform pointer width to be 32, 64, or 128 bits"
+}
+
+// Includes re-exports used by macros.
+//
+// This module is not intended to be part of the public API. In general, any
+// `doc(hidden)` code is not part of Tokio's public and stable API.
+#[macro_use]
+#[doc(hidden)]
+pub mod macros;
+
+cfg_fs! {
+    pub mod fs;
+}
+
+mod future;
+
+pub mod io;
+pub mod net;
+
+mod loom;
+mod park;
+
+cfg_process! {
+    pub mod process;
+}
+
+#[cfg(any(feature = "net", feature = "fs", feature = "io-std"))]
+mod blocking;
+
+cfg_rt! {
+    pub mod runtime;
+}
+
+pub(crate) mod coop;
+
+cfg_signal! {
+    pub mod signal;
+}
+
+cfg_signal_internal! {
+    #[cfg(not(feature = "signal"))]
+    #[allow(dead_code)]
+    #[allow(unreachable_pub)]
+    pub(crate) mod signal;
+}
+
+cfg_sync! {
+    pub mod sync;
+}
+cfg_not_sync! {
+    mod sync;
+}
+
+pub mod task;
+cfg_rt! {
+    pub use task::spawn;
+}
+
+cfg_time! {
+    pub mod time;
+}
+
+mod util;
+
+/// Due to the `Stream` trait's inclusion in `std` landing later than Tokio's 1.0
+/// release, most of the Tokio stream utilities have been moved into the [`tokio-stream`]
+/// crate.
+///
+/// # Why was `Stream` not included in Tokio 1.0?
+///
+/// Originally, we had planned to ship Tokio 1.0 with a stable `Stream` type
+/// but unfortunately the [RFC] had not been merged in time for `Stream` to
+/// reach `std` on a stable compiler in time for the 1.0 release of Tokio. For
+/// this reason, the team has decided to move all `Stream` based utilities to
+/// the [`tokio-stream`] crate. While this is not ideal, once `Stream` has made
+/// it into the standard library and the MSRV period has passed, we will implement
+/// stream for our different types.
+///
+/// While this may seem unfortunate, not all is lost as you can get much of the
+/// `Stream` support with `async/await` and `while let` loops. It is also possible
+/// to create a `impl Stream` from `async fn` using the [`async-stream`] crate.
+///
+/// [`tokio-stream`]: https://docs.rs/tokio-stream
+/// [`async-stream`]: https://docs.rs/async-stream
+/// [RFC]: https://github.com/rust-lang/rfcs/pull/2996
+///
+/// # Example
+///
+/// Convert a [`sync::mpsc::Receiver`] to an `impl Stream`.
+///
+/// ```rust,no_run
+/// use tokio::sync::mpsc;
+///
+/// let (tx, mut rx) = mpsc::channel::<usize>(16);
+///
+/// let stream = async_stream::stream! {
+///     while let Some(item) = rx.recv().await {
+///         yield item;
+///     }
+/// };
+/// ```
+pub mod stream {}
+
+// local re-exports of platform specific things, allowing for decent
+// documentation to be shimmed in on docs.rs
+
+#[cfg(docsrs)]
+pub mod doc;
+
+#[cfg(docsrs)]
+#[allow(unused)]
+pub(crate) use self::doc::os;
+
+#[cfg(not(docsrs))]
+#[allow(unused)]
+pub(crate) use std::os;
+
+#[cfg(docsrs)]
+#[allow(unused)]
+pub(crate) use self::doc::winapi;
+
+#[cfg(all(not(docsrs), windows, feature = "net"))]
+#[allow(unused)]
+pub(crate) use ::winapi;
+
+cfg_macros! {
+    /// Implementation detail of the `select!` macro. This macro is **not**
+    /// intended to be used as part of the public API and is permitted to
+    /// change.
+    #[doc(hidden)]
+    pub use tokio_macros::select_priv_declare_output_enum;
+
+    /// Implementation detail of the `select!` macro. This macro is **not**
+    /// intended to be used as part of the public API and is permitted to
+    /// change.
+    #[doc(hidden)]
+    pub use tokio_macros::select_priv_clean_pattern;
+
+    cfg_rt! {
+        #[cfg(feature = "rt-multi-thread")]
+        #[cfg(not(test))] // Work around for rust-lang/rust#62127
+        #[cfg_attr(docsrs, doc(cfg(feature = "macros")))]
+        #[doc(inline)]
+        pub use tokio_macros::main;
+
+        #[cfg(feature = "rt-multi-thread")]
+        #[cfg_attr(docsrs, doc(cfg(feature = "macros")))]
+        #[doc(inline)]
+        pub use tokio_macros::test;
+
+        cfg_not_rt_multi_thread! {
+            #[cfg(not(test))] // Work around for rust-lang/rust#62127
+            #[doc(inline)]
+            pub use tokio_macros::main_rt as main;
+
+            #[doc(inline)]
+            pub use tokio_macros::test_rt as test;
+        }
+    }
+
+    // Always fail if rt is not enabled.
+    cfg_not_rt! {
+        #[cfg(not(test))]
+        #[doc(inline)]
+        pub use tokio_macros::main_fail as main;
+
+        #[doc(inline)]
+        pub use tokio_macros::test_fail as test;
+    }
+}
+
+// TODO: rm
+#[cfg(feature = "io-util")]
+#[cfg(test)]
+fn is_unpin<T: Unpin>() {}
diff --git a/third_party/rust/tokio/src/loom/mocked.rs b/third_party/rust/tokio/src/loom/mocked.rs
new file mode 100644
index 0000000000..367d59b43a
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/mocked.rs
@@ -0,0 +1,40 @@
+pub(crate) use loom::*;
+
+pub(crate) mod sync {
+
+    pub(crate) use loom::sync::MutexGuard;
+
+    #[derive(Debug)]
+    pub(crate) struct Mutex<T>(loom::sync::Mutex<T>);
+
+    #[allow(dead_code)]
+    impl<T> Mutex<T> {
+        #[inline]
+        pub(crate) fn new(t: T) -> Mutex<T> {
+            Mutex(loom::sync::Mutex::new(t))
+        }
+
+        #[inline]
+        pub(crate) fn lock(&self) -> MutexGuard<'_, T> {
+            self.0.lock().unwrap()
+        }
+
+        #[inline]
+        pub(crate) fn try_lock(&self) -> Option<MutexGuard<'_, T>> {
+            self.0.try_lock().ok()
+        }
+    }
+    pub(crate) use loom::sync::*;
+}
+
+pub(crate) mod rand {
+    pub(crate) fn seed() -> u64 {
+        1
+    }
+}
+
+pub(crate) mod sys {
+    pub(crate) fn num_cpus() -> usize {
+        2
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/mod.rs b/third_party/rust/tokio/src/loom/mod.rs
new file mode 100644
index 0000000000..5957b5377d
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/mod.rs
@@ -0,0 +1,14 @@
+//! This module abstracts over `loom` and `std::sync` depending on whether we
+//! are running tests or not.
+
+#![allow(unused)]
+
+#[cfg(not(all(test, loom)))]
+mod std;
+#[cfg(not(all(test, loom)))]
+pub(crate) use self::std::*;
+
+#[cfg(all(test, loom))]
+mod mocked;
+#[cfg(all(test, loom))]
+pub(crate) use self::mocked::*;
diff --git a/third_party/rust/tokio/src/loom/std/atomic_ptr.rs b/third_party/rust/tokio/src/loom/std/atomic_ptr.rs
new file mode 100644
index 0000000000..236645f037
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/atomic_ptr.rs
@@ -0,0 +1,34 @@
+use std::fmt;
+use std::ops::{Deref, DerefMut};
+
+/// `AtomicPtr` providing an additional `load_unsync` function.
+pub(crate) struct AtomicPtr<T> {
+    inner: std::sync::atomic::AtomicPtr<T>,
+}
+
+impl<T> AtomicPtr<T> {
+    pub(crate) fn new(ptr: *mut T) -> AtomicPtr<T> {
+        let inner = std::sync::atomic::AtomicPtr::new(ptr);
+        AtomicPtr { inner }
+    }
+}
+
+impl<T> Deref for AtomicPtr<T> {
+    type Target = std::sync::atomic::AtomicPtr<T>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+impl<T> DerefMut for AtomicPtr<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        &mut self.inner
+    }
+}
+
+impl<T> fmt::Debug for AtomicPtr<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.deref().fmt(fmt)
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/std/atomic_u16.rs b/third_party/rust/tokio/src/loom/std/atomic_u16.rs
new file mode 100644
index 0000000000..c1c531208c
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/atomic_u16.rs
@@ -0,0 +1,44 @@
+use std::cell::UnsafeCell;
+use std::fmt;
+use std::ops::Deref;
+
+/// `AtomicU16` providing an additional `load_unsync` function.
+pub(crate) struct AtomicU16 {
+    inner: UnsafeCell<std::sync::atomic::AtomicU16>,
+}
+
+unsafe impl Send for AtomicU16 {}
+unsafe impl Sync for AtomicU16 {}
+
+impl AtomicU16 {
+    pub(crate) const fn new(val: u16) -> AtomicU16 {
+        let inner = UnsafeCell::new(std::sync::atomic::AtomicU16::new(val));
+        AtomicU16 { inner }
+    }
+
+    /// Performs an unsynchronized load.
+    ///
+    /// # Safety
+    ///
+    /// All mutations must have happened before the unsynchronized load.
+    /// Additionally, there must be no concurrent mutations.
+    pub(crate) unsafe fn unsync_load(&self) -> u16 {
+        *(*self.inner.get()).get_mut()
+    }
+}
+
+impl Deref for AtomicU16 {
+    type Target = std::sync::atomic::AtomicU16;
+
+    fn deref(&self) -> &Self::Target {
+        // safety: it is always safe to access `&self` fns on the inner value as
+        // we never perform unsafe mutations.
+        unsafe { &*self.inner.get() }
+    }
+}
+
+impl fmt::Debug for AtomicU16 {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.deref().fmt(fmt)
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/std/atomic_u32.rs b/third_party/rust/tokio/src/loom/std/atomic_u32.rs
new file mode 100644
index 0000000000..61f95fb30c
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/atomic_u32.rs
@@ -0,0 +1,34 @@
+use std::cell::UnsafeCell;
+use std::fmt;
+use std::ops::Deref;
+
+/// `AtomicU32` providing an additional `load_unsync` function.
+pub(crate) struct AtomicU32 {
+    inner: UnsafeCell<std::sync::atomic::AtomicU32>,
+}
+
+unsafe impl Send for AtomicU32 {}
+unsafe impl Sync for AtomicU32 {}
+
+impl AtomicU32 {
+    pub(crate) const fn new(val: u32) -> AtomicU32 {
+        let inner = UnsafeCell::new(std::sync::atomic::AtomicU32::new(val));
+        AtomicU32 { inner }
+    }
+}
+
+impl Deref for AtomicU32 {
+    type Target = std::sync::atomic::AtomicU32;
+
+    fn deref(&self) -> &Self::Target {
+        // safety: it is always safe to access `&self` fns on the inner value as
+        // we never perform unsafe mutations.
+        unsafe { &*self.inner.get() }
+    }
+}
+
+impl fmt::Debug for AtomicU32 {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.deref().fmt(fmt)
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/std/atomic_u64.rs b/third_party/rust/tokio/src/loom/std/atomic_u64.rs
new file mode 100644
index 0000000000..113992d977
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/atomic_u64.rs
@@ -0,0 +1,78 @@
+//! Implementation of an atomic u64 cell. On 64 bit platforms, this is a
+//! re-export of `AtomicU64`. On 32 bit platforms, this is implemented using a
+//! `Mutex`.
+
+// `AtomicU64` can only be used on targets with `target_has_atomic` is 64 or greater.
+// Once `cfg_target_has_atomic` feature is stable, we can replace it with
+// `#[cfg(target_has_atomic = "64")]`.
+// Refs: https://github.com/rust-lang/rust/tree/master/src/librustc_target
+cfg_has_atomic_u64! {
+    pub(crate) use std::sync::atomic::AtomicU64;
+}
+
+cfg_not_has_atomic_u64! {
+    use crate::loom::sync::Mutex;
+    use std::sync::atomic::Ordering;
+
+    #[derive(Debug)]
+    pub(crate) struct AtomicU64 {
+        inner: Mutex<u64>,
+    }
+
+    impl AtomicU64 {
+        pub(crate) fn new(val: u64) -> Self {
+            Self {
+                inner: Mutex::new(val),
+            }
+        }
+
+        pub(crate) fn load(&self, _: Ordering) -> u64 {
+            *self.inner.lock()
+        }
+
+        pub(crate) fn store(&self, val: u64, _: Ordering) {
+            *self.inner.lock() = val;
+        }
+
+        pub(crate) fn fetch_add(&self, val: u64, _: Ordering) -> u64 {
+            let mut lock = self.inner.lock();
+            let prev = *lock;
+            *lock = prev + val;
+            prev
+        }
+
+        pub(crate) fn fetch_or(&self, val: u64, _: Ordering) -> u64 {
+            let mut lock = self.inner.lock();
+            let prev = *lock;
+            *lock = prev | val;
+            prev
+        }
+
+        pub(crate) fn compare_exchange(
+            &self,
+            current: u64,
+            new: u64,
+            _success: Ordering,
+            _failure: Ordering,
+        ) -> Result<u64, u64> {
+            let mut lock = self.inner.lock();
+
+            if *lock == current {
+                *lock = new;
+                Ok(current)
+            } else {
+                Err(*lock)
+            }
+        }
+
+        pub(crate) fn compare_exchange_weak(
+            &self,
+            current: u64,
+            new: u64,
+            success: Ordering,
+            failure: Ordering,
+        ) -> Result<u64, u64> {
+            self.compare_exchange(current, new, success, failure)
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/std/atomic_u8.rs b/third_party/rust/tokio/src/loom/std/atomic_u8.rs
new file mode 100644
index 0000000000..408aea338c
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/atomic_u8.rs
@@ -0,0 +1,34 @@
+use std::cell::UnsafeCell;
+use std::fmt;
+use std::ops::Deref;
+
+/// `AtomicU8` providing an additional `load_unsync` function.
+pub(crate) struct AtomicU8 {
+    inner: UnsafeCell<std::sync::atomic::AtomicU8>,
+}
+
+unsafe impl Send for AtomicU8 {}
+unsafe impl Sync for AtomicU8 {}
+
+impl AtomicU8 {
+    pub(crate) const fn new(val: u8) -> AtomicU8 {
+        let inner = UnsafeCell::new(std::sync::atomic::AtomicU8::new(val));
+        AtomicU8 { inner }
+    }
+}
+
+impl Deref for AtomicU8 {
+    type Target = std::sync::atomic::AtomicU8;
+
+    fn deref(&self) -> &Self::Target {
+        // safety: it is always safe to access `&self` fns on the inner value as
+        // we never perform unsafe mutations.
+        unsafe { &*self.inner.get() }
+    }
+}
+
+impl fmt::Debug for AtomicU8 {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.deref().fmt(fmt)
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/std/atomic_usize.rs b/third_party/rust/tokio/src/loom/std/atomic_usize.rs
new file mode 100644
index 0000000000..0d5f36e431
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/atomic_usize.rs
@@ -0,0 +1,56 @@
+use std::cell::UnsafeCell;
+use std::fmt;
+use std::ops;
+
+/// `AtomicUsize` providing an additional `load_unsync` function.
+pub(crate) struct AtomicUsize {
+    inner: UnsafeCell<std::sync::atomic::AtomicUsize>,
+}
+
+unsafe impl Send for AtomicUsize {}
+unsafe impl Sync for AtomicUsize {}
+
+impl AtomicUsize {
+    pub(crate) const fn new(val: usize) -> AtomicUsize {
+        let inner = UnsafeCell::new(std::sync::atomic::AtomicUsize::new(val));
+        AtomicUsize { inner }
+    }
+
+    /// Performs an unsynchronized load.
+    ///
+    /// # Safety
+    ///
+    /// All mutations must have happened before the unsynchronized load.
+    /// Additionally, there must be no concurrent mutations.
+    pub(crate) unsafe fn unsync_load(&self) -> usize {
+        *(*self.inner.get()).get_mut()
+    }
+
+    pub(crate) fn with_mut<R>(&mut self, f: impl FnOnce(&mut usize) -> R) -> R {
+        // safety: we have mutable access
+        f(unsafe { (*self.inner.get()).get_mut() })
+    }
+}
+
+impl ops::Deref for AtomicUsize {
+    type Target = std::sync::atomic::AtomicUsize;
+
+    fn deref(&self) -> &Self::Target {
+        // safety: it is always safe to access `&self` fns on the inner value as
+        // we never perform unsafe mutations.
+        unsafe { &*self.inner.get() }
+    }
+}
+
+impl ops::DerefMut for AtomicUsize {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        // safety: we hold `&mut self`
+        unsafe { &mut *self.inner.get() }
+    }
+}
+
+impl fmt::Debug for AtomicUsize {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(fmt)
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/std/mod.rs b/third_party/rust/tokio/src/loom/std/mod.rs
new file mode 100644
index 0000000000..0c70bee74e
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/mod.rs
@@ -0,0 +1,108 @@
+#![cfg_attr(any(not(feature = "full"), loom), allow(unused_imports, dead_code))]
+
+mod atomic_ptr;
+mod atomic_u16;
+mod atomic_u32;
+mod atomic_u64;
+mod atomic_u8;
+mod atomic_usize;
+mod mutex;
+#[cfg(feature = "parking_lot")]
+mod parking_lot;
+mod unsafe_cell;
+
+pub(crate) mod cell {
+    pub(crate) use super::unsafe_cell::UnsafeCell;
+}
+
+#[cfg(any(
+    feature = "net",
+    feature = "process",
+    feature = "signal",
+    feature = "sync",
+))]
+pub(crate) mod future {
+    pub(crate) use crate::sync::AtomicWaker;
+}
+
+pub(crate) mod hint {
+    pub(crate) use std::hint::spin_loop;
+}
+
+pub(crate) mod rand {
+    use std::collections::hash_map::RandomState;
+    use std::hash::{BuildHasher, Hash, Hasher};
+    use std::sync::atomic::AtomicU32;
+    use std::sync::atomic::Ordering::Relaxed;
+
+    static COUNTER: AtomicU32 = AtomicU32::new(1);
+
+    pub(crate) fn seed() -> u64 {
+        let rand_state = RandomState::new();
+
+        let mut hasher = rand_state.build_hasher();
+
+        // Hash some unique-ish data to generate some new state
+        COUNTER.fetch_add(1, Relaxed).hash(&mut hasher);
+
+        // Get the seed
+        hasher.finish()
+    }
+}
+
+pub(crate) mod sync {
+    pub(crate) use std::sync::{Arc, Weak};
+
+    // Below, make sure all the feature-influenced types are exported for
+    // internal use. Note however that some are not _currently_ named by
+    // consuming code.
+
+    #[cfg(feature = "parking_lot")]
+    #[allow(unused_imports)]
+    pub(crate) use crate::loom::std::parking_lot::{
+        Condvar, Mutex, MutexGuard, RwLock, RwLockReadGuard, WaitTimeoutResult,
+    };
+
+    #[cfg(not(feature = "parking_lot"))]
+    #[allow(unused_imports)]
+    pub(crate) use std::sync::{Condvar, MutexGuard, RwLock, RwLockReadGuard, WaitTimeoutResult};
+
+    #[cfg(not(feature = "parking_lot"))]
+    pub(crate) use crate::loom::std::mutex::Mutex;
+
+    pub(crate) mod atomic {
+        pub(crate) use crate::loom::std::atomic_ptr::AtomicPtr;
+        pub(crate) use crate::loom::std::atomic_u16::AtomicU16;
+        pub(crate) use crate::loom::std::atomic_u32::AtomicU32;
+        pub(crate) use crate::loom::std::atomic_u64::AtomicU64;
+        pub(crate) use crate::loom::std::atomic_u8::AtomicU8;
+        pub(crate) use crate::loom::std::atomic_usize::AtomicUsize;
+
+        pub(crate) use std::sync::atomic::{fence, AtomicBool, Ordering};
+    }
+}
+
+pub(crate) mod sys {
+    #[cfg(feature = "rt-multi-thread")]
+    pub(crate) fn num_cpus() -> usize {
+        usize::max(1, num_cpus::get())
+    }
+
+    #[cfg(not(feature = "rt-multi-thread"))]
+    pub(crate) fn num_cpus() -> usize {
+        1
+    }
+}
+
+pub(crate) mod thread {
+    #[inline]
+    pub(crate) fn yield_now() {
+        std::hint::spin_loop();
+    }
+
+    #[allow(unused_imports)]
+    pub(crate) use std::thread::{
+        current, panicking, park, park_timeout, sleep, spawn, Builder, JoinHandle, LocalKey,
+        Result, Thread, ThreadId,
+    };
+}
diff --git a/third_party/rust/tokio/src/loom/std/mutex.rs b/third_party/rust/tokio/src/loom/std/mutex.rs
new file mode 100644
index 0000000000..3f686e0a78
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/mutex.rs
@@ -0,0 +1,31 @@
+use std::sync::{self, MutexGuard, TryLockError};
+
+/// Adapter for `std::Mutex` that removes the poisoning aspects
+/// from its api.
+#[derive(Debug)]
+pub(crate) struct Mutex<T: ?Sized>(sync::Mutex<T>);
+
+#[allow(dead_code)]
+impl<T> Mutex<T> {
+    #[inline]
+    pub(crate) fn new(t: T) -> Mutex<T> {
+        Mutex(sync::Mutex::new(t))
+    }
+
+    #[inline]
+    pub(crate) fn lock(&self) -> MutexGuard<'_, T> {
+        match self.0.lock() {
+            Ok(guard) => guard,
+            Err(p_err) => p_err.into_inner(),
+        }
+    }
+
+    #[inline]
+    pub(crate) fn try_lock(&self) -> Option<MutexGuard<'_, T>> {
+        match self.0.try_lock() {
+            Ok(guard) => Some(guard),
+            Err(TryLockError::Poisoned(p_err)) => Some(p_err.into_inner()),
+            Err(TryLockError::WouldBlock) => None,
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/std/parking_lot.rs b/third_party/rust/tokio/src/loom/std/parking_lot.rs
new file mode 100644
index 0000000000..034a0ce69a
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/parking_lot.rs
@@ -0,0 +1,184 @@
+//! A minimal adaption of the `parking_lot` synchronization primitives to the
+//! equivalent `std::sync` types.
+//!
+//! This can be extended to additional types/methods as required.
+
+use std::fmt;
+use std::marker::PhantomData;
+use std::ops::{Deref, DerefMut};
+use std::sync::LockResult;
+use std::time::Duration;
+
+// All types in this file are marked with PhantomData to ensure that
+// parking_lot's send_guard feature does not leak through and affect when Tokio
+// types are Send.
+//
+// See <https://github.com/tokio-rs/tokio/pull/4359> for more info.
+
+// Types that do not need wrapping
+pub(crate) use parking_lot::WaitTimeoutResult;
+
+#[derive(Debug)]
+pub(crate) struct Mutex<T: ?Sized>(PhantomData<std::sync::Mutex<T>>, parking_lot::Mutex<T>);
+
+#[derive(Debug)]
+pub(crate) struct RwLock<T>(PhantomData<std::sync::RwLock<T>>, parking_lot::RwLock<T>);
+
+#[derive(Debug)]
+pub(crate) struct Condvar(PhantomData<std::sync::Condvar>, parking_lot::Condvar);
+
+#[derive(Debug)]
+pub(crate) struct MutexGuard<'a, T: ?Sized>(
+    PhantomData<std::sync::MutexGuard<'a, T>>,
+    parking_lot::MutexGuard<'a, T>,
+);
+
+#[derive(Debug)]
+pub(crate) struct RwLockReadGuard<'a, T: ?Sized>(
+    PhantomData<std::sync::RwLockReadGuard<'a, T>>,
+    parking_lot::RwLockReadGuard<'a, T>,
+);
+
+#[derive(Debug)]
+pub(crate) struct RwLockWriteGuard<'a, T: ?Sized>(
+    PhantomData<std::sync::RwLockWriteGuard<'a, T>>,
+    parking_lot::RwLockWriteGuard<'a, T>,
+);
+
+impl<T> Mutex<T> {
+    #[inline]
+    pub(crate) fn new(t: T) -> Mutex<T> {
+        Mutex(PhantomData, parking_lot::Mutex::new(t))
+    }
+
+    #[inline]
+    #[cfg(all(feature = "parking_lot", not(all(loom, test)),))]
+    #[cfg_attr(docsrs, doc(cfg(all(feature = "parking_lot",))))]
+    pub(crate) const fn const_new(t: T) -> Mutex<T> {
+        Mutex(PhantomData, parking_lot::const_mutex(t))
+    }
+
+    #[inline]
+    pub(crate) fn lock(&self) -> MutexGuard<'_, T> {
+        MutexGuard(PhantomData, self.1.lock())
+    }
+
+    #[inline]
+    pub(crate) fn try_lock(&self) -> Option<MutexGuard<'_, T>> {
+        self.1
+            .try_lock()
+            .map(|guard| MutexGuard(PhantomData, guard))
+    }
+
+    #[inline]
+    pub(crate) fn get_mut(&mut self) -> &mut T {
+        self.1.get_mut()
+    }
+
+    // Note: Additional methods `is_poisoned` and `into_inner`, can be
+    // provided here as needed.
+}
+
+impl<'a, T: ?Sized> Deref for MutexGuard<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        self.1.deref()
+    }
+}
+
+impl<'a, T: ?Sized> DerefMut for MutexGuard<'a, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        self.1.deref_mut()
+    }
+}
+
+impl<T> RwLock<T> {
+    pub(crate) fn new(t: T) -> RwLock<T> {
+        RwLock(PhantomData, parking_lot::RwLock::new(t))
+    }
+
+    pub(crate) fn read(&self) -> LockResult<RwLockReadGuard<'_, T>> {
+        Ok(RwLockReadGuard(PhantomData, self.1.read()))
+    }
+
+    pub(crate) fn write(&self) -> LockResult<RwLockWriteGuard<'_, T>> {
+        Ok(RwLockWriteGuard(PhantomData, self.1.write()))
+    }
+}
+
+impl<'a, T: ?Sized> Deref for RwLockReadGuard<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        self.1.deref()
+    }
+}
+
+impl<'a, T: ?Sized> Deref for RwLockWriteGuard<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &T {
+        self.1.deref()
+    }
+}
+
+impl<'a, T: ?Sized> DerefMut for RwLockWriteGuard<'a, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        self.1.deref_mut()
+    }
+}
+
+impl Condvar {
+    #[inline]
+    pub(crate) fn new() -> Condvar {
+        Condvar(PhantomData, parking_lot::Condvar::new())
+    }
+
+    #[inline]
+    pub(crate) fn notify_one(&self) {
+        self.1.notify_one();
+    }
+
+    #[inline]
+    pub(crate) fn notify_all(&self) {
+        self.1.notify_all();
+    }
+
+    #[inline]
+    pub(crate) fn wait<'a, T>(
+        &self,
+        mut guard: MutexGuard<'a, T>,
+    ) -> LockResult<MutexGuard<'a, T>> {
+        self.1.wait(&mut guard.1);
+        Ok(guard)
+    }
+
+    #[inline]
+    pub(crate) fn wait_timeout<'a, T>(
+        &self,
+        mut guard: MutexGuard<'a, T>,
+        timeout: Duration,
+    ) -> LockResult<(MutexGuard<'a, T>, WaitTimeoutResult)> {
+        let wtr = self.1.wait_for(&mut guard.1, timeout);
+        Ok((guard, wtr))
+    }
+
+    // Note: Additional methods `wait_timeout_ms`, `wait_timeout_until`,
+    // `wait_until` can be provided here as needed.
+}
+
+impl<'a, T: ?Sized + fmt::Display> fmt::Display for MutexGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.1, f)
+    }
+}
+
+impl<'a, T: ?Sized + fmt::Display> fmt::Display for RwLockReadGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.1, f)
+    }
+}
+
+impl<'a, T: ?Sized + fmt::Display> fmt::Display for RwLockWriteGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&self.1, f)
+    }
+}
diff --git a/third_party/rust/tokio/src/loom/std/unsafe_cell.rs b/third_party/rust/tokio/src/loom/std/unsafe_cell.rs
new file mode 100644
index 0000000000..66c1d7943e
--- /dev/null
+++ b/third_party/rust/tokio/src/loom/std/unsafe_cell.rs
@@ -0,0 +1,16 @@
+#[derive(Debug)]
+pub(crate) struct UnsafeCell<T>(std::cell::UnsafeCell<T>);
+
+impl<T> UnsafeCell<T> {
+    pub(crate) const fn new(data: T) -> UnsafeCell<T> {
+        UnsafeCell(std::cell::UnsafeCell::new(data))
+    }
+
+    pub(crate) fn with<R>(&self, f: impl FnOnce(*const T) -> R) -> R {
+        f(self.0.get())
+    }
+
+    pub(crate) fn with_mut<R>(&self, f: impl FnOnce(*mut T) -> R) -> R {
+        f(self.0.get())
+    }
+}
diff --git a/third_party/rust/tokio/src/macros/cfg.rs b/third_party/rust/tokio/src/macros/cfg.rs
new file mode 100644
index 0000000000..b6beb3d695
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/cfg.rs
@@ -0,0 +1,457 @@
+#![allow(unused_macros)]
+
+macro_rules! feature {
+    (
+        #![$meta:meta]
+        $($item:item)*
+    ) => {
+        $(
+            #[cfg($meta)]
+            #[cfg_attr(docsrs, doc(cfg($meta)))]
+            $item
+        )*
+    }
+}
+
+/// Enables enter::block_on.
+macro_rules! cfg_block_on {
+    ($($item:item)*) => {
+        $(
+            #[cfg(any(
+                    feature = "fs",
+                    feature = "net",
+                    feature = "io-std",
+                    feature = "rt",
+                    ))]
+            $item
+        )*
+    }
+}
+
+/// Enables internal `AtomicWaker` impl.
+macro_rules! cfg_atomic_waker_impl {
+    ($($item:item)*) => {
+        $(
+            #[cfg(any(
+                feature = "net",
+                feature = "process",
+                feature = "rt",
+                feature = "signal",
+                feature = "time",
+            ))]
+            #[cfg(not(loom))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_aio {
+    ($($item:item)*) => {
+        $(
+            #[cfg(all(any(docsrs, target_os = "freebsd"), feature = "net"))]
+            #[cfg_attr(docsrs,
+                doc(cfg(all(target_os = "freebsd", feature = "net")))
+            )]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_fs {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "fs")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "fs")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_io_blocking {
+    ($($item:item)*) => {
+        $( #[cfg(any(feature = "io-std", feature = "fs"))] $item )*
+    }
+}
+
+macro_rules! cfg_io_driver {
+    ($($item:item)*) => {
+        $(
+            #[cfg(any(
+                feature = "net",
+                feature = "process",
+                all(unix, feature = "signal"),
+            ))]
+            #[cfg_attr(docsrs, doc(cfg(any(
+                feature = "net",
+                feature = "process",
+                all(unix, feature = "signal"),
+            ))))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_io_driver_impl {
+    ( $( $item:item )* ) => {
+        $(
+            #[cfg(any(
+                feature = "net",
+                feature = "process",
+                all(unix, feature = "signal"),
+            ))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_not_io_driver {
+    ($($item:item)*) => {
+        $(
+            #[cfg(not(any(
+                feature = "net",
+                feature = "process",
+                all(unix, feature = "signal"),
+            )))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_io_readiness {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "net")]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_io_std {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "io-std")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "io-std")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_io_util {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "io-util")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "io-util")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_not_io_util {
+    ($($item:item)*) => {
+        $( #[cfg(not(feature = "io-util"))] $item )*
+    }
+}
+
+macro_rules! cfg_loom {
+    ($($item:item)*) => {
+        $( #[cfg(loom)] $item )*
+    }
+}
+
+macro_rules! cfg_not_loom {
+    ($($item:item)*) => {
+        $( #[cfg(not(loom))] $item )*
+    }
+}
+
+macro_rules! cfg_macros {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "macros")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "macros")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_metrics {
+    ($($item:item)*) => {
+        $(
+            // For now, metrics is only disabled in loom tests.
+            // When stabilized, it might have a dedicated feature flag.
+            #[cfg(all(tokio_unstable, not(loom)))]
+            #[cfg_attr(docsrs, doc(cfg(tokio_unstable)))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_not_metrics {
+    ($($item:item)*) => {
+        $(
+            #[cfg(not(all(tokio_unstable, not(loom))))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_net {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "net")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "net")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_net_unix {
+    ($($item:item)*) => {
+        $(
+            #[cfg(all(unix, feature = "net"))]
+            #[cfg_attr(docsrs, doc(cfg(all(unix, feature = "net"))))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_net_windows {
+    ($($item:item)*) => {
+        $(
+            #[cfg(all(any(all(doc, docsrs), windows), feature = "net"))]
+            #[cfg_attr(docsrs, doc(cfg(all(windows, feature = "net"))))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_process {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "process")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "process")))]
+            #[cfg(not(loom))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_process_driver {
+    ($($item:item)*) => {
+        #[cfg(unix)]
+        #[cfg(not(loom))]
+        cfg_process! { $($item)* }
+    }
+}
+
+macro_rules! cfg_not_process_driver {
+    ($($item:item)*) => {
+        $(
+            #[cfg(not(all(unix, not(loom), feature = "process")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_signal {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "signal")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "signal")))]
+            #[cfg(not(loom))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_signal_internal {
+    ($($item:item)*) => {
+        $(
+            #[cfg(any(feature = "signal", all(unix, feature = "process")))]
+            #[cfg(not(loom))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_not_signal_internal {
+    ($($item:item)*) => {
+        $(
+            #[cfg(any(loom, not(unix), not(any(feature = "signal", all(unix, feature = "process")))))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_sync {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "sync")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "sync")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_not_sync {
+    ($($item:item)*) => {
+        $( #[cfg(not(feature = "sync"))] $item )*
+    }
+}
+
+macro_rules! cfg_rt {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "rt")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "rt")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_not_rt {
+    ($($item:item)*) => {
+        $( #[cfg(not(feature = "rt"))] $item )*
+    }
+}
+
+macro_rules! cfg_rt_multi_thread {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "rt-multi-thread")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "rt-multi-thread")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_not_rt_multi_thread {
+    ($($item:item)*) => {
+        $( #[cfg(not(feature = "rt-multi-thread"))] $item )*
+    }
+}
+
+macro_rules! cfg_test_util {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "test-util")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "test-util")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_not_test_util {
+    ($($item:item)*) => {
+        $( #[cfg(not(feature = "test-util"))] $item )*
+    }
+}
+
+macro_rules! cfg_time {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "time")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "time")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_not_time {
+    ($($item:item)*) => {
+        $( #[cfg(not(feature = "time"))] $item )*
+    }
+}
+
+macro_rules! cfg_trace {
+    ($($item:item)*) => {
+        $(
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            #[cfg_attr(docsrs, doc(cfg(all(tokio_unstable, feature = "tracing"))))]
+            $item
+        )*
+    };
+}
+
+macro_rules! cfg_unstable {
+    ($($item:item)*) => {
+        $(
+            #[cfg(tokio_unstable)]
+            #[cfg_attr(docsrs, doc(cfg(tokio_unstable)))]
+            $item
+        )*
+    };
+}
+
+macro_rules! cfg_not_trace {
+    ($($item:item)*) => {
+        $(
+            #[cfg(any(not(tokio_unstable), not(feature = "tracing")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_coop {
+    ($($item:item)*) => {
+        $(
+            #[cfg(any(
+                    feature = "fs",
+                    feature = "io-std",
+                    feature = "net",
+                    feature = "process",
+                    feature = "rt",
+                    feature = "signal",
+                    feature = "sync",
+                    feature = "time",
+                    ))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_not_coop {
+    ($($item:item)*) => {
+        $(
+            #[cfg(not(any(
+                    feature = "fs",
+                    feature = "io-std",
+                    feature = "net",
+                    feature = "process",
+                    feature = "rt",
+                    feature = "signal",
+                    feature = "sync",
+                    feature = "time",
+                    )))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_has_atomic_u64 {
+    ($($item:item)*) => {
+        $(
+            #[cfg(not(any(
+                    target_arch = "arm",
+                    target_arch = "mips",
+                    target_arch = "powerpc",
+                    target_arch = "riscv32"
+                    )))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_not_has_atomic_u64 {
+    ($($item:item)*) => {
+        $(
+            #[cfg(any(
+                    target_arch = "arm",
+                    target_arch = "mips",
+                    target_arch = "powerpc",
+                    target_arch = "riscv32"
+                    ))]
+            $item
+        )*
+    }
+}
diff --git a/third_party/rust/tokio/src/macros/join.rs b/third_party/rust/tokio/src/macros/join.rs
new file mode 100644
index 0000000000..f91b5f1914
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/join.rs
@@ -0,0 +1,119 @@
+/// Waits on multiple concurrent branches, returning when **all** branches
+/// complete.
+///
+/// The `join!` macro must be used inside of async functions, closures, and
+/// blocks.
+///
+/// The `join!` macro takes a list of async expressions and evaluates them
+/// concurrently on the same task. Each async expression evaluates to a future
+/// and the futures from each expression are multiplexed on the current task.
+///
+/// When working with async expressions returning `Result`, `join!` will wait
+/// for **all** branches complete regardless if any complete with `Err`. Use
+/// [`try_join!`] to return early when `Err` is encountered.
+///
+/// [`try_join!`]: macro@try_join
+///
+/// # Notes
+///
+/// The supplied futures are stored inline and does not require allocating a
+/// `Vec`.
+///
+/// ### Runtime characteristics
+///
+/// By running all async expressions on the current task, the expressions are
+/// able to run **concurrently** but not in **parallel**. This means all
+/// expressions are run on the same thread and if one branch blocks the thread,
+/// all other expressions will be unable to continue. If parallelism is
+/// required, spawn each async expression using [`tokio::spawn`] and pass the
+/// join handle to `join!`.
+///
+/// [`tokio::spawn`]: crate::spawn
+///
+/// # Examples
+///
+/// Basic join with two branches
+///
+/// ```
+/// async fn do_stuff_async() {
+///     // async work
+/// }
+///
+/// async fn more_async_work() {
+///     // more here
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let (first, second) = tokio::join!(
+///         do_stuff_async(),
+///         more_async_work());
+///
+///     // do something with the values
+/// }
+/// ```
+#[macro_export]
+#[cfg_attr(docsrs, doc(cfg(feature = "macros")))]
+macro_rules! join {
+    (@ {
+        // One `_` for each branch in the `join!` macro. This is not used once
+        // normalization is complete.
+        ( $($count:tt)* )
+
+        // Normalized join! branches
+        $( ( $($skip:tt)* ) $e:expr, )*
+
+    }) => {{
+        use $crate::macros::support::{maybe_done, poll_fn, Future, Pin};
+        use $crate::macros::support::Poll::{Ready, Pending};
+
+        // Safety: nothing must be moved out of `futures`. This is to satisfy
+        // the requirement of `Pin::new_unchecked` called below.
+        let mut futures = ( $( maybe_done($e), )* );
+
+        poll_fn(move |cx| {
+            let mut is_pending = false;
+
+            $(
+                // Extract the future for this branch from the tuple.
+                let ( $($skip,)* fut, .. ) = &mut futures;
+
+                // Safety: future is stored on the stack above
+                // and never moved.
+                let mut fut = unsafe { Pin::new_unchecked(fut) };
+
+                // Try polling
+                if fut.poll(cx).is_pending() {
+                    is_pending = true;
+                }
+            )*
+
+            if is_pending {
+                Pending
+            } else {
+                Ready(($({
+                    // Extract the future for this branch from the tuple.
+                    let ( $($skip,)* fut, .. ) = &mut futures;
+
+                    // Safety: future is stored on the stack above
+                    // and never moved.
+                    let mut fut = unsafe { Pin::new_unchecked(fut) };
+
+                    fut.take_output().expect("expected completed future")
+                },)*))
+            }
+        }).await
+    }};
+
+    // ===== Normalize =====
+
+    (@ { ( $($s:tt)* ) $($t:tt)* } $e:expr, $($r:tt)* ) => {
+        $crate::join!(@{ ($($s)* _) $($t)* ($($s)*) $e, } $($r)*)
+    };
+
+    // ===== Entry point =====
+
+    ( $($e:expr),* $(,)?) => {
+        $crate::join!(@{ () } $($e,)*)
+    };
+}
diff --git a/third_party/rust/tokio/src/macros/loom.rs b/third_party/rust/tokio/src/macros/loom.rs
new file mode 100644
index 0000000000..d57d9fb0f7
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/loom.rs
@@ -0,0 +1,12 @@
+macro_rules! if_loom {
+    ($($t:tt)*) => {{
+        #[cfg(loom)]
+        const LOOM: bool = true;
+        #[cfg(not(loom))]
+        const LOOM: bool = false;
+
+        if LOOM {
+            $($t)*
+        }
+    }}
+}
diff --git a/third_party/rust/tokio/src/macros/mod.rs b/third_party/rust/tokio/src/macros/mod.rs
new file mode 100644
index 0000000000..a1839c8305
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/mod.rs
@@ -0,0 +1,40 @@
+#![cfg_attr(not(feature = "full"), allow(unused_macros))]
+
+#[macro_use]
+mod cfg;
+
+#[macro_use]
+mod loom;
+
+#[macro_use]
+mod pin;
+
+#[macro_use]
+mod ready;
+
+#[macro_use]
+mod thread_local;
+
+cfg_trace! {
+    #[macro_use]
+    mod trace;
+}
+
+#[macro_use]
+#[cfg(feature = "rt")]
+pub(crate) mod scoped_tls;
+
+cfg_macros! {
+    #[macro_use]
+    mod select;
+
+    #[macro_use]
+    mod join;
+
+    #[macro_use]
+    mod try_join;
+}
+
+// Includes re-exports needed to implement macros
+#[doc(hidden)]
+pub mod support;
diff --git a/third_party/rust/tokio/src/macros/pin.rs b/third_party/rust/tokio/src/macros/pin.rs
new file mode 100644
index 0000000000..7af9ce7d1f
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/pin.rs
@@ -0,0 +1,144 @@
+/// Pins a value on the stack.
+///
+/// Calls to `async fn` return anonymous [`Future`] values that are `!Unpin`.
+/// These values must be pinned before they can be polled. Calling `.await` will
+/// handle this, but consumes the future. If it is required to call `.await` on
+/// a `&mut _` reference, the caller is responsible for pinning the future.
+///
+/// Pinning may be done by allocating with [`Box::pin`] or by using the stack
+/// with the `pin!` macro.
+///
+/// The following will **fail to compile**:
+///
+/// ```compile_fail
+/// async fn my_async_fn() {
+///     // async logic here
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let mut future = my_async_fn();
+///     (&mut future).await;
+/// }
+/// ```
+///
+/// To make this work requires pinning:
+///
+/// ```
+/// use tokio::pin;
+///
+/// async fn my_async_fn() {
+///     // async logic here
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let future = my_async_fn();
+///     pin!(future);
+///
+///     (&mut future).await;
+/// }
+/// ```
+///
+/// Pinning is useful when using `select!` and stream operators that require `T:
+/// Stream + Unpin`.
+///
+/// [`Future`]: trait@std::future::Future
+/// [`Box::pin`]: std::boxed::Box::pin
+///
+/// # Usage
+///
+/// The `pin!` macro takes **identifiers** as arguments. It does **not** work
+/// with expressions.
+///
+/// The following does not compile as an expression is passed to `pin!`.
+///
+/// ```compile_fail
+/// async fn my_async_fn() {
+///     // async logic here
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let mut future = pin!(my_async_fn());
+///     (&mut future).await;
+/// }
+/// ```
+///
+/// # Examples
+///
+/// Using with select:
+///
+/// ```
+/// use tokio::{pin, select};
+/// use tokio_stream::{self as stream, StreamExt};
+///
+/// async fn my_async_fn() {
+///     // async logic here
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let mut stream = stream::iter(vec![1, 2, 3, 4]);
+///
+///     let future = my_async_fn();
+///     pin!(future);
+///
+///     loop {
+///         select! {
+///             _ = &mut future => {
+///                 // Stop looping `future` will be polled after completion
+///                 break;
+///             }
+///             Some(val) = stream.next() => {
+///                 println!("got value = {}", val);
+///             }
+///         }
+///     }
+/// }
+/// ```
+///
+/// Because assigning to a variable followed by pinning is common, there is also
+/// a variant of the macro that supports doing both in one go.
+///
+/// ```
+/// use tokio::{pin, select};
+///
+/// async fn my_async_fn() {
+///     // async logic here
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+///     pin! {
+///         let future1 = my_async_fn();
+///         let future2 = my_async_fn();
+///     }
+///
+///     select! {
+///         _ = &mut future1 => {}
+///         _ = &mut future2 => {}
+///     }
+/// }
+/// ```
+#[macro_export]
+macro_rules! pin {
+    ($($x:ident),*) => { $(
+        // Move the value to ensure that it is owned
+        let mut $x = $x;
+        // Shadow the original binding so that it can't be directly accessed
+        // ever again.
+        #[allow(unused_mut)]
+        let mut $x = unsafe {
+            $crate::macros::support::Pin::new_unchecked(&mut $x)
+        };
+    )* };
+    ($(
+            let $x:ident = $init:expr;
+    )*) => {
+        $(
+            let $x = $init;
+            $crate::pin!($x);
+        )*
+    };
+}
diff --git a/third_party/rust/tokio/src/macros/ready.rs b/third_party/rust/tokio/src/macros/ready.rs
new file mode 100644
index 0000000000..1f48623b80
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/ready.rs
@@ -0,0 +1,8 @@
+macro_rules! ready {
+    ($e:expr $(,)?) => {
+        match $e {
+            std::task::Poll::Ready(t) => t,
+            std::task::Poll::Pending => return std::task::Poll::Pending,
+        }
+    };
+}
diff --git a/third_party/rust/tokio/src/macros/scoped_tls.rs b/third_party/rust/tokio/src/macros/scoped_tls.rs
new file mode 100644
index 0000000000..f2504cbadf
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/scoped_tls.rs
@@ -0,0 +1,77 @@
+use crate::loom::thread::LocalKey;
+
+use std::cell::Cell;
+use std::marker;
+
+/// Sets a reference as a thread-local.
+macro_rules! scoped_thread_local {
+    ($(#[$attrs:meta])* $vis:vis static $name:ident: $ty:ty) => (
+        $(#[$attrs])*
+        $vis static $name: $crate::macros::scoped_tls::ScopedKey<$ty>
+            = $crate::macros::scoped_tls::ScopedKey {
+                inner: {
+                    thread_local!(static FOO: ::std::cell::Cell<*const ()> = {
+                        std::cell::Cell::new(::std::ptr::null())
+                    });
+                    &FOO
+                },
+                _marker: ::std::marker::PhantomData,
+            };
+    )
+}
+
+/// Type representing a thread local storage key corresponding to a reference
+/// to the type parameter `T`.
+pub(crate) struct ScopedKey<T> {
+    pub(crate) inner: &'static LocalKey<Cell<*const ()>>,
+    pub(crate) _marker: marker::PhantomData<T>,
+}
+
+unsafe impl<T> Sync for ScopedKey<T> {}
+
+impl<T> ScopedKey<T> {
+    /// Inserts a value into this scoped thread local storage slot for a
+    /// duration of a closure.
+    pub(crate) fn set<F, R>(&'static self, t: &T, f: F) -> R
+    where
+        F: FnOnce() -> R,
+    {
+        struct Reset {
+            key: &'static LocalKey<Cell<*const ()>>,
+            val: *const (),
+        }
+
+        impl Drop for Reset {
+            fn drop(&mut self) {
+                self.key.with(|c| c.set(self.val));
+            }
+        }
+
+        let prev = self.inner.with(|c| {
+            let prev = c.get();
+            c.set(t as *const _ as *const ());
+            prev
+        });
+
+        let _reset = Reset {
+            key: self.inner,
+            val: prev,
+        };
+
+        f()
+    }
+
+    /// Gets a value out of this scoped variable.
+    pub(crate) fn with<F, R>(&'static self, f: F) -> R
+    where
+        F: FnOnce(Option<&T>) -> R,
+    {
+        let val = self.inner.with(|c| c.get());
+
+        if val.is_null() {
+            f(None)
+        } else {
+            unsafe { f(Some(&*(val as *const T))) }
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/macros/select.rs b/third_party/rust/tokio/src/macros/select.rs
new file mode 100644
index 0000000000..051f8cb72a
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/select.rs
@@ -0,0 +1,1001 @@
+/// Waits on multiple concurrent branches, returning when the **first** branch
+/// completes, cancelling the remaining branches.
+///
+/// The `select!` macro must be used inside of async functions, closures, and
+/// blocks.
+///
+/// The `select!` macro accepts one or more branches with the following pattern:
+///
+/// ```text
+/// <pattern> = <async expression> (, if <precondition>)? => <handler>,
+/// ```
+///
+/// Additionally, the `select!` macro may include a single, optional `else`
+/// branch, which evaluates if none of the other branches match their patterns:
+///
+/// ```text
+/// else => <expression>
+/// ```
+///
+/// The macro aggregates all `<async expression>` expressions and runs them
+/// concurrently on the **current** task. Once the **first** expression
+/// completes with a value that matches its `<pattern>`, the `select!` macro
+/// returns the result of evaluating the completed branch's `<handler>`
+/// expression.
+///
+/// Additionally, each branch may include an optional `if` precondition. If the
+/// precondition returns `false`, then the branch is disabled. The provided
+/// `<async expression>` is still evaluated but the resulting future is never
+/// polled. This capability is useful when using `select!` within a loop.
+///
+/// The complete lifecycle of a `select!` expression is as follows:
+///
+/// 1. Evaluate all provided `<precondition>` expressions. If the precondition
+///    returns `false`, disable the branch for the remainder of the current call
+///    to `select!`. Re-entering `select!` due to a loop clears the "disabled"
+///    state.
+/// 2. Aggregate the `<async expression>`s from each branch, including the
+///    disabled ones. If the branch is disabled, `<async expression>` is still
+///    evaluated, but the resulting future is not polled.
+/// 3. Concurrently await on the results for all remaining `<async expression>`s.
+/// 4. Once an `<async expression>` returns a value, attempt to apply the value
+///    to the provided `<pattern>`, if the pattern matches, evaluate `<handler>`
+///    and return. If the pattern **does not** match, disable the current branch
+///    and for the remainder of the current call to `select!`. Continue from step 3.
+/// 5. If **all** branches are disabled, evaluate the `else` expression. If no
+///    else branch is provided, panic.
+///
+/// # Runtime characteristics
+///
+/// By running all async expressions on the current task, the expressions are
+/// able to run **concurrently** but not in **parallel**. This means all
+/// expressions are run on the same thread and if one branch blocks the thread,
+/// all other expressions will be unable to continue. If parallelism is
+/// required, spawn each async expression using [`tokio::spawn`] and pass the
+/// join handle to `select!`.
+///
+/// [`tokio::spawn`]: crate::spawn
+///
+/// # Fairness
+///
+/// By default, `select!` randomly picks a branch to check first. This provides
+/// some level of fairness when calling `select!` in a loop with branches that
+/// are always ready.
+///
+/// This behavior can be overridden by adding `biased;` to the beginning of the
+/// macro usage. See the examples for details. This will cause `select` to poll
+/// the futures in the order they appear from top to bottom. There are a few
+/// reasons you may want this:
+///
+/// - The random number generation of `tokio::select!` has a non-zero CPU cost
+/// - Your futures may interact in a way where known polling order is significant
+///
+/// But there is an important caveat to this mode. It becomes your responsibility
+/// to ensure that the polling order of your futures is fair. If for example you
+/// are selecting between a stream and a shutdown future, and the stream has a
+/// huge volume of messages and zero or nearly zero time between them, you should
+/// place the shutdown future earlier in the `select!` list to ensure that it is
+/// always polled, and will not be ignored due to the stream being constantly
+/// ready.
+///
+/// # Panics
+///
+/// The `select!` macro panics if all branches are disabled **and** there is no
+/// provided `else` branch. A branch is disabled when the provided `if`
+/// precondition returns `false` **or** when the pattern does not match the
+/// result of `<async expression>`.
+///
+/// # Cancellation safety
+///
+/// When using `select!` in a loop to receive messages from multiple sources,
+/// you should make sure that the receive call is cancellation safe to avoid
+/// losing messages. This section goes through various common methods and
+/// describes whether they are cancel safe.  The lists in this section are not
+/// exhaustive.
+///
+/// The following methods are cancellation safe:
+///
+///  * [`tokio::sync::mpsc::Receiver::recv`](crate::sync::mpsc::Receiver::recv)
+///  * [`tokio::sync::mpsc::UnboundedReceiver::recv`](crate::sync::mpsc::UnboundedReceiver::recv)
+///  * [`tokio::sync::broadcast::Receiver::recv`](crate::sync::broadcast::Receiver::recv)
+///  * [`tokio::sync::watch::Receiver::changed`](crate::sync::watch::Receiver::changed)
+///  * [`tokio::net::TcpListener::accept`](crate::net::TcpListener::accept)
+///  * [`tokio::net::UnixListener::accept`](crate::net::UnixListener::accept)
+///  * [`tokio::io::AsyncReadExt::read`](crate::io::AsyncReadExt::read) on any `AsyncRead`
+///  * [`tokio::io::AsyncReadExt::read_buf`](crate::io::AsyncReadExt::read_buf) on any `AsyncRead`
+///  * [`tokio::io::AsyncWriteExt::write`](crate::io::AsyncWriteExt::write) on any `AsyncWrite`
+///  * [`tokio::io::AsyncWriteExt::write_buf`](crate::io::AsyncWriteExt::write_buf) on any `AsyncWrite`
+///  * [`tokio_stream::StreamExt::next`](https://docs.rs/tokio-stream/0.1/tokio_stream/trait.StreamExt.html#method.next) on any `Stream`
+///  * [`futures::stream::StreamExt::next`](https://docs.rs/futures/0.3/futures/stream/trait.StreamExt.html#method.next) on any `Stream`
+///
+/// The following methods are not cancellation safe and can lead to loss of data:
+///
+///  * [`tokio::io::AsyncReadExt::read_exact`](crate::io::AsyncReadExt::read_exact)
+///  * [`tokio::io::AsyncReadExt::read_to_end`](crate::io::AsyncReadExt::read_to_end)
+///  * [`tokio::io::AsyncReadExt::read_to_string`](crate::io::AsyncReadExt::read_to_string)
+///  * [`tokio::io::AsyncWriteExt::write_all`](crate::io::AsyncWriteExt::write_all)
+///
+/// The following methods are not cancellation safe because they use a queue for
+/// fairness and cancellation makes you lose your place in the queue:
+///
+///  * [`tokio::sync::Mutex::lock`](crate::sync::Mutex::lock)
+///  * [`tokio::sync::RwLock::read`](crate::sync::RwLock::read)
+///  * [`tokio::sync::RwLock::write`](crate::sync::RwLock::write)
+///  * [`tokio::sync::Semaphore::acquire`](crate::sync::Semaphore::acquire)
+///  * [`tokio::sync::Notify::notified`](crate::sync::Notify::notified)
+///
+/// To determine whether your own methods are cancellation safe, look for the
+/// location of uses of `.await`. This is because when an asynchronous method is
+/// cancelled, that always happens at an `.await`. If your function behaves
+/// correctly even if it is restarted while waiting at an `.await`, then it is
+/// cancellation safe.
+///
+/// Be aware that cancelling something that is not cancellation safe is not
+/// necessarily wrong. For example, if you are cancelling a task because the
+/// application is shutting down, then you probably don't care that partially
+/// read data is lost.
+///
+/// # Examples
+///
+/// Basic select with two branches.
+///
+/// ```
+/// async fn do_stuff_async() {
+///     // async work
+/// }
+///
+/// async fn more_async_work() {
+///     // more here
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+///     tokio::select! {
+///         _ = do_stuff_async() => {
+///             println!("do_stuff_async() completed first")
+///         }
+///         _ = more_async_work() => {
+///             println!("more_async_work() completed first")
+///         }
+///     };
+/// }
+/// ```
+///
+/// Basic stream selecting.
+///
+/// ```
+/// use tokio_stream::{self as stream, StreamExt};
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let mut stream1 = stream::iter(vec![1, 2, 3]);
+///     let mut stream2 = stream::iter(vec![4, 5, 6]);
+///
+///     let next = tokio::select! {
+///         v = stream1.next() => v.unwrap(),
+///         v = stream2.next() => v.unwrap(),
+///     };
+///
+///     assert!(next == 1 || next == 4);
+/// }
+/// ```
+///
+/// Collect the contents of two streams. In this example, we rely on pattern
+/// matching and the fact that `stream::iter` is "fused", i.e. once the stream
+/// is complete, all calls to `next()` return `None`.
+///
+/// ```
+/// use tokio_stream::{self as stream, StreamExt};
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let mut stream1 = stream::iter(vec![1, 2, 3]);
+///     let mut stream2 = stream::iter(vec![4, 5, 6]);
+///
+///     let mut values = vec![];
+///
+///     loop {
+///         tokio::select! {
+///             Some(v) = stream1.next() => values.push(v),
+///             Some(v) = stream2.next() => values.push(v),
+///             else => break,
+///         }
+///     }
+///
+///     values.sort();
+///     assert_eq!(&[1, 2, 3, 4, 5, 6], &values[..]);
+/// }
+/// ```
+///
+/// Using the same future in multiple `select!` expressions can be done by passing
+/// a reference to the future. Doing so requires the future to be [`Unpin`]. A
+/// future can be made [`Unpin`] by either using [`Box::pin`] or stack pinning.
+///
+/// [`Unpin`]: std::marker::Unpin
+/// [`Box::pin`]: std::boxed::Box::pin
+///
+/// Here, a stream is consumed for at most 1 second.
+///
+/// ```
+/// use tokio_stream::{self as stream, StreamExt};
+/// use tokio::time::{self, Duration};
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let mut stream = stream::iter(vec![1, 2, 3]);
+///     let sleep = time::sleep(Duration::from_secs(1));
+///     tokio::pin!(sleep);
+///
+///     loop {
+///         tokio::select! {
+///             maybe_v = stream.next() => {
+///                 if let Some(v) = maybe_v {
+///                     println!("got = {}", v);
+///                 } else {
+///                     break;
+///                 }
+///             }
+///             _ = &mut sleep => {
+///                 println!("timeout");
+///                 break;
+///             }
+///         }
+///     }
+/// }
+/// ```
+///
+/// Joining two values using `select!`.
+///
+/// ```
+/// use tokio::sync::oneshot;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let (tx1, mut rx1) = oneshot::channel();
+///     let (tx2, mut rx2) = oneshot::channel();
+///
+///     tokio::spawn(async move {
+///         tx1.send("first").unwrap();
+///     });
+///
+///     tokio::spawn(async move {
+///         tx2.send("second").unwrap();
+///     });
+///
+///     let mut a = None;
+///     let mut b = None;
+///
+///     while a.is_none() || b.is_none() {
+///         tokio::select! {
+///             v1 = (&mut rx1), if a.is_none() => a = Some(v1.unwrap()),
+///             v2 = (&mut rx2), if b.is_none() => b = Some(v2.unwrap()),
+///         }
+///     }
+///
+///     let res = (a.unwrap(), b.unwrap());
+///
+///     assert_eq!(res.0, "first");
+///     assert_eq!(res.1, "second");
+/// }
+/// ```
+///
+/// Using the `biased;` mode to control polling order.
+///
+/// ```
+/// #[tokio::main]
+/// async fn main() {
+///     let mut count = 0u8;
+///
+///     loop {
+///         tokio::select! {
+///             // If you run this example without `biased;`, the polling order is
+///             // pseudo-random, and the assertions on the value of count will
+///             // (probably) fail.
+///             biased;
+///
+///             _ = async {}, if count < 1 => {
+///                 count += 1;
+///                 assert_eq!(count, 1);
+///             }
+///             _ = async {}, if count < 2 => {
+///                 count += 1;
+///                 assert_eq!(count, 2);
+///             }
+///             _ = async {}, if count < 3 => {
+///                 count += 1;
+///                 assert_eq!(count, 3);
+///             }
+///             _ = async {}, if count < 4 => {
+///                 count += 1;
+///                 assert_eq!(count, 4);
+///             }
+///
+///             else => {
+///                 break;
+///             }
+///         };
+///     }
+/// }
+/// ```
+///
+/// ## Avoid racy `if` preconditions
+///
+/// Given that `if` preconditions are used to disable `select!` branches, some
+/// caution must be used to avoid missing values.
+///
+/// For example, here is **incorrect** usage of `sleep` with `if`. The objective
+/// is to repeatedly run an asynchronous task for up to 50 milliseconds.
+/// However, there is a potential for the `sleep` completion to be missed.
+///
+/// ```no_run,should_panic
+/// use tokio::time::{self, Duration};
+///
+/// async fn some_async_work() {
+///     // do work
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let sleep = time::sleep(Duration::from_millis(50));
+///     tokio::pin!(sleep);
+///
+///     while !sleep.is_elapsed() {
+///         tokio::select! {
+///             _ = &mut sleep, if !sleep.is_elapsed() => {
+///                 println!("operation timed out");
+///             }
+///             _ = some_async_work() => {
+///                 println!("operation completed");
+///             }
+///         }
+///     }
+///
+///     panic!("This example shows how not to do it!");
+/// }
+/// ```
+///
+/// In the above example, `sleep.is_elapsed()` may return `true` even if
+/// `sleep.poll()` never returned `Ready`. This opens up a potential race
+/// condition where `sleep` expires between the `while !sleep.is_elapsed()`
+/// check and the call to `select!` resulting in the `some_async_work()` call to
+/// run uninterrupted despite the sleep having elapsed.
+///
+/// One way to write the above example without the race would be:
+///
+/// ```
+/// use tokio::time::{self, Duration};
+///
+/// async fn some_async_work() {
+/// # time::sleep(Duration::from_millis(10)).await;
+///     // do work
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let sleep = time::sleep(Duration::from_millis(50));
+///     tokio::pin!(sleep);
+///
+///     loop {
+///         tokio::select! {
+///             _ = &mut sleep => {
+///                 println!("operation timed out");
+///                 break;
+///             }
+///             _ = some_async_work() => {
+///                 println!("operation completed");
+///             }
+///         }
+///     }
+/// }
+/// ```
+#[macro_export]
+#[cfg_attr(docsrs, doc(cfg(feature = "macros")))]
+macro_rules! select {
+    // Uses a declarative macro to do **most** of the work. While it is possible
+    // to implement fully with a declarative macro, a procedural macro is used
+    // to enable improved error messages.
+    //
+    // The macro is structured as a tt-muncher. All branches are processed and
+    // normalized. Once the input is normalized, it is passed to the top-most
+    // rule. When entering the macro, `@{ }` is inserted at the front. This is
+    // used to collect the normalized input.
+    //
+    // The macro only recurses once per branch. This allows using `select!`
+    // without requiring the user to increase the recursion limit.
+
+    // All input is normalized, now transform.
+    (@ {
+        // The index of the future to poll first (in bias mode), or the RNG
+        // expression to use to pick a future to poll first.
+        start=$start:expr;
+
+        // One `_` for each branch in the `select!` macro. Passing this to
+        // `count!` converts $skip to an integer.
+        ( $($count:tt)* )
+
+        // Normalized select branches. `( $skip )` is a set of `_` characters.
+        // There is one `_` for each select branch **before** this one. Given
+        // that all input futures are stored in a tuple, $skip is useful for
+        // generating a pattern to reference the future for the current branch.
+        // $skip is also used as an argument to `count!`, returning the index of
+        // the current select branch.
+        $( ( $($skip:tt)* ) $bind:pat = $fut:expr, if $c:expr => $handle:expr, )+
+
+        // Fallback expression used when all select branches have been disabled.
+        ; $else:expr
+
+    }) => {{
+        // Enter a context where stable "function-like" proc macros can be used.
+        //
+        // This module is defined within a scope and should not leak out of this
+        // macro.
+        mod util {
+            // Generate an enum with one variant per select branch
+            $crate::select_priv_declare_output_enum!( ( $($count)* ) );
+        }
+
+        // `tokio::macros::support` is a public, but doc(hidden) module
+        // including a re-export of all types needed by this macro.
+        use $crate::macros::support::Future;
+        use $crate::macros::support::Pin;
+        use $crate::macros::support::Poll::{Ready, Pending};
+
+        const BRANCHES: u32 = $crate::count!( $($count)* );
+
+        let mut disabled: util::Mask = Default::default();
+
+        // First, invoke all the pre-conditions. For any that return true,
+        // set the appropriate bit in `disabled`.
+        $(
+            if !$c {
+                let mask: util::Mask = 1 << $crate::count!( $($skip)* );
+                disabled |= mask;
+            }
+        )*
+
+        // Create a scope to separate polling from handling the output. This
+        // adds borrow checker flexibility when using the macro.
+        let mut output = {
+            // Safety: Nothing must be moved out of `futures`. This is to
+            // satisfy the requirement of `Pin::new_unchecked` called below.
+            let mut futures = ( $( $fut , )+ );
+
+            $crate::macros::support::poll_fn(|cx| {
+                // Track if any branch returns pending. If no branch completes
+                // **or** returns pending, this implies that all branches are
+                // disabled.
+                let mut is_pending = false;
+
+                // Choose a starting index to begin polling the futures at. In
+                // practice, this will either be a pseudo-randomly generated
+                // number by default, or the constant 0 if `biased;` is
+                // supplied.
+                let start = $start;
+
+                for i in 0..BRANCHES {
+                    let branch;
+                    #[allow(clippy::modulo_one)]
+                    {
+                        branch = (start + i) % BRANCHES;
+                    }
+                    match branch {
+                        $(
+                            #[allow(unreachable_code)]
+                            $crate::count!( $($skip)* ) => {
+                                // First, if the future has previously been
+                                // disabled, do not poll it again. This is done
+                                // by checking the associated bit in the
+                                // `disabled` bit field.
+                                let mask = 1 << branch;
+
+                                if disabled & mask == mask {
+                                    // The future has been disabled.
+                                    continue;
+                                }
+
+                                // Extract the future for this branch from the
+                                // tuple
+                                let ( $($skip,)* fut, .. ) = &mut futures;
+
+                                // Safety: future is stored on the stack above
+                                // and never moved.
+                                let mut fut = unsafe { Pin::new_unchecked(fut) };
+
+                                // Try polling it
+                                let out = match Future::poll(fut, cx) {
+                                    Ready(out) => out,
+                                    Pending => {
+                                        // Track that at least one future is
+                                        // still pending and continue polling.
+                                        is_pending = true;
+                                        continue;
+                                    }
+                                };
+
+                                // Disable the future from future polling.
+                                disabled |= mask;
+
+                                // The future returned a value, check if matches
+                                // the specified pattern.
+                                #[allow(unused_variables)]
+                                #[allow(unused_mut)]
+                                match &out {
+                                    $crate::select_priv_clean_pattern!($bind) => {}
+                                    _ => continue,
+                                }
+
+                                // The select is complete, return the value
+                                return Ready($crate::select_variant!(util::Out, ($($skip)*))(out));
+                            }
+                        )*
+                        _ => unreachable!("reaching this means there probably is an off by one bug"),
+                    }
+                }
+
+                if is_pending {
+                    Pending
+                } else {
+                    // All branches have been disabled.
+                    Ready(util::Out::Disabled)
+                }
+            }).await
+        };
+
+        match output {
+            $(
+                $crate::select_variant!(util::Out, ($($skip)*) ($bind)) => $handle,
+            )*
+            util::Out::Disabled => $else,
+            _ => unreachable!("failed to match bind"),
+        }
+    }};
+
+    // ==== Normalize =====
+
+    // These rules match a single `select!` branch and normalize it for
+    // processing by the first rule.
+
+    (@ { start=$start:expr; $($t:tt)* } ) => {
+        // No `else` branch
+        $crate::select!(@{ start=$start; $($t)*; panic!("all branches are disabled and there is no else branch") })
+    };
+    (@ { start=$start:expr; $($t:tt)* } else => $else:expr $(,)?) => {
+        $crate::select!(@{ start=$start; $($t)*; $else })
+    };
+    (@ { start=$start:expr; ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr, if $c:expr => $h:block, $($r:tt)* ) => {
+        $crate::select!(@{ start=$start; ($($s)* _) $($t)* ($($s)*) $p = $f, if $c => $h, } $($r)*)
+    };
+    (@ { start=$start:expr; ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr => $h:block, $($r:tt)* ) => {
+        $crate::select!(@{ start=$start; ($($s)* _) $($t)* ($($s)*) $p = $f, if true => $h, } $($r)*)
+    };
+    (@ { start=$start:expr; ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr, if $c:expr => $h:block $($r:tt)* ) => {
+        $crate::select!(@{ start=$start; ($($s)* _) $($t)* ($($s)*) $p = $f, if $c => $h, } $($r)*)
+    };
+    (@ { start=$start:expr; ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr => $h:block $($r:tt)* ) => {
+        $crate::select!(@{ start=$start; ($($s)* _) $($t)* ($($s)*) $p = $f, if true => $h, } $($r)*)
+    };
+    (@ { start=$start:expr; ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr, if $c:expr => $h:expr ) => {
+        $crate::select!(@{ start=$start; ($($s)* _) $($t)* ($($s)*) $p = $f, if $c => $h, })
+    };
+    (@ { start=$start:expr; ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr => $h:expr ) => {
+        $crate::select!(@{ start=$start; ($($s)* _) $($t)* ($($s)*) $p = $f, if true => $h, })
+    };
+    (@ { start=$start:expr; ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr, if $c:expr => $h:expr, $($r:tt)* ) => {
+        $crate::select!(@{ start=$start; ($($s)* _) $($t)* ($($s)*) $p = $f, if $c => $h, } $($r)*)
+    };
+    (@ { start=$start:expr; ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr => $h:expr, $($r:tt)* ) => {
+        $crate::select!(@{ start=$start; ($($s)* _) $($t)* ($($s)*) $p = $f, if true => $h, } $($r)*)
+    };
+
+    // ===== Entry point =====
+
+    (biased; $p:pat = $($t:tt)* ) => {
+        $crate::select!(@{ start=0; () } $p = $($t)*)
+    };
+
+    ( $p:pat = $($t:tt)* ) => {
+        // Randomly generate a starting point. This makes `select!` a bit more
+        // fair and avoids always polling the first future.
+        $crate::select!(@{ start={ $crate::macros::support::thread_rng_n(BRANCHES) }; () } $p = $($t)*)
+    };
+    () => {
+        compile_error!("select! requires at least one branch.")
+    };
+}
+
+// And here... we manually list out matches for up to 64 branches... I'm not
+// happy about it either, but this is how we manage to use a declarative macro!
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! count {
+    () => {
+        0
+    };
+    (_) => {
+        1
+    };
+    (_ _) => {
+        2
+    };
+    (_ _ _) => {
+        3
+    };
+    (_ _ _ _) => {
+        4
+    };
+    (_ _ _ _ _) => {
+        5
+    };
+    (_ _ _ _ _ _) => {
+        6
+    };
+    (_ _ _ _ _ _ _) => {
+        7
+    };
+    (_ _ _ _ _ _ _ _) => {
+        8
+    };
+    (_ _ _ _ _ _ _ _ _) => {
+        9
+    };
+    (_ _ _ _ _ _ _ _ _ _) => {
+        10
+    };
+    (_ _ _ _ _ _ _ _ _ _ _) => {
+        11
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _) => {
+        12
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        13
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        14
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        15
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        16
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        17
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        18
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        19
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        20
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        21
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        22
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        23
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        24
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        25
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        26
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        27
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        28
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        29
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        30
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        31
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        32
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        33
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        34
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        35
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        36
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        37
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        38
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        39
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        40
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        41
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        42
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        43
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        44
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        45
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        46
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        47
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        48
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        49
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        50
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        51
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        52
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        53
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        54
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        55
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        56
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        57
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        58
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        59
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        60
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        61
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        62
+    };
+    (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) => {
+        63
+    };
+}
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! select_variant {
+    ($($p:ident)::*, () $($t:tt)*) => {
+        $($p)::*::_0 $($t)*
+    };
+    ($($p:ident)::*, (_) $($t:tt)*) => {
+        $($p)::*::_1 $($t)*
+    };
+    ($($p:ident)::*, (_ _) $($t:tt)*) => {
+        $($p)::*::_2 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _) $($t:tt)*) => {
+        $($p)::*::_3 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _) $($t:tt)*) => {
+        $($p)::*::_4 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_5 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_6 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_7 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_8 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_9 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_10 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_11 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_12 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_13 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_14 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_15 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_16 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_17 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_18 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_19 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_20 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_21 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_22 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_23 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_24 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_25 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_26 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_27 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_28 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_29 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_30 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_31 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_32 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_33 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_34 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_35 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_36 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_37 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_38 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_39 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_40 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_41 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_42 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_43 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_44 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_45 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_46 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_47 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_48 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_49 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_50 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_51 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_52 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_53 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_54 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_55 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_56 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_57 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_58 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_59 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_60 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_61 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_62 $($t)*
+    };
+    ($($p:ident)::*, (_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _) $($t:tt)*) => {
+        $($p)::*::_63 $($t)*
+    };
+}
diff --git a/third_party/rust/tokio/src/macros/support.rs b/third_party/rust/tokio/src/macros/support.rs
new file mode 100644
index 0000000000..7f11bc6800
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/support.rs
@@ -0,0 +1,9 @@
+cfg_macros! {
+    pub use crate::future::poll_fn;
+    pub use crate::future::maybe_done::maybe_done;
+    pub use crate::util::thread_rng_n;
+}
+
+pub use std::future::Future;
+pub use std::pin::Pin;
+pub use std::task::Poll;
diff --git a/third_party/rust/tokio/src/macros/thread_local.rs b/third_party/rust/tokio/src/macros/thread_local.rs
new file mode 100644
index 0000000000..d848947350
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/thread_local.rs
@@ -0,0 +1,4 @@
+#[cfg(all(loom, test))]
+macro_rules! thread_local {
+    ($($tts:tt)+) => { loom::thread_local!{ $($tts)+ } }
+}
diff --git a/third_party/rust/tokio/src/macros/trace.rs b/third_party/rust/tokio/src/macros/trace.rs
new file mode 100644
index 0000000000..80a257e189
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/trace.rs
@@ -0,0 +1,26 @@
+cfg_trace! {
+    macro_rules! trace_op {
+        ($name:expr, $readiness:literal) => {
+            tracing::trace!(
+                target: "runtime::resource::poll_op",
+                op_name = $name,
+                is_ready = $readiness
+            );
+        }
+    }
+
+    macro_rules! trace_poll_op {
+        ($name:expr, $poll:expr $(,)*) => {
+            match $poll {
+                std::task::Poll::Ready(t) => {
+                    trace_op!($name, true);
+                    std::task::Poll::Ready(t)
+                }
+                std::task::Poll::Pending => {
+                    trace_op!($name, false);
+                    return std::task::Poll::Pending;
+                }
+            }
+        };
+    }
+}
diff --git a/third_party/rust/tokio/src/macros/try_join.rs b/third_party/rust/tokio/src/macros/try_join.rs
new file mode 100644
index 0000000000..6d3a893b7e
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/try_join.rs
@@ -0,0 +1,171 @@
+/// Waits on multiple concurrent branches, returning when **all** branches
+/// complete with `Ok(_)` or on the first `Err(_)`.
+///
+/// The `try_join!` macro must be used inside of async functions, closures, and
+/// blocks.
+///
+/// Similar to [`join!`], the `try_join!` macro takes a list of async
+/// expressions and evaluates them concurrently on the same task. Each async
+/// expression evaluates to a future and the futures from each expression are
+/// multiplexed on the current task. The `try_join!` macro returns when **all**
+/// branches return with `Ok` or when the **first** branch returns with `Err`.
+///
+/// [`join!`]: macro@join
+///
+/// # Notes
+///
+/// The supplied futures are stored inline and does not require allocating a
+/// `Vec`.
+///
+/// ### Runtime characteristics
+///
+/// By running all async expressions on the current task, the expressions are
+/// able to run **concurrently** but not in **parallel**. This means all
+/// expressions are run on the same thread and if one branch blocks the thread,
+/// all other expressions will be unable to continue. If parallelism is
+/// required, spawn each async expression using [`tokio::spawn`] and pass the
+/// join handle to `try_join!`.
+///
+/// [`tokio::spawn`]: crate::spawn
+///
+/// # Examples
+///
+/// Basic try_join with two branches.
+///
+/// ```
+/// async fn do_stuff_async() -> Result<(), &'static str> {
+///     // async work
+/// # Ok(())
+/// }
+///
+/// async fn more_async_work() -> Result<(), &'static str> {
+///     // more here
+/// # Ok(())
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let res = tokio::try_join!(
+///         do_stuff_async(),
+///         more_async_work());
+///
+///     match res {
+///          Ok((first, second)) => {
+///              // do something with the values
+///          }
+///          Err(err) => {
+///             println!("processing failed; error = {}", err);
+///          }
+///     }
+/// }
+/// ```
+///
+/// Using `try_join!` with spawned tasks.
+///
+/// ```
+/// use tokio::task::JoinHandle;
+///
+/// async fn do_stuff_async() -> Result<(), &'static str> {
+///     // async work
+/// # Err("failed")
+/// }
+///
+/// async fn more_async_work() -> Result<(), &'static str> {
+///     // more here
+/// # Ok(())
+/// }
+///
+/// async fn flatten<T>(handle: JoinHandle<Result<T, &'static str>>) -> Result<T, &'static str> {
+///     match handle.await {
+///         Ok(Ok(result)) => Ok(result),
+///         Ok(Err(err)) => Err(err),
+///         Err(err) => Err("handling failed"),
+///     }
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let handle1 = tokio::spawn(do_stuff_async());
+///     let handle2 = tokio::spawn(more_async_work());
+///     match tokio::try_join!(flatten(handle1), flatten(handle2)) {
+///         Ok(val) => {
+///             // do something with the values
+///         }
+///         Err(err) => {
+///             println!("Failed with {}.", err);
+///             # assert_eq!(err, "failed");
+///         }
+///     }
+/// }
+/// ```
+#[macro_export]
+#[cfg_attr(docsrs, doc(cfg(feature = "macros")))]
+macro_rules! try_join {
+    (@ {
+        // One `_` for each branch in the `try_join!` macro. This is not used once
+        // normalization is complete.
+        ( $($count:tt)* )
+
+        // Normalized try_join! branches
+        $( ( $($skip:tt)* ) $e:expr, )*
+
+    }) => {{
+        use $crate::macros::support::{maybe_done, poll_fn, Future, Pin};
+        use $crate::macros::support::Poll::{Ready, Pending};
+
+        // Safety: nothing must be moved out of `futures`. This is to satisfy
+        // the requirement of `Pin::new_unchecked` called below.
+        let mut futures = ( $( maybe_done($e), )* );
+
+        poll_fn(move |cx| {
+            let mut is_pending = false;
+
+            $(
+                // Extract the future for this branch from the tuple.
+                let ( $($skip,)* fut, .. ) = &mut futures;
+
+                // Safety: future is stored on the stack above
+                // and never moved.
+                let mut fut = unsafe { Pin::new_unchecked(fut) };
+
+                // Try polling
+                if fut.as_mut().poll(cx).is_pending() {
+                    is_pending = true;
+                } else if fut.as_mut().output_mut().expect("expected completed future").is_err() {
+                    return Ready(Err(fut.take_output().expect("expected completed future").err().unwrap()))
+                }
+            )*
+
+            if is_pending {
+                Pending
+            } else {
+                Ready(Ok(($({
+                    // Extract the future for this branch from the tuple.
+                    let ( $($skip,)* fut, .. ) = &mut futures;
+
+                    // Safety: future is stored on the stack above
+                    // and never moved.
+                    let mut fut = unsafe { Pin::new_unchecked(fut) };
+
+                    fut
+                        .take_output()
+                        .expect("expected completed future")
+                        .ok()
+                        .expect("expected Ok(_)")
+                },)*)))
+            }
+        }).await
+    }};
+
+    // ===== Normalize =====
+
+    (@ { ( $($s:tt)* ) $($t:tt)* } $e:expr, $($r:tt)* ) => {
+        $crate::try_join!(@{ ($($s)* _) $($t)* ($($s)*) $e, } $($r)*)
+    };
+
+    // ===== Entry point =====
+
+    ( $($e:expr),* $(,)?) => {
+        $crate::try_join!(@{ () } $($e,)*)
+    };
+}
diff --git a/third_party/rust/tokio/src/net/addr.rs b/third_party/rust/tokio/src/net/addr.rs
new file mode 100644
index 0000000000..13f743c962
--- /dev/null
+++ b/third_party/rust/tokio/src/net/addr.rs
@@ -0,0 +1,318 @@
+use std::future;
+use std::io;
+use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr, SocketAddrV4, SocketAddrV6};
+
+/// Converts or resolves without blocking to one or more `SocketAddr` values.
+///
+/// # DNS
+///
+/// Implementations of `ToSocketAddrs` for string types require a DNS lookup.
+///
+/// # Calling
+///
+/// Currently, this trait is only used as an argument to Tokio functions that
+/// need to reference a target socket address. To perform a `SocketAddr`
+/// conversion directly, use [`lookup_host()`](super::lookup_host()).
+///
+/// This trait is sealed and is intended to be opaque. The details of the trait
+/// will change. Stabilization is pending enhancements to the Rust language.
+pub trait ToSocketAddrs: sealed::ToSocketAddrsPriv {}
+
+type ReadyFuture<T> = future::Ready<io::Result<T>>;
+
+cfg_net! {
+    pub(crate) fn to_socket_addrs<T>(arg: T) -> T::Future
+    where
+        T: ToSocketAddrs,
+    {
+        arg.to_socket_addrs(sealed::Internal)
+    }
+}
+
+// ===== impl &impl ToSocketAddrs =====
+
+impl<T: ToSocketAddrs + ?Sized> ToSocketAddrs for &T {}
+
+impl<T> sealed::ToSocketAddrsPriv for &T
+where
+    T: sealed::ToSocketAddrsPriv + ?Sized,
+{
+    type Iter = T::Iter;
+    type Future = T::Future;
+
+    fn to_socket_addrs(&self, _: sealed::Internal) -> Self::Future {
+        (**self).to_socket_addrs(sealed::Internal)
+    }
+}
+
+// ===== impl SocketAddr =====
+
+impl ToSocketAddrs for SocketAddr {}
+
+impl sealed::ToSocketAddrsPriv for SocketAddr {
+    type Iter = std::option::IntoIter<SocketAddr>;
+    type Future = ReadyFuture<Self::Iter>;
+
+    fn to_socket_addrs(&self, _: sealed::Internal) -> Self::Future {
+        let iter = Some(*self).into_iter();
+        future::ready(Ok(iter))
+    }
+}
+
+// ===== impl SocketAddrV4 =====
+
+impl ToSocketAddrs for SocketAddrV4 {}
+
+impl sealed::ToSocketAddrsPriv for SocketAddrV4 {
+    type Iter = std::option::IntoIter<SocketAddr>;
+    type Future = ReadyFuture<Self::Iter>;
+
+    fn to_socket_addrs(&self, _: sealed::Internal) -> Self::Future {
+        SocketAddr::V4(*self).to_socket_addrs(sealed::Internal)
+    }
+}
+
+// ===== impl SocketAddrV6 =====
+
+impl ToSocketAddrs for SocketAddrV6 {}
+
+impl sealed::ToSocketAddrsPriv for SocketAddrV6 {
+    type Iter = std::option::IntoIter<SocketAddr>;
+    type Future = ReadyFuture<Self::Iter>;
+
+    fn to_socket_addrs(&self, _: sealed::Internal) -> Self::Future {
+        SocketAddr::V6(*self).to_socket_addrs(sealed::Internal)
+    }
+}
+
+// ===== impl (IpAddr, u16) =====
+
+impl ToSocketAddrs for (IpAddr, u16) {}
+
+impl sealed::ToSocketAddrsPriv for (IpAddr, u16) {
+    type Iter = std::option::IntoIter<SocketAddr>;
+    type Future = ReadyFuture<Self::Iter>;
+
+    fn to_socket_addrs(&self, _: sealed::Internal) -> Self::Future {
+        let iter = Some(SocketAddr::from(*self)).into_iter();
+        future::ready(Ok(iter))
+    }
+}
+
+// ===== impl (Ipv4Addr, u16) =====
+
+impl ToSocketAddrs for (Ipv4Addr, u16) {}
+
+impl sealed::ToSocketAddrsPriv for (Ipv4Addr, u16) {
+    type Iter = std::option::IntoIter<SocketAddr>;
+    type Future = ReadyFuture<Self::Iter>;
+
+    fn to_socket_addrs(&self, _: sealed::Internal) -> Self::Future {
+        let (ip, port) = *self;
+        SocketAddrV4::new(ip, port).to_socket_addrs(sealed::Internal)
+    }
+}
+
+// ===== impl (Ipv6Addr, u16) =====
+
+impl ToSocketAddrs for (Ipv6Addr, u16) {}
+
+impl sealed::ToSocketAddrsPriv for (Ipv6Addr, u16) {
+    type Iter = std::option::IntoIter<SocketAddr>;
+    type Future = ReadyFuture<Self::Iter>;
+
+    fn to_socket_addrs(&self, _: sealed::Internal) -> Self::Future {
+        let (ip, port) = *self;
+        SocketAddrV6::new(ip, port, 0, 0).to_socket_addrs(sealed::Internal)
+    }
+}
+
+// ===== impl &[SocketAddr] =====
+
+impl ToSocketAddrs for &[SocketAddr] {}
+
+impl sealed::ToSocketAddrsPriv for &[SocketAddr] {
+    type Iter = std::vec::IntoIter<SocketAddr>;
+    type Future = ReadyFuture<Self::Iter>;
+
+    fn to_socket_addrs(&self, _: sealed::Internal) -> Self::Future {
+        let iter = self.to_vec().into_iter();
+        future::ready(Ok(iter))
+    }
+}
+
+cfg_net! {
+    // ===== impl str =====
+
+    impl ToSocketAddrs for str {}
+
+    impl sealed::ToSocketAddrsPriv for str {
+        type Iter = sealed::OneOrMore;
+        type Future = sealed::MaybeReady;
+
+        fn to_socket_addrs(&self, _: sealed::Internal) -> Self::Future {
+            use crate::blocking::spawn_blocking;
+            use sealed::MaybeReady;
+
+            // First check if the input parses as a socket address
+            let res: Result<SocketAddr, _> = self.parse();
+
+            if let Ok(addr) = res {
+                return MaybeReady(sealed::State::Ready(Some(addr)));
+            }
+
+            // Run DNS lookup on the blocking pool
+            let s = self.to_owned();
+
+            MaybeReady(sealed::State::Blocking(spawn_blocking(move || {
+                std::net::ToSocketAddrs::to_socket_addrs(&s)
+            })))
+        }
+    }
+
+    // ===== impl (&str, u16) =====
+
+    impl ToSocketAddrs for (&str, u16) {}
+
+    impl sealed::ToSocketAddrsPriv for (&str, u16) {
+        type Iter = sealed::OneOrMore;
+        type Future = sealed::MaybeReady;
+
+        fn to_socket_addrs(&self, _: sealed::Internal) -> Self::Future {
+            use crate::blocking::spawn_blocking;
+            use sealed::MaybeReady;
+
+            let (host, port) = *self;
+
+            // try to parse the host as a regular IP address first
+            if let Ok(addr) = host.parse::<Ipv4Addr>() {
+                let addr = SocketAddrV4::new(addr, port);
+                let addr = SocketAddr::V4(addr);
+
+                return MaybeReady(sealed::State::Ready(Some(addr)));
+            }
+
+            if let Ok(addr) = host.parse::<Ipv6Addr>() {
+                let addr = SocketAddrV6::new(addr, port, 0, 0);
+                let addr = SocketAddr::V6(addr);
+
+                return MaybeReady(sealed::State::Ready(Some(addr)));
+            }
+
+            let host = host.to_owned();
+
+            MaybeReady(sealed::State::Blocking(spawn_blocking(move || {
+                std::net::ToSocketAddrs::to_socket_addrs(&(&host[..], port))
+            })))
+        }
+    }
+
+    // ===== impl (String, u16) =====
+
+    impl ToSocketAddrs for (String, u16) {}
+
+    impl sealed::ToSocketAddrsPriv for (String, u16) {
+        type Iter = sealed::OneOrMore;
+        type Future = sealed::MaybeReady;
+
+        fn to_socket_addrs(&self, _: sealed::Internal) -> Self::Future {
+            (self.0.as_str(), self.1).to_socket_addrs(sealed::Internal)
+        }
+    }
+
+    // ===== impl String =====
+
+    impl ToSocketAddrs for String {}
+
+    impl sealed::ToSocketAddrsPriv for String {
+        type Iter = <str as sealed::ToSocketAddrsPriv>::Iter;
+        type Future = <str as sealed::ToSocketAddrsPriv>::Future;
+
+        fn to_socket_addrs(&self, _: sealed::Internal) -> Self::Future {
+            (&self[..]).to_socket_addrs(sealed::Internal)
+        }
+    }
+}
+
+pub(crate) mod sealed {
+    //! The contents of this trait are intended to remain private and __not__
+    //! part of the `ToSocketAddrs` public API. The details will change over
+    //! time.
+
+    use std::future::Future;
+    use std::io;
+    use std::net::SocketAddr;
+
+    #[doc(hidden)]
+    pub trait ToSocketAddrsPriv {
+        type Iter: Iterator<Item = SocketAddr> + Send + 'static;
+        type Future: Future<Output = io::Result<Self::Iter>> + Send + 'static;
+
+        fn to_socket_addrs(&self, internal: Internal) -> Self::Future;
+    }
+
+    #[allow(missing_debug_implementations)]
+    pub struct Internal;
+
+    cfg_net! {
+        use crate::blocking::JoinHandle;
+
+        use std::option;
+        use std::pin::Pin;
+        use std::task::{Context, Poll};
+        use std::vec;
+
+        #[doc(hidden)]
+        #[derive(Debug)]
+        pub struct MaybeReady(pub(super) State);
+
+        #[derive(Debug)]
+        pub(super) enum State {
+            Ready(Option<SocketAddr>),
+            Blocking(JoinHandle<io::Result<vec::IntoIter<SocketAddr>>>),
+        }
+
+        #[doc(hidden)]
+        #[derive(Debug)]
+        pub enum OneOrMore {
+            One(option::IntoIter<SocketAddr>),
+            More(vec::IntoIter<SocketAddr>),
+        }
+
+        impl Future for MaybeReady {
+            type Output = io::Result<OneOrMore>;
+
+            fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+                match self.0 {
+                    State::Ready(ref mut i) => {
+                        let iter = OneOrMore::One(i.take().into_iter());
+                        Poll::Ready(Ok(iter))
+                    }
+                    State::Blocking(ref mut rx) => {
+                        let res = ready!(Pin::new(rx).poll(cx))?.map(OneOrMore::More);
+
+                        Poll::Ready(res)
+                    }
+                }
+            }
+        }
+
+        impl Iterator for OneOrMore {
+            type Item = SocketAddr;
+
+            fn next(&mut self) -> Option<Self::Item> {
+                match self {
+                    OneOrMore::One(i) => i.next(),
+                    OneOrMore::More(i) => i.next(),
+                }
+            }
+
+            fn size_hint(&self) -> (usize, Option<usize>) {
+                match self {
+                    OneOrMore::One(i) => i.size_hint(),
+                    OneOrMore::More(i) => i.size_hint(),
+                }
+            }
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/net/lookup_host.rs b/third_party/rust/tokio/src/net/lookup_host.rs
new file mode 100644
index 0000000000..28861849e4
--- /dev/null
+++ b/third_party/rust/tokio/src/net/lookup_host.rs
@@ -0,0 +1,38 @@
+cfg_net! {
+    use crate::net::addr::{self, ToSocketAddrs};
+
+    use std::io;
+    use std::net::SocketAddr;
+
+    /// Performs a DNS resolution.
+    ///
+    /// The returned iterator may not actually yield any values depending on the
+    /// outcome of any resolution performed.
+    ///
+    /// This API is not intended to cover all DNS use cases. Anything beyond the
+    /// basic use case should be done with a specialized library.
+    ///
+    /// # Examples
+    ///
+    /// To resolve a DNS entry:
+    ///
+    /// ```no_run
+    /// use tokio::net;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     for addr in net::lookup_host("localhost:3000").await? {
+    ///         println!("socket address is {}", addr);
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn lookup_host<T>(host: T) -> io::Result<impl Iterator<Item = SocketAddr>>
+    where
+        T: ToSocketAddrs
+    {
+        addr::to_socket_addrs(host).await
+    }
+}
diff --git a/third_party/rust/tokio/src/net/mod.rs b/third_party/rust/tokio/src/net/mod.rs
new file mode 100644
index 0000000000..0b8c1ecd19
--- /dev/null
+++ b/third_party/rust/tokio/src/net/mod.rs
@@ -0,0 +1,52 @@
+#![cfg(not(loom))]
+
+//! TCP/UDP/Unix bindings for `tokio`.
+//!
+//! This module contains the TCP/UDP/Unix networking types, similar to the standard
+//! library, which can be used to implement networking protocols.
+//!
+//! # Organization
+//!
+//! * [`TcpListener`] and [`TcpStream`] provide functionality for communication over TCP
+//! * [`UdpSocket`] provides functionality for communication over UDP
+//! * [`UnixListener`] and [`UnixStream`] provide functionality for communication over a
+//! Unix Domain Stream Socket **(available on Unix only)**
+//! * [`UnixDatagram`] provides functionality for communication
+//! over Unix Domain Datagram Socket **(available on Unix only)**
+
+//!
+//! [`TcpListener`]: TcpListener
+//! [`TcpStream`]: TcpStream
+//! [`UdpSocket`]: UdpSocket
+//! [`UnixListener`]: UnixListener
+//! [`UnixStream`]: UnixStream
+//! [`UnixDatagram`]: UnixDatagram
+
+mod addr;
+#[cfg(feature = "net")]
+pub(crate) use addr::to_socket_addrs;
+pub use addr::ToSocketAddrs;
+
+cfg_net! {
+    mod lookup_host;
+    pub use lookup_host::lookup_host;
+
+    pub mod tcp;
+    pub use tcp::listener::TcpListener;
+    pub use tcp::socket::TcpSocket;
+    pub use tcp::stream::TcpStream;
+
+    mod udp;
+    pub use udp::UdpSocket;
+}
+
+cfg_net_unix! {
+    pub mod unix;
+    pub use unix::datagram::socket::UnixDatagram;
+    pub use unix::listener::UnixListener;
+    pub use unix::stream::UnixStream;
+}
+
+cfg_net_windows! {
+    pub mod windows;
+}
diff --git a/third_party/rust/tokio/src/net/tcp/listener.rs b/third_party/rust/tokio/src/net/tcp/listener.rs
new file mode 100644
index 0000000000..8aecb21aaa
--- /dev/null
+++ b/third_party/rust/tokio/src/net/tcp/listener.rs
@@ -0,0 +1,397 @@
+use crate::io::{Interest, PollEvented};
+use crate::net::tcp::TcpStream;
+use crate::net::{to_socket_addrs, ToSocketAddrs};
+
+use std::convert::TryFrom;
+use std::fmt;
+use std::io;
+use std::net::{self, SocketAddr};
+use std::task::{Context, Poll};
+
+cfg_net! {
+    /// A TCP socket server, listening for connections.
+    ///
+    /// You can accept a new connection by using the [`accept`](`TcpListener::accept`)
+    /// method.
+    ///
+    /// A `TcpListener` can be turned into a `Stream` with [`TcpListenerStream`].
+    ///
+    /// [`TcpListenerStream`]: https://docs.rs/tokio-stream/0.1/tokio_stream/wrappers/struct.TcpListenerStream.html
+    ///
+    /// # Errors
+    ///
+    /// Note that accepting a connection can lead to various errors and not all
+    /// of them are necessarily fatal ‒ for example having too many open file
+    /// descriptors or the other side closing the connection while it waits in
+    /// an accept queue. These would terminate the stream if not handled in any
+    /// way.
+    ///
+    /// # Examples
+    ///
+    /// Using `accept`:
+    /// ```no_run
+    /// use tokio::net::TcpListener;
+    ///
+    /// use std::io;
+    ///
+    /// async fn process_socket<T>(socket: T) {
+    ///     # drop(socket);
+    ///     // do work with socket here
+    /// }
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let listener = TcpListener::bind("127.0.0.1:8080").await?;
+    ///
+    ///     loop {
+    ///         let (socket, _) = listener.accept().await?;
+    ///         process_socket(socket).await;
+    ///     }
+    /// }
+    /// ```
+    pub struct TcpListener {
+        io: PollEvented<mio::net::TcpListener>,
+    }
+}
+
+impl TcpListener {
+    /// Creates a new TcpListener, which will be bound to the specified address.
+    ///
+    /// The returned listener is ready for accepting connections.
+    ///
+    /// Binding with a port number of 0 will request that the OS assigns a port
+    /// to this listener. The port allocated can be queried via the `local_addr`
+    /// method.
+    ///
+    /// The address type can be any implementor of the [`ToSocketAddrs`] trait.
+    /// If `addr` yields multiple addresses, bind will be attempted with each of
+    /// the addresses until one succeeds and returns the listener. If none of
+    /// the addresses succeed in creating a listener, the error returned from
+    /// the last attempt (the last address) is returned.
+    ///
+    /// This function sets the `SO_REUSEADDR` option on the socket.
+    ///
+    /// To configure the socket before binding, you can use the [`TcpSocket`]
+    /// type.
+    ///
+    /// [`ToSocketAddrs`]: trait@crate::net::ToSocketAddrs
+    /// [`TcpSocket`]: struct@crate::net::TcpSocket
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpListener;
+    ///
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let listener = TcpListener::bind("127.0.0.1:2345").await?;
+    ///
+    ///     // use the listener
+    ///
+    ///     # let _ = listener;
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn bind<A: ToSocketAddrs>(addr: A) -> io::Result<TcpListener> {
+        let addrs = to_socket_addrs(addr).await?;
+
+        let mut last_err = None;
+
+        for addr in addrs {
+            match TcpListener::bind_addr(addr) {
+                Ok(listener) => return Ok(listener),
+                Err(e) => last_err = Some(e),
+            }
+        }
+
+        Err(last_err.unwrap_or_else(|| {
+            io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "could not resolve to any address",
+            )
+        }))
+    }
+
+    fn bind_addr(addr: SocketAddr) -> io::Result<TcpListener> {
+        let listener = mio::net::TcpListener::bind(addr)?;
+        TcpListener::new(listener)
+    }
+
+    /// Accepts a new incoming connection from this listener.
+    ///
+    /// This function will yield once a new TCP connection is established. When
+    /// established, the corresponding [`TcpStream`] and the remote peer's
+    /// address will be returned.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. If the method is used as the event in a
+    /// [`tokio::select!`](crate::select) statement and some other branch
+    /// completes first, then it is guaranteed that no new connections were
+    /// accepted by this method.
+    ///
+    /// [`TcpStream`]: struct@crate::net::TcpStream
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpListener;
+    ///
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let listener = TcpListener::bind("127.0.0.1:8080").await?;
+    ///
+    ///     match listener.accept().await {
+    ///         Ok((_socket, addr)) => println!("new client: {:?}", addr),
+    ///         Err(e) => println!("couldn't get client: {:?}", e),
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn accept(&self) -> io::Result<(TcpStream, SocketAddr)> {
+        let (mio, addr) = self
+            .io
+            .registration()
+            .async_io(Interest::READABLE, || self.io.accept())
+            .await?;
+
+        let stream = TcpStream::new(mio)?;
+        Ok((stream, addr))
+    }
+
+    /// Polls to accept a new incoming connection to this listener.
+    ///
+    /// If there is no connection to accept, `Poll::Pending` is returned and the
+    /// current task will be notified by a waker.  Note that on multiple calls
+    /// to `poll_accept`, only the `Waker` from the `Context` passed to the most
+    /// recent call is scheduled to receive a wakeup.
+    pub fn poll_accept(&self, cx: &mut Context<'_>) -> Poll<io::Result<(TcpStream, SocketAddr)>> {
+        loop {
+            let ev = ready!(self.io.registration().poll_read_ready(cx))?;
+
+            match self.io.accept() {
+                Ok((io, addr)) => {
+                    let io = TcpStream::new(io)?;
+                    return Poll::Ready(Ok((io, addr)));
+                }
+                Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+                    self.io.registration().clear_readiness(ev);
+                }
+                Err(e) => return Poll::Ready(Err(e)),
+            }
+        }
+    }
+
+    /// Creates new `TcpListener` from a `std::net::TcpListener`.
+    ///
+    /// This function is intended to be used to wrap a TCP listener from the
+    /// standard library in the Tokio equivalent. The conversion assumes nothing
+    /// about the underlying listener; it is left up to the user to set it in
+    /// non-blocking mode.
+    ///
+    /// This API is typically paired with the `socket2` crate and the `Socket`
+    /// type to build up and customize a listener before it's shipped off to the
+    /// backing event loop. This allows configuration of options like
+    /// `SO_REUSEPORT`, binding to multiple addresses, etc.
+    ///
+    /// # Examples
+    ///
+    /// ```rust,no_run
+    /// use std::error::Error;
+    /// use tokio::net::TcpListener;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let std_listener = std::net::TcpListener::bind("127.0.0.1:0")?;
+    ///     std_listener.set_nonblocking(true)?;
+    ///     let listener = TcpListener::from_std(std_listener)?;
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// This function panics if thread-local runtime is not set.
+    ///
+    /// The runtime is usually set implicitly when this function is called
+    /// from a future driven by a tokio runtime, otherwise runtime can be set
+    /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter) function.
+    pub fn from_std(listener: net::TcpListener) -> io::Result<TcpListener> {
+        let io = mio::net::TcpListener::from_std(listener);
+        let io = PollEvented::new(io)?;
+        Ok(TcpListener { io })
+    }
+
+    /// Turns a [`tokio::net::TcpListener`] into a [`std::net::TcpListener`].
+    ///
+    /// The returned [`std::net::TcpListener`] will have nonblocking mode set as
+    /// `true`.  Use [`set_nonblocking`] to change the blocking mode if needed.
+    ///
+    /// # Examples
+    ///
+    /// ```rust,no_run
+    /// use std::error::Error;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let tokio_listener = tokio::net::TcpListener::bind("127.0.0.1:0").await?;
+    ///     let std_listener = tokio_listener.into_std()?;
+    ///     std_listener.set_nonblocking(false)?;
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// [`tokio::net::TcpListener`]: TcpListener
+    /// [`std::net::TcpListener`]: std::net::TcpListener
+    /// [`set_nonblocking`]: fn@std::net::TcpListener::set_nonblocking
+    pub fn into_std(self) -> io::Result<std::net::TcpListener> {
+        #[cfg(unix)]
+        {
+            use std::os::unix::io::{FromRawFd, IntoRawFd};
+            self.io
+                .into_inner()
+                .map(|io| io.into_raw_fd())
+                .map(|raw_fd| unsafe { std::net::TcpListener::from_raw_fd(raw_fd) })
+        }
+
+        #[cfg(windows)]
+        {
+            use std::os::windows::io::{FromRawSocket, IntoRawSocket};
+            self.io
+                .into_inner()
+                .map(|io| io.into_raw_socket())
+                .map(|raw_socket| unsafe { std::net::TcpListener::from_raw_socket(raw_socket) })
+        }
+    }
+
+    pub(crate) fn new(listener: mio::net::TcpListener) -> io::Result<TcpListener> {
+        let io = PollEvented::new(listener)?;
+        Ok(TcpListener { io })
+    }
+
+    /// Returns the local address that this listener is bound to.
+    ///
+    /// This can be useful, for example, when binding to port 0 to figure out
+    /// which port was actually bound.
+    ///
+    /// # Examples
+    ///
+    /// ```rust,no_run
+    /// use tokio::net::TcpListener;
+    ///
+    /// use std::io;
+    /// use std::net::{Ipv4Addr, SocketAddr, SocketAddrV4};
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let listener = TcpListener::bind("127.0.0.1:8080").await?;
+    ///
+    ///     assert_eq!(listener.local_addr()?,
+    ///                SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(127, 0, 0, 1), 8080)));
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn local_addr(&self) -> io::Result<SocketAddr> {
+        self.io.local_addr()
+    }
+
+    /// Gets the value of the `IP_TTL` option for this socket.
+    ///
+    /// For more information about this option, see [`set_ttl`].
+    ///
+    /// [`set_ttl`]: method@Self::set_ttl
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpListener;
+    ///
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///    let listener = TcpListener::bind("127.0.0.1:0").await?;
+    ///
+    ///    listener.set_ttl(100).expect("could not set TTL");
+    ///    assert_eq!(listener.ttl()?, 100);
+    ///
+    ///    Ok(())
+    /// }
+    /// ```
+    pub fn ttl(&self) -> io::Result<u32> {
+        self.io.ttl()
+    }
+
+    /// Sets the value for the `IP_TTL` option on this socket.
+    ///
+    /// This value sets the time-to-live field that is used in every packet sent
+    /// from this socket.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpListener;
+    ///
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let listener = TcpListener::bind("127.0.0.1:0").await?;
+    ///
+    ///     listener.set_ttl(100).expect("could not set TTL");
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn set_ttl(&self, ttl: u32) -> io::Result<()> {
+        self.io.set_ttl(ttl)
+    }
+}
+
+impl TryFrom<net::TcpListener> for TcpListener {
+    type Error = io::Error;
+
+    /// Consumes stream, returning the tokio I/O object.
+    ///
+    /// This is equivalent to
+    /// [`TcpListener::from_std(stream)`](TcpListener::from_std).
+    fn try_from(stream: net::TcpListener) -> Result<Self, Self::Error> {
+        Self::from_std(stream)
+    }
+}
+
+impl fmt::Debug for TcpListener {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.io.fmt(f)
+    }
+}
+
+#[cfg(unix)]
+mod sys {
+    use super::TcpListener;
+    use std::os::unix::prelude::*;
+
+    impl AsRawFd for TcpListener {
+        fn as_raw_fd(&self) -> RawFd {
+            self.io.as_raw_fd()
+        }
+    }
+}
+
+#[cfg(windows)]
+mod sys {
+    use super::TcpListener;
+    use std::os::windows::prelude::*;
+
+    impl AsRawSocket for TcpListener {
+        fn as_raw_socket(&self) -> RawSocket {
+            self.io.as_raw_socket()
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/net/tcp/mod.rs b/third_party/rust/tokio/src/net/tcp/mod.rs
new file mode 100644
index 0000000000..cb8a8b238b
--- /dev/null
+++ b/third_party/rust/tokio/src/net/tcp/mod.rs
@@ -0,0 +1,14 @@
+//! TCP utility types.
+
+pub(crate) mod listener;
+
+pub(crate) mod socket;
+
+mod split;
+pub use split::{ReadHalf, WriteHalf};
+
+mod split_owned;
+pub use split_owned::{OwnedReadHalf, OwnedWriteHalf, ReuniteError};
+
+pub(crate) mod stream;
+pub(crate) use stream::TcpStream;
diff --git a/third_party/rust/tokio/src/net/tcp/socket.rs b/third_party/rust/tokio/src/net/tcp/socket.rs
new file mode 100644
index 0000000000..171e240189
--- /dev/null
+++ b/third_party/rust/tokio/src/net/tcp/socket.rs
@@ -0,0 +1,690 @@
+use crate::net::{TcpListener, TcpStream};
+
+use std::fmt;
+use std::io;
+use std::net::SocketAddr;
+
+#[cfg(unix)]
+use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
+#[cfg(windows)]
+use std::os::windows::io::{AsRawSocket, FromRawSocket, IntoRawSocket, RawSocket};
+use std::time::Duration;
+
+cfg_net! {
+    /// A TCP socket that has not yet been converted to a `TcpStream` or
+    /// `TcpListener`.
+    ///
+    /// `TcpSocket` wraps an operating system socket and enables the caller to
+    /// configure the socket before establishing a TCP connection or accepting
+    /// inbound connections. The caller is able to set socket option and explicitly
+    /// bind the socket with a socket address.
+    ///
+    /// The underlying socket is closed when the `TcpSocket` value is dropped.
+    ///
+    /// `TcpSocket` should only be used directly if the default configuration used
+    /// by `TcpStream::connect` and `TcpListener::bind` does not meet the required
+    /// use case.
+    ///
+    /// Calling `TcpStream::connect("127.0.0.1:8080")` is equivalent to:
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpSocket;
+    ///
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let addr = "127.0.0.1:8080".parse().unwrap();
+    ///
+    ///     let socket = TcpSocket::new_v4()?;
+    ///     let stream = socket.connect(addr).await?;
+    /// # drop(stream);
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// Calling `TcpListener::bind("127.0.0.1:8080")` is equivalent to:
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpSocket;
+    ///
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let addr = "127.0.0.1:8080".parse().unwrap();
+    ///
+    ///     let socket = TcpSocket::new_v4()?;
+    ///     // On platforms with Berkeley-derived sockets, this allows to quickly
+    ///     // rebind a socket, without needing to wait for the OS to clean up the
+    ///     // previous one.
+    ///     //
+    ///     // On Windows, this allows rebinding sockets which are actively in use,
+    ///     // which allows “socket hijacking”, so we explicitly don't set it here.
+    ///     // https://docs.microsoft.com/en-us/windows/win32/winsock/using-so-reuseaddr-and-so-exclusiveaddruse
+    ///     socket.set_reuseaddr(true)?;
+    ///     socket.bind(addr)?;
+    ///
+    ///     let listener = socket.listen(1024)?;
+    /// # drop(listener);
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// Setting socket options not explicitly provided by `TcpSocket` may be done by
+    /// accessing the `RawFd`/`RawSocket` using [`AsRawFd`]/[`AsRawSocket`] and
+    /// setting the option with a crate like [`socket2`].
+    ///
+    /// [`RawFd`]: https://doc.rust-lang.org/std/os/unix/io/type.RawFd.html
+    /// [`RawSocket`]: https://doc.rust-lang.org/std/os/windows/io/type.RawSocket.html
+    /// [`AsRawFd`]: https://doc.rust-lang.org/std/os/unix/io/trait.AsRawFd.html
+    /// [`AsRawSocket`]: https://doc.rust-lang.org/std/os/windows/io/trait.AsRawSocket.html
+    /// [`socket2`]: https://docs.rs/socket2/
+    #[cfg_attr(docsrs, doc(alias = "connect_std"))]
+    pub struct TcpSocket {
+        inner: socket2::Socket,
+    }
+}
+
+impl TcpSocket {
+    /// Creates a new socket configured for IPv4.
+    ///
+    /// Calls `socket(2)` with `AF_INET` and `SOCK_STREAM`.
+    ///
+    /// # Returns
+    ///
+    /// On success, the newly created `TcpSocket` is returned. If an error is
+    /// encountered, it is returned instead.
+    ///
+    /// # Examples
+    ///
+    /// Create a new IPv4 socket and start listening.
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpSocket;
+    ///
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let addr = "127.0.0.1:8080".parse().unwrap();
+    ///     let socket = TcpSocket::new_v4()?;
+    ///     socket.bind(addr)?;
+    ///
+    ///     let listener = socket.listen(128)?;
+    /// # drop(listener);
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn new_v4() -> io::Result<TcpSocket> {
+        TcpSocket::new(socket2::Domain::IPV4)
+    }
+
+    /// Creates a new socket configured for IPv6.
+    ///
+    /// Calls `socket(2)` with `AF_INET6` and `SOCK_STREAM`.
+    ///
+    /// # Returns
+    ///
+    /// On success, the newly created `TcpSocket` is returned. If an error is
+    /// encountered, it is returned instead.
+    ///
+    /// # Examples
+    ///
+    /// Create a new IPv6 socket and start listening.
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpSocket;
+    ///
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let addr = "[::1]:8080".parse().unwrap();
+    ///     let socket = TcpSocket::new_v6()?;
+    ///     socket.bind(addr)?;
+    ///
+    ///     let listener = socket.listen(128)?;
+    /// # drop(listener);
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn new_v6() -> io::Result<TcpSocket> {
+        TcpSocket::new(socket2::Domain::IPV6)
+    }
+
+    fn new(domain: socket2::Domain) -> io::Result<TcpSocket> {
+        let ty = socket2::Type::STREAM;
+        #[cfg(any(
+            target_os = "android",
+            target_os = "dragonfly",
+            target_os = "freebsd",
+            target_os = "fuchsia",
+            target_os = "illumos",
+            target_os = "linux",
+            target_os = "netbsd",
+            target_os = "openbsd"
+        ))]
+        let ty = ty.nonblocking();
+        let inner = socket2::Socket::new(domain, ty, Some(socket2::Protocol::TCP))?;
+        #[cfg(not(any(
+            target_os = "android",
+            target_os = "dragonfly",
+            target_os = "freebsd",
+            target_os = "fuchsia",
+            target_os = "illumos",
+            target_os = "linux",
+            target_os = "netbsd",
+            target_os = "openbsd"
+        )))]
+        inner.set_nonblocking(true)?;
+        Ok(TcpSocket { inner })
+    }
+
+    /// Allows the socket to bind to an in-use address.
+    ///
+    /// Behavior is platform specific. Refer to the target platform's
+    /// documentation for more details.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpSocket;
+    ///
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let addr = "127.0.0.1:8080".parse().unwrap();
+    ///
+    ///     let socket = TcpSocket::new_v4()?;
+    ///     socket.set_reuseaddr(true)?;
+    ///     socket.bind(addr)?;
+    ///
+    ///     let listener = socket.listen(1024)?;
+    /// # drop(listener);
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn set_reuseaddr(&self, reuseaddr: bool) -> io::Result<()> {
+        self.inner.set_reuse_address(reuseaddr)
+    }
+
+    /// Retrieves the value set for `SO_REUSEADDR` on this socket.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpSocket;
+    ///
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let addr = "127.0.0.1:8080".parse().unwrap();
+    ///
+    ///     let socket = TcpSocket::new_v4()?;
+    ///     socket.set_reuseaddr(true)?;
+    ///     assert!(socket.reuseaddr().unwrap());
+    ///     socket.bind(addr)?;
+    ///
+    ///     let listener = socket.listen(1024)?;
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn reuseaddr(&self) -> io::Result<bool> {
+        self.inner.reuse_address()
+    }
+
+    /// Allows the socket to bind to an in-use port. Only available for unix systems
+    /// (excluding Solaris & Illumos).
+    ///
+    /// Behavior is platform specific. Refer to the target platform's
+    /// documentation for more details.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpSocket;
+    ///
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let addr = "127.0.0.1:8080".parse().unwrap();
+    ///
+    ///     let socket = TcpSocket::new_v4()?;
+    ///     socket.set_reuseport(true)?;
+    ///     socket.bind(addr)?;
+    ///
+    ///     let listener = socket.listen(1024)?;
+    ///     Ok(())
+    /// }
+    /// ```
+    #[cfg(all(unix, not(target_os = "solaris"), not(target_os = "illumos")))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(all(unix, not(target_os = "solaris"), not(target_os = "illumos"))))
+    )]
+    pub fn set_reuseport(&self, reuseport: bool) -> io::Result<()> {
+        self.inner.set_reuse_port(reuseport)
+    }
+
+    /// Allows the socket to bind to an in-use port. Only available for unix systems
+    /// (excluding Solaris & Illumos).
+    ///
+    /// Behavior is platform specific. Refer to the target platform's
+    /// documentation for more details.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpSocket;
+    ///
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let addr = "127.0.0.1:8080".parse().unwrap();
+    ///
+    ///     let socket = TcpSocket::new_v4()?;
+    ///     socket.set_reuseport(true)?;
+    ///     assert!(socket.reuseport().unwrap());
+    ///     socket.bind(addr)?;
+    ///
+    ///     let listener = socket.listen(1024)?;
+    ///     Ok(())
+    /// }
+    /// ```
+    #[cfg(all(unix, not(target_os = "solaris"), not(target_os = "illumos")))]
+    #[cfg_attr(
+        docsrs,
+        doc(cfg(all(unix, not(target_os = "solaris"), not(target_os = "illumos"))))
+    )]
+    pub fn reuseport(&self) -> io::Result<bool> {
+        self.inner.reuse_port()
+    }
+
+    /// Sets the size of the TCP send buffer on this socket.
+    ///
+    /// On most operating systems, this sets the `SO_SNDBUF` socket option.
+    pub fn set_send_buffer_size(&self, size: u32) -> io::Result<()> {
+        self.inner.set_send_buffer_size(size as usize)
+    }
+
+    /// Returns the size of the TCP send buffer for this socket.
+    ///
+    /// On most operating systems, this is the value of the `SO_SNDBUF` socket
+    /// option.
+    ///
+    /// Note that if [`set_send_buffer_size`] has been called on this socket
+    /// previously, the value returned by this function may not be the same as
+    /// the argument provided to `set_send_buffer_size`. This is for the
+    /// following reasons:
+    ///
+    /// * Most operating systems have minimum and maximum allowed sizes for the
+    ///   send buffer, and will clamp the provided value if it is below the
+    ///   minimum or above the maximum. The minimum and maximum buffer sizes are
+    ///   OS-dependent.
+    /// * Linux will double the buffer size to account for internal bookkeeping
+    ///   data, and returns the doubled value from `getsockopt(2)`. As per `man
+    ///   7 socket`:
+    ///   > Sets or gets the maximum socket send buffer in bytes. The
+    ///   > kernel doubles this value (to allow space for bookkeeping
+    ///   > overhead) when it is set using `setsockopt(2)`, and this doubled
+    ///   > value is returned by `getsockopt(2)`.
+    ///
+    /// [`set_send_buffer_size`]: #method.set_send_buffer_size
+    pub fn send_buffer_size(&self) -> io::Result<u32> {
+        self.inner.send_buffer_size().map(|n| n as u32)
+    }
+
+    /// Sets the size of the TCP receive buffer on this socket.
+    ///
+    /// On most operating systems, this sets the `SO_RCVBUF` socket option.
+    pub fn set_recv_buffer_size(&self, size: u32) -> io::Result<()> {
+        self.inner.set_recv_buffer_size(size as usize)
+    }
+
+    /// Returns the size of the TCP receive buffer for this socket.
+    ///
+    /// On most operating systems, this is the value of the `SO_RCVBUF` socket
+    /// option.
+    ///
+    /// Note that if [`set_recv_buffer_size`] has been called on this socket
+    /// previously, the value returned by this function may not be the same as
+    /// the argument provided to `set_send_buffer_size`. This is for the
+    /// following reasons:
+    ///
+    /// * Most operating systems have minimum and maximum allowed sizes for the
+    ///   receive buffer, and will clamp the provided value if it is below the
+    ///   minimum or above the maximum. The minimum and maximum buffer sizes are
+    ///   OS-dependent.
+    /// * Linux will double the buffer size to account for internal bookkeeping
+    ///   data, and returns the doubled value from `getsockopt(2)`. As per `man
+    ///   7 socket`:
+    ///   > Sets or gets the maximum socket send buffer in bytes. The
+    ///   > kernel doubles this value (to allow space for bookkeeping
+    ///   > overhead) when it is set using `setsockopt(2)`, and this doubled
+    ///   > value is returned by `getsockopt(2)`.
+    ///
+    /// [`set_recv_buffer_size`]: #method.set_recv_buffer_size
+    pub fn recv_buffer_size(&self) -> io::Result<u32> {
+        self.inner.recv_buffer_size().map(|n| n as u32)
+    }
+
+    /// Sets the linger duration of this socket by setting the SO_LINGER option.
+    ///
+    /// This option controls the action taken when a stream has unsent messages and the stream is
+    /// closed. If SO_LINGER is set, the system shall block the process until it can transmit the
+    /// data or until the time expires.
+    ///
+    /// If SO_LINGER is not specified, and the socket is closed, the system handles the call in a
+    /// way that allows the process to continue as quickly as possible.
+    pub fn set_linger(&self, dur: Option<Duration>) -> io::Result<()> {
+        self.inner.set_linger(dur)
+    }
+
+    /// Reads the linger duration for this socket by getting the `SO_LINGER`
+    /// option.
+    ///
+    /// For more information about this option, see [`set_linger`].
+    ///
+    /// [`set_linger`]: TcpSocket::set_linger
+    pub fn linger(&self) -> io::Result<Option<Duration>> {
+        self.inner.linger()
+    }
+
+    /// Gets the local address of this socket.
+    ///
+    /// Will fail on windows if called before `bind`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpSocket;
+    ///
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let addr = "127.0.0.1:8080".parse().unwrap();
+    ///
+    ///     let socket = TcpSocket::new_v4()?;
+    ///     socket.bind(addr)?;
+    ///     assert_eq!(socket.local_addr().unwrap().to_string(), "127.0.0.1:8080");
+    ///     let listener = socket.listen(1024)?;
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn local_addr(&self) -> io::Result<SocketAddr> {
+        self.inner.local_addr().and_then(convert_address)
+    }
+
+    /// Binds the socket to the given address.
+    ///
+    /// This calls the `bind(2)` operating-system function. Behavior is
+    /// platform specific. Refer to the target platform's documentation for more
+    /// details.
+    ///
+    /// # Examples
+    ///
+    /// Bind a socket before listening.
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpSocket;
+    ///
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let addr = "127.0.0.1:8080".parse().unwrap();
+    ///
+    ///     let socket = TcpSocket::new_v4()?;
+    ///     socket.bind(addr)?;
+    ///
+    ///     let listener = socket.listen(1024)?;
+    /// # drop(listener);
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn bind(&self, addr: SocketAddr) -> io::Result<()> {
+        self.inner.bind(&addr.into())
+    }
+
+    /// Establishes a TCP connection with a peer at the specified socket address.
+    ///
+    /// The `TcpSocket` is consumed. Once the connection is established, a
+    /// connected [`TcpStream`] is returned. If the connection fails, the
+    /// encountered error is returned.
+    ///
+    /// [`TcpStream`]: TcpStream
+    ///
+    /// This calls the `connect(2)` operating-system function. Behavior is
+    /// platform specific. Refer to the target platform's documentation for more
+    /// details.
+    ///
+    /// # Examples
+    ///
+    /// Connecting to a peer.
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpSocket;
+    ///
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let addr = "127.0.0.1:8080".parse().unwrap();
+    ///
+    ///     let socket = TcpSocket::new_v4()?;
+    ///     let stream = socket.connect(addr).await?;
+    /// # drop(stream);
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn connect(self, addr: SocketAddr) -> io::Result<TcpStream> {
+        if let Err(err) = self.inner.connect(&addr.into()) {
+            #[cfg(unix)]
+            if err.raw_os_error() != Some(libc::EINPROGRESS) {
+                return Err(err);
+            }
+            #[cfg(windows)]
+            if err.kind() != io::ErrorKind::WouldBlock {
+                return Err(err);
+            }
+        }
+        #[cfg(unix)]
+        let mio = {
+            use std::os::unix::io::{FromRawFd, IntoRawFd};
+
+            let raw_fd = self.inner.into_raw_fd();
+            unsafe { mio::net::TcpStream::from_raw_fd(raw_fd) }
+        };
+
+        #[cfg(windows)]
+        let mio = {
+            use std::os::windows::io::{FromRawSocket, IntoRawSocket};
+
+            let raw_socket = self.inner.into_raw_socket();
+            unsafe { mio::net::TcpStream::from_raw_socket(raw_socket) }
+        };
+
+        TcpStream::connect_mio(mio).await
+    }
+
+    /// Converts the socket into a `TcpListener`.
+    ///
+    /// `backlog` defines the maximum number of pending connections are queued
+    /// by the operating system at any given time. Connection are removed from
+    /// the queue with [`TcpListener::accept`]. When the queue is full, the
+    /// operating-system will start rejecting connections.
+    ///
+    /// [`TcpListener::accept`]: TcpListener::accept
+    ///
+    /// This calls the `listen(2)` operating-system function, marking the socket
+    /// as a passive socket. Behavior is platform specific. Refer to the target
+    /// platform's documentation for more details.
+    ///
+    /// # Examples
+    ///
+    /// Create a `TcpListener`.
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpSocket;
+    ///
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let addr = "127.0.0.1:8080".parse().unwrap();
+    ///
+    ///     let socket = TcpSocket::new_v4()?;
+    ///     socket.bind(addr)?;
+    ///
+    ///     let listener = socket.listen(1024)?;
+    /// # drop(listener);
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn listen(self, backlog: u32) -> io::Result<TcpListener> {
+        self.inner.listen(backlog as i32)?;
+        #[cfg(unix)]
+        let mio = {
+            use std::os::unix::io::{FromRawFd, IntoRawFd};
+
+            let raw_fd = self.inner.into_raw_fd();
+            unsafe { mio::net::TcpListener::from_raw_fd(raw_fd) }
+        };
+
+        #[cfg(windows)]
+        let mio = {
+            use std::os::windows::io::{FromRawSocket, IntoRawSocket};
+
+            let raw_socket = self.inner.into_raw_socket();
+            unsafe { mio::net::TcpListener::from_raw_socket(raw_socket) }
+        };
+
+        TcpListener::new(mio)
+    }
+
+    /// Converts a [`std::net::TcpStream`] into a `TcpSocket`. The provided
+    /// socket must not have been connected prior to calling this function. This
+    /// function is typically used together with crates such as [`socket2`] to
+    /// configure socket options that are not available on `TcpSocket`.
+    ///
+    /// [`std::net::TcpStream`]: struct@std::net::TcpStream
+    /// [`socket2`]: https://docs.rs/socket2/
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::net::TcpSocket;
+    /// use socket2::{Domain, Socket, Type};
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> std::io::Result<()> {
+    ///
+    ///     let socket2_socket = Socket::new(Domain::IPV4, Type::STREAM, None)?;
+    ///
+    ///     let socket = TcpSocket::from_std_stream(socket2_socket.into());
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn from_std_stream(std_stream: std::net::TcpStream) -> TcpSocket {
+        #[cfg(unix)]
+        {
+            use std::os::unix::io::{FromRawFd, IntoRawFd};
+
+            let raw_fd = std_stream.into_raw_fd();
+            unsafe { TcpSocket::from_raw_fd(raw_fd) }
+        }
+
+        #[cfg(windows)]
+        {
+            use std::os::windows::io::{FromRawSocket, IntoRawSocket};
+
+            let raw_socket = std_stream.into_raw_socket();
+            unsafe { TcpSocket::from_raw_socket(raw_socket) }
+        }
+    }
+}
+
+fn convert_address(address: socket2::SockAddr) -> io::Result<SocketAddr> {
+    match address.as_socket() {
+        Some(address) => Ok(address),
+        None => Err(io::Error::new(
+            io::ErrorKind::InvalidInput,
+            "invalid address family (not IPv4 or IPv6)",
+        )),
+    }
+}
+
+impl fmt::Debug for TcpSocket {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.inner.fmt(fmt)
+    }
+}
+
+#[cfg(unix)]
+impl AsRawFd for TcpSocket {
+    fn as_raw_fd(&self) -> RawFd {
+        self.inner.as_raw_fd()
+    }
+}
+
+#[cfg(unix)]
+impl FromRawFd for TcpSocket {
+    /// Converts a `RawFd` to a `TcpSocket`.
+    ///
+    /// # Notes
+    ///
+    /// The caller is responsible for ensuring that the socket is in
+    /// non-blocking mode.
+    unsafe fn from_raw_fd(fd: RawFd) -> TcpSocket {
+        let inner = socket2::Socket::from_raw_fd(fd);
+        TcpSocket { inner }
+    }
+}
+
+#[cfg(unix)]
+impl IntoRawFd for TcpSocket {
+    fn into_raw_fd(self) -> RawFd {
+        self.inner.into_raw_fd()
+    }
+}
+
+#[cfg(windows)]
+impl IntoRawSocket for TcpSocket {
+    fn into_raw_socket(self) -> RawSocket {
+        self.inner.into_raw_socket()
+    }
+}
+
+#[cfg(windows)]
+impl AsRawSocket for TcpSocket {
+    fn as_raw_socket(&self) -> RawSocket {
+        self.inner.as_raw_socket()
+    }
+}
+
+#[cfg(windows)]
+impl FromRawSocket for TcpSocket {
+    /// Converts a `RawSocket` to a `TcpStream`.
+    ///
+    /// # Notes
+    ///
+    /// The caller is responsible for ensuring that the socket is in
+    /// non-blocking mode.
+    unsafe fn from_raw_socket(socket: RawSocket) -> TcpSocket {
+        let inner = socket2::Socket::from_raw_socket(socket);
+        TcpSocket { inner }
+    }
+}
diff --git a/third_party/rust/tokio/src/net/tcp/split.rs b/third_party/rust/tokio/src/net/tcp/split.rs
new file mode 100644
index 0000000000..0e02928495
--- /dev/null
+++ b/third_party/rust/tokio/src/net/tcp/split.rs
@@ -0,0 +1,401 @@
+//! `TcpStream` split support.
+//!
+//! A `TcpStream` can be split into a `ReadHalf` and a
+//! `WriteHalf` with the `TcpStream::split` method. `ReadHalf`
+//! implements `AsyncRead` while `WriteHalf` implements `AsyncWrite`.
+//!
+//! Compared to the generic split of `AsyncRead + AsyncWrite`, this specialized
+//! split has no associated overhead and enforces all invariants at the type
+//! level.
+
+use crate::future::poll_fn;
+use crate::io::{AsyncRead, AsyncWrite, Interest, ReadBuf, Ready};
+use crate::net::TcpStream;
+
+use std::io;
+use std::net::{Shutdown, SocketAddr};
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+cfg_io_util! {
+    use bytes::BufMut;
+}
+
+/// Borrowed read half of a [`TcpStream`], created by [`split`].
+///
+/// Reading from a `ReadHalf` is usually done using the convenience methods found on the
+/// [`AsyncReadExt`] trait.
+///
+/// [`TcpStream`]: TcpStream
+/// [`split`]: TcpStream::split()
+/// [`AsyncReadExt`]: trait@crate::io::AsyncReadExt
+#[derive(Debug)]
+pub struct ReadHalf<'a>(&'a TcpStream);
+
+/// Borrowed write half of a [`TcpStream`], created by [`split`].
+///
+/// Note that in the [`AsyncWrite`] implementation of this type, [`poll_shutdown`] will
+/// shut down the TCP stream in the write direction.
+///
+/// Writing to an `WriteHalf` is usually done using the convenience methods found
+/// on the [`AsyncWriteExt`] trait.
+///
+/// [`TcpStream`]: TcpStream
+/// [`split`]: TcpStream::split()
+/// [`AsyncWrite`]: trait@crate::io::AsyncWrite
+/// [`poll_shutdown`]: fn@crate::io::AsyncWrite::poll_shutdown
+/// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+#[derive(Debug)]
+pub struct WriteHalf<'a>(&'a TcpStream);
+
+pub(crate) fn split(stream: &mut TcpStream) -> (ReadHalf<'_>, WriteHalf<'_>) {
+    (ReadHalf(&*stream), WriteHalf(&*stream))
+}
+
+impl ReadHalf<'_> {
+    /// Attempts to receive data on the socket, without removing that data from
+    /// the queue, registering the current task for wakeup if data is not yet
+    /// available.
+    ///
+    /// Note that on multiple calls to `poll_peek` or `poll_read`, only the
+    /// `Waker` from the `Context` passed to the most recent call is scheduled
+    /// to receive a wakeup.
+    ///
+    /// See the [`TcpStream::poll_peek`] level documentation for more details.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::io::{self, ReadBuf};
+    /// use tokio::net::TcpStream;
+    ///
+    /// use futures::future::poll_fn;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let mut stream = TcpStream::connect("127.0.0.1:8000").await?;
+    ///     let (mut read_half, _) = stream.split();
+    ///     let mut buf = [0; 10];
+    ///     let mut buf = ReadBuf::new(&mut buf);
+    ///
+    ///     poll_fn(|cx| {
+    ///         read_half.poll_peek(cx, &mut buf)
+    ///     }).await?;
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// [`TcpStream::poll_peek`]: TcpStream::poll_peek
+    pub fn poll_peek(
+        &mut self,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<usize>> {
+        self.0.poll_peek(cx, buf)
+    }
+
+    /// Receives data on the socket from the remote address to which it is
+    /// connected, without removing that data from the queue. On success,
+    /// returns the number of bytes peeked.
+    ///
+    /// See the [`TcpStream::peek`] level documentation for more details.
+    ///
+    /// [`TcpStream::peek`]: TcpStream::peek
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    /// use tokio::io::AsyncReadExt;
+    /// use std::error::Error;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let mut stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///     let (mut read_half, _) = stream.split();
+    ///
+    ///     let mut b1 = [0; 10];
+    ///     let mut b2 = [0; 10];
+    ///
+    ///     // Peek at the data
+    ///     let n = read_half.peek(&mut b1).await?;
+    ///
+    ///     // Read the data
+    ///     assert_eq!(n, read_half.read(&mut b2[..n]).await?);
+    ///     assert_eq!(&b1[..n], &b2[..n]);
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// The [`read`] method is defined on the [`AsyncReadExt`] trait.
+    ///
+    /// [`read`]: fn@crate::io::AsyncReadExt::read
+    /// [`AsyncReadExt`]: trait@crate::io::AsyncReadExt
+    pub async fn peek(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        let mut buf = ReadBuf::new(buf);
+        poll_fn(|cx| self.poll_peek(cx, &mut buf)).await
+    }
+
+    /// Waits for any of the requested ready states.
+    ///
+    /// This function is usually paired with `try_read()` or `try_write()`. It
+    /// can be used to concurrently read / write to the same socket on a single
+    /// task without splitting the socket.
+    ///
+    /// This function is equivalent to [`TcpStream::ready`].
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read or write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    pub async fn ready(&self, interest: Interest) -> io::Result<Ready> {
+        self.0.ready(interest).await
+    }
+
+    /// Waits for the socket to become readable.
+    ///
+    /// This function is equivalent to `ready(Interest::READABLE)` and is usually
+    /// paired with `try_read()`.
+    ///
+    /// This function is also equivalent to [`TcpStream::ready`].
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    pub async fn readable(&self) -> io::Result<()> {
+        self.0.readable().await
+    }
+
+    /// Tries to read data from the stream into the provided buffer, returning how
+    /// many bytes were read.
+    ///
+    /// Receives any pending data from the socket but does not wait for new data
+    /// to arrive. On success, returns the number of bytes read. Because
+    /// `try_read()` is non-blocking, the buffer does not have to be stored by
+    /// the async task and can exist entirely on the stack.
+    ///
+    /// Usually, [`readable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`readable()`]: Self::readable()
+    /// [`ready()`]: Self::ready()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+    /// and will no longer yield data. If the stream is not ready to read data
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    pub fn try_read(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.0.try_read(buf)
+    }
+
+    /// Tries to read data from the stream into the provided buffers, returning
+    /// how many bytes were read.
+    ///
+    /// Data is copied to fill each buffer in order, with the final buffer
+    /// written to possibly being only partially filled. This method behaves
+    /// equivalently to a single call to [`try_read()`] with concatenated
+    /// buffers.
+    ///
+    /// Receives any pending data from the socket but does not wait for new data
+    /// to arrive. On success, returns the number of bytes read. Because
+    /// `try_read_vectored()` is non-blocking, the buffer does not have to be
+    /// stored by the async task and can exist entirely on the stack.
+    ///
+    /// Usually, [`readable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`try_read()`]: Self::try_read()
+    /// [`readable()`]: Self::readable()
+    /// [`ready()`]: Self::ready()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+    /// and will no longer yield data. If the stream is not ready to read data
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    pub fn try_read_vectored(&self, bufs: &mut [io::IoSliceMut<'_>]) -> io::Result<usize> {
+        self.0.try_read_vectored(bufs)
+    }
+
+    cfg_io_util! {
+        /// Tries to read data from the stream into the provided buffer, advancing the
+        /// buffer's internal cursor, returning how many bytes were read.
+        ///
+        /// Receives any pending data from the socket but does not wait for new data
+        /// to arrive. On success, returns the number of bytes read. Because
+        /// `try_read_buf()` is non-blocking, the buffer does not have to be stored by
+        /// the async task and can exist entirely on the stack.
+        ///
+        /// Usually, [`readable()`] or [`ready()`] is used with this function.
+        ///
+        /// [`readable()`]: Self::readable()
+        /// [`ready()`]: Self::ready()
+        ///
+        /// # Return
+        ///
+        /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+        /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+        /// and will no longer yield data. If the stream is not ready to read data
+        /// `Err(io::ErrorKind::WouldBlock)` is returned.
+        pub fn try_read_buf<B: BufMut>(&self, buf: &mut B) -> io::Result<usize> {
+            self.0.try_read_buf(buf)
+        }
+    }
+
+    /// Returns the remote address that this stream is connected to.
+    pub fn peer_addr(&self) -> io::Result<SocketAddr> {
+        self.0.peer_addr()
+    }
+
+    /// Returns the local address that this stream is bound to.
+    pub fn local_addr(&self) -> io::Result<SocketAddr> {
+        self.0.local_addr()
+    }
+}
+
+impl WriteHalf<'_> {
+    /// Waits for any of the requested ready states.
+    ///
+    /// This function is usually paired with `try_read()` or `try_write()`. It
+    /// can be used to concurrently read / write to the same socket on a single
+    /// task without splitting the socket.
+    ///
+    /// This function is equivalent to [`TcpStream::ready`].
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read or write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    pub async fn ready(&self, interest: Interest) -> io::Result<Ready> {
+        self.0.ready(interest).await
+    }
+
+    /// Waits for the socket to become writable.
+    ///
+    /// This function is equivalent to `ready(Interest::WRITABLE)` and is usually
+    /// paired with `try_write()`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    pub async fn writable(&self) -> io::Result<()> {
+        self.0.writable().await
+    }
+
+    /// Tries to write a buffer to the stream, returning how many bytes were
+    /// written.
+    ///
+    /// The function will attempt to write the entire contents of `buf`, but
+    /// only part of the buffer may be written.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// # Return
+    ///
+    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
+    /// number of bytes written. If the stream is not ready to write data,
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    pub fn try_write(&self, buf: &[u8]) -> io::Result<usize> {
+        self.0.try_write(buf)
+    }
+
+    /// Tries to write several buffers to the stream, returning how many bytes
+    /// were written.
+    ///
+    /// Data is written from each buffer in order, with the final buffer read
+    /// from possible being only partially consumed. This method behaves
+    /// equivalently to a single call to [`try_write()`] with concatenated
+    /// buffers.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// [`try_write()`]: Self::try_write()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
+    /// number of bytes written. If the stream is not ready to write data,
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    pub fn try_write_vectored(&self, bufs: &[io::IoSlice<'_>]) -> io::Result<usize> {
+        self.0.try_write_vectored(bufs)
+    }
+
+    /// Returns the remote address that this stream is connected to.
+    pub fn peer_addr(&self) -> io::Result<SocketAddr> {
+        self.0.peer_addr()
+    }
+
+    /// Returns the local address that this stream is bound to.
+    pub fn local_addr(&self) -> io::Result<SocketAddr> {
+        self.0.local_addr()
+    }
+}
+
+impl AsyncRead for ReadHalf<'_> {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        self.0.poll_read_priv(cx, buf)
+    }
+}
+
+impl AsyncWrite for WriteHalf<'_> {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.0.poll_write_priv(cx, buf)
+    }
+
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.0.poll_write_vectored_priv(cx, bufs)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        self.0.is_write_vectored()
+    }
+
+    #[inline]
+    fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        // tcp flush is a no-op
+        Poll::Ready(Ok(()))
+    }
+
+    // `poll_shutdown` on a write half shutdowns the stream in the "write" direction.
+    fn poll_shutdown(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.0.shutdown_std(Shutdown::Write).into()
+    }
+}
+
+impl AsRef<TcpStream> for ReadHalf<'_> {
+    fn as_ref(&self) -> &TcpStream {
+        self.0
+    }
+}
+
+impl AsRef<TcpStream> for WriteHalf<'_> {
+    fn as_ref(&self) -> &TcpStream {
+        self.0
+    }
+}
diff --git a/third_party/rust/tokio/src/net/tcp/split_owned.rs b/third_party/rust/tokio/src/net/tcp/split_owned.rs
new file mode 100644
index 0000000000..ef4e7b5361
--- /dev/null
+++ b/third_party/rust/tokio/src/net/tcp/split_owned.rs
@@ -0,0 +1,485 @@
+//! `TcpStream` owned split support.
+//!
+//! A `TcpStream` can be split into an `OwnedReadHalf` and a `OwnedWriteHalf`
+//! with the `TcpStream::into_split` method.  `OwnedReadHalf` implements
+//! `AsyncRead` while `OwnedWriteHalf` implements `AsyncWrite`.
+//!
+//! Compared to the generic split of `AsyncRead + AsyncWrite`, this specialized
+//! split has no associated overhead and enforces all invariants at the type
+//! level.
+
+use crate::future::poll_fn;
+use crate::io::{AsyncRead, AsyncWrite, Interest, ReadBuf, Ready};
+use crate::net::TcpStream;
+
+use std::error::Error;
+use std::net::{Shutdown, SocketAddr};
+use std::pin::Pin;
+use std::sync::Arc;
+use std::task::{Context, Poll};
+use std::{fmt, io};
+
+cfg_io_util! {
+    use bytes::BufMut;
+}
+
+/// Owned read half of a [`TcpStream`], created by [`into_split`].
+///
+/// Reading from an `OwnedReadHalf` is usually done using the convenience methods found
+/// on the [`AsyncReadExt`] trait.
+///
+/// [`TcpStream`]: TcpStream
+/// [`into_split`]: TcpStream::into_split()
+/// [`AsyncReadExt`]: trait@crate::io::AsyncReadExt
+#[derive(Debug)]
+pub struct OwnedReadHalf {
+    inner: Arc<TcpStream>,
+}
+
+/// Owned write half of a [`TcpStream`], created by [`into_split`].
+///
+/// Note that in the [`AsyncWrite`] implementation of this type, [`poll_shutdown`] will
+/// shut down the TCP stream in the write direction.  Dropping the write half
+/// will also shut down the write half of the TCP stream.
+///
+/// Writing to an `OwnedWriteHalf` is usually done using the convenience methods found
+/// on the [`AsyncWriteExt`] trait.
+///
+/// [`TcpStream`]: TcpStream
+/// [`into_split`]: TcpStream::into_split()
+/// [`AsyncWrite`]: trait@crate::io::AsyncWrite
+/// [`poll_shutdown`]: fn@crate::io::AsyncWrite::poll_shutdown
+/// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+#[derive(Debug)]
+pub struct OwnedWriteHalf {
+    inner: Arc<TcpStream>,
+    shutdown_on_drop: bool,
+}
+
+pub(crate) fn split_owned(stream: TcpStream) -> (OwnedReadHalf, OwnedWriteHalf) {
+    let arc = Arc::new(stream);
+    let read = OwnedReadHalf {
+        inner: Arc::clone(&arc),
+    };
+    let write = OwnedWriteHalf {
+        inner: arc,
+        shutdown_on_drop: true,
+    };
+    (read, write)
+}
+
+pub(crate) fn reunite(
+    read: OwnedReadHalf,
+    write: OwnedWriteHalf,
+) -> Result<TcpStream, ReuniteError> {
+    if Arc::ptr_eq(&read.inner, &write.inner) {
+        write.forget();
+        // This unwrap cannot fail as the api does not allow creating more than two Arcs,
+        // and we just dropped the other half.
+        Ok(Arc::try_unwrap(read.inner).expect("TcpStream: try_unwrap failed in reunite"))
+    } else {
+        Err(ReuniteError(read, write))
+    }
+}
+
+/// Error indicating that two halves were not from the same socket, and thus could
+/// not be reunited.
+#[derive(Debug)]
+pub struct ReuniteError(pub OwnedReadHalf, pub OwnedWriteHalf);
+
+impl fmt::Display for ReuniteError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(
+            f,
+            "tried to reunite halves that are not from the same socket"
+        )
+    }
+}
+
+impl Error for ReuniteError {}
+
+impl OwnedReadHalf {
+    /// Attempts to put the two halves of a `TcpStream` back together and
+    /// recover the original socket. Succeeds only if the two halves
+    /// originated from the same call to [`into_split`].
+    ///
+    /// [`into_split`]: TcpStream::into_split()
+    pub fn reunite(self, other: OwnedWriteHalf) -> Result<TcpStream, ReuniteError> {
+        reunite(self, other)
+    }
+
+    /// Attempt to receive data on the socket, without removing that data from
+    /// the queue, registering the current task for wakeup if data is not yet
+    /// available.
+    ///
+    /// Note that on multiple calls to `poll_peek` or `poll_read`, only the
+    /// `Waker` from the `Context` passed to the most recent call is scheduled
+    /// to receive a wakeup.
+    ///
+    /// See the [`TcpStream::poll_peek`] level documentation for more details.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::io::{self, ReadBuf};
+    /// use tokio::net::TcpStream;
+    ///
+    /// use futures::future::poll_fn;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let stream = TcpStream::connect("127.0.0.1:8000").await?;
+    ///     let (mut read_half, _) = stream.into_split();
+    ///     let mut buf = [0; 10];
+    ///     let mut buf = ReadBuf::new(&mut buf);
+    ///
+    ///     poll_fn(|cx| {
+    ///         read_half.poll_peek(cx, &mut buf)
+    ///     }).await?;
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// [`TcpStream::poll_peek`]: TcpStream::poll_peek
+    pub fn poll_peek(
+        &mut self,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<usize>> {
+        self.inner.poll_peek(cx, buf)
+    }
+
+    /// Receives data on the socket from the remote address to which it is
+    /// connected, without removing that data from the queue. On success,
+    /// returns the number of bytes peeked.
+    ///
+    /// See the [`TcpStream::peek`] level documentation for more details.
+    ///
+    /// [`TcpStream::peek`]: TcpStream::peek
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    /// use tokio::io::AsyncReadExt;
+    /// use std::error::Error;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///     let (mut read_half, _) = stream.into_split();
+    ///
+    ///     let mut b1 = [0; 10];
+    ///     let mut b2 = [0; 10];
+    ///
+    ///     // Peek at the data
+    ///     let n = read_half.peek(&mut b1).await?;
+    ///
+    ///     // Read the data
+    ///     assert_eq!(n, read_half.read(&mut b2[..n]).await?);
+    ///     assert_eq!(&b1[..n], &b2[..n]);
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// The [`read`] method is defined on the [`AsyncReadExt`] trait.
+    ///
+    /// [`read`]: fn@crate::io::AsyncReadExt::read
+    /// [`AsyncReadExt`]: trait@crate::io::AsyncReadExt
+    pub async fn peek(&mut self, buf: &mut [u8]) -> io::Result<usize> {
+        let mut buf = ReadBuf::new(buf);
+        poll_fn(|cx| self.poll_peek(cx, &mut buf)).await
+    }
+
+    /// Waits for any of the requested ready states.
+    ///
+    /// This function is usually paired with `try_read()` or `try_write()`. It
+    /// can be used to concurrently read / write to the same socket on a single
+    /// task without splitting the socket.
+    ///
+    /// This function is equivalent to [`TcpStream::ready`].
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read or write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    pub async fn ready(&self, interest: Interest) -> io::Result<Ready> {
+        self.inner.ready(interest).await
+    }
+
+    /// Waits for the socket to become readable.
+    ///
+    /// This function is equivalent to `ready(Interest::READABLE)` and is usually
+    /// paired with `try_read()`.
+    ///
+    /// This function is also equivalent to [`TcpStream::ready`].
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    pub async fn readable(&self) -> io::Result<()> {
+        self.inner.readable().await
+    }
+
+    /// Tries to read data from the stream into the provided buffer, returning how
+    /// many bytes were read.
+    ///
+    /// Receives any pending data from the socket but does not wait for new data
+    /// to arrive. On success, returns the number of bytes read. Because
+    /// `try_read()` is non-blocking, the buffer does not have to be stored by
+    /// the async task and can exist entirely on the stack.
+    ///
+    /// Usually, [`readable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`readable()`]: Self::readable()
+    /// [`ready()`]: Self::ready()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+    /// and will no longer yield data. If the stream is not ready to read data
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    pub fn try_read(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.inner.try_read(buf)
+    }
+
+    /// Tries to read data from the stream into the provided buffers, returning
+    /// how many bytes were read.
+    ///
+    /// Data is copied to fill each buffer in order, with the final buffer
+    /// written to possibly being only partially filled. This method behaves
+    /// equivalently to a single call to [`try_read()`] with concatenated
+    /// buffers.
+    ///
+    /// Receives any pending data from the socket but does not wait for new data
+    /// to arrive. On success, returns the number of bytes read. Because
+    /// `try_read_vectored()` is non-blocking, the buffer does not have to be
+    /// stored by the async task and can exist entirely on the stack.
+    ///
+    /// Usually, [`readable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`try_read()`]: Self::try_read()
+    /// [`readable()`]: Self::readable()
+    /// [`ready()`]: Self::ready()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+    /// and will no longer yield data. If the stream is not ready to read data
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    pub fn try_read_vectored(&self, bufs: &mut [io::IoSliceMut<'_>]) -> io::Result<usize> {
+        self.inner.try_read_vectored(bufs)
+    }
+
+    cfg_io_util! {
+        /// Tries to read data from the stream into the provided buffer, advancing the
+        /// buffer's internal cursor, returning how many bytes were read.
+        ///
+        /// Receives any pending data from the socket but does not wait for new data
+        /// to arrive. On success, returns the number of bytes read. Because
+        /// `try_read_buf()` is non-blocking, the buffer does not have to be stored by
+        /// the async task and can exist entirely on the stack.
+        ///
+        /// Usually, [`readable()`] or [`ready()`] is used with this function.
+        ///
+        /// [`readable()`]: Self::readable()
+        /// [`ready()`]: Self::ready()
+        ///
+        /// # Return
+        ///
+        /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+        /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+        /// and will no longer yield data. If the stream is not ready to read data
+        /// `Err(io::ErrorKind::WouldBlock)` is returned.
+        pub fn try_read_buf<B: BufMut>(&self, buf: &mut B) -> io::Result<usize> {
+            self.inner.try_read_buf(buf)
+        }
+    }
+
+    /// Returns the remote address that this stream is connected to.
+    pub fn peer_addr(&self) -> io::Result<SocketAddr> {
+        self.inner.peer_addr()
+    }
+
+    /// Returns the local address that this stream is bound to.
+    pub fn local_addr(&self) -> io::Result<SocketAddr> {
+        self.inner.local_addr()
+    }
+}
+
+impl AsyncRead for OwnedReadHalf {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        self.inner.poll_read_priv(cx, buf)
+    }
+}
+
+impl OwnedWriteHalf {
+    /// Attempts to put the two halves of a `TcpStream` back together and
+    /// recover the original socket. Succeeds only if the two halves
+    /// originated from the same call to [`into_split`].
+    ///
+    /// [`into_split`]: TcpStream::into_split()
+    pub fn reunite(self, other: OwnedReadHalf) -> Result<TcpStream, ReuniteError> {
+        reunite(other, self)
+    }
+
+    /// Destroys the write half, but don't close the write half of the stream
+    /// until the read half is dropped. If the read half has already been
+    /// dropped, this closes the stream.
+    pub fn forget(mut self) {
+        self.shutdown_on_drop = false;
+        drop(self);
+    }
+
+    /// Waits for any of the requested ready states.
+    ///
+    /// This function is usually paired with `try_read()` or `try_write()`. It
+    /// can be used to concurrently read / write to the same socket on a single
+    /// task without splitting the socket.
+    ///
+    /// This function is equivalent to [`TcpStream::ready`].
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read or write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    pub async fn ready(&self, interest: Interest) -> io::Result<Ready> {
+        self.inner.ready(interest).await
+    }
+
+    /// Waits for the socket to become writable.
+    ///
+    /// This function is equivalent to `ready(Interest::WRITABLE)` and is usually
+    /// paired with `try_write()`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    pub async fn writable(&self) -> io::Result<()> {
+        self.inner.writable().await
+    }
+
+    /// Tries to write a buffer to the stream, returning how many bytes were
+    /// written.
+    ///
+    /// The function will attempt to write the entire contents of `buf`, but
+    /// only part of the buffer may be written.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// # Return
+    ///
+    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
+    /// number of bytes written. If the stream is not ready to write data,
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    pub fn try_write(&self, buf: &[u8]) -> io::Result<usize> {
+        self.inner.try_write(buf)
+    }
+
+    /// Tries to write several buffers to the stream, returning how many bytes
+    /// were written.
+    ///
+    /// Data is written from each buffer in order, with the final buffer read
+    /// from possible being only partially consumed. This method behaves
+    /// equivalently to a single call to [`try_write()`] with concatenated
+    /// buffers.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// [`try_write()`]: Self::try_write()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
+    /// number of bytes written. If the stream is not ready to write data,
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    pub fn try_write_vectored(&self, bufs: &[io::IoSlice<'_>]) -> io::Result<usize> {
+        self.inner.try_write_vectored(bufs)
+    }
+
+    /// Returns the remote address that this stream is connected to.
+    pub fn peer_addr(&self) -> io::Result<SocketAddr> {
+        self.inner.peer_addr()
+    }
+
+    /// Returns the local address that this stream is bound to.
+    pub fn local_addr(&self) -> io::Result<SocketAddr> {
+        self.inner.local_addr()
+    }
+}
+
+impl Drop for OwnedWriteHalf {
+    fn drop(&mut self) {
+        if self.shutdown_on_drop {
+            let _ = self.inner.shutdown_std(Shutdown::Write);
+        }
+    }
+}
+
+impl AsyncWrite for OwnedWriteHalf {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.inner.poll_write_priv(cx, buf)
+    }
+
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.inner.poll_write_vectored_priv(cx, bufs)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        self.inner.is_write_vectored()
+    }
+
+    #[inline]
+    fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        // tcp flush is a no-op
+        Poll::Ready(Ok(()))
+    }
+
+    // `poll_shutdown` on a write half shutdowns the stream in the "write" direction.
+    fn poll_shutdown(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        let res = self.inner.shutdown_std(Shutdown::Write);
+        if res.is_ok() {
+            Pin::into_inner(self).shutdown_on_drop = false;
+        }
+        res.into()
+    }
+}
+
+impl AsRef<TcpStream> for OwnedReadHalf {
+    fn as_ref(&self) -> &TcpStream {
+        &*self.inner
+    }
+}
+
+impl AsRef<TcpStream> for OwnedWriteHalf {
+    fn as_ref(&self) -> &TcpStream {
+        &*self.inner
+    }
+}
diff --git a/third_party/rust/tokio/src/net/tcp/stream.rs b/third_party/rust/tokio/src/net/tcp/stream.rs
new file mode 100644
index 0000000000..ebb67b84d1
--- /dev/null
+++ b/third_party/rust/tokio/src/net/tcp/stream.rs
@@ -0,0 +1,1310 @@
+use crate::future::poll_fn;
+use crate::io::{AsyncRead, AsyncWrite, Interest, PollEvented, ReadBuf, Ready};
+use crate::net::tcp::split::{split, ReadHalf, WriteHalf};
+use crate::net::tcp::split_owned::{split_owned, OwnedReadHalf, OwnedWriteHalf};
+use crate::net::{to_socket_addrs, ToSocketAddrs};
+
+use std::convert::TryFrom;
+use std::fmt;
+use std::io;
+use std::net::{Shutdown, SocketAddr};
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use std::time::Duration;
+
+cfg_io_util! {
+    use bytes::BufMut;
+}
+
+cfg_net! {
+    /// A TCP stream between a local and a remote socket.
+    ///
+    /// A TCP stream can either be created by connecting to an endpoint, via the
+    /// [`connect`] method, or by [accepting] a connection from a [listener]. A
+    /// TCP stream can also be created via the [`TcpSocket`] type.
+    ///
+    /// Reading and writing to a `TcpStream` is usually done using the
+    /// convenience methods found on the [`AsyncReadExt`] and [`AsyncWriteExt`]
+    /// traits.
+    ///
+    /// [`connect`]: method@TcpStream::connect
+    /// [accepting]: method@crate::net::TcpListener::accept
+    /// [listener]: struct@crate::net::TcpListener
+    /// [`TcpSocket`]: struct@crate::net::TcpSocket
+    /// [`AsyncReadExt`]: trait@crate::io::AsyncReadExt
+    /// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    /// use tokio::io::AsyncWriteExt;
+    /// use std::error::Error;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let mut stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    ///     // Write some data.
+    ///     stream.write_all(b"hello world!").await?;
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// The [`write_all`] method is defined on the [`AsyncWriteExt`] trait.
+    ///
+    /// [`write_all`]: fn@crate::io::AsyncWriteExt::write_all
+    /// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+    ///
+    /// To shut down the stream in the write direction, you can call the
+    /// [`shutdown()`] method. This will cause the other peer to receive a read of
+    /// length 0, indicating that no more data will be sent. This only closes
+    /// the stream in one direction.
+    ///
+    /// [`shutdown()`]: fn@crate::io::AsyncWriteExt::shutdown
+    pub struct TcpStream {
+        io: PollEvented<mio::net::TcpStream>,
+    }
+}
+
+impl TcpStream {
+    /// Opens a TCP connection to a remote host.
+    ///
+    /// `addr` is an address of the remote host. Anything which implements the
+    /// [`ToSocketAddrs`] trait can be supplied as the address.  If `addr`
+    /// yields multiple addresses, connect will be attempted with each of the
+    /// addresses until a connection is successful. If none of the addresses
+    /// result in a successful connection, the error returned from the last
+    /// connection attempt (the last address) is returned.
+    ///
+    /// To configure the socket before connecting, you can use the [`TcpSocket`]
+    /// type.
+    ///
+    /// [`ToSocketAddrs`]: trait@crate::net::ToSocketAddrs
+    /// [`TcpSocket`]: struct@crate::net::TcpSocket
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    /// use tokio::io::AsyncWriteExt;
+    /// use std::error::Error;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let mut stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    ///     // Write some data.
+    ///     stream.write_all(b"hello world!").await?;
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// The [`write_all`] method is defined on the [`AsyncWriteExt`] trait.
+    ///
+    /// [`write_all`]: fn@crate::io::AsyncWriteExt::write_all
+    /// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+    pub async fn connect<A: ToSocketAddrs>(addr: A) -> io::Result<TcpStream> {
+        let addrs = to_socket_addrs(addr).await?;
+
+        let mut last_err = None;
+
+        for addr in addrs {
+            match TcpStream::connect_addr(addr).await {
+                Ok(stream) => return Ok(stream),
+                Err(e) => last_err = Some(e),
+            }
+        }
+
+        Err(last_err.unwrap_or_else(|| {
+            io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "could not resolve to any address",
+            )
+        }))
+    }
+
+    /// Establishes a connection to the specified `addr`.
+    async fn connect_addr(addr: SocketAddr) -> io::Result<TcpStream> {
+        let sys = mio::net::TcpStream::connect(addr)?;
+        TcpStream::connect_mio(sys).await
+    }
+
+    pub(crate) async fn connect_mio(sys: mio::net::TcpStream) -> io::Result<TcpStream> {
+        let stream = TcpStream::new(sys)?;
+
+        // Once we've connected, wait for the stream to be writable as
+        // that's when the actual connection has been initiated. Once we're
+        // writable we check for `take_socket_error` to see if the connect
+        // actually hit an error or not.
+        //
+        // If all that succeeded then we ship everything on up.
+        poll_fn(|cx| stream.io.registration().poll_write_ready(cx)).await?;
+
+        if let Some(e) = stream.io.take_error()? {
+            return Err(e);
+        }
+
+        Ok(stream)
+    }
+
+    pub(crate) fn new(connected: mio::net::TcpStream) -> io::Result<TcpStream> {
+        let io = PollEvented::new(connected)?;
+        Ok(TcpStream { io })
+    }
+
+    /// Creates new `TcpStream` from a `std::net::TcpStream`.
+    ///
+    /// This function is intended to be used to wrap a TCP stream from the
+    /// standard library in the Tokio equivalent. The conversion assumes nothing
+    /// about the underlying stream; it is left up to the user to set it in
+    /// non-blocking mode.
+    ///
+    /// # Examples
+    ///
+    /// ```rust,no_run
+    /// use std::error::Error;
+    /// use tokio::net::TcpStream;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let std_stream = std::net::TcpStream::connect("127.0.0.1:34254")?;
+    ///     std_stream.set_nonblocking(true)?;
+    ///     let stream = TcpStream::from_std(std_stream)?;
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// This function panics if thread-local runtime is not set.
+    ///
+    /// The runtime is usually set implicitly when this function is called
+    /// from a future driven by a tokio runtime, otherwise runtime can be set
+    /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter) function.
+    pub fn from_std(stream: std::net::TcpStream) -> io::Result<TcpStream> {
+        let io = mio::net::TcpStream::from_std(stream);
+        let io = PollEvented::new(io)?;
+        Ok(TcpStream { io })
+    }
+
+    /// Turns a [`tokio::net::TcpStream`] into a [`std::net::TcpStream`].
+    ///
+    /// The returned [`std::net::TcpStream`] will have nonblocking mode set as `true`.
+    /// Use [`set_nonblocking`] to change the blocking mode if needed.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::error::Error;
+    /// use std::io::Read;
+    /// use tokio::net::TcpListener;
+    /// # use tokio::net::TcpStream;
+    /// # use tokio::io::AsyncWriteExt;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let mut data = [0u8; 12];
+    ///     let listener = TcpListener::bind("127.0.0.1:34254").await?;
+    /// #   let handle = tokio::spawn(async {
+    /// #       let mut stream: TcpStream = TcpStream::connect("127.0.0.1:34254").await.unwrap();
+    /// #       stream.write(b"Hello world!").await.unwrap();
+    /// #   });
+    ///     let (tokio_tcp_stream, _) = listener.accept().await?;
+    ///     let mut std_tcp_stream = tokio_tcp_stream.into_std()?;
+    /// #   handle.await.expect("The task being joined has panicked");
+    ///     std_tcp_stream.set_nonblocking(false)?;
+    ///     std_tcp_stream.read_exact(&mut data)?;
+    /// #   assert_eq!(b"Hello world!", &data);
+    ///     Ok(())
+    /// }
+    /// ```
+    /// [`tokio::net::TcpStream`]: TcpStream
+    /// [`std::net::TcpStream`]: std::net::TcpStream
+    /// [`set_nonblocking`]: fn@std::net::TcpStream::set_nonblocking
+    pub fn into_std(self) -> io::Result<std::net::TcpStream> {
+        #[cfg(unix)]
+        {
+            use std::os::unix::io::{FromRawFd, IntoRawFd};
+            self.io
+                .into_inner()
+                .map(|io| io.into_raw_fd())
+                .map(|raw_fd| unsafe { std::net::TcpStream::from_raw_fd(raw_fd) })
+        }
+
+        #[cfg(windows)]
+        {
+            use std::os::windows::io::{FromRawSocket, IntoRawSocket};
+            self.io
+                .into_inner()
+                .map(|io| io.into_raw_socket())
+                .map(|raw_socket| unsafe { std::net::TcpStream::from_raw_socket(raw_socket) })
+        }
+    }
+
+    /// Returns the local address that this stream is bound to.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    ///
+    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
+    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    /// println!("{:?}", stream.local_addr()?);
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn local_addr(&self) -> io::Result<SocketAddr> {
+        self.io.local_addr()
+    }
+
+    /// Returns the remote address that this stream is connected to.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    ///
+    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
+    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    /// println!("{:?}", stream.peer_addr()?);
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn peer_addr(&self) -> io::Result<SocketAddr> {
+        self.io.peer_addr()
+    }
+
+    /// Attempts to receive data on the socket, without removing that data from
+    /// the queue, registering the current task for wakeup if data is not yet
+    /// available.
+    ///
+    /// Note that on multiple calls to `poll_peek`, `poll_read` or
+    /// `poll_read_ready`, only the `Waker` from the `Context` passed to the
+    /// most recent call is scheduled to receive a wakeup. (However,
+    /// `poll_write` retains a second, independent waker.)
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if data is not yet available.
+    /// * `Poll::Ready(Ok(n))` if data is available. `n` is the number of bytes peeked.
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::io::{self, ReadBuf};
+    /// use tokio::net::TcpStream;
+    ///
+    /// use futures::future::poll_fn;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let stream = TcpStream::connect("127.0.0.1:8000").await?;
+    ///     let mut buf = [0; 10];
+    ///     let mut buf = ReadBuf::new(&mut buf);
+    ///
+    ///     poll_fn(|cx| {
+    ///         stream.poll_peek(cx, &mut buf)
+    ///     }).await?;
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn poll_peek(
+        &self,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<usize>> {
+        loop {
+            let ev = ready!(self.io.registration().poll_read_ready(cx))?;
+
+            let b = unsafe {
+                &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8])
+            };
+
+            match self.io.peek(b) {
+                Ok(ret) => {
+                    unsafe { buf.assume_init(ret) };
+                    buf.advance(ret);
+                    return Poll::Ready(Ok(ret));
+                }
+                Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+                    self.io.registration().clear_readiness(ev);
+                }
+                Err(e) => return Poll::Ready(Err(e)),
+            }
+        }
+    }
+
+    /// Waits for any of the requested ready states.
+    ///
+    /// This function is usually paired with `try_read()` or `try_write()`. It
+    /// can be used to concurrently read / write to the same socket on a single
+    /// task without splitting the socket.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read or write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    ///
+    /// # Examples
+    ///
+    /// Concurrently read and write to the stream on the same task without
+    /// splitting.
+    ///
+    /// ```no_run
+    /// use tokio::io::Interest;
+    /// use tokio::net::TcpStream;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    ///     loop {
+    ///         let ready = stream.ready(Interest::READABLE | Interest::WRITABLE).await?;
+    ///
+    ///         if ready.is_readable() {
+    ///             let mut data = vec![0; 1024];
+    ///             // Try to read data, this may still fail with `WouldBlock`
+    ///             // if the readiness event is a false positive.
+    ///             match stream.try_read(&mut data) {
+    ///                 Ok(n) => {
+    ///                     println!("read {} bytes", n);
+    ///                 }
+    ///                 Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                     continue;
+    ///                 }
+    ///                 Err(e) => {
+    ///                     return Err(e.into());
+    ///                 }
+    ///             }
+    ///
+    ///         }
+    ///
+    ///         if ready.is_writable() {
+    ///             // Try to write data, this may still fail with `WouldBlock`
+    ///             // if the readiness event is a false positive.
+    ///             match stream.try_write(b"hello world") {
+    ///                 Ok(n) => {
+    ///                     println!("write {} bytes", n);
+    ///                 }
+    ///                 Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                     continue
+    ///                 }
+    ///                 Err(e) => {
+    ///                     return Err(e.into());
+    ///                 }
+    ///             }
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    pub async fn ready(&self, interest: Interest) -> io::Result<Ready> {
+        let event = self.io.registration().readiness(interest).await?;
+        Ok(event.ready)
+    }
+
+    /// Waits for the socket to become readable.
+    ///
+    /// This function is equivalent to `ready(Interest::READABLE)` and is usually
+    /// paired with `try_read()`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    ///     let mut msg = vec![0; 1024];
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be readable
+    ///         stream.readable().await?;
+    ///
+    ///         // Try to read data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match stream.try_read(&mut msg) {
+    ///             Ok(n) => {
+    ///                 msg.truncate(n);
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     println!("GOT = {:?}", msg);
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn readable(&self) -> io::Result<()> {
+        self.ready(Interest::READABLE).await?;
+        Ok(())
+    }
+
+    /// Polls for read readiness.
+    ///
+    /// If the tcp stream is not currently ready for reading, this method will
+    /// store a clone of the `Waker` from the provided `Context`. When the tcp
+    /// stream becomes ready for reading, `Waker::wake` will be called on the
+    /// waker.
+    ///
+    /// Note that on multiple calls to `poll_read_ready`, `poll_read` or
+    /// `poll_peek`, only the `Waker` from the `Context` passed to the most
+    /// recent call is scheduled to receive a wakeup. (However,
+    /// `poll_write_ready` retains a second, independent waker.)
+    ///
+    /// This function is intended for cases where creating and pinning a future
+    /// via [`readable`] is not feasible. Where possible, using [`readable`] is
+    /// preferred, as this supports polling from multiple tasks at once.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the tcp stream is not ready for reading.
+    /// * `Poll::Ready(Ok(()))` if the tcp stream is ready for reading.
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// [`readable`]: method@Self::readable
+    pub fn poll_read_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.io.registration().poll_read_ready(cx).map_ok(|_| ())
+    }
+
+    /// Tries to read data from the stream into the provided buffer, returning how
+    /// many bytes were read.
+    ///
+    /// Receives any pending data from the socket but does not wait for new data
+    /// to arrive. On success, returns the number of bytes read. Because
+    /// `try_read()` is non-blocking, the buffer does not have to be stored by
+    /// the async task and can exist entirely on the stack.
+    ///
+    /// Usually, [`readable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`readable()`]: TcpStream::readable()
+    /// [`ready()`]: TcpStream::ready()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+    /// and will no longer yield data. If the stream is not ready to read data
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be readable
+    ///         stream.readable().await?;
+    ///
+    ///         // Creating the buffer **after** the `await` prevents it from
+    ///         // being stored in the async task.
+    ///         let mut buf = [0; 4096];
+    ///
+    ///         // Try to read data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match stream.try_read(&mut buf) {
+    ///             Ok(0) => break,
+    ///             Ok(n) => {
+    ///                 println!("read {} bytes", n);
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_read(&self, buf: &mut [u8]) -> io::Result<usize> {
+        use std::io::Read;
+
+        self.io
+            .registration()
+            .try_io(Interest::READABLE, || (&*self.io).read(buf))
+    }
+
+    /// Tries to read data from the stream into the provided buffers, returning
+    /// how many bytes were read.
+    ///
+    /// Data is copied to fill each buffer in order, with the final buffer
+    /// written to possibly being only partially filled. This method behaves
+    /// equivalently to a single call to [`try_read()`] with concatenated
+    /// buffers.
+    ///
+    /// Receives any pending data from the socket but does not wait for new data
+    /// to arrive. On success, returns the number of bytes read. Because
+    /// `try_read_vectored()` is non-blocking, the buffer does not have to be
+    /// stored by the async task and can exist entirely on the stack.
+    ///
+    /// Usually, [`readable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`try_read()`]: TcpStream::try_read()
+    /// [`readable()`]: TcpStream::readable()
+    /// [`ready()`]: TcpStream::ready()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+    /// and will no longer yield data. If the stream is not ready to read data
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    /// use std::error::Error;
+    /// use std::io::{self, IoSliceMut};
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be readable
+    ///         stream.readable().await?;
+    ///
+    ///         // Creating the buffer **after** the `await` prevents it from
+    ///         // being stored in the async task.
+    ///         let mut buf_a = [0; 512];
+    ///         let mut buf_b = [0; 1024];
+    ///         let mut bufs = [
+    ///             IoSliceMut::new(&mut buf_a),
+    ///             IoSliceMut::new(&mut buf_b),
+    ///         ];
+    ///
+    ///         // Try to read data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match stream.try_read_vectored(&mut bufs) {
+    ///             Ok(0) => break,
+    ///             Ok(n) => {
+    ///                 println!("read {} bytes", n);
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_read_vectored(&self, bufs: &mut [io::IoSliceMut<'_>]) -> io::Result<usize> {
+        use std::io::Read;
+
+        self.io
+            .registration()
+            .try_io(Interest::READABLE, || (&*self.io).read_vectored(bufs))
+    }
+
+    cfg_io_util! {
+        /// Tries to read data from the stream into the provided buffer, advancing the
+        /// buffer's internal cursor, returning how many bytes were read.
+        ///
+        /// Receives any pending data from the socket but does not wait for new data
+        /// to arrive. On success, returns the number of bytes read. Because
+        /// `try_read_buf()` is non-blocking, the buffer does not have to be stored by
+        /// the async task and can exist entirely on the stack.
+        ///
+        /// Usually, [`readable()`] or [`ready()`] is used with this function.
+        ///
+        /// [`readable()`]: TcpStream::readable()
+        /// [`ready()`]: TcpStream::ready()
+        ///
+        /// # Return
+        ///
+        /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+        /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+        /// and will no longer yield data. If the stream is not ready to read data
+        /// `Err(io::ErrorKind::WouldBlock)` is returned.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::net::TcpStream;
+        /// use std::error::Error;
+        /// use std::io;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> Result<(), Box<dyn Error>> {
+        ///     // Connect to a peer
+        ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
+        ///
+        ///     loop {
+        ///         // Wait for the socket to be readable
+        ///         stream.readable().await?;
+        ///
+        ///         let mut buf = Vec::with_capacity(4096);
+        ///
+        ///         // Try to read data, this may still fail with `WouldBlock`
+        ///         // if the readiness event is a false positive.
+        ///         match stream.try_read_buf(&mut buf) {
+        ///             Ok(0) => break,
+        ///             Ok(n) => {
+        ///                 println!("read {} bytes", n);
+        ///             }
+        ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+        ///                 continue;
+        ///             }
+        ///             Err(e) => {
+        ///                 return Err(e.into());
+        ///             }
+        ///         }
+        ///     }
+        ///
+        ///     Ok(())
+        /// }
+        /// ```
+        pub fn try_read_buf<B: BufMut>(&self, buf: &mut B) -> io::Result<usize> {
+            self.io.registration().try_io(Interest::READABLE, || {
+                use std::io::Read;
+
+                let dst = buf.chunk_mut();
+                let dst =
+                    unsafe { &mut *(dst as *mut _ as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]) };
+
+                // Safety: We trust `TcpStream::read` to have filled up `n` bytes in the
+                // buffer.
+                let n = (&*self.io).read(dst)?;
+
+                unsafe {
+                    buf.advance_mut(n);
+                }
+
+                Ok(n)
+            })
+        }
+    }
+
+    /// Waits for the socket to become writable.
+    ///
+    /// This function is equivalent to `ready(Interest::WRITABLE)` and is usually
+    /// paired with `try_write()`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be writable
+    ///         stream.writable().await?;
+    ///
+    ///         // Try to write data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match stream.try_write(b"hello world") {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn writable(&self) -> io::Result<()> {
+        self.ready(Interest::WRITABLE).await?;
+        Ok(())
+    }
+
+    /// Polls for write readiness.
+    ///
+    /// If the tcp stream is not currently ready for writing, this method will
+    /// store a clone of the `Waker` from the provided `Context`. When the tcp
+    /// stream becomes ready for writing, `Waker::wake` will be called on the
+    /// waker.
+    ///
+    /// Note that on multiple calls to `poll_write_ready` or `poll_write`, only
+    /// the `Waker` from the `Context` passed to the most recent call is
+    /// scheduled to receive a wakeup. (However, `poll_read_ready` retains a
+    /// second, independent waker.)
+    ///
+    /// This function is intended for cases where creating and pinning a future
+    /// via [`writable`] is not feasible. Where possible, using [`writable`] is
+    /// preferred, as this supports polling from multiple tasks at once.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the tcp stream is not ready for writing.
+    /// * `Poll::Ready(Ok(()))` if the tcp stream is ready for writing.
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// [`writable`]: method@Self::writable
+    pub fn poll_write_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.io.registration().poll_write_ready(cx).map_ok(|_| ())
+    }
+
+    /// Try to write a buffer to the stream, returning how many bytes were
+    /// written.
+    ///
+    /// The function will attempt to write the entire contents of `buf`, but
+    /// only part of the buffer may be written.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// # Return
+    ///
+    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
+    /// number of bytes written. If the stream is not ready to write data,
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be writable
+    ///         stream.writable().await?;
+    ///
+    ///         // Try to write data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match stream.try_write(b"hello world") {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_write(&self, buf: &[u8]) -> io::Result<usize> {
+        use std::io::Write;
+
+        self.io
+            .registration()
+            .try_io(Interest::WRITABLE, || (&*self.io).write(buf))
+    }
+
+    /// Tries to write several buffers to the stream, returning how many bytes
+    /// were written.
+    ///
+    /// Data is written from each buffer in order, with the final buffer read
+    /// from possible being only partially consumed. This method behaves
+    /// equivalently to a single call to [`try_write()`] with concatenated
+    /// buffers.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// [`try_write()`]: TcpStream::try_write()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
+    /// number of bytes written. If the stream is not ready to write data,
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    ///     let bufs = [io::IoSlice::new(b"hello "), io::IoSlice::new(b"world")];
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be writable
+    ///         stream.writable().await?;
+    ///
+    ///         // Try to write data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match stream.try_write_vectored(&bufs) {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_write_vectored(&self, bufs: &[io::IoSlice<'_>]) -> io::Result<usize> {
+        use std::io::Write;
+
+        self.io
+            .registration()
+            .try_io(Interest::WRITABLE, || (&*self.io).write_vectored(bufs))
+    }
+
+    /// Tries to read or write from the socket using a user-provided IO operation.
+    ///
+    /// If the socket is ready, the provided closure is called. The closure
+    /// should attempt to perform IO operation from the socket by manually
+    /// calling the appropriate syscall. If the operation fails because the
+    /// socket is not actually ready, then the closure should return a
+    /// `WouldBlock` error and the readiness flag is cleared. The return value
+    /// of the closure is then returned by `try_io`.
+    ///
+    /// If the socket is not ready, then the closure is not called
+    /// and a `WouldBlock` error is returned.
+    ///
+    /// The closure should only return a `WouldBlock` error if it has performed
+    /// an IO operation on the socket that failed due to the socket not being
+    /// ready. Returning a `WouldBlock` error in any other situation will
+    /// incorrectly clear the readiness flag, which can cause the socket to
+    /// behave incorrectly.
+    ///
+    /// The closure should not perform the IO operation using any of the methods
+    /// defined on the Tokio `TcpStream` type, as this will mess with the
+    /// readiness flag and can cause the socket to behave incorrectly.
+    ///
+    /// Usually, [`readable()`], [`writable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`readable()`]: TcpStream::readable()
+    /// [`writable()`]: TcpStream::writable()
+    /// [`ready()`]: TcpStream::ready()
+    pub fn try_io<R>(
+        &self,
+        interest: Interest,
+        f: impl FnOnce() -> io::Result<R>,
+    ) -> io::Result<R> {
+        self.io.registration().try_io(interest, f)
+    }
+
+    /// Receives data on the socket from the remote address to which it is
+    /// connected, without removing that data from the queue. On success,
+    /// returns the number of bytes peeked.
+    ///
+    /// Successive calls return the same data. This is accomplished by passing
+    /// `MSG_PEEK` as a flag to the underlying recv system call.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    /// use tokio::io::AsyncReadExt;
+    /// use std::error::Error;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let mut stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    ///     let mut b1 = [0; 10];
+    ///     let mut b2 = [0; 10];
+    ///
+    ///     // Peek at the data
+    ///     let n = stream.peek(&mut b1).await?;
+    ///
+    ///     // Read the data
+    ///     assert_eq!(n, stream.read(&mut b2[..n]).await?);
+    ///     assert_eq!(&b1[..n], &b2[..n]);
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// The [`read`] method is defined on the [`AsyncReadExt`] trait.
+    ///
+    /// [`read`]: fn@crate::io::AsyncReadExt::read
+    /// [`AsyncReadExt`]: trait@crate::io::AsyncReadExt
+    pub async fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .async_io(Interest::READABLE, || self.io.peek(buf))
+            .await
+    }
+
+    /// Shuts down the read, write, or both halves of this connection.
+    ///
+    /// This function will cause all pending and future I/O on the specified
+    /// portions to return immediately with an appropriate value (see the
+    /// documentation of `Shutdown`).
+    pub(super) fn shutdown_std(&self, how: Shutdown) -> io::Result<()> {
+        self.io.shutdown(how)
+    }
+
+    /// Gets the value of the `TCP_NODELAY` option on this socket.
+    ///
+    /// For more information about this option, see [`set_nodelay`].
+    ///
+    /// [`set_nodelay`]: TcpStream::set_nodelay
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    ///
+    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
+    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    /// println!("{:?}", stream.nodelay()?);
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn nodelay(&self) -> io::Result<bool> {
+        self.io.nodelay()
+    }
+
+    /// Sets the value of the `TCP_NODELAY` option on this socket.
+    ///
+    /// If set, this option disables the Nagle algorithm. This means that
+    /// segments are always sent as soon as possible, even if there is only a
+    /// small amount of data. When not set, data is buffered until there is a
+    /// sufficient amount to send out, thereby avoiding the frequent sending of
+    /// small packets.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    ///
+    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
+    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    /// stream.set_nodelay(true)?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn set_nodelay(&self, nodelay: bool) -> io::Result<()> {
+        self.io.set_nodelay(nodelay)
+    }
+
+    /// Reads the linger duration for this socket by getting the `SO_LINGER`
+    /// option.
+    ///
+    /// For more information about this option, see [`set_linger`].
+    ///
+    /// [`set_linger`]: TcpStream::set_linger
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    ///
+    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
+    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    /// println!("{:?}", stream.linger()?);
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn linger(&self) -> io::Result<Option<Duration>> {
+        socket2::SockRef::from(self).linger()
+    }
+
+    /// Sets the linger duration of this socket by setting the SO_LINGER option.
+    ///
+    /// This option controls the action taken when a stream has unsent messages and the stream is
+    /// closed. If SO_LINGER is set, the system shall block the process until it can transmit the
+    /// data or until the time expires.
+    ///
+    /// If SO_LINGER is not specified, and the stream is closed, the system handles the call in a
+    /// way that allows the process to continue as quickly as possible.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    ///
+    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
+    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    /// stream.set_linger(None)?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn set_linger(&self, dur: Option<Duration>) -> io::Result<()> {
+        socket2::SockRef::from(self).set_linger(dur)
+    }
+
+    /// Gets the value of the `IP_TTL` option for this socket.
+    ///
+    /// For more information about this option, see [`set_ttl`].
+    ///
+    /// [`set_ttl`]: TcpStream::set_ttl
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    ///
+    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
+    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    /// println!("{:?}", stream.ttl()?);
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn ttl(&self) -> io::Result<u32> {
+        self.io.ttl()
+    }
+
+    /// Sets the value for the `IP_TTL` option on this socket.
+    ///
+    /// This value sets the time-to-live field that is used in every packet sent
+    /// from this socket.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::TcpStream;
+    ///
+    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
+    /// let stream = TcpStream::connect("127.0.0.1:8080").await?;
+    ///
+    /// stream.set_ttl(123)?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn set_ttl(&self, ttl: u32) -> io::Result<()> {
+        self.io.set_ttl(ttl)
+    }
+
+    // These lifetime markers also appear in the generated documentation, and make
+    // it more clear that this is a *borrowed* split.
+    #[allow(clippy::needless_lifetimes)]
+    /// Splits a `TcpStream` into a read half and a write half, which can be used
+    /// to read and write the stream concurrently.
+    ///
+    /// This method is more efficient than [`into_split`], but the halves cannot be
+    /// moved into independently spawned tasks.
+    ///
+    /// [`into_split`]: TcpStream::into_split()
+    pub fn split<'a>(&'a mut self) -> (ReadHalf<'a>, WriteHalf<'a>) {
+        split(self)
+    }
+
+    /// Splits a `TcpStream` into a read half and a write half, which can be used
+    /// to read and write the stream concurrently.
+    ///
+    /// Unlike [`split`], the owned halves can be moved to separate tasks, however
+    /// this comes at the cost of a heap allocation.
+    ///
+    /// **Note:** Dropping the write half will shut down the write half of the TCP
+    /// stream. This is equivalent to calling [`shutdown()`] on the `TcpStream`.
+    ///
+    /// [`split`]: TcpStream::split()
+    /// [`shutdown()`]: fn@crate::io::AsyncWriteExt::shutdown
+    pub fn into_split(self) -> (OwnedReadHalf, OwnedWriteHalf) {
+        split_owned(self)
+    }
+
+    // == Poll IO functions that takes `&self` ==
+    //
+    // To read or write without mutable access to the `UnixStream`, combine the
+    // `poll_read_ready` or `poll_write_ready` methods with the `try_read` or
+    // `try_write` methods.
+
+    pub(crate) fn poll_read_priv(
+        &self,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        // Safety: `TcpStream::read` correctly handles reads into uninitialized memory
+        unsafe { self.io.poll_read(cx, buf) }
+    }
+
+    pub(super) fn poll_write_priv(
+        &self,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.io.poll_write(cx, buf)
+    }
+
+    pub(super) fn poll_write_vectored_priv(
+        &self,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.io.poll_write_vectored(cx, bufs)
+    }
+}
+
+impl TryFrom<std::net::TcpStream> for TcpStream {
+    type Error = io::Error;
+
+    /// Consumes stream, returning the tokio I/O object.
+    ///
+    /// This is equivalent to
+    /// [`TcpStream::from_std(stream)`](TcpStream::from_std).
+    fn try_from(stream: std::net::TcpStream) -> Result<Self, Self::Error> {
+        Self::from_std(stream)
+    }
+}
+
+// ===== impl Read / Write =====
+
+impl AsyncRead for TcpStream {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        self.poll_read_priv(cx, buf)
+    }
+}
+
+impl AsyncWrite for TcpStream {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.poll_write_priv(cx, buf)
+    }
+
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.poll_write_vectored_priv(cx, bufs)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        true
+    }
+
+    #[inline]
+    fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        // tcp flush is a no-op
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.shutdown_std(std::net::Shutdown::Write)?;
+        Poll::Ready(Ok(()))
+    }
+}
+
+impl fmt::Debug for TcpStream {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.io.fmt(f)
+    }
+}
+
+#[cfg(unix)]
+mod sys {
+    use super::TcpStream;
+    use std::os::unix::prelude::*;
+
+    impl AsRawFd for TcpStream {
+        fn as_raw_fd(&self) -> RawFd {
+            self.io.as_raw_fd()
+        }
+    }
+}
+
+#[cfg(windows)]
+mod sys {
+    use super::TcpStream;
+    use std::os::windows::prelude::*;
+
+    impl AsRawSocket for TcpStream {
+        fn as_raw_socket(&self) -> RawSocket {
+            self.io.as_raw_socket()
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/net/udp.rs b/third_party/rust/tokio/src/net/udp.rs
new file mode 100644
index 0000000000..12af5152c2
--- /dev/null
+++ b/third_party/rust/tokio/src/net/udp.rs
@@ -0,0 +1,1589 @@
+use crate::io::{Interest, PollEvented, ReadBuf, Ready};
+use crate::net::{to_socket_addrs, ToSocketAddrs};
+
+use std::convert::TryFrom;
+use std::fmt;
+use std::io;
+use std::net::{self, Ipv4Addr, Ipv6Addr, SocketAddr};
+use std::task::{Context, Poll};
+
+cfg_io_util! {
+    use bytes::BufMut;
+}
+
+cfg_net! {
+    /// A UDP socket.
+    ///
+    /// UDP is "connectionless", unlike TCP. Meaning, regardless of what address you've bound to, a `UdpSocket`
+    /// is free to communicate with many different remotes. In tokio there are basically two main ways to use `UdpSocket`:
+    ///
+    /// * one to many: [`bind`](`UdpSocket::bind`) and use [`send_to`](`UdpSocket::send_to`)
+    ///   and [`recv_from`](`UdpSocket::recv_from`) to communicate with many different addresses
+    /// * one to one: [`connect`](`UdpSocket::connect`) and associate with a single address, using [`send`](`UdpSocket::send`)
+    ///   and [`recv`](`UdpSocket::recv`) to communicate only with that remote address
+    ///
+    /// This type does not provide a `split` method, because this functionality
+    /// can be achieved by instead wrapping the socket in an [`Arc`]. Note that
+    /// you do not need a `Mutex` to share the `UdpSocket` — an `Arc<UdpSocket>`
+    /// is enough. This is because all of the methods take `&self` instead of
+    /// `&mut self`. Once you have wrapped it in an `Arc`, you can call
+    /// `.clone()` on the `Arc<UdpSocket>` to get multiple shared handles to the
+    /// same socket. An example of such usage can be found further down.
+    ///
+    /// [`Arc`]: std::sync::Arc
+    ///
+    /// # Streams
+    ///
+    /// If you need to listen over UDP and produce a [`Stream`], you can look
+    /// at [`UdpFramed`].
+    ///
+    /// [`UdpFramed`]: https://docs.rs/tokio-util/latest/tokio_util/udp/struct.UdpFramed.html
+    /// [`Stream`]: https://docs.rs/futures/0.3/futures/stream/trait.Stream.html
+    ///
+    /// # Example: one to many (bind)
+    ///
+    /// Using `bind` we can create a simple echo server that sends and recv's with many different clients:
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let sock = UdpSocket::bind("0.0.0.0:8080").await?;
+    ///     let mut buf = [0; 1024];
+    ///     loop {
+    ///         let (len, addr) = sock.recv_from(&mut buf).await?;
+    ///         println!("{:?} bytes received from {:?}", len, addr);
+    ///
+    ///         let len = sock.send_to(&buf[..len], addr).await?;
+    ///         println!("{:?} bytes sent", len);
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// # Example: one to one (connect)
+    ///
+    /// Or using `connect` we can echo with a single remote address using `send` and `recv`:
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let sock = UdpSocket::bind("0.0.0.0:8080").await?;
+    ///
+    ///     let remote_addr = "127.0.0.1:59611";
+    ///     sock.connect(remote_addr).await?;
+    ///     let mut buf = [0; 1024];
+    ///     loop {
+    ///         let len = sock.recv(&mut buf).await?;
+    ///         println!("{:?} bytes received from {:?}", len, remote_addr);
+    ///
+    ///         let len = sock.send(&buf[..len]).await?;
+    ///         println!("{:?} bytes sent", len);
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// # Example: Splitting with `Arc`
+    ///
+    /// Because `send_to` and `recv_from` take `&self`. It's perfectly alright
+    /// to use an `Arc<UdpSocket>` and share the references to multiple tasks.
+    /// Here is a similar "echo" example that supports concurrent
+    /// sending/receiving:
+    ///
+    /// ```no_run
+    /// use tokio::{net::UdpSocket, sync::mpsc};
+    /// use std::{io, net::SocketAddr, sync::Arc};
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let sock = UdpSocket::bind("0.0.0.0:8080".parse::<SocketAddr>().unwrap()).await?;
+    ///     let r = Arc::new(sock);
+    ///     let s = r.clone();
+    ///     let (tx, mut rx) = mpsc::channel::<(Vec<u8>, SocketAddr)>(1_000);
+    ///
+    ///     tokio::spawn(async move {
+    ///         while let Some((bytes, addr)) = rx.recv().await {
+    ///             let len = s.send_to(&bytes, &addr).await.unwrap();
+    ///             println!("{:?} bytes sent", len);
+    ///         }
+    ///     });
+    ///
+    ///     let mut buf = [0; 1024];
+    ///     loop {
+    ///         let (len, addr) = r.recv_from(&mut buf).await?;
+    ///         println!("{:?} bytes received from {:?}", len, addr);
+    ///         tx.send((buf[..len].to_vec(), addr)).await.unwrap();
+    ///     }
+    /// }
+    /// ```
+    ///
+    pub struct UdpSocket {
+        io: PollEvented<mio::net::UdpSocket>,
+    }
+}
+
+impl UdpSocket {
+    /// This function will create a new UDP socket and attempt to bind it to
+    /// the `addr` provided.
+    ///
+    /// Binding with a port number of 0 will request that the OS assigns a port
+    /// to this listener. The port allocated can be queried via the `local_addr`
+    /// method.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let sock = UdpSocket::bind("0.0.0.0:8080").await?;
+    ///     // use `sock`
+    /// #   let _ = sock;
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn bind<A: ToSocketAddrs>(addr: A) -> io::Result<UdpSocket> {
+        let addrs = to_socket_addrs(addr).await?;
+        let mut last_err = None;
+
+        for addr in addrs {
+            match UdpSocket::bind_addr(addr) {
+                Ok(socket) => return Ok(socket),
+                Err(e) => last_err = Some(e),
+            }
+        }
+
+        Err(last_err.unwrap_or_else(|| {
+            io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "could not resolve to any address",
+            )
+        }))
+    }
+
+    fn bind_addr(addr: SocketAddr) -> io::Result<UdpSocket> {
+        let sys = mio::net::UdpSocket::bind(addr)?;
+        UdpSocket::new(sys)
+    }
+
+    fn new(socket: mio::net::UdpSocket) -> io::Result<UdpSocket> {
+        let io = PollEvented::new(socket)?;
+        Ok(UdpSocket { io })
+    }
+
+    /// Creates new `UdpSocket` from a previously bound `std::net::UdpSocket`.
+    ///
+    /// This function is intended to be used to wrap a UDP socket from the
+    /// standard library in the Tokio equivalent. The conversion assumes nothing
+    /// about the underlying socket; it is left up to the user to set it in
+    /// non-blocking mode.
+    ///
+    /// This can be used in conjunction with socket2's `Socket` interface to
+    /// configure a socket before it's handed off, such as setting options like
+    /// `reuse_address` or binding to multiple addresses.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if thread-local runtime is not set.
+    ///
+    /// The runtime is usually set implicitly when this function is called
+    /// from a future driven by a tokio runtime, otherwise runtime can be set
+    /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter) function.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// # use std::{io, net::SocketAddr};
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() -> io::Result<()> {
+    /// let addr = "0.0.0.0:8080".parse::<SocketAddr>().unwrap();
+    /// let std_sock = std::net::UdpSocket::bind(addr)?;
+    /// std_sock.set_nonblocking(true)?;
+    /// let sock = UdpSocket::from_std(std_sock)?;
+    /// // use `sock`
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn from_std(socket: net::UdpSocket) -> io::Result<UdpSocket> {
+        let io = mio::net::UdpSocket::from_std(socket);
+        UdpSocket::new(io)
+    }
+
+    /// Turns a [`tokio::net::UdpSocket`] into a [`std::net::UdpSocket`].
+    ///
+    /// The returned [`std::net::UdpSocket`] will have nonblocking mode set as
+    /// `true`.  Use [`set_nonblocking`] to change the blocking mode if needed.
+    ///
+    /// # Examples
+    ///
+    /// ```rust,no_run
+    /// use std::error::Error;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let tokio_socket = tokio::net::UdpSocket::bind("127.0.0.1:0").await?;
+    ///     let std_socket = tokio_socket.into_std()?;
+    ///     std_socket.set_nonblocking(false)?;
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// [`tokio::net::UdpSocket`]: UdpSocket
+    /// [`std::net::UdpSocket`]: std::net::UdpSocket
+    /// [`set_nonblocking`]: fn@std::net::UdpSocket::set_nonblocking
+    pub fn into_std(self) -> io::Result<std::net::UdpSocket> {
+        #[cfg(unix)]
+        {
+            use std::os::unix::io::{FromRawFd, IntoRawFd};
+            self.io
+                .into_inner()
+                .map(|io| io.into_raw_fd())
+                .map(|raw_fd| unsafe { std::net::UdpSocket::from_raw_fd(raw_fd) })
+        }
+
+        #[cfg(windows)]
+        {
+            use std::os::windows::io::{FromRawSocket, IntoRawSocket};
+            self.io
+                .into_inner()
+                .map(|io| io.into_raw_socket())
+                .map(|raw_socket| unsafe { std::net::UdpSocket::from_raw_socket(raw_socket) })
+        }
+    }
+
+    /// Returns the local address that this socket is bound to.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// # use std::{io, net::SocketAddr};
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() -> io::Result<()> {
+    /// let addr = "0.0.0.0:8080".parse::<SocketAddr>().unwrap();
+    /// let sock = UdpSocket::bind(addr).await?;
+    /// // the address the socket is bound to
+    /// let local_addr = sock.local_addr()?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn local_addr(&self) -> io::Result<SocketAddr> {
+        self.io.local_addr()
+    }
+
+    /// Connects the UDP socket setting the default destination for send() and
+    /// limiting packets that are read via recv from the address specified in
+    /// `addr`.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// # use std::{io, net::SocketAddr};
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() -> io::Result<()> {
+    /// let sock = UdpSocket::bind("0.0.0.0:8080".parse::<SocketAddr>().unwrap()).await?;
+    ///
+    /// let remote_addr = "127.0.0.1:59600".parse::<SocketAddr>().unwrap();
+    /// sock.connect(remote_addr).await?;
+    /// let mut buf = [0u8; 32];
+    /// // recv from remote_addr
+    /// let len = sock.recv(&mut buf).await?;
+    /// // send to remote_addr
+    /// let _len = sock.send(&buf[..len]).await?;
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn connect<A: ToSocketAddrs>(&self, addr: A) -> io::Result<()> {
+        let addrs = to_socket_addrs(addr).await?;
+        let mut last_err = None;
+
+        for addr in addrs {
+            match self.io.connect(addr) {
+                Ok(_) => return Ok(()),
+                Err(e) => last_err = Some(e),
+            }
+        }
+
+        Err(last_err.unwrap_or_else(|| {
+            io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "could not resolve to any address",
+            )
+        }))
+    }
+
+    /// Waits for any of the requested ready states.
+    ///
+    /// This function is usually paired with `try_recv()` or `try_send()`. It
+    /// can be used to concurrently recv / send to the same socket on a single
+    /// task without splitting the socket.
+    ///
+    /// The function may complete without the socket being ready. This is a
+    /// false-positive and attempting an operation will return with
+    /// `io::ErrorKind::WouldBlock`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read or write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    ///
+    /// # Examples
+    ///
+    /// Concurrently receive from and send to the socket on the same task
+    /// without splitting.
+    ///
+    /// ```no_run
+    /// use tokio::io::{self, Interest};
+    /// use tokio::net::UdpSocket;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
+    ///     socket.connect("127.0.0.1:8081").await?;
+    ///
+    ///     loop {
+    ///         let ready = socket.ready(Interest::READABLE | Interest::WRITABLE).await?;
+    ///
+    ///         if ready.is_readable() {
+    ///             // The buffer is **not** included in the async task and will only exist
+    ///             // on the stack.
+    ///             let mut data = [0; 1024];
+    ///             match socket.try_recv(&mut data[..]) {
+    ///                 Ok(n) => {
+    ///                     println!("received {:?}", &data[..n]);
+    ///                 }
+    ///                 // False-positive, continue
+    ///                 Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {}
+    ///                 Err(e) => {
+    ///                     return Err(e);
+    ///                 }
+    ///             }
+    ///         }
+    ///
+    ///         if ready.is_writable() {
+    ///             // Write some data
+    ///             match socket.try_send(b"hello world") {
+    ///                 Ok(n) => {
+    ///                     println!("sent {} bytes", n);
+    ///                 }
+    ///                 // False-positive, continue
+    ///                 Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {}
+    ///                 Err(e) => {
+    ///                     return Err(e);
+    ///                 }
+    ///             }
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    pub async fn ready(&self, interest: Interest) -> io::Result<Ready> {
+        let event = self.io.registration().readiness(interest).await?;
+        Ok(event.ready)
+    }
+
+    /// Waits for the socket to become writable.
+    ///
+    /// This function is equivalent to `ready(Interest::WRITABLE)` and is
+    /// usually paired with `try_send()` or `try_send_to()`.
+    ///
+    /// The function may complete without the socket being writable. This is a
+    /// false-positive and attempting a `try_send()` will return with
+    /// `io::ErrorKind::WouldBlock`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     // Bind socket
+    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
+    ///     socket.connect("127.0.0.1:8081").await?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be writable
+    ///         socket.writable().await?;
+    ///
+    ///         // Try to send data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match socket.try_send(b"hello world") {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e);
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn writable(&self) -> io::Result<()> {
+        self.ready(Interest::WRITABLE).await?;
+        Ok(())
+    }
+
+    /// Polls for write/send readiness.
+    ///
+    /// If the udp stream is not currently ready for sending, this method will
+    /// store a clone of the `Waker` from the provided `Context`. When the udp
+    /// stream becomes ready for sending, `Waker::wake` will be called on the
+    /// waker.
+    ///
+    /// Note that on multiple calls to `poll_send_ready` or `poll_send`, only
+    /// the `Waker` from the `Context` passed to the most recent call is
+    /// scheduled to receive a wakeup. (However, `poll_recv_ready` retains a
+    /// second, independent waker.)
+    ///
+    /// This function is intended for cases where creating and pinning a future
+    /// via [`writable`] is not feasible. Where possible, using [`writable`] is
+    /// preferred, as this supports polling from multiple tasks at once.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the udp stream is not ready for writing.
+    /// * `Poll::Ready(Ok(()))` if the udp stream is ready for writing.
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// [`writable`]: method@Self::writable
+    pub fn poll_send_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.io.registration().poll_write_ready(cx).map_ok(|_| ())
+    }
+
+    /// Sends data on the socket to the remote address that the socket is
+    /// connected to.
+    ///
+    /// The [`connect`] method will connect this socket to a remote address.
+    /// This method will fail if the socket is not connected.
+    ///
+    /// [`connect`]: method@Self::connect
+    ///
+    /// # Return
+    ///
+    /// On success, the number of bytes sent is returned, otherwise, the
+    /// encountered error is returned.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. If `send` is used as the event in a
+    /// [`tokio::select!`](crate::select) statement and some other branch
+    /// completes first, then it is guaranteed that the message was not sent.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::io;
+    /// use tokio::net::UdpSocket;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     // Bind socket
+    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
+    ///     socket.connect("127.0.0.1:8081").await?;
+    ///
+    ///     // Send a message
+    ///     socket.send(b"hello world").await?;
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn send(&self, buf: &[u8]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .async_io(Interest::WRITABLE, || self.io.send(buf))
+            .await
+    }
+
+    /// Attempts to send data on the socket to the remote address to which it
+    /// was previously `connect`ed.
+    ///
+    /// The [`connect`] method will connect this socket to a remote address.
+    /// This method will fail if the socket is not connected.
+    ///
+    /// Note that on multiple calls to a `poll_*` method in the send direction,
+    /// only the `Waker` from the `Context` passed to the most recent call will
+    /// be scheduled to receive a wakeup.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the socket is not available to write
+    /// * `Poll::Ready(Ok(n))` `n` is the number of bytes sent
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// [`connect`]: method@Self::connect
+    pub fn poll_send(&self, cx: &mut Context<'_>, buf: &[u8]) -> Poll<io::Result<usize>> {
+        self.io
+            .registration()
+            .poll_write_io(cx, || self.io.send(buf))
+    }
+
+    /// Tries to send data on the socket to the remote address to which it is
+    /// connected.
+    ///
+    /// When the socket buffer is full, `Err(io::ErrorKind::WouldBlock)` is
+    /// returned. This function is usually paired with `writable()`.
+    ///
+    /// # Returns
+    ///
+    /// If successful, `Ok(n)` is returned, where `n` is the number of bytes
+    /// sent. If the socket is not ready to send data,
+    /// `Err(ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     // Bind a UDP socket
+    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
+    ///
+    ///     // Connect to a peer
+    ///     socket.connect("127.0.0.1:8081").await?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be writable
+    ///         socket.writable().await?;
+    ///
+    ///         // Try to send data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match socket.try_send(b"hello world") {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e);
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_send(&self, buf: &[u8]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::WRITABLE, || self.io.send(buf))
+    }
+
+    /// Waits for the socket to become readable.
+    ///
+    /// This function is equivalent to `ready(Interest::READABLE)` and is usually
+    /// paired with `try_recv()`.
+    ///
+    /// The function may complete without the socket being readable. This is a
+    /// false-positive and attempting a `try_recv()` will return with
+    /// `io::ErrorKind::WouldBlock`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     // Connect to a peer
+    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
+    ///     socket.connect("127.0.0.1:8081").await?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be readable
+    ///         socket.readable().await?;
+    ///
+    ///         // The buffer is **not** included in the async task and will
+    ///         // only exist on the stack.
+    ///         let mut buf = [0; 1024];
+    ///
+    ///         // Try to recv data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match socket.try_recv(&mut buf) {
+    ///             Ok(n) => {
+    ///                 println!("GOT {:?}", &buf[..n]);
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e);
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn readable(&self) -> io::Result<()> {
+        self.ready(Interest::READABLE).await?;
+        Ok(())
+    }
+
+    /// Polls for read/receive readiness.
+    ///
+    /// If the udp stream is not currently ready for receiving, this method will
+    /// store a clone of the `Waker` from the provided `Context`. When the udp
+    /// socket becomes ready for reading, `Waker::wake` will be called on the
+    /// waker.
+    ///
+    /// Note that on multiple calls to `poll_recv_ready`, `poll_recv` or
+    /// `poll_peek`, only the `Waker` from the `Context` passed to the most
+    /// recent call is scheduled to receive a wakeup. (However,
+    /// `poll_send_ready` retains a second, independent waker.)
+    ///
+    /// This function is intended for cases where creating and pinning a future
+    /// via [`readable`] is not feasible. Where possible, using [`readable`] is
+    /// preferred, as this supports polling from multiple tasks at once.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the udp stream is not ready for reading.
+    /// * `Poll::Ready(Ok(()))` if the udp stream is ready for reading.
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// [`readable`]: method@Self::readable
+    pub fn poll_recv_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.io.registration().poll_read_ready(cx).map_ok(|_| ())
+    }
+
+    /// Receives a single datagram message on the socket from the remote address
+    /// to which it is connected. On success, returns the number of bytes read.
+    ///
+    /// The function must be called with valid byte array `buf` of sufficient
+    /// size to hold the message bytes. If a message is too long to fit in the
+    /// supplied buffer, excess bytes may be discarded.
+    ///
+    /// The [`connect`] method will connect this socket to a remote address.
+    /// This method will fail if the socket is not connected.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. If `recv_from` is used as the event in a
+    /// [`tokio::select!`](crate::select) statement and some other branch
+    /// completes first, it is guaranteed that no messages were received on this
+    /// socket.
+    ///
+    /// [`connect`]: method@Self::connect
+    ///
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     // Bind socket
+    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
+    ///     socket.connect("127.0.0.1:8081").await?;
+    ///
+    ///     let mut buf = vec![0; 10];
+    ///     let n = socket.recv(&mut buf).await?;
+    ///
+    ///     println!("received {} bytes {:?}", n, &buf[..n]);
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn recv(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .async_io(Interest::READABLE, || self.io.recv(buf))
+            .await
+    }
+
+    /// Attempts to receive a single datagram message on the socket from the remote
+    /// address to which it is `connect`ed.
+    ///
+    /// The [`connect`] method will connect this socket to a remote address. This method
+    /// resolves to an error if the socket is not connected.
+    ///
+    /// Note that on multiple calls to a `poll_*` method in the recv direction, only the
+    /// `Waker` from the `Context` passed to the most recent call will be scheduled to
+    /// receive a wakeup.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the socket is not ready to read
+    /// * `Poll::Ready(Ok(()))` reads data `ReadBuf` if the socket is ready
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// [`connect`]: method@Self::connect
+    pub fn poll_recv(&self, cx: &mut Context<'_>, buf: &mut ReadBuf<'_>) -> Poll<io::Result<()>> {
+        let n = ready!(self.io.registration().poll_read_io(cx, || {
+            // Safety: will not read the maybe uninitialized bytes.
+            let b = unsafe {
+                &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8])
+            };
+
+            self.io.recv(b)
+        }))?;
+
+        // Safety: We trust `recv` to have filled up `n` bytes in the buffer.
+        unsafe {
+            buf.assume_init(n);
+        }
+        buf.advance(n);
+        Poll::Ready(Ok(()))
+    }
+
+    /// Tries to receive a single datagram message on the socket from the remote
+    /// address to which it is connected. On success, returns the number of
+    /// bytes read.
+    ///
+    /// The function must be called with valid byte array buf of sufficient size
+    /// to hold the message bytes. If a message is too long to fit in the
+    /// supplied buffer, excess bytes may be discarded.
+    ///
+    /// When there is no pending data, `Err(io::ErrorKind::WouldBlock)` is
+    /// returned. This function is usually paired with `readable()`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     // Connect to a peer
+    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
+    ///     socket.connect("127.0.0.1:8081").await?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be readable
+    ///         socket.readable().await?;
+    ///
+    ///         // The buffer is **not** included in the async task and will
+    ///         // only exist on the stack.
+    ///         let mut buf = [0; 1024];
+    ///
+    ///         // Try to recv data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match socket.try_recv(&mut buf) {
+    ///             Ok(n) => {
+    ///                 println!("GOT {:?}", &buf[..n]);
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e);
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_recv(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::READABLE, || self.io.recv(buf))
+    }
+
+    cfg_io_util! {
+        /// Tries to receive data from the stream into the provided buffer, advancing the
+        /// buffer's internal cursor, returning how many bytes were read.
+        ///
+        /// The function must be called with valid byte array buf of sufficient size
+        /// to hold the message bytes. If a message is too long to fit in the
+        /// supplied buffer, excess bytes may be discarded.
+        ///
+        /// When there is no pending data, `Err(io::ErrorKind::WouldBlock)` is
+        /// returned. This function is usually paired with `readable()`.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::net::UdpSocket;
+        /// use std::io;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     // Connect to a peer
+        ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
+        ///     socket.connect("127.0.0.1:8081").await?;
+        ///
+        ///     loop {
+        ///         // Wait for the socket to be readable
+        ///         socket.readable().await?;
+        ///
+        ///         let mut buf = Vec::with_capacity(1024);
+        ///
+        ///         // Try to recv data, this may still fail with `WouldBlock`
+        ///         // if the readiness event is a false positive.
+        ///         match socket.try_recv_buf(&mut buf) {
+        ///             Ok(n) => {
+        ///                 println!("GOT {:?}", &buf[..n]);
+        ///                 break;
+        ///             }
+        ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+        ///                 continue;
+        ///             }
+        ///             Err(e) => {
+        ///                 return Err(e);
+        ///             }
+        ///         }
+        ///     }
+        ///
+        ///     Ok(())
+        /// }
+        /// ```
+        pub fn try_recv_buf<B: BufMut>(&self, buf: &mut B) -> io::Result<usize> {
+            self.io.registration().try_io(Interest::READABLE, || {
+                let dst = buf.chunk_mut();
+                let dst =
+                    unsafe { &mut *(dst as *mut _ as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]) };
+
+                // Safety: We trust `UdpSocket::recv` to have filled up `n` bytes in the
+                // buffer.
+                let n = (&*self.io).recv(dst)?;
+
+                unsafe {
+                    buf.advance_mut(n);
+                }
+
+                Ok(n)
+            })
+        }
+
+        /// Tries to receive a single datagram message on the socket. On success,
+        /// returns the number of bytes read and the origin.
+        ///
+        /// The function must be called with valid byte array buf of sufficient size
+        /// to hold the message bytes. If a message is too long to fit in the
+        /// supplied buffer, excess bytes may be discarded.
+        ///
+        /// When there is no pending data, `Err(io::ErrorKind::WouldBlock)` is
+        /// returned. This function is usually paired with `readable()`.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::net::UdpSocket;
+        /// use std::io;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     // Connect to a peer
+        ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
+        ///
+        ///     loop {
+        ///         // Wait for the socket to be readable
+        ///         socket.readable().await?;
+        ///
+        ///         let mut buf = Vec::with_capacity(1024);
+        ///
+        ///         // Try to recv data, this may still fail with `WouldBlock`
+        ///         // if the readiness event is a false positive.
+        ///         match socket.try_recv_buf_from(&mut buf) {
+        ///             Ok((n, _addr)) => {
+        ///                 println!("GOT {:?}", &buf[..n]);
+        ///                 break;
+        ///             }
+        ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+        ///                 continue;
+        ///             }
+        ///             Err(e) => {
+        ///                 return Err(e);
+        ///             }
+        ///         }
+        ///     }
+        ///
+        ///     Ok(())
+        /// }
+        /// ```
+        pub fn try_recv_buf_from<B: BufMut>(&self, buf: &mut B) -> io::Result<(usize, SocketAddr)> {
+            self.io.registration().try_io(Interest::READABLE, || {
+                let dst = buf.chunk_mut();
+                let dst =
+                    unsafe { &mut *(dst as *mut _ as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]) };
+
+                // Safety: We trust `UdpSocket::recv_from` to have filled up `n` bytes in the
+                // buffer.
+                let (n, addr) = (&*self.io).recv_from(dst)?;
+
+                unsafe {
+                    buf.advance_mut(n);
+                }
+
+                Ok((n, addr))
+            })
+        }
+    }
+
+    /// Sends data on the socket to the given address. On success, returns the
+    /// number of bytes written.
+    ///
+    /// Address type can be any implementor of [`ToSocketAddrs`] trait. See its
+    /// documentation for concrete examples.
+    ///
+    /// It is possible for `addr` to yield multiple addresses, but `send_to`
+    /// will only send data to the first address yielded by `addr`.
+    ///
+    /// This will return an error when the IP version of the local socket does
+    /// not match that returned from [`ToSocketAddrs`].
+    ///
+    /// [`ToSocketAddrs`]: crate::net::ToSocketAddrs
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. If `send_to` is used as the event in a
+    /// [`tokio::select!`](crate::select) statement and some other branch
+    /// completes first, then it is guaranteed that the message was not sent.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
+    ///     let len = socket.send_to(b"hello world", "127.0.0.1:8081").await?;
+    ///
+    ///     println!("Sent {} bytes", len);
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn send_to<A: ToSocketAddrs>(&self, buf: &[u8], target: A) -> io::Result<usize> {
+        let mut addrs = to_socket_addrs(target).await?;
+
+        match addrs.next() {
+            Some(target) => self.send_to_addr(buf, target).await,
+            None => Err(io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "no addresses to send data to",
+            )),
+        }
+    }
+
+    /// Attempts to send data on the socket to a given address.
+    ///
+    /// Note that on multiple calls to a `poll_*` method in the send direction, only the
+    /// `Waker` from the `Context` passed to the most recent call will be scheduled to
+    /// receive a wakeup.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the socket is not ready to write
+    /// * `Poll::Ready(Ok(n))` `n` is the number of bytes sent.
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    pub fn poll_send_to(
+        &self,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+        target: SocketAddr,
+    ) -> Poll<io::Result<usize>> {
+        self.io
+            .registration()
+            .poll_write_io(cx, || self.io.send_to(buf, target))
+    }
+
+    /// Tries to send data on the socket to the given address, but if the send is
+    /// blocked this will return right away.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// # Returns
+    ///
+    /// If successful, returns the number of bytes sent
+    ///
+    /// Users should ensure that when the remote cannot receive, the
+    /// [`ErrorKind::WouldBlock`] is properly handled. An error can also occur
+    /// if the IP version of the socket does not match that of `target`.
+    ///
+    /// [`ErrorKind::WouldBlock`]: std::io::ErrorKind::WouldBlock
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
+    ///
+    ///     let dst = "127.0.0.1:8081".parse()?;
+    ///
+    ///     loop {
+    ///         socket.writable().await?;
+    ///
+    ///         match socket.try_send_to(&b"hello world"[..], dst) {
+    ///             Ok(sent) => {
+    ///                 println!("sent {} bytes", sent);
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 // Writable false positive.
+    ///                 continue;
+    ///             }
+    ///             Err(e) => return Err(e.into()),
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_send_to(&self, buf: &[u8], target: SocketAddr) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::WRITABLE, || self.io.send_to(buf, target))
+    }
+
+    async fn send_to_addr(&self, buf: &[u8], target: SocketAddr) -> io::Result<usize> {
+        self.io
+            .registration()
+            .async_io(Interest::WRITABLE, || self.io.send_to(buf, target))
+            .await
+    }
+
+    /// Receives a single datagram message on the socket. On success, returns
+    /// the number of bytes read and the origin.
+    ///
+    /// The function must be called with valid byte array `buf` of sufficient
+    /// size to hold the message bytes. If a message is too long to fit in the
+    /// supplied buffer, excess bytes may be discarded.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. If `recv_from` is used as the event in a
+    /// [`tokio::select!`](crate::select) statement and some other branch
+    /// completes first, it is guaranteed that no messages were received on this
+    /// socket.
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
+    ///
+    ///     let mut buf = vec![0u8; 32];
+    ///     let (len, addr) = socket.recv_from(&mut buf).await?;
+    ///
+    ///     println!("received {:?} bytes from {:?}", len, addr);
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
+        self.io
+            .registration()
+            .async_io(Interest::READABLE, || self.io.recv_from(buf))
+            .await
+    }
+
+    /// Attempts to receive a single datagram on the socket.
+    ///
+    /// Note that on multiple calls to a `poll_*` method in the recv direction, only the
+    /// `Waker` from the `Context` passed to the most recent call will be scheduled to
+    /// receive a wakeup.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the socket is not ready to read
+    /// * `Poll::Ready(Ok(addr))` reads data from `addr` into `ReadBuf` if the socket is ready
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    pub fn poll_recv_from(
+        &self,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<SocketAddr>> {
+        let (n, addr) = ready!(self.io.registration().poll_read_io(cx, || {
+            // Safety: will not read the maybe uninitialized bytes.
+            let b = unsafe {
+                &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8])
+            };
+
+            self.io.recv_from(b)
+        }))?;
+
+        // Safety: We trust `recv` to have filled up `n` bytes in the buffer.
+        unsafe {
+            buf.assume_init(n);
+        }
+        buf.advance(n);
+        Poll::Ready(Ok(addr))
+    }
+
+    /// Tries to receive a single datagram message on the socket. On success,
+    /// returns the number of bytes read and the origin.
+    ///
+    /// The function must be called with valid byte array buf of sufficient size
+    /// to hold the message bytes. If a message is too long to fit in the
+    /// supplied buffer, excess bytes may be discarded.
+    ///
+    /// When there is no pending data, `Err(io::ErrorKind::WouldBlock)` is
+    /// returned. This function is usually paired with `readable()`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     // Connect to a peer
+    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be readable
+    ///         socket.readable().await?;
+    ///
+    ///         // The buffer is **not** included in the async task and will
+    ///         // only exist on the stack.
+    ///         let mut buf = [0; 1024];
+    ///
+    ///         // Try to recv data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match socket.try_recv_from(&mut buf) {
+    ///             Ok((n, _addr)) => {
+    ///                 println!("GOT {:?}", &buf[..n]);
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e);
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
+        self.io
+            .registration()
+            .try_io(Interest::READABLE, || self.io.recv_from(buf))
+    }
+
+    /// Tries to read or write from the socket using a user-provided IO operation.
+    ///
+    /// If the socket is ready, the provided closure is called. The closure
+    /// should attempt to perform IO operation from the socket by manually
+    /// calling the appropriate syscall. If the operation fails because the
+    /// socket is not actually ready, then the closure should return a
+    /// `WouldBlock` error and the readiness flag is cleared. The return value
+    /// of the closure is then returned by `try_io`.
+    ///
+    /// If the socket is not ready, then the closure is not called
+    /// and a `WouldBlock` error is returned.
+    ///
+    /// The closure should only return a `WouldBlock` error if it has performed
+    /// an IO operation on the socket that failed due to the socket not being
+    /// ready. Returning a `WouldBlock` error in any other situation will
+    /// incorrectly clear the readiness flag, which can cause the socket to
+    /// behave incorrectly.
+    ///
+    /// The closure should not perform the IO operation using any of the methods
+    /// defined on the Tokio `UdpSocket` type, as this will mess with the
+    /// readiness flag and can cause the socket to behave incorrectly.
+    ///
+    /// Usually, [`readable()`], [`writable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`readable()`]: UdpSocket::readable()
+    /// [`writable()`]: UdpSocket::writable()
+    /// [`ready()`]: UdpSocket::ready()
+    pub fn try_io<R>(
+        &self,
+        interest: Interest,
+        f: impl FnOnce() -> io::Result<R>,
+    ) -> io::Result<R> {
+        self.io.registration().try_io(interest, f)
+    }
+
+    /// Receives data from the socket, without removing it from the input queue.
+    /// On success, returns the number of bytes read and the address from whence
+    /// the data came.
+    ///
+    /// # Notes
+    ///
+    /// On Windows, if the data is larger than the buffer specified, the buffer
+    /// is filled with the first part of the data, and peek_from returns the error
+    /// WSAEMSGSIZE(10040). The excess data is lost.
+    /// Make sure to always use a sufficiently large buffer to hold the
+    /// maximum UDP packet size, which can be up to 65536 bytes in size.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let socket = UdpSocket::bind("127.0.0.1:8080").await?;
+    ///
+    ///     let mut buf = vec![0u8; 32];
+    ///     let (len, addr) = socket.peek_from(&mut buf).await?;
+    ///
+    ///     println!("peeked {:?} bytes from {:?}", len, addr);
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn peek_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
+        self.io
+            .registration()
+            .async_io(Interest::READABLE, || self.io.peek_from(buf))
+            .await
+    }
+
+    /// Receives data from the socket, without removing it from the input queue.
+    /// On success, returns the number of bytes read.
+    ///
+    /// # Notes
+    ///
+    /// Note that on multiple calls to a `poll_*` method in the recv direction, only the
+    /// `Waker` from the `Context` passed to the most recent call will be scheduled to
+    /// receive a wakeup
+    ///
+    /// On Windows, if the data is larger than the buffer specified, the buffer
+    /// is filled with the first part of the data, and peek returns the error
+    /// WSAEMSGSIZE(10040). The excess data is lost.
+    /// Make sure to always use a sufficiently large buffer to hold the
+    /// maximum UDP packet size, which can be up to 65536 bytes in size.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the socket is not ready to read
+    /// * `Poll::Ready(Ok(addr))` reads data from `addr` into `ReadBuf` if the socket is ready
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    pub fn poll_peek_from(
+        &self,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<SocketAddr>> {
+        let (n, addr) = ready!(self.io.registration().poll_read_io(cx, || {
+            // Safety: will not read the maybe uninitialized bytes.
+            let b = unsafe {
+                &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8])
+            };
+
+            self.io.peek_from(b)
+        }))?;
+
+        // Safety: We trust `recv` to have filled up `n` bytes in the buffer.
+        unsafe {
+            buf.assume_init(n);
+        }
+        buf.advance(n);
+        Poll::Ready(Ok(addr))
+    }
+
+    /// Gets the value of the `SO_BROADCAST` option for this socket.
+    ///
+    /// For more information about this option, see [`set_broadcast`].
+    ///
+    /// [`set_broadcast`]: method@Self::set_broadcast
+    pub fn broadcast(&self) -> io::Result<bool> {
+        self.io.broadcast()
+    }
+
+    /// Sets the value of the `SO_BROADCAST` option for this socket.
+    ///
+    /// When enabled, this socket is allowed to send packets to a broadcast
+    /// address.
+    pub fn set_broadcast(&self, on: bool) -> io::Result<()> {
+        self.io.set_broadcast(on)
+    }
+
+    /// Gets the value of the `IP_MULTICAST_LOOP` option for this socket.
+    ///
+    /// For more information about this option, see [`set_multicast_loop_v4`].
+    ///
+    /// [`set_multicast_loop_v4`]: method@Self::set_multicast_loop_v4
+    pub fn multicast_loop_v4(&self) -> io::Result<bool> {
+        self.io.multicast_loop_v4()
+    }
+
+    /// Sets the value of the `IP_MULTICAST_LOOP` option for this socket.
+    ///
+    /// If enabled, multicast packets will be looped back to the local socket.
+    ///
+    /// # Note
+    ///
+    /// This may not have any affect on IPv6 sockets.
+    pub fn set_multicast_loop_v4(&self, on: bool) -> io::Result<()> {
+        self.io.set_multicast_loop_v4(on)
+    }
+
+    /// Gets the value of the `IP_MULTICAST_TTL` option for this socket.
+    ///
+    /// For more information about this option, see [`set_multicast_ttl_v4`].
+    ///
+    /// [`set_multicast_ttl_v4`]: method@Self::set_multicast_ttl_v4
+    pub fn multicast_ttl_v4(&self) -> io::Result<u32> {
+        self.io.multicast_ttl_v4()
+    }
+
+    /// Sets the value of the `IP_MULTICAST_TTL` option for this socket.
+    ///
+    /// Indicates the time-to-live value of outgoing multicast packets for
+    /// this socket. The default value is 1 which means that multicast packets
+    /// don't leave the local network unless explicitly requested.
+    ///
+    /// # Note
+    ///
+    /// This may not have any affect on IPv6 sockets.
+    pub fn set_multicast_ttl_v4(&self, ttl: u32) -> io::Result<()> {
+        self.io.set_multicast_ttl_v4(ttl)
+    }
+
+    /// Gets the value of the `IPV6_MULTICAST_LOOP` option for this socket.
+    ///
+    /// For more information about this option, see [`set_multicast_loop_v6`].
+    ///
+    /// [`set_multicast_loop_v6`]: method@Self::set_multicast_loop_v6
+    pub fn multicast_loop_v6(&self) -> io::Result<bool> {
+        self.io.multicast_loop_v6()
+    }
+
+    /// Sets the value of the `IPV6_MULTICAST_LOOP` option for this socket.
+    ///
+    /// Controls whether this socket sees the multicast packets it sends itself.
+    ///
+    /// # Note
+    ///
+    /// This may not have any affect on IPv4 sockets.
+    pub fn set_multicast_loop_v6(&self, on: bool) -> io::Result<()> {
+        self.io.set_multicast_loop_v6(on)
+    }
+
+    /// Gets the value of the `IP_TTL` option for this socket.
+    ///
+    /// For more information about this option, see [`set_ttl`].
+    ///
+    /// [`set_ttl`]: method@Self::set_ttl
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// # use std::io;
+    ///
+    /// # async fn dox() -> io::Result<()> {
+    /// let sock = UdpSocket::bind("127.0.0.1:8080").await?;
+    ///
+    /// println!("{:?}", sock.ttl()?);
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn ttl(&self) -> io::Result<u32> {
+        self.io.ttl()
+    }
+
+    /// Sets the value for the `IP_TTL` option on this socket.
+    ///
+    /// This value sets the time-to-live field that is used in every packet sent
+    /// from this socket.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UdpSocket;
+    /// # use std::io;
+    ///
+    /// # async fn dox() -> io::Result<()> {
+    /// let sock = UdpSocket::bind("127.0.0.1:8080").await?;
+    /// sock.set_ttl(60)?;
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn set_ttl(&self, ttl: u32) -> io::Result<()> {
+        self.io.set_ttl(ttl)
+    }
+
+    /// Executes an operation of the `IP_ADD_MEMBERSHIP` type.
+    ///
+    /// This function specifies a new multicast group for this socket to join.
+    /// The address must be a valid multicast address, and `interface` is the
+    /// address of the local interface with which the system should join the
+    /// multicast group. If it's equal to `INADDR_ANY` then an appropriate
+    /// interface is chosen by the system.
+    pub fn join_multicast_v4(&self, multiaddr: Ipv4Addr, interface: Ipv4Addr) -> io::Result<()> {
+        self.io.join_multicast_v4(&multiaddr, &interface)
+    }
+
+    /// Executes an operation of the `IPV6_ADD_MEMBERSHIP` type.
+    ///
+    /// This function specifies a new multicast group for this socket to join.
+    /// The address must be a valid multicast address, and `interface` is the
+    /// index of the interface to join/leave (or 0 to indicate any interface).
+    pub fn join_multicast_v6(&self, multiaddr: &Ipv6Addr, interface: u32) -> io::Result<()> {
+        self.io.join_multicast_v6(multiaddr, interface)
+    }
+
+    /// Executes an operation of the `IP_DROP_MEMBERSHIP` type.
+    ///
+    /// For more information about this option, see [`join_multicast_v4`].
+    ///
+    /// [`join_multicast_v4`]: method@Self::join_multicast_v4
+    pub fn leave_multicast_v4(&self, multiaddr: Ipv4Addr, interface: Ipv4Addr) -> io::Result<()> {
+        self.io.leave_multicast_v4(&multiaddr, &interface)
+    }
+
+    /// Executes an operation of the `IPV6_DROP_MEMBERSHIP` type.
+    ///
+    /// For more information about this option, see [`join_multicast_v6`].
+    ///
+    /// [`join_multicast_v6`]: method@Self::join_multicast_v6
+    pub fn leave_multicast_v6(&self, multiaddr: &Ipv6Addr, interface: u32) -> io::Result<()> {
+        self.io.leave_multicast_v6(multiaddr, interface)
+    }
+
+    /// Returns the value of the `SO_ERROR` option.
+    ///
+    /// # Examples
+    /// ```
+    /// use tokio::net::UdpSocket;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     // Create a socket
+    ///     let socket = UdpSocket::bind("0.0.0.0:8080").await?;
+    ///
+    ///     if let Ok(Some(err)) = socket.take_error() {
+    ///         println!("Got error: {:?}", err);
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn take_error(&self) -> io::Result<Option<io::Error>> {
+        self.io.take_error()
+    }
+}
+
+impl TryFrom<std::net::UdpSocket> for UdpSocket {
+    type Error = io::Error;
+
+    /// Consumes stream, returning the tokio I/O object.
+    ///
+    /// This is equivalent to
+    /// [`UdpSocket::from_std(stream)`](UdpSocket::from_std).
+    fn try_from(stream: std::net::UdpSocket) -> Result<Self, Self::Error> {
+        Self::from_std(stream)
+    }
+}
+
+impl fmt::Debug for UdpSocket {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.io.fmt(f)
+    }
+}
+
+#[cfg(all(unix))]
+mod sys {
+    use super::UdpSocket;
+    use std::os::unix::prelude::*;
+
+    impl AsRawFd for UdpSocket {
+        fn as_raw_fd(&self) -> RawFd {
+            self.io.as_raw_fd()
+        }
+    }
+}
+
+#[cfg(windows)]
+mod sys {
+    use super::UdpSocket;
+    use std::os::windows::prelude::*;
+
+    impl AsRawSocket for UdpSocket {
+        fn as_raw_socket(&self) -> RawSocket {
+            self.io.as_raw_socket()
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/net/unix/datagram/mod.rs b/third_party/rust/tokio/src/net/unix/datagram/mod.rs
new file mode 100644
index 0000000000..6268b4ac90
--- /dev/null
+++ b/third_party/rust/tokio/src/net/unix/datagram/mod.rs
@@ -0,0 +1,3 @@
+//! Unix datagram types.
+
+pub(crate) mod socket;
diff --git a/third_party/rust/tokio/src/net/unix/datagram/socket.rs b/third_party/rust/tokio/src/net/unix/datagram/socket.rs
new file mode 100644
index 0000000000..d5b618663d
--- /dev/null
+++ b/third_party/rust/tokio/src/net/unix/datagram/socket.rs
@@ -0,0 +1,1422 @@
+use crate::io::{Interest, PollEvented, ReadBuf, Ready};
+use crate::net::unix::SocketAddr;
+
+use std::convert::TryFrom;
+use std::fmt;
+use std::io;
+use std::net::Shutdown;
+use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
+use std::os::unix::net;
+use std::path::Path;
+use std::task::{Context, Poll};
+
+cfg_io_util! {
+    use bytes::BufMut;
+}
+
+cfg_net_unix! {
+    /// An I/O object representing a Unix datagram socket.
+    ///
+    /// A socket can be either named (associated with a filesystem path) or
+    /// unnamed.
+    ///
+    /// This type does not provide a `split` method, because this functionality
+    /// can be achieved by wrapping the socket in an [`Arc`]. Note that you do
+    /// not need a `Mutex` to share the `UnixDatagram` — an `Arc<UnixDatagram>`
+    /// is enough. This is because all of the methods take `&self` instead of
+    /// `&mut self`.
+    ///
+    /// **Note:** named sockets are persisted even after the object is dropped
+    /// and the program has exited, and cannot be reconnected. It is advised
+    /// that you either check for and unlink the existing socket if it exists,
+    /// or use a temporary file that is guaranteed to not already exist.
+    ///
+    /// [`Arc`]: std::sync::Arc
+    ///
+    /// # Examples
+    /// Using named sockets, associated with a filesystem path:
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    /// use tempfile::tempdir;
+    ///
+    /// // We use a temporary directory so that the socket
+    /// // files left by the bound sockets will get cleaned up.
+    /// let tmp = tempdir()?;
+    ///
+    /// // Bind each socket to a filesystem path
+    /// let tx_path = tmp.path().join("tx");
+    /// let tx = UnixDatagram::bind(&tx_path)?;
+    /// let rx_path = tmp.path().join("rx");
+    /// let rx = UnixDatagram::bind(&rx_path)?;
+    ///
+    /// let bytes = b"hello world";
+    /// tx.send_to(bytes, &rx_path).await?;
+    ///
+    /// let mut buf = vec![0u8; 24];
+    /// let (size, addr) = rx.recv_from(&mut buf).await?;
+    ///
+    /// let dgram = &buf[..size];
+    /// assert_eq!(dgram, bytes);
+    /// assert_eq!(addr.as_pathname().unwrap(), &tx_path);
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// Using unnamed sockets, created as a pair
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    ///
+    /// // Create the pair of sockets
+    /// let (sock1, sock2) = UnixDatagram::pair()?;
+    ///
+    /// // Since the sockets are paired, the paired send/recv
+    /// // functions can be used
+    /// let bytes = b"hello world";
+    /// sock1.send(bytes).await?;
+    ///
+    /// let mut buff = vec![0u8; 24];
+    /// let size = sock2.recv(&mut buff).await?;
+    ///
+    /// let dgram = &buff[..size];
+    /// assert_eq!(dgram, bytes);
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub struct UnixDatagram {
+        io: PollEvented<mio::net::UnixDatagram>,
+    }
+}
+
+impl UnixDatagram {
+    /// Waits for any of the requested ready states.
+    ///
+    /// This function is usually paired with `try_recv()` or `try_send()`. It
+    /// can be used to concurrently recv / send to the same socket on a single
+    /// task without splitting the socket.
+    ///
+    /// The function may complete without the socket being ready. This is a
+    /// false-positive and attempting an operation will return with
+    /// `io::ErrorKind::WouldBlock`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read or write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    ///
+    /// # Examples
+    ///
+    /// Concurrently receive from and send to the socket on the same task
+    /// without splitting.
+    ///
+    /// ```no_run
+    /// use tokio::io::Interest;
+    /// use tokio::net::UnixDatagram;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let dir = tempfile::tempdir().unwrap();
+    ///     let client_path = dir.path().join("client.sock");
+    ///     let server_path = dir.path().join("server.sock");
+    ///     let socket = UnixDatagram::bind(&client_path)?;
+    ///     socket.connect(&server_path)?;
+    ///
+    ///     loop {
+    ///         let ready = socket.ready(Interest::READABLE | Interest::WRITABLE).await?;
+    ///
+    ///         if ready.is_readable() {
+    ///             let mut data = [0; 1024];
+    ///             match socket.try_recv(&mut data[..]) {
+    ///                 Ok(n) => {
+    ///                     println!("received {:?}", &data[..n]);
+    ///                 }
+    ///                 // False-positive, continue
+    ///                 Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {}
+    ///                 Err(e) => {
+    ///                     return Err(e);
+    ///                 }
+    ///             }
+    ///         }
+    ///
+    ///         if ready.is_writable() {
+    ///             // Write some data
+    ///             match socket.try_send(b"hello world") {
+    ///                 Ok(n) => {
+    ///                     println!("sent {} bytes", n);
+    ///                 }
+    ///                 // False-positive, continue
+    ///                 Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {}
+    ///                 Err(e) => {
+    ///                     return Err(e);
+    ///                 }
+    ///             }
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    pub async fn ready(&self, interest: Interest) -> io::Result<Ready> {
+        let event = self.io.registration().readiness(interest).await?;
+        Ok(event.ready)
+    }
+
+    /// Waits for the socket to become writable.
+    ///
+    /// This function is equivalent to `ready(Interest::WRITABLE)` and is
+    /// usually paired with `try_send()` or `try_send_to()`.
+    ///
+    /// The function may complete without the socket being writable. This is a
+    /// false-positive and attempting a `try_send()` will return with
+    /// `io::ErrorKind::WouldBlock`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UnixDatagram;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let dir = tempfile::tempdir().unwrap();
+    ///     let client_path = dir.path().join("client.sock");
+    ///     let server_path = dir.path().join("server.sock");
+    ///     let socket = UnixDatagram::bind(&client_path)?;
+    ///     socket.connect(&server_path)?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be writable
+    ///         socket.writable().await?;
+    ///
+    ///         // Try to send data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match socket.try_send(b"hello world") {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e);
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn writable(&self) -> io::Result<()> {
+        self.ready(Interest::WRITABLE).await?;
+        Ok(())
+    }
+
+    /// Polls for write/send readiness.
+    ///
+    /// If the socket is not currently ready for sending, this method will
+    /// store a clone of the `Waker` from the provided `Context`. When the socket
+    /// becomes ready for sending, `Waker::wake` will be called on the
+    /// waker.
+    ///
+    /// Note that on multiple calls to `poll_send_ready` or `poll_send`, only
+    /// the `Waker` from the `Context` passed to the most recent call is
+    /// scheduled to receive a wakeup. (However, `poll_recv_ready` retains a
+    /// second, independent waker.)
+    ///
+    /// This function is intended for cases where creating and pinning a future
+    /// via [`writable`] is not feasible. Where possible, using [`writable`] is
+    /// preferred, as this supports polling from multiple tasks at once.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the socket is not ready for writing.
+    /// * `Poll::Ready(Ok(()))` if the socket is ready for writing.
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// [`writable`]: method@Self::writable
+    pub fn poll_send_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.io.registration().poll_write_ready(cx).map_ok(|_| ())
+    }
+
+    /// Waits for the socket to become readable.
+    ///
+    /// This function is equivalent to `ready(Interest::READABLE)` and is usually
+    /// paired with `try_recv()`.
+    ///
+    /// The function may complete without the socket being readable. This is a
+    /// false-positive and attempting a `try_recv()` will return with
+    /// `io::ErrorKind::WouldBlock`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UnixDatagram;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     // Connect to a peer
+    ///     let dir = tempfile::tempdir().unwrap();
+    ///     let client_path = dir.path().join("client.sock");
+    ///     let server_path = dir.path().join("server.sock");
+    ///     let socket = UnixDatagram::bind(&client_path)?;
+    ///     socket.connect(&server_path)?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be readable
+    ///         socket.readable().await?;
+    ///
+    ///         // The buffer is **not** included in the async task and will
+    ///         // only exist on the stack.
+    ///         let mut buf = [0; 1024];
+    ///
+    ///         // Try to recv data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match socket.try_recv(&mut buf) {
+    ///             Ok(n) => {
+    ///                 println!("GOT {:?}", &buf[..n]);
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e);
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn readable(&self) -> io::Result<()> {
+        self.ready(Interest::READABLE).await?;
+        Ok(())
+    }
+
+    /// Polls for read/receive readiness.
+    ///
+    /// If the socket is not currently ready for receiving, this method will
+    /// store a clone of the `Waker` from the provided `Context`. When the
+    /// socket becomes ready for reading, `Waker::wake` will be called on the
+    /// waker.
+    ///
+    /// Note that on multiple calls to `poll_recv_ready`, `poll_recv` or
+    /// `poll_peek`, only the `Waker` from the `Context` passed to the most
+    /// recent call is scheduled to receive a wakeup. (However,
+    /// `poll_send_ready` retains a second, independent waker.)
+    ///
+    /// This function is intended for cases where creating and pinning a future
+    /// via [`readable`] is not feasible. Where possible, using [`readable`] is
+    /// preferred, as this supports polling from multiple tasks at once.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the socket is not ready for reading.
+    /// * `Poll::Ready(Ok(()))` if the socket is ready for reading.
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// [`readable`]: method@Self::readable
+    pub fn poll_recv_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.io.registration().poll_read_ready(cx).map_ok(|_| ())
+    }
+
+    /// Creates a new `UnixDatagram` bound to the specified path.
+    ///
+    /// # Examples
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    /// use tempfile::tempdir;
+    ///
+    /// // We use a temporary directory so that the socket
+    /// // files left by the bound sockets will get cleaned up.
+    /// let tmp = tempdir()?;
+    ///
+    /// // Bind the socket to a filesystem path
+    /// let socket_path = tmp.path().join("socket");
+    /// let socket = UnixDatagram::bind(&socket_path)?;
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn bind<P>(path: P) -> io::Result<UnixDatagram>
+    where
+        P: AsRef<Path>,
+    {
+        let socket = mio::net::UnixDatagram::bind(path)?;
+        UnixDatagram::new(socket)
+    }
+
+    /// Creates an unnamed pair of connected sockets.
+    ///
+    /// This function will create a pair of interconnected Unix sockets for
+    /// communicating back and forth between one another.
+    ///
+    /// # Examples
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    ///
+    /// // Create the pair of sockets
+    /// let (sock1, sock2) = UnixDatagram::pair()?;
+    ///
+    /// // Since the sockets are paired, the paired send/recv
+    /// // functions can be used
+    /// let bytes = b"hail eris";
+    /// sock1.send(bytes).await?;
+    ///
+    /// let mut buff = vec![0u8; 24];
+    /// let size = sock2.recv(&mut buff).await?;
+    ///
+    /// let dgram = &buff[..size];
+    /// assert_eq!(dgram, bytes);
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn pair() -> io::Result<(UnixDatagram, UnixDatagram)> {
+        let (a, b) = mio::net::UnixDatagram::pair()?;
+        let a = UnixDatagram::new(a)?;
+        let b = UnixDatagram::new(b)?;
+
+        Ok((a, b))
+    }
+
+    /// Creates new `UnixDatagram` from a `std::os::unix::net::UnixDatagram`.
+    ///
+    /// This function is intended to be used to wrap a UnixDatagram from the
+    /// standard library in the Tokio equivalent. The conversion assumes
+    /// nothing about the underlying datagram; it is left up to the user to set
+    /// it in non-blocking mode.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if thread-local runtime is not set.
+    ///
+    /// The runtime is usually set implicitly when this function is called
+    /// from a future driven by a Tokio runtime, otherwise runtime can be set
+    /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter) function.
+    /// # Examples
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    /// use std::os::unix::net::UnixDatagram as StdUDS;
+    /// use tempfile::tempdir;
+    ///
+    /// // We use a temporary directory so that the socket
+    /// // files left by the bound sockets will get cleaned up.
+    /// let tmp = tempdir()?;
+    ///
+    /// // Bind the socket to a filesystem path
+    /// let socket_path = tmp.path().join("socket");
+    /// let std_socket = StdUDS::bind(&socket_path)?;
+    /// std_socket.set_nonblocking(true)?;
+    /// let tokio_socket = UnixDatagram::from_std(std_socket)?;
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn from_std(datagram: net::UnixDatagram) -> io::Result<UnixDatagram> {
+        let socket = mio::net::UnixDatagram::from_std(datagram);
+        let io = PollEvented::new(socket)?;
+        Ok(UnixDatagram { io })
+    }
+
+    /// Turns a [`tokio::net::UnixDatagram`] into a [`std::os::unix::net::UnixDatagram`].
+    ///
+    /// The returned [`std::os::unix::net::UnixDatagram`] will have nonblocking
+    /// mode set as `true`.  Use [`set_nonblocking`] to change the blocking mode
+    /// if needed.
+    ///
+    /// # Examples
+    ///
+    /// ```rust,no_run
+    /// use std::error::Error;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let tokio_socket = tokio::net::UnixDatagram::bind("127.0.0.1:0")?;
+    ///     let std_socket = tokio_socket.into_std()?;
+    ///     std_socket.set_nonblocking(false)?;
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// [`tokio::net::UnixDatagram`]: UnixDatagram
+    /// [`std::os::unix::net::UnixDatagram`]: std::os::unix::net::UnixDatagram
+    /// [`set_nonblocking`]: fn@std::os::unix::net::UnixDatagram::set_nonblocking
+    pub fn into_std(self) -> io::Result<std::os::unix::net::UnixDatagram> {
+        self.io
+            .into_inner()
+            .map(|io| io.into_raw_fd())
+            .map(|raw_fd| unsafe { std::os::unix::net::UnixDatagram::from_raw_fd(raw_fd) })
+    }
+
+    fn new(socket: mio::net::UnixDatagram) -> io::Result<UnixDatagram> {
+        let io = PollEvented::new(socket)?;
+        Ok(UnixDatagram { io })
+    }
+
+    /// Creates a new `UnixDatagram` which is not bound to any address.
+    ///
+    /// # Examples
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    /// use tempfile::tempdir;
+    ///
+    /// // Create an unbound socket
+    /// let tx = UnixDatagram::unbound()?;
+    ///
+    /// // Create another, bound socket
+    /// let tmp = tempdir()?;
+    /// let rx_path = tmp.path().join("rx");
+    /// let rx = UnixDatagram::bind(&rx_path)?;
+    ///
+    /// // Send to the bound socket
+    /// let bytes = b"hello world";
+    /// tx.send_to(bytes, &rx_path).await?;
+    ///
+    /// let mut buf = vec![0u8; 24];
+    /// let (size, addr) = rx.recv_from(&mut buf).await?;
+    ///
+    /// let dgram = &buf[..size];
+    /// assert_eq!(dgram, bytes);
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn unbound() -> io::Result<UnixDatagram> {
+        let socket = mio::net::UnixDatagram::unbound()?;
+        UnixDatagram::new(socket)
+    }
+
+    /// Connects the socket to the specified address.
+    ///
+    /// The `send` method may be used to send data to the specified address.
+    /// `recv` and `recv_from` will only receive data from that address.
+    ///
+    /// # Examples
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    /// use tempfile::tempdir;
+    ///
+    /// // Create an unbound socket
+    /// let tx = UnixDatagram::unbound()?;
+    ///
+    /// // Create another, bound socket
+    /// let tmp = tempdir()?;
+    /// let rx_path = tmp.path().join("rx");
+    /// let rx = UnixDatagram::bind(&rx_path)?;
+    ///
+    /// // Connect to the bound socket
+    /// tx.connect(&rx_path)?;
+    ///
+    /// // Send to the bound socket
+    /// let bytes = b"hello world";
+    /// tx.send(bytes).await?;
+    ///
+    /// let mut buf = vec![0u8; 24];
+    /// let (size, addr) = rx.recv_from(&mut buf).await?;
+    ///
+    /// let dgram = &buf[..size];
+    /// assert_eq!(dgram, bytes);
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn connect<P: AsRef<Path>>(&self, path: P) -> io::Result<()> {
+        self.io.connect(path)
+    }
+
+    /// Sends data on the socket to the socket's peer.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. If `send` is used as the event in a
+    /// [`tokio::select!`](crate::select) statement and some other branch
+    /// completes first, then it is guaranteed that the message was not sent.
+    ///
+    /// # Examples
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    ///
+    /// // Create the pair of sockets
+    /// let (sock1, sock2) = UnixDatagram::pair()?;
+    ///
+    /// // Since the sockets are paired, the paired send/recv
+    /// // functions can be used
+    /// let bytes = b"hello world";
+    /// sock1.send(bytes).await?;
+    ///
+    /// let mut buff = vec![0u8; 24];
+    /// let size = sock2.recv(&mut buff).await?;
+    ///
+    /// let dgram = &buff[..size];
+    /// assert_eq!(dgram, bytes);
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn send(&self, buf: &[u8]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .async_io(Interest::WRITABLE, || self.io.send(buf))
+            .await
+    }
+
+    /// Tries to send a datagram to the peer without waiting.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UnixDatagram;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let dir = tempfile::tempdir().unwrap();
+    ///     let client_path = dir.path().join("client.sock");
+    ///     let server_path = dir.path().join("server.sock");
+    ///     let socket = UnixDatagram::bind(&client_path)?;
+    ///     socket.connect(&server_path)?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be writable
+    ///         socket.writable().await?;
+    ///
+    ///         // Try to send data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match socket.try_send(b"hello world") {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e);
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_send(&self, buf: &[u8]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::WRITABLE, || self.io.send(buf))
+    }
+
+    /// Tries to send a datagram to the peer without waiting.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UnixDatagram;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let dir = tempfile::tempdir().unwrap();
+    ///     let client_path = dir.path().join("client.sock");
+    ///     let server_path = dir.path().join("server.sock");
+    ///     let socket = UnixDatagram::bind(&client_path)?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be writable
+    ///         socket.writable().await?;
+    ///
+    ///         // Try to send data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match socket.try_send_to(b"hello world", &server_path) {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e);
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_send_to<P>(&self, buf: &[u8], target: P) -> io::Result<usize>
+    where
+        P: AsRef<Path>,
+    {
+        self.io
+            .registration()
+            .try_io(Interest::WRITABLE, || self.io.send_to(buf, target))
+    }
+
+    /// Receives data from the socket.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. If `recv` is used as the event in a
+    /// [`tokio::select!`](crate::select) statement and some other branch
+    /// completes first, it is guaranteed that no messages were received on this
+    /// socket.
+    ///
+    /// # Examples
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    ///
+    /// // Create the pair of sockets
+    /// let (sock1, sock2) = UnixDatagram::pair()?;
+    ///
+    /// // Since the sockets are paired, the paired send/recv
+    /// // functions can be used
+    /// let bytes = b"hello world";
+    /// sock1.send(bytes).await?;
+    ///
+    /// let mut buff = vec![0u8; 24];
+    /// let size = sock2.recv(&mut buff).await?;
+    ///
+    /// let dgram = &buff[..size];
+    /// assert_eq!(dgram, bytes);
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn recv(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .async_io(Interest::READABLE, || self.io.recv(buf))
+            .await
+    }
+
+    /// Tries to receive a datagram from the peer without waiting.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UnixDatagram;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     // Connect to a peer
+    ///     let dir = tempfile::tempdir().unwrap();
+    ///     let client_path = dir.path().join("client.sock");
+    ///     let server_path = dir.path().join("server.sock");
+    ///     let socket = UnixDatagram::bind(&client_path)?;
+    ///     socket.connect(&server_path)?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be readable
+    ///         socket.readable().await?;
+    ///
+    ///         // The buffer is **not** included in the async task and will
+    ///         // only exist on the stack.
+    ///         let mut buf = [0; 1024];
+    ///
+    ///         // Try to recv data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match socket.try_recv(&mut buf) {
+    ///             Ok(n) => {
+    ///                 println!("GOT {:?}", &buf[..n]);
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e);
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_recv(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::READABLE, || self.io.recv(buf))
+    }
+
+    cfg_io_util! {
+        /// Tries to receive data from the socket without waiting.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::net::UnixDatagram;
+        /// use std::io;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     // Connect to a peer
+        ///     let dir = tempfile::tempdir().unwrap();
+        ///     let client_path = dir.path().join("client.sock");
+        ///     let server_path = dir.path().join("server.sock");
+        ///     let socket = UnixDatagram::bind(&client_path)?;
+        ///
+        ///     loop {
+        ///         // Wait for the socket to be readable
+        ///         socket.readable().await?;
+        ///
+        ///         let mut buf = Vec::with_capacity(1024);
+        ///
+        ///         // Try to recv data, this may still fail with `WouldBlock`
+        ///         // if the readiness event is a false positive.
+        ///         match socket.try_recv_buf_from(&mut buf) {
+        ///             Ok((n, _addr)) => {
+        ///                 println!("GOT {:?}", &buf[..n]);
+        ///                 break;
+        ///             }
+        ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+        ///                 continue;
+        ///             }
+        ///             Err(e) => {
+        ///                 return Err(e);
+        ///             }
+        ///         }
+        ///     }
+        ///
+        ///     Ok(())
+        /// }
+        /// ```
+        pub fn try_recv_buf_from<B: BufMut>(&self, buf: &mut B) -> io::Result<(usize, SocketAddr)> {
+            let (n, addr) = self.io.registration().try_io(Interest::READABLE, || {
+                let dst = buf.chunk_mut();
+                let dst =
+                    unsafe { &mut *(dst as *mut _ as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]) };
+
+                // Safety: We trust `UnixDatagram::recv_from` to have filled up `n` bytes in the
+                // buffer.
+                let (n, addr) = (&*self.io).recv_from(dst)?;
+
+                unsafe {
+                    buf.advance_mut(n);
+                }
+
+                Ok((n, addr))
+            })?;
+
+            Ok((n, SocketAddr(addr)))
+        }
+
+        /// Tries to read data from the stream into the provided buffer, advancing the
+        /// buffer's internal cursor, returning how many bytes were read.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::net::UnixDatagram;
+        /// use std::io;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> io::Result<()> {
+        ///     // Connect to a peer
+        ///     let dir = tempfile::tempdir().unwrap();
+        ///     let client_path = dir.path().join("client.sock");
+        ///     let server_path = dir.path().join("server.sock");
+        ///     let socket = UnixDatagram::bind(&client_path)?;
+        ///     socket.connect(&server_path)?;
+        ///
+        ///     loop {
+        ///         // Wait for the socket to be readable
+        ///         socket.readable().await?;
+        ///
+        ///         let mut buf = Vec::with_capacity(1024);
+        ///
+        ///         // Try to recv data, this may still fail with `WouldBlock`
+        ///         // if the readiness event is a false positive.
+        ///         match socket.try_recv_buf(&mut buf) {
+        ///             Ok(n) => {
+        ///                 println!("GOT {:?}", &buf[..n]);
+        ///                 break;
+        ///             }
+        ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+        ///                 continue;
+        ///             }
+        ///             Err(e) => {
+        ///                 return Err(e);
+        ///             }
+        ///         }
+        ///     }
+        ///
+        ///     Ok(())
+        /// }
+        /// ```
+        pub fn try_recv_buf<B: BufMut>(&self, buf: &mut B) -> io::Result<usize> {
+            self.io.registration().try_io(Interest::READABLE, || {
+                let dst = buf.chunk_mut();
+                let dst =
+                    unsafe { &mut *(dst as *mut _ as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]) };
+
+                // Safety: We trust `UnixDatagram::recv` to have filled up `n` bytes in the
+                // buffer.
+                let n = (&*self.io).recv(dst)?;
+
+                unsafe {
+                    buf.advance_mut(n);
+                }
+
+                Ok(n)
+            })
+        }
+    }
+
+    /// Sends data on the socket to the specified address.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. If `send_to` is used as the event in a
+    /// [`tokio::select!`](crate::select) statement and some other branch
+    /// completes first, then it is guaranteed that the message was not sent.
+    ///
+    /// # Examples
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    /// use tempfile::tempdir;
+    ///
+    /// // We use a temporary directory so that the socket
+    /// // files left by the bound sockets will get cleaned up.
+    /// let tmp = tempdir()?;
+    ///
+    /// // Bind each socket to a filesystem path
+    /// let tx_path = tmp.path().join("tx");
+    /// let tx = UnixDatagram::bind(&tx_path)?;
+    /// let rx_path = tmp.path().join("rx");
+    /// let rx = UnixDatagram::bind(&rx_path)?;
+    ///
+    /// let bytes = b"hello world";
+    /// tx.send_to(bytes, &rx_path).await?;
+    ///
+    /// let mut buf = vec![0u8; 24];
+    /// let (size, addr) = rx.recv_from(&mut buf).await?;
+    ///
+    /// let dgram = &buf[..size];
+    /// assert_eq!(dgram, bytes);
+    /// assert_eq!(addr.as_pathname().unwrap(), &tx_path);
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn send_to<P>(&self, buf: &[u8], target: P) -> io::Result<usize>
+    where
+        P: AsRef<Path>,
+    {
+        self.io
+            .registration()
+            .async_io(Interest::WRITABLE, || self.io.send_to(buf, target.as_ref()))
+            .await
+    }
+
+    /// Receives data from the socket.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. If `recv_from` is used as the event in a
+    /// [`tokio::select!`](crate::select) statement and some other branch
+    /// completes first, it is guaranteed that no messages were received on this
+    /// socket.
+    ///
+    /// # Examples
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    /// use tempfile::tempdir;
+    ///
+    /// // We use a temporary directory so that the socket
+    /// // files left by the bound sockets will get cleaned up.
+    /// let tmp = tempdir()?;
+    ///
+    /// // Bind each socket to a filesystem path
+    /// let tx_path = tmp.path().join("tx");
+    /// let tx = UnixDatagram::bind(&tx_path)?;
+    /// let rx_path = tmp.path().join("rx");
+    /// let rx = UnixDatagram::bind(&rx_path)?;
+    ///
+    /// let bytes = b"hello world";
+    /// tx.send_to(bytes, &rx_path).await?;
+    ///
+    /// let mut buf = vec![0u8; 24];
+    /// let (size, addr) = rx.recv_from(&mut buf).await?;
+    ///
+    /// let dgram = &buf[..size];
+    /// assert_eq!(dgram, bytes);
+    /// assert_eq!(addr.as_pathname().unwrap(), &tx_path);
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub async fn recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
+        let (n, addr) = self
+            .io
+            .registration()
+            .async_io(Interest::READABLE, || self.io.recv_from(buf))
+            .await?;
+
+        Ok((n, SocketAddr(addr)))
+    }
+
+    /// Attempts to receive a single datagram on the specified address.
+    ///
+    /// Note that on multiple calls to a `poll_*` method in the recv direction, only the
+    /// `Waker` from the `Context` passed to the most recent call will be scheduled to
+    /// receive a wakeup.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the socket is not ready to read
+    /// * `Poll::Ready(Ok(addr))` reads data from `addr` into `ReadBuf` if the socket is ready
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    pub fn poll_recv_from(
+        &self,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<SocketAddr>> {
+        let (n, addr) = ready!(self.io.registration().poll_read_io(cx, || {
+            // Safety: will not read the maybe uninitialized bytes.
+            let b = unsafe {
+                &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8])
+            };
+
+            self.io.recv_from(b)
+        }))?;
+
+        // Safety: We trust `recv` to have filled up `n` bytes in the buffer.
+        unsafe {
+            buf.assume_init(n);
+        }
+        buf.advance(n);
+        Poll::Ready(Ok(SocketAddr(addr)))
+    }
+
+    /// Attempts to send data to the specified address.
+    ///
+    /// Note that on multiple calls to a `poll_*` method in the send direction, only the
+    /// `Waker` from the `Context` passed to the most recent call will be scheduled to
+    /// receive a wakeup.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the socket is not ready to write
+    /// * `Poll::Ready(Ok(n))` `n` is the number of bytes sent.
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    pub fn poll_send_to<P>(
+        &self,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+        target: P,
+    ) -> Poll<io::Result<usize>>
+    where
+        P: AsRef<Path>,
+    {
+        self.io
+            .registration()
+            .poll_write_io(cx, || self.io.send_to(buf, target.as_ref()))
+    }
+
+    /// Attempts to send data on the socket to the remote address to which it
+    /// was previously `connect`ed.
+    ///
+    /// The [`connect`] method will connect this socket to a remote address.
+    /// This method will fail if the socket is not connected.
+    ///
+    /// Note that on multiple calls to a `poll_*` method in the send direction,
+    /// only the `Waker` from the `Context` passed to the most recent call will
+    /// be scheduled to receive a wakeup.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the socket is not available to write
+    /// * `Poll::Ready(Ok(n))` `n` is the number of bytes sent
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// [`connect`]: method@Self::connect
+    pub fn poll_send(&self, cx: &mut Context<'_>, buf: &[u8]) -> Poll<io::Result<usize>> {
+        self.io
+            .registration()
+            .poll_write_io(cx, || self.io.send(buf))
+    }
+
+    /// Attempts to receive a single datagram message on the socket from the remote
+    /// address to which it is `connect`ed.
+    ///
+    /// The [`connect`] method will connect this socket to a remote address. This method
+    /// resolves to an error if the socket is not connected.
+    ///
+    /// Note that on multiple calls to a `poll_*` method in the recv direction, only the
+    /// `Waker` from the `Context` passed to the most recent call will be scheduled to
+    /// receive a wakeup.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the socket is not ready to read
+    /// * `Poll::Ready(Ok(()))` reads data `ReadBuf` if the socket is ready
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// [`connect`]: method@Self::connect
+    pub fn poll_recv(&self, cx: &mut Context<'_>, buf: &mut ReadBuf<'_>) -> Poll<io::Result<()>> {
+        let n = ready!(self.io.registration().poll_read_io(cx, || {
+            // Safety: will not read the maybe uninitialized bytes.
+            let b = unsafe {
+                &mut *(buf.unfilled_mut() as *mut [std::mem::MaybeUninit<u8>] as *mut [u8])
+            };
+
+            self.io.recv(b)
+        }))?;
+
+        // Safety: We trust `recv` to have filled up `n` bytes in the buffer.
+        unsafe {
+            buf.assume_init(n);
+        }
+        buf.advance(n);
+        Poll::Ready(Ok(()))
+    }
+
+    /// Tries to receive data from the socket without waiting.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UnixDatagram;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     // Connect to a peer
+    ///     let dir = tempfile::tempdir().unwrap();
+    ///     let client_path = dir.path().join("client.sock");
+    ///     let server_path = dir.path().join("server.sock");
+    ///     let socket = UnixDatagram::bind(&client_path)?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be readable
+    ///         socket.readable().await?;
+    ///
+    ///         // The buffer is **not** included in the async task and will
+    ///         // only exist on the stack.
+    ///         let mut buf = [0; 1024];
+    ///
+    ///         // Try to recv data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match socket.try_recv_from(&mut buf) {
+    ///             Ok((n, _addr)) => {
+    ///                 println!("GOT {:?}", &buf[..n]);
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e);
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
+        let (n, addr) = self
+            .io
+            .registration()
+            .try_io(Interest::READABLE, || self.io.recv_from(buf))?;
+
+        Ok((n, SocketAddr(addr)))
+    }
+
+    /// Tries to read or write from the socket using a user-provided IO operation.
+    ///
+    /// If the socket is ready, the provided closure is called. The closure
+    /// should attempt to perform IO operation from the socket by manually
+    /// calling the appropriate syscall. If the operation fails because the
+    /// socket is not actually ready, then the closure should return a
+    /// `WouldBlock` error and the readiness flag is cleared. The return value
+    /// of the closure is then returned by `try_io`.
+    ///
+    /// If the socket is not ready, then the closure is not called
+    /// and a `WouldBlock` error is returned.
+    ///
+    /// The closure should only return a `WouldBlock` error if it has performed
+    /// an IO operation on the socket that failed due to the socket not being
+    /// ready. Returning a `WouldBlock` error in any other situation will
+    /// incorrectly clear the readiness flag, which can cause the socket to
+    /// behave incorrectly.
+    ///
+    /// The closure should not perform the IO operation using any of the methods
+    /// defined on the Tokio `UnixDatagram` type, as this will mess with the
+    /// readiness flag and can cause the socket to behave incorrectly.
+    ///
+    /// Usually, [`readable()`], [`writable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`readable()`]: UnixDatagram::readable()
+    /// [`writable()`]: UnixDatagram::writable()
+    /// [`ready()`]: UnixDatagram::ready()
+    pub fn try_io<R>(
+        &self,
+        interest: Interest,
+        f: impl FnOnce() -> io::Result<R>,
+    ) -> io::Result<R> {
+        self.io.registration().try_io(interest, f)
+    }
+
+    /// Returns the local address that this socket is bound to.
+    ///
+    /// # Examples
+    /// For a socket bound to a local path
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    /// use tempfile::tempdir;
+    ///
+    /// // We use a temporary directory so that the socket
+    /// // files left by the bound sockets will get cleaned up.
+    /// let tmp = tempdir()?;
+    ///
+    /// // Bind socket to a filesystem path
+    /// let socket_path = tmp.path().join("socket");
+    /// let socket = UnixDatagram::bind(&socket_path)?;
+    ///
+    /// assert_eq!(socket.local_addr()?.as_pathname().unwrap(), &socket_path);
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// For an unbound socket
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    ///
+    /// // Create an unbound socket
+    /// let socket = UnixDatagram::unbound()?;
+    ///
+    /// assert!(socket.local_addr()?.is_unnamed());
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn local_addr(&self) -> io::Result<SocketAddr> {
+        self.io.local_addr().map(SocketAddr)
+    }
+
+    /// Returns the address of this socket's peer.
+    ///
+    /// The `connect` method will connect the socket to a peer.
+    ///
+    /// # Examples
+    /// For a peer with a local path
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    /// use tempfile::tempdir;
+    ///
+    /// // Create an unbound socket
+    /// let tx = UnixDatagram::unbound()?;
+    ///
+    /// // Create another, bound socket
+    /// let tmp = tempdir()?;
+    /// let rx_path = tmp.path().join("rx");
+    /// let rx = UnixDatagram::bind(&rx_path)?;
+    ///
+    /// // Connect to the bound socket
+    /// tx.connect(&rx_path)?;
+    ///
+    /// assert_eq!(tx.peer_addr()?.as_pathname().unwrap(), &rx_path);
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// For an unbound peer
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    ///
+    /// // Create the pair of sockets
+    /// let (sock1, sock2) = UnixDatagram::pair()?;
+    ///
+    /// assert!(sock1.peer_addr()?.is_unnamed());
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn peer_addr(&self) -> io::Result<SocketAddr> {
+        self.io.peer_addr().map(SocketAddr)
+    }
+
+    /// Returns the value of the `SO_ERROR` option.
+    ///
+    /// # Examples
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    ///
+    /// // Create an unbound socket
+    /// let socket = UnixDatagram::unbound()?;
+    ///
+    /// if let Ok(Some(err)) = socket.take_error() {
+    ///     println!("Got error: {:?}", err);
+    /// }
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn take_error(&self) -> io::Result<Option<io::Error>> {
+        self.io.take_error()
+    }
+
+    /// Shuts down the read, write, or both halves of this connection.
+    ///
+    /// This function will cause all pending and future I/O calls on the
+    /// specified portions to immediately return with an appropriate value
+    /// (see the documentation of `Shutdown`).
+    ///
+    /// # Examples
+    /// ```
+    /// # use std::error::Error;
+    /// # #[tokio::main]
+    /// # async fn main() -> Result<(), Box<dyn Error>> {
+    /// use tokio::net::UnixDatagram;
+    /// use std::net::Shutdown;
+    ///
+    /// // Create an unbound socket
+    /// let (socket, other) = UnixDatagram::pair()?;
+    ///
+    /// socket.shutdown(Shutdown::Both)?;
+    ///
+    /// // NOTE: the following commented out code does NOT work as expected.
+    /// // Due to an underlying issue, the recv call will block indefinitely.
+    /// // See: https://github.com/tokio-rs/tokio/issues/1679
+    /// //let mut buff = vec![0u8; 24];
+    /// //let size = socket.recv(&mut buff).await?;
+    /// //assert_eq!(size, 0);
+    ///
+    /// let send_result = socket.send(b"hello world").await;
+    /// assert!(send_result.is_err());
+    ///
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn shutdown(&self, how: Shutdown) -> io::Result<()> {
+        self.io.shutdown(how)
+    }
+}
+
+impl TryFrom<std::os::unix::net::UnixDatagram> for UnixDatagram {
+    type Error = io::Error;
+
+    /// Consumes stream, returning the Tokio I/O object.
+    ///
+    /// This is equivalent to
+    /// [`UnixDatagram::from_std(stream)`](UnixDatagram::from_std).
+    fn try_from(stream: std::os::unix::net::UnixDatagram) -> Result<Self, Self::Error> {
+        Self::from_std(stream)
+    }
+}
+
+impl fmt::Debug for UnixDatagram {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.io.fmt(f)
+    }
+}
+
+impl AsRawFd for UnixDatagram {
+    fn as_raw_fd(&self) -> RawFd {
+        self.io.as_raw_fd()
+    }
+}
diff --git a/third_party/rust/tokio/src/net/unix/listener.rs b/third_party/rust/tokio/src/net/unix/listener.rs
new file mode 100644
index 0000000000..1785f8b0f7
--- /dev/null
+++ b/third_party/rust/tokio/src/net/unix/listener.rs
@@ -0,0 +1,186 @@
+use crate::io::{Interest, PollEvented};
+use crate::net::unix::{SocketAddr, UnixStream};
+
+use std::convert::TryFrom;
+use std::fmt;
+use std::io;
+use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
+use std::os::unix::net;
+use std::path::Path;
+use std::task::{Context, Poll};
+
+cfg_net_unix! {
+    /// A Unix socket which can accept connections from other Unix sockets.
+    ///
+    /// You can accept a new connection by using the [`accept`](`UnixListener::accept`) method.
+    ///
+    /// A `UnixListener` can be turned into a `Stream` with [`UnixListenerStream`].
+    ///
+    /// [`UnixListenerStream`]: https://docs.rs/tokio-stream/0.1/tokio_stream/wrappers/struct.UnixListenerStream.html
+    ///
+    /// # Errors
+    ///
+    /// Note that accepting a connection can lead to various errors and not all
+    /// of them are necessarily fatal ‒ for example having too many open file
+    /// descriptors or the other side closing the connection while it waits in
+    /// an accept queue. These would terminate the stream if not handled in any
+    /// way.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UnixListener;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let listener = UnixListener::bind("/path/to/the/socket").unwrap();
+    ///     loop {
+    ///         match listener.accept().await {
+    ///             Ok((stream, _addr)) => {
+    ///                 println!("new client!");
+    ///             }
+    ///             Err(e) => { /* connection failed */ }
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    pub struct UnixListener {
+        io: PollEvented<mio::net::UnixListener>,
+    }
+}
+
+impl UnixListener {
+    /// Creates a new `UnixListener` bound to the specified path.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if thread-local runtime is not set.
+    ///
+    /// The runtime is usually set implicitly when this function is called
+    /// from a future driven by a tokio runtime, otherwise runtime can be set
+    /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter) function.
+    pub fn bind<P>(path: P) -> io::Result<UnixListener>
+    where
+        P: AsRef<Path>,
+    {
+        let listener = mio::net::UnixListener::bind(path)?;
+        let io = PollEvented::new(listener)?;
+        Ok(UnixListener { io })
+    }
+
+    /// Creates new `UnixListener` from a `std::os::unix::net::UnixListener `.
+    ///
+    /// This function is intended to be used to wrap a UnixListener from the
+    /// standard library in the Tokio equivalent. The conversion assumes
+    /// nothing about the underlying listener; it is left up to the user to set
+    /// it in non-blocking mode.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if thread-local runtime is not set.
+    ///
+    /// The runtime is usually set implicitly when this function is called
+    /// from a future driven by a tokio runtime, otherwise runtime can be set
+    /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter) function.
+    pub fn from_std(listener: net::UnixListener) -> io::Result<UnixListener> {
+        let listener = mio::net::UnixListener::from_std(listener);
+        let io = PollEvented::new(listener)?;
+        Ok(UnixListener { io })
+    }
+
+    /// Turns a [`tokio::net::UnixListener`] into a [`std::os::unix::net::UnixListener`].
+    ///
+    /// The returned [`std::os::unix::net::UnixListener`] will have nonblocking mode
+    /// set as `true`.  Use [`set_nonblocking`] to change the blocking mode if needed.
+    ///
+    /// # Examples
+    ///
+    /// ```rust,no_run
+    /// use std::error::Error;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let tokio_listener = tokio::net::UnixListener::bind("127.0.0.1:0")?;
+    ///     let std_listener = tokio_listener.into_std()?;
+    ///     std_listener.set_nonblocking(false)?;
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// [`tokio::net::UnixListener`]: UnixListener
+    /// [`std::os::unix::net::UnixListener`]: std::os::unix::net::UnixListener
+    /// [`set_nonblocking`]: fn@std::os::unix::net::UnixListener::set_nonblocking
+    pub fn into_std(self) -> io::Result<std::os::unix::net::UnixListener> {
+        self.io
+            .into_inner()
+            .map(|io| io.into_raw_fd())
+            .map(|raw_fd| unsafe { net::UnixListener::from_raw_fd(raw_fd) })
+    }
+
+    /// Returns the local socket address of this listener.
+    pub fn local_addr(&self) -> io::Result<SocketAddr> {
+        self.io.local_addr().map(SocketAddr)
+    }
+
+    /// Returns the value of the `SO_ERROR` option.
+    pub fn take_error(&self) -> io::Result<Option<io::Error>> {
+        self.io.take_error()
+    }
+
+    /// Accepts a new incoming connection to this listener.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. If the method is used as the event in a
+    /// [`tokio::select!`](crate::select) statement and some other branch
+    /// completes first, then it is guaranteed that no new connections were
+    /// accepted by this method.
+    pub async fn accept(&self) -> io::Result<(UnixStream, SocketAddr)> {
+        let (mio, addr) = self
+            .io
+            .registration()
+            .async_io(Interest::READABLE, || self.io.accept())
+            .await?;
+
+        let addr = SocketAddr(addr);
+        let stream = UnixStream::new(mio)?;
+        Ok((stream, addr))
+    }
+
+    /// Polls to accept a new incoming connection to this listener.
+    ///
+    /// If there is no connection to accept, `Poll::Pending` is returned and the
+    /// current task will be notified by a waker.  Note that on multiple calls
+    /// to `poll_accept`, only the `Waker` from the `Context` passed to the most
+    /// recent call is scheduled to receive a wakeup.
+    pub fn poll_accept(&self, cx: &mut Context<'_>) -> Poll<io::Result<(UnixStream, SocketAddr)>> {
+        let (sock, addr) = ready!(self.io.registration().poll_read_io(cx, || self.io.accept()))?;
+        let addr = SocketAddr(addr);
+        let sock = UnixStream::new(sock)?;
+        Poll::Ready(Ok((sock, addr)))
+    }
+}
+
+impl TryFrom<std::os::unix::net::UnixListener> for UnixListener {
+    type Error = io::Error;
+
+    /// Consumes stream, returning the tokio I/O object.
+    ///
+    /// This is equivalent to
+    /// [`UnixListener::from_std(stream)`](UnixListener::from_std).
+    fn try_from(stream: std::os::unix::net::UnixListener) -> io::Result<Self> {
+        Self::from_std(stream)
+    }
+}
+
+impl fmt::Debug for UnixListener {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.io.fmt(f)
+    }
+}
+
+impl AsRawFd for UnixListener {
+    fn as_raw_fd(&self) -> RawFd {
+        self.io.as_raw_fd()
+    }
+}
diff --git a/third_party/rust/tokio/src/net/unix/mod.rs b/third_party/rust/tokio/src/net/unix/mod.rs
new file mode 100644
index 0000000000..14cb456705
--- /dev/null
+++ b/third_party/rust/tokio/src/net/unix/mod.rs
@@ -0,0 +1,24 @@
+//! Unix domain socket utility types.
+
+// This module does not currently provide any public API, but it was
+// unintentionally defined as a public module. Hide it from the documentation
+// instead of changing it to a private module to avoid breakage.
+#[doc(hidden)]
+pub mod datagram;
+
+pub(crate) mod listener;
+
+mod split;
+pub use split::{ReadHalf, WriteHalf};
+
+mod split_owned;
+pub use split_owned::{OwnedReadHalf, OwnedWriteHalf, ReuniteError};
+
+mod socketaddr;
+pub use socketaddr::SocketAddr;
+
+pub(crate) mod stream;
+pub(crate) use stream::UnixStream;
+
+mod ucred;
+pub use ucred::UCred;
diff --git a/third_party/rust/tokio/src/net/unix/socketaddr.rs b/third_party/rust/tokio/src/net/unix/socketaddr.rs
new file mode 100644
index 0000000000..48f7b96b8c
--- /dev/null
+++ b/third_party/rust/tokio/src/net/unix/socketaddr.rs
@@ -0,0 +1,31 @@
+use std::fmt;
+use std::path::Path;
+
+/// An address associated with a Tokio Unix socket.
+pub struct SocketAddr(pub(super) mio::net::SocketAddr);
+
+impl SocketAddr {
+    /// Returns `true` if the address is unnamed.
+    ///
+    /// Documentation reflected in [`SocketAddr`]
+    ///
+    /// [`SocketAddr`]: std::os::unix::net::SocketAddr
+    pub fn is_unnamed(&self) -> bool {
+        self.0.is_unnamed()
+    }
+
+    /// Returns the contents of this address if it is a `pathname` address.
+    ///
+    /// Documentation reflected in [`SocketAddr`]
+    ///
+    /// [`SocketAddr`]: std::os::unix::net::SocketAddr
+    pub fn as_pathname(&self) -> Option<&Path> {
+        self.0.as_pathname()
+    }
+}
+
+impl fmt::Debug for SocketAddr {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.0.fmt(fmt)
+    }
+}
diff --git a/third_party/rust/tokio/src/net/unix/split.rs b/third_party/rust/tokio/src/net/unix/split.rs
new file mode 100644
index 0000000000..d4686c22d7
--- /dev/null
+++ b/third_party/rust/tokio/src/net/unix/split.rs
@@ -0,0 +1,305 @@
+//! `UnixStream` split support.
+//!
+//! A `UnixStream` can be split into a read half and a write half with
+//! `UnixStream::split`. The read half implements `AsyncRead` while the write
+//! half implements `AsyncWrite`.
+//!
+//! Compared to the generic split of `AsyncRead + AsyncWrite`, this specialized
+//! split has no associated overhead and enforces all invariants at the type
+//! level.
+
+use crate::io::{AsyncRead, AsyncWrite, Interest, ReadBuf, Ready};
+use crate::net::UnixStream;
+
+use crate::net::unix::SocketAddr;
+use std::io;
+use std::net::Shutdown;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+cfg_io_util! {
+    use bytes::BufMut;
+}
+
+/// Borrowed read half of a [`UnixStream`], created by [`split`].
+///
+/// Reading from a `ReadHalf` is usually done using the convenience methods found on the
+/// [`AsyncReadExt`] trait.
+///
+/// [`UnixStream`]: UnixStream
+/// [`split`]: UnixStream::split()
+/// [`AsyncReadExt`]: trait@crate::io::AsyncReadExt
+#[derive(Debug)]
+pub struct ReadHalf<'a>(&'a UnixStream);
+
+/// Borrowed write half of a [`UnixStream`], created by [`split`].
+///
+/// Note that in the [`AsyncWrite`] implementation of this type, [`poll_shutdown`] will
+/// shut down the UnixStream stream in the write direction.
+///
+/// Writing to an `WriteHalf` is usually done using the convenience methods found
+/// on the [`AsyncWriteExt`] trait.
+///
+/// [`UnixStream`]: UnixStream
+/// [`split`]: UnixStream::split()
+/// [`AsyncWrite`]: trait@crate::io::AsyncWrite
+/// [`poll_shutdown`]: fn@crate::io::AsyncWrite::poll_shutdown
+/// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+#[derive(Debug)]
+pub struct WriteHalf<'a>(&'a UnixStream);
+
+pub(crate) fn split(stream: &mut UnixStream) -> (ReadHalf<'_>, WriteHalf<'_>) {
+    (ReadHalf(stream), WriteHalf(stream))
+}
+
+impl ReadHalf<'_> {
+    /// Wait for any of the requested ready states.
+    ///
+    /// This function is usually paired with `try_read()` or `try_write()`. It
+    /// can be used to concurrently read / write to the same socket on a single
+    /// task without splitting the socket.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read or write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    pub async fn ready(&self, interest: Interest) -> io::Result<Ready> {
+        self.0.ready(interest).await
+    }
+
+    /// Waits for the socket to become readable.
+    ///
+    /// This function is equivalent to `ready(Interest::READABLE)` and is usually
+    /// paired with `try_read()`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    pub async fn readable(&self) -> io::Result<()> {
+        self.0.readable().await
+    }
+
+    /// Tries to read data from the stream into the provided buffer, returning how
+    /// many bytes were read.
+    ///
+    /// Receives any pending data from the socket but does not wait for new data
+    /// to arrive. On success, returns the number of bytes read. Because
+    /// `try_read()` is non-blocking, the buffer does not have to be stored by
+    /// the async task and can exist entirely on the stack.
+    ///
+    /// Usually, [`readable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`readable()`]: Self::readable()
+    /// [`ready()`]: Self::ready()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+    /// and will no longer yield data. If the stream is not ready to read data
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    pub fn try_read(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.0.try_read(buf)
+    }
+
+    cfg_io_util! {
+        /// Tries to read data from the stream into the provided buffer, advancing the
+        /// buffer's internal cursor, returning how many bytes were read.
+        ///
+        /// Receives any pending data from the socket but does not wait for new data
+        /// to arrive. On success, returns the number of bytes read. Because
+        /// `try_read_buf()` is non-blocking, the buffer does not have to be stored by
+        /// the async task and can exist entirely on the stack.
+        ///
+        /// Usually, [`readable()`] or [`ready()`] is used with this function.
+        ///
+        /// [`readable()`]: Self::readable()
+        /// [`ready()`]: Self::ready()
+        ///
+        /// # Return
+        ///
+        /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+        /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+        /// and will no longer yield data. If the stream is not ready to read data
+        pub fn try_read_buf<B: BufMut>(&self, buf: &mut B) -> io::Result<usize> {
+            self.0.try_read_buf(buf)
+        }
+    }
+
+    /// Tries to read data from the stream into the provided buffers, returning
+    /// how many bytes were read.
+    ///
+    /// Data is copied to fill each buffer in order, with the final buffer
+    /// written to possibly being only partially filled. This method behaves
+    /// equivalently to a single call to [`try_read()`] with concatenated
+    /// buffers.
+    ///
+    /// Receives any pending data from the socket but does not wait for new data
+    /// to arrive. On success, returns the number of bytes read. Because
+    /// `try_read_vectored()` is non-blocking, the buffer does not have to be
+    /// stored by the async task and can exist entirely on the stack.
+    ///
+    /// Usually, [`readable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`try_read()`]: Self::try_read()
+    /// [`readable()`]: Self::readable()
+    /// [`ready()`]: Self::ready()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+    /// and will no longer yield data. If the stream is not ready to read data
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    pub fn try_read_vectored(&self, bufs: &mut [io::IoSliceMut<'_>]) -> io::Result<usize> {
+        self.0.try_read_vectored(bufs)
+    }
+
+    /// Returns the socket address of the remote half of this connection.
+    pub fn peer_addr(&self) -> io::Result<SocketAddr> {
+        self.0.peer_addr()
+    }
+
+    /// Returns the socket address of the local half of this connection.
+    pub fn local_addr(&self) -> io::Result<SocketAddr> {
+        self.0.local_addr()
+    }
+}
+
+impl WriteHalf<'_> {
+    /// Waits for any of the requested ready states.
+    ///
+    /// This function is usually paired with `try_read()` or `try_write()`. It
+    /// can be used to concurrently read / write to the same socket on a single
+    /// task without splitting the socket.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read or write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    pub async fn ready(&self, interest: Interest) -> io::Result<Ready> {
+        self.0.ready(interest).await
+    }
+
+    /// Waits for the socket to become writable.
+    ///
+    /// This function is equivalent to `ready(Interest::WRITABLE)` and is usually
+    /// paired with `try_write()`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    pub async fn writable(&self) -> io::Result<()> {
+        self.0.writable().await
+    }
+
+    /// Tries to write a buffer to the stream, returning how many bytes were
+    /// written.
+    ///
+    /// The function will attempt to write the entire contents of `buf`, but
+    /// only part of the buffer may be written.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// # Return
+    ///
+    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
+    /// number of bytes written. If the stream is not ready to write data,
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    pub fn try_write(&self, buf: &[u8]) -> io::Result<usize> {
+        self.0.try_write(buf)
+    }
+
+    /// Tries to write several buffers to the stream, returning how many bytes
+    /// were written.
+    ///
+    /// Data is written from each buffer in order, with the final buffer read
+    /// from possible being only partially consumed. This method behaves
+    /// equivalently to a single call to [`try_write()`] with concatenated
+    /// buffers.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// [`try_write()`]: Self::try_write()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
+    /// number of bytes written. If the stream is not ready to write data,
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    pub fn try_write_vectored(&self, buf: &[io::IoSlice<'_>]) -> io::Result<usize> {
+        self.0.try_write_vectored(buf)
+    }
+
+    /// Returns the socket address of the remote half of this connection.
+    pub fn peer_addr(&self) -> io::Result<SocketAddr> {
+        self.0.peer_addr()
+    }
+
+    /// Returns the socket address of the local half of this connection.
+    pub fn local_addr(&self) -> io::Result<SocketAddr> {
+        self.0.local_addr()
+    }
+}
+
+impl AsyncRead for ReadHalf<'_> {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        self.0.poll_read_priv(cx, buf)
+    }
+}
+
+impl AsyncWrite for WriteHalf<'_> {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.0.poll_write_priv(cx, buf)
+    }
+
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.0.poll_write_vectored_priv(cx, bufs)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        self.0.is_write_vectored()
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.0.shutdown_std(Shutdown::Write).into()
+    }
+}
+
+impl AsRef<UnixStream> for ReadHalf<'_> {
+    fn as_ref(&self) -> &UnixStream {
+        self.0
+    }
+}
+
+impl AsRef<UnixStream> for WriteHalf<'_> {
+    fn as_ref(&self) -> &UnixStream {
+        self.0
+    }
+}
diff --git a/third_party/rust/tokio/src/net/unix/split_owned.rs b/third_party/rust/tokio/src/net/unix/split_owned.rs
new file mode 100644
index 0000000000..9c3a2a4177
--- /dev/null
+++ b/third_party/rust/tokio/src/net/unix/split_owned.rs
@@ -0,0 +1,393 @@
+//! `UnixStream` owned split support.
+//!
+//! A `UnixStream` can be split into an `OwnedReadHalf` and a `OwnedWriteHalf`
+//! with the `UnixStream::into_split` method.  `OwnedReadHalf` implements
+//! `AsyncRead` while `OwnedWriteHalf` implements `AsyncWrite`.
+//!
+//! Compared to the generic split of `AsyncRead + AsyncWrite`, this specialized
+//! split has no associated overhead and enforces all invariants at the type
+//! level.
+
+use crate::io::{AsyncRead, AsyncWrite, Interest, ReadBuf, Ready};
+use crate::net::UnixStream;
+
+use crate::net::unix::SocketAddr;
+use std::error::Error;
+use std::net::Shutdown;
+use std::pin::Pin;
+use std::sync::Arc;
+use std::task::{Context, Poll};
+use std::{fmt, io};
+
+cfg_io_util! {
+    use bytes::BufMut;
+}
+
+/// Owned read half of a [`UnixStream`], created by [`into_split`].
+///
+/// Reading from an `OwnedReadHalf` is usually done using the convenience methods found
+/// on the [`AsyncReadExt`] trait.
+///
+/// [`UnixStream`]: crate::net::UnixStream
+/// [`into_split`]: crate::net::UnixStream::into_split()
+/// [`AsyncReadExt`]: trait@crate::io::AsyncReadExt
+#[derive(Debug)]
+pub struct OwnedReadHalf {
+    inner: Arc<UnixStream>,
+}
+
+/// Owned write half of a [`UnixStream`], created by [`into_split`].
+///
+/// Note that in the [`AsyncWrite`] implementation of this type,
+/// [`poll_shutdown`] will shut down the stream in the write direction.
+/// Dropping the write half will also shut down the write half of the stream.
+///
+/// Writing to an `OwnedWriteHalf` is usually done using the convenience methods
+/// found on the [`AsyncWriteExt`] trait.
+///
+/// [`UnixStream`]: crate::net::UnixStream
+/// [`into_split`]: crate::net::UnixStream::into_split()
+/// [`AsyncWrite`]: trait@crate::io::AsyncWrite
+/// [`poll_shutdown`]: fn@crate::io::AsyncWrite::poll_shutdown
+/// [`AsyncWriteExt`]: trait@crate::io::AsyncWriteExt
+#[derive(Debug)]
+pub struct OwnedWriteHalf {
+    inner: Arc<UnixStream>,
+    shutdown_on_drop: bool,
+}
+
+pub(crate) fn split_owned(stream: UnixStream) -> (OwnedReadHalf, OwnedWriteHalf) {
+    let arc = Arc::new(stream);
+    let read = OwnedReadHalf {
+        inner: Arc::clone(&arc),
+    };
+    let write = OwnedWriteHalf {
+        inner: arc,
+        shutdown_on_drop: true,
+    };
+    (read, write)
+}
+
+pub(crate) fn reunite(
+    read: OwnedReadHalf,
+    write: OwnedWriteHalf,
+) -> Result<UnixStream, ReuniteError> {
+    if Arc::ptr_eq(&read.inner, &write.inner) {
+        write.forget();
+        // This unwrap cannot fail as the api does not allow creating more than two Arcs,
+        // and we just dropped the other half.
+        Ok(Arc::try_unwrap(read.inner).expect("UnixStream: try_unwrap failed in reunite"))
+    } else {
+        Err(ReuniteError(read, write))
+    }
+}
+
+/// Error indicating that two halves were not from the same socket, and thus could
+/// not be reunited.
+#[derive(Debug)]
+pub struct ReuniteError(pub OwnedReadHalf, pub OwnedWriteHalf);
+
+impl fmt::Display for ReuniteError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(
+            f,
+            "tried to reunite halves that are not from the same socket"
+        )
+    }
+}
+
+impl Error for ReuniteError {}
+
+impl OwnedReadHalf {
+    /// Attempts to put the two halves of a `UnixStream` back together and
+    /// recover the original socket. Succeeds only if the two halves
+    /// originated from the same call to [`into_split`].
+    ///
+    /// [`into_split`]: crate::net::UnixStream::into_split()
+    pub fn reunite(self, other: OwnedWriteHalf) -> Result<UnixStream, ReuniteError> {
+        reunite(self, other)
+    }
+
+    /// Waits for any of the requested ready states.
+    ///
+    /// This function is usually paired with `try_read()` or `try_write()`. It
+    /// can be used to concurrently read / write to the same socket on a single
+    /// task without splitting the socket.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read or write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    pub async fn ready(&self, interest: Interest) -> io::Result<Ready> {
+        self.inner.ready(interest).await
+    }
+
+    /// Waits for the socket to become readable.
+    ///
+    /// This function is equivalent to `ready(Interest::READABLE)` and is usually
+    /// paired with `try_read()`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    pub async fn readable(&self) -> io::Result<()> {
+        self.inner.readable().await
+    }
+
+    /// Tries to read data from the stream into the provided buffer, returning how
+    /// many bytes were read.
+    ///
+    /// Receives any pending data from the socket but does not wait for new data
+    /// to arrive. On success, returns the number of bytes read. Because
+    /// `try_read()` is non-blocking, the buffer does not have to be stored by
+    /// the async task and can exist entirely on the stack.
+    ///
+    /// Usually, [`readable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`readable()`]: Self::readable()
+    /// [`ready()`]: Self::ready()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+    /// and will no longer yield data. If the stream is not ready to read data
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    pub fn try_read(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.inner.try_read(buf)
+    }
+
+    cfg_io_util! {
+        /// Tries to read data from the stream into the provided buffer, advancing the
+        /// buffer's internal cursor, returning how many bytes were read.
+        ///
+        /// Receives any pending data from the socket but does not wait for new data
+        /// to arrive. On success, returns the number of bytes read. Because
+        /// `try_read_buf()` is non-blocking, the buffer does not have to be stored by
+        /// the async task and can exist entirely on the stack.
+        ///
+        /// Usually, [`readable()`] or [`ready()`] is used with this function.
+        ///
+        /// [`readable()`]: Self::readable()
+        /// [`ready()`]: Self::ready()
+        ///
+        /// # Return
+        ///
+        /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+        /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+        /// and will no longer yield data. If the stream is not ready to read data
+        /// `Err(io::ErrorKind::WouldBlock)` is returned.
+        pub fn try_read_buf<B: BufMut>(&self, buf: &mut B) -> io::Result<usize> {
+            self.inner.try_read_buf(buf)
+        }
+    }
+
+    /// Tries to read data from the stream into the provided buffers, returning
+    /// how many bytes were read.
+    ///
+    /// Data is copied to fill each buffer in order, with the final buffer
+    /// written to possibly being only partially filled. This method behaves
+    /// equivalently to a single call to [`try_read()`] with concatenated
+    /// buffers.
+    ///
+    /// Receives any pending data from the socket but does not wait for new data
+    /// to arrive. On success, returns the number of bytes read. Because
+    /// `try_read_vectored()` is non-blocking, the buffer does not have to be
+    /// stored by the async task and can exist entirely on the stack.
+    ///
+    /// Usually, [`readable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`try_read()`]: Self::try_read()
+    /// [`readable()`]: Self::readable()
+    /// [`ready()`]: Self::ready()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+    /// and will no longer yield data. If the stream is not ready to read data
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    pub fn try_read_vectored(&self, bufs: &mut [io::IoSliceMut<'_>]) -> io::Result<usize> {
+        self.inner.try_read_vectored(bufs)
+    }
+
+    /// Returns the socket address of the remote half of this connection.
+    pub fn peer_addr(&self) -> io::Result<SocketAddr> {
+        self.inner.peer_addr()
+    }
+
+    /// Returns the socket address of the local half of this connection.
+    pub fn local_addr(&self) -> io::Result<SocketAddr> {
+        self.inner.local_addr()
+    }
+}
+
+impl AsyncRead for OwnedReadHalf {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        self.inner.poll_read_priv(cx, buf)
+    }
+}
+
+impl OwnedWriteHalf {
+    /// Attempts to put the two halves of a `UnixStream` back together and
+    /// recover the original socket. Succeeds only if the two halves
+    /// originated from the same call to [`into_split`].
+    ///
+    /// [`into_split`]: crate::net::UnixStream::into_split()
+    pub fn reunite(self, other: OwnedReadHalf) -> Result<UnixStream, ReuniteError> {
+        reunite(other, self)
+    }
+
+    /// Destroys the write half, but don't close the write half of the stream
+    /// until the read half is dropped. If the read half has already been
+    /// dropped, this closes the stream.
+    pub fn forget(mut self) {
+        self.shutdown_on_drop = false;
+        drop(self);
+    }
+
+    /// Waits for any of the requested ready states.
+    ///
+    /// This function is usually paired with `try_read()` or `try_write()`. It
+    /// can be used to concurrently read / write to the same socket on a single
+    /// task without splitting the socket.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read or write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    pub async fn ready(&self, interest: Interest) -> io::Result<Ready> {
+        self.inner.ready(interest).await
+    }
+
+    /// Waits for the socket to become writable.
+    ///
+    /// This function is equivalent to `ready(Interest::WRITABLE)` and is usually
+    /// paired with `try_write()`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    pub async fn writable(&self) -> io::Result<()> {
+        self.inner.writable().await
+    }
+
+    /// Tries to write a buffer to the stream, returning how many bytes were
+    /// written.
+    ///
+    /// The function will attempt to write the entire contents of `buf`, but
+    /// only part of the buffer may be written.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// # Return
+    ///
+    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
+    /// number of bytes written. If the stream is not ready to write data,
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    pub fn try_write(&self, buf: &[u8]) -> io::Result<usize> {
+        self.inner.try_write(buf)
+    }
+
+    /// Tries to write several buffers to the stream, returning how many bytes
+    /// were written.
+    ///
+    /// Data is written from each buffer in order, with the final buffer read
+    /// from possible being only partially consumed. This method behaves
+    /// equivalently to a single call to [`try_write()`] with concatenated
+    /// buffers.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// [`try_write()`]: Self::try_write()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
+    /// number of bytes written. If the stream is not ready to write data,
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    pub fn try_write_vectored(&self, buf: &[io::IoSlice<'_>]) -> io::Result<usize> {
+        self.inner.try_write_vectored(buf)
+    }
+
+    /// Returns the socket address of the remote half of this connection.
+    pub fn peer_addr(&self) -> io::Result<SocketAddr> {
+        self.inner.peer_addr()
+    }
+
+    /// Returns the socket address of the local half of this connection.
+    pub fn local_addr(&self) -> io::Result<SocketAddr> {
+        self.inner.local_addr()
+    }
+}
+
+impl Drop for OwnedWriteHalf {
+    fn drop(&mut self) {
+        if self.shutdown_on_drop {
+            let _ = self.inner.shutdown_std(Shutdown::Write);
+        }
+    }
+}
+
+impl AsyncWrite for OwnedWriteHalf {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.inner.poll_write_priv(cx, buf)
+    }
+
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.inner.poll_write_vectored_priv(cx, bufs)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        self.inner.is_write_vectored()
+    }
+
+    #[inline]
+    fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        // flush is a no-op
+        Poll::Ready(Ok(()))
+    }
+
+    // `poll_shutdown` on a write half shutdowns the stream in the "write" direction.
+    fn poll_shutdown(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        let res = self.inner.shutdown_std(Shutdown::Write);
+        if res.is_ok() {
+            Pin::into_inner(self).shutdown_on_drop = false;
+        }
+        res.into()
+    }
+}
+
+impl AsRef<UnixStream> for OwnedReadHalf {
+    fn as_ref(&self) -> &UnixStream {
+        &*self.inner
+    }
+}
+
+impl AsRef<UnixStream> for OwnedWriteHalf {
+    fn as_ref(&self) -> &UnixStream {
+        &*self.inner
+    }
+}
diff --git a/third_party/rust/tokio/src/net/unix/stream.rs b/third_party/rust/tokio/src/net/unix/stream.rs
new file mode 100644
index 0000000000..4e7ef87b41
--- /dev/null
+++ b/third_party/rust/tokio/src/net/unix/stream.rs
@@ -0,0 +1,960 @@
+use crate::future::poll_fn;
+use crate::io::{AsyncRead, AsyncWrite, Interest, PollEvented, ReadBuf, Ready};
+use crate::net::unix::split::{split, ReadHalf, WriteHalf};
+use crate::net::unix::split_owned::{split_owned, OwnedReadHalf, OwnedWriteHalf};
+use crate::net::unix::ucred::{self, UCred};
+use crate::net::unix::SocketAddr;
+
+use std::convert::TryFrom;
+use std::fmt;
+use std::io::{self, Read, Write};
+use std::net::Shutdown;
+use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
+use std::os::unix::net;
+use std::path::Path;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+cfg_io_util! {
+    use bytes::BufMut;
+}
+
+cfg_net_unix! {
+    /// A structure representing a connected Unix socket.
+    ///
+    /// This socket can be connected directly with `UnixStream::connect` or accepted
+    /// from a listener with `UnixListener::incoming`. Additionally, a pair of
+    /// anonymous Unix sockets can be created with `UnixStream::pair`.
+    ///
+    /// To shut down the stream in the write direction, you can call the
+    /// [`shutdown()`] method. This will cause the other peer to receive a read of
+    /// length 0, indicating that no more data will be sent. This only closes
+    /// the stream in one direction.
+    ///
+    /// [`shutdown()`]: fn@crate::io::AsyncWriteExt::shutdown
+    pub struct UnixStream {
+        io: PollEvented<mio::net::UnixStream>,
+    }
+}
+
+impl UnixStream {
+    /// Connects to the socket named by `path`.
+    ///
+    /// This function will create a new Unix socket and connect to the path
+    /// specified, associating the returned stream with the default event loop's
+    /// handle.
+    pub async fn connect<P>(path: P) -> io::Result<UnixStream>
+    where
+        P: AsRef<Path>,
+    {
+        let stream = mio::net::UnixStream::connect(path)?;
+        let stream = UnixStream::new(stream)?;
+
+        poll_fn(|cx| stream.io.registration().poll_write_ready(cx)).await?;
+
+        if let Some(e) = stream.io.take_error()? {
+            return Err(e);
+        }
+
+        Ok(stream)
+    }
+
+    /// Waits for any of the requested ready states.
+    ///
+    /// This function is usually paired with `try_read()` or `try_write()`. It
+    /// can be used to concurrently read / write to the same socket on a single
+    /// task without splitting the socket.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read or write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    ///
+    /// # Examples
+    ///
+    /// Concurrently read and write to the stream on the same task without
+    /// splitting.
+    ///
+    /// ```no_run
+    /// use tokio::io::Interest;
+    /// use tokio::net::UnixStream;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let dir = tempfile::tempdir().unwrap();
+    ///     let bind_path = dir.path().join("bind_path");
+    ///     let stream = UnixStream::connect(bind_path).await?;
+    ///
+    ///     loop {
+    ///         let ready = stream.ready(Interest::READABLE | Interest::WRITABLE).await?;
+    ///
+    ///         if ready.is_readable() {
+    ///             let mut data = vec![0; 1024];
+    ///             // Try to read data, this may still fail with `WouldBlock`
+    ///             // if the readiness event is a false positive.
+    ///             match stream.try_read(&mut data) {
+    ///                 Ok(n) => {
+    ///                     println!("read {} bytes", n);        
+    ///                 }
+    ///                 Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                     continue;
+    ///                 }
+    ///                 Err(e) => {
+    ///                     return Err(e.into());
+    ///                 }
+    ///             }
+    ///
+    ///         }
+    ///
+    ///         if ready.is_writable() {
+    ///             // Try to write data, this may still fail with `WouldBlock`
+    ///             // if the readiness event is a false positive.
+    ///             match stream.try_write(b"hello world") {
+    ///                 Ok(n) => {
+    ///                     println!("write {} bytes", n);
+    ///                 }
+    ///                 Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                     continue;
+    ///                 }
+    ///                 Err(e) => {
+    ///                     return Err(e.into());
+    ///                 }
+    ///             }
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    pub async fn ready(&self, interest: Interest) -> io::Result<Ready> {
+        let event = self.io.registration().readiness(interest).await?;
+        Ok(event.ready)
+    }
+
+    /// Waits for the socket to become readable.
+    ///
+    /// This function is equivalent to `ready(Interest::READABLE)` and is usually
+    /// paired with `try_read()`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to read that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UnixStream;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let dir = tempfile::tempdir().unwrap();
+    ///     let bind_path = dir.path().join("bind_path");
+    ///     let stream = UnixStream::connect(bind_path).await?;
+    ///
+    ///     let mut msg = vec![0; 1024];
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be readable
+    ///         stream.readable().await?;
+    ///
+    ///         // Try to read data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match stream.try_read(&mut msg) {
+    ///             Ok(n) => {
+    ///                 msg.truncate(n);
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     println!("GOT = {:?}", msg);
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn readable(&self) -> io::Result<()> {
+        self.ready(Interest::READABLE).await?;
+        Ok(())
+    }
+
+    /// Polls for read readiness.
+    ///
+    /// If the unix stream is not currently ready for reading, this method will
+    /// store a clone of the `Waker` from the provided `Context`. When the unix
+    /// stream becomes ready for reading, `Waker::wake` will be called on the
+    /// waker.
+    ///
+    /// Note that on multiple calls to `poll_read_ready` or `poll_read`, only
+    /// the `Waker` from the `Context` passed to the most recent call is
+    /// scheduled to receive a wakeup. (However, `poll_write_ready` retains a
+    /// second, independent waker.)
+    ///
+    /// This function is intended for cases where creating and pinning a future
+    /// via [`readable`] is not feasible. Where possible, using [`readable`] is
+    /// preferred, as this supports polling from multiple tasks at once.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the unix stream is not ready for reading.
+    /// * `Poll::Ready(Ok(()))` if the unix stream is ready for reading.
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// [`readable`]: method@Self::readable
+    pub fn poll_read_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.io.registration().poll_read_ready(cx).map_ok(|_| ())
+    }
+
+    /// Try to read data from the stream into the provided buffer, returning how
+    /// many bytes were read.
+    ///
+    /// Receives any pending data from the socket but does not wait for new data
+    /// to arrive. On success, returns the number of bytes read. Because
+    /// `try_read()` is non-blocking, the buffer does not have to be stored by
+    /// the async task and can exist entirely on the stack.
+    ///
+    /// Usually, [`readable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`readable()`]: UnixStream::readable()
+    /// [`ready()`]: UnixStream::ready()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+    /// and will no longer yield data. If the stream is not ready to read data
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UnixStream;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let dir = tempfile::tempdir().unwrap();
+    ///     let bind_path = dir.path().join("bind_path");
+    ///     let stream = UnixStream::connect(bind_path).await?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be readable
+    ///         stream.readable().await?;
+    ///
+    ///         // Creating the buffer **after** the `await` prevents it from
+    ///         // being stored in the async task.
+    ///         let mut buf = [0; 4096];
+    ///
+    ///         // Try to read data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match stream.try_read(&mut buf) {
+    ///             Ok(0) => break,
+    ///             Ok(n) => {
+    ///                 println!("read {} bytes", n);
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_read(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::READABLE, || (&*self.io).read(buf))
+    }
+
+    /// Tries to read data from the stream into the provided buffers, returning
+    /// how many bytes were read.
+    ///
+    /// Data is copied to fill each buffer in order, with the final buffer
+    /// written to possibly being only partially filled. This method behaves
+    /// equivalently to a single call to [`try_read()`] with concatenated
+    /// buffers.
+    ///
+    /// Receives any pending data from the socket but does not wait for new data
+    /// to arrive. On success, returns the number of bytes read. Because
+    /// `try_read_vectored()` is non-blocking, the buffer does not have to be
+    /// stored by the async task and can exist entirely on the stack.
+    ///
+    /// Usually, [`readable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`try_read()`]: UnixStream::try_read()
+    /// [`readable()`]: UnixStream::readable()
+    /// [`ready()`]: UnixStream::ready()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+    /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+    /// and will no longer yield data. If the stream is not ready to read data
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UnixStream;
+    /// use std::error::Error;
+    /// use std::io::{self, IoSliceMut};
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let dir = tempfile::tempdir().unwrap();
+    ///     let bind_path = dir.path().join("bind_path");
+    ///     let stream = UnixStream::connect(bind_path).await?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be readable
+    ///         stream.readable().await?;
+    ///
+    ///         // Creating the buffer **after** the `await` prevents it from
+    ///         // being stored in the async task.
+    ///         let mut buf_a = [0; 512];
+    ///         let mut buf_b = [0; 1024];
+    ///         let mut bufs = [
+    ///             IoSliceMut::new(&mut buf_a),
+    ///             IoSliceMut::new(&mut buf_b),
+    ///         ];
+    ///
+    ///         // Try to read data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match stream.try_read_vectored(&mut bufs) {
+    ///             Ok(0) => break,
+    ///             Ok(n) => {
+    ///                 println!("read {} bytes", n);
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_read_vectored(&self, bufs: &mut [io::IoSliceMut<'_>]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::READABLE, || (&*self.io).read_vectored(bufs))
+    }
+
+    cfg_io_util! {
+        /// Tries to read data from the stream into the provided buffer, advancing the
+        /// buffer's internal cursor, returning how many bytes were read.
+        ///
+        /// Receives any pending data from the socket but does not wait for new data
+        /// to arrive. On success, returns the number of bytes read. Because
+        /// `try_read_buf()` is non-blocking, the buffer does not have to be stored by
+        /// the async task and can exist entirely on the stack.
+        ///
+        /// Usually, [`readable()`] or [`ready()`] is used with this function.
+        ///
+        /// [`readable()`]: UnixStream::readable()
+        /// [`ready()`]: UnixStream::ready()
+        ///
+        /// # Return
+        ///
+        /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+        /// number of bytes read. `Ok(0)` indicates the stream's read half is closed
+        /// and will no longer yield data. If the stream is not ready to read data
+        /// `Err(io::ErrorKind::WouldBlock)` is returned.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::net::UnixStream;
+        /// use std::error::Error;
+        /// use std::io;
+        ///
+        /// #[tokio::main]
+        /// async fn main() -> Result<(), Box<dyn Error>> {
+        ///     // Connect to a peer
+        ///     let dir = tempfile::tempdir().unwrap();
+        ///     let bind_path = dir.path().join("bind_path");
+        ///     let stream = UnixStream::connect(bind_path).await?;
+        ///
+        ///     loop {
+        ///         // Wait for the socket to be readable
+        ///         stream.readable().await?;
+        ///
+        ///         let mut buf = Vec::with_capacity(4096);
+        ///
+        ///         // Try to read data, this may still fail with `WouldBlock`
+        ///         // if the readiness event is a false positive.
+        ///         match stream.try_read_buf(&mut buf) {
+        ///             Ok(0) => break,
+        ///             Ok(n) => {
+        ///                 println!("read {} bytes", n);
+        ///             }
+        ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+        ///                 continue;
+        ///             }
+        ///             Err(e) => {
+        ///                 return Err(e.into());
+        ///             }
+        ///         }
+        ///     }
+        ///
+        ///     Ok(())
+        /// }
+        /// ```
+        pub fn try_read_buf<B: BufMut>(&self, buf: &mut B) -> io::Result<usize> {
+            self.io.registration().try_io(Interest::READABLE, || {
+                use std::io::Read;
+
+                let dst = buf.chunk_mut();
+                let dst =
+                    unsafe { &mut *(dst as *mut _ as *mut [std::mem::MaybeUninit<u8>] as *mut [u8]) };
+
+                // Safety: We trust `UnixStream::read` to have filled up `n` bytes in the
+                // buffer.
+                let n = (&*self.io).read(dst)?;
+
+                unsafe {
+                    buf.advance_mut(n);
+                }
+
+                Ok(n)
+            })
+        }
+    }
+
+    /// Waits for the socket to become writable.
+    ///
+    /// This function is equivalent to `ready(Interest::WRITABLE)` and is usually
+    /// paired with `try_write()`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once a readiness event occurs, the method
+    /// will continue to return immediately until the readiness event is
+    /// consumed by an attempt to write that fails with `WouldBlock` or
+    /// `Poll::Pending`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UnixStream;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let dir = tempfile::tempdir().unwrap();
+    ///     let bind_path = dir.path().join("bind_path");
+    ///     let stream = UnixStream::connect(bind_path).await?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be writable
+    ///         stream.writable().await?;
+    ///
+    ///         // Try to write data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match stream.try_write(b"hello world") {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn writable(&self) -> io::Result<()> {
+        self.ready(Interest::WRITABLE).await?;
+        Ok(())
+    }
+
+    /// Polls for write readiness.
+    ///
+    /// If the unix stream is not currently ready for writing, this method will
+    /// store a clone of the `Waker` from the provided `Context`. When the unix
+    /// stream becomes ready for writing, `Waker::wake` will be called on the
+    /// waker.
+    ///
+    /// Note that on multiple calls to `poll_write_ready` or `poll_write`, only
+    /// the `Waker` from the `Context` passed to the most recent call is
+    /// scheduled to receive a wakeup. (However, `poll_read_ready` retains a
+    /// second, independent waker.)
+    ///
+    /// This function is intended for cases where creating and pinning a future
+    /// via [`writable`] is not feasible. Where possible, using [`writable`] is
+    /// preferred, as this supports polling from multiple tasks at once.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the unix stream is not ready for writing.
+    /// * `Poll::Ready(Ok(()))` if the unix stream is ready for writing.
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// [`writable`]: method@Self::writable
+    pub fn poll_write_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.io.registration().poll_write_ready(cx).map_ok(|_| ())
+    }
+
+    /// Tries to write a buffer to the stream, returning how many bytes were
+    /// written.
+    ///
+    /// The function will attempt to write the entire contents of `buf`, but
+    /// only part of the buffer may be written.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// # Return
+    ///
+    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
+    /// number of bytes written. If the stream is not ready to write data,
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UnixStream;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let dir = tempfile::tempdir().unwrap();
+    ///     let bind_path = dir.path().join("bind_path");
+    ///     let stream = UnixStream::connect(bind_path).await?;
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be writable
+    ///         stream.writable().await?;
+    ///
+    ///         // Try to write data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match stream.try_write(b"hello world") {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_write(&self, buf: &[u8]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::WRITABLE, || (&*self.io).write(buf))
+    }
+
+    /// Tries to write several buffers to the stream, returning how many bytes
+    /// were written.
+    ///
+    /// Data is written from each buffer in order, with the final buffer read
+    /// from possible being only partially consumed. This method behaves
+    /// equivalently to a single call to [`try_write()`] with concatenated
+    /// buffers.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// [`try_write()`]: UnixStream::try_write()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
+    /// number of bytes written. If the stream is not ready to write data,
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UnixStream;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     // Connect to a peer
+    ///     let dir = tempfile::tempdir().unwrap();
+    ///     let bind_path = dir.path().join("bind_path");
+    ///     let stream = UnixStream::connect(bind_path).await?;
+    ///
+    ///     let bufs = [io::IoSlice::new(b"hello "), io::IoSlice::new(b"world")];
+    ///
+    ///     loop {
+    ///         // Wait for the socket to be writable
+    ///         stream.writable().await?;
+    ///
+    ///         // Try to write data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match stream.try_write_vectored(&bufs) {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_write_vectored(&self, buf: &[io::IoSlice<'_>]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::WRITABLE, || (&*self.io).write_vectored(buf))
+    }
+
+    /// Tries to read or write from the socket using a user-provided IO operation.
+    ///
+    /// If the socket is ready, the provided closure is called. The closure
+    /// should attempt to perform IO operation from the socket by manually
+    /// calling the appropriate syscall. If the operation fails because the
+    /// socket is not actually ready, then the closure should return a
+    /// `WouldBlock` error and the readiness flag is cleared. The return value
+    /// of the closure is then returned by `try_io`.
+    ///
+    /// If the socket is not ready, then the closure is not called
+    /// and a `WouldBlock` error is returned.
+    ///
+    /// The closure should only return a `WouldBlock` error if it has performed
+    /// an IO operation on the socket that failed due to the socket not being
+    /// ready. Returning a `WouldBlock` error in any other situation will
+    /// incorrectly clear the readiness flag, which can cause the socket to
+    /// behave incorrectly.
+    ///
+    /// The closure should not perform the IO operation using any of the methods
+    /// defined on the Tokio `UnixStream` type, as this will mess with the
+    /// readiness flag and can cause the socket to behave incorrectly.
+    ///
+    /// Usually, [`readable()`], [`writable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`readable()`]: UnixStream::readable()
+    /// [`writable()`]: UnixStream::writable()
+    /// [`ready()`]: UnixStream::ready()
+    pub fn try_io<R>(
+        &self,
+        interest: Interest,
+        f: impl FnOnce() -> io::Result<R>,
+    ) -> io::Result<R> {
+        self.io.registration().try_io(interest, f)
+    }
+
+    /// Creates new `UnixStream` from a `std::os::unix::net::UnixStream`.
+    ///
+    /// This function is intended to be used to wrap a UnixStream from the
+    /// standard library in the Tokio equivalent. The conversion assumes
+    /// nothing about the underlying stream; it is left up to the user to set
+    /// it in non-blocking mode.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if thread-local runtime is not set.
+    ///
+    /// The runtime is usually set implicitly when this function is called
+    /// from a future driven by a tokio runtime, otherwise runtime can be set
+    /// explicitly with [`Runtime::enter`](crate::runtime::Runtime::enter) function.
+    pub fn from_std(stream: net::UnixStream) -> io::Result<UnixStream> {
+        let stream = mio::net::UnixStream::from_std(stream);
+        let io = PollEvented::new(stream)?;
+
+        Ok(UnixStream { io })
+    }
+
+    /// Turns a [`tokio::net::UnixStream`] into a [`std::os::unix::net::UnixStream`].
+    ///
+    /// The returned [`std::os::unix::net::UnixStream`] will have nonblocking
+    /// mode set as `true`.  Use [`set_nonblocking`] to change the blocking
+    /// mode if needed.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::error::Error;
+    /// use std::io::Read;
+    /// use tokio::net::UnixListener;
+    /// # use tokio::net::UnixStream;
+    /// # use tokio::io::AsyncWriteExt;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let dir = tempfile::tempdir().unwrap();
+    ///     let bind_path = dir.path().join("bind_path");
+    ///
+    ///     let mut data = [0u8; 12];
+    ///     let listener = UnixListener::bind(&bind_path)?;
+    /// #   let handle = tokio::spawn(async {
+    /// #       let mut stream = UnixStream::connect(bind_path).await.unwrap();
+    /// #       stream.write(b"Hello world!").await.unwrap();
+    /// #   });
+    ///     let (tokio_unix_stream, _) = listener.accept().await?;
+    ///     let mut std_unix_stream = tokio_unix_stream.into_std()?;
+    /// #   handle.await.expect("The task being joined has panicked");
+    ///     std_unix_stream.set_nonblocking(false)?;
+    ///     std_unix_stream.read_exact(&mut data)?;
+    /// #   assert_eq!(b"Hello world!", &data);
+    ///     Ok(())
+    /// }
+    /// ```
+    /// [`tokio::net::UnixStream`]: UnixStream
+    /// [`std::os::unix::net::UnixStream`]: std::os::unix::net::UnixStream
+    /// [`set_nonblocking`]: fn@std::os::unix::net::UnixStream::set_nonblocking
+    pub fn into_std(self) -> io::Result<std::os::unix::net::UnixStream> {
+        self.io
+            .into_inner()
+            .map(|io| io.into_raw_fd())
+            .map(|raw_fd| unsafe { std::os::unix::net::UnixStream::from_raw_fd(raw_fd) })
+    }
+
+    /// Creates an unnamed pair of connected sockets.
+    ///
+    /// This function will create a pair of interconnected Unix sockets for
+    /// communicating back and forth between one another. Each socket will
+    /// be associated with the default event loop's handle.
+    pub fn pair() -> io::Result<(UnixStream, UnixStream)> {
+        let (a, b) = mio::net::UnixStream::pair()?;
+        let a = UnixStream::new(a)?;
+        let b = UnixStream::new(b)?;
+
+        Ok((a, b))
+    }
+
+    pub(crate) fn new(stream: mio::net::UnixStream) -> io::Result<UnixStream> {
+        let io = PollEvented::new(stream)?;
+        Ok(UnixStream { io })
+    }
+
+    /// Returns the socket address of the local half of this connection.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UnixStream;
+    ///
+    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
+    /// let dir = tempfile::tempdir().unwrap();
+    /// let bind_path = dir.path().join("bind_path");
+    /// let stream = UnixStream::connect(bind_path).await?;
+    ///
+    /// println!("{:?}", stream.local_addr()?);
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn local_addr(&self) -> io::Result<SocketAddr> {
+        self.io.local_addr().map(SocketAddr)
+    }
+
+    /// Returns the socket address of the remote half of this connection.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::UnixStream;
+    ///
+    /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
+    /// let dir = tempfile::tempdir().unwrap();
+    /// let bind_path = dir.path().join("bind_path");
+    /// let stream = UnixStream::connect(bind_path).await?;
+    ///
+    /// println!("{:?}", stream.peer_addr()?);
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn peer_addr(&self) -> io::Result<SocketAddr> {
+        self.io.peer_addr().map(SocketAddr)
+    }
+
+    /// Returns effective credentials of the process which called `connect` or `pair`.
+    pub fn peer_cred(&self) -> io::Result<UCred> {
+        ucred::get_peer_cred(self)
+    }
+
+    /// Returns the value of the `SO_ERROR` option.
+    pub fn take_error(&self) -> io::Result<Option<io::Error>> {
+        self.io.take_error()
+    }
+
+    /// Shuts down the read, write, or both halves of this connection.
+    ///
+    /// This function will cause all pending and future I/O calls on the
+    /// specified portions to immediately return with an appropriate value
+    /// (see the documentation of `Shutdown`).
+    pub(super) fn shutdown_std(&self, how: Shutdown) -> io::Result<()> {
+        self.io.shutdown(how)
+    }
+
+    // These lifetime markers also appear in the generated documentation, and make
+    // it more clear that this is a *borrowed* split.
+    #[allow(clippy::needless_lifetimes)]
+    /// Splits a `UnixStream` into a read half and a write half, which can be used
+    /// to read and write the stream concurrently.
+    ///
+    /// This method is more efficient than [`into_split`], but the halves cannot be
+    /// moved into independently spawned tasks.
+    ///
+    /// [`into_split`]: Self::into_split()
+    pub fn split<'a>(&'a mut self) -> (ReadHalf<'a>, WriteHalf<'a>) {
+        split(self)
+    }
+
+    /// Splits a `UnixStream` into a read half and a write half, which can be used
+    /// to read and write the stream concurrently.
+    ///
+    /// Unlike [`split`], the owned halves can be moved to separate tasks, however
+    /// this comes at the cost of a heap allocation.
+    ///
+    /// **Note:** Dropping the write half will shut down the write half of the
+    /// stream. This is equivalent to calling [`shutdown()`] on the `UnixStream`.
+    ///
+    /// [`split`]: Self::split()
+    /// [`shutdown()`]: fn@crate::io::AsyncWriteExt::shutdown
+    pub fn into_split(self) -> (OwnedReadHalf, OwnedWriteHalf) {
+        split_owned(self)
+    }
+}
+
+impl TryFrom<net::UnixStream> for UnixStream {
+    type Error = io::Error;
+
+    /// Consumes stream, returning the tokio I/O object.
+    ///
+    /// This is equivalent to
+    /// [`UnixStream::from_std(stream)`](UnixStream::from_std).
+    fn try_from(stream: net::UnixStream) -> io::Result<Self> {
+        Self::from_std(stream)
+    }
+}
+
+impl AsyncRead for UnixStream {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        self.poll_read_priv(cx, buf)
+    }
+}
+
+impl AsyncWrite for UnixStream {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.poll_write_priv(cx, buf)
+    }
+
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.poll_write_vectored_priv(cx, bufs)
+    }
+
+    fn is_write_vectored(&self) -> bool {
+        true
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.shutdown_std(std::net::Shutdown::Write)?;
+        Poll::Ready(Ok(()))
+    }
+}
+
+impl UnixStream {
+    // == Poll IO functions that takes `&self` ==
+    //
+    // To read or write without mutable access to the `UnixStream`, combine the
+    // `poll_read_ready` or `poll_write_ready` methods with the `try_read` or
+    // `try_write` methods.
+
+    pub(crate) fn poll_read_priv(
+        &self,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        // Safety: `UnixStream::read` correctly handles reads into uninitialized memory
+        unsafe { self.io.poll_read(cx, buf) }
+    }
+
+    pub(crate) fn poll_write_priv(
+        &self,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.io.poll_write(cx, buf)
+    }
+
+    pub(super) fn poll_write_vectored_priv(
+        &self,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.io.poll_write_vectored(cx, bufs)
+    }
+}
+
+impl fmt::Debug for UnixStream {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.io.fmt(f)
+    }
+}
+
+impl AsRawFd for UnixStream {
+    fn as_raw_fd(&self) -> RawFd {
+        self.io.as_raw_fd()
+    }
+}
diff --git a/third_party/rust/tokio/src/net/unix/ucred.rs b/third_party/rust/tokio/src/net/unix/ucred.rs
new file mode 100644
index 0000000000..865303b4ce
--- /dev/null
+++ b/third_party/rust/tokio/src/net/unix/ucred.rs
@@ -0,0 +1,252 @@
+use libc::{gid_t, pid_t, uid_t};
+
+/// Credentials of a process.
+#[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
+pub struct UCred {
+    /// PID (process ID) of the process.
+    pid: Option<pid_t>,
+    /// UID (user ID) of the process.
+    uid: uid_t,
+    /// GID (group ID) of the process.
+    gid: gid_t,
+}
+
+impl UCred {
+    /// Gets UID (user ID) of the process.
+    pub fn uid(&self) -> uid_t {
+        self.uid
+    }
+
+    /// Gets GID (group ID) of the process.
+    pub fn gid(&self) -> gid_t {
+        self.gid
+    }
+
+    /// Gets PID (process ID) of the process.
+    ///
+    /// This is only implemented under Linux, Android, iOS, macOS, Solaris and
+    /// Illumos. On other platforms this will always return `None`.
+    pub fn pid(&self) -> Option<pid_t> {
+        self.pid
+    }
+}
+
+#[cfg(any(target_os = "linux", target_os = "android", target_os = "openbsd"))]
+pub(crate) use self::impl_linux::get_peer_cred;
+
+#[cfg(any(target_os = "netbsd"))]
+pub(crate) use self::impl_netbsd::get_peer_cred;
+
+#[cfg(any(target_os = "dragonfly", target_os = "freebsd"))]
+pub(crate) use self::impl_bsd::get_peer_cred;
+
+#[cfg(any(target_os = "macos", target_os = "ios"))]
+pub(crate) use self::impl_macos::get_peer_cred;
+
+#[cfg(any(target_os = "solaris", target_os = "illumos"))]
+pub(crate) use self::impl_solaris::get_peer_cred;
+
+#[cfg(any(target_os = "linux", target_os = "android", target_os = "openbsd"))]
+pub(crate) mod impl_linux {
+    use crate::net::unix::UnixStream;
+
+    use libc::{c_void, getsockopt, socklen_t, SOL_SOCKET, SO_PEERCRED};
+    use std::{io, mem};
+
+    #[cfg(target_os = "openbsd")]
+    use libc::sockpeercred as ucred;
+    #[cfg(any(target_os = "linux", target_os = "android"))]
+    use libc::ucred;
+
+    pub(crate) fn get_peer_cred(sock: &UnixStream) -> io::Result<super::UCred> {
+        use std::os::unix::io::AsRawFd;
+
+        unsafe {
+            let raw_fd = sock.as_raw_fd();
+
+            let mut ucred = ucred {
+                pid: 0,
+                uid: 0,
+                gid: 0,
+            };
+
+            let ucred_size = mem::size_of::<ucred>();
+
+            // These paranoid checks should be optimized-out
+            assert!(mem::size_of::<u32>() <= mem::size_of::<usize>());
+            assert!(ucred_size <= u32::MAX as usize);
+
+            let mut ucred_size = ucred_size as socklen_t;
+
+            let ret = getsockopt(
+                raw_fd,
+                SOL_SOCKET,
+                SO_PEERCRED,
+                &mut ucred as *mut ucred as *mut c_void,
+                &mut ucred_size,
+            );
+            if ret == 0 && ucred_size as usize == mem::size_of::<ucred>() {
+                Ok(super::UCred {
+                    uid: ucred.uid,
+                    gid: ucred.gid,
+                    pid: Some(ucred.pid),
+                })
+            } else {
+                Err(io::Error::last_os_error())
+            }
+        }
+    }
+}
+
+#[cfg(any(target_os = "netbsd"))]
+pub(crate) mod impl_netbsd {
+    use crate::net::unix::UnixStream;
+
+    use libc::{c_void, getsockopt, socklen_t, unpcbid, LOCAL_PEEREID, SOL_SOCKET};
+    use std::io;
+    use std::mem::size_of;
+    use std::os::unix::io::AsRawFd;
+
+    pub(crate) fn get_peer_cred(sock: &UnixStream) -> io::Result<super::UCred> {
+        unsafe {
+            let raw_fd = sock.as_raw_fd();
+
+            let mut unpcbid = unpcbid {
+                unp_pid: 0,
+                unp_euid: 0,
+                unp_egid: 0,
+            };
+
+            let unpcbid_size = size_of::<unpcbid>();
+            let mut unpcbid_size = unpcbid_size as socklen_t;
+
+            let ret = getsockopt(
+                raw_fd,
+                SOL_SOCKET,
+                LOCAL_PEEREID,
+                &mut unpcbid as *mut unpcbid as *mut c_void,
+                &mut unpcbid_size,
+            );
+            if ret == 0 && unpcbid_size as usize == size_of::<unpcbid>() {
+                Ok(super::UCred {
+                    uid: unpcbid.unp_euid,
+                    gid: unpcbid.unp_egid,
+                    pid: Some(unpcbid.unp_pid),
+                })
+            } else {
+                Err(io::Error::last_os_error())
+            }
+        }
+    }
+}
+
+#[cfg(any(target_os = "dragonfly", target_os = "freebsd"))]
+pub(crate) mod impl_bsd {
+    use crate::net::unix::UnixStream;
+
+    use libc::getpeereid;
+    use std::io;
+    use std::mem::MaybeUninit;
+    use std::os::unix::io::AsRawFd;
+
+    pub(crate) fn get_peer_cred(sock: &UnixStream) -> io::Result<super::UCred> {
+        unsafe {
+            let raw_fd = sock.as_raw_fd();
+
+            let mut uid = MaybeUninit::uninit();
+            let mut gid = MaybeUninit::uninit();
+
+            let ret = getpeereid(raw_fd, uid.as_mut_ptr(), gid.as_mut_ptr());
+
+            if ret == 0 {
+                Ok(super::UCred {
+                    uid: uid.assume_init(),
+                    gid: gid.assume_init(),
+                    pid: None,
+                })
+            } else {
+                Err(io::Error::last_os_error())
+            }
+        }
+    }
+}
+
+#[cfg(any(target_os = "macos", target_os = "ios"))]
+pub(crate) mod impl_macos {
+    use crate::net::unix::UnixStream;
+
+    use libc::{c_void, getpeereid, getsockopt, pid_t, LOCAL_PEEREPID, SOL_LOCAL};
+    use std::io;
+    use std::mem::size_of;
+    use std::mem::MaybeUninit;
+    use std::os::unix::io::AsRawFd;
+
+    pub(crate) fn get_peer_cred(sock: &UnixStream) -> io::Result<super::UCred> {
+        unsafe {
+            let raw_fd = sock.as_raw_fd();
+
+            let mut uid = MaybeUninit::uninit();
+            let mut gid = MaybeUninit::uninit();
+            let mut pid: MaybeUninit<pid_t> = MaybeUninit::uninit();
+            let mut pid_size: MaybeUninit<u32> = MaybeUninit::new(size_of::<pid_t>() as u32);
+
+            if getsockopt(
+                raw_fd,
+                SOL_LOCAL,
+                LOCAL_PEEREPID,
+                pid.as_mut_ptr() as *mut c_void,
+                pid_size.as_mut_ptr(),
+            ) != 0
+            {
+                return Err(io::Error::last_os_error());
+            }
+
+            assert!(pid_size.assume_init() == (size_of::<pid_t>() as u32));
+
+            let ret = getpeereid(raw_fd, uid.as_mut_ptr(), gid.as_mut_ptr());
+
+            if ret == 0 {
+                Ok(super::UCred {
+                    uid: uid.assume_init(),
+                    gid: gid.assume_init(),
+                    pid: Some(pid.assume_init()),
+                })
+            } else {
+                Err(io::Error::last_os_error())
+            }
+        }
+    }
+}
+
+#[cfg(any(target_os = "solaris", target_os = "illumos"))]
+pub(crate) mod impl_solaris {
+    use crate::net::unix::UnixStream;
+    use std::io;
+    use std::os::unix::io::AsRawFd;
+    use std::ptr;
+
+    pub(crate) fn get_peer_cred(sock: &UnixStream) -> io::Result<super::UCred> {
+        unsafe {
+            let raw_fd = sock.as_raw_fd();
+
+            let mut cred = ptr::null_mut();
+            let ret = libc::getpeerucred(raw_fd, &mut cred);
+
+            if ret == 0 {
+                let uid = libc::ucred_geteuid(cred);
+                let gid = libc::ucred_getegid(cred);
+                let pid = libc::ucred_getpid(cred);
+
+                libc::ucred_free(cred);
+
+                Ok(super::UCred {
+                    uid,
+                    gid,
+                    pid: Some(pid),
+                })
+            } else {
+                Err(io::Error::last_os_error())
+            }
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/net/windows/mod.rs b/third_party/rust/tokio/src/net/windows/mod.rs
new file mode 100644
index 0000000000..060b68e663
--- /dev/null
+++ b/third_party/rust/tokio/src/net/windows/mod.rs
@@ -0,0 +1,3 @@
+//! Windows specific network types.
+
+pub mod named_pipe;
diff --git a/third_party/rust/tokio/src/net/windows/named_pipe.rs b/third_party/rust/tokio/src/net/windows/named_pipe.rs
new file mode 100644
index 0000000000..550fd4df2b
--- /dev/null
+++ b/third_party/rust/tokio/src/net/windows/named_pipe.rs
@@ -0,0 +1,2250 @@
+//! Tokio support for [Windows named pipes].
+//!
+//! [Windows named pipes]: https://docs.microsoft.com/en-us/windows/win32/ipc/named-pipes
+
+use std::ffi::c_void;
+use std::ffi::OsStr;
+use std::io::{self, Read, Write};
+use std::pin::Pin;
+use std::ptr;
+use std::task::{Context, Poll};
+
+use crate::io::{AsyncRead, AsyncWrite, Interest, PollEvented, ReadBuf, Ready};
+use crate::os::windows::io::{AsRawHandle, FromRawHandle, RawHandle};
+
+// Hide imports which are not used when generating documentation.
+#[cfg(not(docsrs))]
+mod doc {
+    pub(super) use crate::os::windows::ffi::OsStrExt;
+    pub(super) use crate::winapi::shared::minwindef::{DWORD, FALSE};
+    pub(super) use crate::winapi::um::fileapi;
+    pub(super) use crate::winapi::um::handleapi;
+    pub(super) use crate::winapi::um::namedpipeapi;
+    pub(super) use crate::winapi::um::winbase;
+    pub(super) use crate::winapi::um::winnt;
+
+    pub(super) use mio::windows as mio_windows;
+}
+
+// NB: none of these shows up in public API, so don't document them.
+#[cfg(docsrs)]
+mod doc {
+    pub type DWORD = crate::doc::NotDefinedHere;
+
+    pub(super) mod mio_windows {
+        pub type NamedPipe = crate::doc::NotDefinedHere;
+    }
+}
+
+use self::doc::*;
+
+/// A [Windows named pipe] server.
+///
+/// Accepting client connections involves creating a server with
+/// [`ServerOptions::create`] and waiting for clients to connect using
+/// [`NamedPipeServer::connect`].
+///
+/// To avoid having clients sporadically fail with
+/// [`std::io::ErrorKind::NotFound`] when they connect to a server, we must
+/// ensure that at least one server instance is available at all times. This
+/// means that the typical listen loop for a server is a bit involved, because
+/// we have to ensure that we never drop a server accidentally while a client
+/// might connect.
+///
+/// So a correctly implemented server looks like this:
+///
+/// ```no_run
+/// use std::io;
+/// use tokio::net::windows::named_pipe::ServerOptions;
+///
+/// const PIPE_NAME: &str = r"\\.\pipe\named-pipe-idiomatic-server";
+///
+/// # #[tokio::main] async fn main() -> std::io::Result<()> {
+/// // The first server needs to be constructed early so that clients can
+/// // be correctly connected. Otherwise calling .wait will cause the client to
+/// // error.
+/// //
+/// // Here we also make use of `first_pipe_instance`, which will ensure that
+/// // there are no other servers up and running already.
+/// let mut server = ServerOptions::new()
+///     .first_pipe_instance(true)
+///     .create(PIPE_NAME)?;
+///
+/// // Spawn the server loop.
+/// let server = tokio::spawn(async move {
+///     loop {
+///         // Wait for a client to connect.
+///         let connected = server.connect().await?;
+///
+///         // Construct the next server to be connected before sending the one
+///         // we already have of onto a task. This ensures that the server
+///         // isn't closed (after it's done in the task) before a new one is
+///         // available. Otherwise the client might error with
+///         // `io::ErrorKind::NotFound`.
+///         server = ServerOptions::new().create(PIPE_NAME)?;
+///
+///         let client = tokio::spawn(async move {
+///             /* use the connected client */
+/// #           Ok::<_, std::io::Error>(())
+///         });
+/// #       if true { break } // needed for type inference to work
+///     }
+///
+///     Ok::<_, io::Error>(())
+/// });
+///
+/// /* do something else not server related here */
+/// # Ok(()) }
+/// ```
+///
+/// [`ERROR_PIPE_BUSY`]: crate::winapi::shared::winerror::ERROR_PIPE_BUSY
+/// [Windows named pipe]: https://docs.microsoft.com/en-us/windows/win32/ipc/named-pipes
+#[derive(Debug)]
+pub struct NamedPipeServer {
+    io: PollEvented<mio_windows::NamedPipe>,
+}
+
+impl NamedPipeServer {
+    /// Constructs a new named pipe server from the specified raw handle.
+    ///
+    /// This function will consume ownership of the handle given, passing
+    /// responsibility for closing the handle to the returned object.
+    ///
+    /// This function is also unsafe as the primitives currently returned have
+    /// the contract that they are the sole owner of the file descriptor they
+    /// are wrapping. Usage of this function could accidentally allow violating
+    /// this contract which can cause memory unsafety in code that relies on it
+    /// being true.
+    ///
+    /// # Errors
+    ///
+    /// This errors if called outside of a [Tokio Runtime], or in a runtime that
+    /// has not [enabled I/O], or if any OS-specific I/O errors occur.
+    ///
+    /// [Tokio Runtime]: crate::runtime::Runtime
+    /// [enabled I/O]: crate::runtime::Builder::enable_io
+    pub unsafe fn from_raw_handle(handle: RawHandle) -> io::Result<Self> {
+        let named_pipe = mio_windows::NamedPipe::from_raw_handle(handle);
+
+        Ok(Self {
+            io: PollEvented::new(named_pipe)?,
+        })
+    }
+
+    /// Retrieves information about the named pipe the server is associated
+    /// with.
+    ///
+    /// ```no_run
+    /// use tokio::net::windows::named_pipe::{PipeEnd, PipeMode, ServerOptions};
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-server-info";
+    ///
+    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
+    /// let server = ServerOptions::new()
+    ///     .pipe_mode(PipeMode::Message)
+    ///     .max_instances(5)
+    ///     .create(PIPE_NAME)?;
+    ///
+    /// let server_info = server.info()?;
+    ///
+    /// assert_eq!(server_info.end, PipeEnd::Server);
+    /// assert_eq!(server_info.mode, PipeMode::Message);
+    /// assert_eq!(server_info.max_instances, 5);
+    /// # Ok(()) }
+    /// ```
+    pub fn info(&self) -> io::Result<PipeInfo> {
+        // Safety: we're ensuring the lifetime of the named pipe.
+        unsafe { named_pipe_info(self.io.as_raw_handle()) }
+    }
+
+    /// Enables a named pipe server process to wait for a client process to
+    /// connect to an instance of a named pipe. A client process connects by
+    /// creating a named pipe with the same name.
+    ///
+    /// This corresponds to the [`ConnectNamedPipe`] system call.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancellation safe in the sense that if it is used as the
+    /// event in a [`select!`](crate::select) statement and some other branch
+    /// completes first, then no connection events have been lost.
+    ///
+    /// [`ConnectNamedPipe`]: https://docs.microsoft.com/en-us/windows/win32/api/namedpipeapi/nf-namedpipeapi-connectnamedpipe
+    ///
+    /// # Example
+    ///
+    /// ```no_run
+    /// use tokio::net::windows::named_pipe::ServerOptions;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\mynamedpipe";
+    ///
+    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
+    /// let pipe = ServerOptions::new().create(PIPE_NAME)?;
+    ///
+    /// // Wait for a client to connect.
+    /// pipe.connect().await?;
+    ///
+    /// // Use the connected client...
+    /// # Ok(()) }
+    /// ```
+    pub async fn connect(&self) -> io::Result<()> {
+        loop {
+            match self.io.connect() {
+                Ok(()) => break,
+                Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+                    self.io.registration().readiness(Interest::WRITABLE).await?;
+                }
+                Err(e) => return Err(e),
+            }
+        }
+
+        Ok(())
+    }
+
+    /// Disconnects the server end of a named pipe instance from a client
+    /// process.
+    ///
+    /// ```
+    /// use tokio::io::AsyncWriteExt;
+    /// use tokio::net::windows::named_pipe::{ClientOptions, ServerOptions};
+    /// use winapi::shared::winerror;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-disconnect";
+    ///
+    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
+    /// let server = ServerOptions::new()
+    ///     .create(PIPE_NAME)?;
+    ///
+    /// let mut client = ClientOptions::new()
+    ///     .open(PIPE_NAME)?;
+    ///
+    /// // Wait for a client to become connected.
+    /// server.connect().await?;
+    ///
+    /// // Forcibly disconnect the client.
+    /// server.disconnect()?;
+    ///
+    /// // Write fails with an OS-specific error after client has been
+    /// // disconnected.
+    /// let e = client.write(b"ping").await.unwrap_err();
+    /// assert_eq!(e.raw_os_error(), Some(winerror::ERROR_PIPE_NOT_CONNECTED as i32));
+    /// # Ok(()) }
+    /// ```
+    pub fn disconnect(&self) -> io::Result<()> {
+        self.io.disconnect()
+    }
+
+    /// Waits for any of the requested ready states.
+    ///
+    /// This function is usually paired with `try_read()` or `try_write()`. It
+    /// can be used to concurrently read / write to the same pipe on a single
+    /// task without splitting the pipe.
+    ///
+    /// # Examples
+    ///
+    /// Concurrently read and write to the pipe on the same task without
+    /// splitting.
+    ///
+    /// ```no_run
+    /// use tokio::io::Interest;
+    /// use tokio::net::windows::named_pipe;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-server-ready";
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let server = named_pipe::ServerOptions::new()
+    ///         .create(PIPE_NAME)?;
+    ///
+    ///     loop {
+    ///         let ready = server.ready(Interest::READABLE | Interest::WRITABLE).await?;
+    ///
+    ///         if ready.is_readable() {
+    ///             let mut data = vec![0; 1024];
+    ///             // Try to read data, this may still fail with `WouldBlock`
+    ///             // if the readiness event is a false positive.
+    ///             match server.try_read(&mut data) {
+    ///                 Ok(n) => {
+    ///                     println!("read {} bytes", n);
+    ///                 }
+    ///                 Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                     continue;
+    ///                 }
+    ///                 Err(e) => {
+    ///                     return Err(e.into());
+    ///                 }
+    ///             }
+    ///         }
+    ///
+    ///         if ready.is_writable() {
+    ///             // Try to write data, this may still fail with `WouldBlock`
+    ///             // if the readiness event is a false positive.
+    ///             match server.try_write(b"hello world") {
+    ///                 Ok(n) => {
+    ///                     println!("write {} bytes", n);
+    ///                 }
+    ///                 Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                     continue;
+    ///                 }
+    ///                 Err(e) => {
+    ///                     return Err(e.into());
+    ///                 }
+    ///             }
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    pub async fn ready(&self, interest: Interest) -> io::Result<Ready> {
+        let event = self.io.registration().readiness(interest).await?;
+        Ok(event.ready)
+    }
+
+    /// Waits for the pipe to become readable.
+    ///
+    /// This function is equivalent to `ready(Interest::READABLE)` and is usually
+    /// paired with `try_read()`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::windows::named_pipe;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-server-readable";
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let server = named_pipe::ServerOptions::new()
+    ///         .create(PIPE_NAME)?;
+    ///
+    ///     let mut msg = vec![0; 1024];
+    ///
+    ///     loop {
+    ///         // Wait for the pipe to be readable
+    ///         server.readable().await?;
+    ///
+    ///         // Try to read data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match server.try_read(&mut msg) {
+    ///             Ok(n) => {
+    ///                 msg.truncate(n);
+    ///                 break;
+    ///             }
+    ///             Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     println!("GOT = {:?}", msg);
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn readable(&self) -> io::Result<()> {
+        self.ready(Interest::READABLE).await?;
+        Ok(())
+    }
+
+    /// Polls for read readiness.
+    ///
+    /// If the pipe is not currently ready for reading, this method will
+    /// store a clone of the `Waker` from the provided `Context`. When the pipe
+    /// becomes ready for reading, `Waker::wake` will be called on the waker.
+    ///
+    /// Note that on multiple calls to `poll_read_ready` or `poll_read`, only
+    /// the `Waker` from the `Context` passed to the most recent call is
+    /// scheduled to receive a wakeup. (However, `poll_write_ready` retains a
+    /// second, independent waker.)
+    ///
+    /// This function is intended for cases where creating and pinning a future
+    /// via [`readable`] is not feasible. Where possible, using [`readable`] is
+    /// preferred, as this supports polling from multiple tasks at once.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the pipe is not ready for reading.
+    /// * `Poll::Ready(Ok(()))` if the pipe is ready for reading.
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// [`readable`]: method@Self::readable
+    pub fn poll_read_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.io.registration().poll_read_ready(cx).map_ok(|_| ())
+    }
+
+    /// Tries to read data from the pipe into the provided buffer, returning how
+    /// many bytes were read.
+    ///
+    /// Receives any pending data from the pipe but does not wait for new data
+    /// to arrive. On success, returns the number of bytes read. Because
+    /// `try_read()` is non-blocking, the buffer does not have to be stored by
+    /// the async task and can exist entirely on the stack.
+    ///
+    /// Usually, [`readable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`readable()`]: NamedPipeServer::readable()
+    /// [`ready()`]: NamedPipeServer::ready()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+    /// number of bytes read. `Ok(0)` indicates the pipe's read half is closed
+    /// and will no longer yield data. If the pipe is not ready to read data
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::windows::named_pipe;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-server-try-read";
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let server = named_pipe::ServerOptions::new()
+    ///         .create(PIPE_NAME)?;
+    ///
+    ///     loop {
+    ///         // Wait for the pipe to be readable
+    ///         server.readable().await?;
+    ///
+    ///         // Creating the buffer **after** the `await` prevents it from
+    ///         // being stored in the async task.
+    ///         let mut buf = [0; 4096];
+    ///
+    ///         // Try to read data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match server.try_read(&mut buf) {
+    ///             Ok(0) => break,
+    ///             Ok(n) => {
+    ///                 println!("read {} bytes", n);
+    ///             }
+    ///             Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_read(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::READABLE, || (&*self.io).read(buf))
+    }
+
+    /// Tries to read data from the pipe into the provided buffers, returning
+    /// how many bytes were read.
+    ///
+    /// Data is copied to fill each buffer in order, with the final buffer
+    /// written to possibly being only partially filled. This method behaves
+    /// equivalently to a single call to [`try_read()`] with concatenated
+    /// buffers.
+    ///
+    /// Receives any pending data from the pipe but does not wait for new data
+    /// to arrive. On success, returns the number of bytes read. Because
+    /// `try_read_vectored()` is non-blocking, the buffer does not have to be
+    /// stored by the async task and can exist entirely on the stack.
+    ///
+    /// Usually, [`readable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`try_read()`]: NamedPipeServer::try_read()
+    /// [`readable()`]: NamedPipeServer::readable()
+    /// [`ready()`]: NamedPipeServer::ready()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+    /// number of bytes read. `Ok(0)` indicates the pipe's read half is closed
+    /// and will no longer yield data. If the pipe is not ready to read data
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::windows::named_pipe;
+    /// use std::error::Error;
+    /// use std::io::{self, IoSliceMut};
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-server-try-read-vectored";
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let server = named_pipe::ServerOptions::new()
+    ///         .create(PIPE_NAME)?;
+    ///
+    ///     loop {
+    ///         // Wait for the pipe to be readable
+    ///         server.readable().await?;
+    ///
+    ///         // Creating the buffer **after** the `await` prevents it from
+    ///         // being stored in the async task.
+    ///         let mut buf_a = [0; 512];
+    ///         let mut buf_b = [0; 1024];
+    ///         let mut bufs = [
+    ///             IoSliceMut::new(&mut buf_a),
+    ///             IoSliceMut::new(&mut buf_b),
+    ///         ];
+    ///
+    ///         // Try to read data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match server.try_read_vectored(&mut bufs) {
+    ///             Ok(0) => break,
+    ///             Ok(n) => {
+    ///                 println!("read {} bytes", n);
+    ///             }
+    ///             Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_read_vectored(&self, bufs: &mut [io::IoSliceMut<'_>]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::READABLE, || (&*self.io).read_vectored(bufs))
+    }
+
+    /// Waits for the pipe to become writable.
+    ///
+    /// This function is equivalent to `ready(Interest::WRITABLE)` and is usually
+    /// paired with `try_write()`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::windows::named_pipe;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-server-writable";
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let server = named_pipe::ServerOptions::new()
+    ///         .create(PIPE_NAME)?;
+    ///
+    ///     loop {
+    ///         // Wait for the pipe to be writable
+    ///         server.writable().await?;
+    ///
+    ///         // Try to write data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match server.try_write(b"hello world") {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn writable(&self) -> io::Result<()> {
+        self.ready(Interest::WRITABLE).await?;
+        Ok(())
+    }
+
+    /// Polls for write readiness.
+    ///
+    /// If the pipe is not currently ready for writing, this method will
+    /// store a clone of the `Waker` from the provided `Context`. When the pipe
+    /// becomes ready for writing, `Waker::wake` will be called on the waker.
+    ///
+    /// Note that on multiple calls to `poll_write_ready` or `poll_write`, only
+    /// the `Waker` from the `Context` passed to the most recent call is
+    /// scheduled to receive a wakeup. (However, `poll_read_ready` retains a
+    /// second, independent waker.)
+    ///
+    /// This function is intended for cases where creating and pinning a future
+    /// via [`writable`] is not feasible. Where possible, using [`writable`] is
+    /// preferred, as this supports polling from multiple tasks at once.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the pipe is not ready for writing.
+    /// * `Poll::Ready(Ok(()))` if the pipe is ready for writing.
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// [`writable`]: method@Self::writable
+    pub fn poll_write_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.io.registration().poll_write_ready(cx).map_ok(|_| ())
+    }
+
+    /// Tries to write a buffer to the pipe, returning how many bytes were
+    /// written.
+    ///
+    /// The function will attempt to write the entire contents of `buf`, but
+    /// only part of the buffer may be written.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// # Return
+    ///
+    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
+    /// number of bytes written. If the pipe is not ready to write data,
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::windows::named_pipe;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-server-try-write";
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let server = named_pipe::ServerOptions::new()
+    ///         .create(PIPE_NAME)?;
+    ///
+    ///     loop {
+    ///         // Wait for the pipe to be writable
+    ///         server.writable().await?;
+    ///
+    ///         // Try to write data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match server.try_write(b"hello world") {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_write(&self, buf: &[u8]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::WRITABLE, || (&*self.io).write(buf))
+    }
+
+    /// Tries to write several buffers to the pipe, returning how many bytes
+    /// were written.
+    ///
+    /// Data is written from each buffer in order, with the final buffer read
+    /// from possible being only partially consumed. This method behaves
+    /// equivalently to a single call to [`try_write()`] with concatenated
+    /// buffers.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// [`try_write()`]: NamedPipeServer::try_write()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
+    /// number of bytes written. If the pipe is not ready to write data,
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::windows::named_pipe;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-server-try-write-vectored";
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let server = named_pipe::ServerOptions::new()
+    ///         .create(PIPE_NAME)?;
+    ///
+    ///     let bufs = [io::IoSlice::new(b"hello "), io::IoSlice::new(b"world")];
+    ///
+    ///     loop {
+    ///         // Wait for the pipe to be writable
+    ///         server.writable().await?;
+    ///
+    ///         // Try to write data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match server.try_write_vectored(&bufs) {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_write_vectored(&self, buf: &[io::IoSlice<'_>]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::WRITABLE, || (&*self.io).write_vectored(buf))
+    }
+
+    /// Tries to read or write from the socket using a user-provided IO operation.
+    ///
+    /// If the socket is ready, the provided closure is called. The closure
+    /// should attempt to perform IO operation from the socket by manually
+    /// calling the appropriate syscall. If the operation fails because the
+    /// socket is not actually ready, then the closure should return a
+    /// `WouldBlock` error and the readiness flag is cleared. The return value
+    /// of the closure is then returned by `try_io`.
+    ///
+    /// If the socket is not ready, then the closure is not called
+    /// and a `WouldBlock` error is returned.
+    ///
+    /// The closure should only return a `WouldBlock` error if it has performed
+    /// an IO operation on the socket that failed due to the socket not being
+    /// ready. Returning a `WouldBlock` error in any other situation will
+    /// incorrectly clear the readiness flag, which can cause the socket to
+    /// behave incorrectly.
+    ///
+    /// The closure should not perform the IO operation using any of the
+    /// methods defined on the Tokio `NamedPipeServer` type, as this will mess with
+    /// the readiness flag and can cause the socket to behave incorrectly.
+    ///
+    /// Usually, [`readable()`], [`writable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`readable()`]: NamedPipeServer::readable()
+    /// [`writable()`]: NamedPipeServer::writable()
+    /// [`ready()`]: NamedPipeServer::ready()
+    pub fn try_io<R>(
+        &self,
+        interest: Interest,
+        f: impl FnOnce() -> io::Result<R>,
+    ) -> io::Result<R> {
+        self.io.registration().try_io(interest, f)
+    }
+}
+
+impl AsyncRead for NamedPipeServer {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        unsafe { self.io.poll_read(cx, buf) }
+    }
+}
+
+impl AsyncWrite for NamedPipeServer {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.io.poll_write(cx, buf)
+    }
+
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.io.poll_write_vectored(cx, bufs)
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.poll_flush(cx)
+    }
+}
+
+impl AsRawHandle for NamedPipeServer {
+    fn as_raw_handle(&self) -> RawHandle {
+        self.io.as_raw_handle()
+    }
+}
+
+/// A [Windows named pipe] client.
+///
+/// Constructed using [`ClientOptions::open`].
+///
+/// Connecting a client correctly involves a few steps. When connecting through
+/// [`ClientOptions::open`], it might error indicating one of two things:
+///
+/// * [`std::io::ErrorKind::NotFound`] - There is no server available.
+/// * [`ERROR_PIPE_BUSY`] - There is a server available, but it is busy. Sleep
+///   for a while and try again.
+///
+/// So a correctly implemented client looks like this:
+///
+/// ```no_run
+/// use std::time::Duration;
+/// use tokio::net::windows::named_pipe::ClientOptions;
+/// use tokio::time;
+/// use winapi::shared::winerror;
+///
+/// const PIPE_NAME: &str = r"\\.\pipe\named-pipe-idiomatic-client";
+///
+/// # #[tokio::main] async fn main() -> std::io::Result<()> {
+/// let client = loop {
+///     match ClientOptions::new().open(PIPE_NAME) {
+///         Ok(client) => break client,
+///         Err(e) if e.raw_os_error() == Some(winerror::ERROR_PIPE_BUSY as i32) => (),
+///         Err(e) => return Err(e),
+///     }
+///
+///     time::sleep(Duration::from_millis(50)).await;
+/// };
+///
+/// /* use the connected client */
+/// # Ok(()) }
+/// ```
+///
+/// [`ERROR_PIPE_BUSY`]: crate::winapi::shared::winerror::ERROR_PIPE_BUSY
+/// [Windows named pipe]: https://docs.microsoft.com/en-us/windows/win32/ipc/named-pipes
+#[derive(Debug)]
+pub struct NamedPipeClient {
+    io: PollEvented<mio_windows::NamedPipe>,
+}
+
+impl NamedPipeClient {
+    /// Constructs a new named pipe client from the specified raw handle.
+    ///
+    /// This function will consume ownership of the handle given, passing
+    /// responsibility for closing the handle to the returned object.
+    ///
+    /// This function is also unsafe as the primitives currently returned have
+    /// the contract that they are the sole owner of the file descriptor they
+    /// are wrapping. Usage of this function could accidentally allow violating
+    /// this contract which can cause memory unsafety in code that relies on it
+    /// being true.
+    ///
+    /// # Errors
+    ///
+    /// This errors if called outside of a [Tokio Runtime], or in a runtime that
+    /// has not [enabled I/O], or if any OS-specific I/O errors occur.
+    ///
+    /// [Tokio Runtime]: crate::runtime::Runtime
+    /// [enabled I/O]: crate::runtime::Builder::enable_io
+    pub unsafe fn from_raw_handle(handle: RawHandle) -> io::Result<Self> {
+        let named_pipe = mio_windows::NamedPipe::from_raw_handle(handle);
+
+        Ok(Self {
+            io: PollEvented::new(named_pipe)?,
+        })
+    }
+
+    /// Retrieves information about the named pipe the client is associated
+    /// with.
+    ///
+    /// ```no_run
+    /// use tokio::net::windows::named_pipe::{ClientOptions, PipeEnd, PipeMode};
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-client-info";
+    ///
+    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
+    /// let client = ClientOptions::new()
+    ///     .open(PIPE_NAME)?;
+    ///
+    /// let client_info = client.info()?;
+    ///
+    /// assert_eq!(client_info.end, PipeEnd::Client);
+    /// assert_eq!(client_info.mode, PipeMode::Message);
+    /// assert_eq!(client_info.max_instances, 5);
+    /// # Ok(()) }
+    /// ```
+    pub fn info(&self) -> io::Result<PipeInfo> {
+        // Safety: we're ensuring the lifetime of the named pipe.
+        unsafe { named_pipe_info(self.io.as_raw_handle()) }
+    }
+
+    /// Waits for any of the requested ready states.
+    ///
+    /// This function is usually paired with `try_read()` or `try_write()`. It
+    /// can be used to concurrently read / write to the same pipe on a single
+    /// task without splitting the pipe.
+    ///
+    /// # Examples
+    ///
+    /// Concurrently read and write to the pipe on the same task without
+    /// splitting.
+    ///
+    /// ```no_run
+    /// use tokio::io::Interest;
+    /// use tokio::net::windows::named_pipe;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-client-ready";
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let client = named_pipe::ClientOptions::new().open(PIPE_NAME)?;
+    ///
+    ///     loop {
+    ///         let ready = client.ready(Interest::READABLE | Interest::WRITABLE).await?;
+    ///
+    ///         if ready.is_readable() {
+    ///             let mut data = vec![0; 1024];
+    ///             // Try to read data, this may still fail with `WouldBlock`
+    ///             // if the readiness event is a false positive.
+    ///             match client.try_read(&mut data) {
+    ///                 Ok(n) => {
+    ///                     println!("read {} bytes", n);
+    ///                 }
+    ///                 Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                     continue;
+    ///                 }
+    ///                 Err(e) => {
+    ///                     return Err(e.into());
+    ///                 }
+    ///             }
+    ///         }
+    ///
+    ///         if ready.is_writable() {
+    ///             // Try to write data, this may still fail with `WouldBlock`
+    ///             // if the readiness event is a false positive.
+    ///             match client.try_write(b"hello world") {
+    ///                 Ok(n) => {
+    ///                     println!("write {} bytes", n);
+    ///                 }
+    ///                 Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                     continue;
+    ///                 }
+    ///                 Err(e) => {
+    ///                     return Err(e.into());
+    ///                 }
+    ///             }
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    pub async fn ready(&self, interest: Interest) -> io::Result<Ready> {
+        let event = self.io.registration().readiness(interest).await?;
+        Ok(event.ready)
+    }
+
+    /// Waits for the pipe to become readable.
+    ///
+    /// This function is equivalent to `ready(Interest::READABLE)` and is usually
+    /// paired with `try_read()`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::windows::named_pipe;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-client-readable";
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let client = named_pipe::ClientOptions::new().open(PIPE_NAME)?;
+    ///
+    ///     let mut msg = vec![0; 1024];
+    ///
+    ///     loop {
+    ///         // Wait for the pipe to be readable
+    ///         client.readable().await?;
+    ///
+    ///         // Try to read data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match client.try_read(&mut msg) {
+    ///             Ok(n) => {
+    ///                 msg.truncate(n);
+    ///                 break;
+    ///             }
+    ///             Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     println!("GOT = {:?}", msg);
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn readable(&self) -> io::Result<()> {
+        self.ready(Interest::READABLE).await?;
+        Ok(())
+    }
+
+    /// Polls for read readiness.
+    ///
+    /// If the pipe is not currently ready for reading, this method will
+    /// store a clone of the `Waker` from the provided `Context`. When the pipe
+    /// becomes ready for reading, `Waker::wake` will be called on the waker.
+    ///
+    /// Note that on multiple calls to `poll_read_ready` or `poll_read`, only
+    /// the `Waker` from the `Context` passed to the most recent call is
+    /// scheduled to receive a wakeup. (However, `poll_write_ready` retains a
+    /// second, independent waker.)
+    ///
+    /// This function is intended for cases where creating and pinning a future
+    /// via [`readable`] is not feasible. Where possible, using [`readable`] is
+    /// preferred, as this supports polling from multiple tasks at once.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the pipe is not ready for reading.
+    /// * `Poll::Ready(Ok(()))` if the pipe is ready for reading.
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// [`readable`]: method@Self::readable
+    pub fn poll_read_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.io.registration().poll_read_ready(cx).map_ok(|_| ())
+    }
+
+    /// Tries to read data from the pipe into the provided buffer, returning how
+    /// many bytes were read.
+    ///
+    /// Receives any pending data from the pipe but does not wait for new data
+    /// to arrive. On success, returns the number of bytes read. Because
+    /// `try_read()` is non-blocking, the buffer does not have to be stored by
+    /// the async task and can exist entirely on the stack.
+    ///
+    /// Usually, [`readable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`readable()`]: NamedPipeClient::readable()
+    /// [`ready()`]: NamedPipeClient::ready()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+    /// number of bytes read. `Ok(0)` indicates the pipe's read half is closed
+    /// and will no longer yield data. If the pipe is not ready to read data
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::windows::named_pipe;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-client-try-read";
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let client = named_pipe::ClientOptions::new().open(PIPE_NAME)?;
+    ///
+    ///     loop {
+    ///         // Wait for the pipe to be readable
+    ///         client.readable().await?;
+    ///
+    ///         // Creating the buffer **after** the `await` prevents it from
+    ///         // being stored in the async task.
+    ///         let mut buf = [0; 4096];
+    ///
+    ///         // Try to read data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match client.try_read(&mut buf) {
+    ///             Ok(0) => break,
+    ///             Ok(n) => {
+    ///                 println!("read {} bytes", n);
+    ///             }
+    ///             Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_read(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::READABLE, || (&*self.io).read(buf))
+    }
+
+    /// Tries to read data from the pipe into the provided buffers, returning
+    /// how many bytes were read.
+    ///
+    /// Data is copied to fill each buffer in order, with the final buffer
+    /// written to possibly being only partially filled. This method behaves
+    /// equivalently to a single call to [`try_read()`] with concatenated
+    /// buffers.
+    ///
+    /// Receives any pending data from the pipe but does not wait for new data
+    /// to arrive. On success, returns the number of bytes read. Because
+    /// `try_read_vectored()` is non-blocking, the buffer does not have to be
+    /// stored by the async task and can exist entirely on the stack.
+    ///
+    /// Usually, [`readable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`try_read()`]: NamedPipeClient::try_read()
+    /// [`readable()`]: NamedPipeClient::readable()
+    /// [`ready()`]: NamedPipeClient::ready()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully read, `Ok(n)` is returned, where `n` is the
+    /// number of bytes read. `Ok(0)` indicates the pipe's read half is closed
+    /// and will no longer yield data. If the pipe is not ready to read data
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::windows::named_pipe;
+    /// use std::error::Error;
+    /// use std::io::{self, IoSliceMut};
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-client-try-read-vectored";
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let client = named_pipe::ClientOptions::new().open(PIPE_NAME)?;
+    ///
+    ///     loop {
+    ///         // Wait for the pipe to be readable
+    ///         client.readable().await?;
+    ///
+    ///         // Creating the buffer **after** the `await` prevents it from
+    ///         // being stored in the async task.
+    ///         let mut buf_a = [0; 512];
+    ///         let mut buf_b = [0; 1024];
+    ///         let mut bufs = [
+    ///             IoSliceMut::new(&mut buf_a),
+    ///             IoSliceMut::new(&mut buf_b),
+    ///         ];
+    ///
+    ///         // Try to read data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match client.try_read_vectored(&mut bufs) {
+    ///             Ok(0) => break,
+    ///             Ok(n) => {
+    ///                 println!("read {} bytes", n);
+    ///             }
+    ///             Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_read_vectored(&self, bufs: &mut [io::IoSliceMut<'_>]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::READABLE, || (&*self.io).read_vectored(bufs))
+    }
+
+    /// Waits for the pipe to become writable.
+    ///
+    /// This function is equivalent to `ready(Interest::WRITABLE)` and is usually
+    /// paired with `try_write()`.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::windows::named_pipe;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-client-writable";
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let client = named_pipe::ClientOptions::new().open(PIPE_NAME)?;
+    ///
+    ///     loop {
+    ///         // Wait for the pipe to be writable
+    ///         client.writable().await?;
+    ///
+    ///         // Try to write data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match client.try_write(b"hello world") {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn writable(&self) -> io::Result<()> {
+        self.ready(Interest::WRITABLE).await?;
+        Ok(())
+    }
+
+    /// Polls for write readiness.
+    ///
+    /// If the pipe is not currently ready for writing, this method will
+    /// store a clone of the `Waker` from the provided `Context`. When the pipe
+    /// becomes ready for writing, `Waker::wake` will be called on the waker.
+    ///
+    /// Note that on multiple calls to `poll_write_ready` or `poll_write`, only
+    /// the `Waker` from the `Context` passed to the most recent call is
+    /// scheduled to receive a wakeup. (However, `poll_read_ready` retains a
+    /// second, independent waker.)
+    ///
+    /// This function is intended for cases where creating and pinning a future
+    /// via [`writable`] is not feasible. Where possible, using [`writable`] is
+    /// preferred, as this supports polling from multiple tasks at once.
+    ///
+    /// # Return value
+    ///
+    /// The function returns:
+    ///
+    /// * `Poll::Pending` if the pipe is not ready for writing.
+    /// * `Poll::Ready(Ok(()))` if the pipe is ready for writing.
+    /// * `Poll::Ready(Err(e))` if an error is encountered.
+    ///
+    /// # Errors
+    ///
+    /// This function may encounter any standard I/O error except `WouldBlock`.
+    ///
+    /// [`writable`]: method@Self::writable
+    pub fn poll_write_ready(&self, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.io.registration().poll_write_ready(cx).map_ok(|_| ())
+    }
+
+    /// Tries to write a buffer to the pipe, returning how many bytes were
+    /// written.
+    ///
+    /// The function will attempt to write the entire contents of `buf`, but
+    /// only part of the buffer may be written.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// # Return
+    ///
+    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
+    /// number of bytes written. If the pipe is not ready to write data,
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::windows::named_pipe;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-client-try-write";
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let client = named_pipe::ClientOptions::new().open(PIPE_NAME)?;
+    ///
+    ///     loop {
+    ///         // Wait for the pipe to be writable
+    ///         client.writable().await?;
+    ///
+    ///         // Try to write data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match client.try_write(b"hello world") {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_write(&self, buf: &[u8]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::WRITABLE, || (&*self.io).write(buf))
+    }
+
+    /// Tries to write several buffers to the pipe, returning how many bytes
+    /// were written.
+    ///
+    /// Data is written from each buffer in order, with the final buffer read
+    /// from possible being only partially consumed. This method behaves
+    /// equivalently to a single call to [`try_write()`] with concatenated
+    /// buffers.
+    ///
+    /// This function is usually paired with `writable()`.
+    ///
+    /// [`try_write()`]: NamedPipeClient::try_write()
+    ///
+    /// # Return
+    ///
+    /// If data is successfully written, `Ok(n)` is returned, where `n` is the
+    /// number of bytes written. If the pipe is not ready to write data,
+    /// `Err(io::ErrorKind::WouldBlock)` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// use tokio::net::windows::named_pipe;
+    /// use std::error::Error;
+    /// use std::io;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-client-try-write-vectored";
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn Error>> {
+    ///     let client = named_pipe::ClientOptions::new().open(PIPE_NAME)?;
+    ///
+    ///     let bufs = [io::IoSlice::new(b"hello "), io::IoSlice::new(b"world")];
+    ///
+    ///     loop {
+    ///         // Wait for the pipe to be writable
+    ///         client.writable().await?;
+    ///
+    ///         // Try to write data, this may still fail with `WouldBlock`
+    ///         // if the readiness event is a false positive.
+    ///         match client.try_write_vectored(&bufs) {
+    ///             Ok(n) => {
+    ///                 break;
+    ///             }
+    ///             Err(e) if e.kind() == io::ErrorKind::WouldBlock => {
+    ///                 continue;
+    ///             }
+    ///             Err(e) => {
+    ///                 return Err(e.into());
+    ///             }
+    ///         }
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn try_write_vectored(&self, buf: &[io::IoSlice<'_>]) -> io::Result<usize> {
+        self.io
+            .registration()
+            .try_io(Interest::WRITABLE, || (&*self.io).write_vectored(buf))
+    }
+
+    /// Tries to read or write from the socket using a user-provided IO operation.
+    ///
+    /// If the socket is ready, the provided closure is called. The closure
+    /// should attempt to perform IO operation from the socket by manually
+    /// calling the appropriate syscall. If the operation fails because the
+    /// socket is not actually ready, then the closure should return a
+    /// `WouldBlock` error and the readiness flag is cleared. The return value
+    /// of the closure is then returned by `try_io`.
+    ///
+    /// If the socket is not ready, then the closure is not called
+    /// and a `WouldBlock` error is returned.
+    ///
+    /// The closure should only return a `WouldBlock` error if it has performed
+    /// an IO operation on the socket that failed due to the socket not being
+    /// ready. Returning a `WouldBlock` error in any other situation will
+    /// incorrectly clear the readiness flag, which can cause the socket to
+    /// behave incorrectly.
+    ///
+    /// The closure should not perform the IO operation using any of the methods
+    /// defined on the Tokio `NamedPipeClient` type, as this will mess with the
+    /// readiness flag and can cause the socket to behave incorrectly.
+    ///
+    /// Usually, [`readable()`], [`writable()`] or [`ready()`] is used with this function.
+    ///
+    /// [`readable()`]: NamedPipeClient::readable()
+    /// [`writable()`]: NamedPipeClient::writable()
+    /// [`ready()`]: NamedPipeClient::ready()
+    pub fn try_io<R>(
+        &self,
+        interest: Interest,
+        f: impl FnOnce() -> io::Result<R>,
+    ) -> io::Result<R> {
+        self.io.registration().try_io(interest, f)
+    }
+}
+
+impl AsyncRead for NamedPipeClient {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        unsafe { self.io.poll_read(cx, buf) }
+    }
+}
+
+impl AsyncWrite for NamedPipeClient {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.io.poll_write(cx, buf)
+    }
+
+    fn poll_write_vectored(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        bufs: &[io::IoSlice<'_>],
+    ) -> Poll<io::Result<usize>> {
+        self.io.poll_write_vectored(cx, bufs)
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        self.poll_flush(cx)
+    }
+}
+
+impl AsRawHandle for NamedPipeClient {
+    fn as_raw_handle(&self) -> RawHandle {
+        self.io.as_raw_handle()
+    }
+}
+
+// Helper to set a boolean flag as a bitfield.
+macro_rules! bool_flag {
+    ($f:expr, $t:expr, $flag:expr) => {{
+        let current = $f;
+
+        if $t {
+            $f = current | $flag;
+        } else {
+            $f = current & !$flag;
+        };
+    }};
+}
+
+/// A builder structure for construct a named pipe with named pipe-specific
+/// options. This is required to use for named pipe servers who wants to modify
+/// pipe-related options.
+///
+/// See [`ServerOptions::create`].
+#[derive(Debug, Clone)]
+pub struct ServerOptions {
+    open_mode: DWORD,
+    pipe_mode: DWORD,
+    max_instances: DWORD,
+    out_buffer_size: DWORD,
+    in_buffer_size: DWORD,
+    default_timeout: DWORD,
+}
+
+impl ServerOptions {
+    /// Creates a new named pipe builder with the default settings.
+    ///
+    /// ```
+    /// use tokio::net::windows::named_pipe::ServerOptions;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-new";
+    ///
+    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
+    /// let server = ServerOptions::new().create(PIPE_NAME)?;
+    /// # Ok(()) }
+    /// ```
+    pub fn new() -> ServerOptions {
+        ServerOptions {
+            open_mode: winbase::PIPE_ACCESS_DUPLEX | winbase::FILE_FLAG_OVERLAPPED,
+            pipe_mode: winbase::PIPE_TYPE_BYTE | winbase::PIPE_REJECT_REMOTE_CLIENTS,
+            max_instances: winbase::PIPE_UNLIMITED_INSTANCES,
+            out_buffer_size: 65536,
+            in_buffer_size: 65536,
+            default_timeout: 0,
+        }
+    }
+
+    /// The pipe mode.
+    ///
+    /// The default pipe mode is [`PipeMode::Byte`]. See [`PipeMode`] for
+    /// documentation of what each mode means.
+    ///
+    /// This corresponding to specifying [`dwPipeMode`].
+    ///
+    /// [`dwPipeMode`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea
+    pub fn pipe_mode(&mut self, pipe_mode: PipeMode) -> &mut Self {
+        self.pipe_mode = match pipe_mode {
+            PipeMode::Byte => winbase::PIPE_TYPE_BYTE,
+            PipeMode::Message => winbase::PIPE_TYPE_MESSAGE,
+        };
+
+        self
+    }
+
+    /// The flow of data in the pipe goes from client to server only.
+    ///
+    /// This corresponds to setting [`PIPE_ACCESS_INBOUND`].
+    ///
+    /// [`PIPE_ACCESS_INBOUND`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea#pipe_access_inbound
+    ///
+    /// # Errors
+    ///
+    /// Server side prevents connecting by denying inbound access, client errors
+    /// with [`std::io::ErrorKind::PermissionDenied`] when attempting to create
+    /// the connection.
+    ///
+    /// ```
+    /// use std::io;
+    /// use tokio::net::windows::named_pipe::{ClientOptions, ServerOptions};
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-access-inbound-err1";
+    ///
+    /// # #[tokio::main] async fn main() -> io::Result<()> {
+    /// let _server = ServerOptions::new()
+    ///     .access_inbound(false)
+    ///     .create(PIPE_NAME)?;
+    ///
+    /// let e = ClientOptions::new()
+    ///     .open(PIPE_NAME)
+    ///     .unwrap_err();
+    ///
+    /// assert_eq!(e.kind(), io::ErrorKind::PermissionDenied);
+    /// # Ok(()) }
+    /// ```
+    ///
+    /// Disabling writing allows a client to connect, but errors with
+    /// [`std::io::ErrorKind::PermissionDenied`] if a write is attempted.
+    ///
+    /// ```
+    /// use std::io;
+    /// use tokio::io::AsyncWriteExt;
+    /// use tokio::net::windows::named_pipe::{ClientOptions, ServerOptions};
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-access-inbound-err2";
+    ///
+    /// # #[tokio::main] async fn main() -> io::Result<()> {
+    /// let server = ServerOptions::new()
+    ///     .access_inbound(false)
+    ///     .create(PIPE_NAME)?;
+    ///
+    /// let mut client = ClientOptions::new()
+    ///     .write(false)
+    ///     .open(PIPE_NAME)?;
+    ///
+    /// server.connect().await?;
+    ///
+    /// let e = client.write(b"ping").await.unwrap_err();
+    /// assert_eq!(e.kind(), io::ErrorKind::PermissionDenied);
+    /// # Ok(()) }
+    /// ```
+    ///
+    /// # Examples
+    ///
+    /// A unidirectional named pipe that only supports server-to-client
+    /// communication.
+    ///
+    /// ```
+    /// use std::io;
+    /// use tokio::io::{AsyncReadExt, AsyncWriteExt};
+    /// use tokio::net::windows::named_pipe::{ClientOptions, ServerOptions};
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-access-inbound";
+    ///
+    /// # #[tokio::main] async fn main() -> io::Result<()> {
+    /// let mut server = ServerOptions::new()
+    ///     .access_inbound(false)
+    ///     .create(PIPE_NAME)?;
+    ///
+    /// let mut client = ClientOptions::new()
+    ///     .write(false)
+    ///     .open(PIPE_NAME)?;
+    ///
+    /// server.connect().await?;
+    ///
+    /// let write = server.write_all(b"ping");
+    ///
+    /// let mut buf = [0u8; 4];
+    /// let read = client.read_exact(&mut buf);
+    ///
+    /// let ((), read) = tokio::try_join!(write, read)?;
+    ///
+    /// assert_eq!(read, 4);
+    /// assert_eq!(&buf[..], b"ping");
+    /// # Ok(()) }
+    /// ```
+    pub fn access_inbound(&mut self, allowed: bool) -> &mut Self {
+        bool_flag!(self.open_mode, allowed, winbase::PIPE_ACCESS_INBOUND);
+        self
+    }
+
+    /// The flow of data in the pipe goes from server to client only.
+    ///
+    /// This corresponds to setting [`PIPE_ACCESS_OUTBOUND`].
+    ///
+    /// [`PIPE_ACCESS_OUTBOUND`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea#pipe_access_outbound
+    ///
+    /// # Errors
+    ///
+    /// Server side prevents connecting by denying outbound access, client
+    /// errors with [`std::io::ErrorKind::PermissionDenied`] when attempting to
+    /// create the connection.
+    ///
+    /// ```
+    /// use std::io;
+    /// use tokio::net::windows::named_pipe::{ClientOptions, ServerOptions};
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-access-outbound-err1";
+    ///
+    /// # #[tokio::main] async fn main() -> io::Result<()> {
+    /// let server = ServerOptions::new()
+    ///     .access_outbound(false)
+    ///     .create(PIPE_NAME)?;
+    ///
+    /// let e = ClientOptions::new()
+    ///     .open(PIPE_NAME)
+    ///     .unwrap_err();
+    ///
+    /// assert_eq!(e.kind(), io::ErrorKind::PermissionDenied);
+    /// # Ok(()) }
+    /// ```
+    ///
+    /// Disabling reading allows a client to connect, but attempting to read
+    /// will error with [`std::io::ErrorKind::PermissionDenied`].
+    ///
+    /// ```
+    /// use std::io;
+    /// use tokio::io::AsyncReadExt;
+    /// use tokio::net::windows::named_pipe::{ClientOptions, ServerOptions};
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-access-outbound-err2";
+    ///
+    /// # #[tokio::main] async fn main() -> io::Result<()> {
+    /// let server = ServerOptions::new()
+    ///     .access_outbound(false)
+    ///     .create(PIPE_NAME)?;
+    ///
+    /// let mut client = ClientOptions::new()
+    ///     .read(false)
+    ///     .open(PIPE_NAME)?;
+    ///
+    /// server.connect().await?;
+    ///
+    /// let mut buf = [0u8; 4];
+    /// let e = client.read(&mut buf).await.unwrap_err();
+    /// assert_eq!(e.kind(), io::ErrorKind::PermissionDenied);
+    /// # Ok(()) }
+    /// ```
+    ///
+    /// # Examples
+    ///
+    /// A unidirectional named pipe that only supports client-to-server
+    /// communication.
+    ///
+    /// ```
+    /// use tokio::io::{AsyncReadExt, AsyncWriteExt};
+    /// use tokio::net::windows::named_pipe::{ClientOptions, ServerOptions};
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-access-outbound";
+    ///
+    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
+    /// let mut server = ServerOptions::new()
+    ///     .access_outbound(false)
+    ///     .create(PIPE_NAME)?;
+    ///
+    /// let mut client = ClientOptions::new()
+    ///     .read(false)
+    ///     .open(PIPE_NAME)?;
+    ///
+    /// server.connect().await?;
+    ///
+    /// let write = client.write_all(b"ping");
+    ///
+    /// let mut buf = [0u8; 4];
+    /// let read = server.read_exact(&mut buf);
+    ///
+    /// let ((), read) = tokio::try_join!(write, read)?;
+    ///
+    /// println!("done reading and writing");
+    ///
+    /// assert_eq!(read, 4);
+    /// assert_eq!(&buf[..], b"ping");
+    /// # Ok(()) }
+    /// ```
+    pub fn access_outbound(&mut self, allowed: bool) -> &mut Self {
+        bool_flag!(self.open_mode, allowed, winbase::PIPE_ACCESS_OUTBOUND);
+        self
+    }
+
+    /// If you attempt to create multiple instances of a pipe with this flag
+    /// set, creation of the first server instance succeeds, but creation of any
+    /// subsequent instances will fail with
+    /// [`std::io::ErrorKind::PermissionDenied`].
+    ///
+    /// This option is intended to be used with servers that want to ensure that
+    /// they are the only process listening for clients on a given named pipe.
+    /// This is accomplished by enabling it for the first server instance
+    /// created in a process.
+    ///
+    /// This corresponds to setting [`FILE_FLAG_FIRST_PIPE_INSTANCE`].
+    ///
+    /// # Errors
+    ///
+    /// If this option is set and more than one instance of the server for a
+    /// given named pipe exists, calling [`create`] will fail with
+    /// [`std::io::ErrorKind::PermissionDenied`].
+    ///
+    /// ```
+    /// use std::io;
+    /// use tokio::net::windows::named_pipe::ServerOptions;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-first-instance-error";
+    ///
+    /// # #[tokio::main] async fn main() -> io::Result<()> {
+    /// let server1 = ServerOptions::new()
+    ///     .first_pipe_instance(true)
+    ///     .create(PIPE_NAME)?;
+    ///
+    /// // Second server errs, since it's not the first instance.
+    /// let e = ServerOptions::new()
+    ///     .first_pipe_instance(true)
+    ///     .create(PIPE_NAME)
+    ///     .unwrap_err();
+    ///
+    /// assert_eq!(e.kind(), io::ErrorKind::PermissionDenied);
+    /// # Ok(()) }
+    /// ```
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::io;
+    /// use tokio::net::windows::named_pipe::ServerOptions;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-first-instance";
+    ///
+    /// # #[tokio::main] async fn main() -> io::Result<()> {
+    /// let mut builder = ServerOptions::new();
+    /// builder.first_pipe_instance(true);
+    ///
+    /// let server = builder.create(PIPE_NAME)?;
+    /// let e = builder.create(PIPE_NAME).unwrap_err();
+    /// assert_eq!(e.kind(), io::ErrorKind::PermissionDenied);
+    /// drop(server);
+    ///
+    /// // OK: since, we've closed the other instance.
+    /// let _server2 = builder.create(PIPE_NAME)?;
+    /// # Ok(()) }
+    /// ```
+    ///
+    /// [`create`]: ServerOptions::create
+    /// [`FILE_FLAG_FIRST_PIPE_INSTANCE`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea#pipe_first_pipe_instance
+    pub fn first_pipe_instance(&mut self, first: bool) -> &mut Self {
+        bool_flag!(
+            self.open_mode,
+            first,
+            winbase::FILE_FLAG_FIRST_PIPE_INSTANCE
+        );
+        self
+    }
+
+    /// Indicates whether this server can accept remote clients or not. Remote
+    /// clients are disabled by default.
+    ///
+    /// This corresponds to setting [`PIPE_REJECT_REMOTE_CLIENTS`].
+    ///
+    /// [`PIPE_REJECT_REMOTE_CLIENTS`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea#pipe_reject_remote_clients
+    pub fn reject_remote_clients(&mut self, reject: bool) -> &mut Self {
+        bool_flag!(self.pipe_mode, reject, winbase::PIPE_REJECT_REMOTE_CLIENTS);
+        self
+    }
+
+    /// The maximum number of instances that can be created for this pipe. The
+    /// first instance of the pipe can specify this value; the same number must
+    /// be specified for other instances of the pipe. Acceptable values are in
+    /// the range 1 through 254. The default value is unlimited.
+    ///
+    /// This corresponds to specifying [`nMaxInstances`].
+    ///
+    /// [`nMaxInstances`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea
+    ///
+    /// # Errors
+    ///
+    /// The same numbers of `max_instances` have to be used by all servers. Any
+    /// additional servers trying to be built which uses a mismatching value
+    /// might error.
+    ///
+    /// ```
+    /// use std::io;
+    /// use tokio::net::windows::named_pipe::{ServerOptions, ClientOptions};
+    /// use winapi::shared::winerror;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-max-instances";
+    ///
+    /// # #[tokio::main] async fn main() -> io::Result<()> {
+    /// let mut server = ServerOptions::new();
+    /// server.max_instances(2);
+    ///
+    /// let s1 = server.create(PIPE_NAME)?;
+    /// let c1 = ClientOptions::new().open(PIPE_NAME);
+    ///
+    /// let s2 = server.create(PIPE_NAME)?;
+    /// let c2 = ClientOptions::new().open(PIPE_NAME);
+    ///
+    /// // Too many servers!
+    /// let e = server.create(PIPE_NAME).unwrap_err();
+    /// assert_eq!(e.raw_os_error(), Some(winerror::ERROR_PIPE_BUSY as i32));
+    ///
+    /// // Still too many servers even if we specify a higher value!
+    /// let e = server.max_instances(100).create(PIPE_NAME).unwrap_err();
+    /// assert_eq!(e.raw_os_error(), Some(winerror::ERROR_PIPE_BUSY as i32));
+    /// # Ok(()) }
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if more than 254 instances are specified. If
+    /// you do not wish to set an instance limit, leave it unspecified.
+    ///
+    /// ```should_panic
+    /// use tokio::net::windows::named_pipe::ServerOptions;
+    ///
+    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
+    /// let builder = ServerOptions::new().max_instances(255);
+    /// # Ok(()) }
+    /// ```
+    pub fn max_instances(&mut self, instances: usize) -> &mut Self {
+        assert!(instances < 255, "cannot specify more than 254 instances");
+        self.max_instances = instances as DWORD;
+        self
+    }
+
+    /// The number of bytes to reserve for the output buffer.
+    ///
+    /// This corresponds to specifying [`nOutBufferSize`].
+    ///
+    /// [`nOutBufferSize`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea
+    pub fn out_buffer_size(&mut self, buffer: u32) -> &mut Self {
+        self.out_buffer_size = buffer as DWORD;
+        self
+    }
+
+    /// The number of bytes to reserve for the input buffer.
+    ///
+    /// This corresponds to specifying [`nInBufferSize`].
+    ///
+    /// [`nInBufferSize`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea
+    pub fn in_buffer_size(&mut self, buffer: u32) -> &mut Self {
+        self.in_buffer_size = buffer as DWORD;
+        self
+    }
+
+    /// Creates the named pipe identified by `addr` for use as a server.
+    ///
+    /// This uses the [`CreateNamedPipe`] function.
+    ///
+    /// [`CreateNamedPipe`]: https://docs.microsoft.com/en-us/windows/win32/api/winbase/nf-winbase-createnamedpipea
+    ///
+    /// # Errors
+    ///
+    /// This errors if called outside of a [Tokio Runtime], or in a runtime that
+    /// has not [enabled I/O], or if any OS-specific I/O errors occur.
+    ///
+    /// [Tokio Runtime]: crate::runtime::Runtime
+    /// [enabled I/O]: crate::runtime::Builder::enable_io
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::net::windows::named_pipe::ServerOptions;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-create";
+    ///
+    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
+    /// let server = ServerOptions::new().create(PIPE_NAME)?;
+    /// # Ok(()) }
+    /// ```
+    pub fn create(&self, addr: impl AsRef<OsStr>) -> io::Result<NamedPipeServer> {
+        // Safety: We're calling create_with_security_attributes_raw w/ a null
+        // pointer which disables it.
+        unsafe { self.create_with_security_attributes_raw(addr, ptr::null_mut()) }
+    }
+
+    /// Creates the named pipe identified by `addr` for use as a server.
+    ///
+    /// This is the same as [`create`] except that it supports providing the raw
+    /// pointer to a structure of [`SECURITY_ATTRIBUTES`] which will be passed
+    /// as the `lpSecurityAttributes` argument to [`CreateFile`].
+    ///
+    /// # Errors
+    ///
+    /// This errors if called outside of a [Tokio Runtime], or in a runtime that
+    /// has not [enabled I/O], or if any OS-specific I/O errors occur.
+    ///
+    /// [Tokio Runtime]: crate::runtime::Runtime
+    /// [enabled I/O]: crate::runtime::Builder::enable_io
+    ///
+    /// # Safety
+    ///
+    /// The `attrs` argument must either be null or point at a valid instance of
+    /// the [`SECURITY_ATTRIBUTES`] structure. If the argument is null, the
+    /// behavior is identical to calling the [`create`] method.
+    ///
+    /// [`create`]: ServerOptions::create
+    /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilew
+    /// [`SECURITY_ATTRIBUTES`]: crate::winapi::um::minwinbase::SECURITY_ATTRIBUTES
+    pub unsafe fn create_with_security_attributes_raw(
+        &self,
+        addr: impl AsRef<OsStr>,
+        attrs: *mut c_void,
+    ) -> io::Result<NamedPipeServer> {
+        let addr = encode_addr(addr);
+
+        let h = namedpipeapi::CreateNamedPipeW(
+            addr.as_ptr(),
+            self.open_mode,
+            self.pipe_mode,
+            self.max_instances,
+            self.out_buffer_size,
+            self.in_buffer_size,
+            self.default_timeout,
+            attrs as *mut _,
+        );
+
+        if h == handleapi::INVALID_HANDLE_VALUE {
+            return Err(io::Error::last_os_error());
+        }
+
+        NamedPipeServer::from_raw_handle(h)
+    }
+}
+
+/// A builder suitable for building and interacting with named pipes from the
+/// client side.
+///
+/// See [`ClientOptions::open`].
+#[derive(Debug, Clone)]
+pub struct ClientOptions {
+    desired_access: DWORD,
+    security_qos_flags: DWORD,
+}
+
+impl ClientOptions {
+    /// Creates a new named pipe builder with the default settings.
+    ///
+    /// ```
+    /// use tokio::net::windows::named_pipe::{ServerOptions, ClientOptions};
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\tokio-named-pipe-client-new";
+    ///
+    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
+    /// // Server must be created in order for the client creation to succeed.
+    /// let server = ServerOptions::new().create(PIPE_NAME)?;
+    /// let client = ClientOptions::new().open(PIPE_NAME)?;
+    /// # Ok(()) }
+    /// ```
+    pub fn new() -> Self {
+        Self {
+            desired_access: winnt::GENERIC_READ | winnt::GENERIC_WRITE,
+            security_qos_flags: winbase::SECURITY_IDENTIFICATION | winbase::SECURITY_SQOS_PRESENT,
+        }
+    }
+
+    /// If the client supports reading data. This is enabled by default.
+    ///
+    /// This corresponds to setting [`GENERIC_READ`] in the call to [`CreateFile`].
+    ///
+    /// [`GENERIC_READ`]: https://docs.microsoft.com/en-us/windows/win32/secauthz/generic-access-rights
+    /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilew
+    pub fn read(&mut self, allowed: bool) -> &mut Self {
+        bool_flag!(self.desired_access, allowed, winnt::GENERIC_READ);
+        self
+    }
+
+    /// If the created pipe supports writing data. This is enabled by default.
+    ///
+    /// This corresponds to setting [`GENERIC_WRITE`] in the call to [`CreateFile`].
+    ///
+    /// [`GENERIC_WRITE`]: https://docs.microsoft.com/en-us/windows/win32/secauthz/generic-access-rights
+    /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilew
+    pub fn write(&mut self, allowed: bool) -> &mut Self {
+        bool_flag!(self.desired_access, allowed, winnt::GENERIC_WRITE);
+        self
+    }
+
+    /// Sets qos flags which are combined with other flags and attributes in the
+    /// call to [`CreateFile`].
+    ///
+    /// By default `security_qos_flags` is set to [`SECURITY_IDENTIFICATION`],
+    /// calling this function would override that value completely with the
+    /// argument specified.
+    ///
+    /// When `security_qos_flags` is not set, a malicious program can gain the
+    /// elevated privileges of a privileged Rust process when it allows opening
+    /// user-specified paths, by tricking it into opening a named pipe. So
+    /// arguably `security_qos_flags` should also be set when opening arbitrary
+    /// paths. However the bits can then conflict with other flags, specifically
+    /// `FILE_FLAG_OPEN_NO_RECALL`.
+    ///
+    /// For information about possible values, see [Impersonation Levels] on the
+    /// Windows Dev Center site. The `SECURITY_SQOS_PRESENT` flag is set
+    /// automatically when using this method.
+    ///
+    /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea
+    /// [`SECURITY_IDENTIFICATION`]: crate::winapi::um::winbase::SECURITY_IDENTIFICATION
+    /// [Impersonation Levels]: https://docs.microsoft.com/en-us/windows/win32/api/winnt/ne-winnt-security_impersonation_level
+    pub fn security_qos_flags(&mut self, flags: u32) -> &mut Self {
+        // See: https://github.com/rust-lang/rust/pull/58216
+        self.security_qos_flags = flags | winbase::SECURITY_SQOS_PRESENT;
+        self
+    }
+
+    /// Opens the named pipe identified by `addr`.
+    ///
+    /// This opens the client using [`CreateFile`] with the
+    /// `dwCreationDisposition` option set to `OPEN_EXISTING`.
+    ///
+    /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea
+    ///
+    /// # Errors
+    ///
+    /// This errors if called outside of a [Tokio Runtime], or in a runtime that
+    /// has not [enabled I/O], or if any OS-specific I/O errors occur.
+    ///
+    /// There are a few errors you need to take into account when creating a
+    /// named pipe on the client side:
+    ///
+    /// * [`std::io::ErrorKind::NotFound`] - This indicates that the named pipe
+    ///   does not exist. Presumably the server is not up.
+    /// * [`ERROR_PIPE_BUSY`] - This error is raised when the named pipe exists,
+    ///   but the server is not currently waiting for a connection. Please see the
+    ///   examples for how to check for this error.
+    ///
+    /// [`ERROR_PIPE_BUSY`]: crate::winapi::shared::winerror::ERROR_PIPE_BUSY
+    /// [`winapi`]: crate::winapi
+    /// [enabled I/O]: crate::runtime::Builder::enable_io
+    /// [Tokio Runtime]: crate::runtime::Runtime
+    ///
+    /// A connect loop that waits until a pipe becomes available looks like
+    /// this:
+    ///
+    /// ```no_run
+    /// use std::time::Duration;
+    /// use tokio::net::windows::named_pipe::ClientOptions;
+    /// use tokio::time;
+    /// use winapi::shared::winerror;
+    ///
+    /// const PIPE_NAME: &str = r"\\.\pipe\mynamedpipe";
+    ///
+    /// # #[tokio::main] async fn main() -> std::io::Result<()> {
+    /// let client = loop {
+    ///     match ClientOptions::new().open(PIPE_NAME) {
+    ///         Ok(client) => break client,
+    ///         Err(e) if e.raw_os_error() == Some(winerror::ERROR_PIPE_BUSY as i32) => (),
+    ///         Err(e) => return Err(e),
+    ///     }
+    ///
+    ///     time::sleep(Duration::from_millis(50)).await;
+    /// };
+    ///
+    /// // use the connected client.
+    /// # Ok(()) }
+    /// ```
+    pub fn open(&self, addr: impl AsRef<OsStr>) -> io::Result<NamedPipeClient> {
+        // Safety: We're calling open_with_security_attributes_raw w/ a null
+        // pointer which disables it.
+        unsafe { self.open_with_security_attributes_raw(addr, ptr::null_mut()) }
+    }
+
+    /// Opens the named pipe identified by `addr`.
+    ///
+    /// This is the same as [`open`] except that it supports providing the raw
+    /// pointer to a structure of [`SECURITY_ATTRIBUTES`] which will be passed
+    /// as the `lpSecurityAttributes` argument to [`CreateFile`].
+    ///
+    /// # Safety
+    ///
+    /// The `attrs` argument must either be null or point at a valid instance of
+    /// the [`SECURITY_ATTRIBUTES`] structure. If the argument is null, the
+    /// behavior is identical to calling the [`open`] method.
+    ///
+    /// [`open`]: ClientOptions::open
+    /// [`CreateFile`]: https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilew
+    /// [`SECURITY_ATTRIBUTES`]: crate::winapi::um::minwinbase::SECURITY_ATTRIBUTES
+    pub unsafe fn open_with_security_attributes_raw(
+        &self,
+        addr: impl AsRef<OsStr>,
+        attrs: *mut c_void,
+    ) -> io::Result<NamedPipeClient> {
+        let addr = encode_addr(addr);
+
+        // NB: We could use a platform specialized `OpenOptions` here, but since
+        // we have access to winapi it ultimately doesn't hurt to use
+        // `CreateFile` explicitly since it allows the use of our already
+        // well-structured wide `addr` to pass into CreateFileW.
+        let h = fileapi::CreateFileW(
+            addr.as_ptr(),
+            self.desired_access,
+            0,
+            attrs as *mut _,
+            fileapi::OPEN_EXISTING,
+            self.get_flags(),
+            ptr::null_mut(),
+        );
+
+        if h == handleapi::INVALID_HANDLE_VALUE {
+            return Err(io::Error::last_os_error());
+        }
+
+        NamedPipeClient::from_raw_handle(h)
+    }
+
+    fn get_flags(&self) -> u32 {
+        self.security_qos_flags | winbase::FILE_FLAG_OVERLAPPED
+    }
+}
+
+/// The pipe mode of a named pipe.
+///
+/// Set through [`ServerOptions::pipe_mode`].
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+#[non_exhaustive]
+pub enum PipeMode {
+    /// Data is written to the pipe as a stream of bytes. The pipe does not
+    /// distinguish bytes written during different write operations.
+    ///
+    /// Corresponds to [`PIPE_TYPE_BYTE`][crate::winapi::um::winbase::PIPE_TYPE_BYTE].
+    Byte,
+    /// Data is written to the pipe as a stream of messages. The pipe treats the
+    /// bytes written during each write operation as a message unit. Any reading
+    /// on a named pipe returns [`ERROR_MORE_DATA`] when a message is not read
+    /// completely.
+    ///
+    /// Corresponds to [`PIPE_TYPE_MESSAGE`][crate::winapi::um::winbase::PIPE_TYPE_MESSAGE].
+    ///
+    /// [`ERROR_MORE_DATA`]: crate::winapi::shared::winerror::ERROR_MORE_DATA
+    Message,
+}
+
+/// Indicates the end of a named pipe.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+#[non_exhaustive]
+pub enum PipeEnd {
+    /// The named pipe refers to the client end of a named pipe instance.
+    ///
+    /// Corresponds to [`PIPE_CLIENT_END`][crate::winapi::um::winbase::PIPE_CLIENT_END].
+    Client,
+    /// The named pipe refers to the server end of a named pipe instance.
+    ///
+    /// Corresponds to [`PIPE_SERVER_END`][crate::winapi::um::winbase::PIPE_SERVER_END].
+    Server,
+}
+
+/// Information about a named pipe.
+///
+/// Constructed through [`NamedPipeServer::info`] or [`NamedPipeClient::info`].
+#[derive(Debug)]
+#[non_exhaustive]
+pub struct PipeInfo {
+    /// Indicates the mode of a named pipe.
+    pub mode: PipeMode,
+    /// Indicates the end of a named pipe.
+    pub end: PipeEnd,
+    /// The maximum number of instances that can be created for this pipe.
+    pub max_instances: u32,
+    /// The number of bytes to reserve for the output buffer.
+    pub out_buffer_size: u32,
+    /// The number of bytes to reserve for the input buffer.
+    pub in_buffer_size: u32,
+}
+
+/// Encodes an address so that it is a null-terminated wide string.
+fn encode_addr(addr: impl AsRef<OsStr>) -> Box<[u16]> {
+    let len = addr.as_ref().encode_wide().count();
+    let mut vec = Vec::with_capacity(len + 1);
+    vec.extend(addr.as_ref().encode_wide());
+    vec.push(0);
+    vec.into_boxed_slice()
+}
+
+/// Internal function to get the info out of a raw named pipe.
+unsafe fn named_pipe_info(handle: RawHandle) -> io::Result<PipeInfo> {
+    let mut flags = 0;
+    let mut out_buffer_size = 0;
+    let mut in_buffer_size = 0;
+    let mut max_instances = 0;
+
+    let result = namedpipeapi::GetNamedPipeInfo(
+        handle,
+        &mut flags,
+        &mut out_buffer_size,
+        &mut in_buffer_size,
+        &mut max_instances,
+    );
+
+    if result == FALSE {
+        return Err(io::Error::last_os_error());
+    }
+
+    let mut end = PipeEnd::Client;
+    let mut mode = PipeMode::Byte;
+
+    if flags & winbase::PIPE_SERVER_END != 0 {
+        end = PipeEnd::Server;
+    }
+
+    if flags & winbase::PIPE_TYPE_MESSAGE != 0 {
+        mode = PipeMode::Message;
+    }
+
+    Ok(PipeInfo {
+        end,
+        mode,
+        out_buffer_size,
+        in_buffer_size,
+        max_instances,
+    })
+}
diff --git a/third_party/rust/tokio/src/park/either.rs b/third_party/rust/tokio/src/park/either.rs
new file mode 100644
index 0000000000..ee02ec158b
--- /dev/null
+++ b/third_party/rust/tokio/src/park/either.rs
@@ -0,0 +1,74 @@
+#![cfg_attr(not(feature = "full"), allow(dead_code))]
+
+use crate::park::{Park, Unpark};
+
+use std::fmt;
+use std::time::Duration;
+
+pub(crate) enum Either<A, B> {
+    A(A),
+    B(B),
+}
+
+impl<A, B> Park for Either<A, B>
+where
+    A: Park,
+    B: Park,
+{
+    type Unpark = Either<A::Unpark, B::Unpark>;
+    type Error = Either<A::Error, B::Error>;
+
+    fn unpark(&self) -> Self::Unpark {
+        match self {
+            Either::A(a) => Either::A(a.unpark()),
+            Either::B(b) => Either::B(b.unpark()),
+        }
+    }
+
+    fn park(&mut self) -> Result<(), Self::Error> {
+        match self {
+            Either::A(a) => a.park().map_err(Either::A),
+            Either::B(b) => b.park().map_err(Either::B),
+        }
+    }
+
+    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
+        match self {
+            Either::A(a) => a.park_timeout(duration).map_err(Either::A),
+            Either::B(b) => b.park_timeout(duration).map_err(Either::B),
+        }
+    }
+
+    fn shutdown(&mut self) {
+        match self {
+            Either::A(a) => a.shutdown(),
+            Either::B(b) => b.shutdown(),
+        }
+    }
+}
+
+impl<A, B> Unpark for Either<A, B>
+where
+    A: Unpark,
+    B: Unpark,
+{
+    fn unpark(&self) {
+        match self {
+            Either::A(a) => a.unpark(),
+            Either::B(b) => b.unpark(),
+        }
+    }
+}
+
+impl<A, B> fmt::Debug for Either<A, B>
+where
+    A: fmt::Debug,
+    B: fmt::Debug,
+{
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Either::A(a) => a.fmt(fmt),
+            Either::B(b) => b.fmt(fmt),
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/park/mod.rs b/third_party/rust/tokio/src/park/mod.rs
new file mode 100644
index 0000000000..87d04ff78e
--- /dev/null
+++ b/third_party/rust/tokio/src/park/mod.rs
@@ -0,0 +1,117 @@
+//! Abstraction over blocking and unblocking the current thread.
+//!
+//! Provides an abstraction over blocking the current thread. This is similar to
+//! the park / unpark constructs provided by `std` but made generic. This allows
+//! embedding custom functionality to perform when the thread is blocked.
+//!
+//! A blocked `Park` instance is unblocked by calling `unpark` on its
+//! `Unpark` handle.
+//!
+//! The `ParkThread` struct implements `Park` using `thread::park` to put the
+//! thread to sleep. The Tokio reactor also implements park, but uses
+//! `mio::Poll` to block the thread instead.
+//!
+//! The `Park` trait is composable. A timer implementation might decorate a
+//! `Park` implementation by checking if any timeouts have elapsed after the
+//! inner `Park` implementation unblocks.
+//!
+//! # Model
+//!
+//! Conceptually, each `Park` instance has an associated token, which is
+//! initially not present:
+//!
+//! * The `park` method blocks the current thread unless or until the token is
+//!   available, at which point it atomically consumes the token.
+//! * The `unpark` method atomically makes the token available if it wasn't
+//!   already.
+//!
+//! Some things to note:
+//!
+//! * If `unpark` is called before `park`, the next call to `park` will
+//!   **not** block the thread.
+//! * **Spurious** wakeups are permitted, i.e., the `park` method may unblock
+//!   even if `unpark` was not called.
+//! * `park_timeout` does the same as `park` but allows specifying a maximum
+//!   time to block the thread for.
+
+cfg_rt! {
+    pub(crate) mod either;
+}
+
+#[cfg(any(feature = "rt", feature = "sync"))]
+pub(crate) mod thread;
+
+use std::fmt::Debug;
+use std::sync::Arc;
+use std::time::Duration;
+
+/// Blocks the current thread.
+pub(crate) trait Park {
+    /// Unpark handle type for the `Park` implementation.
+    type Unpark: Unpark;
+
+    /// Error returned by `park`.
+    type Error: Debug;
+
+    /// Gets a new `Unpark` handle associated with this `Park` instance.
+    fn unpark(&self) -> Self::Unpark;
+
+    /// Blocks the current thread unless or until the token is available.
+    ///
+    /// A call to `park` does not guarantee that the thread will remain blocked
+    /// forever, and callers should be prepared for this possibility. This
+    /// function may wakeup spuriously for any reason.
+    ///
+    /// # Panics
+    ///
+    /// This function **should** not panic, but ultimately, panics are left as
+    /// an implementation detail. Refer to the documentation for the specific
+    /// `Park` implementation.
+    fn park(&mut self) -> Result<(), Self::Error>;
+
+    /// Parks the current thread for at most `duration`.
+    ///
+    /// This function is the same as `park` but allows specifying a maximum time
+    /// to block the thread for.
+    ///
+    /// Same as `park`, there is no guarantee that the thread will remain
+    /// blocked for any amount of time. Spurious wakeups are permitted for any
+    /// reason.
+    ///
+    /// # Panics
+    ///
+    /// This function **should** not panic, but ultimately, panics are left as
+    /// an implementation detail. Refer to the documentation for the specific
+    /// `Park` implementation.
+    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error>;
+
+    /// Releases all resources holded by the parker for proper leak-free shutdown.
+    fn shutdown(&mut self);
+}
+
+/// Unblock a thread blocked by the associated `Park` instance.
+pub(crate) trait Unpark: Sync + Send + 'static {
+    /// Unblocks a thread that is blocked by the associated `Park` handle.
+    ///
+    /// Calling `unpark` atomically makes available the unpark token, if it is
+    /// not already available.
+    ///
+    /// # Panics
+    ///
+    /// This function **should** not panic, but ultimately, panics are left as
+    /// an implementation detail. Refer to the documentation for the specific
+    /// `Unpark` implementation.
+    fn unpark(&self);
+}
+
+impl Unpark for Box<dyn Unpark> {
+    fn unpark(&self) {
+        (**self).unpark()
+    }
+}
+
+impl Unpark for Arc<dyn Unpark> {
+    fn unpark(&self) {
+        (**self).unpark()
+    }
+}
diff --git a/third_party/rust/tokio/src/park/thread.rs b/third_party/rust/tokio/src/park/thread.rs
new file mode 100644
index 0000000000..27ce202439
--- /dev/null
+++ b/third_party/rust/tokio/src/park/thread.rs
@@ -0,0 +1,346 @@
+#![cfg_attr(not(feature = "full"), allow(dead_code))]
+
+use crate::loom::sync::atomic::AtomicUsize;
+use crate::loom::sync::{Arc, Condvar, Mutex};
+use crate::park::{Park, Unpark};
+
+use std::sync::atomic::Ordering::SeqCst;
+use std::time::Duration;
+
+#[derive(Debug)]
+pub(crate) struct ParkThread {
+    inner: Arc<Inner>,
+}
+
+pub(crate) type ParkError = ();
+
+/// Unblocks a thread that was blocked by `ParkThread`.
+#[derive(Clone, Debug)]
+pub(crate) struct UnparkThread {
+    inner: Arc<Inner>,
+}
+
+#[derive(Debug)]
+struct Inner {
+    state: AtomicUsize,
+    mutex: Mutex<()>,
+    condvar: Condvar,
+}
+
+const EMPTY: usize = 0;
+const PARKED: usize = 1;
+const NOTIFIED: usize = 2;
+
+thread_local! {
+    static CURRENT_PARKER: ParkThread = ParkThread::new();
+}
+
+// ==== impl ParkThread ====
+
+impl ParkThread {
+    pub(crate) fn new() -> Self {
+        Self {
+            inner: Arc::new(Inner {
+                state: AtomicUsize::new(EMPTY),
+                mutex: Mutex::new(()),
+                condvar: Condvar::new(),
+            }),
+        }
+    }
+}
+
+impl Park for ParkThread {
+    type Unpark = UnparkThread;
+    type Error = ParkError;
+
+    fn unpark(&self) -> Self::Unpark {
+        let inner = self.inner.clone();
+        UnparkThread { inner }
+    }
+
+    fn park(&mut self) -> Result<(), Self::Error> {
+        self.inner.park();
+        Ok(())
+    }
+
+    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
+        self.inner.park_timeout(duration);
+        Ok(())
+    }
+
+    fn shutdown(&mut self) {
+        self.inner.shutdown();
+    }
+}
+
+// ==== impl Inner ====
+
+impl Inner {
+    /// Parks the current thread for at most `dur`.
+    fn park(&self) {
+        // If we were previously notified then we consume this notification and
+        // return quickly.
+        if self
+            .state
+            .compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst)
+            .is_ok()
+        {
+            return;
+        }
+
+        // Otherwise we need to coordinate going to sleep
+        let mut m = self.mutex.lock();
+
+        match self.state.compare_exchange(EMPTY, PARKED, SeqCst, SeqCst) {
+            Ok(_) => {}
+            Err(NOTIFIED) => {
+                // We must read here, even though we know it will be `NOTIFIED`.
+                // This is because `unpark` may have been called again since we read
+                // `NOTIFIED` in the `compare_exchange` above. We must perform an
+                // acquire operation that synchronizes with that `unpark` to observe
+                // any writes it made before the call to unpark. To do that we must
+                // read from the write it made to `state`.
+                let old = self.state.swap(EMPTY, SeqCst);
+                debug_assert_eq!(old, NOTIFIED, "park state changed unexpectedly");
+
+                return;
+            }
+            Err(actual) => panic!("inconsistent park state; actual = {}", actual),
+        }
+
+        loop {
+            m = self.condvar.wait(m).unwrap();
+
+            if self
+                .state
+                .compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst)
+                .is_ok()
+            {
+                // got a notification
+                return;
+            }
+
+            // spurious wakeup, go back to sleep
+        }
+    }
+
+    fn park_timeout(&self, dur: Duration) {
+        // Like `park` above we have a fast path for an already-notified thread,
+        // and afterwards we start coordinating for a sleep. Return quickly.
+        if self
+            .state
+            .compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst)
+            .is_ok()
+        {
+            return;
+        }
+
+        if dur == Duration::from_millis(0) {
+            return;
+        }
+
+        let m = self.mutex.lock();
+
+        match self.state.compare_exchange(EMPTY, PARKED, SeqCst, SeqCst) {
+            Ok(_) => {}
+            Err(NOTIFIED) => {
+                // We must read again here, see `park`.
+                let old = self.state.swap(EMPTY, SeqCst);
+                debug_assert_eq!(old, NOTIFIED, "park state changed unexpectedly");
+
+                return;
+            }
+            Err(actual) => panic!("inconsistent park_timeout state; actual = {}", actual),
+        }
+
+        // Wait with a timeout, and if we spuriously wake up or otherwise wake up
+        // from a notification, we just want to unconditionally set the state back to
+        // empty, either consuming a notification or un-flagging ourselves as
+        // parked.
+        let (_m, _result) = self.condvar.wait_timeout(m, dur).unwrap();
+
+        match self.state.swap(EMPTY, SeqCst) {
+            NOTIFIED => {} // got a notification, hurray!
+            PARKED => {}   // no notification, alas
+            n => panic!("inconsistent park_timeout state: {}", n),
+        }
+    }
+
+    fn unpark(&self) {
+        // To ensure the unparked thread will observe any writes we made before
+        // this call, we must perform a release operation that `park` can
+        // synchronize with. To do that we must write `NOTIFIED` even if `state`
+        // is already `NOTIFIED`. That is why this must be a swap rather than a
+        // compare-and-swap that returns if it reads `NOTIFIED` on failure.
+        match self.state.swap(NOTIFIED, SeqCst) {
+            EMPTY => return,    // no one was waiting
+            NOTIFIED => return, // already unparked
+            PARKED => {}        // gotta go wake someone up
+            _ => panic!("inconsistent state in unpark"),
+        }
+
+        // There is a period between when the parked thread sets `state` to
+        // `PARKED` (or last checked `state` in the case of a spurious wake
+        // up) and when it actually waits on `cvar`. If we were to notify
+        // during this period it would be ignored and then when the parked
+        // thread went to sleep it would never wake up. Fortunately, it has
+        // `lock` locked at this stage so we can acquire `lock` to wait until
+        // it is ready to receive the notification.
+        //
+        // Releasing `lock` before the call to `notify_one` means that when the
+        // parked thread wakes it doesn't get woken only to have to wait for us
+        // to release `lock`.
+        drop(self.mutex.lock());
+
+        self.condvar.notify_one()
+    }
+
+    fn shutdown(&self) {
+        self.condvar.notify_all();
+    }
+}
+
+impl Default for ParkThread {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+// ===== impl UnparkThread =====
+
+impl Unpark for UnparkThread {
+    fn unpark(&self) {
+        self.inner.unpark();
+    }
+}
+
+use std::future::Future;
+use std::marker::PhantomData;
+use std::mem;
+use std::rc::Rc;
+use std::task::{RawWaker, RawWakerVTable, Waker};
+
+/// Blocks the current thread using a condition variable.
+#[derive(Debug)]
+pub(crate) struct CachedParkThread {
+    _anchor: PhantomData<Rc<()>>,
+}
+
+impl CachedParkThread {
+    /// Creates a new `ParkThread` handle for the current thread.
+    ///
+    /// This type cannot be moved to other threads, so it should be created on
+    /// the thread that the caller intends to park.
+    pub(crate) fn new() -> CachedParkThread {
+        CachedParkThread {
+            _anchor: PhantomData,
+        }
+    }
+
+    pub(crate) fn get_unpark(&self) -> Result<UnparkThread, ParkError> {
+        self.with_current(|park_thread| park_thread.unpark())
+    }
+
+    /// Gets a reference to the `ParkThread` handle for this thread.
+    fn with_current<F, R>(&self, f: F) -> Result<R, ParkError>
+    where
+        F: FnOnce(&ParkThread) -> R,
+    {
+        CURRENT_PARKER.try_with(|inner| f(inner)).map_err(|_| ())
+    }
+
+    pub(crate) fn block_on<F: Future>(&mut self, f: F) -> Result<F::Output, ParkError> {
+        use std::task::Context;
+        use std::task::Poll::Ready;
+
+        // `get_unpark()` should not return a Result
+        let waker = self.get_unpark()?.into_waker();
+        let mut cx = Context::from_waker(&waker);
+
+        pin!(f);
+
+        loop {
+            if let Ready(v) = crate::coop::budget(|| f.as_mut().poll(&mut cx)) {
+                return Ok(v);
+            }
+
+            self.park()?;
+        }
+    }
+}
+
+impl Park for CachedParkThread {
+    type Unpark = UnparkThread;
+    type Error = ParkError;
+
+    fn unpark(&self) -> Self::Unpark {
+        self.get_unpark().unwrap()
+    }
+
+    fn park(&mut self) -> Result<(), Self::Error> {
+        self.with_current(|park_thread| park_thread.inner.park())?;
+        Ok(())
+    }
+
+    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
+        self.with_current(|park_thread| park_thread.inner.park_timeout(duration))?;
+        Ok(())
+    }
+
+    fn shutdown(&mut self) {
+        let _ = self.with_current(|park_thread| park_thread.inner.shutdown());
+    }
+}
+
+impl UnparkThread {
+    pub(crate) fn into_waker(self) -> Waker {
+        unsafe {
+            let raw = unparker_to_raw_waker(self.inner);
+            Waker::from_raw(raw)
+        }
+    }
+}
+
+impl Inner {
+    #[allow(clippy::wrong_self_convention)]
+    fn into_raw(this: Arc<Inner>) -> *const () {
+        Arc::into_raw(this) as *const ()
+    }
+
+    unsafe fn from_raw(ptr: *const ()) -> Arc<Inner> {
+        Arc::from_raw(ptr as *const Inner)
+    }
+}
+
+unsafe fn unparker_to_raw_waker(unparker: Arc<Inner>) -> RawWaker {
+    RawWaker::new(
+        Inner::into_raw(unparker),
+        &RawWakerVTable::new(clone, wake, wake_by_ref, drop_waker),
+    )
+}
+
+unsafe fn clone(raw: *const ()) -> RawWaker {
+    let unparker = Inner::from_raw(raw);
+
+    // Increment the ref count
+    mem::forget(unparker.clone());
+
+    unparker_to_raw_waker(unparker)
+}
+
+unsafe fn drop_waker(raw: *const ()) {
+    let _ = Inner::from_raw(raw);
+}
+
+unsafe fn wake(raw: *const ()) {
+    let unparker = Inner::from_raw(raw);
+    unparker.unpark();
+}
+
+unsafe fn wake_by_ref(raw: *const ()) {
+    let unparker = Inner::from_raw(raw);
+    unparker.unpark();
+
+    // We don't actually own a reference to the unparker
+    mem::forget(unparker);
+}
diff --git a/third_party/rust/tokio/src/process/kill.rs b/third_party/rust/tokio/src/process/kill.rs
new file mode 100644
index 0000000000..a1f1652281
--- /dev/null
+++ b/third_party/rust/tokio/src/process/kill.rs
@@ -0,0 +1,13 @@
+use std::io;
+
+/// An interface for killing a running process.
+pub(crate) trait Kill {
+    /// Forcefully kills the process.
+    fn kill(&mut self) -> io::Result<()>;
+}
+
+impl<T: Kill> Kill for &mut T {
+    fn kill(&mut self) -> io::Result<()> {
+        (**self).kill()
+    }
+}
diff --git a/third_party/rust/tokio/src/process/mod.rs b/third_party/rust/tokio/src/process/mod.rs
new file mode 100644
index 0000000000..4e1a21dd44
--- /dev/null
+++ b/third_party/rust/tokio/src/process/mod.rs
@@ -0,0 +1,1534 @@
+//! An implementation of asynchronous process management for Tokio.
+//!
+//! This module provides a [`Command`] struct that imitates the interface of the
+//! [`std::process::Command`] type in the standard library, but provides asynchronous versions of
+//! functions that create processes. These functions (`spawn`, `status`, `output` and their
+//! variants) return "future aware" types that interoperate with Tokio. The asynchronous process
+//! support is provided through signal handling on Unix and system APIs on Windows.
+//!
+//! [`std::process::Command`]: std::process::Command
+//!
+//! # Examples
+//!
+//! Here's an example program which will spawn `echo hello world` and then wait
+//! for it complete.
+//!
+//! ```no_run
+//! use tokio::process::Command;
+//!
+//! #[tokio::main]
+//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
+//!     // The usage is similar as with the standard library's `Command` type
+//!     let mut child = Command::new("echo")
+//!         .arg("hello")
+//!         .arg("world")
+//!         .spawn()
+//!         .expect("failed to spawn");
+//!
+//!     // Await until the command completes
+//!     let status = child.wait().await?;
+//!     println!("the command exited with: {}", status);
+//!     Ok(())
+//! }
+//! ```
+//!
+//! Next, let's take a look at an example where we not only spawn `echo hello
+//! world` but we also capture its output.
+//!
+//! ```no_run
+//! use tokio::process::Command;
+//!
+//! #[tokio::main]
+//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
+//!     // Like above, but use `output` which returns a future instead of
+//!     // immediately returning the `Child`.
+//!     let output = Command::new("echo").arg("hello").arg("world")
+//!                         .output();
+//!
+//!     let output = output.await?;
+//!
+//!     assert!(output.status.success());
+//!     assert_eq!(output.stdout, b"hello world\n");
+//!     Ok(())
+//! }
+//! ```
+//!
+//! We can also read input line by line.
+//!
+//! ```no_run
+//! use tokio::io::{BufReader, AsyncBufReadExt};
+//! use tokio::process::Command;
+//!
+//! use std::process::Stdio;
+//!
+//! #[tokio::main]
+//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
+//!     let mut cmd = Command::new("cat");
+//!
+//!     // Specify that we want the command's standard output piped back to us.
+//!     // By default, standard input/output/error will be inherited from the
+//!     // current process (for example, this means that standard input will
+//!     // come from the keyboard and standard output/error will go directly to
+//!     // the terminal if this process is invoked from the command line).
+//!     cmd.stdout(Stdio::piped());
+//!
+//!     let mut child = cmd.spawn()
+//!         .expect("failed to spawn command");
+//!
+//!     let stdout = child.stdout.take()
+//!         .expect("child did not have a handle to stdout");
+//!
+//!     let mut reader = BufReader::new(stdout).lines();
+//!
+//!     // Ensure the child process is spawned in the runtime so it can
+//!     // make progress on its own while we await for any output.
+//!     tokio::spawn(async move {
+//!         let status = child.wait().await
+//!             .expect("child process encountered an error");
+//!
+//!         println!("child status was: {}", status);
+//!     });
+//!
+//!     while let Some(line) = reader.next_line().await? {
+//!         println!("Line: {}", line);
+//!     }
+//!
+//!     Ok(())
+//! }
+//! ```
+//!
+//! Here is another example using `sort` writing into the child process
+//! standard input, capturing the output of the sorted text.
+//!
+//! ```no_run
+//! use tokio::io::AsyncWriteExt;
+//! use tokio::process::Command;
+//!
+//! use std::process::Stdio;
+//!
+//! #[tokio::main]
+//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
+//!     let mut cmd = Command::new("sort");
+//!
+//!     // Specifying that we want pipe both the output and the input.
+//!     // Similarily to capturing the output, by configuring the pipe
+//!     // to stdin it can now be used as an asynchronous writer.
+//!     cmd.stdout(Stdio::piped());
+//!     cmd.stdin(Stdio::piped());
+//!
+//!     let mut child = cmd.spawn().expect("failed to spawn command");
+//!
+//!     // These are the animals we want to sort
+//!     let animals: &[&str] = &["dog", "bird", "frog", "cat", "fish"];
+//!
+//!     let mut stdin = child
+//!         .stdin
+//!         .take()
+//!         .expect("child did not have a handle to stdin");
+//!
+//!     // Write our animals to the child process
+//!     // Note that the behavior of `sort` is to buffer _all input_ before writing any output.
+//!     // In the general sense, it is recommended to write to the child in a separate task as
+//!     // awaiting its exit (or output) to avoid deadlocks (for example, the child tries to write
+//!     // some output but gets stuck waiting on the parent to read from it, meanwhile the parent
+//!     // is stuck waiting to write its input completely before reading the output).
+//!     stdin
+//!         .write(animals.join("\n").as_bytes())
+//!         .await
+//!         .expect("could not write to stdin");
+//!
+//!     // We drop the handle here which signals EOF to the child process.
+//!     // This tells the child process that it there is no more data on the pipe.
+//!     drop(stdin);
+//!
+//!     let op = child.wait_with_output().await?;
+//!
+//!     // Results should come back in sorted order
+//!     assert_eq!(op.stdout, "bird\ncat\ndog\nfish\nfrog\n".as_bytes());
+//!
+//!     Ok(())
+//! }
+//! ```
+//!
+//! With some coordination, we can also pipe the output of one command into
+//! another.
+//!
+//! ```no_run
+//! use tokio::join;
+//! use tokio::process::Command;
+//! use std::convert::TryInto;
+//! use std::process::Stdio;
+//!
+//! #[tokio::main]
+//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
+//!     let mut echo = Command::new("echo")
+//!         .arg("hello world!")
+//!         .stdout(Stdio::piped())
+//!         .spawn()
+//!         .expect("failed to spawn echo");
+//!
+//!     let tr_stdin: Stdio = echo
+//!         .stdout
+//!         .take()
+//!         .unwrap()
+//!         .try_into()
+//!         .expect("failed to convert to Stdio");
+//!
+//!     let tr = Command::new("tr")
+//!         .arg("a-z")
+//!         .arg("A-Z")
+//!         .stdin(tr_stdin)
+//!         .stdout(Stdio::piped())
+//!         .spawn()
+//!         .expect("failed to spawn tr");
+//!
+//!     let (echo_result, tr_output) = join!(echo.wait(), tr.wait_with_output());
+//!
+//!     assert!(echo_result.unwrap().success());
+//!
+//!     let tr_output = tr_output.expect("failed to await tr");
+//!     assert!(tr_output.status.success());
+//!
+//!     assert_eq!(tr_output.stdout, b"HELLO WORLD!\n");
+//!
+//!     Ok(())
+//! }
+//! ```
+//!
+//! # Caveats
+//!
+//! ## Dropping/Cancellation
+//!
+//! Similar to the behavior to the standard library, and unlike the futures
+//! paradigm of dropping-implies-cancellation, a spawned process will, by
+//! default, continue to execute even after the `Child` handle has been dropped.
+//!
+//! The [`Command::kill_on_drop`] method can be used to modify this behavior
+//! and kill the child process if the `Child` wrapper is dropped before it
+//! has exited.
+//!
+//! ## Unix Processes
+//!
+//! On Unix platforms processes must be "reaped" by their parent process after
+//! they have exited in order to release all OS resources. A child process which
+//! has exited, but has not yet been reaped by its parent is considered a "zombie"
+//! process. Such processes continue to count against limits imposed by the system,
+//! and having too many zombie processes present can prevent additional processes
+//! from being spawned.
+//!
+//! The tokio runtime will, on a best-effort basis, attempt to reap and clean up
+//! any process which it has spawned. No additional guarantees are made with regards
+//! how quickly or how often this procedure will take place.
+//!
+//! It is recommended to avoid dropping a [`Child`] process handle before it has been
+//! fully `await`ed if stricter cleanup guarantees are required.
+//!
+//! [`Command`]: crate::process::Command
+//! [`Command::kill_on_drop`]: crate::process::Command::kill_on_drop
+//! [`Child`]: crate::process::Child
+
+#[path = "unix/mod.rs"]
+#[cfg(unix)]
+mod imp;
+
+#[cfg(unix)]
+pub(crate) mod unix {
+    pub(crate) use super::imp::*;
+}
+
+#[path = "windows.rs"]
+#[cfg(windows)]
+mod imp;
+
+mod kill;
+
+use crate::io::{AsyncRead, AsyncWrite, ReadBuf};
+use crate::process::kill::Kill;
+
+use std::convert::TryInto;
+use std::ffi::OsStr;
+use std::future::Future;
+use std::io;
+#[cfg(unix)]
+use std::os::unix::process::CommandExt;
+#[cfg(windows)]
+use std::os::windows::io::{AsRawHandle, RawHandle};
+#[cfg(windows)]
+use std::os::windows::process::CommandExt;
+use std::path::Path;
+use std::pin::Pin;
+use std::process::{Command as StdCommand, ExitStatus, Output, Stdio};
+use std::task::Context;
+use std::task::Poll;
+
+/// This structure mimics the API of [`std::process::Command`] found in the standard library, but
+/// replaces functions that create a process with an asynchronous variant. The main provided
+/// asynchronous functions are [spawn](Command::spawn), [status](Command::status), and
+/// [output](Command::output).
+///
+/// `Command` uses asynchronous versions of some `std` types (for example [`Child`]).
+///
+/// [`std::process::Command`]: std::process::Command
+/// [`Child`]: struct@Child
+#[derive(Debug)]
+pub struct Command {
+    std: StdCommand,
+    kill_on_drop: bool,
+}
+
+pub(crate) struct SpawnedChild {
+    child: imp::Child,
+    stdin: Option<imp::ChildStdio>,
+    stdout: Option<imp::ChildStdio>,
+    stderr: Option<imp::ChildStdio>,
+}
+
+impl Command {
+    /// Constructs a new `Command` for launching the program at
+    /// path `program`, with the following default configuration:
+    ///
+    /// * No arguments to the program
+    /// * Inherit the current process's environment
+    /// * Inherit the current process's working directory
+    /// * Inherit stdin/stdout/stderr for `spawn` or `status`, but create pipes for `output`
+    ///
+    /// Builder methods are provided to change these defaults and
+    /// otherwise configure the process.
+    ///
+    /// If `program` is not an absolute path, the `PATH` will be searched in
+    /// an OS-defined way.
+    ///
+    /// The search path to be used may be controlled by setting the
+    /// `PATH` environment variable on the Command,
+    /// but this has some implementation limitations on Windows
+    /// (see issue [rust-lang/rust#37519]).
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```no_run
+    /// use tokio::process::Command;
+    /// let command = Command::new("sh");
+    /// ```
+    ///
+    /// [rust-lang/rust#37519]: https://github.com/rust-lang/rust/issues/37519
+    pub fn new<S: AsRef<OsStr>>(program: S) -> Command {
+        Self::from(StdCommand::new(program))
+    }
+
+    /// Cheaply convert to a `&std::process::Command` for places where the type from the standard
+    /// library is expected.
+    pub fn as_std(&self) -> &StdCommand {
+        &self.std
+    }
+
+    /// Adds an argument to pass to the program.
+    ///
+    /// Only one argument can be passed per use. So instead of:
+    ///
+    /// ```no_run
+    /// tokio::process::Command::new("sh")
+    ///   .arg("-C /path/to/repo");
+    /// ```
+    ///
+    /// usage would be:
+    ///
+    /// ```no_run
+    /// tokio::process::Command::new("sh")
+    ///   .arg("-C")
+    ///   .arg("/path/to/repo");
+    /// ```
+    ///
+    /// To pass multiple arguments see [`args`].
+    ///
+    /// [`args`]: method@Self::args
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```no_run
+    /// use tokio::process::Command;
+    ///
+    /// let command = Command::new("ls")
+    ///         .arg("-l")
+    ///         .arg("-a");
+    /// ```
+    pub fn arg<S: AsRef<OsStr>>(&mut self, arg: S) -> &mut Command {
+        self.std.arg(arg);
+        self
+    }
+
+    /// Adds multiple arguments to pass to the program.
+    ///
+    /// To pass a single argument see [`arg`].
+    ///
+    /// [`arg`]: method@Self::arg
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```no_run
+    /// use tokio::process::Command;
+    ///
+    /// let command = Command::new("ls")
+    ///         .args(&["-l", "-a"]);
+    /// ```
+    pub fn args<I, S>(&mut self, args: I) -> &mut Command
+    where
+        I: IntoIterator<Item = S>,
+        S: AsRef<OsStr>,
+    {
+        self.std.args(args);
+        self
+    }
+
+    /// Inserts or updates an environment variable mapping.
+    ///
+    /// Note that environment variable names are case-insensitive (but case-preserving) on Windows,
+    /// and case-sensitive on all other platforms.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```no_run
+    /// use tokio::process::Command;
+    ///
+    /// let command = Command::new("ls")
+    ///         .env("PATH", "/bin");
+    /// ```
+    pub fn env<K, V>(&mut self, key: K, val: V) -> &mut Command
+    where
+        K: AsRef<OsStr>,
+        V: AsRef<OsStr>,
+    {
+        self.std.env(key, val);
+        self
+    }
+
+    /// Adds or updates multiple environment variable mappings.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```no_run
+    /// use tokio::process::Command;
+    /// use std::process::{Stdio};
+    /// use std::env;
+    /// use std::collections::HashMap;
+    ///
+    /// let filtered_env : HashMap<String, String> =
+    ///     env::vars().filter(|&(ref k, _)|
+    ///         k == "TERM" || k == "TZ" || k == "LANG" || k == "PATH"
+    ///     ).collect();
+    ///
+    /// let command = Command::new("printenv")
+    ///         .stdin(Stdio::null())
+    ///         .stdout(Stdio::inherit())
+    ///         .env_clear()
+    ///         .envs(&filtered_env);
+    /// ```
+    pub fn envs<I, K, V>(&mut self, vars: I) -> &mut Command
+    where
+        I: IntoIterator<Item = (K, V)>,
+        K: AsRef<OsStr>,
+        V: AsRef<OsStr>,
+    {
+        self.std.envs(vars);
+        self
+    }
+
+    /// Removes an environment variable mapping.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```no_run
+    /// use tokio::process::Command;
+    ///
+    /// let command = Command::new("ls")
+    ///         .env_remove("PATH");
+    /// ```
+    pub fn env_remove<K: AsRef<OsStr>>(&mut self, key: K) -> &mut Command {
+        self.std.env_remove(key);
+        self
+    }
+
+    /// Clears the entire environment map for the child process.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```no_run
+    /// use tokio::process::Command;
+    ///
+    /// let command = Command::new("ls")
+    ///         .env_clear();
+    /// ```
+    pub fn env_clear(&mut self) -> &mut Command {
+        self.std.env_clear();
+        self
+    }
+
+    /// Sets the working directory for the child process.
+    ///
+    /// # Platform-specific behavior
+    ///
+    /// If the program path is relative (e.g., `"./script.sh"`), it's ambiguous
+    /// whether it should be interpreted relative to the parent's working
+    /// directory or relative to `current_dir`. The behavior in this case is
+    /// platform specific and unstable, and it's recommended to use
+    /// [`canonicalize`] to get an absolute program path instead.
+    ///
+    /// [`canonicalize`]: crate::fs::canonicalize()
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```no_run
+    /// use tokio::process::Command;
+    ///
+    /// let command = Command::new("ls")
+    ///         .current_dir("/bin");
+    /// ```
+    pub fn current_dir<P: AsRef<Path>>(&mut self, dir: P) -> &mut Command {
+        self.std.current_dir(dir);
+        self
+    }
+
+    /// Sets configuration for the child process's standard input (stdin) handle.
+    ///
+    /// Defaults to [`inherit`] when used with `spawn` or `status`, and
+    /// defaults to [`piped`] when used with `output`.
+    ///
+    /// [`inherit`]: std::process::Stdio::inherit
+    /// [`piped`]: std::process::Stdio::piped
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```no_run
+    /// use std::process::{Stdio};
+    /// use tokio::process::Command;
+    ///
+    /// let command = Command::new("ls")
+    ///         .stdin(Stdio::null());
+    /// ```
+    pub fn stdin<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Command {
+        self.std.stdin(cfg);
+        self
+    }
+
+    /// Sets configuration for the child process's standard output (stdout) handle.
+    ///
+    /// Defaults to [`inherit`] when used with `spawn` or `status`, and
+    /// defaults to [`piped`] when used with `output`.
+    ///
+    /// [`inherit`]: std::process::Stdio::inherit
+    /// [`piped`]: std::process::Stdio::piped
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```no_run
+    /// use tokio::process::Command;
+    /// use std::process::Stdio;
+    ///
+    /// let command = Command::new("ls")
+    ///         .stdout(Stdio::null());
+    /// ```
+    pub fn stdout<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Command {
+        self.std.stdout(cfg);
+        self
+    }
+
+    /// Sets configuration for the child process's standard error (stderr) handle.
+    ///
+    /// Defaults to [`inherit`] when used with `spawn` or `status`, and
+    /// defaults to [`piped`] when used with `output`.
+    ///
+    /// [`inherit`]: std::process::Stdio::inherit
+    /// [`piped`]: std::process::Stdio::piped
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```no_run
+    /// use tokio::process::Command;
+    /// use std::process::{Stdio};
+    ///
+    /// let command = Command::new("ls")
+    ///         .stderr(Stdio::null());
+    /// ```
+    pub fn stderr<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Command {
+        self.std.stderr(cfg);
+        self
+    }
+
+    /// Controls whether a `kill` operation should be invoked on a spawned child
+    /// process when its corresponding `Child` handle is dropped.
+    ///
+    /// By default, this value is assumed to be `false`, meaning the next spawned
+    /// process will not be killed on drop, similar to the behavior of the standard
+    /// library.
+    ///
+    /// # Caveats
+    ///
+    /// On Unix platforms processes must be "reaped" by their parent process after
+    /// they have exited in order to release all OS resources. A child process which
+    /// has exited, but has not yet been reaped by its parent is considered a "zombie"
+    /// process. Such processes continue to count against limits imposed by the system,
+    /// and having too many zombie processes present can prevent additional processes
+    /// from being spawned.
+    ///
+    /// Although issuing a `kill` signal to the child process is a synchronous
+    /// operation, the resulting zombie process cannot be `.await`ed inside of the
+    /// destructor to avoid blocking other tasks. The tokio runtime will, on a
+    /// best-effort basis, attempt to reap and clean up such processes in the
+    /// background, but makes no additional guarantees are made with regards
+    /// how quickly or how often this procedure will take place.
+    ///
+    /// If stronger guarantees are required, it is recommended to avoid dropping
+    /// a [`Child`] handle where possible, and instead utilize `child.wait().await`
+    /// or `child.kill().await` where possible.
+    pub fn kill_on_drop(&mut self, kill_on_drop: bool) -> &mut Command {
+        self.kill_on_drop = kill_on_drop;
+        self
+    }
+
+    /// Sets the [process creation flags][1] to be passed to `CreateProcess`.
+    ///
+    /// These will always be ORed with `CREATE_UNICODE_ENVIRONMENT`.
+    ///
+    /// [1]: https://msdn.microsoft.com/en-us/library/windows/desktop/ms684863(v=vs.85).aspx
+    #[cfg(windows)]
+    #[cfg_attr(docsrs, doc(cfg(windows)))]
+    pub fn creation_flags(&mut self, flags: u32) -> &mut Command {
+        self.std.creation_flags(flags);
+        self
+    }
+
+    /// Sets the child process's user ID. This translates to a
+    /// `setuid` call in the child process. Failure in the `setuid`
+    /// call will cause the spawn to fail.
+    #[cfg(unix)]
+    #[cfg_attr(docsrs, doc(cfg(unix)))]
+    pub fn uid(&mut self, id: u32) -> &mut Command {
+        self.std.uid(id);
+        self
+    }
+
+    /// Similar to `uid` but sets the group ID of the child process. This has
+    /// the same semantics as the `uid` field.
+    #[cfg(unix)]
+    #[cfg_attr(docsrs, doc(cfg(unix)))]
+    pub fn gid(&mut self, id: u32) -> &mut Command {
+        self.std.gid(id);
+        self
+    }
+
+    /// Sets executable argument.
+    ///
+    /// Set the first process argument, `argv[0]`, to something other than the
+    /// default executable path.
+    #[cfg(unix)]
+    #[cfg_attr(docsrs, doc(cfg(unix)))]
+    pub fn arg0<S>(&mut self, arg: S) -> &mut Command
+    where
+        S: AsRef<OsStr>,
+    {
+        self.std.arg0(arg);
+        self
+    }
+
+    /// Schedules a closure to be run just before the `exec` function is
+    /// invoked.
+    ///
+    /// The closure is allowed to return an I/O error whose OS error code will
+    /// be communicated back to the parent and returned as an error from when
+    /// the spawn was requested.
+    ///
+    /// Multiple closures can be registered and they will be called in order of
+    /// their registration. If a closure returns `Err` then no further closures
+    /// will be called and the spawn operation will immediately return with a
+    /// failure.
+    ///
+    /// # Safety
+    ///
+    /// This closure will be run in the context of the child process after a
+    /// `fork`. This primarily means that any modifications made to memory on
+    /// behalf of this closure will **not** be visible to the parent process.
+    /// This is often a very constrained environment where normal operations
+    /// like `malloc` or acquiring a mutex are not guaranteed to work (due to
+    /// other threads perhaps still running when the `fork` was run).
+    ///
+    /// This also means that all resources such as file descriptors and
+    /// memory-mapped regions got duplicated. It is your responsibility to make
+    /// sure that the closure does not violate library invariants by making
+    /// invalid use of these duplicates.
+    ///
+    /// When this closure is run, aspects such as the stdio file descriptors and
+    /// working directory have successfully been changed, so output to these
+    /// locations may not appear where intended.
+    #[cfg(unix)]
+    #[cfg_attr(docsrs, doc(cfg(unix)))]
+    pub unsafe fn pre_exec<F>(&mut self, f: F) -> &mut Command
+    where
+        F: FnMut() -> io::Result<()> + Send + Sync + 'static,
+    {
+        self.std.pre_exec(f);
+        self
+    }
+
+    /// Executes the command as a child process, returning a handle to it.
+    ///
+    /// By default, stdin, stdout and stderr are inherited from the parent.
+    ///
+    /// This method will spawn the child process synchronously and return a
+    /// handle to a future-aware child process. The `Child` returned implements
+    /// `Future` itself to acquire the `ExitStatus` of the child, and otherwise
+    /// the `Child` has methods to acquire handles to the stdin, stdout, and
+    /// stderr streams.
+    ///
+    /// All I/O this child does will be associated with the current default
+    /// event loop.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```no_run
+    /// use tokio::process::Command;
+    ///
+    /// async fn run_ls() -> std::process::ExitStatus {
+    ///     Command::new("ls")
+    ///         .spawn()
+    ///         .expect("ls command failed to start")
+    ///         .wait()
+    ///         .await
+    ///         .expect("ls command failed to run")
+    /// }
+    /// ```
+    ///
+    /// # Caveats
+    ///
+    /// ## Dropping/Cancellation
+    ///
+    /// Similar to the behavior to the standard library, and unlike the futures
+    /// paradigm of dropping-implies-cancellation, a spawned process will, by
+    /// default, continue to execute even after the `Child` handle has been dropped.
+    ///
+    /// The [`Command::kill_on_drop`] method can be used to modify this behavior
+    /// and kill the child process if the `Child` wrapper is dropped before it
+    /// has exited.
+    ///
+    /// ## Unix Processes
+    ///
+    /// On Unix platforms processes must be "reaped" by their parent process after
+    /// they have exited in order to release all OS resources. A child process which
+    /// has exited, but has not yet been reaped by its parent is considered a "zombie"
+    /// process. Such processes continue to count against limits imposed by the system,
+    /// and having too many zombie processes present can prevent additional processes
+    /// from being spawned.
+    ///
+    /// The tokio runtime will, on a best-effort basis, attempt to reap and clean up
+    /// any process which it has spawned. No additional guarantees are made with regards
+    /// how quickly or how often this procedure will take place.
+    ///
+    /// It is recommended to avoid dropping a [`Child`] process handle before it has been
+    /// fully `await`ed if stricter cleanup guarantees are required.
+    ///
+    /// [`Command`]: crate::process::Command
+    /// [`Command::kill_on_drop`]: crate::process::Command::kill_on_drop
+    /// [`Child`]: crate::process::Child
+    ///
+    /// # Errors
+    ///
+    /// On Unix platforms this method will fail with `std::io::ErrorKind::WouldBlock`
+    /// if the system process limit is reached (which includes other applications
+    /// running on the system).
+    pub fn spawn(&mut self) -> io::Result<Child> {
+        imp::spawn_child(&mut self.std).map(|spawned_child| Child {
+            child: FusedChild::Child(ChildDropGuard {
+                inner: spawned_child.child,
+                kill_on_drop: self.kill_on_drop,
+            }),
+            stdin: spawned_child.stdin.map(|inner| ChildStdin { inner }),
+            stdout: spawned_child.stdout.map(|inner| ChildStdout { inner }),
+            stderr: spawned_child.stderr.map(|inner| ChildStderr { inner }),
+        })
+    }
+
+    /// Executes the command as a child process, waiting for it to finish and
+    /// collecting its exit status.
+    ///
+    /// By default, stdin, stdout and stderr are inherited from the parent.
+    /// If any input/output handles are set to a pipe then they will be immediately
+    /// closed after the child is spawned.
+    ///
+    /// All I/O this child does will be associated with the current default
+    /// event loop.
+    ///
+    /// The destructor of the future returned by this function will kill
+    /// the child if [`kill_on_drop`] is set to true.
+    ///
+    /// [`kill_on_drop`]: fn@Self::kill_on_drop
+    ///
+    /// # Errors
+    ///
+    /// This future will return an error if the child process cannot be spawned
+    /// or if there is an error while awaiting its status.
+    ///
+    /// On Unix platforms this method will fail with `std::io::ErrorKind::WouldBlock`
+    /// if the system process limit is reached (which includes other applications
+    /// running on the system).
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```no_run
+    /// use tokio::process::Command;
+    ///
+    /// async fn run_ls() -> std::process::ExitStatus {
+    ///     Command::new("ls")
+    ///         .status()
+    ///         .await
+    ///         .expect("ls command failed to run")
+    /// }
+    /// ```
+    pub fn status(&mut self) -> impl Future<Output = io::Result<ExitStatus>> {
+        let child = self.spawn();
+
+        async {
+            let mut child = child?;
+
+            // Ensure we close any stdio handles so we can't deadlock
+            // waiting on the child which may be waiting to read/write
+            // to a pipe we're holding.
+            child.stdin.take();
+            child.stdout.take();
+            child.stderr.take();
+
+            child.wait().await
+        }
+    }
+
+    /// Executes the command as a child process, waiting for it to finish and
+    /// collecting all of its output.
+    ///
+    /// > **Note**: this method, unlike the standard library, will
+    /// > unconditionally configure the stdout/stderr handles to be pipes, even
+    /// > if they have been previously configured. If this is not desired then
+    /// > the `spawn` method should be used in combination with the
+    /// > `wait_with_output` method on child.
+    ///
+    /// This method will return a future representing the collection of the
+    /// child process's stdout/stderr. It will resolve to
+    /// the `Output` type in the standard library, containing `stdout` and
+    /// `stderr` as `Vec<u8>` along with an `ExitStatus` representing how the
+    /// process exited.
+    ///
+    /// All I/O this child does will be associated with the current default
+    /// event loop.
+    ///
+    /// The destructor of the future returned by this function will kill
+    /// the child if [`kill_on_drop`] is set to true.
+    ///
+    /// [`kill_on_drop`]: fn@Self::kill_on_drop
+    ///
+    /// # Errors
+    ///
+    /// This future will return an error if the child process cannot be spawned
+    /// or if there is an error while awaiting its status.
+    ///
+    /// On Unix platforms this method will fail with `std::io::ErrorKind::WouldBlock`
+    /// if the system process limit is reached (which includes other applications
+    /// running on the system).
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```no_run
+    /// use tokio::process::Command;
+    ///
+    /// async fn run_ls() {
+    ///     let output: std::process::Output = Command::new("ls")
+    ///         .output()
+    ///         .await
+    ///         .expect("ls command failed to run");
+    ///     println!("stderr of ls: {:?}", output.stderr);
+    /// }
+    /// ```
+    pub fn output(&mut self) -> impl Future<Output = io::Result<Output>> {
+        self.std.stdout(Stdio::piped());
+        self.std.stderr(Stdio::piped());
+
+        let child = self.spawn();
+
+        async { child?.wait_with_output().await }
+    }
+}
+
+impl From<StdCommand> for Command {
+    fn from(std: StdCommand) -> Command {
+        Command {
+            std,
+            kill_on_drop: false,
+        }
+    }
+}
+
+/// A drop guard which can ensure the child process is killed on drop if specified.
+#[derive(Debug)]
+struct ChildDropGuard<T: Kill> {
+    inner: T,
+    kill_on_drop: bool,
+}
+
+impl<T: Kill> Kill for ChildDropGuard<T> {
+    fn kill(&mut self) -> io::Result<()> {
+        let ret = self.inner.kill();
+
+        if ret.is_ok() {
+            self.kill_on_drop = false;
+        }
+
+        ret
+    }
+}
+
+impl<T: Kill> Drop for ChildDropGuard<T> {
+    fn drop(&mut self) {
+        if self.kill_on_drop {
+            drop(self.kill());
+        }
+    }
+}
+
+impl<T, E, F> Future for ChildDropGuard<F>
+where
+    F: Future<Output = Result<T, E>> + Kill + Unpin,
+{
+    type Output = Result<T, E>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        // Keep track of task budget
+        let coop = ready!(crate::coop::poll_proceed(cx));
+
+        let ret = Pin::new(&mut self.inner).poll(cx);
+
+        if let Poll::Ready(Ok(_)) = ret {
+            // Avoid the overhead of trying to kill a reaped process
+            self.kill_on_drop = false;
+        }
+
+        if ret.is_ready() {
+            coop.made_progress();
+        }
+
+        ret
+    }
+}
+
+/// Keeps track of the exit status of a child process without worrying about
+/// polling the underlying futures even after they have completed.
+#[derive(Debug)]
+enum FusedChild {
+    Child(ChildDropGuard<imp::Child>),
+    Done(ExitStatus),
+}
+
+/// Representation of a child process spawned onto an event loop.
+///
+/// # Caveats
+/// Similar to the behavior to the standard library, and unlike the futures
+/// paradigm of dropping-implies-cancellation, a spawned process will, by
+/// default, continue to execute even after the `Child` handle has been dropped.
+///
+/// The `Command::kill_on_drop` method can be used to modify this behavior
+/// and kill the child process if the `Child` wrapper is dropped before it
+/// has exited.
+#[derive(Debug)]
+pub struct Child {
+    child: FusedChild,
+
+    /// The handle for writing to the child's standard input (stdin), if it has
+    /// been captured. To avoid partially moving the `child` and thus blocking
+    /// yourself from calling functions on `child` while using `stdin`, you might
+    /// find it helpful to do:
+    ///
+    /// ```no_run
+    /// # let mut child = tokio::process::Command::new("echo").spawn().unwrap();
+    /// let stdin = child.stdin.take().unwrap();
+    /// ```
+    pub stdin: Option<ChildStdin>,
+
+    /// The handle for reading from the child's standard output (stdout), if it
+    /// has been captured. You might find it helpful to do
+    ///
+    /// ```no_run
+    /// # let mut child = tokio::process::Command::new("echo").spawn().unwrap();
+    /// let stdout = child.stdout.take().unwrap();
+    /// ```
+    ///
+    /// to avoid partially moving the `child` and thus blocking yourself from calling
+    /// functions on `child` while using `stdout`.
+    pub stdout: Option<ChildStdout>,
+
+    /// The handle for reading from the child's standard error (stderr), if it
+    /// has been captured. You might find it helpful to do
+    ///
+    /// ```no_run
+    /// # let mut child = tokio::process::Command::new("echo").spawn().unwrap();
+    /// let stderr = child.stderr.take().unwrap();
+    /// ```
+    ///
+    /// to avoid partially moving the `child` and thus blocking yourself from calling
+    /// functions on `child` while using `stderr`.
+    pub stderr: Option<ChildStderr>,
+}
+
+impl Child {
+    /// Returns the OS-assigned process identifier associated with this child
+    /// while it is still running.
+    ///
+    /// Once the child has been polled to completion this will return `None`.
+    /// This is done to avoid confusion on platforms like Unix where the OS
+    /// identifier could be reused once the process has completed.
+    pub fn id(&self) -> Option<u32> {
+        match &self.child {
+            FusedChild::Child(child) => Some(child.inner.id()),
+            FusedChild::Done(_) => None,
+        }
+    }
+
+    /// Extracts the raw handle of the process associated with this child while
+    /// it is still running. Returns `None` if the child has exited.
+    #[cfg(windows)]
+    pub fn raw_handle(&self) -> Option<RawHandle> {
+        match &self.child {
+            FusedChild::Child(c) => Some(c.inner.as_raw_handle()),
+            FusedChild::Done(_) => None,
+        }
+    }
+
+    /// Attempts to force the child to exit, but does not wait for the request
+    /// to take effect.
+    ///
+    /// On Unix platforms, this is the equivalent to sending a SIGKILL. Note
+    /// that on Unix platforms it is possible for a zombie process to remain
+    /// after a kill is sent; to avoid this, the caller should ensure that either
+    /// `child.wait().await` or `child.try_wait()` is invoked successfully.
+    pub fn start_kill(&mut self) -> io::Result<()> {
+        match &mut self.child {
+            FusedChild::Child(child) => child.kill(),
+            FusedChild::Done(_) => Err(io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "invalid argument: can't kill an exited process",
+            )),
+        }
+    }
+
+    /// Forces the child to exit.
+    ///
+    /// This is equivalent to sending a SIGKILL on unix platforms.
+    ///
+    /// If the child has to be killed remotely, it is possible to do it using
+    /// a combination of the select! macro and a oneshot channel. In the following
+    /// example, the child will run until completion unless a message is sent on
+    /// the oneshot channel. If that happens, the child is killed immediately
+    /// using the `.kill()` method.
+    ///
+    /// ```no_run
+    /// use tokio::process::Command;
+    /// use tokio::sync::oneshot::channel;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (send, recv) = channel::<()>();
+    ///     let mut child = Command::new("sleep").arg("1").spawn().unwrap();
+    ///     tokio::spawn(async move { send.send(()) });
+    ///     tokio::select! {
+    ///         _ = child.wait() => {}
+    ///         _ = recv => child.kill().await.expect("kill failed"),
+    ///     }
+    /// }
+    /// ```
+    pub async fn kill(&mut self) -> io::Result<()> {
+        self.start_kill()?;
+        self.wait().await?;
+        Ok(())
+    }
+
+    /// Waits for the child to exit completely, returning the status that it
+    /// exited with. This function will continue to have the same return value
+    /// after it has been called at least once.
+    ///
+    /// The stdin handle to the child process, if any, will be closed
+    /// before waiting. This helps avoid deadlock: it ensures that the
+    /// child does not block waiting for input from the parent, while
+    /// the parent waits for the child to exit.
+    ///
+    /// If the caller wishes to explicitly control when the child's stdin
+    /// handle is closed, they may `.take()` it before calling `.wait()`:
+    ///
+    /// ```
+    /// # #[cfg(not(unix))]fn main(){}
+    /// # #[cfg(unix)]
+    /// use tokio::io::AsyncWriteExt;
+    /// # #[cfg(unix)]
+    /// use tokio::process::Command;
+    /// # #[cfg(unix)]
+    /// use std::process::Stdio;
+    ///
+    /// # #[cfg(unix)]
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let mut child = Command::new("cat")
+    ///         .stdin(Stdio::piped())
+    ///         .spawn()
+    ///         .unwrap();
+    ///
+    ///     let mut stdin = child.stdin.take().unwrap();
+    ///     tokio::spawn(async move {
+    ///         // do something with stdin here...
+    ///         stdin.write_all(b"hello world\n").await.unwrap();
+    ///
+    ///         // then drop when finished
+    ///         drop(stdin);
+    ///     });
+    ///
+    ///     // wait for the process to complete
+    ///     let _ = child.wait().await;
+    /// }
+    /// ```
+    pub async fn wait(&mut self) -> io::Result<ExitStatus> {
+        // Ensure stdin is closed so the child isn't stuck waiting on
+        // input while the parent is waiting for it to exit.
+        drop(self.stdin.take());
+
+        match &mut self.child {
+            FusedChild::Done(exit) => Ok(*exit),
+            FusedChild::Child(child) => {
+                let ret = child.await;
+
+                if let Ok(exit) = ret {
+                    self.child = FusedChild::Done(exit);
+                }
+
+                ret
+            }
+        }
+    }
+
+    /// Attempts to collect the exit status of the child if it has already
+    /// exited.
+    ///
+    /// This function will not block the calling thread and will only
+    /// check to see if the child process has exited or not. If the child has
+    /// exited then on Unix the process ID is reaped. This function is
+    /// guaranteed to repeatedly return a successful exit status so long as the
+    /// child has already exited.
+    ///
+    /// If the child has exited, then `Ok(Some(status))` is returned. If the
+    /// exit status is not available at this time then `Ok(None)` is returned.
+    /// If an error occurs, then that error is returned.
+    ///
+    /// Note that unlike `wait`, this function will not attempt to drop stdin,
+    /// nor will it wake the current task if the child exits.
+    pub fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
+        match &mut self.child {
+            FusedChild::Done(exit) => Ok(Some(*exit)),
+            FusedChild::Child(guard) => {
+                let ret = guard.inner.try_wait();
+
+                if let Ok(Some(exit)) = ret {
+                    // Avoid the overhead of trying to kill a reaped process
+                    guard.kill_on_drop = false;
+                    self.child = FusedChild::Done(exit);
+                }
+
+                ret
+            }
+        }
+    }
+
+    /// Returns a future that will resolve to an `Output`, containing the exit
+    /// status, stdout, and stderr of the child process.
+    ///
+    /// The returned future will simultaneously waits for the child to exit and
+    /// collect all remaining output on the stdout/stderr handles, returning an
+    /// `Output` instance.
+    ///
+    /// The stdin handle to the child process, if any, will be closed before
+    /// waiting. This helps avoid deadlock: it ensures that the child does not
+    /// block waiting for input from the parent, while the parent waits for the
+    /// child to exit.
+    ///
+    /// By default, stdin, stdout and stderr are inherited from the parent. In
+    /// order to capture the output into this `Output` it is necessary to create
+    /// new pipes between parent and child. Use `stdout(Stdio::piped())` or
+    /// `stderr(Stdio::piped())`, respectively, when creating a `Command`.
+    pub async fn wait_with_output(mut self) -> io::Result<Output> {
+        use crate::future::try_join3;
+
+        async fn read_to_end<A: AsyncRead + Unpin>(io: &mut Option<A>) -> io::Result<Vec<u8>> {
+            let mut vec = Vec::new();
+            if let Some(io) = io.as_mut() {
+                crate::io::util::read_to_end(io, &mut vec).await?;
+            }
+            Ok(vec)
+        }
+
+        let mut stdout_pipe = self.stdout.take();
+        let mut stderr_pipe = self.stderr.take();
+
+        let stdout_fut = read_to_end(&mut stdout_pipe);
+        let stderr_fut = read_to_end(&mut stderr_pipe);
+
+        let (status, stdout, stderr) = try_join3(self.wait(), stdout_fut, stderr_fut).await?;
+
+        // Drop happens after `try_join` due to <https://github.com/tokio-rs/tokio/issues/4309>
+        drop(stdout_pipe);
+        drop(stderr_pipe);
+
+        Ok(Output {
+            status,
+            stdout,
+            stderr,
+        })
+    }
+}
+
+/// The standard input stream for spawned children.
+///
+/// This type implements the `AsyncWrite` trait to pass data to the stdin handle of
+/// handle of a child process asynchronously.
+#[derive(Debug)]
+pub struct ChildStdin {
+    inner: imp::ChildStdio,
+}
+
+/// The standard output stream for spawned children.
+///
+/// This type implements the `AsyncRead` trait to read data from the stdout
+/// handle of a child process asynchronously.
+#[derive(Debug)]
+pub struct ChildStdout {
+    inner: imp::ChildStdio,
+}
+
+/// The standard error stream for spawned children.
+///
+/// This type implements the `AsyncRead` trait to read data from the stderr
+/// handle of a child process asynchronously.
+#[derive(Debug)]
+pub struct ChildStderr {
+    inner: imp::ChildStdio,
+}
+
+impl ChildStdin {
+    /// Creates an asynchronous `ChildStdin` from a synchronous one.
+    ///
+    /// # Errors
+    ///
+    /// This method may fail if an error is encountered when setting the pipe to
+    /// non-blocking mode, or when registering the pipe with the runtime's IO
+    /// driver.
+    pub fn from_std(inner: std::process::ChildStdin) -> io::Result<Self> {
+        Ok(Self {
+            inner: imp::stdio(inner)?,
+        })
+    }
+}
+
+impl ChildStdout {
+    /// Creates an asynchronous `ChildStderr` from a synchronous one.
+    ///
+    /// # Errors
+    ///
+    /// This method may fail if an error is encountered when setting the pipe to
+    /// non-blocking mode, or when registering the pipe with the runtime's IO
+    /// driver.
+    pub fn from_std(inner: std::process::ChildStdout) -> io::Result<Self> {
+        Ok(Self {
+            inner: imp::stdio(inner)?,
+        })
+    }
+}
+
+impl ChildStderr {
+    /// Creates an asynchronous `ChildStderr` from a synchronous one.
+    ///
+    /// # Errors
+    ///
+    /// This method may fail if an error is encountered when setting the pipe to
+    /// non-blocking mode, or when registering the pipe with the runtime's IO
+    /// driver.
+    pub fn from_std(inner: std::process::ChildStderr) -> io::Result<Self> {
+        Ok(Self {
+            inner: imp::stdio(inner)?,
+        })
+    }
+}
+
+impl AsyncWrite for ChildStdin {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        self.inner.poll_write(cx, buf)
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn poll_shutdown(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        Poll::Ready(Ok(()))
+    }
+}
+
+impl AsyncRead for ChildStdout {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        // Safety: pipes support reading into uninitialized memory
+        unsafe { self.inner.poll_read(cx, buf) }
+    }
+}
+
+impl AsyncRead for ChildStderr {
+    fn poll_read(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        // Safety: pipes support reading into uninitialized memory
+        unsafe { self.inner.poll_read(cx, buf) }
+    }
+}
+
+impl TryInto<Stdio> for ChildStdin {
+    type Error = io::Error;
+
+    fn try_into(self) -> Result<Stdio, Self::Error> {
+        imp::convert_to_stdio(self.inner)
+    }
+}
+
+impl TryInto<Stdio> for ChildStdout {
+    type Error = io::Error;
+
+    fn try_into(self) -> Result<Stdio, Self::Error> {
+        imp::convert_to_stdio(self.inner)
+    }
+}
+
+impl TryInto<Stdio> for ChildStderr {
+    type Error = io::Error;
+
+    fn try_into(self) -> Result<Stdio, Self::Error> {
+        imp::convert_to_stdio(self.inner)
+    }
+}
+
+#[cfg(unix)]
+mod sys {
+    use std::os::unix::io::{AsRawFd, RawFd};
+
+    use super::{ChildStderr, ChildStdin, ChildStdout};
+
+    impl AsRawFd for ChildStdin {
+        fn as_raw_fd(&self) -> RawFd {
+            self.inner.as_raw_fd()
+        }
+    }
+
+    impl AsRawFd for ChildStdout {
+        fn as_raw_fd(&self) -> RawFd {
+            self.inner.as_raw_fd()
+        }
+    }
+
+    impl AsRawFd for ChildStderr {
+        fn as_raw_fd(&self) -> RawFd {
+            self.inner.as_raw_fd()
+        }
+    }
+}
+
+#[cfg(windows)]
+mod sys {
+    use std::os::windows::io::{AsRawHandle, RawHandle};
+
+    use super::{ChildStderr, ChildStdin, ChildStdout};
+
+    impl AsRawHandle for ChildStdin {
+        fn as_raw_handle(&self) -> RawHandle {
+            self.inner.as_raw_handle()
+        }
+    }
+
+    impl AsRawHandle for ChildStdout {
+        fn as_raw_handle(&self) -> RawHandle {
+            self.inner.as_raw_handle()
+        }
+    }
+
+    impl AsRawHandle for ChildStderr {
+        fn as_raw_handle(&self) -> RawHandle {
+            self.inner.as_raw_handle()
+        }
+    }
+}
+
+#[cfg(all(test, not(loom)))]
+mod test {
+    use super::kill::Kill;
+    use super::ChildDropGuard;
+
+    use futures::future::FutureExt;
+    use std::future::Future;
+    use std::io;
+    use std::pin::Pin;
+    use std::task::{Context, Poll};
+
+    struct Mock {
+        num_kills: usize,
+        num_polls: usize,
+        poll_result: Poll<Result<(), ()>>,
+    }
+
+    impl Mock {
+        fn new() -> Self {
+            Self::with_result(Poll::Pending)
+        }
+
+        fn with_result(result: Poll<Result<(), ()>>) -> Self {
+            Self {
+                num_kills: 0,
+                num_polls: 0,
+                poll_result: result,
+            }
+        }
+    }
+
+    impl Kill for Mock {
+        fn kill(&mut self) -> io::Result<()> {
+            self.num_kills += 1;
+            Ok(())
+        }
+    }
+
+    impl Future for Mock {
+        type Output = Result<(), ()>;
+
+        fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Self::Output> {
+            let inner = Pin::get_mut(self);
+            inner.num_polls += 1;
+            inner.poll_result
+        }
+    }
+
+    #[test]
+    fn kills_on_drop_if_specified() {
+        let mut mock = Mock::new();
+
+        {
+            let guard = ChildDropGuard {
+                inner: &mut mock,
+                kill_on_drop: true,
+            };
+            drop(guard);
+        }
+
+        assert_eq!(1, mock.num_kills);
+        assert_eq!(0, mock.num_polls);
+    }
+
+    #[test]
+    fn no_kill_on_drop_by_default() {
+        let mut mock = Mock::new();
+
+        {
+            let guard = ChildDropGuard {
+                inner: &mut mock,
+                kill_on_drop: false,
+            };
+            drop(guard);
+        }
+
+        assert_eq!(0, mock.num_kills);
+        assert_eq!(0, mock.num_polls);
+    }
+
+    #[test]
+    fn no_kill_if_already_killed() {
+        let mut mock = Mock::new();
+
+        {
+            let mut guard = ChildDropGuard {
+                inner: &mut mock,
+                kill_on_drop: true,
+            };
+            let _ = guard.kill();
+            drop(guard);
+        }
+
+        assert_eq!(1, mock.num_kills);
+        assert_eq!(0, mock.num_polls);
+    }
+
+    #[test]
+    fn no_kill_if_reaped() {
+        let mut mock_pending = Mock::with_result(Poll::Pending);
+        let mut mock_reaped = Mock::with_result(Poll::Ready(Ok(())));
+        let mut mock_err = Mock::with_result(Poll::Ready(Err(())));
+
+        let waker = futures::task::noop_waker();
+        let mut context = Context::from_waker(&waker);
+        {
+            let mut guard = ChildDropGuard {
+                inner: &mut mock_pending,
+                kill_on_drop: true,
+            };
+            let _ = guard.poll_unpin(&mut context);
+
+            let mut guard = ChildDropGuard {
+                inner: &mut mock_reaped,
+                kill_on_drop: true,
+            };
+            let _ = guard.poll_unpin(&mut context);
+
+            let mut guard = ChildDropGuard {
+                inner: &mut mock_err,
+                kill_on_drop: true,
+            };
+            let _ = guard.poll_unpin(&mut context);
+        }
+
+        assert_eq!(1, mock_pending.num_kills);
+        assert_eq!(1, mock_pending.num_polls);
+
+        assert_eq!(0, mock_reaped.num_kills);
+        assert_eq!(1, mock_reaped.num_polls);
+
+        assert_eq!(1, mock_err.num_kills);
+        assert_eq!(1, mock_err.num_polls);
+    }
+}
diff --git a/third_party/rust/tokio/src/process/unix/driver.rs b/third_party/rust/tokio/src/process/unix/driver.rs
new file mode 100644
index 0000000000..84dc8fbd02
--- /dev/null
+++ b/third_party/rust/tokio/src/process/unix/driver.rs
@@ -0,0 +1,58 @@
+#![cfg_attr(not(feature = "rt"), allow(dead_code))]
+
+//! Process driver.
+
+use crate::park::Park;
+use crate::process::unix::GlobalOrphanQueue;
+use crate::signal::unix::driver::{Driver as SignalDriver, Handle as SignalHandle};
+
+use std::io;
+use std::time::Duration;
+
+/// Responsible for cleaning up orphaned child processes on Unix platforms.
+#[derive(Debug)]
+pub(crate) struct Driver {
+    park: SignalDriver,
+    signal_handle: SignalHandle,
+}
+
+// ===== impl Driver =====
+
+impl Driver {
+    /// Creates a new signal `Driver` instance that delegates wakeups to `park`.
+    pub(crate) fn new(park: SignalDriver) -> Self {
+        let signal_handle = park.handle();
+
+        Self {
+            park,
+            signal_handle,
+        }
+    }
+}
+
+// ===== impl Park for Driver =====
+
+impl Park for Driver {
+    type Unpark = <SignalDriver as Park>::Unpark;
+    type Error = io::Error;
+
+    fn unpark(&self) -> Self::Unpark {
+        self.park.unpark()
+    }
+
+    fn park(&mut self) -> Result<(), Self::Error> {
+        self.park.park()?;
+        GlobalOrphanQueue::reap_orphans(&self.signal_handle);
+        Ok(())
+    }
+
+    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
+        self.park.park_timeout(duration)?;
+        GlobalOrphanQueue::reap_orphans(&self.signal_handle);
+        Ok(())
+    }
+
+    fn shutdown(&mut self) {
+        self.park.shutdown()
+    }
+}
diff --git a/third_party/rust/tokio/src/process/unix/mod.rs b/third_party/rust/tokio/src/process/unix/mod.rs
new file mode 100644
index 0000000000..576fe6cb47
--- /dev/null
+++ b/third_party/rust/tokio/src/process/unix/mod.rs
@@ -0,0 +1,250 @@
+//! Unix handling of child processes.
+//!
+//! Right now the only "fancy" thing about this is how we implement the
+//! `Future` implementation on `Child` to get the exit status. Unix offers
+//! no way to register a child with epoll, and the only real way to get a
+//! notification when a process exits is the SIGCHLD signal.
+//!
+//! Signal handling in general is *super* hairy and complicated, and it's even
+//! more complicated here with the fact that signals are coalesced, so we may
+//! not get a SIGCHLD-per-child.
+//!
+//! Our best approximation here is to check *all spawned processes* for all
+//! SIGCHLD signals received. To do that we create a `Signal`, implemented in
+//! the `tokio-net` crate, which is a stream over signals being received.
+//!
+//! Later when we poll the process's exit status we simply check to see if a
+//! SIGCHLD has happened since we last checked, and while that returns "yes" we
+//! keep trying.
+//!
+//! Note that this means that this isn't really scalable, but then again
+//! processes in general aren't scalable (e.g. millions) so it shouldn't be that
+//! bad in theory...
+
+pub(crate) mod driver;
+
+pub(crate) mod orphan;
+use orphan::{OrphanQueue, OrphanQueueImpl, Wait};
+
+mod reap;
+use reap::Reaper;
+
+use crate::io::PollEvented;
+use crate::process::kill::Kill;
+use crate::process::SpawnedChild;
+use crate::signal::unix::driver::Handle as SignalHandle;
+use crate::signal::unix::{signal, Signal, SignalKind};
+
+use mio::event::Source;
+use mio::unix::SourceFd;
+use once_cell::sync::Lazy;
+use std::fmt;
+use std::fs::File;
+use std::future::Future;
+use std::io;
+use std::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
+use std::pin::Pin;
+use std::process::{Child as StdChild, ExitStatus, Stdio};
+use std::task::Context;
+use std::task::Poll;
+
+impl Wait for StdChild {
+    fn id(&self) -> u32 {
+        self.id()
+    }
+
+    fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
+        self.try_wait()
+    }
+}
+
+impl Kill for StdChild {
+    fn kill(&mut self) -> io::Result<()> {
+        self.kill()
+    }
+}
+
+static ORPHAN_QUEUE: Lazy<OrphanQueueImpl<StdChild>> = Lazy::new(OrphanQueueImpl::new);
+
+pub(crate) struct GlobalOrphanQueue;
+
+impl fmt::Debug for GlobalOrphanQueue {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        ORPHAN_QUEUE.fmt(fmt)
+    }
+}
+
+impl GlobalOrphanQueue {
+    fn reap_orphans(handle: &SignalHandle) {
+        ORPHAN_QUEUE.reap_orphans(handle)
+    }
+}
+
+impl OrphanQueue<StdChild> for GlobalOrphanQueue {
+    fn push_orphan(&self, orphan: StdChild) {
+        ORPHAN_QUEUE.push_orphan(orphan)
+    }
+}
+
+#[must_use = "futures do nothing unless polled"]
+pub(crate) struct Child {
+    inner: Reaper<StdChild, GlobalOrphanQueue, Signal>,
+}
+
+impl fmt::Debug for Child {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Child")
+            .field("pid", &self.inner.id())
+            .finish()
+    }
+}
+
+pub(crate) fn spawn_child(cmd: &mut std::process::Command) -> io::Result<SpawnedChild> {
+    let mut child = cmd.spawn()?;
+    let stdin = child.stdin.take().map(stdio).transpose()?;
+    let stdout = child.stdout.take().map(stdio).transpose()?;
+    let stderr = child.stderr.take().map(stdio).transpose()?;
+
+    let signal = signal(SignalKind::child())?;
+
+    Ok(SpawnedChild {
+        child: Child {
+            inner: Reaper::new(child, GlobalOrphanQueue, signal),
+        },
+        stdin,
+        stdout,
+        stderr,
+    })
+}
+
+impl Child {
+    pub(crate) fn id(&self) -> u32 {
+        self.inner.id()
+    }
+
+    pub(crate) fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
+        self.inner.inner_mut().try_wait()
+    }
+}
+
+impl Kill for Child {
+    fn kill(&mut self) -> io::Result<()> {
+        self.inner.kill()
+    }
+}
+
+impl Future for Child {
+    type Output = io::Result<ExitStatus>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        Pin::new(&mut self.inner).poll(cx)
+    }
+}
+
+#[derive(Debug)]
+pub(crate) struct Pipe {
+    // Actually a pipe and not a File. However, we are reusing `File` to get
+    // close on drop. This is a similar trick as `mio`.
+    fd: File,
+}
+
+impl<T: IntoRawFd> From<T> for Pipe {
+    fn from(fd: T) -> Self {
+        let fd = unsafe { File::from_raw_fd(fd.into_raw_fd()) };
+        Self { fd }
+    }
+}
+
+impl<'a> io::Read for &'a Pipe {
+    fn read(&mut self, bytes: &mut [u8]) -> io::Result<usize> {
+        (&self.fd).read(bytes)
+    }
+}
+
+impl<'a> io::Write for &'a Pipe {
+    fn write(&mut self, bytes: &[u8]) -> io::Result<usize> {
+        (&self.fd).write(bytes)
+    }
+
+    fn flush(&mut self) -> io::Result<()> {
+        (&self.fd).flush()
+    }
+}
+
+impl AsRawFd for Pipe {
+    fn as_raw_fd(&self) -> RawFd {
+        self.fd.as_raw_fd()
+    }
+}
+
+pub(crate) fn convert_to_stdio(io: PollEvented<Pipe>) -> io::Result<Stdio> {
+    let mut fd = io.into_inner()?.fd;
+
+    // Ensure that the fd to be inherited is set to *blocking* mode, as this
+    // is the default that virtually all programs expect to have. Those
+    // programs that know how to work with nonblocking stdio will know how to
+    // change it to nonblocking mode.
+    set_nonblocking(&mut fd, false)?;
+
+    Ok(Stdio::from(fd))
+}
+
+impl Source for Pipe {
+    fn register(
+        &mut self,
+        registry: &mio::Registry,
+        token: mio::Token,
+        interest: mio::Interest,
+    ) -> io::Result<()> {
+        SourceFd(&self.as_raw_fd()).register(registry, token, interest)
+    }
+
+    fn reregister(
+        &mut self,
+        registry: &mio::Registry,
+        token: mio::Token,
+        interest: mio::Interest,
+    ) -> io::Result<()> {
+        SourceFd(&self.as_raw_fd()).reregister(registry, token, interest)
+    }
+
+    fn deregister(&mut self, registry: &mio::Registry) -> io::Result<()> {
+        SourceFd(&self.as_raw_fd()).deregister(registry)
+    }
+}
+
+pub(crate) type ChildStdio = PollEvented<Pipe>;
+
+fn set_nonblocking<T: AsRawFd>(fd: &mut T, nonblocking: bool) -> io::Result<()> {
+    unsafe {
+        let fd = fd.as_raw_fd();
+        let previous = libc::fcntl(fd, libc::F_GETFL);
+        if previous == -1 {
+            return Err(io::Error::last_os_error());
+        }
+
+        let new = if nonblocking {
+            previous | libc::O_NONBLOCK
+        } else {
+            previous & !libc::O_NONBLOCK
+        };
+
+        let r = libc::fcntl(fd, libc::F_SETFL, new);
+        if r == -1 {
+            return Err(io::Error::last_os_error());
+        }
+    }
+
+    Ok(())
+}
+
+pub(super) fn stdio<T>(io: T) -> io::Result<PollEvented<Pipe>>
+where
+    T: IntoRawFd,
+{
+    // Set the fd to nonblocking before we pass it to the event loop
+    let mut pipe = Pipe::from(io);
+    set_nonblocking(&mut pipe, true)?;
+
+    PollEvented::new(pipe)
+}
diff --git a/third_party/rust/tokio/src/process/unix/orphan.rs b/third_party/rust/tokio/src/process/unix/orphan.rs
new file mode 100644
index 0000000000..0e52530c37
--- /dev/null
+++ b/third_party/rust/tokio/src/process/unix/orphan.rs
@@ -0,0 +1,321 @@
+use crate::loom::sync::{Mutex, MutexGuard};
+use crate::signal::unix::driver::Handle as SignalHandle;
+use crate::signal::unix::{signal_with_handle, SignalKind};
+use crate::sync::watch;
+use std::io;
+use std::process::ExitStatus;
+
+/// An interface for waiting on a process to exit.
+pub(crate) trait Wait {
+    /// Get the identifier for this process or diagnostics.
+    fn id(&self) -> u32;
+    /// Try waiting for a process to exit in a non-blocking manner.
+    fn try_wait(&mut self) -> io::Result<Option<ExitStatus>>;
+}
+
+impl<T: Wait> Wait for &mut T {
+    fn id(&self) -> u32 {
+        (**self).id()
+    }
+
+    fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
+        (**self).try_wait()
+    }
+}
+
+/// An interface for queueing up an orphaned process so that it can be reaped.
+pub(crate) trait OrphanQueue<T> {
+    /// Adds an orphan to the queue.
+    fn push_orphan(&self, orphan: T);
+}
+
+impl<T, O: OrphanQueue<T>> OrphanQueue<T> for &O {
+    fn push_orphan(&self, orphan: T) {
+        (**self).push_orphan(orphan);
+    }
+}
+
+/// An implementation of `OrphanQueue`.
+#[derive(Debug)]
+pub(crate) struct OrphanQueueImpl<T> {
+    sigchild: Mutex<Option<watch::Receiver<()>>>,
+    queue: Mutex<Vec<T>>,
+}
+
+impl<T> OrphanQueueImpl<T> {
+    pub(crate) fn new() -> Self {
+        Self {
+            sigchild: Mutex::new(None),
+            queue: Mutex::new(Vec::new()),
+        }
+    }
+
+    #[cfg(test)]
+    fn len(&self) -> usize {
+        self.queue.lock().len()
+    }
+
+    pub(crate) fn push_orphan(&self, orphan: T)
+    where
+        T: Wait,
+    {
+        self.queue.lock().push(orphan)
+    }
+
+    /// Attempts to reap every process in the queue, ignoring any errors and
+    /// enqueueing any orphans which have not yet exited.
+    pub(crate) fn reap_orphans(&self, handle: &SignalHandle)
+    where
+        T: Wait,
+    {
+        // If someone else is holding the lock, they will be responsible for draining
+        // the queue as necessary, so we can safely bail if that happens
+        if let Some(mut sigchild_guard) = self.sigchild.try_lock() {
+            match &mut *sigchild_guard {
+                Some(sigchild) => {
+                    if sigchild.try_has_changed().and_then(Result::ok).is_some() {
+                        drain_orphan_queue(self.queue.lock());
+                    }
+                }
+                None => {
+                    let queue = self.queue.lock();
+
+                    // Be lazy and only initialize the SIGCHLD listener if there
+                    // are any orphaned processes in the queue.
+                    if !queue.is_empty() {
+                        // An errors shouldn't really happen here, but if it does it
+                        // means that the signal driver isn't running, in
+                        // which case there isn't anything we can
+                        // register/initialize here, so we can try again later
+                        if let Ok(sigchild) = signal_with_handle(SignalKind::child(), handle) {
+                            *sigchild_guard = Some(sigchild);
+                            drain_orphan_queue(queue);
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+fn drain_orphan_queue<T>(mut queue: MutexGuard<'_, Vec<T>>)
+where
+    T: Wait,
+{
+    for i in (0..queue.len()).rev() {
+        match queue[i].try_wait() {
+            Ok(None) => {}
+            Ok(Some(_)) | Err(_) => {
+                // The stdlib handles interruption errors (EINTR) when polling a child process.
+                // All other errors represent invalid inputs or pids that have already been
+                // reaped, so we can drop the orphan in case an error is raised.
+                queue.swap_remove(i);
+            }
+        }
+    }
+
+    drop(queue);
+}
+
+#[cfg(all(test, not(loom)))]
+pub(crate) mod test {
+    use super::*;
+    use crate::io::driver::Driver as IoDriver;
+    use crate::signal::unix::driver::{Driver as SignalDriver, Handle as SignalHandle};
+    use crate::sync::watch;
+    use std::cell::{Cell, RefCell};
+    use std::io;
+    use std::os::unix::process::ExitStatusExt;
+    use std::process::ExitStatus;
+    use std::rc::Rc;
+
+    pub(crate) struct MockQueue<W> {
+        pub(crate) all_enqueued: RefCell<Vec<W>>,
+    }
+
+    impl<W> MockQueue<W> {
+        pub(crate) fn new() -> Self {
+            Self {
+                all_enqueued: RefCell::new(Vec::new()),
+            }
+        }
+    }
+
+    impl<W> OrphanQueue<W> for MockQueue<W> {
+        fn push_orphan(&self, orphan: W) {
+            self.all_enqueued.borrow_mut().push(orphan);
+        }
+    }
+
+    struct MockWait {
+        total_waits: Rc<Cell<usize>>,
+        num_wait_until_status: usize,
+        return_err: bool,
+    }
+
+    impl MockWait {
+        fn new(num_wait_until_status: usize) -> Self {
+            Self {
+                total_waits: Rc::new(Cell::new(0)),
+                num_wait_until_status,
+                return_err: false,
+            }
+        }
+
+        fn with_err() -> Self {
+            Self {
+                total_waits: Rc::new(Cell::new(0)),
+                num_wait_until_status: 0,
+                return_err: true,
+            }
+        }
+    }
+
+    impl Wait for MockWait {
+        fn id(&self) -> u32 {
+            42
+        }
+
+        fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
+            let waits = self.total_waits.get();
+
+            let ret = if self.num_wait_until_status == waits {
+                if self.return_err {
+                    Ok(Some(ExitStatus::from_raw(0)))
+                } else {
+                    Err(io::Error::new(io::ErrorKind::Other, "mock err"))
+                }
+            } else {
+                Ok(None)
+            };
+
+            self.total_waits.set(waits + 1);
+            ret
+        }
+    }
+
+    #[test]
+    fn drain_attempts_a_single_reap_of_all_queued_orphans() {
+        let first_orphan = MockWait::new(0);
+        let second_orphan = MockWait::new(1);
+        let third_orphan = MockWait::new(2);
+        let fourth_orphan = MockWait::with_err();
+
+        let first_waits = first_orphan.total_waits.clone();
+        let second_waits = second_orphan.total_waits.clone();
+        let third_waits = third_orphan.total_waits.clone();
+        let fourth_waits = fourth_orphan.total_waits.clone();
+
+        let orphanage = OrphanQueueImpl::new();
+        orphanage.push_orphan(first_orphan);
+        orphanage.push_orphan(third_orphan);
+        orphanage.push_orphan(second_orphan);
+        orphanage.push_orphan(fourth_orphan);
+
+        assert_eq!(orphanage.len(), 4);
+
+        drain_orphan_queue(orphanage.queue.lock());
+        assert_eq!(orphanage.len(), 2);
+        assert_eq!(first_waits.get(), 1);
+        assert_eq!(second_waits.get(), 1);
+        assert_eq!(third_waits.get(), 1);
+        assert_eq!(fourth_waits.get(), 1);
+
+        drain_orphan_queue(orphanage.queue.lock());
+        assert_eq!(orphanage.len(), 1);
+        assert_eq!(first_waits.get(), 1);
+        assert_eq!(second_waits.get(), 2);
+        assert_eq!(third_waits.get(), 2);
+        assert_eq!(fourth_waits.get(), 1);
+
+        drain_orphan_queue(orphanage.queue.lock());
+        assert_eq!(orphanage.len(), 0);
+        assert_eq!(first_waits.get(), 1);
+        assert_eq!(second_waits.get(), 2);
+        assert_eq!(third_waits.get(), 3);
+        assert_eq!(fourth_waits.get(), 1);
+
+        // Safe to reap when empty
+        drain_orphan_queue(orphanage.queue.lock());
+    }
+
+    #[test]
+    fn no_reap_if_no_signal_received() {
+        let (tx, rx) = watch::channel(());
+
+        let handle = SignalHandle::default();
+
+        let orphanage = OrphanQueueImpl::new();
+        *orphanage.sigchild.lock() = Some(rx);
+
+        let orphan = MockWait::new(2);
+        let waits = orphan.total_waits.clone();
+        orphanage.push_orphan(orphan);
+
+        orphanage.reap_orphans(&handle);
+        assert_eq!(waits.get(), 0);
+
+        orphanage.reap_orphans(&handle);
+        assert_eq!(waits.get(), 0);
+
+        tx.send(()).unwrap();
+        orphanage.reap_orphans(&handle);
+        assert_eq!(waits.get(), 1);
+    }
+
+    #[test]
+    fn no_reap_if_signal_lock_held() {
+        let handle = SignalHandle::default();
+
+        let orphanage = OrphanQueueImpl::new();
+        let signal_guard = orphanage.sigchild.lock();
+
+        let orphan = MockWait::new(2);
+        let waits = orphan.total_waits.clone();
+        orphanage.push_orphan(orphan);
+
+        orphanage.reap_orphans(&handle);
+        assert_eq!(waits.get(), 0);
+
+        drop(signal_guard);
+    }
+
+    #[cfg_attr(miri, ignore)] // Miri does not support epoll.
+    #[test]
+    fn does_not_register_signal_if_queue_empty() {
+        let signal_driver = IoDriver::new().and_then(SignalDriver::new).unwrap();
+        let handle = signal_driver.handle();
+
+        let orphanage = OrphanQueueImpl::new();
+        assert!(orphanage.sigchild.lock().is_none()); // Sanity
+
+        // No register when queue empty
+        orphanage.reap_orphans(&handle);
+        assert!(orphanage.sigchild.lock().is_none());
+
+        let orphan = MockWait::new(2);
+        let waits = orphan.total_waits.clone();
+        orphanage.push_orphan(orphan);
+
+        orphanage.reap_orphans(&handle);
+        assert!(orphanage.sigchild.lock().is_some());
+        assert_eq!(waits.get(), 1); // Eager reap when registering listener
+    }
+
+    #[test]
+    fn does_nothing_if_signal_could_not_be_registered() {
+        let handle = SignalHandle::default();
+
+        let orphanage = OrphanQueueImpl::new();
+        assert!(orphanage.sigchild.lock().is_none());
+
+        let orphan = MockWait::new(2);
+        let waits = orphan.total_waits.clone();
+        orphanage.push_orphan(orphan);
+
+        // Signal handler has "gone away", nothing to register or reap
+        orphanage.reap_orphans(&handle);
+        assert!(orphanage.sigchild.lock().is_none());
+        assert_eq!(waits.get(), 0);
+    }
+}
diff --git a/third_party/rust/tokio/src/process/unix/reap.rs b/third_party/rust/tokio/src/process/unix/reap.rs
new file mode 100644
index 0000000000..f7f4d3cc70
--- /dev/null
+++ b/third_party/rust/tokio/src/process/unix/reap.rs
@@ -0,0 +1,298 @@
+use crate::process::imp::orphan::{OrphanQueue, Wait};
+use crate::process::kill::Kill;
+use crate::signal::unix::InternalStream;
+
+use std::future::Future;
+use std::io;
+use std::ops::Deref;
+use std::pin::Pin;
+use std::process::ExitStatus;
+use std::task::Context;
+use std::task::Poll;
+
+/// Orchestrates between registering interest for receiving signals when a
+/// child process has exited, and attempting to poll for process completion.
+#[derive(Debug)]
+pub(crate) struct Reaper<W, Q, S>
+where
+    W: Wait,
+    Q: OrphanQueue<W>,
+{
+    inner: Option<W>,
+    orphan_queue: Q,
+    signal: S,
+}
+
+impl<W, Q, S> Deref for Reaper<W, Q, S>
+where
+    W: Wait,
+    Q: OrphanQueue<W>,
+{
+    type Target = W;
+
+    fn deref(&self) -> &Self::Target {
+        self.inner()
+    }
+}
+
+impl<W, Q, S> Reaper<W, Q, S>
+where
+    W: Wait,
+    Q: OrphanQueue<W>,
+{
+    pub(crate) fn new(inner: W, orphan_queue: Q, signal: S) -> Self {
+        Self {
+            inner: Some(inner),
+            orphan_queue,
+            signal,
+        }
+    }
+
+    fn inner(&self) -> &W {
+        self.inner.as_ref().expect("inner has gone away")
+    }
+
+    pub(crate) fn inner_mut(&mut self) -> &mut W {
+        self.inner.as_mut().expect("inner has gone away")
+    }
+}
+
+impl<W, Q, S> Future for Reaper<W, Q, S>
+where
+    W: Wait + Unpin,
+    Q: OrphanQueue<W> + Unpin,
+    S: InternalStream + Unpin,
+{
+    type Output = io::Result<ExitStatus>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        loop {
+            // If the child hasn't exited yet, then it's our responsibility to
+            // ensure the current task gets notified when it might be able to
+            // make progress. We can use the delivery of a SIGCHLD signal as a
+            // sign that we can potentially make progress.
+            //
+            // However, we will register for a notification on the next signal
+            // BEFORE we poll the child. Otherwise it is possible that the child
+            // can exit and the signal can arrive after we last polled the child,
+            // but before we've registered for a notification on the next signal
+            // (this can cause a deadlock if there are no more spawned children
+            // which can generate a different signal for us). A side effect of
+            // pre-registering for signal notifications is that when the child
+            // exits, we will have already registered for an additional
+            // notification we don't need to consume. If another signal arrives,
+            // this future's task will be notified/woken up again. Since the
+            // futures model allows for spurious wake ups this extra wakeup
+            // should not cause significant issues with parent futures.
+            let registered_interest = self.signal.poll_recv(cx).is_pending();
+
+            if let Some(status) = self.inner_mut().try_wait()? {
+                return Poll::Ready(Ok(status));
+            }
+
+            // If our attempt to poll for the next signal was not ready, then
+            // we've arranged for our task to get notified and we can bail out.
+            if registered_interest {
+                return Poll::Pending;
+            } else {
+                // Otherwise, if the signal stream delivered a signal to us, we
+                // won't get notified at the next signal, so we'll loop and try
+                // again.
+                continue;
+            }
+        }
+    }
+}
+
+impl<W, Q, S> Kill for Reaper<W, Q, S>
+where
+    W: Kill + Wait,
+    Q: OrphanQueue<W>,
+{
+    fn kill(&mut self) -> io::Result<()> {
+        self.inner_mut().kill()
+    }
+}
+
+impl<W, Q, S> Drop for Reaper<W, Q, S>
+where
+    W: Wait,
+    Q: OrphanQueue<W>,
+{
+    fn drop(&mut self) {
+        if let Ok(Some(_)) = self.inner_mut().try_wait() {
+            return;
+        }
+
+        let orphan = self.inner.take().unwrap();
+        self.orphan_queue.push_orphan(orphan);
+    }
+}
+
+#[cfg(all(test, not(loom)))]
+mod test {
+    use super::*;
+
+    use crate::process::unix::orphan::test::MockQueue;
+    use futures::future::FutureExt;
+    use std::os::unix::process::ExitStatusExt;
+    use std::process::ExitStatus;
+    use std::task::Context;
+    use std::task::Poll;
+
+    #[derive(Debug)]
+    struct MockWait {
+        total_kills: usize,
+        total_waits: usize,
+        num_wait_until_status: usize,
+        status: ExitStatus,
+    }
+
+    impl MockWait {
+        fn new(status: ExitStatus, num_wait_until_status: usize) -> Self {
+            Self {
+                total_kills: 0,
+                total_waits: 0,
+                num_wait_until_status,
+                status,
+            }
+        }
+    }
+
+    impl Wait for MockWait {
+        fn id(&self) -> u32 {
+            0
+        }
+
+        fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
+            let ret = if self.num_wait_until_status == self.total_waits {
+                Some(self.status)
+            } else {
+                None
+            };
+
+            self.total_waits += 1;
+            Ok(ret)
+        }
+    }
+
+    impl Kill for MockWait {
+        fn kill(&mut self) -> io::Result<()> {
+            self.total_kills += 1;
+            Ok(())
+        }
+    }
+
+    struct MockStream {
+        total_polls: usize,
+        values: Vec<Option<()>>,
+    }
+
+    impl MockStream {
+        fn new(values: Vec<Option<()>>) -> Self {
+            Self {
+                total_polls: 0,
+                values,
+            }
+        }
+    }
+
+    impl InternalStream for MockStream {
+        fn poll_recv(&mut self, _cx: &mut Context<'_>) -> Poll<Option<()>> {
+            self.total_polls += 1;
+            match self.values.remove(0) {
+                Some(()) => Poll::Ready(Some(())),
+                None => Poll::Pending,
+            }
+        }
+    }
+
+    #[test]
+    fn reaper() {
+        let exit = ExitStatus::from_raw(0);
+        let mock = MockWait::new(exit, 3);
+        let mut grim = Reaper::new(
+            mock,
+            MockQueue::new(),
+            MockStream::new(vec![None, Some(()), None, None, None]),
+        );
+
+        let waker = futures::task::noop_waker();
+        let mut context = Context::from_waker(&waker);
+
+        // Not yet exited, interest registered
+        assert!(grim.poll_unpin(&mut context).is_pending());
+        assert_eq!(1, grim.signal.total_polls);
+        assert_eq!(1, grim.total_waits);
+        assert!(grim.orphan_queue.all_enqueued.borrow().is_empty());
+
+        // Not yet exited, couldn't register interest the first time
+        // but managed to register interest the second time around
+        assert!(grim.poll_unpin(&mut context).is_pending());
+        assert_eq!(3, grim.signal.total_polls);
+        assert_eq!(3, grim.total_waits);
+        assert!(grim.orphan_queue.all_enqueued.borrow().is_empty());
+
+        // Exited
+        if let Poll::Ready(r) = grim.poll_unpin(&mut context) {
+            assert!(r.is_ok());
+            let exit_code = r.unwrap();
+            assert_eq!(exit_code, exit);
+        } else {
+            unreachable!();
+        }
+        assert_eq!(4, grim.signal.total_polls);
+        assert_eq!(4, grim.total_waits);
+        assert!(grim.orphan_queue.all_enqueued.borrow().is_empty());
+    }
+
+    #[test]
+    fn kill() {
+        let exit = ExitStatus::from_raw(0);
+        let mut grim = Reaper::new(
+            MockWait::new(exit, 0),
+            MockQueue::new(),
+            MockStream::new(vec![None]),
+        );
+
+        grim.kill().unwrap();
+        assert_eq!(1, grim.total_kills);
+        assert!(grim.orphan_queue.all_enqueued.borrow().is_empty());
+    }
+
+    #[test]
+    fn drop_reaps_if_possible() {
+        let exit = ExitStatus::from_raw(0);
+        let mut mock = MockWait::new(exit, 0);
+
+        {
+            let queue = MockQueue::new();
+
+            let grim = Reaper::new(&mut mock, &queue, MockStream::new(vec![]));
+
+            drop(grim);
+
+            assert!(queue.all_enqueued.borrow().is_empty());
+        }
+
+        assert_eq!(1, mock.total_waits);
+        assert_eq!(0, mock.total_kills);
+    }
+
+    #[test]
+    fn drop_enqueues_orphan_if_wait_fails() {
+        let exit = ExitStatus::from_raw(0);
+        let mut mock = MockWait::new(exit, 2);
+
+        {
+            let queue = MockQueue::<&mut MockWait>::new();
+            let grim = Reaper::new(&mut mock, &queue, MockStream::new(vec![]));
+            drop(grim);
+
+            assert_eq!(1, queue.all_enqueued.borrow().len());
+        }
+
+        assert_eq!(1, mock.total_waits);
+        assert_eq!(0, mock.total_kills);
+    }
+}
diff --git a/third_party/rust/tokio/src/process/windows.rs b/third_party/rust/tokio/src/process/windows.rs
new file mode 100644
index 0000000000..136d5b0cab
--- /dev/null
+++ b/third_party/rust/tokio/src/process/windows.rs
@@ -0,0 +1,205 @@
+//! Windows asynchronous process handling.
+//!
+//! Like with Unix we don't actually have a way of registering a process with an
+//! IOCP object. As a result we similarly need another mechanism for getting a
+//! signal when a process has exited. For now this is implemented with the
+//! `RegisterWaitForSingleObject` function in the kernel32.dll.
+//!
+//! This strategy is the same that libuv takes and essentially just queues up a
+//! wait for the process in a kernel32-specific thread pool. Once the object is
+//! notified (e.g. the process exits) then we have a callback that basically
+//! just completes a `Oneshot`.
+//!
+//! The `poll_exit` implementation will attempt to wait for the process in a
+//! nonblocking fashion, but failing that it'll fire off a
+//! `RegisterWaitForSingleObject` and then wait on the other end of the oneshot
+//! from then on out.
+
+use crate::io::PollEvented;
+use crate::process::kill::Kill;
+use crate::process::SpawnedChild;
+use crate::sync::oneshot;
+
+use mio::windows::NamedPipe;
+use std::fmt;
+use std::future::Future;
+use std::io;
+use std::os::windows::prelude::{AsRawHandle, FromRawHandle, IntoRawHandle, RawHandle};
+use std::pin::Pin;
+use std::process::Stdio;
+use std::process::{Child as StdChild, Command as StdCommand, ExitStatus};
+use std::ptr;
+use std::task::Context;
+use std::task::Poll;
+use winapi::shared::minwindef::{DWORD, FALSE};
+use winapi::um::handleapi::{DuplicateHandle, INVALID_HANDLE_VALUE};
+use winapi::um::processthreadsapi::GetCurrentProcess;
+use winapi::um::threadpoollegacyapiset::UnregisterWaitEx;
+use winapi::um::winbase::{RegisterWaitForSingleObject, INFINITE};
+use winapi::um::winnt::{
+    BOOLEAN, DUPLICATE_SAME_ACCESS, HANDLE, PVOID, WT_EXECUTEINWAITTHREAD, WT_EXECUTEONLYONCE,
+};
+
+#[must_use = "futures do nothing unless polled"]
+pub(crate) struct Child {
+    child: StdChild,
+    waiting: Option<Waiting>,
+}
+
+impl fmt::Debug for Child {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Child")
+            .field("pid", &self.id())
+            .field("child", &self.child)
+            .field("waiting", &"..")
+            .finish()
+    }
+}
+
+struct Waiting {
+    rx: oneshot::Receiver<()>,
+    wait_object: HANDLE,
+    tx: *mut Option<oneshot::Sender<()>>,
+}
+
+unsafe impl Sync for Waiting {}
+unsafe impl Send for Waiting {}
+
+pub(crate) fn spawn_child(cmd: &mut StdCommand) -> io::Result<SpawnedChild> {
+    let mut child = cmd.spawn()?;
+    let stdin = child.stdin.take().map(stdio).transpose()?;
+    let stdout = child.stdout.take().map(stdio).transpose()?;
+    let stderr = child.stderr.take().map(stdio).transpose()?;
+
+    Ok(SpawnedChild {
+        child: Child {
+            child,
+            waiting: None,
+        },
+        stdin,
+        stdout,
+        stderr,
+    })
+}
+
+impl Child {
+    pub(crate) fn id(&self) -> u32 {
+        self.child.id()
+    }
+
+    pub(crate) fn try_wait(&mut self) -> io::Result<Option<ExitStatus>> {
+        self.child.try_wait()
+    }
+}
+
+impl Kill for Child {
+    fn kill(&mut self) -> io::Result<()> {
+        self.child.kill()
+    }
+}
+
+impl Future for Child {
+    type Output = io::Result<ExitStatus>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let inner = Pin::get_mut(self);
+        loop {
+            if let Some(ref mut w) = inner.waiting {
+                match Pin::new(&mut w.rx).poll(cx) {
+                    Poll::Ready(Ok(())) => {}
+                    Poll::Ready(Err(_)) => panic!("should not be canceled"),
+                    Poll::Pending => return Poll::Pending,
+                }
+                let status = inner.try_wait()?.expect("not ready yet");
+                return Poll::Ready(Ok(status));
+            }
+
+            if let Some(e) = inner.try_wait()? {
+                return Poll::Ready(Ok(e));
+            }
+            let (tx, rx) = oneshot::channel();
+            let ptr = Box::into_raw(Box::new(Some(tx)));
+            let mut wait_object = ptr::null_mut();
+            let rc = unsafe {
+                RegisterWaitForSingleObject(
+                    &mut wait_object,
+                    inner.child.as_raw_handle(),
+                    Some(callback),
+                    ptr as *mut _,
+                    INFINITE,
+                    WT_EXECUTEINWAITTHREAD | WT_EXECUTEONLYONCE,
+                )
+            };
+            if rc == 0 {
+                let err = io::Error::last_os_error();
+                drop(unsafe { Box::from_raw(ptr) });
+                return Poll::Ready(Err(err));
+            }
+            inner.waiting = Some(Waiting {
+                rx,
+                wait_object,
+                tx: ptr,
+            });
+        }
+    }
+}
+
+impl AsRawHandle for Child {
+    fn as_raw_handle(&self) -> RawHandle {
+        self.child.as_raw_handle()
+    }
+}
+
+impl Drop for Waiting {
+    fn drop(&mut self) {
+        unsafe {
+            let rc = UnregisterWaitEx(self.wait_object, INVALID_HANDLE_VALUE);
+            if rc == 0 {
+                panic!("failed to unregister: {}", io::Error::last_os_error());
+            }
+            drop(Box::from_raw(self.tx));
+        }
+    }
+}
+
+unsafe extern "system" fn callback(ptr: PVOID, _timer_fired: BOOLEAN) {
+    let complete = &mut *(ptr as *mut Option<oneshot::Sender<()>>);
+    let _ = complete.take().unwrap().send(());
+}
+
+pub(crate) type ChildStdio = PollEvented<NamedPipe>;
+
+pub(super) fn stdio<T>(io: T) -> io::Result<PollEvented<NamedPipe>>
+where
+    T: IntoRawHandle,
+{
+    let pipe = unsafe { NamedPipe::from_raw_handle(io.into_raw_handle()) };
+    PollEvented::new(pipe)
+}
+
+pub(crate) fn convert_to_stdio(io: PollEvented<NamedPipe>) -> io::Result<Stdio> {
+    let named_pipe = io.into_inner()?;
+
+    // Mio does not implement `IntoRawHandle` for `NamedPipe`, so we'll manually
+    // duplicate the handle here...
+    unsafe {
+        let mut dup_handle = INVALID_HANDLE_VALUE;
+        let cur_proc = GetCurrentProcess();
+
+        let status = DuplicateHandle(
+            cur_proc,
+            named_pipe.as_raw_handle(),
+            cur_proc,
+            &mut dup_handle,
+            0 as DWORD,
+            FALSE,
+            DUPLICATE_SAME_ACCESS,
+        );
+
+        if status == 0 {
+            return Err(io::Error::last_os_error());
+        }
+
+        Ok(Stdio::from_raw_handle(dup_handle))
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/basic_scheduler.rs b/third_party/rust/tokio/src/runtime/basic_scheduler.rs
new file mode 100644
index 0000000000..401f55b3f2
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/basic_scheduler.rs
@@ -0,0 +1,574 @@
+use crate::future::poll_fn;
+use crate::loom::sync::atomic::AtomicBool;
+use crate::loom::sync::{Arc, Mutex};
+use crate::park::{Park, Unpark};
+use crate::runtime::context::EnterGuard;
+use crate::runtime::driver::Driver;
+use crate::runtime::task::{self, JoinHandle, OwnedTasks, Schedule, Task};
+use crate::runtime::Callback;
+use crate::runtime::{MetricsBatch, SchedulerMetrics, WorkerMetrics};
+use crate::sync::notify::Notify;
+use crate::util::atomic_cell::AtomicCell;
+use crate::util::{waker_ref, Wake, WakerRef};
+
+use std::cell::RefCell;
+use std::collections::VecDeque;
+use std::fmt;
+use std::future::Future;
+use std::sync::atomic::Ordering::{AcqRel, Release};
+use std::task::Poll::{Pending, Ready};
+use std::time::Duration;
+
+/// Executes tasks on the current thread
+pub(crate) struct BasicScheduler {
+    /// Core scheduler data is acquired by a thread entering `block_on`.
+    core: AtomicCell<Core>,
+
+    /// Notifier for waking up other threads to steal the
+    /// driver.
+    notify: Notify,
+
+    /// Sendable task spawner
+    spawner: Spawner,
+
+    /// This is usually None, but right before dropping the BasicScheduler, it
+    /// is changed to `Some` with the context being the runtime's own context.
+    /// This ensures that any tasks dropped in the `BasicScheduler`s destructor
+    /// run in that runtime's context.
+    context_guard: Option<EnterGuard>,
+}
+
+/// Data required for executing the scheduler. The struct is passed around to
+/// a function that will perform the scheduling work and acts as a capability token.
+struct Core {
+    /// Scheduler run queue
+    tasks: VecDeque<task::Notified<Arc<Shared>>>,
+
+    /// Sendable task spawner
+    spawner: Spawner,
+
+    /// Current tick
+    tick: u8,
+
+    /// Runtime driver
+    ///
+    /// The driver is removed before starting to park the thread
+    driver: Option<Driver>,
+
+    /// Metrics batch
+    metrics: MetricsBatch,
+}
+
+#[derive(Clone)]
+pub(crate) struct Spawner {
+    shared: Arc<Shared>,
+}
+
+/// Scheduler state shared between threads.
+struct Shared {
+    /// Remote run queue. None if the `Runtime` has been dropped.
+    queue: Mutex<Option<VecDeque<task::Notified<Arc<Shared>>>>>,
+
+    /// Collection of all active tasks spawned onto this executor.
+    owned: OwnedTasks<Arc<Shared>>,
+
+    /// Unpark the blocked thread.
+    unpark: <Driver as Park>::Unpark,
+
+    /// Indicates whether the blocked on thread was woken.
+    woken: AtomicBool,
+
+    /// Callback for a worker parking itself
+    before_park: Option<Callback>,
+
+    /// Callback for a worker unparking itself
+    after_unpark: Option<Callback>,
+
+    /// Keeps track of various runtime metrics.
+    scheduler_metrics: SchedulerMetrics,
+
+    /// This scheduler only has one worker.
+    worker_metrics: WorkerMetrics,
+}
+
+/// Thread-local context.
+struct Context {
+    /// Handle to the spawner
+    spawner: Spawner,
+
+    /// Scheduler core, enabling the holder of `Context` to execute the
+    /// scheduler.
+    core: RefCell<Option<Box<Core>>>,
+}
+
+/// Initial queue capacity.
+const INITIAL_CAPACITY: usize = 64;
+
+/// Max number of tasks to poll per tick.
+#[cfg(loom)]
+const MAX_TASKS_PER_TICK: usize = 4;
+#[cfg(not(loom))]
+const MAX_TASKS_PER_TICK: usize = 61;
+
+/// How often to check the remote queue first.
+const REMOTE_FIRST_INTERVAL: u8 = 31;
+
+// Tracks the current BasicScheduler.
+scoped_thread_local!(static CURRENT: Context);
+
+impl BasicScheduler {
+    pub(crate) fn new(
+        driver: Driver,
+        before_park: Option<Callback>,
+        after_unpark: Option<Callback>,
+    ) -> BasicScheduler {
+        let unpark = driver.unpark();
+
+        let spawner = Spawner {
+            shared: Arc::new(Shared {
+                queue: Mutex::new(Some(VecDeque::with_capacity(INITIAL_CAPACITY))),
+                owned: OwnedTasks::new(),
+                unpark,
+                woken: AtomicBool::new(false),
+                before_park,
+                after_unpark,
+                scheduler_metrics: SchedulerMetrics::new(),
+                worker_metrics: WorkerMetrics::new(),
+            }),
+        };
+
+        let core = AtomicCell::new(Some(Box::new(Core {
+            tasks: VecDeque::with_capacity(INITIAL_CAPACITY),
+            spawner: spawner.clone(),
+            tick: 0,
+            driver: Some(driver),
+            metrics: MetricsBatch::new(),
+        })));
+
+        BasicScheduler {
+            core,
+            notify: Notify::new(),
+            spawner,
+            context_guard: None,
+        }
+    }
+
+    pub(crate) fn spawner(&self) -> &Spawner {
+        &self.spawner
+    }
+
+    pub(crate) fn block_on<F: Future>(&self, future: F) -> F::Output {
+        pin!(future);
+
+        // Attempt to steal the scheduler core and block_on the future if we can
+        // there, otherwise, lets select on a notification that the core is
+        // available or the future is complete.
+        loop {
+            if let Some(core) = self.take_core() {
+                return core.block_on(future);
+            } else {
+                let mut enter = crate::runtime::enter(false);
+
+                let notified = self.notify.notified();
+                pin!(notified);
+
+                if let Some(out) = enter
+                    .block_on(poll_fn(|cx| {
+                        if notified.as_mut().poll(cx).is_ready() {
+                            return Ready(None);
+                        }
+
+                        if let Ready(out) = future.as_mut().poll(cx) {
+                            return Ready(Some(out));
+                        }
+
+                        Pending
+                    }))
+                    .expect("Failed to `Enter::block_on`")
+                {
+                    return out;
+                }
+            }
+        }
+    }
+
+    fn take_core(&self) -> Option<CoreGuard<'_>> {
+        let core = self.core.take()?;
+
+        Some(CoreGuard {
+            context: Context {
+                spawner: self.spawner.clone(),
+                core: RefCell::new(Some(core)),
+            },
+            basic_scheduler: self,
+        })
+    }
+
+    pub(super) fn set_context_guard(&mut self, guard: EnterGuard) {
+        self.context_guard = Some(guard);
+    }
+}
+
+impl Drop for BasicScheduler {
+    fn drop(&mut self) {
+        // Avoid a double panic if we are currently panicking and
+        // the lock may be poisoned.
+
+        let core = match self.take_core() {
+            Some(core) => core,
+            None if std::thread::panicking() => return,
+            None => panic!("Oh no! We never placed the Core back, this is a bug!"),
+        };
+
+        core.enter(|mut core, context| {
+            // Drain the OwnedTasks collection. This call also closes the
+            // collection, ensuring that no tasks are ever pushed after this
+            // call returns.
+            context.spawner.shared.owned.close_and_shutdown_all();
+
+            // Drain local queue
+            // We already shut down every task, so we just need to drop the task.
+            while let Some(task) = core.pop_task() {
+                drop(task);
+            }
+
+            // Drain remote queue and set it to None
+            let remote_queue = core.spawner.shared.queue.lock().take();
+
+            // Using `Option::take` to replace the shared queue with `None`.
+            // We already shut down every task, so we just need to drop the task.
+            if let Some(remote_queue) = remote_queue {
+                for task in remote_queue {
+                    drop(task);
+                }
+            }
+
+            assert!(context.spawner.shared.owned.is_empty());
+
+            // Submit metrics
+            core.metrics.submit(&core.spawner.shared.worker_metrics);
+
+            (core, ())
+        });
+    }
+}
+
+impl fmt::Debug for BasicScheduler {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("BasicScheduler").finish()
+    }
+}
+
+// ===== impl Core =====
+
+impl Core {
+    fn pop_task(&mut self) -> Option<task::Notified<Arc<Shared>>> {
+        let ret = self.tasks.pop_front();
+        self.spawner
+            .shared
+            .worker_metrics
+            .set_queue_depth(self.tasks.len());
+        ret
+    }
+
+    fn push_task(&mut self, task: task::Notified<Arc<Shared>>) {
+        self.tasks.push_back(task);
+        self.metrics.inc_local_schedule_count();
+        self.spawner
+            .shared
+            .worker_metrics
+            .set_queue_depth(self.tasks.len());
+    }
+}
+
+// ===== impl Context =====
+
+impl Context {
+    /// Execute the closure with the given scheduler core stored in the
+    /// thread-local context.
+    fn run_task<R>(&self, mut core: Box<Core>, f: impl FnOnce() -> R) -> (Box<Core>, R) {
+        core.metrics.incr_poll_count();
+        self.enter(core, || crate::coop::budget(f))
+    }
+
+    /// Blocks the current thread until an event is received by the driver,
+    /// including I/O events, timer events, ...
+    fn park(&self, mut core: Box<Core>) -> Box<Core> {
+        let mut driver = core.driver.take().expect("driver missing");
+
+        if let Some(f) = &self.spawner.shared.before_park {
+            // Incorrect lint, the closures are actually different types so `f`
+            // cannot be passed as an argument to `enter`.
+            #[allow(clippy::redundant_closure)]
+            let (c, _) = self.enter(core, || f());
+            core = c;
+        }
+
+        // This check will fail if `before_park` spawns a task for us to run
+        // instead of parking the thread
+        if core.tasks.is_empty() {
+            // Park until the thread is signaled
+            core.metrics.about_to_park();
+            core.metrics.submit(&core.spawner.shared.worker_metrics);
+
+            let (c, _) = self.enter(core, || {
+                driver.park().expect("failed to park");
+            });
+
+            core = c;
+            core.metrics.returned_from_park();
+        }
+
+        if let Some(f) = &self.spawner.shared.after_unpark {
+            // Incorrect lint, the closures are actually different types so `f`
+            // cannot be passed as an argument to `enter`.
+            #[allow(clippy::redundant_closure)]
+            let (c, _) = self.enter(core, || f());
+            core = c;
+        }
+
+        core.driver = Some(driver);
+        core
+    }
+
+    /// Checks the driver for new events without blocking the thread.
+    fn park_yield(&self, mut core: Box<Core>) -> Box<Core> {
+        let mut driver = core.driver.take().expect("driver missing");
+
+        core.metrics.submit(&core.spawner.shared.worker_metrics);
+        let (mut core, _) = self.enter(core, || {
+            driver
+                .park_timeout(Duration::from_millis(0))
+                .expect("failed to park");
+        });
+
+        core.driver = Some(driver);
+        core
+    }
+
+    fn enter<R>(&self, core: Box<Core>, f: impl FnOnce() -> R) -> (Box<Core>, R) {
+        // Store the scheduler core in the thread-local context
+        //
+        // A drop-guard is employed at a higher level.
+        *self.core.borrow_mut() = Some(core);
+
+        // Execute the closure while tracking the execution budget
+        let ret = f();
+
+        // Take the scheduler core back
+        let core = self.core.borrow_mut().take().expect("core missing");
+        (core, ret)
+    }
+}
+
+// ===== impl Spawner =====
+
+impl Spawner {
+    /// Spawns a future onto the basic scheduler
+    pub(crate) fn spawn<F>(&self, future: F) -> JoinHandle<F::Output>
+    where
+        F: crate::future::Future + Send + 'static,
+        F::Output: Send + 'static,
+    {
+        let (handle, notified) = self.shared.owned.bind(future, self.shared.clone());
+
+        if let Some(notified) = notified {
+            self.shared.schedule(notified);
+        }
+
+        handle
+    }
+
+    fn pop(&self) -> Option<task::Notified<Arc<Shared>>> {
+        match self.shared.queue.lock().as_mut() {
+            Some(queue) => queue.pop_front(),
+            None => None,
+        }
+    }
+
+    fn waker_ref(&self) -> WakerRef<'_> {
+        // Set woken to true when enter block_on, ensure outer future
+        // be polled for the first time when enter loop
+        self.shared.woken.store(true, Release);
+        waker_ref(&self.shared)
+    }
+
+    // reset woken to false and return original value
+    pub(crate) fn reset_woken(&self) -> bool {
+        self.shared.woken.swap(false, AcqRel)
+    }
+}
+
+cfg_metrics! {
+    impl Spawner {
+        pub(crate) fn scheduler_metrics(&self) -> &SchedulerMetrics {
+            &self.shared.scheduler_metrics
+        }
+
+        pub(crate) fn injection_queue_depth(&self) -> usize {
+            // TODO: avoid having to lock. The multi-threaded injection queue
+            // could probably be used here.
+            self.shared.queue.lock()
+                .as_ref()
+                .map(|queue| queue.len())
+                .unwrap_or(0)
+        }
+
+        pub(crate) fn worker_metrics(&self, worker: usize) -> &WorkerMetrics {
+            assert_eq!(0, worker);
+            &self.shared.worker_metrics
+        }
+    }
+}
+
+impl fmt::Debug for Spawner {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Spawner").finish()
+    }
+}
+
+// ===== impl Shared =====
+
+impl Schedule for Arc<Shared> {
+    fn release(&self, task: &Task<Self>) -> Option<Task<Self>> {
+        self.owned.remove(task)
+    }
+
+    fn schedule(&self, task: task::Notified<Self>) {
+        CURRENT.with(|maybe_cx| match maybe_cx {
+            Some(cx) if Arc::ptr_eq(self, &cx.spawner.shared) => {
+                let mut core = cx.core.borrow_mut();
+
+                // If `None`, the runtime is shutting down, so there is no need
+                // to schedule the task.
+                if let Some(core) = core.as_mut() {
+                    core.push_task(task);
+                }
+            }
+            _ => {
+                // Track that a task was scheduled from **outside** of the runtime.
+                self.scheduler_metrics.inc_remote_schedule_count();
+
+                // If the queue is None, then the runtime has shut down. We
+                // don't need to do anything with the notification in that case.
+                let mut guard = self.queue.lock();
+                if let Some(queue) = guard.as_mut() {
+                    queue.push_back(task);
+                    drop(guard);
+                    self.unpark.unpark();
+                }
+            }
+        });
+    }
+}
+
+impl Wake for Shared {
+    fn wake(arc_self: Arc<Self>) {
+        Wake::wake_by_ref(&arc_self)
+    }
+
+    /// Wake by reference
+    fn wake_by_ref(arc_self: &Arc<Self>) {
+        arc_self.woken.store(true, Release);
+        arc_self.unpark.unpark();
+    }
+}
+
+// ===== CoreGuard =====
+
+/// Used to ensure we always place the `Core` value back into its slot in
+/// `BasicScheduler`, even if the future panics.
+struct CoreGuard<'a> {
+    context: Context,
+    basic_scheduler: &'a BasicScheduler,
+}
+
+impl CoreGuard<'_> {
+    fn block_on<F: Future>(self, future: F) -> F::Output {
+        self.enter(|mut core, context| {
+            let _enter = crate::runtime::enter(false);
+            let waker = context.spawner.waker_ref();
+            let mut cx = std::task::Context::from_waker(&waker);
+
+            pin!(future);
+
+            'outer: loop {
+                if core.spawner.reset_woken() {
+                    let (c, res) = context.enter(core, || {
+                        crate::coop::budget(|| future.as_mut().poll(&mut cx))
+                    });
+
+                    core = c;
+
+                    if let Ready(v) = res {
+                        return (core, v);
+                    }
+                }
+
+                for _ in 0..MAX_TASKS_PER_TICK {
+                    // Get and increment the current tick
+                    let tick = core.tick;
+                    core.tick = core.tick.wrapping_add(1);
+
+                    let entry = if tick % REMOTE_FIRST_INTERVAL == 0 {
+                        core.spawner.pop().or_else(|| core.tasks.pop_front())
+                    } else {
+                        core.tasks.pop_front().or_else(|| core.spawner.pop())
+                    };
+
+                    let task = match entry {
+                        Some(entry) => entry,
+                        None => {
+                            core = context.park(core);
+
+                            // Try polling the `block_on` future next
+                            continue 'outer;
+                        }
+                    };
+
+                    let task = context.spawner.shared.owned.assert_owner(task);
+
+                    let (c, _) = context.run_task(core, || {
+                        task.run();
+                    });
+
+                    core = c;
+                }
+
+                // Yield to the driver, this drives the timer and pulls any
+                // pending I/O events.
+                core = context.park_yield(core);
+            }
+        })
+    }
+
+    /// Enters the scheduler context. This sets the queue and other necessary
+    /// scheduler state in the thread-local.
+    fn enter<F, R>(self, f: F) -> R
+    where
+        F: FnOnce(Box<Core>, &Context) -> (Box<Core>, R),
+    {
+        // Remove `core` from `context` to pass into the closure.
+        let core = self.context.core.borrow_mut().take().expect("core missing");
+
+        // Call the closure and place `core` back
+        let (core, ret) = CURRENT.set(&self.context, || f(core, &self.context));
+
+        *self.context.core.borrow_mut() = Some(core);
+
+        ret
+    }
+}
+
+impl Drop for CoreGuard<'_> {
+    fn drop(&mut self) {
+        if let Some(core) = self.context.core.borrow_mut().take() {
+            // Replace old scheduler back into the state to allow
+            // other threads to pick it up and drive it.
+            self.basic_scheduler.core.set(core);
+
+            // Wake up other possible threads that could steal the driver.
+            self.basic_scheduler.notify.notify_one()
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/blocking/mod.rs b/third_party/rust/tokio/src/runtime/blocking/mod.rs
new file mode 100644
index 0000000000..15fe05c9ad
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/blocking/mod.rs
@@ -0,0 +1,48 @@
+//! Abstracts out the APIs necessary to `Runtime` for integrating the blocking
+//! pool. When the `blocking` feature flag is **not** enabled, these APIs are
+//! shells. This isolates the complexity of dealing with conditional
+//! compilation.
+
+mod pool;
+pub(crate) use pool::{spawn_blocking, BlockingPool, Mandatory, Spawner, Task};
+
+cfg_fs! {
+    pub(crate) use pool::spawn_mandatory_blocking;
+}
+
+mod schedule;
+mod shutdown;
+mod task;
+pub(crate) use schedule::NoopSchedule;
+pub(crate) use task::BlockingTask;
+
+use crate::runtime::Builder;
+
+pub(crate) fn create_blocking_pool(builder: &Builder, thread_cap: usize) -> BlockingPool {
+    BlockingPool::new(builder, thread_cap)
+}
+
+/*
+cfg_not_blocking_impl! {
+    use crate::runtime::Builder;
+    use std::time::Duration;
+
+    #[derive(Debug, Clone)]
+    pub(crate) struct BlockingPool {}
+
+    pub(crate) use BlockingPool as Spawner;
+
+    pub(crate) fn create_blocking_pool(_builder: &Builder, _thread_cap: usize) -> BlockingPool {
+        BlockingPool {}
+    }
+
+    impl BlockingPool {
+        pub(crate) fn spawner(&self) -> &BlockingPool {
+            self
+        }
+
+        pub(crate) fn shutdown(&mut self, _duration: Option<Duration>) {
+        }
+    }
+}
+*/
diff --git a/third_party/rust/tokio/src/runtime/blocking/pool.rs b/third_party/rust/tokio/src/runtime/blocking/pool.rs
new file mode 100644
index 0000000000..daf1f63fac
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/blocking/pool.rs
@@ -0,0 +1,396 @@
+//! Thread pool for blocking operations
+
+use crate::loom::sync::{Arc, Condvar, Mutex};
+use crate::loom::thread;
+use crate::runtime::blocking::schedule::NoopSchedule;
+use crate::runtime::blocking::shutdown;
+use crate::runtime::builder::ThreadNameFn;
+use crate::runtime::context;
+use crate::runtime::task::{self, JoinHandle};
+use crate::runtime::{Builder, Callback, Handle};
+
+use std::collections::{HashMap, VecDeque};
+use std::fmt;
+use std::time::Duration;
+
+pub(crate) struct BlockingPool {
+    spawner: Spawner,
+    shutdown_rx: shutdown::Receiver,
+}
+
+#[derive(Clone)]
+pub(crate) struct Spawner {
+    inner: Arc<Inner>,
+}
+
+struct Inner {
+    /// State shared between worker threads.
+    shared: Mutex<Shared>,
+
+    /// Pool threads wait on this.
+    condvar: Condvar,
+
+    /// Spawned threads use this name.
+    thread_name: ThreadNameFn,
+
+    /// Spawned thread stack size.
+    stack_size: Option<usize>,
+
+    /// Call after a thread starts.
+    after_start: Option<Callback>,
+
+    /// Call before a thread stops.
+    before_stop: Option<Callback>,
+
+    // Maximum number of threads.
+    thread_cap: usize,
+
+    // Customizable wait timeout.
+    keep_alive: Duration,
+}
+
+struct Shared {
+    queue: VecDeque<Task>,
+    num_th: usize,
+    num_idle: u32,
+    num_notify: u32,
+    shutdown: bool,
+    shutdown_tx: Option<shutdown::Sender>,
+    /// Prior to shutdown, we clean up JoinHandles by having each timed-out
+    /// thread join on the previous timed-out thread. This is not strictly
+    /// necessary but helps avoid Valgrind false positives, see
+    /// <https://github.com/tokio-rs/tokio/commit/646fbae76535e397ef79dbcaacb945d4c829f666>
+    /// for more information.
+    last_exiting_thread: Option<thread::JoinHandle<()>>,
+    /// This holds the JoinHandles for all running threads; on shutdown, the thread
+    /// calling shutdown handles joining on these.
+    worker_threads: HashMap<usize, thread::JoinHandle<()>>,
+    /// This is a counter used to iterate worker_threads in a consistent order (for loom's
+    /// benefit).
+    worker_thread_index: usize,
+}
+
+pub(crate) struct Task {
+    task: task::UnownedTask<NoopSchedule>,
+    mandatory: Mandatory,
+}
+
+#[derive(PartialEq, Eq)]
+pub(crate) enum Mandatory {
+    #[cfg_attr(not(fs), allow(dead_code))]
+    Mandatory,
+    NonMandatory,
+}
+
+impl Task {
+    pub(crate) fn new(task: task::UnownedTask<NoopSchedule>, mandatory: Mandatory) -> Task {
+        Task { task, mandatory }
+    }
+
+    fn run(self) {
+        self.task.run();
+    }
+
+    fn shutdown_or_run_if_mandatory(self) {
+        match self.mandatory {
+            Mandatory::NonMandatory => self.task.shutdown(),
+            Mandatory::Mandatory => self.task.run(),
+        }
+    }
+}
+
+const KEEP_ALIVE: Duration = Duration::from_secs(10);
+
+/// Runs the provided function on an executor dedicated to blocking operations.
+/// Tasks will be scheduled as non-mandatory, meaning they may not get executed
+/// in case of runtime shutdown.
+pub(crate) fn spawn_blocking<F, R>(func: F) -> JoinHandle<R>
+where
+    F: FnOnce() -> R + Send + 'static,
+    R: Send + 'static,
+{
+    let rt = context::current();
+    rt.spawn_blocking(func)
+}
+
+cfg_fs! {
+    #[cfg_attr(any(
+        all(loom, not(test)), // the function is covered by loom tests
+        test
+    ), allow(dead_code))]
+    /// Runs the provided function on an executor dedicated to blocking
+    /// operations. Tasks will be scheduled as mandatory, meaning they are
+    /// guaranteed to run unless a shutdown is already taking place. In case a
+    /// shutdown is already taking place, `None` will be returned.
+    pub(crate) fn spawn_mandatory_blocking<F, R>(func: F) -> Option<JoinHandle<R>>
+    where
+        F: FnOnce() -> R + Send + 'static,
+        R: Send + 'static,
+    {
+        let rt = context::current();
+        rt.spawn_mandatory_blocking(func)
+    }
+}
+
+// ===== impl BlockingPool =====
+
+impl BlockingPool {
+    pub(crate) fn new(builder: &Builder, thread_cap: usize) -> BlockingPool {
+        let (shutdown_tx, shutdown_rx) = shutdown::channel();
+        let keep_alive = builder.keep_alive.unwrap_or(KEEP_ALIVE);
+
+        BlockingPool {
+            spawner: Spawner {
+                inner: Arc::new(Inner {
+                    shared: Mutex::new(Shared {
+                        queue: VecDeque::new(),
+                        num_th: 0,
+                        num_idle: 0,
+                        num_notify: 0,
+                        shutdown: false,
+                        shutdown_tx: Some(shutdown_tx),
+                        last_exiting_thread: None,
+                        worker_threads: HashMap::new(),
+                        worker_thread_index: 0,
+                    }),
+                    condvar: Condvar::new(),
+                    thread_name: builder.thread_name.clone(),
+                    stack_size: builder.thread_stack_size,
+                    after_start: builder.after_start.clone(),
+                    before_stop: builder.before_stop.clone(),
+                    thread_cap,
+                    keep_alive,
+                }),
+            },
+            shutdown_rx,
+        }
+    }
+
+    pub(crate) fn spawner(&self) -> &Spawner {
+        &self.spawner
+    }
+
+    pub(crate) fn shutdown(&mut self, timeout: Option<Duration>) {
+        let mut shared = self.spawner.inner.shared.lock();
+
+        // The function can be called multiple times. First, by explicitly
+        // calling `shutdown` then by the drop handler calling `shutdown`. This
+        // prevents shutting down twice.
+        if shared.shutdown {
+            return;
+        }
+
+        shared.shutdown = true;
+        shared.shutdown_tx = None;
+        self.spawner.inner.condvar.notify_all();
+
+        let last_exited_thread = std::mem::take(&mut shared.last_exiting_thread);
+        let workers = std::mem::take(&mut shared.worker_threads);
+
+        drop(shared);
+
+        if self.shutdown_rx.wait(timeout) {
+            let _ = last_exited_thread.map(|th| th.join());
+
+            // Loom requires that execution be deterministic, so sort by thread ID before joining.
+            // (HashMaps use a randomly-seeded hash function, so the order is nondeterministic)
+            let mut workers: Vec<(usize, thread::JoinHandle<()>)> = workers.into_iter().collect();
+            workers.sort_by_key(|(id, _)| *id);
+
+            for (_id, handle) in workers.into_iter() {
+                let _ = handle.join();
+            }
+        }
+    }
+}
+
+impl Drop for BlockingPool {
+    fn drop(&mut self) {
+        self.shutdown(None);
+    }
+}
+
+impl fmt::Debug for BlockingPool {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("BlockingPool").finish()
+    }
+}
+
+// ===== impl Spawner =====
+
+impl Spawner {
+    pub(crate) fn spawn(&self, task: Task, rt: &Handle) -> Result<(), ()> {
+        let mut shared = self.inner.shared.lock();
+
+        if shared.shutdown {
+            // Shutdown the task: it's fine to shutdown this task (even if
+            // mandatory) because it was scheduled after the shutdown of the
+            // runtime began.
+            task.task.shutdown();
+
+            // no need to even push this task; it would never get picked up
+            return Err(());
+        }
+
+        shared.queue.push_back(task);
+
+        if shared.num_idle == 0 {
+            // No threads are able to process the task.
+
+            if shared.num_th == self.inner.thread_cap {
+                // At max number of threads
+            } else {
+                shared.num_th += 1;
+                assert!(shared.shutdown_tx.is_some());
+                let shutdown_tx = shared.shutdown_tx.clone();
+
+                if let Some(shutdown_tx) = shutdown_tx {
+                    let id = shared.worker_thread_index;
+                    shared.worker_thread_index += 1;
+
+                    let handle = self.spawn_thread(shutdown_tx, rt, id);
+
+                    shared.worker_threads.insert(id, handle);
+                }
+            }
+        } else {
+            // Notify an idle worker thread. The notification counter
+            // is used to count the needed amount of notifications
+            // exactly. Thread libraries may generate spurious
+            // wakeups, this counter is used to keep us in a
+            // consistent state.
+            shared.num_idle -= 1;
+            shared.num_notify += 1;
+            self.inner.condvar.notify_one();
+        }
+
+        Ok(())
+    }
+
+    fn spawn_thread(
+        &self,
+        shutdown_tx: shutdown::Sender,
+        rt: &Handle,
+        id: usize,
+    ) -> thread::JoinHandle<()> {
+        let mut builder = thread::Builder::new().name((self.inner.thread_name)());
+
+        if let Some(stack_size) = self.inner.stack_size {
+            builder = builder.stack_size(stack_size);
+        }
+
+        let rt = rt.clone();
+
+        builder
+            .spawn(move || {
+                // Only the reference should be moved into the closure
+                let _enter = crate::runtime::context::enter(rt.clone());
+                rt.blocking_spawner.inner.run(id);
+                drop(shutdown_tx);
+            })
+            .expect("OS can't spawn a new worker thread")
+    }
+}
+
+impl Inner {
+    fn run(&self, worker_thread_id: usize) {
+        if let Some(f) = &self.after_start {
+            f()
+        }
+
+        let mut shared = self.shared.lock();
+        let mut join_on_thread = None;
+
+        'main: loop {
+            // BUSY
+            while let Some(task) = shared.queue.pop_front() {
+                drop(shared);
+                task.run();
+
+                shared = self.shared.lock();
+            }
+
+            // IDLE
+            shared.num_idle += 1;
+
+            while !shared.shutdown {
+                let lock_result = self.condvar.wait_timeout(shared, self.keep_alive).unwrap();
+
+                shared = lock_result.0;
+                let timeout_result = lock_result.1;
+
+                if shared.num_notify != 0 {
+                    // We have received a legitimate wakeup,
+                    // acknowledge it by decrementing the counter
+                    // and transition to the BUSY state.
+                    shared.num_notify -= 1;
+                    break;
+                }
+
+                // Even if the condvar "timed out", if the pool is entering the
+                // shutdown phase, we want to perform the cleanup logic.
+                if !shared.shutdown && timeout_result.timed_out() {
+                    // We'll join the prior timed-out thread's JoinHandle after dropping the lock.
+                    // This isn't done when shutting down, because the thread calling shutdown will
+                    // handle joining everything.
+                    let my_handle = shared.worker_threads.remove(&worker_thread_id);
+                    join_on_thread = std::mem::replace(&mut shared.last_exiting_thread, my_handle);
+
+                    break 'main;
+                }
+
+                // Spurious wakeup detected, go back to sleep.
+            }
+
+            if shared.shutdown {
+                // Drain the queue
+                while let Some(task) = shared.queue.pop_front() {
+                    drop(shared);
+
+                    task.shutdown_or_run_if_mandatory();
+
+                    shared = self.shared.lock();
+                }
+
+                // Work was produced, and we "took" it (by decrementing num_notify).
+                // This means that num_idle was decremented once for our wakeup.
+                // But, since we are exiting, we need to "undo" that, as we'll stay idle.
+                shared.num_idle += 1;
+                // NOTE: Technically we should also do num_notify++ and notify again,
+                // but since we're shutting down anyway, that won't be necessary.
+                break;
+            }
+        }
+
+        // Thread exit
+        shared.num_th -= 1;
+
+        // num_idle should now be tracked exactly, panic
+        // with a descriptive message if it is not the
+        // case.
+        shared.num_idle = shared
+            .num_idle
+            .checked_sub(1)
+            .expect("num_idle underflowed on thread exit");
+
+        if shared.shutdown && shared.num_th == 0 {
+            self.condvar.notify_one();
+        }
+
+        drop(shared);
+
+        if let Some(f) = &self.before_stop {
+            f()
+        }
+
+        if let Some(handle) = join_on_thread {
+            let _ = handle.join();
+        }
+    }
+}
+
+impl fmt::Debug for Spawner {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("blocking::Spawner").finish()
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/blocking/schedule.rs b/third_party/rust/tokio/src/runtime/blocking/schedule.rs
new file mode 100644
index 0000000000..54252241d9
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/blocking/schedule.rs
@@ -0,0 +1,19 @@
+use crate::runtime::task::{self, Task};
+
+/// `task::Schedule` implementation that does nothing. This is unique to the
+/// blocking scheduler as tasks scheduled are not really futures but blocking
+/// operations.
+///
+/// We avoid storing the task by forgetting it in `bind` and re-materializing it
+/// in `release.
+pub(crate) struct NoopSchedule;
+
+impl task::Schedule for NoopSchedule {
+    fn release(&self, _task: &Task<Self>) -> Option<Task<Self>> {
+        None
+    }
+
+    fn schedule(&self, _task: task::Notified<Self>) {
+        unreachable!();
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/blocking/shutdown.rs b/third_party/rust/tokio/src/runtime/blocking/shutdown.rs
new file mode 100644
index 0000000000..e6f4674183
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/blocking/shutdown.rs
@@ -0,0 +1,71 @@
+//! A shutdown channel.
+//!
+//! Each worker holds the `Sender` half. When all the `Sender` halves are
+//! dropped, the `Receiver` receives a notification.
+
+use crate::loom::sync::Arc;
+use crate::sync::oneshot;
+
+use std::time::Duration;
+
+#[derive(Debug, Clone)]
+pub(super) struct Sender {
+    _tx: Arc<oneshot::Sender<()>>,
+}
+
+#[derive(Debug)]
+pub(super) struct Receiver {
+    rx: oneshot::Receiver<()>,
+}
+
+pub(super) fn channel() -> (Sender, Receiver) {
+    let (tx, rx) = oneshot::channel();
+    let tx = Sender { _tx: Arc::new(tx) };
+    let rx = Receiver { rx };
+
+    (tx, rx)
+}
+
+impl Receiver {
+    /// Blocks the current thread until all `Sender` handles drop.
+    ///
+    /// If `timeout` is `Some`, the thread is blocked for **at most** `timeout`
+    /// duration. If `timeout` is `None`, then the thread is blocked until the
+    /// shutdown signal is received.
+    ///
+    /// If the timeout has elapsed, it returns `false`, otherwise it returns `true`.
+    pub(crate) fn wait(&mut self, timeout: Option<Duration>) -> bool {
+        use crate::runtime::enter::try_enter;
+
+        if timeout == Some(Duration::from_nanos(0)) {
+            return false;
+        }
+
+        let mut e = match try_enter(false) {
+            Some(enter) => enter,
+            _ => {
+                if std::thread::panicking() {
+                    // Don't panic in a panic
+                    return false;
+                } else {
+                    panic!(
+                        "Cannot drop a runtime in a context where blocking is not allowed. \
+                        This happens when a runtime is dropped from within an asynchronous context."
+                    );
+                }
+            }
+        };
+
+        // The oneshot completes with an Err
+        //
+        // If blocking fails to wait, this indicates a problem parking the
+        // current thread (usually, shutting down a runtime stored in a
+        // thread-local).
+        if let Some(timeout) = timeout {
+            e.block_on_timeout(&mut self.rx, timeout).is_ok()
+        } else {
+            let _ = e.block_on(&mut self.rx);
+            true
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/blocking/task.rs b/third_party/rust/tokio/src/runtime/blocking/task.rs
new file mode 100644
index 0000000000..0b7803a6c0
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/blocking/task.rs
@@ -0,0 +1,44 @@
+use std::future::Future;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+/// Converts a function to a future that completes on poll.
+pub(crate) struct BlockingTask<T> {
+    func: Option<T>,
+}
+
+impl<T> BlockingTask<T> {
+    /// Initializes a new blocking task from the given function.
+    pub(crate) fn new(func: T) -> BlockingTask<T> {
+        BlockingTask { func: Some(func) }
+    }
+}
+
+// The closure `F` is never pinned
+impl<T> Unpin for BlockingTask<T> {}
+
+impl<T, R> Future for BlockingTask<T>
+where
+    T: FnOnce() -> R + Send + 'static,
+    R: Send + 'static,
+{
+    type Output = R;
+
+    fn poll(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<R> {
+        let me = &mut *self;
+        let func = me
+            .func
+            .take()
+            .expect("[internal exception] blocking task ran twice.");
+
+        // This is a little subtle:
+        // For convenience, we'd like _every_ call tokio ever makes to Task::poll() to be budgeted
+        // using coop. However, the way things are currently modeled, even running a blocking task
+        // currently goes through Task::poll(), and so is subject to budgeting. That isn't really
+        // what we want; a blocking task may itself want to run tasks (it might be a Worker!), so
+        // we want it to start without any budgeting.
+        crate::coop::stop();
+
+        Poll::Ready(func())
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/builder.rs b/third_party/rust/tokio/src/runtime/builder.rs
new file mode 100644
index 0000000000..91c365fd51
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/builder.rs
@@ -0,0 +1,718 @@
+use crate::runtime::handle::Handle;
+use crate::runtime::{blocking, driver, Callback, Runtime, Spawner};
+
+use std::fmt;
+use std::io;
+use std::time::Duration;
+
+/// Builds Tokio Runtime with custom configuration values.
+///
+/// Methods can be chained in order to set the configuration values. The
+/// Runtime is constructed by calling [`build`].
+///
+/// New instances of `Builder` are obtained via [`Builder::new_multi_thread`]
+/// or [`Builder::new_current_thread`].
+///
+/// See function level documentation for details on the various configuration
+/// settings.
+///
+/// [`build`]: method@Self::build
+/// [`Builder::new_multi_thread`]: method@Self::new_multi_thread
+/// [`Builder::new_current_thread`]: method@Self::new_current_thread
+///
+/// # Examples
+///
+/// ```
+/// use tokio::runtime::Builder;
+///
+/// fn main() {
+///     // build runtime
+///     let runtime = Builder::new_multi_thread()
+///         .worker_threads(4)
+///         .thread_name("my-custom-name")
+///         .thread_stack_size(3 * 1024 * 1024)
+///         .build()
+///         .unwrap();
+///
+///     // use runtime ...
+/// }
+/// ```
+pub struct Builder {
+    /// Runtime type
+    kind: Kind,
+
+    /// Whether or not to enable the I/O driver
+    enable_io: bool,
+
+    /// Whether or not to enable the time driver
+    enable_time: bool,
+
+    /// Whether or not the clock should start paused.
+    start_paused: bool,
+
+    /// The number of worker threads, used by Runtime.
+    ///
+    /// Only used when not using the current-thread executor.
+    worker_threads: Option<usize>,
+
+    /// Cap on thread usage.
+    max_blocking_threads: usize,
+
+    /// Name fn used for threads spawned by the runtime.
+    pub(super) thread_name: ThreadNameFn,
+
+    /// Stack size used for threads spawned by the runtime.
+    pub(super) thread_stack_size: Option<usize>,
+
+    /// Callback to run after each thread starts.
+    pub(super) after_start: Option<Callback>,
+
+    /// To run before each worker thread stops
+    pub(super) before_stop: Option<Callback>,
+
+    /// To run before each worker thread is parked.
+    pub(super) before_park: Option<Callback>,
+
+    /// To run after each thread is unparked.
+    pub(super) after_unpark: Option<Callback>,
+
+    /// Customizable keep alive timeout for BlockingPool
+    pub(super) keep_alive: Option<Duration>,
+}
+
+pub(crate) type ThreadNameFn = std::sync::Arc<dyn Fn() -> String + Send + Sync + 'static>;
+
+pub(crate) enum Kind {
+    CurrentThread,
+    #[cfg(feature = "rt-multi-thread")]
+    MultiThread,
+}
+
+impl Builder {
+    /// Returns a new builder with the current thread scheduler selected.
+    ///
+    /// Configuration methods can be chained on the return value.
+    ///
+    /// To spawn non-`Send` tasks on the resulting runtime, combine it with a
+    /// [`LocalSet`].
+    ///
+    /// [`LocalSet`]: crate::task::LocalSet
+    pub fn new_current_thread() -> Builder {
+        Builder::new(Kind::CurrentThread)
+    }
+
+    /// Returns a new builder with the multi thread scheduler selected.
+    ///
+    /// Configuration methods can be chained on the return value.
+    #[cfg(feature = "rt-multi-thread")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "rt-multi-thread")))]
+    pub fn new_multi_thread() -> Builder {
+        Builder::new(Kind::MultiThread)
+    }
+
+    /// Returns a new runtime builder initialized with default configuration
+    /// values.
+    ///
+    /// Configuration methods can be chained on the return value.
+    pub(crate) fn new(kind: Kind) -> Builder {
+        Builder {
+            kind,
+
+            // I/O defaults to "off"
+            enable_io: false,
+
+            // Time defaults to "off"
+            enable_time: false,
+
+            // The clock starts not-paused
+            start_paused: false,
+
+            // Default to lazy auto-detection (one thread per CPU core)
+            worker_threads: None,
+
+            max_blocking_threads: 512,
+
+            // Default thread name
+            thread_name: std::sync::Arc::new(|| "tokio-runtime-worker".into()),
+
+            // Do not set a stack size by default
+            thread_stack_size: None,
+
+            // No worker thread callbacks
+            after_start: None,
+            before_stop: None,
+            before_park: None,
+            after_unpark: None,
+
+            keep_alive: None,
+        }
+    }
+
+    /// Enables both I/O and time drivers.
+    ///
+    /// Doing this is a shorthand for calling `enable_io` and `enable_time`
+    /// individually. If additional components are added to Tokio in the future,
+    /// `enable_all` will include these future components.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime;
+    ///
+    /// let rt = runtime::Builder::new_multi_thread()
+    ///     .enable_all()
+    ///     .build()
+    ///     .unwrap();
+    /// ```
+    pub fn enable_all(&mut self) -> &mut Self {
+        #[cfg(any(feature = "net", feature = "process", all(unix, feature = "signal")))]
+        self.enable_io();
+        #[cfg(feature = "time")]
+        self.enable_time();
+
+        self
+    }
+
+    /// Sets the number of worker threads the `Runtime` will use.
+    ///
+    /// This can be any number above 0 though it is advised to keep this value
+    /// on the smaller side.
+    ///
+    /// # Default
+    ///
+    /// The default value is the number of cores available to the system.
+    ///
+    /// # Panic
+    ///
+    /// When using the `current_thread` runtime this method will panic, since
+    /// those variants do not allow setting worker thread counts.
+    ///
+    ///
+    /// # Examples
+    ///
+    /// ## Multi threaded runtime with 4 threads
+    ///
+    /// ```
+    /// use tokio::runtime;
+    ///
+    /// // This will spawn a work-stealing runtime with 4 worker threads.
+    /// let rt = runtime::Builder::new_multi_thread()
+    ///     .worker_threads(4)
+    ///     .build()
+    ///     .unwrap();
+    ///
+    /// rt.spawn(async move {});
+    /// ```
+    ///
+    /// ## Current thread runtime (will only run on the current thread via `Runtime::block_on`)
+    ///
+    /// ```
+    /// use tokio::runtime;
+    ///
+    /// // Create a runtime that _must_ be driven from a call
+    /// // to `Runtime::block_on`.
+    /// let rt = runtime::Builder::new_current_thread()
+    ///     .build()
+    ///     .unwrap();
+    ///
+    /// // This will run the runtime and future on the current thread
+    /// rt.block_on(async move {});
+    /// ```
+    ///
+    /// # Panic
+    ///
+    /// This will panic if `val` is not larger than `0`.
+    pub fn worker_threads(&mut self, val: usize) -> &mut Self {
+        assert!(val > 0, "Worker threads cannot be set to 0");
+        self.worker_threads = Some(val);
+        self
+    }
+
+    /// Specifies the limit for additional threads spawned by the Runtime.
+    ///
+    /// These threads are used for blocking operations like tasks spawned
+    /// through [`spawn_blocking`]. Unlike the [`worker_threads`], they are not
+    /// always active and will exit if left idle for too long. You can change
+    /// this timeout duration with [`thread_keep_alive`].
+    ///
+    /// The default value is 512.
+    ///
+    /// # Panic
+    ///
+    /// This will panic if `val` is not larger than `0`.
+    ///
+    /// # Upgrading from 0.x
+    ///
+    /// In old versions `max_threads` limited both blocking and worker threads, but the
+    /// current `max_blocking_threads` does not include async worker threads in the count.
+    ///
+    /// [`spawn_blocking`]: fn@crate::task::spawn_blocking
+    /// [`worker_threads`]: Self::worker_threads
+    /// [`thread_keep_alive`]: Self::thread_keep_alive
+    #[cfg_attr(docsrs, doc(alias = "max_threads"))]
+    pub fn max_blocking_threads(&mut self, val: usize) -> &mut Self {
+        assert!(val > 0, "Max blocking threads cannot be set to 0");
+        self.max_blocking_threads = val;
+        self
+    }
+
+    /// Sets name of threads spawned by the `Runtime`'s thread pool.
+    ///
+    /// The default name is "tokio-runtime-worker".
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use tokio::runtime;
+    ///
+    /// # pub fn main() {
+    /// let rt = runtime::Builder::new_multi_thread()
+    ///     .thread_name("my-pool")
+    ///     .build();
+    /// # }
+    /// ```
+    pub fn thread_name(&mut self, val: impl Into<String>) -> &mut Self {
+        let val = val.into();
+        self.thread_name = std::sync::Arc::new(move || val.clone());
+        self
+    }
+
+    /// Sets a function used to generate the name of threads spawned by the `Runtime`'s thread pool.
+    ///
+    /// The default name fn is `|| "tokio-runtime-worker".into()`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use tokio::runtime;
+    /// # use std::sync::atomic::{AtomicUsize, Ordering};
+    ///
+    /// # pub fn main() {
+    /// let rt = runtime::Builder::new_multi_thread()
+    ///     .thread_name_fn(|| {
+    ///        static ATOMIC_ID: AtomicUsize = AtomicUsize::new(0);
+    ///        let id = ATOMIC_ID.fetch_add(1, Ordering::SeqCst);
+    ///        format!("my-pool-{}", id)
+    ///     })
+    ///     .build();
+    /// # }
+    /// ```
+    pub fn thread_name_fn<F>(&mut self, f: F) -> &mut Self
+    where
+        F: Fn() -> String + Send + Sync + 'static,
+    {
+        self.thread_name = std::sync::Arc::new(f);
+        self
+    }
+
+    /// Sets the stack size (in bytes) for worker threads.
+    ///
+    /// The actual stack size may be greater than this value if the platform
+    /// specifies minimal stack size.
+    ///
+    /// The default stack size for spawned threads is 2 MiB, though this
+    /// particular stack size is subject to change in the future.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use tokio::runtime;
+    ///
+    /// # pub fn main() {
+    /// let rt = runtime::Builder::new_multi_thread()
+    ///     .thread_stack_size(32 * 1024)
+    ///     .build();
+    /// # }
+    /// ```
+    pub fn thread_stack_size(&mut self, val: usize) -> &mut Self {
+        self.thread_stack_size = Some(val);
+        self
+    }
+
+    /// Executes function `f` after each thread is started but before it starts
+    /// doing work.
+    ///
+    /// This is intended for bookkeeping and monitoring use cases.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use tokio::runtime;
+    ///
+    /// # pub fn main() {
+    /// let runtime = runtime::Builder::new_multi_thread()
+    ///     .on_thread_start(|| {
+    ///         println!("thread started");
+    ///     })
+    ///     .build();
+    /// # }
+    /// ```
+    #[cfg(not(loom))]
+    pub fn on_thread_start<F>(&mut self, f: F) -> &mut Self
+    where
+        F: Fn() + Send + Sync + 'static,
+    {
+        self.after_start = Some(std::sync::Arc::new(f));
+        self
+    }
+
+    /// Executes function `f` before each thread stops.
+    ///
+    /// This is intended for bookkeeping and monitoring use cases.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use tokio::runtime;
+    ///
+    /// # pub fn main() {
+    /// let runtime = runtime::Builder::new_multi_thread()
+    ///     .on_thread_stop(|| {
+    ///         println!("thread stopping");
+    ///     })
+    ///     .build();
+    /// # }
+    /// ```
+    #[cfg(not(loom))]
+    pub fn on_thread_stop<F>(&mut self, f: F) -> &mut Self
+    where
+        F: Fn() + Send + Sync + 'static,
+    {
+        self.before_stop = Some(std::sync::Arc::new(f));
+        self
+    }
+
+    /// Executes function `f` just before a thread is parked (goes idle).
+    /// `f` is called within the Tokio context, so functions like [`tokio::spawn`](crate::spawn)
+    /// can be called, and may result in this thread being unparked immediately.
+    ///
+    /// This can be used to start work only when the executor is idle, or for bookkeeping
+    /// and monitoring purposes.
+    ///
+    /// Note: There can only be one park callback for a runtime; calling this function
+    /// more than once replaces the last callback defined, rather than adding to it.
+    ///
+    /// # Examples
+    ///
+    /// ## Multithreaded executor
+    /// ```
+    /// # use std::sync::Arc;
+    /// # use std::sync::atomic::{AtomicBool, Ordering};
+    /// # use tokio::runtime;
+    /// # use tokio::sync::Barrier;
+    /// # pub fn main() {
+    /// let once = AtomicBool::new(true);
+    /// let barrier = Arc::new(Barrier::new(2));
+    ///
+    /// let runtime = runtime::Builder::new_multi_thread()
+    ///     .worker_threads(1)
+    ///     .on_thread_park({
+    ///         let barrier = barrier.clone();
+    ///         move || {
+    ///             let barrier = barrier.clone();
+    ///             if once.swap(false, Ordering::Relaxed) {
+    ///                 tokio::spawn(async move { barrier.wait().await; });
+    ///            }
+    ///         }
+    ///     })
+    ///     .build()
+    ///     .unwrap();
+    ///
+    /// runtime.block_on(async {
+    ///    barrier.wait().await;
+    /// })
+    /// # }
+    /// ```
+    /// ## Current thread executor
+    /// ```
+    /// # use std::sync::Arc;
+    /// # use std::sync::atomic::{AtomicBool, Ordering};
+    /// # use tokio::runtime;
+    /// # use tokio::sync::Barrier;
+    /// # pub fn main() {
+    /// let once = AtomicBool::new(true);
+    /// let barrier = Arc::new(Barrier::new(2));
+    ///
+    /// let runtime = runtime::Builder::new_current_thread()
+    ///     .on_thread_park({
+    ///         let barrier = barrier.clone();
+    ///         move || {
+    ///             let barrier = barrier.clone();
+    ///             if once.swap(false, Ordering::Relaxed) {
+    ///                 tokio::spawn(async move { barrier.wait().await; });
+    ///            }
+    ///         }
+    ///     })
+    ///     .build()
+    ///     .unwrap();
+    ///
+    /// runtime.block_on(async {
+    ///    barrier.wait().await;
+    /// })
+    /// # }
+    /// ```
+    #[cfg(not(loom))]
+    pub fn on_thread_park<F>(&mut self, f: F) -> &mut Self
+    where
+        F: Fn() + Send + Sync + 'static,
+    {
+        self.before_park = Some(std::sync::Arc::new(f));
+        self
+    }
+
+    /// Executes function `f` just after a thread unparks (starts executing tasks).
+    ///
+    /// This is intended for bookkeeping and monitoring use cases; note that work
+    /// in this callback will increase latencies when the application has allowed one or
+    /// more runtime threads to go idle.
+    ///
+    /// Note: There can only be one unpark callback for a runtime; calling this function
+    /// more than once replaces the last callback defined, rather than adding to it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use tokio::runtime;
+    ///
+    /// # pub fn main() {
+    /// let runtime = runtime::Builder::new_multi_thread()
+    ///     .on_thread_unpark(|| {
+    ///         println!("thread unparking");
+    ///     })
+    ///     .build();
+    ///
+    /// runtime.unwrap().block_on(async {
+    ///    tokio::task::yield_now().await;
+    ///    println!("Hello from Tokio!");
+    /// })
+    /// # }
+    /// ```
+    #[cfg(not(loom))]
+    pub fn on_thread_unpark<F>(&mut self, f: F) -> &mut Self
+    where
+        F: Fn() + Send + Sync + 'static,
+    {
+        self.after_unpark = Some(std::sync::Arc::new(f));
+        self
+    }
+
+    /// Creates the configured `Runtime`.
+    ///
+    /// The returned `Runtime` instance is ready to spawn tasks.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Builder;
+    ///
+    /// let rt  = Builder::new_multi_thread().build().unwrap();
+    ///
+    /// rt.block_on(async {
+    ///     println!("Hello from the Tokio runtime");
+    /// });
+    /// ```
+    pub fn build(&mut self) -> io::Result<Runtime> {
+        match &self.kind {
+            Kind::CurrentThread => self.build_basic_runtime(),
+            #[cfg(feature = "rt-multi-thread")]
+            Kind::MultiThread => self.build_threaded_runtime(),
+        }
+    }
+
+    fn get_cfg(&self) -> driver::Cfg {
+        driver::Cfg {
+            enable_pause_time: match self.kind {
+                Kind::CurrentThread => true,
+                #[cfg(feature = "rt-multi-thread")]
+                Kind::MultiThread => false,
+            },
+            enable_io: self.enable_io,
+            enable_time: self.enable_time,
+            start_paused: self.start_paused,
+        }
+    }
+
+    /// Sets a custom timeout for a thread in the blocking pool.
+    ///
+    /// By default, the timeout for a thread is set to 10 seconds. This can
+    /// be overridden using .thread_keep_alive().
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use tokio::runtime;
+    /// # use std::time::Duration;
+    ///
+    /// # pub fn main() {
+    /// let rt = runtime::Builder::new_multi_thread()
+    ///     .thread_keep_alive(Duration::from_millis(100))
+    ///     .build();
+    /// # }
+    /// ```
+    pub fn thread_keep_alive(&mut self, duration: Duration) -> &mut Self {
+        self.keep_alive = Some(duration);
+        self
+    }
+
+    fn build_basic_runtime(&mut self) -> io::Result<Runtime> {
+        use crate::runtime::{BasicScheduler, Kind};
+
+        let (driver, resources) = driver::Driver::new(self.get_cfg())?;
+
+        // And now put a single-threaded scheduler on top of the timer. When
+        // there are no futures ready to do something, it'll let the timer or
+        // the reactor to generate some new stimuli for the futures to continue
+        // in their life.
+        let scheduler =
+            BasicScheduler::new(driver, self.before_park.clone(), self.after_unpark.clone());
+        let spawner = Spawner::Basic(scheduler.spawner().clone());
+
+        // Blocking pool
+        let blocking_pool = blocking::create_blocking_pool(self, self.max_blocking_threads);
+        let blocking_spawner = blocking_pool.spawner().clone();
+
+        Ok(Runtime {
+            kind: Kind::CurrentThread(scheduler),
+            handle: Handle {
+                spawner,
+                io_handle: resources.io_handle,
+                time_handle: resources.time_handle,
+                signal_handle: resources.signal_handle,
+                clock: resources.clock,
+                blocking_spawner,
+            },
+            blocking_pool,
+        })
+    }
+}
+
+cfg_io_driver! {
+    impl Builder {
+        /// Enables the I/O driver.
+        ///
+        /// Doing this enables using net, process, signal, and some I/O types on
+        /// the runtime.
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// use tokio::runtime;
+        ///
+        /// let rt = runtime::Builder::new_multi_thread()
+        ///     .enable_io()
+        ///     .build()
+        ///     .unwrap();
+        /// ```
+        pub fn enable_io(&mut self) -> &mut Self {
+            self.enable_io = true;
+            self
+        }
+    }
+}
+
+cfg_time! {
+    impl Builder {
+        /// Enables the time driver.
+        ///
+        /// Doing this enables using `tokio::time` on the runtime.
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// use tokio::runtime;
+        ///
+        /// let rt = runtime::Builder::new_multi_thread()
+        ///     .enable_time()
+        ///     .build()
+        ///     .unwrap();
+        /// ```
+        pub fn enable_time(&mut self) -> &mut Self {
+            self.enable_time = true;
+            self
+        }
+    }
+}
+
+cfg_test_util! {
+    impl Builder {
+        /// Controls if the runtime's clock starts paused or advancing.
+        ///
+        /// Pausing time requires the current-thread runtime; construction of
+        /// the runtime will panic otherwise.
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// use tokio::runtime;
+        ///
+        /// let rt = runtime::Builder::new_current_thread()
+        ///     .enable_time()
+        ///     .start_paused(true)
+        ///     .build()
+        ///     .unwrap();
+        /// ```
+        pub fn start_paused(&mut self, start_paused: bool) -> &mut Self {
+            self.start_paused = start_paused;
+            self
+        }
+    }
+}
+
+cfg_rt_multi_thread! {
+    impl Builder {
+        fn build_threaded_runtime(&mut self) -> io::Result<Runtime> {
+            use crate::loom::sys::num_cpus;
+            use crate::runtime::{Kind, ThreadPool};
+            use crate::runtime::park::Parker;
+
+            let core_threads = self.worker_threads.unwrap_or_else(num_cpus);
+
+            let (driver, resources) = driver::Driver::new(self.get_cfg())?;
+
+            let (scheduler, launch) = ThreadPool::new(core_threads, Parker::new(driver), self.before_park.clone(), self.after_unpark.clone());
+            let spawner = Spawner::ThreadPool(scheduler.spawner().clone());
+
+            // Create the blocking pool
+            let blocking_pool = blocking::create_blocking_pool(self, self.max_blocking_threads + core_threads);
+            let blocking_spawner = blocking_pool.spawner().clone();
+
+            // Create the runtime handle
+            let handle = Handle {
+                spawner,
+                io_handle: resources.io_handle,
+                time_handle: resources.time_handle,
+                signal_handle: resources.signal_handle,
+                clock: resources.clock,
+                blocking_spawner,
+            };
+
+            // Spawn the thread pool workers
+            let _enter = crate::runtime::context::enter(handle.clone());
+            launch.launch();
+
+            Ok(Runtime {
+                kind: Kind::ThreadPool(scheduler),
+                handle,
+                blocking_pool,
+            })
+        }
+    }
+}
+
+impl fmt::Debug for Builder {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Builder")
+            .field("worker_threads", &self.worker_threads)
+            .field("max_blocking_threads", &self.max_blocking_threads)
+            .field(
+                "thread_name",
+                &"<dyn Fn() -> String + Send + Sync + 'static>",
+            )
+            .field("thread_stack_size", &self.thread_stack_size)
+            .field("after_start", &self.after_start.as_ref().map(|_| "..."))
+            .field("before_stop", &self.before_stop.as_ref().map(|_| "..."))
+            .field("before_park", &self.before_park.as_ref().map(|_| "..."))
+            .field("after_unpark", &self.after_unpark.as_ref().map(|_| "..."))
+            .finish()
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/context.rs b/third_party/rust/tokio/src/runtime/context.rs
new file mode 100644
index 0000000000..1f44a53402
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/context.rs
@@ -0,0 +1,111 @@
+//! Thread local runtime context
+use crate::runtime::{Handle, TryCurrentError};
+
+use std::cell::RefCell;
+
+thread_local! {
+    static CONTEXT: RefCell<Option<Handle>> = RefCell::new(None)
+}
+
+pub(crate) fn try_current() -> Result<Handle, crate::runtime::TryCurrentError> {
+    match CONTEXT.try_with(|ctx| ctx.borrow().clone()) {
+        Ok(Some(handle)) => Ok(handle),
+        Ok(None) => Err(TryCurrentError::new_no_context()),
+        Err(_access_error) => Err(TryCurrentError::new_thread_local_destroyed()),
+    }
+}
+
+pub(crate) fn current() -> Handle {
+    match try_current() {
+        Ok(handle) => handle,
+        Err(e) => panic!("{}", e),
+    }
+}
+
+cfg_io_driver! {
+    pub(crate) fn io_handle() -> crate::runtime::driver::IoHandle {
+        match CONTEXT.try_with(|ctx| {
+            let ctx = ctx.borrow();
+            ctx.as_ref().expect(crate::util::error::CONTEXT_MISSING_ERROR).io_handle.clone()
+        }) {
+            Ok(io_handle) => io_handle,
+            Err(_) => panic!("{}", crate::util::error::THREAD_LOCAL_DESTROYED_ERROR),
+        }
+    }
+}
+
+cfg_signal_internal! {
+    #[cfg(unix)]
+    pub(crate) fn signal_handle() -> crate::runtime::driver::SignalHandle {
+        match CONTEXT.try_with(|ctx| {
+            let ctx = ctx.borrow();
+            ctx.as_ref().expect(crate::util::error::CONTEXT_MISSING_ERROR).signal_handle.clone()
+        }) {
+            Ok(signal_handle) => signal_handle,
+            Err(_) => panic!("{}", crate::util::error::THREAD_LOCAL_DESTROYED_ERROR),
+        }
+    }
+}
+
+cfg_time! {
+    pub(crate) fn time_handle() -> crate::runtime::driver::TimeHandle {
+        match CONTEXT.try_with(|ctx| {
+            let ctx = ctx.borrow();
+            ctx.as_ref().expect(crate::util::error::CONTEXT_MISSING_ERROR).time_handle.clone()
+        }) {
+            Ok(time_handle) => time_handle,
+            Err(_) => panic!("{}", crate::util::error::THREAD_LOCAL_DESTROYED_ERROR),
+        }
+    }
+
+    cfg_test_util! {
+        pub(crate) fn clock() -> Option<crate::runtime::driver::Clock> {
+            match CONTEXT.try_with(|ctx| (*ctx.borrow()).as_ref().map(|ctx| ctx.clock.clone())) {
+                Ok(clock) => clock,
+                Err(_) => panic!("{}", crate::util::error::THREAD_LOCAL_DESTROYED_ERROR),
+            }
+        }
+    }
+}
+
+cfg_rt! {
+    pub(crate) fn spawn_handle() -> Option<crate::runtime::Spawner> {
+        match CONTEXT.try_with(|ctx| (*ctx.borrow()).as_ref().map(|ctx| ctx.spawner.clone())) {
+            Ok(spawner) => spawner,
+            Err(_) => panic!("{}", crate::util::error::THREAD_LOCAL_DESTROYED_ERROR),
+        }
+    }
+}
+
+/// Sets this [`Handle`] as the current active [`Handle`].
+///
+/// [`Handle`]: Handle
+pub(crate) fn enter(new: Handle) -> EnterGuard {
+    match try_enter(new) {
+        Some(guard) => guard,
+        None => panic!("{}", crate::util::error::THREAD_LOCAL_DESTROYED_ERROR),
+    }
+}
+
+/// Sets this [`Handle`] as the current active [`Handle`].
+///
+/// [`Handle`]: Handle
+pub(crate) fn try_enter(new: Handle) -> Option<EnterGuard> {
+    CONTEXT
+        .try_with(|ctx| {
+            let old = ctx.borrow_mut().replace(new);
+            EnterGuard(old)
+        })
+        .ok()
+}
+
+#[derive(Debug)]
+pub(crate) struct EnterGuard(Option<Handle>);
+
+impl Drop for EnterGuard {
+    fn drop(&mut self) {
+        CONTEXT.with(|ctx| {
+            *ctx.borrow_mut() = self.0.take();
+        });
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/driver.rs b/third_party/rust/tokio/src/runtime/driver.rs
new file mode 100644
index 0000000000..7e459779bb
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/driver.rs
@@ -0,0 +1,208 @@
+//! Abstracts out the entire chain of runtime sub-drivers into common types.
+use crate::park::thread::ParkThread;
+use crate::park::Park;
+
+use std::io;
+use std::time::Duration;
+
+// ===== io driver =====
+
+cfg_io_driver! {
+    type IoDriver = crate::io::driver::Driver;
+    type IoStack = crate::park::either::Either<ProcessDriver, ParkThread>;
+    pub(crate) type IoHandle = Option<crate::io::driver::Handle>;
+
+    fn create_io_stack(enabled: bool) -> io::Result<(IoStack, IoHandle, SignalHandle)> {
+        use crate::park::either::Either;
+
+        #[cfg(loom)]
+        assert!(!enabled);
+
+        let ret = if enabled {
+            let io_driver = crate::io::driver::Driver::new()?;
+            let io_handle = io_driver.handle();
+
+            let (signal_driver, signal_handle) = create_signal_driver(io_driver)?;
+            let process_driver = create_process_driver(signal_driver);
+
+            (Either::A(process_driver), Some(io_handle), signal_handle)
+        } else {
+            (Either::B(ParkThread::new()), Default::default(), Default::default())
+        };
+
+        Ok(ret)
+    }
+}
+
+cfg_not_io_driver! {
+    pub(crate) type IoHandle = ();
+    type IoStack = ParkThread;
+
+    fn create_io_stack(_enabled: bool) -> io::Result<(IoStack, IoHandle, SignalHandle)> {
+        Ok((ParkThread::new(), Default::default(), Default::default()))
+    }
+}
+
+// ===== signal driver =====
+
+macro_rules! cfg_signal_internal_and_unix {
+    ($($item:item)*) => {
+        #[cfg(unix)]
+        cfg_signal_internal! { $($item)* }
+    }
+}
+
+cfg_signal_internal_and_unix! {
+    type SignalDriver = crate::signal::unix::driver::Driver;
+    pub(crate) type SignalHandle = Option<crate::signal::unix::driver::Handle>;
+
+    fn create_signal_driver(io_driver: IoDriver) -> io::Result<(SignalDriver, SignalHandle)> {
+        let driver = crate::signal::unix::driver::Driver::new(io_driver)?;
+        let handle = driver.handle();
+        Ok((driver, Some(handle)))
+    }
+}
+
+cfg_not_signal_internal! {
+    pub(crate) type SignalHandle = ();
+
+    cfg_io_driver! {
+        type SignalDriver = IoDriver;
+
+        fn create_signal_driver(io_driver: IoDriver) -> io::Result<(SignalDriver, SignalHandle)> {
+            Ok((io_driver, ()))
+        }
+    }
+}
+
+// ===== process driver =====
+
+cfg_process_driver! {
+    type ProcessDriver = crate::process::unix::driver::Driver;
+
+    fn create_process_driver(signal_driver: SignalDriver) -> ProcessDriver {
+        crate::process::unix::driver::Driver::new(signal_driver)
+    }
+}
+
+cfg_not_process_driver! {
+    cfg_io_driver! {
+        type ProcessDriver = SignalDriver;
+
+        fn create_process_driver(signal_driver: SignalDriver) -> ProcessDriver {
+            signal_driver
+        }
+    }
+}
+
+// ===== time driver =====
+
+cfg_time! {
+    type TimeDriver = crate::park::either::Either<crate::time::driver::Driver<IoStack>, IoStack>;
+
+    pub(crate) type Clock = crate::time::Clock;
+    pub(crate) type TimeHandle = Option<crate::time::driver::Handle>;
+
+    fn create_clock(enable_pausing: bool, start_paused: bool) -> Clock {
+        crate::time::Clock::new(enable_pausing, start_paused)
+    }
+
+    fn create_time_driver(
+        enable: bool,
+        io_stack: IoStack,
+        clock: Clock,
+    ) -> (TimeDriver, TimeHandle) {
+        use crate::park::either::Either;
+
+        if enable {
+            let driver = crate::time::driver::Driver::new(io_stack, clock);
+            let handle = driver.handle();
+
+            (Either::A(driver), Some(handle))
+        } else {
+            (Either::B(io_stack), None)
+        }
+    }
+}
+
+cfg_not_time! {
+    type TimeDriver = IoStack;
+
+    pub(crate) type Clock = ();
+    pub(crate) type TimeHandle = ();
+
+    fn create_clock(_enable_pausing: bool, _start_paused: bool) -> Clock {
+        ()
+    }
+
+    fn create_time_driver(
+        _enable: bool,
+        io_stack: IoStack,
+        _clock: Clock,
+    ) -> (TimeDriver, TimeHandle) {
+        (io_stack, ())
+    }
+}
+
+// ===== runtime driver =====
+
+#[derive(Debug)]
+pub(crate) struct Driver {
+    inner: TimeDriver,
+}
+
+pub(crate) struct Resources {
+    pub(crate) io_handle: IoHandle,
+    pub(crate) signal_handle: SignalHandle,
+    pub(crate) time_handle: TimeHandle,
+    pub(crate) clock: Clock,
+}
+
+pub(crate) struct Cfg {
+    pub(crate) enable_io: bool,
+    pub(crate) enable_time: bool,
+    pub(crate) enable_pause_time: bool,
+    pub(crate) start_paused: bool,
+}
+
+impl Driver {
+    pub(crate) fn new(cfg: Cfg) -> io::Result<(Self, Resources)> {
+        let (io_stack, io_handle, signal_handle) = create_io_stack(cfg.enable_io)?;
+
+        let clock = create_clock(cfg.enable_pause_time, cfg.start_paused);
+
+        let (time_driver, time_handle) =
+            create_time_driver(cfg.enable_time, io_stack, clock.clone());
+
+        Ok((
+            Self { inner: time_driver },
+            Resources {
+                io_handle,
+                signal_handle,
+                time_handle,
+                clock,
+            },
+        ))
+    }
+}
+
+impl Park for Driver {
+    type Unpark = <TimeDriver as Park>::Unpark;
+    type Error = <TimeDriver as Park>::Error;
+
+    fn unpark(&self) -> Self::Unpark {
+        self.inner.unpark()
+    }
+
+    fn park(&mut self) -> Result<(), Self::Error> {
+        self.inner.park()
+    }
+
+    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
+        self.inner.park_timeout(duration)
+    }
+
+    fn shutdown(&mut self) {
+        self.inner.shutdown()
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/enter.rs b/third_party/rust/tokio/src/runtime/enter.rs
new file mode 100644
index 0000000000..3f14cb5878
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/enter.rs
@@ -0,0 +1,205 @@
+use std::cell::{Cell, RefCell};
+use std::fmt;
+use std::marker::PhantomData;
+
+#[derive(Debug, Clone, Copy)]
+pub(crate) enum EnterContext {
+    #[cfg_attr(not(feature = "rt"), allow(dead_code))]
+    Entered {
+        allow_blocking: bool,
+    },
+    NotEntered,
+}
+
+impl EnterContext {
+    pub(crate) fn is_entered(self) -> bool {
+        matches!(self, EnterContext::Entered { .. })
+    }
+}
+
+thread_local!(static ENTERED: Cell<EnterContext> = Cell::new(EnterContext::NotEntered));
+
+/// Represents an executor context.
+pub(crate) struct Enter {
+    _p: PhantomData<RefCell<()>>,
+}
+
+cfg_rt! {
+    use crate::park::thread::ParkError;
+
+    use std::time::Duration;
+
+    /// Marks the current thread as being within the dynamic extent of an
+    /// executor.
+    pub(crate) fn enter(allow_blocking: bool) -> Enter {
+        if let Some(enter) = try_enter(allow_blocking) {
+            return enter;
+        }
+
+        panic!(
+            "Cannot start a runtime from within a runtime. This happens \
+            because a function (like `block_on`) attempted to block the \
+            current thread while the thread is being used to drive \
+            asynchronous tasks."
+        );
+    }
+
+    /// Tries to enter a runtime context, returns `None` if already in a runtime
+    /// context.
+    pub(crate) fn try_enter(allow_blocking: bool) -> Option<Enter> {
+        ENTERED.with(|c| {
+            if c.get().is_entered() {
+                None
+            } else {
+                c.set(EnterContext::Entered { allow_blocking });
+                Some(Enter { _p: PhantomData })
+            }
+        })
+    }
+}
+
+// Forces the current "entered" state to be cleared while the closure
+// is executed.
+//
+// # Warning
+//
+// This is hidden for a reason. Do not use without fully understanding
+// executors. Misusing can easily cause your program to deadlock.
+cfg_rt_multi_thread! {
+    pub(crate) fn exit<F: FnOnce() -> R, R>(f: F) -> R {
+        // Reset in case the closure panics
+        struct Reset(EnterContext);
+        impl Drop for Reset {
+            fn drop(&mut self) {
+                ENTERED.with(|c| {
+                    assert!(!c.get().is_entered(), "closure claimed permanent executor");
+                    c.set(self.0);
+                });
+            }
+        }
+
+        let was = ENTERED.with(|c| {
+            let e = c.get();
+            assert!(e.is_entered(), "asked to exit when not entered");
+            c.set(EnterContext::NotEntered);
+            e
+        });
+
+        let _reset = Reset(was);
+        // dropping _reset after f() will reset ENTERED
+        f()
+    }
+}
+
+cfg_rt! {
+    /// Disallows blocking in the current runtime context until the guard is dropped.
+    pub(crate) fn disallow_blocking() -> DisallowBlockingGuard {
+        let reset = ENTERED.with(|c| {
+            if let EnterContext::Entered {
+                allow_blocking: true,
+            } = c.get()
+            {
+                c.set(EnterContext::Entered {
+                    allow_blocking: false,
+                });
+                true
+            } else {
+                false
+            }
+        });
+        DisallowBlockingGuard(reset)
+    }
+
+    pub(crate) struct DisallowBlockingGuard(bool);
+    impl Drop for DisallowBlockingGuard {
+        fn drop(&mut self) {
+            if self.0 {
+                // XXX: Do we want some kind of assertion here, or is "best effort" okay?
+                ENTERED.with(|c| {
+                    if let EnterContext::Entered {
+                        allow_blocking: false,
+                    } = c.get()
+                    {
+                        c.set(EnterContext::Entered {
+                            allow_blocking: true,
+                        });
+                    }
+                })
+            }
+        }
+    }
+}
+
+cfg_rt_multi_thread! {
+    /// Returns true if in a runtime context.
+    pub(crate) fn context() -> EnterContext {
+        ENTERED.with(|c| c.get())
+    }
+}
+
+cfg_rt! {
+    impl Enter {
+        /// Blocks the thread on the specified future, returning the value with
+        /// which that future completes.
+        pub(crate) fn block_on<F>(&mut self, f: F) -> Result<F::Output, ParkError>
+        where
+            F: std::future::Future,
+        {
+            use crate::park::thread::CachedParkThread;
+
+            let mut park = CachedParkThread::new();
+            park.block_on(f)
+        }
+
+        /// Blocks the thread on the specified future for **at most** `timeout`
+        ///
+        /// If the future completes before `timeout`, the result is returned. If
+        /// `timeout` elapses, then `Err` is returned.
+        pub(crate) fn block_on_timeout<F>(&mut self, f: F, timeout: Duration) -> Result<F::Output, ParkError>
+        where
+            F: std::future::Future,
+        {
+            use crate::park::Park;
+            use crate::park::thread::CachedParkThread;
+            use std::task::Context;
+            use std::task::Poll::Ready;
+            use std::time::Instant;
+
+            let mut park = CachedParkThread::new();
+            let waker = park.get_unpark()?.into_waker();
+            let mut cx = Context::from_waker(&waker);
+
+            pin!(f);
+            let when = Instant::now() + timeout;
+
+            loop {
+                if let Ready(v) = crate::coop::budget(|| f.as_mut().poll(&mut cx)) {
+                    return Ok(v);
+                }
+
+                let now = Instant::now();
+
+                if now >= when {
+                    return Err(());
+                }
+
+                park.park_timeout(when - now)?;
+            }
+        }
+    }
+}
+
+impl fmt::Debug for Enter {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("Enter").finish()
+    }
+}
+
+impl Drop for Enter {
+    fn drop(&mut self) {
+        ENTERED.with(|c| {
+            assert!(c.get().is_entered());
+            c.set(EnterContext::NotEntered);
+        });
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/handle.rs b/third_party/rust/tokio/src/runtime/handle.rs
new file mode 100644
index 0000000000..9dbe6774dd
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/handle.rs
@@ -0,0 +1,435 @@
+use crate::runtime::blocking::{BlockingTask, NoopSchedule};
+use crate::runtime::task::{self, JoinHandle};
+use crate::runtime::{blocking, context, driver, Spawner};
+use crate::util::error::{CONTEXT_MISSING_ERROR, THREAD_LOCAL_DESTROYED_ERROR};
+
+use std::future::Future;
+use std::marker::PhantomData;
+use std::{error, fmt};
+
+/// Handle to the runtime.
+///
+/// The handle is internally reference-counted and can be freely cloned. A handle can be
+/// obtained using the [`Runtime::handle`] method.
+///
+/// [`Runtime::handle`]: crate::runtime::Runtime::handle()
+#[derive(Debug, Clone)]
+pub struct Handle {
+    pub(super) spawner: Spawner,
+
+    /// Handles to the I/O drivers
+    #[cfg_attr(
+        not(any(feature = "net", feature = "process", all(unix, feature = "signal"))),
+        allow(dead_code)
+    )]
+    pub(super) io_handle: driver::IoHandle,
+
+    /// Handles to the signal drivers
+    #[cfg_attr(
+        any(
+            loom,
+            not(all(unix, feature = "signal")),
+            not(all(unix, feature = "process")),
+        ),
+        allow(dead_code)
+    )]
+    pub(super) signal_handle: driver::SignalHandle,
+
+    /// Handles to the time drivers
+    #[cfg_attr(not(feature = "time"), allow(dead_code))]
+    pub(super) time_handle: driver::TimeHandle,
+
+    /// Source of `Instant::now()`
+    #[cfg_attr(not(all(feature = "time", feature = "test-util")), allow(dead_code))]
+    pub(super) clock: driver::Clock,
+
+    /// Blocking pool spawner
+    pub(super) blocking_spawner: blocking::Spawner,
+}
+
+/// Runtime context guard.
+///
+/// Returned by [`Runtime::enter`] and [`Handle::enter`], the context guard exits
+/// the runtime context on drop.
+///
+/// [`Runtime::enter`]: fn@crate::runtime::Runtime::enter
+#[derive(Debug)]
+#[must_use = "Creating and dropping a guard does nothing"]
+pub struct EnterGuard<'a> {
+    _guard: context::EnterGuard,
+    _handle_lifetime: PhantomData<&'a Handle>,
+}
+
+impl Handle {
+    /// Enters the runtime context. This allows you to construct types that must
+    /// have an executor available on creation such as [`Sleep`] or [`TcpStream`].
+    /// It will also allow you to call methods such as [`tokio::spawn`].
+    ///
+    /// [`Sleep`]: struct@crate::time::Sleep
+    /// [`TcpStream`]: struct@crate::net::TcpStream
+    /// [`tokio::spawn`]: fn@crate::spawn
+    pub fn enter(&self) -> EnterGuard<'_> {
+        EnterGuard {
+            _guard: context::enter(self.clone()),
+            _handle_lifetime: PhantomData,
+        }
+    }
+
+    /// Returns a `Handle` view over the currently running `Runtime`.
+    ///
+    /// # Panic
+    ///
+    /// This will panic if called outside the context of a Tokio runtime. That means that you must
+    /// call this on one of the threads **being run by the runtime**. Calling this from within a
+    /// thread created by `std::thread::spawn` (for example) will cause a panic.
+    ///
+    /// # Examples
+    ///
+    /// This can be used to obtain the handle of the surrounding runtime from an async
+    /// block or function running on that runtime.
+    ///
+    /// ```
+    /// # use std::thread;
+    /// # use tokio::runtime::Runtime;
+    /// # fn dox() {
+    /// # let rt = Runtime::new().unwrap();
+    /// # rt.spawn(async {
+    /// use tokio::runtime::Handle;
+    ///
+    /// // Inside an async block or function.
+    /// let handle = Handle::current();
+    /// handle.spawn(async {
+    ///     println!("now running in the existing Runtime");
+    /// });
+    ///
+    /// # let handle =
+    /// thread::spawn(move || {
+    ///     // Notice that the handle is created outside of this thread and then moved in
+    ///     handle.spawn(async { /* ... */ })
+    ///     // This next line would cause a panic
+    ///     // let handle2 = Handle::current();
+    /// });
+    /// # handle.join().unwrap();
+    /// # });
+    /// # }
+    /// ```
+    pub fn current() -> Self {
+        context::current()
+    }
+
+    /// Returns a Handle view over the currently running Runtime
+    ///
+    /// Returns an error if no Runtime has been started
+    ///
+    /// Contrary to `current`, this never panics
+    pub fn try_current() -> Result<Self, TryCurrentError> {
+        context::try_current()
+    }
+
+    /// Spawns a future onto the Tokio runtime.
+    ///
+    /// This spawns the given future onto the runtime's executor, usually a
+    /// thread pool. The thread pool is then responsible for polling the future
+    /// until it completes.
+    ///
+    /// See [module level][mod] documentation for more details.
+    ///
+    /// [mod]: index.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Runtime;
+    ///
+    /// # fn dox() {
+    /// // Create the runtime
+    /// let rt = Runtime::new().unwrap();
+    /// // Get a handle from this runtime
+    /// let handle = rt.handle();
+    ///
+    /// // Spawn a future onto the runtime using the handle
+    /// handle.spawn(async {
+    ///     println!("now running on a worker thread");
+    /// });
+    /// # }
+    /// ```
+    #[track_caller]
+    pub fn spawn<F>(&self, future: F) -> JoinHandle<F::Output>
+    where
+        F: Future + Send + 'static,
+        F::Output: Send + 'static,
+    {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let future = crate::util::trace::task(future, "task", None);
+        self.spawner.spawn(future)
+    }
+
+    /// Runs the provided function on an executor dedicated to blocking.
+    /// operations.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Runtime;
+    ///
+    /// # fn dox() {
+    /// // Create the runtime
+    /// let rt = Runtime::new().unwrap();
+    /// // Get a handle from this runtime
+    /// let handle = rt.handle();
+    ///
+    /// // Spawn a blocking function onto the runtime using the handle
+    /// handle.spawn_blocking(|| {
+    ///     println!("now running on a worker thread");
+    /// });
+    /// # }
+    #[track_caller]
+    pub fn spawn_blocking<F, R>(&self, func: F) -> JoinHandle<R>
+    where
+        F: FnOnce() -> R + Send + 'static,
+        R: Send + 'static,
+    {
+        let (join_handle, _was_spawned) =
+            if cfg!(debug_assertions) && std::mem::size_of::<F>() > 2048 {
+                self.spawn_blocking_inner(Box::new(func), blocking::Mandatory::NonMandatory, None)
+            } else {
+                self.spawn_blocking_inner(func, blocking::Mandatory::NonMandatory, None)
+            };
+
+        join_handle
+    }
+
+    cfg_fs! {
+        #[track_caller]
+        #[cfg_attr(any(
+            all(loom, not(test)), // the function is covered by loom tests
+            test
+        ), allow(dead_code))]
+        pub(crate) fn spawn_mandatory_blocking<F, R>(&self, func: F) -> Option<JoinHandle<R>>
+        where
+            F: FnOnce() -> R + Send + 'static,
+            R: Send + 'static,
+        {
+            let (join_handle, was_spawned) = if cfg!(debug_assertions) && std::mem::size_of::<F>() > 2048 {
+                self.spawn_blocking_inner(
+                    Box::new(func),
+                    blocking::Mandatory::Mandatory,
+                    None
+                )
+            } else {
+                self.spawn_blocking_inner(
+                    func,
+                    blocking::Mandatory::Mandatory,
+                    None
+                )
+            };
+
+            if was_spawned {
+                Some(join_handle)
+            } else {
+                None
+            }
+        }
+    }
+
+    #[track_caller]
+    pub(crate) fn spawn_blocking_inner<F, R>(
+        &self,
+        func: F,
+        is_mandatory: blocking::Mandatory,
+        name: Option<&str>,
+    ) -> (JoinHandle<R>, bool)
+    where
+        F: FnOnce() -> R + Send + 'static,
+        R: Send + 'static,
+    {
+        let fut = BlockingTask::new(func);
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let fut = {
+            use tracing::Instrument;
+            let location = std::panic::Location::caller();
+            let span = tracing::trace_span!(
+                target: "tokio::task::blocking",
+                "runtime.spawn",
+                kind = %"blocking",
+                task.name = %name.unwrap_or_default(),
+                "fn" = %std::any::type_name::<F>(),
+                spawn.location = %format_args!("{}:{}:{}", location.file(), location.line(), location.column()),
+            );
+            fut.instrument(span)
+        };
+
+        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+        let _ = name;
+
+        let (task, handle) = task::unowned(fut, NoopSchedule);
+        let spawned = self
+            .blocking_spawner
+            .spawn(blocking::Task::new(task, is_mandatory), self);
+        (handle, spawned.is_ok())
+    }
+
+    /// Runs a future to completion on this `Handle`'s associated `Runtime`.
+    ///
+    /// This runs the given future on the current thread, blocking until it is
+    /// complete, and yielding its resolved result. Any tasks or timers which
+    /// the future spawns internally will be executed on the runtime.
+    ///
+    /// When this is used on a `current_thread` runtime, only the
+    /// [`Runtime::block_on`] method can drive the IO and timer drivers, but the
+    /// `Handle::block_on` method cannot drive them. This means that, when using
+    /// this method on a current_thread runtime, anything that relies on IO or
+    /// timers will not work unless there is another thread currently calling
+    /// [`Runtime::block_on`] on the same runtime.
+    ///
+    /// # If the runtime has been shut down
+    ///
+    /// If the `Handle`'s associated `Runtime` has been shut down (through
+    /// [`Runtime::shutdown_background`], [`Runtime::shutdown_timeout`], or by
+    /// dropping it) and `Handle::block_on` is used it might return an error or
+    /// panic. Specifically IO resources will return an error and timers will
+    /// panic. Runtime independent futures will run as normal.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if the provided future panics, if called within an
+    /// asynchronous execution context, or if a timer future is executed on a
+    /// runtime that has been shut down.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Runtime;
+    ///
+    /// // Create the runtime
+    /// let rt  = Runtime::new().unwrap();
+    ///
+    /// // Get a handle from this runtime
+    /// let handle = rt.handle();
+    ///
+    /// // Execute the future, blocking the current thread until completion
+    /// handle.block_on(async {
+    ///     println!("hello");
+    /// });
+    /// ```
+    ///
+    /// Or using `Handle::current`:
+    ///
+    /// ```
+    /// use tokio::runtime::Handle;
+    ///
+    /// #[tokio::main]
+    /// async fn main () {
+    ///     let handle = Handle::current();
+    ///     std::thread::spawn(move || {
+    ///         // Using Handle::block_on to run async code in the new thread.
+    ///         handle.block_on(async {
+    ///             println!("hello");
+    ///         });
+    ///     });
+    /// }
+    /// ```
+    ///
+    /// [`JoinError`]: struct@crate::task::JoinError
+    /// [`JoinHandle`]: struct@crate::task::JoinHandle
+    /// [`Runtime::block_on`]: fn@crate::runtime::Runtime::block_on
+    /// [`Runtime::shutdown_background`]: fn@crate::runtime::Runtime::shutdown_background
+    /// [`Runtime::shutdown_timeout`]: fn@crate::runtime::Runtime::shutdown_timeout
+    /// [`spawn_blocking`]: crate::task::spawn_blocking
+    /// [`tokio::fs`]: crate::fs
+    /// [`tokio::net`]: crate::net
+    /// [`tokio::time`]: crate::time
+    #[track_caller]
+    pub fn block_on<F: Future>(&self, future: F) -> F::Output {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let future = crate::util::trace::task(future, "block_on", None);
+
+        // Enter the **runtime** context. This configures spawning, the current I/O driver, ...
+        let _rt_enter = self.enter();
+
+        // Enter a **blocking** context. This prevents blocking from a runtime.
+        let mut blocking_enter = crate::runtime::enter(true);
+
+        // Block on the future
+        blocking_enter
+            .block_on(future)
+            .expect("failed to park thread")
+    }
+
+    pub(crate) fn shutdown(mut self) {
+        self.spawner.shutdown();
+    }
+}
+
+cfg_metrics! {
+    use crate::runtime::RuntimeMetrics;
+
+    impl Handle {
+        /// Returns a view that lets you get information about how the runtime
+        /// is performing.
+        pub fn metrics(&self) -> RuntimeMetrics {
+            RuntimeMetrics::new(self.clone())
+        }
+    }
+}
+
+/// Error returned by `try_current` when no Runtime has been started
+#[derive(Debug)]
+pub struct TryCurrentError {
+    kind: TryCurrentErrorKind,
+}
+
+impl TryCurrentError {
+    pub(crate) fn new_no_context() -> Self {
+        Self {
+            kind: TryCurrentErrorKind::NoContext,
+        }
+    }
+
+    pub(crate) fn new_thread_local_destroyed() -> Self {
+        Self {
+            kind: TryCurrentErrorKind::ThreadLocalDestroyed,
+        }
+    }
+
+    /// Returns true if the call failed because there is currently no runtime in
+    /// the Tokio context.
+    pub fn is_missing_context(&self) -> bool {
+        matches!(self.kind, TryCurrentErrorKind::NoContext)
+    }
+
+    /// Returns true if the call failed because the Tokio context thread-local
+    /// had been destroyed. This can usually only happen if in the destructor of
+    /// other thread-locals.
+    pub fn is_thread_local_destroyed(&self) -> bool {
+        matches!(self.kind, TryCurrentErrorKind::ThreadLocalDestroyed)
+    }
+}
+
+enum TryCurrentErrorKind {
+    NoContext,
+    ThreadLocalDestroyed,
+}
+
+impl fmt::Debug for TryCurrentErrorKind {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use TryCurrentErrorKind::*;
+        match self {
+            NoContext => f.write_str("NoContext"),
+            ThreadLocalDestroyed => f.write_str("ThreadLocalDestroyed"),
+        }
+    }
+}
+
+impl fmt::Display for TryCurrentError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use TryCurrentErrorKind::*;
+        match self.kind {
+            NoContext => f.write_str(CONTEXT_MISSING_ERROR),
+            ThreadLocalDestroyed => f.write_str(THREAD_LOCAL_DESTROYED_ERROR),
+        }
+    }
+}
+
+impl error::Error for TryCurrentError {}
diff --git a/third_party/rust/tokio/src/runtime/metrics/batch.rs b/third_party/rust/tokio/src/runtime/metrics/batch.rs
new file mode 100644
index 0000000000..f1c3fa6b74
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/metrics/batch.rs
@@ -0,0 +1,105 @@
+use crate::runtime::WorkerMetrics;
+
+use std::convert::TryFrom;
+use std::sync::atomic::Ordering::Relaxed;
+use std::time::Instant;
+
+pub(crate) struct MetricsBatch {
+    /// Number of times the worker parked.
+    park_count: u64,
+
+    /// Number of times the worker woke w/o doing work.
+    noop_count: u64,
+
+    /// Number of times stolen.
+    steal_count: u64,
+
+    /// Number of tasks that were polled by the worker.
+    poll_count: u64,
+
+    /// Number of tasks polled when the worker entered park. This is used to
+    /// track the noop count.
+    poll_count_on_last_park: u64,
+
+    /// Number of tasks that were scheduled locally on this worker.
+    local_schedule_count: u64,
+
+    /// Number of tasks moved to the global queue to make space in the local
+    /// queue
+    overflow_count: u64,
+
+    /// The total busy duration in nanoseconds.
+    busy_duration_total: u64,
+    last_resume_time: Instant,
+}
+
+impl MetricsBatch {
+    pub(crate) fn new() -> MetricsBatch {
+        MetricsBatch {
+            park_count: 0,
+            noop_count: 0,
+            steal_count: 0,
+            poll_count: 0,
+            poll_count_on_last_park: 0,
+            local_schedule_count: 0,
+            overflow_count: 0,
+            busy_duration_total: 0,
+            last_resume_time: Instant::now(),
+        }
+    }
+
+    pub(crate) fn submit(&mut self, worker: &WorkerMetrics) {
+        worker.park_count.store(self.park_count, Relaxed);
+        worker.noop_count.store(self.noop_count, Relaxed);
+        worker.steal_count.store(self.steal_count, Relaxed);
+        worker.poll_count.store(self.poll_count, Relaxed);
+
+        worker
+            .busy_duration_total
+            .store(self.busy_duration_total, Relaxed);
+
+        worker
+            .local_schedule_count
+            .store(self.local_schedule_count, Relaxed);
+        worker.overflow_count.store(self.overflow_count, Relaxed);
+    }
+
+    /// The worker is about to park.
+    pub(crate) fn about_to_park(&mut self) {
+        self.park_count += 1;
+
+        if self.poll_count_on_last_park == self.poll_count {
+            self.noop_count += 1;
+        } else {
+            self.poll_count_on_last_park = self.poll_count;
+        }
+
+        let busy_duration = self.last_resume_time.elapsed();
+        let busy_duration = u64::try_from(busy_duration.as_nanos()).unwrap_or(u64::MAX);
+        self.busy_duration_total += busy_duration;
+    }
+
+    pub(crate) fn returned_from_park(&mut self) {
+        self.last_resume_time = Instant::now();
+    }
+
+    pub(crate) fn inc_local_schedule_count(&mut self) {
+        self.local_schedule_count += 1;
+    }
+
+    pub(crate) fn incr_poll_count(&mut self) {
+        self.poll_count += 1;
+    }
+}
+
+cfg_rt_multi_thread! {
+    impl MetricsBatch {
+        pub(crate) fn incr_steal_count(&mut self, by: u16) {
+            self.steal_count += by as u64;
+        }
+
+        pub(crate) fn incr_overflow_count(&mut self) {
+            self.overflow_count += 1;
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/metrics/mock.rs b/third_party/rust/tokio/src/runtime/metrics/mock.rs
new file mode 100644
index 0000000000..6b9cf704f4
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/metrics/mock.rs
@@ -0,0 +1,43 @@
+//! This file contains mocks of the types in src/runtime/metrics
+
+pub(crate) struct SchedulerMetrics {}
+
+pub(crate) struct WorkerMetrics {}
+
+pub(crate) struct MetricsBatch {}
+
+impl SchedulerMetrics {
+    pub(crate) fn new() -> Self {
+        Self {}
+    }
+
+    /// Increment the number of tasks scheduled externally
+    pub(crate) fn inc_remote_schedule_count(&self) {}
+}
+
+impl WorkerMetrics {
+    pub(crate) fn new() -> Self {
+        Self {}
+    }
+
+    pub(crate) fn set_queue_depth(&self, _len: usize) {}
+}
+
+impl MetricsBatch {
+    pub(crate) fn new() -> Self {
+        Self {}
+    }
+
+    pub(crate) fn submit(&mut self, _to: &WorkerMetrics) {}
+    pub(crate) fn about_to_park(&mut self) {}
+    pub(crate) fn returned_from_park(&mut self) {}
+    pub(crate) fn incr_poll_count(&mut self) {}
+    pub(crate) fn inc_local_schedule_count(&mut self) {}
+}
+
+cfg_rt_multi_thread! {
+    impl MetricsBatch {
+        pub(crate) fn incr_steal_count(&mut self, _by: u16) {}
+        pub(crate) fn incr_overflow_count(&mut self) {}
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/metrics/mod.rs b/third_party/rust/tokio/src/runtime/metrics/mod.rs
new file mode 100644
index 0000000000..ca643a5904
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/metrics/mod.rs
@@ -0,0 +1,30 @@
+//! This module contains information need to view information about how the
+//! runtime is performing.
+//!
+//! **Note**: This is an [unstable API][unstable]. The public API of types in
+//! this module may break in 1.x releases. See [the documentation on unstable
+//! features][unstable] for details.
+//!
+//! [unstable]: crate#unstable-features
+#![allow(clippy::module_inception)]
+
+cfg_metrics! {
+    mod batch;
+    pub(crate) use batch::MetricsBatch;
+
+    mod runtime;
+    #[allow(unreachable_pub)] // rust-lang/rust#57411
+    pub use runtime::RuntimeMetrics;
+
+    mod scheduler;
+    pub(crate) use scheduler::SchedulerMetrics;
+
+    mod worker;
+    pub(crate) use worker::WorkerMetrics;
+}
+
+cfg_not_metrics! {
+    mod mock;
+
+    pub(crate) use mock::{SchedulerMetrics, WorkerMetrics, MetricsBatch};
+}
diff --git a/third_party/rust/tokio/src/runtime/metrics/runtime.rs b/third_party/rust/tokio/src/runtime/metrics/runtime.rs
new file mode 100644
index 0000000000..0f8055907f
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/metrics/runtime.rs
@@ -0,0 +1,449 @@
+use crate::runtime::Handle;
+
+use std::sync::atomic::Ordering::Relaxed;
+use std::time::Duration;
+
+/// Handle to the runtime's metrics.
+///
+/// This handle is internally reference-counted and can be freely cloned. A
+/// `RuntimeMetrics` handle is obtained using the [`Runtime::metrics`] method.
+///
+/// [`Runtime::metrics`]: crate::runtime::Runtime::metrics()
+#[derive(Clone, Debug)]
+pub struct RuntimeMetrics {
+    handle: Handle,
+}
+
+impl RuntimeMetrics {
+    pub(crate) fn new(handle: Handle) -> RuntimeMetrics {
+        RuntimeMetrics { handle }
+    }
+
+    /// Returns the number of worker threads used by the runtime.
+    ///
+    /// The number of workers is set by configuring `worker_threads` on
+    /// `runtime::Builder`. When using the `current_thread` runtime, the return
+    /// value is always `1`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Handle;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let metrics = Handle::current().metrics();
+    ///
+    ///     let n = metrics.num_workers();
+    ///     println!("Runtime is using {} workers", n);
+    /// }
+    /// ```
+    pub fn num_workers(&self) -> usize {
+        self.handle.spawner.num_workers()
+    }
+
+    /// Returns the number of tasks scheduled from **outside** of the runtime.
+    ///
+    /// The remote schedule count starts at zero when the runtime is created and
+    /// increases by one each time a task is woken from **outside** of the
+    /// runtime. This usually means that a task is spawned or notified from a
+    /// non-runtime thread and must be queued using the Runtime's injection
+    /// queue, which tends to be slower.
+    ///
+    /// The counter is monotonically increasing. It is never decremented or
+    /// reset to zero.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Handle;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let metrics = Handle::current().metrics();
+    ///
+    ///     let n = metrics.remote_schedule_count();
+    ///     println!("{} tasks were scheduled from outside the runtime", n);
+    /// }
+    /// ```
+    pub fn remote_schedule_count(&self) -> u64 {
+        self.handle
+            .spawner
+            .scheduler_metrics()
+            .remote_schedule_count
+            .load(Relaxed)
+    }
+
+    /// Returns the total number of times the given worker thread has parked.
+    ///
+    /// The worker park count starts at zero when the runtime is created and
+    /// increases by one each time the worker parks the thread waiting for new
+    /// inbound events to process. This usually means the worker has processed
+    /// all pending work and is currently idle.
+    ///
+    /// The counter is monotonically increasing. It is never decremented or
+    /// reset to zero.
+    ///
+    /// # Arguments
+    ///
+    /// `worker` is the index of the worker being queried. The given value must
+    /// be between 0 and `num_workers()`. The index uniquely identifies a single
+    /// worker and will continue to indentify the worker throughout the lifetime
+    /// of the runtime instance.
+    ///
+    /// # Panics
+    ///
+    /// The method panics when `worker` represents an invalid worker, i.e. is
+    /// greater than or equal to `num_workers()`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Handle;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let metrics = Handle::current().metrics();
+    ///
+    ///     let n = metrics.worker_park_count(0);
+    ///     println!("worker 0 parked {} times", n);
+    /// }
+    /// ```
+    pub fn worker_park_count(&self, worker: usize) -> u64 {
+        self.handle
+            .spawner
+            .worker_metrics(worker)
+            .park_count
+            .load(Relaxed)
+    }
+
+    /// Returns the number of times the given worker thread unparked but
+    /// performed no work before parking again.
+    ///
+    /// The worker no-op count starts at zero when the runtime is created and
+    /// increases by one each time the worker unparks the thread but finds no
+    /// new work and goes back to sleep. This indicates a false-positive wake up.
+    ///
+    /// The counter is monotonically increasing. It is never decremented or
+    /// reset to zero.
+    ///
+    /// # Arguments
+    ///
+    /// `worker` is the index of the worker being queried. The given value must
+    /// be between 0 and `num_workers()`. The index uniquely identifies a single
+    /// worker and will continue to indentify the worker throughout the lifetime
+    /// of the runtime instance.
+    ///
+    /// # Panics
+    ///
+    /// The method panics when `worker` represents an invalid worker, i.e. is
+    /// greater than or equal to `num_workers()`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Handle;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let metrics = Handle::current().metrics();
+    ///
+    ///     let n = metrics.worker_noop_count(0);
+    ///     println!("worker 0 had {} no-op unparks", n);
+    /// }
+    /// ```
+    pub fn worker_noop_count(&self, worker: usize) -> u64 {
+        self.handle
+            .spawner
+            .worker_metrics(worker)
+            .noop_count
+            .load(Relaxed)
+    }
+
+    /// Returns the number of times the given worker thread stole tasks from
+    /// another worker thread.
+    ///
+    /// This metric only applies to the **multi-threaded** runtime and will always return `0` when using the current thread runtime.
+    ///
+    /// The worker steal count starts at zero when the runtime is created and
+    /// increases by one each time the worker has processed its scheduled queue
+    /// and successfully steals more pending tasks from another worker.
+    ///
+    /// The counter is monotonically increasing. It is never decremented or
+    /// reset to zero.
+    ///
+    /// # Arguments
+    ///
+    /// `worker` is the index of the worker being queried. The given value must
+    /// be between 0 and `num_workers()`. The index uniquely identifies a single
+    /// worker and will continue to indentify the worker throughout the lifetime
+    /// of the runtime instance.
+    ///
+    /// # Panics
+    ///
+    /// The method panics when `worker` represents an invalid worker, i.e. is
+    /// greater than or equal to `num_workers()`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Handle;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let metrics = Handle::current().metrics();
+    ///
+    ///     let n = metrics.worker_noop_count(0);
+    ///     println!("worker 0 has stolen tasks {} times", n);
+    /// }
+    /// ```
+    pub fn worker_steal_count(&self, worker: usize) -> u64 {
+        self.handle
+            .spawner
+            .worker_metrics(worker)
+            .steal_count
+            .load(Relaxed)
+    }
+
+    /// Returns the number of tasks the given worker thread has polled.
+    ///
+    /// The worker poll count starts at zero when the runtime is created and
+    /// increases by one each time the worker polls a scheduled task.
+    ///
+    /// The counter is monotonically increasing. It is never decremented or
+    /// reset to zero.
+    ///
+    /// # Arguments
+    ///
+    /// `worker` is the index of the worker being queried. The given value must
+    /// be between 0 and `num_workers()`. The index uniquely identifies a single
+    /// worker and will continue to indentify the worker throughout the lifetime
+    /// of the runtime instance.
+    ///
+    /// # Panics
+    ///
+    /// The method panics when `worker` represents an invalid worker, i.e. is
+    /// greater than or equal to `num_workers()`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Handle;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let metrics = Handle::current().metrics();
+    ///
+    ///     let n = metrics.worker_poll_count(0);
+    ///     println!("worker 0 has polled {} tasks", n);
+    /// }
+    /// ```
+    pub fn worker_poll_count(&self, worker: usize) -> u64 {
+        self.handle
+            .spawner
+            .worker_metrics(worker)
+            .poll_count
+            .load(Relaxed)
+    }
+
+    /// Returns the amount of time the given worker thread has been busy.
+    ///
+    /// The worker busy duration starts at zero when the runtime is created and
+    /// increases whenever the worker is spending time processing work. Using
+    /// this value can indicate the load of the given worker. If a lot of time
+    /// is spent busy, then the worker is under load and will check for inbound
+    /// events less often.
+    ///
+    /// The timer is monotonically increasing. It is never decremented or reset
+    /// to zero.
+    ///
+    /// # Arguments
+    ///
+    /// `worker` is the index of the worker being queried. The given value must
+    /// be between 0 and `num_workers()`. The index uniquely identifies a single
+    /// worker and will continue to indentify the worker throughout the lifetime
+    /// of the runtime instance.
+    ///
+    /// # Panics
+    ///
+    /// The method panics when `worker` represents an invalid worker, i.e. is
+    /// greater than or equal to `num_workers()`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Handle;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let metrics = Handle::current().metrics();
+    ///
+    ///     let n = metrics.worker_poll_count(0);
+    ///     println!("worker 0 has polled {} tasks", n);
+    /// }
+    /// ```
+    pub fn worker_total_busy_duration(&self, worker: usize) -> Duration {
+        let nanos = self
+            .handle
+            .spawner
+            .worker_metrics(worker)
+            .busy_duration_total
+            .load(Relaxed);
+        Duration::from_nanos(nanos)
+    }
+
+    /// Returns the number of tasks scheduled from **within** the runtime on the
+    /// given worker's local queue.
+    ///
+    /// The local schedule count starts at zero when the runtime is created and
+    /// increases by one each time a task is woken from **inside** of the
+    /// runtime on the given worker. This usually means that a task is spawned
+    /// or notified from within a runtime thread and will be queued on the
+    /// worker-local queue.
+    ///
+    /// The counter is monotonically increasing. It is never decremented or
+    /// reset to zero.
+    ///
+    /// # Arguments
+    ///
+    /// `worker` is the index of the worker being queried. The given value must
+    /// be between 0 and `num_workers()`. The index uniquely identifies a single
+    /// worker and will continue to indentify the worker throughout the lifetime
+    /// of the runtime instance.
+    ///
+    /// # Panics
+    ///
+    /// The method panics when `worker` represents an invalid worker, i.e. is
+    /// greater than or equal to `num_workers()`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Handle;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let metrics = Handle::current().metrics();
+    ///
+    ///     let n = metrics.worker_local_schedule_count(0);
+    ///     println!("{} tasks were scheduled on the worker's local queue", n);
+    /// }
+    /// ```
+    pub fn worker_local_schedule_count(&self, worker: usize) -> u64 {
+        self.handle
+            .spawner
+            .worker_metrics(worker)
+            .local_schedule_count
+            .load(Relaxed)
+    }
+
+    /// Returns the number of times the given worker thread saturated its local
+    /// queue.
+    ///
+    /// This metric only applies to the **multi-threaded** scheduler.
+    ///
+    /// The worker steal count starts at zero when the runtime is created and
+    /// increases by one each time the worker attempts to schedule a task
+    /// locally, but its local queue is full. When this happens, half of the
+    /// local queue is moved to the injection queue.
+    ///
+    /// The counter is monotonically increasing. It is never decremented or
+    /// reset to zero.
+    ///
+    /// # Arguments
+    ///
+    /// `worker` is the index of the worker being queried. The given value must
+    /// be between 0 and `num_workers()`. The index uniquely identifies a single
+    /// worker and will continue to indentify the worker throughout the lifetime
+    /// of the runtime instance.
+    ///
+    /// # Panics
+    ///
+    /// The method panics when `worker` represents an invalid worker, i.e. is
+    /// greater than or equal to `num_workers()`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Handle;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let metrics = Handle::current().metrics();
+    ///
+    ///     let n = metrics.worker_overflow_count(0);
+    ///     println!("worker 0 has overflowed its queue {} times", n);
+    /// }
+    /// ```
+    pub fn worker_overflow_count(&self, worker: usize) -> u64 {
+        self.handle
+            .spawner
+            .worker_metrics(worker)
+            .overflow_count
+            .load(Relaxed)
+    }
+
+    /// Returns the number of tasks currently scheduled in the runtime's
+    /// injection queue.
+    ///
+    /// Tasks that are spanwed or notified from a non-runtime thread are
+    /// scheduled using the runtime's injection queue. This metric returns the
+    /// **current** number of tasks pending in the injection queue. As such, the
+    /// returned value may increase or decrease as new tasks are scheduled and
+    /// processed.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Handle;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let metrics = Handle::current().metrics();
+    ///
+    ///     let n = metrics.injection_queue_depth();
+    ///     println!("{} tasks currently pending in the runtime's injection queue", n);
+    /// }
+    /// ```
+    pub fn injection_queue_depth(&self) -> usize {
+        self.handle.spawner.injection_queue_depth()
+    }
+
+    /// Returns the number of tasks currently scheduled in the given worker's
+    /// local queue.
+    ///
+    /// Tasks that are spawned or notified from within a runtime thread are
+    /// scheduled using that worker's local queue. This metric returns the
+    /// **current** number of tasks pending in the worker's local queue. As
+    /// such, the returned value may increase or decrease as new tasks are
+    /// scheduled and processed.
+    ///
+    /// # Arguments
+    ///
+    /// `worker` is the index of the worker being queried. The given value must
+    /// be between 0 and `num_workers()`. The index uniquely identifies a single
+    /// worker and will continue to indentify the worker throughout the lifetime
+    /// of the runtime instance.
+    ///
+    /// # Panics
+    ///
+    /// The method panics when `worker` represents an invalid worker, i.e. is
+    /// greater than or equal to `num_workers()`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::runtime::Handle;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let metrics = Handle::current().metrics();
+    ///
+    ///     let n = metrics.worker_local_queue_depth(0);
+    ///     println!("{} tasks currently pending in worker 0's local queue", n);
+    /// }
+    /// ```
+    pub fn worker_local_queue_depth(&self, worker: usize) -> usize {
+        self.handle.spawner.worker_local_queue_depth(worker)
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/metrics/scheduler.rs b/third_party/rust/tokio/src/runtime/metrics/scheduler.rs
new file mode 100644
index 0000000000..d1ba3b6442
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/metrics/scheduler.rs
@@ -0,0 +1,27 @@
+use crate::loom::sync::atomic::{AtomicU64, Ordering::Relaxed};
+
+/// Retrieves metrics from the Tokio runtime.
+///
+/// **Note**: This is an [unstable API][unstable]. The public API of this type
+/// may break in 1.x releases. See [the documentation on unstable
+/// features][unstable] for details.
+///
+/// [unstable]: crate#unstable-features
+#[derive(Debug)]
+pub(crate) struct SchedulerMetrics {
+    /// Number of tasks that are scheduled from outside the runtime.
+    pub(super) remote_schedule_count: AtomicU64,
+}
+
+impl SchedulerMetrics {
+    pub(crate) fn new() -> SchedulerMetrics {
+        SchedulerMetrics {
+            remote_schedule_count: AtomicU64::new(0),
+        }
+    }
+
+    /// Increment the number of tasks scheduled externally
+    pub(crate) fn inc_remote_schedule_count(&self) {
+        self.remote_schedule_count.fetch_add(1, Relaxed);
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/metrics/worker.rs b/third_party/rust/tokio/src/runtime/metrics/worker.rs
new file mode 100644
index 0000000000..c9b85e48e4
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/metrics/worker.rs
@@ -0,0 +1,61 @@
+use crate::loom::sync::atomic::Ordering::Relaxed;
+use crate::loom::sync::atomic::{AtomicU64, AtomicUsize};
+
+/// Retreive runtime worker metrics.
+///
+/// **Note**: This is an [unstable API][unstable]. The public API of this type
+/// may break in 1.x releases. See [the documentation on unstable
+/// features][unstable] for details.
+///
+/// [unstable]: crate#unstable-features
+#[derive(Debug)]
+#[repr(align(128))]
+pub(crate) struct WorkerMetrics {
+    ///  Number of times the worker parked.
+    pub(crate) park_count: AtomicU64,
+
+    /// Number of times the worker woke then parked again without doing work.
+    pub(crate) noop_count: AtomicU64,
+
+    /// Number of times the worker attempted to steal.
+    pub(crate) steal_count: AtomicU64,
+
+    /// Number of tasks the worker polled.
+    pub(crate) poll_count: AtomicU64,
+
+    /// Amount of time the worker spent doing work vs. parking.
+    pub(crate) busy_duration_total: AtomicU64,
+
+    /// Number of tasks scheduled for execution on the worker's local queue.
+    pub(crate) local_schedule_count: AtomicU64,
+
+    /// Number of tasks moved from the local queue to the global queue to free space.
+    pub(crate) overflow_count: AtomicU64,
+
+    /// Number of tasks currently in the local queue. Used only by the
+    /// current-thread scheduler.
+    pub(crate) queue_depth: AtomicUsize,
+}
+
+impl WorkerMetrics {
+    pub(crate) fn new() -> WorkerMetrics {
+        WorkerMetrics {
+            park_count: AtomicU64::new(0),
+            noop_count: AtomicU64::new(0),
+            steal_count: AtomicU64::new(0),
+            poll_count: AtomicU64::new(0),
+            overflow_count: AtomicU64::new(0),
+            busy_duration_total: AtomicU64::new(0),
+            local_schedule_count: AtomicU64::new(0),
+            queue_depth: AtomicUsize::new(0),
+        }
+    }
+
+    pub(crate) fn queue_depth(&self) -> usize {
+        self.queue_depth.load(Relaxed)
+    }
+
+    pub(crate) fn set_queue_depth(&self, len: usize) {
+        self.queue_depth.store(len, Relaxed);
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/mod.rs b/third_party/rust/tokio/src/runtime/mod.rs
new file mode 100644
index 0000000000..7c381b0bbd
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/mod.rs
@@ -0,0 +1,623 @@
+//! The Tokio runtime.
+//!
+//! Unlike other Rust programs, asynchronous applications require runtime
+//! support. In particular, the following runtime services are necessary:
+//!
+//! * An **I/O event loop**, called the driver, which drives I/O resources and
+//!   dispatches I/O events to tasks that depend on them.
+//! * A **scheduler** to execute [tasks] that use these I/O resources.
+//! * A **timer** for scheduling work to run after a set period of time.
+//!
+//! Tokio's [`Runtime`] bundles all of these services as a single type, allowing
+//! them to be started, shut down, and configured together. However, often it is
+//! not required to configure a [`Runtime`] manually, and a user may just use the
+//! [`tokio::main`] attribute macro, which creates a [`Runtime`] under the hood.
+//!
+//! # Usage
+//!
+//! When no fine tuning is required, the [`tokio::main`] attribute macro can be
+//! used.
+//!
+//! ```no_run
+//! use tokio::net::TcpListener;
+//! use tokio::io::{AsyncReadExt, AsyncWriteExt};
+//!
+//! #[tokio::main]
+//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
+//!     let listener = TcpListener::bind("127.0.0.1:8080").await?;
+//!
+//!     loop {
+//!         let (mut socket, _) = listener.accept().await?;
+//!
+//!         tokio::spawn(async move {
+//!             let mut buf = [0; 1024];
+//!
+//!             // In a loop, read data from the socket and write the data back.
+//!             loop {
+//!                 let n = match socket.read(&mut buf).await {
+//!                     // socket closed
+//!                     Ok(n) if n == 0 => return,
+//!                     Ok(n) => n,
+//!                     Err(e) => {
+//!                         println!("failed to read from socket; err = {:?}", e);
+//!                         return;
+//!                     }
+//!                 };
+//!
+//!                 // Write the data back
+//!                 if let Err(e) = socket.write_all(&buf[0..n]).await {
+//!                     println!("failed to write to socket; err = {:?}", e);
+//!                     return;
+//!                 }
+//!             }
+//!         });
+//!     }
+//! }
+//! ```
+//!
+//! From within the context of the runtime, additional tasks are spawned using
+//! the [`tokio::spawn`] function. Futures spawned using this function will be
+//! executed on the same thread pool used by the [`Runtime`].
+//!
+//! A [`Runtime`] instance can also be used directly.
+//!
+//! ```no_run
+//! use tokio::net::TcpListener;
+//! use tokio::io::{AsyncReadExt, AsyncWriteExt};
+//! use tokio::runtime::Runtime;
+//!
+//! fn main() -> Result<(), Box<dyn std::error::Error>> {
+//!     // Create the runtime
+//!     let rt  = Runtime::new()?;
+//!
+//!     // Spawn the root task
+//!     rt.block_on(async {
+//!         let listener = TcpListener::bind("127.0.0.1:8080").await?;
+//!
+//!         loop {
+//!             let (mut socket, _) = listener.accept().await?;
+//!
+//!             tokio::spawn(async move {
+//!                 let mut buf = [0; 1024];
+//!
+//!                 // In a loop, read data from the socket and write the data back.
+//!                 loop {
+//!                     let n = match socket.read(&mut buf).await {
+//!                         // socket closed
+//!                         Ok(n) if n == 0 => return,
+//!                         Ok(n) => n,
+//!                         Err(e) => {
+//!                             println!("failed to read from socket; err = {:?}", e);
+//!                             return;
+//!                         }
+//!                     };
+//!
+//!                     // Write the data back
+//!                     if let Err(e) = socket.write_all(&buf[0..n]).await {
+//!                         println!("failed to write to socket; err = {:?}", e);
+//!                         return;
+//!                     }
+//!                 }
+//!             });
+//!         }
+//!     })
+//! }
+//! ```
+//!
+//! ## Runtime Configurations
+//!
+//! Tokio provides multiple task scheduling strategies, suitable for different
+//! applications. The [runtime builder] or `#[tokio::main]` attribute may be
+//! used to select which scheduler to use.
+//!
+//! #### Multi-Thread Scheduler
+//!
+//! The multi-thread scheduler executes futures on a _thread pool_, using a
+//! work-stealing strategy. By default, it will start a worker thread for each
+//! CPU core available on the system. This tends to be the ideal configuration
+//! for most applications. The multi-thread scheduler requires the `rt-multi-thread`
+//! feature flag, and is selected by default:
+//! ```
+//! use tokio::runtime;
+//!
+//! # fn main() -> Result<(), Box<dyn std::error::Error>> {
+//! let threaded_rt = runtime::Runtime::new()?;
+//! # Ok(()) }
+//! ```
+//!
+//! Most applications should use the multi-thread scheduler, except in some
+//! niche use-cases, such as when running only a single thread is required.
+//!
+//! #### Current-Thread Scheduler
+//!
+//! The current-thread scheduler provides a _single-threaded_ future executor.
+//! All tasks will be created and executed on the current thread. This requires
+//! the `rt` feature flag.
+//! ```
+//! use tokio::runtime;
+//!
+//! # fn main() -> Result<(), Box<dyn std::error::Error>> {
+//! let basic_rt = runtime::Builder::new_current_thread()
+//!     .build()?;
+//! # Ok(()) }
+//! ```
+//!
+//! #### Resource drivers
+//!
+//! When configuring a runtime by hand, no resource drivers are enabled by
+//! default. In this case, attempting to use networking types or time types will
+//! fail. In order to enable these types, the resource drivers must be enabled.
+//! This is done with [`Builder::enable_io`] and [`Builder::enable_time`]. As a
+//! shorthand, [`Builder::enable_all`] enables both resource drivers.
+//!
+//! ## Lifetime of spawned threads
+//!
+//! The runtime may spawn threads depending on its configuration and usage. The
+//! multi-thread scheduler spawns threads to schedule tasks and for `spawn_blocking`
+//! calls.
+//!
+//! While the `Runtime` is active, threads may shutdown after periods of being
+//! idle. Once `Runtime` is dropped, all runtime threads are forcibly shutdown.
+//! Any tasks that have not yet completed will be dropped.
+//!
+//! [tasks]: crate::task
+//! [`Runtime`]: Runtime
+//! [`tokio::spawn`]: crate::spawn
+//! [`tokio::main`]: ../attr.main.html
+//! [runtime builder]: crate::runtime::Builder
+//! [`Runtime::new`]: crate::runtime::Runtime::new
+//! [`Builder::basic_scheduler`]: crate::runtime::Builder::basic_scheduler
+//! [`Builder::threaded_scheduler`]: crate::runtime::Builder::threaded_scheduler
+//! [`Builder::enable_io`]: crate::runtime::Builder::enable_io
+//! [`Builder::enable_time`]: crate::runtime::Builder::enable_time
+//! [`Builder::enable_all`]: crate::runtime::Builder::enable_all
+
+// At the top due to macros
+#[cfg(test)]
+#[cfg(not(target_arch = "wasm32"))]
+#[macro_use]
+mod tests;
+
+pub(crate) mod enter;
+
+pub(crate) mod task;
+
+cfg_metrics! {
+    mod metrics;
+    pub use metrics::RuntimeMetrics;
+
+    pub(crate) use metrics::{MetricsBatch, SchedulerMetrics, WorkerMetrics};
+}
+
+cfg_not_metrics! {
+    pub(crate) mod metrics;
+    pub(crate) use metrics::{SchedulerMetrics, WorkerMetrics, MetricsBatch};
+}
+
+cfg_rt! {
+    mod basic_scheduler;
+    use basic_scheduler::BasicScheduler;
+
+    mod blocking;
+    use blocking::BlockingPool;
+    pub(crate) use blocking::spawn_blocking;
+
+    cfg_trace! {
+        pub(crate) use blocking::Mandatory;
+    }
+
+    cfg_fs! {
+        pub(crate) use blocking::spawn_mandatory_blocking;
+    }
+
+    mod builder;
+    pub use self::builder::Builder;
+
+    pub(crate) mod context;
+    pub(crate) mod driver;
+
+    use self::enter::enter;
+
+    mod handle;
+    pub use handle::{EnterGuard, Handle, TryCurrentError};
+
+    mod spawner;
+    use self::spawner::Spawner;
+}
+
+cfg_rt_multi_thread! {
+    mod park;
+    use park::Parker;
+}
+
+cfg_rt_multi_thread! {
+    mod queue;
+
+    pub(crate) mod thread_pool;
+    use self::thread_pool::ThreadPool;
+}
+
+cfg_rt! {
+    use crate::task::JoinHandle;
+
+    use std::future::Future;
+    use std::time::Duration;
+
+    /// The Tokio runtime.
+    ///
+    /// The runtime provides an I/O driver, task scheduler, [timer], and
+    /// blocking pool, necessary for running asynchronous tasks.
+    ///
+    /// Instances of `Runtime` can be created using [`new`], or [`Builder`].
+    /// However, most users will use the `#[tokio::main]` annotation on their
+    /// entry point instead.
+    ///
+    /// See [module level][mod] documentation for more details.
+    ///
+    /// # Shutdown
+    ///
+    /// Shutting down the runtime is done by dropping the value. The current
+    /// thread will block until the shut down operation has completed.
+    ///
+    /// * Drain any scheduled work queues.
+    /// * Drop any futures that have not yet completed.
+    /// * Drop the reactor.
+    ///
+    /// Once the reactor has dropped, any outstanding I/O resources bound to
+    /// that reactor will no longer function. Calling any method on them will
+    /// result in an error.
+    ///
+    /// # Sharing
+    ///
+    /// The Tokio runtime implements `Sync` and `Send` to allow you to wrap it
+    /// in a `Arc`. Most fn take `&self` to allow you to call them concurrently
+    /// across multiple threads.
+    ///
+    /// Calls to `shutdown` and `shutdown_timeout` require exclusive ownership of
+    /// the runtime type and this can be achieved via `Arc::try_unwrap` when only
+    /// one strong count reference is left over.
+    ///
+    /// [timer]: crate::time
+    /// [mod]: index.html
+    /// [`new`]: method@Self::new
+    /// [`Builder`]: struct@Builder
+    #[derive(Debug)]
+    pub struct Runtime {
+        /// Task executor
+        kind: Kind,
+
+        /// Handle to runtime, also contains driver handles
+        handle: Handle,
+
+        /// Blocking pool handle, used to signal shutdown
+        blocking_pool: BlockingPool,
+    }
+
+    /// The runtime executor is either a thread-pool or a current-thread executor.
+    #[derive(Debug)]
+    enum Kind {
+        /// Execute all tasks on the current-thread.
+        CurrentThread(BasicScheduler),
+
+        /// Execute tasks across multiple threads.
+        #[cfg(feature = "rt-multi-thread")]
+        ThreadPool(ThreadPool),
+    }
+
+    /// After thread starts / before thread stops
+    type Callback = std::sync::Arc<dyn Fn() + Send + Sync>;
+
+    impl Runtime {
+        /// Creates a new runtime instance with default configuration values.
+        ///
+        /// This results in the multi threaded scheduler, I/O driver, and time driver being
+        /// initialized.
+        ///
+        /// Most applications will not need to call this function directly. Instead,
+        /// they will use the  [`#[tokio::main]` attribute][main]. When a more complex
+        /// configuration is necessary, the [runtime builder] may be used.
+        ///
+        /// See [module level][mod] documentation for more details.
+        ///
+        /// # Examples
+        ///
+        /// Creating a new `Runtime` with default configuration values.
+        ///
+        /// ```
+        /// use tokio::runtime::Runtime;
+        ///
+        /// let rt = Runtime::new()
+        ///     .unwrap();
+        ///
+        /// // Use the runtime...
+        /// ```
+        ///
+        /// [mod]: index.html
+        /// [main]: ../attr.main.html
+        /// [threaded scheduler]: index.html#threaded-scheduler
+        /// [basic scheduler]: index.html#basic-scheduler
+        /// [runtime builder]: crate::runtime::Builder
+        #[cfg(feature = "rt-multi-thread")]
+        #[cfg_attr(docsrs, doc(cfg(feature = "rt-multi-thread")))]
+        pub fn new() -> std::io::Result<Runtime> {
+            Builder::new_multi_thread().enable_all().build()
+        }
+
+        /// Returns a handle to the runtime's spawner.
+        ///
+        /// The returned handle can be used to spawn tasks that run on this runtime, and can
+        /// be cloned to allow moving the `Handle` to other threads.
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// use tokio::runtime::Runtime;
+        ///
+        /// let rt = Runtime::new()
+        ///     .unwrap();
+        ///
+        /// let handle = rt.handle();
+        ///
+        /// // Use the handle...
+        /// ```
+        pub fn handle(&self) -> &Handle {
+            &self.handle
+        }
+
+        /// Spawns a future onto the Tokio runtime.
+        ///
+        /// This spawns the given future onto the runtime's executor, usually a
+        /// thread pool. The thread pool is then responsible for polling the future
+        /// until it completes.
+        ///
+        /// See [module level][mod] documentation for more details.
+        ///
+        /// [mod]: index.html
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// use tokio::runtime::Runtime;
+        ///
+        /// # fn dox() {
+        /// // Create the runtime
+        /// let rt = Runtime::new().unwrap();
+        ///
+        /// // Spawn a future onto the runtime
+        /// rt.spawn(async {
+        ///     println!("now running on a worker thread");
+        /// });
+        /// # }
+        /// ```
+        #[track_caller]
+        pub fn spawn<F>(&self, future: F) -> JoinHandle<F::Output>
+        where
+            F: Future + Send + 'static,
+            F::Output: Send + 'static,
+        {
+            self.handle.spawn(future)
+        }
+
+        /// Runs the provided function on an executor dedicated to blocking operations.
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// use tokio::runtime::Runtime;
+        ///
+        /// # fn dox() {
+        /// // Create the runtime
+        /// let rt = Runtime::new().unwrap();
+        ///
+        /// // Spawn a blocking function onto the runtime
+        /// rt.spawn_blocking(|| {
+        ///     println!("now running on a worker thread");
+        /// });
+        /// # }
+        #[track_caller]
+        pub fn spawn_blocking<F, R>(&self, func: F) -> JoinHandle<R>
+        where
+            F: FnOnce() -> R + Send + 'static,
+            R: Send + 'static,
+        {
+            self.handle.spawn_blocking(func)
+        }
+
+        /// Runs a future to completion on the Tokio runtime. This is the
+        /// runtime's entry point.
+        ///
+        /// This runs the given future on the current thread, blocking until it is
+        /// complete, and yielding its resolved result. Any tasks or timers
+        /// which the future spawns internally will be executed on the runtime.
+        ///
+        /// # Multi thread scheduler
+        ///
+        /// When the multi thread scheduler is used this will allow futures
+        /// to run within the io driver and timer context of the overall runtime.
+        ///
+        /// # Current thread scheduler
+        ///
+        /// When the current thread scheduler is enabled `block_on`
+        /// can be called concurrently from multiple threads. The first call
+        /// will take ownership of the io and timer drivers. This means
+        /// other threads which do not own the drivers will hook into that one.
+        /// When the first `block_on` completes, other threads will be able to
+        /// "steal" the driver to allow continued execution of their futures.
+        ///
+        /// # Panics
+        ///
+        /// This function panics if the provided future panics, or if called within an
+        /// asynchronous execution context.
+        ///
+        /// # Examples
+        ///
+        /// ```no_run
+        /// use tokio::runtime::Runtime;
+        ///
+        /// // Create the runtime
+        /// let rt  = Runtime::new().unwrap();
+        ///
+        /// // Execute the future, blocking the current thread until completion
+        /// rt.block_on(async {
+        ///     println!("hello");
+        /// });
+        /// ```
+        ///
+        /// [handle]: fn@Handle::block_on
+        #[track_caller]
+        pub fn block_on<F: Future>(&self, future: F) -> F::Output {
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            let future = crate::util::trace::task(future, "block_on", None);
+
+            let _enter = self.enter();
+
+            match &self.kind {
+                Kind::CurrentThread(exec) => exec.block_on(future),
+                #[cfg(feature = "rt-multi-thread")]
+                Kind::ThreadPool(exec) => exec.block_on(future),
+            }
+        }
+
+        /// Enters the runtime context.
+        ///
+        /// This allows you to construct types that must have an executor
+        /// available on creation such as [`Sleep`] or [`TcpStream`]. It will
+        /// also allow you to call methods such as [`tokio::spawn`].
+        ///
+        /// [`Sleep`]: struct@crate::time::Sleep
+        /// [`TcpStream`]: struct@crate::net::TcpStream
+        /// [`tokio::spawn`]: fn@crate::spawn
+        ///
+        /// # Example
+        ///
+        /// ```
+        /// use tokio::runtime::Runtime;
+        ///
+        /// fn function_that_spawns(msg: String) {
+        ///     // Had we not used `rt.enter` below, this would panic.
+        ///     tokio::spawn(async move {
+        ///         println!("{}", msg);
+        ///     });
+        /// }
+        ///
+        /// fn main() {
+        ///     let rt = Runtime::new().unwrap();
+        ///
+        ///     let s = "Hello World!".to_string();
+        ///
+        ///     // By entering the context, we tie `tokio::spawn` to this executor.
+        ///     let _guard = rt.enter();
+        ///     function_that_spawns(s);
+        /// }
+        /// ```
+        pub fn enter(&self) -> EnterGuard<'_> {
+            self.handle.enter()
+        }
+
+        /// Shuts down the runtime, waiting for at most `duration` for all spawned
+        /// task to shutdown.
+        ///
+        /// Usually, dropping a `Runtime` handle is sufficient as tasks are able to
+        /// shutdown in a timely fashion. However, dropping a `Runtime` will wait
+        /// indefinitely for all tasks to terminate, and there are cases where a long
+        /// blocking task has been spawned, which can block dropping `Runtime`.
+        ///
+        /// In this case, calling `shutdown_timeout` with an explicit wait timeout
+        /// can work. The `shutdown_timeout` will signal all tasks to shutdown and
+        /// will wait for at most `duration` for all spawned tasks to terminate. If
+        /// `timeout` elapses before all tasks are dropped, the function returns and
+        /// outstanding tasks are potentially leaked.
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// use tokio::runtime::Runtime;
+        /// use tokio::task;
+        ///
+        /// use std::thread;
+        /// use std::time::Duration;
+        ///
+        /// fn main() {
+        ///    let runtime = Runtime::new().unwrap();
+        ///
+        ///    runtime.block_on(async move {
+        ///        task::spawn_blocking(move || {
+        ///            thread::sleep(Duration::from_secs(10_000));
+        ///        });
+        ///    });
+        ///
+        ///    runtime.shutdown_timeout(Duration::from_millis(100));
+        /// }
+        /// ```
+        pub fn shutdown_timeout(mut self, duration: Duration) {
+            // Wakeup and shutdown all the worker threads
+            self.handle.clone().shutdown();
+            self.blocking_pool.shutdown(Some(duration));
+        }
+
+        /// Shuts down the runtime, without waiting for any spawned tasks to shutdown.
+        ///
+        /// This can be useful if you want to drop a runtime from within another runtime.
+        /// Normally, dropping a runtime will block indefinitely for spawned blocking tasks
+        /// to complete, which would normally not be permitted within an asynchronous context.
+        /// By calling `shutdown_background()`, you can drop the runtime from such a context.
+        ///
+        /// Note however, that because we do not wait for any blocking tasks to complete, this
+        /// may result in a resource leak (in that any blocking tasks are still running until they
+        /// return.
+        ///
+        /// This function is equivalent to calling `shutdown_timeout(Duration::of_nanos(0))`.
+        ///
+        /// ```
+        /// use tokio::runtime::Runtime;
+        ///
+        /// fn main() {
+        ///    let runtime = Runtime::new().unwrap();
+        ///
+        ///    runtime.block_on(async move {
+        ///        let inner_runtime = Runtime::new().unwrap();
+        ///        // ...
+        ///        inner_runtime.shutdown_background();
+        ///    });
+        /// }
+        /// ```
+        pub fn shutdown_background(self) {
+            self.shutdown_timeout(Duration::from_nanos(0))
+        }
+    }
+
+    #[allow(clippy::single_match)] // there are comments in the error branch, so we don't want if-let
+    impl Drop for Runtime {
+        fn drop(&mut self) {
+            match &mut self.kind {
+                Kind::CurrentThread(basic) => {
+                    // This ensures that tasks spawned on the basic runtime are dropped inside the
+                    // runtime's context.
+                    match self::context::try_enter(self.handle.clone()) {
+                        Some(guard) => basic.set_context_guard(guard),
+                        None => {
+                            // The context thread-local has already been destroyed.
+                            //
+                            // We don't set the guard in this case. Calls to tokio::spawn in task
+                            // destructors would fail regardless if this happens.
+                        },
+                    }
+                },
+                #[cfg(feature = "rt-multi-thread")]
+                Kind::ThreadPool(_) => {
+                    // The threaded scheduler drops its tasks on its worker threads, which is
+                    // already in the runtime's context.
+                },
+            }
+        }
+    }
+
+    cfg_metrics! {
+        impl Runtime {
+            /// TODO
+            pub fn metrics(&self) -> RuntimeMetrics {
+                self.handle.metrics()
+            }
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/park.rs b/third_party/rust/tokio/src/runtime/park.rs
new file mode 100644
index 0000000000..033b9f20be
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/park.rs
@@ -0,0 +1,257 @@
+//! Parks the runtime.
+//!
+//! A combination of the various resource driver park handles.
+
+use crate::loom::sync::atomic::AtomicUsize;
+use crate::loom::sync::{Arc, Condvar, Mutex};
+use crate::loom::thread;
+use crate::park::{Park, Unpark};
+use crate::runtime::driver::Driver;
+use crate::util::TryLock;
+
+use std::sync::atomic::Ordering::SeqCst;
+use std::time::Duration;
+
+pub(crate) struct Parker {
+    inner: Arc<Inner>,
+}
+
+pub(crate) struct Unparker {
+    inner: Arc<Inner>,
+}
+
+struct Inner {
+    /// Avoids entering the park if possible
+    state: AtomicUsize,
+
+    /// Used to coordinate access to the driver / condvar
+    mutex: Mutex<()>,
+
+    /// Condvar to block on if the driver is unavailable.
+    condvar: Condvar,
+
+    /// Resource (I/O, time, ...) driver
+    shared: Arc<Shared>,
+}
+
+const EMPTY: usize = 0;
+const PARKED_CONDVAR: usize = 1;
+const PARKED_DRIVER: usize = 2;
+const NOTIFIED: usize = 3;
+
+/// Shared across multiple Parker handles
+struct Shared {
+    /// Shared driver. Only one thread at a time can use this
+    driver: TryLock<Driver>,
+
+    /// Unpark handle
+    handle: <Driver as Park>::Unpark,
+}
+
+impl Parker {
+    pub(crate) fn new(driver: Driver) -> Parker {
+        let handle = driver.unpark();
+
+        Parker {
+            inner: Arc::new(Inner {
+                state: AtomicUsize::new(EMPTY),
+                mutex: Mutex::new(()),
+                condvar: Condvar::new(),
+                shared: Arc::new(Shared {
+                    driver: TryLock::new(driver),
+                    handle,
+                }),
+            }),
+        }
+    }
+}
+
+impl Clone for Parker {
+    fn clone(&self) -> Parker {
+        Parker {
+            inner: Arc::new(Inner {
+                state: AtomicUsize::new(EMPTY),
+                mutex: Mutex::new(()),
+                condvar: Condvar::new(),
+                shared: self.inner.shared.clone(),
+            }),
+        }
+    }
+}
+
+impl Park for Parker {
+    type Unpark = Unparker;
+    type Error = ();
+
+    fn unpark(&self) -> Unparker {
+        Unparker {
+            inner: self.inner.clone(),
+        }
+    }
+
+    fn park(&mut self) -> Result<(), Self::Error> {
+        self.inner.park();
+        Ok(())
+    }
+
+    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
+        // Only parking with zero is supported...
+        assert_eq!(duration, Duration::from_millis(0));
+
+        if let Some(mut driver) = self.inner.shared.driver.try_lock() {
+            driver.park_timeout(duration).map_err(|_| ())
+        } else {
+            Ok(())
+        }
+    }
+
+    fn shutdown(&mut self) {
+        self.inner.shutdown();
+    }
+}
+
+impl Unpark for Unparker {
+    fn unpark(&self) {
+        self.inner.unpark();
+    }
+}
+
+impl Inner {
+    /// Parks the current thread for at most `dur`.
+    fn park(&self) {
+        for _ in 0..3 {
+            // If we were previously notified then we consume this notification and
+            // return quickly.
+            if self
+                .state
+                .compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst)
+                .is_ok()
+            {
+                return;
+            }
+
+            thread::yield_now();
+        }
+
+        if let Some(mut driver) = self.shared.driver.try_lock() {
+            self.park_driver(&mut driver);
+        } else {
+            self.park_condvar();
+        }
+    }
+
+    fn park_condvar(&self) {
+        // Otherwise we need to coordinate going to sleep
+        let mut m = self.mutex.lock();
+
+        match self
+            .state
+            .compare_exchange(EMPTY, PARKED_CONDVAR, SeqCst, SeqCst)
+        {
+            Ok(_) => {}
+            Err(NOTIFIED) => {
+                // We must read here, even though we know it will be `NOTIFIED`.
+                // This is because `unpark` may have been called again since we read
+                // `NOTIFIED` in the `compare_exchange` above. We must perform an
+                // acquire operation that synchronizes with that `unpark` to observe
+                // any writes it made before the call to unpark. To do that we must
+                // read from the write it made to `state`.
+                let old = self.state.swap(EMPTY, SeqCst);
+                debug_assert_eq!(old, NOTIFIED, "park state changed unexpectedly");
+
+                return;
+            }
+            Err(actual) => panic!("inconsistent park state; actual = {}", actual),
+        }
+
+        loop {
+            m = self.condvar.wait(m).unwrap();
+
+            if self
+                .state
+                .compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst)
+                .is_ok()
+            {
+                // got a notification
+                return;
+            }
+
+            // spurious wakeup, go back to sleep
+        }
+    }
+
+    fn park_driver(&self, driver: &mut Driver) {
+        match self
+            .state
+            .compare_exchange(EMPTY, PARKED_DRIVER, SeqCst, SeqCst)
+        {
+            Ok(_) => {}
+            Err(NOTIFIED) => {
+                // We must read here, even though we know it will be `NOTIFIED`.
+                // This is because `unpark` may have been called again since we read
+                // `NOTIFIED` in the `compare_exchange` above. We must perform an
+                // acquire operation that synchronizes with that `unpark` to observe
+                // any writes it made before the call to unpark. To do that we must
+                // read from the write it made to `state`.
+                let old = self.state.swap(EMPTY, SeqCst);
+                debug_assert_eq!(old, NOTIFIED, "park state changed unexpectedly");
+
+                return;
+            }
+            Err(actual) => panic!("inconsistent park state; actual = {}", actual),
+        }
+
+        // TODO: don't unwrap
+        driver.park().unwrap();
+
+        match self.state.swap(EMPTY, SeqCst) {
+            NOTIFIED => {}      // got a notification, hurray!
+            PARKED_DRIVER => {} // no notification, alas
+            n => panic!("inconsistent park_timeout state: {}", n),
+        }
+    }
+
+    fn unpark(&self) {
+        // To ensure the unparked thread will observe any writes we made before
+        // this call, we must perform a release operation that `park` can
+        // synchronize with. To do that we must write `NOTIFIED` even if `state`
+        // is already `NOTIFIED`. That is why this must be a swap rather than a
+        // compare-and-swap that returns if it reads `NOTIFIED` on failure.
+        match self.state.swap(NOTIFIED, SeqCst) {
+            EMPTY => {}    // no one was waiting
+            NOTIFIED => {} // already unparked
+            PARKED_CONDVAR => self.unpark_condvar(),
+            PARKED_DRIVER => self.unpark_driver(),
+            actual => panic!("inconsistent state in unpark; actual = {}", actual),
+        }
+    }
+
+    fn unpark_condvar(&self) {
+        // There is a period between when the parked thread sets `state` to
+        // `PARKED` (or last checked `state` in the case of a spurious wake
+        // up) and when it actually waits on `cvar`. If we were to notify
+        // during this period it would be ignored and then when the parked
+        // thread went to sleep it would never wake up. Fortunately, it has
+        // `lock` locked at this stage so we can acquire `lock` to wait until
+        // it is ready to receive the notification.
+        //
+        // Releasing `lock` before the call to `notify_one` means that when the
+        // parked thread wakes it doesn't get woken only to have to wait for us
+        // to release `lock`.
+        drop(self.mutex.lock());
+
+        self.condvar.notify_one()
+    }
+
+    fn unpark_driver(&self) {
+        self.shared.handle.unpark();
+    }
+
+    fn shutdown(&self) {
+        if let Some(mut driver) = self.shared.driver.try_lock() {
+            driver.shutdown();
+        }
+
+        self.condvar.notify_all();
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/queue.rs b/third_party/rust/tokio/src/runtime/queue.rs
new file mode 100644
index 0000000000..ad9085a654
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/queue.rs
@@ -0,0 +1,511 @@
+//! Run-queue structures to support a work-stealing scheduler
+
+use crate::loom::cell::UnsafeCell;
+use crate::loom::sync::atomic::{AtomicU16, AtomicU32};
+use crate::loom::sync::Arc;
+use crate::runtime::task::{self, Inject};
+use crate::runtime::MetricsBatch;
+
+use std::mem::MaybeUninit;
+use std::ptr;
+use std::sync::atomic::Ordering::{AcqRel, Acquire, Relaxed, Release};
+
+/// Producer handle. May only be used from a single thread.
+pub(super) struct Local<T: 'static> {
+    inner: Arc<Inner<T>>,
+}
+
+/// Consumer handle. May be used from many threads.
+pub(super) struct Steal<T: 'static>(Arc<Inner<T>>);
+
+pub(super) struct Inner<T: 'static> {
+    /// Concurrently updated by many threads.
+    ///
+    /// Contains two `u16` values. The LSB byte is the "real" head of the queue.
+    /// The `u16` in the MSB is set by a stealer in process of stealing values.
+    /// It represents the first value being stolen in the batch. `u16` is used
+    /// in order to distinguish between `head == tail` and `head == tail -
+    /// capacity`.
+    ///
+    /// When both `u16` values are the same, there is no active stealer.
+    ///
+    /// Tracking an in-progress stealer prevents a wrapping scenario.
+    head: AtomicU32,
+
+    /// Only updated by producer thread but read by many threads.
+    tail: AtomicU16,
+
+    /// Elements
+    buffer: Box<[UnsafeCell<MaybeUninit<task::Notified<T>>>; LOCAL_QUEUE_CAPACITY]>,
+}
+
+unsafe impl<T> Send for Inner<T> {}
+unsafe impl<T> Sync for Inner<T> {}
+
+#[cfg(not(loom))]
+const LOCAL_QUEUE_CAPACITY: usize = 256;
+
+// Shrink the size of the local queue when using loom. This shouldn't impact
+// logic, but allows loom to test more edge cases in a reasonable a mount of
+// time.
+#[cfg(loom)]
+const LOCAL_QUEUE_CAPACITY: usize = 4;
+
+const MASK: usize = LOCAL_QUEUE_CAPACITY - 1;
+
+// Constructing the fixed size array directly is very awkward. The only way to
+// do it is to repeat `UnsafeCell::new(MaybeUninit::uninit())` 256 times, as
+// the contents are not Copy. The trick with defining a const doesn't work for
+// generic types.
+fn make_fixed_size<T>(buffer: Box<[T]>) -> Box<[T; LOCAL_QUEUE_CAPACITY]> {
+    assert_eq!(buffer.len(), LOCAL_QUEUE_CAPACITY);
+
+    // safety: We check that the length is correct.
+    unsafe { Box::from_raw(Box::into_raw(buffer).cast()) }
+}
+
+/// Create a new local run-queue
+pub(super) fn local<T: 'static>() -> (Steal<T>, Local<T>) {
+    let mut buffer = Vec::with_capacity(LOCAL_QUEUE_CAPACITY);
+
+    for _ in 0..LOCAL_QUEUE_CAPACITY {
+        buffer.push(UnsafeCell::new(MaybeUninit::uninit()));
+    }
+
+    let inner = Arc::new(Inner {
+        head: AtomicU32::new(0),
+        tail: AtomicU16::new(0),
+        buffer: make_fixed_size(buffer.into_boxed_slice()),
+    });
+
+    let local = Local {
+        inner: inner.clone(),
+    };
+
+    let remote = Steal(inner);
+
+    (remote, local)
+}
+
+impl<T> Local<T> {
+    /// Returns true if the queue has entries that can be stealed.
+    pub(super) fn is_stealable(&self) -> bool {
+        !self.inner.is_empty()
+    }
+
+    /// Returns false if there are any entries in the queue
+    ///
+    /// Separate to is_stealable so that refactors of is_stealable to "protect"
+    /// some tasks from stealing won't affect this
+    pub(super) fn has_tasks(&self) -> bool {
+        !self.inner.is_empty()
+    }
+
+    /// Pushes a task to the back of the local queue, skipping the LIFO slot.
+    pub(super) fn push_back(
+        &mut self,
+        mut task: task::Notified<T>,
+        inject: &Inject<T>,
+        metrics: &mut MetricsBatch,
+    ) {
+        let tail = loop {
+            let head = self.inner.head.load(Acquire);
+            let (steal, real) = unpack(head);
+
+            // safety: this is the **only** thread that updates this cell.
+            let tail = unsafe { self.inner.tail.unsync_load() };
+
+            if tail.wrapping_sub(steal) < LOCAL_QUEUE_CAPACITY as u16 {
+                // There is capacity for the task
+                break tail;
+            } else if steal != real {
+                // Concurrently stealing, this will free up capacity, so only
+                // push the task onto the inject queue
+                inject.push(task);
+                return;
+            } else {
+                // Push the current task and half of the queue into the
+                // inject queue.
+                match self.push_overflow(task, real, tail, inject, metrics) {
+                    Ok(_) => return,
+                    // Lost the race, try again
+                    Err(v) => {
+                        task = v;
+                    }
+                }
+            }
+        };
+
+        // Map the position to a slot index.
+        let idx = tail as usize & MASK;
+
+        self.inner.buffer[idx].with_mut(|ptr| {
+            // Write the task to the slot
+            //
+            // Safety: There is only one producer and the above `if`
+            // condition ensures we don't touch a cell if there is a
+            // value, thus no consumer.
+            unsafe {
+                ptr::write((*ptr).as_mut_ptr(), task);
+            }
+        });
+
+        // Make the task available. Synchronizes with a load in
+        // `steal_into2`.
+        self.inner.tail.store(tail.wrapping_add(1), Release);
+    }
+
+    /// Moves a batch of tasks into the inject queue.
+    ///
+    /// This will temporarily make some of the tasks unavailable to stealers.
+    /// Once `push_overflow` is done, a notification is sent out, so if other
+    /// workers "missed" some of the tasks during a steal, they will get
+    /// another opportunity.
+    #[inline(never)]
+    fn push_overflow(
+        &mut self,
+        task: task::Notified<T>,
+        head: u16,
+        tail: u16,
+        inject: &Inject<T>,
+        metrics: &mut MetricsBatch,
+    ) -> Result<(), task::Notified<T>> {
+        /// How many elements are we taking from the local queue.
+        ///
+        /// This is one less than the number of tasks pushed to the inject
+        /// queue as we are also inserting the `task` argument.
+        const NUM_TASKS_TAKEN: u16 = (LOCAL_QUEUE_CAPACITY / 2) as u16;
+
+        assert_eq!(
+            tail.wrapping_sub(head) as usize,
+            LOCAL_QUEUE_CAPACITY,
+            "queue is not full; tail = {}; head = {}",
+            tail,
+            head
+        );
+
+        let prev = pack(head, head);
+
+        // Claim a bunch of tasks
+        //
+        // We are claiming the tasks **before** reading them out of the buffer.
+        // This is safe because only the **current** thread is able to push new
+        // tasks.
+        //
+        // There isn't really any need for memory ordering... Relaxed would
+        // work. This is because all tasks are pushed into the queue from the
+        // current thread (or memory has been acquired if the local queue handle
+        // moved).
+        if self
+            .inner
+            .head
+            .compare_exchange(
+                prev,
+                pack(
+                    head.wrapping_add(NUM_TASKS_TAKEN),
+                    head.wrapping_add(NUM_TASKS_TAKEN),
+                ),
+                Release,
+                Relaxed,
+            )
+            .is_err()
+        {
+            // We failed to claim the tasks, losing the race. Return out of
+            // this function and try the full `push` routine again. The queue
+            // may not be full anymore.
+            return Err(task);
+        }
+
+        /// An iterator that takes elements out of the run queue.
+        struct BatchTaskIter<'a, T: 'static> {
+            buffer: &'a [UnsafeCell<MaybeUninit<task::Notified<T>>>; LOCAL_QUEUE_CAPACITY],
+            head: u32,
+            i: u32,
+        }
+        impl<'a, T: 'static> Iterator for BatchTaskIter<'a, T> {
+            type Item = task::Notified<T>;
+
+            #[inline]
+            fn next(&mut self) -> Option<task::Notified<T>> {
+                if self.i == u32::from(NUM_TASKS_TAKEN) {
+                    None
+                } else {
+                    let i_idx = self.i.wrapping_add(self.head) as usize & MASK;
+                    let slot = &self.buffer[i_idx];
+
+                    // safety: Our CAS from before has assumed exclusive ownership
+                    // of the task pointers in this range.
+                    let task = slot.with(|ptr| unsafe { ptr::read((*ptr).as_ptr()) });
+
+                    self.i += 1;
+                    Some(task)
+                }
+            }
+        }
+
+        // safety: The CAS above ensures that no consumer will look at these
+        // values again, and we are the only producer.
+        let batch_iter = BatchTaskIter {
+            buffer: &*self.inner.buffer,
+            head: head as u32,
+            i: 0,
+        };
+        inject.push_batch(batch_iter.chain(std::iter::once(task)));
+
+        // Add 1 to factor in the task currently being scheduled.
+        metrics.incr_overflow_count();
+
+        Ok(())
+    }
+
+    /// Pops a task from the local queue.
+    pub(super) fn pop(&mut self) -> Option<task::Notified<T>> {
+        let mut head = self.inner.head.load(Acquire);
+
+        let idx = loop {
+            let (steal, real) = unpack(head);
+
+            // safety: this is the **only** thread that updates this cell.
+            let tail = unsafe { self.inner.tail.unsync_load() };
+
+            if real == tail {
+                // queue is empty
+                return None;
+            }
+
+            let next_real = real.wrapping_add(1);
+
+            // If `steal == real` there are no concurrent stealers. Both `steal`
+            // and `real` are updated.
+            let next = if steal == real {
+                pack(next_real, next_real)
+            } else {
+                assert_ne!(steal, next_real);
+                pack(steal, next_real)
+            };
+
+            // Attempt to claim a task.
+            let res = self
+                .inner
+                .head
+                .compare_exchange(head, next, AcqRel, Acquire);
+
+            match res {
+                Ok(_) => break real as usize & MASK,
+                Err(actual) => head = actual,
+            }
+        };
+
+        Some(self.inner.buffer[idx].with(|ptr| unsafe { ptr::read(ptr).assume_init() }))
+    }
+}
+
+impl<T> Steal<T> {
+    pub(super) fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+
+    /// Steals half the tasks from self and place them into `dst`.
+    pub(super) fn steal_into(
+        &self,
+        dst: &mut Local<T>,
+        dst_metrics: &mut MetricsBatch,
+    ) -> Option<task::Notified<T>> {
+        // Safety: the caller is the only thread that mutates `dst.tail` and
+        // holds a mutable reference.
+        let dst_tail = unsafe { dst.inner.tail.unsync_load() };
+
+        // To the caller, `dst` may **look** empty but still have values
+        // contained in the buffer. If another thread is concurrently stealing
+        // from `dst` there may not be enough capacity to steal.
+        let (steal, _) = unpack(dst.inner.head.load(Acquire));
+
+        if dst_tail.wrapping_sub(steal) > LOCAL_QUEUE_CAPACITY as u16 / 2 {
+            // we *could* try to steal less here, but for simplicity, we're just
+            // going to abort.
+            return None;
+        }
+
+        // Steal the tasks into `dst`'s buffer. This does not yet expose the
+        // tasks in `dst`.
+        let mut n = self.steal_into2(dst, dst_tail);
+
+        if n == 0 {
+            // No tasks were stolen
+            return None;
+        }
+
+        dst_metrics.incr_steal_count(n);
+
+        // We are returning a task here
+        n -= 1;
+
+        let ret_pos = dst_tail.wrapping_add(n);
+        let ret_idx = ret_pos as usize & MASK;
+
+        // safety: the value was written as part of `steal_into2` and not
+        // exposed to stealers, so no other thread can access it.
+        let ret = dst.inner.buffer[ret_idx].with(|ptr| unsafe { ptr::read((*ptr).as_ptr()) });
+
+        if n == 0 {
+            // The `dst` queue is empty, but a single task was stolen
+            return Some(ret);
+        }
+
+        // Make the stolen items available to consumers
+        dst.inner.tail.store(dst_tail.wrapping_add(n), Release);
+
+        Some(ret)
+    }
+
+    // Steal tasks from `self`, placing them into `dst`. Returns the number of
+    // tasks that were stolen.
+    fn steal_into2(&self, dst: &mut Local<T>, dst_tail: u16) -> u16 {
+        let mut prev_packed = self.0.head.load(Acquire);
+        let mut next_packed;
+
+        let n = loop {
+            let (src_head_steal, src_head_real) = unpack(prev_packed);
+            let src_tail = self.0.tail.load(Acquire);
+
+            // If these two do not match, another thread is concurrently
+            // stealing from the queue.
+            if src_head_steal != src_head_real {
+                return 0;
+            }
+
+            // Number of available tasks to steal
+            let n = src_tail.wrapping_sub(src_head_real);
+            let n = n - n / 2;
+
+            if n == 0 {
+                // No tasks available to steal
+                return 0;
+            }
+
+            // Update the real head index to acquire the tasks.
+            let steal_to = src_head_real.wrapping_add(n);
+            assert_ne!(src_head_steal, steal_to);
+            next_packed = pack(src_head_steal, steal_to);
+
+            // Claim all those tasks. This is done by incrementing the "real"
+            // head but not the steal. By doing this, no other thread is able to
+            // steal from this queue until the current thread completes.
+            let res = self
+                .0
+                .head
+                .compare_exchange(prev_packed, next_packed, AcqRel, Acquire);
+
+            match res {
+                Ok(_) => break n,
+                Err(actual) => prev_packed = actual,
+            }
+        };
+
+        assert!(n <= LOCAL_QUEUE_CAPACITY as u16 / 2, "actual = {}", n);
+
+        let (first, _) = unpack(next_packed);
+
+        // Take all the tasks
+        for i in 0..n {
+            // Compute the positions
+            let src_pos = first.wrapping_add(i);
+            let dst_pos = dst_tail.wrapping_add(i);
+
+            // Map to slots
+            let src_idx = src_pos as usize & MASK;
+            let dst_idx = dst_pos as usize & MASK;
+
+            // Read the task
+            //
+            // safety: We acquired the task with the atomic exchange above.
+            let task = self.0.buffer[src_idx].with(|ptr| unsafe { ptr::read((*ptr).as_ptr()) });
+
+            // Write the task to the new slot
+            //
+            // safety: `dst` queue is empty and we are the only producer to
+            // this queue.
+            dst.inner.buffer[dst_idx]
+                .with_mut(|ptr| unsafe { ptr::write((*ptr).as_mut_ptr(), task) });
+        }
+
+        let mut prev_packed = next_packed;
+
+        // Update `src_head_steal` to match `src_head_real` signalling that the
+        // stealing routine is complete.
+        loop {
+            let head = unpack(prev_packed).1;
+            next_packed = pack(head, head);
+
+            let res = self
+                .0
+                .head
+                .compare_exchange(prev_packed, next_packed, AcqRel, Acquire);
+
+            match res {
+                Ok(_) => return n,
+                Err(actual) => {
+                    let (actual_steal, actual_real) = unpack(actual);
+
+                    assert_ne!(actual_steal, actual_real);
+
+                    prev_packed = actual;
+                }
+            }
+        }
+    }
+}
+
+cfg_metrics! {
+    impl<T> Steal<T> {
+        pub(crate) fn len(&self) -> usize {
+            self.0.len() as _
+        }
+    }
+}
+
+impl<T> Clone for Steal<T> {
+    fn clone(&self) -> Steal<T> {
+        Steal(self.0.clone())
+    }
+}
+
+impl<T> Drop for Local<T> {
+    fn drop(&mut self) {
+        if !std::thread::panicking() {
+            assert!(self.pop().is_none(), "queue not empty");
+        }
+    }
+}
+
+impl<T> Inner<T> {
+    fn len(&self) -> u16 {
+        let (_, head) = unpack(self.head.load(Acquire));
+        let tail = self.tail.load(Acquire);
+
+        tail.wrapping_sub(head)
+    }
+
+    fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+}
+
+/// Split the head value into the real head and the index a stealer is working
+/// on.
+fn unpack(n: u32) -> (u16, u16) {
+    let real = n & u16::MAX as u32;
+    let steal = n >> 16;
+
+    (steal as u16, real as u16)
+}
+
+/// Join the two head values
+fn pack(steal: u16, real: u16) -> u32 {
+    (real as u32) | ((steal as u32) << 16)
+}
+
+#[test]
+fn test_local_queue_capacity() {
+    assert!(LOCAL_QUEUE_CAPACITY - 1 <= u8::MAX as usize);
+}
diff --git a/third_party/rust/tokio/src/runtime/spawner.rs b/third_party/rust/tokio/src/runtime/spawner.rs
new file mode 100644
index 0000000000..d81a806cb5
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/spawner.rs
@@ -0,0 +1,83 @@
+use crate::future::Future;
+use crate::runtime::basic_scheduler;
+use crate::task::JoinHandle;
+
+cfg_rt_multi_thread! {
+    use crate::runtime::thread_pool;
+}
+
+#[derive(Debug, Clone)]
+pub(crate) enum Spawner {
+    Basic(basic_scheduler::Spawner),
+    #[cfg(feature = "rt-multi-thread")]
+    ThreadPool(thread_pool::Spawner),
+}
+
+impl Spawner {
+    pub(crate) fn shutdown(&mut self) {
+        #[cfg(feature = "rt-multi-thread")]
+        {
+            if let Spawner::ThreadPool(spawner) = self {
+                spawner.shutdown();
+            }
+        }
+    }
+
+    pub(crate) fn spawn<F>(&self, future: F) -> JoinHandle<F::Output>
+    where
+        F: Future + Send + 'static,
+        F::Output: Send + 'static,
+    {
+        match self {
+            Spawner::Basic(spawner) => spawner.spawn(future),
+            #[cfg(feature = "rt-multi-thread")]
+            Spawner::ThreadPool(spawner) => spawner.spawn(future),
+        }
+    }
+}
+
+cfg_metrics! {
+    use crate::runtime::{SchedulerMetrics, WorkerMetrics};
+
+    impl Spawner {
+        pub(crate) fn num_workers(&self) -> usize {
+            match self {
+                Spawner::Basic(_) => 1,
+                #[cfg(feature = "rt-multi-thread")]
+                Spawner::ThreadPool(spawner) => spawner.num_workers(),
+            }
+        }
+
+        pub(crate) fn scheduler_metrics(&self) -> &SchedulerMetrics {
+            match self {
+                Spawner::Basic(spawner) => spawner.scheduler_metrics(),
+                #[cfg(feature = "rt-multi-thread")]
+                Spawner::ThreadPool(spawner) => spawner.scheduler_metrics(),
+            }
+        }
+
+        pub(crate) fn worker_metrics(&self, worker: usize) -> &WorkerMetrics {
+            match self {
+                Spawner::Basic(spawner) => spawner.worker_metrics(worker),
+                #[cfg(feature = "rt-multi-thread")]
+                Spawner::ThreadPool(spawner) => spawner.worker_metrics(worker),
+            }
+        }
+
+        pub(crate) fn injection_queue_depth(&self) -> usize {
+            match self {
+                Spawner::Basic(spawner) => spawner.injection_queue_depth(),
+                #[cfg(feature = "rt-multi-thread")]
+                Spawner::ThreadPool(spawner) => spawner.injection_queue_depth(),
+            }
+        }
+
+        pub(crate) fn worker_local_queue_depth(&self, worker: usize) -> usize {
+            match self {
+                Spawner::Basic(spawner) => spawner.worker_metrics(worker).queue_depth(),
+                #[cfg(feature = "rt-multi-thread")]
+                Spawner::ThreadPool(spawner) => spawner.worker_local_queue_depth(worker),
+            }
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/task/core.rs b/third_party/rust/tokio/src/runtime/task/core.rs
new file mode 100644
index 0000000000..776e8341f3
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/task/core.rs
@@ -0,0 +1,267 @@
+//! Core task module.
+//!
+//! # Safety
+//!
+//! The functions in this module are private to the `task` module. All of them
+//! should be considered `unsafe` to use, but are not marked as such since it
+//! would be too noisy.
+//!
+//! Make sure to consult the relevant safety section of each function before
+//! use.
+
+use crate::future::Future;
+use crate::loom::cell::UnsafeCell;
+use crate::runtime::task::raw::{self, Vtable};
+use crate::runtime::task::state::State;
+use crate::runtime::task::Schedule;
+use crate::util::linked_list;
+
+use std::pin::Pin;
+use std::ptr::NonNull;
+use std::task::{Context, Poll, Waker};
+
+/// The task cell. Contains the components of the task.
+///
+/// It is critical for `Header` to be the first field as the task structure will
+/// be referenced by both *mut Cell and *mut Header.
+#[repr(C)]
+pub(super) struct Cell<T: Future, S> {
+    /// Hot task state data
+    pub(super) header: Header,
+
+    /// Either the future or output, depending on the execution stage.
+    pub(super) core: Core<T, S>,
+
+    /// Cold data
+    pub(super) trailer: Trailer,
+}
+
+pub(super) struct CoreStage<T: Future> {
+    stage: UnsafeCell<Stage<T>>,
+}
+
+/// The core of the task.
+///
+/// Holds the future or output, depending on the stage of execution.
+pub(super) struct Core<T: Future, S> {
+    /// Scheduler used to drive this future.
+    pub(super) scheduler: S,
+
+    /// Either the future or the output.
+    pub(super) stage: CoreStage<T>,
+}
+
+/// Crate public as this is also needed by the pool.
+#[repr(C)]
+pub(crate) struct Header {
+    /// Task state.
+    pub(super) state: State,
+
+    pub(super) owned: UnsafeCell<linked_list::Pointers<Header>>,
+
+    /// Pointer to next task, used with the injection queue.
+    pub(super) queue_next: UnsafeCell<Option<NonNull<Header>>>,
+
+    /// Table of function pointers for executing actions on the task.
+    pub(super) vtable: &'static Vtable,
+
+    /// This integer contains the id of the OwnedTasks or LocalOwnedTasks that
+    /// this task is stored in. If the task is not in any list, should be the
+    /// id of the list that it was previously in, or zero if it has never been
+    /// in any list.
+    ///
+    /// Once a task has been bound to a list, it can never be bound to another
+    /// list, even if removed from the first list.
+    ///
+    /// The id is not unset when removed from a list because we want to be able
+    /// to read the id without synchronization, even if it is concurrently being
+    /// removed from the list.
+    pub(super) owner_id: UnsafeCell<u64>,
+
+    /// The tracing ID for this instrumented task.
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    pub(super) id: Option<tracing::Id>,
+}
+
+unsafe impl Send for Header {}
+unsafe impl Sync for Header {}
+
+/// Cold data is stored after the future.
+pub(super) struct Trailer {
+    /// Consumer task waiting on completion of this task.
+    pub(super) waker: UnsafeCell<Option<Waker>>,
+}
+
+/// Either the future or the output.
+pub(super) enum Stage<T: Future> {
+    Running(T),
+    Finished(super::Result<T::Output>),
+    Consumed,
+}
+
+impl<T: Future, S: Schedule> Cell<T, S> {
+    /// Allocates a new task cell, containing the header, trailer, and core
+    /// structures.
+    pub(super) fn new(future: T, scheduler: S, state: State) -> Box<Cell<T, S>> {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let id = future.id();
+        Box::new(Cell {
+            header: Header {
+                state,
+                owned: UnsafeCell::new(linked_list::Pointers::new()),
+                queue_next: UnsafeCell::new(None),
+                vtable: raw::vtable::<T, S>(),
+                owner_id: UnsafeCell::new(0),
+                #[cfg(all(tokio_unstable, feature = "tracing"))]
+                id,
+            },
+            core: Core {
+                scheduler,
+                stage: CoreStage {
+                    stage: UnsafeCell::new(Stage::Running(future)),
+                },
+            },
+            trailer: Trailer {
+                waker: UnsafeCell::new(None),
+            },
+        })
+    }
+}
+
+impl<T: Future> CoreStage<T> {
+    pub(super) fn with_mut<R>(&self, f: impl FnOnce(*mut Stage<T>) -> R) -> R {
+        self.stage.with_mut(f)
+    }
+
+    /// Polls the future.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure it is safe to mutate the `state` field. This
+    /// requires ensuring mutual exclusion between any concurrent thread that
+    /// might modify the future or output field.
+    ///
+    /// The mutual exclusion is implemented by `Harness` and the `Lifecycle`
+    /// component of the task state.
+    ///
+    /// `self` must also be pinned. This is handled by storing the task on the
+    /// heap.
+    pub(super) fn poll(&self, mut cx: Context<'_>) -> Poll<T::Output> {
+        let res = {
+            self.stage.with_mut(|ptr| {
+                // Safety: The caller ensures mutual exclusion to the field.
+                let future = match unsafe { &mut *ptr } {
+                    Stage::Running(future) => future,
+                    _ => unreachable!("unexpected stage"),
+                };
+
+                // Safety: The caller ensures the future is pinned.
+                let future = unsafe { Pin::new_unchecked(future) };
+
+                future.poll(&mut cx)
+            })
+        };
+
+        if res.is_ready() {
+            self.drop_future_or_output();
+        }
+
+        res
+    }
+
+    /// Drops the future.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure it is safe to mutate the `stage` field.
+    pub(super) fn drop_future_or_output(&self) {
+        // Safety: the caller ensures mutual exclusion to the field.
+        unsafe {
+            self.set_stage(Stage::Consumed);
+        }
+    }
+
+    /// Stores the task output.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure it is safe to mutate the `stage` field.
+    pub(super) fn store_output(&self, output: super::Result<T::Output>) {
+        // Safety: the caller ensures mutual exclusion to the field.
+        unsafe {
+            self.set_stage(Stage::Finished(output));
+        }
+    }
+
+    /// Takes the task output.
+    ///
+    /// # Safety
+    ///
+    /// The caller must ensure it is safe to mutate the `stage` field.
+    pub(super) fn take_output(&self) -> super::Result<T::Output> {
+        use std::mem;
+
+        self.stage.with_mut(|ptr| {
+            // Safety:: the caller ensures mutual exclusion to the field.
+            match mem::replace(unsafe { &mut *ptr }, Stage::Consumed) {
+                Stage::Finished(output) => output,
+                _ => panic!("JoinHandle polled after completion"),
+            }
+        })
+    }
+
+    unsafe fn set_stage(&self, stage: Stage<T>) {
+        self.stage.with_mut(|ptr| *ptr = stage)
+    }
+}
+
+cfg_rt_multi_thread! {
+    impl Header {
+        pub(super) unsafe fn set_next(&self, next: Option<NonNull<Header>>) {
+            self.queue_next.with_mut(|ptr| *ptr = next);
+        }
+    }
+}
+
+impl Header {
+    // safety: The caller must guarantee exclusive access to this field, and
+    // must ensure that the id is either 0 or the id of the OwnedTasks
+    // containing this task.
+    pub(super) unsafe fn set_owner_id(&self, owner: u64) {
+        self.owner_id.with_mut(|ptr| *ptr = owner);
+    }
+
+    pub(super) fn get_owner_id(&self) -> u64 {
+        // safety: If there are concurrent writes, then that write has violated
+        // the safety requirements on `set_owner_id`.
+        unsafe { self.owner_id.with(|ptr| *ptr) }
+    }
+}
+
+impl Trailer {
+    pub(super) unsafe fn set_waker(&self, waker: Option<Waker>) {
+        self.waker.with_mut(|ptr| {
+            *ptr = waker;
+        });
+    }
+
+    pub(super) unsafe fn will_wake(&self, waker: &Waker) -> bool {
+        self.waker
+            .with(|ptr| (*ptr).as_ref().unwrap().will_wake(waker))
+    }
+
+    pub(super) fn wake_join(&self) {
+        self.waker.with(|ptr| match unsafe { &*ptr } {
+            Some(waker) => waker.wake_by_ref(),
+            None => panic!("waker missing"),
+        });
+    }
+}
+
+#[test]
+#[cfg(not(loom))]
+fn header_lte_cache_line() {
+    use std::mem::size_of;
+
+    assert!(size_of::<Header>() <= 8 * size_of::<*const ()>());
+}
diff --git a/third_party/rust/tokio/src/runtime/task/error.rs b/third_party/rust/tokio/src/runtime/task/error.rs
new file mode 100644
index 0000000000..1a8129b2b6
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/task/error.rs
@@ -0,0 +1,146 @@
+use std::any::Any;
+use std::fmt;
+use std::io;
+
+use crate::util::SyncWrapper;
+
+cfg_rt! {
+    /// Task failed to execute to completion.
+    pub struct JoinError {
+        repr: Repr,
+    }
+}
+
+enum Repr {
+    Cancelled,
+    Panic(SyncWrapper<Box<dyn Any + Send + 'static>>),
+}
+
+impl JoinError {
+    pub(crate) fn cancelled() -> JoinError {
+        JoinError {
+            repr: Repr::Cancelled,
+        }
+    }
+
+    pub(crate) fn panic(err: Box<dyn Any + Send + 'static>) -> JoinError {
+        JoinError {
+            repr: Repr::Panic(SyncWrapper::new(err)),
+        }
+    }
+
+    /// Returns true if the error was caused by the task being cancelled.
+    pub fn is_cancelled(&self) -> bool {
+        matches!(&self.repr, Repr::Cancelled)
+    }
+
+    /// Returns true if the error was caused by the task panicking.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::panic;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let err = tokio::spawn(async {
+    ///         panic!("boom");
+    ///     }).await.unwrap_err();
+    ///
+    ///     assert!(err.is_panic());
+    /// }
+    /// ```
+    pub fn is_panic(&self) -> bool {
+        matches!(&self.repr, Repr::Panic(_))
+    }
+
+    /// Consumes the join error, returning the object with which the task panicked.
+    ///
+    /// # Panics
+    ///
+    /// `into_panic()` panics if the `Error` does not represent the underlying
+    /// task terminating with a panic. Use `is_panic` to check the error reason
+    /// or `try_into_panic` for a variant that does not panic.
+    ///
+    /// # Examples
+    ///
+    /// ```should_panic
+    /// use std::panic;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let err = tokio::spawn(async {
+    ///         panic!("boom");
+    ///     }).await.unwrap_err();
+    ///
+    ///     if err.is_panic() {
+    ///         // Resume the panic on the main task
+    ///         panic::resume_unwind(err.into_panic());
+    ///     }
+    /// }
+    /// ```
+    pub fn into_panic(self) -> Box<dyn Any + Send + 'static> {
+        self.try_into_panic()
+            .expect("`JoinError` reason is not a panic.")
+    }
+
+    /// Consumes the join error, returning the object with which the task
+    /// panicked if the task terminated due to a panic. Otherwise, `self` is
+    /// returned.
+    ///
+    /// # Examples
+    ///
+    /// ```should_panic
+    /// use std::panic;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let err = tokio::spawn(async {
+    ///         panic!("boom");
+    ///     }).await.unwrap_err();
+    ///
+    ///     if let Ok(reason) = err.try_into_panic() {
+    ///         // Resume the panic on the main task
+    ///         panic::resume_unwind(reason);
+    ///     }
+    /// }
+    /// ```
+    pub fn try_into_panic(self) -> Result<Box<dyn Any + Send + 'static>, JoinError> {
+        match self.repr {
+            Repr::Panic(p) => Ok(p.into_inner()),
+            _ => Err(self),
+        }
+    }
+}
+
+impl fmt::Display for JoinError {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match &self.repr {
+            Repr::Cancelled => write!(fmt, "cancelled"),
+            Repr::Panic(_) => write!(fmt, "panic"),
+        }
+    }
+}
+
+impl fmt::Debug for JoinError {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match &self.repr {
+            Repr::Cancelled => write!(fmt, "JoinError::Cancelled"),
+            Repr::Panic(_) => write!(fmt, "JoinError::Panic(...)"),
+        }
+    }
+}
+
+impl std::error::Error for JoinError {}
+
+impl From<JoinError> for io::Error {
+    fn from(src: JoinError) -> io::Error {
+        io::Error::new(
+            io::ErrorKind::Other,
+            match src.repr {
+                Repr::Cancelled => "task was cancelled",
+                Repr::Panic(_) => "task panicked",
+            },
+        )
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/task/harness.rs b/third_party/rust/tokio/src/runtime/task/harness.rs
new file mode 100644
index 0000000000..261dccea41
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/task/harness.rs
@@ -0,0 +1,485 @@
+use crate::future::Future;
+use crate::runtime::task::core::{Cell, Core, CoreStage, Header, Trailer};
+use crate::runtime::task::state::Snapshot;
+use crate::runtime::task::waker::waker_ref;
+use crate::runtime::task::{JoinError, Notified, Schedule, Task};
+
+use std::mem;
+use std::mem::ManuallyDrop;
+use std::panic;
+use std::ptr::NonNull;
+use std::task::{Context, Poll, Waker};
+
+/// Typed raw task handle.
+pub(super) struct Harness<T: Future, S: 'static> {
+    cell: NonNull<Cell<T, S>>,
+}
+
+impl<T, S> Harness<T, S>
+where
+    T: Future,
+    S: 'static,
+{
+    pub(super) unsafe fn from_raw(ptr: NonNull<Header>) -> Harness<T, S> {
+        Harness {
+            cell: ptr.cast::<Cell<T, S>>(),
+        }
+    }
+
+    fn header_ptr(&self) -> NonNull<Header> {
+        self.cell.cast()
+    }
+
+    fn header(&self) -> &Header {
+        unsafe { &self.cell.as_ref().header }
+    }
+
+    fn trailer(&self) -> &Trailer {
+        unsafe { &self.cell.as_ref().trailer }
+    }
+
+    fn core(&self) -> &Core<T, S> {
+        unsafe { &self.cell.as_ref().core }
+    }
+}
+
+impl<T, S> Harness<T, S>
+where
+    T: Future,
+    S: Schedule,
+{
+    /// Polls the inner future. A ref-count is consumed.
+    ///
+    /// All necessary state checks and transitions are performed.
+    /// Panics raised while polling the future are handled.
+    pub(super) fn poll(self) {
+        // We pass our ref-count to `poll_inner`.
+        match self.poll_inner() {
+            PollFuture::Notified => {
+                // The `poll_inner` call has given us two ref-counts back.
+                // We give one of them to a new task and call `yield_now`.
+                self.core()
+                    .scheduler
+                    .yield_now(Notified(self.get_new_task()));
+
+                // The remaining ref-count is now dropped. We kept the extra
+                // ref-count until now to ensure that even if the `yield_now`
+                // call drops the provided task, the task isn't deallocated
+                // before after `yield_now` returns.
+                self.drop_reference();
+            }
+            PollFuture::Complete => {
+                self.complete();
+            }
+            PollFuture::Dealloc => {
+                self.dealloc();
+            }
+            PollFuture::Done => (),
+        }
+    }
+
+    /// Polls the task and cancel it if necessary. This takes ownership of a
+    /// ref-count.
+    ///
+    /// If the return value is Notified, the caller is given ownership of two
+    /// ref-counts.
+    ///
+    /// If the return value is Complete, the caller is given ownership of a
+    /// single ref-count, which should be passed on to `complete`.
+    ///
+    /// If the return value is Dealloc, then this call consumed the last
+    /// ref-count and the caller should call `dealloc`.
+    ///
+    /// Otherwise the ref-count is consumed and the caller should not access
+    /// `self` again.
+    fn poll_inner(&self) -> PollFuture {
+        use super::state::{TransitionToIdle, TransitionToRunning};
+
+        match self.header().state.transition_to_running() {
+            TransitionToRunning::Success => {
+                let header_ptr = self.header_ptr();
+                let waker_ref = waker_ref::<T, S>(&header_ptr);
+                let cx = Context::from_waker(&*waker_ref);
+                let res = poll_future(&self.core().stage, cx);
+
+                if res == Poll::Ready(()) {
+                    // The future completed. Move on to complete the task.
+                    return PollFuture::Complete;
+                }
+
+                match self.header().state.transition_to_idle() {
+                    TransitionToIdle::Ok => PollFuture::Done,
+                    TransitionToIdle::OkNotified => PollFuture::Notified,
+                    TransitionToIdle::OkDealloc => PollFuture::Dealloc,
+                    TransitionToIdle::Cancelled => {
+                        // The transition to idle failed because the task was
+                        // cancelled during the poll.
+
+                        cancel_task(&self.core().stage);
+                        PollFuture::Complete
+                    }
+                }
+            }
+            TransitionToRunning::Cancelled => {
+                cancel_task(&self.core().stage);
+                PollFuture::Complete
+            }
+            TransitionToRunning::Failed => PollFuture::Done,
+            TransitionToRunning::Dealloc => PollFuture::Dealloc,
+        }
+    }
+
+    /// Forcibly shuts down the task.
+    ///
+    /// Attempt to transition to `Running` in order to forcibly shutdown the
+    /// task. If the task is currently running or in a state of completion, then
+    /// there is nothing further to do. When the task completes running, it will
+    /// notice the `CANCELLED` bit and finalize the task.
+    pub(super) fn shutdown(self) {
+        if !self.header().state.transition_to_shutdown() {
+            // The task is concurrently running. No further work needed.
+            self.drop_reference();
+            return;
+        }
+
+        // By transitioning the lifecycle to `Running`, we have permission to
+        // drop the future.
+        cancel_task(&self.core().stage);
+        self.complete();
+    }
+
+    pub(super) fn dealloc(self) {
+        // Release the join waker, if there is one.
+        self.trailer().waker.with_mut(drop);
+
+        // Check causality
+        self.core().stage.with_mut(drop);
+
+        unsafe {
+            drop(Box::from_raw(self.cell.as_ptr()));
+        }
+    }
+
+    // ===== join handle =====
+
+    /// Read the task output into `dst`.
+    pub(super) fn try_read_output(self, dst: &mut Poll<super::Result<T::Output>>, waker: &Waker) {
+        if can_read_output(self.header(), self.trailer(), waker) {
+            *dst = Poll::Ready(self.core().stage.take_output());
+        }
+    }
+
+    /// Try to set the waker notified when the task is complete. Returns true if
+    /// the task has already completed. If this call returns false, then the
+    /// waker will not be notified.
+    pub(super) fn try_set_join_waker(self, waker: &Waker) -> bool {
+        can_read_output(self.header(), self.trailer(), waker)
+    }
+
+    pub(super) fn drop_join_handle_slow(self) {
+        // Try to unset `JOIN_INTEREST`. This must be done as a first step in
+        // case the task concurrently completed.
+        if self.header().state.unset_join_interested().is_err() {
+            // It is our responsibility to drop the output. This is critical as
+            // the task output may not be `Send` and as such must remain with
+            // the scheduler or `JoinHandle`. i.e. if the output remains in the
+            // task structure until the task is deallocated, it may be dropped
+            // by a Waker on any arbitrary thread.
+            //
+            // Panics are delivered to the user via the `JoinHandle`. Given that
+            // they are dropping the `JoinHandle`, we assume they are not
+            // interested in the panic and swallow it.
+            let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+                self.core().stage.drop_future_or_output();
+            }));
+        }
+
+        // Drop the `JoinHandle` reference, possibly deallocating the task
+        self.drop_reference();
+    }
+
+    /// Remotely aborts the task.
+    ///
+    /// The caller should hold a ref-count, but we do not consume it.
+    ///
+    /// This is similar to `shutdown` except that it asks the runtime to perform
+    /// the shutdown. This is necessary to avoid the shutdown happening in the
+    /// wrong thread for non-Send tasks.
+    pub(super) fn remote_abort(self) {
+        if self.header().state.transition_to_notified_and_cancel() {
+            // The transition has created a new ref-count, which we turn into
+            // a Notified and pass to the task.
+            //
+            // Since the caller holds a ref-count, the task cannot be destroyed
+            // before the call to `schedule` returns even if the call drops the
+            // `Notified` internally.
+            self.core()
+                .scheduler
+                .schedule(Notified(self.get_new_task()));
+        }
+    }
+
+    // ===== waker behavior =====
+
+    /// This call consumes a ref-count and notifies the task. This will create a
+    /// new Notified and submit it if necessary.
+    ///
+    /// The caller does not need to hold a ref-count besides the one that was
+    /// passed to this call.
+    pub(super) fn wake_by_val(self) {
+        use super::state::TransitionToNotifiedByVal;
+
+        match self.header().state.transition_to_notified_by_val() {
+            TransitionToNotifiedByVal::Submit => {
+                // The caller has given us a ref-count, and the transition has
+                // created a new ref-count, so we now hold two. We turn the new
+                // ref-count Notified and pass it to the call to `schedule`.
+                //
+                // The old ref-count is retained for now to ensure that the task
+                // is not dropped during the call to `schedule` if the call
+                // drops the task it was given.
+                self.core()
+                    .scheduler
+                    .schedule(Notified(self.get_new_task()));
+
+                // Now that we have completed the call to schedule, we can
+                // release our ref-count.
+                self.drop_reference();
+            }
+            TransitionToNotifiedByVal::Dealloc => {
+                self.dealloc();
+            }
+            TransitionToNotifiedByVal::DoNothing => {}
+        }
+    }
+
+    /// This call notifies the task. It will not consume any ref-counts, but the
+    /// caller should hold a ref-count.  This will create a new Notified and
+    /// submit it if necessary.
+    pub(super) fn wake_by_ref(&self) {
+        use super::state::TransitionToNotifiedByRef;
+
+        match self.header().state.transition_to_notified_by_ref() {
+            TransitionToNotifiedByRef::Submit => {
+                // The transition above incremented the ref-count for a new task
+                // and the caller also holds a ref-count. The caller's ref-count
+                // ensures that the task is not destroyed even if the new task
+                // is dropped before `schedule` returns.
+                self.core()
+                    .scheduler
+                    .schedule(Notified(self.get_new_task()));
+            }
+            TransitionToNotifiedByRef::DoNothing => {}
+        }
+    }
+
+    pub(super) fn drop_reference(self) {
+        if self.header().state.ref_dec() {
+            self.dealloc();
+        }
+    }
+
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    pub(super) fn id(&self) -> Option<&tracing::Id> {
+        self.header().id.as_ref()
+    }
+
+    // ====== internal ======
+
+    /// Completes the task. This method assumes that the state is RUNNING.
+    fn complete(self) {
+        // The future has completed and its output has been written to the task
+        // stage. We transition from running to complete.
+
+        let snapshot = self.header().state.transition_to_complete();
+
+        // We catch panics here in case dropping the future or waking the
+        // JoinHandle panics.
+        let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+            if !snapshot.is_join_interested() {
+                // The `JoinHandle` is not interested in the output of
+                // this task. It is our responsibility to drop the
+                // output.
+                self.core().stage.drop_future_or_output();
+            } else if snapshot.has_join_waker() {
+                // Notify the join handle. The previous transition obtains the
+                // lock on the waker cell.
+                self.trailer().wake_join();
+            }
+        }));
+
+        // The task has completed execution and will no longer be scheduled.
+        let num_release = self.release();
+
+        if self.header().state.transition_to_terminal(num_release) {
+            self.dealloc();
+        }
+    }
+
+    /// Releases the task from the scheduler. Returns the number of ref-counts
+    /// that should be decremented.
+    fn release(&self) -> usize {
+        // We don't actually increment the ref-count here, but the new task is
+        // never destroyed, so that's ok.
+        let me = ManuallyDrop::new(self.get_new_task());
+
+        if let Some(task) = self.core().scheduler.release(&me) {
+            mem::forget(task);
+            2
+        } else {
+            1
+        }
+    }
+
+    /// Creates a new task that holds its own ref-count.
+    ///
+    /// # Safety
+    ///
+    /// Any use of `self` after this call must ensure that a ref-count to the
+    /// task holds the task alive until after the use of `self`. Passing the
+    /// returned Task to any method on `self` is unsound if dropping the Task
+    /// could drop `self` before the call on `self` returned.
+    fn get_new_task(&self) -> Task<S> {
+        // safety: The header is at the beginning of the cell, so this cast is
+        // safe.
+        unsafe { Task::from_raw(self.cell.cast()) }
+    }
+}
+
+fn can_read_output(header: &Header, trailer: &Trailer, waker: &Waker) -> bool {
+    // Load a snapshot of the current task state
+    let snapshot = header.state.load();
+
+    debug_assert!(snapshot.is_join_interested());
+
+    if !snapshot.is_complete() {
+        // The waker must be stored in the task struct.
+        let res = if snapshot.has_join_waker() {
+            // There already is a waker stored in the struct. If it matches
+            // the provided waker, then there is no further work to do.
+            // Otherwise, the waker must be swapped.
+            let will_wake = unsafe {
+                // Safety: when `JOIN_INTEREST` is set, only `JOIN_HANDLE`
+                // may mutate the `waker` field.
+                trailer.will_wake(waker)
+            };
+
+            if will_wake {
+                // The task is not complete **and** the waker is up to date,
+                // there is nothing further that needs to be done.
+                return false;
+            }
+
+            // Unset the `JOIN_WAKER` to gain mutable access to the `waker`
+            // field then update the field with the new join worker.
+            //
+            // This requires two atomic operations, unsetting the bit and
+            // then resetting it. If the task transitions to complete
+            // concurrently to either one of those operations, then setting
+            // the join waker fails and we proceed to reading the task
+            // output.
+            header
+                .state
+                .unset_waker()
+                .and_then(|snapshot| set_join_waker(header, trailer, waker.clone(), snapshot))
+        } else {
+            set_join_waker(header, trailer, waker.clone(), snapshot)
+        };
+
+        match res {
+            Ok(_) => return false,
+            Err(snapshot) => {
+                assert!(snapshot.is_complete());
+            }
+        }
+    }
+    true
+}
+
+fn set_join_waker(
+    header: &Header,
+    trailer: &Trailer,
+    waker: Waker,
+    snapshot: Snapshot,
+) -> Result<Snapshot, Snapshot> {
+    assert!(snapshot.is_join_interested());
+    assert!(!snapshot.has_join_waker());
+
+    // Safety: Only the `JoinHandle` may set the `waker` field. When
+    // `JOIN_INTEREST` is **not** set, nothing else will touch the field.
+    unsafe {
+        trailer.set_waker(Some(waker));
+    }
+
+    // Update the `JoinWaker` state accordingly
+    let res = header.state.set_join_waker();
+
+    // If the state could not be updated, then clear the join waker
+    if res.is_err() {
+        unsafe {
+            trailer.set_waker(None);
+        }
+    }
+
+    res
+}
+
+enum PollFuture {
+    Complete,
+    Notified,
+    Done,
+    Dealloc,
+}
+
+/// Cancels the task and store the appropriate error in the stage field.
+fn cancel_task<T: Future>(stage: &CoreStage<T>) {
+    // Drop the future from a panic guard.
+    let res = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+        stage.drop_future_or_output();
+    }));
+
+    match res {
+        Ok(()) => {
+            stage.store_output(Err(JoinError::cancelled()));
+        }
+        Err(panic) => {
+            stage.store_output(Err(JoinError::panic(panic)));
+        }
+    }
+}
+
+/// Polls the future. If the future completes, the output is written to the
+/// stage field.
+fn poll_future<T: Future>(core: &CoreStage<T>, cx: Context<'_>) -> Poll<()> {
+    // Poll the future.
+    let output = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+        struct Guard<'a, T: Future> {
+            core: &'a CoreStage<T>,
+        }
+        impl<'a, T: Future> Drop for Guard<'a, T> {
+            fn drop(&mut self) {
+                // If the future panics on poll, we drop it inside the panic
+                // guard.
+                self.core.drop_future_or_output();
+            }
+        }
+        let guard = Guard { core };
+        let res = guard.core.poll(cx);
+        mem::forget(guard);
+        res
+    }));
+
+    // Prepare output for being placed in the core stage.
+    let output = match output {
+        Ok(Poll::Pending) => return Poll::Pending,
+        Ok(Poll::Ready(output)) => Ok(output),
+        Err(panic) => Err(JoinError::panic(panic)),
+    };
+
+    // Catch and ignore panics if the future panics on drop.
+    let _ = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+        core.store_output(output);
+    }));
+
+    Poll::Ready(())
+}
diff --git a/third_party/rust/tokio/src/runtime/task/inject.rs b/third_party/rust/tokio/src/runtime/task/inject.rs
new file mode 100644
index 0000000000..1585e13a01
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/task/inject.rs
@@ -0,0 +1,220 @@
+//! Inject queue used to send wakeups to a work-stealing scheduler
+
+use crate::loom::sync::atomic::AtomicUsize;
+use crate::loom::sync::Mutex;
+use crate::runtime::task;
+
+use std::marker::PhantomData;
+use std::ptr::NonNull;
+use std::sync::atomic::Ordering::{Acquire, Release};
+
+/// Growable, MPMC queue used to inject new tasks into the scheduler and as an
+/// overflow queue when the local, fixed-size, array queue overflows.
+pub(crate) struct Inject<T: 'static> {
+    /// Pointers to the head and tail of the queue.
+    pointers: Mutex<Pointers>,
+
+    /// Number of pending tasks in the queue. This helps prevent unnecessary
+    /// locking in the hot path.
+    len: AtomicUsize,
+
+    _p: PhantomData<T>,
+}
+
+struct Pointers {
+    /// True if the queue is closed.
+    is_closed: bool,
+
+    /// Linked-list head.
+    head: Option<NonNull<task::Header>>,
+
+    /// Linked-list tail.
+    tail: Option<NonNull<task::Header>>,
+}
+
+unsafe impl<T> Send for Inject<T> {}
+unsafe impl<T> Sync for Inject<T> {}
+
+impl<T: 'static> Inject<T> {
+    pub(crate) fn new() -> Inject<T> {
+        Inject {
+            pointers: Mutex::new(Pointers {
+                is_closed: false,
+                head: None,
+                tail: None,
+            }),
+            len: AtomicUsize::new(0),
+            _p: PhantomData,
+        }
+    }
+
+    pub(crate) fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Closes the injection queue, returns `true` if the queue is open when the
+    /// transition is made.
+    pub(crate) fn close(&self) -> bool {
+        let mut p = self.pointers.lock();
+
+        if p.is_closed {
+            return false;
+        }
+
+        p.is_closed = true;
+        true
+    }
+
+    pub(crate) fn is_closed(&self) -> bool {
+        self.pointers.lock().is_closed
+    }
+
+    pub(crate) fn len(&self) -> usize {
+        self.len.load(Acquire)
+    }
+
+    /// Pushes a value into the queue.
+    ///
+    /// This does nothing if the queue is closed.
+    pub(crate) fn push(&self, task: task::Notified<T>) {
+        // Acquire queue lock
+        let mut p = self.pointers.lock();
+
+        if p.is_closed {
+            return;
+        }
+
+        // safety: only mutated with the lock held
+        let len = unsafe { self.len.unsync_load() };
+        let task = task.into_raw();
+
+        // The next pointer should already be null
+        debug_assert!(get_next(task).is_none());
+
+        if let Some(tail) = p.tail {
+            // safety: Holding the Notified for a task guarantees exclusive
+            // access to the `queue_next` field.
+            set_next(tail, Some(task));
+        } else {
+            p.head = Some(task);
+        }
+
+        p.tail = Some(task);
+
+        self.len.store(len + 1, Release);
+    }
+
+    /// Pushes several values into the queue.
+    #[inline]
+    pub(crate) fn push_batch<I>(&self, mut iter: I)
+    where
+        I: Iterator<Item = task::Notified<T>>,
+    {
+        let first = match iter.next() {
+            Some(first) => first.into_raw(),
+            None => return,
+        };
+
+        // Link up all the tasks.
+        let mut prev = first;
+        let mut counter = 1;
+
+        // We are going to be called with an `std::iter::Chain`, and that
+        // iterator overrides `for_each` to something that is easier for the
+        // compiler to optimize than a loop.
+        iter.for_each(|next| {
+            let next = next.into_raw();
+
+            // safety: Holding the Notified for a task guarantees exclusive
+            // access to the `queue_next` field.
+            set_next(prev, Some(next));
+            prev = next;
+            counter += 1;
+        });
+
+        // Now that the tasks are linked together, insert them into the
+        // linked list.
+        self.push_batch_inner(first, prev, counter);
+    }
+
+    /// Inserts several tasks that have been linked together into the queue.
+    ///
+    /// The provided head and tail may be be the same task. In this case, a
+    /// single task is inserted.
+    #[inline]
+    fn push_batch_inner(
+        &self,
+        batch_head: NonNull<task::Header>,
+        batch_tail: NonNull<task::Header>,
+        num: usize,
+    ) {
+        debug_assert!(get_next(batch_tail).is_none());
+
+        let mut p = self.pointers.lock();
+
+        if let Some(tail) = p.tail {
+            set_next(tail, Some(batch_head));
+        } else {
+            p.head = Some(batch_head);
+        }
+
+        p.tail = Some(batch_tail);
+
+        // Increment the count.
+        //
+        // safety: All updates to the len atomic are guarded by the mutex. As
+        // such, a non-atomic load followed by a store is safe.
+        let len = unsafe { self.len.unsync_load() };
+
+        self.len.store(len + num, Release);
+    }
+
+    pub(crate) fn pop(&self) -> Option<task::Notified<T>> {
+        // Fast path, if len == 0, then there are no values
+        if self.is_empty() {
+            return None;
+        }
+
+        let mut p = self.pointers.lock();
+
+        // It is possible to hit null here if another thread popped the last
+        // task between us checking `len` and acquiring the lock.
+        let task = p.head?;
+
+        p.head = get_next(task);
+
+        if p.head.is_none() {
+            p.tail = None;
+        }
+
+        set_next(task, None);
+
+        // Decrement the count.
+        //
+        // safety: All updates to the len atomic are guarded by the mutex. As
+        // such, a non-atomic load followed by a store is safe.
+        self.len
+            .store(unsafe { self.len.unsync_load() } - 1, Release);
+
+        // safety: a `Notified` is pushed into the queue and now it is popped!
+        Some(unsafe { task::Notified::from_raw(task) })
+    }
+}
+
+impl<T: 'static> Drop for Inject<T> {
+    fn drop(&mut self) {
+        if !std::thread::panicking() {
+            assert!(self.pop().is_none(), "queue not empty");
+        }
+    }
+}
+
+fn get_next(header: NonNull<task::Header>) -> Option<NonNull<task::Header>> {
+    unsafe { header.as_ref().queue_next.with(|ptr| *ptr) }
+}
+
+fn set_next(header: NonNull<task::Header>, val: Option<NonNull<task::Header>>) {
+    unsafe {
+        header.as_ref().set_next(val);
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/task/join.rs b/third_party/rust/tokio/src/runtime/task/join.rs
new file mode 100644
index 0000000000..8beed2eaac
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/task/join.rs
@@ -0,0 +1,275 @@
+use crate::runtime::task::RawTask;
+
+use std::fmt;
+use std::future::Future;
+use std::marker::PhantomData;
+use std::panic::{RefUnwindSafe, UnwindSafe};
+use std::pin::Pin;
+use std::task::{Context, Poll, Waker};
+
+cfg_rt! {
+    /// An owned permission to join on a task (await its termination).
+    ///
+    /// This can be thought of as the equivalent of [`std::thread::JoinHandle`] for
+    /// a task rather than a thread.
+    ///
+    /// A `JoinHandle` *detaches* the associated task when it is dropped, which
+    /// means that there is no longer any handle to the task, and no way to `join`
+    /// on it.
+    ///
+    /// This `struct` is created by the [`task::spawn`] and [`task::spawn_blocking`]
+    /// functions.
+    ///
+    /// # Examples
+    ///
+    /// Creation from [`task::spawn`]:
+    ///
+    /// ```
+    /// use tokio::task;
+    ///
+    /// # async fn doc() {
+    /// let join_handle: task::JoinHandle<_> = task::spawn(async {
+    ///     // some work here
+    /// });
+    /// # }
+    /// ```
+    ///
+    /// Creation from [`task::spawn_blocking`]:
+    ///
+    /// ```
+    /// use tokio::task;
+    ///
+    /// # async fn doc() {
+    /// let join_handle: task::JoinHandle<_> = task::spawn_blocking(|| {
+    ///     // some blocking work here
+    /// });
+    /// # }
+    /// ```
+    ///
+    /// The generic parameter `T` in `JoinHandle<T>` is the return type of the spawned task.
+    /// If the return value is an i32, the join handle has type `JoinHandle<i32>`:
+    ///
+    /// ```
+    /// use tokio::task;
+    ///
+    /// # async fn doc() {
+    /// let join_handle: task::JoinHandle<i32> = task::spawn(async {
+    ///     5 + 3
+    /// });
+    /// # }
+    ///
+    /// ```
+    ///
+    /// If the task does not have a return value, the join handle has type `JoinHandle<()>`:
+    ///
+    /// ```
+    /// use tokio::task;
+    ///
+    /// # async fn doc() {
+    /// let join_handle: task::JoinHandle<()> = task::spawn(async {
+    ///     println!("I return nothing.");
+    /// });
+    /// # }
+    /// ```
+    ///
+    /// Note that `handle.await` doesn't give you the return type directly. It is wrapped in a
+    /// `Result` because panics in the spawned task are caught by Tokio. The `?` operator has
+    /// to be double chained to extract the returned value:
+    ///
+    /// ```
+    /// use tokio::task;
+    /// use std::io;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let join_handle: task::JoinHandle<Result<i32, io::Error>> = tokio::spawn(async {
+    ///         Ok(5 + 3)
+    ///     });
+    ///
+    ///     let result = join_handle.await??;
+    ///     assert_eq!(result, 8);
+    ///     Ok(())
+    /// }
+    /// ```
+    ///
+    /// If the task panics, the error is a [`JoinError`] that contains the panic:
+    ///
+    /// ```
+    /// use tokio::task;
+    /// use std::io;
+    /// use std::panic;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let join_handle: task::JoinHandle<Result<i32, io::Error>> = tokio::spawn(async {
+    ///         panic!("boom");
+    ///     });
+    ///
+    ///     let err = join_handle.await.unwrap_err();
+    ///     assert!(err.is_panic());
+    ///     Ok(())
+    /// }
+    ///
+    /// ```
+    /// Child being detached and outliving its parent:
+    ///
+    /// ```no_run
+    /// use tokio::task;
+    /// use tokio::time;
+    /// use std::time::Duration;
+    ///
+    /// # #[tokio::main] async fn main() {
+    /// let original_task = task::spawn(async {
+    ///     let _detached_task = task::spawn(async {
+    ///         // Here we sleep to make sure that the first task returns before.
+    ///         time::sleep(Duration::from_millis(10)).await;
+    ///         // This will be called, even though the JoinHandle is dropped.
+    ///         println!("♫ Still alive ♫");
+    ///     });
+    /// });
+    ///
+    /// original_task.await.expect("The task being joined has panicked");
+    /// println!("Original task is joined.");
+    ///
+    /// // We make sure that the new task has time to run, before the main
+    /// // task returns.
+    ///
+    /// time::sleep(Duration::from_millis(1000)).await;
+    /// # }
+    /// ```
+    ///
+    /// [`task::spawn`]: crate::task::spawn()
+    /// [`task::spawn_blocking`]: crate::task::spawn_blocking
+    /// [`std::thread::JoinHandle`]: std::thread::JoinHandle
+    /// [`JoinError`]: crate::task::JoinError
+    pub struct JoinHandle<T> {
+        raw: Option<RawTask>,
+        _p: PhantomData<T>,
+    }
+}
+
+unsafe impl<T: Send> Send for JoinHandle<T> {}
+unsafe impl<T: Send> Sync for JoinHandle<T> {}
+
+impl<T> UnwindSafe for JoinHandle<T> {}
+impl<T> RefUnwindSafe for JoinHandle<T> {}
+
+impl<T> JoinHandle<T> {
+    pub(super) fn new(raw: RawTask) -> JoinHandle<T> {
+        JoinHandle {
+            raw: Some(raw),
+            _p: PhantomData,
+        }
+    }
+
+    /// Abort the task associated with the handle.
+    ///
+    /// Awaiting a cancelled task might complete as usual if the task was
+    /// already completed at the time it was cancelled, but most likely it
+    /// will fail with a [cancelled] `JoinError`.
+    ///
+    /// ```rust
+    /// use tokio::time;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///    let mut handles = Vec::new();
+    ///
+    ///    handles.push(tokio::spawn(async {
+    ///       time::sleep(time::Duration::from_secs(10)).await;
+    ///       true
+    ///    }));
+    ///
+    ///    handles.push(tokio::spawn(async {
+    ///       time::sleep(time::Duration::from_secs(10)).await;
+    ///       false
+    ///    }));
+    ///
+    ///    for handle in &handles {
+    ///        handle.abort();
+    ///    }
+    ///
+    ///    for handle in handles {
+    ///        assert!(handle.await.unwrap_err().is_cancelled());
+    ///    }
+    /// }
+    /// ```
+    /// [cancelled]: method@super::error::JoinError::is_cancelled
+    pub fn abort(&self) {
+        if let Some(raw) = self.raw {
+            raw.remote_abort();
+        }
+    }
+
+    /// Set the waker that is notified when the task completes.
+    pub(crate) fn set_join_waker(&mut self, waker: &Waker) {
+        if let Some(raw) = self.raw {
+            if raw.try_set_join_waker(waker) {
+                // In this case the task has already completed. We wake the waker immediately.
+                waker.wake_by_ref();
+            }
+        }
+    }
+}
+
+impl<T> Unpin for JoinHandle<T> {}
+
+impl<T> Future for JoinHandle<T> {
+    type Output = super::Result<T>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut ret = Poll::Pending;
+
+        // Keep track of task budget
+        let coop = ready!(crate::coop::poll_proceed(cx));
+
+        // Raw should always be set. If it is not, this is due to polling after
+        // completion
+        let raw = self
+            .raw
+            .as_ref()
+            .expect("polling after `JoinHandle` already completed");
+
+        // Try to read the task output. If the task is not yet complete, the
+        // waker is stored and is notified once the task does complete.
+        //
+        // The function must go via the vtable, which requires erasing generic
+        // types. To do this, the function "return" is placed on the stack
+        // **before** calling the function and is passed into the function using
+        // `*mut ()`.
+        //
+        // Safety:
+        //
+        // The type of `T` must match the task's output type.
+        unsafe {
+            raw.try_read_output(&mut ret as *mut _ as *mut (), cx.waker());
+        }
+
+        if ret.is_ready() {
+            coop.made_progress();
+        }
+
+        ret
+    }
+}
+
+impl<T> Drop for JoinHandle<T> {
+    fn drop(&mut self) {
+        if let Some(raw) = self.raw.take() {
+            if raw.header().state.drop_join_handle_fast().is_ok() {
+                return;
+            }
+
+            raw.drop_join_handle_slow();
+        }
+    }
+}
+
+impl<T> fmt::Debug for JoinHandle<T>
+where
+    T: fmt::Debug,
+{
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("JoinHandle").finish()
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/task/list.rs b/third_party/rust/tokio/src/runtime/task/list.rs
new file mode 100644
index 0000000000..7758f8db7a
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/task/list.rs
@@ -0,0 +1,297 @@
+//! This module has containers for storing the tasks spawned on a scheduler. The
+//! `OwnedTasks` container is thread-safe but can only store tasks that
+//! implement Send. The `LocalOwnedTasks` container is not thread safe, but can
+//! store non-Send tasks.
+//!
+//! The collections can be closed to prevent adding new tasks during shutdown of
+//! the scheduler with the collection.
+
+use crate::future::Future;
+use crate::loom::cell::UnsafeCell;
+use crate::loom::sync::Mutex;
+use crate::runtime::task::{JoinHandle, LocalNotified, Notified, Schedule, Task};
+use crate::util::linked_list::{Link, LinkedList};
+
+use std::marker::PhantomData;
+
+// The id from the module below is used to verify whether a given task is stored
+// in this OwnedTasks, or some other task. The counter starts at one so we can
+// use zero for tasks not owned by any list.
+//
+// The safety checks in this file can technically be violated if the counter is
+// overflown, but the checks are not supposed to ever fail unless there is a
+// bug in Tokio, so we accept that certain bugs would not be caught if the two
+// mixed up runtimes happen to have the same id.
+
+cfg_has_atomic_u64! {
+    use std::sync::atomic::{AtomicU64, Ordering};
+
+    static NEXT_OWNED_TASKS_ID: AtomicU64 = AtomicU64::new(1);
+
+    fn get_next_id() -> u64 {
+        loop {
+            let id = NEXT_OWNED_TASKS_ID.fetch_add(1, Ordering::Relaxed);
+            if id != 0 {
+                return id;
+            }
+        }
+    }
+}
+
+cfg_not_has_atomic_u64! {
+    use std::sync::atomic::{AtomicU32, Ordering};
+
+    static NEXT_OWNED_TASKS_ID: AtomicU32 = AtomicU32::new(1);
+
+    fn get_next_id() -> u64 {
+        loop {
+            let id = NEXT_OWNED_TASKS_ID.fetch_add(1, Ordering::Relaxed);
+            if id != 0 {
+                return u64::from(id);
+            }
+        }
+    }
+}
+
+pub(crate) struct OwnedTasks<S: 'static> {
+    inner: Mutex<OwnedTasksInner<S>>,
+    id: u64,
+}
+pub(crate) struct LocalOwnedTasks<S: 'static> {
+    inner: UnsafeCell<OwnedTasksInner<S>>,
+    id: u64,
+    _not_send_or_sync: PhantomData<*const ()>,
+}
+struct OwnedTasksInner<S: 'static> {
+    list: LinkedList<Task<S>, <Task<S> as Link>::Target>,
+    closed: bool,
+}
+
+impl<S: 'static> OwnedTasks<S> {
+    pub(crate) fn new() -> Self {
+        Self {
+            inner: Mutex::new(OwnedTasksInner {
+                list: LinkedList::new(),
+                closed: false,
+            }),
+            id: get_next_id(),
+        }
+    }
+
+    /// Binds the provided task to this OwnedTasks instance. This fails if the
+    /// OwnedTasks has been closed.
+    pub(crate) fn bind<T>(
+        &self,
+        task: T,
+        scheduler: S,
+    ) -> (JoinHandle<T::Output>, Option<Notified<S>>)
+    where
+        S: Schedule,
+        T: Future + Send + 'static,
+        T::Output: Send + 'static,
+    {
+        let (task, notified, join) = super::new_task(task, scheduler);
+
+        unsafe {
+            // safety: We just created the task, so we have exclusive access
+            // to the field.
+            task.header().set_owner_id(self.id);
+        }
+
+        let mut lock = self.inner.lock();
+        if lock.closed {
+            drop(lock);
+            drop(notified);
+            task.shutdown();
+            (join, None)
+        } else {
+            lock.list.push_front(task);
+            (join, Some(notified))
+        }
+    }
+
+    /// Asserts that the given task is owned by this OwnedTasks and convert it to
+    /// a LocalNotified, giving the thread permission to poll this task.
+    #[inline]
+    pub(crate) fn assert_owner(&self, task: Notified<S>) -> LocalNotified<S> {
+        assert_eq!(task.header().get_owner_id(), self.id);
+
+        // safety: All tasks bound to this OwnedTasks are Send, so it is safe
+        // to poll it on this thread no matter what thread we are on.
+        LocalNotified {
+            task: task.0,
+            _not_send: PhantomData,
+        }
+    }
+
+    /// Shuts down all tasks in the collection. This call also closes the
+    /// collection, preventing new items from being added.
+    pub(crate) fn close_and_shutdown_all(&self)
+    where
+        S: Schedule,
+    {
+        // The first iteration of the loop was unrolled so it can set the
+        // closed bool.
+        let first_task = {
+            let mut lock = self.inner.lock();
+            lock.closed = true;
+            lock.list.pop_back()
+        };
+        match first_task {
+            Some(task) => task.shutdown(),
+            None => return,
+        }
+
+        loop {
+            let task = match self.inner.lock().list.pop_back() {
+                Some(task) => task,
+                None => return,
+            };
+
+            task.shutdown();
+        }
+    }
+
+    pub(crate) fn remove(&self, task: &Task<S>) -> Option<Task<S>> {
+        let task_id = task.header().get_owner_id();
+        if task_id == 0 {
+            // The task is unowned.
+            return None;
+        }
+
+        assert_eq!(task_id, self.id);
+
+        // safety: We just checked that the provided task is not in some other
+        // linked list.
+        unsafe { self.inner.lock().list.remove(task.header().into()) }
+    }
+
+    pub(crate) fn is_empty(&self) -> bool {
+        self.inner.lock().list.is_empty()
+    }
+}
+
+impl<S: 'static> LocalOwnedTasks<S> {
+    pub(crate) fn new() -> Self {
+        Self {
+            inner: UnsafeCell::new(OwnedTasksInner {
+                list: LinkedList::new(),
+                closed: false,
+            }),
+            id: get_next_id(),
+            _not_send_or_sync: PhantomData,
+        }
+    }
+
+    pub(crate) fn bind<T>(
+        &self,
+        task: T,
+        scheduler: S,
+    ) -> (JoinHandle<T::Output>, Option<Notified<S>>)
+    where
+        S: Schedule,
+        T: Future + 'static,
+        T::Output: 'static,
+    {
+        let (task, notified, join) = super::new_task(task, scheduler);
+
+        unsafe {
+            // safety: We just created the task, so we have exclusive access
+            // to the field.
+            task.header().set_owner_id(self.id);
+        }
+
+        if self.is_closed() {
+            drop(notified);
+            task.shutdown();
+            (join, None)
+        } else {
+            self.with_inner(|inner| {
+                inner.list.push_front(task);
+            });
+            (join, Some(notified))
+        }
+    }
+
+    /// Shuts down all tasks in the collection. This call also closes the
+    /// collection, preventing new items from being added.
+    pub(crate) fn close_and_shutdown_all(&self)
+    where
+        S: Schedule,
+    {
+        self.with_inner(|inner| inner.closed = true);
+
+        while let Some(task) = self.with_inner(|inner| inner.list.pop_back()) {
+            task.shutdown();
+        }
+    }
+
+    pub(crate) fn remove(&self, task: &Task<S>) -> Option<Task<S>> {
+        let task_id = task.header().get_owner_id();
+        if task_id == 0 {
+            // The task is unowned.
+            return None;
+        }
+
+        assert_eq!(task_id, self.id);
+
+        self.with_inner(|inner|
+            // safety: We just checked that the provided task is not in some
+            // other linked list.
+            unsafe { inner.list.remove(task.header().into()) })
+    }
+
+    /// Asserts that the given task is owned by this LocalOwnedTasks and convert
+    /// it to a LocalNotified, giving the thread permission to poll this task.
+    #[inline]
+    pub(crate) fn assert_owner(&self, task: Notified<S>) -> LocalNotified<S> {
+        assert_eq!(task.header().get_owner_id(), self.id);
+
+        // safety: The task was bound to this LocalOwnedTasks, and the
+        // LocalOwnedTasks is not Send or Sync, so we are on the right thread
+        // for polling this task.
+        LocalNotified {
+            task: task.0,
+            _not_send: PhantomData,
+        }
+    }
+
+    #[inline]
+    fn with_inner<F, T>(&self, f: F) -> T
+    where
+        F: FnOnce(&mut OwnedTasksInner<S>) -> T,
+    {
+        // safety: This type is not Sync, so concurrent calls of this method
+        // can't happen.  Furthermore, all uses of this method in this file make
+        // sure that they don't call `with_inner` recursively.
+        self.inner.with_mut(|ptr| unsafe { f(&mut *ptr) })
+    }
+
+    pub(crate) fn is_closed(&self) -> bool {
+        self.with_inner(|inner| inner.closed)
+    }
+
+    pub(crate) fn is_empty(&self) -> bool {
+        self.with_inner(|inner| inner.list.is_empty())
+    }
+}
+
+#[cfg(all(test))]
+mod tests {
+    use super::*;
+
+    // This test may run in parallel with other tests, so we only test that ids
+    // come in increasing order.
+    #[test]
+    fn test_id_not_broken() {
+        let mut last_id = get_next_id();
+        assert_ne!(last_id, 0);
+
+        for _ in 0..1000 {
+            let next_id = get_next_id();
+            assert_ne!(next_id, 0);
+            assert!(last_id < next_id);
+            last_id = next_id;
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/task/mod.rs b/third_party/rust/tokio/src/runtime/task/mod.rs
new file mode 100644
index 0000000000..2a492dc985
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/task/mod.rs
@@ -0,0 +1,445 @@
+//! The task module.
+//!
+//! The task module contains the code that manages spawned tasks and provides a
+//! safe API for the rest of the runtime to use. Each task in a runtime is
+//! stored in an OwnedTasks or LocalOwnedTasks object.
+//!
+//! # Task reference types
+//!
+//! A task is usually referenced by multiple handles, and there are several
+//! types of handles.
+//!
+//!  * OwnedTask - tasks stored in an OwnedTasks or LocalOwnedTasks are of this
+//!    reference type.
+//!
+//!  * JoinHandle - each task has a JoinHandle that allows access to the output
+//!    of the task.
+//!
+//!  * Waker - every waker for a task has this reference type. There can be any
+//!    number of waker references.
+//!
+//!  * Notified - tracks whether the task is notified.
+//!
+//!  * Unowned - this task reference type is used for tasks not stored in any
+//!    runtime. Mainly used for blocking tasks, but also in tests.
+//!
+//! The task uses a reference count to keep track of how many active references
+//! exist. The Unowned reference type takes up two ref-counts. All other
+//! reference types take up a single ref-count.
+//!
+//! Besides the waker type, each task has at most one of each reference type.
+//!
+//! # State
+//!
+//! The task stores its state in an atomic usize with various bitfields for the
+//! necessary information. The state has the following bitfields:
+//!
+//!  * RUNNING - Tracks whether the task is currently being polled or cancelled.
+//!    This bit functions as a lock around the task.
+//!
+//!  * COMPLETE - Is one once the future has fully completed and has been
+//!    dropped. Never unset once set. Never set together with RUNNING.
+//!
+//!  * NOTIFIED - Tracks whether a Notified object currently exists.
+//!
+//!  * CANCELLED - Is set to one for tasks that should be cancelled as soon as
+//!    possible. May take any value for completed tasks.
+//!
+//!  * JOIN_INTEREST - Is set to one if there exists a JoinHandle.
+//!
+//!  * JOIN_WAKER - Is set to one if the JoinHandle has set a waker.
+//!
+//! The rest of the bits are used for the ref-count.
+//!
+//! # Fields in the task
+//!
+//! The task has various fields. This section describes how and when it is safe
+//! to access a field.
+//!
+//!  * The state field is accessed with atomic instructions.
+//!
+//!  * The OwnedTask reference has exclusive access to the `owned` field.
+//!
+//!  * The Notified reference has exclusive access to the `queue_next` field.
+//!
+//!  * The `owner_id` field can be set as part of construction of the task, but
+//!    is otherwise immutable and anyone can access the field immutably without
+//!    synchronization.
+//!
+//!  * If COMPLETE is one, then the JoinHandle has exclusive access to the
+//!    stage field. If COMPLETE is zero, then the RUNNING bitfield functions as
+//!    a lock for the stage field, and it can be accessed only by the thread
+//!    that set RUNNING to one.
+//!
+//!  * If JOIN_WAKER is zero, then the JoinHandle has exclusive access to the
+//!    join handle waker. If JOIN_WAKER and COMPLETE are both one, then the
+//!    thread that set COMPLETE to one has exclusive access to the join handle
+//!    waker.
+//!
+//! All other fields are immutable and can be accessed immutably without
+//! synchronization by anyone.
+//!
+//! # Safety
+//!
+//! This section goes through various situations and explains why the API is
+//! safe in that situation.
+//!
+//! ## Polling or dropping the future
+//!
+//! Any mutable access to the future happens after obtaining a lock by modifying
+//! the RUNNING field, so exclusive access is ensured.
+//!
+//! When the task completes, exclusive access to the output is transferred to
+//! the JoinHandle. If the JoinHandle is already dropped when the transition to
+//! complete happens, the thread performing that transition retains exclusive
+//! access to the output and should immediately drop it.
+//!
+//! ## Non-Send futures
+//!
+//! If a future is not Send, then it is bound to a LocalOwnedTasks.  The future
+//! will only ever be polled or dropped given a LocalNotified or inside a call
+//! to LocalOwnedTasks::shutdown_all. In either case, it is guaranteed that the
+//! future is on the right thread.
+//!
+//! If the task is never removed from the LocalOwnedTasks, then it is leaked, so
+//! there is no risk that the task is dropped on some other thread when the last
+//! ref-count drops.
+//!
+//! ## Non-Send output
+//!
+//! When a task completes, the output is placed in the stage of the task. Then,
+//! a transition that sets COMPLETE to true is performed, and the value of
+//! JOIN_INTEREST when this transition happens is read.
+//!
+//! If JOIN_INTEREST is zero when the transition to COMPLETE happens, then the
+//! output is immediately dropped.
+//!
+//! If JOIN_INTEREST is one when the transition to COMPLETE happens, then the
+//! JoinHandle is responsible for cleaning up the output. If the output is not
+//! Send, then this happens:
+//!
+//!  1. The output is created on the thread that the future was polled on. Since
+//!     only non-Send futures can have non-Send output, the future was polled on
+//!     the thread that the future was spawned from.
+//!  2. Since JoinHandle<Output> is not Send if Output is not Send, the
+//!     JoinHandle is also on the thread that the future was spawned from.
+//!  3. Thus, the JoinHandle will not move the output across threads when it
+//!     takes or drops the output.
+//!
+//! ## Recursive poll/shutdown
+//!
+//! Calling poll from inside a shutdown call or vice-versa is not prevented by
+//! the API exposed by the task module, so this has to be safe. In either case,
+//! the lock in the RUNNING bitfield makes the inner call return immediately. If
+//! the inner call is a `shutdown` call, then the CANCELLED bit is set, and the
+//! poll call will notice it when the poll finishes, and the task is cancelled
+//! at that point.
+
+// Some task infrastructure is here to support `JoinSet`, which is currently
+// unstable. This should be removed once `JoinSet` is stabilized.
+#![cfg_attr(not(tokio_unstable), allow(dead_code))]
+
+mod core;
+use self::core::Cell;
+use self::core::Header;
+
+mod error;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::error::JoinError;
+
+mod harness;
+use self::harness::Harness;
+
+cfg_rt_multi_thread! {
+    mod inject;
+    pub(super) use self::inject::Inject;
+}
+
+mod join;
+#[allow(unreachable_pub)] // https://github.com/rust-lang/rust/issues/57411
+pub use self::join::JoinHandle;
+
+mod list;
+pub(crate) use self::list::{LocalOwnedTasks, OwnedTasks};
+
+mod raw;
+use self::raw::RawTask;
+
+mod state;
+use self::state::State;
+
+mod waker;
+
+use crate::future::Future;
+use crate::util::linked_list;
+
+use std::marker::PhantomData;
+use std::ptr::NonNull;
+use std::{fmt, mem};
+
+/// An owned handle to the task, tracked by ref count.
+#[repr(transparent)]
+pub(crate) struct Task<S: 'static> {
+    raw: RawTask,
+    _p: PhantomData<S>,
+}
+
+unsafe impl<S> Send for Task<S> {}
+unsafe impl<S> Sync for Task<S> {}
+
+/// A task was notified.
+#[repr(transparent)]
+pub(crate) struct Notified<S: 'static>(Task<S>);
+
+// safety: This type cannot be used to touch the task without first verifying
+// that the value is on a thread where it is safe to poll the task.
+unsafe impl<S: Schedule> Send for Notified<S> {}
+unsafe impl<S: Schedule> Sync for Notified<S> {}
+
+/// A non-Send variant of Notified with the invariant that it is on a thread
+/// where it is safe to poll it.
+#[repr(transparent)]
+pub(crate) struct LocalNotified<S: 'static> {
+    task: Task<S>,
+    _not_send: PhantomData<*const ()>,
+}
+
+/// A task that is not owned by any OwnedTasks. Used for blocking tasks.
+/// This type holds two ref-counts.
+pub(crate) struct UnownedTask<S: 'static> {
+    raw: RawTask,
+    _p: PhantomData<S>,
+}
+
+// safety: This type can only be created given a Send task.
+unsafe impl<S> Send for UnownedTask<S> {}
+unsafe impl<S> Sync for UnownedTask<S> {}
+
+/// Task result sent back.
+pub(crate) type Result<T> = std::result::Result<T, JoinError>;
+
+pub(crate) trait Schedule: Sync + Sized + 'static {
+    /// The task has completed work and is ready to be released. The scheduler
+    /// should release it immediately and return it. The task module will batch
+    /// the ref-dec with setting other options.
+    ///
+    /// If the scheduler has already released the task, then None is returned.
+    fn release(&self, task: &Task<Self>) -> Option<Task<Self>>;
+
+    /// Schedule the task
+    fn schedule(&self, task: Notified<Self>);
+
+    /// Schedule the task to run in the near future, yielding the thread to
+    /// other tasks.
+    fn yield_now(&self, task: Notified<Self>) {
+        self.schedule(task);
+    }
+}
+
+cfg_rt! {
+    /// This is the constructor for a new task. Three references to the task are
+    /// created. The first task reference is usually put into an OwnedTasks
+    /// immediately. The Notified is sent to the scheduler as an ordinary
+    /// notification.
+    fn new_task<T, S>(
+        task: T,
+        scheduler: S
+    ) -> (Task<S>, Notified<S>, JoinHandle<T::Output>)
+    where
+        S: Schedule,
+        T: Future + 'static,
+        T::Output: 'static,
+    {
+        let raw = RawTask::new::<T, S>(task, scheduler);
+        let task = Task {
+            raw,
+            _p: PhantomData,
+        };
+        let notified = Notified(Task {
+            raw,
+            _p: PhantomData,
+        });
+        let join = JoinHandle::new(raw);
+
+        (task, notified, join)
+    }
+
+    /// Creates a new task with an associated join handle. This method is used
+    /// only when the task is not going to be stored in an `OwnedTasks` list.
+    ///
+    /// Currently only blocking tasks use this method.
+    pub(crate) fn unowned<T, S>(task: T, scheduler: S) -> (UnownedTask<S>, JoinHandle<T::Output>)
+    where
+        S: Schedule,
+        T: Send + Future + 'static,
+        T::Output: Send + 'static,
+    {
+        let (task, notified, join) = new_task(task, scheduler);
+
+        // This transfers the ref-count of task and notified into an UnownedTask.
+        // This is valid because an UnownedTask holds two ref-counts.
+        let unowned = UnownedTask {
+            raw: task.raw,
+            _p: PhantomData,
+        };
+        std::mem::forget(task);
+        std::mem::forget(notified);
+
+        (unowned, join)
+    }
+}
+
+impl<S: 'static> Task<S> {
+    unsafe fn from_raw(ptr: NonNull<Header>) -> Task<S> {
+        Task {
+            raw: RawTask::from_raw(ptr),
+            _p: PhantomData,
+        }
+    }
+
+    fn header(&self) -> &Header {
+        self.raw.header()
+    }
+}
+
+impl<S: 'static> Notified<S> {
+    fn header(&self) -> &Header {
+        self.0.header()
+    }
+}
+
+cfg_rt_multi_thread! {
+    impl<S: 'static> Notified<S> {
+        unsafe fn from_raw(ptr: NonNull<Header>) -> Notified<S> {
+            Notified(Task::from_raw(ptr))
+        }
+    }
+
+    impl<S: 'static> Task<S> {
+        fn into_raw(self) -> NonNull<Header> {
+            let ret = self.raw.header_ptr();
+            mem::forget(self);
+            ret
+        }
+    }
+
+    impl<S: 'static> Notified<S> {
+        fn into_raw(self) -> NonNull<Header> {
+            self.0.into_raw()
+        }
+    }
+}
+
+impl<S: Schedule> Task<S> {
+    /// Pre-emptively cancels the task as part of the shutdown process.
+    pub(crate) fn shutdown(self) {
+        let raw = self.raw;
+        mem::forget(self);
+        raw.shutdown();
+    }
+}
+
+impl<S: Schedule> LocalNotified<S> {
+    /// Runs the task.
+    pub(crate) fn run(self) {
+        let raw = self.task.raw;
+        mem::forget(self);
+        raw.poll();
+    }
+}
+
+impl<S: Schedule> UnownedTask<S> {
+    // Used in test of the inject queue.
+    #[cfg(test)]
+    #[cfg_attr(target_arch = "wasm32", allow(dead_code))]
+    pub(super) fn into_notified(self) -> Notified<S> {
+        Notified(self.into_task())
+    }
+
+    fn into_task(self) -> Task<S> {
+        // Convert into a task.
+        let task = Task {
+            raw: self.raw,
+            _p: PhantomData,
+        };
+        mem::forget(self);
+
+        // Drop a ref-count since an UnownedTask holds two.
+        task.header().state.ref_dec();
+
+        task
+    }
+
+    pub(crate) fn run(self) {
+        let raw = self.raw;
+        mem::forget(self);
+
+        // Transfer one ref-count to a Task object.
+        let task = Task::<S> {
+            raw,
+            _p: PhantomData,
+        };
+
+        // Use the other ref-count to poll the task.
+        raw.poll();
+        // Decrement our extra ref-count
+        drop(task);
+    }
+
+    pub(crate) fn shutdown(self) {
+        self.into_task().shutdown()
+    }
+}
+
+impl<S: 'static> Drop for Task<S> {
+    fn drop(&mut self) {
+        // Decrement the ref count
+        if self.header().state.ref_dec() {
+            // Deallocate if this is the final ref count
+            self.raw.dealloc();
+        }
+    }
+}
+
+impl<S: 'static> Drop for UnownedTask<S> {
+    fn drop(&mut self) {
+        // Decrement the ref count
+        if self.raw.header().state.ref_dec_twice() {
+            // Deallocate if this is the final ref count
+            self.raw.dealloc();
+        }
+    }
+}
+
+impl<S> fmt::Debug for Task<S> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(fmt, "Task({:p})", self.header())
+    }
+}
+
+impl<S> fmt::Debug for Notified<S> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(fmt, "task::Notified({:p})", self.0.header())
+    }
+}
+
+/// # Safety
+///
+/// Tasks are pinned.
+unsafe impl<S> linked_list::Link for Task<S> {
+    type Handle = Task<S>;
+    type Target = Header;
+
+    fn as_raw(handle: &Task<S>) -> NonNull<Header> {
+        handle.raw.header_ptr()
+    }
+
+    unsafe fn from_raw(ptr: NonNull<Header>) -> Task<S> {
+        Task::from_raw(ptr)
+    }
+
+    unsafe fn pointers(target: NonNull<Header>) -> NonNull<linked_list::Pointers<Header>> {
+        // Not super great as it avoids some of looms checking...
+        NonNull::from(target.as_ref().owned.with_mut(|ptr| &mut *ptr))
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/task/raw.rs b/third_party/rust/tokio/src/runtime/task/raw.rs
new file mode 100644
index 0000000000..2e4420b5c1
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/task/raw.rs
@@ -0,0 +1,165 @@
+use crate::future::Future;
+use crate::runtime::task::{Cell, Harness, Header, Schedule, State};
+
+use std::ptr::NonNull;
+use std::task::{Poll, Waker};
+
+/// Raw task handle
+pub(super) struct RawTask {
+    ptr: NonNull<Header>,
+}
+
+pub(super) struct Vtable {
+    /// Polls the future.
+    pub(super) poll: unsafe fn(NonNull<Header>),
+
+    /// Deallocates the memory.
+    pub(super) dealloc: unsafe fn(NonNull<Header>),
+
+    /// Reads the task output, if complete.
+    pub(super) try_read_output: unsafe fn(NonNull<Header>, *mut (), &Waker),
+
+    /// Try to set the waker notified when the task is complete. Returns true if
+    /// the task has already completed. If this call returns false, then the
+    /// waker will not be notified.
+    pub(super) try_set_join_waker: unsafe fn(NonNull<Header>, &Waker) -> bool,
+
+    /// The join handle has been dropped.
+    pub(super) drop_join_handle_slow: unsafe fn(NonNull<Header>),
+
+    /// The task is remotely aborted.
+    pub(super) remote_abort: unsafe fn(NonNull<Header>),
+
+    /// Scheduler is being shutdown.
+    pub(super) shutdown: unsafe fn(NonNull<Header>),
+}
+
+/// Get the vtable for the requested `T` and `S` generics.
+pub(super) fn vtable<T: Future, S: Schedule>() -> &'static Vtable {
+    &Vtable {
+        poll: poll::<T, S>,
+        dealloc: dealloc::<T, S>,
+        try_read_output: try_read_output::<T, S>,
+        try_set_join_waker: try_set_join_waker::<T, S>,
+        drop_join_handle_slow: drop_join_handle_slow::<T, S>,
+        remote_abort: remote_abort::<T, S>,
+        shutdown: shutdown::<T, S>,
+    }
+}
+
+impl RawTask {
+    pub(super) fn new<T, S>(task: T, scheduler: S) -> RawTask
+    where
+        T: Future,
+        S: Schedule,
+    {
+        let ptr = Box::into_raw(Cell::<_, S>::new(task, scheduler, State::new()));
+        let ptr = unsafe { NonNull::new_unchecked(ptr as *mut Header) };
+
+        RawTask { ptr }
+    }
+
+    pub(super) unsafe fn from_raw(ptr: NonNull<Header>) -> RawTask {
+        RawTask { ptr }
+    }
+
+    pub(super) fn header_ptr(&self) -> NonNull<Header> {
+        self.ptr
+    }
+
+    /// Returns a reference to the task's meta structure.
+    ///
+    /// Safe as `Header` is `Sync`.
+    pub(super) fn header(&self) -> &Header {
+        unsafe { self.ptr.as_ref() }
+    }
+
+    /// Safety: mutual exclusion is required to call this function.
+    pub(super) fn poll(self) {
+        let vtable = self.header().vtable;
+        unsafe { (vtable.poll)(self.ptr) }
+    }
+
+    pub(super) fn dealloc(self) {
+        let vtable = self.header().vtable;
+        unsafe {
+            (vtable.dealloc)(self.ptr);
+        }
+    }
+
+    /// Safety: `dst` must be a `*mut Poll<super::Result<T::Output>>` where `T`
+    /// is the future stored by the task.
+    pub(super) unsafe fn try_read_output(self, dst: *mut (), waker: &Waker) {
+        let vtable = self.header().vtable;
+        (vtable.try_read_output)(self.ptr, dst, waker);
+    }
+
+    pub(super) fn try_set_join_waker(self, waker: &Waker) -> bool {
+        let vtable = self.header().vtable;
+        unsafe { (vtable.try_set_join_waker)(self.ptr, waker) }
+    }
+
+    pub(super) fn drop_join_handle_slow(self) {
+        let vtable = self.header().vtable;
+        unsafe { (vtable.drop_join_handle_slow)(self.ptr) }
+    }
+
+    pub(super) fn shutdown(self) {
+        let vtable = self.header().vtable;
+        unsafe { (vtable.shutdown)(self.ptr) }
+    }
+
+    pub(super) fn remote_abort(self) {
+        let vtable = self.header().vtable;
+        unsafe { (vtable.remote_abort)(self.ptr) }
+    }
+}
+
+impl Clone for RawTask {
+    fn clone(&self) -> Self {
+        RawTask { ptr: self.ptr }
+    }
+}
+
+impl Copy for RawTask {}
+
+unsafe fn poll<T: Future, S: Schedule>(ptr: NonNull<Header>) {
+    let harness = Harness::<T, S>::from_raw(ptr);
+    harness.poll();
+}
+
+unsafe fn dealloc<T: Future, S: Schedule>(ptr: NonNull<Header>) {
+    let harness = Harness::<T, S>::from_raw(ptr);
+    harness.dealloc();
+}
+
+unsafe fn try_read_output<T: Future, S: Schedule>(
+    ptr: NonNull<Header>,
+    dst: *mut (),
+    waker: &Waker,
+) {
+    let out = &mut *(dst as *mut Poll<super::Result<T::Output>>);
+
+    let harness = Harness::<T, S>::from_raw(ptr);
+    harness.try_read_output(out, waker);
+}
+
+unsafe fn try_set_join_waker<T: Future, S: Schedule>(ptr: NonNull<Header>, waker: &Waker) -> bool {
+    let harness = Harness::<T, S>::from_raw(ptr);
+    harness.try_set_join_waker(waker)
+}
+
+unsafe fn drop_join_handle_slow<T: Future, S: Schedule>(ptr: NonNull<Header>) {
+    let harness = Harness::<T, S>::from_raw(ptr);
+    harness.drop_join_handle_slow()
+}
+
+unsafe fn remote_abort<T: Future, S: Schedule>(ptr: NonNull<Header>) {
+    let harness = Harness::<T, S>::from_raw(ptr);
+    harness.remote_abort()
+}
+
+unsafe fn shutdown<T: Future, S: Schedule>(ptr: NonNull<Header>) {
+    let harness = Harness::<T, S>::from_raw(ptr);
+    harness.shutdown()
+}
diff --git a/third_party/rust/tokio/src/runtime/task/state.rs b/third_party/rust/tokio/src/runtime/task/state.rs
new file mode 100644
index 0000000000..c2d5b28eac
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/task/state.rs
@@ -0,0 +1,595 @@
+use crate::loom::sync::atomic::AtomicUsize;
+
+use std::fmt;
+use std::sync::atomic::Ordering::{AcqRel, Acquire, Release};
+use std::usize;
+
+pub(super) struct State {
+    val: AtomicUsize,
+}
+
+/// Current state value.
+#[derive(Copy, Clone)]
+pub(super) struct Snapshot(usize);
+
+type UpdateResult = Result<Snapshot, Snapshot>;
+
+/// The task is currently being run.
+const RUNNING: usize = 0b0001;
+
+/// The task is complete.
+///
+/// Once this bit is set, it is never unset.
+const COMPLETE: usize = 0b0010;
+
+/// Extracts the task's lifecycle value from the state.
+const LIFECYCLE_MASK: usize = 0b11;
+
+/// Flag tracking if the task has been pushed into a run queue.
+const NOTIFIED: usize = 0b100;
+
+/// The join handle is still around.
+#[allow(clippy::unusual_byte_groupings)] // https://github.com/rust-lang/rust-clippy/issues/6556
+const JOIN_INTEREST: usize = 0b1_000;
+
+/// A join handle waker has been set.
+#[allow(clippy::unusual_byte_groupings)] // https://github.com/rust-lang/rust-clippy/issues/6556
+const JOIN_WAKER: usize = 0b10_000;
+
+/// The task has been forcibly cancelled.
+#[allow(clippy::unusual_byte_groupings)] // https://github.com/rust-lang/rust-clippy/issues/6556
+const CANCELLED: usize = 0b100_000;
+
+/// All bits.
+const STATE_MASK: usize = LIFECYCLE_MASK | NOTIFIED | JOIN_INTEREST | JOIN_WAKER | CANCELLED;
+
+/// Bits used by the ref count portion of the state.
+const REF_COUNT_MASK: usize = !STATE_MASK;
+
+/// Number of positions to shift the ref count.
+const REF_COUNT_SHIFT: usize = REF_COUNT_MASK.count_zeros() as usize;
+
+/// One ref count.
+const REF_ONE: usize = 1 << REF_COUNT_SHIFT;
+
+/// State a task is initialized with.
+///
+/// A task is initialized with three references:
+///
+///  * A reference that will be stored in an OwnedTasks or LocalOwnedTasks.
+///  * A reference that will be sent to the scheduler as an ordinary notification.
+///  * A reference for the JoinHandle.
+///
+/// As the task starts with a `JoinHandle`, `JOIN_INTEREST` is set.
+/// As the task starts with a `Notified`, `NOTIFIED` is set.
+const INITIAL_STATE: usize = (REF_ONE * 3) | JOIN_INTEREST | NOTIFIED;
+
+#[must_use]
+pub(super) enum TransitionToRunning {
+    Success,
+    Cancelled,
+    Failed,
+    Dealloc,
+}
+
+#[must_use]
+pub(super) enum TransitionToIdle {
+    Ok,
+    OkNotified,
+    OkDealloc,
+    Cancelled,
+}
+
+#[must_use]
+pub(super) enum TransitionToNotifiedByVal {
+    DoNothing,
+    Submit,
+    Dealloc,
+}
+
+#[must_use]
+pub(super) enum TransitionToNotifiedByRef {
+    DoNothing,
+    Submit,
+}
+
+/// All transitions are performed via RMW operations. This establishes an
+/// unambiguous modification order.
+impl State {
+    /// Returns a task's initial state.
+    pub(super) fn new() -> State {
+        // The raw task returned by this method has a ref-count of three. See
+        // the comment on INITIAL_STATE for more.
+        State {
+            val: AtomicUsize::new(INITIAL_STATE),
+        }
+    }
+
+    /// Loads the current state, establishes `Acquire` ordering.
+    pub(super) fn load(&self) -> Snapshot {
+        Snapshot(self.val.load(Acquire))
+    }
+
+    /// Attempts to transition the lifecycle to `Running`. This sets the
+    /// notified bit to false so notifications during the poll can be detected.
+    pub(super) fn transition_to_running(&self) -> TransitionToRunning {
+        self.fetch_update_action(|mut next| {
+            let action;
+            assert!(next.is_notified());
+
+            if !next.is_idle() {
+                // This happens if the task is either currently running or if it
+                // has already completed, e.g. if it was cancelled during
+                // shutdown. Consume the ref-count and return.
+                next.ref_dec();
+                if next.ref_count() == 0 {
+                    action = TransitionToRunning::Dealloc;
+                } else {
+                    action = TransitionToRunning::Failed;
+                }
+            } else {
+                // We are able to lock the RUNNING bit.
+                next.set_running();
+                next.unset_notified();
+
+                if next.is_cancelled() {
+                    action = TransitionToRunning::Cancelled;
+                } else {
+                    action = TransitionToRunning::Success;
+                }
+            }
+            (action, Some(next))
+        })
+    }
+
+    /// Transitions the task from `Running` -> `Idle`.
+    ///
+    /// Returns `true` if the transition to `Idle` is successful, `false` otherwise.
+    /// The transition to `Idle` fails if the task has been flagged to be
+    /// cancelled.
+    pub(super) fn transition_to_idle(&self) -> TransitionToIdle {
+        self.fetch_update_action(|curr| {
+            assert!(curr.is_running());
+
+            if curr.is_cancelled() {
+                return (TransitionToIdle::Cancelled, None);
+            }
+
+            let mut next = curr;
+            let action;
+            next.unset_running();
+
+            if !next.is_notified() {
+                // Polling the future consumes the ref-count of the Notified.
+                next.ref_dec();
+                if next.ref_count() == 0 {
+                    action = TransitionToIdle::OkDealloc;
+                } else {
+                    action = TransitionToIdle::Ok;
+                }
+            } else {
+                // The caller will schedule a new notification, so we create a
+                // new ref-count for the notification. Our own ref-count is kept
+                // for now, and the caller will drop it shortly.
+                next.ref_inc();
+                action = TransitionToIdle::OkNotified;
+            }
+
+            (action, Some(next))
+        })
+    }
+
+    /// Transitions the task from `Running` -> `Complete`.
+    pub(super) fn transition_to_complete(&self) -> Snapshot {
+        const DELTA: usize = RUNNING | COMPLETE;
+
+        let prev = Snapshot(self.val.fetch_xor(DELTA, AcqRel));
+        assert!(prev.is_running());
+        assert!(!prev.is_complete());
+
+        Snapshot(prev.0 ^ DELTA)
+    }
+
+    /// Transitions from `Complete` -> `Terminal`, decrementing the reference
+    /// count the specified number of times.
+    ///
+    /// Returns true if the task should be deallocated.
+    pub(super) fn transition_to_terminal(&self, count: usize) -> bool {
+        let prev = Snapshot(self.val.fetch_sub(count * REF_ONE, AcqRel));
+        assert!(
+            prev.ref_count() >= count,
+            "current: {}, sub: {}",
+            prev.ref_count(),
+            count
+        );
+        prev.ref_count() == count
+    }
+
+    /// Transitions the state to `NOTIFIED`.
+    ///
+    /// If no task needs to be submitted, a ref-count is consumed.
+    ///
+    /// If a task needs to be submitted, the ref-count is incremented for the
+    /// new Notified.
+    pub(super) fn transition_to_notified_by_val(&self) -> TransitionToNotifiedByVal {
+        self.fetch_update_action(|mut snapshot| {
+            let action;
+
+            if snapshot.is_running() {
+                // If the task is running, we mark it as notified, but we should
+                // not submit anything as the thread currently running the
+                // future is responsible for that.
+                snapshot.set_notified();
+                snapshot.ref_dec();
+
+                // The thread that set the running bit also holds a ref-count.
+                assert!(snapshot.ref_count() > 0);
+
+                action = TransitionToNotifiedByVal::DoNothing;
+            } else if snapshot.is_complete() || snapshot.is_notified() {
+                // We do not need to submit any notifications, but we have to
+                // decrement the ref-count.
+                snapshot.ref_dec();
+
+                if snapshot.ref_count() == 0 {
+                    action = TransitionToNotifiedByVal::Dealloc;
+                } else {
+                    action = TransitionToNotifiedByVal::DoNothing;
+                }
+            } else {
+                // We create a new notified that we can submit. The caller
+                // retains ownership of the ref-count they passed in.
+                snapshot.set_notified();
+                snapshot.ref_inc();
+                action = TransitionToNotifiedByVal::Submit;
+            }
+
+            (action, Some(snapshot))
+        })
+    }
+
+    /// Transitions the state to `NOTIFIED`.
+    pub(super) fn transition_to_notified_by_ref(&self) -> TransitionToNotifiedByRef {
+        self.fetch_update_action(|mut snapshot| {
+            if snapshot.is_complete() || snapshot.is_notified() {
+                // There is nothing to do in this case.
+                (TransitionToNotifiedByRef::DoNothing, None)
+            } else if snapshot.is_running() {
+                // If the task is running, we mark it as notified, but we should
+                // not submit as the thread currently running the future is
+                // responsible for that.
+                snapshot.set_notified();
+                (TransitionToNotifiedByRef::DoNothing, Some(snapshot))
+            } else {
+                // The task is idle and not notified. We should submit a
+                // notification.
+                snapshot.set_notified();
+                snapshot.ref_inc();
+                (TransitionToNotifiedByRef::Submit, Some(snapshot))
+            }
+        })
+    }
+
+    /// Sets the cancelled bit and transitions the state to `NOTIFIED` if idle.
+    ///
+    /// Returns `true` if the task needs to be submitted to the pool for
+    /// execution.
+    pub(super) fn transition_to_notified_and_cancel(&self) -> bool {
+        self.fetch_update_action(|mut snapshot| {
+            if snapshot.is_cancelled() || snapshot.is_complete() {
+                // Aborts to completed or cancelled tasks are no-ops.
+                (false, None)
+            } else if snapshot.is_running() {
+                // If the task is running, we mark it as cancelled. The thread
+                // running the task will notice the cancelled bit when it
+                // stops polling and it will kill the task.
+                //
+                // The set_notified() call is not strictly necessary but it will
+                // in some cases let a wake_by_ref call return without having
+                // to perform a compare_exchange.
+                snapshot.set_notified();
+                snapshot.set_cancelled();
+                (false, Some(snapshot))
+            } else {
+                // The task is idle. We set the cancelled and notified bits and
+                // submit a notification if the notified bit was not already
+                // set.
+                snapshot.set_cancelled();
+                if !snapshot.is_notified() {
+                    snapshot.set_notified();
+                    snapshot.ref_inc();
+                    (true, Some(snapshot))
+                } else {
+                    (false, Some(snapshot))
+                }
+            }
+        })
+    }
+
+    /// Sets the `CANCELLED` bit and attempts to transition to `Running`.
+    ///
+    /// Returns `true` if the transition to `Running` succeeded.
+    pub(super) fn transition_to_shutdown(&self) -> bool {
+        let mut prev = Snapshot(0);
+
+        let _ = self.fetch_update(|mut snapshot| {
+            prev = snapshot;
+
+            if snapshot.is_idle() {
+                snapshot.set_running();
+            }
+
+            // If the task was not idle, the thread currently running the task
+            // will notice the cancelled bit and cancel it once the poll
+            // completes.
+            snapshot.set_cancelled();
+            Some(snapshot)
+        });
+
+        prev.is_idle()
+    }
+
+    /// Optimistically tries to swap the state assuming the join handle is
+    /// __immediately__ dropped on spawn.
+    pub(super) fn drop_join_handle_fast(&self) -> Result<(), ()> {
+        use std::sync::atomic::Ordering::Relaxed;
+
+        // Relaxed is acceptable as if this function is called and succeeds,
+        // then nothing has been done w/ the join handle.
+        //
+        // The moment the join handle is used (polled), the `JOIN_WAKER` flag is
+        // set, at which point the CAS will fail.
+        //
+        // Given this, there is no risk if this operation is reordered.
+        self.val
+            .compare_exchange_weak(
+                INITIAL_STATE,
+                (INITIAL_STATE - REF_ONE) & !JOIN_INTEREST,
+                Release,
+                Relaxed,
+            )
+            .map(|_| ())
+            .map_err(|_| ())
+    }
+
+    /// Tries to unset the JOIN_INTEREST flag.
+    ///
+    /// Returns `Ok` if the operation happens before the task transitions to a
+    /// completed state, `Err` otherwise.
+    pub(super) fn unset_join_interested(&self) -> UpdateResult {
+        self.fetch_update(|curr| {
+            assert!(curr.is_join_interested());
+
+            if curr.is_complete() {
+                return None;
+            }
+
+            let mut next = curr;
+            next.unset_join_interested();
+
+            Some(next)
+        })
+    }
+
+    /// Sets the `JOIN_WAKER` bit.
+    ///
+    /// Returns `Ok` if the bit is set, `Err` otherwise. This operation fails if
+    /// the task has completed.
+    pub(super) fn set_join_waker(&self) -> UpdateResult {
+        self.fetch_update(|curr| {
+            assert!(curr.is_join_interested());
+            assert!(!curr.has_join_waker());
+
+            if curr.is_complete() {
+                return None;
+            }
+
+            let mut next = curr;
+            next.set_join_waker();
+
+            Some(next)
+        })
+    }
+
+    /// Unsets the `JOIN_WAKER` bit.
+    ///
+    /// Returns `Ok` has been unset, `Err` otherwise. This operation fails if
+    /// the task has completed.
+    pub(super) fn unset_waker(&self) -> UpdateResult {
+        self.fetch_update(|curr| {
+            assert!(curr.is_join_interested());
+            assert!(curr.has_join_waker());
+
+            if curr.is_complete() {
+                return None;
+            }
+
+            let mut next = curr;
+            next.unset_join_waker();
+
+            Some(next)
+        })
+    }
+
+    pub(super) fn ref_inc(&self) {
+        use std::process;
+        use std::sync::atomic::Ordering::Relaxed;
+
+        // Using a relaxed ordering is alright here, as knowledge of the
+        // original reference prevents other threads from erroneously deleting
+        // the object.
+        //
+        // As explained in the [Boost documentation][1], Increasing the
+        // reference counter can always be done with memory_order_relaxed: New
+        // references to an object can only be formed from an existing
+        // reference, and passing an existing reference from one thread to
+        // another must already provide any required synchronization.
+        //
+        // [1]: (www.boost.org/doc/libs/1_55_0/doc/html/atomic/usage_examples.html)
+        let prev = self.val.fetch_add(REF_ONE, Relaxed);
+
+        // If the reference count overflowed, abort.
+        if prev > isize::MAX as usize {
+            process::abort();
+        }
+    }
+
+    /// Returns `true` if the task should be released.
+    pub(super) fn ref_dec(&self) -> bool {
+        let prev = Snapshot(self.val.fetch_sub(REF_ONE, AcqRel));
+        assert!(prev.ref_count() >= 1);
+        prev.ref_count() == 1
+    }
+
+    /// Returns `true` if the task should be released.
+    pub(super) fn ref_dec_twice(&self) -> bool {
+        let prev = Snapshot(self.val.fetch_sub(2 * REF_ONE, AcqRel));
+        assert!(prev.ref_count() >= 2);
+        prev.ref_count() == 2
+    }
+
+    fn fetch_update_action<F, T>(&self, mut f: F) -> T
+    where
+        F: FnMut(Snapshot) -> (T, Option<Snapshot>),
+    {
+        let mut curr = self.load();
+
+        loop {
+            let (output, next) = f(curr);
+            let next = match next {
+                Some(next) => next,
+                None => return output,
+            };
+
+            let res = self.val.compare_exchange(curr.0, next.0, AcqRel, Acquire);
+
+            match res {
+                Ok(_) => return output,
+                Err(actual) => curr = Snapshot(actual),
+            }
+        }
+    }
+
+    fn fetch_update<F>(&self, mut f: F) -> Result<Snapshot, Snapshot>
+    where
+        F: FnMut(Snapshot) -> Option<Snapshot>,
+    {
+        let mut curr = self.load();
+
+        loop {
+            let next = match f(curr) {
+                Some(next) => next,
+                None => return Err(curr),
+            };
+
+            let res = self.val.compare_exchange(curr.0, next.0, AcqRel, Acquire);
+
+            match res {
+                Ok(_) => return Ok(next),
+                Err(actual) => curr = Snapshot(actual),
+            }
+        }
+    }
+}
+
+// ===== impl Snapshot =====
+
+impl Snapshot {
+    /// Returns `true` if the task is in an idle state.
+    pub(super) fn is_idle(self) -> bool {
+        self.0 & (RUNNING | COMPLETE) == 0
+    }
+
+    /// Returns `true` if the task has been flagged as notified.
+    pub(super) fn is_notified(self) -> bool {
+        self.0 & NOTIFIED == NOTIFIED
+    }
+
+    fn unset_notified(&mut self) {
+        self.0 &= !NOTIFIED
+    }
+
+    fn set_notified(&mut self) {
+        self.0 |= NOTIFIED
+    }
+
+    pub(super) fn is_running(self) -> bool {
+        self.0 & RUNNING == RUNNING
+    }
+
+    fn set_running(&mut self) {
+        self.0 |= RUNNING;
+    }
+
+    fn unset_running(&mut self) {
+        self.0 &= !RUNNING;
+    }
+
+    pub(super) fn is_cancelled(self) -> bool {
+        self.0 & CANCELLED == CANCELLED
+    }
+
+    fn set_cancelled(&mut self) {
+        self.0 |= CANCELLED;
+    }
+
+    /// Returns `true` if the task's future has completed execution.
+    pub(super) fn is_complete(self) -> bool {
+        self.0 & COMPLETE == COMPLETE
+    }
+
+    pub(super) fn is_join_interested(self) -> bool {
+        self.0 & JOIN_INTEREST == JOIN_INTEREST
+    }
+
+    fn unset_join_interested(&mut self) {
+        self.0 &= !JOIN_INTEREST
+    }
+
+    pub(super) fn has_join_waker(self) -> bool {
+        self.0 & JOIN_WAKER == JOIN_WAKER
+    }
+
+    fn set_join_waker(&mut self) {
+        self.0 |= JOIN_WAKER;
+    }
+
+    fn unset_join_waker(&mut self) {
+        self.0 &= !JOIN_WAKER
+    }
+
+    pub(super) fn ref_count(self) -> usize {
+        (self.0 & REF_COUNT_MASK) >> REF_COUNT_SHIFT
+    }
+
+    fn ref_inc(&mut self) {
+        assert!(self.0 <= isize::MAX as usize);
+        self.0 += REF_ONE;
+    }
+
+    pub(super) fn ref_dec(&mut self) {
+        assert!(self.ref_count() > 0);
+        self.0 -= REF_ONE
+    }
+}
+
+impl fmt::Debug for State {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let snapshot = self.load();
+        snapshot.fmt(fmt)
+    }
+}
+
+impl fmt::Debug for Snapshot {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Snapshot")
+            .field("is_running", &self.is_running())
+            .field("is_complete", &self.is_complete())
+            .field("is_notified", &self.is_notified())
+            .field("is_cancelled", &self.is_cancelled())
+            .field("is_join_interested", &self.is_join_interested())
+            .field("has_join_waker", &self.has_join_waker())
+            .field("ref_count", &self.ref_count())
+            .finish()
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/task/waker.rs b/third_party/rust/tokio/src/runtime/task/waker.rs
new file mode 100644
index 0000000000..74a29f4a84
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/task/waker.rs
@@ -0,0 +1,130 @@
+use crate::future::Future;
+use crate::runtime::task::harness::Harness;
+use crate::runtime::task::{Header, Schedule};
+
+use std::marker::PhantomData;
+use std::mem::ManuallyDrop;
+use std::ops;
+use std::ptr::NonNull;
+use std::task::{RawWaker, RawWakerVTable, Waker};
+
+pub(super) struct WakerRef<'a, S: 'static> {
+    waker: ManuallyDrop<Waker>,
+    _p: PhantomData<(&'a Header, S)>,
+}
+
+/// Returns a `WakerRef` which avoids having to pre-emptively increase the
+/// refcount if there is no need to do so.
+pub(super) fn waker_ref<T, S>(header: &NonNull<Header>) -> WakerRef<'_, S>
+where
+    T: Future,
+    S: Schedule,
+{
+    // `Waker::will_wake` uses the VTABLE pointer as part of the check. This
+    // means that `will_wake` will always return false when using the current
+    // task's waker. (discussion at rust-lang/rust#66281).
+    //
+    // To fix this, we use a single vtable. Since we pass in a reference at this
+    // point and not an *owned* waker, we must ensure that `drop` is never
+    // called on this waker instance. This is done by wrapping it with
+    // `ManuallyDrop` and then never calling drop.
+    let waker = unsafe { ManuallyDrop::new(Waker::from_raw(raw_waker::<T, S>(*header))) };
+
+    WakerRef {
+        waker,
+        _p: PhantomData,
+    }
+}
+
+impl<S> ops::Deref for WakerRef<'_, S> {
+    type Target = Waker;
+
+    fn deref(&self) -> &Waker {
+        &self.waker
+    }
+}
+
+cfg_trace! {
+    macro_rules! trace {
+        ($harness:expr, $op:expr) => {
+            if let Some(id) = $harness.id() {
+                tracing::trace!(
+                    target: "tokio::task::waker",
+                    op = $op,
+                    task.id = id.into_u64(),
+                );
+            }
+        }
+    }
+}
+
+cfg_not_trace! {
+    macro_rules! trace {
+        ($harness:expr, $op:expr) => {
+            // noop
+            let _ = &$harness;
+        }
+    }
+}
+
+unsafe fn clone_waker<T, S>(ptr: *const ()) -> RawWaker
+where
+    T: Future,
+    S: Schedule,
+{
+    let header = ptr as *const Header;
+    let ptr = NonNull::new_unchecked(ptr as *mut Header);
+    let harness = Harness::<T, S>::from_raw(ptr);
+    trace!(harness, "waker.clone");
+    (*header).state.ref_inc();
+    raw_waker::<T, S>(ptr)
+}
+
+unsafe fn drop_waker<T, S>(ptr: *const ())
+where
+    T: Future,
+    S: Schedule,
+{
+    let ptr = NonNull::new_unchecked(ptr as *mut Header);
+    let harness = Harness::<T, S>::from_raw(ptr);
+    trace!(harness, "waker.drop");
+    harness.drop_reference();
+}
+
+unsafe fn wake_by_val<T, S>(ptr: *const ())
+where
+    T: Future,
+    S: Schedule,
+{
+    let ptr = NonNull::new_unchecked(ptr as *mut Header);
+    let harness = Harness::<T, S>::from_raw(ptr);
+    trace!(harness, "waker.wake");
+    harness.wake_by_val();
+}
+
+// Wake without consuming the waker
+unsafe fn wake_by_ref<T, S>(ptr: *const ())
+where
+    T: Future,
+    S: Schedule,
+{
+    let ptr = NonNull::new_unchecked(ptr as *mut Header);
+    let harness = Harness::<T, S>::from_raw(ptr);
+    trace!(harness, "waker.wake_by_ref");
+    harness.wake_by_ref();
+}
+
+fn raw_waker<T, S>(header: NonNull<Header>) -> RawWaker
+where
+    T: Future,
+    S: Schedule,
+{
+    let ptr = header.as_ptr() as *const ();
+    let vtable = &RawWakerVTable::new(
+        clone_waker::<T, S>,
+        wake_by_val::<T, S>,
+        wake_by_ref::<T, S>,
+        drop_waker::<T, S>,
+    );
+    RawWaker::new(ptr, vtable)
+}
diff --git a/third_party/rust/tokio/src/runtime/tests/loom_basic_scheduler.rs b/third_party/rust/tokio/src/runtime/tests/loom_basic_scheduler.rs
new file mode 100644
index 0000000000..a772603f71
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/tests/loom_basic_scheduler.rs
@@ -0,0 +1,142 @@
+use crate::loom::sync::atomic::AtomicUsize;
+use crate::loom::sync::Arc;
+use crate::loom::thread;
+use crate::runtime::{Builder, Runtime};
+use crate::sync::oneshot::{self, Receiver};
+use crate::task;
+use std::future::Future;
+use std::pin::Pin;
+use std::sync::atomic::Ordering::{Acquire, Release};
+use std::task::{Context, Poll};
+
+fn assert_at_most_num_polls(rt: Arc<Runtime>, at_most_polls: usize) {
+    let (tx, rx) = oneshot::channel();
+    let num_polls = Arc::new(AtomicUsize::new(0));
+    rt.spawn(async move {
+        for _ in 0..12 {
+            task::yield_now().await;
+        }
+        tx.send(()).unwrap();
+    });
+
+    rt.block_on(async {
+        BlockedFuture {
+            rx,
+            num_polls: num_polls.clone(),
+        }
+        .await;
+    });
+
+    let polls = num_polls.load(Acquire);
+    assert!(polls <= at_most_polls);
+}
+
+#[test]
+fn block_on_num_polls() {
+    loom::model(|| {
+        // we expect at most 4 number of polls because there are three points at
+        // which we poll the future and an opportunity for a false-positive.. At
+        // any of these points it can be ready:
+        //
+        // - when we fail to steal the parker and we block on a notification
+        //   that it is available.
+        //
+        // - when we steal the parker and we schedule the future
+        //
+        // - when the future is woken up and we have ran the max number of tasks
+        //   for the current tick or there are no more tasks to run.
+        //
+        // - a thread is notified that the parker is available but a third
+        //   thread acquires it before the notified thread can.
+        //
+        let at_most = 4;
+
+        let rt1 = Arc::new(Builder::new_current_thread().build().unwrap());
+        let rt2 = rt1.clone();
+        let rt3 = rt1.clone();
+
+        let th1 = thread::spawn(move || assert_at_most_num_polls(rt1, at_most));
+        let th2 = thread::spawn(move || assert_at_most_num_polls(rt2, at_most));
+        let th3 = thread::spawn(move || assert_at_most_num_polls(rt3, at_most));
+
+        th1.join().unwrap();
+        th2.join().unwrap();
+        th3.join().unwrap();
+    });
+}
+
+#[test]
+fn assert_no_unnecessary_polls() {
+    loom::model(|| {
+        // // After we poll outer future, woken should reset to false
+        let rt = Builder::new_current_thread().build().unwrap();
+        let (tx, rx) = oneshot::channel();
+        let pending_cnt = Arc::new(AtomicUsize::new(0));
+
+        rt.spawn(async move {
+            for _ in 0..24 {
+                task::yield_now().await;
+            }
+            tx.send(()).unwrap();
+        });
+
+        let pending_cnt_clone = pending_cnt.clone();
+        rt.block_on(async move {
+            // use task::yield_now() to ensure woken set to true
+            // ResetFuture will be polled at most once
+            // Here comes two cases
+            // 1. recv no message from channel, ResetFuture will be polled
+            //    but get Pending and we record ResetFuture.pending_cnt ++.
+            //    Then when message arrive, ResetFuture returns Ready. So we
+            //    expect ResetFuture.pending_cnt = 1
+            // 2. recv message from channel, ResetFuture returns Ready immediately.
+            //    We expect ResetFuture.pending_cnt = 0
+            task::yield_now().await;
+            ResetFuture {
+                rx,
+                pending_cnt: pending_cnt_clone,
+            }
+            .await;
+        });
+
+        let pending_cnt = pending_cnt.load(Acquire);
+        assert!(pending_cnt <= 1);
+    });
+}
+
+struct BlockedFuture {
+    rx: Receiver<()>,
+    num_polls: Arc<AtomicUsize>,
+}
+
+impl Future for BlockedFuture {
+    type Output = ();
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.num_polls.fetch_add(1, Release);
+
+        match Pin::new(&mut self.rx).poll(cx) {
+            Poll::Pending => Poll::Pending,
+            _ => Poll::Ready(()),
+        }
+    }
+}
+
+struct ResetFuture {
+    rx: Receiver<()>,
+    pending_cnt: Arc<AtomicUsize>,
+}
+
+impl Future for ResetFuture {
+    type Output = ();
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match Pin::new(&mut self.rx).poll(cx) {
+            Poll::Pending => {
+                self.pending_cnt.fetch_add(1, Release);
+                Poll::Pending
+            }
+            _ => Poll::Ready(()),
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/tests/loom_blocking.rs b/third_party/rust/tokio/src/runtime/tests/loom_blocking.rs
new file mode 100644
index 0000000000..89de85e436
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/tests/loom_blocking.rs
@@ -0,0 +1,81 @@
+use crate::runtime::{self, Runtime};
+
+use std::sync::Arc;
+
+#[test]
+fn blocking_shutdown() {
+    loom::model(|| {
+        let v = Arc::new(());
+
+        let rt = mk_runtime(1);
+        {
+            let _enter = rt.enter();
+            for _ in 0..2 {
+                let v = v.clone();
+                crate::task::spawn_blocking(move || {
+                    assert!(1 < Arc::strong_count(&v));
+                });
+            }
+        }
+
+        drop(rt);
+        assert_eq!(1, Arc::strong_count(&v));
+    });
+}
+
+#[test]
+fn spawn_mandatory_blocking_should_always_run() {
+    use crate::runtime::tests::loom_oneshot;
+    loom::model(|| {
+        let rt = runtime::Builder::new_current_thread().build().unwrap();
+
+        let (tx, rx) = loom_oneshot::channel();
+        let _enter = rt.enter();
+        runtime::spawn_blocking(|| {});
+        runtime::spawn_mandatory_blocking(move || {
+            let _ = tx.send(());
+        })
+        .unwrap();
+
+        drop(rt);
+
+        // This call will deadlock if `spawn_mandatory_blocking` doesn't run.
+        let () = rx.recv();
+    });
+}
+
+#[test]
+fn spawn_mandatory_blocking_should_run_even_when_shutting_down_from_other_thread() {
+    use crate::runtime::tests::loom_oneshot;
+    loom::model(|| {
+        let rt = runtime::Builder::new_current_thread().build().unwrap();
+        let handle = rt.handle().clone();
+
+        // Drop the runtime in a different thread
+        {
+            loom::thread::spawn(move || {
+                drop(rt);
+            });
+        }
+
+        let _enter = handle.enter();
+        let (tx, rx) = loom_oneshot::channel();
+        let handle = runtime::spawn_mandatory_blocking(move || {
+            let _ = tx.send(());
+        });
+
+        // handle.is_some() means that `spawn_mandatory_blocking`
+        // promised us to run the blocking task
+        if handle.is_some() {
+            // This call will deadlock if `spawn_mandatory_blocking` doesn't run.
+            let () = rx.recv();
+        }
+    });
+}
+
+fn mk_runtime(num_threads: usize) -> Runtime {
+    runtime::Builder::new_multi_thread()
+        .worker_threads(num_threads)
+        .build()
+        .unwrap()
+}
diff --git a/third_party/rust/tokio/src/runtime/tests/loom_join_set.rs b/third_party/rust/tokio/src/runtime/tests/loom_join_set.rs
new file mode 100644
index 0000000000..e87ddb0140
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/tests/loom_join_set.rs
@@ -0,0 +1,82 @@
+use crate::runtime::Builder;
+use crate::task::JoinSet;
+
+#[test]
+fn test_join_set() {
+    loom::model(|| {
+        let rt = Builder::new_multi_thread()
+            .worker_threads(1)
+            .build()
+            .unwrap();
+        let mut set = JoinSet::new();
+
+        rt.block_on(async {
+            assert_eq!(set.len(), 0);
+            set.spawn(async { () });
+            assert_eq!(set.len(), 1);
+            set.spawn(async { () });
+            assert_eq!(set.len(), 2);
+            let () = set.join_one().await.unwrap().unwrap();
+            assert_eq!(set.len(), 1);
+            set.spawn(async { () });
+            assert_eq!(set.len(), 2);
+            let () = set.join_one().await.unwrap().unwrap();
+            assert_eq!(set.len(), 1);
+            let () = set.join_one().await.unwrap().unwrap();
+            assert_eq!(set.len(), 0);
+            set.spawn(async { () });
+            assert_eq!(set.len(), 1);
+        });
+
+        drop(set);
+        drop(rt);
+    });
+}
+
+#[test]
+fn abort_all_during_completion() {
+    use std::sync::{
+        atomic::{AtomicBool, Ordering::SeqCst},
+        Arc,
+    };
+
+    // These booleans assert that at least one execution had the task complete first, and that at
+    // least one execution had the task be cancelled before it completed.
+    let complete_happened = Arc::new(AtomicBool::new(false));
+    let cancel_happened = Arc::new(AtomicBool::new(false));
+
+    {
+        let complete_happened = complete_happened.clone();
+        let cancel_happened = cancel_happened.clone();
+        loom::model(move || {
+            let rt = Builder::new_multi_thread()
+                .worker_threads(1)
+                .build()
+                .unwrap();
+
+            let mut set = JoinSet::new();
+
+            rt.block_on(async {
+                set.spawn(async { () });
+                set.abort_all();
+
+                match set.join_one().await {
+                    Ok(Some(())) => complete_happened.store(true, SeqCst),
+                    Err(err) if err.is_cancelled() => cancel_happened.store(true, SeqCst),
+                    Err(err) => panic!("fail: {}", err),
+                    Ok(None) => {
+                        unreachable!("Aborting the task does not remove it from the JoinSet.")
+                    }
+                }
+
+                assert!(matches!(set.join_one().await, Ok(None)));
+            });
+
+            drop(set);
+            drop(rt);
+        });
+    }
+
+    assert!(complete_happened.load(SeqCst));
+    assert!(cancel_happened.load(SeqCst));
+}
diff --git a/third_party/rust/tokio/src/runtime/tests/loom_local.rs b/third_party/rust/tokio/src/runtime/tests/loom_local.rs
new file mode 100644
index 0000000000..d9a07a45f0
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/tests/loom_local.rs
@@ -0,0 +1,47 @@
+use crate::runtime::tests::loom_oneshot as oneshot;
+use crate::runtime::Builder;
+use crate::task::LocalSet;
+
+use std::task::Poll;
+
+/// Waking a runtime will attempt to push a task into a queue of notifications
+/// in the runtime, however the tasks in such a queue usually have a reference
+/// to the runtime itself. This means that if they are not properly removed at
+/// runtime shutdown, this will cause a memory leak.
+///
+/// This test verifies that waking something during shutdown of a LocalSet does
+/// not result in tasks lingering in the queue once shutdown is complete. This
+/// is verified using loom's leak finder.
+#[test]
+fn wake_during_shutdown() {
+    loom::model(|| {
+        let rt = Builder::new_current_thread().build().unwrap();
+        let ls = LocalSet::new();
+
+        let (send, recv) = oneshot::channel();
+
+        ls.spawn_local(async move {
+            let mut send = Some(send);
+
+            let () = futures::future::poll_fn(|cx| {
+                if let Some(send) = send.take() {
+                    send.send(cx.waker().clone());
+                }
+
+                Poll::Pending
+            })
+            .await;
+        });
+
+        let handle = loom::thread::spawn(move || {
+            let waker = recv.recv();
+            waker.wake();
+        });
+
+        ls.block_on(&rt, crate::task::yield_now());
+
+        drop(ls);
+        handle.join().unwrap();
+        drop(rt);
+    });
+}
diff --git a/third_party/rust/tokio/src/runtime/tests/loom_oneshot.rs b/third_party/rust/tokio/src/runtime/tests/loom_oneshot.rs
new file mode 100644
index 0000000000..87eb638642
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/tests/loom_oneshot.rs
@@ -0,0 +1,48 @@
+use crate::loom::sync::{Arc, Mutex};
+use loom::sync::Notify;
+
+pub(crate) fn channel<T>() -> (Sender<T>, Receiver<T>) {
+    let inner = Arc::new(Inner {
+        notify: Notify::new(),
+        value: Mutex::new(None),
+    });
+
+    let tx = Sender {
+        inner: inner.clone(),
+    };
+    let rx = Receiver { inner };
+
+    (tx, rx)
+}
+
+pub(crate) struct Sender<T> {
+    inner: Arc<Inner<T>>,
+}
+
+pub(crate) struct Receiver<T> {
+    inner: Arc<Inner<T>>,
+}
+
+struct Inner<T> {
+    notify: Notify,
+    value: Mutex<Option<T>>,
+}
+
+impl<T> Sender<T> {
+    pub(crate) fn send(self, value: T) {
+        *self.inner.value.lock() = Some(value);
+        self.inner.notify.notify();
+    }
+}
+
+impl<T> Receiver<T> {
+    pub(crate) fn recv(self) -> T {
+        loop {
+            if let Some(v) = self.inner.value.lock().take() {
+                return v;
+            }
+
+            self.inner.notify.wait();
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/tests/loom_pool.rs b/third_party/rust/tokio/src/runtime/tests/loom_pool.rs
new file mode 100644
index 0000000000..b3ecd43124
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/tests/loom_pool.rs
@@ -0,0 +1,430 @@
+/// Full runtime loom tests. These are heavy tests and take significant time to
+/// run on CI.
+///
+/// Use `LOOM_MAX_PREEMPTIONS=1` to do a "quick" run as a smoke test.
+///
+/// In order to speed up the C
+use crate::future::poll_fn;
+use crate::runtime::tests::loom_oneshot as oneshot;
+use crate::runtime::{self, Runtime};
+use crate::{spawn, task};
+use tokio_test::assert_ok;
+
+use loom::sync::atomic::{AtomicBool, AtomicUsize};
+use loom::sync::Arc;
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::pin::Pin;
+use std::sync::atomic::Ordering::{Relaxed, SeqCst};
+use std::task::{Context, Poll};
+
+mod atomic_take {
+    use loom::sync::atomic::AtomicBool;
+    use std::mem::MaybeUninit;
+    use std::sync::atomic::Ordering::SeqCst;
+
+    pub(super) struct AtomicTake<T> {
+        inner: MaybeUninit<T>,
+        taken: AtomicBool,
+    }
+
+    impl<T> AtomicTake<T> {
+        pub(super) fn new(value: T) -> Self {
+            Self {
+                inner: MaybeUninit::new(value),
+                taken: AtomicBool::new(false),
+            }
+        }
+
+        pub(super) fn take(&self) -> Option<T> {
+            // safety: Only one thread will see the boolean change from false
+            // to true, so that thread is able to take the value.
+            match self.taken.fetch_or(true, SeqCst) {
+                false => unsafe { Some(std::ptr::read(self.inner.as_ptr())) },
+                true => None,
+            }
+        }
+    }
+
+    impl<T> Drop for AtomicTake<T> {
+        fn drop(&mut self) {
+            drop(self.take());
+        }
+    }
+}
+
+#[derive(Clone)]
+struct AtomicOneshot<T> {
+    value: std::sync::Arc<atomic_take::AtomicTake<oneshot::Sender<T>>>,
+}
+impl<T> AtomicOneshot<T> {
+    fn new(sender: oneshot::Sender<T>) -> Self {
+        Self {
+            value: std::sync::Arc::new(atomic_take::AtomicTake::new(sender)),
+        }
+    }
+
+    fn assert_send(&self, value: T) {
+        self.value.take().unwrap().send(value);
+    }
+}
+
+/// Tests are divided into groups to make the runs faster on CI.
+mod group_a {
+    use super::*;
+
+    #[test]
+    fn racy_shutdown() {
+        loom::model(|| {
+            let pool = mk_pool(1);
+
+            // here's the case we want to exercise:
+            //
+            // a worker that still has tasks in its local queue gets sent to the blocking pool (due to
+            // block_in_place). the blocking pool is shut down, so drops the worker. the worker's
+            // shutdown method never gets run.
+            //
+            // we do this by spawning two tasks on one worker, the first of which does block_in_place,
+            // and then immediately drop the pool.
+
+            pool.spawn(track(async {
+                crate::task::block_in_place(|| {});
+            }));
+            pool.spawn(track(async {}));
+            drop(pool);
+        });
+    }
+
+    #[test]
+    fn pool_multi_spawn() {
+        loom::model(|| {
+            let pool = mk_pool(2);
+            let c1 = Arc::new(AtomicUsize::new(0));
+
+            let (tx, rx) = oneshot::channel();
+            let tx1 = AtomicOneshot::new(tx);
+
+            // Spawn a task
+            let c2 = c1.clone();
+            let tx2 = tx1.clone();
+            pool.spawn(track(async move {
+                spawn(track(async move {
+                    if 1 == c1.fetch_add(1, Relaxed) {
+                        tx1.assert_send(());
+                    }
+                }));
+            }));
+
+            // Spawn a second task
+            pool.spawn(track(async move {
+                spawn(track(async move {
+                    if 1 == c2.fetch_add(1, Relaxed) {
+                        tx2.assert_send(());
+                    }
+                }));
+            }));
+
+            rx.recv();
+        });
+    }
+
+    fn only_blocking_inner(first_pending: bool) {
+        loom::model(move || {
+            let pool = mk_pool(1);
+            let (block_tx, block_rx) = oneshot::channel();
+
+            pool.spawn(track(async move {
+                crate::task::block_in_place(move || {
+                    block_tx.send(());
+                });
+                if first_pending {
+                    task::yield_now().await
+                }
+            }));
+
+            block_rx.recv();
+            drop(pool);
+        });
+    }
+
+    #[test]
+    fn only_blocking_without_pending() {
+        only_blocking_inner(false)
+    }
+
+    #[test]
+    fn only_blocking_with_pending() {
+        only_blocking_inner(true)
+    }
+}
+
+mod group_b {
+    use super::*;
+
+    fn blocking_and_regular_inner(first_pending: bool) {
+        const NUM: usize = 3;
+        loom::model(move || {
+            let pool = mk_pool(1);
+            let cnt = Arc::new(AtomicUsize::new(0));
+
+            let (block_tx, block_rx) = oneshot::channel();
+            let (done_tx, done_rx) = oneshot::channel();
+            let done_tx = AtomicOneshot::new(done_tx);
+
+            pool.spawn(track(async move {
+                crate::task::block_in_place(move || {
+                    block_tx.send(());
+                });
+                if first_pending {
+                    task::yield_now().await
+                }
+            }));
+
+            for _ in 0..NUM {
+                let cnt = cnt.clone();
+                let done_tx = done_tx.clone();
+
+                pool.spawn(track(async move {
+                    if NUM == cnt.fetch_add(1, Relaxed) + 1 {
+                        done_tx.assert_send(());
+                    }
+                }));
+            }
+
+            done_rx.recv();
+            block_rx.recv();
+
+            drop(pool);
+        });
+    }
+
+    #[test]
+    fn blocking_and_regular() {
+        blocking_and_regular_inner(false);
+    }
+
+    #[test]
+    fn blocking_and_regular_with_pending() {
+        blocking_and_regular_inner(true);
+    }
+
+    #[test]
+    fn join_output() {
+        loom::model(|| {
+            let rt = mk_pool(1);
+
+            rt.block_on(async {
+                let t = crate::spawn(track(async { "hello" }));
+
+                let out = assert_ok!(t.await);
+                assert_eq!("hello", out.into_inner());
+            });
+        });
+    }
+
+    #[test]
+    fn poll_drop_handle_then_drop() {
+        loom::model(|| {
+            let rt = mk_pool(1);
+
+            rt.block_on(async move {
+                let mut t = crate::spawn(track(async { "hello" }));
+
+                poll_fn(|cx| {
+                    let _ = Pin::new(&mut t).poll(cx);
+                    Poll::Ready(())
+                })
+                .await;
+            });
+        })
+    }
+
+    #[test]
+    fn complete_block_on_under_load() {
+        loom::model(|| {
+            let pool = mk_pool(1);
+
+            pool.block_on(async {
+                // Trigger a re-schedule
+                crate::spawn(track(async {
+                    for _ in 0..2 {
+                        task::yield_now().await;
+                    }
+                }));
+
+                gated2(true).await
+            });
+        });
+    }
+
+    #[test]
+    fn shutdown_with_notification() {
+        use crate::sync::oneshot;
+
+        loom::model(|| {
+            let rt = mk_pool(2);
+            let (done_tx, done_rx) = oneshot::channel::<()>();
+
+            rt.spawn(track(async move {
+                let (tx, rx) = oneshot::channel::<()>();
+
+                crate::spawn(async move {
+                    crate::task::spawn_blocking(move || {
+                        let _ = tx.send(());
+                    });
+
+                    let _ = done_rx.await;
+                });
+
+                let _ = rx.await;
+
+                let _ = done_tx.send(());
+            }));
+        });
+    }
+}
+
+mod group_c {
+    use super::*;
+
+    #[test]
+    fn pool_shutdown() {
+        loom::model(|| {
+            let pool = mk_pool(2);
+
+            pool.spawn(track(async move {
+                gated2(true).await;
+            }));
+
+            pool.spawn(track(async move {
+                gated2(false).await;
+            }));
+
+            drop(pool);
+        });
+    }
+}
+
+mod group_d {
+    use super::*;
+
+    #[test]
+    fn pool_multi_notify() {
+        loom::model(|| {
+            let pool = mk_pool(2);
+
+            let c1 = Arc::new(AtomicUsize::new(0));
+
+            let (done_tx, done_rx) = oneshot::channel();
+            let done_tx1 = AtomicOneshot::new(done_tx);
+            let done_tx2 = done_tx1.clone();
+
+            // Spawn a task
+            let c2 = c1.clone();
+            pool.spawn(track(async move {
+                gated().await;
+                gated().await;
+
+                if 1 == c1.fetch_add(1, Relaxed) {
+                    done_tx1.assert_send(());
+                }
+            }));
+
+            // Spawn a second task
+            pool.spawn(track(async move {
+                gated().await;
+                gated().await;
+
+                if 1 == c2.fetch_add(1, Relaxed) {
+                    done_tx2.assert_send(());
+                }
+            }));
+
+            done_rx.recv();
+        });
+    }
+}
+
+fn mk_pool(num_threads: usize) -> Runtime {
+    runtime::Builder::new_multi_thread()
+        .worker_threads(num_threads)
+        .build()
+        .unwrap()
+}
+
+fn gated() -> impl Future<Output = &'static str> {
+    gated2(false)
+}
+
+fn gated2(thread: bool) -> impl Future<Output = &'static str> {
+    use loom::thread;
+    use std::sync::Arc;
+
+    let gate = Arc::new(AtomicBool::new(false));
+    let mut fired = false;
+
+    poll_fn(move |cx| {
+        if !fired {
+            let gate = gate.clone();
+            let waker = cx.waker().clone();
+
+            if thread {
+                thread::spawn(move || {
+                    gate.store(true, SeqCst);
+                    waker.wake_by_ref();
+                });
+            } else {
+                spawn(track(async move {
+                    gate.store(true, SeqCst);
+                    waker.wake_by_ref();
+                }));
+            }
+
+            fired = true;
+
+            return Poll::Pending;
+        }
+
+        if gate.load(SeqCst) {
+            Poll::Ready("hello world")
+        } else {
+            Poll::Pending
+        }
+    })
+}
+
+fn track<T: Future>(f: T) -> Track<T> {
+    Track {
+        inner: f,
+        arc: Arc::new(()),
+    }
+}
+
+pin_project! {
+    struct Track<T> {
+        #[pin]
+        inner: T,
+        // Arc is used to hook into loom's leak tracking.
+        arc: Arc<()>,
+    }
+}
+
+impl<T> Track<T> {
+    fn into_inner(self) -> T {
+        self.inner
+    }
+}
+
+impl<T: Future> Future for Track<T> {
+    type Output = Track<T::Output>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let me = self.project();
+
+        Poll::Ready(Track {
+            inner: ready!(me.inner.poll(cx)),
+            arc: me.arc.clone(),
+        })
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/tests/loom_queue.rs b/third_party/rust/tokio/src/runtime/tests/loom_queue.rs
new file mode 100644
index 0000000000..b5f78d7ebe
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/tests/loom_queue.rs
@@ -0,0 +1,208 @@
+use crate::runtime::blocking::NoopSchedule;
+use crate::runtime::task::Inject;
+use crate::runtime::{queue, MetricsBatch};
+
+use loom::thread;
+
+#[test]
+fn basic() {
+    loom::model(|| {
+        let (steal, mut local) = queue::local();
+        let inject = Inject::new();
+        let mut metrics = MetricsBatch::new();
+
+        let th = thread::spawn(move || {
+            let mut metrics = MetricsBatch::new();
+            let (_, mut local) = queue::local();
+            let mut n = 0;
+
+            for _ in 0..3 {
+                if steal.steal_into(&mut local, &mut metrics).is_some() {
+                    n += 1;
+                }
+
+                while local.pop().is_some() {
+                    n += 1;
+                }
+            }
+
+            n
+        });
+
+        let mut n = 0;
+
+        for _ in 0..2 {
+            for _ in 0..2 {
+                let (task, _) = super::unowned(async {});
+                local.push_back(task, &inject, &mut metrics);
+            }
+
+            if local.pop().is_some() {
+                n += 1;
+            }
+
+            // Push another task
+            let (task, _) = super::unowned(async {});
+            local.push_back(task, &inject, &mut metrics);
+
+            while local.pop().is_some() {
+                n += 1;
+            }
+        }
+
+        while inject.pop().is_some() {
+            n += 1;
+        }
+
+        n += th.join().unwrap();
+
+        assert_eq!(6, n);
+    });
+}
+
+#[test]
+fn steal_overflow() {
+    loom::model(|| {
+        let (steal, mut local) = queue::local();
+        let inject = Inject::new();
+        let mut metrics = MetricsBatch::new();
+
+        let th = thread::spawn(move || {
+            let mut metrics = MetricsBatch::new();
+            let (_, mut local) = queue::local();
+            let mut n = 0;
+
+            if steal.steal_into(&mut local, &mut metrics).is_some() {
+                n += 1;
+            }
+
+            while local.pop().is_some() {
+                n += 1;
+            }
+
+            n
+        });
+
+        let mut n = 0;
+
+        // push a task, pop a task
+        let (task, _) = super::unowned(async {});
+        local.push_back(task, &inject, &mut metrics);
+
+        if local.pop().is_some() {
+            n += 1;
+        }
+
+        for _ in 0..6 {
+            let (task, _) = super::unowned(async {});
+            local.push_back(task, &inject, &mut metrics);
+        }
+
+        n += th.join().unwrap();
+
+        while local.pop().is_some() {
+            n += 1;
+        }
+
+        while inject.pop().is_some() {
+            n += 1;
+        }
+
+        assert_eq!(7, n);
+    });
+}
+
+#[test]
+fn multi_stealer() {
+    const NUM_TASKS: usize = 5;
+
+    fn steal_tasks(steal: queue::Steal<NoopSchedule>) -> usize {
+        let mut metrics = MetricsBatch::new();
+        let (_, mut local) = queue::local();
+
+        if steal.steal_into(&mut local, &mut metrics).is_none() {
+            return 0;
+        }
+
+        let mut n = 1;
+
+        while local.pop().is_some() {
+            n += 1;
+        }
+
+        n
+    }
+
+    loom::model(|| {
+        let (steal, mut local) = queue::local();
+        let inject = Inject::new();
+        let mut metrics = MetricsBatch::new();
+
+        // Push work
+        for _ in 0..NUM_TASKS {
+            let (task, _) = super::unowned(async {});
+            local.push_back(task, &inject, &mut metrics);
+        }
+
+        let th1 = {
+            let steal = steal.clone();
+            thread::spawn(move || steal_tasks(steal))
+        };
+
+        let th2 = thread::spawn(move || steal_tasks(steal));
+
+        let mut n = 0;
+
+        while local.pop().is_some() {
+            n += 1;
+        }
+
+        while inject.pop().is_some() {
+            n += 1;
+        }
+
+        n += th1.join().unwrap();
+        n += th2.join().unwrap();
+
+        assert_eq!(n, NUM_TASKS);
+    });
+}
+
+#[test]
+fn chained_steal() {
+    loom::model(|| {
+        let mut metrics = MetricsBatch::new();
+        let (s1, mut l1) = queue::local();
+        let (s2, mut l2) = queue::local();
+        let inject = Inject::new();
+
+        // Load up some tasks
+        for _ in 0..4 {
+            let (task, _) = super::unowned(async {});
+            l1.push_back(task, &inject, &mut metrics);
+
+            let (task, _) = super::unowned(async {});
+            l2.push_back(task, &inject, &mut metrics);
+        }
+
+        // Spawn a task to steal from **our** queue
+        let th = thread::spawn(move || {
+            let mut metrics = MetricsBatch::new();
+            let (_, mut local) = queue::local();
+            s1.steal_into(&mut local, &mut metrics);
+
+            while local.pop().is_some() {}
+        });
+
+        // Drain our tasks, then attempt to steal
+        while l1.pop().is_some() {}
+
+        s2.steal_into(&mut l1, &mut metrics);
+
+        th.join().unwrap();
+
+        while l1.pop().is_some() {}
+        while l2.pop().is_some() {}
+        while inject.pop().is_some() {}
+    });
+}
diff --git a/third_party/rust/tokio/src/runtime/tests/loom_shutdown_join.rs b/third_party/rust/tokio/src/runtime/tests/loom_shutdown_join.rs
new file mode 100644
index 0000000000..6fbc4bfded
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/tests/loom_shutdown_join.rs
@@ -0,0 +1,28 @@
+use crate::runtime::{Builder, Handle};
+
+#[test]
+fn join_handle_cancel_on_shutdown() {
+    let mut builder = loom::model::Builder::new();
+    builder.preemption_bound = Some(2);
+    builder.check(|| {
+        use futures::future::FutureExt;
+
+        let rt = Builder::new_multi_thread()
+            .worker_threads(2)
+            .build()
+            .unwrap();
+
+        let handle = rt.block_on(async move { Handle::current() });
+
+        let jh1 = handle.spawn(futures::future::pending::<()>());
+
+        drop(rt);
+
+        let jh2 = handle.spawn(futures::future::pending::<()>());
+
+        let err1 = jh1.now_or_never().unwrap().unwrap_err();
+        let err2 = jh2.now_or_never().unwrap().unwrap_err();
+        assert!(err1.is_cancelled());
+        assert!(err2.is_cancelled());
+    });
+}
diff --git a/third_party/rust/tokio/src/runtime/tests/mod.rs b/third_party/rust/tokio/src/runtime/tests/mod.rs
new file mode 100644
index 0000000000..4b49698a86
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/tests/mod.rs
@@ -0,0 +1,50 @@
+use self::unowned_wrapper::unowned;
+
+mod unowned_wrapper {
+    use crate::runtime::blocking::NoopSchedule;
+    use crate::runtime::task::{JoinHandle, Notified};
+
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    pub(crate) fn unowned<T>(task: T) -> (Notified<NoopSchedule>, JoinHandle<T::Output>)
+    where
+        T: std::future::Future + Send + 'static,
+        T::Output: Send + 'static,
+    {
+        use tracing::Instrument;
+        let span = tracing::trace_span!("test_span");
+        let task = task.instrument(span);
+        let (task, handle) = crate::runtime::task::unowned(task, NoopSchedule);
+        (task.into_notified(), handle)
+    }
+
+    #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+    pub(crate) fn unowned<T>(task: T) -> (Notified<NoopSchedule>, JoinHandle<T::Output>)
+    where
+        T: std::future::Future + Send + 'static,
+        T::Output: Send + 'static,
+    {
+        let (task, handle) = crate::runtime::task::unowned(task, NoopSchedule);
+        (task.into_notified(), handle)
+    }
+}
+
+cfg_loom! {
+    mod loom_basic_scheduler;
+    mod loom_blocking;
+    mod loom_local;
+    mod loom_oneshot;
+    mod loom_pool;
+    mod loom_queue;
+    mod loom_shutdown_join;
+    mod loom_join_set;
+}
+
+cfg_not_loom! {
+    mod queue;
+
+    #[cfg(not(miri))]
+    mod task_combinations;
+
+    #[cfg(miri)]
+    mod task;
+}
diff --git a/third_party/rust/tokio/src/runtime/tests/queue.rs b/third_party/rust/tokio/src/runtime/tests/queue.rs
new file mode 100644
index 0000000000..0fd1e0c6d9
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/tests/queue.rs
@@ -0,0 +1,248 @@
+use crate::runtime::queue;
+use crate::runtime::task::{self, Inject, Schedule, Task};
+use crate::runtime::MetricsBatch;
+
+use std::thread;
+use std::time::Duration;
+
+#[allow(unused)]
+macro_rules! assert_metrics {
+    ($metrics:ident, $field:ident == $v:expr) => {{
+        use crate::runtime::WorkerMetrics;
+        use std::sync::atomic::Ordering::Relaxed;
+
+        let worker = WorkerMetrics::new();
+        $metrics.submit(&worker);
+
+        let expect = $v;
+        let actual = worker.$field.load(Relaxed);
+
+        assert!(actual == expect, "expect = {}; actual = {}", expect, actual)
+    }};
+}
+
+#[test]
+fn fits_256() {
+    let (_, mut local) = queue::local();
+    let inject = Inject::new();
+    let mut metrics = MetricsBatch::new();
+
+    for _ in 0..256 {
+        let (task, _) = super::unowned(async {});
+        local.push_back(task, &inject, &mut metrics);
+    }
+
+    cfg_metrics! {
+        assert_metrics!(metrics, overflow_count == 0);
+    }
+
+    assert!(inject.pop().is_none());
+
+    while local.pop().is_some() {}
+}
+
+#[test]
+fn overflow() {
+    let (_, mut local) = queue::local();
+    let inject = Inject::new();
+    let mut metrics = MetricsBatch::new();
+
+    for _ in 0..257 {
+        let (task, _) = super::unowned(async {});
+        local.push_back(task, &inject, &mut metrics);
+    }
+
+    cfg_metrics! {
+        assert_metrics!(metrics, overflow_count == 1);
+    }
+
+    let mut n = 0;
+
+    while inject.pop().is_some() {
+        n += 1;
+    }
+
+    while local.pop().is_some() {
+        n += 1;
+    }
+
+    assert_eq!(n, 257);
+}
+
+#[test]
+fn steal_batch() {
+    let mut metrics = MetricsBatch::new();
+
+    let (steal1, mut local1) = queue::local();
+    let (_, mut local2) = queue::local();
+    let inject = Inject::new();
+
+    for _ in 0..4 {
+        let (task, _) = super::unowned(async {});
+        local1.push_back(task, &inject, &mut metrics);
+    }
+
+    assert!(steal1.steal_into(&mut local2, &mut metrics).is_some());
+
+    cfg_metrics! {
+        assert_metrics!(metrics, steal_count == 2);
+    }
+
+    for _ in 0..1 {
+        assert!(local2.pop().is_some());
+    }
+
+    assert!(local2.pop().is_none());
+
+    for _ in 0..2 {
+        assert!(local1.pop().is_some());
+    }
+
+    assert!(local1.pop().is_none());
+}
+
+const fn normal_or_miri(normal: usize, miri: usize) -> usize {
+    if cfg!(miri) {
+        miri
+    } else {
+        normal
+    }
+}
+
+#[test]
+fn stress1() {
+    const NUM_ITER: usize = 1;
+    const NUM_STEAL: usize = normal_or_miri(1_000, 10);
+    const NUM_LOCAL: usize = normal_or_miri(1_000, 10);
+    const NUM_PUSH: usize = normal_or_miri(500, 10);
+    const NUM_POP: usize = normal_or_miri(250, 10);
+
+    let mut metrics = MetricsBatch::new();
+
+    for _ in 0..NUM_ITER {
+        let (steal, mut local) = queue::local();
+        let inject = Inject::new();
+
+        let th = thread::spawn(move || {
+            let mut metrics = MetricsBatch::new();
+            let (_, mut local) = queue::local();
+            let mut n = 0;
+
+            for _ in 0..NUM_STEAL {
+                if steal.steal_into(&mut local, &mut metrics).is_some() {
+                    n += 1;
+                }
+
+                while local.pop().is_some() {
+                    n += 1;
+                }
+
+                thread::yield_now();
+            }
+
+            cfg_metrics! {
+                assert_metrics!(metrics, steal_count == n as _);
+            }
+
+            n
+        });
+
+        let mut n = 0;
+
+        for _ in 0..NUM_LOCAL {
+            for _ in 0..NUM_PUSH {
+                let (task, _) = super::unowned(async {});
+                local.push_back(task, &inject, &mut metrics);
+            }
+
+            for _ in 0..NUM_POP {
+                if local.pop().is_some() {
+                    n += 1;
+                } else {
+                    break;
+                }
+            }
+        }
+
+        while inject.pop().is_some() {
+            n += 1;
+        }
+
+        n += th.join().unwrap();
+
+        assert_eq!(n, NUM_LOCAL * NUM_PUSH);
+    }
+}
+
+#[test]
+fn stress2() {
+    const NUM_ITER: usize = 1;
+    const NUM_TASKS: usize = normal_or_miri(1_000_000, 50);
+    const NUM_STEAL: usize = normal_or_miri(1_000, 10);
+
+    let mut metrics = MetricsBatch::new();
+
+    for _ in 0..NUM_ITER {
+        let (steal, mut local) = queue::local();
+        let inject = Inject::new();
+
+        let th = thread::spawn(move || {
+            let mut stats = MetricsBatch::new();
+            let (_, mut local) = queue::local();
+            let mut n = 0;
+
+            for _ in 0..NUM_STEAL {
+                if steal.steal_into(&mut local, &mut stats).is_some() {
+                    n += 1;
+                }
+
+                while local.pop().is_some() {
+                    n += 1;
+                }
+
+                thread::sleep(Duration::from_micros(10));
+            }
+
+            n
+        });
+
+        let mut num_pop = 0;
+
+        for i in 0..NUM_TASKS {
+            let (task, _) = super::unowned(async {});
+            local.push_back(task, &inject, &mut metrics);
+
+            if i % 128 == 0 && local.pop().is_some() {
+                num_pop += 1;
+            }
+
+            while inject.pop().is_some() {
+                num_pop += 1;
+            }
+        }
+
+        num_pop += th.join().unwrap();
+
+        while local.pop().is_some() {
+            num_pop += 1;
+        }
+
+        while inject.pop().is_some() {
+            num_pop += 1;
+        }
+
+        assert_eq!(num_pop, NUM_TASKS);
+    }
+}
+
+struct Runtime;
+
+impl Schedule for Runtime {
+    fn release(&self, _task: &Task<Self>) -> Option<Task<Self>> {
+        None
+    }
+
+    fn schedule(&self, _task: task::Notified<Self>) {
+        unreachable!();
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/tests/task.rs b/third_party/rust/tokio/src/runtime/tests/task.rs
new file mode 100644
index 0000000000..04e1b56e77
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/tests/task.rs
@@ -0,0 +1,288 @@
+use crate::runtime::blocking::NoopSchedule;
+use crate::runtime::task::{self, unowned, JoinHandle, OwnedTasks, Schedule, Task};
+use crate::util::TryLock;
+
+use std::collections::VecDeque;
+use std::future::Future;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::Arc;
+
+struct AssertDropHandle {
+    is_dropped: Arc<AtomicBool>,
+}
+impl AssertDropHandle {
+    #[track_caller]
+    fn assert_dropped(&self) {
+        assert!(self.is_dropped.load(Ordering::SeqCst));
+    }
+
+    #[track_caller]
+    fn assert_not_dropped(&self) {
+        assert!(!self.is_dropped.load(Ordering::SeqCst));
+    }
+}
+
+struct AssertDrop {
+    is_dropped: Arc<AtomicBool>,
+}
+impl AssertDrop {
+    fn new() -> (Self, AssertDropHandle) {
+        let shared = Arc::new(AtomicBool::new(false));
+        (
+            AssertDrop {
+                is_dropped: shared.clone(),
+            },
+            AssertDropHandle {
+                is_dropped: shared.clone(),
+            },
+        )
+    }
+}
+impl Drop for AssertDrop {
+    fn drop(&mut self) {
+        self.is_dropped.store(true, Ordering::SeqCst);
+    }
+}
+
+// A Notified does not shut down on drop, but it is dropped once the ref-count
+// hits zero.
+#[test]
+fn create_drop1() {
+    let (ad, handle) = AssertDrop::new();
+    let (notified, join) = unowned(
+        async {
+            drop(ad);
+            unreachable!()
+        },
+        NoopSchedule,
+    );
+    drop(notified);
+    handle.assert_not_dropped();
+    drop(join);
+    handle.assert_dropped();
+}
+
+#[test]
+fn create_drop2() {
+    let (ad, handle) = AssertDrop::new();
+    let (notified, join) = unowned(
+        async {
+            drop(ad);
+            unreachable!()
+        },
+        NoopSchedule,
+    );
+    drop(join);
+    handle.assert_not_dropped();
+    drop(notified);
+    handle.assert_dropped();
+}
+
+// Shutting down through Notified works
+#[test]
+fn create_shutdown1() {
+    let (ad, handle) = AssertDrop::new();
+    let (notified, join) = unowned(
+        async {
+            drop(ad);
+            unreachable!()
+        },
+        NoopSchedule,
+    );
+    drop(join);
+    handle.assert_not_dropped();
+    notified.shutdown();
+    handle.assert_dropped();
+}
+
+#[test]
+fn create_shutdown2() {
+    let (ad, handle) = AssertDrop::new();
+    let (notified, join) = unowned(
+        async {
+            drop(ad);
+            unreachable!()
+        },
+        NoopSchedule,
+    );
+    handle.assert_not_dropped();
+    notified.shutdown();
+    handle.assert_dropped();
+    drop(join);
+}
+
+#[test]
+fn unowned_poll() {
+    let (task, _) = unowned(async {}, NoopSchedule);
+    task.run();
+}
+
+#[test]
+fn schedule() {
+    with(|rt| {
+        rt.spawn(async {
+            crate::task::yield_now().await;
+        });
+
+        assert_eq!(2, rt.tick());
+        rt.shutdown();
+    })
+}
+
+#[test]
+fn shutdown() {
+    with(|rt| {
+        rt.spawn(async {
+            loop {
+                crate::task::yield_now().await;
+            }
+        });
+
+        rt.tick_max(1);
+
+        rt.shutdown();
+    })
+}
+
+#[test]
+fn shutdown_immediately() {
+    with(|rt| {
+        rt.spawn(async {
+            loop {
+                crate::task::yield_now().await;
+            }
+        });
+
+        rt.shutdown();
+    })
+}
+
+#[test]
+fn spawn_during_shutdown() {
+    static DID_SPAWN: AtomicBool = AtomicBool::new(false);
+
+    struct SpawnOnDrop(Runtime);
+    impl Drop for SpawnOnDrop {
+        fn drop(&mut self) {
+            DID_SPAWN.store(true, Ordering::SeqCst);
+            self.0.spawn(async {});
+        }
+    }
+
+    with(|rt| {
+        let rt2 = rt.clone();
+        rt.spawn(async move {
+            let _spawn_on_drop = SpawnOnDrop(rt2);
+
+            loop {
+                crate::task::yield_now().await;
+            }
+        });
+
+        rt.tick_max(1);
+        rt.shutdown();
+    });
+
+    assert!(DID_SPAWN.load(Ordering::SeqCst));
+}
+
+fn with(f: impl FnOnce(Runtime)) {
+    struct Reset;
+
+    impl Drop for Reset {
+        fn drop(&mut self) {
+            let _rt = CURRENT.try_lock().unwrap().take();
+        }
+    }
+
+    let _reset = Reset;
+
+    let rt = Runtime(Arc::new(Inner {
+        owned: OwnedTasks::new(),
+        core: TryLock::new(Core {
+            queue: VecDeque::new(),
+        }),
+    }));
+
+    *CURRENT.try_lock().unwrap() = Some(rt.clone());
+    f(rt)
+}
+
+#[derive(Clone)]
+struct Runtime(Arc<Inner>);
+
+struct Inner {
+    core: TryLock<Core>,
+    owned: OwnedTasks<Runtime>,
+}
+
+struct Core {
+    queue: VecDeque<task::Notified<Runtime>>,
+}
+
+static CURRENT: TryLock<Option<Runtime>> = TryLock::new(None);
+
+impl Runtime {
+    fn spawn<T>(&self, future: T) -> JoinHandle<T::Output>
+    where
+        T: 'static + Send + Future,
+        T::Output: 'static + Send,
+    {
+        let (handle, notified) = self.0.owned.bind(future, self.clone());
+
+        if let Some(notified) = notified {
+            self.schedule(notified);
+        }
+
+        handle
+    }
+
+    fn tick(&self) -> usize {
+        self.tick_max(usize::MAX)
+    }
+
+    fn tick_max(&self, max: usize) -> usize {
+        let mut n = 0;
+
+        while !self.is_empty() && n < max {
+            let task = self.next_task();
+            n += 1;
+            let task = self.0.owned.assert_owner(task);
+            task.run();
+        }
+
+        n
+    }
+
+    fn is_empty(&self) -> bool {
+        self.0.core.try_lock().unwrap().queue.is_empty()
+    }
+
+    fn next_task(&self) -> task::Notified<Runtime> {
+        self.0.core.try_lock().unwrap().queue.pop_front().unwrap()
+    }
+
+    fn shutdown(&self) {
+        let mut core = self.0.core.try_lock().unwrap();
+
+        self.0.owned.close_and_shutdown_all();
+
+        while let Some(task) = core.queue.pop_back() {
+            drop(task);
+        }
+
+        drop(core);
+
+        assert!(self.0.owned.is_empty());
+    }
+}
+
+impl Schedule for Runtime {
+    fn release(&self, task: &Task<Self>) -> Option<Task<Self>> {
+        self.0.owned.remove(task)
+    }
+
+    fn schedule(&self, task: task::Notified<Self>) {
+        self.0.core.try_lock().unwrap().queue.push_back(task);
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/tests/task_combinations.rs b/third_party/rust/tokio/src/runtime/tests/task_combinations.rs
new file mode 100644
index 0000000000..76ce2330c2
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/tests/task_combinations.rs
@@ -0,0 +1,380 @@
+use std::future::Future;
+use std::panic;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+use crate::runtime::Builder;
+use crate::sync::oneshot;
+use crate::task::JoinHandle;
+
+use futures::future::FutureExt;
+
+// Enums for each option in the combinations being tested
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+enum CombiRuntime {
+    CurrentThread,
+    Multi1,
+    Multi2,
+}
+#[derive(Copy, Clone, Debug, PartialEq)]
+enum CombiLocalSet {
+    Yes,
+    No,
+}
+#[derive(Copy, Clone, Debug, PartialEq)]
+enum CombiTask {
+    PanicOnRun,
+    PanicOnDrop,
+    PanicOnRunAndDrop,
+    NoPanic,
+}
+#[derive(Copy, Clone, Debug, PartialEq)]
+enum CombiOutput {
+    PanicOnDrop,
+    NoPanic,
+}
+#[derive(Copy, Clone, Debug, PartialEq)]
+enum CombiJoinInterest {
+    Polled,
+    NotPolled,
+}
+#[allow(clippy::enum_variant_names)] // we aren't using glob imports
+#[derive(Copy, Clone, Debug, PartialEq)]
+enum CombiJoinHandle {
+    DropImmediately = 1,
+    DropFirstPoll = 2,
+    DropAfterNoConsume = 3,
+    DropAfterConsume = 4,
+}
+#[derive(Copy, Clone, Debug, PartialEq)]
+enum CombiAbort {
+    NotAborted = 0,
+    AbortedImmediately = 1,
+    AbortedFirstPoll = 2,
+    AbortedAfterFinish = 3,
+    AbortedAfterConsumeOutput = 4,
+}
+
+#[test]
+fn test_combinations() {
+    let mut rt = &[
+        CombiRuntime::CurrentThread,
+        CombiRuntime::Multi1,
+        CombiRuntime::Multi2,
+    ][..];
+
+    if cfg!(miri) {
+        rt = &[CombiRuntime::CurrentThread];
+    }
+
+    let ls = [CombiLocalSet::Yes, CombiLocalSet::No];
+    let task = [
+        CombiTask::NoPanic,
+        CombiTask::PanicOnRun,
+        CombiTask::PanicOnDrop,
+        CombiTask::PanicOnRunAndDrop,
+    ];
+    let output = [CombiOutput::NoPanic, CombiOutput::PanicOnDrop];
+    let ji = [CombiJoinInterest::Polled, CombiJoinInterest::NotPolled];
+    let jh = [
+        CombiJoinHandle::DropImmediately,
+        CombiJoinHandle::DropFirstPoll,
+        CombiJoinHandle::DropAfterNoConsume,
+        CombiJoinHandle::DropAfterConsume,
+    ];
+    let abort = [
+        CombiAbort::NotAborted,
+        CombiAbort::AbortedImmediately,
+        CombiAbort::AbortedFirstPoll,
+        CombiAbort::AbortedAfterFinish,
+        CombiAbort::AbortedAfterConsumeOutput,
+    ];
+
+    for rt in rt.iter().copied() {
+        for ls in ls.iter().copied() {
+            for task in task.iter().copied() {
+                for output in output.iter().copied() {
+                    for ji in ji.iter().copied() {
+                        for jh in jh.iter().copied() {
+                            for abort in abort.iter().copied() {
+                                test_combination(rt, ls, task, output, ji, jh, abort);
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+fn test_combination(
+    rt: CombiRuntime,
+    ls: CombiLocalSet,
+    task: CombiTask,
+    output: CombiOutput,
+    ji: CombiJoinInterest,
+    jh: CombiJoinHandle,
+    abort: CombiAbort,
+) {
+    if (jh as usize) < (abort as usize) {
+        // drop before abort not possible
+        return;
+    }
+    if (task == CombiTask::PanicOnDrop) && (output == CombiOutput::PanicOnDrop) {
+        // this causes double panic
+        return;
+    }
+    if (task == CombiTask::PanicOnRunAndDrop) && (abort != CombiAbort::AbortedImmediately) {
+        // this causes double panic
+        return;
+    }
+
+    println!("Runtime {:?}, LocalSet {:?}, Task {:?}, Output {:?}, JoinInterest {:?}, JoinHandle {:?}, Abort {:?}", rt, ls, task, output, ji, jh, abort);
+
+    // A runtime optionally with a LocalSet
+    struct Rt {
+        rt: crate::runtime::Runtime,
+        ls: Option<crate::task::LocalSet>,
+    }
+    impl Rt {
+        fn new(rt: CombiRuntime, ls: CombiLocalSet) -> Self {
+            let rt = match rt {
+                CombiRuntime::CurrentThread => Builder::new_current_thread().build().unwrap(),
+                CombiRuntime::Multi1 => Builder::new_multi_thread()
+                    .worker_threads(1)
+                    .build()
+                    .unwrap(),
+                CombiRuntime::Multi2 => Builder::new_multi_thread()
+                    .worker_threads(2)
+                    .build()
+                    .unwrap(),
+            };
+
+            let ls = match ls {
+                CombiLocalSet::Yes => Some(crate::task::LocalSet::new()),
+                CombiLocalSet::No => None,
+            };
+
+            Self { rt, ls }
+        }
+        fn block_on<T>(&self, task: T) -> T::Output
+        where
+            T: Future,
+        {
+            match &self.ls {
+                Some(ls) => ls.block_on(&self.rt, task),
+                None => self.rt.block_on(task),
+            }
+        }
+        fn spawn<T>(&self, task: T) -> JoinHandle<T::Output>
+        where
+            T: Future + Send + 'static,
+            T::Output: Send + 'static,
+        {
+            match &self.ls {
+                Some(ls) => ls.spawn_local(task),
+                None => self.rt.spawn(task),
+            }
+        }
+    }
+
+    // The type used for the output of the future
+    struct Output {
+        panic_on_drop: bool,
+        on_drop: Option<oneshot::Sender<()>>,
+    }
+    impl Output {
+        fn disarm(&mut self) {
+            self.panic_on_drop = false;
+        }
+    }
+    impl Drop for Output {
+        fn drop(&mut self) {
+            let _ = self.on_drop.take().unwrap().send(());
+            if self.panic_on_drop {
+                panic!("Panicking in Output");
+            }
+        }
+    }
+
+    // A wrapper around the future that is spawned
+    struct FutWrapper<F> {
+        inner: F,
+        on_drop: Option<oneshot::Sender<()>>,
+        panic_on_drop: bool,
+    }
+    impl<F: Future> Future for FutWrapper<F> {
+        type Output = F::Output;
+        fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<F::Output> {
+            unsafe {
+                let me = Pin::into_inner_unchecked(self);
+                let inner = Pin::new_unchecked(&mut me.inner);
+                inner.poll(cx)
+            }
+        }
+    }
+    impl<F> Drop for FutWrapper<F> {
+        fn drop(&mut self) {
+            let _: Result<(), ()> = self.on_drop.take().unwrap().send(());
+            if self.panic_on_drop {
+                panic!("Panicking in FutWrapper");
+            }
+        }
+    }
+
+    // The channels passed to the task
+    struct Signals {
+        on_first_poll: Option<oneshot::Sender<()>>,
+        wait_complete: Option<oneshot::Receiver<()>>,
+        on_output_drop: Option<oneshot::Sender<()>>,
+    }
+
+    // The task we will spawn
+    async fn my_task(mut signal: Signals, task: CombiTask, out: CombiOutput) -> Output {
+        // Signal that we have been polled once
+        let _ = signal.on_first_poll.take().unwrap().send(());
+
+        // Wait for a signal, then complete the future
+        let _ = signal.wait_complete.take().unwrap().await;
+
+        // If the task gets past wait_complete without yielding, then aborts
+        // may not be caught without this yield_now.
+        crate::task::yield_now().await;
+
+        if task == CombiTask::PanicOnRun || task == CombiTask::PanicOnRunAndDrop {
+            panic!("Panicking in my_task on {:?}", std::thread::current().id());
+        }
+
+        Output {
+            panic_on_drop: out == CombiOutput::PanicOnDrop,
+            on_drop: signal.on_output_drop.take(),
+        }
+    }
+
+    let rt = Rt::new(rt, ls);
+
+    let (on_first_poll, wait_first_poll) = oneshot::channel();
+    let (on_complete, wait_complete) = oneshot::channel();
+    let (on_future_drop, wait_future_drop) = oneshot::channel();
+    let (on_output_drop, wait_output_drop) = oneshot::channel();
+    let signal = Signals {
+        on_first_poll: Some(on_first_poll),
+        wait_complete: Some(wait_complete),
+        on_output_drop: Some(on_output_drop),
+    };
+
+    // === Spawn task ===
+    let mut handle = Some(rt.spawn(FutWrapper {
+        inner: my_task(signal, task, output),
+        on_drop: Some(on_future_drop),
+        panic_on_drop: task == CombiTask::PanicOnDrop || task == CombiTask::PanicOnRunAndDrop,
+    }));
+
+    // Keep track of whether the task has been killed with an abort
+    let mut aborted = false;
+
+    // If we want to poll the JoinHandle, do it now
+    if ji == CombiJoinInterest::Polled {
+        assert!(
+            handle.as_mut().unwrap().now_or_never().is_none(),
+            "Polling handle succeeded"
+        );
+    }
+
+    if abort == CombiAbort::AbortedImmediately {
+        handle.as_mut().unwrap().abort();
+        aborted = true;
+    }
+    if jh == CombiJoinHandle::DropImmediately {
+        drop(handle.take().unwrap());
+    }
+
+    // === Wait for first poll ===
+    let got_polled = rt.block_on(wait_first_poll).is_ok();
+    if !got_polled {
+        // it's possible that we are aborted but still got polled
+        assert!(
+            aborted,
+            "Task completed without ever being polled but was not aborted."
+        );
+    }
+
+    if abort == CombiAbort::AbortedFirstPoll {
+        handle.as_mut().unwrap().abort();
+        aborted = true;
+    }
+    if jh == CombiJoinHandle::DropFirstPoll {
+        drop(handle.take().unwrap());
+    }
+
+    // Signal the future that it can return now
+    let _ = on_complete.send(());
+    // === Wait for future to be dropped ===
+    assert!(
+        rt.block_on(wait_future_drop).is_ok(),
+        "The future should always be dropped."
+    );
+
+    if abort == CombiAbort::AbortedAfterFinish {
+        // Don't set aborted to true here as the task already finished
+        handle.as_mut().unwrap().abort();
+    }
+    if jh == CombiJoinHandle::DropAfterNoConsume {
+        // The runtime will usually have dropped every ref-count at this point,
+        // in which case dropping the JoinHandle drops the output.
+        //
+        // (But it might race and still hold a ref-count)
+        let panic = panic::catch_unwind(panic::AssertUnwindSafe(|| {
+            drop(handle.take().unwrap());
+        }));
+        if panic.is_err() {
+            assert!(
+                (output == CombiOutput::PanicOnDrop)
+                    && (!matches!(task, CombiTask::PanicOnRun | CombiTask::PanicOnRunAndDrop))
+                    && !aborted,
+                "Dropping JoinHandle shouldn't panic here"
+            );
+        }
+    }
+
+    // Check whether we drop after consuming the output
+    if jh == CombiJoinHandle::DropAfterConsume {
+        // Using as_mut() to not immediately drop the handle
+        let result = rt.block_on(handle.as_mut().unwrap());
+
+        match result {
+            Ok(mut output) => {
+                // Don't panic here.
+                output.disarm();
+                assert!(!aborted, "Task was aborted but returned output");
+            }
+            Err(err) if err.is_cancelled() => assert!(aborted, "Cancelled output but not aborted"),
+            Err(err) if err.is_panic() => {
+                assert!(
+                    (task == CombiTask::PanicOnRun)
+                        || (task == CombiTask::PanicOnDrop)
+                        || (task == CombiTask::PanicOnRunAndDrop)
+                        || (output == CombiOutput::PanicOnDrop),
+                    "Panic but nothing should panic"
+                );
+            }
+            _ => unreachable!(),
+        }
+
+        let handle = handle.take().unwrap();
+        if abort == CombiAbort::AbortedAfterConsumeOutput {
+            handle.abort();
+        }
+        drop(handle);
+    }
+
+    // The output should have been dropped now. Check whether the output
+    // object was created at all.
+    let output_created = rt.block_on(wait_output_drop).is_ok();
+    assert_eq!(
+        output_created,
+        (!matches!(task, CombiTask::PanicOnRun | CombiTask::PanicOnRunAndDrop)) && !aborted,
+        "Creation of output object"
+    );
+}
diff --git a/third_party/rust/tokio/src/runtime/thread_pool/idle.rs b/third_party/rust/tokio/src/runtime/thread_pool/idle.rs
new file mode 100644
index 0000000000..a57bf6a0b1
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/thread_pool/idle.rs
@@ -0,0 +1,226 @@
+//! Coordinates idling workers
+
+use crate::loom::sync::atomic::AtomicUsize;
+use crate::loom::sync::Mutex;
+
+use std::fmt;
+use std::sync::atomic::Ordering::{self, SeqCst};
+
+pub(super) struct Idle {
+    /// Tracks both the number of searching workers and the number of unparked
+    /// workers.
+    ///
+    /// Used as a fast-path to avoid acquiring the lock when needed.
+    state: AtomicUsize,
+
+    /// Sleeping workers
+    sleepers: Mutex<Vec<usize>>,
+
+    /// Total number of workers.
+    num_workers: usize,
+}
+
+const UNPARK_SHIFT: usize = 16;
+const UNPARK_MASK: usize = !SEARCH_MASK;
+const SEARCH_MASK: usize = (1 << UNPARK_SHIFT) - 1;
+
+#[derive(Copy, Clone)]
+struct State(usize);
+
+impl Idle {
+    pub(super) fn new(num_workers: usize) -> Idle {
+        let init = State::new(num_workers);
+
+        Idle {
+            state: AtomicUsize::new(init.into()),
+            sleepers: Mutex::new(Vec::with_capacity(num_workers)),
+            num_workers,
+        }
+    }
+
+    /// If there are no workers actively searching, returns the index of a
+    /// worker currently sleeping.
+    pub(super) fn worker_to_notify(&self) -> Option<usize> {
+        // If at least one worker is spinning, work being notified will
+        // eventually be found. A searching thread will find **some** work and
+        // notify another worker, eventually leading to our work being found.
+        //
+        // For this to happen, this load must happen before the thread
+        // transitioning `num_searching` to zero. Acquire / Release does not
+        // provide sufficient guarantees, so this load is done with `SeqCst` and
+        // will pair with the `fetch_sub(1)` when transitioning out of
+        // searching.
+        if !self.notify_should_wakeup() {
+            return None;
+        }
+
+        // Acquire the lock
+        let mut sleepers = self.sleepers.lock();
+
+        // Check again, now that the lock is acquired
+        if !self.notify_should_wakeup() {
+            return None;
+        }
+
+        // A worker should be woken up, atomically increment the number of
+        // searching workers as well as the number of unparked workers.
+        State::unpark_one(&self.state, 1);
+
+        // Get the worker to unpark
+        let ret = sleepers.pop();
+        debug_assert!(ret.is_some());
+
+        ret
+    }
+
+    /// Returns `true` if the worker needs to do a final check for submitted
+    /// work.
+    pub(super) fn transition_worker_to_parked(&self, worker: usize, is_searching: bool) -> bool {
+        // Acquire the lock
+        let mut sleepers = self.sleepers.lock();
+
+        // Decrement the number of unparked threads
+        let ret = State::dec_num_unparked(&self.state, is_searching);
+
+        // Track the sleeping worker
+        sleepers.push(worker);
+
+        ret
+    }
+
+    pub(super) fn transition_worker_to_searching(&self) -> bool {
+        let state = State::load(&self.state, SeqCst);
+        if 2 * state.num_searching() >= self.num_workers {
+            return false;
+        }
+
+        // It is possible for this routine to allow more than 50% of the workers
+        // to search. That is OK. Limiting searchers is only an optimization to
+        // prevent too much contention.
+        State::inc_num_searching(&self.state, SeqCst);
+        true
+    }
+
+    /// A lightweight transition from searching -> running.
+    ///
+    /// Returns `true` if this is the final searching worker. The caller
+    /// **must** notify a new worker.
+    pub(super) fn transition_worker_from_searching(&self) -> bool {
+        State::dec_num_searching(&self.state)
+    }
+
+    /// Unpark a specific worker. This happens if tasks are submitted from
+    /// within the worker's park routine.
+    ///
+    /// Returns `true` if the worker was parked before calling the method.
+    pub(super) fn unpark_worker_by_id(&self, worker_id: usize) -> bool {
+        let mut sleepers = self.sleepers.lock();
+
+        for index in 0..sleepers.len() {
+            if sleepers[index] == worker_id {
+                sleepers.swap_remove(index);
+
+                // Update the state accordingly while the lock is held.
+                State::unpark_one(&self.state, 0);
+
+                return true;
+            }
+        }
+
+        false
+    }
+
+    /// Returns `true` if `worker_id` is contained in the sleep set.
+    pub(super) fn is_parked(&self, worker_id: usize) -> bool {
+        let sleepers = self.sleepers.lock();
+        sleepers.contains(&worker_id)
+    }
+
+    fn notify_should_wakeup(&self) -> bool {
+        let state = State(self.state.fetch_add(0, SeqCst));
+        state.num_searching() == 0 && state.num_unparked() < self.num_workers
+    }
+}
+
+impl State {
+    fn new(num_workers: usize) -> State {
+        // All workers start in the unparked state
+        let ret = State(num_workers << UNPARK_SHIFT);
+        debug_assert_eq!(num_workers, ret.num_unparked());
+        debug_assert_eq!(0, ret.num_searching());
+        ret
+    }
+
+    fn load(cell: &AtomicUsize, ordering: Ordering) -> State {
+        State(cell.load(ordering))
+    }
+
+    fn unpark_one(cell: &AtomicUsize, num_searching: usize) {
+        cell.fetch_add(num_searching | (1 << UNPARK_SHIFT), SeqCst);
+    }
+
+    fn inc_num_searching(cell: &AtomicUsize, ordering: Ordering) {
+        cell.fetch_add(1, ordering);
+    }
+
+    /// Returns `true` if this is the final searching worker
+    fn dec_num_searching(cell: &AtomicUsize) -> bool {
+        let state = State(cell.fetch_sub(1, SeqCst));
+        state.num_searching() == 1
+    }
+
+    /// Track a sleeping worker
+    ///
+    /// Returns `true` if this is the final searching worker.
+    fn dec_num_unparked(cell: &AtomicUsize, is_searching: bool) -> bool {
+        let mut dec = 1 << UNPARK_SHIFT;
+
+        if is_searching {
+            dec += 1;
+        }
+
+        let prev = State(cell.fetch_sub(dec, SeqCst));
+        is_searching && prev.num_searching() == 1
+    }
+
+    /// Number of workers currently searching
+    fn num_searching(self) -> usize {
+        self.0 & SEARCH_MASK
+    }
+
+    /// Number of workers currently unparked
+    fn num_unparked(self) -> usize {
+        (self.0 & UNPARK_MASK) >> UNPARK_SHIFT
+    }
+}
+
+impl From<usize> for State {
+    fn from(src: usize) -> State {
+        State(src)
+    }
+}
+
+impl From<State> for usize {
+    fn from(src: State) -> usize {
+        src.0
+    }
+}
+
+impl fmt::Debug for State {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("worker::State")
+            .field("num_unparked", &self.num_unparked())
+            .field("num_searching", &self.num_searching())
+            .finish()
+    }
+}
+
+#[test]
+fn test_state() {
+    assert_eq!(0, UNPARK_MASK & SEARCH_MASK);
+    assert_eq!(0, !(UNPARK_MASK | SEARCH_MASK));
+
+    let state = State::new(10);
+    assert_eq!(10, state.num_unparked());
+    assert_eq!(0, state.num_searching());
+}
diff --git a/third_party/rust/tokio/src/runtime/thread_pool/mod.rs b/third_party/rust/tokio/src/runtime/thread_pool/mod.rs
new file mode 100644
index 0000000000..d3f46517cb
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/thread_pool/mod.rs
@@ -0,0 +1,136 @@
+//! Threadpool
+
+mod idle;
+use self::idle::Idle;
+
+mod worker;
+pub(crate) use worker::Launch;
+
+pub(crate) use worker::block_in_place;
+
+use crate::loom::sync::Arc;
+use crate::runtime::task::JoinHandle;
+use crate::runtime::{Callback, Parker};
+
+use std::fmt;
+use std::future::Future;
+
+/// Work-stealing based thread pool for executing futures.
+pub(crate) struct ThreadPool {
+    spawner: Spawner,
+}
+
+/// Submits futures to the associated thread pool for execution.
+///
+/// A `Spawner` instance is a handle to a single thread pool that allows the owner
+/// of the handle to spawn futures onto the thread pool.
+///
+/// The `Spawner` handle is *only* used for spawning new futures. It does not
+/// impact the lifecycle of the thread pool in any way. The thread pool may
+/// shut down while there are outstanding `Spawner` instances.
+///
+/// `Spawner` instances are obtained by calling [`ThreadPool::spawner`].
+///
+/// [`ThreadPool::spawner`]: method@ThreadPool::spawner
+#[derive(Clone)]
+pub(crate) struct Spawner {
+    shared: Arc<worker::Shared>,
+}
+
+// ===== impl ThreadPool =====
+
+impl ThreadPool {
+    pub(crate) fn new(
+        size: usize,
+        parker: Parker,
+        before_park: Option<Callback>,
+        after_unpark: Option<Callback>,
+    ) -> (ThreadPool, Launch) {
+        let (shared, launch) = worker::create(size, parker, before_park, after_unpark);
+        let spawner = Spawner { shared };
+        let thread_pool = ThreadPool { spawner };
+
+        (thread_pool, launch)
+    }
+
+    /// Returns reference to `Spawner`.
+    ///
+    /// The `Spawner` handle can be cloned and enables spawning tasks from other
+    /// threads.
+    pub(crate) fn spawner(&self) -> &Spawner {
+        &self.spawner
+    }
+
+    /// Blocks the current thread waiting for the future to complete.
+    ///
+    /// The future will execute on the current thread, but all spawned tasks
+    /// will be executed on the thread pool.
+    pub(crate) fn block_on<F>(&self, future: F) -> F::Output
+    where
+        F: Future,
+    {
+        let mut enter = crate::runtime::enter(true);
+        enter.block_on(future).expect("failed to park thread")
+    }
+}
+
+impl fmt::Debug for ThreadPool {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("ThreadPool").finish()
+    }
+}
+
+impl Drop for ThreadPool {
+    fn drop(&mut self) {
+        self.spawner.shutdown();
+    }
+}
+
+// ==== impl Spawner =====
+
+impl Spawner {
+    /// Spawns a future onto the thread pool
+    pub(crate) fn spawn<F>(&self, future: F) -> JoinHandle<F::Output>
+    where
+        F: crate::future::Future + Send + 'static,
+        F::Output: Send + 'static,
+    {
+        worker::Shared::bind_new_task(&self.shared, future)
+    }
+
+    pub(crate) fn shutdown(&mut self) {
+        self.shared.close();
+    }
+}
+
+cfg_metrics! {
+    use crate::runtime::{SchedulerMetrics, WorkerMetrics};
+
+    impl Spawner {
+        pub(crate) fn num_workers(&self) -> usize {
+            self.shared.worker_metrics.len()
+        }
+
+        pub(crate) fn scheduler_metrics(&self) -> &SchedulerMetrics {
+            &self.shared.scheduler_metrics
+        }
+
+        pub(crate) fn worker_metrics(&self, worker: usize) -> &WorkerMetrics {
+            &self.shared.worker_metrics[worker]
+        }
+
+        pub(crate) fn injection_queue_depth(&self) -> usize {
+            self.shared.injection_queue_depth()
+        }
+
+        pub(crate) fn worker_local_queue_depth(&self, worker: usize) -> usize {
+            self.shared.worker_local_queue_depth(worker)
+        }
+    }
+}
+
+impl fmt::Debug for Spawner {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Spawner").finish()
+    }
+}
diff --git a/third_party/rust/tokio/src/runtime/thread_pool/worker.rs b/third_party/rust/tokio/src/runtime/thread_pool/worker.rs
new file mode 100644
index 0000000000..7e4989701e
--- /dev/null
+++ b/third_party/rust/tokio/src/runtime/thread_pool/worker.rs
@@ -0,0 +1,848 @@
+//! A scheduler is initialized with a fixed number of workers. Each worker is
+//! driven by a thread. Each worker has a "core" which contains data such as the
+//! run queue and other state. When `block_in_place` is called, the worker's
+//! "core" is handed off to a new thread allowing the scheduler to continue to
+//! make progress while the originating thread blocks.
+//!
+//! # Shutdown
+//!
+//! Shutting down the runtime involves the following steps:
+//!
+//!  1. The Shared::close method is called. This closes the inject queue and
+//!     OwnedTasks instance and wakes up all worker threads.
+//!
+//!  2. Each worker thread observes the close signal next time it runs
+//!     Core::maintenance by checking whether the inject queue is closed.
+//!     The Core::is_shutdown flag is set to true.
+//!
+//!  3. The worker thread calls `pre_shutdown` in parallel. Here, the worker
+//!     will keep removing tasks from OwnedTasks until it is empty. No new
+//!     tasks can be pushed to the OwnedTasks during or after this step as it
+//!     was closed in step 1.
+//!
+//!  5. The workers call Shared::shutdown to enter the single-threaded phase of
+//!     shutdown. These calls will push their core to Shared::shutdown_cores,
+//!     and the last thread to push its core will finish the shutdown procedure.
+//!
+//!  6. The local run queue of each core is emptied, then the inject queue is
+//!     emptied.
+//!
+//! At this point, shutdown has completed. It is not possible for any of the
+//! collections to contain any tasks at this point, as each collection was
+//! closed first, then emptied afterwards.
+//!
+//! ## Spawns during shutdown
+//!
+//! When spawning tasks during shutdown, there are two cases:
+//!
+//!  * The spawner observes the OwnedTasks being open, and the inject queue is
+//!    closed.
+//!  * The spawner observes the OwnedTasks being closed and doesn't check the
+//!    inject queue.
+//!
+//! The first case can only happen if the OwnedTasks::bind call happens before
+//! or during step 1 of shutdown. In this case, the runtime will clean up the
+//! task in step 3 of shutdown.
+//!
+//! In the latter case, the task was not spawned and the task is immediately
+//! cancelled by the spawner.
+//!
+//! The correctness of shutdown requires both the inject queue and OwnedTasks
+//! collection to have a closed bit. With a close bit on only the inject queue,
+//! spawning could run in to a situation where a task is successfully bound long
+//! after the runtime has shut down. With a close bit on only the OwnedTasks,
+//! the first spawning situation could result in the notification being pushed
+//! to the inject queue after step 6 of shutdown, which would leave a task in
+//! the inject queue indefinitely. This would be a ref-count cycle and a memory
+//! leak.
+
+use crate::coop;
+use crate::future::Future;
+use crate::loom::rand::seed;
+use crate::loom::sync::{Arc, Mutex};
+use crate::park::{Park, Unpark};
+use crate::runtime;
+use crate::runtime::enter::EnterContext;
+use crate::runtime::park::{Parker, Unparker};
+use crate::runtime::task::{Inject, JoinHandle, OwnedTasks};
+use crate::runtime::thread_pool::Idle;
+use crate::runtime::{queue, task, Callback, MetricsBatch, SchedulerMetrics, WorkerMetrics};
+use crate::util::atomic_cell::AtomicCell;
+use crate::util::FastRand;
+
+use std::cell::RefCell;
+use std::time::Duration;
+
+/// A scheduler worker
+pub(super) struct Worker {
+    /// Reference to shared state
+    shared: Arc<Shared>,
+
+    /// Index holding this worker's remote state
+    index: usize,
+
+    /// Used to hand-off a worker's core to another thread.
+    core: AtomicCell<Core>,
+}
+
+/// Core data
+struct Core {
+    /// Used to schedule bookkeeping tasks every so often.
+    tick: u8,
+
+    /// When a task is scheduled from a worker, it is stored in this slot. The
+    /// worker will check this slot for a task **before** checking the run
+    /// queue. This effectively results in the **last** scheduled task to be run
+    /// next (LIFO). This is an optimization for message passing patterns and
+    /// helps to reduce latency.
+    lifo_slot: Option<Notified>,
+
+    /// The worker-local run queue.
+    run_queue: queue::Local<Arc<Shared>>,
+
+    /// True if the worker is currently searching for more work. Searching
+    /// involves attempting to steal from other workers.
+    is_searching: bool,
+
+    /// True if the scheduler is being shutdown
+    is_shutdown: bool,
+
+    /// Parker
+    ///
+    /// Stored in an `Option` as the parker is added / removed to make the
+    /// borrow checker happy.
+    park: Option<Parker>,
+
+    /// Batching metrics so they can be submitted to RuntimeMetrics.
+    metrics: MetricsBatch,
+
+    /// Fast random number generator.
+    rand: FastRand,
+}
+
+/// State shared across all workers
+pub(super) struct Shared {
+    /// Per-worker remote state. All other workers have access to this and is
+    /// how they communicate between each other.
+    remotes: Box<[Remote]>,
+
+    /// Submits work to the scheduler while **not** currently on a worker thread.
+    inject: Inject<Arc<Shared>>,
+
+    /// Coordinates idle workers
+    idle: Idle,
+
+    /// Collection of all active tasks spawned onto this executor.
+    owned: OwnedTasks<Arc<Shared>>,
+
+    /// Cores that have observed the shutdown signal
+    ///
+    /// The core is **not** placed back in the worker to avoid it from being
+    /// stolen by a thread that was spawned as part of `block_in_place`.
+    #[allow(clippy::vec_box)] // we're moving an already-boxed value
+    shutdown_cores: Mutex<Vec<Box<Core>>>,
+
+    /// Callback for a worker parking itself
+    before_park: Option<Callback>,
+    /// Callback for a worker unparking itself
+    after_unpark: Option<Callback>,
+
+    /// Collects metrics from the runtime.
+    pub(super) scheduler_metrics: SchedulerMetrics,
+
+    pub(super) worker_metrics: Box<[WorkerMetrics]>,
+}
+
+/// Used to communicate with a worker from other threads.
+struct Remote {
+    /// Steals tasks from this worker.
+    steal: queue::Steal<Arc<Shared>>,
+
+    /// Unparks the associated worker thread
+    unpark: Unparker,
+}
+
+/// Thread-local context
+struct Context {
+    /// Worker
+    worker: Arc<Worker>,
+
+    /// Core data
+    core: RefCell<Option<Box<Core>>>,
+}
+
+/// Starts the workers
+pub(crate) struct Launch(Vec<Arc<Worker>>);
+
+/// Running a task may consume the core. If the core is still available when
+/// running the task completes, it is returned. Otherwise, the worker will need
+/// to stop processing.
+type RunResult = Result<Box<Core>, ()>;
+
+/// A task handle
+type Task = task::Task<Arc<Shared>>;
+
+/// A notified task handle
+type Notified = task::Notified<Arc<Shared>>;
+
+// Tracks thread-local state
+scoped_thread_local!(static CURRENT: Context);
+
+pub(super) fn create(
+    size: usize,
+    park: Parker,
+    before_park: Option<Callback>,
+    after_unpark: Option<Callback>,
+) -> (Arc<Shared>, Launch) {
+    let mut cores = vec![];
+    let mut remotes = vec![];
+    let mut worker_metrics = vec![];
+
+    // Create the local queues
+    for _ in 0..size {
+        let (steal, run_queue) = queue::local();
+
+        let park = park.clone();
+        let unpark = park.unpark();
+
+        cores.push(Box::new(Core {
+            tick: 0,
+            lifo_slot: None,
+            run_queue,
+            is_searching: false,
+            is_shutdown: false,
+            park: Some(park),
+            metrics: MetricsBatch::new(),
+            rand: FastRand::new(seed()),
+        }));
+
+        remotes.push(Remote { steal, unpark });
+        worker_metrics.push(WorkerMetrics::new());
+    }
+
+    let shared = Arc::new(Shared {
+        remotes: remotes.into_boxed_slice(),
+        inject: Inject::new(),
+        idle: Idle::new(size),
+        owned: OwnedTasks::new(),
+        shutdown_cores: Mutex::new(vec![]),
+        before_park,
+        after_unpark,
+        scheduler_metrics: SchedulerMetrics::new(),
+        worker_metrics: worker_metrics.into_boxed_slice(),
+    });
+
+    let mut launch = Launch(vec![]);
+
+    for (index, core) in cores.drain(..).enumerate() {
+        launch.0.push(Arc::new(Worker {
+            shared: shared.clone(),
+            index,
+            core: AtomicCell::new(Some(core)),
+        }));
+    }
+
+    (shared, launch)
+}
+
+pub(crate) fn block_in_place<F, R>(f: F) -> R
+where
+    F: FnOnce() -> R,
+{
+    // Try to steal the worker core back
+    struct Reset(coop::Budget);
+
+    impl Drop for Reset {
+        fn drop(&mut self) {
+            CURRENT.with(|maybe_cx| {
+                if let Some(cx) = maybe_cx {
+                    let core = cx.worker.core.take();
+                    let mut cx_core = cx.core.borrow_mut();
+                    assert!(cx_core.is_none());
+                    *cx_core = core;
+
+                    // Reset the task budget as we are re-entering the
+                    // runtime.
+                    coop::set(self.0);
+                }
+            });
+        }
+    }
+
+    let mut had_entered = false;
+
+    CURRENT.with(|maybe_cx| {
+        match (crate::runtime::enter::context(), maybe_cx.is_some()) {
+            (EnterContext::Entered { .. }, true) => {
+                // We are on a thread pool runtime thread, so we just need to
+                // set up blocking.
+                had_entered = true;
+            }
+            (EnterContext::Entered { allow_blocking }, false) => {
+                // We are on an executor, but _not_ on the thread pool.  That is
+                // _only_ okay if we are in a thread pool runtime's block_on
+                // method:
+                if allow_blocking {
+                    had_entered = true;
+                    return;
+                } else {
+                    // This probably means we are on the basic_scheduler or in a
+                    // LocalSet, where it is _not_ okay to block.
+                    panic!("can call blocking only when running on the multi-threaded runtime");
+                }
+            }
+            (EnterContext::NotEntered, true) => {
+                // This is a nested call to block_in_place (we already exited).
+                // All the necessary setup has already been done.
+                return;
+            }
+            (EnterContext::NotEntered, false) => {
+                // We are outside of the tokio runtime, so blocking is fine.
+                // We can also skip all of the thread pool blocking setup steps.
+                return;
+            }
+        }
+
+        let cx = maybe_cx.expect("no .is_some() == false cases above should lead here");
+
+        // Get the worker core. If none is set, then blocking is fine!
+        let core = match cx.core.borrow_mut().take() {
+            Some(core) => core,
+            None => return,
+        };
+
+        // The parker should be set here
+        assert!(core.park.is_some());
+
+        // In order to block, the core must be sent to another thread for
+        // execution.
+        //
+        // First, move the core back into the worker's shared core slot.
+        cx.worker.core.set(core);
+
+        // Next, clone the worker handle and send it to a new thread for
+        // processing.
+        //
+        // Once the blocking task is done executing, we will attempt to
+        // steal the core back.
+        let worker = cx.worker.clone();
+        runtime::spawn_blocking(move || run(worker));
+    });
+
+    if had_entered {
+        // Unset the current task's budget. Blocking sections are not
+        // constrained by task budgets.
+        let _reset = Reset(coop::stop());
+
+        crate::runtime::enter::exit(f)
+    } else {
+        f()
+    }
+}
+
+/// After how many ticks is the global queue polled. This helps to ensure
+/// fairness.
+///
+/// The number is fairly arbitrary. I believe this value was copied from golang.
+const GLOBAL_POLL_INTERVAL: u8 = 61;
+
+impl Launch {
+    pub(crate) fn launch(mut self) {
+        for worker in self.0.drain(..) {
+            runtime::spawn_blocking(move || run(worker));
+        }
+    }
+}
+
+fn run(worker: Arc<Worker>) {
+    // Acquire a core. If this fails, then another thread is running this
+    // worker and there is nothing further to do.
+    let core = match worker.core.take() {
+        Some(core) => core,
+        None => return,
+    };
+
+    // Set the worker context.
+    let cx = Context {
+        worker,
+        core: RefCell::new(None),
+    };
+
+    let _enter = crate::runtime::enter(true);
+
+    CURRENT.set(&cx, || {
+        // This should always be an error. It only returns a `Result` to support
+        // using `?` to short circuit.
+        assert!(cx.run(core).is_err());
+    });
+}
+
+impl Context {
+    fn run(&self, mut core: Box<Core>) -> RunResult {
+        while !core.is_shutdown {
+            // Increment the tick
+            core.tick();
+
+            // Run maintenance, if needed
+            core = self.maintenance(core);
+
+            // First, check work available to the current worker.
+            if let Some(task) = core.next_task(&self.worker) {
+                core = self.run_task(task, core)?;
+                continue;
+            }
+
+            // There is no more **local** work to process, try to steal work
+            // from other workers.
+            if let Some(task) = core.steal_work(&self.worker) {
+                core = self.run_task(task, core)?;
+            } else {
+                // Wait for work
+                core = self.park(core);
+            }
+        }
+
+        core.pre_shutdown(&self.worker);
+
+        // Signal shutdown
+        self.worker.shared.shutdown(core);
+        Err(())
+    }
+
+    fn run_task(&self, task: Notified, mut core: Box<Core>) -> RunResult {
+        let task = self.worker.shared.owned.assert_owner(task);
+
+        // Make sure the worker is not in the **searching** state. This enables
+        // another idle worker to try to steal work.
+        core.transition_from_searching(&self.worker);
+
+        // Make the core available to the runtime context
+        core.metrics.incr_poll_count();
+        *self.core.borrow_mut() = Some(core);
+
+        // Run the task
+        coop::budget(|| {
+            task.run();
+
+            // As long as there is budget remaining and a task exists in the
+            // `lifo_slot`, then keep running.
+            loop {
+                // Check if we still have the core. If not, the core was stolen
+                // by another worker.
+                let mut core = match self.core.borrow_mut().take() {
+                    Some(core) => core,
+                    None => return Err(()),
+                };
+
+                // Check for a task in the LIFO slot
+                let task = match core.lifo_slot.take() {
+                    Some(task) => task,
+                    None => return Ok(core),
+                };
+
+                if coop::has_budget_remaining() {
+                    // Run the LIFO task, then loop
+                    core.metrics.incr_poll_count();
+                    *self.core.borrow_mut() = Some(core);
+                    let task = self.worker.shared.owned.assert_owner(task);
+                    task.run();
+                } else {
+                    // Not enough budget left to run the LIFO task, push it to
+                    // the back of the queue and return.
+                    core.run_queue
+                        .push_back(task, self.worker.inject(), &mut core.metrics);
+                    return Ok(core);
+                }
+            }
+        })
+    }
+
+    fn maintenance(&self, mut core: Box<Core>) -> Box<Core> {
+        if core.tick % GLOBAL_POLL_INTERVAL == 0 {
+            // Call `park` with a 0 timeout. This enables the I/O driver, timer, ...
+            // to run without actually putting the thread to sleep.
+            core = self.park_timeout(core, Some(Duration::from_millis(0)));
+
+            // Run regularly scheduled maintenance
+            core.maintenance(&self.worker);
+        }
+
+        core
+    }
+
+    fn park(&self, mut core: Box<Core>) -> Box<Core> {
+        if let Some(f) = &self.worker.shared.before_park {
+            f();
+        }
+
+        if core.transition_to_parked(&self.worker) {
+            while !core.is_shutdown {
+                core.metrics.about_to_park();
+                core = self.park_timeout(core, None);
+                core.metrics.returned_from_park();
+
+                // Run regularly scheduled maintenance
+                core.maintenance(&self.worker);
+
+                if core.transition_from_parked(&self.worker) {
+                    break;
+                }
+            }
+        }
+
+        if let Some(f) = &self.worker.shared.after_unpark {
+            f();
+        }
+        core
+    }
+
+    fn park_timeout(&self, mut core: Box<Core>, duration: Option<Duration>) -> Box<Core> {
+        // Take the parker out of core
+        let mut park = core.park.take().expect("park missing");
+
+        // Store `core` in context
+        *self.core.borrow_mut() = Some(core);
+
+        // Park thread
+        if let Some(timeout) = duration {
+            park.park_timeout(timeout).expect("park failed");
+        } else {
+            park.park().expect("park failed");
+        }
+
+        // Remove `core` from context
+        core = self.core.borrow_mut().take().expect("core missing");
+
+        // Place `park` back in `core`
+        core.park = Some(park);
+
+        // If there are tasks available to steal, but this worker is not
+        // looking for tasks to steal, notify another worker.
+        if !core.is_searching && core.run_queue.is_stealable() {
+            self.worker.shared.notify_parked();
+        }
+
+        core
+    }
+}
+
+impl Core {
+    /// Increment the tick
+    fn tick(&mut self) {
+        self.tick = self.tick.wrapping_add(1);
+    }
+
+    /// Return the next notified task available to this worker.
+    fn next_task(&mut self, worker: &Worker) -> Option<Notified> {
+        if self.tick % GLOBAL_POLL_INTERVAL == 0 {
+            worker.inject().pop().or_else(|| self.next_local_task())
+        } else {
+            self.next_local_task().or_else(|| worker.inject().pop())
+        }
+    }
+
+    fn next_local_task(&mut self) -> Option<Notified> {
+        self.lifo_slot.take().or_else(|| self.run_queue.pop())
+    }
+
+    fn steal_work(&mut self, worker: &Worker) -> Option<Notified> {
+        if !self.transition_to_searching(worker) {
+            return None;
+        }
+
+        let num = worker.shared.remotes.len();
+        // Start from a random worker
+        let start = self.rand.fastrand_n(num as u32) as usize;
+
+        for i in 0..num {
+            let i = (start + i) % num;
+
+            // Don't steal from ourself! We know we don't have work.
+            if i == worker.index {
+                continue;
+            }
+
+            let target = &worker.shared.remotes[i];
+            if let Some(task) = target
+                .steal
+                .steal_into(&mut self.run_queue, &mut self.metrics)
+            {
+                return Some(task);
+            }
+        }
+
+        // Fallback on checking the global queue
+        worker.shared.inject.pop()
+    }
+
+    fn transition_to_searching(&mut self, worker: &Worker) -> bool {
+        if !self.is_searching {
+            self.is_searching = worker.shared.idle.transition_worker_to_searching();
+        }
+
+        self.is_searching
+    }
+
+    fn transition_from_searching(&mut self, worker: &Worker) {
+        if !self.is_searching {
+            return;
+        }
+
+        self.is_searching = false;
+        worker.shared.transition_worker_from_searching();
+    }
+
+    /// Prepares the worker state for parking.
+    ///
+    /// Returns true if the transition happend, false if there is work to do first.
+    fn transition_to_parked(&mut self, worker: &Worker) -> bool {
+        // Workers should not park if they have work to do
+        if self.lifo_slot.is_some() || self.run_queue.has_tasks() {
+            return false;
+        }
+
+        // When the final worker transitions **out** of searching to parked, it
+        // must check all the queues one last time in case work materialized
+        // between the last work scan and transitioning out of searching.
+        let is_last_searcher = worker
+            .shared
+            .idle
+            .transition_worker_to_parked(worker.index, self.is_searching);
+
+        // The worker is no longer searching. Setting this is the local cache
+        // only.
+        self.is_searching = false;
+
+        if is_last_searcher {
+            worker.shared.notify_if_work_pending();
+        }
+
+        true
+    }
+
+    /// Returns `true` if the transition happened.
+    fn transition_from_parked(&mut self, worker: &Worker) -> bool {
+        // If a task is in the lifo slot, then we must unpark regardless of
+        // being notified
+        if self.lifo_slot.is_some() {
+            // When a worker wakes, it should only transition to the "searching"
+            // state when the wake originates from another worker *or* a new task
+            // is pushed. We do *not* want the worker to transition to "searching"
+            // when it wakes when the I/O driver receives new events.
+            self.is_searching = !worker.shared.idle.unpark_worker_by_id(worker.index);
+            return true;
+        }
+
+        if worker.shared.idle.is_parked(worker.index) {
+            return false;
+        }
+
+        // When unparked, the worker is in the searching state.
+        self.is_searching = true;
+        true
+    }
+
+    /// Runs maintenance work such as checking the pool's state.
+    fn maintenance(&mut self, worker: &Worker) {
+        self.metrics
+            .submit(&worker.shared.worker_metrics[worker.index]);
+
+        if !self.is_shutdown {
+            // Check if the scheduler has been shutdown
+            self.is_shutdown = worker.inject().is_closed();
+        }
+    }
+
+    /// Signals all tasks to shut down, and waits for them to complete. Must run
+    /// before we enter the single-threaded phase of shutdown processing.
+    fn pre_shutdown(&mut self, worker: &Worker) {
+        // Signal to all tasks to shut down.
+        worker.shared.owned.close_and_shutdown_all();
+
+        self.metrics
+            .submit(&worker.shared.worker_metrics[worker.index]);
+    }
+
+    /// Shuts down the core.
+    fn shutdown(&mut self) {
+        // Take the core
+        let mut park = self.park.take().expect("park missing");
+
+        // Drain the queue
+        while self.next_local_task().is_some() {}
+
+        park.shutdown();
+    }
+}
+
+impl Worker {
+    /// Returns a reference to the scheduler's injection queue.
+    fn inject(&self) -> &Inject<Arc<Shared>> {
+        &self.shared.inject
+    }
+}
+
+impl task::Schedule for Arc<Shared> {
+    fn release(&self, task: &Task) -> Option<Task> {
+        self.owned.remove(task)
+    }
+
+    fn schedule(&self, task: Notified) {
+        (**self).schedule(task, false);
+    }
+
+    fn yield_now(&self, task: Notified) {
+        (**self).schedule(task, true);
+    }
+}
+
+impl Shared {
+    pub(super) fn bind_new_task<T>(me: &Arc<Self>, future: T) -> JoinHandle<T::Output>
+    where
+        T: Future + Send + 'static,
+        T::Output: Send + 'static,
+    {
+        let (handle, notified) = me.owned.bind(future, me.clone());
+
+        if let Some(notified) = notified {
+            me.schedule(notified, false);
+        }
+
+        handle
+    }
+
+    pub(super) fn schedule(&self, task: Notified, is_yield: bool) {
+        CURRENT.with(|maybe_cx| {
+            if let Some(cx) = maybe_cx {
+                // Make sure the task is part of the **current** scheduler.
+                if self.ptr_eq(&cx.worker.shared) {
+                    // And the current thread still holds a core
+                    if let Some(core) = cx.core.borrow_mut().as_mut() {
+                        self.schedule_local(core, task, is_yield);
+                        return;
+                    }
+                }
+            }
+
+            // Otherwise, use the inject queue.
+            self.inject.push(task);
+            self.scheduler_metrics.inc_remote_schedule_count();
+            self.notify_parked();
+        })
+    }
+
+    fn schedule_local(&self, core: &mut Core, task: Notified, is_yield: bool) {
+        core.metrics.inc_local_schedule_count();
+
+        // Spawning from the worker thread. If scheduling a "yield" then the
+        // task must always be pushed to the back of the queue, enabling other
+        // tasks to be executed. If **not** a yield, then there is more
+        // flexibility and the task may go to the front of the queue.
+        let should_notify = if is_yield {
+            core.run_queue
+                .push_back(task, &self.inject, &mut core.metrics);
+            true
+        } else {
+            // Push to the LIFO slot
+            let prev = core.lifo_slot.take();
+            let ret = prev.is_some();
+
+            if let Some(prev) = prev {
+                core.run_queue
+                    .push_back(prev, &self.inject, &mut core.metrics);
+            }
+
+            core.lifo_slot = Some(task);
+
+            ret
+        };
+
+        // Only notify if not currently parked. If `park` is `None`, then the
+        // scheduling is from a resource driver. As notifications often come in
+        // batches, the notification is delayed until the park is complete.
+        if should_notify && core.park.is_some() {
+            self.notify_parked();
+        }
+    }
+
+    pub(super) fn close(&self) {
+        if self.inject.close() {
+            self.notify_all();
+        }
+    }
+
+    fn notify_parked(&self) {
+        if let Some(index) = self.idle.worker_to_notify() {
+            self.remotes[index].unpark.unpark();
+        }
+    }
+
+    fn notify_all(&self) {
+        for remote in &self.remotes[..] {
+            remote.unpark.unpark();
+        }
+    }
+
+    fn notify_if_work_pending(&self) {
+        for remote in &self.remotes[..] {
+            if !remote.steal.is_empty() {
+                self.notify_parked();
+                return;
+            }
+        }
+
+        if !self.inject.is_empty() {
+            self.notify_parked();
+        }
+    }
+
+    fn transition_worker_from_searching(&self) {
+        if self.idle.transition_worker_from_searching() {
+            // We are the final searching worker. Because work was found, we
+            // need to notify another worker.
+            self.notify_parked();
+        }
+    }
+
+    /// Signals that a worker has observed the shutdown signal and has replaced
+    /// its core back into its handle.
+    ///
+    /// If all workers have reached this point, the final cleanup is performed.
+    fn shutdown(&self, core: Box<Core>) {
+        let mut cores = self.shutdown_cores.lock();
+        cores.push(core);
+
+        if cores.len() != self.remotes.len() {
+            return;
+        }
+
+        debug_assert!(self.owned.is_empty());
+
+        for mut core in cores.drain(..) {
+            core.shutdown();
+        }
+
+        // Drain the injection queue
+        //
+        // We already shut down every task, so we can simply drop the tasks.
+        while let Some(task) = self.inject.pop() {
+            drop(task);
+        }
+    }
+
+    fn ptr_eq(&self, other: &Shared) -> bool {
+        std::ptr::eq(self, other)
+    }
+}
+
+cfg_metrics! {
+    impl Shared {
+        pub(super) fn injection_queue_depth(&self) -> usize {
+            self.inject.len()
+        }
+
+        pub(super) fn worker_local_queue_depth(&self, worker: usize) -> usize {
+            self.remotes[worker].steal.len()
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/signal/ctrl_c.rs b/third_party/rust/tokio/src/signal/ctrl_c.rs
new file mode 100644
index 0000000000..b26ab7ead6
--- /dev/null
+++ b/third_party/rust/tokio/src/signal/ctrl_c.rs
@@ -0,0 +1,62 @@
+#[cfg(unix)]
+use super::unix::{self as os_impl};
+#[cfg(windows)]
+use super::windows::{self as os_impl};
+
+use std::io;
+
+/// Completes when a "ctrl-c" notification is sent to the process.
+///
+/// While signals are handled very differently between Unix and Windows, both
+/// platforms support receiving a signal on "ctrl-c". This function provides a
+/// portable API for receiving this notification.
+///
+/// Once the returned future is polled, a listener is registered. The future
+/// will complete on the first received `ctrl-c` **after** the initial call to
+/// either `Future::poll` or `.await`.
+///
+/// # Caveats
+///
+/// On Unix platforms, the first time that a `Signal` instance is registered for a
+/// particular signal kind, an OS signal-handler is installed which replaces the
+/// default platform behavior when that signal is received, **for the duration of
+/// the entire process**.
+///
+/// For example, Unix systems will terminate a process by default when it
+/// receives a signal generated by "CTRL+C" on the terminal. But, when a
+/// `ctrl_c` stream is created to listen for this signal, the time it arrives,
+/// it will be translated to a stream event, and the process will continue to
+/// execute.  **Even if this `Signal` instance is dropped, subsequent SIGINT
+/// deliveries will end up captured by Tokio, and the default platform behavior
+/// will NOT be reset**.
+///
+/// Thus, applications should take care to ensure the expected signal behavior
+/// occurs as expected after listening for specific signals.
+///
+/// # Examples
+///
+/// ```rust,no_run
+/// use tokio::signal;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     println!("waiting for ctrl-c");
+///
+///     signal::ctrl_c().await.expect("failed to listen for event");
+///
+///     println!("received ctrl-c event");
+/// }
+/// ```
+///
+/// Listen in the background:
+///
+/// ```rust,no_run
+/// tokio::spawn(async move {
+///     tokio::signal::ctrl_c().await.unwrap();
+///     // Your handler here
+/// });
+/// ```
+pub async fn ctrl_c() -> io::Result<()> {
+    os_impl::ctrl_c()?.recv().await;
+    Ok(())
+}
diff --git a/third_party/rust/tokio/src/signal/mod.rs b/third_party/rust/tokio/src/signal/mod.rs
new file mode 100644
index 0000000000..882218a0f6
--- /dev/null
+++ b/third_party/rust/tokio/src/signal/mod.rs
@@ -0,0 +1,100 @@
+//! Asynchronous signal handling for Tokio.
+//!
+//! Note that signal handling is in general a very tricky topic and should be
+//! used with great care. This crate attempts to implement 'best practice' for
+//! signal handling, but it should be evaluated for your own applications' needs
+//! to see if it's suitable.
+//!
+//! There are some fundamental limitations of this crate documented on the OS
+//! specific structures, as well.
+//!
+//! # Examples
+//!
+//! Print on "ctrl-c" notification.
+//!
+//! ```rust,no_run
+//! use tokio::signal;
+//!
+//! #[tokio::main]
+//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
+//!     signal::ctrl_c().await?;
+//!     println!("ctrl-c received!");
+//!     Ok(())
+//! }
+//! ```
+//!
+//! Wait for SIGHUP on Unix
+//!
+//! ```rust,no_run
+//! # #[cfg(unix)] {
+//! use tokio::signal::unix::{signal, SignalKind};
+//!
+//! #[tokio::main]
+//! async fn main() -> Result<(), Box<dyn std::error::Error>> {
+//!     // An infinite stream of hangup signals.
+//!     let mut stream = signal(SignalKind::hangup())?;
+//!
+//!     // Print whenever a HUP signal is received
+//!     loop {
+//!         stream.recv().await;
+//!         println!("got signal HUP");
+//!     }
+//! }
+//! # }
+//! ```
+use crate::sync::watch::Receiver;
+use std::task::{Context, Poll};
+
+mod ctrl_c;
+pub use ctrl_c::ctrl_c;
+
+mod registry;
+
+mod os {
+    #[cfg(unix)]
+    pub(crate) use super::unix::{OsExtraData, OsStorage};
+
+    #[cfg(windows)]
+    pub(crate) use super::windows::{OsExtraData, OsStorage};
+}
+
+pub mod unix;
+pub mod windows;
+
+mod reusable_box;
+use self::reusable_box::ReusableBoxFuture;
+
+#[derive(Debug)]
+struct RxFuture {
+    inner: ReusableBoxFuture<Receiver<()>>,
+}
+
+async fn make_future(mut rx: Receiver<()>) -> Receiver<()> {
+    match rx.changed().await {
+        Ok(()) => rx,
+        Err(_) => panic!("signal sender went away"),
+    }
+}
+
+impl RxFuture {
+    fn new(rx: Receiver<()>) -> Self {
+        Self {
+            inner: ReusableBoxFuture::new(make_future(rx)),
+        }
+    }
+
+    async fn recv(&mut self) -> Option<()> {
+        use crate::future::poll_fn;
+        poll_fn(|cx| self.poll_recv(cx)).await
+    }
+
+    fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>> {
+        match self.inner.poll(cx) {
+            Poll::Pending => Poll::Pending,
+            Poll::Ready(rx) => {
+                self.inner.set(make_future(rx));
+                Poll::Ready(Some(()))
+            }
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/signal/registry.rs b/third_party/rust/tokio/src/signal/registry.rs
new file mode 100644
index 0000000000..6d8eb9e748
--- /dev/null
+++ b/third_party/rust/tokio/src/signal/registry.rs
@@ -0,0 +1,279 @@
+#![allow(clippy::unit_arg)]
+
+use crate::signal::os::{OsExtraData, OsStorage};
+
+use crate::sync::watch;
+
+use once_cell::sync::Lazy;
+use std::ops;
+use std::pin::Pin;
+use std::sync::atomic::{AtomicBool, Ordering};
+
+pub(crate) type EventId = usize;
+
+/// State for a specific event, whether a notification is pending delivery,
+/// and what listeners are registered.
+#[derive(Debug)]
+pub(crate) struct EventInfo {
+    pending: AtomicBool,
+    tx: watch::Sender<()>,
+}
+
+impl Default for EventInfo {
+    fn default() -> Self {
+        let (tx, _rx) = watch::channel(());
+
+        Self {
+            pending: AtomicBool::new(false),
+            tx,
+        }
+    }
+}
+
+/// An interface for retrieving the `EventInfo` for a particular eventId.
+pub(crate) trait Storage {
+    /// Gets the `EventInfo` for `id` if it exists.
+    fn event_info(&self, id: EventId) -> Option<&EventInfo>;
+
+    /// Invokes `f` once for each defined `EventInfo` in this storage.
+    fn for_each<'a, F>(&'a self, f: F)
+    where
+        F: FnMut(&'a EventInfo);
+}
+
+impl Storage for Vec<EventInfo> {
+    fn event_info(&self, id: EventId) -> Option<&EventInfo> {
+        self.get(id)
+    }
+
+    fn for_each<'a, F>(&'a self, f: F)
+    where
+        F: FnMut(&'a EventInfo),
+    {
+        self.iter().for_each(f)
+    }
+}
+
+/// An interface for initializing a type. Useful for situations where we cannot
+/// inject a configured instance in the constructor of another type.
+pub(crate) trait Init {
+    fn init() -> Self;
+}
+
+/// Manages and distributes event notifications to any registered listeners.
+///
+/// Generic over the underlying storage to allow for domain specific
+/// optimizations (e.g. eventIds may or may not be contiguous).
+#[derive(Debug)]
+pub(crate) struct Registry<S> {
+    storage: S,
+}
+
+impl<S> Registry<S> {
+    fn new(storage: S) -> Self {
+        Self { storage }
+    }
+}
+
+impl<S: Storage> Registry<S> {
+    /// Registers a new listener for `event_id`.
+    fn register_listener(&self, event_id: EventId) -> watch::Receiver<()> {
+        self.storage
+            .event_info(event_id)
+            .unwrap_or_else(|| panic!("invalid event_id: {}", event_id))
+            .tx
+            .subscribe()
+    }
+
+    /// Marks `event_id` as having been delivered, without broadcasting it to
+    /// any listeners.
+    fn record_event(&self, event_id: EventId) {
+        if let Some(event_info) = self.storage.event_info(event_id) {
+            event_info.pending.store(true, Ordering::SeqCst)
+        }
+    }
+
+    /// Broadcasts all previously recorded events to their respective listeners.
+    ///
+    /// Returns `true` if an event was delivered to at least one listener.
+    fn broadcast(&self) -> bool {
+        let mut did_notify = false;
+        self.storage.for_each(|event_info| {
+            // Any signal of this kind arrived since we checked last?
+            if !event_info.pending.swap(false, Ordering::SeqCst) {
+                return;
+            }
+
+            // Ignore errors if there are no listeners
+            if event_info.tx.send(()).is_ok() {
+                did_notify = true;
+            }
+        });
+
+        did_notify
+    }
+}
+
+pub(crate) struct Globals {
+    extra: OsExtraData,
+    registry: Registry<OsStorage>,
+}
+
+impl ops::Deref for Globals {
+    type Target = OsExtraData;
+
+    fn deref(&self) -> &Self::Target {
+        &self.extra
+    }
+}
+
+impl Globals {
+    /// Registers a new listener for `event_id`.
+    pub(crate) fn register_listener(&self, event_id: EventId) -> watch::Receiver<()> {
+        self.registry.register_listener(event_id)
+    }
+
+    /// Marks `event_id` as having been delivered, without broadcasting it to
+    /// any listeners.
+    pub(crate) fn record_event(&self, event_id: EventId) {
+        self.registry.record_event(event_id);
+    }
+
+    /// Broadcasts all previously recorded events to their respective listeners.
+    ///
+    /// Returns `true` if an event was delivered to at least one listener.
+    pub(crate) fn broadcast(&self) -> bool {
+        self.registry.broadcast()
+    }
+
+    #[cfg(unix)]
+    pub(crate) fn storage(&self) -> &OsStorage {
+        &self.registry.storage
+    }
+}
+
+pub(crate) fn globals() -> Pin<&'static Globals>
+where
+    OsExtraData: 'static + Send + Sync + Init,
+    OsStorage: 'static + Send + Sync + Init,
+{
+    static GLOBALS: Lazy<Pin<Box<Globals>>> = Lazy::new(|| {
+        Box::pin(Globals {
+            extra: OsExtraData::init(),
+            registry: Registry::new(OsStorage::init()),
+        })
+    });
+
+    GLOBALS.as_ref()
+}
+
+#[cfg(all(test, not(loom)))]
+mod tests {
+    use super::*;
+    use crate::runtime::{self, Runtime};
+    use crate::sync::{oneshot, watch};
+
+    use futures::future;
+
+    #[test]
+    fn smoke() {
+        let rt = rt();
+        rt.block_on(async move {
+            let registry = Registry::new(vec![
+                EventInfo::default(),
+                EventInfo::default(),
+                EventInfo::default(),
+            ]);
+
+            let first = registry.register_listener(0);
+            let second = registry.register_listener(1);
+            let third = registry.register_listener(2);
+
+            let (fire, wait) = oneshot::channel();
+
+            crate::spawn(async {
+                wait.await.expect("wait failed");
+
+                // Record some events which should get coalesced
+                registry.record_event(0);
+                registry.record_event(0);
+                registry.record_event(1);
+                registry.record_event(1);
+                registry.broadcast();
+
+                // Yield so the previous broadcast can get received
+                //
+                // This yields many times since the block_on task is only polled every 61
+                // ticks.
+                for _ in 0..100 {
+                    crate::task::yield_now().await;
+                }
+
+                // Send subsequent signal
+                registry.record_event(0);
+                registry.broadcast();
+
+                drop(registry);
+            });
+
+            let _ = fire.send(());
+            let all = future::join3(collect(first), collect(second), collect(third));
+
+            let (first_results, second_results, third_results) = all.await;
+            assert_eq!(2, first_results.len());
+            assert_eq!(1, second_results.len());
+            assert_eq!(0, third_results.len());
+        });
+    }
+
+    #[test]
+    #[should_panic = "invalid event_id: 1"]
+    fn register_panics_on_invalid_input() {
+        let registry = Registry::new(vec![EventInfo::default()]);
+
+        registry.register_listener(1);
+    }
+
+    #[test]
+    fn record_invalid_event_does_nothing() {
+        let registry = Registry::new(vec![EventInfo::default()]);
+        registry.record_event(42);
+    }
+
+    #[test]
+    fn broadcast_returns_if_at_least_one_event_fired() {
+        let registry = Registry::new(vec![EventInfo::default(), EventInfo::default()]);
+
+        registry.record_event(0);
+        assert!(!registry.broadcast());
+
+        let first = registry.register_listener(0);
+        let second = registry.register_listener(1);
+
+        registry.record_event(0);
+        assert!(registry.broadcast());
+
+        drop(first);
+        registry.record_event(0);
+        assert!(!registry.broadcast());
+
+        drop(second);
+    }
+
+    fn rt() -> Runtime {
+        runtime::Builder::new_current_thread()
+            .enable_time()
+            .build()
+            .unwrap()
+    }
+
+    async fn collect(mut rx: watch::Receiver<()>) -> Vec<()> {
+        let mut ret = vec![];
+
+        while let Ok(v) = rx.changed().await {
+            ret.push(v);
+        }
+
+        ret
+    }
+}
diff --git a/third_party/rust/tokio/src/signal/reusable_box.rs b/third_party/rust/tokio/src/signal/reusable_box.rs
new file mode 100644
index 0000000000..02f32474b1
--- /dev/null
+++ b/third_party/rust/tokio/src/signal/reusable_box.rs
@@ -0,0 +1,228 @@
+use std::alloc::Layout;
+use std::future::Future;
+use std::panic::AssertUnwindSafe;
+use std::pin::Pin;
+use std::ptr::{self, NonNull};
+use std::task::{Context, Poll};
+use std::{fmt, panic};
+
+/// A reusable `Pin<Box<dyn Future<Output = T> + Send>>`.
+///
+/// This type lets you replace the future stored in the box without
+/// reallocating when the size and alignment permits this.
+pub(crate) struct ReusableBoxFuture<T> {
+    boxed: NonNull<dyn Future<Output = T> + Send>,
+}
+
+impl<T> ReusableBoxFuture<T> {
+    /// Create a new `ReusableBoxFuture<T>` containing the provided future.
+    pub(crate) fn new<F>(future: F) -> Self
+    where
+        F: Future<Output = T> + Send + 'static,
+    {
+        let boxed: Box<dyn Future<Output = T> + Send> = Box::new(future);
+
+        let boxed = Box::into_raw(boxed);
+
+        // SAFETY: Box::into_raw does not return null pointers.
+        let boxed = unsafe { NonNull::new_unchecked(boxed) };
+
+        Self { boxed }
+    }
+
+    /// Replaces the future currently stored in this box.
+    ///
+    /// This reallocates if and only if the layout of the provided future is
+    /// different from the layout of the currently stored future.
+    pub(crate) fn set<F>(&mut self, future: F)
+    where
+        F: Future<Output = T> + Send + 'static,
+    {
+        if let Err(future) = self.try_set(future) {
+            *self = Self::new(future);
+        }
+    }
+
+    /// Replaces the future currently stored in this box.
+    ///
+    /// This function never reallocates, but returns an error if the provided
+    /// future has a different size or alignment from the currently stored
+    /// future.
+    pub(crate) fn try_set<F>(&mut self, future: F) -> Result<(), F>
+    where
+        F: Future<Output = T> + Send + 'static,
+    {
+        // SAFETY: The pointer is not dangling.
+        let self_layout = {
+            let dyn_future: &(dyn Future<Output = T> + Send) = unsafe { self.boxed.as_ref() };
+            Layout::for_value(dyn_future)
+        };
+
+        if Layout::new::<F>() == self_layout {
+            // SAFETY: We just checked that the layout of F is correct.
+            unsafe {
+                self.set_same_layout(future);
+            }
+
+            Ok(())
+        } else {
+            Err(future)
+        }
+    }
+
+    /// Sets the current future.
+    ///
+    /// # Safety
+    ///
+    /// This function requires that the layout of the provided future is the
+    /// same as `self.layout`.
+    unsafe fn set_same_layout<F>(&mut self, future: F)
+    where
+        F: Future<Output = T> + Send + 'static,
+    {
+        // Drop the existing future, catching any panics.
+        let result = panic::catch_unwind(AssertUnwindSafe(|| {
+            ptr::drop_in_place(self.boxed.as_ptr());
+        }));
+
+        // Overwrite the future behind the pointer. This is safe because the
+        // allocation was allocated with the same size and alignment as the type F.
+        let self_ptr: *mut F = self.boxed.as_ptr() as *mut F;
+        ptr::write(self_ptr, future);
+
+        // Update the vtable of self.boxed. The pointer is not null because we
+        // just got it from self.boxed, which is not null.
+        self.boxed = NonNull::new_unchecked(self_ptr);
+
+        // If the old future's destructor panicked, resume unwinding.
+        match result {
+            Ok(()) => {}
+            Err(payload) => {
+                panic::resume_unwind(payload);
+            }
+        }
+    }
+
+    /// Gets a pinned reference to the underlying future.
+    pub(crate) fn get_pin(&mut self) -> Pin<&mut (dyn Future<Output = T> + Send)> {
+        // SAFETY: The user of this box cannot move the box, and we do not move it
+        // either.
+        unsafe { Pin::new_unchecked(self.boxed.as_mut()) }
+    }
+
+    /// Polls the future stored inside this box.
+    pub(crate) fn poll(&mut self, cx: &mut Context<'_>) -> Poll<T> {
+        self.get_pin().poll(cx)
+    }
+}
+
+impl<T> Future for ReusableBoxFuture<T> {
+    type Output = T;
+
+    /// Polls the future stored inside this box.
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
+        Pin::into_inner(self).get_pin().poll(cx)
+    }
+}
+
+// The future stored inside ReusableBoxFuture<T> must be Send.
+unsafe impl<T> Send for ReusableBoxFuture<T> {}
+
+// The only method called on self.boxed is poll, which takes &mut self, so this
+// struct being Sync does not permit any invalid access to the Future, even if
+// the future is not Sync.
+unsafe impl<T> Sync for ReusableBoxFuture<T> {}
+
+// Just like a Pin<Box<dyn Future>> is always Unpin, so is this type.
+impl<T> Unpin for ReusableBoxFuture<T> {}
+
+impl<T> Drop for ReusableBoxFuture<T> {
+    fn drop(&mut self) {
+        unsafe {
+            drop(Box::from_raw(self.boxed.as_ptr()));
+        }
+    }
+}
+
+impl<T> fmt::Debug for ReusableBoxFuture<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("ReusableBoxFuture").finish()
+    }
+}
+
+#[cfg(test)]
+#[cfg(not(miri))] // Miri breaks when you use Pin<&mut dyn Future>
+mod test {
+    use super::ReusableBoxFuture;
+    use futures::future::FutureExt;
+    use std::alloc::Layout;
+    use std::future::Future;
+    use std::pin::Pin;
+    use std::task::{Context, Poll};
+
+    #[test]
+    fn test_different_futures() {
+        let fut = async move { 10 };
+        // Not zero sized!
+        assert_eq!(Layout::for_value(&fut).size(), 1);
+
+        let mut b = ReusableBoxFuture::new(fut);
+
+        assert_eq!(b.get_pin().now_or_never(), Some(10));
+
+        b.try_set(async move { 20 })
+            .unwrap_or_else(|_| panic!("incorrect size"));
+
+        assert_eq!(b.get_pin().now_or_never(), Some(20));
+
+        b.try_set(async move { 30 })
+            .unwrap_or_else(|_| panic!("incorrect size"));
+
+        assert_eq!(b.get_pin().now_or_never(), Some(30));
+    }
+
+    #[test]
+    fn test_different_sizes() {
+        let fut1 = async move { 10 };
+        let val = [0u32; 1000];
+        let fut2 = async move { val[0] };
+        let fut3 = ZeroSizedFuture {};
+
+        assert_eq!(Layout::for_value(&fut1).size(), 1);
+        assert_eq!(Layout::for_value(&fut2).size(), 4004);
+        assert_eq!(Layout::for_value(&fut3).size(), 0);
+
+        let mut b = ReusableBoxFuture::new(fut1);
+        assert_eq!(b.get_pin().now_or_never(), Some(10));
+        b.set(fut2);
+        assert_eq!(b.get_pin().now_or_never(), Some(0));
+        b.set(fut3);
+        assert_eq!(b.get_pin().now_or_never(), Some(5));
+    }
+
+    struct ZeroSizedFuture {}
+    impl Future for ZeroSizedFuture {
+        type Output = u32;
+        fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<u32> {
+            Poll::Ready(5)
+        }
+    }
+
+    #[test]
+    fn test_zero_sized() {
+        let fut = ZeroSizedFuture {};
+        // Zero sized!
+        assert_eq!(Layout::for_value(&fut).size(), 0);
+
+        let mut b = ReusableBoxFuture::new(fut);
+
+        assert_eq!(b.get_pin().now_or_never(), Some(5));
+        assert_eq!(b.get_pin().now_or_never(), Some(5));
+
+        b.try_set(ZeroSizedFuture {})
+            .unwrap_or_else(|_| panic!("incorrect size"));
+
+        assert_eq!(b.get_pin().now_or_never(), Some(5));
+        assert_eq!(b.get_pin().now_or_never(), Some(5));
+    }
+}
diff --git a/third_party/rust/tokio/src/signal/unix.rs b/third_party/rust/tokio/src/signal/unix.rs
new file mode 100644
index 0000000000..86ea9a93ee
--- /dev/null
+++ b/third_party/rust/tokio/src/signal/unix.rs
@@ -0,0 +1,477 @@
+//! Unix-specific types for signal handling.
+//!
+//! This module is only defined on Unix platforms and contains the primary
+//! `Signal` type for receiving notifications of signals.
+
+#![cfg(unix)]
+#![cfg_attr(docsrs, doc(cfg(all(unix, feature = "signal"))))]
+
+use crate::signal::registry::{globals, EventId, EventInfo, Globals, Init, Storage};
+use crate::signal::RxFuture;
+use crate::sync::watch;
+
+use mio::net::UnixStream;
+use std::io::{self, Error, ErrorKind, Write};
+use std::pin::Pin;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::Once;
+use std::task::{Context, Poll};
+
+pub(crate) mod driver;
+use self::driver::Handle;
+
+pub(crate) type OsStorage = Vec<SignalInfo>;
+
+// Number of different unix signals
+// (FreeBSD has 33)
+const SIGNUM: usize = 33;
+
+impl Init for OsStorage {
+    fn init() -> Self {
+        (0..SIGNUM).map(|_| SignalInfo::default()).collect()
+    }
+}
+
+impl Storage for OsStorage {
+    fn event_info(&self, id: EventId) -> Option<&EventInfo> {
+        self.get(id).map(|si| &si.event_info)
+    }
+
+    fn for_each<'a, F>(&'a self, f: F)
+    where
+        F: FnMut(&'a EventInfo),
+    {
+        self.iter().map(|si| &si.event_info).for_each(f)
+    }
+}
+
+#[derive(Debug)]
+pub(crate) struct OsExtraData {
+    sender: UnixStream,
+    receiver: UnixStream,
+}
+
+impl Init for OsExtraData {
+    fn init() -> Self {
+        let (receiver, sender) = UnixStream::pair().expect("failed to create UnixStream");
+
+        Self { sender, receiver }
+    }
+}
+
+/// Represents the specific kind of signal to listen for.
+#[derive(Debug, Clone, Copy)]
+pub struct SignalKind(libc::c_int);
+
+impl SignalKind {
+    /// Allows for listening to any valid OS signal.
+    ///
+    /// For example, this can be used for listening for platform-specific
+    /// signals.
+    /// ```rust,no_run
+    /// # use tokio::signal::unix::SignalKind;
+    /// # let signum = -1;
+    /// // let signum = libc::OS_SPECIFIC_SIGNAL;
+    /// let kind = SignalKind::from_raw(signum);
+    /// ```
+    // Use `std::os::raw::c_int` on public API to prevent leaking a non-stable
+    // type alias from libc.
+    // `libc::c_int` and `std::os::raw::c_int` are currently the same type, and are
+    // unlikely to change to other types, but technically libc can change this
+    // in the future minor version.
+    // See https://github.com/tokio-rs/tokio/issues/3767 for more.
+    pub fn from_raw(signum: std::os::raw::c_int) -> Self {
+        Self(signum as libc::c_int)
+    }
+
+    /// Represents the SIGALRM signal.
+    ///
+    /// On Unix systems this signal is sent when a real-time timer has expired.
+    /// By default, the process is terminated by this signal.
+    pub fn alarm() -> Self {
+        Self(libc::SIGALRM)
+    }
+
+    /// Represents the SIGCHLD signal.
+    ///
+    /// On Unix systems this signal is sent when the status of a child process
+    /// has changed. By default, this signal is ignored.
+    pub fn child() -> Self {
+        Self(libc::SIGCHLD)
+    }
+
+    /// Represents the SIGHUP signal.
+    ///
+    /// On Unix systems this signal is sent when the terminal is disconnected.
+    /// By default, the process is terminated by this signal.
+    pub fn hangup() -> Self {
+        Self(libc::SIGHUP)
+    }
+
+    /// Represents the SIGINFO signal.
+    ///
+    /// On Unix systems this signal is sent to request a status update from the
+    /// process. By default, this signal is ignored.
+    #[cfg(any(
+        target_os = "dragonfly",
+        target_os = "freebsd",
+        target_os = "macos",
+        target_os = "netbsd",
+        target_os = "openbsd"
+    ))]
+    pub fn info() -> Self {
+        Self(libc::SIGINFO)
+    }
+
+    /// Represents the SIGINT signal.
+    ///
+    /// On Unix systems this signal is sent to interrupt a program.
+    /// By default, the process is terminated by this signal.
+    pub fn interrupt() -> Self {
+        Self(libc::SIGINT)
+    }
+
+    /// Represents the SIGIO signal.
+    ///
+    /// On Unix systems this signal is sent when I/O operations are possible
+    /// on some file descriptor. By default, this signal is ignored.
+    pub fn io() -> Self {
+        Self(libc::SIGIO)
+    }
+
+    /// Represents the SIGPIPE signal.
+    ///
+    /// On Unix systems this signal is sent when the process attempts to write
+    /// to a pipe which has no reader. By default, the process is terminated by
+    /// this signal.
+    pub fn pipe() -> Self {
+        Self(libc::SIGPIPE)
+    }
+
+    /// Represents the SIGQUIT signal.
+    ///
+    /// On Unix systems this signal is sent to issue a shutdown of the
+    /// process, after which the OS will dump the process core.
+    /// By default, the process is terminated by this signal.
+    pub fn quit() -> Self {
+        Self(libc::SIGQUIT)
+    }
+
+    /// Represents the SIGTERM signal.
+    ///
+    /// On Unix systems this signal is sent to issue a shutdown of the
+    /// process. By default, the process is terminated by this signal.
+    pub fn terminate() -> Self {
+        Self(libc::SIGTERM)
+    }
+
+    /// Represents the SIGUSR1 signal.
+    ///
+    /// On Unix systems this is a user defined signal.
+    /// By default, the process is terminated by this signal.
+    pub fn user_defined1() -> Self {
+        Self(libc::SIGUSR1)
+    }
+
+    /// Represents the SIGUSR2 signal.
+    ///
+    /// On Unix systems this is a user defined signal.
+    /// By default, the process is terminated by this signal.
+    pub fn user_defined2() -> Self {
+        Self(libc::SIGUSR2)
+    }
+
+    /// Represents the SIGWINCH signal.
+    ///
+    /// On Unix systems this signal is sent when the terminal window is resized.
+    /// By default, this signal is ignored.
+    pub fn window_change() -> Self {
+        Self(libc::SIGWINCH)
+    }
+}
+
+pub(crate) struct SignalInfo {
+    event_info: EventInfo,
+    init: Once,
+    initialized: AtomicBool,
+}
+
+impl Default for SignalInfo {
+    fn default() -> SignalInfo {
+        SignalInfo {
+            event_info: Default::default(),
+            init: Once::new(),
+            initialized: AtomicBool::new(false),
+        }
+    }
+}
+
+/// Our global signal handler for all signals registered by this module.
+///
+/// The purpose of this signal handler is to primarily:
+///
+/// 1. Flag that our specific signal was received (e.g. store an atomic flag)
+/// 2. Wake up the driver by writing a byte to a pipe
+///
+/// Those two operations should both be async-signal safe.
+fn action(globals: Pin<&'static Globals>, signal: libc::c_int) {
+    globals.record_event(signal as EventId);
+
+    // Send a wakeup, ignore any errors (anything reasonably possible is
+    // full pipe and then it will wake up anyway).
+    let mut sender = &globals.sender;
+    drop(sender.write(&[1]));
+}
+
+/// Enables this module to receive signal notifications for the `signal`
+/// provided.
+///
+/// This will register the signal handler if it hasn't already been registered,
+/// returning any error along the way if that fails.
+fn signal_enable(signal: SignalKind, handle: &Handle) -> io::Result<()> {
+    let signal = signal.0;
+    if signal < 0 || signal_hook_registry::FORBIDDEN.contains(&signal) {
+        return Err(Error::new(
+            ErrorKind::Other,
+            format!("Refusing to register signal {}", signal),
+        ));
+    }
+
+    // Check that we have a signal driver running
+    handle.check_inner()?;
+
+    let globals = globals();
+    let siginfo = match globals.storage().get(signal as EventId) {
+        Some(slot) => slot,
+        None => return Err(io::Error::new(io::ErrorKind::Other, "signal too large")),
+    };
+    let mut registered = Ok(());
+    siginfo.init.call_once(|| {
+        registered = unsafe {
+            signal_hook_registry::register(signal, move || action(globals, signal)).map(|_| ())
+        };
+        if registered.is_ok() {
+            siginfo.initialized.store(true, Ordering::Relaxed);
+        }
+    });
+    registered?;
+    // If the call_once failed, it won't be retried on the next attempt to register the signal. In
+    // such case it is not run, registered is still `Ok(())`, initialized is still `false`.
+    if siginfo.initialized.load(Ordering::Relaxed) {
+        Ok(())
+    } else {
+        Err(Error::new(
+            ErrorKind::Other,
+            "Failed to register signal handler",
+        ))
+    }
+}
+
+/// A stream of events for receiving a particular type of OS signal.
+///
+/// In general signal handling on Unix is a pretty tricky topic, and this
+/// structure is no exception! There are some important limitations to keep in
+/// mind when using `Signal` streams:
+///
+/// * Signals handling in Unix already necessitates coalescing signals
+///   together sometimes. This `Signal` stream is also no exception here in
+///   that it will also coalesce signals. That is, even if the signal handler
+///   for this process runs multiple times, the `Signal` stream may only return
+///   one signal notification. Specifically, before `poll` is called, all
+///   signal notifications are coalesced into one item returned from `poll`.
+///   Once `poll` has been called, however, a further signal is guaranteed to
+///   be yielded as an item.
+///
+///   Put another way, any element pulled off the returned stream corresponds to
+///   *at least one* signal, but possibly more.
+///
+/// * Signal handling in general is relatively inefficient. Although some
+///   improvements are possible in this crate, it's recommended to not plan on
+///   having millions of signal channels open.
+///
+/// If you've got any questions about this feel free to open an issue on the
+/// repo! New approaches to alleviate some of these limitations are always
+/// appreciated!
+///
+/// # Caveats
+///
+/// The first time that a `Signal` instance is registered for a particular
+/// signal kind, an OS signal-handler is installed which replaces the default
+/// platform behavior when that signal is received, **for the duration of the
+/// entire process**.
+///
+/// For example, Unix systems will terminate a process by default when it
+/// receives SIGINT. But, when a `Signal` instance is created to listen for
+/// this signal, the next SIGINT that arrives will be translated to a stream
+/// event, and the process will continue to execute. **Even if this `Signal`
+/// instance is dropped, subsequent SIGINT deliveries will end up captured by
+/// Tokio, and the default platform behavior will NOT be reset**.
+///
+/// Thus, applications should take care to ensure the expected signal behavior
+/// occurs as expected after listening for specific signals.
+///
+/// # Examples
+///
+/// Wait for SIGHUP
+///
+/// ```rust,no_run
+/// use tokio::signal::unix::{signal, SignalKind};
+///
+/// #[tokio::main]
+/// async fn main() -> Result<(), Box<dyn std::error::Error>> {
+///     // An infinite stream of hangup signals.
+///     let mut stream = signal(SignalKind::hangup())?;
+///
+///     // Print whenever a HUP signal is received
+///     loop {
+///         stream.recv().await;
+///         println!("got signal HUP");
+///     }
+/// }
+/// ```
+#[must_use = "streams do nothing unless polled"]
+#[derive(Debug)]
+pub struct Signal {
+    inner: RxFuture,
+}
+
+/// Creates a new stream which will receive notifications when the current
+/// process receives the specified signal `kind`.
+///
+/// This function will create a new stream which binds to the default reactor.
+/// The `Signal` stream is an infinite stream which will receive
+/// notifications whenever a signal is received. More documentation can be
+/// found on `Signal` itself, but to reiterate:
+///
+/// * Signals may be coalesced beyond what the kernel already does.
+/// * Once a signal handler is registered with the process the underlying
+///   libc signal handler is never unregistered.
+///
+/// A `Signal` stream can be created for a particular signal number
+/// multiple times. When a signal is received then all the associated
+/// channels will receive the signal notification.
+///
+/// # Errors
+///
+/// * If the lower-level C functions fail for some reason.
+/// * If the previous initialization of this specific signal failed.
+/// * If the signal is one of
+///   [`signal_hook::FORBIDDEN`](fn@signal_hook_registry::register#panics)
+pub fn signal(kind: SignalKind) -> io::Result<Signal> {
+    let rx = signal_with_handle(kind, &Handle::current())?;
+
+    Ok(Signal {
+        inner: RxFuture::new(rx),
+    })
+}
+
+pub(crate) fn signal_with_handle(
+    kind: SignalKind,
+    handle: &Handle,
+) -> io::Result<watch::Receiver<()>> {
+    // Turn the signal delivery on once we are ready for it
+    signal_enable(kind, handle)?;
+
+    Ok(globals().register_listener(kind.0 as EventId))
+}
+
+impl Signal {
+    /// Receives the next signal notification event.
+    ///
+    /// `None` is returned if no more events can be received by this stream.
+    ///
+    /// # Examples
+    ///
+    /// Wait for SIGHUP
+    ///
+    /// ```rust,no_run
+    /// use tokio::signal::unix::{signal, SignalKind};
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    ///     // An infinite stream of hangup signals.
+    ///     let mut stream = signal(SignalKind::hangup())?;
+    ///
+    ///     // Print whenever a HUP signal is received
+    ///     loop {
+    ///         stream.recv().await;
+    ///         println!("got signal HUP");
+    ///     }
+    /// }
+    /// ```
+    pub async fn recv(&mut self) -> Option<()> {
+        self.inner.recv().await
+    }
+
+    /// Polls to receive the next signal notification event, outside of an
+    /// `async` context.
+    ///
+    /// This method returns:
+    ///
+    ///  * `Poll::Pending` if no signals are available but the channel is not
+    ///    closed.
+    ///  * `Poll::Ready(Some(()))` if a signal is available.
+    ///  * `Poll::Ready(None)` if the channel has been closed and all signals
+    ///    sent before it was closed have been received.
+    ///
+    /// # Examples
+    ///
+    /// Polling from a manually implemented future
+    ///
+    /// ```rust,no_run
+    /// use std::pin::Pin;
+    /// use std::future::Future;
+    /// use std::task::{Context, Poll};
+    /// use tokio::signal::unix::Signal;
+    ///
+    /// struct MyFuture {
+    ///     signal: Signal,
+    /// }
+    ///
+    /// impl Future for MyFuture {
+    ///     type Output = Option<()>;
+    ///
+    ///     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+    ///         println!("polling MyFuture");
+    ///         self.signal.poll_recv(cx)
+    ///     }
+    /// }
+    /// ```
+    pub fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>> {
+        self.inner.poll_recv(cx)
+    }
+}
+
+// Work around for abstracting streams internally
+pub(crate) trait InternalStream {
+    fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>>;
+}
+
+impl InternalStream for Signal {
+    fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>> {
+        self.poll_recv(cx)
+    }
+}
+
+pub(crate) fn ctrl_c() -> io::Result<Signal> {
+    signal(SignalKind::interrupt())
+}
+
+#[cfg(all(test, not(loom)))]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn signal_enable_error_on_invalid_input() {
+        signal_enable(SignalKind::from_raw(-1), &Handle::default()).unwrap_err();
+    }
+
+    #[test]
+    fn signal_enable_error_on_forbidden_input() {
+        signal_enable(
+            SignalKind::from_raw(signal_hook_registry::FORBIDDEN[0]),
+            &Handle::default(),
+        )
+        .unwrap_err();
+    }
+}
diff --git a/third_party/rust/tokio/src/signal/unix/driver.rs b/third_party/rust/tokio/src/signal/unix/driver.rs
new file mode 100644
index 0000000000..5fe7c354c5
--- /dev/null
+++ b/third_party/rust/tokio/src/signal/unix/driver.rs
@@ -0,0 +1,207 @@
+#![cfg_attr(not(feature = "rt"), allow(dead_code))]
+
+//! Signal driver
+
+use crate::io::driver::{Driver as IoDriver, Interest};
+use crate::io::PollEvented;
+use crate::park::Park;
+use crate::signal::registry::globals;
+
+use mio::net::UnixStream;
+use std::io::{self, Read};
+use std::ptr;
+use std::sync::{Arc, Weak};
+use std::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
+use std::time::Duration;
+
+/// Responsible for registering wakeups when an OS signal is received, and
+/// subsequently dispatching notifications to any signal listeners as appropriate.
+///
+/// Note: this driver relies on having an enabled IO driver in order to listen to
+/// pipe write wakeups.
+#[derive(Debug)]
+pub(crate) struct Driver {
+    /// Thread parker. The `Driver` park implementation delegates to this.
+    park: IoDriver,
+
+    /// A pipe for receiving wake events from the signal handler
+    receiver: PollEvented<UnixStream>,
+
+    /// Shared state
+    inner: Arc<Inner>,
+}
+
+#[derive(Clone, Debug, Default)]
+pub(crate) struct Handle {
+    inner: Weak<Inner>,
+}
+
+#[derive(Debug)]
+pub(super) struct Inner(());
+
+// ===== impl Driver =====
+
+impl Driver {
+    /// Creates a new signal `Driver` instance that delegates wakeups to `park`.
+    pub(crate) fn new(park: IoDriver) -> io::Result<Self> {
+        use std::mem::ManuallyDrop;
+        use std::os::unix::io::{AsRawFd, FromRawFd};
+
+        // NB: We give each driver a "fresh" receiver file descriptor to avoid
+        // the issues described in alexcrichton/tokio-process#42.
+        //
+        // In the past we would reuse the actual receiver file descriptor and
+        // swallow any errors around double registration of the same descriptor.
+        // I'm not sure if the second (failed) registration simply doesn't end
+        // up receiving wake up notifications, or there could be some race
+        // condition when consuming readiness events, but having distinct
+        // descriptors for distinct PollEvented instances appears to mitigate
+        // this.
+        //
+        // Unfortunately we cannot just use a single global PollEvented instance
+        // either, since we can't compare Handles or assume they will always
+        // point to the exact same reactor.
+        //
+        // Mio 0.7 removed `try_clone()` as an API due to unexpected behavior
+        // with registering dups with the same reactor. In this case, duping is
+        // safe as each dup is registered with separate reactors **and** we
+        // only expect at least one dup to receive the notification.
+
+        // Manually drop as we don't actually own this instance of UnixStream.
+        let receiver_fd = globals().receiver.as_raw_fd();
+
+        // safety: there is nothing unsafe about this, but the `from_raw_fd` fn is marked as unsafe.
+        let original =
+            ManuallyDrop::new(unsafe { std::os::unix::net::UnixStream::from_raw_fd(receiver_fd) });
+        let receiver = UnixStream::from_std(original.try_clone()?);
+        let receiver = PollEvented::new_with_interest_and_handle(
+            receiver,
+            Interest::READABLE | Interest::WRITABLE,
+            park.handle(),
+        )?;
+
+        Ok(Self {
+            park,
+            receiver,
+            inner: Arc::new(Inner(())),
+        })
+    }
+
+    /// Returns a handle to this event loop which can be sent across threads
+    /// and can be used as a proxy to the event loop itself.
+    pub(crate) fn handle(&self) -> Handle {
+        Handle {
+            inner: Arc::downgrade(&self.inner),
+        }
+    }
+
+    fn process(&self) {
+        // Check if the pipe is ready to read and therefore has "woken" us up
+        //
+        // To do so, we will `poll_read_ready` with a noop waker, since we don't
+        // need to actually be notified when read ready...
+        let waker = unsafe { Waker::from_raw(RawWaker::new(ptr::null(), &NOOP_WAKER_VTABLE)) };
+        let mut cx = Context::from_waker(&waker);
+
+        let ev = match self.receiver.registration().poll_read_ready(&mut cx) {
+            Poll::Ready(Ok(ev)) => ev,
+            Poll::Ready(Err(e)) => panic!("reactor gone: {}", e),
+            Poll::Pending => return, // No wake has arrived, bail
+        };
+
+        // Drain the pipe completely so we can receive a new readiness event
+        // if another signal has come in.
+        let mut buf = [0; 128];
+        loop {
+            match (&*self.receiver).read(&mut buf) {
+                Ok(0) => panic!("EOF on self-pipe"),
+                Ok(_) => continue, // Keep reading
+                Err(e) if e.kind() == io::ErrorKind::WouldBlock => break,
+                Err(e) => panic!("Bad read on self-pipe: {}", e),
+            }
+        }
+
+        self.receiver.registration().clear_readiness(ev);
+
+        // Broadcast any signals which were received
+        globals().broadcast();
+    }
+}
+
+const NOOP_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new(noop_clone, noop, noop, noop);
+
+unsafe fn noop_clone(_data: *const ()) -> RawWaker {
+    RawWaker::new(ptr::null(), &NOOP_WAKER_VTABLE)
+}
+
+unsafe fn noop(_data: *const ()) {}
+
+// ===== impl Park for Driver =====
+
+impl Park for Driver {
+    type Unpark = <IoDriver as Park>::Unpark;
+    type Error = io::Error;
+
+    fn unpark(&self) -> Self::Unpark {
+        self.park.unpark()
+    }
+
+    fn park(&mut self) -> Result<(), Self::Error> {
+        self.park.park()?;
+        self.process();
+        Ok(())
+    }
+
+    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
+        self.park.park_timeout(duration)?;
+        self.process();
+        Ok(())
+    }
+
+    fn shutdown(&mut self) {
+        self.park.shutdown()
+    }
+}
+
+// ===== impl Handle =====
+
+impl Handle {
+    pub(super) fn check_inner(&self) -> io::Result<()> {
+        if self.inner.strong_count() > 0 {
+            Ok(())
+        } else {
+            Err(io::Error::new(io::ErrorKind::Other, "signal driver gone"))
+        }
+    }
+}
+
+cfg_rt! {
+    impl Handle {
+        /// Returns a handle to the current driver
+        ///
+        /// # Panics
+        ///
+        /// This function panics if there is no current signal driver set.
+        pub(super) fn current() -> Self {
+            crate::runtime::context::signal_handle().expect(
+                "there is no signal driver running, must be called from the context of Tokio runtime",
+            )
+        }
+    }
+}
+
+cfg_not_rt! {
+    impl Handle {
+        /// Returns a handle to the current driver
+        ///
+        /// # Panics
+        ///
+        /// This function panics if there is no current signal driver set.
+        pub(super) fn current() -> Self {
+            panic!(
+                "there is no signal driver running, must be called from the context of Tokio runtime or with\
+                `rt` enabled.",
+            )
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/signal/windows.rs b/third_party/rust/tokio/src/signal/windows.rs
new file mode 100644
index 0000000000..11ec6cb08c
--- /dev/null
+++ b/third_party/rust/tokio/src/signal/windows.rs
@@ -0,0 +1,223 @@
+//! Windows-specific types for signal handling.
+//!
+//! This module is only defined on Windows and allows receiving "ctrl-c"
+//! and "ctrl-break" notifications. These events are listened for via the
+//! `SetConsoleCtrlHandler` function which receives events of the type
+//! `CTRL_C_EVENT` and `CTRL_BREAK_EVENT`.
+
+#![cfg(any(windows, docsrs))]
+#![cfg_attr(docsrs, doc(cfg(all(windows, feature = "signal"))))]
+
+use crate::signal::RxFuture;
+use std::io;
+use std::task::{Context, Poll};
+
+#[cfg(not(docsrs))]
+#[path = "windows/sys.rs"]
+mod imp;
+#[cfg(not(docsrs))]
+pub(crate) use self::imp::{OsExtraData, OsStorage};
+
+#[cfg(docsrs)]
+#[path = "windows/stub.rs"]
+mod imp;
+
+/// Creates a new stream which receives "ctrl-c" notifications sent to the
+/// process.
+///
+/// # Examples
+///
+/// ```rust,no_run
+/// use tokio::signal::windows::ctrl_c;
+///
+/// #[tokio::main]
+/// async fn main() -> Result<(), Box<dyn std::error::Error>> {
+///     // An infinite stream of CTRL-C events.
+///     let mut stream = ctrl_c()?;
+///
+///     // Print whenever a CTRL-C event is received.
+///     for countdown in (0..3).rev() {
+///         stream.recv().await;
+///         println!("got CTRL-C. {} more to exit", countdown);
+///     }
+///
+///     Ok(())
+/// }
+/// ```
+pub fn ctrl_c() -> io::Result<CtrlC> {
+    Ok(CtrlC {
+        inner: self::imp::ctrl_c()?,
+    })
+}
+
+/// Represents a stream which receives "ctrl-c" notifications sent to the process
+/// via `SetConsoleCtrlHandler`.
+///
+/// A notification to this process notifies *all* streams listening for
+/// this event. Moreover, the notifications **are coalesced** if they aren't processed
+/// quickly enough. This means that if two notifications are received back-to-back,
+/// then the stream may only receive one item about the two notifications.
+#[must_use = "streams do nothing unless polled"]
+#[derive(Debug)]
+pub struct CtrlC {
+    inner: RxFuture,
+}
+
+impl CtrlC {
+    /// Receives the next signal notification event.
+    ///
+    /// `None` is returned if no more events can be received by this stream.
+    ///
+    /// # Examples
+    ///
+    /// ```rust,no_run
+    /// use tokio::signal::windows::ctrl_c;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    ///     // An infinite stream of CTRL-C events.
+    ///     let mut stream = ctrl_c()?;
+    ///
+    ///     // Print whenever a CTRL-C event is received.
+    ///     for countdown in (0..3).rev() {
+    ///         stream.recv().await;
+    ///         println!("got CTRL-C. {} more to exit", countdown);
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    /// ```
+    pub async fn recv(&mut self) -> Option<()> {
+        self.inner.recv().await
+    }
+
+    /// Polls to receive the next signal notification event, outside of an
+    /// `async` context.
+    ///
+    /// `None` is returned if no more events can be received by this stream.
+    ///
+    /// # Examples
+    ///
+    /// Polling from a manually implemented future
+    ///
+    /// ```rust,no_run
+    /// use std::pin::Pin;
+    /// use std::future::Future;
+    /// use std::task::{Context, Poll};
+    /// use tokio::signal::windows::CtrlC;
+    ///
+    /// struct MyFuture {
+    ///     ctrl_c: CtrlC,
+    /// }
+    ///
+    /// impl Future for MyFuture {
+    ///     type Output = Option<()>;
+    ///
+    ///     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+    ///         println!("polling MyFuture");
+    ///         self.ctrl_c.poll_recv(cx)
+    ///     }
+    /// }
+    /// ```
+    pub fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>> {
+        self.inner.poll_recv(cx)
+    }
+}
+
+/// Represents a stream which receives "ctrl-break" notifications sent to the process
+/// via `SetConsoleCtrlHandler`.
+///
+/// A notification to this process notifies *all* streams listening for
+/// this event. Moreover, the notifications **are coalesced** if they aren't processed
+/// quickly enough. This means that if two notifications are received back-to-back,
+/// then the stream may only receive one item about the two notifications.
+#[must_use = "streams do nothing unless polled"]
+#[derive(Debug)]
+pub struct CtrlBreak {
+    inner: RxFuture,
+}
+
+impl CtrlBreak {
+    /// Receives the next signal notification event.
+    ///
+    /// `None` is returned if no more events can be received by this stream.
+    ///
+    /// # Examples
+    ///
+    /// ```rust,no_run
+    /// use tokio::signal::windows::ctrl_break;
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    ///     // An infinite stream of CTRL-BREAK events.
+    ///     let mut stream = ctrl_break()?;
+    ///
+    ///     // Print whenever a CTRL-BREAK event is received.
+    ///     loop {
+    ///         stream.recv().await;
+    ///         println!("got signal CTRL-BREAK");
+    ///     }
+    /// }
+    /// ```
+    pub async fn recv(&mut self) -> Option<()> {
+        self.inner.recv().await
+    }
+
+    /// Polls to receive the next signal notification event, outside of an
+    /// `async` context.
+    ///
+    /// `None` is returned if no more events can be received by this stream.
+    ///
+    /// # Examples
+    ///
+    /// Polling from a manually implemented future
+    ///
+    /// ```rust,no_run
+    /// use std::pin::Pin;
+    /// use std::future::Future;
+    /// use std::task::{Context, Poll};
+    /// use tokio::signal::windows::CtrlBreak;
+    ///
+    /// struct MyFuture {
+    ///     ctrl_break: CtrlBreak,
+    /// }
+    ///
+    /// impl Future for MyFuture {
+    ///     type Output = Option<()>;
+    ///
+    ///     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+    ///         println!("polling MyFuture");
+    ///         self.ctrl_break.poll_recv(cx)
+    ///     }
+    /// }
+    /// ```
+    pub fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<()>> {
+        self.inner.poll_recv(cx)
+    }
+}
+
+/// Creates a new stream which receives "ctrl-break" notifications sent to the
+/// process.
+///
+/// # Examples
+///
+/// ```rust,no_run
+/// use tokio::signal::windows::ctrl_break;
+///
+/// #[tokio::main]
+/// async fn main() -> Result<(), Box<dyn std::error::Error>> {
+///     // An infinite stream of CTRL-BREAK events.
+///     let mut stream = ctrl_break()?;
+///
+///     // Print whenever a CTRL-BREAK event is received.
+///     loop {
+///         stream.recv().await;
+///         println!("got signal CTRL-BREAK");
+///     }
+/// }
+/// ```
+pub fn ctrl_break() -> io::Result<CtrlBreak> {
+    Ok(CtrlBreak {
+        inner: self::imp::ctrl_break()?,
+    })
+}
diff --git a/third_party/rust/tokio/src/signal/windows/stub.rs b/third_party/rust/tokio/src/signal/windows/stub.rs
new file mode 100644
index 0000000000..88630543da
--- /dev/null
+++ b/third_party/rust/tokio/src/signal/windows/stub.rs
@@ -0,0 +1,13 @@
+//! Stub implementations for the platform API so that rustdoc can build linkable
+//! documentation on non-windows platforms.
+
+use crate::signal::RxFuture;
+use std::io;
+
+pub(super) fn ctrl_c() -> io::Result<RxFuture> {
+    panic!()
+}
+
+pub(super) fn ctrl_break() -> io::Result<RxFuture> {
+    panic!()
+}
diff --git a/third_party/rust/tokio/src/signal/windows/sys.rs b/third_party/rust/tokio/src/signal/windows/sys.rs
new file mode 100644
index 0000000000..8d29c357b6
--- /dev/null
+++ b/third_party/rust/tokio/src/signal/windows/sys.rs
@@ -0,0 +1,153 @@
+use std::convert::TryFrom;
+use std::io;
+use std::sync::Once;
+
+use crate::signal::registry::{globals, EventId, EventInfo, Init, Storage};
+use crate::signal::RxFuture;
+
+use winapi::shared::minwindef::{BOOL, DWORD, FALSE, TRUE};
+use winapi::um::consoleapi::SetConsoleCtrlHandler;
+use winapi::um::wincon::{CTRL_BREAK_EVENT, CTRL_C_EVENT};
+
+pub(super) fn ctrl_c() -> io::Result<RxFuture> {
+    new(CTRL_C_EVENT)
+}
+
+pub(super) fn ctrl_break() -> io::Result<RxFuture> {
+    new(CTRL_BREAK_EVENT)
+}
+
+fn new(signum: DWORD) -> io::Result<RxFuture> {
+    global_init()?;
+    let rx = globals().register_listener(signum as EventId);
+    Ok(RxFuture::new(rx))
+}
+
+#[derive(Debug)]
+pub(crate) struct OsStorage {
+    ctrl_c: EventInfo,
+    ctrl_break: EventInfo,
+}
+
+impl Init for OsStorage {
+    fn init() -> Self {
+        Self {
+            ctrl_c: EventInfo::default(),
+            ctrl_break: EventInfo::default(),
+        }
+    }
+}
+
+impl Storage for OsStorage {
+    fn event_info(&self, id: EventId) -> Option<&EventInfo> {
+        match DWORD::try_from(id) {
+            Ok(CTRL_C_EVENT) => Some(&self.ctrl_c),
+            Ok(CTRL_BREAK_EVENT) => Some(&self.ctrl_break),
+            _ => None,
+        }
+    }
+
+    fn for_each<'a, F>(&'a self, mut f: F)
+    where
+        F: FnMut(&'a EventInfo),
+    {
+        f(&self.ctrl_c);
+        f(&self.ctrl_break);
+    }
+}
+
+#[derive(Debug)]
+pub(crate) struct OsExtraData {}
+
+impl Init for OsExtraData {
+    fn init() -> Self {
+        Self {}
+    }
+}
+
+fn global_init() -> io::Result<()> {
+    static INIT: Once = Once::new();
+
+    let mut init = None;
+
+    INIT.call_once(|| unsafe {
+        let rc = SetConsoleCtrlHandler(Some(handler), TRUE);
+        let ret = if rc == 0 {
+            Err(io::Error::last_os_error())
+        } else {
+            Ok(())
+        };
+
+        init = Some(ret);
+    });
+
+    init.unwrap_or_else(|| Ok(()))
+}
+
+unsafe extern "system" fn handler(ty: DWORD) -> BOOL {
+    let globals = globals();
+    globals.record_event(ty as EventId);
+
+    // According to https://docs.microsoft.com/en-us/windows/console/handlerroutine
+    // the handler routine is always invoked in a new thread, thus we don't
+    // have the same restrictions as in Unix signal handlers, meaning we can
+    // go ahead and perform the broadcast here.
+    if globals.broadcast() {
+        TRUE
+    } else {
+        // No one is listening for this notification any more
+        // let the OS fire the next (possibly the default) handler.
+        FALSE
+    }
+}
+
+#[cfg(all(test, not(loom)))]
+mod tests {
+    use super::*;
+    use crate::runtime::Runtime;
+
+    use tokio_test::{assert_ok, assert_pending, assert_ready_ok, task};
+
+    #[test]
+    fn ctrl_c() {
+        let rt = rt();
+        let _enter = rt.enter();
+
+        let mut ctrl_c = task::spawn(crate::signal::ctrl_c());
+
+        assert_pending!(ctrl_c.poll());
+
+        // Windows doesn't have a good programmatic way of sending events
+        // like sending signals on Unix, so we'll stub out the actual OS
+        // integration and test that our handling works.
+        unsafe {
+            super::handler(CTRL_C_EVENT);
+        }
+
+        assert_ready_ok!(ctrl_c.poll());
+    }
+
+    #[test]
+    fn ctrl_break() {
+        let rt = rt();
+
+        rt.block_on(async {
+            let mut ctrl_break = assert_ok!(crate::signal::windows::ctrl_break());
+
+            // Windows doesn't have a good programmatic way of sending events
+            // like sending signals on Unix, so we'll stub out the actual OS
+            // integration and test that our handling works.
+            unsafe {
+                super::handler(CTRL_BREAK_EVENT);
+            }
+
+            ctrl_break.recv().await.unwrap();
+        });
+    }
+
+    fn rt() -> Runtime {
+        crate::runtime::Builder::new_current_thread()
+            .build()
+            .unwrap()
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/barrier.rs b/third_party/rust/tokio/src/sync/barrier.rs
new file mode 100644
index 0000000000..dfc76a40eb
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/barrier.rs
@@ -0,0 +1,206 @@
+use crate::loom::sync::Mutex;
+use crate::sync::watch;
+#[cfg(all(tokio_unstable, feature = "tracing"))]
+use crate::util::trace;
+
+/// A barrier enables multiple tasks to synchronize the beginning of some computation.
+///
+/// ```
+/// # #[tokio::main]
+/// # async fn main() {
+/// use tokio::sync::Barrier;
+/// use std::sync::Arc;
+///
+/// let mut handles = Vec::with_capacity(10);
+/// let barrier = Arc::new(Barrier::new(10));
+/// for _ in 0..10 {
+///     let c = barrier.clone();
+///     // The same messages will be printed together.
+///     // You will NOT see any interleaving.
+///     handles.push(tokio::spawn(async move {
+///         println!("before wait");
+///         let wait_result = c.wait().await;
+///         println!("after wait");
+///         wait_result
+///     }));
+/// }
+///
+/// // Will not resolve until all "after wait" messages have been printed
+/// let mut num_leaders = 0;
+/// for handle in handles {
+///     let wait_result = handle.await.unwrap();
+///     if wait_result.is_leader() {
+///         num_leaders += 1;
+///     }
+/// }
+///
+/// // Exactly one barrier will resolve as the "leader"
+/// assert_eq!(num_leaders, 1);
+/// # }
+/// ```
+#[derive(Debug)]
+pub struct Barrier {
+    state: Mutex<BarrierState>,
+    wait: watch::Receiver<usize>,
+    n: usize,
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    resource_span: tracing::Span,
+}
+
+#[derive(Debug)]
+struct BarrierState {
+    waker: watch::Sender<usize>,
+    arrived: usize,
+    generation: usize,
+}
+
+impl Barrier {
+    /// Creates a new barrier that can block a given number of tasks.
+    ///
+    /// A barrier will block `n`-1 tasks which call [`Barrier::wait`] and then wake up all
+    /// tasks at once when the `n`th task calls `wait`.
+    #[track_caller]
+    pub fn new(mut n: usize) -> Barrier {
+        let (waker, wait) = crate::sync::watch::channel(0);
+
+        if n == 0 {
+            // if n is 0, it's not clear what behavior the user wants.
+            // in std::sync::Barrier, an n of 0 exhibits the same behavior as n == 1, where every
+            // .wait() immediately unblocks, so we adopt that here as well.
+            n = 1;
+        }
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = {
+            let location = std::panic::Location::caller();
+            let resource_span = tracing::trace_span!(
+                "runtime.resource",
+                concrete_type = "Barrier",
+                kind = "Sync",
+                loc.file = location.file(),
+                loc.line = location.line(),
+                loc.col = location.column(),
+            );
+
+            resource_span.in_scope(|| {
+                tracing::trace!(
+                    target: "runtime::resource::state_update",
+                    size = n,
+                );
+
+                tracing::trace!(
+                    target: "runtime::resource::state_update",
+                    arrived = 0,
+                )
+            });
+            resource_span
+        };
+
+        Barrier {
+            state: Mutex::new(BarrierState {
+                waker,
+                arrived: 0,
+                generation: 1,
+            }),
+            n,
+            wait,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span: resource_span,
+        }
+    }
+
+    /// Does not resolve until all tasks have rendezvoused here.
+    ///
+    /// Barriers are re-usable after all tasks have rendezvoused once, and can
+    /// be used continuously.
+    ///
+    /// A single (arbitrary) future will receive a [`BarrierWaitResult`] that returns `true` from
+    /// [`BarrierWaitResult::is_leader`] when returning from this function, and all other tasks
+    /// will receive a result that will return `false` from `is_leader`.
+    pub async fn wait(&self) -> BarrierWaitResult {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        return trace::async_op(
+            || self.wait_internal(),
+            self.resource_span.clone(),
+            "Barrier::wait",
+            "poll",
+            false,
+        )
+        .await;
+
+        #[cfg(any(not(tokio_unstable), not(feature = "tracing")))]
+        return self.wait_internal().await;
+    }
+    async fn wait_internal(&self) -> BarrierWaitResult {
+        // NOTE: we are taking a _synchronous_ lock here.
+        // It is okay to do so because the critical section is fast and never yields, so it cannot
+        // deadlock even if another future is concurrently holding the lock.
+        // It is _desireable_ to do so as synchronous Mutexes are, at least in theory, faster than
+        // the asynchronous counter-parts, so we should use them where possible [citation needed].
+        // NOTE: the extra scope here is so that the compiler doesn't think `state` is held across
+        // a yield point, and thus marks the returned future as !Send.
+        let generation = {
+            let mut state = self.state.lock();
+            let generation = state.generation;
+            state.arrived += 1;
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            tracing::trace!(
+                target: "runtime::resource::state_update",
+                arrived = 1,
+                arrived.op = "add",
+            );
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            tracing::trace!(
+                target: "runtime::resource::async_op::state_update",
+                arrived = true,
+            );
+            if state.arrived == self.n {
+                #[cfg(all(tokio_unstable, feature = "tracing"))]
+                tracing::trace!(
+                    target: "runtime::resource::async_op::state_update",
+                    is_leader = true,
+                );
+                // we are the leader for this generation
+                // wake everyone, increment the generation, and return
+                state
+                    .waker
+                    .send(state.generation)
+                    .expect("there is at least one receiver");
+                state.arrived = 0;
+                state.generation += 1;
+                return BarrierWaitResult(true);
+            }
+
+            generation
+        };
+
+        // we're going to have to wait for the last of the generation to arrive
+        let mut wait = self.wait.clone();
+
+        loop {
+            let _ = wait.changed().await;
+
+            // note that the first time through the loop, this _will_ yield a generation
+            // immediately, since we cloned a receiver that has never seen any values.
+            if *wait.borrow() >= generation {
+                break;
+            }
+        }
+
+        BarrierWaitResult(false)
+    }
+}
+
+/// A `BarrierWaitResult` is returned by `wait` when all tasks in the `Barrier` have rendezvoused.
+#[derive(Debug, Clone)]
+pub struct BarrierWaitResult(bool);
+
+impl BarrierWaitResult {
+    /// Returns `true` if this task from wait is the "leader task".
+    ///
+    /// Only one task will have `true` returned from their result, all other tasks will have
+    /// `false` returned.
+    pub fn is_leader(&self) -> bool {
+        self.0
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/batch_semaphore.rs b/third_party/rust/tokio/src/sync/batch_semaphore.rs
new file mode 100644
index 0000000000..4f5effff31
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/batch_semaphore.rs
@@ -0,0 +1,727 @@
+#![cfg_attr(not(feature = "sync"), allow(unreachable_pub, dead_code))]
+//! # Implementation Details.
+//!
+//! The semaphore is implemented using an intrusive linked list of waiters. An
+//! atomic counter tracks the number of available permits. If the semaphore does
+//! not contain the required number of permits, the task attempting to acquire
+//! permits places its waker at the end of a queue. When new permits are made
+//! available (such as by releasing an initial acquisition), they are assigned
+//! to the task at the front of the queue, waking that task if its requested
+//! number of permits is met.
+//!
+//! Because waiters are enqueued at the back of the linked list and dequeued
+//! from the front, the semaphore is fair. Tasks trying to acquire large numbers
+//! of permits at a time will always be woken eventually, even if many other
+//! tasks are acquiring smaller numbers of permits. This means that in a
+//! use-case like tokio's read-write lock, writers will not be starved by
+//! readers.
+use crate::loom::cell::UnsafeCell;
+use crate::loom::sync::atomic::AtomicUsize;
+use crate::loom::sync::{Mutex, MutexGuard};
+use crate::util::linked_list::{self, LinkedList};
+#[cfg(all(tokio_unstable, feature = "tracing"))]
+use crate::util::trace;
+use crate::util::WakeList;
+
+use std::future::Future;
+use std::marker::PhantomPinned;
+use std::pin::Pin;
+use std::ptr::NonNull;
+use std::sync::atomic::Ordering::*;
+use std::task::Poll::*;
+use std::task::{Context, Poll, Waker};
+use std::{cmp, fmt};
+
+/// An asynchronous counting semaphore which permits waiting on multiple permits at once.
+pub(crate) struct Semaphore {
+    waiters: Mutex<Waitlist>,
+    /// The current number of available permits in the semaphore.
+    permits: AtomicUsize,
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    resource_span: tracing::Span,
+}
+
+struct Waitlist {
+    queue: LinkedList<Waiter, <Waiter as linked_list::Link>::Target>,
+    closed: bool,
+}
+
+/// Error returned from the [`Semaphore::try_acquire`] function.
+///
+/// [`Semaphore::try_acquire`]: crate::sync::Semaphore::try_acquire
+#[derive(Debug, PartialEq)]
+pub enum TryAcquireError {
+    /// The semaphore has been [closed] and cannot issue new permits.
+    ///
+    /// [closed]: crate::sync::Semaphore::close
+    Closed,
+
+    /// The semaphore has no available permits.
+    NoPermits,
+}
+/// Error returned from the [`Semaphore::acquire`] function.
+///
+/// An `acquire` operation can only fail if the semaphore has been
+/// [closed].
+///
+/// [closed]: crate::sync::Semaphore::close
+/// [`Semaphore::acquire`]: crate::sync::Semaphore::acquire
+#[derive(Debug)]
+pub struct AcquireError(());
+
+pub(crate) struct Acquire<'a> {
+    node: Waiter,
+    semaphore: &'a Semaphore,
+    num_permits: u32,
+    queued: bool,
+}
+
+/// An entry in the wait queue.
+struct Waiter {
+    /// The current state of the waiter.
+    ///
+    /// This is either the number of remaining permits required by
+    /// the waiter, or a flag indicating that the waiter is not yet queued.
+    state: AtomicUsize,
+
+    /// The waker to notify the task awaiting permits.
+    ///
+    /// # Safety
+    ///
+    /// This may only be accessed while the wait queue is locked.
+    waker: UnsafeCell<Option<Waker>>,
+
+    /// Intrusive linked-list pointers.
+    ///
+    /// # Safety
+    ///
+    /// This may only be accessed while the wait queue is locked.
+    ///
+    /// TODO: Ideally, we would be able to use loom to enforce that
+    /// this isn't accessed concurrently. However, it is difficult to
+    /// use a `UnsafeCell` here, since the `Link` trait requires _returning_
+    /// references to `Pointers`, and `UnsafeCell` requires that checked access
+    /// take place inside a closure. We should consider changing `Pointers` to
+    /// use `UnsafeCell` internally.
+    pointers: linked_list::Pointers<Waiter>,
+
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    ctx: trace::AsyncOpTracingCtx,
+
+    /// Should not be `Unpin`.
+    _p: PhantomPinned,
+}
+
+impl Semaphore {
+    /// The maximum number of permits which a semaphore can hold.
+    ///
+    /// Note that this reserves three bits of flags in the permit counter, but
+    /// we only actually use one of them. However, the previous semaphore
+    /// implementation used three bits, so we will continue to reserve them to
+    /// avoid a breaking change if additional flags need to be added in the
+    /// future.
+    pub(crate) const MAX_PERMITS: usize = std::usize::MAX >> 3;
+    const CLOSED: usize = 1;
+    // The least-significant bit in the number of permits is reserved to use
+    // as a flag indicating that the semaphore has been closed. Consequently
+    // PERMIT_SHIFT is used to leave that bit for that purpose.
+    const PERMIT_SHIFT: usize = 1;
+
+    /// Creates a new semaphore with the initial number of permits
+    ///
+    /// Maximum number of permits on 32-bit platforms is `1<<29`.
+    pub(crate) fn new(permits: usize) -> Self {
+        assert!(
+            permits <= Self::MAX_PERMITS,
+            "a semaphore may not have more than MAX_PERMITS permits ({})",
+            Self::MAX_PERMITS
+        );
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = {
+            let resource_span = tracing::trace_span!(
+                "runtime.resource",
+                concrete_type = "Semaphore",
+                kind = "Sync",
+                is_internal = true
+            );
+
+            resource_span.in_scope(|| {
+                tracing::trace!(
+                    target: "runtime::resource::state_update",
+                    permits = permits,
+                    permits.op = "override",
+                )
+            });
+            resource_span
+        };
+
+        Self {
+            permits: AtomicUsize::new(permits << Self::PERMIT_SHIFT),
+            waiters: Mutex::new(Waitlist {
+                queue: LinkedList::new(),
+                closed: false,
+            }),
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+
+    /// Creates a new semaphore with the initial number of permits.
+    ///
+    /// Maximum number of permits on 32-bit platforms is `1<<29`.
+    ///
+    /// If the specified number of permits exceeds the maximum permit amount
+    /// Then the value will get clamped to the maximum number of permits.
+    #[cfg(all(feature = "parking_lot", not(all(loom, test))))]
+    pub(crate) const fn const_new(mut permits: usize) -> Self {
+        // NOTE: assertions and by extension panics are still being worked on: https://github.com/rust-lang/rust/issues/74925
+        // currently we just clamp the permit count when it exceeds the max
+        permits &= Self::MAX_PERMITS;
+
+        Self {
+            permits: AtomicUsize::new(permits << Self::PERMIT_SHIFT),
+            waiters: Mutex::const_new(Waitlist {
+                queue: LinkedList::new(),
+                closed: false,
+            }),
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span: tracing::Span::none(),
+        }
+    }
+
+    /// Returns the current number of available permits.
+    pub(crate) fn available_permits(&self) -> usize {
+        self.permits.load(Acquire) >> Self::PERMIT_SHIFT
+    }
+
+    /// Adds `added` new permits to the semaphore.
+    ///
+    /// The maximum number of permits is `usize::MAX >> 3`, and this function will panic if the limit is exceeded.
+    pub(crate) fn release(&self, added: usize) {
+        if added == 0 {
+            return;
+        }
+
+        // Assign permits to the wait queue
+        self.add_permits_locked(added, self.waiters.lock());
+    }
+
+    /// Closes the semaphore. This prevents the semaphore from issuing new
+    /// permits and notifies all pending waiters.
+    pub(crate) fn close(&self) {
+        let mut waiters = self.waiters.lock();
+        // If the semaphore's permits counter has enough permits for an
+        // unqueued waiter to acquire all the permits it needs immediately,
+        // it won't touch the wait list. Therefore, we have to set a bit on
+        // the permit counter as well. However, we must do this while
+        // holding the lock --- otherwise, if we set the bit and then wait
+        // to acquire the lock we'll enter an inconsistent state where the
+        // permit counter is closed, but the wait list is not.
+        self.permits.fetch_or(Self::CLOSED, Release);
+        waiters.closed = true;
+        while let Some(mut waiter) = waiters.queue.pop_back() {
+            let waker = unsafe { waiter.as_mut().waker.with_mut(|waker| (*waker).take()) };
+            if let Some(waker) = waker {
+                waker.wake();
+            }
+        }
+    }
+
+    /// Returns true if the semaphore is closed.
+    pub(crate) fn is_closed(&self) -> bool {
+        self.permits.load(Acquire) & Self::CLOSED == Self::CLOSED
+    }
+
+    pub(crate) fn try_acquire(&self, num_permits: u32) -> Result<(), TryAcquireError> {
+        assert!(
+            num_permits as usize <= Self::MAX_PERMITS,
+            "a semaphore may not have more than MAX_PERMITS permits ({})",
+            Self::MAX_PERMITS
+        );
+        let num_permits = (num_permits as usize) << Self::PERMIT_SHIFT;
+        let mut curr = self.permits.load(Acquire);
+        loop {
+            // Has the semaphore closed?
+            if curr & Self::CLOSED == Self::CLOSED {
+                return Err(TryAcquireError::Closed);
+            }
+
+            // Are there enough permits remaining?
+            if curr < num_permits {
+                return Err(TryAcquireError::NoPermits);
+            }
+
+            let next = curr - num_permits;
+
+            match self.permits.compare_exchange(curr, next, AcqRel, Acquire) {
+                Ok(_) => {
+                    // TODO: Instrument once issue has been solved}
+                    return Ok(());
+                }
+                Err(actual) => curr = actual,
+            }
+        }
+    }
+
+    pub(crate) fn acquire(&self, num_permits: u32) -> Acquire<'_> {
+        Acquire::new(self, num_permits)
+    }
+
+    /// Release `rem` permits to the semaphore's wait list, starting from the
+    /// end of the queue.
+    ///
+    /// If `rem` exceeds the number of permits needed by the wait list, the
+    /// remainder are assigned back to the semaphore.
+    fn add_permits_locked(&self, mut rem: usize, waiters: MutexGuard<'_, Waitlist>) {
+        let mut wakers = WakeList::new();
+        let mut lock = Some(waiters);
+        let mut is_empty = false;
+        while rem > 0 {
+            let mut waiters = lock.take().unwrap_or_else(|| self.waiters.lock());
+            'inner: while wakers.can_push() {
+                // Was the waiter assigned enough permits to wake it?
+                match waiters.queue.last() {
+                    Some(waiter) => {
+                        if !waiter.assign_permits(&mut rem) {
+                            break 'inner;
+                        }
+                    }
+                    None => {
+                        is_empty = true;
+                        // If we assigned permits to all the waiters in the queue, and there are
+                        // still permits left over, assign them back to the semaphore.
+                        break 'inner;
+                    }
+                };
+                let mut waiter = waiters.queue.pop_back().unwrap();
+                if let Some(waker) =
+                    unsafe { waiter.as_mut().waker.with_mut(|waker| (*waker).take()) }
+                {
+                    wakers.push(waker);
+                }
+            }
+
+            if rem > 0 && is_empty {
+                let permits = rem;
+                assert!(
+                    permits <= Self::MAX_PERMITS,
+                    "cannot add more than MAX_PERMITS permits ({})",
+                    Self::MAX_PERMITS
+                );
+                let prev = self.permits.fetch_add(rem << Self::PERMIT_SHIFT, Release);
+                let prev = prev >> Self::PERMIT_SHIFT;
+                assert!(
+                    prev + permits <= Self::MAX_PERMITS,
+                    "number of added permits ({}) would overflow MAX_PERMITS ({})",
+                    rem,
+                    Self::MAX_PERMITS
+                );
+
+                // add remaining permits back
+                #[cfg(all(tokio_unstable, feature = "tracing"))]
+                self.resource_span.in_scope(|| {
+                    tracing::trace!(
+                    target: "runtime::resource::state_update",
+                    permits = rem,
+                    permits.op = "add",
+                    )
+                });
+
+                rem = 0;
+            }
+
+            drop(waiters); // release the lock
+
+            wakers.wake_all();
+        }
+
+        assert_eq!(rem, 0);
+    }
+
+    fn poll_acquire(
+        &self,
+        cx: &mut Context<'_>,
+        num_permits: u32,
+        node: Pin<&mut Waiter>,
+        queued: bool,
+    ) -> Poll<Result<(), AcquireError>> {
+        let mut acquired = 0;
+
+        let needed = if queued {
+            node.state.load(Acquire) << Self::PERMIT_SHIFT
+        } else {
+            (num_permits as usize) << Self::PERMIT_SHIFT
+        };
+
+        let mut lock = None;
+        // First, try to take the requested number of permits from the
+        // semaphore.
+        let mut curr = self.permits.load(Acquire);
+        let mut waiters = loop {
+            // Has the semaphore closed?
+            if curr & Self::CLOSED > 0 {
+                return Ready(Err(AcquireError::closed()));
+            }
+
+            let mut remaining = 0;
+            let total = curr
+                .checked_add(acquired)
+                .expect("number of permits must not overflow");
+            let (next, acq) = if total >= needed {
+                let next = curr - (needed - acquired);
+                (next, needed >> Self::PERMIT_SHIFT)
+            } else {
+                remaining = (needed - acquired) - curr;
+                (0, curr >> Self::PERMIT_SHIFT)
+            };
+
+            if remaining > 0 && lock.is_none() {
+                // No permits were immediately available, so this permit will
+                // (probably) need to wait. We'll need to acquire a lock on the
+                // wait queue before continuing. We need to do this _before_ the
+                // CAS that sets the new value of the semaphore's `permits`
+                // counter. Otherwise, if we subtract the permits and then
+                // acquire the lock, we might miss additional permits being
+                // added while waiting for the lock.
+                lock = Some(self.waiters.lock());
+            }
+
+            match self.permits.compare_exchange(curr, next, AcqRel, Acquire) {
+                Ok(_) => {
+                    acquired += acq;
+                    if remaining == 0 {
+                        if !queued {
+                            #[cfg(all(tokio_unstable, feature = "tracing"))]
+                            self.resource_span.in_scope(|| {
+                                tracing::trace!(
+                                    target: "runtime::resource::state_update",
+                                    permits = acquired,
+                                    permits.op = "sub",
+                                );
+                                tracing::trace!(
+                                    target: "runtime::resource::async_op::state_update",
+                                    permits_obtained = acquired,
+                                    permits.op = "add",
+                                )
+                            });
+
+                            return Ready(Ok(()));
+                        } else if lock.is_none() {
+                            break self.waiters.lock();
+                        }
+                    }
+                    break lock.expect("lock must be acquired before waiting");
+                }
+                Err(actual) => curr = actual,
+            }
+        };
+
+        if waiters.closed {
+            return Ready(Err(AcquireError::closed()));
+        }
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+                target: "runtime::resource::state_update",
+                permits = acquired,
+                permits.op = "sub",
+            )
+        });
+
+        if node.assign_permits(&mut acquired) {
+            self.add_permits_locked(acquired, waiters);
+            return Ready(Ok(()));
+        }
+
+        assert_eq!(acquired, 0);
+
+        // Otherwise, register the waker & enqueue the node.
+        node.waker.with_mut(|waker| {
+            // Safety: the wait list is locked, so we may modify the waker.
+            let waker = unsafe { &mut *waker };
+            // Do we need to register the new waker?
+            if waker
+                .as_ref()
+                .map(|waker| !waker.will_wake(cx.waker()))
+                .unwrap_or(true)
+            {
+                *waker = Some(cx.waker().clone());
+            }
+        });
+
+        // If the waiter is not already in the wait queue, enqueue it.
+        if !queued {
+            let node = unsafe {
+                let node = Pin::into_inner_unchecked(node) as *mut _;
+                NonNull::new_unchecked(node)
+            };
+
+            waiters.queue.push_front(node);
+        }
+
+        Pending
+    }
+}
+
+impl fmt::Debug for Semaphore {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Semaphore")
+            .field("permits", &self.available_permits())
+            .finish()
+    }
+}
+
+impl Waiter {
+    fn new(
+        num_permits: u32,
+        #[cfg(all(tokio_unstable, feature = "tracing"))] ctx: trace::AsyncOpTracingCtx,
+    ) -> Self {
+        Waiter {
+            waker: UnsafeCell::new(None),
+            state: AtomicUsize::new(num_permits as usize),
+            pointers: linked_list::Pointers::new(),
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            ctx,
+            _p: PhantomPinned,
+        }
+    }
+
+    /// Assign permits to the waiter.
+    ///
+    /// Returns `true` if the waiter should be removed from the queue
+    fn assign_permits(&self, n: &mut usize) -> bool {
+        let mut curr = self.state.load(Acquire);
+        loop {
+            let assign = cmp::min(curr, *n);
+            let next = curr - assign;
+            match self.state.compare_exchange(curr, next, AcqRel, Acquire) {
+                Ok(_) => {
+                    *n -= assign;
+                    #[cfg(all(tokio_unstable, feature = "tracing"))]
+                    self.ctx.async_op_span.in_scope(|| {
+                        tracing::trace!(
+                            target: "runtime::resource::async_op::state_update",
+                            permits_obtained = assign,
+                            permits.op = "add",
+                        );
+                    });
+                    return next == 0;
+                }
+                Err(actual) => curr = actual,
+            }
+        }
+    }
+}
+
+impl Future for Acquire<'_> {
+    type Output = Result<(), AcquireError>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let _resource_span = self.node.ctx.resource_span.clone().entered();
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let _async_op_span = self.node.ctx.async_op_span.clone().entered();
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let _async_op_poll_span = self.node.ctx.async_op_poll_span.clone().entered();
+
+        let (node, semaphore, needed, queued) = self.project();
+
+        // First, ensure the current task has enough budget to proceed.
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let coop = ready!(trace_poll_op!(
+            "poll_acquire",
+            crate::coop::poll_proceed(cx),
+        ));
+
+        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+        let coop = ready!(crate::coop::poll_proceed(cx));
+
+        let result = match semaphore.poll_acquire(cx, needed, node, *queued) {
+            Pending => {
+                *queued = true;
+                Pending
+            }
+            Ready(r) => {
+                coop.made_progress();
+                r?;
+                *queued = false;
+                Ready(Ok(()))
+            }
+        };
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        return trace_poll_op!("poll_acquire", result);
+
+        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+        return result;
+    }
+}
+
+impl<'a> Acquire<'a> {
+    fn new(semaphore: &'a Semaphore, num_permits: u32) -> Self {
+        #[cfg(any(not(tokio_unstable), not(feature = "tracing")))]
+        return Self {
+            node: Waiter::new(num_permits),
+            semaphore,
+            num_permits,
+            queued: false,
+        };
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        return semaphore.resource_span.in_scope(|| {
+            let async_op_span =
+                tracing::trace_span!("runtime.resource.async_op", source = "Acquire::new");
+            let async_op_poll_span = async_op_span.in_scope(|| {
+                tracing::trace!(
+                    target: "runtime::resource::async_op::state_update",
+                    permits_requested = num_permits,
+                    permits.op = "override",
+                );
+
+                tracing::trace!(
+                    target: "runtime::resource::async_op::state_update",
+                    permits_obtained = 0 as usize,
+                    permits.op = "override",
+                );
+
+                tracing::trace_span!("runtime.resource.async_op.poll")
+            });
+
+            let ctx = trace::AsyncOpTracingCtx {
+                async_op_span,
+                async_op_poll_span,
+                resource_span: semaphore.resource_span.clone(),
+            };
+
+            Self {
+                node: Waiter::new(num_permits, ctx),
+                semaphore,
+                num_permits,
+                queued: false,
+            }
+        });
+    }
+
+    fn project(self: Pin<&mut Self>) -> (Pin<&mut Waiter>, &Semaphore, u32, &mut bool) {
+        fn is_unpin<T: Unpin>() {}
+        unsafe {
+            // Safety: all fields other than `node` are `Unpin`
+
+            is_unpin::<&Semaphore>();
+            is_unpin::<&mut bool>();
+            is_unpin::<u32>();
+
+            let this = self.get_unchecked_mut();
+            (
+                Pin::new_unchecked(&mut this.node),
+                this.semaphore,
+                this.num_permits,
+                &mut this.queued,
+            )
+        }
+    }
+}
+
+impl Drop for Acquire<'_> {
+    fn drop(&mut self) {
+        // If the future is completed, there is no node in the wait list, so we
+        // can skip acquiring the lock.
+        if !self.queued {
+            return;
+        }
+
+        // This is where we ensure safety. The future is being dropped,
+        // which means we must ensure that the waiter entry is no longer stored
+        // in the linked list.
+        let mut waiters = self.semaphore.waiters.lock();
+
+        // remove the entry from the list
+        let node = NonNull::from(&mut self.node);
+        // Safety: we have locked the wait list.
+        unsafe { waiters.queue.remove(node) };
+
+        let acquired_permits = self.num_permits as usize - self.node.state.load(Acquire);
+        if acquired_permits > 0 {
+            self.semaphore.add_permits_locked(acquired_permits, waiters);
+        }
+    }
+}
+
+// Safety: the `Acquire` future is not `Sync` automatically because it contains
+// a `Waiter`, which, in turn, contains an `UnsafeCell`. However, the
+// `UnsafeCell` is only accessed when the future is borrowed mutably (either in
+// `poll` or in `drop`). Therefore, it is safe (although not particularly
+// _useful_) for the future to be borrowed immutably across threads.
+unsafe impl Sync for Acquire<'_> {}
+
+// ===== impl AcquireError ====
+
+impl AcquireError {
+    fn closed() -> AcquireError {
+        AcquireError(())
+    }
+}
+
+impl fmt::Display for AcquireError {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(fmt, "semaphore closed")
+    }
+}
+
+impl std::error::Error for AcquireError {}
+
+// ===== impl TryAcquireError =====
+
+impl TryAcquireError {
+    /// Returns `true` if the error was caused by a closed semaphore.
+    #[allow(dead_code)] // may be used later!
+    pub(crate) fn is_closed(&self) -> bool {
+        matches!(self, TryAcquireError::Closed)
+    }
+
+    /// Returns `true` if the error was caused by calling `try_acquire` on a
+    /// semaphore with no available permits.
+    #[allow(dead_code)] // may be used later!
+    pub(crate) fn is_no_permits(&self) -> bool {
+        matches!(self, TryAcquireError::NoPermits)
+    }
+}
+
+impl fmt::Display for TryAcquireError {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            TryAcquireError::Closed => write!(fmt, "semaphore closed"),
+            TryAcquireError::NoPermits => write!(fmt, "no permits available"),
+        }
+    }
+}
+
+impl std::error::Error for TryAcquireError {}
+
+/// # Safety
+///
+/// `Waiter` is forced to be !Unpin.
+unsafe impl linked_list::Link for Waiter {
+    // XXX: ideally, we would be able to use `Pin` here, to enforce the
+    // invariant that list entries may not move while in the list. However, we
+    // can't do this currently, as using `Pin<&'a mut Waiter>` as the `Handle`
+    // type would require `Semaphore` to be generic over a lifetime. We can't
+    // use `Pin<*mut Waiter>`, as raw pointers are `Unpin` regardless of whether
+    // or not they dereference to an `!Unpin` target.
+    type Handle = NonNull<Waiter>;
+    type Target = Waiter;
+
+    fn as_raw(handle: &Self::Handle) -> NonNull<Waiter> {
+        *handle
+    }
+
+    unsafe fn from_raw(ptr: NonNull<Waiter>) -> NonNull<Waiter> {
+        ptr
+    }
+
+    unsafe fn pointers(mut target: NonNull<Waiter>) -> NonNull<linked_list::Pointers<Waiter>> {
+        NonNull::from(&mut target.as_mut().pointers)
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/broadcast.rs b/third_party/rust/tokio/src/sync/broadcast.rs
new file mode 100644
index 0000000000..0d9cd3bc17
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/broadcast.rs
@@ -0,0 +1,1078 @@
+//! A multi-producer, multi-consumer broadcast queue. Each sent value is seen by
+//! all consumers.
+//!
+//! A [`Sender`] is used to broadcast values to **all** connected [`Receiver`]
+//! values. [`Sender`] handles are clone-able, allowing concurrent send and
+//! receive actions. [`Sender`] and [`Receiver`] are both `Send` and `Sync` as
+//! long as `T` is also `Send` or `Sync` respectively.
+//!
+//! When a value is sent, **all** [`Receiver`] handles are notified and will
+//! receive the value. The value is stored once inside the channel and cloned on
+//! demand for each receiver. Once all receivers have received a clone of the
+//! value, the value is released from the channel.
+//!
+//! A channel is created by calling [`channel`], specifying the maximum number
+//! of messages the channel can retain at any given time.
+//!
+//! New [`Receiver`] handles are created by calling [`Sender::subscribe`]. The
+//! returned [`Receiver`] will receive values sent **after** the call to
+//! `subscribe`.
+//!
+//! ## Lagging
+//!
+//! As sent messages must be retained until **all** [`Receiver`] handles receive
+//! a clone, broadcast channels are susceptible to the "slow receiver" problem.
+//! In this case, all but one receiver are able to receive values at the rate
+//! they are sent. Because one receiver is stalled, the channel starts to fill
+//! up.
+//!
+//! This broadcast channel implementation handles this case by setting a hard
+//! upper bound on the number of values the channel may retain at any given
+//! time. This upper bound is passed to the [`channel`] function as an argument.
+//!
+//! If a value is sent when the channel is at capacity, the oldest value
+//! currently held by the channel is released. This frees up space for the new
+//! value. Any receiver that has not yet seen the released value will return
+//! [`RecvError::Lagged`] the next time [`recv`] is called.
+//!
+//! Once [`RecvError::Lagged`] is returned, the lagging receiver's position is
+//! updated to the oldest value contained by the channel. The next call to
+//! [`recv`] will return this value.
+//!
+//! This behavior enables a receiver to detect when it has lagged so far behind
+//! that data has been dropped. The caller may decide how to respond to this:
+//! either by aborting its task or by tolerating lost messages and resuming
+//! consumption of the channel.
+//!
+//! ## Closing
+//!
+//! When **all** [`Sender`] handles have been dropped, no new values may be
+//! sent. At this point, the channel is "closed". Once a receiver has received
+//! all values retained by the channel, the next call to [`recv`] will return
+//! with [`RecvError::Closed`].
+//!
+//! [`Sender`]: crate::sync::broadcast::Sender
+//! [`Sender::subscribe`]: crate::sync::broadcast::Sender::subscribe
+//! [`Receiver`]: crate::sync::broadcast::Receiver
+//! [`channel`]: crate::sync::broadcast::channel
+//! [`RecvError::Lagged`]: crate::sync::broadcast::error::RecvError::Lagged
+//! [`RecvError::Closed`]: crate::sync::broadcast::error::RecvError::Closed
+//! [`recv`]: crate::sync::broadcast::Receiver::recv
+//!
+//! # Examples
+//!
+//! Basic usage
+//!
+//! ```
+//! use tokio::sync::broadcast;
+//!
+//! #[tokio::main]
+//! async fn main() {
+//!     let (tx, mut rx1) = broadcast::channel(16);
+//!     let mut rx2 = tx.subscribe();
+//!
+//!     tokio::spawn(async move {
+//!         assert_eq!(rx1.recv().await.unwrap(), 10);
+//!         assert_eq!(rx1.recv().await.unwrap(), 20);
+//!     });
+//!
+//!     tokio::spawn(async move {
+//!         assert_eq!(rx2.recv().await.unwrap(), 10);
+//!         assert_eq!(rx2.recv().await.unwrap(), 20);
+//!     });
+//!
+//!     tx.send(10).unwrap();
+//!     tx.send(20).unwrap();
+//! }
+//! ```
+//!
+//! Handling lag
+//!
+//! ```
+//! use tokio::sync::broadcast;
+//!
+//! #[tokio::main]
+//! async fn main() {
+//!     let (tx, mut rx) = broadcast::channel(2);
+//!
+//!     tx.send(10).unwrap();
+//!     tx.send(20).unwrap();
+//!     tx.send(30).unwrap();
+//!
+//!     // The receiver lagged behind
+//!     assert!(rx.recv().await.is_err());
+//!
+//!     // At this point, we can abort or continue with lost messages
+//!
+//!     assert_eq!(20, rx.recv().await.unwrap());
+//!     assert_eq!(30, rx.recv().await.unwrap());
+//! }
+//! ```
+
+use crate::loom::cell::UnsafeCell;
+use crate::loom::sync::atomic::AtomicUsize;
+use crate::loom::sync::{Arc, Mutex, RwLock, RwLockReadGuard};
+use crate::util::linked_list::{self, LinkedList};
+
+use std::fmt;
+use std::future::Future;
+use std::marker::PhantomPinned;
+use std::pin::Pin;
+use std::ptr::NonNull;
+use std::sync::atomic::Ordering::SeqCst;
+use std::task::{Context, Poll, Waker};
+use std::usize;
+
+/// Sending-half of the [`broadcast`] channel.
+///
+/// May be used from many threads. Messages can be sent with
+/// [`send`][Sender::send].
+///
+/// # Examples
+///
+/// ```
+/// use tokio::sync::broadcast;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let (tx, mut rx1) = broadcast::channel(16);
+///     let mut rx2 = tx.subscribe();
+///
+///     tokio::spawn(async move {
+///         assert_eq!(rx1.recv().await.unwrap(), 10);
+///         assert_eq!(rx1.recv().await.unwrap(), 20);
+///     });
+///
+///     tokio::spawn(async move {
+///         assert_eq!(rx2.recv().await.unwrap(), 10);
+///         assert_eq!(rx2.recv().await.unwrap(), 20);
+///     });
+///
+///     tx.send(10).unwrap();
+///     tx.send(20).unwrap();
+/// }
+/// ```
+///
+/// [`broadcast`]: crate::sync::broadcast
+pub struct Sender<T> {
+    shared: Arc<Shared<T>>,
+}
+
+/// Receiving-half of the [`broadcast`] channel.
+///
+/// Must not be used concurrently. Messages may be retrieved using
+/// [`recv`][Receiver::recv].
+///
+/// To turn this receiver into a `Stream`, you can use the [`BroadcastStream`]
+/// wrapper.
+///
+/// [`BroadcastStream`]: https://docs.rs/tokio-stream/0.1/tokio_stream/wrappers/struct.BroadcastStream.html
+///
+/// # Examples
+///
+/// ```
+/// use tokio::sync::broadcast;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let (tx, mut rx1) = broadcast::channel(16);
+///     let mut rx2 = tx.subscribe();
+///
+///     tokio::spawn(async move {
+///         assert_eq!(rx1.recv().await.unwrap(), 10);
+///         assert_eq!(rx1.recv().await.unwrap(), 20);
+///     });
+///
+///     tokio::spawn(async move {
+///         assert_eq!(rx2.recv().await.unwrap(), 10);
+///         assert_eq!(rx2.recv().await.unwrap(), 20);
+///     });
+///
+///     tx.send(10).unwrap();
+///     tx.send(20).unwrap();
+/// }
+/// ```
+///
+/// [`broadcast`]: crate::sync::broadcast
+pub struct Receiver<T> {
+    /// State shared with all receivers and senders.
+    shared: Arc<Shared<T>>,
+
+    /// Next position to read from
+    next: u64,
+}
+
+pub mod error {
+    //! Broadcast error types
+
+    use std::fmt;
+
+    /// Error returned by from the [`send`] function on a [`Sender`].
+    ///
+    /// A **send** operation can only fail if there are no active receivers,
+    /// implying that the message could never be received. The error contains the
+    /// message being sent as a payload so it can be recovered.
+    ///
+    /// [`send`]: crate::sync::broadcast::Sender::send
+    /// [`Sender`]: crate::sync::broadcast::Sender
+    #[derive(Debug)]
+    pub struct SendError<T>(pub T);
+
+    impl<T> fmt::Display for SendError<T> {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            write!(f, "channel closed")
+        }
+    }
+
+    impl<T: fmt::Debug> std::error::Error for SendError<T> {}
+
+    /// An error returned from the [`recv`] function on a [`Receiver`].
+    ///
+    /// [`recv`]: crate::sync::broadcast::Receiver::recv
+    /// [`Receiver`]: crate::sync::broadcast::Receiver
+    #[derive(Debug, PartialEq)]
+    pub enum RecvError {
+        /// There are no more active senders implying no further messages will ever
+        /// be sent.
+        Closed,
+
+        /// The receiver lagged too far behind. Attempting to receive again will
+        /// return the oldest message still retained by the channel.
+        ///
+        /// Includes the number of skipped messages.
+        Lagged(u64),
+    }
+
+    impl fmt::Display for RecvError {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            match self {
+                RecvError::Closed => write!(f, "channel closed"),
+                RecvError::Lagged(amt) => write!(f, "channel lagged by {}", amt),
+            }
+        }
+    }
+
+    impl std::error::Error for RecvError {}
+
+    /// An error returned from the [`try_recv`] function on a [`Receiver`].
+    ///
+    /// [`try_recv`]: crate::sync::broadcast::Receiver::try_recv
+    /// [`Receiver`]: crate::sync::broadcast::Receiver
+    #[derive(Debug, PartialEq)]
+    pub enum TryRecvError {
+        /// The channel is currently empty. There are still active
+        /// [`Sender`] handles, so data may yet become available.
+        ///
+        /// [`Sender`]: crate::sync::broadcast::Sender
+        Empty,
+
+        /// There are no more active senders implying no further messages will ever
+        /// be sent.
+        Closed,
+
+        /// The receiver lagged too far behind and has been forcibly disconnected.
+        /// Attempting to receive again will return the oldest message still
+        /// retained by the channel.
+        ///
+        /// Includes the number of skipped messages.
+        Lagged(u64),
+    }
+
+    impl fmt::Display for TryRecvError {
+        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+            match self {
+                TryRecvError::Empty => write!(f, "channel empty"),
+                TryRecvError::Closed => write!(f, "channel closed"),
+                TryRecvError::Lagged(amt) => write!(f, "channel lagged by {}", amt),
+            }
+        }
+    }
+
+    impl std::error::Error for TryRecvError {}
+}
+
+use self::error::*;
+
+/// Data shared between senders and receivers.
+struct Shared<T> {
+    /// slots in the channel.
+    buffer: Box<[RwLock<Slot<T>>]>,
+
+    /// Mask a position -> index.
+    mask: usize,
+
+    /// Tail of the queue. Includes the rx wait list.
+    tail: Mutex<Tail>,
+
+    /// Number of outstanding Sender handles.
+    num_tx: AtomicUsize,
+}
+
+/// Next position to write a value.
+struct Tail {
+    /// Next position to write to.
+    pos: u64,
+
+    /// Number of active receivers.
+    rx_cnt: usize,
+
+    /// True if the channel is closed.
+    closed: bool,
+
+    /// Receivers waiting for a value.
+    waiters: LinkedList<Waiter, <Waiter as linked_list::Link>::Target>,
+}
+
+/// Slot in the buffer.
+struct Slot<T> {
+    /// Remaining number of receivers that are expected to see this value.
+    ///
+    /// When this goes to zero, the value is released.
+    ///
+    /// An atomic is used as it is mutated concurrently with the slot read lock
+    /// acquired.
+    rem: AtomicUsize,
+
+    /// Uniquely identifies the `send` stored in the slot.
+    pos: u64,
+
+    /// True signals the channel is closed.
+    closed: bool,
+
+    /// The value being broadcast.
+    ///
+    /// The value is set by `send` when the write lock is held. When a reader
+    /// drops, `rem` is decremented. When it hits zero, the value is dropped.
+    val: UnsafeCell<Option<T>>,
+}
+
+/// An entry in the wait queue.
+struct Waiter {
+    /// True if queued.
+    queued: bool,
+
+    /// Task waiting on the broadcast channel.
+    waker: Option<Waker>,
+
+    /// Intrusive linked-list pointers.
+    pointers: linked_list::Pointers<Waiter>,
+
+    /// Should not be `Unpin`.
+    _p: PhantomPinned,
+}
+
+struct RecvGuard<'a, T> {
+    slot: RwLockReadGuard<'a, Slot<T>>,
+}
+
+/// Receive a value future.
+struct Recv<'a, T> {
+    /// Receiver being waited on.
+    receiver: &'a mut Receiver<T>,
+
+    /// Entry in the waiter `LinkedList`.
+    waiter: UnsafeCell<Waiter>,
+}
+
+unsafe impl<'a, T: Send> Send for Recv<'a, T> {}
+unsafe impl<'a, T: Send> Sync for Recv<'a, T> {}
+
+/// Max number of receivers. Reserve space to lock.
+const MAX_RECEIVERS: usize = usize::MAX >> 2;
+
+/// Create a bounded, multi-producer, multi-consumer channel where each sent
+/// value is broadcasted to all active receivers.
+///
+/// All data sent on [`Sender`] will become available on every active
+/// [`Receiver`] in the same order as it was sent.
+///
+/// The `Sender` can be cloned to `send` to the same channel from multiple
+/// points in the process or it can be used concurrently from an `Arc`. New
+/// `Receiver` handles are created by calling [`Sender::subscribe`].
+///
+/// If all [`Receiver`] handles are dropped, the `send` method will return a
+/// [`SendError`]. Similarly, if all [`Sender`] handles are dropped, the [`recv`]
+/// method will return a [`RecvError`].
+///
+/// [`Sender`]: crate::sync::broadcast::Sender
+/// [`Sender::subscribe`]: crate::sync::broadcast::Sender::subscribe
+/// [`Receiver`]: crate::sync::broadcast::Receiver
+/// [`recv`]: crate::sync::broadcast::Receiver::recv
+/// [`SendError`]: crate::sync::broadcast::error::SendError
+/// [`RecvError`]: crate::sync::broadcast::error::RecvError
+///
+/// # Examples
+///
+/// ```
+/// use tokio::sync::broadcast;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let (tx, mut rx1) = broadcast::channel(16);
+///     let mut rx2 = tx.subscribe();
+///
+///     tokio::spawn(async move {
+///         assert_eq!(rx1.recv().await.unwrap(), 10);
+///         assert_eq!(rx1.recv().await.unwrap(), 20);
+///     });
+///
+///     tokio::spawn(async move {
+///         assert_eq!(rx2.recv().await.unwrap(), 10);
+///         assert_eq!(rx2.recv().await.unwrap(), 20);
+///     });
+///
+///     tx.send(10).unwrap();
+///     tx.send(20).unwrap();
+/// }
+/// ```
+pub fn channel<T: Clone>(mut capacity: usize) -> (Sender<T>, Receiver<T>) {
+    assert!(capacity > 0, "capacity is empty");
+    assert!(capacity <= usize::MAX >> 1, "requested capacity too large");
+
+    // Round to a power of two
+    capacity = capacity.next_power_of_two();
+
+    let mut buffer = Vec::with_capacity(capacity);
+
+    for i in 0..capacity {
+        buffer.push(RwLock::new(Slot {
+            rem: AtomicUsize::new(0),
+            pos: (i as u64).wrapping_sub(capacity as u64),
+            closed: false,
+            val: UnsafeCell::new(None),
+        }));
+    }
+
+    let shared = Arc::new(Shared {
+        buffer: buffer.into_boxed_slice(),
+        mask: capacity - 1,
+        tail: Mutex::new(Tail {
+            pos: 0,
+            rx_cnt: 1,
+            closed: false,
+            waiters: LinkedList::new(),
+        }),
+        num_tx: AtomicUsize::new(1),
+    });
+
+    let rx = Receiver {
+        shared: shared.clone(),
+        next: 0,
+    };
+
+    let tx = Sender { shared };
+
+    (tx, rx)
+}
+
+unsafe impl<T: Send> Send for Sender<T> {}
+unsafe impl<T: Send> Sync for Sender<T> {}
+
+unsafe impl<T: Send> Send for Receiver<T> {}
+unsafe impl<T: Send> Sync for Receiver<T> {}
+
+impl<T> Sender<T> {
+    /// Attempts to send a value to all active [`Receiver`] handles, returning
+    /// it back if it could not be sent.
+    ///
+    /// A successful send occurs when there is at least one active [`Receiver`]
+    /// handle. An unsuccessful send would be one where all associated
+    /// [`Receiver`] handles have already been dropped.
+    ///
+    /// # Return
+    ///
+    /// On success, the number of subscribed [`Receiver`] handles is returned.
+    /// This does not mean that this number of receivers will see the message as
+    /// a receiver may drop before receiving the message.
+    ///
+    /// # Note
+    ///
+    /// A return value of `Ok` **does not** mean that the sent value will be
+    /// observed by all or any of the active [`Receiver`] handles. [`Receiver`]
+    /// handles may be dropped before receiving the sent message.
+    ///
+    /// A return value of `Err` **does not** mean that future calls to `send`
+    /// will fail. New [`Receiver`] handles may be created by calling
+    /// [`subscribe`].
+    ///
+    /// [`Receiver`]: crate::sync::broadcast::Receiver
+    /// [`subscribe`]: crate::sync::broadcast::Sender::subscribe
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::broadcast;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx1) = broadcast::channel(16);
+    ///     let mut rx2 = tx.subscribe();
+    ///
+    ///     tokio::spawn(async move {
+    ///         assert_eq!(rx1.recv().await.unwrap(), 10);
+    ///         assert_eq!(rx1.recv().await.unwrap(), 20);
+    ///     });
+    ///
+    ///     tokio::spawn(async move {
+    ///         assert_eq!(rx2.recv().await.unwrap(), 10);
+    ///         assert_eq!(rx2.recv().await.unwrap(), 20);
+    ///     });
+    ///
+    ///     tx.send(10).unwrap();
+    ///     tx.send(20).unwrap();
+    /// }
+    /// ```
+    pub fn send(&self, value: T) -> Result<usize, SendError<T>> {
+        self.send2(Some(value))
+            .map_err(|SendError(maybe_v)| SendError(maybe_v.unwrap()))
+    }
+
+    /// Creates a new [`Receiver`] handle that will receive values sent **after**
+    /// this call to `subscribe`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::broadcast;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, _rx) = broadcast::channel(16);
+    ///
+    ///     // Will not be seen
+    ///     tx.send(10).unwrap();
+    ///
+    ///     let mut rx = tx.subscribe();
+    ///
+    ///     tx.send(20).unwrap();
+    ///
+    ///     let value = rx.recv().await.unwrap();
+    ///     assert_eq!(20, value);
+    /// }
+    /// ```
+    pub fn subscribe(&self) -> Receiver<T> {
+        let shared = self.shared.clone();
+        new_receiver(shared)
+    }
+
+    /// Returns the number of active receivers
+    ///
+    /// An active receiver is a [`Receiver`] handle returned from [`channel`] or
+    /// [`subscribe`]. These are the handles that will receive values sent on
+    /// this [`Sender`].
+    ///
+    /// # Note
+    ///
+    /// It is not guaranteed that a sent message will reach this number of
+    /// receivers. Active receivers may never call [`recv`] again before
+    /// dropping.
+    ///
+    /// [`recv`]: crate::sync::broadcast::Receiver::recv
+    /// [`Receiver`]: crate::sync::broadcast::Receiver
+    /// [`Sender`]: crate::sync::broadcast::Sender
+    /// [`subscribe`]: crate::sync::broadcast::Sender::subscribe
+    /// [`channel`]: crate::sync::broadcast::channel
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::broadcast;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, _rx1) = broadcast::channel(16);
+    ///
+    ///     assert_eq!(1, tx.receiver_count());
+    ///
+    ///     let mut _rx2 = tx.subscribe();
+    ///
+    ///     assert_eq!(2, tx.receiver_count());
+    ///
+    ///     tx.send(10).unwrap();
+    /// }
+    /// ```
+    pub fn receiver_count(&self) -> usize {
+        let tail = self.shared.tail.lock();
+        tail.rx_cnt
+    }
+
+    fn send2(&self, value: Option<T>) -> Result<usize, SendError<Option<T>>> {
+        let mut tail = self.shared.tail.lock();
+
+        if tail.rx_cnt == 0 {
+            return Err(SendError(value));
+        }
+
+        // Position to write into
+        let pos = tail.pos;
+        let rem = tail.rx_cnt;
+        let idx = (pos & self.shared.mask as u64) as usize;
+
+        // Update the tail position
+        tail.pos = tail.pos.wrapping_add(1);
+
+        // Get the slot
+        let mut slot = self.shared.buffer[idx].write().unwrap();
+
+        // Track the position
+        slot.pos = pos;
+
+        // Set remaining receivers
+        slot.rem.with_mut(|v| *v = rem);
+
+        // Set the closed bit if the value is `None`; otherwise write the value
+        if value.is_none() {
+            tail.closed = true;
+            slot.closed = true;
+        } else {
+            slot.val.with_mut(|ptr| unsafe { *ptr = value });
+        }
+
+        // Release the slot lock before notifying the receivers.
+        drop(slot);
+
+        tail.notify_rx();
+
+        // Release the mutex. This must happen after the slot lock is released,
+        // otherwise the writer lock bit could be cleared while another thread
+        // is in the critical section.
+        drop(tail);
+
+        Ok(rem)
+    }
+}
+
+fn new_receiver<T>(shared: Arc<Shared<T>>) -> Receiver<T> {
+    let mut tail = shared.tail.lock();
+
+    if tail.rx_cnt == MAX_RECEIVERS {
+        panic!("max receivers");
+    }
+
+    tail.rx_cnt = tail.rx_cnt.checked_add(1).expect("overflow");
+
+    let next = tail.pos;
+
+    drop(tail);
+
+    Receiver { shared, next }
+}
+
+impl Tail {
+    fn notify_rx(&mut self) {
+        while let Some(mut waiter) = self.waiters.pop_back() {
+            // Safety: `waiters` lock is still held.
+            let waiter = unsafe { waiter.as_mut() };
+
+            assert!(waiter.queued);
+            waiter.queued = false;
+
+            let waker = waiter.waker.take().unwrap();
+            waker.wake();
+        }
+    }
+}
+
+impl<T> Clone for Sender<T> {
+    fn clone(&self) -> Sender<T> {
+        let shared = self.shared.clone();
+        shared.num_tx.fetch_add(1, SeqCst);
+
+        Sender { shared }
+    }
+}
+
+impl<T> Drop for Sender<T> {
+    fn drop(&mut self) {
+        if 1 == self.shared.num_tx.fetch_sub(1, SeqCst) {
+            let _ = self.send2(None);
+        }
+    }
+}
+
+impl<T> Receiver<T> {
+    /// Locks the next value if there is one.
+    fn recv_ref(
+        &mut self,
+        waiter: Option<(&UnsafeCell<Waiter>, &Waker)>,
+    ) -> Result<RecvGuard<'_, T>, TryRecvError> {
+        let idx = (self.next & self.shared.mask as u64) as usize;
+
+        // The slot holding the next value to read
+        let mut slot = self.shared.buffer[idx].read().unwrap();
+
+        if slot.pos != self.next {
+            let next_pos = slot.pos.wrapping_add(self.shared.buffer.len() as u64);
+
+            // The receiver has read all current values in the channel and there
+            // is no waiter to register
+            if waiter.is_none() && next_pos == self.next {
+                return Err(TryRecvError::Empty);
+            }
+
+            // Release the `slot` lock before attempting to acquire the `tail`
+            // lock. This is required because `send2` acquires the tail lock
+            // first followed by the slot lock. Acquiring the locks in reverse
+            // order here would result in a potential deadlock: `recv_ref`
+            // acquires the `slot` lock and attempts to acquire the `tail` lock
+            // while `send2` acquired the `tail` lock and attempts to acquire
+            // the slot lock.
+            drop(slot);
+
+            let mut tail = self.shared.tail.lock();
+
+            // Acquire slot lock again
+            slot = self.shared.buffer[idx].read().unwrap();
+
+            // Make sure the position did not change. This could happen in the
+            // unlikely event that the buffer is wrapped between dropping the
+            // read lock and acquiring the tail lock.
+            if slot.pos != self.next {
+                let next_pos = slot.pos.wrapping_add(self.shared.buffer.len() as u64);
+
+                if next_pos == self.next {
+                    // Store the waker
+                    if let Some((waiter, waker)) = waiter {
+                        // Safety: called while locked.
+                        unsafe {
+                            // Only queue if not already queued
+                            waiter.with_mut(|ptr| {
+                                // If there is no waker **or** if the currently
+                                // stored waker references a **different** task,
+                                // track the tasks' waker to be notified on
+                                // receipt of a new value.
+                                match (*ptr).waker {
+                                    Some(ref w) if w.will_wake(waker) => {}
+                                    _ => {
+                                        (*ptr).waker = Some(waker.clone());
+                                    }
+                                }
+
+                                if !(*ptr).queued {
+                                    (*ptr).queued = true;
+                                    tail.waiters.push_front(NonNull::new_unchecked(&mut *ptr));
+                                }
+                            });
+                        }
+                    }
+
+                    return Err(TryRecvError::Empty);
+                }
+
+                // At this point, the receiver has lagged behind the sender by
+                // more than the channel capacity. The receiver will attempt to
+                // catch up by skipping dropped messages and setting the
+                // internal cursor to the **oldest** message stored by the
+                // channel.
+                //
+                // However, finding the oldest position is a bit more
+                // complicated than `tail-position - buffer-size`. When
+                // the channel is closed, the tail position is incremented to
+                // signal a new `None` message, but `None` is not stored in the
+                // channel itself (see issue #2425 for why).
+                //
+                // To account for this, if the channel is closed, the tail
+                // position is decremented by `buffer-size + 1`.
+                let mut adjust = 0;
+                if tail.closed {
+                    adjust = 1
+                }
+                let next = tail
+                    .pos
+                    .wrapping_sub(self.shared.buffer.len() as u64 + adjust);
+
+                let missed = next.wrapping_sub(self.next);
+
+                drop(tail);
+
+                // The receiver is slow but no values have been missed
+                if missed == 0 {
+                    self.next = self.next.wrapping_add(1);
+
+                    return Ok(RecvGuard { slot });
+                }
+
+                self.next = next;
+
+                return Err(TryRecvError::Lagged(missed));
+            }
+        }
+
+        self.next = self.next.wrapping_add(1);
+
+        if slot.closed {
+            return Err(TryRecvError::Closed);
+        }
+
+        Ok(RecvGuard { slot })
+    }
+}
+
+impl<T: Clone> Receiver<T> {
+    /// Receives the next value for this receiver.
+    ///
+    /// Each [`Receiver`] handle will receive a clone of all values sent
+    /// **after** it has subscribed.
+    ///
+    /// `Err(RecvError::Closed)` is returned when all `Sender` halves have
+    /// dropped, indicating that no further values can be sent on the channel.
+    ///
+    /// If the [`Receiver`] handle falls behind, once the channel is full, newly
+    /// sent values will overwrite old values. At this point, a call to [`recv`]
+    /// will return with `Err(RecvError::Lagged)` and the [`Receiver`]'s
+    /// internal cursor is updated to point to the oldest value still held by
+    /// the channel. A subsequent call to [`recv`] will return this value
+    /// **unless** it has been since overwritten.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. If `recv` is used as the event in a
+    /// [`tokio::select!`](crate::select) statement and some other branch
+    /// completes first, it is guaranteed that no messages were received on this
+    /// channel.
+    ///
+    /// [`Receiver`]: crate::sync::broadcast::Receiver
+    /// [`recv`]: crate::sync::broadcast::Receiver::recv
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::broadcast;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx1) = broadcast::channel(16);
+    ///     let mut rx2 = tx.subscribe();
+    ///
+    ///     tokio::spawn(async move {
+    ///         assert_eq!(rx1.recv().await.unwrap(), 10);
+    ///         assert_eq!(rx1.recv().await.unwrap(), 20);
+    ///     });
+    ///
+    ///     tokio::spawn(async move {
+    ///         assert_eq!(rx2.recv().await.unwrap(), 10);
+    ///         assert_eq!(rx2.recv().await.unwrap(), 20);
+    ///     });
+    ///
+    ///     tx.send(10).unwrap();
+    ///     tx.send(20).unwrap();
+    /// }
+    /// ```
+    ///
+    /// Handling lag
+    ///
+    /// ```
+    /// use tokio::sync::broadcast;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = broadcast::channel(2);
+    ///
+    ///     tx.send(10).unwrap();
+    ///     tx.send(20).unwrap();
+    ///     tx.send(30).unwrap();
+    ///
+    ///     // The receiver lagged behind
+    ///     assert!(rx.recv().await.is_err());
+    ///
+    ///     // At this point, we can abort or continue with lost messages
+    ///
+    ///     assert_eq!(20, rx.recv().await.unwrap());
+    ///     assert_eq!(30, rx.recv().await.unwrap());
+    /// }
+    /// ```
+    pub async fn recv(&mut self) -> Result<T, RecvError> {
+        let fut = Recv::new(self);
+        fut.await
+    }
+
+    /// Attempts to return a pending value on this receiver without awaiting.
+    ///
+    /// This is useful for a flavor of "optimistic check" before deciding to
+    /// await on a receiver.
+    ///
+    /// Compared with [`recv`], this function has three failure cases instead of two
+    /// (one for closed, one for an empty buffer, one for a lagging receiver).
+    ///
+    /// `Err(TryRecvError::Closed)` is returned when all `Sender` halves have
+    /// dropped, indicating that no further values can be sent on the channel.
+    ///
+    /// If the [`Receiver`] handle falls behind, once the channel is full, newly
+    /// sent values will overwrite old values. At this point, a call to [`recv`]
+    /// will return with `Err(TryRecvError::Lagged)` and the [`Receiver`]'s
+    /// internal cursor is updated to point to the oldest value still held by
+    /// the channel. A subsequent call to [`try_recv`] will return this value
+    /// **unless** it has been since overwritten. If there are no values to
+    /// receive, `Err(TryRecvError::Empty)` is returned.
+    ///
+    /// [`recv`]: crate::sync::broadcast::Receiver::recv
+    /// [`try_recv`]: crate::sync::broadcast::Receiver::try_recv
+    /// [`Receiver`]: crate::sync::broadcast::Receiver
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::broadcast;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = broadcast::channel(16);
+    ///
+    ///     assert!(rx.try_recv().is_err());
+    ///
+    ///     tx.send(10).unwrap();
+    ///
+    ///     let value = rx.try_recv().unwrap();
+    ///     assert_eq!(10, value);
+    /// }
+    /// ```
+    pub fn try_recv(&mut self) -> Result<T, TryRecvError> {
+        let guard = self.recv_ref(None)?;
+        guard.clone_value().ok_or(TryRecvError::Closed)
+    }
+}
+
+impl<T> Drop for Receiver<T> {
+    fn drop(&mut self) {
+        let mut tail = self.shared.tail.lock();
+
+        tail.rx_cnt -= 1;
+        let until = tail.pos;
+
+        drop(tail);
+
+        while self.next < until {
+            match self.recv_ref(None) {
+                Ok(_) => {}
+                // The channel is closed
+                Err(TryRecvError::Closed) => break,
+                // Ignore lagging, we will catch up
+                Err(TryRecvError::Lagged(..)) => {}
+                // Can't be empty
+                Err(TryRecvError::Empty) => panic!("unexpected empty broadcast channel"),
+            }
+        }
+    }
+}
+
+impl<'a, T> Recv<'a, T> {
+    fn new(receiver: &'a mut Receiver<T>) -> Recv<'a, T> {
+        Recv {
+            receiver,
+            waiter: UnsafeCell::new(Waiter {
+                queued: false,
+                waker: None,
+                pointers: linked_list::Pointers::new(),
+                _p: PhantomPinned,
+            }),
+        }
+    }
+
+    /// A custom `project` implementation is used in place of `pin-project-lite`
+    /// as a custom drop implementation is needed.
+    fn project(self: Pin<&mut Self>) -> (&mut Receiver<T>, &UnsafeCell<Waiter>) {
+        unsafe {
+            // Safety: Receiver is Unpin
+            is_unpin::<&mut Receiver<T>>();
+
+            let me = self.get_unchecked_mut();
+            (me.receiver, &me.waiter)
+        }
+    }
+}
+
+impl<'a, T> Future for Recv<'a, T>
+where
+    T: Clone,
+{
+    type Output = Result<T, RecvError>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<T, RecvError>> {
+        let (receiver, waiter) = self.project();
+
+        let guard = match receiver.recv_ref(Some((waiter, cx.waker()))) {
+            Ok(value) => value,
+            Err(TryRecvError::Empty) => return Poll::Pending,
+            Err(TryRecvError::Lagged(n)) => return Poll::Ready(Err(RecvError::Lagged(n))),
+            Err(TryRecvError::Closed) => return Poll::Ready(Err(RecvError::Closed)),
+        };
+
+        Poll::Ready(guard.clone_value().ok_or(RecvError::Closed))
+    }
+}
+
+impl<'a, T> Drop for Recv<'a, T> {
+    fn drop(&mut self) {
+        // Acquire the tail lock. This is required for safety before accessing
+        // the waiter node.
+        let mut tail = self.receiver.shared.tail.lock();
+
+        // safety: tail lock is held
+        let queued = self.waiter.with(|ptr| unsafe { (*ptr).queued });
+
+        if queued {
+            // Remove the node
+            //
+            // safety: tail lock is held and the wait node is verified to be in
+            // the list.
+            unsafe {
+                self.waiter.with_mut(|ptr| {
+                    tail.waiters.remove((&mut *ptr).into());
+                });
+            }
+        }
+    }
+}
+
+/// # Safety
+///
+/// `Waiter` is forced to be !Unpin.
+unsafe impl linked_list::Link for Waiter {
+    type Handle = NonNull<Waiter>;
+    type Target = Waiter;
+
+    fn as_raw(handle: &NonNull<Waiter>) -> NonNull<Waiter> {
+        *handle
+    }
+
+    unsafe fn from_raw(ptr: NonNull<Waiter>) -> NonNull<Waiter> {
+        ptr
+    }
+
+    unsafe fn pointers(mut target: NonNull<Waiter>) -> NonNull<linked_list::Pointers<Waiter>> {
+        NonNull::from(&mut target.as_mut().pointers)
+    }
+}
+
+impl<T> fmt::Debug for Sender<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(fmt, "broadcast::Sender")
+    }
+}
+
+impl<T> fmt::Debug for Receiver<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(fmt, "broadcast::Receiver")
+    }
+}
+
+impl<'a, T> RecvGuard<'a, T> {
+    fn clone_value(&self) -> Option<T>
+    where
+        T: Clone,
+    {
+        self.slot.val.with(|ptr| unsafe { (*ptr).clone() })
+    }
+}
+
+impl<'a, T> Drop for RecvGuard<'a, T> {
+    fn drop(&mut self) {
+        // Decrement the remaining counter
+        if 1 == self.slot.rem.fetch_sub(1, SeqCst) {
+            // Safety: Last receiver, drop the value
+            self.slot.val.with_mut(|ptr| unsafe { *ptr = None });
+        }
+    }
+}
+
+fn is_unpin<T: Unpin>() {}
diff --git a/third_party/rust/tokio/src/sync/mod.rs b/third_party/rust/tokio/src/sync/mod.rs
new file mode 100644
index 0000000000..457e6ab294
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/mod.rs
@@ -0,0 +1,499 @@
+#![cfg_attr(loom, allow(dead_code, unreachable_pub, unused_imports))]
+
+//! Synchronization primitives for use in asynchronous contexts.
+//!
+//! Tokio programs tend to be organized as a set of [tasks] where each task
+//! operates independently and may be executed on separate physical threads. The
+//! synchronization primitives provided in this module permit these independent
+//! tasks to communicate together.
+//!
+//! [tasks]: crate::task
+//!
+//! # Message passing
+//!
+//! The most common form of synchronization in a Tokio program is message
+//! passing. Two tasks operate independently and send messages to each other to
+//! synchronize. Doing so has the advantage of avoiding shared state.
+//!
+//! Message passing is implemented using channels. A channel supports sending a
+//! message from one producer task to one or more consumer tasks. There are a
+//! few flavors of channels provided by Tokio. Each channel flavor supports
+//! different message passing patterns. When a channel supports multiple
+//! producers, many separate tasks may **send** messages. When a channel
+//! supports multiple consumers, many different separate tasks may **receive**
+//! messages.
+//!
+//! Tokio provides many different channel flavors as different message passing
+//! patterns are best handled with different implementations.
+//!
+//! ## `oneshot` channel
+//!
+//! The [`oneshot` channel][oneshot] supports sending a **single** value from a
+//! single producer to a single consumer. This channel is usually used to send
+//! the result of a computation to a waiter.
+//!
+//! **Example:** using a [`oneshot` channel][oneshot] to receive the result of a
+//! computation.
+//!
+//! ```
+//! use tokio::sync::oneshot;
+//!
+//! async fn some_computation() -> String {
+//!     "represents the result of the computation".to_string()
+//! }
+//!
+//! #[tokio::main]
+//! async fn main() {
+//!     let (tx, rx) = oneshot::channel();
+//!
+//!     tokio::spawn(async move {
+//!         let res = some_computation().await;
+//!         tx.send(res).unwrap();
+//!     });
+//!
+//!     // Do other work while the computation is happening in the background
+//!
+//!     // Wait for the computation result
+//!     let res = rx.await.unwrap();
+//! }
+//! ```
+//!
+//! Note, if the task produces a computation result as its final
+//! action before terminating, the [`JoinHandle`] can be used to
+//! receive that value instead of allocating resources for the
+//! `oneshot` channel. Awaiting on [`JoinHandle`] returns `Result`. If
+//! the task panics, the `Joinhandle` yields `Err` with the panic
+//! cause.
+//!
+//! **Example:**
+//!
+//! ```
+//! async fn some_computation() -> String {
+//!     "the result of the computation".to_string()
+//! }
+//!
+//! #[tokio::main]
+//! async fn main() {
+//!     let join_handle = tokio::spawn(async move {
+//!         some_computation().await
+//!     });
+//!
+//!     // Do other work while the computation is happening in the background
+//!
+//!     // Wait for the computation result
+//!     let res = join_handle.await.unwrap();
+//! }
+//! ```
+//!
+//! [oneshot]: oneshot
+//! [`JoinHandle`]: crate::task::JoinHandle
+//!
+//! ## `mpsc` channel
+//!
+//! The [`mpsc` channel][mpsc] supports sending **many** values from **many**
+//! producers to a single consumer. This channel is often used to send work to a
+//! task or to receive the result of many computations.
+//!
+//! **Example:** using an mpsc to incrementally stream the results of a series
+//! of computations.
+//!
+//! ```
+//! use tokio::sync::mpsc;
+//!
+//! async fn some_computation(input: u32) -> String {
+//!     format!("the result of computation {}", input)
+//! }
+//!
+//! #[tokio::main]
+//! async fn main() {
+//!     let (tx, mut rx) = mpsc::channel(100);
+//!
+//!     tokio::spawn(async move {
+//!         for i in 0..10 {
+//!             let res = some_computation(i).await;
+//!             tx.send(res).await.unwrap();
+//!         }
+//!     });
+//!
+//!     while let Some(res) = rx.recv().await {
+//!         println!("got = {}", res);
+//!     }
+//! }
+//! ```
+//!
+//! The argument to `mpsc::channel` is the channel capacity. This is the maximum
+//! number of values that can be stored in the channel pending receipt at any
+//! given time. Properly setting this value is key in implementing robust
+//! programs as the channel capacity plays a critical part in handling back
+//! pressure.
+//!
+//! A common concurrency pattern for resource management is to spawn a task
+//! dedicated to managing that resource and using message passing between other
+//! tasks to interact with the resource. The resource may be anything that may
+//! not be concurrently used. Some examples include a socket and program state.
+//! For example, if multiple tasks need to send data over a single socket, spawn
+//! a task to manage the socket and use a channel to synchronize.
+//!
+//! **Example:** sending data from many tasks over a single socket using message
+//! passing.
+//!
+//! ```no_run
+//! use tokio::io::{self, AsyncWriteExt};
+//! use tokio::net::TcpStream;
+//! use tokio::sync::mpsc;
+//!
+//! #[tokio::main]
+//! async fn main() -> io::Result<()> {
+//!     let mut socket = TcpStream::connect("www.example.com:1234").await?;
+//!     let (tx, mut rx) = mpsc::channel(100);
+//!
+//!     for _ in 0..10 {
+//!         // Each task needs its own `tx` handle. This is done by cloning the
+//!         // original handle.
+//!         let tx = tx.clone();
+//!
+//!         tokio::spawn(async move {
+//!             tx.send(&b"data to write"[..]).await.unwrap();
+//!         });
+//!     }
+//!
+//!     // The `rx` half of the channel returns `None` once **all** `tx` clones
+//!     // drop. To ensure `None` is returned, drop the handle owned by the
+//!     // current task. If this `tx` handle is not dropped, there will always
+//!     // be a single outstanding `tx` handle.
+//!     drop(tx);
+//!
+//!     while let Some(res) = rx.recv().await {
+//!         socket.write_all(res).await?;
+//!     }
+//!
+//!     Ok(())
+//! }
+//! ```
+//!
+//! The [`mpsc`][mpsc] and [`oneshot`][oneshot] channels can be combined to
+//! provide a request / response type synchronization pattern with a shared
+//! resource. A task is spawned to synchronize a resource and waits on commands
+//! received on a [`mpsc`][mpsc] channel. Each command includes a
+//! [`oneshot`][oneshot] `Sender` on which the result of the command is sent.
+//!
+//! **Example:** use a task to synchronize a `u64` counter. Each task sends an
+//! "fetch and increment" command. The counter value **before** the increment is
+//! sent over the provided `oneshot` channel.
+//!
+//! ```
+//! use tokio::sync::{oneshot, mpsc};
+//! use Command::Increment;
+//!
+//! enum Command {
+//!     Increment,
+//!     // Other commands can be added here
+//! }
+//!
+//! #[tokio::main]
+//! async fn main() {
+//!     let (cmd_tx, mut cmd_rx) = mpsc::channel::<(Command, oneshot::Sender<u64>)>(100);
+//!
+//!     // Spawn a task to manage the counter
+//!     tokio::spawn(async move {
+//!         let mut counter: u64 = 0;
+//!
+//!         while let Some((cmd, response)) = cmd_rx.recv().await {
+//!             match cmd {
+//!                 Increment => {
+//!                     let prev = counter;
+//!                     counter += 1;
+//!                     response.send(prev).unwrap();
+//!                 }
+//!             }
+//!         }
+//!     });
+//!
+//!     let mut join_handles = vec![];
+//!
+//!     // Spawn tasks that will send the increment command.
+//!     for _ in 0..10 {
+//!         let cmd_tx = cmd_tx.clone();
+//!
+//!         join_handles.push(tokio::spawn(async move {
+//!             let (resp_tx, resp_rx) = oneshot::channel();
+//!
+//!             cmd_tx.send((Increment, resp_tx)).await.ok().unwrap();
+//!             let res = resp_rx.await.unwrap();
+//!
+//!             println!("previous value = {}", res);
+//!         }));
+//!     }
+//!
+//!     // Wait for all tasks to complete
+//!     for join_handle in join_handles.drain(..) {
+//!         join_handle.await.unwrap();
+//!     }
+//! }
+//! ```
+//!
+//! [mpsc]: mpsc
+//!
+//! ## `broadcast` channel
+//!
+//! The [`broadcast` channel] supports sending **many** values from
+//! **many** producers to **many** consumers. Each consumer will receive
+//! **each** value. This channel can be used to implement "fan out" style
+//! patterns common with pub / sub or "chat" systems.
+//!
+//! This channel tends to be used less often than `oneshot` and `mpsc` but still
+//! has its use cases.
+//!
+//! Basic usage
+//!
+//! ```
+//! use tokio::sync::broadcast;
+//!
+//! #[tokio::main]
+//! async fn main() {
+//!     let (tx, mut rx1) = broadcast::channel(16);
+//!     let mut rx2 = tx.subscribe();
+//!
+//!     tokio::spawn(async move {
+//!         assert_eq!(rx1.recv().await.unwrap(), 10);
+//!         assert_eq!(rx1.recv().await.unwrap(), 20);
+//!     });
+//!
+//!     tokio::spawn(async move {
+//!         assert_eq!(rx2.recv().await.unwrap(), 10);
+//!         assert_eq!(rx2.recv().await.unwrap(), 20);
+//!     });
+//!
+//!     tx.send(10).unwrap();
+//!     tx.send(20).unwrap();
+//! }
+//! ```
+//!
+//! [`broadcast` channel]: crate::sync::broadcast
+//!
+//! ## `watch` channel
+//!
+//! The [`watch` channel] supports sending **many** values from a **single**
+//! producer to **many** consumers. However, only the **most recent** value is
+//! stored in the channel. Consumers are notified when a new value is sent, but
+//! there is no guarantee that consumers will see **all** values.
+//!
+//! The [`watch` channel] is similar to a [`broadcast` channel] with capacity 1.
+//!
+//! Use cases for the [`watch` channel] include broadcasting configuration
+//! changes or signalling program state changes, such as transitioning to
+//! shutdown.
+//!
+//! **Example:** use a [`watch` channel] to notify tasks of configuration
+//! changes. In this example, a configuration file is checked periodically. When
+//! the file changes, the configuration changes are signalled to consumers.
+//!
+//! ```
+//! use tokio::sync::watch;
+//! use tokio::time::{self, Duration, Instant};
+//!
+//! use std::io;
+//!
+//! #[derive(Debug, Clone, Eq, PartialEq)]
+//! struct Config {
+//!     timeout: Duration,
+//! }
+//!
+//! impl Config {
+//!     async fn load_from_file() -> io::Result<Config> {
+//!         // file loading and deserialization logic here
+//! # Ok(Config { timeout: Duration::from_secs(1) })
+//!     }
+//! }
+//!
+//! async fn my_async_operation() {
+//!     // Do something here
+//! }
+//!
+//! #[tokio::main]
+//! async fn main() {
+//!     // Load initial configuration value
+//!     let mut config = Config::load_from_file().await.unwrap();
+//!
+//!     // Create the watch channel, initialized with the loaded configuration
+//!     let (tx, rx) = watch::channel(config.clone());
+//!
+//!     // Spawn a task to monitor the file.
+//!     tokio::spawn(async move {
+//!         loop {
+//!             // Wait 10 seconds between checks
+//!             time::sleep(Duration::from_secs(10)).await;
+//!
+//!             // Load the configuration file
+//!             let new_config = Config::load_from_file().await.unwrap();
+//!
+//!             // If the configuration changed, send the new config value
+//!             // on the watch channel.
+//!             if new_config != config {
+//!                 tx.send(new_config.clone()).unwrap();
+//!                 config = new_config;
+//!             }
+//!         }
+//!     });
+//!
+//!     let mut handles = vec![];
+//!
+//!     // Spawn tasks that runs the async operation for at most `timeout`. If
+//!     // the timeout elapses, restart the operation.
+//!     //
+//!     // The task simultaneously watches the `Config` for changes. When the
+//!     // timeout duration changes, the timeout is updated without restarting
+//!     // the in-flight operation.
+//!     for _ in 0..5 {
+//!         // Clone a config watch handle for use in this task
+//!         let mut rx = rx.clone();
+//!
+//!         let handle = tokio::spawn(async move {
+//!             // Start the initial operation and pin the future to the stack.
+//!             // Pinning to the stack is required to resume the operation
+//!             // across multiple calls to `select!`
+//!             let op = my_async_operation();
+//!             tokio::pin!(op);
+//!
+//!             // Get the initial config value
+//!             let mut conf = rx.borrow().clone();
+//!
+//!             let mut op_start = Instant::now();
+//!             let sleep = time::sleep_until(op_start + conf.timeout);
+//!             tokio::pin!(sleep);
+//!
+//!             loop {
+//!                 tokio::select! {
+//!                     _ = &mut sleep => {
+//!                         // The operation elapsed. Restart it
+//!                         op.set(my_async_operation());
+//!
+//!                         // Track the new start time
+//!                         op_start = Instant::now();
+//!
+//!                         // Restart the timeout
+//!                         sleep.set(time::sleep_until(op_start + conf.timeout));
+//!                     }
+//!                     _ = rx.changed() => {
+//!                         conf = rx.borrow().clone();
+//!
+//!                         // The configuration has been updated. Update the
+//!                         // `sleep` using the new `timeout` value.
+//!                         sleep.as_mut().reset(op_start + conf.timeout);
+//!                     }
+//!                     _ = &mut op => {
+//!                         // The operation completed!
+//!                         return
+//!                     }
+//!                 }
+//!             }
+//!         });
+//!
+//!         handles.push(handle);
+//!     }
+//!
+//!     for handle in handles.drain(..) {
+//!         handle.await.unwrap();
+//!     }
+//! }
+//! ```
+//!
+//! [`watch` channel]: mod@crate::sync::watch
+//! [`broadcast` channel]: mod@crate::sync::broadcast
+//!
+//! # State synchronization
+//!
+//! The remaining synchronization primitives focus on synchronizing state.
+//! These are asynchronous equivalents to versions provided by `std`. They
+//! operate in a similar way as their `std` counterparts but will wait
+//! asynchronously instead of blocking the thread.
+//!
+//! * [`Barrier`](Barrier) Ensures multiple tasks will wait for each other to
+//!   reach a point in the program, before continuing execution all together.
+//!
+//! * [`Mutex`](Mutex) Mutual Exclusion mechanism, which ensures that at most
+//!   one thread at a time is able to access some data.
+//!
+//! * [`Notify`](Notify) Basic task notification. `Notify` supports notifying a
+//!   receiving task without sending data. In this case, the task wakes up and
+//!   resumes processing.
+//!
+//! * [`RwLock`](RwLock) Provides a mutual exclusion mechanism which allows
+//!   multiple readers at the same time, while allowing only one writer at a
+//!   time. In some cases, this can be more efficient than a mutex.
+//!
+//! * [`Semaphore`](Semaphore) Limits the amount of concurrency. A semaphore
+//!   holds a number of permits, which tasks may request in order to enter a
+//!   critical section. Semaphores are useful for implementing limiting or
+//!   bounding of any kind.
+
+cfg_sync! {
+    /// Named future types.
+    pub mod futures {
+        pub use super::notify::Notified;
+    }
+
+    mod barrier;
+    pub use barrier::{Barrier, BarrierWaitResult};
+
+    pub mod broadcast;
+
+    pub mod mpsc;
+
+    mod mutex;
+    pub use mutex::{Mutex, MutexGuard, TryLockError, OwnedMutexGuard, MappedMutexGuard};
+
+    pub(crate) mod notify;
+    pub use notify::Notify;
+
+    pub mod oneshot;
+
+    pub(crate) mod batch_semaphore;
+    pub use batch_semaphore::{AcquireError, TryAcquireError};
+
+    mod semaphore;
+    pub use semaphore::{Semaphore, SemaphorePermit, OwnedSemaphorePermit};
+
+    mod rwlock;
+    pub use rwlock::RwLock;
+    pub use rwlock::owned_read_guard::OwnedRwLockReadGuard;
+    pub use rwlock::owned_write_guard::OwnedRwLockWriteGuard;
+    pub use rwlock::owned_write_guard_mapped::OwnedRwLockMappedWriteGuard;
+    pub use rwlock::read_guard::RwLockReadGuard;
+    pub use rwlock::write_guard::RwLockWriteGuard;
+    pub use rwlock::write_guard_mapped::RwLockMappedWriteGuard;
+
+    mod task;
+    pub(crate) use task::AtomicWaker;
+
+    mod once_cell;
+    pub use self::once_cell::{OnceCell, SetError};
+
+    pub mod watch;
+}
+
+cfg_not_sync! {
+    cfg_fs! {
+        pub(crate) mod batch_semaphore;
+        mod mutex;
+        pub(crate) use mutex::Mutex;
+    }
+
+    #[cfg(any(feature = "rt", feature = "signal", all(unix, feature = "process")))]
+    pub(crate) mod notify;
+
+    #[cfg(any(feature = "rt", all(windows, feature = "process")))]
+    pub(crate) mod oneshot;
+
+    cfg_atomic_waker_impl! {
+        mod task;
+        pub(crate) use task::AtomicWaker;
+    }
+
+    #[cfg(any(feature = "signal", all(unix, feature = "process")))]
+    pub(crate) mod watch;
+}
+
+/// Unit tests
+#[cfg(test)]
+mod tests;
diff --git a/third_party/rust/tokio/src/sync/mpsc/block.rs b/third_party/rust/tokio/src/sync/mpsc/block.rs
new file mode 100644
index 0000000000..58f4a9f6cc
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/mpsc/block.rs
@@ -0,0 +1,385 @@
+use crate::loom::cell::UnsafeCell;
+use crate::loom::sync::atomic::{AtomicPtr, AtomicUsize};
+
+use std::mem::MaybeUninit;
+use std::ops;
+use std::ptr::{self, NonNull};
+use std::sync::atomic::Ordering::{self, AcqRel, Acquire, Release};
+
+/// A block in a linked list.
+///
+/// Each block in the list can hold up to `BLOCK_CAP` messages.
+pub(crate) struct Block<T> {
+    /// The start index of this block.
+    ///
+    /// Slots in this block have indices in `start_index .. start_index + BLOCK_CAP`.
+    start_index: usize,
+
+    /// The next block in the linked list.
+    next: AtomicPtr<Block<T>>,
+
+    /// Bitfield tracking slots that are ready to have their values consumed.
+    ready_slots: AtomicUsize,
+
+    /// The observed `tail_position` value *after* the block has been passed by
+    /// `block_tail`.
+    observed_tail_position: UnsafeCell<usize>,
+
+    /// Array containing values pushed into the block. Values are stored in a
+    /// continuous array in order to improve cache line behavior when reading.
+    /// The values must be manually dropped.
+    values: Values<T>,
+}
+
+pub(crate) enum Read<T> {
+    Value(T),
+    Closed,
+}
+
+struct Values<T>([UnsafeCell<MaybeUninit<T>>; BLOCK_CAP]);
+
+use super::BLOCK_CAP;
+
+/// Masks an index to get the block identifier.
+const BLOCK_MASK: usize = !(BLOCK_CAP - 1);
+
+/// Masks an index to get the value offset in a block.
+const SLOT_MASK: usize = BLOCK_CAP - 1;
+
+/// Flag tracking that a block has gone through the sender's release routine.
+///
+/// When this is set, the receiver may consider freeing the block.
+const RELEASED: usize = 1 << BLOCK_CAP;
+
+/// Flag tracking all senders dropped.
+///
+/// When this flag is set, the send half of the channel has closed.
+const TX_CLOSED: usize = RELEASED << 1;
+
+/// Mask covering all bits used to track slot readiness.
+const READY_MASK: usize = RELEASED - 1;
+
+/// Returns the index of the first slot in the block referenced by `slot_index`.
+#[inline(always)]
+pub(crate) fn start_index(slot_index: usize) -> usize {
+    BLOCK_MASK & slot_index
+}
+
+/// Returns the offset into the block referenced by `slot_index`.
+#[inline(always)]
+pub(crate) fn offset(slot_index: usize) -> usize {
+    SLOT_MASK & slot_index
+}
+
+impl<T> Block<T> {
+    pub(crate) fn new(start_index: usize) -> Block<T> {
+        Block {
+            // The absolute index in the channel of the first slot in the block.
+            start_index,
+
+            // Pointer to the next block in the linked list.
+            next: AtomicPtr::new(ptr::null_mut()),
+
+            ready_slots: AtomicUsize::new(0),
+
+            observed_tail_position: UnsafeCell::new(0),
+
+            // Value storage
+            values: unsafe { Values::uninitialized() },
+        }
+    }
+
+    /// Returns `true` if the block matches the given index.
+    pub(crate) fn is_at_index(&self, index: usize) -> bool {
+        debug_assert!(offset(index) == 0);
+        self.start_index == index
+    }
+
+    /// Returns the number of blocks between `self` and the block at the
+    /// specified index.
+    ///
+    /// `start_index` must represent a block *after* `self`.
+    pub(crate) fn distance(&self, other_index: usize) -> usize {
+        debug_assert!(offset(other_index) == 0);
+        other_index.wrapping_sub(self.start_index) / BLOCK_CAP
+    }
+
+    /// Reads the value at the given offset.
+    ///
+    /// Returns `None` if the slot is empty.
+    ///
+    /// # Safety
+    ///
+    /// To maintain safety, the caller must ensure:
+    ///
+    /// * No concurrent access to the slot.
+    pub(crate) unsafe fn read(&self, slot_index: usize) -> Option<Read<T>> {
+        let offset = offset(slot_index);
+
+        let ready_bits = self.ready_slots.load(Acquire);
+
+        if !is_ready(ready_bits, offset) {
+            if is_tx_closed(ready_bits) {
+                return Some(Read::Closed);
+            }
+
+            return None;
+        }
+
+        // Get the value
+        let value = self.values[offset].with(|ptr| ptr::read(ptr));
+
+        Some(Read::Value(value.assume_init()))
+    }
+
+    /// Writes a value to the block at the given offset.
+    ///
+    /// # Safety
+    ///
+    /// To maintain safety, the caller must ensure:
+    ///
+    /// * The slot is empty.
+    /// * No concurrent access to the slot.
+    pub(crate) unsafe fn write(&self, slot_index: usize, value: T) {
+        // Get the offset into the block
+        let slot_offset = offset(slot_index);
+
+        self.values[slot_offset].with_mut(|ptr| {
+            ptr::write(ptr, MaybeUninit::new(value));
+        });
+
+        // Release the value. After this point, the slot ref may no longer
+        // be used. It is possible for the receiver to free the memory at
+        // any point.
+        self.set_ready(slot_offset);
+    }
+
+    /// Signal to the receiver that the sender half of the list is closed.
+    pub(crate) unsafe fn tx_close(&self) {
+        self.ready_slots.fetch_or(TX_CLOSED, Release);
+    }
+
+    /// Resets the block to a blank state. This enables reusing blocks in the
+    /// channel.
+    ///
+    /// # Safety
+    ///
+    /// To maintain safety, the caller must ensure:
+    ///
+    /// * All slots are empty.
+    /// * The caller holds a unique pointer to the block.
+    pub(crate) unsafe fn reclaim(&mut self) {
+        self.start_index = 0;
+        self.next = AtomicPtr::new(ptr::null_mut());
+        self.ready_slots = AtomicUsize::new(0);
+    }
+
+    /// Releases the block to the rx half for freeing.
+    ///
+    /// This function is called by the tx half once it can be guaranteed that no
+    /// more senders will attempt to access the block.
+    ///
+    /// # Safety
+    ///
+    /// To maintain safety, the caller must ensure:
+    ///
+    /// * The block will no longer be accessed by any sender.
+    pub(crate) unsafe fn tx_release(&self, tail_position: usize) {
+        // Track the observed tail_position. Any sender targeting a greater
+        // tail_position is guaranteed to not access this block.
+        self.observed_tail_position
+            .with_mut(|ptr| *ptr = tail_position);
+
+        // Set the released bit, signalling to the receiver that it is safe to
+        // free the block's memory as soon as all slots **prior** to
+        // `observed_tail_position` have been filled.
+        self.ready_slots.fetch_or(RELEASED, Release);
+    }
+
+    /// Mark a slot as ready
+    fn set_ready(&self, slot: usize) {
+        let mask = 1 << slot;
+        self.ready_slots.fetch_or(mask, Release);
+    }
+
+    /// Returns `true` when all slots have their `ready` bits set.
+    ///
+    /// This indicates that the block is in its final state and will no longer
+    /// be mutated.
+    ///
+    /// # Implementation
+    ///
+    /// The implementation walks each slot checking the `ready` flag. It might
+    /// be that it would make more sense to coalesce ready flags as bits in a
+    /// single atomic cell. However, this could have negative impact on cache
+    /// behavior as there would be many more mutations to a single slot.
+    pub(crate) fn is_final(&self) -> bool {
+        self.ready_slots.load(Acquire) & READY_MASK == READY_MASK
+    }
+
+    /// Returns the `observed_tail_position` value, if set
+    pub(crate) fn observed_tail_position(&self) -> Option<usize> {
+        if 0 == RELEASED & self.ready_slots.load(Acquire) {
+            None
+        } else {
+            Some(self.observed_tail_position.with(|ptr| unsafe { *ptr }))
+        }
+    }
+
+    /// Loads the next block
+    pub(crate) fn load_next(&self, ordering: Ordering) -> Option<NonNull<Block<T>>> {
+        let ret = NonNull::new(self.next.load(ordering));
+
+        debug_assert!(unsafe {
+            ret.map(|block| block.as_ref().start_index == self.start_index.wrapping_add(BLOCK_CAP))
+                .unwrap_or(true)
+        });
+
+        ret
+    }
+
+    /// Pushes `block` as the next block in the link.
+    ///
+    /// Returns Ok if successful, otherwise, a pointer to the next block in
+    /// the list is returned.
+    ///
+    /// This requires that the next pointer is null.
+    ///
+    /// # Ordering
+    ///
+    /// This performs a compare-and-swap on `next` using AcqRel ordering.
+    ///
+    /// # Safety
+    ///
+    /// To maintain safety, the caller must ensure:
+    ///
+    /// * `block` is not freed until it has been removed from the list.
+    pub(crate) unsafe fn try_push(
+        &self,
+        block: &mut NonNull<Block<T>>,
+        success: Ordering,
+        failure: Ordering,
+    ) -> Result<(), NonNull<Block<T>>> {
+        block.as_mut().start_index = self.start_index.wrapping_add(BLOCK_CAP);
+
+        let next_ptr = self
+            .next
+            .compare_exchange(ptr::null_mut(), block.as_ptr(), success, failure)
+            .unwrap_or_else(|x| x);
+
+        match NonNull::new(next_ptr) {
+            Some(next_ptr) => Err(next_ptr),
+            None => Ok(()),
+        }
+    }
+
+    /// Grows the `Block` linked list by allocating and appending a new block.
+    ///
+    /// The next block in the linked list is returned. This may or may not be
+    /// the one allocated by the function call.
+    ///
+    /// # Implementation
+    ///
+    /// It is assumed that `self.next` is null. A new block is allocated with
+    /// `start_index` set to be the next block. A compare-and-swap is performed
+    /// with AcqRel memory ordering. If the compare-and-swap is successful, the
+    /// newly allocated block is released to other threads walking the block
+    /// linked list. If the compare-and-swap fails, the current thread acquires
+    /// the next block in the linked list, allowing the current thread to access
+    /// the slots.
+    pub(crate) fn grow(&self) -> NonNull<Block<T>> {
+        // Create the new block. It is assumed that the block will become the
+        // next one after `&self`. If this turns out to not be the case,
+        // `start_index` is updated accordingly.
+        let new_block = Box::new(Block::new(self.start_index + BLOCK_CAP));
+
+        let mut new_block = unsafe { NonNull::new_unchecked(Box::into_raw(new_block)) };
+
+        // Attempt to store the block. The first compare-and-swap attempt is
+        // "unrolled" due to minor differences in logic
+        //
+        // `AcqRel` is used as the ordering **only** when attempting the
+        // compare-and-swap on self.next.
+        //
+        // If the compare-and-swap fails, then the actual value of the cell is
+        // returned from this function and accessed by the caller. Given this,
+        // the memory must be acquired.
+        //
+        // `Release` ensures that the newly allocated block is available to
+        // other threads acquiring the next pointer.
+        let next = NonNull::new(
+            self.next
+                .compare_exchange(ptr::null_mut(), new_block.as_ptr(), AcqRel, Acquire)
+                .unwrap_or_else(|x| x),
+        );
+
+        let next = match next {
+            Some(next) => next,
+            None => {
+                // The compare-and-swap succeeded and the newly allocated block
+                // is successfully pushed.
+                return new_block;
+            }
+        };
+
+        // There already is a next block in the linked list. The newly allocated
+        // block could be dropped and the discovered next block returned;
+        // however, that would be wasteful. Instead, the linked list is walked
+        // by repeatedly attempting to compare-and-swap the pointer into the
+        // `next` register until the compare-and-swap succeed.
+        //
+        // Care is taken to update new_block's start_index field as appropriate.
+
+        let mut curr = next;
+
+        // TODO: Should this iteration be capped?
+        loop {
+            let actual = unsafe { curr.as_ref().try_push(&mut new_block, AcqRel, Acquire) };
+
+            curr = match actual {
+                Ok(_) => {
+                    return next;
+                }
+                Err(curr) => curr,
+            };
+
+            crate::loom::thread::yield_now();
+        }
+    }
+}
+
+/// Returns `true` if the specified slot has a value ready to be consumed.
+fn is_ready(bits: usize, slot: usize) -> bool {
+    let mask = 1 << slot;
+    mask == mask & bits
+}
+
+/// Returns `true` if the closed flag has been set.
+fn is_tx_closed(bits: usize) -> bool {
+    TX_CLOSED == bits & TX_CLOSED
+}
+
+impl<T> Values<T> {
+    unsafe fn uninitialized() -> Values<T> {
+        let mut vals = MaybeUninit::uninit();
+
+        // When fuzzing, `UnsafeCell` needs to be initialized.
+        if_loom! {
+            let p = vals.as_mut_ptr() as *mut UnsafeCell<MaybeUninit<T>>;
+            for i in 0..BLOCK_CAP {
+                p.add(i)
+                    .write(UnsafeCell::new(MaybeUninit::uninit()));
+            }
+        }
+
+        Values(vals.assume_init())
+    }
+}
+
+impl<T> ops::Index<usize> for Values<T> {
+    type Output = UnsafeCell<MaybeUninit<T>>;
+
+    fn index(&self, index: usize) -> &Self::Output {
+        self.0.index(index)
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/mpsc/bounded.rs b/third_party/rust/tokio/src/sync/mpsc/bounded.rs
new file mode 100644
index 0000000000..ddded8ebb3
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/mpsc/bounded.rs
@@ -0,0 +1,1197 @@
+use crate::sync::batch_semaphore::{self as semaphore, TryAcquireError};
+use crate::sync::mpsc::chan;
+use crate::sync::mpsc::error::{SendError, TryRecvError, TrySendError};
+
+cfg_time! {
+    use crate::sync::mpsc::error::SendTimeoutError;
+    use crate::time::Duration;
+}
+
+use std::fmt;
+use std::task::{Context, Poll};
+
+/// Sends values to the associated `Receiver`.
+///
+/// Instances are created by the [`channel`](channel) function.
+///
+/// To convert the `Sender` into a `Sink` or use it in a poll function, you can
+/// use the [`PollSender`] utility.
+///
+/// [`PollSender`]: https://docs.rs/tokio-util/0.6/tokio_util/sync/struct.PollSender.html
+pub struct Sender<T> {
+    chan: chan::Tx<T, Semaphore>,
+}
+
+/// Permits to send one value into the channel.
+///
+/// `Permit` values are returned by [`Sender::reserve()`] and [`Sender::try_reserve()`]
+/// and are used to guarantee channel capacity before generating a message to send.
+///
+/// [`Sender::reserve()`]: Sender::reserve
+/// [`Sender::try_reserve()`]: Sender::try_reserve
+pub struct Permit<'a, T> {
+    chan: &'a chan::Tx<T, Semaphore>,
+}
+
+/// Owned permit to send one value into the channel.
+///
+/// This is identical to the [`Permit`] type, except that it moves the sender
+/// rather than borrowing it.
+///
+/// `OwnedPermit` values are returned by [`Sender::reserve_owned()`] and
+/// [`Sender::try_reserve_owned()`] and are used to guarantee channel capacity
+/// before generating a message to send.
+///
+/// [`Permit`]: Permit
+/// [`Sender::reserve_owned()`]: Sender::reserve_owned
+/// [`Sender::try_reserve_owned()`]: Sender::try_reserve_owned
+pub struct OwnedPermit<T> {
+    chan: Option<chan::Tx<T, Semaphore>>,
+}
+
+/// Receives values from the associated `Sender`.
+///
+/// Instances are created by the [`channel`](channel) function.
+///
+/// This receiver can be turned into a `Stream` using [`ReceiverStream`].
+///
+/// [`ReceiverStream`]: https://docs.rs/tokio-stream/0.1/tokio_stream/wrappers/struct.ReceiverStream.html
+pub struct Receiver<T> {
+    /// The channel receiver.
+    chan: chan::Rx<T, Semaphore>,
+}
+
+/// Creates a bounded mpsc channel for communicating between asynchronous tasks
+/// with backpressure.
+///
+/// The channel will buffer up to the provided number of messages.  Once the
+/// buffer is full, attempts to send new messages will wait until a message is
+/// received from the channel. The provided buffer capacity must be at least 1.
+///
+/// All data sent on `Sender` will become available on `Receiver` in the same
+/// order as it was sent.
+///
+/// The `Sender` can be cloned to `send` to the same channel from multiple code
+/// locations. Only one `Receiver` is supported.
+///
+/// If the `Receiver` is disconnected while trying to `send`, the `send` method
+/// will return a `SendError`. Similarly, if `Sender` is disconnected while
+/// trying to `recv`, the `recv` method will return `None`.
+///
+/// # Panics
+///
+/// Panics if the buffer capacity is 0.
+///
+/// # Examples
+///
+/// ```rust
+/// use tokio::sync::mpsc;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let (tx, mut rx) = mpsc::channel(100);
+///
+///     tokio::spawn(async move {
+///         for i in 0..10 {
+///             if let Err(_) = tx.send(i).await {
+///                 println!("receiver dropped");
+///                 return;
+///             }
+///         }
+///     });
+///
+///     while let Some(i) = rx.recv().await {
+///         println!("got = {}", i);
+///     }
+/// }
+/// ```
+pub fn channel<T>(buffer: usize) -> (Sender<T>, Receiver<T>) {
+    assert!(buffer > 0, "mpsc bounded channel requires buffer > 0");
+    let semaphore = (semaphore::Semaphore::new(buffer), buffer);
+    let (tx, rx) = chan::channel(semaphore);
+
+    let tx = Sender::new(tx);
+    let rx = Receiver::new(rx);
+
+    (tx, rx)
+}
+
+/// Channel semaphore is a tuple of the semaphore implementation and a `usize`
+/// representing the channel bound.
+type Semaphore = (semaphore::Semaphore, usize);
+
+impl<T> Receiver<T> {
+    pub(crate) fn new(chan: chan::Rx<T, Semaphore>) -> Receiver<T> {
+        Receiver { chan }
+    }
+
+    /// Receives the next value for this receiver.
+    ///
+    /// This method returns `None` if the channel has been closed and there are
+    /// no remaining messages in the channel's buffer. This indicates that no
+    /// further values can ever be received from this `Receiver`. The channel is
+    /// closed when all senders have been dropped, or when [`close`] is called.
+    ///
+    /// If there are no messages in the channel's buffer, but the channel has
+    /// not yet been closed, this method will sleep until a message is sent or
+    /// the channel is closed.  Note that if [`close`] is called, but there are
+    /// still outstanding [`Permits`] from before it was closed, the channel is
+    /// not considered closed by `recv` until the permits are released.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. If `recv` is used as the event in a
+    /// [`tokio::select!`](crate::select) statement and some other branch
+    /// completes first, it is guaranteed that no messages were received on this
+    /// channel.
+    ///
+    /// [`close`]: Self::close
+    /// [`Permits`]: struct@crate::sync::mpsc::Permit
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::channel(100);
+    ///
+    ///     tokio::spawn(async move {
+    ///         tx.send("hello").await.unwrap();
+    ///     });
+    ///
+    ///     assert_eq!(Some("hello"), rx.recv().await);
+    ///     assert_eq!(None, rx.recv().await);
+    /// }
+    /// ```
+    ///
+    /// Values are buffered:
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::channel(100);
+    ///
+    ///     tx.send("hello").await.unwrap();
+    ///     tx.send("world").await.unwrap();
+    ///
+    ///     assert_eq!(Some("hello"), rx.recv().await);
+    ///     assert_eq!(Some("world"), rx.recv().await);
+    /// }
+    /// ```
+    pub async fn recv(&mut self) -> Option<T> {
+        use crate::future::poll_fn;
+        poll_fn(|cx| self.chan.recv(cx)).await
+    }
+
+    /// Tries to receive the next value for this receiver.
+    ///
+    /// This method returns the [`Empty`] error if the channel is currently
+    /// empty, but there are still outstanding [senders] or [permits].
+    ///
+    /// This method returns the [`Disconnected`] error if the channel is
+    /// currently empty, and there are no outstanding [senders] or [permits].
+    ///
+    /// Unlike the [`poll_recv`] method, this method will never return an
+    /// [`Empty`] error spuriously.
+    ///
+    /// [`Empty`]: crate::sync::mpsc::error::TryRecvError::Empty
+    /// [`Disconnected`]: crate::sync::mpsc::error::TryRecvError::Disconnected
+    /// [`poll_recv`]: Self::poll_recv
+    /// [senders]: crate::sync::mpsc::Sender
+    /// [permits]: crate::sync::mpsc::Permit
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    /// use tokio::sync::mpsc::error::TryRecvError;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::channel(100);
+    ///
+    ///     tx.send("hello").await.unwrap();
+    ///
+    ///     assert_eq!(Ok("hello"), rx.try_recv());
+    ///     assert_eq!(Err(TryRecvError::Empty), rx.try_recv());
+    ///
+    ///     tx.send("hello").await.unwrap();
+    ///     // Drop the last sender, closing the channel.
+    ///     drop(tx);
+    ///
+    ///     assert_eq!(Ok("hello"), rx.try_recv());
+    ///     assert_eq!(Err(TryRecvError::Disconnected), rx.try_recv());
+    /// }
+    /// ```
+    pub fn try_recv(&mut self) -> Result<T, TryRecvError> {
+        self.chan.try_recv()
+    }
+
+    /// Blocking receive to call outside of asynchronous contexts.
+    ///
+    /// This method returns `None` if the channel has been closed and there are
+    /// no remaining messages in the channel's buffer. This indicates that no
+    /// further values can ever be received from this `Receiver`. The channel is
+    /// closed when all senders have been dropped, or when [`close`] is called.
+    ///
+    /// If there are no messages in the channel's buffer, but the channel has
+    /// not yet been closed, this method will block until a message is sent or
+    /// the channel is closed.
+    ///
+    /// This method is intended for use cases where you are sending from
+    /// asynchronous code to synchronous code, and will work even if the sender
+    /// is not using [`blocking_send`] to send the message.
+    ///
+    /// Note that if [`close`] is called, but there are still outstanding
+    /// [`Permits`] from before it was closed, the channel is not considered
+    /// closed by `blocking_recv` until the permits are released.
+    ///
+    /// [`close`]: Self::close
+    /// [`Permits`]: struct@crate::sync::mpsc::Permit
+    /// [`blocking_send`]: fn@crate::sync::mpsc::Sender::blocking_send
+    ///
+    /// # Panics
+    ///
+    /// This function panics if called within an asynchronous execution
+    /// context.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::thread;
+    /// use tokio::runtime::Runtime;
+    /// use tokio::sync::mpsc;
+    ///
+    /// fn main() {
+    ///     let (tx, mut rx) = mpsc::channel::<u8>(10);
+    ///
+    ///     let sync_code = thread::spawn(move || {
+    ///         assert_eq!(Some(10), rx.blocking_recv());
+    ///     });
+    ///
+    ///     Runtime::new()
+    ///         .unwrap()
+    ///         .block_on(async move {
+    ///             let _ = tx.send(10).await;
+    ///         });
+    ///     sync_code.join().unwrap()
+    /// }
+    /// ```
+    #[cfg(feature = "sync")]
+    pub fn blocking_recv(&mut self) -> Option<T> {
+        crate::future::block_on(self.recv())
+    }
+
+    /// Closes the receiving half of a channel without dropping it.
+    ///
+    /// This prevents any further messages from being sent on the channel while
+    /// still enabling the receiver to drain messages that are buffered. Any
+    /// outstanding [`Permit`] values will still be able to send messages.
+    ///
+    /// To guarantee that no messages are dropped, after calling `close()`,
+    /// `recv()` must be called until `None` is returned. If there are
+    /// outstanding [`Permit`] or [`OwnedPermit`] values, the `recv` method will
+    /// not return `None` until those are released.
+    ///
+    /// [`Permit`]: Permit
+    /// [`OwnedPermit`]: OwnedPermit
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::channel(20);
+    ///
+    ///     tokio::spawn(async move {
+    ///         let mut i = 0;
+    ///         while let Ok(permit) = tx.reserve().await {
+    ///             permit.send(i);
+    ///             i += 1;
+    ///         }
+    ///     });
+    ///
+    ///     rx.close();
+    ///
+    ///     while let Some(msg) = rx.recv().await {
+    ///         println!("got {}", msg);
+    ///     }
+    ///
+    ///     // Channel closed and no messages are lost.
+    /// }
+    /// ```
+    pub fn close(&mut self) {
+        self.chan.close();
+    }
+
+    /// Polls to receive the next message on this channel.
+    ///
+    /// This method returns:
+    ///
+    ///  * `Poll::Pending` if no messages are available but the channel is not
+    ///    closed, or if a spurious failure happens.
+    ///  * `Poll::Ready(Some(message))` if a message is available.
+    ///  * `Poll::Ready(None)` if the channel has been closed and all messages
+    ///    sent before it was closed have been received.
+    ///
+    /// When the method returns `Poll::Pending`, the `Waker` in the provided
+    /// `Context` is scheduled to receive a wakeup when a message is sent on any
+    /// receiver, or when the channel is closed.  Note that on multiple calls to
+    /// `poll_recv`, only the `Waker` from the `Context` passed to the most
+    /// recent call is scheduled to receive a wakeup.
+    ///
+    /// If this method returns `Poll::Pending` due to a spurious failure, then
+    /// the `Waker` will be notified when the situation causing the spurious
+    /// failure has been resolved. Note that receiving such a wakeup does not
+    /// guarantee that the next call will succeed — it could fail with another
+    /// spurious failure.
+    pub fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<T>> {
+        self.chan.recv(cx)
+    }
+}
+
+impl<T> fmt::Debug for Receiver<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Receiver")
+            .field("chan", &self.chan)
+            .finish()
+    }
+}
+
+impl<T> Unpin for Receiver<T> {}
+
+impl<T> Sender<T> {
+    pub(crate) fn new(chan: chan::Tx<T, Semaphore>) -> Sender<T> {
+        Sender { chan }
+    }
+
+    /// Sends a value, waiting until there is capacity.
+    ///
+    /// A successful send occurs when it is determined that the other end of the
+    /// channel has not hung up already. An unsuccessful send would be one where
+    /// the corresponding receiver has already been closed. Note that a return
+    /// value of `Err` means that the data will never be received, but a return
+    /// value of `Ok` does not mean that the data will be received. It is
+    /// possible for the corresponding receiver to hang up immediately after
+    /// this function returns `Ok`.
+    ///
+    /// # Errors
+    ///
+    /// If the receive half of the channel is closed, either due to [`close`]
+    /// being called or the [`Receiver`] handle dropping, the function returns
+    /// an error. The error includes the value passed to `send`.
+    ///
+    /// [`close`]: Receiver::close
+    /// [`Receiver`]: Receiver
+    ///
+    /// # Cancel safety
+    ///
+    /// If `send` is used as the event in a [`tokio::select!`](crate::select)
+    /// statement and some other branch completes first, then it is guaranteed
+    /// that the message was not sent.
+    ///
+    /// This channel uses a queue to ensure that calls to `send` and `reserve`
+    /// complete in the order they were requested.  Cancelling a call to
+    /// `send` makes you lose your place in the queue.
+    ///
+    /// # Examples
+    ///
+    /// In the following example, each call to `send` will block until the
+    /// previously sent value was received.
+    ///
+    /// ```rust
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::channel(1);
+    ///
+    ///     tokio::spawn(async move {
+    ///         for i in 0..10 {
+    ///             if let Err(_) = tx.send(i).await {
+    ///                 println!("receiver dropped");
+    ///                 return;
+    ///             }
+    ///         }
+    ///     });
+    ///
+    ///     while let Some(i) = rx.recv().await {
+    ///         println!("got = {}", i);
+    ///     }
+    /// }
+    /// ```
+    pub async fn send(&self, value: T) -> Result<(), SendError<T>> {
+        match self.reserve().await {
+            Ok(permit) => {
+                permit.send(value);
+                Ok(())
+            }
+            Err(_) => Err(SendError(value)),
+        }
+    }
+
+    /// Completes when the receiver has dropped.
+    ///
+    /// This allows the producers to get notified when interest in the produced
+    /// values is canceled and immediately stop doing work.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once the channel is closed, it stays closed
+    /// forever and all future calls to `closed` will return immediately.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx1, rx) = mpsc::channel::<()>(1);
+    ///     let tx2 = tx1.clone();
+    ///     let tx3 = tx1.clone();
+    ///     let tx4 = tx1.clone();
+    ///     let tx5 = tx1.clone();
+    ///     tokio::spawn(async move {
+    ///         drop(rx);
+    ///     });
+    ///
+    ///     futures::join!(
+    ///         tx1.closed(),
+    ///         tx2.closed(),
+    ///         tx3.closed(),
+    ///         tx4.closed(),
+    ///         tx5.closed()
+    ///     );
+    ///     println!("Receiver dropped");
+    /// }
+    /// ```
+    pub async fn closed(&self) {
+        self.chan.closed().await
+    }
+
+    /// Attempts to immediately send a message on this `Sender`
+    ///
+    /// This method differs from [`send`] by returning immediately if the channel's
+    /// buffer is full or no receiver is waiting to acquire some data. Compared
+    /// with [`send`], this function has two failure cases instead of one (one for
+    /// disconnection, one for a full buffer).
+    ///
+    /// # Errors
+    ///
+    /// If the channel capacity has been reached, i.e., the channel has `n`
+    /// buffered values where `n` is the argument passed to [`channel`], then an
+    /// error is returned.
+    ///
+    /// If the receive half of the channel is closed, either due to [`close`]
+    /// being called or the [`Receiver`] handle dropping, the function returns
+    /// an error. The error includes the value passed to `send`.
+    ///
+    /// [`send`]: Sender::send
+    /// [`channel`]: channel
+    /// [`close`]: Receiver::close
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     // Create a channel with buffer size 1
+    ///     let (tx1, mut rx) = mpsc::channel(1);
+    ///     let tx2 = tx1.clone();
+    ///
+    ///     tokio::spawn(async move {
+    ///         tx1.send(1).await.unwrap();
+    ///         tx1.send(2).await.unwrap();
+    ///         // task waits until the receiver receives a value.
+    ///     });
+    ///
+    ///     tokio::spawn(async move {
+    ///         // This will return an error and send
+    ///         // no message if the buffer is full
+    ///         let _ = tx2.try_send(3);
+    ///     });
+    ///
+    ///     let mut msg;
+    ///     msg = rx.recv().await.unwrap();
+    ///     println!("message {} received", msg);
+    ///
+    ///     msg = rx.recv().await.unwrap();
+    ///     println!("message {} received", msg);
+    ///
+    ///     // Third message may have never been sent
+    ///     match rx.recv().await {
+    ///         Some(msg) => println!("message {} received", msg),
+    ///         None => println!("the third message was never sent"),
+    ///     }
+    /// }
+    /// ```
+    pub fn try_send(&self, message: T) -> Result<(), TrySendError<T>> {
+        match self.chan.semaphore().0.try_acquire(1) {
+            Ok(_) => {}
+            Err(TryAcquireError::Closed) => return Err(TrySendError::Closed(message)),
+            Err(TryAcquireError::NoPermits) => return Err(TrySendError::Full(message)),
+        }
+
+        // Send the message
+        self.chan.send(message);
+        Ok(())
+    }
+
+    /// Sends a value, waiting until there is capacity, but only for a limited time.
+    ///
+    /// Shares the same success and error conditions as [`send`], adding one more
+    /// condition for an unsuccessful send, which is when the provided timeout has
+    /// elapsed, and there is no capacity available.
+    ///
+    /// [`send`]: Sender::send
+    ///
+    /// # Errors
+    ///
+    /// If the receive half of the channel is closed, either due to [`close`]
+    /// being called or the [`Receiver`] having been dropped,
+    /// the function returns an error. The error includes the value passed to `send`.
+    ///
+    /// [`close`]: Receiver::close
+    /// [`Receiver`]: Receiver
+    ///
+    /// # Panics
+    ///
+    /// This function panics if it is called outside the context of a Tokio
+    /// runtime [with time enabled](crate::runtime::Builder::enable_time).
+    ///
+    /// # Examples
+    ///
+    /// In the following example, each call to `send_timeout` will block until the
+    /// previously sent value was received, unless the timeout has elapsed.
+    ///
+    /// ```rust
+    /// use tokio::sync::mpsc;
+    /// use tokio::time::{sleep, Duration};
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::channel(1);
+    ///
+    ///     tokio::spawn(async move {
+    ///         for i in 0..10 {
+    ///             if let Err(e) = tx.send_timeout(i, Duration::from_millis(100)).await {
+    ///                 println!("send error: #{:?}", e);
+    ///                 return;
+    ///             }
+    ///         }
+    ///     });
+    ///
+    ///     while let Some(i) = rx.recv().await {
+    ///         println!("got = {}", i);
+    ///         sleep(Duration::from_millis(200)).await;
+    ///     }
+    /// }
+    /// ```
+    #[cfg(feature = "time")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "time")))]
+    pub async fn send_timeout(
+        &self,
+        value: T,
+        timeout: Duration,
+    ) -> Result<(), SendTimeoutError<T>> {
+        let permit = match crate::time::timeout(timeout, self.reserve()).await {
+            Err(_) => {
+                return Err(SendTimeoutError::Timeout(value));
+            }
+            Ok(Err(_)) => {
+                return Err(SendTimeoutError::Closed(value));
+            }
+            Ok(Ok(permit)) => permit,
+        };
+
+        permit.send(value);
+        Ok(())
+    }
+
+    /// Blocking send to call outside of asynchronous contexts.
+    ///
+    /// This method is intended for use cases where you are sending from
+    /// synchronous code to asynchronous code, and will work even if the
+    /// receiver is not using [`blocking_recv`] to receive the message.
+    ///
+    /// [`blocking_recv`]: fn@crate::sync::mpsc::Receiver::blocking_recv
+    ///
+    /// # Panics
+    ///
+    /// This function panics if called within an asynchronous execution
+    /// context.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::thread;
+    /// use tokio::runtime::Runtime;
+    /// use tokio::sync::mpsc;
+    ///
+    /// fn main() {
+    ///     let (tx, mut rx) = mpsc::channel::<u8>(1);
+    ///
+    ///     let sync_code = thread::spawn(move || {
+    ///         tx.blocking_send(10).unwrap();
+    ///     });
+    ///
+    ///     Runtime::new().unwrap().block_on(async move {
+    ///         assert_eq!(Some(10), rx.recv().await);
+    ///     });
+    ///     sync_code.join().unwrap()
+    /// }
+    /// ```
+    #[cfg(feature = "sync")]
+    pub fn blocking_send(&self, value: T) -> Result<(), SendError<T>> {
+        crate::future::block_on(self.send(value))
+    }
+
+    /// Checks if the channel has been closed. This happens when the
+    /// [`Receiver`] is dropped, or when the [`Receiver::close`] method is
+    /// called.
+    ///
+    /// [`Receiver`]: crate::sync::mpsc::Receiver
+    /// [`Receiver::close`]: crate::sync::mpsc::Receiver::close
+    ///
+    /// ```
+    /// let (tx, rx) = tokio::sync::mpsc::channel::<()>(42);
+    /// assert!(!tx.is_closed());
+    ///
+    /// let tx2 = tx.clone();
+    /// assert!(!tx2.is_closed());
+    ///
+    /// drop(rx);
+    /// assert!(tx.is_closed());
+    /// assert!(tx2.is_closed());
+    /// ```
+    pub fn is_closed(&self) -> bool {
+        self.chan.is_closed()
+    }
+
+    /// Waits for channel capacity. Once capacity to send one message is
+    /// available, it is reserved for the caller.
+    ///
+    /// If the channel is full, the function waits for the number of unreceived
+    /// messages to become less than the channel capacity. Capacity to send one
+    /// message is reserved for the caller. A [`Permit`] is returned to track
+    /// the reserved capacity. The [`send`] function on [`Permit`] consumes the
+    /// reserved capacity.
+    ///
+    /// Dropping [`Permit`] without sending a message releases the capacity back
+    /// to the channel.
+    ///
+    /// [`Permit`]: Permit
+    /// [`send`]: Permit::send
+    ///
+    /// # Cancel safety
+    ///
+    /// This channel uses a queue to ensure that calls to `send` and `reserve`
+    /// complete in the order they were requested.  Cancelling a call to
+    /// `reserve` makes you lose your place in the queue.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::channel(1);
+    ///
+    ///     // Reserve capacity
+    ///     let permit = tx.reserve().await.unwrap();
+    ///
+    ///     // Trying to send directly on the `tx` will fail due to no
+    ///     // available capacity.
+    ///     assert!(tx.try_send(123).is_err());
+    ///
+    ///     // Sending on the permit succeeds
+    ///     permit.send(456);
+    ///
+    ///     // The value sent on the permit is received
+    ///     assert_eq!(rx.recv().await.unwrap(), 456);
+    /// }
+    /// ```
+    pub async fn reserve(&self) -> Result<Permit<'_, T>, SendError<()>> {
+        self.reserve_inner().await?;
+        Ok(Permit { chan: &self.chan })
+    }
+
+    /// Waits for channel capacity, moving the `Sender` and returning an owned
+    /// permit. Once capacity to send one message is available, it is reserved
+    /// for the caller.
+    ///
+    /// This moves the sender _by value_, and returns an owned permit that can
+    /// be used to send a message into the channel. Unlike [`Sender::reserve`],
+    /// this method may be used in cases where the permit must be valid for the
+    /// `'static` lifetime. `Sender`s may be cloned cheaply (`Sender::clone` is
+    /// essentially a reference count increment, comparable to [`Arc::clone`]),
+    /// so when multiple [`OwnedPermit`]s are needed or the `Sender` cannot be
+    /// moved, it can be cloned prior to calling `reserve_owned`.
+    ///
+    /// If the channel is full, the function waits for the number of unreceived
+    /// messages to become less than the channel capacity. Capacity to send one
+    /// message is reserved for the caller. An [`OwnedPermit`] is returned to
+    /// track the reserved capacity. The [`send`] function on [`OwnedPermit`]
+    /// consumes the reserved capacity.
+    ///
+    /// Dropping the [`OwnedPermit`] without sending a message releases the
+    /// capacity back to the channel.
+    ///
+    /// # Cancel safety
+    ///
+    /// This channel uses a queue to ensure that calls to `send` and `reserve`
+    /// complete in the order they were requested.  Cancelling a call to
+    /// `reserve_owned` makes you lose your place in the queue.
+    ///
+    /// # Examples
+    /// Sending a message using an [`OwnedPermit`]:
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::channel(1);
+    ///
+    ///     // Reserve capacity, moving the sender.
+    ///     let permit = tx.reserve_owned().await.unwrap();
+    ///
+    ///     // Send a message, consuming the permit and returning
+    ///     // the moved sender.
+    ///     let tx = permit.send(123);
+    ///
+    ///     // The value sent on the permit is received.
+    ///     assert_eq!(rx.recv().await.unwrap(), 123);
+    ///
+    ///     // The sender can now be used again.
+    ///     tx.send(456).await.unwrap();
+    /// }
+    /// ```
+    ///
+    /// When multiple [`OwnedPermit`]s are needed, or the sender cannot be moved
+    /// by value, it can be inexpensively cloned before calling `reserve_owned`:
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::channel(1);
+    ///
+    ///     // Clone the sender and reserve capacity.
+    ///     let permit = tx.clone().reserve_owned().await.unwrap();
+    ///
+    ///     // Trying to send directly on the `tx` will fail due to no
+    ///     // available capacity.
+    ///     assert!(tx.try_send(123).is_err());
+    ///
+    ///     // Sending on the permit succeeds.
+    ///     permit.send(456);
+    ///
+    ///     // The value sent on the permit is received
+    ///     assert_eq!(rx.recv().await.unwrap(), 456);
+    /// }
+    /// ```
+    ///
+    /// [`Sender::reserve`]: Sender::reserve
+    /// [`OwnedPermit`]: OwnedPermit
+    /// [`send`]: OwnedPermit::send
+    /// [`Arc::clone`]: std::sync::Arc::clone
+    pub async fn reserve_owned(self) -> Result<OwnedPermit<T>, SendError<()>> {
+        self.reserve_inner().await?;
+        Ok(OwnedPermit {
+            chan: Some(self.chan),
+        })
+    }
+
+    async fn reserve_inner(&self) -> Result<(), SendError<()>> {
+        match self.chan.semaphore().0.acquire(1).await {
+            Ok(_) => Ok(()),
+            Err(_) => Err(SendError(())),
+        }
+    }
+
+    /// Tries to acquire a slot in the channel without waiting for the slot to become
+    /// available.
+    ///
+    /// If the channel is full this function will return [`TrySendError`], otherwise
+    /// if there is a slot available it will return a [`Permit`] that will then allow you
+    /// to [`send`] on the channel with a guaranteed slot. This function is similar to
+    /// [`reserve`] except it does not await for the slot to become available.
+    ///
+    /// Dropping [`Permit`] without sending a message releases the capacity back
+    /// to the channel.
+    ///
+    /// [`Permit`]: Permit
+    /// [`send`]: Permit::send
+    /// [`reserve`]: Sender::reserve
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::channel(1);
+    ///
+    ///     // Reserve capacity
+    ///     let permit = tx.try_reserve().unwrap();
+    ///
+    ///     // Trying to send directly on the `tx` will fail due to no
+    ///     // available capacity.
+    ///     assert!(tx.try_send(123).is_err());
+    ///
+    ///     // Trying to reserve an additional slot on the `tx` will
+    ///     // fail because there is no capacity.
+    ///     assert!(tx.try_reserve().is_err());
+    ///
+    ///     // Sending on the permit succeeds
+    ///     permit.send(456);
+    ///
+    ///     // The value sent on the permit is received
+    ///     assert_eq!(rx.recv().await.unwrap(), 456);
+    ///
+    /// }
+    /// ```
+    pub fn try_reserve(&self) -> Result<Permit<'_, T>, TrySendError<()>> {
+        match self.chan.semaphore().0.try_acquire(1) {
+            Ok(_) => {}
+            Err(TryAcquireError::Closed) => return Err(TrySendError::Closed(())),
+            Err(TryAcquireError::NoPermits) => return Err(TrySendError::Full(())),
+        }
+
+        Ok(Permit { chan: &self.chan })
+    }
+
+    /// Tries to acquire a slot in the channel without waiting for the slot to become
+    /// available, returning an owned permit.
+    ///
+    /// This moves the sender _by value_, and returns an owned permit that can
+    /// be used to send a message into the channel. Unlike [`Sender::try_reserve`],
+    /// this method may be used in cases where the permit must be valid for the
+    /// `'static` lifetime.  `Sender`s may be cloned cheaply (`Sender::clone` is
+    /// essentially a reference count increment, comparable to [`Arc::clone`]),
+    /// so when multiple [`OwnedPermit`]s are needed or the `Sender` cannot be
+    /// moved, it can be cloned prior to calling `try_reserve_owned`.
+    ///
+    /// If the channel is full this function will return a [`TrySendError`].
+    /// Since the sender is taken by value, the `TrySendError` returned in this
+    /// case contains the sender, so that it may be used again. Otherwise, if
+    /// there is a slot available, this method will return an [`OwnedPermit`]
+    /// that can then be used to [`send`] on the channel with a guaranteed slot.
+    /// This function is similar to  [`reserve_owned`] except it does not await
+    /// for the slot to become available.
+    ///
+    /// Dropping the [`OwnedPermit`] without sending a message releases the capacity back
+    /// to the channel.
+    ///
+    /// [`OwnedPermit`]: OwnedPermit
+    /// [`send`]: OwnedPermit::send
+    /// [`reserve_owned`]: Sender::reserve_owned
+    /// [`Arc::clone`]: std::sync::Arc::clone
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::channel(1);
+    ///
+    ///     // Reserve capacity
+    ///     let permit = tx.clone().try_reserve_owned().unwrap();
+    ///
+    ///     // Trying to send directly on the `tx` will fail due to no
+    ///     // available capacity.
+    ///     assert!(tx.try_send(123).is_err());
+    ///
+    ///     // Trying to reserve an additional slot on the `tx` will
+    ///     // fail because there is no capacity.
+    ///     assert!(tx.try_reserve().is_err());
+    ///
+    ///     // Sending on the permit succeeds
+    ///     permit.send(456);
+    ///
+    ///     // The value sent on the permit is received
+    ///     assert_eq!(rx.recv().await.unwrap(), 456);
+    ///
+    /// }
+    /// ```
+    pub fn try_reserve_owned(self) -> Result<OwnedPermit<T>, TrySendError<Self>> {
+        match self.chan.semaphore().0.try_acquire(1) {
+            Ok(_) => {}
+            Err(TryAcquireError::Closed) => return Err(TrySendError::Closed(self)),
+            Err(TryAcquireError::NoPermits) => return Err(TrySendError::Full(self)),
+        }
+
+        Ok(OwnedPermit {
+            chan: Some(self.chan),
+        })
+    }
+
+    /// Returns `true` if senders belong to the same channel.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let (tx, rx) = tokio::sync::mpsc::channel::<()>(1);
+    /// let  tx2 = tx.clone();
+    /// assert!(tx.same_channel(&tx2));
+    ///
+    /// let (tx3, rx3) = tokio::sync::mpsc::channel::<()>(1);
+    /// assert!(!tx3.same_channel(&tx2));
+    /// ```
+    pub fn same_channel(&self, other: &Self) -> bool {
+        self.chan.same_channel(&other.chan)
+    }
+
+    /// Returns the current capacity of the channel.
+    ///
+    /// The capacity goes down when sending a value by calling [`send`] or by reserving capacity
+    /// with [`reserve`]. The capacity goes up when values are received by the [`Receiver`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::channel::<()>(5);
+    ///
+    ///     assert_eq!(tx.capacity(), 5);
+    ///
+    ///     // Making a reservation drops the capacity by one.
+    ///     let permit = tx.reserve().await.unwrap();
+    ///     assert_eq!(tx.capacity(), 4);
+    ///
+    ///     // Sending and receiving a value increases the capacity by one.
+    ///     permit.send(());
+    ///     rx.recv().await.unwrap();
+    ///     assert_eq!(tx.capacity(), 5);
+    /// }
+    /// ```
+    ///
+    /// [`send`]: Sender::send
+    /// [`reserve`]: Sender::reserve
+    pub fn capacity(&self) -> usize {
+        self.chan.semaphore().0.available_permits()
+    }
+}
+
+impl<T> Clone for Sender<T> {
+    fn clone(&self) -> Self {
+        Sender {
+            chan: self.chan.clone(),
+        }
+    }
+}
+
+impl<T> fmt::Debug for Sender<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Sender")
+            .field("chan", &self.chan)
+            .finish()
+    }
+}
+
+// ===== impl Permit =====
+
+impl<T> Permit<'_, T> {
+    /// Sends a value using the reserved capacity.
+    ///
+    /// Capacity for the message has already been reserved. The message is sent
+    /// to the receiver and the permit is consumed. The operation will succeed
+    /// even if the receiver half has been closed. See [`Receiver::close`] for
+    /// more details on performing a clean shutdown.
+    ///
+    /// [`Receiver::close`]: Receiver::close
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::channel(1);
+    ///
+    ///     // Reserve capacity
+    ///     let permit = tx.reserve().await.unwrap();
+    ///
+    ///     // Trying to send directly on the `tx` will fail due to no
+    ///     // available capacity.
+    ///     assert!(tx.try_send(123).is_err());
+    ///
+    ///     // Send a message on the permit
+    ///     permit.send(456);
+    ///
+    ///     // The value sent on the permit is received
+    ///     assert_eq!(rx.recv().await.unwrap(), 456);
+    /// }
+    /// ```
+    pub fn send(self, value: T) {
+        use std::mem;
+
+        self.chan.send(value);
+
+        // Avoid the drop logic
+        mem::forget(self);
+    }
+}
+
+impl<T> Drop for Permit<'_, T> {
+    fn drop(&mut self) {
+        use chan::Semaphore;
+
+        let semaphore = self.chan.semaphore();
+
+        // Add the permit back to the semaphore
+        semaphore.add_permit();
+
+        // If this is the last sender for this channel, wake the receiver so
+        // that it can be notified that the channel is closed.
+        if semaphore.is_closed() && semaphore.is_idle() {
+            self.chan.wake_rx();
+        }
+    }
+}
+
+impl<T> fmt::Debug for Permit<'_, T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Permit")
+            .field("chan", &self.chan)
+            .finish()
+    }
+}
+
+// ===== impl Permit =====
+
+impl<T> OwnedPermit<T> {
+    /// Sends a value using the reserved capacity.
+    ///
+    /// Capacity for the message has already been reserved. The message is sent
+    /// to the receiver and the permit is consumed. The operation will succeed
+    /// even if the receiver half has been closed. See [`Receiver::close`] for
+    /// more details on performing a clean shutdown.
+    ///
+    /// Unlike [`Permit::send`], this method returns the [`Sender`] from which
+    /// the `OwnedPermit` was reserved.
+    ///
+    /// [`Receiver::close`]: Receiver::close
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::channel(1);
+    ///
+    ///     // Reserve capacity
+    ///     let permit = tx.reserve_owned().await.unwrap();
+    ///
+    ///     // Send a message on the permit, returning the sender.
+    ///     let tx = permit.send(456);
+    ///
+    ///     // The value sent on the permit is received
+    ///     assert_eq!(rx.recv().await.unwrap(), 456);
+    ///
+    ///     // We may now reuse `tx` to send another message.
+    ///     tx.send(789).await.unwrap();
+    /// }
+    /// ```
+    pub fn send(mut self, value: T) -> Sender<T> {
+        let chan = self.chan.take().unwrap_or_else(|| {
+            unreachable!("OwnedPermit channel is only taken when the permit is moved")
+        });
+        chan.send(value);
+
+        Sender { chan }
+    }
+
+    /// Releases the reserved capacity *without* sending a message, returning the
+    /// [`Sender`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, rx) = mpsc::channel(1);
+    ///
+    ///     // Clone the sender and reserve capacity
+    ///     let permit = tx.clone().reserve_owned().await.unwrap();
+    ///
+    ///     // Trying to send on the original `tx` will fail, since the `permit`
+    ///     // has reserved all the available capacity.
+    ///     assert!(tx.try_send(123).is_err());
+    ///
+    ///     // Release the permit without sending a message, returning the clone
+    ///     // of the sender.
+    ///     let tx2 = permit.release();
+    ///
+    ///     // We may now reuse `tx` to send another message.
+    ///     tx.send(789).await.unwrap();
+    ///     # drop(rx); drop(tx2);
+    /// }
+    /// ```
+    ///
+    /// [`Sender`]: Sender
+    pub fn release(mut self) -> Sender<T> {
+        use chan::Semaphore;
+
+        let chan = self.chan.take().unwrap_or_else(|| {
+            unreachable!("OwnedPermit channel is only taken when the permit is moved")
+        });
+
+        // Add the permit back to the semaphore
+        chan.semaphore().add_permit();
+        Sender { chan }
+    }
+}
+
+impl<T> Drop for OwnedPermit<T> {
+    fn drop(&mut self) {
+        use chan::Semaphore;
+
+        // Are we still holding onto the sender?
+        if let Some(chan) = self.chan.take() {
+            let semaphore = chan.semaphore();
+
+            // Add the permit back to the semaphore
+            semaphore.add_permit();
+
+            // If this `OwnedPermit` is holding the last sender for this
+            // channel, wake the receiver so that it can be notified that the
+            // channel is closed.
+            if semaphore.is_closed() && semaphore.is_idle() {
+                chan.wake_rx();
+            }
+        }
+
+        // Otherwise, do nothing.
+    }
+}
+
+impl<T> fmt::Debug for OwnedPermit<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("OwnedPermit")
+            .field("chan", &self.chan)
+            .finish()
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/mpsc/chan.rs b/third_party/rust/tokio/src/sync/mpsc/chan.rs
new file mode 100644
index 0000000000..c3007de89c
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/mpsc/chan.rs
@@ -0,0 +1,405 @@
+use crate::loom::cell::UnsafeCell;
+use crate::loom::future::AtomicWaker;
+use crate::loom::sync::atomic::AtomicUsize;
+use crate::loom::sync::Arc;
+use crate::park::thread::CachedParkThread;
+use crate::park::Park;
+use crate::sync::mpsc::error::TryRecvError;
+use crate::sync::mpsc::list;
+use crate::sync::notify::Notify;
+
+use std::fmt;
+use std::process;
+use std::sync::atomic::Ordering::{AcqRel, Relaxed};
+use std::task::Poll::{Pending, Ready};
+use std::task::{Context, Poll};
+
+/// Channel sender.
+pub(crate) struct Tx<T, S> {
+    inner: Arc<Chan<T, S>>,
+}
+
+impl<T, S: fmt::Debug> fmt::Debug for Tx<T, S> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Tx").field("inner", &self.inner).finish()
+    }
+}
+
+/// Channel receiver.
+pub(crate) struct Rx<T, S: Semaphore> {
+    inner: Arc<Chan<T, S>>,
+}
+
+impl<T, S: Semaphore + fmt::Debug> fmt::Debug for Rx<T, S> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Rx").field("inner", &self.inner).finish()
+    }
+}
+
+pub(crate) trait Semaphore {
+    fn is_idle(&self) -> bool;
+
+    fn add_permit(&self);
+
+    fn close(&self);
+
+    fn is_closed(&self) -> bool;
+}
+
+struct Chan<T, S> {
+    /// Notifies all tasks listening for the receiver being dropped.
+    notify_rx_closed: Notify,
+
+    /// Handle to the push half of the lock-free list.
+    tx: list::Tx<T>,
+
+    /// Coordinates access to channel's capacity.
+    semaphore: S,
+
+    /// Receiver waker. Notified when a value is pushed into the channel.
+    rx_waker: AtomicWaker,
+
+    /// Tracks the number of outstanding sender handles.
+    ///
+    /// When this drops to zero, the send half of the channel is closed.
+    tx_count: AtomicUsize,
+
+    /// Only accessed by `Rx` handle.
+    rx_fields: UnsafeCell<RxFields<T>>,
+}
+
+impl<T, S> fmt::Debug for Chan<T, S>
+where
+    S: fmt::Debug,
+{
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Chan")
+            .field("tx", &self.tx)
+            .field("semaphore", &self.semaphore)
+            .field("rx_waker", &self.rx_waker)
+            .field("tx_count", &self.tx_count)
+            .field("rx_fields", &"...")
+            .finish()
+    }
+}
+
+/// Fields only accessed by `Rx` handle.
+struct RxFields<T> {
+    /// Channel receiver. This field is only accessed by the `Receiver` type.
+    list: list::Rx<T>,
+
+    /// `true` if `Rx::close` is called.
+    rx_closed: bool,
+}
+
+impl<T> fmt::Debug for RxFields<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("RxFields")
+            .field("list", &self.list)
+            .field("rx_closed", &self.rx_closed)
+            .finish()
+    }
+}
+
+unsafe impl<T: Send, S: Send> Send for Chan<T, S> {}
+unsafe impl<T: Send, S: Sync> Sync for Chan<T, S> {}
+
+pub(crate) fn channel<T, S: Semaphore>(semaphore: S) -> (Tx<T, S>, Rx<T, S>) {
+    let (tx, rx) = list::channel();
+
+    let chan = Arc::new(Chan {
+        notify_rx_closed: Notify::new(),
+        tx,
+        semaphore,
+        rx_waker: AtomicWaker::new(),
+        tx_count: AtomicUsize::new(1),
+        rx_fields: UnsafeCell::new(RxFields {
+            list: rx,
+            rx_closed: false,
+        }),
+    });
+
+    (Tx::new(chan.clone()), Rx::new(chan))
+}
+
+// ===== impl Tx =====
+
+impl<T, S> Tx<T, S> {
+    fn new(chan: Arc<Chan<T, S>>) -> Tx<T, S> {
+        Tx { inner: chan }
+    }
+
+    pub(super) fn semaphore(&self) -> &S {
+        &self.inner.semaphore
+    }
+
+    /// Send a message and notify the receiver.
+    pub(crate) fn send(&self, value: T) {
+        self.inner.send(value);
+    }
+
+    /// Wake the receive half
+    pub(crate) fn wake_rx(&self) {
+        self.inner.rx_waker.wake();
+    }
+
+    /// Returns `true` if senders belong to the same channel.
+    pub(crate) fn same_channel(&self, other: &Self) -> bool {
+        Arc::ptr_eq(&self.inner, &other.inner)
+    }
+}
+
+impl<T, S: Semaphore> Tx<T, S> {
+    pub(crate) fn is_closed(&self) -> bool {
+        self.inner.semaphore.is_closed()
+    }
+
+    pub(crate) async fn closed(&self) {
+        // In order to avoid a race condition, we first request a notification,
+        // **then** check whether the semaphore is closed. If the semaphore is
+        // closed the notification request is dropped.
+        let notified = self.inner.notify_rx_closed.notified();
+
+        if self.inner.semaphore.is_closed() {
+            return;
+        }
+        notified.await;
+    }
+}
+
+impl<T, S> Clone for Tx<T, S> {
+    fn clone(&self) -> Tx<T, S> {
+        // Using a Relaxed ordering here is sufficient as the caller holds a
+        // strong ref to `self`, preventing a concurrent decrement to zero.
+        self.inner.tx_count.fetch_add(1, Relaxed);
+
+        Tx {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+impl<T, S> Drop for Tx<T, S> {
+    fn drop(&mut self) {
+        if self.inner.tx_count.fetch_sub(1, AcqRel) != 1 {
+            return;
+        }
+
+        // Close the list, which sends a `Close` message
+        self.inner.tx.close();
+
+        // Notify the receiver
+        self.wake_rx();
+    }
+}
+
+// ===== impl Rx =====
+
+impl<T, S: Semaphore> Rx<T, S> {
+    fn new(chan: Arc<Chan<T, S>>) -> Rx<T, S> {
+        Rx { inner: chan }
+    }
+
+    pub(crate) fn close(&mut self) {
+        self.inner.rx_fields.with_mut(|rx_fields_ptr| {
+            let rx_fields = unsafe { &mut *rx_fields_ptr };
+
+            if rx_fields.rx_closed {
+                return;
+            }
+
+            rx_fields.rx_closed = true;
+        });
+
+        self.inner.semaphore.close();
+        self.inner.notify_rx_closed.notify_waiters();
+    }
+
+    /// Receive the next value
+    pub(crate) fn recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<T>> {
+        use super::block::Read::*;
+
+        // Keep track of task budget
+        let coop = ready!(crate::coop::poll_proceed(cx));
+
+        self.inner.rx_fields.with_mut(|rx_fields_ptr| {
+            let rx_fields = unsafe { &mut *rx_fields_ptr };
+
+            macro_rules! try_recv {
+                () => {
+                    match rx_fields.list.pop(&self.inner.tx) {
+                        Some(Value(value)) => {
+                            self.inner.semaphore.add_permit();
+                            coop.made_progress();
+                            return Ready(Some(value));
+                        }
+                        Some(Closed) => {
+                            // TODO: This check may not be required as it most
+                            // likely can only return `true` at this point. A
+                            // channel is closed when all tx handles are
+                            // dropped. Dropping a tx handle releases memory,
+                            // which ensures that if dropping the tx handle is
+                            // visible, then all messages sent are also visible.
+                            assert!(self.inner.semaphore.is_idle());
+                            coop.made_progress();
+                            return Ready(None);
+                        }
+                        None => {} // fall through
+                    }
+                };
+            }
+
+            try_recv!();
+
+            self.inner.rx_waker.register_by_ref(cx.waker());
+
+            // It is possible that a value was pushed between attempting to read
+            // and registering the task, so we have to check the channel a
+            // second time here.
+            try_recv!();
+
+            if rx_fields.rx_closed && self.inner.semaphore.is_idle() {
+                coop.made_progress();
+                Ready(None)
+            } else {
+                Pending
+            }
+        })
+    }
+
+    /// Try to receive the next value.
+    pub(crate) fn try_recv(&mut self) -> Result<T, TryRecvError> {
+        use super::list::TryPopResult;
+
+        self.inner.rx_fields.with_mut(|rx_fields_ptr| {
+            let rx_fields = unsafe { &mut *rx_fields_ptr };
+
+            macro_rules! try_recv {
+                () => {
+                    match rx_fields.list.try_pop(&self.inner.tx) {
+                        TryPopResult::Ok(value) => {
+                            self.inner.semaphore.add_permit();
+                            return Ok(value);
+                        }
+                        TryPopResult::Closed => return Err(TryRecvError::Disconnected),
+                        TryPopResult::Empty => return Err(TryRecvError::Empty),
+                        TryPopResult::Busy => {} // fall through
+                    }
+                };
+            }
+
+            try_recv!();
+
+            // If a previous `poll_recv` call has set a waker, we wake it here.
+            // This allows us to put our own CachedParkThread waker in the
+            // AtomicWaker slot instead.
+            //
+            // This is not a spurious wakeup to `poll_recv` since we just got a
+            // Busy from `try_pop`, which only happens if there are messages in
+            // the queue.
+            self.inner.rx_waker.wake();
+
+            // Park the thread until the problematic send has completed.
+            let mut park = CachedParkThread::new();
+            let waker = park.unpark().into_waker();
+            loop {
+                self.inner.rx_waker.register_by_ref(&waker);
+                // It is possible that the problematic send has now completed,
+                // so we have to check for messages again.
+                try_recv!();
+                park.park().expect("park failed");
+            }
+        })
+    }
+}
+
+impl<T, S: Semaphore> Drop for Rx<T, S> {
+    fn drop(&mut self) {
+        use super::block::Read::Value;
+
+        self.close();
+
+        self.inner.rx_fields.with_mut(|rx_fields_ptr| {
+            let rx_fields = unsafe { &mut *rx_fields_ptr };
+
+            while let Some(Value(_)) = rx_fields.list.pop(&self.inner.tx) {
+                self.inner.semaphore.add_permit();
+            }
+        })
+    }
+}
+
+// ===== impl Chan =====
+
+impl<T, S> Chan<T, S> {
+    fn send(&self, value: T) {
+        // Push the value
+        self.tx.push(value);
+
+        // Notify the rx task
+        self.rx_waker.wake();
+    }
+}
+
+impl<T, S> Drop for Chan<T, S> {
+    fn drop(&mut self) {
+        use super::block::Read::Value;
+
+        // Safety: the only owner of the rx fields is Chan, and eing
+        // inside its own Drop means we're the last ones to touch it.
+        self.rx_fields.with_mut(|rx_fields_ptr| {
+            let rx_fields = unsafe { &mut *rx_fields_ptr };
+
+            while let Some(Value(_)) = rx_fields.list.pop(&self.tx) {}
+            unsafe { rx_fields.list.free_blocks() };
+        });
+    }
+}
+
+// ===== impl Semaphore for (::Semaphore, capacity) =====
+
+impl Semaphore for (crate::sync::batch_semaphore::Semaphore, usize) {
+    fn add_permit(&self) {
+        self.0.release(1)
+    }
+
+    fn is_idle(&self) -> bool {
+        self.0.available_permits() == self.1
+    }
+
+    fn close(&self) {
+        self.0.close();
+    }
+
+    fn is_closed(&self) -> bool {
+        self.0.is_closed()
+    }
+}
+
+// ===== impl Semaphore for AtomicUsize =====
+
+use std::sync::atomic::Ordering::{Acquire, Release};
+use std::usize;
+
+impl Semaphore for AtomicUsize {
+    fn add_permit(&self) {
+        let prev = self.fetch_sub(2, Release);
+
+        if prev >> 1 == 0 {
+            // Something went wrong
+            process::abort();
+        }
+    }
+
+    fn is_idle(&self) -> bool {
+        self.load(Acquire) >> 1 == 0
+    }
+
+    fn close(&self) {
+        self.fetch_or(1, Release);
+    }
+
+    fn is_closed(&self) -> bool {
+        self.load(Acquire) & 1 == 1
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/mpsc/error.rs b/third_party/rust/tokio/src/sync/mpsc/error.rs
new file mode 100644
index 0000000000..3fe6bac5e1
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/mpsc/error.rs
@@ -0,0 +1,125 @@
+//! Channel error types.
+
+use std::error::Error;
+use std::fmt;
+
+/// Error returned by the `Sender`.
+#[derive(Debug)]
+pub struct SendError<T>(pub T);
+
+impl<T> fmt::Display for SendError<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(fmt, "channel closed")
+    }
+}
+
+impl<T: fmt::Debug> std::error::Error for SendError<T> {}
+
+// ===== TrySendError =====
+
+/// This enumeration is the list of the possible error outcomes for the
+/// [try_send](super::Sender::try_send) method.
+#[derive(Debug, Eq, PartialEq)]
+pub enum TrySendError<T> {
+    /// The data could not be sent on the channel because the channel is
+    /// currently full and sending would require blocking.
+    Full(T),
+
+    /// The receive half of the channel was explicitly closed or has been
+    /// dropped.
+    Closed(T),
+}
+
+impl<T: fmt::Debug> Error for TrySendError<T> {}
+
+impl<T> fmt::Display for TrySendError<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(
+            fmt,
+            "{}",
+            match self {
+                TrySendError::Full(..) => "no available capacity",
+                TrySendError::Closed(..) => "channel closed",
+            }
+        )
+    }
+}
+
+impl<T> From<SendError<T>> for TrySendError<T> {
+    fn from(src: SendError<T>) -> TrySendError<T> {
+        TrySendError::Closed(src.0)
+    }
+}
+
+// ===== TryRecvError =====
+
+/// Error returned by `try_recv`.
+#[derive(PartialEq, Eq, Clone, Copy, Debug)]
+pub enum TryRecvError {
+    /// This **channel** is currently empty, but the **Sender**(s) have not yet
+    /// disconnected, so data may yet become available.
+    Empty,
+    /// The **channel**'s sending half has become disconnected, and there will
+    /// never be any more data received on it.
+    Disconnected,
+}
+
+impl fmt::Display for TryRecvError {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            TryRecvError::Empty => "receiving on an empty channel".fmt(fmt),
+            TryRecvError::Disconnected => "receiving on a closed channel".fmt(fmt),
+        }
+    }
+}
+
+impl Error for TryRecvError {}
+
+// ===== RecvError =====
+
+/// Error returned by `Receiver`.
+#[derive(Debug)]
+#[doc(hidden)]
+#[deprecated(note = "This type is unused because recv returns an Option.")]
+pub struct RecvError(());
+
+#[allow(deprecated)]
+impl fmt::Display for RecvError {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(fmt, "channel closed")
+    }
+}
+
+#[allow(deprecated)]
+impl Error for RecvError {}
+
+cfg_time! {
+    // ===== SendTimeoutError =====
+
+    #[derive(Debug, Eq, PartialEq)]
+    /// Error returned by [`Sender::send_timeout`](super::Sender::send_timeout)].
+    pub enum SendTimeoutError<T> {
+        /// The data could not be sent on the channel because the channel is
+        /// full, and the timeout to send has elapsed.
+        Timeout(T),
+
+        /// The receive half of the channel was explicitly closed or has been
+        /// dropped.
+        Closed(T),
+    }
+
+    impl<T: fmt::Debug> Error for SendTimeoutError<T> {}
+
+    impl<T> fmt::Display for SendTimeoutError<T> {
+        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+            write!(
+                fmt,
+                "{}",
+                match self {
+                    SendTimeoutError::Timeout(..) => "timed out waiting on send operation",
+                    SendTimeoutError::Closed(..) => "channel closed",
+                }
+            )
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/mpsc/list.rs b/third_party/rust/tokio/src/sync/mpsc/list.rs
new file mode 100644
index 0000000000..e4eeb45411
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/mpsc/list.rs
@@ -0,0 +1,371 @@
+//! A concurrent, lock-free, FIFO list.
+
+use crate::loom::sync::atomic::{AtomicPtr, AtomicUsize};
+use crate::loom::thread;
+use crate::sync::mpsc::block::{self, Block};
+
+use std::fmt;
+use std::ptr::NonNull;
+use std::sync::atomic::Ordering::{AcqRel, Acquire, Relaxed, Release};
+
+/// List queue transmit handle.
+pub(crate) struct Tx<T> {
+    /// Tail in the `Block` mpmc list.
+    block_tail: AtomicPtr<Block<T>>,
+
+    /// Position to push the next message. This references a block and offset
+    /// into the block.
+    tail_position: AtomicUsize,
+}
+
+/// List queue receive handle
+pub(crate) struct Rx<T> {
+    /// Pointer to the block being processed.
+    head: NonNull<Block<T>>,
+
+    /// Next slot index to process.
+    index: usize,
+
+    /// Pointer to the next block pending release.
+    free_head: NonNull<Block<T>>,
+}
+
+/// Return value of `Rx::try_pop`.
+pub(crate) enum TryPopResult<T> {
+    /// Successfully popped a value.
+    Ok(T),
+    /// The channel is empty.
+    Empty,
+    /// The channel is empty and closed.
+    Closed,
+    /// The channel is not empty, but the first value is being written.
+    Busy,
+}
+
+pub(crate) fn channel<T>() -> (Tx<T>, Rx<T>) {
+    // Create the initial block shared between the tx and rx halves.
+    let initial_block = Box::new(Block::new(0));
+    let initial_block_ptr = Box::into_raw(initial_block);
+
+    let tx = Tx {
+        block_tail: AtomicPtr::new(initial_block_ptr),
+        tail_position: AtomicUsize::new(0),
+    };
+
+    let head = NonNull::new(initial_block_ptr).unwrap();
+
+    let rx = Rx {
+        head,
+        index: 0,
+        free_head: head,
+    };
+
+    (tx, rx)
+}
+
+impl<T> Tx<T> {
+    /// Pushes a value into the list.
+    pub(crate) fn push(&self, value: T) {
+        // First, claim a slot for the value. `Acquire` is used here to
+        // synchronize with the `fetch_add` in `reclaim_blocks`.
+        let slot_index = self.tail_position.fetch_add(1, Acquire);
+
+        // Load the current block and write the value
+        let block = self.find_block(slot_index);
+
+        unsafe {
+            // Write the value to the block
+            block.as_ref().write(slot_index, value);
+        }
+    }
+
+    /// Closes the send half of the list.
+    ///
+    /// Similar process as pushing a value, but instead of writing the value &
+    /// setting the ready flag, the TX_CLOSED flag is set on the block.
+    pub(crate) fn close(&self) {
+        // First, claim a slot for the value. This is the last slot that will be
+        // claimed.
+        let slot_index = self.tail_position.fetch_add(1, Acquire);
+
+        let block = self.find_block(slot_index);
+
+        unsafe { block.as_ref().tx_close() }
+    }
+
+    fn find_block(&self, slot_index: usize) -> NonNull<Block<T>> {
+        // The start index of the block that contains `index`.
+        let start_index = block::start_index(slot_index);
+
+        // The index offset into the block
+        let offset = block::offset(slot_index);
+
+        // Load the current head of the block
+        let mut block_ptr = self.block_tail.load(Acquire);
+
+        let block = unsafe { &*block_ptr };
+
+        // Calculate the distance between the tail ptr and the target block
+        let distance = block.distance(start_index);
+
+        // Decide if this call to `find_block` should attempt to update the
+        // `block_tail` pointer.
+        //
+        // Updating `block_tail` is not always performed in order to reduce
+        // contention.
+        //
+        // When set, as the routine walks the linked list, it attempts to update
+        // `block_tail`. If the update cannot be performed, `try_updating_tail`
+        // is unset.
+        let mut try_updating_tail = distance > offset;
+
+        // Walk the linked list of blocks until the block with `start_index` is
+        // found.
+        loop {
+            let block = unsafe { &(*block_ptr) };
+
+            if block.is_at_index(start_index) {
+                return unsafe { NonNull::new_unchecked(block_ptr) };
+            }
+
+            let next_block = block
+                .load_next(Acquire)
+                // There is no allocated next block, grow the linked list.
+                .unwrap_or_else(|| block.grow());
+
+            // If the block is **not** final, then the tail pointer cannot be
+            // advanced any more.
+            try_updating_tail &= block.is_final();
+
+            if try_updating_tail {
+                // Advancing `block_tail` must happen when walking the linked
+                // list. `block_tail` may not advance passed any blocks that are
+                // not "final". At the point a block is finalized, it is unknown
+                // if there are any prior blocks that are unfinalized, which
+                // makes it impossible to advance `block_tail`.
+                //
+                // While walking the linked list, `block_tail` can be advanced
+                // as long as finalized blocks are traversed.
+                //
+                // Release ordering is used to ensure that any subsequent reads
+                // are able to see the memory pointed to by `block_tail`.
+                //
+                // Acquire is not needed as any "actual" value is not accessed.
+                // At this point, the linked list is walked to acquire blocks.
+                if self
+                    .block_tail
+                    .compare_exchange(block_ptr, next_block.as_ptr(), Release, Relaxed)
+                    .is_ok()
+                {
+                    // Synchronize with any senders
+                    let tail_position = self.tail_position.fetch_add(0, Release);
+
+                    unsafe {
+                        block.tx_release(tail_position);
+                    }
+                } else {
+                    // A concurrent sender is also working on advancing
+                    // `block_tail` and this thread is falling behind.
+                    //
+                    // Stop trying to advance the tail pointer
+                    try_updating_tail = false;
+                }
+            }
+
+            block_ptr = next_block.as_ptr();
+
+            thread::yield_now();
+        }
+    }
+
+    pub(crate) unsafe fn reclaim_block(&self, mut block: NonNull<Block<T>>) {
+        // The block has been removed from the linked list and ownership
+        // is reclaimed.
+        //
+        // Before dropping the block, see if it can be reused by
+        // inserting it back at the end of the linked list.
+        //
+        // First, reset the data
+        block.as_mut().reclaim();
+
+        let mut reused = false;
+
+        // Attempt to insert the block at the end
+        //
+        // Walk at most three times
+        //
+        let curr_ptr = self.block_tail.load(Acquire);
+
+        // The pointer can never be null
+        debug_assert!(!curr_ptr.is_null());
+
+        let mut curr = NonNull::new_unchecked(curr_ptr);
+
+        // TODO: Unify this logic with Block::grow
+        for _ in 0..3 {
+            match curr.as_ref().try_push(&mut block, AcqRel, Acquire) {
+                Ok(_) => {
+                    reused = true;
+                    break;
+                }
+                Err(next) => {
+                    curr = next;
+                }
+            }
+        }
+
+        if !reused {
+            let _ = Box::from_raw(block.as_ptr());
+        }
+    }
+}
+
+impl<T> fmt::Debug for Tx<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Tx")
+            .field("block_tail", &self.block_tail.load(Relaxed))
+            .field("tail_position", &self.tail_position.load(Relaxed))
+            .finish()
+    }
+}
+
+impl<T> Rx<T> {
+    /// Pops the next value off the queue.
+    pub(crate) fn pop(&mut self, tx: &Tx<T>) -> Option<block::Read<T>> {
+        // Advance `head`, if needed
+        if !self.try_advancing_head() {
+            return None;
+        }
+
+        self.reclaim_blocks(tx);
+
+        unsafe {
+            let block = self.head.as_ref();
+
+            let ret = block.read(self.index);
+
+            if let Some(block::Read::Value(..)) = ret {
+                self.index = self.index.wrapping_add(1);
+            }
+
+            ret
+        }
+    }
+
+    /// Pops the next value off the queue, detecting whether the block
+    /// is busy or empty on failure.
+    ///
+    /// This function exists because `Rx::pop` can return `None` even if the
+    /// channel's queue contains a message that has been completely written.
+    /// This can happen if the fully delivered message is behind another message
+    /// that is in the middle of being written to the block, since the channel
+    /// can't return the messages out of order.
+    pub(crate) fn try_pop(&mut self, tx: &Tx<T>) -> TryPopResult<T> {
+        let tail_position = tx.tail_position.load(Acquire);
+        let result = self.pop(tx);
+
+        match result {
+            Some(block::Read::Value(t)) => TryPopResult::Ok(t),
+            Some(block::Read::Closed) => TryPopResult::Closed,
+            None if tail_position == self.index => TryPopResult::Empty,
+            None => TryPopResult::Busy,
+        }
+    }
+
+    /// Tries advancing the block pointer to the block referenced by `self.index`.
+    ///
+    /// Returns `true` if successful, `false` if there is no next block to load.
+    fn try_advancing_head(&mut self) -> bool {
+        let block_index = block::start_index(self.index);
+
+        loop {
+            let next_block = {
+                let block = unsafe { self.head.as_ref() };
+
+                if block.is_at_index(block_index) {
+                    return true;
+                }
+
+                block.load_next(Acquire)
+            };
+
+            let next_block = match next_block {
+                Some(next_block) => next_block,
+                None => {
+                    return false;
+                }
+            };
+
+            self.head = next_block;
+
+            thread::yield_now();
+        }
+    }
+
+    fn reclaim_blocks(&mut self, tx: &Tx<T>) {
+        while self.free_head != self.head {
+            unsafe {
+                // Get a handle to the block that will be freed and update
+                // `free_head` to point to the next block.
+                let block = self.free_head;
+
+                let observed_tail_position = block.as_ref().observed_tail_position();
+
+                let required_index = match observed_tail_position {
+                    Some(i) => i,
+                    None => return,
+                };
+
+                if required_index > self.index {
+                    return;
+                }
+
+                // We may read the next pointer with `Relaxed` ordering as it is
+                // guaranteed that the `reclaim_blocks` routine trails the `recv`
+                // routine. Any memory accessed by `reclaim_blocks` has already
+                // been acquired by `recv`.
+                let next_block = block.as_ref().load_next(Relaxed);
+
+                // Update the free list head
+                self.free_head = next_block.unwrap();
+
+                // Push the emptied block onto the back of the queue, making it
+                // available to senders.
+                tx.reclaim_block(block);
+            }
+
+            thread::yield_now();
+        }
+    }
+
+    /// Effectively `Drop` all the blocks. Should only be called once, when
+    /// the list is dropping.
+    pub(super) unsafe fn free_blocks(&mut self) {
+        debug_assert_ne!(self.free_head, NonNull::dangling());
+
+        let mut cur = Some(self.free_head);
+
+        #[cfg(debug_assertions)]
+        {
+            // to trigger the debug assert above so as to catch that we
+            // don't call `free_blocks` more than once.
+            self.free_head = NonNull::dangling();
+            self.head = NonNull::dangling();
+        }
+
+        while let Some(block) = cur {
+            cur = block.as_ref().load_next(Relaxed);
+            drop(Box::from_raw(block.as_ptr()));
+        }
+    }
+}
+
+impl<T> fmt::Debug for Rx<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Rx")
+            .field("head", &self.head)
+            .field("index", &self.index)
+            .field("free_head", &self.free_head)
+            .finish()
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/mpsc/mod.rs b/third_party/rust/tokio/src/sync/mpsc/mod.rs
new file mode 100644
index 0000000000..b1513a9da5
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/mpsc/mod.rs
@@ -0,0 +1,115 @@
+#![cfg_attr(not(feature = "sync"), allow(dead_code, unreachable_pub))]
+
+//! A multi-producer, single-consumer queue for sending values between
+//! asynchronous tasks.
+//!
+//! This module provides two variants of the channel: bounded and unbounded. The
+//! bounded variant has a limit on the number of messages that the channel can
+//! store, and if this limit is reached, trying to send another message will
+//! wait until a message is received from the channel. An unbounded channel has
+//! an infinite capacity, so the `send` method will always complete immediately.
+//! This makes the [`UnboundedSender`] usable from both synchronous and
+//! asynchronous code.
+//!
+//! Similar to the `mpsc` channels provided by `std`, the channel constructor
+//! functions provide separate send and receive handles, [`Sender`] and
+//! [`Receiver`] for the bounded channel, [`UnboundedSender`] and
+//! [`UnboundedReceiver`] for the unbounded channel. If there is no message to read,
+//! the current task will be notified when a new value is sent. [`Sender`] and
+//! [`UnboundedSender`] allow sending values into the channel. If the bounded
+//! channel is at capacity, the send is rejected and the task will be notified
+//! when additional capacity is available. In other words, the channel provides
+//! backpressure.
+//!
+//!
+//! # Disconnection
+//!
+//! When all [`Sender`] handles have been dropped, it is no longer
+//! possible to send values into the channel. This is considered the termination
+//! event of the stream. As such, `Receiver::poll` returns `Ok(Ready(None))`.
+//!
+//! If the [`Receiver`] handle is dropped, then messages can no longer
+//! be read out of the channel. In this case, all further attempts to send will
+//! result in an error.
+//!
+//! # Clean Shutdown
+//!
+//! When the [`Receiver`] is dropped, it is possible for unprocessed messages to
+//! remain in the channel. Instead, it is usually desirable to perform a "clean"
+//! shutdown. To do this, the receiver first calls `close`, which will prevent
+//! any further messages to be sent into the channel. Then, the receiver
+//! consumes the channel to completion, at which point the receiver can be
+//! dropped.
+//!
+//! # Communicating between sync and async code
+//!
+//! When you want to communicate between synchronous and asynchronous code, there
+//! are two situations to consider:
+//!
+//! **Bounded channel**: If you need a bounded channel, you should use a bounded
+//! Tokio `mpsc` channel for both directions of communication. Instead of calling
+//! the async [`send`][bounded-send] or [`recv`][bounded-recv] methods, in
+//! synchronous code you will need to use the [`blocking_send`][blocking-send] or
+//! [`blocking_recv`][blocking-recv] methods.
+//!
+//! **Unbounded channel**: You should use the kind of channel that matches where
+//! the receiver is. So for sending a message _from async to sync_, you should
+//! use [the standard library unbounded channel][std-unbounded] or
+//! [crossbeam][crossbeam-unbounded].  Similarly, for sending a message _from sync
+//! to async_, you should use an unbounded Tokio `mpsc` channel.
+//!
+//! Please be aware that the above remarks were written with the `mpsc` channel
+//! in mind, but they can also be generalized to other kinds of channels. In
+//! general, any channel method that isn't marked async can be called anywhere,
+//! including outside of the runtime. For example, sending a message on a
+//! oneshot channel from outside the runtime is perfectly fine.
+//!
+//! # Multiple runtimes
+//!
+//! The mpsc channel does not care about which runtime you use it in, and can be
+//! used to send messages from one runtime to another. It can also be used in
+//! non-Tokio runtimes.
+//!
+//! There is one exception to the above: the [`send_timeout`] must be used from
+//! within a Tokio runtime, however it is still not tied to one specific Tokio
+//! runtime, and the sender may be moved from one Tokio runtime to another.
+//!
+//! [`Sender`]: crate::sync::mpsc::Sender
+//! [`Receiver`]: crate::sync::mpsc::Receiver
+//! [bounded-send]: crate::sync::mpsc::Sender::send()
+//! [bounded-recv]: crate::sync::mpsc::Receiver::recv()
+//! [blocking-send]: crate::sync::mpsc::Sender::blocking_send()
+//! [blocking-recv]: crate::sync::mpsc::Receiver::blocking_recv()
+//! [`UnboundedSender`]: crate::sync::mpsc::UnboundedSender
+//! [`UnboundedReceiver`]: crate::sync::mpsc::UnboundedReceiver
+//! [`Handle::block_on`]: crate::runtime::Handle::block_on()
+//! [std-unbounded]: std::sync::mpsc::channel
+//! [crossbeam-unbounded]: https://docs.rs/crossbeam/*/crossbeam/channel/fn.unbounded.html
+//! [`send_timeout`]: crate::sync::mpsc::Sender::send_timeout
+
+pub(super) mod block;
+
+mod bounded;
+pub use self::bounded::{channel, OwnedPermit, Permit, Receiver, Sender};
+
+mod chan;
+
+pub(super) mod list;
+
+mod unbounded;
+pub use self::unbounded::{unbounded_channel, UnboundedReceiver, UnboundedSender};
+
+pub mod error;
+
+/// The number of values a block can contain.
+///
+/// This value must be a power of 2. It also must be smaller than the number of
+/// bits in `usize`.
+#[cfg(all(target_pointer_width = "64", not(loom)))]
+const BLOCK_CAP: usize = 32;
+
+#[cfg(all(not(target_pointer_width = "64"), not(loom)))]
+const BLOCK_CAP: usize = 16;
+
+#[cfg(loom)]
+const BLOCK_CAP: usize = 2;
diff --git a/third_party/rust/tokio/src/sync/mpsc/unbounded.rs b/third_party/rust/tokio/src/sync/mpsc/unbounded.rs
new file mode 100644
index 0000000000..b133f9f35e
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/mpsc/unbounded.rs
@@ -0,0 +1,373 @@
+use crate::loom::sync::atomic::AtomicUsize;
+use crate::sync::mpsc::chan;
+use crate::sync::mpsc::error::{SendError, TryRecvError};
+
+use std::fmt;
+use std::task::{Context, Poll};
+
+/// Send values to the associated `UnboundedReceiver`.
+///
+/// Instances are created by the
+/// [`unbounded_channel`](unbounded_channel) function.
+pub struct UnboundedSender<T> {
+    chan: chan::Tx<T, Semaphore>,
+}
+
+impl<T> Clone for UnboundedSender<T> {
+    fn clone(&self) -> Self {
+        UnboundedSender {
+            chan: self.chan.clone(),
+        }
+    }
+}
+
+impl<T> fmt::Debug for UnboundedSender<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("UnboundedSender")
+            .field("chan", &self.chan)
+            .finish()
+    }
+}
+
+/// Receive values from the associated `UnboundedSender`.
+///
+/// Instances are created by the
+/// [`unbounded_channel`](unbounded_channel) function.
+///
+/// This receiver can be turned into a `Stream` using [`UnboundedReceiverStream`].
+///
+/// [`UnboundedReceiverStream`]: https://docs.rs/tokio-stream/0.1/tokio_stream/wrappers/struct.UnboundedReceiverStream.html
+pub struct UnboundedReceiver<T> {
+    /// The channel receiver
+    chan: chan::Rx<T, Semaphore>,
+}
+
+impl<T> fmt::Debug for UnboundedReceiver<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("UnboundedReceiver")
+            .field("chan", &self.chan)
+            .finish()
+    }
+}
+
+/// Creates an unbounded mpsc channel for communicating between asynchronous
+/// tasks without backpressure.
+///
+/// A `send` on this channel will always succeed as long as the receive half has
+/// not been closed. If the receiver falls behind, messages will be arbitrarily
+/// buffered.
+///
+/// **Note** that the amount of available system memory is an implicit bound to
+/// the channel. Using an `unbounded` channel has the ability of causing the
+/// process to run out of memory. In this case, the process will be aborted.
+pub fn unbounded_channel<T>() -> (UnboundedSender<T>, UnboundedReceiver<T>) {
+    let (tx, rx) = chan::channel(AtomicUsize::new(0));
+
+    let tx = UnboundedSender::new(tx);
+    let rx = UnboundedReceiver::new(rx);
+
+    (tx, rx)
+}
+
+/// No capacity
+type Semaphore = AtomicUsize;
+
+impl<T> UnboundedReceiver<T> {
+    pub(crate) fn new(chan: chan::Rx<T, Semaphore>) -> UnboundedReceiver<T> {
+        UnboundedReceiver { chan }
+    }
+
+    /// Receives the next value for this receiver.
+    ///
+    /// `None` is returned when all `Sender` halves have dropped, indicating
+    /// that no further values can be sent on the channel.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. If `recv` is used as the event in a
+    /// [`tokio::select!`](crate::select) statement and some other branch
+    /// completes first, it is guaranteed that no messages were received on this
+    /// channel.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::unbounded_channel();
+    ///
+    ///     tokio::spawn(async move {
+    ///         tx.send("hello").unwrap();
+    ///     });
+    ///
+    ///     assert_eq!(Some("hello"), rx.recv().await);
+    ///     assert_eq!(None, rx.recv().await);
+    /// }
+    /// ```
+    ///
+    /// Values are buffered:
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::unbounded_channel();
+    ///
+    ///     tx.send("hello").unwrap();
+    ///     tx.send("world").unwrap();
+    ///
+    ///     assert_eq!(Some("hello"), rx.recv().await);
+    ///     assert_eq!(Some("world"), rx.recv().await);
+    /// }
+    /// ```
+    pub async fn recv(&mut self) -> Option<T> {
+        use crate::future::poll_fn;
+
+        poll_fn(|cx| self.poll_recv(cx)).await
+    }
+
+    /// Tries to receive the next value for this receiver.
+    ///
+    /// This method returns the [`Empty`] error if the channel is currently
+    /// empty, but there are still outstanding [senders] or [permits].
+    ///
+    /// This method returns the [`Disconnected`] error if the channel is
+    /// currently empty, and there are no outstanding [senders] or [permits].
+    ///
+    /// Unlike the [`poll_recv`] method, this method will never return an
+    /// [`Empty`] error spuriously.
+    ///
+    /// [`Empty`]: crate::sync::mpsc::error::TryRecvError::Empty
+    /// [`Disconnected`]: crate::sync::mpsc::error::TryRecvError::Disconnected
+    /// [`poll_recv`]: Self::poll_recv
+    /// [senders]: crate::sync::mpsc::Sender
+    /// [permits]: crate::sync::mpsc::Permit
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    /// use tokio::sync::mpsc::error::TryRecvError;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::unbounded_channel();
+    ///
+    ///     tx.send("hello").unwrap();
+    ///
+    ///     assert_eq!(Ok("hello"), rx.try_recv());
+    ///     assert_eq!(Err(TryRecvError::Empty), rx.try_recv());
+    ///
+    ///     tx.send("hello").unwrap();
+    ///     // Drop the last sender, closing the channel.
+    ///     drop(tx);
+    ///
+    ///     assert_eq!(Ok("hello"), rx.try_recv());
+    ///     assert_eq!(Err(TryRecvError::Disconnected), rx.try_recv());
+    /// }
+    /// ```
+    pub fn try_recv(&mut self) -> Result<T, TryRecvError> {
+        self.chan.try_recv()
+    }
+
+    /// Blocking receive to call outside of asynchronous contexts.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if called within an asynchronous execution
+    /// context.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::thread;
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = mpsc::unbounded_channel::<u8>();
+    ///
+    ///     let sync_code = thread::spawn(move || {
+    ///         assert_eq!(Some(10), rx.blocking_recv());
+    ///     });
+    ///
+    ///     let _ = tx.send(10);
+    ///     sync_code.join().unwrap();
+    /// }
+    /// ```
+    #[cfg(feature = "sync")]
+    pub fn blocking_recv(&mut self) -> Option<T> {
+        crate::future::block_on(self.recv())
+    }
+
+    /// Closes the receiving half of a channel, without dropping it.
+    ///
+    /// This prevents any further messages from being sent on the channel while
+    /// still enabling the receiver to drain messages that are buffered.
+    pub fn close(&mut self) {
+        self.chan.close();
+    }
+
+    /// Polls to receive the next message on this channel.
+    ///
+    /// This method returns:
+    ///
+    ///  * `Poll::Pending` if no messages are available but the channel is not
+    ///    closed, or if a spurious failure happens.
+    ///  * `Poll::Ready(Some(message))` if a message is available.
+    ///  * `Poll::Ready(None)` if the channel has been closed and all messages
+    ///    sent before it was closed have been received.
+    ///
+    /// When the method returns `Poll::Pending`, the `Waker` in the provided
+    /// `Context` is scheduled to receive a wakeup when a message is sent on any
+    /// receiver, or when the channel is closed.  Note that on multiple calls to
+    /// `poll_recv`, only the `Waker` from the `Context` passed to the most
+    /// recent call is scheduled to receive a wakeup.
+    ///
+    /// If this method returns `Poll::Pending` due to a spurious failure, then
+    /// the `Waker` will be notified when the situation causing the spurious
+    /// failure has been resolved. Note that receiving such a wakeup does not
+    /// guarantee that the next call will succeed — it could fail with another
+    /// spurious failure.
+    pub fn poll_recv(&mut self, cx: &mut Context<'_>) -> Poll<Option<T>> {
+        self.chan.recv(cx)
+    }
+}
+
+impl<T> UnboundedSender<T> {
+    pub(crate) fn new(chan: chan::Tx<T, Semaphore>) -> UnboundedSender<T> {
+        UnboundedSender { chan }
+    }
+
+    /// Attempts to send a message on this `UnboundedSender` without blocking.
+    ///
+    /// This method is not marked async because sending a message to an unbounded channel
+    /// never requires any form of waiting. Because of this, the `send` method can be
+    /// used in both synchronous and asynchronous code without problems.
+    ///
+    /// If the receive half of the channel is closed, either due to [`close`]
+    /// being called or the [`UnboundedReceiver`] having been dropped, this
+    /// function returns an error. The error includes the value passed to `send`.
+    ///
+    /// [`close`]: UnboundedReceiver::close
+    /// [`UnboundedReceiver`]: UnboundedReceiver
+    pub fn send(&self, message: T) -> Result<(), SendError<T>> {
+        if !self.inc_num_messages() {
+            return Err(SendError(message));
+        }
+
+        self.chan.send(message);
+        Ok(())
+    }
+
+    fn inc_num_messages(&self) -> bool {
+        use std::process;
+        use std::sync::atomic::Ordering::{AcqRel, Acquire};
+
+        let mut curr = self.chan.semaphore().load(Acquire);
+
+        loop {
+            if curr & 1 == 1 {
+                return false;
+            }
+
+            if curr == usize::MAX ^ 1 {
+                // Overflowed the ref count. There is no safe way to recover, so
+                // abort the process. In practice, this should never happen.
+                process::abort()
+            }
+
+            match self
+                .chan
+                .semaphore()
+                .compare_exchange(curr, curr + 2, AcqRel, Acquire)
+            {
+                Ok(_) => return true,
+                Err(actual) => {
+                    curr = actual;
+                }
+            }
+        }
+    }
+
+    /// Completes when the receiver has dropped.
+    ///
+    /// This allows the producers to get notified when interest in the produced
+    /// values is canceled and immediately stop doing work.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once the channel is closed, it stays closed
+    /// forever and all future calls to `closed` will return immediately.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::mpsc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx1, rx) = mpsc::unbounded_channel::<()>();
+    ///     let tx2 = tx1.clone();
+    ///     let tx3 = tx1.clone();
+    ///     let tx4 = tx1.clone();
+    ///     let tx5 = tx1.clone();
+    ///     tokio::spawn(async move {
+    ///         drop(rx);
+    ///     });
+    ///
+    ///     futures::join!(
+    ///         tx1.closed(),
+    ///         tx2.closed(),
+    ///         tx3.closed(),
+    ///         tx4.closed(),
+    ///         tx5.closed()
+    ///     );
+    ////     println!("Receiver dropped");
+    /// }
+    /// ```
+    pub async fn closed(&self) {
+        self.chan.closed().await
+    }
+
+    /// Checks if the channel has been closed. This happens when the
+    /// [`UnboundedReceiver`] is dropped, or when the
+    /// [`UnboundedReceiver::close`] method is called.
+    ///
+    /// [`UnboundedReceiver`]: crate::sync::mpsc::UnboundedReceiver
+    /// [`UnboundedReceiver::close`]: crate::sync::mpsc::UnboundedReceiver::close
+    ///
+    /// ```
+    /// let (tx, rx) = tokio::sync::mpsc::unbounded_channel::<()>();
+    /// assert!(!tx.is_closed());
+    ///
+    /// let tx2 = tx.clone();
+    /// assert!(!tx2.is_closed());
+    ///
+    /// drop(rx);
+    /// assert!(tx.is_closed());
+    /// assert!(tx2.is_closed());
+    /// ```
+    pub fn is_closed(&self) -> bool {
+        self.chan.is_closed()
+    }
+
+    /// Returns `true` if senders belong to the same channel.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let (tx, rx) = tokio::sync::mpsc::unbounded_channel::<()>();
+    /// let  tx2 = tx.clone();
+    /// assert!(tx.same_channel(&tx2));
+    ///
+    /// let (tx3, rx3) = tokio::sync::mpsc::unbounded_channel::<()>();
+    /// assert!(!tx3.same_channel(&tx2));
+    /// ```
+    pub fn same_channel(&self, other: &Self) -> bool {
+        self.chan.same_channel(&other.chan)
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/mutex.rs b/third_party/rust/tokio/src/sync/mutex.rs
new file mode 100644
index 0000000000..b8d5ba74e7
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/mutex.rs
@@ -0,0 +1,967 @@
+#![cfg_attr(not(feature = "sync"), allow(unreachable_pub, dead_code))]
+
+use crate::sync::batch_semaphore as semaphore;
+#[cfg(all(tokio_unstable, feature = "tracing"))]
+use crate::util::trace;
+
+use std::cell::UnsafeCell;
+use std::error::Error;
+use std::ops::{Deref, DerefMut};
+use std::sync::Arc;
+use std::{fmt, marker, mem};
+
+/// An asynchronous `Mutex`-like type.
+///
+/// This type acts similarly to [`std::sync::Mutex`], with two major
+/// differences: [`lock`] is an async method so does not block, and the lock
+/// guard is designed to be held across `.await` points.
+///
+/// # Which kind of mutex should you use?
+///
+/// Contrary to popular belief, it is ok and often preferred to use the ordinary
+/// [`Mutex`][std] from the standard library in asynchronous code.
+///
+/// The feature that the async mutex offers over the blocking mutex is the
+/// ability to keep it locked across an `.await` point. This makes the async
+/// mutex more expensive than the blocking mutex, so the blocking mutex should
+/// be preferred in the cases where it can be used. The primary use case for the
+/// async mutex is to provide shared mutable access to IO resources such as a
+/// database connection. If the value behind the mutex is just data, it's
+/// usually appropriate to use a blocking mutex such as the one in the standard
+/// library or [`parking_lot`].
+///
+/// Note that, although the compiler will not prevent the std `Mutex` from holding
+/// its guard across `.await` points in situations where the task is not movable
+/// between threads, this virtually never leads to correct concurrent code in
+/// practice as it can easily lead to deadlocks.
+///
+/// A common pattern is to wrap the `Arc<Mutex<...>>` in a struct that provides
+/// non-async methods for performing operations on the data within, and only
+/// lock the mutex inside these methods. The [mini-redis] example provides an
+/// illustration of this pattern.
+///
+/// Additionally, when you _do_ want shared access to an IO resource, it is
+/// often better to spawn a task to manage the IO resource, and to use message
+/// passing to communicate with that task.
+///
+/// [std]: std::sync::Mutex
+/// [`parking_lot`]: https://docs.rs/parking_lot
+/// [mini-redis]: https://github.com/tokio-rs/mini-redis/blob/master/src/db.rs
+///
+/// # Examples:
+///
+/// ```rust,no_run
+/// use tokio::sync::Mutex;
+/// use std::sync::Arc;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let data1 = Arc::new(Mutex::new(0));
+///     let data2 = Arc::clone(&data1);
+///
+///     tokio::spawn(async move {
+///         let mut lock = data2.lock().await;
+///         *lock += 1;
+///     });
+///
+///     let mut lock = data1.lock().await;
+///     *lock += 1;
+/// }
+/// ```
+///
+///
+/// ```rust,no_run
+/// use tokio::sync::Mutex;
+/// use std::sync::Arc;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let count = Arc::new(Mutex::new(0));
+///
+///     for i in 0..5 {
+///         let my_count = Arc::clone(&count);
+///         tokio::spawn(async move {
+///             for j in 0..10 {
+///                 let mut lock = my_count.lock().await;
+///                 *lock += 1;
+///                 println!("{} {} {}", i, j, lock);
+///             }
+///         });
+///     }
+///
+///     loop {
+///         if *count.lock().await >= 50 {
+///             break;
+///         }
+///     }
+///     println!("Count hit 50.");
+/// }
+/// ```
+/// There are a few things of note here to pay attention to in this example.
+/// 1. The mutex is wrapped in an [`Arc`] to allow it to be shared across
+///    threads.
+/// 2. Each spawned task obtains a lock and releases it on every iteration.
+/// 3. Mutation of the data protected by the Mutex is done by de-referencing
+///    the obtained lock as seen on lines 12 and 19.
+///
+/// Tokio's Mutex works in a simple FIFO (first in, first out) style where all
+/// calls to [`lock`] complete in the order they were performed. In that way the
+/// Mutex is "fair" and predictable in how it distributes the locks to inner
+/// data. Locks are released and reacquired after every iteration, so basically,
+/// each thread goes to the back of the line after it increments the value once.
+/// Note that there's some unpredictability to the timing between when the
+/// threads are started, but once they are going they alternate predictably.
+/// Finally, since there is only a single valid lock at any given time, there is
+/// no possibility of a race condition when mutating the inner value.
+///
+/// Note that in contrast to [`std::sync::Mutex`], this implementation does not
+/// poison the mutex when a thread holding the [`MutexGuard`] panics. In such a
+/// case, the mutex will be unlocked. If the panic is caught, this might leave
+/// the data protected by the mutex in an inconsistent state.
+///
+/// [`Mutex`]: struct@Mutex
+/// [`MutexGuard`]: struct@MutexGuard
+/// [`Arc`]: struct@std::sync::Arc
+/// [`std::sync::Mutex`]: struct@std::sync::Mutex
+/// [`Send`]: trait@std::marker::Send
+/// [`lock`]: method@Mutex::lock
+pub struct Mutex<T: ?Sized> {
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    resource_span: tracing::Span,
+    s: semaphore::Semaphore,
+    c: UnsafeCell<T>,
+}
+
+/// A handle to a held `Mutex`. The guard can be held across any `.await` point
+/// as it is [`Send`].
+///
+/// As long as you have this guard, you have exclusive access to the underlying
+/// `T`. The guard internally borrows the `Mutex`, so the mutex will not be
+/// dropped while a guard exists.
+///
+/// The lock is automatically released whenever the guard is dropped, at which
+/// point `lock` will succeed yet again.
+pub struct MutexGuard<'a, T: ?Sized> {
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    resource_span: tracing::Span,
+    lock: &'a Mutex<T>,
+}
+
+/// An owned handle to a held `Mutex`.
+///
+/// This guard is only available from a `Mutex` that is wrapped in an [`Arc`]. It
+/// is identical to `MutexGuard`, except that rather than borrowing the `Mutex`,
+/// it clones the `Arc`, incrementing the reference count. This means that
+/// unlike `MutexGuard`, it will have the `'static` lifetime.
+///
+/// As long as you have this guard, you have exclusive access to the underlying
+/// `T`. The guard internally keeps a reference-counted pointer to the original
+/// `Mutex`, so even if the lock goes away, the guard remains valid.
+///
+/// The lock is automatically released whenever the guard is dropped, at which
+/// point `lock` will succeed yet again.
+///
+/// [`Arc`]: std::sync::Arc
+pub struct OwnedMutexGuard<T: ?Sized> {
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    resource_span: tracing::Span,
+    lock: Arc<Mutex<T>>,
+}
+
+/// A handle to a held `Mutex` that has had a function applied to it via [`MutexGuard::map`].
+///
+/// This can be used to hold a subfield of the protected data.
+///
+/// [`MutexGuard::map`]: method@MutexGuard::map
+#[must_use = "if unused the Mutex will immediately unlock"]
+pub struct MappedMutexGuard<'a, T: ?Sized> {
+    s: &'a semaphore::Semaphore,
+    data: *mut T,
+    // Needed to tell the borrow checker that we are holding a `&mut T`
+    marker: marker::PhantomData<&'a mut T>,
+}
+
+// As long as T: Send, it's fine to send and share Mutex<T> between threads.
+// If T was not Send, sending and sharing a Mutex<T> would be bad, since you can
+// access T through Mutex<T>.
+unsafe impl<T> Send for Mutex<T> where T: ?Sized + Send {}
+unsafe impl<T> Sync for Mutex<T> where T: ?Sized + Send {}
+unsafe impl<T> Sync for MutexGuard<'_, T> where T: ?Sized + Send + Sync {}
+unsafe impl<T> Sync for OwnedMutexGuard<T> where T: ?Sized + Send + Sync {}
+unsafe impl<'a, T> Sync for MappedMutexGuard<'a, T> where T: ?Sized + Sync + 'a {}
+unsafe impl<'a, T> Send for MappedMutexGuard<'a, T> where T: ?Sized + Send + 'a {}
+
+/// Error returned from the [`Mutex::try_lock`], [`RwLock::try_read`] and
+/// [`RwLock::try_write`] functions.
+///
+/// `Mutex::try_lock` operation will only fail if the mutex is already locked.
+///
+/// `RwLock::try_read` operation will only fail if the lock is currently held
+/// by an exclusive writer.
+///
+/// `RwLock::try_write` operation will if lock is held by any reader or by an
+/// exclusive writer.
+///
+/// [`Mutex::try_lock`]: Mutex::try_lock
+/// [`RwLock::try_read`]: fn@super::RwLock::try_read
+/// [`RwLock::try_write`]: fn@super::RwLock::try_write
+#[derive(Debug)]
+pub struct TryLockError(pub(super) ());
+
+impl fmt::Display for TryLockError {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(fmt, "operation would block")
+    }
+}
+
+impl Error for TryLockError {}
+
+#[test]
+#[cfg(not(loom))]
+fn bounds() {
+    fn check_send<T: Send>() {}
+    fn check_unpin<T: Unpin>() {}
+    // This has to take a value, since the async fn's return type is unnameable.
+    fn check_send_sync_val<T: Send + Sync>(_t: T) {}
+    fn check_send_sync<T: Send + Sync>() {}
+    fn check_static<T: 'static>() {}
+    fn check_static_val<T: 'static>(_t: T) {}
+
+    check_send::<MutexGuard<'_, u32>>();
+    check_send::<OwnedMutexGuard<u32>>();
+    check_unpin::<Mutex<u32>>();
+    check_send_sync::<Mutex<u32>>();
+    check_static::<OwnedMutexGuard<u32>>();
+
+    let mutex = Mutex::new(1);
+    check_send_sync_val(mutex.lock());
+    let arc_mutex = Arc::new(Mutex::new(1));
+    check_send_sync_val(arc_mutex.clone().lock_owned());
+    check_static_val(arc_mutex.lock_owned());
+}
+
+impl<T: ?Sized> Mutex<T> {
+    /// Creates a new lock in an unlocked state ready for use.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Mutex;
+    ///
+    /// let lock = Mutex::new(5);
+    /// ```
+    #[track_caller]
+    pub fn new(t: T) -> Self
+    where
+        T: Sized,
+    {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = {
+            let location = std::panic::Location::caller();
+
+            tracing::trace_span!(
+                "runtime.resource",
+                concrete_type = "Mutex",
+                kind = "Sync",
+                loc.file = location.file(),
+                loc.line = location.line(),
+                loc.col = location.column(),
+            )
+        };
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let s = resource_span.in_scope(|| {
+            tracing::trace!(
+                target: "runtime::resource::state_update",
+                locked = false,
+            );
+            semaphore::Semaphore::new(1)
+        });
+
+        #[cfg(any(not(tokio_unstable), not(feature = "tracing")))]
+        let s = semaphore::Semaphore::new(1);
+
+        Self {
+            c: UnsafeCell::new(t),
+            s,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+
+    /// Creates a new lock in an unlocked state ready for use.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Mutex;
+    ///
+    /// static LOCK: Mutex<i32> = Mutex::const_new(5);
+    /// ```
+    #[cfg(all(feature = "parking_lot", not(all(loom, test)),))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "parking_lot")))]
+    pub const fn const_new(t: T) -> Self
+    where
+        T: Sized,
+    {
+        Self {
+            c: UnsafeCell::new(t),
+            s: semaphore::Semaphore::const_new(1),
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span: tracing::Span::none(),
+        }
+    }
+
+    /// Locks this mutex, causing the current task to yield until the lock has
+    /// been acquired.  When the lock has been acquired, function returns a
+    /// [`MutexGuard`].
+    ///
+    /// # Cancel safety
+    ///
+    /// This method uses a queue to fairly distribute locks in the order they
+    /// were requested. Cancelling a call to `lock` makes you lose your place in
+    /// the queue.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Mutex;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let mutex = Mutex::new(1);
+    ///
+    ///     let mut n = mutex.lock().await;
+    ///     *n = 2;
+    /// }
+    /// ```
+    pub async fn lock(&self) -> MutexGuard<'_, T> {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        trace::async_op(
+            || self.acquire(),
+            self.resource_span.clone(),
+            "Mutex::lock",
+            "poll",
+            false,
+        )
+        .await;
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+                target: "runtime::resource::state_update",
+                locked = true,
+            );
+        });
+
+        #[cfg(any(not(tokio_unstable), not(feature = "tracing")))]
+        self.acquire().await;
+
+        MutexGuard {
+            lock: self,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span: self.resource_span.clone(),
+        }
+    }
+
+    /// Blockingly locks this `Mutex`. When the lock has been acquired, function returns a
+    /// [`MutexGuard`].
+    ///
+    /// This method is intended for use cases where you
+    /// need to use this mutex in asynchronous code as well as in synchronous code.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if called within an asynchronous execution context.
+    ///
+    ///   - If you find yourself in an asynchronous execution context and needing
+    ///     to call some (synchronous) function which performs one of these
+    ///     `blocking_` operations, then consider wrapping that call inside
+    ///     [`spawn_blocking()`][crate::runtime::Handle::spawn_blocking]
+    ///     (or [`block_in_place()`][crate::task::block_in_place]).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::Mutex;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let mutex =  Arc::new(Mutex::new(1));
+    ///     let lock = mutex.lock().await;
+    ///
+    ///     let mutex1 = Arc::clone(&mutex);
+    ///     let blocking_task = tokio::task::spawn_blocking(move || {
+    ///         // This shall block until the `lock` is released.
+    ///         let mut n = mutex1.blocking_lock();
+    ///         *n = 2;
+    ///     });
+    ///
+    ///     assert_eq!(*lock, 1);
+    ///     // Release the lock.
+    ///     drop(lock);
+    ///
+    ///     // Await the completion of the blocking task.
+    ///     blocking_task.await.unwrap();
+    ///
+    ///     // Assert uncontended.
+    ///     let n = mutex.try_lock().unwrap();
+    ///     assert_eq!(*n, 2);
+    /// }
+    ///
+    /// ```
+    #[cfg(feature = "sync")]
+    pub fn blocking_lock(&self) -> MutexGuard<'_, T> {
+        crate::future::block_on(self.lock())
+    }
+
+    /// Locks this mutex, causing the current task to yield until the lock has
+    /// been acquired. When the lock has been acquired, this returns an
+    /// [`OwnedMutexGuard`].
+    ///
+    /// This method is identical to [`Mutex::lock`], except that the returned
+    /// guard references the `Mutex` with an [`Arc`] rather than by borrowing
+    /// it. Therefore, the `Mutex` must be wrapped in an `Arc` to call this
+    /// method, and the guard will live for the `'static` lifetime, as it keeps
+    /// the `Mutex` alive by holding an `Arc`.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method uses a queue to fairly distribute locks in the order they
+    /// were requested. Cancelling a call to `lock_owned` makes you lose your
+    /// place in the queue.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Mutex;
+    /// use std::sync::Arc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let mutex = Arc::new(Mutex::new(1));
+    ///
+    ///     let mut n = mutex.clone().lock_owned().await;
+    ///     *n = 2;
+    /// }
+    /// ```
+    ///
+    /// [`Arc`]: std::sync::Arc
+    pub async fn lock_owned(self: Arc<Self>) -> OwnedMutexGuard<T> {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        trace::async_op(
+            || self.acquire(),
+            self.resource_span.clone(),
+            "Mutex::lock_owned",
+            "poll",
+            false,
+        )
+        .await;
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+                target: "runtime::resource::state_update",
+                locked = true,
+            );
+        });
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = self.resource_span.clone();
+
+        #[cfg(any(not(tokio_unstable), not(feature = "tracing")))]
+        self.acquire().await;
+
+        OwnedMutexGuard {
+            lock: self,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+
+    async fn acquire(&self) {
+        self.s.acquire(1).await.unwrap_or_else(|_| {
+            // The semaphore was closed. but, we never explicitly close it, and
+            // we own it exclusively, which means that this can never happen.
+            unreachable!()
+        });
+    }
+
+    /// Attempts to acquire the lock, and returns [`TryLockError`] if the
+    /// lock is currently held somewhere else.
+    ///
+    /// [`TryLockError`]: TryLockError
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Mutex;
+    /// # async fn dox() -> Result<(), tokio::sync::TryLockError> {
+    ///
+    /// let mutex = Mutex::new(1);
+    ///
+    /// let n = mutex.try_lock()?;
+    /// assert_eq!(*n, 1);
+    /// # Ok(())
+    /// # }
+    /// ```
+    pub fn try_lock(&self) -> Result<MutexGuard<'_, T>, TryLockError> {
+        match self.s.try_acquire(1) {
+            Ok(_) => {
+                #[cfg(all(tokio_unstable, feature = "tracing"))]
+                self.resource_span.in_scope(|| {
+                    tracing::trace!(
+                        target: "runtime::resource::state_update",
+                        locked = true,
+                    );
+                });
+
+                Ok(MutexGuard {
+                    lock: self,
+                    #[cfg(all(tokio_unstable, feature = "tracing"))]
+                    resource_span: self.resource_span.clone(),
+                })
+            }
+            Err(_) => Err(TryLockError(())),
+        }
+    }
+
+    /// Returns a mutable reference to the underlying data.
+    ///
+    /// Since this call borrows the `Mutex` mutably, no actual locking needs to
+    /// take place -- the mutable borrow statically guarantees no locks exist.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Mutex;
+    ///
+    /// fn main() {
+    ///     let mut mutex = Mutex::new(1);
+    ///
+    ///     let n = mutex.get_mut();
+    ///     *n = 2;
+    /// }
+    /// ```
+    pub fn get_mut(&mut self) -> &mut T {
+        unsafe {
+            // Safety: This is https://github.com/rust-lang/rust/pull/76936
+            &mut *self.c.get()
+        }
+    }
+
+    /// Attempts to acquire the lock, and returns [`TryLockError`] if the lock
+    /// is currently held somewhere else.
+    ///
+    /// This method is identical to [`Mutex::try_lock`], except that the
+    /// returned  guard references the `Mutex` with an [`Arc`] rather than by
+    /// borrowing it. Therefore, the `Mutex` must be wrapped in an `Arc` to call
+    /// this method, and the guard will live for the `'static` lifetime, as it
+    /// keeps the `Mutex` alive by holding an `Arc`.
+    ///
+    /// [`TryLockError`]: TryLockError
+    /// [`Arc`]: std::sync::Arc
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Mutex;
+    /// use std::sync::Arc;
+    /// # async fn dox() -> Result<(), tokio::sync::TryLockError> {
+    ///
+    /// let mutex = Arc::new(Mutex::new(1));
+    ///
+    /// let n = mutex.clone().try_lock_owned()?;
+    /// assert_eq!(*n, 1);
+    /// # Ok(())
+    /// # }
+    pub fn try_lock_owned(self: Arc<Self>) -> Result<OwnedMutexGuard<T>, TryLockError> {
+        match self.s.try_acquire(1) {
+            Ok(_) => {
+                #[cfg(all(tokio_unstable, feature = "tracing"))]
+                self.resource_span.in_scope(|| {
+                    tracing::trace!(
+                        target: "runtime::resource::state_update",
+                        locked = true,
+                    );
+                });
+
+                #[cfg(all(tokio_unstable, feature = "tracing"))]
+                let resource_span = self.resource_span.clone();
+
+                Ok(OwnedMutexGuard {
+                    lock: self,
+                    #[cfg(all(tokio_unstable, feature = "tracing"))]
+                    resource_span,
+                })
+            }
+            Err(_) => Err(TryLockError(())),
+        }
+    }
+
+    /// Consumes the mutex, returning the underlying data.
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Mutex;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let mutex = Mutex::new(1);
+    ///
+    ///     let n = mutex.into_inner();
+    ///     assert_eq!(n, 1);
+    /// }
+    /// ```
+    pub fn into_inner(self) -> T
+    where
+        T: Sized,
+    {
+        self.c.into_inner()
+    }
+}
+
+impl<T> From<T> for Mutex<T> {
+    fn from(s: T) -> Self {
+        Self::new(s)
+    }
+}
+
+impl<T> Default for Mutex<T>
+where
+    T: Default,
+{
+    fn default() -> Self {
+        Self::new(T::default())
+    }
+}
+
+impl<T: ?Sized> std::fmt::Debug for Mutex<T>
+where
+    T: std::fmt::Debug,
+{
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let mut d = f.debug_struct("Mutex");
+        match self.try_lock() {
+            Ok(inner) => d.field("data", &&*inner),
+            Err(_) => d.field("data", &format_args!("<locked>")),
+        };
+        d.finish()
+    }
+}
+
+// === impl MutexGuard ===
+
+impl<'a, T: ?Sized> MutexGuard<'a, T> {
+    /// Makes a new [`MappedMutexGuard`] for a component of the locked data.
+    ///
+    /// This operation cannot fail as the [`MutexGuard`] passed in already locked the mutex.
+    ///
+    /// This is an associated function that needs to be used as `MutexGuard::map(...)`. A method
+    /// would interfere with methods of the same name on the contents of the locked data.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::{Mutex, MutexGuard};
+    ///
+    /// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    /// struct Foo(u32);
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let foo = Mutex::new(Foo(1));
+    ///
+    /// {
+    ///     let mut mapped = MutexGuard::map(foo.lock().await, |f| &mut f.0);
+    ///     *mapped = 2;
+    /// }
+    ///
+    /// assert_eq!(Foo(2), *foo.lock().await);
+    /// # }
+    /// ```
+    ///
+    /// [`MutexGuard`]: struct@MutexGuard
+    /// [`MappedMutexGuard`]: struct@MappedMutexGuard
+    #[inline]
+    pub fn map<U, F>(mut this: Self, f: F) -> MappedMutexGuard<'a, U>
+    where
+        F: FnOnce(&mut T) -> &mut U,
+    {
+        let data = f(&mut *this) as *mut U;
+        let s = &this.lock.s;
+        mem::forget(this);
+        MappedMutexGuard {
+            s,
+            data,
+            marker: marker::PhantomData,
+        }
+    }
+
+    /// Attempts to make a new [`MappedMutexGuard`] for a component of the locked data. The
+    /// original guard is returned if the closure returns `None`.
+    ///
+    /// This operation cannot fail as the [`MutexGuard`] passed in already locked the mutex.
+    ///
+    /// This is an associated function that needs to be used as `MutexGuard::try_map(...)`. A
+    /// method would interfere with methods of the same name on the contents of the locked data.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::{Mutex, MutexGuard};
+    ///
+    /// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    /// struct Foo(u32);
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let foo = Mutex::new(Foo(1));
+    ///
+    /// {
+    ///     let mut mapped = MutexGuard::try_map(foo.lock().await, |f| Some(&mut f.0))
+    ///         .expect("should not fail");
+    ///     *mapped = 2;
+    /// }
+    ///
+    /// assert_eq!(Foo(2), *foo.lock().await);
+    /// # }
+    /// ```
+    ///
+    /// [`MutexGuard`]: struct@MutexGuard
+    /// [`MappedMutexGuard`]: struct@MappedMutexGuard
+    #[inline]
+    pub fn try_map<U, F>(mut this: Self, f: F) -> Result<MappedMutexGuard<'a, U>, Self>
+    where
+        F: FnOnce(&mut T) -> Option<&mut U>,
+    {
+        let data = match f(&mut *this) {
+            Some(data) => data as *mut U,
+            None => return Err(this),
+        };
+        let s = &this.lock.s;
+        mem::forget(this);
+        Ok(MappedMutexGuard {
+            s,
+            data,
+            marker: marker::PhantomData,
+        })
+    }
+
+    /// Returns a reference to the original `Mutex`.
+    ///
+    /// ```
+    /// use tokio::sync::{Mutex, MutexGuard};
+    ///
+    /// async fn unlock_and_relock<'l>(guard: MutexGuard<'l, u32>) -> MutexGuard<'l, u32> {
+    ///     println!("1. contains: {:?}", *guard);
+    ///     let mutex = MutexGuard::mutex(&guard);
+    ///     drop(guard);
+    ///     let guard = mutex.lock().await;
+    ///     println!("2. contains: {:?}", *guard);
+    ///     guard
+    /// }
+    /// #
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// #     let mutex = Mutex::new(0u32);
+    /// #     let guard = mutex.lock().await;
+    /// #     unlock_and_relock(guard).await;
+    /// # }
+    /// ```
+    #[inline]
+    pub fn mutex(this: &Self) -> &'a Mutex<T> {
+        this.lock
+    }
+}
+
+impl<T: ?Sized> Drop for MutexGuard<'_, T> {
+    fn drop(&mut self) {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+                target: "runtime::resource::state_update",
+                locked = false,
+            );
+        });
+        self.lock.s.release(1);
+    }
+}
+
+impl<T: ?Sized> Deref for MutexGuard<'_, T> {
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        unsafe { &*self.lock.c.get() }
+    }
+}
+
+impl<T: ?Sized> DerefMut for MutexGuard<'_, T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        unsafe { &mut *self.lock.c.get() }
+    }
+}
+
+impl<T: ?Sized + fmt::Debug> fmt::Debug for MutexGuard<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<T: ?Sized + fmt::Display> fmt::Display for MutexGuard<'_, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+// === impl OwnedMutexGuard ===
+
+impl<T: ?Sized> OwnedMutexGuard<T> {
+    /// Returns a reference to the original `Arc<Mutex>`.
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::{Mutex, OwnedMutexGuard};
+    ///
+    /// async fn unlock_and_relock(guard: OwnedMutexGuard<u32>) -> OwnedMutexGuard<u32> {
+    ///     println!("1. contains: {:?}", *guard);
+    ///     let mutex: Arc<Mutex<u32>> = OwnedMutexGuard::mutex(&guard).clone();
+    ///     drop(guard);
+    ///     let guard = mutex.lock_owned().await;
+    ///     println!("2. contains: {:?}", *guard);
+    ///     guard
+    /// }
+    /// #
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// #     let mutex = Arc::new(Mutex::new(0u32));
+    /// #     let guard = mutex.lock_owned().await;
+    /// #     unlock_and_relock(guard).await;
+    /// # }
+    /// ```
+    #[inline]
+    pub fn mutex(this: &Self) -> &Arc<Mutex<T>> {
+        &this.lock
+    }
+}
+
+impl<T: ?Sized> Drop for OwnedMutexGuard<T> {
+    fn drop(&mut self) {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+                target: "runtime::resource::state_update",
+                locked = false,
+            );
+        });
+        self.lock.s.release(1)
+    }
+}
+
+impl<T: ?Sized> Deref for OwnedMutexGuard<T> {
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        unsafe { &*self.lock.c.get() }
+    }
+}
+
+impl<T: ?Sized> DerefMut for OwnedMutexGuard<T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        unsafe { &mut *self.lock.c.get() }
+    }
+}
+
+impl<T: ?Sized + fmt::Debug> fmt::Debug for OwnedMutexGuard<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<T: ?Sized + fmt::Display> fmt::Display for OwnedMutexGuard<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+// === impl MappedMutexGuard ===
+
+impl<'a, T: ?Sized> MappedMutexGuard<'a, T> {
+    /// Makes a new [`MappedMutexGuard`] for a component of the locked data.
+    ///
+    /// This operation cannot fail as the [`MappedMutexGuard`] passed in already locked the mutex.
+    ///
+    /// This is an associated function that needs to be used as `MappedMutexGuard::map(...)`. A
+    /// method would interfere with methods of the same name on the contents of the locked data.
+    ///
+    /// [`MappedMutexGuard`]: struct@MappedMutexGuard
+    #[inline]
+    pub fn map<U, F>(mut this: Self, f: F) -> MappedMutexGuard<'a, U>
+    where
+        F: FnOnce(&mut T) -> &mut U,
+    {
+        let data = f(&mut *this) as *mut U;
+        let s = this.s;
+        mem::forget(this);
+        MappedMutexGuard {
+            s,
+            data,
+            marker: marker::PhantomData,
+        }
+    }
+
+    /// Attempts to make a new [`MappedMutexGuard`] for a component of the locked data. The
+    /// original guard is returned if the closure returns `None`.
+    ///
+    /// This operation cannot fail as the [`MappedMutexGuard`] passed in already locked the mutex.
+    ///
+    /// This is an associated function that needs to be used as `MappedMutexGuard::try_map(...)`. A
+    /// method would interfere with methods of the same name on the contents of the locked data.
+    ///
+    /// [`MappedMutexGuard`]: struct@MappedMutexGuard
+    #[inline]
+    pub fn try_map<U, F>(mut this: Self, f: F) -> Result<MappedMutexGuard<'a, U>, Self>
+    where
+        F: FnOnce(&mut T) -> Option<&mut U>,
+    {
+        let data = match f(&mut *this) {
+            Some(data) => data as *mut U,
+            None => return Err(this),
+        };
+        let s = this.s;
+        mem::forget(this);
+        Ok(MappedMutexGuard {
+            s,
+            data,
+            marker: marker::PhantomData,
+        })
+    }
+}
+
+impl<'a, T: ?Sized> Drop for MappedMutexGuard<'a, T> {
+    fn drop(&mut self) {
+        self.s.release(1)
+    }
+}
+
+impl<'a, T: ?Sized> Deref for MappedMutexGuard<'a, T> {
+    type Target = T;
+    fn deref(&self) -> &Self::Target {
+        unsafe { &*self.data }
+    }
+}
+
+impl<'a, T: ?Sized> DerefMut for MappedMutexGuard<'a, T> {
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        unsafe { &mut *self.data }
+    }
+}
+
+impl<'a, T: ?Sized + fmt::Debug> fmt::Debug for MappedMutexGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'a, T: ?Sized + fmt::Display> fmt::Display for MappedMutexGuard<'a, T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/notify.rs b/third_party/rust/tokio/src/sync/notify.rs
new file mode 100644
index 0000000000..83d0de4fbe
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/notify.rs
@@ -0,0 +1,740 @@
+// Allow `unreachable_pub` warnings when sync is not enabled
+// due to the usage of `Notify` within the `rt` feature set.
+// When this module is compiled with `sync` enabled we will warn on
+// this lint. When `rt` is enabled we use `pub(crate)` which
+// triggers this warning but it is safe to ignore in this case.
+#![cfg_attr(not(feature = "sync"), allow(unreachable_pub, dead_code))]
+
+use crate::loom::sync::atomic::AtomicUsize;
+use crate::loom::sync::Mutex;
+use crate::util::linked_list::{self, LinkedList};
+use crate::util::WakeList;
+
+use std::cell::UnsafeCell;
+use std::future::Future;
+use std::marker::PhantomPinned;
+use std::pin::Pin;
+use std::ptr::NonNull;
+use std::sync::atomic::Ordering::SeqCst;
+use std::task::{Context, Poll, Waker};
+
+type WaitList = LinkedList<Waiter, <Waiter as linked_list::Link>::Target>;
+
+/// Notifies a single task to wake up.
+///
+/// `Notify` provides a basic mechanism to notify a single task of an event.
+/// `Notify` itself does not carry any data. Instead, it is to be used to signal
+/// another task to perform an operation.
+///
+/// `Notify` can be thought of as a [`Semaphore`] starting with 0 permits.
+/// [`notified().await`] waits for a permit to become available, and [`notify_one()`]
+/// sets a permit **if there currently are no available permits**.
+///
+/// The synchronization details of `Notify` are similar to
+/// [`thread::park`][park] and [`Thread::unpark`][unpark] from std. A [`Notify`]
+/// value contains a single permit. [`notified().await`] waits for the permit to
+/// be made available, consumes the permit, and resumes.  [`notify_one()`] sets the
+/// permit, waking a pending task if there is one.
+///
+/// If `notify_one()` is called **before** `notified().await`, then the next call to
+/// `notified().await` will complete immediately, consuming the permit. Any
+/// subsequent calls to `notified().await` will wait for a new permit.
+///
+/// If `notify_one()` is called **multiple** times before `notified().await`, only a
+/// **single** permit is stored. The next call to `notified().await` will
+/// complete immediately, but the one after will wait for a new permit.
+///
+/// # Examples
+///
+/// Basic usage.
+///
+/// ```
+/// use tokio::sync::Notify;
+/// use std::sync::Arc;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let notify = Arc::new(Notify::new());
+///     let notify2 = notify.clone();
+///
+///     let handle = tokio::spawn(async move {
+///         notify2.notified().await;
+///         println!("received notification");
+///     });
+///
+///     println!("sending notification");
+///     notify.notify_one();
+///
+///     // Wait for task to receive notification.
+///     handle.await.unwrap();
+/// }
+/// ```
+///
+/// Unbound mpsc channel.
+///
+/// ```
+/// use tokio::sync::Notify;
+///
+/// use std::collections::VecDeque;
+/// use std::sync::Mutex;
+///
+/// struct Channel<T> {
+///     values: Mutex<VecDeque<T>>,
+///     notify: Notify,
+/// }
+///
+/// impl<T> Channel<T> {
+///     pub fn send(&self, value: T) {
+///         self.values.lock().unwrap()
+///             .push_back(value);
+///
+///         // Notify the consumer a value is available
+///         self.notify.notify_one();
+///     }
+///
+///     pub async fn recv(&self) -> T {
+///         loop {
+///             // Drain values
+///             if let Some(value) = self.values.lock().unwrap().pop_front() {
+///                 return value;
+///             }
+///
+///             // Wait for values to be available
+///             self.notify.notified().await;
+///         }
+///     }
+/// }
+/// ```
+///
+/// [park]: std::thread::park
+/// [unpark]: std::thread::Thread::unpark
+/// [`notified().await`]: Notify::notified()
+/// [`notify_one()`]: Notify::notify_one()
+/// [`Semaphore`]: crate::sync::Semaphore
+#[derive(Debug)]
+pub struct Notify {
+    // This uses 2 bits to store one of `EMPTY`,
+    // `WAITING` or `NOTIFIED`. The rest of the bits
+    // are used to store the number of times `notify_waiters`
+    // was called.
+    state: AtomicUsize,
+    waiters: Mutex<WaitList>,
+}
+
+#[derive(Debug, Clone, Copy)]
+enum NotificationType {
+    // Notification triggered by calling `notify_waiters`
+    AllWaiters,
+    // Notification triggered by calling `notify_one`
+    OneWaiter,
+}
+
+#[derive(Debug)]
+#[repr(C)] // required by `linked_list::Link` impl
+struct Waiter {
+    /// Intrusive linked-list pointers.
+    pointers: linked_list::Pointers<Waiter>,
+
+    /// Waiting task's waker.
+    waker: Option<Waker>,
+
+    /// `true` if the notification has been assigned to this waiter.
+    notified: Option<NotificationType>,
+
+    /// Should not be `Unpin`.
+    _p: PhantomPinned,
+}
+
+/// Future returned from [`Notify::notified()`]
+#[derive(Debug)]
+pub struct Notified<'a> {
+    /// The `Notify` being received on.
+    notify: &'a Notify,
+
+    /// The current state of the receiving process.
+    state: State,
+
+    /// Entry in the waiter `LinkedList`.
+    waiter: UnsafeCell<Waiter>,
+}
+
+unsafe impl<'a> Send for Notified<'a> {}
+unsafe impl<'a> Sync for Notified<'a> {}
+
+#[derive(Debug)]
+enum State {
+    Init(usize),
+    Waiting,
+    Done,
+}
+
+const NOTIFY_WAITERS_SHIFT: usize = 2;
+const STATE_MASK: usize = (1 << NOTIFY_WAITERS_SHIFT) - 1;
+const NOTIFY_WAITERS_CALLS_MASK: usize = !STATE_MASK;
+
+/// Initial "idle" state.
+const EMPTY: usize = 0;
+
+/// One or more threads are currently waiting to be notified.
+const WAITING: usize = 1;
+
+/// Pending notification.
+const NOTIFIED: usize = 2;
+
+fn set_state(data: usize, state: usize) -> usize {
+    (data & NOTIFY_WAITERS_CALLS_MASK) | (state & STATE_MASK)
+}
+
+fn get_state(data: usize) -> usize {
+    data & STATE_MASK
+}
+
+fn get_num_notify_waiters_calls(data: usize) -> usize {
+    (data & NOTIFY_WAITERS_CALLS_MASK) >> NOTIFY_WAITERS_SHIFT
+}
+
+fn inc_num_notify_waiters_calls(data: usize) -> usize {
+    data + (1 << NOTIFY_WAITERS_SHIFT)
+}
+
+fn atomic_inc_num_notify_waiters_calls(data: &AtomicUsize) {
+    data.fetch_add(1 << NOTIFY_WAITERS_SHIFT, SeqCst);
+}
+
+impl Notify {
+    /// Create a new `Notify`, initialized without a permit.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Notify;
+    ///
+    /// let notify = Notify::new();
+    /// ```
+    pub fn new() -> Notify {
+        Notify {
+            state: AtomicUsize::new(0),
+            waiters: Mutex::new(LinkedList::new()),
+        }
+    }
+
+    /// Create a new `Notify`, initialized without a permit.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Notify;
+    ///
+    /// static NOTIFY: Notify = Notify::const_new();
+    /// ```
+    #[cfg(all(feature = "parking_lot", not(all(loom, test))))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "parking_lot")))]
+    pub const fn const_new() -> Notify {
+        Notify {
+            state: AtomicUsize::new(0),
+            waiters: Mutex::const_new(LinkedList::new()),
+        }
+    }
+
+    /// Wait for a notification.
+    ///
+    /// Equivalent to:
+    ///
+    /// ```ignore
+    /// async fn notified(&self);
+    /// ```
+    ///
+    /// Each `Notify` value holds a single permit. If a permit is available from
+    /// an earlier call to [`notify_one()`], then `notified().await` will complete
+    /// immediately, consuming that permit. Otherwise, `notified().await` waits
+    /// for a permit to be made available by the next call to `notify_one()`.
+    ///
+    /// [`notify_one()`]: Notify::notify_one
+    ///
+    /// # Cancel safety
+    ///
+    /// This method uses a queue to fairly distribute notifications in the order
+    /// they were requested. Cancelling a call to `notified` makes you lose your
+    /// place in the queue.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Notify;
+    /// use std::sync::Arc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let notify = Arc::new(Notify::new());
+    ///     let notify2 = notify.clone();
+    ///
+    ///     tokio::spawn(async move {
+    ///         notify2.notified().await;
+    ///         println!("received notification");
+    ///     });
+    ///
+    ///     println!("sending notification");
+    ///     notify.notify_one();
+    /// }
+    /// ```
+    pub fn notified(&self) -> Notified<'_> {
+        // we load the number of times notify_waiters
+        // was called and store that in our initial state
+        let state = self.state.load(SeqCst);
+        Notified {
+            notify: self,
+            state: State::Init(state >> NOTIFY_WAITERS_SHIFT),
+            waiter: UnsafeCell::new(Waiter {
+                pointers: linked_list::Pointers::new(),
+                waker: None,
+                notified: None,
+                _p: PhantomPinned,
+            }),
+        }
+    }
+
+    /// Notifies a waiting task.
+    ///
+    /// If a task is currently waiting, that task is notified. Otherwise, a
+    /// permit is stored in this `Notify` value and the **next** call to
+    /// [`notified().await`] will complete immediately consuming the permit made
+    /// available by this call to `notify_one()`.
+    ///
+    /// At most one permit may be stored by `Notify`. Many sequential calls to
+    /// `notify_one` will result in a single permit being stored. The next call to
+    /// `notified().await` will complete immediately, but the one after that
+    /// will wait.
+    ///
+    /// [`notified().await`]: Notify::notified()
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Notify;
+    /// use std::sync::Arc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let notify = Arc::new(Notify::new());
+    ///     let notify2 = notify.clone();
+    ///
+    ///     tokio::spawn(async move {
+    ///         notify2.notified().await;
+    ///         println!("received notification");
+    ///     });
+    ///
+    ///     println!("sending notification");
+    ///     notify.notify_one();
+    /// }
+    /// ```
+    // Alias for old name in 0.x
+    #[cfg_attr(docsrs, doc(alias = "notify"))]
+    pub fn notify_one(&self) {
+        // Load the current state
+        let mut curr = self.state.load(SeqCst);
+
+        // If the state is `EMPTY`, transition to `NOTIFIED` and return.
+        while let EMPTY | NOTIFIED = get_state(curr) {
+            // The compare-exchange from `NOTIFIED` -> `NOTIFIED` is intended. A
+            // happens-before synchronization must happen between this atomic
+            // operation and a task calling `notified().await`.
+            let new = set_state(curr, NOTIFIED);
+            let res = self.state.compare_exchange(curr, new, SeqCst, SeqCst);
+
+            match res {
+                // No waiters, no further work to do
+                Ok(_) => return,
+                Err(actual) => {
+                    curr = actual;
+                }
+            }
+        }
+
+        // There are waiters, the lock must be acquired to notify.
+        let mut waiters = self.waiters.lock();
+
+        // The state must be reloaded while the lock is held. The state may only
+        // transition out of WAITING while the lock is held.
+        curr = self.state.load(SeqCst);
+
+        if let Some(waker) = notify_locked(&mut waiters, &self.state, curr) {
+            drop(waiters);
+            waker.wake();
+        }
+    }
+
+    /// Notifies all waiting tasks.
+    ///
+    /// If a task is currently waiting, that task is notified. Unlike with
+    /// `notify_one()`, no permit is stored to be used by the next call to
+    /// `notified().await`. The purpose of this method is to notify all
+    /// already registered waiters. Registering for notification is done by
+    /// acquiring an instance of the `Notified` future via calling `notified()`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Notify;
+    /// use std::sync::Arc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let notify = Arc::new(Notify::new());
+    ///     let notify2 = notify.clone();
+    ///
+    ///     let notified1 = notify.notified();
+    ///     let notified2 = notify.notified();
+    ///
+    ///     let handle = tokio::spawn(async move {
+    ///         println!("sending notifications");
+    ///         notify2.notify_waiters();
+    ///     });
+    ///
+    ///     notified1.await;
+    ///     notified2.await;
+    ///     println!("received notifications");
+    /// }
+    /// ```
+    pub fn notify_waiters(&self) {
+        let mut wakers = WakeList::new();
+
+        // There are waiters, the lock must be acquired to notify.
+        let mut waiters = self.waiters.lock();
+
+        // The state must be reloaded while the lock is held. The state may only
+        // transition out of WAITING while the lock is held.
+        let curr = self.state.load(SeqCst);
+
+        if let EMPTY | NOTIFIED = get_state(curr) {
+            // There are no waiting tasks. All we need to do is increment the
+            // number of times this method was called.
+            atomic_inc_num_notify_waiters_calls(&self.state);
+            return;
+        }
+
+        // At this point, it is guaranteed that the state will not
+        // concurrently change, as holding the lock is required to
+        // transition **out** of `WAITING`.
+        'outer: loop {
+            while wakers.can_push() {
+                match waiters.pop_back() {
+                    Some(mut waiter) => {
+                        // Safety: `waiters` lock is still held.
+                        let waiter = unsafe { waiter.as_mut() };
+
+                        assert!(waiter.notified.is_none());
+
+                        waiter.notified = Some(NotificationType::AllWaiters);
+
+                        if let Some(waker) = waiter.waker.take() {
+                            wakers.push(waker);
+                        }
+                    }
+                    None => {
+                        break 'outer;
+                    }
+                }
+            }
+
+            drop(waiters);
+
+            wakers.wake_all();
+
+            // Acquire the lock again.
+            waiters = self.waiters.lock();
+        }
+
+        // All waiters will be notified, the state must be transitioned to
+        // `EMPTY`. As transitioning **from** `WAITING` requires the lock to be
+        // held, a `store` is sufficient.
+        let new = set_state(inc_num_notify_waiters_calls(curr), EMPTY);
+        self.state.store(new, SeqCst);
+
+        // Release the lock before notifying
+        drop(waiters);
+
+        wakers.wake_all();
+    }
+}
+
+impl Default for Notify {
+    fn default() -> Notify {
+        Notify::new()
+    }
+}
+
+fn notify_locked(waiters: &mut WaitList, state: &AtomicUsize, curr: usize) -> Option<Waker> {
+    loop {
+        match get_state(curr) {
+            EMPTY | NOTIFIED => {
+                let res = state.compare_exchange(curr, set_state(curr, NOTIFIED), SeqCst, SeqCst);
+
+                match res {
+                    Ok(_) => return None,
+                    Err(actual) => {
+                        let actual_state = get_state(actual);
+                        assert!(actual_state == EMPTY || actual_state == NOTIFIED);
+                        state.store(set_state(actual, NOTIFIED), SeqCst);
+                        return None;
+                    }
+                }
+            }
+            WAITING => {
+                // At this point, it is guaranteed that the state will not
+                // concurrently change as holding the lock is required to
+                // transition **out** of `WAITING`.
+                //
+                // Get a pending waiter
+                let mut waiter = waiters.pop_back().unwrap();
+
+                // Safety: `waiters` lock is still held.
+                let waiter = unsafe { waiter.as_mut() };
+
+                assert!(waiter.notified.is_none());
+
+                waiter.notified = Some(NotificationType::OneWaiter);
+                let waker = waiter.waker.take();
+
+                if waiters.is_empty() {
+                    // As this the **final** waiter in the list, the state
+                    // must be transitioned to `EMPTY`. As transitioning
+                    // **from** `WAITING` requires the lock to be held, a
+                    // `store` is sufficient.
+                    state.store(set_state(curr, EMPTY), SeqCst);
+                }
+
+                return waker;
+            }
+            _ => unreachable!(),
+        }
+    }
+}
+
+// ===== impl Notified =====
+
+impl Notified<'_> {
+    /// A custom `project` implementation is used in place of `pin-project-lite`
+    /// as a custom drop implementation is needed.
+    fn project(self: Pin<&mut Self>) -> (&Notify, &mut State, &UnsafeCell<Waiter>) {
+        unsafe {
+            // Safety: both `notify` and `state` are `Unpin`.
+
+            is_unpin::<&Notify>();
+            is_unpin::<AtomicUsize>();
+
+            let me = self.get_unchecked_mut();
+            (me.notify, &mut me.state, &me.waiter)
+        }
+    }
+}
+
+impl Future for Notified<'_> {
+    type Output = ();
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
+        use State::*;
+
+        let (notify, state, waiter) = self.project();
+
+        loop {
+            match *state {
+                Init(initial_notify_waiters_calls) => {
+                    let curr = notify.state.load(SeqCst);
+
+                    // Optimistically try acquiring a pending notification
+                    let res = notify.state.compare_exchange(
+                        set_state(curr, NOTIFIED),
+                        set_state(curr, EMPTY),
+                        SeqCst,
+                        SeqCst,
+                    );
+
+                    if res.is_ok() {
+                        // Acquired the notification
+                        *state = Done;
+                        return Poll::Ready(());
+                    }
+
+                    // Clone the waker before locking, a waker clone can be
+                    // triggering arbitrary code.
+                    let waker = cx.waker().clone();
+
+                    // Acquire the lock and attempt to transition to the waiting
+                    // state.
+                    let mut waiters = notify.waiters.lock();
+
+                    // Reload the state with the lock held
+                    let mut curr = notify.state.load(SeqCst);
+
+                    // if notify_waiters has been called after the future
+                    // was created, then we are done
+                    if get_num_notify_waiters_calls(curr) != initial_notify_waiters_calls {
+                        *state = Done;
+                        return Poll::Ready(());
+                    }
+
+                    // Transition the state to WAITING.
+                    loop {
+                        match get_state(curr) {
+                            EMPTY => {
+                                // Transition to WAITING
+                                let res = notify.state.compare_exchange(
+                                    set_state(curr, EMPTY),
+                                    set_state(curr, WAITING),
+                                    SeqCst,
+                                    SeqCst,
+                                );
+
+                                if let Err(actual) = res {
+                                    assert_eq!(get_state(actual), NOTIFIED);
+                                    curr = actual;
+                                } else {
+                                    break;
+                                }
+                            }
+                            WAITING => break,
+                            NOTIFIED => {
+                                // Try consuming the notification
+                                let res = notify.state.compare_exchange(
+                                    set_state(curr, NOTIFIED),
+                                    set_state(curr, EMPTY),
+                                    SeqCst,
+                                    SeqCst,
+                                );
+
+                                match res {
+                                    Ok(_) => {
+                                        // Acquired the notification
+                                        *state = Done;
+                                        return Poll::Ready(());
+                                    }
+                                    Err(actual) => {
+                                        assert_eq!(get_state(actual), EMPTY);
+                                        curr = actual;
+                                    }
+                                }
+                            }
+                            _ => unreachable!(),
+                        }
+                    }
+
+                    // Safety: called while locked.
+                    unsafe {
+                        (*waiter.get()).waker = Some(waker);
+                    }
+
+                    // Insert the waiter into the linked list
+                    //
+                    // safety: pointers from `UnsafeCell` are never null.
+                    waiters.push_front(unsafe { NonNull::new_unchecked(waiter.get()) });
+
+                    *state = Waiting;
+
+                    return Poll::Pending;
+                }
+                Waiting => {
+                    // Currently in the "Waiting" state, implying the caller has
+                    // a waiter stored in the waiter list (guarded by
+                    // `notify.waiters`). In order to access the waker fields,
+                    // we must hold the lock.
+
+                    let waiters = notify.waiters.lock();
+
+                    // Safety: called while locked
+                    let w = unsafe { &mut *waiter.get() };
+
+                    if w.notified.is_some() {
+                        // Our waker has been notified. Reset the fields and
+                        // remove it from the list.
+                        w.waker = None;
+                        w.notified = None;
+
+                        *state = Done;
+                    } else {
+                        // Update the waker, if necessary.
+                        if !w.waker.as_ref().unwrap().will_wake(cx.waker()) {
+                            w.waker = Some(cx.waker().clone());
+                        }
+
+                        return Poll::Pending;
+                    }
+
+                    // Explicit drop of the lock to indicate the scope that the
+                    // lock is held. Because holding the lock is required to
+                    // ensure safe access to fields not held within the lock, it
+                    // is helpful to visualize the scope of the critical
+                    // section.
+                    drop(waiters);
+                }
+                Done => {
+                    return Poll::Ready(());
+                }
+            }
+        }
+    }
+}
+
+impl Drop for Notified<'_> {
+    fn drop(&mut self) {
+        use State::*;
+
+        // Safety: The type only transitions to a "Waiting" state when pinned.
+        let (notify, state, waiter) = unsafe { Pin::new_unchecked(self).project() };
+
+        // This is where we ensure safety. The `Notified` value is being
+        // dropped, which means we must ensure that the waiter entry is no
+        // longer stored in the linked list.
+        if let Waiting = *state {
+            let mut waiters = notify.waiters.lock();
+            let mut notify_state = notify.state.load(SeqCst);
+
+            // remove the entry from the list (if not already removed)
+            //
+            // safety: the waiter is only added to `waiters` by virtue of it
+            // being the only `LinkedList` available to the type.
+            unsafe { waiters.remove(NonNull::new_unchecked(waiter.get())) };
+
+            if waiters.is_empty() {
+                if let WAITING = get_state(notify_state) {
+                    notify_state = set_state(notify_state, EMPTY);
+                    notify.state.store(notify_state, SeqCst);
+                }
+            }
+
+            // See if the node was notified but not received. In this case, if
+            // the notification was triggered via `notify_one`, it must be sent
+            // to the next waiter.
+            //
+            // Safety: with the entry removed from the linked list, there can be
+            // no concurrent access to the entry
+            if let Some(NotificationType::OneWaiter) = unsafe { (*waiter.get()).notified } {
+                if let Some(waker) = notify_locked(&mut waiters, &notify.state, notify_state) {
+                    drop(waiters);
+                    waker.wake();
+                }
+            }
+        }
+    }
+}
+
+/// # Safety
+///
+/// `Waiter` is forced to be !Unpin.
+unsafe impl linked_list::Link for Waiter {
+    type Handle = NonNull<Waiter>;
+    type Target = Waiter;
+
+    fn as_raw(handle: &NonNull<Waiter>) -> NonNull<Waiter> {
+        *handle
+    }
+
+    unsafe fn from_raw(ptr: NonNull<Waiter>) -> NonNull<Waiter> {
+        ptr
+    }
+
+    unsafe fn pointers(target: NonNull<Waiter>) -> NonNull<linked_list::Pointers<Waiter>> {
+        target.cast()
+    }
+}
+
+fn is_unpin<T: Unpin>() {}
diff --git a/third_party/rust/tokio/src/sync/once_cell.rs b/third_party/rust/tokio/src/sync/once_cell.rs
new file mode 100644
index 0000000000..d31a40e2c8
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/once_cell.rs
@@ -0,0 +1,457 @@
+use super::{Semaphore, SemaphorePermit, TryAcquireError};
+use crate::loom::cell::UnsafeCell;
+use std::error::Error;
+use std::fmt;
+use std::future::Future;
+use std::mem::MaybeUninit;
+use std::ops::Drop;
+use std::ptr;
+use std::sync::atomic::{AtomicBool, Ordering};
+
+// This file contains an implementation of an OnceCell. The principle
+// behind the safety the of the cell is that any thread with an `&OnceCell` may
+// access the `value` field according the following rules:
+//
+//  1. When `value_set` is false, the `value` field may be modified by the
+//     thread holding the permit on the semaphore.
+//  2. When `value_set` is true, the `value` field may be accessed immutably by
+//     any thread.
+//
+// It is an invariant that if the semaphore is closed, then `value_set` is true.
+// The reverse does not necessarily hold — but if not, the semaphore may not
+// have any available permits.
+//
+// A thread with a `&mut OnceCell` may modify the value in any way it wants as
+// long as the invariants are upheld.
+
+/// A thread-safe cell that can be written to only once.
+///
+/// A `OnceCell` is typically used for global variables that need to be
+/// initialized once on first use, but need no further changes. The `OnceCell`
+/// in Tokio allows the initialization procedure to be asynchronous.
+///
+/// # Examples
+///
+/// ```
+/// use tokio::sync::OnceCell;
+///
+/// async fn some_computation() -> u32 {
+///     1 + 1
+/// }
+///
+/// static ONCE: OnceCell<u32> = OnceCell::const_new();
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let result = ONCE.get_or_init(some_computation).await;
+///     assert_eq!(*result, 2);
+/// }
+/// ```
+///
+/// It is often useful to write a wrapper method for accessing the value.
+///
+/// ```
+/// use tokio::sync::OnceCell;
+///
+/// static ONCE: OnceCell<u32> = OnceCell::const_new();
+///
+/// async fn get_global_integer() -> &'static u32 {
+///     ONCE.get_or_init(|| async {
+///         1 + 1
+///     }).await
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let result = get_global_integer().await;
+///     assert_eq!(*result, 2);
+/// }
+/// ```
+pub struct OnceCell<T> {
+    value_set: AtomicBool,
+    value: UnsafeCell<MaybeUninit<T>>,
+    semaphore: Semaphore,
+}
+
+impl<T> Default for OnceCell<T> {
+    fn default() -> OnceCell<T> {
+        OnceCell::new()
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for OnceCell<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("OnceCell")
+            .field("value", &self.get())
+            .finish()
+    }
+}
+
+impl<T: Clone> Clone for OnceCell<T> {
+    fn clone(&self) -> OnceCell<T> {
+        OnceCell::new_with(self.get().cloned())
+    }
+}
+
+impl<T: PartialEq> PartialEq for OnceCell<T> {
+    fn eq(&self, other: &OnceCell<T>) -> bool {
+        self.get() == other.get()
+    }
+}
+
+impl<T: Eq> Eq for OnceCell<T> {}
+
+impl<T> Drop for OnceCell<T> {
+    fn drop(&mut self) {
+        if self.initialized_mut() {
+            unsafe {
+                self.value
+                    .with_mut(|ptr| ptr::drop_in_place((&mut *ptr).as_mut_ptr()));
+            };
+        }
+    }
+}
+
+impl<T> From<T> for OnceCell<T> {
+    fn from(value: T) -> Self {
+        let semaphore = Semaphore::new(0);
+        semaphore.close();
+        OnceCell {
+            value_set: AtomicBool::new(true),
+            value: UnsafeCell::new(MaybeUninit::new(value)),
+            semaphore,
+        }
+    }
+}
+
+impl<T> OnceCell<T> {
+    /// Creates a new empty `OnceCell` instance.
+    pub fn new() -> Self {
+        OnceCell {
+            value_set: AtomicBool::new(false),
+            value: UnsafeCell::new(MaybeUninit::uninit()),
+            semaphore: Semaphore::new(1),
+        }
+    }
+
+    /// Creates a new `OnceCell` that contains the provided value, if any.
+    ///
+    /// If the `Option` is `None`, this is equivalent to `OnceCell::new`.
+    ///
+    /// [`OnceCell::new`]: crate::sync::OnceCell::new
+    pub fn new_with(value: Option<T>) -> Self {
+        if let Some(v) = value {
+            OnceCell::from(v)
+        } else {
+            OnceCell::new()
+        }
+    }
+
+    /// Creates a new empty `OnceCell` instance.
+    ///
+    /// Equivalent to `OnceCell::new`, except that it can be used in static
+    /// variables.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use tokio::sync::OnceCell;
+    ///
+    /// static ONCE: OnceCell<u32> = OnceCell::const_new();
+    ///
+    /// async fn get_global_integer() -> &'static u32 {
+    ///     ONCE.get_or_init(|| async {
+    ///         1 + 1
+    ///     }).await
+    /// }
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let result = get_global_integer().await;
+    ///     assert_eq!(*result, 2);
+    /// }
+    /// ```
+    #[cfg(all(feature = "parking_lot", not(all(loom, test))))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "parking_lot")))]
+    pub const fn const_new() -> Self {
+        OnceCell {
+            value_set: AtomicBool::new(false),
+            value: UnsafeCell::new(MaybeUninit::uninit()),
+            semaphore: Semaphore::const_new(1),
+        }
+    }
+
+    /// Returns `true` if the `OnceCell` currently contains a value, and `false`
+    /// otherwise.
+    pub fn initialized(&self) -> bool {
+        // Using acquire ordering so any threads that read a true from this
+        // atomic is able to read the value.
+        self.value_set.load(Ordering::Acquire)
+    }
+
+    /// Returns `true` if the `OnceCell` currently contains a value, and `false`
+    /// otherwise.
+    fn initialized_mut(&mut self) -> bool {
+        *self.value_set.get_mut()
+    }
+
+    // SAFETY: The OnceCell must not be empty.
+    unsafe fn get_unchecked(&self) -> &T {
+        &*self.value.with(|ptr| (*ptr).as_ptr())
+    }
+
+    // SAFETY: The OnceCell must not be empty.
+    unsafe fn get_unchecked_mut(&mut self) -> &mut T {
+        &mut *self.value.with_mut(|ptr| (*ptr).as_mut_ptr())
+    }
+
+    fn set_value(&self, value: T, permit: SemaphorePermit<'_>) -> &T {
+        // SAFETY: We are holding the only permit on the semaphore.
+        unsafe {
+            self.value.with_mut(|ptr| (*ptr).as_mut_ptr().write(value));
+        }
+
+        // Using release ordering so any threads that read a true from this
+        // atomic is able to read the value we just stored.
+        self.value_set.store(true, Ordering::Release);
+        self.semaphore.close();
+        permit.forget();
+
+        // SAFETY: We just initialized the cell.
+        unsafe { self.get_unchecked() }
+    }
+
+    /// Returns a reference to the value currently stored in the `OnceCell`, or
+    /// `None` if the `OnceCell` is empty.
+    pub fn get(&self) -> Option<&T> {
+        if self.initialized() {
+            Some(unsafe { self.get_unchecked() })
+        } else {
+            None
+        }
+    }
+
+    /// Returns a mutable reference to the value currently stored in the
+    /// `OnceCell`, or `None` if the `OnceCell` is empty.
+    ///
+    /// Since this call borrows the `OnceCell` mutably, it is safe to mutate the
+    /// value inside the `OnceCell` — the mutable borrow statically guarantees
+    /// no other references exist.
+    pub fn get_mut(&mut self) -> Option<&mut T> {
+        if self.initialized_mut() {
+            Some(unsafe { self.get_unchecked_mut() })
+        } else {
+            None
+        }
+    }
+
+    /// Sets the value of the `OnceCell` to the given value if the `OnceCell` is
+    /// empty.
+    ///
+    /// If the `OnceCell` already has a value, this call will fail with an
+    /// [`SetError::AlreadyInitializedError`].
+    ///
+    /// If the `OnceCell` is empty, but some other task is currently trying to
+    /// set the value, this call will fail with [`SetError::InitializingError`].
+    ///
+    /// [`SetError::AlreadyInitializedError`]: crate::sync::SetError::AlreadyInitializedError
+    /// [`SetError::InitializingError`]: crate::sync::SetError::InitializingError
+    pub fn set(&self, value: T) -> Result<(), SetError<T>> {
+        if self.initialized() {
+            return Err(SetError::AlreadyInitializedError(value));
+        }
+
+        // Another task might be initializing the cell, in which case
+        // `try_acquire` will return an error. If we succeed to acquire the
+        // permit, then we can set the value.
+        match self.semaphore.try_acquire() {
+            Ok(permit) => {
+                debug_assert!(!self.initialized());
+                self.set_value(value, permit);
+                Ok(())
+            }
+            Err(TryAcquireError::NoPermits) => {
+                // Some other task is holding the permit. That task is
+                // currently trying to initialize the value.
+                Err(SetError::InitializingError(value))
+            }
+            Err(TryAcquireError::Closed) => {
+                // The semaphore was closed. Some other task has initialized
+                // the value.
+                Err(SetError::AlreadyInitializedError(value))
+            }
+        }
+    }
+
+    /// Gets the value currently in the `OnceCell`, or initialize it with the
+    /// given asynchronous operation.
+    ///
+    /// If some other task is currently working on initializing the `OnceCell`,
+    /// this call will wait for that other task to finish, then return the value
+    /// that the other task produced.
+    ///
+    /// If the provided operation is cancelled or panics, the initialization
+    /// attempt is cancelled. If there are other tasks waiting for the value to
+    /// be initialized, one of them will start another attempt at initializing
+    /// the value.
+    ///
+    /// This will deadlock if `f` tries to initialize the cell recursively.
+    pub async fn get_or_init<F, Fut>(&self, f: F) -> &T
+    where
+        F: FnOnce() -> Fut,
+        Fut: Future<Output = T>,
+    {
+        if self.initialized() {
+            // SAFETY: The OnceCell has been fully initialized.
+            unsafe { self.get_unchecked() }
+        } else {
+            // Here we try to acquire the semaphore permit. Holding the permit
+            // will allow us to set the value of the OnceCell, and prevents
+            // other tasks from initializing the OnceCell while we are holding
+            // it.
+            match self.semaphore.acquire().await {
+                Ok(permit) => {
+                    debug_assert!(!self.initialized());
+
+                    // If `f()` panics or `select!` is called, this
+                    // `get_or_init` call is aborted and the semaphore permit is
+                    // dropped.
+                    let value = f().await;
+
+                    self.set_value(value, permit)
+                }
+                Err(_) => {
+                    debug_assert!(self.initialized());
+
+                    // SAFETY: The semaphore has been closed. This only happens
+                    // when the OnceCell is fully initialized.
+                    unsafe { self.get_unchecked() }
+                }
+            }
+        }
+    }
+
+    /// Gets the value currently in the `OnceCell`, or initialize it with the
+    /// given asynchronous operation.
+    ///
+    /// If some other task is currently working on initializing the `OnceCell`,
+    /// this call will wait for that other task to finish, then return the value
+    /// that the other task produced.
+    ///
+    /// If the provided operation returns an error, is cancelled or panics, the
+    /// initialization attempt is cancelled. If there are other tasks waiting
+    /// for the value to be initialized, one of them will start another attempt
+    /// at initializing the value.
+    ///
+    /// This will deadlock if `f` tries to initialize the cell recursively.
+    pub async fn get_or_try_init<E, F, Fut>(&self, f: F) -> Result<&T, E>
+    where
+        F: FnOnce() -> Fut,
+        Fut: Future<Output = Result<T, E>>,
+    {
+        if self.initialized() {
+            // SAFETY: The OnceCell has been fully initialized.
+            unsafe { Ok(self.get_unchecked()) }
+        } else {
+            // Here we try to acquire the semaphore permit. Holding the permit
+            // will allow us to set the value of the OnceCell, and prevents
+            // other tasks from initializing the OnceCell while we are holding
+            // it.
+            match self.semaphore.acquire().await {
+                Ok(permit) => {
+                    debug_assert!(!self.initialized());
+
+                    // If `f()` panics or `select!` is called, this
+                    // `get_or_try_init` call is aborted and the semaphore
+                    // permit is dropped.
+                    let value = f().await;
+
+                    match value {
+                        Ok(value) => Ok(self.set_value(value, permit)),
+                        Err(e) => Err(e),
+                    }
+                }
+                Err(_) => {
+                    debug_assert!(self.initialized());
+
+                    // SAFETY: The semaphore has been closed. This only happens
+                    // when the OnceCell is fully initialized.
+                    unsafe { Ok(self.get_unchecked()) }
+                }
+            }
+        }
+    }
+
+    /// Takes the value from the cell, destroying the cell in the process.
+    /// Returns `None` if the cell is empty.
+    pub fn into_inner(mut self) -> Option<T> {
+        if self.initialized_mut() {
+            // Set to uninitialized for the destructor of `OnceCell` to work properly
+            *self.value_set.get_mut() = false;
+            Some(unsafe { self.value.with(|ptr| ptr::read(ptr).assume_init()) })
+        } else {
+            None
+        }
+    }
+
+    /// Takes ownership of the current value, leaving the cell empty.  Returns
+    /// `None` if the cell is empty.
+    pub fn take(&mut self) -> Option<T> {
+        std::mem::take(self).into_inner()
+    }
+}
+
+// Since `get` gives us access to immutable references of the OnceCell, OnceCell
+// can only be Sync if T is Sync, otherwise OnceCell would allow sharing
+// references of !Sync values across threads. We need T to be Send in order for
+// OnceCell to by Sync because we can use `set` on `&OnceCell<T>` to send values
+// (of type T) across threads.
+unsafe impl<T: Sync + Send> Sync for OnceCell<T> {}
+
+// Access to OnceCell's value is guarded by the semaphore permit
+// and atomic operations on `value_set`, so as long as T itself is Send
+// it's safe to send it to another thread
+unsafe impl<T: Send> Send for OnceCell<T> {}
+
+/// Errors that can be returned from [`OnceCell::set`].
+///
+/// [`OnceCell::set`]: crate::sync::OnceCell::set
+#[derive(Debug, PartialEq)]
+pub enum SetError<T> {
+    /// The cell was already initialized when [`OnceCell::set`] was called.
+    ///
+    /// [`OnceCell::set`]: crate::sync::OnceCell::set
+    AlreadyInitializedError(T),
+
+    /// The cell is currently being initialized.
+    InitializingError(T),
+}
+
+impl<T> fmt::Display for SetError<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            SetError::AlreadyInitializedError(_) => write!(f, "AlreadyInitializedError"),
+            SetError::InitializingError(_) => write!(f, "InitializingError"),
+        }
+    }
+}
+
+impl<T: fmt::Debug> Error for SetError<T> {}
+
+impl<T> SetError<T> {
+    /// Whether `SetError` is `SetError::AlreadyInitializedError`.
+    pub fn is_already_init_err(&self) -> bool {
+        match self {
+            SetError::AlreadyInitializedError(_) => true,
+            SetError::InitializingError(_) => false,
+        }
+    }
+
+    /// Whether `SetError` is `SetError::InitializingError`
+    pub fn is_initializing_err(&self) -> bool {
+        match self {
+            SetError::AlreadyInitializedError(_) => false,
+            SetError::InitializingError(_) => true,
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/oneshot.rs b/third_party/rust/tokio/src/sync/oneshot.rs
new file mode 100644
index 0000000000..2240074e73
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/oneshot.rs
@@ -0,0 +1,1366 @@
+#![cfg_attr(not(feature = "sync"), allow(dead_code, unreachable_pub))]
+
+//! A one-shot channel is used for sending a single message between
+//! asynchronous tasks. The [`channel`] function is used to create a
+//! [`Sender`] and [`Receiver`] handle pair that form the channel.
+//!
+//! The `Sender` handle is used by the producer to send the value.
+//! The `Receiver` handle is used by the consumer to receive the value.
+//!
+//! Each handle can be used on separate tasks.
+//!
+//! Since the `send` method is not async, it can be used anywhere. This includes
+//! sending between two runtimes, and using it from non-async code.
+//!
+//! # Examples
+//!
+//! ```
+//! use tokio::sync::oneshot;
+//!
+//! #[tokio::main]
+//! async fn main() {
+//!     let (tx, rx) = oneshot::channel();
+//!
+//!     tokio::spawn(async move {
+//!         if let Err(_) = tx.send(3) {
+//!             println!("the receiver dropped");
+//!         }
+//!     });
+//!
+//!     match rx.await {
+//!         Ok(v) => println!("got = {:?}", v),
+//!         Err(_) => println!("the sender dropped"),
+//!     }
+//! }
+//! ```
+//!
+//! If the sender is dropped without sending, the receiver will fail with
+//! [`error::RecvError`]:
+//!
+//! ```
+//! use tokio::sync::oneshot;
+//!
+//! #[tokio::main]
+//! async fn main() {
+//!     let (tx, rx) = oneshot::channel::<u32>();
+//!
+//!     tokio::spawn(async move {
+//!         drop(tx);
+//!     });
+//!
+//!     match rx.await {
+//!         Ok(_) => panic!("This doesn't happen"),
+//!         Err(_) => println!("the sender dropped"),
+//!     }
+//! }
+//! ```
+//!
+//! To use a oneshot channel in a `tokio::select!` loop, add `&mut` in front of
+//! the channel.
+//!
+//! ```
+//! use tokio::sync::oneshot;
+//! use tokio::time::{interval, sleep, Duration};
+//!
+//! #[tokio::main]
+//! # async fn _doc() {}
+//! # #[tokio::main(flavor = "current_thread", start_paused = true)]
+//! async fn main() {
+//!     let (send, mut recv) = oneshot::channel();
+//!     let mut interval = interval(Duration::from_millis(100));
+//!
+//!     # let handle =
+//!     tokio::spawn(async move {
+//!         sleep(Duration::from_secs(1)).await;
+//!         send.send("shut down").unwrap();
+//!     });
+//!
+//!     loop {
+//!         tokio::select! {
+//!             _ = interval.tick() => println!("Another 100ms"),
+//!             msg = &mut recv => {
+//!                 println!("Got message: {}", msg.unwrap());
+//!                 break;
+//!             }
+//!         }
+//!     }
+//!     # handle.await.unwrap();
+//! }
+//! ```
+//!
+//! To use a `Sender` from a destructor, put it in an [`Option`] and call
+//! [`Option::take`].
+//!
+//! ```
+//! use tokio::sync::oneshot;
+//!
+//! struct SendOnDrop {
+//!     sender: Option<oneshot::Sender<&'static str>>,
+//! }
+//! impl Drop for SendOnDrop {
+//!     fn drop(&mut self) {
+//!         if let Some(sender) = self.sender.take() {
+//!             // Using `let _ =` to ignore send errors.
+//!             let _ = sender.send("I got dropped!");
+//!         }
+//!     }
+//! }
+//!
+//! #[tokio::main]
+//! # async fn _doc() {}
+//! # #[tokio::main(flavor = "current_thread")]
+//! async fn main() {
+//!     let (send, recv) = oneshot::channel();
+//!
+//!     let send_on_drop = SendOnDrop { sender: Some(send) };
+//!     drop(send_on_drop);
+//!
+//!     assert_eq!(recv.await, Ok("I got dropped!"));
+//! }
+//! ```
+
+use crate::loom::cell::UnsafeCell;
+use crate::loom::sync::atomic::AtomicUsize;
+use crate::loom::sync::Arc;
+#[cfg(all(tokio_unstable, feature = "tracing"))]
+use crate::util::trace;
+
+use std::fmt;
+use std::future::Future;
+use std::mem::MaybeUninit;
+use std::pin::Pin;
+use std::sync::atomic::Ordering::{self, AcqRel, Acquire};
+use std::task::Poll::{Pending, Ready};
+use std::task::{Context, Poll, Waker};
+
+/// Sends a value to the associated [`Receiver`].
+///
+/// A pair of both a [`Sender`] and a [`Receiver`]  are created by the
+/// [`channel`](fn@channel) function.
+///
+/// # Examples
+///
+/// ```
+/// use tokio::sync::oneshot;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let (tx, rx) = oneshot::channel();
+///
+///     tokio::spawn(async move {
+///         if let Err(_) = tx.send(3) {
+///             println!("the receiver dropped");
+///         }
+///     });
+///
+///     match rx.await {
+///         Ok(v) => println!("got = {:?}", v),
+///         Err(_) => println!("the sender dropped"),
+///     }
+/// }
+/// ```
+///
+/// If the sender is dropped without sending, the receiver will fail with
+/// [`error::RecvError`]:
+///
+/// ```
+/// use tokio::sync::oneshot;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let (tx, rx) = oneshot::channel::<u32>();
+///
+///     tokio::spawn(async move {
+///         drop(tx);
+///     });
+///
+///     match rx.await {
+///         Ok(_) => panic!("This doesn't happen"),
+///         Err(_) => println!("the sender dropped"),
+///     }
+/// }
+/// ```
+///
+/// To use a `Sender` from a destructor, put it in an [`Option`] and call
+/// [`Option::take`].
+///
+/// ```
+/// use tokio::sync::oneshot;
+///
+/// struct SendOnDrop {
+///     sender: Option<oneshot::Sender<&'static str>>,
+/// }
+/// impl Drop for SendOnDrop {
+///     fn drop(&mut self) {
+///         if let Some(sender) = self.sender.take() {
+///             // Using `let _ =` to ignore send errors.
+///             let _ = sender.send("I got dropped!");
+///         }
+///     }
+/// }
+///
+/// #[tokio::main]
+/// # async fn _doc() {}
+/// # #[tokio::main(flavor = "current_thread")]
+/// async fn main() {
+///     let (send, recv) = oneshot::channel();
+///
+///     let send_on_drop = SendOnDrop { sender: Some(send) };
+///     drop(send_on_drop);
+///
+///     assert_eq!(recv.await, Ok("I got dropped!"));
+/// }
+/// ```
+///
+/// [`Option`]: std::option::Option
+/// [`Option::take`]: std::option::Option::take
+#[derive(Debug)]
+pub struct Sender<T> {
+    inner: Option<Arc<Inner<T>>>,
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    resource_span: tracing::Span,
+}
+
+/// Receives a value from the associated [`Sender`].
+///
+/// A pair of both a [`Sender`] and a [`Receiver`]  are created by the
+/// [`channel`](fn@channel) function.
+///
+/// This channel has no `recv` method because the receiver itself implements the
+/// [`Future`] trait. To receive a value, `.await` the `Receiver` object directly.
+///
+/// [`Future`]: trait@std::future::Future
+///
+/// # Examples
+///
+/// ```
+/// use tokio::sync::oneshot;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let (tx, rx) = oneshot::channel();
+///
+///     tokio::spawn(async move {
+///         if let Err(_) = tx.send(3) {
+///             println!("the receiver dropped");
+///         }
+///     });
+///
+///     match rx.await {
+///         Ok(v) => println!("got = {:?}", v),
+///         Err(_) => println!("the sender dropped"),
+///     }
+/// }
+/// ```
+///
+/// If the sender is dropped without sending, the receiver will fail with
+/// [`error::RecvError`]:
+///
+/// ```
+/// use tokio::sync::oneshot;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let (tx, rx) = oneshot::channel::<u32>();
+///
+///     tokio::spawn(async move {
+///         drop(tx);
+///     });
+///
+///     match rx.await {
+///         Ok(_) => panic!("This doesn't happen"),
+///         Err(_) => println!("the sender dropped"),
+///     }
+/// }
+/// ```
+///
+/// To use a `Receiver` in a `tokio::select!` loop, add `&mut` in front of the
+/// channel.
+///
+/// ```
+/// use tokio::sync::oneshot;
+/// use tokio::time::{interval, sleep, Duration};
+///
+/// #[tokio::main]
+/// # async fn _doc() {}
+/// # #[tokio::main(flavor = "current_thread", start_paused = true)]
+/// async fn main() {
+///     let (send, mut recv) = oneshot::channel();
+///     let mut interval = interval(Duration::from_millis(100));
+///
+///     # let handle =
+///     tokio::spawn(async move {
+///         sleep(Duration::from_secs(1)).await;
+///         send.send("shut down").unwrap();
+///     });
+///
+///     loop {
+///         tokio::select! {
+///             _ = interval.tick() => println!("Another 100ms"),
+///             msg = &mut recv => {
+///                 println!("Got message: {}", msg.unwrap());
+///                 break;
+///             }
+///         }
+///     }
+///     # handle.await.unwrap();
+/// }
+/// ```
+#[derive(Debug)]
+pub struct Receiver<T> {
+    inner: Option<Arc<Inner<T>>>,
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    resource_span: tracing::Span,
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    async_op_span: tracing::Span,
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    async_op_poll_span: tracing::Span,
+}
+
+pub mod error {
+    //! Oneshot error types.
+
+    use std::fmt;
+
+    /// Error returned by the `Future` implementation for `Receiver`.
+    #[derive(Debug, Eq, PartialEq)]
+    pub struct RecvError(pub(super) ());
+
+    /// Error returned by the `try_recv` function on `Receiver`.
+    #[derive(Debug, Eq, PartialEq)]
+    pub enum TryRecvError {
+        /// The send half of the channel has not yet sent a value.
+        Empty,
+
+        /// The send half of the channel was dropped without sending a value.
+        Closed,
+    }
+
+    // ===== impl RecvError =====
+
+    impl fmt::Display for RecvError {
+        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+            write!(fmt, "channel closed")
+        }
+    }
+
+    impl std::error::Error for RecvError {}
+
+    // ===== impl TryRecvError =====
+
+    impl fmt::Display for TryRecvError {
+        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+            match self {
+                TryRecvError::Empty => write!(fmt, "channel empty"),
+                TryRecvError::Closed => write!(fmt, "channel closed"),
+            }
+        }
+    }
+
+    impl std::error::Error for TryRecvError {}
+}
+
+use self::error::*;
+
+struct Inner<T> {
+    /// Manages the state of the inner cell.
+    state: AtomicUsize,
+
+    /// The value. This is set by `Sender` and read by `Receiver`. The state of
+    /// the cell is tracked by `state`.
+    value: UnsafeCell<Option<T>>,
+
+    /// The task to notify when the receiver drops without consuming the value.
+    ///
+    /// ## Safety
+    ///
+    /// The `TX_TASK_SET` bit in the `state` field is set if this field is
+    /// initialized. If that bit is unset, this field may be uninitialized.
+    tx_task: Task,
+
+    /// The task to notify when the value is sent.
+    ///
+    /// ## Safety
+    ///
+    /// The `RX_TASK_SET` bit in the `state` field is set if this field is
+    /// initialized. If that bit is unset, this field may be uninitialized.
+    rx_task: Task,
+}
+
+struct Task(UnsafeCell<MaybeUninit<Waker>>);
+
+impl Task {
+    unsafe fn will_wake(&self, cx: &mut Context<'_>) -> bool {
+        self.with_task(|w| w.will_wake(cx.waker()))
+    }
+
+    unsafe fn with_task<F, R>(&self, f: F) -> R
+    where
+        F: FnOnce(&Waker) -> R,
+    {
+        self.0.with(|ptr| {
+            let waker: *const Waker = (&*ptr).as_ptr();
+            f(&*waker)
+        })
+    }
+
+    unsafe fn drop_task(&self) {
+        self.0.with_mut(|ptr| {
+            let ptr: *mut Waker = (&mut *ptr).as_mut_ptr();
+            ptr.drop_in_place();
+        });
+    }
+
+    unsafe fn set_task(&self, cx: &mut Context<'_>) {
+        self.0.with_mut(|ptr| {
+            let ptr: *mut Waker = (&mut *ptr).as_mut_ptr();
+            ptr.write(cx.waker().clone());
+        });
+    }
+}
+
+#[derive(Clone, Copy)]
+struct State(usize);
+
+/// Creates a new one-shot channel for sending single values across asynchronous
+/// tasks.
+///
+/// The function returns separate "send" and "receive" handles. The `Sender`
+/// handle is used by the producer to send the value. The `Receiver` handle is
+/// used by the consumer to receive the value.
+///
+/// Each handle can be used on separate tasks.
+///
+/// # Examples
+///
+/// ```
+/// use tokio::sync::oneshot;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let (tx, rx) = oneshot::channel();
+///
+///     tokio::spawn(async move {
+///         if let Err(_) = tx.send(3) {
+///             println!("the receiver dropped");
+///         }
+///     });
+///
+///     match rx.await {
+///         Ok(v) => println!("got = {:?}", v),
+///         Err(_) => println!("the sender dropped"),
+///     }
+/// }
+/// ```
+#[track_caller]
+pub fn channel<T>() -> (Sender<T>, Receiver<T>) {
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    let resource_span = {
+        let location = std::panic::Location::caller();
+
+        let resource_span = tracing::trace_span!(
+            "runtime.resource",
+            concrete_type = "Sender|Receiver",
+            kind = "Sync",
+            loc.file = location.file(),
+            loc.line = location.line(),
+            loc.col = location.column(),
+        );
+
+        resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            tx_dropped = false,
+            tx_dropped.op = "override",
+            )
+        });
+
+        resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            rx_dropped = false,
+            rx_dropped.op = "override",
+            )
+        });
+
+        resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            value_sent = false,
+            value_sent.op = "override",
+            )
+        });
+
+        resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            value_received = false,
+            value_received.op = "override",
+            )
+        });
+
+        resource_span
+    };
+
+    let inner = Arc::new(Inner {
+        state: AtomicUsize::new(State::new().as_usize()),
+        value: UnsafeCell::new(None),
+        tx_task: Task(UnsafeCell::new(MaybeUninit::uninit())),
+        rx_task: Task(UnsafeCell::new(MaybeUninit::uninit())),
+    });
+
+    let tx = Sender {
+        inner: Some(inner.clone()),
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        resource_span: resource_span.clone(),
+    };
+
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    let async_op_span = resource_span
+        .in_scope(|| tracing::trace_span!("runtime.resource.async_op", source = "Receiver::await"));
+
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    let async_op_poll_span =
+        async_op_span.in_scope(|| tracing::trace_span!("runtime.resource.async_op.poll"));
+
+    let rx = Receiver {
+        inner: Some(inner),
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        resource_span: resource_span,
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        async_op_span,
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        async_op_poll_span,
+    };
+
+    (tx, rx)
+}
+
+impl<T> Sender<T> {
+    /// Attempts to send a value on this channel, returning it back if it could
+    /// not be sent.
+    ///
+    /// This method consumes `self` as only one value may ever be sent on a oneshot
+    /// channel. It is not marked async because sending a message to an oneshot
+    /// channel never requires any form of waiting.  Because of this, the `send`
+    /// method can be used in both synchronous and asynchronous code without
+    /// problems.
+    ///
+    /// A successful send occurs when it is determined that the other end of the
+    /// channel has not hung up already. An unsuccessful send would be one where
+    /// the corresponding receiver has already been deallocated. Note that a
+    /// return value of `Err` means that the data will never be received, but
+    /// a return value of `Ok` does *not* mean that the data will be received.
+    /// It is possible for the corresponding receiver to hang up immediately
+    /// after this function returns `Ok`.
+    ///
+    /// # Examples
+    ///
+    /// Send a value to another task
+    ///
+    /// ```
+    /// use tokio::sync::oneshot;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, rx) = oneshot::channel();
+    ///
+    ///     tokio::spawn(async move {
+    ///         if let Err(_) = tx.send(3) {
+    ///             println!("the receiver dropped");
+    ///         }
+    ///     });
+    ///
+    ///     match rx.await {
+    ///         Ok(v) => println!("got = {:?}", v),
+    ///         Err(_) => println!("the sender dropped"),
+    ///     }
+    /// }
+    /// ```
+    pub fn send(mut self, t: T) -> Result<(), T> {
+        let inner = self.inner.take().unwrap();
+
+        inner.value.with_mut(|ptr| unsafe {
+            // SAFETY: The receiver will not access the `UnsafeCell` unless the
+            // channel has been marked as "complete" (the `VALUE_SENT` state bit
+            // is set).
+            // That bit is only set by the sender later on in this method, and
+            // calling this method consumes `self`. Therefore, if it was possible to
+            // call this method, we know that the `VALUE_SENT` bit is unset, and
+            // the receiver is not currently accessing the `UnsafeCell`.
+            *ptr = Some(t);
+        });
+
+        if !inner.complete() {
+            unsafe {
+                // SAFETY: The receiver will not access the `UnsafeCell` unless
+                // the channel has been marked as "complete". Calling
+                // `complete()` will return true if this bit is set, and false
+                // if it is not set. Thus, if `complete()` returned false, it is
+                // safe for us to access the value, because we know that the
+                // receiver will not.
+                return Err(inner.consume_value().unwrap());
+            }
+        }
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            value_sent = true,
+            value_sent.op = "override",
+            )
+        });
+
+        Ok(())
+    }
+
+    /// Waits for the associated [`Receiver`] handle to close.
+    ///
+    /// A [`Receiver`] is closed by either calling [`close`] explicitly or the
+    /// [`Receiver`] value is dropped.
+    ///
+    /// This function is useful when paired with `select!` to abort a
+    /// computation when the receiver is no longer interested in the result.
+    ///
+    /// # Return
+    ///
+    /// Returns a `Future` which must be awaited on.
+    ///
+    /// [`Receiver`]: Receiver
+    /// [`close`]: Receiver::close
+    ///
+    /// # Examples
+    ///
+    /// Basic usage
+    ///
+    /// ```
+    /// use tokio::sync::oneshot;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (mut tx, rx) = oneshot::channel::<()>();
+    ///
+    ///     tokio::spawn(async move {
+    ///         drop(rx);
+    ///     });
+    ///
+    ///     tx.closed().await;
+    ///     println!("the receiver dropped");
+    /// }
+    /// ```
+    ///
+    /// Paired with select
+    ///
+    /// ```
+    /// use tokio::sync::oneshot;
+    /// use tokio::time::{self, Duration};
+    ///
+    /// async fn compute() -> String {
+    ///     // Complex computation returning a `String`
+    /// # "hello".to_string()
+    /// }
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (mut tx, rx) = oneshot::channel();
+    ///
+    ///     tokio::spawn(async move {
+    ///         tokio::select! {
+    ///             _ = tx.closed() => {
+    ///                 // The receiver dropped, no need to do any further work
+    ///             }
+    ///             value = compute() => {
+    ///                 // The send can fail if the channel was closed at the exact same
+    ///                 // time as when compute() finished, so just ignore the failure.
+    ///                 let _ = tx.send(value);
+    ///             }
+    ///         }
+    ///     });
+    ///
+    ///     // Wait for up to 10 seconds
+    ///     let _ = time::timeout(Duration::from_secs(10), rx).await;
+    /// }
+    /// ```
+    pub async fn closed(&mut self) {
+        use crate::future::poll_fn;
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = self.resource_span.clone();
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let closed = trace::async_op(
+            || poll_fn(|cx| self.poll_closed(cx)),
+            resource_span,
+            "Sender::closed",
+            "poll_closed",
+            false,
+        );
+        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+        let closed = poll_fn(|cx| self.poll_closed(cx));
+
+        closed.await
+    }
+
+    /// Returns `true` if the associated [`Receiver`] handle has been dropped.
+    ///
+    /// A [`Receiver`] is closed by either calling [`close`] explicitly or the
+    /// [`Receiver`] value is dropped.
+    ///
+    /// If `true` is returned, a call to `send` will always result in an error.
+    ///
+    /// [`Receiver`]: Receiver
+    /// [`close`]: Receiver::close
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::oneshot;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, rx) = oneshot::channel();
+    ///
+    ///     assert!(!tx.is_closed());
+    ///
+    ///     drop(rx);
+    ///
+    ///     assert!(tx.is_closed());
+    ///     assert!(tx.send("never received").is_err());
+    /// }
+    /// ```
+    pub fn is_closed(&self) -> bool {
+        let inner = self.inner.as_ref().unwrap();
+
+        let state = State::load(&inner.state, Acquire);
+        state.is_closed()
+    }
+
+    /// Checks whether the oneshot channel has been closed, and if not, schedules the
+    /// `Waker` in the provided `Context` to receive a notification when the channel is
+    /// closed.
+    ///
+    /// A [`Receiver`] is closed by either calling [`close`] explicitly, or when the
+    /// [`Receiver`] value is dropped.
+    ///
+    /// Note that on multiple calls to poll, only the `Waker` from the `Context` passed
+    /// to the most recent call will be scheduled to receive a wakeup.
+    ///
+    /// [`Receiver`]: struct@crate::sync::oneshot::Receiver
+    /// [`close`]: fn@crate::sync::oneshot::Receiver::close
+    ///
+    /// # Return value
+    ///
+    /// This function returns:
+    ///
+    ///  * `Poll::Pending` if the channel is still open.
+    ///  * `Poll::Ready(())` if the channel is closed.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::oneshot;
+    ///
+    /// use futures::future::poll_fn;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (mut tx, mut rx) = oneshot::channel::<()>();
+    ///
+    ///     tokio::spawn(async move {
+    ///         rx.close();
+    ///     });
+    ///
+    ///     poll_fn(|cx| tx.poll_closed(cx)).await;
+    ///
+    ///     println!("the receiver dropped");
+    /// }
+    /// ```
+    pub fn poll_closed(&mut self, cx: &mut Context<'_>) -> Poll<()> {
+        // Keep track of task budget
+        let coop = ready!(crate::coop::poll_proceed(cx));
+
+        let inner = self.inner.as_ref().unwrap();
+
+        let mut state = State::load(&inner.state, Acquire);
+
+        if state.is_closed() {
+            coop.made_progress();
+            return Poll::Ready(());
+        }
+
+        if state.is_tx_task_set() {
+            let will_notify = unsafe { inner.tx_task.will_wake(cx) };
+
+            if !will_notify {
+                state = State::unset_tx_task(&inner.state);
+
+                if state.is_closed() {
+                    // Set the flag again so that the waker is released in drop
+                    State::set_tx_task(&inner.state);
+                    coop.made_progress();
+                    return Ready(());
+                } else {
+                    unsafe { inner.tx_task.drop_task() };
+                }
+            }
+        }
+
+        if !state.is_tx_task_set() {
+            // Attempt to set the task
+            unsafe {
+                inner.tx_task.set_task(cx);
+            }
+
+            // Update the state
+            state = State::set_tx_task(&inner.state);
+
+            if state.is_closed() {
+                coop.made_progress();
+                return Ready(());
+            }
+        }
+
+        Pending
+    }
+}
+
+impl<T> Drop for Sender<T> {
+    fn drop(&mut self) {
+        if let Some(inner) = self.inner.as_ref() {
+            inner.complete();
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            self.resource_span.in_scope(|| {
+                tracing::trace!(
+                target: "runtime::resource::state_update",
+                tx_dropped = true,
+                tx_dropped.op = "override",
+                )
+            });
+        }
+    }
+}
+
+impl<T> Receiver<T> {
+    /// Prevents the associated [`Sender`] handle from sending a value.
+    ///
+    /// Any `send` operation which happens after calling `close` is guaranteed
+    /// to fail. After calling `close`, [`try_recv`] should be called to
+    /// receive a value if one was sent **before** the call to `close`
+    /// completed.
+    ///
+    /// This function is useful to perform a graceful shutdown and ensure that a
+    /// value will not be sent into the channel and never received.
+    ///
+    /// `close` is no-op if a message is already received or the channel
+    /// is already closed.
+    ///
+    /// [`Sender`]: Sender
+    /// [`try_recv`]: Receiver::try_recv
+    ///
+    /// # Examples
+    ///
+    /// Prevent a value from being sent
+    ///
+    /// ```
+    /// use tokio::sync::oneshot;
+    /// use tokio::sync::oneshot::error::TryRecvError;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = oneshot::channel();
+    ///
+    ///     assert!(!tx.is_closed());
+    ///
+    ///     rx.close();
+    ///
+    ///     assert!(tx.is_closed());
+    ///     assert!(tx.send("never received").is_err());
+    ///
+    ///     match rx.try_recv() {
+    ///         Err(TryRecvError::Closed) => {}
+    ///         _ => unreachable!(),
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// Receive a value sent **before** calling `close`
+    ///
+    /// ```
+    /// use tokio::sync::oneshot;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = oneshot::channel();
+    ///
+    ///     assert!(tx.send("will receive").is_ok());
+    ///
+    ///     rx.close();
+    ///
+    ///     let msg = rx.try_recv().unwrap();
+    ///     assert_eq!(msg, "will receive");
+    /// }
+    /// ```
+    pub fn close(&mut self) {
+        if let Some(inner) = self.inner.as_ref() {
+            inner.close();
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            self.resource_span.in_scope(|| {
+                tracing::trace!(
+                target: "runtime::resource::state_update",
+                rx_dropped = true,
+                rx_dropped.op = "override",
+                )
+            });
+        }
+    }
+
+    /// Attempts to receive a value.
+    ///
+    /// If a pending value exists in the channel, it is returned. If no value
+    /// has been sent, the current task **will not** be registered for
+    /// future notification.
+    ///
+    /// This function is useful to call from outside the context of an
+    /// asynchronous task.
+    ///
+    /// # Return
+    ///
+    /// - `Ok(T)` if a value is pending in the channel.
+    /// - `Err(TryRecvError::Empty)` if no value has been sent yet.
+    /// - `Err(TryRecvError::Closed)` if the sender has dropped without sending
+    ///   a value.
+    ///
+    /// # Examples
+    ///
+    /// `try_recv` before a value is sent, then after.
+    ///
+    /// ```
+    /// use tokio::sync::oneshot;
+    /// use tokio::sync::oneshot::error::TryRecvError;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = oneshot::channel();
+    ///
+    ///     match rx.try_recv() {
+    ///         // The channel is currently empty
+    ///         Err(TryRecvError::Empty) => {}
+    ///         _ => unreachable!(),
+    ///     }
+    ///
+    ///     // Send a value
+    ///     tx.send("hello").unwrap();
+    ///
+    ///     match rx.try_recv() {
+    ///         Ok(value) => assert_eq!(value, "hello"),
+    ///         _ => unreachable!(),
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// `try_recv` when the sender dropped before sending a value
+    ///
+    /// ```
+    /// use tokio::sync::oneshot;
+    /// use tokio::sync::oneshot::error::TryRecvError;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = oneshot::channel::<()>();
+    ///
+    ///     drop(tx);
+    ///
+    ///     match rx.try_recv() {
+    ///         // The channel will never receive a value.
+    ///         Err(TryRecvError::Closed) => {}
+    ///         _ => unreachable!(),
+    ///     }
+    /// }
+    /// ```
+    pub fn try_recv(&mut self) -> Result<T, TryRecvError> {
+        let result = if let Some(inner) = self.inner.as_ref() {
+            let state = State::load(&inner.state, Acquire);
+
+            if state.is_complete() {
+                // SAFETY: If `state.is_complete()` returns true, then the
+                // `VALUE_SENT` bit has been set and the sender side of the
+                // channel will no longer attempt to access the inner
+                // `UnsafeCell`. Therefore, it is now safe for us to access the
+                // cell.
+                match unsafe { inner.consume_value() } {
+                    Some(value) => {
+                        #[cfg(all(tokio_unstable, feature = "tracing"))]
+                        self.resource_span.in_scope(|| {
+                            tracing::trace!(
+                            target: "runtime::resource::state_update",
+                            value_received = true,
+                            value_received.op = "override",
+                            )
+                        });
+                        Ok(value)
+                    }
+                    None => Err(TryRecvError::Closed),
+                }
+            } else if state.is_closed() {
+                Err(TryRecvError::Closed)
+            } else {
+                // Not ready, this does not clear `inner`
+                return Err(TryRecvError::Empty);
+            }
+        } else {
+            Err(TryRecvError::Closed)
+        };
+
+        self.inner = None;
+        result
+    }
+
+    /// Blocking receive to call outside of asynchronous contexts.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if called within an asynchronous execution
+    /// context.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::thread;
+    /// use tokio::sync::oneshot;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, rx) = oneshot::channel::<u8>();
+    ///
+    ///     let sync_code = thread::spawn(move || {
+    ///         assert_eq!(Ok(10), rx.blocking_recv());
+    ///     });
+    ///
+    ///     let _ = tx.send(10);
+    ///     sync_code.join().unwrap();
+    /// }
+    /// ```
+    #[cfg(feature = "sync")]
+    pub fn blocking_recv(self) -> Result<T, RecvError> {
+        crate::future::block_on(self)
+    }
+}
+
+impl<T> Drop for Receiver<T> {
+    fn drop(&mut self) {
+        if let Some(inner) = self.inner.as_ref() {
+            inner.close();
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            self.resource_span.in_scope(|| {
+                tracing::trace!(
+                target: "runtime::resource::state_update",
+                rx_dropped = true,
+                rx_dropped.op = "override",
+                )
+            });
+        }
+    }
+}
+
+impl<T> Future for Receiver<T> {
+    type Output = Result<T, RecvError>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        // If `inner` is `None`, then `poll()` has already completed.
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let _res_span = self.resource_span.clone().entered();
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let _ao_span = self.async_op_span.clone().entered();
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let _ao_poll_span = self.async_op_poll_span.clone().entered();
+
+        let ret = if let Some(inner) = self.as_ref().get_ref().inner.as_ref() {
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            let res = ready!(trace_poll_op!("poll_recv", inner.poll_recv(cx)))?;
+
+            #[cfg(any(not(tokio_unstable), not(feature = "tracing")))]
+            let res = ready!(inner.poll_recv(cx))?;
+
+            res
+        } else {
+            panic!("called after complete");
+        };
+
+        self.inner = None;
+        Ready(Ok(ret))
+    }
+}
+
+impl<T> Inner<T> {
+    fn complete(&self) -> bool {
+        let prev = State::set_complete(&self.state);
+
+        if prev.is_closed() {
+            return false;
+        }
+
+        if prev.is_rx_task_set() {
+            // TODO: Consume waker?
+            unsafe {
+                self.rx_task.with_task(Waker::wake_by_ref);
+            }
+        }
+
+        true
+    }
+
+    fn poll_recv(&self, cx: &mut Context<'_>) -> Poll<Result<T, RecvError>> {
+        // Keep track of task budget
+        let coop = ready!(crate::coop::poll_proceed(cx));
+
+        // Load the state
+        let mut state = State::load(&self.state, Acquire);
+
+        if state.is_complete() {
+            coop.made_progress();
+            match unsafe { self.consume_value() } {
+                Some(value) => Ready(Ok(value)),
+                None => Ready(Err(RecvError(()))),
+            }
+        } else if state.is_closed() {
+            coop.made_progress();
+            Ready(Err(RecvError(())))
+        } else {
+            if state.is_rx_task_set() {
+                let will_notify = unsafe { self.rx_task.will_wake(cx) };
+
+                // Check if the task is still the same
+                if !will_notify {
+                    // Unset the task
+                    state = State::unset_rx_task(&self.state);
+                    if state.is_complete() {
+                        // Set the flag again so that the waker is released in drop
+                        State::set_rx_task(&self.state);
+
+                        coop.made_progress();
+                        // SAFETY: If `state.is_complete()` returns true, then the
+                        // `VALUE_SENT` bit has been set and the sender side of the
+                        // channel will no longer attempt to access the inner
+                        // `UnsafeCell`. Therefore, it is now safe for us to access the
+                        // cell.
+                        return match unsafe { self.consume_value() } {
+                            Some(value) => Ready(Ok(value)),
+                            None => Ready(Err(RecvError(()))),
+                        };
+                    } else {
+                        unsafe { self.rx_task.drop_task() };
+                    }
+                }
+            }
+
+            if !state.is_rx_task_set() {
+                // Attempt to set the task
+                unsafe {
+                    self.rx_task.set_task(cx);
+                }
+
+                // Update the state
+                state = State::set_rx_task(&self.state);
+
+                if state.is_complete() {
+                    coop.made_progress();
+                    match unsafe { self.consume_value() } {
+                        Some(value) => Ready(Ok(value)),
+                        None => Ready(Err(RecvError(()))),
+                    }
+                } else {
+                    Pending
+                }
+            } else {
+                Pending
+            }
+        }
+    }
+
+    /// Called by `Receiver` to indicate that the value will never be received.
+    fn close(&self) {
+        let prev = State::set_closed(&self.state);
+
+        if prev.is_tx_task_set() && !prev.is_complete() {
+            unsafe {
+                self.tx_task.with_task(Waker::wake_by_ref);
+            }
+        }
+    }
+
+    /// Consumes the value. This function does not check `state`.
+    ///
+    /// # Safety
+    ///
+    /// Calling this method concurrently on multiple threads will result in a
+    /// data race. The `VALUE_SENT` state bit is used to ensure that only the
+    /// sender *or* the receiver will call this method at a given point in time.
+    /// If `VALUE_SENT` is not set, then only the sender may call this method;
+    /// if it is set, then only the receiver may call this method.
+    unsafe fn consume_value(&self) -> Option<T> {
+        self.value.with_mut(|ptr| (*ptr).take())
+    }
+}
+
+unsafe impl<T: Send> Send for Inner<T> {}
+unsafe impl<T: Send> Sync for Inner<T> {}
+
+fn mut_load(this: &mut AtomicUsize) -> usize {
+    this.with_mut(|v| *v)
+}
+
+impl<T> Drop for Inner<T> {
+    fn drop(&mut self) {
+        let state = State(mut_load(&mut self.state));
+
+        if state.is_rx_task_set() {
+            unsafe {
+                self.rx_task.drop_task();
+            }
+        }
+
+        if state.is_tx_task_set() {
+            unsafe {
+                self.tx_task.drop_task();
+            }
+        }
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for Inner<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use std::sync::atomic::Ordering::Relaxed;
+
+        fmt.debug_struct("Inner")
+            .field("state", &State::load(&self.state, Relaxed))
+            .finish()
+    }
+}
+
+/// Indicates that a waker for the receiving task has been set.
+///
+/// # Safety
+///
+/// If this bit is not set, the `rx_task` field may be uninitialized.
+const RX_TASK_SET: usize = 0b00001;
+/// Indicates that a value has been stored in the channel's inner `UnsafeCell`.
+///
+/// # Safety
+///
+/// This bit controls which side of the channel is permitted to access the
+/// `UnsafeCell`. If it is set, the `UnsafeCell` may ONLY be accessed by the
+/// receiver. If this bit is NOT set, the `UnsafeCell` may ONLY be accessed by
+/// the sender.
+const VALUE_SENT: usize = 0b00010;
+const CLOSED: usize = 0b00100;
+
+/// Indicates that a waker for the sending task has been set.
+///
+/// # Safety
+///
+/// If this bit is not set, the `tx_task` field may be uninitialized.
+const TX_TASK_SET: usize = 0b01000;
+
+impl State {
+    fn new() -> State {
+        State(0)
+    }
+
+    fn is_complete(self) -> bool {
+        self.0 & VALUE_SENT == VALUE_SENT
+    }
+
+    fn set_complete(cell: &AtomicUsize) -> State {
+        // This method is a compare-and-swap loop rather than a fetch-or like
+        // other `set_$WHATEVER` methods on `State`. This is because we must
+        // check if the state has been closed before setting the `VALUE_SENT`
+        // bit.
+        //
+        // We don't want to set both the `VALUE_SENT` bit if the `CLOSED`
+        // bit is already set, because `VALUE_SENT` will tell the receiver that
+        // it's okay to access the inner `UnsafeCell`. Immediately after calling
+        // `set_complete`, if the channel was closed, the sender will _also_
+        // access the `UnsafeCell` to take the value back out, so if a
+        // `poll_recv` or `try_recv` call is occurring concurrently, both
+        // threads may try to access the `UnsafeCell` if we were to set the
+        // `VALUE_SENT` bit on a closed channel.
+        let mut state = cell.load(Ordering::Relaxed);
+        loop {
+            if State(state).is_closed() {
+                break;
+            }
+            // TODO: This could be `Release`, followed by an `Acquire` fence *if*
+            // the `RX_TASK_SET` flag is set. However, `loom` does not support
+            // fences yet.
+            match cell.compare_exchange_weak(
+                state,
+                state | VALUE_SENT,
+                Ordering::AcqRel,
+                Ordering::Acquire,
+            ) {
+                Ok(_) => break,
+                Err(actual) => state = actual,
+            }
+        }
+        State(state)
+    }
+
+    fn is_rx_task_set(self) -> bool {
+        self.0 & RX_TASK_SET == RX_TASK_SET
+    }
+
+    fn set_rx_task(cell: &AtomicUsize) -> State {
+        let val = cell.fetch_or(RX_TASK_SET, AcqRel);
+        State(val | RX_TASK_SET)
+    }
+
+    fn unset_rx_task(cell: &AtomicUsize) -> State {
+        let val = cell.fetch_and(!RX_TASK_SET, AcqRel);
+        State(val & !RX_TASK_SET)
+    }
+
+    fn is_closed(self) -> bool {
+        self.0 & CLOSED == CLOSED
+    }
+
+    fn set_closed(cell: &AtomicUsize) -> State {
+        // Acquire because we want all later writes (attempting to poll) to be
+        // ordered after this.
+        let val = cell.fetch_or(CLOSED, Acquire);
+        State(val)
+    }
+
+    fn set_tx_task(cell: &AtomicUsize) -> State {
+        let val = cell.fetch_or(TX_TASK_SET, AcqRel);
+        State(val | TX_TASK_SET)
+    }
+
+    fn unset_tx_task(cell: &AtomicUsize) -> State {
+        let val = cell.fetch_and(!TX_TASK_SET, AcqRel);
+        State(val & !TX_TASK_SET)
+    }
+
+    fn is_tx_task_set(self) -> bool {
+        self.0 & TX_TASK_SET == TX_TASK_SET
+    }
+
+    fn as_usize(self) -> usize {
+        self.0
+    }
+
+    fn load(cell: &AtomicUsize, order: Ordering) -> State {
+        let val = cell.load(order);
+        State(val)
+    }
+}
+
+impl fmt::Debug for State {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("State")
+            .field("is_complete", &self.is_complete())
+            .field("is_closed", &self.is_closed())
+            .field("is_rx_task_set", &self.is_rx_task_set())
+            .field("is_tx_task_set", &self.is_tx_task_set())
+            .finish()
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/rwlock.rs b/third_party/rust/tokio/src/sync/rwlock.rs
new file mode 100644
index 0000000000..b856cfc856
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/rwlock.rs
@@ -0,0 +1,1078 @@
+use crate::sync::batch_semaphore::{Semaphore, TryAcquireError};
+use crate::sync::mutex::TryLockError;
+#[cfg(all(tokio_unstable, feature = "tracing"))]
+use crate::util::trace;
+use std::cell::UnsafeCell;
+use std::marker;
+use std::marker::PhantomData;
+use std::mem::ManuallyDrop;
+use std::sync::Arc;
+
+pub(crate) mod owned_read_guard;
+pub(crate) mod owned_write_guard;
+pub(crate) mod owned_write_guard_mapped;
+pub(crate) mod read_guard;
+pub(crate) mod write_guard;
+pub(crate) mod write_guard_mapped;
+pub(crate) use owned_read_guard::OwnedRwLockReadGuard;
+pub(crate) use owned_write_guard::OwnedRwLockWriteGuard;
+pub(crate) use owned_write_guard_mapped::OwnedRwLockMappedWriteGuard;
+pub(crate) use read_guard::RwLockReadGuard;
+pub(crate) use write_guard::RwLockWriteGuard;
+pub(crate) use write_guard_mapped::RwLockMappedWriteGuard;
+
+#[cfg(not(loom))]
+const MAX_READS: u32 = std::u32::MAX >> 3;
+
+#[cfg(loom)]
+const MAX_READS: u32 = 10;
+
+/// An asynchronous reader-writer lock.
+///
+/// This type of lock allows a number of readers or at most one writer at any
+/// point in time. The write portion of this lock typically allows modification
+/// of the underlying data (exclusive access) and the read portion of this lock
+/// typically allows for read-only access (shared access).
+///
+/// In comparison, a [`Mutex`] does not distinguish between readers or writers
+/// that acquire the lock, therefore causing any tasks waiting for the lock to
+/// become available to yield. An `RwLock` will allow any number of readers to
+/// acquire the lock as long as a writer is not holding the lock.
+///
+/// The priority policy of Tokio's read-write lock is _fair_ (or
+/// [_write-preferring_]), in order to ensure that readers cannot starve
+/// writers. Fairness is ensured using a first-in, first-out queue for the tasks
+/// awaiting the lock; if a task that wishes to acquire the write lock is at the
+/// head of the queue, read locks will not be given out until the write lock has
+/// been released. This is in contrast to the Rust standard library's
+/// `std::sync::RwLock`, where the priority policy is dependent on the
+/// operating system's implementation.
+///
+/// The type parameter `T` represents the data that this lock protects. It is
+/// required that `T` satisfies [`Send`] to be shared across threads. The RAII guards
+/// returned from the locking methods implement [`Deref`](trait@std::ops::Deref)
+/// (and [`DerefMut`](trait@std::ops::DerefMut)
+/// for the `write` methods) to allow access to the content of the lock.
+///
+/// # Examples
+///
+/// ```
+/// use tokio::sync::RwLock;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let lock = RwLock::new(5);
+///
+///     // many reader locks can be held at once
+///     {
+///         let r1 = lock.read().await;
+///         let r2 = lock.read().await;
+///         assert_eq!(*r1, 5);
+///         assert_eq!(*r2, 5);
+///     } // read locks are dropped at this point
+///
+///     // only one write lock may be held, however
+///     {
+///         let mut w = lock.write().await;
+///         *w += 1;
+///         assert_eq!(*w, 6);
+///     } // write lock is dropped here
+/// }
+/// ```
+///
+/// [`Mutex`]: struct@super::Mutex
+/// [`RwLock`]: struct@RwLock
+/// [`RwLockReadGuard`]: struct@RwLockReadGuard
+/// [`RwLockWriteGuard`]: struct@RwLockWriteGuard
+/// [`Send`]: trait@std::marker::Send
+/// [_write-preferring_]: https://en.wikipedia.org/wiki/Readers%E2%80%93writer_lock#Priority_policies
+#[derive(Debug)]
+pub struct RwLock<T: ?Sized> {
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    resource_span: tracing::Span,
+
+    // maximum number of concurrent readers
+    mr: u32,
+
+    //semaphore to coordinate read and write access to T
+    s: Semaphore,
+
+    //inner data T
+    c: UnsafeCell<T>,
+}
+
+#[test]
+#[cfg(not(loom))]
+fn bounds() {
+    fn check_send<T: Send>() {}
+    fn check_sync<T: Sync>() {}
+    fn check_unpin<T: Unpin>() {}
+    // This has to take a value, since the async fn's return type is unnameable.
+    fn check_send_sync_val<T: Send + Sync>(_t: T) {}
+
+    check_send::<RwLock<u32>>();
+    check_sync::<RwLock<u32>>();
+    check_unpin::<RwLock<u32>>();
+
+    check_send::<RwLockReadGuard<'_, u32>>();
+    check_sync::<RwLockReadGuard<'_, u32>>();
+    check_unpin::<RwLockReadGuard<'_, u32>>();
+
+    check_send::<OwnedRwLockReadGuard<u32, i32>>();
+    check_sync::<OwnedRwLockReadGuard<u32, i32>>();
+    check_unpin::<OwnedRwLockReadGuard<u32, i32>>();
+
+    check_send::<RwLockWriteGuard<'_, u32>>();
+    check_sync::<RwLockWriteGuard<'_, u32>>();
+    check_unpin::<RwLockWriteGuard<'_, u32>>();
+
+    check_send::<RwLockMappedWriteGuard<'_, u32>>();
+    check_sync::<RwLockMappedWriteGuard<'_, u32>>();
+    check_unpin::<RwLockMappedWriteGuard<'_, u32>>();
+
+    check_send::<OwnedRwLockWriteGuard<u32>>();
+    check_sync::<OwnedRwLockWriteGuard<u32>>();
+    check_unpin::<OwnedRwLockWriteGuard<u32>>();
+
+    check_send::<OwnedRwLockMappedWriteGuard<u32, i32>>();
+    check_sync::<OwnedRwLockMappedWriteGuard<u32, i32>>();
+    check_unpin::<OwnedRwLockMappedWriteGuard<u32, i32>>();
+
+    let rwlock = Arc::new(RwLock::new(0));
+    check_send_sync_val(rwlock.read());
+    check_send_sync_val(Arc::clone(&rwlock).read_owned());
+    check_send_sync_val(rwlock.write());
+    check_send_sync_val(Arc::clone(&rwlock).write_owned());
+}
+
+// As long as T: Send + Sync, it's fine to send and share RwLock<T> between threads.
+// If T were not Send, sending and sharing a RwLock<T> would be bad, since you can access T through
+// RwLock<T>.
+unsafe impl<T> Send for RwLock<T> where T: ?Sized + Send {}
+unsafe impl<T> Sync for RwLock<T> where T: ?Sized + Send + Sync {}
+// NB: These impls need to be explicit since we're storing a raw pointer.
+// Safety: Stores a raw pointer to `T`, so if `T` is `Sync`, the lock guard over
+// `T` is `Send`.
+unsafe impl<T> Send for RwLockReadGuard<'_, T> where T: ?Sized + Sync {}
+unsafe impl<T> Sync for RwLockReadGuard<'_, T> where T: ?Sized + Send + Sync {}
+// T is required to be `Send` because an OwnedRwLockReadGuard can be used to drop the value held in
+// the RwLock, unlike RwLockReadGuard.
+unsafe impl<T, U> Send for OwnedRwLockReadGuard<T, U>
+where
+    T: ?Sized + Send + Sync,
+    U: ?Sized + Sync,
+{
+}
+unsafe impl<T, U> Sync for OwnedRwLockReadGuard<T, U>
+where
+    T: ?Sized + Send + Sync,
+    U: ?Sized + Send + Sync,
+{
+}
+unsafe impl<T> Sync for RwLockWriteGuard<'_, T> where T: ?Sized + Send + Sync {}
+unsafe impl<T> Sync for OwnedRwLockWriteGuard<T> where T: ?Sized + Send + Sync {}
+unsafe impl<T> Sync for RwLockMappedWriteGuard<'_, T> where T: ?Sized + Send + Sync {}
+unsafe impl<T, U> Sync for OwnedRwLockMappedWriteGuard<T, U>
+where
+    T: ?Sized + Send + Sync,
+    U: ?Sized + Send + Sync,
+{
+}
+// Safety: Stores a raw pointer to `T`, so if `T` is `Sync`, the lock guard over
+// `T` is `Send` - but since this is also provides mutable access, we need to
+// make sure that `T` is `Send` since its value can be sent across thread
+// boundaries.
+unsafe impl<T> Send for RwLockWriteGuard<'_, T> where T: ?Sized + Send + Sync {}
+unsafe impl<T> Send for OwnedRwLockWriteGuard<T> where T: ?Sized + Send + Sync {}
+unsafe impl<T> Send for RwLockMappedWriteGuard<'_, T> where T: ?Sized + Send + Sync {}
+unsafe impl<T, U> Send for OwnedRwLockMappedWriteGuard<T, U>
+where
+    T: ?Sized + Send + Sync,
+    U: ?Sized + Send + Sync,
+{
+}
+
+impl<T: ?Sized> RwLock<T> {
+    /// Creates a new instance of an `RwLock<T>` which is unlocked.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::RwLock;
+    ///
+    /// let lock = RwLock::new(5);
+    /// ```
+    #[track_caller]
+    pub fn new(value: T) -> RwLock<T>
+    where
+        T: Sized,
+    {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = {
+            let location = std::panic::Location::caller();
+            let resource_span = tracing::trace_span!(
+                "runtime.resource",
+                concrete_type = "RwLock",
+                kind = "Sync",
+                loc.file = location.file(),
+                loc.line = location.line(),
+                loc.col = location.column(),
+            );
+
+            resource_span.in_scope(|| {
+                tracing::trace!(
+                    target: "runtime::resource::state_update",
+                    max_readers = MAX_READS,
+                );
+
+                tracing::trace!(
+                    target: "runtime::resource::state_update",
+                    write_locked = false,
+                );
+
+                tracing::trace!(
+                    target: "runtime::resource::state_update",
+                    current_readers = 0,
+                );
+            });
+
+            resource_span
+        };
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let s = resource_span.in_scope(|| Semaphore::new(MAX_READS as usize));
+
+        #[cfg(any(not(tokio_unstable), not(feature = "tracing")))]
+        let s = Semaphore::new(MAX_READS as usize);
+
+        RwLock {
+            mr: MAX_READS,
+            c: UnsafeCell::new(value),
+            s,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+
+    /// Creates a new instance of an `RwLock<T>` which is unlocked
+    /// and allows a maximum of `max_reads` concurrent readers.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::RwLock;
+    ///
+    /// let lock = RwLock::with_max_readers(5, 1024);
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// Panics if `max_reads` is more than `u32::MAX >> 3`.
+    #[track_caller]
+    pub fn with_max_readers(value: T, max_reads: u32) -> RwLock<T>
+    where
+        T: Sized,
+    {
+        assert!(
+            max_reads <= MAX_READS,
+            "a RwLock may not be created with more than {} readers",
+            MAX_READS
+        );
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = {
+            let location = std::panic::Location::caller();
+
+            let resource_span = tracing::trace_span!(
+                "runtime.resource",
+                concrete_type = "RwLock",
+                kind = "Sync",
+                loc.file = location.file(),
+                loc.line = location.line(),
+                loc.col = location.column(),
+            );
+
+            resource_span.in_scope(|| {
+                tracing::trace!(
+                    target: "runtime::resource::state_update",
+                    max_readers = max_reads,
+                );
+
+                tracing::trace!(
+                    target: "runtime::resource::state_update",
+                    write_locked = false,
+                );
+
+                tracing::trace!(
+                    target: "runtime::resource::state_update",
+                    current_readers = 0,
+                );
+            });
+
+            resource_span
+        };
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let s = resource_span.in_scope(|| Semaphore::new(max_reads as usize));
+
+        #[cfg(any(not(tokio_unstable), not(feature = "tracing")))]
+        let s = Semaphore::new(max_reads as usize);
+
+        RwLock {
+            mr: max_reads,
+            c: UnsafeCell::new(value),
+            s,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+
+    /// Creates a new instance of an `RwLock<T>` which is unlocked.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::RwLock;
+    ///
+    /// static LOCK: RwLock<i32> = RwLock::const_new(5);
+    /// ```
+    #[cfg(all(feature = "parking_lot", not(all(loom, test))))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "parking_lot")))]
+    pub const fn const_new(value: T) -> RwLock<T>
+    where
+        T: Sized,
+    {
+        RwLock {
+            mr: MAX_READS,
+            c: UnsafeCell::new(value),
+            s: Semaphore::const_new(MAX_READS as usize),
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span: tracing::Span::none(),
+        }
+    }
+
+    /// Creates a new instance of an `RwLock<T>` which is unlocked
+    /// and allows a maximum of `max_reads` concurrent readers.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::RwLock;
+    ///
+    /// static LOCK: RwLock<i32> = RwLock::const_with_max_readers(5, 1024);
+    /// ```
+    #[cfg(all(feature = "parking_lot", not(all(loom, test))))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "parking_lot")))]
+    pub const fn const_with_max_readers(value: T, mut max_reads: u32) -> RwLock<T>
+    where
+        T: Sized,
+    {
+        max_reads &= MAX_READS;
+        RwLock {
+            mr: max_reads,
+            c: UnsafeCell::new(value),
+            s: Semaphore::const_new(max_reads as usize),
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span: tracing::Span::none(),
+        }
+    }
+
+    /// Locks this `RwLock` with shared read access, causing the current task
+    /// to yield until the lock has been acquired.
+    ///
+    /// The calling task will yield until there are no writers which hold the
+    /// lock. There may be other readers inside the lock when the task resumes.
+    ///
+    /// Note that under the priority policy of [`RwLock`], read locks are not
+    /// granted until prior write locks, to prevent starvation. Therefore
+    /// deadlock may occur if a read lock is held by the current task, a write
+    /// lock attempt is made, and then a subsequent read lock attempt is made
+    /// by the current task.
+    ///
+    /// Returns an RAII guard which will drop this read access of the `RwLock`
+    /// when dropped.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method uses a queue to fairly distribute locks in the order they
+    /// were requested. Cancelling a call to `read` makes you lose your place in
+    /// the queue.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::RwLock;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let lock = Arc::new(RwLock::new(1));
+    ///     let c_lock = lock.clone();
+    ///
+    ///     let n = lock.read().await;
+    ///     assert_eq!(*n, 1);
+    ///
+    ///     tokio::spawn(async move {
+    ///         // While main has an active read lock, we acquire one too.
+    ///         let r = c_lock.read().await;
+    ///         assert_eq!(*r, 1);
+    ///     }).await.expect("The spawned task has panicked");
+    ///
+    ///     // Drop the guard after the spawned task finishes.
+    ///     drop(n);
+    /// }
+    /// ```
+    pub async fn read(&self) -> RwLockReadGuard<'_, T> {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let inner = trace::async_op(
+            || self.s.acquire(1),
+            self.resource_span.clone(),
+            "RwLock::read",
+            "poll",
+            false,
+        );
+
+        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+        let inner = self.s.acquire(1);
+
+        inner.await.unwrap_or_else(|_| {
+            // The semaphore was closed. but, we never explicitly close it, and we have a
+            // handle to it through the Arc, which means that this can never happen.
+            unreachable!()
+        });
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            current_readers = 1,
+            current_readers.op = "add",
+            )
+        });
+
+        RwLockReadGuard {
+            s: &self.s,
+            data: self.c.get(),
+            marker: marker::PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span: self.resource_span.clone(),
+        }
+    }
+
+    /// Blockingly locks this `RwLock` with shared read access.
+    ///
+    /// This method is intended for use cases where you
+    /// need to use this rwlock in asynchronous code as well as in synchronous code.
+    ///
+    /// Returns an RAII guard which will drop the read access of this `RwLock` when dropped.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if called within an asynchronous execution context.
+    ///
+    ///   - If you find yourself in an asynchronous execution context and needing
+    ///     to call some (synchronous) function which performs one of these
+    ///     `blocking_` operations, then consider wrapping that call inside
+    ///     [`spawn_blocking()`][crate::runtime::Handle::spawn_blocking]
+    ///     (or [`block_in_place()`][crate::task::block_in_place]).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::RwLock;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let rwlock = Arc::new(RwLock::new(1));
+    ///     let mut write_lock = rwlock.write().await;
+    ///
+    ///     let blocking_task = tokio::task::spawn_blocking({
+    ///         let rwlock = Arc::clone(&rwlock);
+    ///         move || {
+    ///             // This shall block until the `write_lock` is released.
+    ///             let read_lock = rwlock.blocking_read();
+    ///             assert_eq!(*read_lock, 0);
+    ///         }
+    ///     });
+    ///
+    ///     *write_lock -= 1;
+    ///     drop(write_lock); // release the lock.
+    ///
+    ///     // Await the completion of the blocking task.
+    ///     blocking_task.await.unwrap();
+    ///
+    ///     // Assert uncontended.
+    ///     assert!(rwlock.try_write().is_ok());
+    /// }
+    /// ```
+    #[cfg(feature = "sync")]
+    pub fn blocking_read(&self) -> RwLockReadGuard<'_, T> {
+        crate::future::block_on(self.read())
+    }
+
+    /// Locks this `RwLock` with shared read access, causing the current task
+    /// to yield until the lock has been acquired.
+    ///
+    /// The calling task will yield until there are no writers which hold the
+    /// lock. There may be other readers inside the lock when the task resumes.
+    ///
+    /// This method is identical to [`RwLock::read`], except that the returned
+    /// guard references the `RwLock` with an [`Arc`] rather than by borrowing
+    /// it. Therefore, the `RwLock` must be wrapped in an `Arc` to call this
+    /// method, and the guard will live for the `'static` lifetime, as it keeps
+    /// the `RwLock` alive by holding an `Arc`.
+    ///
+    /// Note that under the priority policy of [`RwLock`], read locks are not
+    /// granted until prior write locks, to prevent starvation. Therefore
+    /// deadlock may occur if a read lock is held by the current task, a write
+    /// lock attempt is made, and then a subsequent read lock attempt is made
+    /// by the current task.
+    ///
+    /// Returns an RAII guard which will drop this read access of the `RwLock`
+    /// when dropped.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method uses a queue to fairly distribute locks in the order they
+    /// were requested. Cancelling a call to `read_owned` makes you lose your
+    /// place in the queue.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::RwLock;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let lock = Arc::new(RwLock::new(1));
+    ///     let c_lock = lock.clone();
+    ///
+    ///     let n = lock.read_owned().await;
+    ///     assert_eq!(*n, 1);
+    ///
+    ///     tokio::spawn(async move {
+    ///         // While main has an active read lock, we acquire one too.
+    ///         let r = c_lock.read_owned().await;
+    ///         assert_eq!(*r, 1);
+    ///     }).await.expect("The spawned task has panicked");
+    ///
+    ///     // Drop the guard after the spawned task finishes.
+    ///     drop(n);
+    ///}
+    /// ```
+    pub async fn read_owned(self: Arc<Self>) -> OwnedRwLockReadGuard<T> {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let inner = trace::async_op(
+            || self.s.acquire(1),
+            self.resource_span.clone(),
+            "RwLock::read_owned",
+            "poll",
+            false,
+        );
+
+        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+        let inner = self.s.acquire(1);
+
+        inner.await.unwrap_or_else(|_| {
+            // The semaphore was closed. but, we never explicitly close it, and we have a
+            // handle to it through the Arc, which means that this can never happen.
+            unreachable!()
+        });
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            current_readers = 1,
+            current_readers.op = "add",
+            )
+        });
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = self.resource_span.clone();
+
+        OwnedRwLockReadGuard {
+            data: self.c.get(),
+            lock: ManuallyDrop::new(self),
+            _p: PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+
+    /// Attempts to acquire this `RwLock` with shared read access.
+    ///
+    /// If the access couldn't be acquired immediately, returns [`TryLockError`].
+    /// Otherwise, an RAII guard is returned which will release read access
+    /// when dropped.
+    ///
+    /// [`TryLockError`]: TryLockError
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::RwLock;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let lock = Arc::new(RwLock::new(1));
+    ///     let c_lock = lock.clone();
+    ///
+    ///     let v = lock.try_read().unwrap();
+    ///     assert_eq!(*v, 1);
+    ///
+    ///     tokio::spawn(async move {
+    ///         // While main has an active read lock, we acquire one too.
+    ///         let n = c_lock.read().await;
+    ///         assert_eq!(*n, 1);
+    ///     }).await.expect("The spawned task has panicked");
+    ///
+    ///     // Drop the guard when spawned task finishes.
+    ///     drop(v);
+    /// }
+    /// ```
+    pub fn try_read(&self) -> Result<RwLockReadGuard<'_, T>, TryLockError> {
+        match self.s.try_acquire(1) {
+            Ok(permit) => permit,
+            Err(TryAcquireError::NoPermits) => return Err(TryLockError(())),
+            Err(TryAcquireError::Closed) => unreachable!(),
+        }
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            current_readers = 1,
+            current_readers.op = "add",
+            )
+        });
+
+        Ok(RwLockReadGuard {
+            s: &self.s,
+            data: self.c.get(),
+            marker: marker::PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span: self.resource_span.clone(),
+        })
+    }
+
+    /// Attempts to acquire this `RwLock` with shared read access.
+    ///
+    /// If the access couldn't be acquired immediately, returns [`TryLockError`].
+    /// Otherwise, an RAII guard is returned which will release read access
+    /// when dropped.
+    ///
+    /// This method is identical to [`RwLock::try_read`], except that the
+    /// returned guard references the `RwLock` with an [`Arc`] rather than by
+    /// borrowing it. Therefore, the `RwLock` must be wrapped in an `Arc` to
+    /// call this method, and the guard will live for the `'static` lifetime,
+    /// as it keeps the `RwLock` alive by holding an `Arc`.
+    ///
+    /// [`TryLockError`]: TryLockError
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::RwLock;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let lock = Arc::new(RwLock::new(1));
+    ///     let c_lock = lock.clone();
+    ///
+    ///     let v = lock.try_read_owned().unwrap();
+    ///     assert_eq!(*v, 1);
+    ///
+    ///     tokio::spawn(async move {
+    ///         // While main has an active read lock, we acquire one too.
+    ///         let n = c_lock.read_owned().await;
+    ///         assert_eq!(*n, 1);
+    ///     }).await.expect("The spawned task has panicked");
+    ///
+    ///     // Drop the guard when spawned task finishes.
+    ///     drop(v);
+    /// }
+    /// ```
+    pub fn try_read_owned(self: Arc<Self>) -> Result<OwnedRwLockReadGuard<T>, TryLockError> {
+        match self.s.try_acquire(1) {
+            Ok(permit) => permit,
+            Err(TryAcquireError::NoPermits) => return Err(TryLockError(())),
+            Err(TryAcquireError::Closed) => unreachable!(),
+        }
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            current_readers = 1,
+            current_readers.op = "add",
+            )
+        });
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = self.resource_span.clone();
+
+        Ok(OwnedRwLockReadGuard {
+            data: self.c.get(),
+            lock: ManuallyDrop::new(self),
+            _p: PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        })
+    }
+
+    /// Locks this `RwLock` with exclusive write access, causing the current
+    /// task to yield until the lock has been acquired.
+    ///
+    /// The calling task will yield while other writers or readers currently
+    /// have access to the lock.
+    ///
+    /// Returns an RAII guard which will drop the write access of this `RwLock`
+    /// when dropped.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method uses a queue to fairly distribute locks in the order they
+    /// were requested. Cancelling a call to `write` makes you lose your place
+    /// in the queue.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::RwLock;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///   let lock = RwLock::new(1);
+    ///
+    ///   let mut n = lock.write().await;
+    ///   *n = 2;
+    ///}
+    /// ```
+    pub async fn write(&self) -> RwLockWriteGuard<'_, T> {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let inner = trace::async_op(
+            || self.s.acquire(self.mr),
+            self.resource_span.clone(),
+            "RwLock::write",
+            "poll",
+            false,
+        );
+
+        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+        let inner = self.s.acquire(self.mr);
+
+        inner.await.unwrap_or_else(|_| {
+            // The semaphore was closed. but, we never explicitly close it, and we have a
+            // handle to it through the Arc, which means that this can never happen.
+            unreachable!()
+        });
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            write_locked = true,
+            write_locked.op = "override",
+            )
+        });
+
+        RwLockWriteGuard {
+            permits_acquired: self.mr,
+            s: &self.s,
+            data: self.c.get(),
+            marker: marker::PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span: self.resource_span.clone(),
+        }
+    }
+
+    /// Blockingly locks this `RwLock` with exclusive write access.
+    ///
+    /// This method is intended for use cases where you
+    /// need to use this rwlock in asynchronous code as well as in synchronous code.
+    ///
+    /// Returns an RAII guard which will drop the write access of this `RwLock` when dropped.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if called within an asynchronous execution context.
+    ///
+    ///   - If you find yourself in an asynchronous execution context and needing
+    ///     to call some (synchronous) function which performs one of these
+    ///     `blocking_` operations, then consider wrapping that call inside
+    ///     [`spawn_blocking()`][crate::runtime::Handle::spawn_blocking]
+    ///     (or [`block_in_place()`][crate::task::block_in_place]).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::{sync::RwLock};
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let rwlock =  Arc::new(RwLock::new(1));
+    ///     let read_lock = rwlock.read().await;
+    ///
+    ///     let blocking_task = tokio::task::spawn_blocking({
+    ///         let rwlock = Arc::clone(&rwlock);
+    ///         move || {
+    ///             // This shall block until the `read_lock` is released.
+    ///             let mut write_lock = rwlock.blocking_write();
+    ///             *write_lock = 2;
+    ///         }
+    ///     });
+    ///
+    ///     assert_eq!(*read_lock, 1);
+    ///     // Release the last outstanding read lock.
+    ///     drop(read_lock);
+    ///
+    ///     // Await the completion of the blocking task.
+    ///     blocking_task.await.unwrap();
+    ///
+    ///     // Assert uncontended.
+    ///     let read_lock = rwlock.try_read().unwrap();
+    ///     assert_eq!(*read_lock, 2);
+    /// }
+    /// ```
+    #[cfg(feature = "sync")]
+    pub fn blocking_write(&self) -> RwLockWriteGuard<'_, T> {
+        crate::future::block_on(self.write())
+    }
+
+    /// Locks this `RwLock` with exclusive write access, causing the current
+    /// task to yield until the lock has been acquired.
+    ///
+    /// The calling task will yield while other writers or readers currently
+    /// have access to the lock.
+    ///
+    /// This method is identical to [`RwLock::write`], except that the returned
+    /// guard references the `RwLock` with an [`Arc`] rather than by borrowing
+    /// it. Therefore, the `RwLock` must be wrapped in an `Arc` to call this
+    /// method, and the guard will live for the `'static` lifetime, as it keeps
+    /// the `RwLock` alive by holding an `Arc`.
+    ///
+    /// Returns an RAII guard which will drop the write access of this `RwLock`
+    /// when dropped.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method uses a queue to fairly distribute locks in the order they
+    /// were requested. Cancelling a call to `write_owned` makes you lose your
+    /// place in the queue.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::RwLock;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///   let lock = Arc::new(RwLock::new(1));
+    ///
+    ///   let mut n = lock.write_owned().await;
+    ///   *n = 2;
+    ///}
+    /// ```
+    pub async fn write_owned(self: Arc<Self>) -> OwnedRwLockWriteGuard<T> {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let inner = trace::async_op(
+            || self.s.acquire(self.mr),
+            self.resource_span.clone(),
+            "RwLock::write_owned",
+            "poll",
+            false,
+        );
+
+        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+        let inner = self.s.acquire(self.mr);
+
+        inner.await.unwrap_or_else(|_| {
+            // The semaphore was closed. but, we never explicitly close it, and we have a
+            // handle to it through the Arc, which means that this can never happen.
+            unreachable!()
+        });
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            write_locked = true,
+            write_locked.op = "override",
+            )
+        });
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = self.resource_span.clone();
+
+        OwnedRwLockWriteGuard {
+            permits_acquired: self.mr,
+            data: self.c.get(),
+            lock: ManuallyDrop::new(self),
+            _p: PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+
+    /// Attempts to acquire this `RwLock` with exclusive write access.
+    ///
+    /// If the access couldn't be acquired immediately, returns [`TryLockError`].
+    /// Otherwise, an RAII guard is returned which will release write access
+    /// when dropped.
+    ///
+    /// [`TryLockError`]: TryLockError
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::RwLock;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let rw = RwLock::new(1);
+    ///
+    ///     let v = rw.read().await;
+    ///     assert_eq!(*v, 1);
+    ///
+    ///     assert!(rw.try_write().is_err());
+    /// }
+    /// ```
+    pub fn try_write(&self) -> Result<RwLockWriteGuard<'_, T>, TryLockError> {
+        match self.s.try_acquire(self.mr) {
+            Ok(permit) => permit,
+            Err(TryAcquireError::NoPermits) => return Err(TryLockError(())),
+            Err(TryAcquireError::Closed) => unreachable!(),
+        }
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            write_locked = true,
+            write_locked.op = "override",
+            )
+        });
+
+        Ok(RwLockWriteGuard {
+            permits_acquired: self.mr,
+            s: &self.s,
+            data: self.c.get(),
+            marker: marker::PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span: self.resource_span.clone(),
+        })
+    }
+
+    /// Attempts to acquire this `RwLock` with exclusive write access.
+    ///
+    /// If the access couldn't be acquired immediately, returns [`TryLockError`].
+    /// Otherwise, an RAII guard is returned which will release write access
+    /// when dropped.
+    ///
+    /// This method is identical to [`RwLock::try_write`], except that the
+    /// returned guard references the `RwLock` with an [`Arc`] rather than by
+    /// borrowing it. Therefore, the `RwLock` must be wrapped in an `Arc` to
+    /// call this method, and the guard will live for the `'static` lifetime,
+    /// as it keeps the `RwLock` alive by holding an `Arc`.
+    ///
+    /// [`TryLockError`]: TryLockError
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::RwLock;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let rw = Arc::new(RwLock::new(1));
+    ///
+    ///     let v = Arc::clone(&rw).read_owned().await;
+    ///     assert_eq!(*v, 1);
+    ///
+    ///     assert!(rw.try_write_owned().is_err());
+    /// }
+    /// ```
+    pub fn try_write_owned(self: Arc<Self>) -> Result<OwnedRwLockWriteGuard<T>, TryLockError> {
+        match self.s.try_acquire(self.mr) {
+            Ok(permit) => permit,
+            Err(TryAcquireError::NoPermits) => return Err(TryLockError(())),
+            Err(TryAcquireError::Closed) => unreachable!(),
+        }
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            write_locked = true,
+            write_locked.op = "override",
+            )
+        });
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = self.resource_span.clone();
+
+        Ok(OwnedRwLockWriteGuard {
+            permits_acquired: self.mr,
+            data: self.c.get(),
+            lock: ManuallyDrop::new(self),
+            _p: PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        })
+    }
+
+    /// Returns a mutable reference to the underlying data.
+    ///
+    /// Since this call borrows the `RwLock` mutably, no actual locking needs to
+    /// take place -- the mutable borrow statically guarantees no locks exist.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::RwLock;
+    ///
+    /// fn main() {
+    ///     let mut lock = RwLock::new(1);
+    ///
+    ///     let n = lock.get_mut();
+    ///     *n = 2;
+    /// }
+    /// ```
+    pub fn get_mut(&mut self) -> &mut T {
+        unsafe {
+            // Safety: This is https://github.com/rust-lang/rust/pull/76936
+            &mut *self.c.get()
+        }
+    }
+
+    /// Consumes the lock, returning the underlying data.
+    pub fn into_inner(self) -> T
+    where
+        T: Sized,
+    {
+        self.c.into_inner()
+    }
+}
+
+impl<T> From<T> for RwLock<T> {
+    fn from(s: T) -> Self {
+        Self::new(s)
+    }
+}
+
+impl<T: ?Sized> Default for RwLock<T>
+where
+    T: Default,
+{
+    fn default() -> Self {
+        Self::new(T::default())
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/rwlock/owned_read_guard.rs b/third_party/rust/tokio/src/sync/rwlock/owned_read_guard.rs
new file mode 100644
index 0000000000..27b71bd988
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/rwlock/owned_read_guard.rs
@@ -0,0 +1,170 @@
+use crate::sync::rwlock::RwLock;
+use std::fmt;
+use std::marker::PhantomData;
+use std::mem;
+use std::mem::ManuallyDrop;
+use std::ops;
+use std::sync::Arc;
+
+/// Owned RAII structure used to release the shared read access of a lock when
+/// dropped.
+///
+/// This structure is created by the [`read_owned`] method on
+/// [`RwLock`].
+///
+/// [`read_owned`]: method@crate::sync::RwLock::read_owned
+/// [`RwLock`]: struct@crate::sync::RwLock
+pub struct OwnedRwLockReadGuard<T: ?Sized, U: ?Sized = T> {
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    pub(super) resource_span: tracing::Span,
+    // ManuallyDrop allows us to destructure into this field without running the destructor.
+    pub(super) lock: ManuallyDrop<Arc<RwLock<T>>>,
+    pub(super) data: *const U,
+    pub(super) _p: PhantomData<T>,
+}
+
+impl<T: ?Sized, U: ?Sized> OwnedRwLockReadGuard<T, U> {
+    /// Makes a new `OwnedRwLockReadGuard` for a component of the locked data.
+    /// This operation cannot fail as the `OwnedRwLockReadGuard` passed in
+    /// already locked the data.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `OwnedRwLockReadGuard::map(...)`. A method would interfere with
+    /// methods of the same name on the contents of the locked data.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::{RwLock, OwnedRwLockReadGuard};
+    ///
+    /// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    /// struct Foo(u32);
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let lock = Arc::new(RwLock::new(Foo(1)));
+    ///
+    /// let guard = lock.read_owned().await;
+    /// let guard = OwnedRwLockReadGuard::map(guard, |f| &f.0);
+    ///
+    /// assert_eq!(1, *guard);
+    /// # }
+    /// ```
+    #[inline]
+    pub fn map<F, V: ?Sized>(mut this: Self, f: F) -> OwnedRwLockReadGuard<T, V>
+    where
+        F: FnOnce(&U) -> &V,
+    {
+        let data = f(&*this) as *const V;
+        let lock = unsafe { ManuallyDrop::take(&mut this.lock) };
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = this.resource_span.clone();
+        // NB: Forget to avoid drop impl from being called.
+        mem::forget(this);
+
+        OwnedRwLockReadGuard {
+            lock: ManuallyDrop::new(lock),
+            data,
+            _p: PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+
+    /// Attempts to make a new [`OwnedRwLockReadGuard`] for a component of the
+    /// locked data. The original guard is returned if the closure returns
+    /// `None`.
+    ///
+    /// This operation cannot fail as the `OwnedRwLockReadGuard` passed in
+    /// already locked the data.
+    ///
+    /// This is an associated function that needs to be used as
+    /// `OwnedRwLockReadGuard::try_map(..)`. A method would interfere with
+    /// methods of the same name on the contents of the locked data.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::{RwLock, OwnedRwLockReadGuard};
+    ///
+    /// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    /// struct Foo(u32);
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let lock = Arc::new(RwLock::new(Foo(1)));
+    ///
+    /// let guard = lock.read_owned().await;
+    /// let guard = OwnedRwLockReadGuard::try_map(guard, |f| Some(&f.0)).expect("should not fail");
+    ///
+    /// assert_eq!(1, *guard);
+    /// # }
+    /// ```
+    #[inline]
+    pub fn try_map<F, V: ?Sized>(mut this: Self, f: F) -> Result<OwnedRwLockReadGuard<T, V>, Self>
+    where
+        F: FnOnce(&U) -> Option<&V>,
+    {
+        let data = match f(&*this) {
+            Some(data) => data as *const V,
+            None => return Err(this),
+        };
+        let lock = unsafe { ManuallyDrop::take(&mut this.lock) };
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = this.resource_span.clone();
+        // NB: Forget to avoid drop impl from being called.
+        mem::forget(this);
+
+        Ok(OwnedRwLockReadGuard {
+            lock: ManuallyDrop::new(lock),
+            data,
+            _p: PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        })
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> ops::Deref for OwnedRwLockReadGuard<T, U> {
+    type Target = U;
+
+    fn deref(&self) -> &U {
+        unsafe { &*self.data }
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> fmt::Debug for OwnedRwLockReadGuard<T, U>
+where
+    U: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> fmt::Display for OwnedRwLockReadGuard<T, U>
+where
+    U: fmt::Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> Drop for OwnedRwLockReadGuard<T, U> {
+    fn drop(&mut self) {
+        self.lock.s.release(1);
+        unsafe { ManuallyDrop::drop(&mut self.lock) };
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            current_readers = 1,
+            current_readers.op = "sub",
+            )
+        });
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/rwlock/owned_write_guard.rs b/third_party/rust/tokio/src/sync/rwlock/owned_write_guard.rs
new file mode 100644
index 0000000000..dbedab4cbb
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/rwlock/owned_write_guard.rs
@@ -0,0 +1,279 @@
+use crate::sync::rwlock::owned_read_guard::OwnedRwLockReadGuard;
+use crate::sync::rwlock::owned_write_guard_mapped::OwnedRwLockMappedWriteGuard;
+use crate::sync::rwlock::RwLock;
+use std::fmt;
+use std::marker::PhantomData;
+use std::mem::{self, ManuallyDrop};
+use std::ops;
+use std::sync::Arc;
+
+/// Owned RAII structure used to release the exclusive write access of a lock when
+/// dropped.
+///
+/// This structure is created by the [`write_owned`] method
+/// on [`RwLock`].
+///
+/// [`write_owned`]: method@crate::sync::RwLock::write_owned
+/// [`RwLock`]: struct@crate::sync::RwLock
+pub struct OwnedRwLockWriteGuard<T: ?Sized> {
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    pub(super) resource_span: tracing::Span,
+    pub(super) permits_acquired: u32,
+    // ManuallyDrop allows us to destructure into this field without running the destructor.
+    pub(super) lock: ManuallyDrop<Arc<RwLock<T>>>,
+    pub(super) data: *mut T,
+    pub(super) _p: PhantomData<T>,
+}
+
+impl<T: ?Sized> OwnedRwLockWriteGuard<T> {
+    /// Makes a new [`OwnedRwLockMappedWriteGuard`] for a component of the locked
+    /// data.
+    ///
+    /// This operation cannot fail as the `OwnedRwLockWriteGuard` passed in
+    /// already locked the data.
+    ///
+    /// This is an associated function that needs to be used as
+    /// `OwnedRwLockWriteGuard::map(..)`. A method would interfere with methods
+    /// of the same name on the contents of the locked data.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::{RwLock, OwnedRwLockWriteGuard};
+    ///
+    /// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    /// struct Foo(u32);
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let lock = Arc::new(RwLock::new(Foo(1)));
+    ///
+    /// {
+    ///     let lock = Arc::clone(&lock);
+    ///     let mut mapped = OwnedRwLockWriteGuard::map(lock.write_owned().await, |f| &mut f.0);
+    ///     *mapped = 2;
+    /// }
+    ///
+    /// assert_eq!(Foo(2), *lock.read().await);
+    /// # }
+    /// ```
+    #[inline]
+    pub fn map<F, U: ?Sized>(mut this: Self, f: F) -> OwnedRwLockMappedWriteGuard<T, U>
+    where
+        F: FnOnce(&mut T) -> &mut U,
+    {
+        let data = f(&mut *this) as *mut U;
+        let lock = unsafe { ManuallyDrop::take(&mut this.lock) };
+        let permits_acquired = this.permits_acquired;
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = this.resource_span.clone();
+        // NB: Forget to avoid drop impl from being called.
+        mem::forget(this);
+
+        OwnedRwLockMappedWriteGuard {
+            permits_acquired,
+            lock: ManuallyDrop::new(lock),
+            data,
+            _p: PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+
+    /// Attempts to make  a new [`OwnedRwLockMappedWriteGuard`] for a component
+    /// of the locked data. The original guard is returned if the closure
+    /// returns `None`.
+    ///
+    /// This operation cannot fail as the `OwnedRwLockWriteGuard` passed in
+    /// already locked the data.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `OwnedRwLockWriteGuard::try_map(...)`. A method would interfere
+    /// with methods of the same name on the contents of the locked data.
+    ///
+    /// [`RwLockMappedWriteGuard`]: struct@crate::sync::RwLockMappedWriteGuard
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::{RwLock, OwnedRwLockWriteGuard};
+    ///
+    /// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    /// struct Foo(u32);
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let lock = Arc::new(RwLock::new(Foo(1)));
+    ///
+    /// {
+    ///     let guard = Arc::clone(&lock).write_owned().await;
+    ///     let mut guard = OwnedRwLockWriteGuard::try_map(guard, |f| Some(&mut f.0)).expect("should not fail");
+    ///     *guard = 2;
+    /// }
+    ///
+    /// assert_eq!(Foo(2), *lock.read().await);
+    /// # }
+    /// ```
+    #[inline]
+    pub fn try_map<F, U: ?Sized>(
+        mut this: Self,
+        f: F,
+    ) -> Result<OwnedRwLockMappedWriteGuard<T, U>, Self>
+    where
+        F: FnOnce(&mut T) -> Option<&mut U>,
+    {
+        let data = match f(&mut *this) {
+            Some(data) => data as *mut U,
+            None => return Err(this),
+        };
+        let permits_acquired = this.permits_acquired;
+        let lock = unsafe { ManuallyDrop::take(&mut this.lock) };
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = this.resource_span.clone();
+
+        // NB: Forget to avoid drop impl from being called.
+        mem::forget(this);
+
+        Ok(OwnedRwLockMappedWriteGuard {
+            permits_acquired,
+            lock: ManuallyDrop::new(lock),
+            data,
+            _p: PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        })
+    }
+
+    /// Converts this `OwnedRwLockWriteGuard` into an
+    /// `OwnedRwLockMappedWriteGuard`. This method can be used to store a
+    /// non-mapped guard in a struct field that expects a mapped guard.
+    ///
+    /// This is equivalent to calling `OwnedRwLockWriteGuard::map(guard, |me| me)`.
+    #[inline]
+    pub fn into_mapped(this: Self) -> OwnedRwLockMappedWriteGuard<T> {
+        Self::map(this, |me| me)
+    }
+
+    /// Atomically downgrades a write lock into a read lock without allowing
+    /// any writers to take exclusive access of the lock in the meantime.
+    ///
+    /// **Note:** This won't *necessarily* allow any additional readers to acquire
+    /// locks, since [`RwLock`] is fair and it is possible that a writer is next
+    /// in line.
+    ///
+    /// Returns an RAII guard which will drop this read access of the `RwLock`
+    /// when dropped.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use tokio::sync::RwLock;
+    /// # use std::sync::Arc;
+    /// #
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let lock = Arc::new(RwLock::new(1));
+    ///
+    /// let n = lock.clone().write_owned().await;
+    ///
+    /// let cloned_lock = lock.clone();
+    /// let handle = tokio::spawn(async move {
+    ///     *cloned_lock.write_owned().await = 2;
+    /// });
+    ///
+    /// let n = n.downgrade();
+    /// assert_eq!(*n, 1, "downgrade is atomic");
+    ///
+    /// drop(n);
+    /// handle.await.unwrap();
+    /// assert_eq!(*lock.read().await, 2, "second writer obtained write lock");
+    /// # }
+    /// ```
+    pub fn downgrade(mut self) -> OwnedRwLockReadGuard<T> {
+        let lock = unsafe { ManuallyDrop::take(&mut self.lock) };
+        let data = self.data;
+        let to_release = (self.permits_acquired - 1) as usize;
+
+        // Release all but one of the permits held by the write guard
+        lock.s.release(to_release);
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            write_locked = false,
+            write_locked.op = "override",
+            )
+        });
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            current_readers = 1,
+            current_readers.op = "add",
+            )
+        });
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = self.resource_span.clone();
+        // NB: Forget to avoid drop impl from being called.
+        mem::forget(self);
+
+        OwnedRwLockReadGuard {
+            lock: ManuallyDrop::new(lock),
+            data,
+            _p: PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+}
+
+impl<T: ?Sized> ops::Deref for OwnedRwLockWriteGuard<T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        unsafe { &*self.data }
+    }
+}
+
+impl<T: ?Sized> ops::DerefMut for OwnedRwLockWriteGuard<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.data }
+    }
+}
+
+impl<T: ?Sized> fmt::Debug for OwnedRwLockWriteGuard<T>
+where
+    T: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<T: ?Sized> fmt::Display for OwnedRwLockWriteGuard<T>
+where
+    T: fmt::Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+impl<T: ?Sized> Drop for OwnedRwLockWriteGuard<T> {
+    fn drop(&mut self) {
+        self.lock.s.release(self.permits_acquired as usize);
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            write_locked = false,
+            write_locked.op = "override",
+            )
+        });
+        unsafe { ManuallyDrop::drop(&mut self.lock) };
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/rwlock/owned_write_guard_mapped.rs b/third_party/rust/tokio/src/sync/rwlock/owned_write_guard_mapped.rs
new file mode 100644
index 0000000000..55a24d96ac
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/rwlock/owned_write_guard_mapped.rs
@@ -0,0 +1,191 @@
+use crate::sync::rwlock::RwLock;
+use std::fmt;
+use std::marker::PhantomData;
+use std::mem::{self, ManuallyDrop};
+use std::ops;
+use std::sync::Arc;
+
+/// Owned RAII structure used to release the exclusive write access of a lock when
+/// dropped.
+///
+/// This structure is created by [mapping] an [`OwnedRwLockWriteGuard`]. It is a
+/// separate type from `OwnedRwLockWriteGuard` to disallow downgrading a mapped
+/// guard, since doing so can cause undefined behavior.
+///
+/// [mapping]: method@crate::sync::OwnedRwLockWriteGuard::map
+/// [`OwnedRwLockWriteGuard`]: struct@crate::sync::OwnedRwLockWriteGuard
+pub struct OwnedRwLockMappedWriteGuard<T: ?Sized, U: ?Sized = T> {
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    pub(super) resource_span: tracing::Span,
+    pub(super) permits_acquired: u32,
+    // ManuallyDrop allows us to destructure into this field without running the destructor.
+    pub(super) lock: ManuallyDrop<Arc<RwLock<T>>>,
+    pub(super) data: *mut U,
+    pub(super) _p: PhantomData<T>,
+}
+
+impl<T: ?Sized, U: ?Sized> OwnedRwLockMappedWriteGuard<T, U> {
+    /// Makes a new `OwnedRwLockMappedWriteGuard` for a component of the locked
+    /// data.
+    ///
+    /// This operation cannot fail as the `OwnedRwLockMappedWriteGuard` passed
+    /// in already locked the data.
+    ///
+    /// This is an associated function that needs to be used as
+    /// `OwnedRwLockWriteGuard::map(..)`. A method would interfere with methods
+    /// of the same name on the contents of the locked data.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::{RwLock, OwnedRwLockWriteGuard};
+    ///
+    /// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    /// struct Foo(u32);
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let lock = Arc::new(RwLock::new(Foo(1)));
+    ///
+    /// {
+    ///     let lock = Arc::clone(&lock);
+    ///     let mut mapped = OwnedRwLockWriteGuard::map(lock.write_owned().await, |f| &mut f.0);
+    ///     *mapped = 2;
+    /// }
+    ///
+    /// assert_eq!(Foo(2), *lock.read().await);
+    /// # }
+    /// ```
+    #[inline]
+    pub fn map<F, V: ?Sized>(mut this: Self, f: F) -> OwnedRwLockMappedWriteGuard<T, V>
+    where
+        F: FnOnce(&mut U) -> &mut V,
+    {
+        let data = f(&mut *this) as *mut V;
+        let lock = unsafe { ManuallyDrop::take(&mut this.lock) };
+        let permits_acquired = this.permits_acquired;
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = this.resource_span.clone();
+        // NB: Forget to avoid drop impl from being called.
+        mem::forget(this);
+
+        OwnedRwLockMappedWriteGuard {
+            permits_acquired,
+            lock: ManuallyDrop::new(lock),
+            data,
+            _p: PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+
+    /// Attempts to make a new `OwnedRwLockMappedWriteGuard` for a component
+    /// of the locked data. The original guard is returned if the closure
+    /// returns `None`.
+    ///
+    /// This operation cannot fail as the `OwnedRwLockMappedWriteGuard` passed
+    /// in already locked the data.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `OwnedRwLockMappedWriteGuard::try_map(...)`. A method would interfere with
+    /// methods of the same name on the contents of the locked data.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::{RwLock, OwnedRwLockWriteGuard};
+    ///
+    /// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    /// struct Foo(u32);
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let lock = Arc::new(RwLock::new(Foo(1)));
+    ///
+    /// {
+    ///     let guard = Arc::clone(&lock).write_owned().await;
+    ///     let mut guard = OwnedRwLockWriteGuard::try_map(guard, |f| Some(&mut f.0)).expect("should not fail");
+    ///     *guard = 2;
+    /// }
+    ///
+    /// assert_eq!(Foo(2), *lock.read().await);
+    /// # }
+    /// ```
+    #[inline]
+    pub fn try_map<F, V: ?Sized>(
+        mut this: Self,
+        f: F,
+    ) -> Result<OwnedRwLockMappedWriteGuard<T, V>, Self>
+    where
+        F: FnOnce(&mut U) -> Option<&mut V>,
+    {
+        let data = match f(&mut *this) {
+            Some(data) => data as *mut V,
+            None => return Err(this),
+        };
+        let lock = unsafe { ManuallyDrop::take(&mut this.lock) };
+        let permits_acquired = this.permits_acquired;
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = this.resource_span.clone();
+        // NB: Forget to avoid drop impl from being called.
+        mem::forget(this);
+
+        Ok(OwnedRwLockMappedWriteGuard {
+            permits_acquired,
+            lock: ManuallyDrop::new(lock),
+            data,
+            _p: PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        })
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> ops::Deref for OwnedRwLockMappedWriteGuard<T, U> {
+    type Target = U;
+
+    fn deref(&self) -> &U {
+        unsafe { &*self.data }
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> ops::DerefMut for OwnedRwLockMappedWriteGuard<T, U> {
+    fn deref_mut(&mut self) -> &mut U {
+        unsafe { &mut *self.data }
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> fmt::Debug for OwnedRwLockMappedWriteGuard<T, U>
+where
+    U: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> fmt::Display for OwnedRwLockMappedWriteGuard<T, U>
+where
+    U: fmt::Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+impl<T: ?Sized, U: ?Sized> Drop for OwnedRwLockMappedWriteGuard<T, U> {
+    fn drop(&mut self) {
+        self.lock.s.release(self.permits_acquired as usize);
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            write_locked = false,
+            write_locked.op = "override",
+            )
+        });
+        unsafe { ManuallyDrop::drop(&mut self.lock) };
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/rwlock/read_guard.rs b/third_party/rust/tokio/src/sync/rwlock/read_guard.rs
new file mode 100644
index 0000000000..3692131992
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/rwlock/read_guard.rs
@@ -0,0 +1,177 @@
+use crate::sync::batch_semaphore::Semaphore;
+use std::fmt;
+use std::marker;
+use std::mem;
+use std::ops;
+
+/// RAII structure used to release the shared read access of a lock when
+/// dropped.
+///
+/// This structure is created by the [`read`] method on
+/// [`RwLock`].
+///
+/// [`read`]: method@crate::sync::RwLock::read
+/// [`RwLock`]: struct@crate::sync::RwLock
+pub struct RwLockReadGuard<'a, T: ?Sized> {
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    pub(super) resource_span: tracing::Span,
+    pub(super) s: &'a Semaphore,
+    pub(super) data: *const T,
+    pub(super) marker: marker::PhantomData<&'a T>,
+}
+
+impl<'a, T: ?Sized> RwLockReadGuard<'a, T> {
+    /// Makes a new `RwLockReadGuard` for a component of the locked data.
+    ///
+    /// This operation cannot fail as the `RwLockReadGuard` passed in already
+    /// locked the data.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `RwLockReadGuard::map(...)`. A method would interfere with
+    /// methods of the same name on the contents of the locked data.
+    ///
+    /// This is an asynchronous version of [`RwLockReadGuard::map`] from the
+    /// [`parking_lot` crate].
+    ///
+    /// [`RwLockReadGuard::map`]: https://docs.rs/lock_api/latest/lock_api/struct.RwLockReadGuard.html#method.map
+    /// [`parking_lot` crate]: https://crates.io/crates/parking_lot
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::{RwLock, RwLockReadGuard};
+    ///
+    /// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    /// struct Foo(u32);
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let lock = RwLock::new(Foo(1));
+    ///
+    /// let guard = lock.read().await;
+    /// let guard = RwLockReadGuard::map(guard, |f| &f.0);
+    ///
+    /// assert_eq!(1, *guard);
+    /// # }
+    /// ```
+    #[inline]
+    pub fn map<F, U: ?Sized>(this: Self, f: F) -> RwLockReadGuard<'a, U>
+    where
+        F: FnOnce(&T) -> &U,
+    {
+        let data = f(&*this) as *const U;
+        let s = this.s;
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = this.resource_span.clone();
+        // NB: Forget to avoid drop impl from being called.
+        mem::forget(this);
+
+        RwLockReadGuard {
+            s,
+            data,
+            marker: marker::PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+
+    /// Attempts to make a new [`RwLockReadGuard`] for a component of the
+    /// locked data. The original guard is returned if the closure returns
+    /// `None`.
+    ///
+    /// This operation cannot fail as the `RwLockReadGuard` passed in already
+    /// locked the data.
+    ///
+    /// This is an associated function that needs to be used as
+    /// `RwLockReadGuard::try_map(..)`. A method would interfere with methods of the
+    /// same name on the contents of the locked data.
+    ///
+    /// This is an asynchronous version of [`RwLockReadGuard::try_map`] from the
+    /// [`parking_lot` crate].
+    ///
+    /// [`RwLockReadGuard::try_map`]: https://docs.rs/lock_api/latest/lock_api/struct.RwLockReadGuard.html#method.try_map
+    /// [`parking_lot` crate]: https://crates.io/crates/parking_lot
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::{RwLock, RwLockReadGuard};
+    ///
+    /// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    /// struct Foo(u32);
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let lock = RwLock::new(Foo(1));
+    ///
+    /// let guard = lock.read().await;
+    /// let guard = RwLockReadGuard::try_map(guard, |f| Some(&f.0)).expect("should not fail");
+    ///
+    /// assert_eq!(1, *guard);
+    /// # }
+    /// ```
+    #[inline]
+    pub fn try_map<F, U: ?Sized>(this: Self, f: F) -> Result<RwLockReadGuard<'a, U>, Self>
+    where
+        F: FnOnce(&T) -> Option<&U>,
+    {
+        let data = match f(&*this) {
+            Some(data) => data as *const U,
+            None => return Err(this),
+        };
+        let s = this.s;
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = this.resource_span.clone();
+        // NB: Forget to avoid drop impl from being called.
+        mem::forget(this);
+
+        Ok(RwLockReadGuard {
+            s,
+            data,
+            marker: marker::PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        })
+    }
+}
+
+impl<T: ?Sized> ops::Deref for RwLockReadGuard<'_, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        unsafe { &*self.data }
+    }
+}
+
+impl<'a, T: ?Sized> fmt::Debug for RwLockReadGuard<'a, T>
+where
+    T: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'a, T: ?Sized> fmt::Display for RwLockReadGuard<'a, T>
+where
+    T: fmt::Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+impl<'a, T: ?Sized> Drop for RwLockReadGuard<'a, T> {
+    fn drop(&mut self) {
+        self.s.release(1);
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            current_readers = 1,
+            current_readers.op = "sub",
+            )
+        });
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/rwlock/write_guard.rs b/third_party/rust/tokio/src/sync/rwlock/write_guard.rs
new file mode 100644
index 0000000000..7cadd74c60
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/rwlock/write_guard.rs
@@ -0,0 +1,282 @@
+use crate::sync::batch_semaphore::Semaphore;
+use crate::sync::rwlock::read_guard::RwLockReadGuard;
+use crate::sync::rwlock::write_guard_mapped::RwLockMappedWriteGuard;
+use std::fmt;
+use std::marker;
+use std::mem;
+use std::ops;
+
+/// RAII structure used to release the exclusive write access of a lock when
+/// dropped.
+///
+/// This structure is created by the [`write`] method
+/// on [`RwLock`].
+///
+/// [`write`]: method@crate::sync::RwLock::write
+/// [`RwLock`]: struct@crate::sync::RwLock
+pub struct RwLockWriteGuard<'a, T: ?Sized> {
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    pub(super) resource_span: tracing::Span,
+    pub(super) permits_acquired: u32,
+    pub(super) s: &'a Semaphore,
+    pub(super) data: *mut T,
+    pub(super) marker: marker::PhantomData<&'a mut T>,
+}
+
+impl<'a, T: ?Sized> RwLockWriteGuard<'a, T> {
+    /// Makes a new [`RwLockMappedWriteGuard`] for a component of the locked data.
+    ///
+    /// This operation cannot fail as the `RwLockWriteGuard` passed in already
+    /// locked the data.
+    ///
+    /// This is an associated function that needs to be used as
+    /// `RwLockWriteGuard::map(..)`. A method would interfere with methods of
+    /// the same name on the contents of the locked data.
+    ///
+    /// This is an asynchronous version of [`RwLockWriteGuard::map`] from the
+    /// [`parking_lot` crate].
+    ///
+    /// [`RwLockMappedWriteGuard`]: struct@crate::sync::RwLockMappedWriteGuard
+    /// [`RwLockWriteGuard::map`]: https://docs.rs/lock_api/latest/lock_api/struct.RwLockWriteGuard.html#method.map
+    /// [`parking_lot` crate]: https://crates.io/crates/parking_lot
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::{RwLock, RwLockWriteGuard};
+    ///
+    /// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    /// struct Foo(u32);
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let lock = RwLock::new(Foo(1));
+    ///
+    /// {
+    ///     let mut mapped = RwLockWriteGuard::map(lock.write().await, |f| &mut f.0);
+    ///     *mapped = 2;
+    /// }
+    ///
+    /// assert_eq!(Foo(2), *lock.read().await);
+    /// # }
+    /// ```
+    #[inline]
+    pub fn map<F, U: ?Sized>(mut this: Self, f: F) -> RwLockMappedWriteGuard<'a, U>
+    where
+        F: FnOnce(&mut T) -> &mut U,
+    {
+        let data = f(&mut *this) as *mut U;
+        let s = this.s;
+        let permits_acquired = this.permits_acquired;
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = this.resource_span.clone();
+        // NB: Forget to avoid drop impl from being called.
+        mem::forget(this);
+        RwLockMappedWriteGuard {
+            permits_acquired,
+            s,
+            data,
+            marker: marker::PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+
+    /// Attempts to make  a new [`RwLockMappedWriteGuard`] for a component of
+    /// the locked data. The original guard is returned if the closure returns
+    /// `None`.
+    ///
+    /// This operation cannot fail as the `RwLockWriteGuard` passed in already
+    /// locked the data.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `RwLockWriteGuard::try_map(...)`. A method would interfere with
+    /// methods of the same name on the contents of the locked data.
+    ///
+    /// This is an asynchronous version of [`RwLockWriteGuard::try_map`] from
+    /// the [`parking_lot` crate].
+    ///
+    /// [`RwLockMappedWriteGuard`]: struct@crate::sync::RwLockMappedWriteGuard
+    /// [`RwLockWriteGuard::try_map`]: https://docs.rs/lock_api/latest/lock_api/struct.RwLockWriteGuard.html#method.try_map
+    /// [`parking_lot` crate]: https://crates.io/crates/parking_lot
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::{RwLock, RwLockWriteGuard};
+    ///
+    /// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    /// struct Foo(u32);
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let lock = RwLock::new(Foo(1));
+    ///
+    /// {
+    ///     let guard = lock.write().await;
+    ///     let mut guard = RwLockWriteGuard::try_map(guard, |f| Some(&mut f.0)).expect("should not fail");
+    ///     *guard = 2;
+    /// }
+    ///
+    /// assert_eq!(Foo(2), *lock.read().await);
+    /// # }
+    /// ```
+    #[inline]
+    pub fn try_map<F, U: ?Sized>(
+        mut this: Self,
+        f: F,
+    ) -> Result<RwLockMappedWriteGuard<'a, U>, Self>
+    where
+        F: FnOnce(&mut T) -> Option<&mut U>,
+    {
+        let data = match f(&mut *this) {
+            Some(data) => data as *mut U,
+            None => return Err(this),
+        };
+        let s = this.s;
+        let permits_acquired = this.permits_acquired;
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = this.resource_span.clone();
+        // NB: Forget to avoid drop impl from being called.
+        mem::forget(this);
+        Ok(RwLockMappedWriteGuard {
+            permits_acquired,
+            s,
+            data,
+            marker: marker::PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        })
+    }
+
+    /// Converts this `RwLockWriteGuard` into an `RwLockMappedWriteGuard`. This
+    /// method can be used to store a non-mapped guard in a struct field that
+    /// expects a mapped guard.
+    ///
+    /// This is equivalent to calling `RwLockWriteGuard::map(guard, |me| me)`.
+    #[inline]
+    pub fn into_mapped(this: Self) -> RwLockMappedWriteGuard<'a, T> {
+        RwLockWriteGuard::map(this, |me| me)
+    }
+
+    /// Atomically downgrades a write lock into a read lock without allowing
+    /// any writers to take exclusive access of the lock in the meantime.
+    ///
+    /// **Note:** This won't *necessarily* allow any additional readers to acquire
+    /// locks, since [`RwLock`] is fair and it is possible that a writer is next
+    /// in line.
+    ///
+    /// Returns an RAII guard which will drop this read access of the `RwLock`
+    /// when dropped.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use tokio::sync::RwLock;
+    /// # use std::sync::Arc;
+    /// #
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let lock = Arc::new(RwLock::new(1));
+    ///
+    /// let n = lock.write().await;
+    ///
+    /// let cloned_lock = lock.clone();
+    /// let handle = tokio::spawn(async move {
+    ///     *cloned_lock.write().await = 2;
+    /// });
+    ///
+    /// let n = n.downgrade();
+    /// assert_eq!(*n, 1, "downgrade is atomic");
+    ///
+    /// drop(n);
+    /// handle.await.unwrap();
+    /// assert_eq!(*lock.read().await, 2, "second writer obtained write lock");
+    /// # }
+    /// ```
+    ///
+    /// [`RwLock`]: struct@crate::sync::RwLock
+    pub fn downgrade(self) -> RwLockReadGuard<'a, T> {
+        let RwLockWriteGuard { s, data, .. } = self;
+        let to_release = (self.permits_acquired - 1) as usize;
+        // Release all but one of the permits held by the write guard
+        s.release(to_release);
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            write_locked = false,
+            write_locked.op = "override",
+            )
+        });
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            current_readers = 1,
+            current_readers.op = "add",
+            )
+        });
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = self.resource_span.clone();
+        // NB: Forget to avoid drop impl from being called.
+        mem::forget(self);
+
+        RwLockReadGuard {
+            s,
+            data,
+            marker: marker::PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+}
+
+impl<T: ?Sized> ops::Deref for RwLockWriteGuard<'_, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        unsafe { &*self.data }
+    }
+}
+
+impl<T: ?Sized> ops::DerefMut for RwLockWriteGuard<'_, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.data }
+    }
+}
+
+impl<'a, T: ?Sized> fmt::Debug for RwLockWriteGuard<'a, T>
+where
+    T: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'a, T: ?Sized> fmt::Display for RwLockWriteGuard<'a, T>
+where
+    T: fmt::Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+impl<'a, T: ?Sized> Drop for RwLockWriteGuard<'a, T> {
+    fn drop(&mut self) {
+        self.s.release(self.permits_acquired as usize);
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            write_locked = false,
+            write_locked.op = "override",
+            )
+        });
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/rwlock/write_guard_mapped.rs b/third_party/rust/tokio/src/sync/rwlock/write_guard_mapped.rs
new file mode 100644
index 0000000000..b5c644a9e8
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/rwlock/write_guard_mapped.rs
@@ -0,0 +1,197 @@
+use crate::sync::batch_semaphore::Semaphore;
+use std::fmt;
+use std::marker;
+use std::mem;
+use std::ops;
+
+/// RAII structure used to release the exclusive write access of a lock when
+/// dropped.
+///
+/// This structure is created by [mapping] an [`RwLockWriteGuard`]. It is a
+/// separate type from `RwLockWriteGuard` to disallow downgrading a mapped
+/// guard, since doing so can cause undefined behavior.
+///
+/// [mapping]: method@crate::sync::RwLockWriteGuard::map
+/// [`RwLockWriteGuard`]: struct@crate::sync::RwLockWriteGuard
+pub struct RwLockMappedWriteGuard<'a, T: ?Sized> {
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    pub(super) resource_span: tracing::Span,
+    pub(super) permits_acquired: u32,
+    pub(super) s: &'a Semaphore,
+    pub(super) data: *mut T,
+    pub(super) marker: marker::PhantomData<&'a mut T>,
+}
+
+impl<'a, T: ?Sized> RwLockMappedWriteGuard<'a, T> {
+    /// Makes a new `RwLockMappedWriteGuard` for a component of the locked data.
+    ///
+    /// This operation cannot fail as the `RwLockMappedWriteGuard` passed in already
+    /// locked the data.
+    ///
+    /// This is an associated function that needs to be used as
+    /// `RwLockMappedWriteGuard::map(..)`. A method would interfere with methods
+    /// of the same name on the contents of the locked data.
+    ///
+    /// This is an asynchronous version of [`RwLockWriteGuard::map`] from the
+    /// [`parking_lot` crate].
+    ///
+    /// [`RwLockWriteGuard::map`]: https://docs.rs/lock_api/latest/lock_api/struct.RwLockWriteGuard.html#method.map
+    /// [`parking_lot` crate]: https://crates.io/crates/parking_lot
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::{RwLock, RwLockWriteGuard};
+    ///
+    /// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    /// struct Foo(u32);
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let lock = RwLock::new(Foo(1));
+    ///
+    /// {
+    ///     let mut mapped = RwLockWriteGuard::map(lock.write().await, |f| &mut f.0);
+    ///     *mapped = 2;
+    /// }
+    ///
+    /// assert_eq!(Foo(2), *lock.read().await);
+    /// # }
+    /// ```
+    #[inline]
+    pub fn map<F, U: ?Sized>(mut this: Self, f: F) -> RwLockMappedWriteGuard<'a, U>
+    where
+        F: FnOnce(&mut T) -> &mut U,
+    {
+        let data = f(&mut *this) as *mut U;
+        let s = this.s;
+        let permits_acquired = this.permits_acquired;
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = this.resource_span.clone();
+        // NB: Forget to avoid drop impl from being called.
+        mem::forget(this);
+
+        RwLockMappedWriteGuard {
+            permits_acquired,
+            s,
+            data,
+            marker: marker::PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+
+    /// Attempts to make a new [`RwLockMappedWriteGuard`] for a component of
+    /// the locked data. The original guard is returned if the closure returns
+    /// `None`.
+    ///
+    /// This operation cannot fail as the `RwLockMappedWriteGuard` passed in already
+    /// locked the data.
+    ///
+    /// This is an associated function that needs to be
+    /// used as `RwLockMappedWriteGuard::try_map(...)`. A method would interfere
+    /// with methods of the same name on the contents of the locked data.
+    ///
+    /// This is an asynchronous version of [`RwLockWriteGuard::try_map`] from
+    /// the [`parking_lot` crate].
+    ///
+    /// [`RwLockWriteGuard::try_map`]: https://docs.rs/lock_api/latest/lock_api/struct.RwLockWriteGuard.html#method.try_map
+    /// [`parking_lot` crate]: https://crates.io/crates/parking_lot
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::{RwLock, RwLockWriteGuard};
+    ///
+    /// #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    /// struct Foo(u32);
+    ///
+    /// # #[tokio::main]
+    /// # async fn main() {
+    /// let lock = RwLock::new(Foo(1));
+    ///
+    /// {
+    ///     let guard = lock.write().await;
+    ///     let mut guard = RwLockWriteGuard::try_map(guard, |f| Some(&mut f.0)).expect("should not fail");
+    ///     *guard = 2;
+    /// }
+    ///
+    /// assert_eq!(Foo(2), *lock.read().await);
+    /// # }
+    /// ```
+    #[inline]
+    pub fn try_map<F, U: ?Sized>(
+        mut this: Self,
+        f: F,
+    ) -> Result<RwLockMappedWriteGuard<'a, U>, Self>
+    where
+        F: FnOnce(&mut T) -> Option<&mut U>,
+    {
+        let data = match f(&mut *this) {
+            Some(data) => data as *mut U,
+            None => return Err(this),
+        };
+        let s = this.s;
+        let permits_acquired = this.permits_acquired;
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = this.resource_span.clone();
+        // NB: Forget to avoid drop impl from being called.
+        mem::forget(this);
+
+        Ok(RwLockMappedWriteGuard {
+            permits_acquired,
+            s,
+            data,
+            marker: marker::PhantomData,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        })
+    }
+}
+
+impl<T: ?Sized> ops::Deref for RwLockMappedWriteGuard<'_, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        unsafe { &*self.data }
+    }
+}
+
+impl<T: ?Sized> ops::DerefMut for RwLockMappedWriteGuard<'_, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.data }
+    }
+}
+
+impl<'a, T: ?Sized> fmt::Debug for RwLockMappedWriteGuard<'a, T>
+where
+    T: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<'a, T: ?Sized> fmt::Display for RwLockMappedWriteGuard<'a, T>
+where
+    T: fmt::Display,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+impl<'a, T: ?Sized> Drop for RwLockMappedWriteGuard<'a, T> {
+    fn drop(&mut self) {
+        self.s.release(self.permits_acquired as usize);
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        self.resource_span.in_scope(|| {
+            tracing::trace!(
+            target: "runtime::resource::state_update",
+            write_locked = false,
+            write_locked.op = "override",
+            )
+        });
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/semaphore.rs b/third_party/rust/tokio/src/sync/semaphore.rs
new file mode 100644
index 0000000000..860f46f399
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/semaphore.rs
@@ -0,0 +1,644 @@
+use super::batch_semaphore as ll; // low level implementation
+use super::{AcquireError, TryAcquireError};
+#[cfg(all(tokio_unstable, feature = "tracing"))]
+use crate::util::trace;
+use std::sync::Arc;
+
+/// Counting semaphore performing asynchronous permit acquisition.
+///
+/// A semaphore maintains a set of permits. Permits are used to synchronize
+/// access to a shared resource. A semaphore differs from a mutex in that it
+/// can allow more than one concurrent caller to access the shared resource at a
+/// time.
+///
+/// When `acquire` is called and the semaphore has remaining permits, the
+/// function immediately returns a permit. However, if no remaining permits are
+/// available, `acquire` (asynchronously) waits until an outstanding permit is
+/// dropped. At this point, the freed permit is assigned to the caller.
+///
+/// This `Semaphore` is fair, which means that permits are given out in the order
+/// they were requested. This fairness is also applied when `acquire_many` gets
+/// involved, so if a call to `acquire_many` at the front of the queue requests
+/// more permits than currently available, this can prevent a call to `acquire`
+/// from completing, even if the semaphore has enough permits complete the call
+/// to `acquire`.
+///
+/// To use the `Semaphore` in a poll function, you can use the [`PollSemaphore`]
+/// utility.
+///
+/// # Examples
+///
+/// Basic usage:
+///
+/// ```
+/// use tokio::sync::{Semaphore, TryAcquireError};
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let semaphore = Semaphore::new(3);
+///
+///     let a_permit = semaphore.acquire().await.unwrap();
+///     let two_permits = semaphore.acquire_many(2).await.unwrap();
+///
+///     assert_eq!(semaphore.available_permits(), 0);
+///
+///     let permit_attempt = semaphore.try_acquire();
+///     assert_eq!(permit_attempt.err(), Some(TryAcquireError::NoPermits));
+/// }
+/// ```
+///
+/// Use [`Semaphore::acquire_owned`] to move permits across tasks:
+///
+/// ```
+/// use std::sync::Arc;
+/// use tokio::sync::Semaphore;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let semaphore = Arc::new(Semaphore::new(3));
+///     let mut join_handles = Vec::new();
+///
+///     for _ in 0..5 {
+///         let permit = semaphore.clone().acquire_owned().await.unwrap();
+///         join_handles.push(tokio::spawn(async move {
+///             // perform task...
+///             // explicitly own `permit` in the task
+///             drop(permit);
+///         }));
+///     }
+///
+///     for handle in join_handles {
+///         handle.await.unwrap();
+///     }
+/// }
+/// ```
+///
+/// [`PollSemaphore`]: https://docs.rs/tokio-util/0.6/tokio_util/sync/struct.PollSemaphore.html
+/// [`Semaphore::acquire_owned`]: crate::sync::Semaphore::acquire_owned
+#[derive(Debug)]
+pub struct Semaphore {
+    /// The low level semaphore
+    ll_sem: ll::Semaphore,
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    resource_span: tracing::Span,
+}
+
+/// A permit from the semaphore.
+///
+/// This type is created by the [`acquire`] method.
+///
+/// [`acquire`]: crate::sync::Semaphore::acquire()
+#[must_use]
+#[derive(Debug)]
+pub struct SemaphorePermit<'a> {
+    sem: &'a Semaphore,
+    permits: u32,
+}
+
+/// An owned permit from the semaphore.
+///
+/// This type is created by the [`acquire_owned`] method.
+///
+/// [`acquire_owned`]: crate::sync::Semaphore::acquire_owned()
+#[must_use]
+#[derive(Debug)]
+pub struct OwnedSemaphorePermit {
+    sem: Arc<Semaphore>,
+    permits: u32,
+}
+
+#[test]
+#[cfg(not(loom))]
+fn bounds() {
+    fn check_unpin<T: Unpin>() {}
+    // This has to take a value, since the async fn's return type is unnameable.
+    fn check_send_sync_val<T: Send + Sync>(_t: T) {}
+    fn check_send_sync<T: Send + Sync>() {}
+    check_unpin::<Semaphore>();
+    check_unpin::<SemaphorePermit<'_>>();
+    check_send_sync::<Semaphore>();
+
+    let semaphore = Semaphore::new(0);
+    check_send_sync_val(semaphore.acquire());
+}
+
+impl Semaphore {
+    /// Creates a new semaphore with the initial number of permits.
+    #[track_caller]
+    pub fn new(permits: usize) -> Self {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = {
+            let location = std::panic::Location::caller();
+
+            tracing::trace_span!(
+                "runtime.resource",
+                concrete_type = "Semaphore",
+                kind = "Sync",
+                loc.file = location.file(),
+                loc.line = location.line(),
+                loc.col = location.column(),
+                inherits_child_attrs = true,
+            )
+        };
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let ll_sem = resource_span.in_scope(|| ll::Semaphore::new(permits));
+
+        #[cfg(any(not(tokio_unstable), not(feature = "tracing")))]
+        let ll_sem = ll::Semaphore::new(permits);
+
+        Self {
+            ll_sem,
+            #[cfg(all(tokio_unstable, feature = "tracing"))]
+            resource_span,
+        }
+    }
+
+    /// Creates a new semaphore with the initial number of permits.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Semaphore;
+    ///
+    /// static SEM: Semaphore = Semaphore::const_new(10);
+    /// ```
+    ///
+    #[cfg(all(feature = "parking_lot", not(all(loom, test))))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "parking_lot")))]
+    pub const fn const_new(permits: usize) -> Self {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        return Self {
+            ll_sem: ll::Semaphore::const_new(permits),
+            resource_span: tracing::Span::none(),
+        };
+
+        #[cfg(any(not(tokio_unstable), not(feature = "tracing")))]
+        return Self {
+            ll_sem: ll::Semaphore::const_new(permits),
+        };
+    }
+
+    /// Returns the current number of available permits.
+    pub fn available_permits(&self) -> usize {
+        self.ll_sem.available_permits()
+    }
+
+    /// Adds `n` new permits to the semaphore.
+    ///
+    /// The maximum number of permits is `usize::MAX >> 3`, and this function will panic if the limit is exceeded.
+    pub fn add_permits(&self, n: usize) {
+        self.ll_sem.release(n);
+    }
+
+    /// Acquires a permit from the semaphore.
+    ///
+    /// If the semaphore has been closed, this returns an [`AcquireError`].
+    /// Otherwise, this returns a [`SemaphorePermit`] representing the
+    /// acquired permit.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method uses a queue to fairly distribute permits in the order they
+    /// were requested. Cancelling a call to `acquire` makes you lose your place
+    /// in the queue.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Semaphore;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let semaphore = Semaphore::new(2);
+    ///
+    ///     let permit_1 = semaphore.acquire().await.unwrap();
+    ///     assert_eq!(semaphore.available_permits(), 1);
+    ///
+    ///     let permit_2 = semaphore.acquire().await.unwrap();
+    ///     assert_eq!(semaphore.available_permits(), 0);
+    ///
+    ///     drop(permit_1);
+    ///     assert_eq!(semaphore.available_permits(), 1);
+    /// }
+    /// ```
+    ///
+    /// [`AcquireError`]: crate::sync::AcquireError
+    /// [`SemaphorePermit`]: crate::sync::SemaphorePermit
+    pub async fn acquire(&self) -> Result<SemaphorePermit<'_>, AcquireError> {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let inner = trace::async_op(
+            || self.ll_sem.acquire(1),
+            self.resource_span.clone(),
+            "Semaphore::acquire",
+            "poll",
+            true,
+        );
+        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+        let inner = self.ll_sem.acquire(1);
+
+        inner.await?;
+        Ok(SemaphorePermit {
+            sem: self,
+            permits: 1,
+        })
+    }
+
+    /// Acquires `n` permits from the semaphore.
+    ///
+    /// If the semaphore has been closed, this returns an [`AcquireError`].
+    /// Otherwise, this returns a [`SemaphorePermit`] representing the
+    /// acquired permits.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method uses a queue to fairly distribute permits in the order they
+    /// were requested. Cancelling a call to `acquire_many` makes you lose your
+    /// place in the queue.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Semaphore;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let semaphore = Semaphore::new(5);
+    ///
+    ///     let permit = semaphore.acquire_many(3).await.unwrap();
+    ///     assert_eq!(semaphore.available_permits(), 2);
+    /// }
+    /// ```
+    ///
+    /// [`AcquireError`]: crate::sync::AcquireError
+    /// [`SemaphorePermit`]: crate::sync::SemaphorePermit
+    pub async fn acquire_many(&self, n: u32) -> Result<SemaphorePermit<'_>, AcquireError> {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        trace::async_op(
+            || self.ll_sem.acquire(n),
+            self.resource_span.clone(),
+            "Semaphore::acquire_many",
+            "poll",
+            true,
+        )
+        .await?;
+
+        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+        self.ll_sem.acquire(n).await?;
+
+        Ok(SemaphorePermit {
+            sem: self,
+            permits: n,
+        })
+    }
+
+    /// Tries to acquire a permit from the semaphore.
+    ///
+    /// If the semaphore has been closed, this returns a [`TryAcquireError::Closed`]
+    /// and a [`TryAcquireError::NoPermits`] if there are no permits left. Otherwise,
+    /// this returns a [`SemaphorePermit`] representing the acquired permits.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::{Semaphore, TryAcquireError};
+    ///
+    /// # fn main() {
+    /// let semaphore = Semaphore::new(2);
+    ///
+    /// let permit_1 = semaphore.try_acquire().unwrap();
+    /// assert_eq!(semaphore.available_permits(), 1);
+    ///
+    /// let permit_2 = semaphore.try_acquire().unwrap();
+    /// assert_eq!(semaphore.available_permits(), 0);
+    ///
+    /// let permit_3 = semaphore.try_acquire();
+    /// assert_eq!(permit_3.err(), Some(TryAcquireError::NoPermits));
+    /// # }
+    /// ```
+    ///
+    /// [`TryAcquireError::Closed`]: crate::sync::TryAcquireError::Closed
+    /// [`TryAcquireError::NoPermits`]: crate::sync::TryAcquireError::NoPermits
+    /// [`SemaphorePermit`]: crate::sync::SemaphorePermit
+    pub fn try_acquire(&self) -> Result<SemaphorePermit<'_>, TryAcquireError> {
+        match self.ll_sem.try_acquire(1) {
+            Ok(_) => Ok(SemaphorePermit {
+                sem: self,
+                permits: 1,
+            }),
+            Err(e) => Err(e),
+        }
+    }
+
+    /// Tries to acquire `n` permits from the semaphore.
+    ///
+    /// If the semaphore has been closed, this returns a [`TryAcquireError::Closed`]
+    /// and a [`TryAcquireError::NoPermits`] if there are not enough permits left.
+    /// Otherwise, this returns a [`SemaphorePermit`] representing the acquired permits.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::{Semaphore, TryAcquireError};
+    ///
+    /// # fn main() {
+    /// let semaphore = Semaphore::new(4);
+    ///
+    /// let permit_1 = semaphore.try_acquire_many(3).unwrap();
+    /// assert_eq!(semaphore.available_permits(), 1);
+    ///
+    /// let permit_2 = semaphore.try_acquire_many(2);
+    /// assert_eq!(permit_2.err(), Some(TryAcquireError::NoPermits));
+    /// # }
+    /// ```
+    ///
+    /// [`TryAcquireError::Closed`]: crate::sync::TryAcquireError::Closed
+    /// [`TryAcquireError::NoPermits`]: crate::sync::TryAcquireError::NoPermits
+    /// [`SemaphorePermit`]: crate::sync::SemaphorePermit
+    pub fn try_acquire_many(&self, n: u32) -> Result<SemaphorePermit<'_>, TryAcquireError> {
+        match self.ll_sem.try_acquire(n) {
+            Ok(_) => Ok(SemaphorePermit {
+                sem: self,
+                permits: n,
+            }),
+            Err(e) => Err(e),
+        }
+    }
+
+    /// Acquires a permit from the semaphore.
+    ///
+    /// The semaphore must be wrapped in an [`Arc`] to call this method.
+    /// If the semaphore has been closed, this returns an [`AcquireError`].
+    /// Otherwise, this returns a [`OwnedSemaphorePermit`] representing the
+    /// acquired permit.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method uses a queue to fairly distribute permits in the order they
+    /// were requested. Cancelling a call to `acquire_owned` makes you lose your
+    /// place in the queue.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::Semaphore;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let semaphore = Arc::new(Semaphore::new(3));
+    ///     let mut join_handles = Vec::new();
+    ///
+    ///     for _ in 0..5 {
+    ///         let permit = semaphore.clone().acquire_owned().await.unwrap();
+    ///         join_handles.push(tokio::spawn(async move {
+    ///             // perform task...
+    ///             // explicitly own `permit` in the task
+    ///             drop(permit);
+    ///         }));
+    ///     }
+    ///
+    ///     for handle in join_handles {
+    ///         handle.await.unwrap();
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// [`Arc`]: std::sync::Arc
+    /// [`AcquireError`]: crate::sync::AcquireError
+    /// [`OwnedSemaphorePermit`]: crate::sync::OwnedSemaphorePermit
+    pub async fn acquire_owned(self: Arc<Self>) -> Result<OwnedSemaphorePermit, AcquireError> {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let inner = trace::async_op(
+            || self.ll_sem.acquire(1),
+            self.resource_span.clone(),
+            "Semaphore::acquire_owned",
+            "poll",
+            true,
+        );
+        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+        let inner = self.ll_sem.acquire(1);
+
+        inner.await?;
+        Ok(OwnedSemaphorePermit {
+            sem: self,
+            permits: 1,
+        })
+    }
+
+    /// Acquires `n` permits from the semaphore.
+    ///
+    /// The semaphore must be wrapped in an [`Arc`] to call this method.
+    /// If the semaphore has been closed, this returns an [`AcquireError`].
+    /// Otherwise, this returns a [`OwnedSemaphorePermit`] representing the
+    /// acquired permit.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method uses a queue to fairly distribute permits in the order they
+    /// were requested. Cancelling a call to `acquire_many_owned` makes you lose
+    /// your place in the queue.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::Semaphore;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let semaphore = Arc::new(Semaphore::new(10));
+    ///     let mut join_handles = Vec::new();
+    ///
+    ///     for _ in 0..5 {
+    ///         let permit = semaphore.clone().acquire_many_owned(2).await.unwrap();
+    ///         join_handles.push(tokio::spawn(async move {
+    ///             // perform task...
+    ///             // explicitly own `permit` in the task
+    ///             drop(permit);
+    ///         }));
+    ///     }
+    ///
+    ///     for handle in join_handles {
+    ///         handle.await.unwrap();
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// [`Arc`]: std::sync::Arc
+    /// [`AcquireError`]: crate::sync::AcquireError
+    /// [`OwnedSemaphorePermit`]: crate::sync::OwnedSemaphorePermit
+    pub async fn acquire_many_owned(
+        self: Arc<Self>,
+        n: u32,
+    ) -> Result<OwnedSemaphorePermit, AcquireError> {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let inner = trace::async_op(
+            || self.ll_sem.acquire(n),
+            self.resource_span.clone(),
+            "Semaphore::acquire_many_owned",
+            "poll",
+            true,
+        );
+        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+        let inner = self.ll_sem.acquire(n);
+
+        inner.await?;
+        Ok(OwnedSemaphorePermit {
+            sem: self,
+            permits: n,
+        })
+    }
+
+    /// Tries to acquire a permit from the semaphore.
+    ///
+    /// The semaphore must be wrapped in an [`Arc`] to call this method. If
+    /// the semaphore has been closed, this returns a [`TryAcquireError::Closed`]
+    /// and a [`TryAcquireError::NoPermits`] if there are no permits left.
+    /// Otherwise, this returns a [`OwnedSemaphorePermit`] representing the
+    /// acquired permit.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::{Semaphore, TryAcquireError};
+    ///
+    /// # fn main() {
+    /// let semaphore = Arc::new(Semaphore::new(2));
+    ///
+    /// let permit_1 = Arc::clone(&semaphore).try_acquire_owned().unwrap();
+    /// assert_eq!(semaphore.available_permits(), 1);
+    ///
+    /// let permit_2 = Arc::clone(&semaphore).try_acquire_owned().unwrap();
+    /// assert_eq!(semaphore.available_permits(), 0);
+    ///
+    /// let permit_3 = semaphore.try_acquire_owned();
+    /// assert_eq!(permit_3.err(), Some(TryAcquireError::NoPermits));
+    /// # }
+    /// ```
+    ///
+    /// [`Arc`]: std::sync::Arc
+    /// [`TryAcquireError::Closed`]: crate::sync::TryAcquireError::Closed
+    /// [`TryAcquireError::NoPermits`]: crate::sync::TryAcquireError::NoPermits
+    /// [`OwnedSemaphorePermit`]: crate::sync::OwnedSemaphorePermit
+    pub fn try_acquire_owned(self: Arc<Self>) -> Result<OwnedSemaphorePermit, TryAcquireError> {
+        match self.ll_sem.try_acquire(1) {
+            Ok(_) => Ok(OwnedSemaphorePermit {
+                sem: self,
+                permits: 1,
+            }),
+            Err(e) => Err(e),
+        }
+    }
+
+    /// Tries to acquire `n` permits from the semaphore.
+    ///
+    /// The semaphore must be wrapped in an [`Arc`] to call this method. If
+    /// the semaphore has been closed, this returns a [`TryAcquireError::Closed`]
+    /// and a [`TryAcquireError::NoPermits`] if there are no permits left.
+    /// Otherwise, this returns a [`OwnedSemaphorePermit`] representing the
+    /// acquired permit.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use std::sync::Arc;
+    /// use tokio::sync::{Semaphore, TryAcquireError};
+    ///
+    /// # fn main() {
+    /// let semaphore = Arc::new(Semaphore::new(4));
+    ///
+    /// let permit_1 = Arc::clone(&semaphore).try_acquire_many_owned(3).unwrap();
+    /// assert_eq!(semaphore.available_permits(), 1);
+    ///
+    /// let permit_2 = semaphore.try_acquire_many_owned(2);
+    /// assert_eq!(permit_2.err(), Some(TryAcquireError::NoPermits));
+    /// # }
+    /// ```
+    ///
+    /// [`Arc`]: std::sync::Arc
+    /// [`TryAcquireError::Closed`]: crate::sync::TryAcquireError::Closed
+    /// [`TryAcquireError::NoPermits`]: crate::sync::TryAcquireError::NoPermits
+    /// [`OwnedSemaphorePermit`]: crate::sync::OwnedSemaphorePermit
+    pub fn try_acquire_many_owned(
+        self: Arc<Self>,
+        n: u32,
+    ) -> Result<OwnedSemaphorePermit, TryAcquireError> {
+        match self.ll_sem.try_acquire(n) {
+            Ok(_) => Ok(OwnedSemaphorePermit {
+                sem: self,
+                permits: n,
+            }),
+            Err(e) => Err(e),
+        }
+    }
+
+    /// Closes the semaphore.
+    ///
+    /// This prevents the semaphore from issuing new permits and notifies all pending waiters.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::Semaphore;
+    /// use std::sync::Arc;
+    /// use tokio::sync::TryAcquireError;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let semaphore = Arc::new(Semaphore::new(1));
+    ///     let semaphore2 = semaphore.clone();
+    ///
+    ///     tokio::spawn(async move {
+    ///         let permit = semaphore.acquire_many(2).await;
+    ///         assert!(permit.is_err());
+    ///         println!("waiter received error");
+    ///     });
+    ///
+    ///     println!("closing semaphore");
+    ///     semaphore2.close();
+    ///
+    ///     // Cannot obtain more permits
+    ///     assert_eq!(semaphore2.try_acquire().err(), Some(TryAcquireError::Closed))
+    /// }
+    /// ```
+    pub fn close(&self) {
+        self.ll_sem.close();
+    }
+
+    /// Returns true if the semaphore is closed
+    pub fn is_closed(&self) -> bool {
+        self.ll_sem.is_closed()
+    }
+}
+
+impl<'a> SemaphorePermit<'a> {
+    /// Forgets the permit **without** releasing it back to the semaphore.
+    /// This can be used to reduce the amount of permits available from a
+    /// semaphore.
+    pub fn forget(mut self) {
+        self.permits = 0;
+    }
+}
+
+impl OwnedSemaphorePermit {
+    /// Forgets the permit **without** releasing it back to the semaphore.
+    /// This can be used to reduce the amount of permits available from a
+    /// semaphore.
+    pub fn forget(mut self) {
+        self.permits = 0;
+    }
+}
+
+impl<'a> Drop for SemaphorePermit<'_> {
+    fn drop(&mut self) {
+        self.sem.add_permits(self.permits as usize);
+    }
+}
+
+impl Drop for OwnedSemaphorePermit {
+    fn drop(&mut self) {
+        self.sem.add_permits(self.permits as usize);
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/task/atomic_waker.rs b/third_party/rust/tokio/src/sync/task/atomic_waker.rs
new file mode 100644
index 0000000000..13aba35448
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/task/atomic_waker.rs
@@ -0,0 +1,382 @@
+#![cfg_attr(any(loom, not(feature = "sync")), allow(dead_code, unreachable_pub))]
+
+use crate::loom::cell::UnsafeCell;
+use crate::loom::hint;
+use crate::loom::sync::atomic::AtomicUsize;
+
+use std::fmt;
+use std::panic::{resume_unwind, AssertUnwindSafe, RefUnwindSafe, UnwindSafe};
+use std::sync::atomic::Ordering::{AcqRel, Acquire, Release};
+use std::task::Waker;
+
+/// A synchronization primitive for task waking.
+///
+/// `AtomicWaker` will coordinate concurrent wakes with the consumer
+/// potentially "waking" the underlying task. This is useful in scenarios
+/// where a computation completes in another thread and wants to wake the
+/// consumer, but the consumer is in the process of being migrated to a new
+/// logical task.
+///
+/// Consumers should call `register` before checking the result of a computation
+/// and producers should call `wake` after producing the computation (this
+/// differs from the usual `thread::park` pattern). It is also permitted for
+/// `wake` to be called **before** `register`. This results in a no-op.
+///
+/// A single `AtomicWaker` may be reused for any number of calls to `register` or
+/// `wake`.
+pub(crate) struct AtomicWaker {
+    state: AtomicUsize,
+    waker: UnsafeCell<Option<Waker>>,
+}
+
+impl RefUnwindSafe for AtomicWaker {}
+impl UnwindSafe for AtomicWaker {}
+
+// `AtomicWaker` is a multi-consumer, single-producer transfer cell. The cell
+// stores a `Waker` value produced by calls to `register` and many threads can
+// race to take the waker by calling `wake`.
+//
+// If a new `Waker` instance is produced by calling `register` before an existing
+// one is consumed, then the existing one is overwritten.
+//
+// While `AtomicWaker` is single-producer, the implementation ensures memory
+// safety. In the event of concurrent calls to `register`, there will be a
+// single winner whose waker will get stored in the cell. The losers will not
+// have their tasks woken. As such, callers should ensure to add synchronization
+// to calls to `register`.
+//
+// The implementation uses a single `AtomicUsize` value to coordinate access to
+// the `Waker` cell. There are two bits that are operated on independently. These
+// are represented by `REGISTERING` and `WAKING`.
+//
+// The `REGISTERING` bit is set when a producer enters the critical section. The
+// `WAKING` bit is set when a consumer enters the critical section. Neither
+// bit being set is represented by `WAITING`.
+//
+// A thread obtains an exclusive lock on the waker cell by transitioning the
+// state from `WAITING` to `REGISTERING` or `WAKING`, depending on the
+// operation the thread wishes to perform. When this transition is made, it is
+// guaranteed that no other thread will access the waker cell.
+//
+// # Registering
+//
+// On a call to `register`, an attempt to transition the state from WAITING to
+// REGISTERING is made. On success, the caller obtains a lock on the waker cell.
+//
+// If the lock is obtained, then the thread sets the waker cell to the waker
+// provided as an argument. Then it attempts to transition the state back from
+// `REGISTERING` -> `WAITING`.
+//
+// If this transition is successful, then the registering process is complete
+// and the next call to `wake` will observe the waker.
+//
+// If the transition fails, then there was a concurrent call to `wake` that
+// was unable to access the waker cell (due to the registering thread holding the
+// lock). To handle this, the registering thread removes the waker it just set
+// from the cell and calls `wake` on it. This call to wake represents the
+// attempt to wake by the other thread (that set the `WAKING` bit). The
+// state is then transitioned from `REGISTERING | WAKING` back to `WAITING`.
+// This transition must succeed because, at this point, the state cannot be
+// transitioned by another thread.
+//
+// # Waking
+//
+// On a call to `wake`, an attempt to transition the state from `WAITING` to
+// `WAKING` is made. On success, the caller obtains a lock on the waker cell.
+//
+// If the lock is obtained, then the thread takes ownership of the current value
+// in the waker cell, and calls `wake` on it. The state is then transitioned
+// back to `WAITING`. This transition must succeed as, at this point, the state
+// cannot be transitioned by another thread.
+//
+// If the thread is unable to obtain the lock, the `WAKING` bit is still set.
+// This is because it has either been set by the current thread but the previous
+// value included the `REGISTERING` bit **or** a concurrent thread is in the
+// `WAKING` critical section. Either way, no action must be taken.
+//
+// If the current thread is the only concurrent call to `wake` and another
+// thread is in the `register` critical section, when the other thread **exits**
+// the `register` critical section, it will observe the `WAKING` bit and
+// handle the waker itself.
+//
+// If another thread is in the `waker` critical section, then it will handle
+// waking the caller task.
+//
+// # A potential race (is safely handled).
+//
+// Imagine the following situation:
+//
+// * Thread A obtains the `wake` lock and wakes a task.
+//
+// * Before thread A releases the `wake` lock, the woken task is scheduled.
+//
+// * Thread B attempts to wake the task. In theory this should result in the
+//   task being woken, but it cannot because thread A still holds the wake
+//   lock.
+//
+// This case is handled by requiring users of `AtomicWaker` to call `register`
+// **before** attempting to observe the application state change that resulted
+// in the task being woken. The wakers also change the application state
+// before calling wake.
+//
+// Because of this, the task will do one of two things.
+//
+// 1) Observe the application state change that Thread B is waking on. In
+//    this case, it is OK for Thread B's wake to be lost.
+//
+// 2) Call register before attempting to observe the application state. Since
+//    Thread A still holds the `wake` lock, the call to `register` will result
+//    in the task waking itself and get scheduled again.
+
+/// Idle state.
+const WAITING: usize = 0;
+
+/// A new waker value is being registered with the `AtomicWaker` cell.
+const REGISTERING: usize = 0b01;
+
+/// The task currently registered with the `AtomicWaker` cell is being woken.
+const WAKING: usize = 0b10;
+
+impl AtomicWaker {
+    /// Create an `AtomicWaker`
+    pub(crate) fn new() -> AtomicWaker {
+        AtomicWaker {
+            state: AtomicUsize::new(WAITING),
+            waker: UnsafeCell::new(None),
+        }
+    }
+
+    /*
+    /// Registers the current waker to be notified on calls to `wake`.
+    pub(crate) fn register(&self, waker: Waker) {
+        self.do_register(waker);
+    }
+    */
+
+    /// Registers the provided waker to be notified on calls to `wake`.
+    ///
+    /// The new waker will take place of any previous wakers that were registered
+    /// by previous calls to `register`. Any calls to `wake` that happen after
+    /// a call to `register` (as defined by the memory ordering rules), will
+    /// wake the `register` caller's task.
+    ///
+    /// It is safe to call `register` with multiple other threads concurrently
+    /// calling `wake`. This will result in the `register` caller's current
+    /// task being woken once.
+    ///
+    /// This function is safe to call concurrently, but this is generally a bad
+    /// idea. Concurrent calls to `register` will attempt to register different
+    /// tasks to be woken. One of the callers will win and have its task set,
+    /// but there is no guarantee as to which caller will succeed.
+    pub(crate) fn register_by_ref(&self, waker: &Waker) {
+        self.do_register(waker);
+    }
+
+    fn do_register<W>(&self, waker: W)
+    where
+        W: WakerRef,
+    {
+        fn catch_unwind<F: FnOnce() -> R, R>(f: F) -> std::thread::Result<R> {
+            std::panic::catch_unwind(AssertUnwindSafe(f))
+        }
+
+        match self
+            .state
+            .compare_exchange(WAITING, REGISTERING, Acquire, Acquire)
+            .unwrap_or_else(|x| x)
+        {
+            WAITING => {
+                unsafe {
+                    // If `into_waker` panics (because it's code outside of
+                    // AtomicWaker) we need to prime a guard that is called on
+                    // unwind to restore the waker to a WAITING state. Otherwise
+                    // any future calls to register will incorrectly be stuck
+                    // believing it's being updated by someone else.
+                    let new_waker_or_panic = catch_unwind(move || waker.into_waker());
+
+                    // Set the field to contain the new waker, or if
+                    // `into_waker` panicked, leave the old value.
+                    let mut maybe_panic = None;
+                    let mut old_waker = None;
+                    match new_waker_or_panic {
+                        Ok(new_waker) => {
+                            old_waker = self.waker.with_mut(|t| (*t).take());
+                            self.waker.with_mut(|t| *t = Some(new_waker));
+                        }
+                        Err(panic) => maybe_panic = Some(panic),
+                    }
+
+                    // Release the lock. If the state transitioned to include
+                    // the `WAKING` bit, this means that a wake has been
+                    // called concurrently, so we have to remove the waker and
+                    // wake it.`
+                    //
+                    // Start by assuming that the state is `REGISTERING` as this
+                    // is what we jut set it to.
+                    let res = self
+                        .state
+                        .compare_exchange(REGISTERING, WAITING, AcqRel, Acquire);
+
+                    match res {
+                        Ok(_) => {
+                            // We don't want to give the caller the panic if it
+                            // was someone else who put in that waker.
+                            let _ = catch_unwind(move || {
+                                drop(old_waker);
+                            });
+                        }
+                        Err(actual) => {
+                            // This branch can only be reached if a
+                            // concurrent thread called `wake`. In this
+                            // case, `actual` **must** be `REGISTERING |
+                            // WAKING`.
+                            debug_assert_eq!(actual, REGISTERING | WAKING);
+
+                            // Take the waker to wake once the atomic operation has
+                            // completed.
+                            let mut waker = self.waker.with_mut(|t| (*t).take());
+
+                            // Just swap, because no one could change state
+                            // while state == `Registering | `Waking`
+                            self.state.swap(WAITING, AcqRel);
+
+                            // If `into_waker` panicked, then the waker in the
+                            // waker slot is actually the old waker.
+                            if maybe_panic.is_some() {
+                                old_waker = waker.take();
+                            }
+
+                            // We don't want to give the caller the panic if it
+                            // was someone else who put in that waker.
+                            if let Some(old_waker) = old_waker {
+                                let _ = catch_unwind(move || {
+                                    old_waker.wake();
+                                });
+                            }
+
+                            // The atomic swap was complete, now wake the waker
+                            // and return.
+                            //
+                            // If this panics, we end up in a consumed state and
+                            // return the panic to the caller.
+                            if let Some(waker) = waker {
+                                debug_assert!(maybe_panic.is_none());
+                                waker.wake();
+                            }
+                        }
+                    }
+
+                    if let Some(panic) = maybe_panic {
+                        // If `into_waker` panicked, return the panic to the caller.
+                        resume_unwind(panic);
+                    }
+                }
+            }
+            WAKING => {
+                // Currently in the process of waking the task, i.e.,
+                // `wake` is currently being called on the old waker.
+                // So, we call wake on the new waker.
+                //
+                // If this panics, someone else is responsible for restoring the
+                // state of the waker.
+                waker.wake();
+
+                // This is equivalent to a spin lock, so use a spin hint.
+                hint::spin_loop();
+            }
+            state => {
+                // In this case, a concurrent thread is holding the
+                // "registering" lock. This probably indicates a bug in the
+                // caller's code as racing to call `register` doesn't make much
+                // sense.
+                //
+                // We just want to maintain memory safety. It is ok to drop the
+                // call to `register`.
+                debug_assert!(state == REGISTERING || state == REGISTERING | WAKING);
+            }
+        }
+    }
+
+    /// Wakes the task that last called `register`.
+    ///
+    /// If `register` has not been called yet, then this does nothing.
+    pub(crate) fn wake(&self) {
+        if let Some(waker) = self.take_waker() {
+            // If wake panics, we've consumed the waker which is a legitimate
+            // outcome.
+            waker.wake();
+        }
+    }
+
+    /// Attempts to take the `Waker` value out of the `AtomicWaker` with the
+    /// intention that the caller will wake the task later.
+    pub(crate) fn take_waker(&self) -> Option<Waker> {
+        // AcqRel ordering is used in order to acquire the value of the `waker`
+        // cell as well as to establish a `release` ordering with whatever
+        // memory the `AtomicWaker` is associated with.
+        match self.state.fetch_or(WAKING, AcqRel) {
+            WAITING => {
+                // The waking lock has been acquired.
+                let waker = unsafe { self.waker.with_mut(|t| (*t).take()) };
+
+                // Release the lock
+                self.state.fetch_and(!WAKING, Release);
+
+                waker
+            }
+            state => {
+                // There is a concurrent thread currently updating the
+                // associated waker.
+                //
+                // Nothing more to do as the `WAKING` bit has been set. It
+                // doesn't matter if there are concurrent registering threads or
+                // not.
+                //
+                debug_assert!(
+                    state == REGISTERING || state == REGISTERING | WAKING || state == WAKING
+                );
+                None
+            }
+        }
+    }
+}
+
+impl Default for AtomicWaker {
+    fn default() -> Self {
+        AtomicWaker::new()
+    }
+}
+
+impl fmt::Debug for AtomicWaker {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(fmt, "AtomicWaker")
+    }
+}
+
+unsafe impl Send for AtomicWaker {}
+unsafe impl Sync for AtomicWaker {}
+
+trait WakerRef {
+    fn wake(self);
+    fn into_waker(self) -> Waker;
+}
+
+impl WakerRef for Waker {
+    fn wake(self) {
+        self.wake()
+    }
+
+    fn into_waker(self) -> Waker {
+        self
+    }
+}
+
+impl WakerRef for &Waker {
+    fn wake(self) {
+        self.wake_by_ref()
+    }
+
+    fn into_waker(self) -> Waker {
+        self.clone()
+    }
+}
diff --git a/third_party/rust/tokio/src/sync/task/mod.rs b/third_party/rust/tokio/src/sync/task/mod.rs
new file mode 100644
index 0000000000..a6bc6ed06e
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/task/mod.rs
@@ -0,0 +1,4 @@
+//! Thread-safe task notification primitives.
+
+mod atomic_waker;
+pub(crate) use self::atomic_waker::AtomicWaker;
diff --git a/third_party/rust/tokio/src/sync/tests/atomic_waker.rs b/third_party/rust/tokio/src/sync/tests/atomic_waker.rs
new file mode 100644
index 0000000000..ec13cbd658
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/tests/atomic_waker.rs
@@ -0,0 +1,77 @@
+use crate::sync::AtomicWaker;
+use tokio_test::task;
+
+use std::task::Waker;
+
+trait AssertSend: Send {}
+trait AssertSync: Send {}
+
+impl AssertSend for AtomicWaker {}
+impl AssertSync for AtomicWaker {}
+
+impl AssertSend for Waker {}
+impl AssertSync for Waker {}
+
+#[cfg(target_arch = "wasm32")]
+use wasm_bindgen_test::wasm_bindgen_test as test;
+
+#[test]
+fn basic_usage() {
+    let mut waker = task::spawn(AtomicWaker::new());
+
+    waker.enter(|cx, waker| waker.register_by_ref(cx.waker()));
+    waker.wake();
+
+    assert!(waker.is_woken());
+}
+
+#[test]
+fn wake_without_register() {
+    let mut waker = task::spawn(AtomicWaker::new());
+    waker.wake();
+
+    // Registering should not result in a notification
+    waker.enter(|cx, waker| waker.register_by_ref(cx.waker()));
+
+    assert!(!waker.is_woken());
+}
+
+#[test]
+#[cfg(not(target_arch = "wasm32"))] // wasm currently doesn't support unwinding
+fn atomic_waker_panic_safe() {
+    use std::panic;
+    use std::ptr;
+    use std::task::{RawWaker, RawWakerVTable, Waker};
+
+    static PANICKING_VTABLE: RawWakerVTable = RawWakerVTable::new(
+        |_| panic!("clone"),
+        |_| unimplemented!("wake"),
+        |_| unimplemented!("wake_by_ref"),
+        |_| (),
+    );
+
+    static NONPANICKING_VTABLE: RawWakerVTable = RawWakerVTable::new(
+        |_| RawWaker::new(ptr::null(), &NONPANICKING_VTABLE),
+        |_| unimplemented!("wake"),
+        |_| unimplemented!("wake_by_ref"),
+        |_| (),
+    );
+
+    let panicking = unsafe { Waker::from_raw(RawWaker::new(ptr::null(), &PANICKING_VTABLE)) };
+    let nonpanicking = unsafe { Waker::from_raw(RawWaker::new(ptr::null(), &NONPANICKING_VTABLE)) };
+
+    let atomic_waker = AtomicWaker::new();
+
+    let panicking = panic::AssertUnwindSafe(&panicking);
+
+    let result = panic::catch_unwind(|| {
+        let panic::AssertUnwindSafe(panicking) = panicking;
+        atomic_waker.register_by_ref(panicking);
+    });
+
+    assert!(result.is_err());
+    assert!(atomic_waker.take_waker().is_none());
+
+    atomic_waker.register_by_ref(&nonpanicking);
+    assert!(atomic_waker.take_waker().is_some());
+}
diff --git a/third_party/rust/tokio/src/sync/tests/loom_atomic_waker.rs b/third_party/rust/tokio/src/sync/tests/loom_atomic_waker.rs
new file mode 100644
index 0000000000..f8bae65d13
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/tests/loom_atomic_waker.rs
@@ -0,0 +1,100 @@
+use crate::sync::task::AtomicWaker;
+
+use futures::future::poll_fn;
+use loom::future::block_on;
+use loom::sync::atomic::AtomicUsize;
+use loom::thread;
+use std::sync::atomic::Ordering::Relaxed;
+use std::sync::Arc;
+use std::task::Poll::{Pending, Ready};
+
+struct Chan {
+    num: AtomicUsize,
+    task: AtomicWaker,
+}
+
+#[test]
+fn basic_notification() {
+    const NUM_NOTIFY: usize = 2;
+
+    loom::model(|| {
+        let chan = Arc::new(Chan {
+            num: AtomicUsize::new(0),
+            task: AtomicWaker::new(),
+        });
+
+        for _ in 0..NUM_NOTIFY {
+            let chan = chan.clone();
+
+            thread::spawn(move || {
+                chan.num.fetch_add(1, Relaxed);
+                chan.task.wake();
+            });
+        }
+
+        block_on(poll_fn(move |cx| {
+            chan.task.register_by_ref(cx.waker());
+
+            if NUM_NOTIFY == chan.num.load(Relaxed) {
+                return Ready(());
+            }
+
+            Pending
+        }));
+    });
+}
+
+#[test]
+fn test_panicky_waker() {
+    use std::panic;
+    use std::ptr;
+    use std::task::{RawWaker, RawWakerVTable, Waker};
+
+    static PANICKING_VTABLE: RawWakerVTable =
+        RawWakerVTable::new(|_| panic!("clone"), |_| (), |_| (), |_| ());
+
+    let panicking = unsafe { Waker::from_raw(RawWaker::new(ptr::null(), &PANICKING_VTABLE)) };
+
+    // If you're working with this test (and I sure hope you never have to!),
+    // uncomment the following section because there will be a lot of panics
+    // which would otherwise log.
+    //
+    // We can't however leaved it uncommented, because it's global.
+    // panic::set_hook(Box::new(|_| ()));
+
+    const NUM_NOTIFY: usize = 2;
+
+    loom::model(move || {
+        let chan = Arc::new(Chan {
+            num: AtomicUsize::new(0),
+            task: AtomicWaker::new(),
+        });
+
+        for _ in 0..NUM_NOTIFY {
+            let chan = chan.clone();
+
+            thread::spawn(move || {
+                chan.num.fetch_add(1, Relaxed);
+                chan.task.wake();
+            });
+        }
+
+        // Note: this panic should have no effect on the overall state of the
+        // waker and it should proceed as normal.
+        //
+        // A thread above might race to flag a wakeup, and a WAKING state will
+        // be preserved if this expected panic races with that so the below
+        // procedure should be allowed to continue uninterrupted.
+        let _ = panic::catch_unwind(|| chan.task.register_by_ref(&panicking));
+
+        block_on(poll_fn(move |cx| {
+            chan.task.register_by_ref(cx.waker());
+
+            if NUM_NOTIFY == chan.num.load(Relaxed) {
+                return Ready(());
+            }
+
+            Pending
+        }));
+    });
+}
diff --git a/third_party/rust/tokio/src/sync/tests/loom_broadcast.rs b/third_party/rust/tokio/src/sync/tests/loom_broadcast.rs
new file mode 100644
index 0000000000..039b01bf43
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/tests/loom_broadcast.rs
@@ -0,0 +1,207 @@
+use crate::sync::broadcast;
+use crate::sync::broadcast::error::RecvError::{Closed, Lagged};
+
+use loom::future::block_on;
+use loom::sync::Arc;
+use loom::thread;
+use tokio_test::{assert_err, assert_ok};
+
+#[test]
+fn broadcast_send() {
+    loom::model(|| {
+        let (tx1, mut rx) = broadcast::channel(2);
+        let tx1 = Arc::new(tx1);
+        let tx2 = tx1.clone();
+
+        let th1 = thread::spawn(move || {
+            block_on(async {
+                assert_ok!(tx1.send("one"));
+                assert_ok!(tx1.send("two"));
+                assert_ok!(tx1.send("three"));
+            });
+        });
+
+        let th2 = thread::spawn(move || {
+            block_on(async {
+                assert_ok!(tx2.send("eins"));
+                assert_ok!(tx2.send("zwei"));
+                assert_ok!(tx2.send("drei"));
+            });
+        });
+
+        block_on(async {
+            let mut num = 0;
+            loop {
+                match rx.recv().await {
+                    Ok(_) => num += 1,
+                    Err(Closed) => break,
+                    Err(Lagged(n)) => num += n as usize,
+                }
+            }
+            assert_eq!(num, 6);
+        });
+
+        assert_ok!(th1.join());
+        assert_ok!(th2.join());
+    });
+}
+
+// An `Arc` is used as the value in order to detect memory leaks.
+#[test]
+fn broadcast_two() {
+    loom::model(|| {
+        let (tx, mut rx1) = broadcast::channel::<Arc<&'static str>>(16);
+        let mut rx2 = tx.subscribe();
+
+        let th1 = thread::spawn(move || {
+            block_on(async {
+                let v = assert_ok!(rx1.recv().await);
+                assert_eq!(*v, "hello");
+
+                let v = assert_ok!(rx1.recv().await);
+                assert_eq!(*v, "world");
+
+                match assert_err!(rx1.recv().await) {
+                    Closed => {}
+                    _ => panic!(),
+                }
+            });
+        });
+
+        let th2 = thread::spawn(move || {
+            block_on(async {
+                let v = assert_ok!(rx2.recv().await);
+                assert_eq!(*v, "hello");
+
+                let v = assert_ok!(rx2.recv().await);
+                assert_eq!(*v, "world");
+
+                match assert_err!(rx2.recv().await) {
+                    Closed => {}
+                    _ => panic!(),
+                }
+            });
+        });
+
+        assert_ok!(tx.send(Arc::new("hello")));
+        assert_ok!(tx.send(Arc::new("world")));
+        drop(tx);
+
+        assert_ok!(th1.join());
+        assert_ok!(th2.join());
+    });
+}
+
+#[test]
+fn broadcast_wrap() {
+    loom::model(|| {
+        let (tx, mut rx1) = broadcast::channel(2);
+        let mut rx2 = tx.subscribe();
+
+        let th1 = thread::spawn(move || {
+            block_on(async {
+                let mut num = 0;
+
+                loop {
+                    match rx1.recv().await {
+                        Ok(_) => num += 1,
+                        Err(Closed) => break,
+                        Err(Lagged(n)) => num += n as usize,
+                    }
+                }
+
+                assert_eq!(num, 3);
+            });
+        });
+
+        let th2 = thread::spawn(move || {
+            block_on(async {
+                let mut num = 0;
+
+                loop {
+                    match rx2.recv().await {
+                        Ok(_) => num += 1,
+                        Err(Closed) => break,
+                        Err(Lagged(n)) => num += n as usize,
+                    }
+                }
+
+                assert_eq!(num, 3);
+            });
+        });
+
+        assert_ok!(tx.send("one"));
+        assert_ok!(tx.send("two"));
+        assert_ok!(tx.send("three"));
+
+        drop(tx);
+
+        assert_ok!(th1.join());
+        assert_ok!(th2.join());
+    });
+}
+
+#[test]
+fn drop_rx() {
+    loom::model(|| {
+        let (tx, mut rx1) = broadcast::channel(16);
+        let rx2 = tx.subscribe();
+
+        let th1 = thread::spawn(move || {
+            block_on(async {
+                let v = assert_ok!(rx1.recv().await);
+                assert_eq!(v, "one");
+
+                let v = assert_ok!(rx1.recv().await);
+                assert_eq!(v, "two");
+
+                let v = assert_ok!(rx1.recv().await);
+                assert_eq!(v, "three");
+
+                match assert_err!(rx1.recv().await) {
+                    Closed => {}
+                    _ => panic!(),
+                }
+            });
+        });
+
+        let th2 = thread::spawn(move || {
+            drop(rx2);
+        });
+
+        assert_ok!(tx.send("one"));
+        assert_ok!(tx.send("two"));
+        assert_ok!(tx.send("three"));
+        drop(tx);
+
+        assert_ok!(th1.join());
+        assert_ok!(th2.join());
+    });
+}
+
+#[test]
+fn drop_multiple_rx_with_overflow() {
+    loom::model(move || {
+        // It is essential to have multiple senders and receivers in this test case.
+        let (tx, mut rx) = broadcast::channel(1);
+        let _rx2 = tx.subscribe();
+
+        let _ = tx.send(());
+        let tx2 = tx.clone();
+        let th1 = thread::spawn(move || {
+            block_on(async {
+                for _ in 0..100 {
+                    let _ = tx2.send(());
+                }
+            });
+        });
+        let _ = tx.send(());
+
+        let th2 = thread::spawn(move || {
+            block_on(async { while let Ok(_) = rx.recv().await {} });
+        });
+
+        assert_ok!(th1.join());
+        assert_ok!(th2.join());
+    });
+}
diff --git a/third_party/rust/tokio/src/sync/tests/loom_list.rs b/third_party/rust/tokio/src/sync/tests/loom_list.rs
new file mode 100644
index 0000000000..4067f865ce
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/tests/loom_list.rs
@@ -0,0 +1,48 @@
+use crate::sync::mpsc::list;
+
+use loom::thread;
+use std::sync::Arc;
+
+#[test]
+fn smoke() {
+    use crate::sync::mpsc::block::Read::*;
+
+    const NUM_TX: usize = 2;
+    const NUM_MSG: usize = 2;
+
+    loom::model(|| {
+        let (tx, mut rx) = list::channel();
+        let tx = Arc::new(tx);
+
+        for th in 0..NUM_TX {
+            let tx = tx.clone();
+
+            thread::spawn(move || {
+                for i in 0..NUM_MSG {
+                    tx.push((th, i));
+                }
+            });
+        }
+
+        let mut next = vec![0; NUM_TX];
+
+        loop {
+            match rx.pop(&tx) {
+                Some(Value((th, v))) => {
+                    assert_eq!(v, next[th]);
+                    next[th] += 1;
+
+                    if next.iter().all(|&i| i == NUM_MSG) {
+                        break;
+                    }
+                }
+                Some(Closed) => {
+                    panic!();
+                }
+                None => {
+                    thread::yield_now();
+                }
+            }
+        }
+    });
+}
diff --git a/third_party/rust/tokio/src/sync/tests/loom_mpsc.rs b/third_party/rust/tokio/src/sync/tests/loom_mpsc.rs
new file mode 100644
index 0000000000..f165e7076e
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/tests/loom_mpsc.rs
@@ -0,0 +1,190 @@
+use crate::sync::mpsc;
+
+use futures::future::poll_fn;
+use loom::future::block_on;
+use loom::sync::Arc;
+use loom::thread;
+use tokio_test::assert_ok;
+
+#[test]
+fn closing_tx() {
+    loom::model(|| {
+        let (tx, mut rx) = mpsc::channel(16);
+
+        thread::spawn(move || {
+            tx.try_send(()).unwrap();
+            drop(tx);
+        });
+
+        let v = block_on(rx.recv());
+        assert!(v.is_some());
+
+        let v = block_on(rx.recv());
+        assert!(v.is_none());
+    });
+}
+
+#[test]
+fn closing_unbounded_tx() {
+    loom::model(|| {
+        let (tx, mut rx) = mpsc::unbounded_channel();
+
+        thread::spawn(move || {
+            tx.send(()).unwrap();
+            drop(tx);
+        });
+
+        let v = block_on(rx.recv());
+        assert!(v.is_some());
+
+        let v = block_on(rx.recv());
+        assert!(v.is_none());
+    });
+}
+
+#[test]
+fn closing_bounded_rx() {
+    loom::model(|| {
+        let (tx1, rx) = mpsc::channel::<()>(16);
+        let tx2 = tx1.clone();
+        thread::spawn(move || {
+            drop(rx);
+        });
+
+        block_on(tx1.closed());
+        block_on(tx2.closed());
+    });
+}
+
+#[test]
+fn closing_and_sending() {
+    loom::model(|| {
+        let (tx1, mut rx) = mpsc::channel::<()>(16);
+        let tx1 = Arc::new(tx1);
+        let tx2 = tx1.clone();
+
+        let th1 = thread::spawn(move || {
+            tx1.try_send(()).unwrap();
+        });
+
+        let th2 = thread::spawn(move || {
+            block_on(tx2.closed());
+        });
+
+        let th3 = thread::spawn(move || {
+            let v = block_on(rx.recv());
+            assert!(v.is_some());
+            drop(rx);
+        });
+
+        assert_ok!(th1.join());
+        assert_ok!(th2.join());
+        assert_ok!(th3.join());
+    });
+}
+
+#[test]
+fn closing_unbounded_rx() {
+    loom::model(|| {
+        let (tx1, rx) = mpsc::unbounded_channel::<()>();
+        let tx2 = tx1.clone();
+        thread::spawn(move || {
+            drop(rx);
+        });
+
+        block_on(tx1.closed());
+        block_on(tx2.closed());
+    });
+}
+
+#[test]
+fn dropping_tx() {
+    loom::model(|| {
+        let (tx, mut rx) = mpsc::channel::<()>(16);
+
+        for _ in 0..2 {
+            let tx = tx.clone();
+            thread::spawn(move || {
+                drop(tx);
+            });
+        }
+        drop(tx);
+
+        let v = block_on(rx.recv());
+        assert!(v.is_none());
+    });
+}
+
+#[test]
+fn dropping_unbounded_tx() {
+    loom::model(|| {
+        let (tx, mut rx) = mpsc::unbounded_channel::<()>();
+
+        for _ in 0..2 {
+            let tx = tx.clone();
+            thread::spawn(move || {
+                drop(tx);
+            });
+        }
+        drop(tx);
+
+        let v = block_on(rx.recv());
+        assert!(v.is_none());
+    });
+}
+
+#[test]
+fn try_recv() {
+    loom::model(|| {
+        use crate::sync::{mpsc, Semaphore};
+        use loom::sync::{Arc, Mutex};
+
+        const PERMITS: usize = 2;
+        const TASKS: usize = 2;
+        const CYCLES: usize = 1;
+
+        struct Context {
+            sem: Arc<Semaphore>,
+            tx: mpsc::Sender<()>,
+            rx: Mutex<mpsc::Receiver<()>>,
+        }
+
+        fn run(ctx: &Context) {
+            block_on(async {
+                let permit = ctx.sem.acquire().await;
+                assert_ok!(ctx.rx.lock().unwrap().try_recv());
+                crate::task::yield_now().await;
+                assert_ok!(ctx.tx.clone().try_send(()));
+                drop(permit);
+            });
+        }
+
+        let (tx, rx) = mpsc::channel(PERMITS);
+        let sem = Arc::new(Semaphore::new(PERMITS));
+        let ctx = Arc::new(Context {
+            sem,
+            tx,
+            rx: Mutex::new(rx),
+        });
+
+        for _ in 0..PERMITS {
+            assert_ok!(ctx.tx.clone().try_send(()));
+        }
+
+        let mut ths = Vec::new();
+
+        for _ in 0..TASKS {
+            let ctx = ctx.clone();
+
+            ths.push(thread::spawn(move || {
+                run(&ctx);
+            }));
+        }
+
+        run(&ctx);
+
+        for th in ths {
+            th.join().unwrap();
+        }
+    });
+}
diff --git a/third_party/rust/tokio/src/sync/tests/loom_notify.rs b/third_party/rust/tokio/src/sync/tests/loom_notify.rs
new file mode 100644
index 0000000000..d484a75817
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/tests/loom_notify.rs
@@ -0,0 +1,140 @@
+use crate::sync::Notify;
+
+use loom::future::block_on;
+use loom::sync::Arc;
+use loom::thread;
+
+#[test]
+fn notify_one() {
+    loom::model(|| {
+        let tx = Arc::new(Notify::new());
+        let rx = tx.clone();
+
+        let th = thread::spawn(move || {
+            block_on(async {
+                rx.notified().await;
+            });
+        });
+
+        tx.notify_one();
+        th.join().unwrap();
+    });
+}
+
+#[test]
+fn notify_waiters() {
+    loom::model(|| {
+        let notify = Arc::new(Notify::new());
+        let tx = notify.clone();
+        let notified1 = notify.notified();
+        let notified2 = notify.notified();
+
+        let th = thread::spawn(move || {
+            tx.notify_waiters();
+        });
+
+        block_on(async {
+            notified1.await;
+            notified2.await;
+        });
+
+        th.join().unwrap();
+    });
+}
+
+#[test]
+fn notify_waiters_and_one() {
+    loom::model(|| {
+        let notify = Arc::new(Notify::new());
+        let tx1 = notify.clone();
+        let tx2 = notify.clone();
+
+        let th1 = thread::spawn(move || {
+            tx1.notify_waiters();
+        });
+
+        let th2 = thread::spawn(move || {
+            tx2.notify_one();
+        });
+
+        let th3 = thread::spawn(move || {
+            let notified = notify.notified();
+
+            block_on(async {
+                notified.await;
+            });
+        });
+
+        th1.join().unwrap();
+        th2.join().unwrap();
+        th3.join().unwrap();
+    });
+}
+
+#[test]
+fn notify_multi() {
+    loom::model(|| {
+        let notify = Arc::new(Notify::new());
+
+        let mut ths = vec![];
+
+        for _ in 0..2 {
+            let notify = notify.clone();
+
+            ths.push(thread::spawn(move || {
+                block_on(async {
+                    notify.notified().await;
+                    notify.notify_one();
+                })
+            }));
+        }
+
+        notify.notify_one();
+
+        for th in ths.drain(..) {
+            th.join().unwrap();
+        }
+
+        block_on(async {
+            notify.notified().await;
+        });
+    });
+}
+
+#[test]
+fn notify_drop() {
+    use crate::future::poll_fn;
+    use std::future::Future;
+    use std::task::Poll;
+
+    loom::model(|| {
+        let notify = Arc::new(Notify::new());
+        let rx1 = notify.clone();
+        let rx2 = notify.clone();
+
+        let th1 = thread::spawn(move || {
+            let mut recv = Box::pin(rx1.notified());
+
+            block_on(poll_fn(|cx| {
+                if recv.as_mut().poll(cx).is_ready() {
+                    rx1.notify_one();
+                }
+                Poll::Ready(())
+            }));
+        });
+
+        let th2 = thread::spawn(move || {
+            block_on(async {
+                rx2.notified().await;
+                // Trigger second notification
+                rx2.notify_one();
+                rx2.notified().await;
+            });
+        });
+
+        notify.notify_one();
+
+        th1.join().unwrap();
+        th2.join().unwrap();
+    });
+}
diff --git a/third_party/rust/tokio/src/sync/tests/loom_oneshot.rs b/third_party/rust/tokio/src/sync/tests/loom_oneshot.rs
new file mode 100644
index 0000000000..c5f7972079
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/tests/loom_oneshot.rs
@@ -0,0 +1,140 @@
+use crate::sync::oneshot;
+
+use futures::future::poll_fn;
+use loom::future::block_on;
+use loom::thread;
+use std::task::Poll::{Pending, Ready};
+
+#[test]
+fn smoke() {
+    loom::model(|| {
+        let (tx, rx) = oneshot::channel();
+
+        thread::spawn(move || {
+            tx.send(1).unwrap();
+        });
+
+        let value = block_on(rx).unwrap();
+        assert_eq!(1, value);
+    });
+}
+
+#[test]
+fn changing_rx_task() {
+    loom::model(|| {
+        let (tx, mut rx) = oneshot::channel();
+
+        thread::spawn(move || {
+            tx.send(1).unwrap();
+        });
+
+        let rx = thread::spawn(move || {
+            let ready = block_on(poll_fn(|cx| match Pin::new(&mut rx).poll(cx) {
+                Ready(Ok(value)) => {
+                    assert_eq!(1, value);
+                    Ready(true)
+                }
+                Ready(Err(_)) => unimplemented!(),
+                Pending => Ready(false),
+            }));
+
+            if ready {
+                None
+            } else {
+                Some(rx)
+            }
+        })
+        .join()
+        .unwrap();
+
+        if let Some(rx) = rx {
+            // Previous task parked, use a new task...
+            let value = block_on(rx).unwrap();
+            assert_eq!(1, value);
+        }
+    });
+}
+
+#[test]
+fn try_recv_close() {
+    // reproduces https://github.com/tokio-rs/tokio/issues/4225
+    loom::model(|| {
+        let (tx, mut rx) = oneshot::channel();
+        thread::spawn(move || {
+            let _ = tx.send(());
+        });
+
+        rx.close();
+        let _ = rx.try_recv();
+    })
+}
+
+#[test]
+fn recv_closed() {
+    // reproduces https://github.com/tokio-rs/tokio/issues/4225
+    loom::model(|| {
+        let (tx, mut rx) = oneshot::channel();
+
+        thread::spawn(move || {
+            let _ = tx.send(1);
+        });
+
+        rx.close();
+        let _ = block_on(rx);
+    });
+}
+
+// TODO: Move this into `oneshot` proper.
+
+use std::future::Future;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+struct OnClose<'a> {
+    tx: &'a mut oneshot::Sender<i32>,
+}
+
+impl<'a> OnClose<'a> {
+    fn new(tx: &'a mut oneshot::Sender<i32>) -> Self {
+        OnClose { tx }
+    }
+}
+
+impl Future for OnClose<'_> {
+    type Output = bool;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<bool> {
+        let fut = self.get_mut().tx.closed();
+        crate::pin!(fut);
+
+        Ready(fut.poll(cx).is_ready())
+    }
+}
+
+#[test]
+fn changing_tx_task() {
+    loom::model(|| {
+        let (mut tx, rx) = oneshot::channel::<i32>();
+
+        thread::spawn(move || {
+            drop(rx);
+        });
+
+        let tx = thread::spawn(move || {
+            let t1 = block_on(OnClose::new(&mut tx));
+
+            if t1 {
+                None
+            } else {
+                Some(tx)
+            }
+        })
+        .join()
+        .unwrap();
+
+        if let Some(mut tx) = tx {
+            // Previous task parked, use a new task...
+            block_on(OnClose::new(&mut tx));
+        }
+    });
+}
diff --git a/third_party/rust/tokio/src/sync/tests/loom_rwlock.rs b/third_party/rust/tokio/src/sync/tests/loom_rwlock.rs
new file mode 100644
index 0000000000..4b5cc7edc6
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/tests/loom_rwlock.rs
@@ -0,0 +1,105 @@
+use crate::sync::rwlock::*;
+
+use loom::future::block_on;
+use loom::thread;
+use std::sync::Arc;
+
+#[test]
+fn concurrent_write() {
+    let b = loom::model::Builder::new();
+
+    b.check(|| {
+        let rwlock = Arc::new(RwLock::<u32>::new(0));
+
+        let rwclone = rwlock.clone();
+        let t1 = thread::spawn(move || {
+            block_on(async {
+                let mut guard = rwclone.write().await;
+                *guard += 5;
+            });
+        });
+
+        let rwclone = rwlock.clone();
+        let t2 = thread::spawn(move || {
+            block_on(async {
+                let mut guard = rwclone.write_owned().await;
+                *guard += 5;
+            });
+        });
+
+        t1.join().expect("thread 1 write should not panic");
+        t2.join().expect("thread 2 write should not panic");
+        //when all threads have finished the value on the lock should be 10
+        let guard = block_on(rwlock.read());
+        assert_eq!(10, *guard);
+    });
+}
+
+#[test]
+fn concurrent_read_write() {
+    let b = loom::model::Builder::new();
+
+    b.check(|| {
+        let rwlock = Arc::new(RwLock::<u32>::new(0));
+
+        let rwclone = rwlock.clone();
+        let t1 = thread::spawn(move || {
+            block_on(async {
+                let mut guard = rwclone.write().await;
+                *guard += 5;
+            });
+        });
+
+        let rwclone = rwlock.clone();
+        let t2 = thread::spawn(move || {
+            block_on(async {
+                let mut guard = rwclone.write_owned().await;
+                *guard += 5;
+            });
+        });
+
+        let rwclone = rwlock.clone();
+        let t3 = thread::spawn(move || {
+            block_on(async {
+                let guard = rwclone.read().await;
+                //at this state the value on the lock may either be 0, 5, or 10
+                assert!(*guard == 0 || *guard == 5 || *guard == 10);
+            });
+        });
+
+        {
+            let guard = block_on(rwlock.clone().read_owned());
+            //at this state the value on the lock may either be 0, 5, or 10
+            assert!(*guard == 0 || *guard == 5 || *guard == 10);
+        }
+
+        t1.join().expect("thread 1 write should not panic");
+        t2.join().expect("thread 2 write should not panic");
+        t3.join().expect("thread 3 read should not panic");
+
+        let guard = block_on(rwlock.read());
+        //when all threads have finished the value on the lock should be 10
+        assert_eq!(10, *guard);
+    });
+}
+#[test]
+fn downgrade() {
+    loom::model(|| {
+        let lock = Arc::new(RwLock::new(1));
+
+        let n = block_on(lock.write());
+
+        let cloned_lock = lock.clone();
+        let handle = thread::spawn(move || {
+            let mut guard = block_on(cloned_lock.write());
+            *guard = 2;
+        });
+
+        let n = n.downgrade();
+        assert_eq!(*n, 1);
+
+        drop(n);
+        handle.join().unwrap();
+        assert_eq!(*block_on(lock.read()), 2);
+    });
+}
diff --git a/third_party/rust/tokio/src/sync/tests/loom_semaphore_batch.rs b/third_party/rust/tokio/src/sync/tests/loom_semaphore_batch.rs
new file mode 100644
index 0000000000..76a1bc0062
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/tests/loom_semaphore_batch.rs
@@ -0,0 +1,215 @@
+use crate::sync::batch_semaphore::*;
+
+use futures::future::poll_fn;
+use loom::future::block_on;
+use loom::sync::atomic::AtomicUsize;
+use loom::thread;
+use std::future::Future;
+use std::pin::Pin;
+use std::sync::atomic::Ordering::SeqCst;
+use std::sync::Arc;
+use std::task::Poll::Ready;
+use std::task::{Context, Poll};
+
+#[test]
+fn basic_usage() {
+    const NUM: usize = 2;
+
+    struct Shared {
+        semaphore: Semaphore,
+        active: AtomicUsize,
+    }
+
+    async fn actor(shared: Arc<Shared>) {
+        shared.semaphore.acquire(1).await.unwrap();
+        let actual = shared.active.fetch_add(1, SeqCst);
+        assert!(actual <= NUM - 1);
+
+        let actual = shared.active.fetch_sub(1, SeqCst);
+        assert!(actual <= NUM);
+        shared.semaphore.release(1);
+    }
+
+    loom::model(|| {
+        let shared = Arc::new(Shared {
+            semaphore: Semaphore::new(NUM),
+            active: AtomicUsize::new(0),
+        });
+
+        for _ in 0..NUM {
+            let shared = shared.clone();
+
+            thread::spawn(move || {
+                block_on(actor(shared));
+            });
+        }
+
+        block_on(actor(shared));
+    });
+}
+
+#[test]
+fn release() {
+    loom::model(|| {
+        let semaphore = Arc::new(Semaphore::new(1));
+
+        {
+            let semaphore = semaphore.clone();
+            thread::spawn(move || {
+                block_on(semaphore.acquire(1)).unwrap();
+                semaphore.release(1);
+            });
+        }
+
+        block_on(semaphore.acquire(1)).unwrap();
+
+        semaphore.release(1);
+    });
+}
+
+#[test]
+fn basic_closing() {
+    const NUM: usize = 2;
+
+    loom::model(|| {
+        let semaphore = Arc::new(Semaphore::new(1));
+
+        for _ in 0..NUM {
+            let semaphore = semaphore.clone();
+
+            thread::spawn(move || {
+                for _ in 0..2 {
+                    block_on(semaphore.acquire(1)).map_err(|_| ())?;
+
+                    semaphore.release(1);
+                }
+
+                Ok::<(), ()>(())
+            });
+        }
+
+        semaphore.close();
+    });
+}
+
+#[test]
+fn concurrent_close() {
+    const NUM: usize = 3;
+
+    loom::model(|| {
+        let semaphore = Arc::new(Semaphore::new(1));
+
+        for _ in 0..NUM {
+            let semaphore = semaphore.clone();
+
+            thread::spawn(move || {
+                block_on(semaphore.acquire(1)).map_err(|_| ())?;
+                semaphore.release(1);
+                semaphore.close();
+
+                Ok::<(), ()>(())
+            });
+        }
+    });
+}
+
+#[test]
+fn concurrent_cancel() {
+    async fn poll_and_cancel(semaphore: Arc<Semaphore>) {
+        let mut acquire1 = Some(semaphore.acquire(1));
+        let mut acquire2 = Some(semaphore.acquire(1));
+        poll_fn(|cx| {
+            // poll the acquire future once, and then immediately throw
+            // it away. this simulates a situation where a future is
+            // polled and then cancelled, such as by a timeout.
+            if let Some(acquire) = acquire1.take() {
+                pin!(acquire);
+                let _ = acquire.poll(cx);
+            }
+            if let Some(acquire) = acquire2.take() {
+                pin!(acquire);
+                let _ = acquire.poll(cx);
+            }
+            Poll::Ready(())
+        })
+        .await
+    }
+
+    loom::model(|| {
+        let semaphore = Arc::new(Semaphore::new(0));
+        let t1 = {
+            let semaphore = semaphore.clone();
+            thread::spawn(move || block_on(poll_and_cancel(semaphore)))
+        };
+        let t2 = {
+            let semaphore = semaphore.clone();
+            thread::spawn(move || block_on(poll_and_cancel(semaphore)))
+        };
+        let t3 = {
+            let semaphore = semaphore.clone();
+            thread::spawn(move || block_on(poll_and_cancel(semaphore)))
+        };
+
+        t1.join().unwrap();
+        semaphore.release(10);
+        t2.join().unwrap();
+        t3.join().unwrap();
+    });
+}
+
+#[test]
+fn batch() {
+    let mut b = loom::model::Builder::new();
+    b.preemption_bound = Some(1);
+
+    b.check(|| {
+        let semaphore = Arc::new(Semaphore::new(10));
+        let active = Arc::new(AtomicUsize::new(0));
+        let mut ths = vec![];
+
+        for _ in 0..2 {
+            let semaphore = semaphore.clone();
+            let active = active.clone();
+
+            ths.push(thread::spawn(move || {
+                for n in &[4, 10, 8] {
+                    block_on(semaphore.acquire(*n)).unwrap();
+
+                    active.fetch_add(*n as usize, SeqCst);
+
+                    let num_active = active.load(SeqCst);
+                    assert!(num_active <= 10);
+
+                    thread::yield_now();
+
+                    active.fetch_sub(*n as usize, SeqCst);
+
+                    semaphore.release(*n as usize);
+                }
+            }));
+        }
+
+        for th in ths.into_iter() {
+            th.join().unwrap();
+        }
+
+        assert_eq!(10, semaphore.available_permits());
+    });
+}
+
+#[test]
+fn release_during_acquire() {
+    loom::model(|| {
+        let semaphore = Arc::new(Semaphore::new(10));
+        semaphore
+            .try_acquire(8)
+            .expect("try_acquire should succeed; semaphore uncontended");
+        let semaphore2 = semaphore.clone();
+        let thread = thread::spawn(move || block_on(semaphore2.acquire(4)).unwrap());
+
+        semaphore.release(8);
+        thread.join().unwrap();
+        semaphore.release(4);
+        assert_eq!(10, semaphore.available_permits());
+    })
+}
diff --git a/third_party/rust/tokio/src/sync/tests/loom_watch.rs b/third_party/rust/tokio/src/sync/tests/loom_watch.rs
new file mode 100644
index 0000000000..c575b5b66c
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/tests/loom_watch.rs
@@ -0,0 +1,36 @@
+use crate::sync::watch;
+
+use loom::future::block_on;
+use loom::thread;
+
+#[test]
+fn smoke() {
+    loom::model(|| {
+        let (tx, mut rx1) = watch::channel(1);
+        let mut rx2 = rx1.clone();
+        let mut rx3 = rx1.clone();
+        let mut rx4 = rx1.clone();
+        let mut rx5 = rx1.clone();
+
+        let th = thread::spawn(move || {
+            tx.send(2).unwrap();
+        });
+
+        block_on(rx1.changed()).unwrap();
+        assert_eq!(*rx1.borrow(), 2);
+
+        block_on(rx2.changed()).unwrap();
+        assert_eq!(*rx2.borrow(), 2);
+
+        block_on(rx3.changed()).unwrap();
+        assert_eq!(*rx3.borrow(), 2);
+
+        block_on(rx4.changed()).unwrap();
+        assert_eq!(*rx4.borrow(), 2);
+
+        block_on(rx5.changed()).unwrap();
+        assert_eq!(*rx5.borrow(), 2);
+
+        th.join().unwrap();
+    })
+}
diff --git a/third_party/rust/tokio/src/sync/tests/mod.rs b/third_party/rust/tokio/src/sync/tests/mod.rs
new file mode 100644
index 0000000000..ee76418ac5
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/tests/mod.rs
@@ -0,0 +1,17 @@
+cfg_not_loom! {
+    mod atomic_waker;
+    mod notify;
+    mod semaphore_batch;
+}
+
+cfg_loom! {
+    mod loom_atomic_waker;
+    mod loom_broadcast;
+    mod loom_list;
+    mod loom_mpsc;
+    mod loom_notify;
+    mod loom_oneshot;
+    mod loom_semaphore_batch;
+    mod loom_watch;
+    mod loom_rwlock;
+}
diff --git a/third_party/rust/tokio/src/sync/tests/notify.rs b/third_party/rust/tokio/src/sync/tests/notify.rs
new file mode 100644
index 0000000000..20153b7a5a
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/tests/notify.rs
@@ -0,0 +1,81 @@
+use crate::sync::Notify;
+use std::future::Future;
+use std::mem::ManuallyDrop;
+use std::sync::Arc;
+use std::task::{Context, RawWaker, RawWakerVTable, Waker};
+
+#[cfg(target_arch = "wasm32")]
+use wasm_bindgen_test::wasm_bindgen_test as test;
+
+#[test]
+fn notify_clones_waker_before_lock() {
+    const VTABLE: &RawWakerVTable = &RawWakerVTable::new(clone_w, wake, wake_by_ref, drop_w);
+
+    unsafe fn clone_w(data: *const ()) -> RawWaker {
+        let arc = ManuallyDrop::new(Arc::<Notify>::from_raw(data as *const Notify));
+        // Or some other arbitrary code that shouldn't be executed while the
+        // Notify wait list is locked.
+        arc.notify_one();
+        let _arc_clone: ManuallyDrop<_> = arc.clone();
+        RawWaker::new(data, VTABLE)
+    }
+
+    unsafe fn drop_w(data: *const ()) {
+        let _ = Arc::<Notify>::from_raw(data as *const Notify);
+    }
+
+    unsafe fn wake(_data: *const ()) {
+        unreachable!()
+    }
+
+    unsafe fn wake_by_ref(_data: *const ()) {
+        unreachable!()
+    }
+
+    let notify = Arc::new(Notify::new());
+    let notify2 = notify.clone();
+
+    let waker =
+        unsafe { Waker::from_raw(RawWaker::new(Arc::into_raw(notify2) as *const _, VTABLE)) };
+    let mut cx = Context::from_waker(&waker);
+
+    let future = notify.notified();
+    pin!(future);
+
+    // The result doesn't matter, we're just testing that we don't deadlock.
+    let _ = future.poll(&mut cx);
+}
+
+#[test]
+fn notify_simple() {
+    let notify = Notify::new();
+
+    let mut fut1 = tokio_test::task::spawn(notify.notified());
+    assert!(fut1.poll().is_pending());
+
+    let mut fut2 = tokio_test::task::spawn(notify.notified());
+    assert!(fut2.poll().is_pending());
+
+    notify.notify_waiters();
+
+    assert!(fut1.poll().is_ready());
+    assert!(fut2.poll().is_ready());
+}
+
+#[test]
+#[cfg(not(target_arch = "wasm32"))]
+fn watch_test() {
+    let rt = crate::runtime::Builder::new_current_thread()
+        .build()
+        .unwrap();
+
+    rt.block_on(async {
+        let (tx, mut rx) = crate::sync::watch::channel(());
+
+        crate::spawn(async move {
+            let _ = tx.send(());
+        });
+
+        let _ = rx.changed().await;
+    });
+}
diff --git a/third_party/rust/tokio/src/sync/tests/semaphore_batch.rs b/third_party/rust/tokio/src/sync/tests/semaphore_batch.rs
new file mode 100644
index 0000000000..d529a9e886
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/tests/semaphore_batch.rs
@@ -0,0 +1,254 @@
+use crate::sync::batch_semaphore::Semaphore;
+use tokio_test::*;
+
+#[cfg(target_arch = "wasm32")]
+use wasm_bindgen_test::wasm_bindgen_test as test;
+
+#[test]
+fn poll_acquire_one_available() {
+    let s = Semaphore::new(100);
+    assert_eq!(s.available_permits(), 100);
+
+    // Polling for a permit succeeds immediately
+    assert_ready_ok!(task::spawn(s.acquire(1)).poll());
+    assert_eq!(s.available_permits(), 99);
+}
+
+#[test]
+fn poll_acquire_many_available() {
+    let s = Semaphore::new(100);
+    assert_eq!(s.available_permits(), 100);
+
+    // Polling for a permit succeeds immediately
+    assert_ready_ok!(task::spawn(s.acquire(5)).poll());
+    assert_eq!(s.available_permits(), 95);
+
+    assert_ready_ok!(task::spawn(s.acquire(5)).poll());
+    assert_eq!(s.available_permits(), 90);
+}
+
+#[test]
+fn try_acquire_one_available() {
+    let s = Semaphore::new(100);
+    assert_eq!(s.available_permits(), 100);
+
+    assert_ok!(s.try_acquire(1));
+    assert_eq!(s.available_permits(), 99);
+
+    assert_ok!(s.try_acquire(1));
+    assert_eq!(s.available_permits(), 98);
+}
+
+#[test]
+fn try_acquire_many_available() {
+    let s = Semaphore::new(100);
+    assert_eq!(s.available_permits(), 100);
+
+    assert_ok!(s.try_acquire(5));
+    assert_eq!(s.available_permits(), 95);
+
+    assert_ok!(s.try_acquire(5));
+    assert_eq!(s.available_permits(), 90);
+}
+
+#[test]
+fn poll_acquire_one_unavailable() {
+    let s = Semaphore::new(1);
+
+    // Acquire the first permit
+    assert_ready_ok!(task::spawn(s.acquire(1)).poll());
+    assert_eq!(s.available_permits(), 0);
+
+    let mut acquire_2 = task::spawn(s.acquire(1));
+    // Try to acquire the second permit
+    assert_pending!(acquire_2.poll());
+    assert_eq!(s.available_permits(), 0);
+
+    s.release(1);
+
+    assert_eq!(s.available_permits(), 0);
+    assert!(acquire_2.is_woken());
+    assert_ready_ok!(acquire_2.poll());
+    assert_eq!(s.available_permits(), 0);
+
+    s.release(1);
+    assert_eq!(s.available_permits(), 1);
+}
+
+#[test]
+fn poll_acquire_many_unavailable() {
+    let s = Semaphore::new(5);
+
+    // Acquire the first permit
+    assert_ready_ok!(task::spawn(s.acquire(1)).poll());
+    assert_eq!(s.available_permits(), 4);
+
+    // Try to acquire the second permit
+    let mut acquire_2 = task::spawn(s.acquire(5));
+    assert_pending!(acquire_2.poll());
+    assert_eq!(s.available_permits(), 0);
+
+    // Try to acquire the third permit
+    let mut acquire_3 = task::spawn(s.acquire(3));
+    assert_pending!(acquire_3.poll());
+    assert_eq!(s.available_permits(), 0);
+
+    s.release(1);
+
+    assert_eq!(s.available_permits(), 0);
+    assert!(acquire_2.is_woken());
+    assert_ready_ok!(acquire_2.poll());
+
+    assert!(!acquire_3.is_woken());
+    assert_eq!(s.available_permits(), 0);
+
+    s.release(1);
+    assert!(!acquire_3.is_woken());
+    assert_eq!(s.available_permits(), 0);
+
+    s.release(2);
+    assert!(acquire_3.is_woken());
+
+    assert_ready_ok!(acquire_3.poll());
+}
+
+#[test]
+fn try_acquire_one_unavailable() {
+    let s = Semaphore::new(1);
+
+    // Acquire the first permit
+    assert_ok!(s.try_acquire(1));
+    assert_eq!(s.available_permits(), 0);
+
+    assert_err!(s.try_acquire(1));
+
+    s.release(1);
+
+    assert_eq!(s.available_permits(), 1);
+    assert_ok!(s.try_acquire(1));
+
+    s.release(1);
+    assert_eq!(s.available_permits(), 1);
+}
+
+#[test]
+fn try_acquire_many_unavailable() {
+    let s = Semaphore::new(5);
+
+    // Acquire the first permit
+    assert_ok!(s.try_acquire(1));
+    assert_eq!(s.available_permits(), 4);
+
+    assert_err!(s.try_acquire(5));
+
+    s.release(1);
+    assert_eq!(s.available_permits(), 5);
+
+    assert_ok!(s.try_acquire(5));
+
+    s.release(1);
+    assert_eq!(s.available_permits(), 1);
+
+    s.release(1);
+    assert_eq!(s.available_permits(), 2);
+}
+
+#[test]
+fn poll_acquire_one_zero_permits() {
+    let s = Semaphore::new(0);
+    assert_eq!(s.available_permits(), 0);
+
+    // Try to acquire the permit
+    let mut acquire = task::spawn(s.acquire(1));
+    assert_pending!(acquire.poll());
+
+    s.release(1);
+
+    assert!(acquire.is_woken());
+    assert_ready_ok!(acquire.poll());
+}
+
+#[test]
+#[should_panic]
+#[cfg(not(target_arch = "wasm32"))] // wasm currently doesn't support unwinding
+fn validates_max_permits() {
+    use std::usize;
+    Semaphore::new((usize::MAX >> 2) + 1);
+}
+
+#[test]
+fn close_semaphore_prevents_acquire() {
+    let s = Semaphore::new(5);
+    s.close();
+
+    assert_eq!(5, s.available_permits());
+
+    assert_ready_err!(task::spawn(s.acquire(1)).poll());
+    assert_eq!(5, s.available_permits());
+
+    assert_ready_err!(task::spawn(s.acquire(1)).poll());
+    assert_eq!(5, s.available_permits());
+}
+
+#[test]
+fn close_semaphore_notifies_permit1() {
+    let s = Semaphore::new(0);
+    let mut acquire = task::spawn(s.acquire(1));
+
+    assert_pending!(acquire.poll());
+
+    s.close();
+
+    assert!(acquire.is_woken());
+    assert_ready_err!(acquire.poll());
+}
+
+#[test]
+fn close_semaphore_notifies_permit2() {
+    let s = Semaphore::new(2);
+
+    // Acquire a couple of permits
+    assert_ready_ok!(task::spawn(s.acquire(1)).poll());
+    assert_ready_ok!(task::spawn(s.acquire(1)).poll());
+
+    let mut acquire3 = task::spawn(s.acquire(1));
+    let mut acquire4 = task::spawn(s.acquire(1));
+    assert_pending!(acquire3.poll());
+    assert_pending!(acquire4.poll());
+
+    s.close();
+
+    assert!(acquire3.is_woken());
+    assert!(acquire4.is_woken());
+
+    assert_ready_err!(acquire3.poll());
+    assert_ready_err!(acquire4.poll());
+
+    assert_eq!(0, s.available_permits());
+
+    s.release(1);
+
+    assert_eq!(1, s.available_permits());
+
+    assert_ready_err!(task::spawn(s.acquire(1)).poll());
+
+    s.release(1);
+
+    assert_eq!(2, s.available_permits());
+}
+
+#[test]
+fn cancel_acquire_releases_permits() {
+    let s = Semaphore::new(10);
+    s.try_acquire(4).expect("uncontended try_acquire succeeds");
+    assert_eq!(6, s.available_permits());
+
+    let mut acquire = task::spawn(s.acquire(8));
+    assert_pending!(acquire.poll());
+
+    assert_eq!(0, s.available_permits());
+    drop(acquire);
+
+    assert_eq!(6, s.available_permits());
+    assert_ok!(s.try_acquire(6));
+}
diff --git a/third_party/rust/tokio/src/sync/watch.rs b/third_party/rust/tokio/src/sync/watch.rs
new file mode 100644
index 0000000000..5673e0fca7
--- /dev/null
+++ b/third_party/rust/tokio/src/sync/watch.rs
@@ -0,0 +1,834 @@
+#![cfg_attr(not(feature = "sync"), allow(dead_code, unreachable_pub))]
+
+//! A single-producer, multi-consumer channel that only retains the *last* sent
+//! value.
+//!
+//! This channel is useful for watching for changes to a value from multiple
+//! points in the code base, for example, changes to configuration values.
+//!
+//! # Usage
+//!
+//! [`channel`] returns a [`Sender`] / [`Receiver`] pair. These are the producer
+//! and sender halves of the channel. The channel is created with an initial
+//! value. The **latest** value stored in the channel is accessed with
+//! [`Receiver::borrow()`]. Awaiting [`Receiver::changed()`] waits for a new
+//! value to sent by the [`Sender`] half.
+//!
+//! # Examples
+//!
+//! ```
+//! use tokio::sync::watch;
+//!
+//! # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
+//!     let (tx, mut rx) = watch::channel("hello");
+//!
+//!     tokio::spawn(async move {
+//!         while rx.changed().await.is_ok() {
+//!             println!("received = {:?}", *rx.borrow());
+//!         }
+//!     });
+//!
+//!     tx.send("world")?;
+//! # Ok(())
+//! # }
+//! ```
+//!
+//! # Closing
+//!
+//! [`Sender::is_closed`] and [`Sender::closed`] allow the producer to detect
+//! when all [`Receiver`] handles have been dropped. This indicates that there
+//! is no further interest in the values being produced and work can be stopped.
+//!
+//! # Thread safety
+//!
+//! Both [`Sender`] and [`Receiver`] are thread safe. They can be moved to other
+//! threads and can be used in a concurrent environment. Clones of [`Receiver`]
+//! handles may be moved to separate threads and also used concurrently.
+//!
+//! [`Sender`]: crate::sync::watch::Sender
+//! [`Receiver`]: crate::sync::watch::Receiver
+//! [`Receiver::changed()`]: crate::sync::watch::Receiver::changed
+//! [`Receiver::borrow()`]: crate::sync::watch::Receiver::borrow
+//! [`channel`]: crate::sync::watch::channel
+//! [`Sender::is_closed`]: crate::sync::watch::Sender::is_closed
+//! [`Sender::closed`]: crate::sync::watch::Sender::closed
+
+use crate::sync::notify::Notify;
+
+use crate::loom::sync::atomic::AtomicUsize;
+use crate::loom::sync::atomic::Ordering::Relaxed;
+use crate::loom::sync::{Arc, RwLock, RwLockReadGuard};
+use std::mem;
+use std::ops;
+
+/// Receives values from the associated [`Sender`](struct@Sender).
+///
+/// Instances are created by the [`channel`](fn@channel) function.
+///
+/// To turn this receiver into a `Stream`, you can use the [`WatchStream`]
+/// wrapper.
+///
+/// [`WatchStream`]: https://docs.rs/tokio-stream/0.1/tokio_stream/wrappers/struct.WatchStream.html
+#[derive(Debug)]
+pub struct Receiver<T> {
+    /// Pointer to the shared state
+    shared: Arc<Shared<T>>,
+
+    /// Last observed version
+    version: Version,
+}
+
+/// Sends values to the associated [`Receiver`](struct@Receiver).
+///
+/// Instances are created by the [`channel`](fn@channel) function.
+#[derive(Debug)]
+pub struct Sender<T> {
+    shared: Arc<Shared<T>>,
+}
+
+/// Returns a reference to the inner value.
+///
+/// Outstanding borrows hold a read lock on the inner value. This means that
+/// long lived borrows could cause the produce half to block. It is recommended
+/// to keep the borrow as short lived as possible.
+///
+/// The priority policy of the lock is dependent on the underlying lock
+/// implementation, and this type does not guarantee that any particular policy
+/// will be used. In particular, a producer which is waiting to acquire the lock
+/// in `send` might or might not block concurrent calls to `borrow`, e.g.:
+///
+/// <details><summary>Potential deadlock example</summary>
+///
+/// ```text
+/// // Task 1 (on thread A)    |  // Task 2 (on thread B)
+/// let _ref1 = rx.borrow();   |
+///                            |  // will block
+///                            |  let _ = tx.send(());
+/// // may deadlock            |
+/// let _ref2 = rx.borrow();   |
+/// ```
+/// </details>
+#[derive(Debug)]
+pub struct Ref<'a, T> {
+    inner: RwLockReadGuard<'a, T>,
+}
+
+#[derive(Debug)]
+struct Shared<T> {
+    /// The most recent value.
+    value: RwLock<T>,
+
+    /// The current version.
+    ///
+    /// The lowest bit represents a "closed" state. The rest of the bits
+    /// represent the current version.
+    state: AtomicState,
+
+    /// Tracks the number of `Receiver` instances.
+    ref_count_rx: AtomicUsize,
+
+    /// Notifies waiting receivers that the value changed.
+    notify_rx: Notify,
+
+    /// Notifies any task listening for `Receiver` dropped events.
+    notify_tx: Notify,
+}
+
+pub mod error {
+    //! Watch error types.
+
+    use std::fmt;
+
+    /// Error produced when sending a value fails.
+    #[derive(Debug)]
+    pub struct SendError<T>(pub T);
+
+    // ===== impl SendError =====
+
+    impl<T: fmt::Debug> fmt::Display for SendError<T> {
+        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+            write!(fmt, "channel closed")
+        }
+    }
+
+    impl<T: fmt::Debug> std::error::Error for SendError<T> {}
+
+    /// Error produced when receiving a change notification.
+    #[derive(Debug)]
+    pub struct RecvError(pub(super) ());
+
+    // ===== impl RecvError =====
+
+    impl fmt::Display for RecvError {
+        fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+            write!(fmt, "channel closed")
+        }
+    }
+
+    impl std::error::Error for RecvError {}
+}
+
+use self::state::{AtomicState, Version};
+mod state {
+    use crate::loom::sync::atomic::AtomicUsize;
+    use crate::loom::sync::atomic::Ordering::SeqCst;
+
+    const CLOSED: usize = 1;
+
+    /// The version part of the state. The lowest bit is always zero.
+    #[derive(Copy, Clone, Debug, Eq, PartialEq)]
+    pub(super) struct Version(usize);
+
+    /// Snapshot of the state. The first bit is used as the CLOSED bit.
+    /// The remaining bits are used as the version.
+    ///
+    /// The CLOSED bit tracks whether the Sender has been dropped. Dropping all
+    /// receivers does not set it.
+    #[derive(Copy, Clone, Debug)]
+    pub(super) struct StateSnapshot(usize);
+
+    /// The state stored in an atomic integer.
+    #[derive(Debug)]
+    pub(super) struct AtomicState(AtomicUsize);
+
+    impl Version {
+        /// Get the initial version when creating the channel.
+        pub(super) fn initial() -> Self {
+            Version(0)
+        }
+    }
+
+    impl StateSnapshot {
+        /// Extract the version from the state.
+        pub(super) fn version(self) -> Version {
+            Version(self.0 & !CLOSED)
+        }
+
+        /// Is the closed bit set?
+        pub(super) fn is_closed(self) -> bool {
+            (self.0 & CLOSED) == CLOSED
+        }
+    }
+
+    impl AtomicState {
+        /// Create a new `AtomicState` that is not closed and which has the
+        /// version set to `Version::initial()`.
+        pub(super) fn new() -> Self {
+            AtomicState(AtomicUsize::new(0))
+        }
+
+        /// Load the current value of the state.
+        pub(super) fn load(&self) -> StateSnapshot {
+            StateSnapshot(self.0.load(SeqCst))
+        }
+
+        /// Increment the version counter.
+        pub(super) fn increment_version(&self) {
+            // Increment by two to avoid touching the CLOSED bit.
+            self.0.fetch_add(2, SeqCst);
+        }
+
+        /// Set the closed bit in the state.
+        pub(super) fn set_closed(&self) {
+            self.0.fetch_or(CLOSED, SeqCst);
+        }
+    }
+}
+
+/// Creates a new watch channel, returning the "send" and "receive" handles.
+///
+/// All values sent by [`Sender`] will become visible to the [`Receiver`] handles.
+/// Only the last value sent is made available to the [`Receiver`] half. All
+/// intermediate values are dropped.
+///
+/// # Examples
+///
+/// ```
+/// use tokio::sync::watch;
+///
+/// # async fn dox() -> Result<(), Box<dyn std::error::Error>> {
+///     let (tx, mut rx) = watch::channel("hello");
+///
+///     tokio::spawn(async move {
+///         while rx.changed().await.is_ok() {
+///             println!("received = {:?}", *rx.borrow());
+///         }
+///     });
+///
+///     tx.send("world")?;
+/// # Ok(())
+/// # }
+/// ```
+///
+/// [`Sender`]: struct@Sender
+/// [`Receiver`]: struct@Receiver
+pub fn channel<T>(init: T) -> (Sender<T>, Receiver<T>) {
+    let shared = Arc::new(Shared {
+        value: RwLock::new(init),
+        state: AtomicState::new(),
+        ref_count_rx: AtomicUsize::new(1),
+        notify_rx: Notify::new(),
+        notify_tx: Notify::new(),
+    });
+
+    let tx = Sender {
+        shared: shared.clone(),
+    };
+
+    let rx = Receiver {
+        shared,
+        version: Version::initial(),
+    };
+
+    (tx, rx)
+}
+
+impl<T> Receiver<T> {
+    fn from_shared(version: Version, shared: Arc<Shared<T>>) -> Self {
+        // No synchronization necessary as this is only used as a counter and
+        // not memory access.
+        shared.ref_count_rx.fetch_add(1, Relaxed);
+
+        Self { shared, version }
+    }
+
+    /// Returns a reference to the most recently sent value.
+    ///
+    /// This method does not mark the returned value as seen, so future calls to
+    /// [`changed`] may return immediately even if you have already seen the
+    /// value with a call to `borrow`.
+    ///
+    /// Outstanding borrows hold a read lock. This means that long lived borrows
+    /// could cause the send half to block. It is recommended to keep the borrow
+    /// as short lived as possible.
+    ///
+    /// The priority policy of the lock is dependent on the underlying lock
+    /// implementation, and this type does not guarantee that any particular policy
+    /// will be used. In particular, a producer which is waiting to acquire the lock
+    /// in `send` might or might not block concurrent calls to `borrow`, e.g.:
+    ///
+    /// <details><summary>Potential deadlock example</summary>
+    ///
+    /// ```text
+    /// // Task 1 (on thread A)    |  // Task 2 (on thread B)
+    /// let _ref1 = rx.borrow();   |
+    ///                            |  // will block
+    ///                            |  let _ = tx.send(());
+    /// // may deadlock            |
+    /// let _ref2 = rx.borrow();   |
+    /// ```
+    /// </details>
+    ///
+    /// [`changed`]: Receiver::changed
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::watch;
+    ///
+    /// let (_, rx) = watch::channel("hello");
+    /// assert_eq!(*rx.borrow(), "hello");
+    /// ```
+    pub fn borrow(&self) -> Ref<'_, T> {
+        let inner = self.shared.value.read().unwrap();
+        Ref { inner }
+    }
+
+    /// Returns a reference to the most recently sent value and mark that value
+    /// as seen.
+    ///
+    /// This method marks the value as seen, so [`changed`] will not return
+    /// immediately if the newest value is one previously returned by
+    /// `borrow_and_update`.
+    ///
+    /// Outstanding borrows hold a read lock. This means that long lived borrows
+    /// could cause the send half to block. It is recommended to keep the borrow
+    /// as short lived as possible.
+    ///
+    /// The priority policy of the lock is dependent on the underlying lock
+    /// implementation, and this type does not guarantee that any particular policy
+    /// will be used. In particular, a producer which is waiting to acquire the lock
+    /// in `send` might or might not block concurrent calls to `borrow`, e.g.:
+    ///
+    /// <details><summary>Potential deadlock example</summary>
+    ///
+    /// ```text
+    /// // Task 1 (on thread A)                |  // Task 2 (on thread B)
+    /// let _ref1 = rx1.borrow_and_update();   |
+    ///                                        |  // will block
+    ///                                        |  let _ = tx.send(());
+    /// // may deadlock                        |
+    /// let _ref2 = rx2.borrow_and_update();   |
+    /// ```
+    /// </details>
+    ///
+    /// [`changed`]: Receiver::changed
+    pub fn borrow_and_update(&mut self) -> Ref<'_, T> {
+        let inner = self.shared.value.read().unwrap();
+        self.version = self.shared.state.load().version();
+        Ref { inner }
+    }
+
+    /// Checks if this channel contains a message that this receiver has not yet
+    /// seen. The new value is not marked as seen.
+    ///
+    /// Although this method is called `has_changed`, it does not check new
+    /// messages for equality, so this call will return true even if the new
+    /// message is equal to the old message.
+    ///
+    /// Returns an error if the channel has been closed.
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::watch;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = watch::channel("hello");
+    ///
+    ///     tx.send("goodbye").unwrap();
+    ///
+    ///     assert!(rx.has_changed().unwrap());
+    ///     assert_eq!(*rx.borrow_and_update(), "goodbye");
+    ///
+    ///     // The value has been marked as seen
+    ///     assert!(!rx.has_changed().unwrap());
+    ///
+    ///     drop(tx);
+    ///     // The `tx` handle has been dropped
+    ///     assert!(rx.has_changed().is_err());
+    /// }
+    /// ```
+    pub fn has_changed(&self) -> Result<bool, error::RecvError> {
+        // Load the version from the state
+        let state = self.shared.state.load();
+        if state.is_closed() {
+            // The sender has dropped.
+            return Err(error::RecvError(()));
+        }
+        let new_version = state.version();
+
+        Ok(self.version != new_version)
+    }
+
+    /// Waits for a change notification, then marks the newest value as seen.
+    ///
+    /// If the newest value in the channel has not yet been marked seen when
+    /// this method is called, the method marks that value seen and returns
+    /// immediately. If the newest value has already been marked seen, then the
+    /// method sleeps until a new message is sent by the [`Sender`] connected to
+    /// this `Receiver`, or until the [`Sender`] is dropped.
+    ///
+    /// This method returns an error if and only if the [`Sender`] is dropped.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. If you use it as the event in a
+    /// [`tokio::select!`](crate::select) statement and some other branch
+    /// completes first, then it is guaranteed that no values have been marked
+    /// seen by this call to `changed`.
+    ///
+    /// [`Sender`]: struct@Sender
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::watch;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, mut rx) = watch::channel("hello");
+    ///
+    ///     tokio::spawn(async move {
+    ///         tx.send("goodbye").unwrap();
+    ///     });
+    ///
+    ///     assert!(rx.changed().await.is_ok());
+    ///     assert_eq!(*rx.borrow(), "goodbye");
+    ///
+    ///     // The `tx` handle has been dropped
+    ///     assert!(rx.changed().await.is_err());
+    /// }
+    /// ```
+    pub async fn changed(&mut self) -> Result<(), error::RecvError> {
+        loop {
+            // In order to avoid a race condition, we first request a notification,
+            // **then** check the current value's version. If a new version exists,
+            // the notification request is dropped.
+            let notified = self.shared.notify_rx.notified();
+
+            if let Some(ret) = maybe_changed(&self.shared, &mut self.version) {
+                return ret;
+            }
+
+            notified.await;
+            // loop around again in case the wake-up was spurious
+        }
+    }
+
+    cfg_process_driver! {
+        pub(crate) fn try_has_changed(&mut self) -> Option<Result<(), error::RecvError>> {
+            maybe_changed(&self.shared, &mut self.version)
+        }
+    }
+}
+
+fn maybe_changed<T>(
+    shared: &Shared<T>,
+    version: &mut Version,
+) -> Option<Result<(), error::RecvError>> {
+    // Load the version from the state
+    let state = shared.state.load();
+    let new_version = state.version();
+
+    if *version != new_version {
+        // Observe the new version and return
+        *version = new_version;
+        return Some(Ok(()));
+    }
+
+    if state.is_closed() {
+        // All receivers have dropped.
+        return Some(Err(error::RecvError(())));
+    }
+
+    None
+}
+
+impl<T> Clone for Receiver<T> {
+    fn clone(&self) -> Self {
+        let version = self.version;
+        let shared = self.shared.clone();
+
+        Self::from_shared(version, shared)
+    }
+}
+
+impl<T> Drop for Receiver<T> {
+    fn drop(&mut self) {
+        // No synchronization necessary as this is only used as a counter and
+        // not memory access.
+        if 1 == self.shared.ref_count_rx.fetch_sub(1, Relaxed) {
+            // This is the last `Receiver` handle, tasks waiting on `Sender::closed()`
+            self.shared.notify_tx.notify_waiters();
+        }
+    }
+}
+
+impl<T> Sender<T> {
+    /// Sends a new value via the channel, notifying all receivers.
+    ///
+    /// This method fails if the channel has been closed, which happens when
+    /// every receiver has been dropped.
+    pub fn send(&self, value: T) -> Result<(), error::SendError<T>> {
+        // This is pretty much only useful as a hint anyway, so synchronization isn't critical.
+        if 0 == self.receiver_count() {
+            return Err(error::SendError(value));
+        }
+
+        self.send_replace(value);
+        Ok(())
+    }
+
+    /// Sends a new value via the channel, notifying all receivers and returning
+    /// the previous value in the channel.
+    ///
+    /// This can be useful for reusing the buffers inside a watched value.
+    /// Additionally, this method permits sending values even when there are no
+    /// receivers.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::watch;
+    ///
+    /// let (tx, _rx) = watch::channel(1);
+    /// assert_eq!(tx.send_replace(2), 1);
+    /// assert_eq!(tx.send_replace(3), 2);
+    /// ```
+    pub fn send_replace(&self, value: T) -> T {
+        let old = {
+            // Acquire the write lock and update the value.
+            let mut lock = self.shared.value.write().unwrap();
+            let old = mem::replace(&mut *lock, value);
+
+            self.shared.state.increment_version();
+
+            // Release the write lock.
+            //
+            // Incrementing the version counter while holding the lock ensures
+            // that receivers are able to figure out the version number of the
+            // value they are currently looking at.
+            drop(lock);
+
+            old
+        };
+
+        // Notify all watchers
+        self.shared.notify_rx.notify_waiters();
+
+        old
+    }
+
+    /// Returns a reference to the most recently sent value
+    ///
+    /// Outstanding borrows hold a read lock. This means that long lived borrows
+    /// could cause the send half to block. It is recommended to keep the borrow
+    /// as short lived as possible.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::watch;
+    ///
+    /// let (tx, _) = watch::channel("hello");
+    /// assert_eq!(*tx.borrow(), "hello");
+    /// ```
+    pub fn borrow(&self) -> Ref<'_, T> {
+        let inner = self.shared.value.read().unwrap();
+        Ref { inner }
+    }
+
+    /// Checks if the channel has been closed. This happens when all receivers
+    /// have dropped.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let (tx, rx) = tokio::sync::watch::channel(());
+    /// assert!(!tx.is_closed());
+    ///
+    /// drop(rx);
+    /// assert!(tx.is_closed());
+    /// ```
+    pub fn is_closed(&self) -> bool {
+        self.receiver_count() == 0
+    }
+
+    /// Completes when all receivers have dropped.
+    ///
+    /// This allows the producer to get notified when interest in the produced
+    /// values is canceled and immediately stop doing work.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancel safe. Once the channel is closed, it stays closed
+    /// forever and all future calls to `closed` will return immediately.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::watch;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, rx) = watch::channel("hello");
+    ///
+    ///     tokio::spawn(async move {
+    ///         // use `rx`
+    ///         drop(rx);
+    ///     });
+    ///
+    ///     // Waits for `rx` to drop
+    ///     tx.closed().await;
+    ///     println!("the `rx` handles dropped")
+    /// }
+    /// ```
+    pub async fn closed(&self) {
+        while self.receiver_count() > 0 {
+            let notified = self.shared.notify_tx.notified();
+
+            if self.receiver_count() == 0 {
+                return;
+            }
+
+            notified.await;
+            // The channel could have been reopened in the meantime by calling
+            // `subscribe`, so we loop again.
+        }
+    }
+
+    /// Creates a new [`Receiver`] connected to this `Sender`.
+    ///
+    /// All messages sent before this call to `subscribe` are initially marked
+    /// as seen by the new `Receiver`.
+    ///
+    /// This method can be called even if there are no other receivers. In this
+    /// case, the channel is reopened.
+    ///
+    /// # Examples
+    ///
+    /// The new channel will receive messages sent on this `Sender`.
+    ///
+    /// ```
+    /// use tokio::sync::watch;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, _rx) = watch::channel(0u64);
+    ///
+    ///     tx.send(5).unwrap();
+    ///
+    ///     let rx = tx.subscribe();
+    ///     assert_eq!(5, *rx.borrow());
+    ///
+    ///     tx.send(10).unwrap();
+    ///     assert_eq!(10, *rx.borrow());
+    /// }
+    /// ```
+    ///
+    /// The most recent message is considered seen by the channel, so this test
+    /// is guaranteed to pass.
+    ///
+    /// ```
+    /// use tokio::sync::watch;
+    /// use tokio::time::Duration;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, _rx) = watch::channel(0u64);
+    ///     tx.send(5).unwrap();
+    ///     let mut rx = tx.subscribe();
+    ///
+    ///     tokio::spawn(async move {
+    ///         // by spawning and sleeping, the message is sent after `main`
+    ///         // hits the call to `changed`.
+    ///         # if false {
+    ///         tokio::time::sleep(Duration::from_millis(10)).await;
+    ///         # }
+    ///         tx.send(100).unwrap();
+    ///     });
+    ///
+    ///     rx.changed().await.unwrap();
+    ///     assert_eq!(100, *rx.borrow());
+    /// }
+    /// ```
+    pub fn subscribe(&self) -> Receiver<T> {
+        let shared = self.shared.clone();
+        let version = shared.state.load().version();
+
+        // The CLOSED bit in the state tracks only whether the sender is
+        // dropped, so we do not need to unset it if this reopens the channel.
+        Receiver::from_shared(version, shared)
+    }
+
+    /// Returns the number of receivers that currently exist.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::sync::watch;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let (tx, rx1) = watch::channel("hello");
+    ///
+    ///     assert_eq!(1, tx.receiver_count());
+    ///
+    ///     let mut _rx2 = rx1.clone();
+    ///
+    ///     assert_eq!(2, tx.receiver_count());
+    /// }
+    /// ```
+    pub fn receiver_count(&self) -> usize {
+        self.shared.ref_count_rx.load(Relaxed)
+    }
+}
+
+impl<T> Drop for Sender<T> {
+    fn drop(&mut self) {
+        self.shared.state.set_closed();
+        self.shared.notify_rx.notify_waiters();
+    }
+}
+
+// ===== impl Ref =====
+
+impl<T> ops::Deref for Ref<'_, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        self.inner.deref()
+    }
+}
+
+#[cfg(all(test, loom))]
+mod tests {
+    use futures::future::FutureExt;
+    use loom::thread;
+
+    // test for https://github.com/tokio-rs/tokio/issues/3168
+    #[test]
+    fn watch_spurious_wakeup() {
+        loom::model(|| {
+            let (send, mut recv) = crate::sync::watch::channel(0i32);
+
+            send.send(1).unwrap();
+
+            let send_thread = thread::spawn(move || {
+                send.send(2).unwrap();
+                send
+            });
+
+            recv.changed().now_or_never();
+
+            let send = send_thread.join().unwrap();
+            let recv_thread = thread::spawn(move || {
+                recv.changed().now_or_never();
+                recv.changed().now_or_never();
+                recv
+            });
+
+            send.send(3).unwrap();
+
+            let mut recv = recv_thread.join().unwrap();
+            let send_thread = thread::spawn(move || {
+                send.send(2).unwrap();
+            });
+
+            recv.changed().now_or_never();
+
+            send_thread.join().unwrap();
+        });
+    }
+
+    #[test]
+    fn watch_borrow() {
+        loom::model(|| {
+            let (send, mut recv) = crate::sync::watch::channel(0i32);
+
+            assert!(send.borrow().eq(&0));
+            assert!(recv.borrow().eq(&0));
+
+            send.send(1).unwrap();
+            assert!(send.borrow().eq(&1));
+
+            let send_thread = thread::spawn(move || {
+                send.send(2).unwrap();
+                send
+            });
+
+            recv.changed().now_or_never();
+
+            let send = send_thread.join().unwrap();
+            let recv_thread = thread::spawn(move || {
+                recv.changed().now_or_never();
+                recv.changed().now_or_never();
+                recv
+            });
+
+            send.send(3).unwrap();
+
+            let recv = recv_thread.join().unwrap();
+            assert!(recv.borrow().eq(&3));
+            assert!(send.borrow().eq(&3));
+
+            send.send(2).unwrap();
+
+            thread::spawn(move || {
+                assert!(recv.borrow().eq(&2));
+            });
+            assert!(send.borrow().eq(&2));
+        });
+    }
+}
diff --git a/third_party/rust/tokio/src/task/blocking.rs b/third_party/rust/tokio/src/task/blocking.rs
new file mode 100644
index 0000000000..5fe358f3e5
--- /dev/null
+++ b/third_party/rust/tokio/src/task/blocking.rs
@@ -0,0 +1,199 @@
+use crate::task::JoinHandle;
+
+cfg_rt_multi_thread! {
+    /// Runs the provided blocking function on the current thread without
+    /// blocking the executor.
+    ///
+    /// In general, issuing a blocking call or performing a lot of compute in a
+    /// future without yielding is problematic, as it may prevent the executor
+    /// from driving other tasks forward. Calling this function informs the
+    /// executor that the currently executing task is about to block the thread,
+    /// so the executor is able to hand off any other tasks it has to a new
+    /// worker thread before that happens. See the [CPU-bound tasks and blocking
+    /// code][blocking] section for more information.
+    ///
+    /// Be aware that although this function avoids starving other independently
+    /// spawned tasks, any other code running concurrently in the same task will
+    /// be suspended during the call to `block_in_place`. This can happen e.g.
+    /// when using the [`join!`] macro. To avoid this issue, use
+    /// [`spawn_blocking`] instead of `block_in_place`.
+    ///
+    /// Note that this function cannot be used within a [`current_thread`] runtime
+    /// because in this case there are no other worker threads to hand off tasks
+    /// to. On the other hand, calling the function outside a runtime is
+    /// allowed. In this case, `block_in_place` just calls the provided closure
+    /// normally.
+    ///
+    /// Code running behind `block_in_place` cannot be cancelled. When you shut
+    /// down the executor, it will wait indefinitely for all blocking operations
+    /// to finish. You can use [`shutdown_timeout`] to stop waiting for them
+    /// after a certain timeout. Be aware that this will still not cancel the
+    /// tasks — they are simply allowed to keep running after the method
+    /// returns.
+    ///
+    /// [blocking]: ../index.html#cpu-bound-tasks-and-blocking-code
+    /// [`spawn_blocking`]: fn@crate::task::spawn_blocking
+    /// [`join!`]: macro@join
+    /// [`thread::spawn`]: fn@std::thread::spawn
+    /// [`shutdown_timeout`]: fn@crate::runtime::Runtime::shutdown_timeout
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::task;
+    ///
+    /// # async fn docs() {
+    /// task::block_in_place(move || {
+    ///     // do some compute-heavy work or call synchronous code
+    /// });
+    /// # }
+    /// ```
+    ///
+    /// Code running inside `block_in_place` may use `block_on` to reenter the
+    /// async context.
+    ///
+    /// ```
+    /// use tokio::task;
+    /// use tokio::runtime::Handle;
+    ///
+    /// # async fn docs() {
+    /// task::block_in_place(move || {
+    ///     Handle::current().block_on(async move {
+    ///         // do something async
+    ///     });
+    /// });
+    /// # }
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// This function panics if called from a [`current_thread`] runtime.
+    ///
+    /// [`current_thread`]: fn@crate::runtime::Builder::new_current_thread
+    pub fn block_in_place<F, R>(f: F) -> R
+    where
+        F: FnOnce() -> R,
+    {
+        crate::runtime::thread_pool::block_in_place(f)
+    }
+}
+
+cfg_rt! {
+    /// Runs the provided closure on a thread where blocking is acceptable.
+    ///
+    /// In general, issuing a blocking call or performing a lot of compute in a
+    /// future without yielding is problematic, as it may prevent the executor from
+    /// driving other futures forward. This function runs the provided closure on a
+    /// thread dedicated to blocking operations. See the [CPU-bound tasks and
+    /// blocking code][blocking] section for more information.
+    ///
+    /// Tokio will spawn more blocking threads when they are requested through this
+    /// function until the upper limit configured on the [`Builder`] is reached.
+    /// After reaching the upper limit, the tasks are put in a queue.
+    /// The thread limit is very large by default, because `spawn_blocking` is often
+    /// used for various kinds of IO operations that cannot be performed
+    /// asynchronously.  When you run CPU-bound code using `spawn_blocking`, you
+    /// should keep this large upper limit in mind. When running many CPU-bound
+    /// computations, a semaphore or some other synchronization primitive should be
+    /// used to limit the number of computation executed in parallel. Specialized
+    /// CPU-bound executors, such as [rayon], may also be a good fit.
+    ///
+    /// This function is intended for non-async operations that eventually finish on
+    /// their own. If you want to spawn an ordinary thread, you should use
+    /// [`thread::spawn`] instead.
+    ///
+    /// Closures spawned using `spawn_blocking` cannot be cancelled. When you shut
+    /// down the executor, it will wait indefinitely for all blocking operations to
+    /// finish. You can use [`shutdown_timeout`] to stop waiting for them after a
+    /// certain timeout. Be aware that this will still not cancel the tasks — they
+    /// are simply allowed to keep running after the method returns.
+    ///
+    /// Note that if you are using the single threaded runtime, this function will
+    /// still spawn additional threads for blocking operations. The basic
+    /// scheduler's single thread is only used for asynchronous code.
+    ///
+    /// # Related APIs and patterns for bridging asynchronous and blocking code
+    ///
+    /// In simple cases, it is sufficient to have the closure accept input
+    /// parameters at creation time and return a single value (or struct/tuple, etc.).
+    ///
+    /// For more complex situations in which it is desirable to stream data to or from
+    /// the synchronous context, the [`mpsc channel`] has `blocking_send` and
+    /// `blocking_recv` methods for use in non-async code such as the thread created
+    /// by `spawn_blocking`.
+    ///
+    /// Another option is [`SyncIoBridge`] for cases where the synchronous context
+    /// is operating on byte streams.  For example, you might use an asynchronous
+    /// HTTP client such as [hyper] to fetch data, but perform complex parsing
+    /// of the payload body using a library written for synchronous I/O.
+    ///
+    /// Finally, see also [Bridging with sync code][bridgesync] for discussions
+    /// around the opposite case of using Tokio as part of a larger synchronous
+    /// codebase.
+    ///
+    /// [`Builder`]: struct@crate::runtime::Builder
+    /// [blocking]: ../index.html#cpu-bound-tasks-and-blocking-code
+    /// [rayon]: https://docs.rs/rayon
+    /// [`mpsc channel`]: crate::sync::mpsc
+    /// [`SyncIoBridge`]: https://docs.rs/tokio-util/0.6/tokio_util/io/struct.SyncIoBridge.html
+    /// [hyper]: https://docs.rs/hyper
+    /// [`thread::spawn`]: fn@std::thread::spawn
+    /// [`shutdown_timeout`]: fn@crate::runtime::Runtime::shutdown_timeout
+    /// [bridgesync]: https://tokio.rs/tokio/topics/bridging
+    ///
+    /// # Examples
+    ///
+    /// Pass an input value and receive result of computation:
+    ///
+    /// ```
+    /// use tokio::task;
+    ///
+    /// # async fn docs() -> Result<(), Box<dyn std::error::Error>>{
+    /// // Initial input
+    /// let mut v = "Hello, ".to_string();
+    /// let res = task::spawn_blocking(move || {
+    ///     // Stand-in for compute-heavy work or using synchronous APIs
+    ///     v.push_str("world");
+    ///     // Pass ownership of the value back to the asynchronous context
+    ///     v
+    /// }).await?;
+    ///
+    /// // `res` is the value returned from the thread
+    /// assert_eq!(res.as_str(), "Hello, world");
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// Use a channel:
+    ///
+    /// ```
+    /// use tokio::task;
+    /// use tokio::sync::mpsc;
+    ///
+    /// # async fn docs() {
+    /// let (tx, mut rx) = mpsc::channel(2);
+    /// let start = 5;
+    /// let worker = task::spawn_blocking(move || {
+    ///     for x in 0..10 {
+    ///         // Stand in for complex computation
+    ///         tx.blocking_send(start + x).unwrap();
+    ///     }
+    /// });
+    ///
+    /// let mut acc = 0;
+    /// while let Some(v) = rx.recv().await {
+    ///     acc += v;
+    /// }
+    /// assert_eq!(acc, 95);
+    /// worker.await.unwrap();
+    /// # }
+    /// ```
+    #[track_caller]
+    pub fn spawn_blocking<F, R>(f: F) -> JoinHandle<R>
+    where
+        F: FnOnce() -> R + Send + 'static,
+        R: Send + 'static,
+    {
+        crate::runtime::spawn_blocking(f)
+    }
+}
diff --git a/third_party/rust/tokio/src/task/builder.rs b/third_party/rust/tokio/src/task/builder.rs
new file mode 100644
index 0000000000..2086302fb9
--- /dev/null
+++ b/third_party/rust/tokio/src/task/builder.rs
@@ -0,0 +1,115 @@
+#![allow(unreachable_pub)]
+use crate::{runtime::context, task::JoinHandle};
+use std::future::Future;
+
+/// Factory which is used to configure the properties of a new task.
+///
+/// **Note**: This is an [unstable API][unstable]. The public API of this type
+/// may break in 1.x releases. See [the documentation on unstable
+/// features][unstable] for details.
+///
+/// Methods can be chained in order to configure it.
+///
+/// Currently, there is only one configuration option:
+///
+/// - [`name`], which specifies an associated name for
+///   the task
+///
+/// There are three types of task that can be spawned from a Builder:
+/// - [`spawn_local`] for executing futures on the current thread
+/// - [`spawn`] for executing [`Send`] futures on the runtime
+/// - [`spawn_blocking`] for executing blocking code in the
+///   blocking thread pool.
+///
+/// ## Example
+///
+/// ```no_run
+/// use tokio::net::{TcpListener, TcpStream};
+///
+/// use std::io;
+///
+/// async fn process(socket: TcpStream) {
+///     // ...
+/// # drop(socket);
+/// }
+///
+/// #[tokio::main]
+/// async fn main() -> io::Result<()> {
+///     let listener = TcpListener::bind("127.0.0.1:8080").await?;
+///
+///     loop {
+///         let (socket, _) = listener.accept().await?;
+///
+///         tokio::task::Builder::new()
+///             .name("tcp connection handler")
+///             .spawn(async move {
+///                 // Process each socket concurrently.
+///                 process(socket).await
+///             });
+///     }
+/// }
+/// ```
+/// [unstable]: crate#unstable-features
+/// [`name`]: Builder::name
+/// [`spawn_local`]: Builder::spawn_local
+/// [`spawn`]: Builder::spawn
+/// [`spawn_blocking`]: Builder::spawn_blocking
+#[derive(Default, Debug)]
+#[cfg_attr(docsrs, doc(cfg(all(tokio_unstable, feature = "tracing"))))]
+pub struct Builder<'a> {
+    name: Option<&'a str>,
+}
+
+impl<'a> Builder<'a> {
+    /// Creates a new task builder.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Assigns a name to the task which will be spawned.
+    pub fn name(&self, name: &'a str) -> Self {
+        Self { name: Some(name) }
+    }
+
+    /// Spawns a task on the executor.
+    ///
+    /// See [`task::spawn`](crate::task::spawn) for
+    /// more details.
+    #[track_caller]
+    pub fn spawn<Fut>(self, future: Fut) -> JoinHandle<Fut::Output>
+    where
+        Fut: Future + Send + 'static,
+        Fut::Output: Send + 'static,
+    {
+        super::spawn::spawn_inner(future, self.name)
+    }
+
+    /// Spawns a task on the current thread.
+    ///
+    /// See [`task::spawn_local`](crate::task::spawn_local)
+    /// for more details.
+    #[track_caller]
+    pub fn spawn_local<Fut>(self, future: Fut) -> JoinHandle<Fut::Output>
+    where
+        Fut: Future + 'static,
+        Fut::Output: 'static,
+    {
+        super::local::spawn_local_inner(future, self.name)
+    }
+
+    /// Spawns blocking code on the blocking threadpool.
+    ///
+    /// See [`task::spawn_blocking`](crate::task::spawn_blocking)
+    /// for more details.
+    #[track_caller]
+    pub fn spawn_blocking<Function, Output>(self, function: Function) -> JoinHandle<Output>
+    where
+        Function: FnOnce() -> Output + Send + 'static,
+        Output: Send + 'static,
+    {
+        use crate::runtime::Mandatory;
+        let (join_handle, _was_spawned) =
+            context::current().spawn_blocking_inner(function, Mandatory::NonMandatory, self.name);
+        join_handle
+    }
+}
diff --git a/third_party/rust/tokio/src/task/join_set.rs b/third_party/rust/tokio/src/task/join_set.rs
new file mode 100644
index 0000000000..8e8f74f66d
--- /dev/null
+++ b/third_party/rust/tokio/src/task/join_set.rs
@@ -0,0 +1,248 @@
+use std::fmt;
+use std::future::Future;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+use crate::runtime::Handle;
+use crate::task::{JoinError, JoinHandle, LocalSet};
+use crate::util::IdleNotifiedSet;
+
+/// A collection of tasks spawned on a Tokio runtime.
+///
+/// A `JoinSet` can be used to await the completion of some or all of the tasks
+/// in the set. The set is not ordered, and the tasks will be returned in the
+/// order they complete.
+///
+/// All of the tasks must have the same return type `T`.
+///
+/// When the `JoinSet` is dropped, all tasks in the `JoinSet` are immediately aborted.
+///
+/// **Note**: This is an [unstable API][unstable]. The public API of this type
+/// may break in 1.x releases. See [the documentation on unstable
+/// features][unstable] for details.
+///
+/// # Examples
+///
+/// Spawn multiple tasks and wait for them.
+///
+/// ```
+/// use tokio::task::JoinSet;
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let mut set = JoinSet::new();
+///
+///     for i in 0..10 {
+///         set.spawn(async move { i });
+///     }
+///
+///     let mut seen = [false; 10];
+///     while let Some(res) = set.join_one().await.unwrap() {
+///         seen[res] = true;
+///     }
+///
+///     for i in 0..10 {
+///         assert!(seen[i]);
+///     }
+/// }
+/// ```
+///
+/// [unstable]: crate#unstable-features
+pub struct JoinSet<T> {
+    inner: IdleNotifiedSet<JoinHandle<T>>,
+}
+
+impl<T> JoinSet<T> {
+    /// Create a new `JoinSet`.
+    pub fn new() -> Self {
+        Self {
+            inner: IdleNotifiedSet::new(),
+        }
+    }
+
+    /// Returns the number of tasks currently in the `JoinSet`.
+    pub fn len(&self) -> usize {
+        self.inner.len()
+    }
+
+    /// Returns whether the `JoinSet` is empty.
+    pub fn is_empty(&self) -> bool {
+        self.inner.is_empty()
+    }
+}
+
+impl<T: 'static> JoinSet<T> {
+    /// Spawn the provided task on the `JoinSet`.
+    ///
+    /// # Panics
+    ///
+    /// This method panics if called outside of a Tokio runtime.
+    pub fn spawn<F>(&mut self, task: F)
+    where
+        F: Future<Output = T>,
+        F: Send + 'static,
+        T: Send,
+    {
+        self.insert(crate::spawn(task));
+    }
+
+    /// Spawn the provided task on the provided runtime and store it in this `JoinSet`.
+    pub fn spawn_on<F>(&mut self, task: F, handle: &Handle)
+    where
+        F: Future<Output = T>,
+        F: Send + 'static,
+        T: Send,
+    {
+        self.insert(handle.spawn(task));
+    }
+
+    /// Spawn the provided task on the current [`LocalSet`] and store it in this `JoinSet`.
+    ///
+    /// # Panics
+    ///
+    /// This method panics if it is called outside of a `LocalSet`.
+    ///
+    /// [`LocalSet`]: crate::task::LocalSet
+    pub fn spawn_local<F>(&mut self, task: F)
+    where
+        F: Future<Output = T>,
+        F: 'static,
+    {
+        self.insert(crate::task::spawn_local(task));
+    }
+
+    /// Spawn the provided task on the provided [`LocalSet`] and store it in this `JoinSet`.
+    ///
+    /// [`LocalSet`]: crate::task::LocalSet
+    pub fn spawn_local_on<F>(&mut self, task: F, local_set: &LocalSet)
+    where
+        F: Future<Output = T>,
+        F: 'static,
+    {
+        self.insert(local_set.spawn_local(task));
+    }
+
+    fn insert(&mut self, jh: JoinHandle<T>) {
+        let mut entry = self.inner.insert_idle(jh);
+
+        // Set the waker that is notified when the task completes.
+        entry.with_value_and_context(|jh, ctx| jh.set_join_waker(ctx.waker()));
+    }
+
+    /// Waits until one of the tasks in the set completes and returns its output.
+    ///
+    /// Returns `None` if the set is empty.
+    ///
+    /// # Cancel Safety
+    ///
+    /// This method is cancel safe. If `join_one` is used as the event in a `tokio::select!`
+    /// statement and some other branch completes first, it is guaranteed that no tasks were
+    /// removed from this `JoinSet`.
+    pub async fn join_one(&mut self) -> Result<Option<T>, JoinError> {
+        crate::future::poll_fn(|cx| self.poll_join_one(cx)).await
+    }
+
+    /// Aborts all tasks and waits for them to finish shutting down.
+    ///
+    /// Calling this method is equivalent to calling [`abort_all`] and then calling [`join_one`] in
+    /// a loop until it returns `Ok(None)`.
+    ///
+    /// This method ignores any panics in the tasks shutting down. When this call returns, the
+    /// `JoinSet` will be empty.
+    ///
+    /// [`abort_all`]: fn@Self::abort_all
+    /// [`join_one`]: fn@Self::join_one
+    pub async fn shutdown(&mut self) {
+        self.abort_all();
+        while self.join_one().await.transpose().is_some() {}
+    }
+
+    /// Aborts all tasks on this `JoinSet`.
+    ///
+    /// This does not remove the tasks from the `JoinSet`. To wait for the tasks to complete
+    /// cancellation, you should call `join_one` in a loop until the `JoinSet` is empty.
+    pub fn abort_all(&mut self) {
+        self.inner.for_each(|jh| jh.abort());
+    }
+
+    /// Removes all tasks from this `JoinSet` without aborting them.
+    ///
+    /// The tasks removed by this call will continue to run in the background even if the `JoinSet`
+    /// is dropped.
+    pub fn detach_all(&mut self) {
+        self.inner.drain(drop);
+    }
+
+    /// Polls for one of the tasks in the set to complete.
+    ///
+    /// If this returns `Poll::Ready(Ok(Some(_)))` or `Poll::Ready(Err(_))`, then the task that
+    /// completed is removed from the set.
+    ///
+    /// When the method returns `Poll::Pending`, the `Waker` in the provided `Context` is scheduled
+    /// to receive a wakeup when a task in the `JoinSet` completes. Note that on multiple calls to
+    /// `poll_join_one`, only the `Waker` from the `Context` passed to the most recent call is
+    /// scheduled to receive a wakeup.
+    ///
+    /// # Returns
+    ///
+    /// This function returns:
+    ///
+    ///  * `Poll::Pending` if the `JoinSet` is not empty but there is no task whose output is
+    ///     available right now.
+    ///  * `Poll::Ready(Ok(Some(value)))` if one of the tasks in this `JoinSet` has completed. The
+    ///    `value` is the return value of one of the tasks that completed.
+    ///  * `Poll::Ready(Err(err))` if one of the tasks in this `JoinSet` has panicked or been
+    ///     aborted.
+    ///  * `Poll::Ready(Ok(None))` if the `JoinSet` is empty.
+    ///
+    /// Note that this method may return `Poll::Pending` even if one of the tasks has completed.
+    /// This can happen if the [coop budget] is reached.
+    ///
+    /// [coop budget]: crate::task#cooperative-scheduling
+    fn poll_join_one(&mut self, cx: &mut Context<'_>) -> Poll<Result<Option<T>, JoinError>> {
+        // The call to `pop_notified` moves the entry to the `idle` list. It is moved back to
+        // the `notified` list if the waker is notified in the `poll` call below.
+        let mut entry = match self.inner.pop_notified(cx.waker()) {
+            Some(entry) => entry,
+            None => {
+                if self.is_empty() {
+                    return Poll::Ready(Ok(None));
+                } else {
+                    // The waker was set by `pop_notified`.
+                    return Poll::Pending;
+                }
+            }
+        };
+
+        let res = entry.with_value_and_context(|jh, ctx| Pin::new(jh).poll(ctx));
+
+        if let Poll::Ready(res) = res {
+            entry.remove();
+            Poll::Ready(Some(res).transpose())
+        } else {
+            // A JoinHandle generally won't emit a wakeup without being ready unless
+            // the coop limit has been reached. We yield to the executor in this
+            // case.
+            cx.waker().wake_by_ref();
+            Poll::Pending
+        }
+    }
+}
+
+impl<T> Drop for JoinSet<T> {
+    fn drop(&mut self) {
+        self.inner.drain(|join_handle| join_handle.abort());
+    }
+}
+
+impl<T> fmt::Debug for JoinSet<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("JoinSet").field("len", &self.len()).finish()
+    }
+}
+
+impl<T> Default for JoinSet<T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
diff --git a/third_party/rust/tokio/src/task/local.rs b/third_party/rust/tokio/src/task/local.rs
new file mode 100644
index 0000000000..2dbd970604
--- /dev/null
+++ b/third_party/rust/tokio/src/task/local.rs
@@ -0,0 +1,698 @@
+//! Runs `!Send` futures on the current thread.
+use crate::loom::sync::{Arc, Mutex};
+use crate::runtime::task::{self, JoinHandle, LocalOwnedTasks, Task};
+use crate::sync::AtomicWaker;
+use crate::util::VecDequeCell;
+
+use std::cell::Cell;
+use std::collections::VecDeque;
+use std::fmt;
+use std::future::Future;
+use std::marker::PhantomData;
+use std::pin::Pin;
+use std::task::Poll;
+
+use pin_project_lite::pin_project;
+
+cfg_rt! {
+    /// A set of tasks which are executed on the same thread.
+    ///
+    /// In some cases, it is necessary to run one or more futures that do not
+    /// implement [`Send`] and thus are unsafe to send between threads. In these
+    /// cases, a [local task set] may be used to schedule one or more `!Send`
+    /// futures to run together on the same thread.
+    ///
+    /// For example, the following code will not compile:
+    ///
+    /// ```rust,compile_fail
+    /// use std::rc::Rc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     // `Rc` does not implement `Send`, and thus may not be sent between
+    ///     // threads safely.
+    ///     let unsend_data = Rc::new("my unsend data...");
+    ///
+    ///     let unsend_data = unsend_data.clone();
+    ///     // Because the `async` block here moves `unsend_data`, the future is `!Send`.
+    ///     // Since `tokio::spawn` requires the spawned future to implement `Send`, this
+    ///     // will not compile.
+    ///     tokio::spawn(async move {
+    ///         println!("{}", unsend_data);
+    ///         // ...
+    ///     }).await.unwrap();
+    /// }
+    /// ```
+    ///
+    /// # Use with `run_until`
+    ///
+    /// To spawn `!Send` futures, we can use a local task set to schedule them
+    /// on the thread calling [`Runtime::block_on`]. When running inside of the
+    /// local task set, we can use [`task::spawn_local`], which can spawn
+    /// `!Send` futures. For example:
+    ///
+    /// ```rust
+    /// use std::rc::Rc;
+    /// use tokio::task;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let unsend_data = Rc::new("my unsend data...");
+    ///
+    ///     // Construct a local task set that can run `!Send` futures.
+    ///     let local = task::LocalSet::new();
+    ///
+    ///     // Run the local task set.
+    ///     local.run_until(async move {
+    ///         let unsend_data = unsend_data.clone();
+    ///         // `spawn_local` ensures that the future is spawned on the local
+    ///         // task set.
+    ///         task::spawn_local(async move {
+    ///             println!("{}", unsend_data);
+    ///             // ...
+    ///         }).await.unwrap();
+    ///     }).await;
+    /// }
+    /// ```
+    /// **Note:** The `run_until` method can only be used in `#[tokio::main]`,
+    /// `#[tokio::test]` or directly inside a call to [`Runtime::block_on`]. It
+    /// cannot be used inside a task spawned with `tokio::spawn`.
+    ///
+    /// ## Awaiting a `LocalSet`
+    ///
+    /// Additionally, a `LocalSet` itself implements `Future`, completing when
+    /// *all* tasks spawned on the `LocalSet` complete. This can be used to run
+    /// several futures on a `LocalSet` and drive the whole set until they
+    /// complete. For example,
+    ///
+    /// ```rust
+    /// use tokio::{task, time};
+    /// use std::rc::Rc;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let unsend_data = Rc::new("world");
+    ///     let local = task::LocalSet::new();
+    ///
+    ///     let unsend_data2 = unsend_data.clone();
+    ///     local.spawn_local(async move {
+    ///         // ...
+    ///         println!("hello {}", unsend_data2)
+    ///     });
+    ///
+    ///     local.spawn_local(async move {
+    ///         time::sleep(time::Duration::from_millis(100)).await;
+    ///         println!("goodbye {}", unsend_data)
+    ///     });
+    ///
+    ///     // ...
+    ///
+    ///     local.await;
+    /// }
+    /// ```
+    /// **Note:** Awaiting a `LocalSet` can only be done inside
+    /// `#[tokio::main]`, `#[tokio::test]` or directly inside a call to
+    /// [`Runtime::block_on`]. It cannot be used inside a task spawned with
+    /// `tokio::spawn`.
+    ///
+    /// ## Use inside `tokio::spawn`
+    ///
+    /// The two methods mentioned above cannot be used inside `tokio::spawn`, so
+    /// to spawn `!Send` futures from inside `tokio::spawn`, we need to do
+    /// something else. The solution is to create the `LocalSet` somewhere else,
+    /// and communicate with it using an [`mpsc`] channel.
+    ///
+    /// The following example puts the `LocalSet` inside a new thread.
+    /// ```
+    /// use tokio::runtime::Builder;
+    /// use tokio::sync::{mpsc, oneshot};
+    /// use tokio::task::LocalSet;
+    ///
+    /// // This struct describes the task you want to spawn. Here we include
+    /// // some simple examples. The oneshot channel allows sending a response
+    /// // to the spawner.
+    /// #[derive(Debug)]
+    /// enum Task {
+    ///     PrintNumber(u32),
+    ///     AddOne(u32, oneshot::Sender<u32>),
+    /// }
+    ///
+    /// #[derive(Clone)]
+    /// struct LocalSpawner {
+    ///    send: mpsc::UnboundedSender<Task>,
+    /// }
+    ///
+    /// impl LocalSpawner {
+    ///     pub fn new() -> Self {
+    ///         let (send, mut recv) = mpsc::unbounded_channel();
+    ///
+    ///         let rt = Builder::new_current_thread()
+    ///             .enable_all()
+    ///             .build()
+    ///             .unwrap();
+    ///
+    ///         std::thread::spawn(move || {
+    ///             let local = LocalSet::new();
+    ///
+    ///             local.spawn_local(async move {
+    ///                 while let Some(new_task) = recv.recv().await {
+    ///                     tokio::task::spawn_local(run_task(new_task));
+    ///                 }
+    ///                 // If the while loop returns, then all the LocalSpawner
+    ///                 // objects have have been dropped.
+    ///             });
+    ///
+    ///             // This will return once all senders are dropped and all
+    ///             // spawned tasks have returned.
+    ///             rt.block_on(local);
+    ///         });
+    ///
+    ///         Self {
+    ///             send,
+    ///         }
+    ///     }
+    ///
+    ///     pub fn spawn(&self, task: Task) {
+    ///         self.send.send(task).expect("Thread with LocalSet has shut down.");
+    ///     }
+    /// }
+    ///
+    /// // This task may do !Send stuff. We use printing a number as an example,
+    /// // but it could be anything.
+    /// //
+    /// // The Task struct is an enum to support spawning many different kinds
+    /// // of operations.
+    /// async fn run_task(task: Task) {
+    ///     match task {
+    ///         Task::PrintNumber(n) => {
+    ///             println!("{}", n);
+    ///         },
+    ///         Task::AddOne(n, response) => {
+    ///             // We ignore failures to send the response.
+    ///             let _ = response.send(n + 1);
+    ///         },
+    ///     }
+    /// }
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let spawner = LocalSpawner::new();
+    ///
+    ///     let (send, response) = oneshot::channel();
+    ///     spawner.spawn(Task::AddOne(10, send));
+    ///     let eleven = response.await.unwrap();
+    ///     assert_eq!(eleven, 11);
+    /// }
+    /// ```
+    ///
+    /// [`Send`]: trait@std::marker::Send
+    /// [local task set]: struct@LocalSet
+    /// [`Runtime::block_on`]: method@crate::runtime::Runtime::block_on
+    /// [`task::spawn_local`]: fn@spawn_local
+    /// [`mpsc`]: mod@crate::sync::mpsc
+    pub struct LocalSet {
+        /// Current scheduler tick.
+        tick: Cell<u8>,
+
+        /// State available from thread-local.
+        context: Context,
+
+        /// This type should not be Send.
+        _not_send: PhantomData<*const ()>,
+    }
+}
+
+/// State available from the thread-local.
+struct Context {
+    /// Collection of all active tasks spawned onto this executor.
+    owned: LocalOwnedTasks<Arc<Shared>>,
+
+    /// Local run queue sender and receiver.
+    queue: VecDequeCell<task::Notified<Arc<Shared>>>,
+
+    /// State shared between threads.
+    shared: Arc<Shared>,
+}
+
+/// LocalSet state shared between threads.
+struct Shared {
+    /// Remote run queue sender.
+    queue: Mutex<Option<VecDeque<task::Notified<Arc<Shared>>>>>,
+
+    /// Wake the `LocalSet` task.
+    waker: AtomicWaker,
+}
+
+pin_project! {
+    #[derive(Debug)]
+    struct RunUntil<'a, F> {
+        local_set: &'a LocalSet,
+        #[pin]
+        future: F,
+    }
+}
+
+scoped_thread_local!(static CURRENT: Context);
+
+cfg_rt! {
+    /// Spawns a `!Send` future on the local task set.
+    ///
+    /// The spawned future will be run on the same thread that called `spawn_local.`
+    /// This may only be called from the context of a local task set.
+    ///
+    /// # Panics
+    ///
+    /// - This function panics if called outside of a local task set.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use std::rc::Rc;
+    /// use tokio::task;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let unsend_data = Rc::new("my unsend data...");
+    ///
+    ///     let local = task::LocalSet::new();
+    ///
+    ///     // Run the local task set.
+    ///     local.run_until(async move {
+    ///         let unsend_data = unsend_data.clone();
+    ///         task::spawn_local(async move {
+    ///             println!("{}", unsend_data);
+    ///             // ...
+    ///         }).await.unwrap();
+    ///     }).await;
+    /// }
+    /// ```
+    #[track_caller]
+    pub fn spawn_local<F>(future: F) -> JoinHandle<F::Output>
+    where
+        F: Future + 'static,
+        F::Output: 'static,
+    {
+        spawn_local_inner(future, None)
+    }
+
+
+    #[track_caller]
+    pub(super) fn spawn_local_inner<F>(future: F, name: Option<&str>) -> JoinHandle<F::Output>
+    where F: Future + 'static,
+          F::Output: 'static
+    {
+        let future = crate::util::trace::task(future, "local", name);
+        CURRENT.with(|maybe_cx| {
+            let cx = maybe_cx
+                .expect("`spawn_local` called from outside of a `task::LocalSet`");
+
+            let (handle, notified) = cx.owned.bind(future, cx.shared.clone());
+
+            if let Some(notified) = notified {
+                cx.shared.schedule(notified);
+            }
+
+            handle
+        })
+    }
+}
+
+/// Initial queue capacity.
+const INITIAL_CAPACITY: usize = 64;
+
+/// Max number of tasks to poll per tick.
+const MAX_TASKS_PER_TICK: usize = 61;
+
+/// How often it check the remote queue first.
+const REMOTE_FIRST_INTERVAL: u8 = 31;
+
+impl LocalSet {
+    /// Returns a new local task set.
+    pub fn new() -> LocalSet {
+        LocalSet {
+            tick: Cell::new(0),
+            context: Context {
+                owned: LocalOwnedTasks::new(),
+                queue: VecDequeCell::with_capacity(INITIAL_CAPACITY),
+                shared: Arc::new(Shared {
+                    queue: Mutex::new(Some(VecDeque::with_capacity(INITIAL_CAPACITY))),
+                    waker: AtomicWaker::new(),
+                }),
+            },
+            _not_send: PhantomData,
+        }
+    }
+
+    /// Spawns a `!Send` task onto the local task set.
+    ///
+    /// This task is guaranteed to be run on the current thread.
+    ///
+    /// Unlike the free function [`spawn_local`], this method may be used to
+    /// spawn local tasks when the task set is _not_ running. For example:
+    /// ```rust
+    /// use tokio::task;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let local = task::LocalSet::new();
+    ///
+    ///     // Spawn a future on the local set. This future will be run when
+    ///     // we call `run_until` to drive the task set.
+    ///     local.spawn_local(async {
+    ///        // ...
+    ///     });
+    ///
+    ///     // Run the local task set.
+    ///     local.run_until(async move {
+    ///         // ...
+    ///     }).await;
+    ///
+    ///     // When `run` finishes, we can spawn _more_ futures, which will
+    ///     // run in subsequent calls to `run_until`.
+    ///     local.spawn_local(async {
+    ///        // ...
+    ///     });
+    ///
+    ///     local.run_until(async move {
+    ///         // ...
+    ///     }).await;
+    /// }
+    /// ```
+    /// [`spawn_local`]: fn@spawn_local
+    #[track_caller]
+    pub fn spawn_local<F>(&self, future: F) -> JoinHandle<F::Output>
+    where
+        F: Future + 'static,
+        F::Output: 'static,
+    {
+        let future = crate::util::trace::task(future, "local", None);
+
+        let (handle, notified) = self.context.owned.bind(future, self.context.shared.clone());
+
+        if let Some(notified) = notified {
+            self.context.shared.schedule(notified);
+        }
+
+        self.context.shared.waker.wake();
+        handle
+    }
+
+    /// Runs a future to completion on the provided runtime, driving any local
+    /// futures spawned on this task set on the current thread.
+    ///
+    /// This runs the given future on the runtime, blocking until it is
+    /// complete, and yielding its resolved result. Any tasks or timers which
+    /// the future spawns internally will be executed on the runtime. The future
+    /// may also call [`spawn_local`] to spawn_local additional local futures on the
+    /// current thread.
+    ///
+    /// This method should not be called from an asynchronous context.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if the executor is at capacity, if the provided
+    /// future panics, or if called within an asynchronous execution context.
+    ///
+    /// # Notes
+    ///
+    /// Since this function internally calls [`Runtime::block_on`], and drives
+    /// futures in the local task set inside that call to `block_on`, the local
+    /// futures may not use [in-place blocking]. If a blocking call needs to be
+    /// issued from a local task, the [`spawn_blocking`] API may be used instead.
+    ///
+    /// For example, this will panic:
+    /// ```should_panic
+    /// use tokio::runtime::Runtime;
+    /// use tokio::task;
+    ///
+    /// let rt  = Runtime::new().unwrap();
+    /// let local = task::LocalSet::new();
+    /// local.block_on(&rt, async {
+    ///     let join = task::spawn_local(async {
+    ///         let blocking_result = task::block_in_place(|| {
+    ///             // ...
+    ///         });
+    ///         // ...
+    ///     });
+    ///     join.await.unwrap();
+    /// })
+    /// ```
+    /// This, however, will not panic:
+    /// ```
+    /// use tokio::runtime::Runtime;
+    /// use tokio::task;
+    ///
+    /// let rt  = Runtime::new().unwrap();
+    /// let local = task::LocalSet::new();
+    /// local.block_on(&rt, async {
+    ///     let join = task::spawn_local(async {
+    ///         let blocking_result = task::spawn_blocking(|| {
+    ///             // ...
+    ///         }).await;
+    ///         // ...
+    ///     });
+    ///     join.await.unwrap();
+    /// })
+    /// ```
+    ///
+    /// [`spawn_local`]: fn@spawn_local
+    /// [`Runtime::block_on`]: method@crate::runtime::Runtime::block_on
+    /// [in-place blocking]: fn@crate::task::block_in_place
+    /// [`spawn_blocking`]: fn@crate::task::spawn_blocking
+    #[cfg(feature = "rt")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "rt")))]
+    pub fn block_on<F>(&self, rt: &crate::runtime::Runtime, future: F) -> F::Output
+    where
+        F: Future,
+    {
+        rt.block_on(self.run_until(future))
+    }
+
+    /// Runs a future to completion on the local set, returning its output.
+    ///
+    /// This returns a future that runs the given future with a local set,
+    /// allowing it to call [`spawn_local`] to spawn additional `!Send` futures.
+    /// Any local futures spawned on the local set will be driven in the
+    /// background until the future passed to `run_until` completes. When the future
+    /// passed to `run` finishes, any local futures which have not completed
+    /// will remain on the local set, and will be driven on subsequent calls to
+    /// `run_until` or when [awaiting the local set] itself.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// use tokio::task;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     task::LocalSet::new().run_until(async {
+    ///         task::spawn_local(async move {
+    ///             // ...
+    ///         }).await.unwrap();
+    ///         // ...
+    ///     }).await;
+    /// }
+    /// ```
+    ///
+    /// [`spawn_local`]: fn@spawn_local
+    /// [awaiting the local set]: #awaiting-a-localset
+    pub async fn run_until<F>(&self, future: F) -> F::Output
+    where
+        F: Future,
+    {
+        let run_until = RunUntil {
+            future,
+            local_set: self,
+        };
+        run_until.await
+    }
+
+    /// Ticks the scheduler, returning whether the local future needs to be
+    /// notified again.
+    fn tick(&self) -> bool {
+        for _ in 0..MAX_TASKS_PER_TICK {
+            match self.next_task() {
+                // Run the task
+                //
+                // Safety: As spawned tasks are `!Send`, `run_unchecked` must be
+                // used. We are responsible for maintaining the invariant that
+                // `run_unchecked` is only called on threads that spawned the
+                // task initially. Because `LocalSet` itself is `!Send`, and
+                // `spawn_local` spawns into the `LocalSet` on the current
+                // thread, the invariant is maintained.
+                Some(task) => crate::coop::budget(|| task.run()),
+                // We have fully drained the queue of notified tasks, so the
+                // local future doesn't need to be notified again — it can wait
+                // until something else wakes a task in the local set.
+                None => return false,
+            }
+        }
+
+        true
+    }
+
+    fn next_task(&self) -> Option<task::LocalNotified<Arc<Shared>>> {
+        let tick = self.tick.get();
+        self.tick.set(tick.wrapping_add(1));
+
+        let task = if tick % REMOTE_FIRST_INTERVAL == 0 {
+            self.context
+                .shared
+                .queue
+                .lock()
+                .as_mut()
+                .and_then(|queue| queue.pop_front())
+                .or_else(|| self.context.queue.pop_front())
+        } else {
+            self.context.queue.pop_front().or_else(|| {
+                self.context
+                    .shared
+                    .queue
+                    .lock()
+                    .as_mut()
+                    .and_then(|queue| queue.pop_front())
+            })
+        };
+
+        task.map(|task| self.context.owned.assert_owner(task))
+    }
+
+    fn with<T>(&self, f: impl FnOnce() -> T) -> T {
+        CURRENT.set(&self.context, f)
+    }
+}
+
+impl fmt::Debug for LocalSet {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("LocalSet").finish()
+    }
+}
+
+impl Future for LocalSet {
+    type Output = ();
+
+    fn poll(self: Pin<&mut Self>, cx: &mut std::task::Context<'_>) -> Poll<Self::Output> {
+        // Register the waker before starting to work
+        self.context.shared.waker.register_by_ref(cx.waker());
+
+        if self.with(|| self.tick()) {
+            // If `tick` returns true, we need to notify the local future again:
+            // there are still tasks remaining in the run queue.
+            cx.waker().wake_by_ref();
+            Poll::Pending
+        } else if self.context.owned.is_empty() {
+            // If the scheduler has no remaining futures, we're done!
+            Poll::Ready(())
+        } else {
+            // There are still futures in the local set, but we've polled all the
+            // futures in the run queue. Therefore, we can just return Pending
+            // since the remaining futures will be woken from somewhere else.
+            Poll::Pending
+        }
+    }
+}
+
+impl Default for LocalSet {
+    fn default() -> LocalSet {
+        LocalSet::new()
+    }
+}
+
+impl Drop for LocalSet {
+    fn drop(&mut self) {
+        self.with(|| {
+            // Shut down all tasks in the LocalOwnedTasks and close it to
+            // prevent new tasks from ever being added.
+            self.context.owned.close_and_shutdown_all();
+
+            // We already called shutdown on all tasks above, so there is no
+            // need to call shutdown.
+            for task in self.context.queue.take() {
+                drop(task);
+            }
+
+            // Take the queue from the Shared object to prevent pushing
+            // notifications to it in the future.
+            let queue = self.context.shared.queue.lock().take().unwrap();
+            for task in queue {
+                drop(task);
+            }
+
+            assert!(self.context.owned.is_empty());
+        });
+    }
+}
+
+// === impl LocalFuture ===
+
+impl<T: Future> Future for RunUntil<'_, T> {
+    type Output = T::Output;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut std::task::Context<'_>) -> Poll<Self::Output> {
+        let me = self.project();
+
+        me.local_set.with(|| {
+            me.local_set
+                .context
+                .shared
+                .waker
+                .register_by_ref(cx.waker());
+
+            let _no_blocking = crate::runtime::enter::disallow_blocking();
+            let f = me.future;
+
+            if let Poll::Ready(output) = crate::coop::budget(|| f.poll(cx)) {
+                return Poll::Ready(output);
+            }
+
+            if me.local_set.tick() {
+                // If `tick` returns `true`, we need to notify the local future again:
+                // there are still tasks remaining in the run queue.
+                cx.waker().wake_by_ref();
+            }
+
+            Poll::Pending
+        })
+    }
+}
+
+impl Shared {
+    /// Schedule the provided task on the scheduler.
+    fn schedule(&self, task: task::Notified<Arc<Self>>) {
+        CURRENT.with(|maybe_cx| match maybe_cx {
+            Some(cx) if cx.shared.ptr_eq(self) => {
+                cx.queue.push_back(task);
+            }
+            _ => {
+                // First check whether the queue is still there (if not, the
+                // LocalSet is dropped). Then push to it if so, and if not,
+                // do nothing.
+                let mut lock = self.queue.lock();
+
+                if let Some(queue) = lock.as_mut() {
+                    queue.push_back(task);
+                    drop(lock);
+                    self.waker.wake();
+                }
+            }
+        });
+    }
+
+    fn ptr_eq(&self, other: &Shared) -> bool {
+        std::ptr::eq(self, other)
+    }
+}
+
+impl task::Schedule for Arc<Shared> {
+    fn release(&self, task: &Task<Self>) -> Option<Task<Self>> {
+        CURRENT.with(|maybe_cx| {
+            let cx = maybe_cx.expect("scheduler context missing");
+            assert!(cx.shared.ptr_eq(self));
+            cx.owned.remove(task)
+        })
+    }
+
+    fn schedule(&self, task: task::Notified<Self>) {
+        Shared::schedule(self, task);
+    }
+}
diff --git a/third_party/rust/tokio/src/task/mod.rs b/third_party/rust/tokio/src/task/mod.rs
new file mode 100644
index 0000000000..d532155a1f
--- /dev/null
+++ b/third_party/rust/tokio/src/task/mod.rs
@@ -0,0 +1,317 @@
+//! Asynchronous green-threads.
+//!
+//! ## What are Tasks?
+//!
+//! A _task_ is a light weight, non-blocking unit of execution. A task is similar
+//! to an OS thread, but rather than being managed by the OS scheduler, they are
+//! managed by the [Tokio runtime][rt]. Another name for this general pattern is
+//! [green threads]. If you are familiar with [Go's goroutines], [Kotlin's
+//! coroutines], or [Erlang's processes], you can think of Tokio's tasks as
+//! something similar.
+//!
+//! Key points about tasks include:
+//!
+//! * Tasks are **light weight**. Because tasks are scheduled by the Tokio
+//!   runtime rather than the operating system, creating new tasks or switching
+//!   between tasks does not require a context switch and has fairly low
+//!   overhead. Creating, running, and destroying large numbers of tasks is
+//!   quite cheap, especially compared to OS threads.
+//!
+//! * Tasks are scheduled **cooperatively**. Most operating systems implement
+//!   _preemptive multitasking_. This is a scheduling technique where the
+//!   operating system allows each thread to run for a period of time, and then
+//!   _preempts_ it, temporarily pausing that thread and switching to another.
+//!   Tasks, on the other hand, implement _cooperative multitasking_. In
+//!   cooperative multitasking, a task is allowed to run until it _yields_,
+//!   indicating to the Tokio runtime's scheduler that it cannot currently
+//!   continue executing. When a task yields, the Tokio runtime switches to
+//!   executing the next task.
+//!
+//! * Tasks are **non-blocking**. Typically, when an OS thread performs I/O or
+//!   must synchronize with another thread, it _blocks_, allowing the OS to
+//!   schedule another thread. When a task cannot continue executing, it must
+//!   yield instead, allowing the Tokio runtime to schedule another task. Tasks
+//!   should generally not perform system calls or other operations that could
+//!   block a thread, as this would prevent other tasks running on the same
+//!   thread from executing as well. Instead, this module provides APIs for
+//!   running blocking operations in an asynchronous context.
+//!
+//! [rt]: crate::runtime
+//! [green threads]: https://en.wikipedia.org/wiki/Green_threads
+//! [Go's goroutines]: https://tour.golang.org/concurrency/1
+//! [Kotlin's coroutines]: https://kotlinlang.org/docs/reference/coroutines-overview.html
+//! [Erlang's processes]: http://erlang.org/doc/getting_started/conc_prog.html#processes
+//!
+//! ## Working with Tasks
+//!
+//! This module provides the following APIs for working with tasks:
+//!
+//! ### Spawning
+//!
+//! Perhaps the most important function in this module is [`task::spawn`]. This
+//! function can be thought of as an async equivalent to the standard library's
+//! [`thread::spawn`][`std::thread::spawn`]. It takes an `async` block or other
+//! [future], and creates a new task to run that work concurrently:
+//!
+//! ```
+//! use tokio::task;
+//!
+//! # async fn doc() {
+//! task::spawn(async {
+//!     // perform some work here...
+//! });
+//! # }
+//! ```
+//!
+//! Like [`std::thread::spawn`], `task::spawn` returns a [`JoinHandle`] struct.
+//! A `JoinHandle` is itself a future which may be used to await the output of
+//! the spawned task. For example:
+//!
+//! ```
+//! use tokio::task;
+//!
+//! # #[tokio::main] async fn main() -> Result<(), Box<dyn std::error::Error>> {
+//! let join = task::spawn(async {
+//!     // ...
+//!     "hello world!"
+//! });
+//!
+//! // ...
+//!
+//! // Await the result of the spawned task.
+//! let result = join.await?;
+//! assert_eq!(result, "hello world!");
+//! # Ok(())
+//! # }
+//! ```
+//!
+//! Again, like `std::thread`'s [`JoinHandle` type][thread_join], if the spawned
+//! task panics, awaiting its `JoinHandle` will return a [`JoinError`]. For
+//! example:
+//!
+//! ```
+//! use tokio::task;
+//!
+//! # #[tokio::main] async fn main() {
+//! let join = task::spawn(async {
+//!     panic!("something bad happened!")
+//! });
+//!
+//! // The returned result indicates that the task failed.
+//! assert!(join.await.is_err());
+//! # }
+//! ```
+//!
+//! `spawn`, `JoinHandle`, and `JoinError` are present when the "rt"
+//! feature flag is enabled.
+//!
+//! [`task::spawn`]: crate::task::spawn()
+//! [future]: std::future::Future
+//! [`std::thread::spawn`]: std::thread::spawn
+//! [`JoinHandle`]: crate::task::JoinHandle
+//! [thread_join]: std::thread::JoinHandle
+//! [`JoinError`]: crate::task::JoinError
+//!
+//! ### Blocking and Yielding
+//!
+//! As we discussed above, code running in asynchronous tasks should not perform
+//! operations that can block. A blocking operation performed in a task running
+//! on a thread that is also running other tasks would block the entire thread,
+//! preventing other tasks from running.
+//!
+//! Instead, Tokio provides two APIs for running blocking operations in an
+//! asynchronous context: [`task::spawn_blocking`] and [`task::block_in_place`].
+//!
+//! Be aware that if you call a non-async method from async code, that non-async
+//! method is still inside the asynchronous context, so you should also avoid
+//! blocking operations there. This includes destructors of objects destroyed in
+//! async code.
+//!
+//! #### spawn_blocking
+//!
+//! The `task::spawn_blocking` function is similar to the `task::spawn` function
+//! discussed in the previous section, but rather than spawning an
+//! _non-blocking_ future on the Tokio runtime, it instead spawns a
+//! _blocking_ function on a dedicated thread pool for blocking tasks. For
+//! example:
+//!
+//! ```
+//! use tokio::task;
+//!
+//! # async fn docs() {
+//! task::spawn_blocking(|| {
+//!     // do some compute-heavy work or call synchronous code
+//! });
+//! # }
+//! ```
+//!
+//! Just like `task::spawn`, `task::spawn_blocking` returns a `JoinHandle`
+//! which we can use to await the result of the blocking operation:
+//!
+//! ```rust
+//! # use tokio::task;
+//! # async fn docs() -> Result<(), Box<dyn std::error::Error>>{
+//! let join = task::spawn_blocking(|| {
+//!     // do some compute-heavy work or call synchronous code
+//!     "blocking completed"
+//! });
+//!
+//! let result = join.await?;
+//! assert_eq!(result, "blocking completed");
+//! # Ok(())
+//! # }
+//! ```
+//!
+//! #### block_in_place
+//!
+//! When using the [multi-threaded runtime][rt-multi-thread], the [`task::block_in_place`]
+//! function is also available. Like `task::spawn_blocking`, this function
+//! allows running a blocking operation from an asynchronous context. Unlike
+//! `spawn_blocking`, however, `block_in_place` works by transitioning the
+//! _current_ worker thread to a blocking thread, moving other tasks running on
+//! that thread to another worker thread. This can improve performance by avoiding
+//! context switches.
+//!
+//! For example:
+//!
+//! ```
+//! use tokio::task;
+//!
+//! # async fn docs() {
+//! let result = task::block_in_place(|| {
+//!     // do some compute-heavy work or call synchronous code
+//!     "blocking completed"
+//! });
+//!
+//! assert_eq!(result, "blocking completed");
+//! # }
+//! ```
+//!
+//! #### yield_now
+//!
+//! In addition, this module provides a [`task::yield_now`] async function
+//! that is analogous to the standard library's [`thread::yield_now`]. Calling
+//! and `await`ing this function will cause the current task to yield to the
+//! Tokio runtime's scheduler, allowing other tasks to be
+//! scheduled. Eventually, the yielding task will be polled again, allowing it
+//! to execute. For example:
+//!
+//! ```rust
+//! use tokio::task;
+//!
+//! # #[tokio::main] async fn main() {
+//! async {
+//!     task::spawn(async {
+//!         // ...
+//!         println!("spawned task done!")
+//!     });
+//!
+//!     // Yield, allowing the newly-spawned task to execute first.
+//!     task::yield_now().await;
+//!     println!("main task done!");
+//! }
+//! # .await;
+//! # }
+//! ```
+//!
+//! ### Cooperative scheduling
+//!
+//! A single call to [`poll`] on a top-level task may potentially do a lot of
+//! work before it returns `Poll::Pending`. If a task runs for a long period of
+//! time without yielding back to the executor, it can starve other tasks
+//! waiting on that executor to execute them, or drive underlying resources.
+//! Since Rust does not have a runtime, it is difficult to forcibly preempt a
+//! long-running task. Instead, this module provides an opt-in mechanism for
+//! futures to collaborate with the executor to avoid starvation.
+//!
+//! Consider a future like this one:
+//!
+//! ```
+//! # use tokio_stream::{Stream, StreamExt};
+//! async fn drop_all<I: Stream + Unpin>(mut input: I) {
+//!     while let Some(_) = input.next().await {}
+//! }
+//! ```
+//!
+//! It may look harmless, but consider what happens under heavy load if the
+//! input stream is _always_ ready. If we spawn `drop_all`, the task will never
+//! yield, and will starve other tasks and resources on the same executor.
+//!
+//! To account for this, Tokio has explicit yield points in a number of library
+//! functions, which force tasks to return to the executor periodically.
+//!
+//!
+//! #### unconstrained
+//!
+//! If necessary, [`task::unconstrained`] lets you opt out a future of Tokio's cooperative
+//! scheduling. When a future is wrapped with `unconstrained`, it will never be forced to yield to
+//! Tokio. For example:
+//!
+//! ```
+//! # #[tokio::main]
+//! # async fn main() {
+//! use tokio::{task, sync::mpsc};
+//!
+//! let fut = async {
+//!     let (tx, mut rx) = mpsc::unbounded_channel();
+//!
+//!     for i in 0..1000 {
+//!         let _ = tx.send(());
+//!         // This will always be ready. If coop was in effect, this code would be forced to yield
+//!         // periodically. However, if left unconstrained, then this code will never yield.
+//!         rx.recv().await;
+//!     }
+//! };
+//!
+//! task::unconstrained(fut).await;
+//! # }
+//! ```
+//!
+//! [`task::spawn_blocking`]: crate::task::spawn_blocking
+//! [`task::block_in_place`]: crate::task::block_in_place
+//! [rt-multi-thread]: ../runtime/index.html#threaded-scheduler
+//! [`task::yield_now`]: crate::task::yield_now()
+//! [`thread::yield_now`]: std::thread::yield_now
+//! [`task::unconstrained`]: crate::task::unconstrained()
+//! [`poll`]: method@std::future::Future::poll
+
+cfg_rt! {
+    pub use crate::runtime::task::{JoinError, JoinHandle};
+
+    mod blocking;
+    pub use blocking::spawn_blocking;
+
+    mod spawn;
+    pub use spawn::spawn;
+
+    cfg_rt_multi_thread! {
+        pub use blocking::block_in_place;
+    }
+
+    mod yield_now;
+    pub use yield_now::yield_now;
+
+    mod local;
+    pub use local::{spawn_local, LocalSet};
+
+    mod task_local;
+    pub use task_local::LocalKey;
+
+    mod unconstrained;
+    pub use unconstrained::{unconstrained, Unconstrained};
+
+    cfg_unstable! {
+        mod join_set;
+        pub use join_set::JoinSet;
+    }
+
+    cfg_trace! {
+        mod builder;
+        pub use builder::Builder;
+    }
+
+    /// Task-related futures.
+    pub mod futures {
+        pub use super::task_local::TaskLocalFuture;
+    }
+}
diff --git a/third_party/rust/tokio/src/task/spawn.rs b/third_party/rust/tokio/src/task/spawn.rs
new file mode 100644
index 0000000000..a9d736674c
--- /dev/null
+++ b/third_party/rust/tokio/src/task/spawn.rs
@@ -0,0 +1,149 @@
+use crate::{task::JoinHandle, util::error::CONTEXT_MISSING_ERROR};
+
+use std::future::Future;
+
+cfg_rt! {
+    /// Spawns a new asynchronous task, returning a
+    /// [`JoinHandle`](super::JoinHandle) for it.
+    ///
+    /// Spawning a task enables the task to execute concurrently to other tasks. The
+    /// spawned task may execute on the current thread, or it may be sent to a
+    /// different thread to be executed. The specifics depend on the current
+    /// [`Runtime`](crate::runtime::Runtime) configuration.
+    ///
+    /// There is no guarantee that a spawned task will execute to completion.
+    /// When a runtime is shutdown, all outstanding tasks are dropped,
+    /// regardless of the lifecycle of that task.
+    ///
+    /// This function must be called from the context of a Tokio runtime. Tasks running on
+    /// the Tokio runtime are always inside its context, but you can also enter the context
+    /// using the [`Runtime::enter`](crate::runtime::Runtime::enter()) method.
+    ///
+    /// # Examples
+    ///
+    /// In this example, a server is started and `spawn` is used to start a new task
+    /// that processes each received connection.
+    ///
+    /// ```no_run
+    /// use tokio::net::{TcpListener, TcpStream};
+    ///
+    /// use std::io;
+    ///
+    /// async fn process(socket: TcpStream) {
+    ///     // ...
+    /// # drop(socket);
+    /// }
+    ///
+    /// #[tokio::main]
+    /// async fn main() -> io::Result<()> {
+    ///     let listener = TcpListener::bind("127.0.0.1:8080").await?;
+    ///
+    ///     loop {
+    ///         let (socket, _) = listener.accept().await?;
+    ///
+    ///         tokio::spawn(async move {
+    ///             // Process each socket concurrently.
+    ///             process(socket).await
+    ///         });
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// Panics if called from **outside** of the Tokio runtime.
+    ///
+    /// # Using `!Send` values from a task
+    ///
+    /// The task supplied to `spawn` must implement `Send`. However, it is
+    /// possible to **use** `!Send` values from the task as long as they only
+    /// exist between calls to `.await`.
+    ///
+    /// For example, this will work:
+    ///
+    /// ```
+    /// use tokio::task;
+    ///
+    /// use std::rc::Rc;
+    ///
+    /// fn use_rc(rc: Rc<()>) {
+    ///     // Do stuff w/ rc
+    /// # drop(rc);
+    /// }
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     tokio::spawn(async {
+    ///         // Force the `Rc` to stay in a scope with no `.await`
+    ///         {
+    ///             let rc = Rc::new(());
+    ///             use_rc(rc.clone());
+    ///         }
+    ///
+    ///         task::yield_now().await;
+    ///     }).await.unwrap();
+    /// }
+    /// ```
+    ///
+    /// This will **not** work:
+    ///
+    /// ```compile_fail
+    /// use tokio::task;
+    ///
+    /// use std::rc::Rc;
+    ///
+    /// fn use_rc(rc: Rc<()>) {
+    ///     // Do stuff w/ rc
+    /// # drop(rc);
+    /// }
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     tokio::spawn(async {
+    ///         let rc = Rc::new(());
+    ///
+    ///         task::yield_now().await;
+    ///
+    ///         use_rc(rc.clone());
+    ///     }).await.unwrap();
+    /// }
+    /// ```
+    ///
+    /// Holding on to a `!Send` value across calls to `.await` will result in
+    /// an unfriendly compile error message similar to:
+    ///
+    /// ```text
+    /// `[... some type ...]` cannot be sent between threads safely
+    /// ```
+    ///
+    /// or:
+    ///
+    /// ```text
+    /// error[E0391]: cycle detected when processing `main`
+    /// ```
+    #[track_caller]
+    pub fn spawn<T>(future: T) -> JoinHandle<T::Output>
+    where
+        T: Future + Send + 'static,
+        T::Output: Send + 'static,
+    {
+        // preventing stack overflows on debug mode, by quickly sending the
+        // task to the heap.
+        if cfg!(debug_assertions) && std::mem::size_of::<T>() > 2048 {
+            spawn_inner(Box::pin(future), None)
+        } else {
+            spawn_inner(future, None)
+        }
+    }
+
+    #[track_caller]
+    pub(super) fn spawn_inner<T>(future: T, name: Option<&str>) -> JoinHandle<T::Output>
+    where
+        T: Future + Send + 'static,
+        T::Output: Send + 'static,
+    {
+        let spawn_handle = crate::runtime::context::spawn_handle().expect(CONTEXT_MISSING_ERROR);
+        let task = crate::util::trace::task(future, "task", name);
+        spawn_handle.spawn(task)
+    }
+}
diff --git a/third_party/rust/tokio/src/task/task_local.rs b/third_party/rust/tokio/src/task/task_local.rs
new file mode 100644
index 0000000000..949bbca3ee
--- /dev/null
+++ b/third_party/rust/tokio/src/task/task_local.rs
@@ -0,0 +1,302 @@
+use pin_project_lite::pin_project;
+use std::cell::RefCell;
+use std::error::Error;
+use std::future::Future;
+use std::marker::PhantomPinned;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use std::{fmt, thread};
+
+/// Declares a new task-local key of type [`tokio::task::LocalKey`].
+///
+/// # Syntax
+///
+/// The macro wraps any number of static declarations and makes them local to the current task.
+/// Publicity and attributes for each static is preserved. For example:
+///
+/// # Examples
+///
+/// ```
+/// # use tokio::task_local;
+/// task_local! {
+///     pub static ONE: u32;
+///
+///     #[allow(unused)]
+///     static TWO: f32;
+/// }
+/// # fn main() {}
+/// ```
+///
+/// See [LocalKey documentation][`tokio::task::LocalKey`] for more
+/// information.
+///
+/// [`tokio::task::LocalKey`]: struct@crate::task::LocalKey
+#[macro_export]
+#[cfg_attr(docsrs, doc(cfg(feature = "rt")))]
+macro_rules! task_local {
+     // empty (base case for the recursion)
+    () => {};
+
+    ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty; $($rest:tt)*) => {
+        $crate::__task_local_inner!($(#[$attr])* $vis $name, $t);
+        $crate::task_local!($($rest)*);
+    };
+
+    ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty) => {
+        $crate::__task_local_inner!($(#[$attr])* $vis $name, $t);
+    }
+}
+
+#[doc(hidden)]
+#[macro_export]
+macro_rules! __task_local_inner {
+    ($(#[$attr:meta])* $vis:vis $name:ident, $t:ty) => {
+        $vis static $name: $crate::task::LocalKey<$t> = {
+            std::thread_local! {
+                static __KEY: std::cell::RefCell<Option<$t>> = std::cell::RefCell::new(None);
+            }
+
+            $crate::task::LocalKey { inner: __KEY }
+        };
+    };
+}
+
+/// A key for task-local data.
+///
+/// This type is generated by the `task_local!` macro.
+///
+/// Unlike [`std::thread::LocalKey`], `tokio::task::LocalKey` will
+/// _not_ lazily initialize the value on first access. Instead, the
+/// value is first initialized when the future containing
+/// the task-local is first polled by a futures executor, like Tokio.
+///
+/// # Examples
+///
+/// ```
+/// # async fn dox() {
+/// tokio::task_local! {
+///     static NUMBER: u32;
+/// }
+///
+/// NUMBER.scope(1, async move {
+///     assert_eq!(NUMBER.get(), 1);
+/// }).await;
+///
+/// NUMBER.scope(2, async move {
+///     assert_eq!(NUMBER.get(), 2);
+///
+///     NUMBER.scope(3, async move {
+///         assert_eq!(NUMBER.get(), 3);
+///     }).await;
+/// }).await;
+/// # }
+/// ```
+/// [`std::thread::LocalKey`]: struct@std::thread::LocalKey
+#[cfg_attr(docsrs, doc(cfg(feature = "rt")))]
+pub struct LocalKey<T: 'static> {
+    #[doc(hidden)]
+    pub inner: thread::LocalKey<RefCell<Option<T>>>,
+}
+
+impl<T: 'static> LocalKey<T> {
+    /// Sets a value `T` as the task-local value for the future `F`.
+    ///
+    /// On completion of `scope`, the task-local will be dropped.
+    ///
+    /// ### Examples
+    ///
+    /// ```
+    /// # async fn dox() {
+    /// tokio::task_local! {
+    ///     static NUMBER: u32;
+    /// }
+    ///
+    /// NUMBER.scope(1, async move {
+    ///     println!("task local value: {}", NUMBER.get());
+    /// }).await;
+    /// # }
+    /// ```
+    pub fn scope<F>(&'static self, value: T, f: F) -> TaskLocalFuture<T, F>
+    where
+        F: Future,
+    {
+        TaskLocalFuture {
+            local: self,
+            slot: Some(value),
+            future: f,
+            _pinned: PhantomPinned,
+        }
+    }
+
+    /// Sets a value `T` as the task-local value for the closure `F`.
+    ///
+    /// On completion of `scope`, the task-local will be dropped.
+    ///
+    /// ### Examples
+    ///
+    /// ```
+    /// # async fn dox() {
+    /// tokio::task_local! {
+    ///     static NUMBER: u32;
+    /// }
+    ///
+    /// NUMBER.sync_scope(1, || {
+    ///     println!("task local value: {}", NUMBER.get());
+    /// });
+    /// # }
+    /// ```
+    pub fn sync_scope<F, R>(&'static self, value: T, f: F) -> R
+    where
+        F: FnOnce() -> R,
+    {
+        let scope = TaskLocalFuture {
+            local: self,
+            slot: Some(value),
+            future: (),
+            _pinned: PhantomPinned,
+        };
+        crate::pin!(scope);
+        scope.with_task(|_| f())
+    }
+
+    /// Accesses the current task-local and runs the provided closure.
+    ///
+    /// # Panics
+    ///
+    /// This function will panic if not called within the context
+    /// of a future containing a task-local with the corresponding key.
+    pub fn with<F, R>(&'static self, f: F) -> R
+    where
+        F: FnOnce(&T) -> R,
+    {
+        self.try_with(f).expect(
+            "cannot access a Task Local Storage value \
+             without setting it via `LocalKey::set`",
+        )
+    }
+
+    /// Accesses the current task-local and runs the provided closure.
+    ///
+    /// If the task-local with the associated key is not present, this
+    /// method will return an `AccessError`. For a panicking variant,
+    /// see `with`.
+    pub fn try_with<F, R>(&'static self, f: F) -> Result<R, AccessError>
+    where
+        F: FnOnce(&T) -> R,
+    {
+        self.inner.with(|v| {
+            if let Some(val) = v.borrow().as_ref() {
+                Ok(f(val))
+            } else {
+                Err(AccessError { _private: () })
+            }
+        })
+    }
+}
+
+impl<T: Copy + 'static> LocalKey<T> {
+    /// Returns a copy of the task-local value
+    /// if the task-local value implements `Copy`.
+    pub fn get(&'static self) -> T {
+        self.with(|v| *v)
+    }
+}
+
+impl<T: 'static> fmt::Debug for LocalKey<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.pad("LocalKey { .. }")
+    }
+}
+
+pin_project! {
+    /// A future that sets a value `T` of a task local for the future `F` during
+    /// its execution.
+    ///
+    /// The value of the task-local must be `'static` and will be dropped on the
+    /// completion of the future.
+    ///
+    /// Created by the function [`LocalKey::scope`](self::LocalKey::scope).
+    ///
+    /// ### Examples
+    ///
+    /// ```
+    /// # async fn dox() {
+    /// tokio::task_local! {
+    ///     static NUMBER: u32;
+    /// }
+    ///
+    /// NUMBER.scope(1, async move {
+    ///     println!("task local value: {}", NUMBER.get());
+    /// }).await;
+    /// # }
+    /// ```
+    pub struct TaskLocalFuture<T, F>
+    where
+        T: 'static
+    {
+        local: &'static LocalKey<T>,
+        slot: Option<T>,
+        #[pin]
+        future: F,
+        #[pin]
+        _pinned: PhantomPinned,
+    }
+}
+
+impl<T: 'static, F> TaskLocalFuture<T, F> {
+    fn with_task<F2: FnOnce(Pin<&mut F>) -> R, R>(self: Pin<&mut Self>, f: F2) -> R {
+        struct Guard<'a, T: 'static> {
+            local: &'static LocalKey<T>,
+            slot: &'a mut Option<T>,
+            prev: Option<T>,
+        }
+
+        impl<T> Drop for Guard<'_, T> {
+            fn drop(&mut self) {
+                let value = self.local.inner.with(|c| c.replace(self.prev.take()));
+                *self.slot = value;
+            }
+        }
+
+        let project = self.project();
+        let val = project.slot.take();
+
+        let prev = project.local.inner.with(|c| c.replace(val));
+
+        let _guard = Guard {
+            prev,
+            slot: project.slot,
+            local: *project.local,
+        };
+
+        f(project.future)
+    }
+}
+
+impl<T: 'static, F: Future> Future for TaskLocalFuture<T, F> {
+    type Output = F::Output;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.with_task(|f| f.poll(cx))
+    }
+}
+
+/// An error returned by [`LocalKey::try_with`](method@LocalKey::try_with).
+#[derive(Clone, Copy, Eq, PartialEq)]
+pub struct AccessError {
+    _private: (),
+}
+
+impl fmt::Debug for AccessError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("AccessError").finish()
+    }
+}
+
+impl fmt::Display for AccessError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt("task-local value not set", f)
+    }
+}
+
+impl Error for AccessError {}
diff --git a/third_party/rust/tokio/src/task/unconstrained.rs b/third_party/rust/tokio/src/task/unconstrained.rs
new file mode 100644
index 0000000000..31c732bfc9
--- /dev/null
+++ b/third_party/rust/tokio/src/task/unconstrained.rs
@@ -0,0 +1,45 @@
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// Future for the [`unconstrained`](unconstrained) method.
+    #[cfg_attr(docsrs, doc(cfg(feature = "rt")))]
+    #[must_use = "Unconstrained does nothing unless polled"]
+    pub struct Unconstrained<F> {
+        #[pin]
+        inner: F,
+    }
+}
+
+impl<F> Future for Unconstrained<F>
+where
+    F: Future,
+{
+    type Output = <F as Future>::Output;
+
+    cfg_coop! {
+        fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+            let inner = self.project().inner;
+            crate::coop::with_unconstrained(|| inner.poll(cx))
+        }
+    }
+
+    cfg_not_coop! {
+        fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+            let inner = self.project().inner;
+            inner.poll(cx)
+        }
+    }
+}
+
+/// Turn off cooperative scheduling for a future. The future will never be forced to yield by
+/// Tokio. Using this exposes your service to starvation if the unconstrained future never yields
+/// otherwise.
+///
+/// See also the usage example in the [task module](index.html#unconstrained).
+#[cfg_attr(docsrs, doc(cfg(feature = "rt")))]
+pub fn unconstrained<F>(inner: F) -> Unconstrained<F> {
+    Unconstrained { inner }
+}
diff --git a/third_party/rust/tokio/src/task/yield_now.rs b/third_party/rust/tokio/src/task/yield_now.rs
new file mode 100644
index 0000000000..148e3dc0c8
--- /dev/null
+++ b/third_party/rust/tokio/src/task/yield_now.rs
@@ -0,0 +1,58 @@
+use std::future::Future;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+/// Yields execution back to the Tokio runtime.
+///
+/// A task yields by awaiting on `yield_now()`, and may resume when that future
+/// completes (with no output.) The current task will be re-added as a pending
+/// task at the _back_ of the pending queue. Any other pending tasks will be
+/// scheduled. No other waking is required for the task to continue.
+///
+/// See also the usage example in the [task module](index.html#yield_now).
+///
+/// ## Non-guarantees
+///
+/// This function may not yield all the way up to the executor if there are any
+/// special combinators above it in the call stack. For example, if a
+/// [`tokio::select!`] has another branch complete during the same poll as the
+/// `yield_now()`, then the yield is not propagated all the way up to the
+/// runtime.
+///
+/// It is generally not guaranteed that the runtime behaves like you expect it
+/// to when deciding which task to schedule next after a call to `yield_now()`.
+/// In particular, the runtime may choose to poll the task that just ran
+/// `yield_now()` again immediately without polling any other tasks first. For
+/// example, the runtime will not drive the IO driver between every poll of a
+/// task, and this could result in the runtime polling the current task again
+/// immediately even if there is another task that could make progress if that
+/// other task is waiting for a notification from the IO driver.
+///
+/// In general, changes to the order in which the runtime polls tasks is not
+/// considered a breaking change, and your program should be correct no matter
+/// which order the runtime polls your tasks in.
+///
+/// [`tokio::select!`]: macro@crate::select
+#[cfg_attr(docsrs, doc(cfg(feature = "rt")))]
+pub async fn yield_now() {
+    /// Yield implementation
+    struct YieldNow {
+        yielded: bool,
+    }
+
+    impl Future for YieldNow {
+        type Output = ();
+
+        fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
+            if self.yielded {
+                return Poll::Ready(());
+            }
+
+            self.yielded = true;
+            cx.waker().wake_by_ref();
+            Poll::Pending
+        }
+    }
+
+    YieldNow { yielded: false }.await
+}
diff --git a/third_party/rust/tokio/src/time/clock.rs b/third_party/rust/tokio/src/time/clock.rs
new file mode 100644
index 0000000000..41be9bac48
--- /dev/null
+++ b/third_party/rust/tokio/src/time/clock.rs
@@ -0,0 +1,233 @@
+#![cfg_attr(not(feature = "rt"), allow(dead_code))]
+
+//! Source of time abstraction.
+//!
+//! By default, `std::time::Instant::now()` is used. However, when the
+//! `test-util` feature flag is enabled, the values returned for `now()` are
+//! configurable.
+
+cfg_not_test_util! {
+    use crate::time::{Instant};
+
+    #[derive(Debug, Clone)]
+    pub(crate) struct Clock {}
+
+    pub(crate) fn now() -> Instant {
+        Instant::from_std(std::time::Instant::now())
+    }
+
+    impl Clock {
+        pub(crate) fn new(_enable_pausing: bool, _start_paused: bool) -> Clock {
+            Clock {}
+        }
+
+        pub(crate) fn now(&self) -> Instant {
+            now()
+        }
+    }
+}
+
+cfg_test_util! {
+    use crate::time::{Duration, Instant};
+    use crate::loom::sync::{Arc, Mutex};
+
+    cfg_rt! {
+        fn clock() -> Option<Clock> {
+            crate::runtime::context::clock()
+        }
+    }
+
+    cfg_not_rt! {
+        fn clock() -> Option<Clock> {
+            None
+        }
+    }
+
+    /// A handle to a source of time.
+    #[derive(Debug, Clone)]
+    pub(crate) struct Clock {
+        inner: Arc<Mutex<Inner>>,
+    }
+
+    #[derive(Debug)]
+    struct Inner {
+        /// True if the ability to pause time is enabled.
+        enable_pausing: bool,
+
+        /// Instant to use as the clock's base instant.
+        base: std::time::Instant,
+
+        /// Instant at which the clock was last unfrozen.
+        unfrozen: Option<std::time::Instant>,
+    }
+
+    /// Pauses time.
+    ///
+    /// The current value of `Instant::now()` is saved and all subsequent calls
+    /// to `Instant::now()` will return the saved value. The saved value can be
+    /// changed by [`advance`] or by the time auto-advancing once the runtime
+    /// has no work to do. This only affects the `Instant` type in Tokio, and
+    /// the `Instant` in std continues to work as normal.
+    ///
+    /// Pausing time requires the `current_thread` Tokio runtime. This is the
+    /// default runtime used by `#[tokio::test]`. The runtime can be initialized
+    /// with time in a paused state using the `Builder::start_paused` method.
+    ///
+    /// For cases where time is immediately paused, it is better to pause
+    /// the time using the `main` or `test` macro:
+    /// ```
+    /// #[tokio::main(flavor = "current_thread", start_paused = true)]
+    /// async fn main() {
+    ///    println!("Hello world");
+    /// }
+    /// ```
+    ///
+    /// # Panics
+    ///
+    /// Panics if time is already frozen or if called from outside of a
+    /// `current_thread` Tokio runtime.
+    ///
+    /// # Auto-advance
+    ///
+    /// If time is paused and the runtime has no work to do, the clock is
+    /// auto-advanced to the next pending timer. This means that [`Sleep`] or
+    /// other timer-backed primitives can cause the runtime to advance the
+    /// current time when awaited.
+    ///
+    /// [`Sleep`]: crate::time::Sleep
+    /// [`advance`]: crate::time::advance
+    pub fn pause() {
+        let clock = clock().expect("time cannot be frozen from outside the Tokio runtime");
+        clock.pause();
+    }
+
+    /// Resumes time.
+    ///
+    /// Clears the saved `Instant::now()` value. Subsequent calls to
+    /// `Instant::now()` will return the value returned by the system call.
+    ///
+    /// # Panics
+    ///
+    /// Panics if time is not frozen or if called from outside of the Tokio
+    /// runtime.
+    pub fn resume() {
+        let clock = clock().expect("time cannot be frozen from outside the Tokio runtime");
+        let mut inner = clock.inner.lock();
+
+        if inner.unfrozen.is_some() {
+            panic!("time is not frozen");
+        }
+
+        inner.unfrozen = Some(std::time::Instant::now());
+    }
+
+    /// Advances time.
+    ///
+    /// Increments the saved `Instant::now()` value by `duration`. Subsequent
+    /// calls to `Instant::now()` will return the result of the increment.
+    ///
+    /// This function will make the current time jump forward by the given
+    /// duration in one jump. This means that all `sleep` calls with a deadline
+    /// before the new time will immediately complete "at the same time", and
+    /// the runtime is free to poll them in any order.  Additionally, this
+    /// method will not wait for the `sleep` calls it advanced past to complete.
+    /// If you want to do that, you should instead call [`sleep`] and rely on
+    /// the runtime's auto-advance feature.
+    ///
+    /// Note that calls to `sleep` are not guaranteed to complete the first time
+    /// they are polled after a call to `advance`. For example, this can happen
+    /// if the runtime has not yet touched the timer driver after the call to
+    /// `advance`. However if they don't, the runtime will poll the task again
+    /// shortly.
+    ///
+    /// # Panics
+    ///
+    /// Panics if time is not frozen or if called from outside of the Tokio
+    /// runtime.
+    ///
+    /// # Auto-advance
+    ///
+    /// If the time is paused and there is no work to do, the runtime advances
+    /// time to the next timer. See [`pause`](pause#auto-advance) for more
+    /// details.
+    ///
+    /// [`sleep`]: fn@crate::time::sleep
+    pub async fn advance(duration: Duration) {
+        let clock = clock().expect("time cannot be frozen from outside the Tokio runtime");
+        clock.advance(duration);
+
+        crate::task::yield_now().await;
+    }
+
+    /// Returns the current instant, factoring in frozen time.
+    pub(crate) fn now() -> Instant {
+        if let Some(clock) = clock() {
+            clock.now()
+        } else {
+            Instant::from_std(std::time::Instant::now())
+        }
+    }
+
+    impl Clock {
+        /// Returns a new `Clock` instance that uses the current execution context's
+        /// source of time.
+        pub(crate) fn new(enable_pausing: bool, start_paused: bool) -> Clock {
+            let now = std::time::Instant::now();
+
+            let clock = Clock {
+                inner: Arc::new(Mutex::new(Inner {
+                    enable_pausing,
+                    base: now,
+                    unfrozen: Some(now),
+                })),
+            };
+
+            if start_paused {
+                clock.pause();
+            }
+
+            clock
+        }
+
+        pub(crate) fn pause(&self) {
+            let mut inner = self.inner.lock();
+
+            if !inner.enable_pausing {
+                drop(inner); // avoid poisoning the lock
+                panic!("`time::pause()` requires the `current_thread` Tokio runtime. \
+                        This is the default Runtime used by `#[tokio::test].");
+            }
+
+            let elapsed = inner.unfrozen.as_ref().expect("time is already frozen").elapsed();
+            inner.base += elapsed;
+            inner.unfrozen = None;
+        }
+
+        pub(crate) fn is_paused(&self) -> bool {
+            let inner = self.inner.lock();
+            inner.unfrozen.is_none()
+        }
+
+        pub(crate) fn advance(&self, duration: Duration) {
+            let mut inner = self.inner.lock();
+
+            if inner.unfrozen.is_some() {
+                panic!("time is not frozen");
+            }
+
+            inner.base += duration;
+        }
+
+        pub(crate) fn now(&self) -> Instant {
+            let inner = self.inner.lock();
+
+            let mut ret = inner.base;
+
+            if let Some(unfrozen) = inner.unfrozen {
+                ret += unfrozen.elapsed();
+            }
+
+            Instant::from_std(ret)
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/time/driver/entry.rs b/third_party/rust/tokio/src/time/driver/entry.rs
new file mode 100644
index 0000000000..f0ea898e12
--- /dev/null
+++ b/third_party/rust/tokio/src/time/driver/entry.rs
@@ -0,0 +1,633 @@
+//! Timer state structures.
+//!
+//! This module contains the heart of the intrusive timer implementation, and as
+//! such the structures inside are full of tricky concurrency and unsafe code.
+//!
+//! # Ground rules
+//!
+//! The heart of the timer implementation here is the [`TimerShared`] structure,
+//! shared between the [`TimerEntry`] and the driver. Generally, we permit access
+//! to [`TimerShared`] ONLY via either 1) a mutable reference to [`TimerEntry`] or
+//! 2) a held driver lock.
+//!
+//! It follows from this that any changes made while holding BOTH 1 and 2 will
+//! be reliably visible, regardless of ordering. This is because of the acq/rel
+//! fences on the driver lock ensuring ordering with 2, and rust mutable
+//! reference rules for 1 (a mutable reference to an object can't be passed
+//! between threads without an acq/rel barrier, and same-thread we have local
+//! happens-before ordering).
+//!
+//! # State field
+//!
+//! Each timer has a state field associated with it. This field contains either
+//! the current scheduled time, or a special flag value indicating its state.
+//! This state can either indicate that the timer is on the 'pending' queue (and
+//! thus will be fired with an `Ok(())` result soon) or that it has already been
+//! fired/deregistered.
+//!
+//! This single state field allows for code that is firing the timer to
+//! synchronize with any racing `reset` calls reliably.
+//!
+//! # Cached vs true timeouts
+//!
+//! To allow for the use case of a timeout that is periodically reset before
+//! expiration to be as lightweight as possible, we support optimistically
+//! lock-free timer resets, in the case where a timer is rescheduled to a later
+//! point than it was originally scheduled for.
+//!
+//! This is accomplished by lazily rescheduling timers. That is, we update the
+//! state field field with the true expiration of the timer from the holder of
+//! the [`TimerEntry`]. When the driver services timers (ie, whenever it's
+//! walking lists of timers), it checks this "true when" value, and reschedules
+//! based on it.
+//!
+//! We do, however, also need to track what the expiration time was when we
+//! originally registered the timer; this is used to locate the right linked
+//! list when the timer is being cancelled. This is referred to as the "cached
+//! when" internally.
+//!
+//! There is of course a race condition between timer reset and timer
+//! expiration. If the driver fails to observe the updated expiration time, it
+//! could trigger expiration of the timer too early. However, because
+//! [`mark_pending`][mark_pending] performs a compare-and-swap, it will identify this race and
+//! refuse to mark the timer as pending.
+//!
+//! [mark_pending]: TimerHandle::mark_pending
+
+use crate::loom::cell::UnsafeCell;
+use crate::loom::sync::atomic::AtomicU64;
+use crate::loom::sync::atomic::Ordering;
+
+use crate::sync::AtomicWaker;
+use crate::time::Instant;
+use crate::util::linked_list;
+
+use super::Handle;
+
+use std::cell::UnsafeCell as StdUnsafeCell;
+use std::task::{Context, Poll, Waker};
+use std::{marker::PhantomPinned, pin::Pin, ptr::NonNull};
+
+type TimerResult = Result<(), crate::time::error::Error>;
+
+const STATE_DEREGISTERED: u64 = u64::MAX;
+const STATE_PENDING_FIRE: u64 = STATE_DEREGISTERED - 1;
+const STATE_MIN_VALUE: u64 = STATE_PENDING_FIRE;
+
+/// This structure holds the current shared state of the timer - its scheduled
+/// time (if registered), or otherwise the result of the timer completing, as
+/// well as the registered waker.
+///
+/// Generally, the StateCell is only permitted to be accessed from two contexts:
+/// Either a thread holding the corresponding &mut TimerEntry, or a thread
+/// holding the timer driver lock. The write actions on the StateCell amount to
+/// passing "ownership" of the StateCell between these contexts; moving a timer
+/// from the TimerEntry to the driver requires _both_ holding the &mut
+/// TimerEntry and the driver lock, while moving it back (firing the timer)
+/// requires only the driver lock.
+pub(super) struct StateCell {
+    /// Holds either the scheduled expiration time for this timer, or (if the
+    /// timer has been fired and is unregistered), `u64::MAX`.
+    state: AtomicU64,
+    /// If the timer is fired (an Acquire order read on state shows
+    /// `u64::MAX`), holds the result that should be returned from
+    /// polling the timer. Otherwise, the contents are unspecified and reading
+    /// without holding the driver lock is undefined behavior.
+    result: UnsafeCell<TimerResult>,
+    /// The currently-registered waker
+    waker: CachePadded<AtomicWaker>,
+}
+
+impl Default for StateCell {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl std::fmt::Debug for StateCell {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "StateCell({:?})", self.read_state())
+    }
+}
+
+impl StateCell {
+    fn new() -> Self {
+        Self {
+            state: AtomicU64::new(STATE_DEREGISTERED),
+            result: UnsafeCell::new(Ok(())),
+            waker: CachePadded(AtomicWaker::new()),
+        }
+    }
+
+    fn is_pending(&self) -> bool {
+        self.state.load(Ordering::Relaxed) == STATE_PENDING_FIRE
+    }
+
+    /// Returns the current expiration time, or None if not currently scheduled.
+    fn when(&self) -> Option<u64> {
+        let cur_state = self.state.load(Ordering::Relaxed);
+
+        if cur_state == u64::MAX {
+            None
+        } else {
+            Some(cur_state)
+        }
+    }
+
+    /// If the timer is completed, returns the result of the timer. Otherwise,
+    /// returns None and registers the waker.
+    fn poll(&self, waker: &Waker) -> Poll<TimerResult> {
+        // We must register first. This ensures that either `fire` will
+        // observe the new waker, or we will observe a racing fire to have set
+        // the state, or both.
+        self.waker.0.register_by_ref(waker);
+
+        self.read_state()
+    }
+
+    fn read_state(&self) -> Poll<TimerResult> {
+        let cur_state = self.state.load(Ordering::Acquire);
+
+        if cur_state == STATE_DEREGISTERED {
+            // SAFETY: The driver has fired this timer; this involves writing
+            // the result, and then writing (with release ordering) the state
+            // field.
+            Poll::Ready(unsafe { self.result.with(|p| *p) })
+        } else {
+            Poll::Pending
+        }
+    }
+
+    /// Marks this timer as being moved to the pending list, if its scheduled
+    /// time is not after `not_after`.
+    ///
+    /// If the timer is scheduled for a time after not_after, returns an Err
+    /// containing the current scheduled time.
+    ///
+    /// SAFETY: Must hold the driver lock.
+    unsafe fn mark_pending(&self, not_after: u64) -> Result<(), u64> {
+        // Quick initial debug check to see if the timer is already fired. Since
+        // firing the timer can only happen with the driver lock held, we know
+        // we shouldn't be able to "miss" a transition to a fired state, even
+        // with relaxed ordering.
+        let mut cur_state = self.state.load(Ordering::Relaxed);
+
+        loop {
+            debug_assert!(cur_state < STATE_MIN_VALUE);
+
+            if cur_state > not_after {
+                break Err(cur_state);
+            }
+
+            match self.state.compare_exchange(
+                cur_state,
+                STATE_PENDING_FIRE,
+                Ordering::AcqRel,
+                Ordering::Acquire,
+            ) {
+                Ok(_) => {
+                    break Ok(());
+                }
+                Err(actual_state) => {
+                    cur_state = actual_state;
+                }
+            }
+        }
+    }
+
+    /// Fires the timer, setting the result to the provided result.
+    ///
+    /// Returns:
+    /// * `Some(waker) - if fired and a waker needs to be invoked once the
+    ///   driver lock is released
+    /// * `None` - if fired and a waker does not need to be invoked, or if
+    ///   already fired
+    ///
+    /// SAFETY: The driver lock must be held.
+    unsafe fn fire(&self, result: TimerResult) -> Option<Waker> {
+        // Quick initial check to see if the timer is already fired. Since
+        // firing the timer can only happen with the driver lock held, we know
+        // we shouldn't be able to "miss" a transition to a fired state, even
+        // with relaxed ordering.
+        let cur_state = self.state.load(Ordering::Relaxed);
+        if cur_state == STATE_DEREGISTERED {
+            return None;
+        }
+
+        // SAFETY: We assume the driver lock is held and the timer is not
+        // fired, so only the driver is accessing this field.
+        //
+        // We perform a release-ordered store to state below, to ensure this
+        // write is visible before the state update is visible.
+        unsafe { self.result.with_mut(|p| *p = result) };
+
+        self.state.store(STATE_DEREGISTERED, Ordering::Release);
+
+        self.waker.0.take_waker()
+    }
+
+    /// Marks the timer as registered (poll will return None) and sets the
+    /// expiration time.
+    ///
+    /// While this function is memory-safe, it should only be called from a
+    /// context holding both `&mut TimerEntry` and the driver lock.
+    fn set_expiration(&self, timestamp: u64) {
+        debug_assert!(timestamp < STATE_MIN_VALUE);
+
+        // We can use relaxed ordering because we hold the driver lock and will
+        // fence when we release the lock.
+        self.state.store(timestamp, Ordering::Relaxed);
+    }
+
+    /// Attempts to adjust the timer to a new timestamp.
+    ///
+    /// If the timer has already been fired, is pending firing, or the new
+    /// timestamp is earlier than the old timestamp, (or occasionally
+    /// spuriously) returns Err without changing the timer's state. In this
+    /// case, the timer must be deregistered and re-registered.
+    fn extend_expiration(&self, new_timestamp: u64) -> Result<(), ()> {
+        let mut prior = self.state.load(Ordering::Relaxed);
+        loop {
+            if new_timestamp < prior || prior >= STATE_MIN_VALUE {
+                return Err(());
+            }
+
+            match self.state.compare_exchange_weak(
+                prior,
+                new_timestamp,
+                Ordering::AcqRel,
+                Ordering::Acquire,
+            ) {
+                Ok(_) => {
+                    return Ok(());
+                }
+                Err(true_prior) => {
+                    prior = true_prior;
+                }
+            }
+        }
+    }
+
+    /// Returns true if the state of this timer indicates that the timer might
+    /// be registered with the driver. This check is performed with relaxed
+    /// ordering, but is conservative - if it returns false, the timer is
+    /// definitely _not_ registered.
+    pub(super) fn might_be_registered(&self) -> bool {
+        self.state.load(Ordering::Relaxed) != u64::MAX
+    }
+}
+
+/// A timer entry.
+///
+/// This is the handle to a timer that is controlled by the requester of the
+/// timer. As this participates in intrusive data structures, it must be pinned
+/// before polling.
+#[derive(Debug)]
+pub(super) struct TimerEntry {
+    /// Arc reference to the driver. We can only free the driver after
+    /// deregistering everything from their respective timer wheels.
+    driver: Handle,
+    /// Shared inner structure; this is part of an intrusive linked list, and
+    /// therefore other references can exist to it while mutable references to
+    /// Entry exist.
+    ///
+    /// This is manipulated only under the inner mutex. TODO: Can we use loom
+    /// cells for this?
+    inner: StdUnsafeCell<TimerShared>,
+    /// Initial deadline for the timer. This is used to register on the first
+    /// poll, as we can't register prior to being pinned.
+    initial_deadline: Option<Instant>,
+    /// Ensure the type is !Unpin
+    _m: std::marker::PhantomPinned,
+}
+
+unsafe impl Send for TimerEntry {}
+unsafe impl Sync for TimerEntry {}
+
+/// An TimerHandle is the (non-enforced) "unique" pointer from the driver to the
+/// timer entry. Generally, at most one TimerHandle exists for a timer at a time
+/// (enforced by the timer state machine).
+///
+/// SAFETY: An TimerHandle is essentially a raw pointer, and the usual caveats
+/// of pointer safety apply. In particular, TimerHandle does not itself enforce
+/// that the timer does still exist; however, normally an TimerHandle is created
+/// immediately before registering the timer, and is consumed when firing the
+/// timer, to help minimize mistakes. Still, because TimerHandle cannot enforce
+/// memory safety, all operations are unsafe.
+#[derive(Debug)]
+pub(crate) struct TimerHandle {
+    inner: NonNull<TimerShared>,
+}
+
+pub(super) type EntryList = crate::util::linked_list::LinkedList<TimerShared, TimerShared>;
+
+/// The shared state structure of a timer. This structure is shared between the
+/// frontend (`Entry`) and driver backend.
+///
+/// Note that this structure is located inside the `TimerEntry` structure.
+#[derive(Debug)]
+#[repr(C)] // required by `link_list::Link` impl
+pub(crate) struct TimerShared {
+    /// Data manipulated by the driver thread itself, only.
+    driver_state: CachePadded<TimerSharedPadded>,
+
+    /// Current state. This records whether the timer entry is currently under
+    /// the ownership of the driver, and if not, its current state (not
+    /// complete, fired, error, etc).
+    state: StateCell,
+
+    _p: PhantomPinned,
+}
+
+impl TimerShared {
+    pub(super) fn new() -> Self {
+        Self {
+            state: StateCell::default(),
+            driver_state: CachePadded(TimerSharedPadded::new()),
+            _p: PhantomPinned,
+        }
+    }
+
+    /// Gets the cached time-of-expiration value.
+    pub(super) fn cached_when(&self) -> u64 {
+        // Cached-when is only accessed under the driver lock, so we can use relaxed
+        self.driver_state.0.cached_when.load(Ordering::Relaxed)
+    }
+
+    /// Gets the true time-of-expiration value, and copies it into the cached
+    /// time-of-expiration value.
+    ///
+    /// SAFETY: Must be called with the driver lock held, and when this entry is
+    /// not in any timer wheel lists.
+    pub(super) unsafe fn sync_when(&self) -> u64 {
+        let true_when = self.true_when();
+
+        self.driver_state
+            .0
+            .cached_when
+            .store(true_when, Ordering::Relaxed);
+
+        true_when
+    }
+
+    /// Sets the cached time-of-expiration value.
+    ///
+    /// SAFETY: Must be called with the driver lock held, and when this entry is
+    /// not in any timer wheel lists.
+    unsafe fn set_cached_when(&self, when: u64) {
+        self.driver_state
+            .0
+            .cached_when
+            .store(when, Ordering::Relaxed);
+    }
+
+    /// Returns the true time-of-expiration value, with relaxed memory ordering.
+    pub(super) fn true_when(&self) -> u64 {
+        self.state.when().expect("Timer already fired")
+    }
+
+    /// Sets the true time-of-expiration value, even if it is less than the
+    /// current expiration or the timer is deregistered.
+    ///
+    /// SAFETY: Must only be called with the driver lock held and the entry not
+    /// in the timer wheel.
+    pub(super) unsafe fn set_expiration(&self, t: u64) {
+        self.state.set_expiration(t);
+        self.driver_state.0.cached_when.store(t, Ordering::Relaxed);
+    }
+
+    /// Sets the true time-of-expiration only if it is after the current.
+    pub(super) fn extend_expiration(&self, t: u64) -> Result<(), ()> {
+        self.state.extend_expiration(t)
+    }
+
+    /// Returns a TimerHandle for this timer.
+    pub(super) fn handle(&self) -> TimerHandle {
+        TimerHandle {
+            inner: NonNull::from(self),
+        }
+    }
+
+    /// Returns true if the state of this timer indicates that the timer might
+    /// be registered with the driver. This check is performed with relaxed
+    /// ordering, but is conservative - if it returns false, the timer is
+    /// definitely _not_ registered.
+    pub(super) fn might_be_registered(&self) -> bool {
+        self.state.might_be_registered()
+    }
+}
+
+/// Additional shared state between the driver and the timer which is cache
+/// padded. This contains the information that the driver thread accesses most
+/// frequently to minimize contention. In particular, we move it away from the
+/// waker, as the waker is updated on every poll.
+#[repr(C)] // required by `link_list::Link` impl
+struct TimerSharedPadded {
+    /// A link within the doubly-linked list of timers on a particular level and
+    /// slot. Valid only if state is equal to Registered.
+    ///
+    /// Only accessed under the entry lock.
+    pointers: linked_list::Pointers<TimerShared>,
+
+    /// The expiration time for which this entry is currently registered.
+    /// Generally owned by the driver, but is accessed by the entry when not
+    /// registered.
+    cached_when: AtomicU64,
+
+    /// The true expiration time. Set by the timer future, read by the driver.
+    true_when: AtomicU64,
+}
+
+impl std::fmt::Debug for TimerSharedPadded {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("TimerSharedPadded")
+            .field("when", &self.true_when.load(Ordering::Relaxed))
+            .field("cached_when", &self.cached_when.load(Ordering::Relaxed))
+            .finish()
+    }
+}
+
+impl TimerSharedPadded {
+    fn new() -> Self {
+        Self {
+            cached_when: AtomicU64::new(0),
+            true_when: AtomicU64::new(0),
+            pointers: linked_list::Pointers::new(),
+        }
+    }
+}
+
+unsafe impl Send for TimerShared {}
+unsafe impl Sync for TimerShared {}
+
+unsafe impl linked_list::Link for TimerShared {
+    type Handle = TimerHandle;
+
+    type Target = TimerShared;
+
+    fn as_raw(handle: &Self::Handle) -> NonNull<Self::Target> {
+        handle.inner
+    }
+
+    unsafe fn from_raw(ptr: NonNull<Self::Target>) -> Self::Handle {
+        TimerHandle { inner: ptr }
+    }
+
+    unsafe fn pointers(
+        target: NonNull<Self::Target>,
+    ) -> NonNull<linked_list::Pointers<Self::Target>> {
+        target.cast()
+    }
+}
+
+// ===== impl Entry =====
+
+impl TimerEntry {
+    pub(crate) fn new(handle: &Handle, deadline: Instant) -> Self {
+        let driver = handle.clone();
+
+        Self {
+            driver,
+            inner: StdUnsafeCell::new(TimerShared::new()),
+            initial_deadline: Some(deadline),
+            _m: std::marker::PhantomPinned,
+        }
+    }
+
+    fn inner(&self) -> &TimerShared {
+        unsafe { &*self.inner.get() }
+    }
+
+    pub(crate) fn is_elapsed(&self) -> bool {
+        !self.inner().state.might_be_registered() && self.initial_deadline.is_none()
+    }
+
+    /// Cancels and deregisters the timer. This operation is irreversible.
+    pub(crate) fn cancel(self: Pin<&mut Self>) {
+        // We need to perform an acq/rel fence with the driver thread, and the
+        // simplest way to do so is to grab the driver lock.
+        //
+        // Why is this necessary? We're about to release this timer's memory for
+        // some other non-timer use. However, we've been doing a bunch of
+        // relaxed (or even non-atomic) writes from the driver thread, and we'll
+        // be doing more from _this thread_ (as this memory is interpreted as
+        // something else).
+        //
+        // It is critical to ensure that, from the point of view of the driver,
+        // those future non-timer writes happen-after the timer is fully fired,
+        // and from the purpose of this thread, the driver's writes all
+        // happen-before we drop the timer. This in turn requires us to perform
+        // an acquire-release barrier in _both_ directions between the driver
+        // and dropping thread.
+        //
+        // The lock acquisition in clear_entry serves this purpose. All of the
+        // driver manipulations happen with the lock held, so we can just take
+        // the lock and be sure that this drop happens-after everything the
+        // driver did so far and happens-before everything the driver does in
+        // the future. While we have the lock held, we also go ahead and
+        // deregister the entry if necessary.
+        unsafe { self.driver.clear_entry(NonNull::from(self.inner())) };
+    }
+
+    pub(crate) fn reset(mut self: Pin<&mut Self>, new_time: Instant) {
+        unsafe { self.as_mut().get_unchecked_mut() }.initial_deadline = None;
+
+        let tick = self.driver.time_source().deadline_to_tick(new_time);
+
+        if self.inner().extend_expiration(tick).is_ok() {
+            return;
+        }
+
+        unsafe {
+            self.driver.reregister(tick, self.inner().into());
+        }
+    }
+
+    pub(crate) fn poll_elapsed(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<(), super::Error>> {
+        if self.driver.is_shutdown() {
+            panic!("{}", crate::util::error::RUNTIME_SHUTTING_DOWN_ERROR);
+        }
+
+        if let Some(deadline) = self.initial_deadline {
+            self.as_mut().reset(deadline);
+        }
+
+        let this = unsafe { self.get_unchecked_mut() };
+
+        this.inner().state.poll(cx.waker())
+    }
+}
+
+impl TimerHandle {
+    pub(super) unsafe fn cached_when(&self) -> u64 {
+        unsafe { self.inner.as_ref().cached_when() }
+    }
+
+    pub(super) unsafe fn sync_when(&self) -> u64 {
+        unsafe { self.inner.as_ref().sync_when() }
+    }
+
+    pub(super) unsafe fn is_pending(&self) -> bool {
+        unsafe { self.inner.as_ref().state.is_pending() }
+    }
+
+    /// Forcibly sets the true and cached expiration times to the given tick.
+    ///
+    /// SAFETY: The caller must ensure that the handle remains valid, the driver
+    /// lock is held, and that the timer is not in any wheel linked lists.
+    pub(super) unsafe fn set_expiration(&self, tick: u64) {
+        self.inner.as_ref().set_expiration(tick);
+    }
+
+    /// Attempts to mark this entry as pending. If the expiration time is after
+    /// `not_after`, however, returns an Err with the current expiration time.
+    ///
+    /// If an `Err` is returned, the `cached_when` value will be updated to this
+    /// new expiration time.
+    ///
+    /// SAFETY: The caller must ensure that the handle remains valid, the driver
+    /// lock is held, and that the timer is not in any wheel linked lists.
+    /// After returning Ok, the entry must be added to the pending list.
+    pub(super) unsafe fn mark_pending(&self, not_after: u64) -> Result<(), u64> {
+        match self.inner.as_ref().state.mark_pending(not_after) {
+            Ok(()) => {
+                // mark this as being on the pending queue in cached_when
+                self.inner.as_ref().set_cached_when(u64::MAX);
+                Ok(())
+            }
+            Err(tick) => {
+                self.inner.as_ref().set_cached_when(tick);
+                Err(tick)
+            }
+        }
+    }
+
+    /// Attempts to transition to a terminal state. If the state is already a
+    /// terminal state, does nothing.
+    ///
+    /// Because the entry might be dropped after the state is moved to a
+    /// terminal state, this function consumes the handle to ensure we don't
+    /// access the entry afterwards.
+    ///
+    /// Returns the last-registered waker, if any.
+    ///
+    /// SAFETY: The driver lock must be held while invoking this function, and
+    /// the entry must not be in any wheel linked lists.
+    pub(super) unsafe fn fire(self, completed_state: TimerResult) -> Option<Waker> {
+        self.inner.as_ref().state.fire(completed_state)
+    }
+}
+
+impl Drop for TimerEntry {
+    fn drop(&mut self) {
+        unsafe { Pin::new_unchecked(self) }.as_mut().cancel()
+    }
+}
+
+#[cfg_attr(target_arch = "x86_64", repr(align(128)))]
+#[cfg_attr(not(target_arch = "x86_64"), repr(align(64)))]
+#[derive(Debug, Default)]
+struct CachePadded<T>(T);
diff --git a/third_party/rust/tokio/src/time/driver/handle.rs b/third_party/rust/tokio/src/time/driver/handle.rs
new file mode 100644
index 0000000000..b61c0476e1
--- /dev/null
+++ b/third_party/rust/tokio/src/time/driver/handle.rs
@@ -0,0 +1,94 @@
+use crate::loom::sync::Arc;
+use crate::time::driver::ClockTime;
+use std::fmt;
+
+/// Handle to time driver instance.
+#[derive(Clone)]
+pub(crate) struct Handle {
+    time_source: ClockTime,
+    inner: Arc<super::Inner>,
+}
+
+impl Handle {
+    /// Creates a new timer `Handle` from a shared `Inner` timer state.
+    pub(super) fn new(inner: Arc<super::Inner>) -> Self {
+        let time_source = inner.state.lock().time_source.clone();
+        Handle { time_source, inner }
+    }
+
+    /// Returns the time source associated with this handle.
+    pub(super) fn time_source(&self) -> &ClockTime {
+        &self.time_source
+    }
+
+    /// Access the driver's inner structure.
+    pub(super) fn get(&self) -> &super::Inner {
+        &*self.inner
+    }
+
+    /// Checks whether the driver has been shutdown.
+    pub(super) fn is_shutdown(&self) -> bool {
+        self.inner.is_shutdown()
+    }
+}
+
+cfg_rt! {
+    impl Handle {
+        /// Tries to get a handle to the current timer.
+        ///
+        /// # Panics
+        ///
+        /// This function panics if there is no current timer set.
+        ///
+        /// It can be triggered when [`Builder::enable_time`] or
+        /// [`Builder::enable_all`] are not included in the builder.
+        ///
+        /// It can also panic whenever a timer is created outside of a
+        /// Tokio runtime. That is why `rt.block_on(sleep(...))` will panic,
+        /// since the function is executed outside of the runtime.
+        /// Whereas `rt.block_on(async {sleep(...).await})` doesn't panic.
+        /// And this is because wrapping the function on an async makes it lazy,
+        /// and so gets executed inside the runtime successfully without
+        /// panicking.
+        ///
+        /// [`Builder::enable_time`]: crate::runtime::Builder::enable_time
+        /// [`Builder::enable_all`]: crate::runtime::Builder::enable_all
+        pub(crate) fn current() -> Self {
+            crate::runtime::context::time_handle()
+                .expect("A Tokio 1.x context was found, but timers are disabled. Call `enable_time` on the runtime builder to enable timers.")
+        }
+    }
+}
+
+cfg_not_rt! {
+    impl Handle {
+        /// Tries to get a handle to the current timer.
+        ///
+        /// # Panics
+        ///
+        /// This function panics if there is no current timer set.
+        ///
+        /// It can be triggered when [`Builder::enable_time`] or
+        /// [`Builder::enable_all`] are not included in the builder.
+        ///
+        /// It can also panic whenever a timer is created outside of a
+        /// Tokio runtime. That is why `rt.block_on(sleep(...))` will panic,
+        /// since the function is executed outside of the runtime.
+        /// Whereas `rt.block_on(async {sleep(...).await})` doesn't panic.
+        /// And this is because wrapping the function on an async makes it lazy,
+        /// and so gets executed inside the runtime successfully without
+        /// panicking.
+        ///
+        /// [`Builder::enable_time`]: crate::runtime::Builder::enable_time
+        /// [`Builder::enable_all`]: crate::runtime::Builder::enable_all
+        pub(crate) fn current() -> Self {
+            panic!("{}", crate::util::error::CONTEXT_MISSING_ERROR)
+        }
+    }
+}
+
+impl fmt::Debug for Handle {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "Handle")
+    }
+}
diff --git a/third_party/rust/tokio/src/time/driver/mod.rs b/third_party/rust/tokio/src/time/driver/mod.rs
new file mode 100644
index 0000000000..9971877479
--- /dev/null
+++ b/third_party/rust/tokio/src/time/driver/mod.rs
@@ -0,0 +1,528 @@
+// Currently, rust warns when an unsafe fn contains an unsafe {} block. However,
+// in the future, this will change to the reverse. For now, suppress this
+// warning and generally stick with being explicit about unsafety.
+#![allow(unused_unsafe)]
+#![cfg_attr(not(feature = "rt"), allow(dead_code))]
+
+//! Time driver.
+
+mod entry;
+pub(self) use self::entry::{EntryList, TimerEntry, TimerHandle, TimerShared};
+
+mod handle;
+pub(crate) use self::handle::Handle;
+
+mod wheel;
+
+pub(super) mod sleep;
+
+use crate::loom::sync::atomic::{AtomicBool, Ordering};
+use crate::loom::sync::{Arc, Mutex};
+use crate::park::{Park, Unpark};
+use crate::time::error::Error;
+use crate::time::{Clock, Duration, Instant};
+
+use std::convert::TryInto;
+use std::fmt;
+use std::{num::NonZeroU64, ptr::NonNull, task::Waker};
+
+/// Time implementation that drives [`Sleep`][sleep], [`Interval`][interval], and [`Timeout`][timeout].
+///
+/// A `Driver` instance tracks the state necessary for managing time and
+/// notifying the [`Sleep`][sleep] instances once their deadlines are reached.
+///
+/// It is expected that a single instance manages many individual [`Sleep`][sleep]
+/// instances. The `Driver` implementation is thread-safe and, as such, is able
+/// to handle callers from across threads.
+///
+/// After creating the `Driver` instance, the caller must repeatedly call `park`
+/// or `park_timeout`. The time driver will perform no work unless `park` or
+/// `park_timeout` is called repeatedly.
+///
+/// The driver has a resolution of one millisecond. Any unit of time that falls
+/// between milliseconds are rounded up to the next millisecond.
+///
+/// When an instance is dropped, any outstanding [`Sleep`][sleep] instance that has not
+/// elapsed will be notified with an error. At this point, calling `poll` on the
+/// [`Sleep`][sleep] instance will result in panic.
+///
+/// # Implementation
+///
+/// The time driver is based on the [paper by Varghese and Lauck][paper].
+///
+/// A hashed timing wheel is a vector of slots, where each slot handles a time
+/// slice. As time progresses, the timer walks over the slot for the current
+/// instant, and processes each entry for that slot. When the timer reaches the
+/// end of the wheel, it starts again at the beginning.
+///
+/// The implementation maintains six wheels arranged in a set of levels. As the
+/// levels go up, the slots of the associated wheel represent larger intervals
+/// of time. At each level, the wheel has 64 slots. Each slot covers a range of
+/// time equal to the wheel at the lower level. At level zero, each slot
+/// represents one millisecond of time.
+///
+/// The wheels are:
+///
+/// * Level 0: 64 x 1 millisecond slots.
+/// * Level 1: 64 x 64 millisecond slots.
+/// * Level 2: 64 x ~4 second slots.
+/// * Level 3: 64 x ~4 minute slots.
+/// * Level 4: 64 x ~4 hour slots.
+/// * Level 5: 64 x ~12 day slots.
+///
+/// When the timer processes entries at level zero, it will notify all the
+/// `Sleep` instances as their deadlines have been reached. For all higher
+/// levels, all entries will be redistributed across the wheel at the next level
+/// down. Eventually, as time progresses, entries with [`Sleep`][sleep] instances will
+/// either be canceled (dropped) or their associated entries will reach level
+/// zero and be notified.
+///
+/// [paper]: http://www.cs.columbia.edu/~nahum/w6998/papers/ton97-timing-wheels.pdf
+/// [sleep]: crate::time::Sleep
+/// [timeout]: crate::time::Timeout
+/// [interval]: crate::time::Interval
+#[derive(Debug)]
+pub(crate) struct Driver<P: Park + 'static> {
+    /// Timing backend in use.
+    time_source: ClockTime,
+
+    /// Shared state.
+    handle: Handle,
+
+    /// Parker to delegate to.
+    park: P,
+
+    // When `true`, a call to `park_timeout` should immediately return and time
+    // should not advance. One reason for this to be `true` is if the task
+    // passed to `Runtime::block_on` called `task::yield_now()`.
+    //
+    // While it may look racy, it only has any effect when the clock is paused
+    // and pausing the clock is restricted to a single-threaded runtime.
+    #[cfg(feature = "test-util")]
+    did_wake: Arc<AtomicBool>,
+}
+
+/// A structure which handles conversion from Instants to u64 timestamps.
+#[derive(Debug, Clone)]
+pub(self) struct ClockTime {
+    clock: super::clock::Clock,
+    start_time: Instant,
+}
+
+impl ClockTime {
+    pub(self) fn new(clock: Clock) -> Self {
+        Self {
+            start_time: clock.now(),
+            clock,
+        }
+    }
+
+    pub(self) fn deadline_to_tick(&self, t: Instant) -> u64 {
+        // Round up to the end of a ms
+        self.instant_to_tick(t + Duration::from_nanos(999_999))
+    }
+
+    pub(self) fn instant_to_tick(&self, t: Instant) -> u64 {
+        // round up
+        let dur: Duration = t
+            .checked_duration_since(self.start_time)
+            .unwrap_or_else(|| Duration::from_secs(0));
+        let ms = dur.as_millis();
+
+        ms.try_into().unwrap_or(u64::MAX)
+    }
+
+    pub(self) fn tick_to_duration(&self, t: u64) -> Duration {
+        Duration::from_millis(t)
+    }
+
+    pub(self) fn now(&self) -> u64 {
+        self.instant_to_tick(self.clock.now())
+    }
+}
+
+/// Timer state shared between `Driver`, `Handle`, and `Registration`.
+struct Inner {
+    // The state is split like this so `Handle` can access `is_shutdown` without locking the mutex
+    pub(super) state: Mutex<InnerState>,
+
+    /// True if the driver is being shutdown.
+    pub(super) is_shutdown: AtomicBool,
+}
+
+/// Time state shared which must be protected by a `Mutex`
+struct InnerState {
+    /// Timing backend in use.
+    time_source: ClockTime,
+
+    /// The last published timer `elapsed` value.
+    elapsed: u64,
+
+    /// The earliest time at which we promise to wake up without unparking.
+    next_wake: Option<NonZeroU64>,
+
+    /// Timer wheel.
+    wheel: wheel::Wheel,
+
+    /// Unparker that can be used to wake the time driver.
+    unpark: Box<dyn Unpark>,
+}
+
+// ===== impl Driver =====
+
+impl<P> Driver<P>
+where
+    P: Park + 'static,
+{
+    /// Creates a new `Driver` instance that uses `park` to block the current
+    /// thread and `time_source` to get the current time and convert to ticks.
+    ///
+    /// Specifying the source of time is useful when testing.
+    pub(crate) fn new(park: P, clock: Clock) -> Driver<P> {
+        let time_source = ClockTime::new(clock);
+
+        let inner = Inner::new(time_source.clone(), Box::new(park.unpark()));
+
+        Driver {
+            time_source,
+            handle: Handle::new(Arc::new(inner)),
+            park,
+            #[cfg(feature = "test-util")]
+            did_wake: Arc::new(AtomicBool::new(false)),
+        }
+    }
+
+    /// Returns a handle to the timer.
+    ///
+    /// The `Handle` is how `Sleep` instances are created. The `Sleep` instances
+    /// can either be created directly or the `Handle` instance can be passed to
+    /// `with_default`, setting the timer as the default timer for the execution
+    /// context.
+    pub(crate) fn handle(&self) -> Handle {
+        self.handle.clone()
+    }
+
+    fn park_internal(&mut self, limit: Option<Duration>) -> Result<(), P::Error> {
+        let mut lock = self.handle.get().state.lock();
+
+        assert!(!self.handle.is_shutdown());
+
+        let next_wake = lock.wheel.next_expiration_time();
+        lock.next_wake =
+            next_wake.map(|t| NonZeroU64::new(t).unwrap_or_else(|| NonZeroU64::new(1).unwrap()));
+
+        drop(lock);
+
+        match next_wake {
+            Some(when) => {
+                let now = self.time_source.now();
+                // Note that we effectively round up to 1ms here - this avoids
+                // very short-duration microsecond-resolution sleeps that the OS
+                // might treat as zero-length.
+                let mut duration = self.time_source.tick_to_duration(when.saturating_sub(now));
+
+                if duration > Duration::from_millis(0) {
+                    if let Some(limit) = limit {
+                        duration = std::cmp::min(limit, duration);
+                    }
+
+                    self.park_timeout(duration)?;
+                } else {
+                    self.park.park_timeout(Duration::from_secs(0))?;
+                }
+            }
+            None => {
+                if let Some(duration) = limit {
+                    self.park_timeout(duration)?;
+                } else {
+                    self.park.park()?;
+                }
+            }
+        }
+
+        // Process pending timers after waking up
+        self.handle.process();
+
+        Ok(())
+    }
+
+    cfg_test_util! {
+        fn park_timeout(&mut self, duration: Duration) -> Result<(), P::Error> {
+            let clock = &self.time_source.clock;
+
+            if clock.is_paused() {
+                self.park.park_timeout(Duration::from_secs(0))?;
+
+                // If the time driver was woken, then the park completed
+                // before the "duration" elapsed (usually caused by a
+                // yield in `Runtime::block_on`). In this case, we don't
+                // advance the clock.
+                if !self.did_wake() {
+                    // Simulate advancing time
+                    clock.advance(duration);
+                }
+            } else {
+                self.park.park_timeout(duration)?;
+            }
+
+            Ok(())
+        }
+
+        fn did_wake(&self) -> bool {
+            self.did_wake.swap(false, Ordering::SeqCst)
+        }
+    }
+
+    cfg_not_test_util! {
+        fn park_timeout(&mut self, duration: Duration) -> Result<(), P::Error> {
+            self.park.park_timeout(duration)
+        }
+    }
+}
+
+impl Handle {
+    /// Runs timer related logic, and returns the next wakeup time
+    pub(self) fn process(&self) {
+        let now = self.time_source().now();
+
+        self.process_at_time(now)
+    }
+
+    pub(self) fn process_at_time(&self, mut now: u64) {
+        let mut waker_list: [Option<Waker>; 32] = Default::default();
+        let mut waker_idx = 0;
+
+        let mut lock = self.get().lock();
+
+        if now < lock.elapsed {
+            // Time went backwards! This normally shouldn't happen as the Rust language
+            // guarantees that an Instant is monotonic, but can happen when running
+            // Linux in a VM on a Windows host due to std incorrectly trusting the
+            // hardware clock to be monotonic.
+            //
+            // See <https://github.com/tokio-rs/tokio/issues/3619> for more information.
+            now = lock.elapsed;
+        }
+
+        while let Some(entry) = lock.wheel.poll(now) {
+            debug_assert!(unsafe { entry.is_pending() });
+
+            // SAFETY: We hold the driver lock, and just removed the entry from any linked lists.
+            if let Some(waker) = unsafe { entry.fire(Ok(())) } {
+                waker_list[waker_idx] = Some(waker);
+
+                waker_idx += 1;
+
+                if waker_idx == waker_list.len() {
+                    // Wake a batch of wakers. To avoid deadlock, we must do this with the lock temporarily dropped.
+                    drop(lock);
+
+                    for waker in waker_list.iter_mut() {
+                        waker.take().unwrap().wake();
+                    }
+
+                    waker_idx = 0;
+
+                    lock = self.get().lock();
+                }
+            }
+        }
+
+        // Update the elapsed cache
+        lock.elapsed = lock.wheel.elapsed();
+        lock.next_wake = lock
+            .wheel
+            .poll_at()
+            .map(|t| NonZeroU64::new(t).unwrap_or_else(|| NonZeroU64::new(1).unwrap()));
+
+        drop(lock);
+
+        for waker in waker_list[0..waker_idx].iter_mut() {
+            waker.take().unwrap().wake();
+        }
+    }
+
+    /// Removes a registered timer from the driver.
+    ///
+    /// The timer will be moved to the cancelled state. Wakers will _not_ be
+    /// invoked. If the timer is already completed, this function is a no-op.
+    ///
+    /// This function always acquires the driver lock, even if the entry does
+    /// not appear to be registered.
+    ///
+    /// SAFETY: The timer must not be registered with some other driver, and
+    /// `add_entry` must not be called concurrently.
+    pub(self) unsafe fn clear_entry(&self, entry: NonNull<TimerShared>) {
+        unsafe {
+            let mut lock = self.get().lock();
+
+            if entry.as_ref().might_be_registered() {
+                lock.wheel.remove(entry);
+            }
+
+            entry.as_ref().handle().fire(Ok(()));
+        }
+    }
+
+    /// Removes and re-adds an entry to the driver.
+    ///
+    /// SAFETY: The timer must be either unregistered, or registered with this
+    /// driver. No other threads are allowed to concurrently manipulate the
+    /// timer at all (the current thread should hold an exclusive reference to
+    /// the `TimerEntry`)
+    pub(self) unsafe fn reregister(&self, new_tick: u64, entry: NonNull<TimerShared>) {
+        let waker = unsafe {
+            let mut lock = self.get().lock();
+
+            // We may have raced with a firing/deregistration, so check before
+            // deregistering.
+            if unsafe { entry.as_ref().might_be_registered() } {
+                lock.wheel.remove(entry);
+            }
+
+            // Now that we have exclusive control of this entry, mint a handle to reinsert it.
+            let entry = entry.as_ref().handle();
+
+            if self.is_shutdown() {
+                unsafe { entry.fire(Err(crate::time::error::Error::shutdown())) }
+            } else {
+                entry.set_expiration(new_tick);
+
+                // Note: We don't have to worry about racing with some other resetting
+                // thread, because add_entry and reregister require exclusive control of
+                // the timer entry.
+                match unsafe { lock.wheel.insert(entry) } {
+                    Ok(when) => {
+                        if lock
+                            .next_wake
+                            .map(|next_wake| when < next_wake.get())
+                            .unwrap_or(true)
+                        {
+                            lock.unpark.unpark();
+                        }
+
+                        None
+                    }
+                    Err((entry, super::error::InsertError::Elapsed)) => unsafe {
+                        entry.fire(Ok(()))
+                    },
+                }
+            }
+
+            // Must release lock before invoking waker to avoid the risk of deadlock.
+        };
+
+        // The timer was fired synchronously as a result of the reregistration.
+        // Wake the waker; this is needed because we might reset _after_ a poll,
+        // and otherwise the task won't be awoken to poll again.
+        if let Some(waker) = waker {
+            waker.wake();
+        }
+    }
+}
+
+impl<P> Park for Driver<P>
+where
+    P: Park + 'static,
+{
+    type Unpark = TimerUnpark<P>;
+    type Error = P::Error;
+
+    fn unpark(&self) -> Self::Unpark {
+        TimerUnpark::new(self)
+    }
+
+    fn park(&mut self) -> Result<(), Self::Error> {
+        self.park_internal(None)
+    }
+
+    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
+        self.park_internal(Some(duration))
+    }
+
+    fn shutdown(&mut self) {
+        if self.handle.is_shutdown() {
+            return;
+        }
+
+        self.handle.get().is_shutdown.store(true, Ordering::SeqCst);
+
+        // Advance time forward to the end of time.
+
+        self.handle.process_at_time(u64::MAX);
+
+        self.park.shutdown();
+    }
+}
+
+impl<P> Drop for Driver<P>
+where
+    P: Park + 'static,
+{
+    fn drop(&mut self) {
+        self.shutdown();
+    }
+}
+
+pub(crate) struct TimerUnpark<P: Park + 'static> {
+    inner: P::Unpark,
+
+    #[cfg(feature = "test-util")]
+    did_wake: Arc<AtomicBool>,
+}
+
+impl<P: Park + 'static> TimerUnpark<P> {
+    fn new(driver: &Driver<P>) -> TimerUnpark<P> {
+        TimerUnpark {
+            inner: driver.park.unpark(),
+
+            #[cfg(feature = "test-util")]
+            did_wake: driver.did_wake.clone(),
+        }
+    }
+}
+
+impl<P: Park + 'static> Unpark for TimerUnpark<P> {
+    fn unpark(&self) {
+        #[cfg(feature = "test-util")]
+        self.did_wake.store(true, Ordering::SeqCst);
+
+        self.inner.unpark();
+    }
+}
+
+// ===== impl Inner =====
+
+impl Inner {
+    pub(self) fn new(time_source: ClockTime, unpark: Box<dyn Unpark>) -> Self {
+        Inner {
+            state: Mutex::new(InnerState {
+                time_source,
+                elapsed: 0,
+                next_wake: None,
+                unpark,
+                wheel: wheel::Wheel::new(),
+            }),
+            is_shutdown: AtomicBool::new(false),
+        }
+    }
+
+    /// Locks the driver's inner structure
+    pub(super) fn lock(&self) -> crate::loom::sync::MutexGuard<'_, InnerState> {
+        self.state.lock()
+    }
+
+    // Check whether the driver has been shutdown
+    pub(super) fn is_shutdown(&self) -> bool {
+        self.is_shutdown.load(Ordering::SeqCst)
+    }
+}
+
+impl fmt::Debug for Inner {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Inner").finish()
+    }
+}
+
+#[cfg(test)]
+mod tests;
diff --git a/third_party/rust/tokio/src/time/driver/sleep.rs b/third_party/rust/tokio/src/time/driver/sleep.rs
new file mode 100644
index 0000000000..7f27ef201f
--- /dev/null
+++ b/third_party/rust/tokio/src/time/driver/sleep.rs
@@ -0,0 +1,438 @@
+#[cfg(all(tokio_unstable, feature = "tracing"))]
+use crate::time::driver::ClockTime;
+use crate::time::driver::{Handle, TimerEntry};
+use crate::time::{error::Error, Duration, Instant};
+use crate::util::trace;
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::panic::Location;
+use std::pin::Pin;
+use std::task::{self, Poll};
+
+/// Waits until `deadline` is reached.
+///
+/// No work is performed while awaiting on the sleep future to complete. `Sleep`
+/// operates at millisecond granularity and should not be used for tasks that
+/// require high-resolution timers.
+///
+/// To run something regularly on a schedule, see [`interval`].
+///
+/// # Cancellation
+///
+/// Canceling a sleep instance is done by dropping the returned future. No additional
+/// cleanup work is required.
+///
+/// # Examples
+///
+/// Wait 100ms and print "100 ms have elapsed".
+///
+/// ```
+/// use tokio::time::{sleep_until, Instant, Duration};
+///
+/// #[tokio::main]
+/// async fn main() {
+///     sleep_until(Instant::now() + Duration::from_millis(100)).await;
+///     println!("100 ms have elapsed");
+/// }
+/// ```
+///
+/// See the documentation for the [`Sleep`] type for more examples.
+///
+/// # Panics
+///
+/// This function panics if there is no current timer set.
+///
+/// It can be triggered when [`Builder::enable_time`] or
+/// [`Builder::enable_all`] are not included in the builder.
+///
+/// It can also panic whenever a timer is created outside of a
+/// Tokio runtime. That is why `rt.block_on(sleep(...))` will panic,
+/// since the function is executed outside of the runtime.
+/// Whereas `rt.block_on(async {sleep(...).await})` doesn't panic.
+/// And this is because wrapping the function on an async makes it lazy,
+/// and so gets executed inside the runtime successfully without
+/// panicking.
+///
+/// [`Sleep`]: struct@crate::time::Sleep
+/// [`interval`]: crate::time::interval()
+/// [`Builder::enable_time`]: crate::runtime::Builder::enable_time
+/// [`Builder::enable_all`]: crate::runtime::Builder::enable_all
+// Alias for old name in 0.x
+#[cfg_attr(docsrs, doc(alias = "delay_until"))]
+#[track_caller]
+pub fn sleep_until(deadline: Instant) -> Sleep {
+    return Sleep::new_timeout(deadline, trace::caller_location());
+}
+
+/// Waits until `duration` has elapsed.
+///
+/// Equivalent to `sleep_until(Instant::now() + duration)`. An asynchronous
+/// analog to `std::thread::sleep`.
+///
+/// No work is performed while awaiting on the sleep future to complete. `Sleep`
+/// operates at millisecond granularity and should not be used for tasks that
+/// require high-resolution timers.
+///
+/// To run something regularly on a schedule, see [`interval`].
+///
+/// The maximum duration for a sleep is 68719476734 milliseconds (approximately 2.2 years).
+///
+/// # Cancellation
+///
+/// Canceling a sleep instance is done by dropping the returned future. No additional
+/// cleanup work is required.
+///
+/// # Examples
+///
+/// Wait 100ms and print "100 ms have elapsed".
+///
+/// ```
+/// use tokio::time::{sleep, Duration};
+///
+/// #[tokio::main]
+/// async fn main() {
+///     sleep(Duration::from_millis(100)).await;
+///     println!("100 ms have elapsed");
+/// }
+/// ```
+///
+/// See the documentation for the [`Sleep`] type for more examples.
+///
+/// # Panics
+///
+/// This function panics if there is no current timer set.
+///
+/// It can be triggered when [`Builder::enable_time`] or
+/// [`Builder::enable_all`] are not included in the builder.
+///
+/// It can also panic whenever a timer is created outside of a
+/// Tokio runtime. That is why `rt.block_on(sleep(...))` will panic,
+/// since the function is executed outside of the runtime.
+/// Whereas `rt.block_on(async {sleep(...).await})` doesn't panic.
+/// And this is because wrapping the function on an async makes it lazy,
+/// and so gets executed inside the runtime successfully without
+/// panicking.
+///
+/// [`Sleep`]: struct@crate::time::Sleep
+/// [`interval`]: crate::time::interval()
+/// [`Builder::enable_time`]: crate::runtime::Builder::enable_time
+/// [`Builder::enable_all`]: crate::runtime::Builder::enable_all
+// Alias for old name in 0.x
+#[cfg_attr(docsrs, doc(alias = "delay_for"))]
+#[cfg_attr(docsrs, doc(alias = "wait"))]
+#[track_caller]
+pub fn sleep(duration: Duration) -> Sleep {
+    let location = trace::caller_location();
+
+    match Instant::now().checked_add(duration) {
+        Some(deadline) => Sleep::new_timeout(deadline, location),
+        None => Sleep::new_timeout(Instant::far_future(), location),
+    }
+}
+
+pin_project! {
+    /// Future returned by [`sleep`](sleep) and [`sleep_until`](sleep_until).
+    ///
+    /// This type does not implement the `Unpin` trait, which means that if you
+    /// use it with [`select!`] or by calling `poll`, you have to pin it first.
+    /// If you use it with `.await`, this does not apply.
+    ///
+    /// # Examples
+    ///
+    /// Wait 100ms and print "100 ms have elapsed".
+    ///
+    /// ```
+    /// use tokio::time::{sleep, Duration};
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     sleep(Duration::from_millis(100)).await;
+    ///     println!("100 ms have elapsed");
+    /// }
+    /// ```
+    ///
+    /// Use with [`select!`]. Pinning the `Sleep` with [`tokio::pin!`] is
+    /// necessary when the same `Sleep` is selected on multiple times.
+    /// ```no_run
+    /// use tokio::time::{self, Duration, Instant};
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let sleep = time::sleep(Duration::from_millis(10));
+    ///     tokio::pin!(sleep);
+    ///
+    ///     loop {
+    ///         tokio::select! {
+    ///             () = &mut sleep => {
+    ///                 println!("timer elapsed");
+    ///                 sleep.as_mut().reset(Instant::now() + Duration::from_millis(50));
+    ///             },
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    /// Use in a struct with boxing. By pinning the `Sleep` with a `Box`, the
+    /// `HasSleep` struct implements `Unpin`, even though `Sleep` does not.
+    /// ```
+    /// use std::future::Future;
+    /// use std::pin::Pin;
+    /// use std::task::{Context, Poll};
+    /// use tokio::time::Sleep;
+    ///
+    /// struct HasSleep {
+    ///     sleep: Pin<Box<Sleep>>,
+    /// }
+    ///
+    /// impl Future for HasSleep {
+    ///     type Output = ();
+    ///
+    ///     fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
+    ///         self.sleep.as_mut().poll(cx)
+    ///     }
+    /// }
+    /// ```
+    /// Use in a struct with pin projection. This method avoids the `Box`, but
+    /// the `HasSleep` struct will not be `Unpin` as a consequence.
+    /// ```
+    /// use std::future::Future;
+    /// use std::pin::Pin;
+    /// use std::task::{Context, Poll};
+    /// use tokio::time::Sleep;
+    /// use pin_project_lite::pin_project;
+    ///
+    /// pin_project! {
+    ///     struct HasSleep {
+    ///         #[pin]
+    ///         sleep: Sleep,
+    ///     }
+    /// }
+    ///
+    /// impl Future for HasSleep {
+    ///     type Output = ();
+    ///
+    ///     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
+    ///         self.project().sleep.poll(cx)
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// [`select!`]: ../macro.select.html
+    /// [`tokio::pin!`]: ../macro.pin.html
+    // Alias for old name in 0.2
+    #[cfg_attr(docsrs, doc(alias = "Delay"))]
+    #[derive(Debug)]
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    pub struct Sleep {
+        inner: Inner,
+
+        // The link between the `Sleep` instance and the timer that drives it.
+        #[pin]
+        entry: TimerEntry,
+    }
+}
+
+cfg_trace! {
+    #[derive(Debug)]
+    struct Inner {
+        deadline: Instant,
+        ctx: trace::AsyncOpTracingCtx,
+        time_source: ClockTime,
+    }
+}
+
+cfg_not_trace! {
+    #[derive(Debug)]
+    struct Inner {
+        deadline: Instant,
+    }
+}
+
+impl Sleep {
+    #[cfg_attr(not(all(tokio_unstable, feature = "tracing")), allow(unused_variables))]
+    pub(crate) fn new_timeout(
+        deadline: Instant,
+        location: Option<&'static Location<'static>>,
+    ) -> Sleep {
+        let handle = Handle::current();
+        let entry = TimerEntry::new(&handle, deadline);
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let inner = {
+            let time_source = handle.time_source().clone();
+            let deadline_tick = time_source.deadline_to_tick(deadline);
+            let duration = deadline_tick.checked_sub(time_source.now()).unwrap_or(0);
+
+            let location = location.expect("should have location if tracing");
+            let resource_span = tracing::trace_span!(
+                "runtime.resource",
+                concrete_type = "Sleep",
+                kind = "timer",
+                loc.file = location.file(),
+                loc.line = location.line(),
+                loc.col = location.column(),
+            );
+
+            let async_op_span = resource_span.in_scope(|| {
+                tracing::trace!(
+                    target: "runtime::resource::state_update",
+                    duration = duration,
+                    duration.unit = "ms",
+                    duration.op = "override",
+                );
+
+                tracing::trace_span!("runtime.resource.async_op", source = "Sleep::new_timeout")
+            });
+
+            let async_op_poll_span =
+                async_op_span.in_scope(|| tracing::trace_span!("runtime.resource.async_op.poll"));
+
+            let ctx = trace::AsyncOpTracingCtx {
+                async_op_span,
+                async_op_poll_span,
+                resource_span,
+            };
+
+            Inner {
+                deadline,
+                ctx,
+                time_source,
+            }
+        };
+
+        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+        let inner = Inner { deadline };
+
+        Sleep { inner, entry }
+    }
+
+    pub(crate) fn far_future(location: Option<&'static Location<'static>>) -> Sleep {
+        Self::new_timeout(Instant::far_future(), location)
+    }
+
+    /// Returns the instant at which the future will complete.
+    pub fn deadline(&self) -> Instant {
+        self.inner.deadline
+    }
+
+    /// Returns `true` if `Sleep` has elapsed.
+    ///
+    /// A `Sleep` instance is elapsed when the requested duration has elapsed.
+    pub fn is_elapsed(&self) -> bool {
+        self.entry.is_elapsed()
+    }
+
+    /// Resets the `Sleep` instance to a new deadline.
+    ///
+    /// Calling this function allows changing the instant at which the `Sleep`
+    /// future completes without having to create new associated state.
+    ///
+    /// This function can be called both before and after the future has
+    /// completed.
+    ///
+    /// To call this method, you will usually combine the call with
+    /// [`Pin::as_mut`], which lets you call the method without consuming the
+    /// `Sleep` itself.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use tokio::time::{Duration, Instant};
+    ///
+    /// # #[tokio::main(flavor = "current_thread")]
+    /// # async fn main() {
+    /// let sleep = tokio::time::sleep(Duration::from_millis(10));
+    /// tokio::pin!(sleep);
+    ///
+    /// sleep.as_mut().reset(Instant::now() + Duration::from_millis(20));
+    /// # }
+    /// ```
+    ///
+    /// See also the top-level examples.
+    ///
+    /// [`Pin::as_mut`]: fn@std::pin::Pin::as_mut
+    pub fn reset(self: Pin<&mut Self>, deadline: Instant) {
+        self.reset_inner(deadline)
+    }
+
+    fn reset_inner(self: Pin<&mut Self>, deadline: Instant) {
+        let me = self.project();
+        me.entry.reset(deadline);
+        (*me.inner).deadline = deadline;
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        {
+            let _resource_enter = me.inner.ctx.resource_span.enter();
+            me.inner.ctx.async_op_span =
+                tracing::trace_span!("runtime.resource.async_op", source = "Sleep::reset");
+            let _async_op_enter = me.inner.ctx.async_op_span.enter();
+
+            me.inner.ctx.async_op_poll_span =
+                tracing::trace_span!("runtime.resource.async_op.poll");
+
+            let duration = {
+                let now = me.inner.time_source.now();
+                let deadline_tick = me.inner.time_source.deadline_to_tick(deadline);
+                deadline_tick.checked_sub(now).unwrap_or(0)
+            };
+
+            tracing::trace!(
+                target: "runtime::resource::state_update",
+                duration = duration,
+                duration.unit = "ms",
+                duration.op = "override",
+            );
+        }
+    }
+
+    fn poll_elapsed(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Result<(), Error>> {
+        let me = self.project();
+
+        // Keep track of task budget
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let coop = ready!(trace_poll_op!(
+            "poll_elapsed",
+            crate::coop::poll_proceed(cx),
+        ));
+
+        #[cfg(any(not(tokio_unstable), not(feature = "tracing")))]
+        let coop = ready!(crate::coop::poll_proceed(cx));
+
+        let result = me.entry.poll_elapsed(cx).map(move |r| {
+            coop.made_progress();
+            r
+        });
+
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        return trace_poll_op!("poll_elapsed", result);
+
+        #[cfg(any(not(tokio_unstable), not(feature = "tracing")))]
+        return result;
+    }
+}
+
+impl Future for Sleep {
+    type Output = ();
+
+    // `poll_elapsed` can return an error in two cases:
+    //
+    // - AtCapacity: this is a pathological case where far too many
+    //   sleep instances have been scheduled.
+    // - Shutdown: No timer has been setup, which is a mis-use error.
+    //
+    // Both cases are extremely rare, and pretty accurately fit into
+    // "logic errors", so we just panic in this case. A user couldn't
+    // really do much better if we passed the error onwards.
+    fn poll(mut self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let _res_span = self.inner.ctx.resource_span.clone().entered();
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let _ao_span = self.inner.ctx.async_op_span.clone().entered();
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let _ao_poll_span = self.inner.ctx.async_op_poll_span.clone().entered();
+        match ready!(self.as_mut().poll_elapsed(cx)) {
+            Ok(()) => Poll::Ready(()),
+            Err(e) => panic!("timer error: {}", e),
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/time/driver/tests/mod.rs b/third_party/rust/tokio/src/time/driver/tests/mod.rs
new file mode 100644
index 0000000000..3ac8c75643
--- /dev/null
+++ b/third_party/rust/tokio/src/time/driver/tests/mod.rs
@@ -0,0 +1,301 @@
+use std::{task::Context, time::Duration};
+
+#[cfg(not(loom))]
+use futures::task::noop_waker_ref;
+
+use crate::loom::sync::Arc;
+use crate::loom::thread;
+use crate::{
+    loom::sync::atomic::{AtomicBool, Ordering},
+    park::Unpark,
+};
+
+use super::{Handle, TimerEntry};
+
+struct MockUnpark {}
+impl Unpark for MockUnpark {
+    fn unpark(&self) {}
+}
+impl MockUnpark {
+    fn mock() -> Box<dyn Unpark> {
+        Box::new(Self {})
+    }
+}
+
+fn block_on<T>(f: impl std::future::Future<Output = T>) -> T {
+    #[cfg(loom)]
+    return loom::future::block_on(f);
+
+    #[cfg(not(loom))]
+    {
+        let rt = crate::runtime::Builder::new_current_thread()
+            .build()
+            .unwrap();
+        rt.block_on(f)
+    }
+}
+
+fn model(f: impl Fn() + Send + Sync + 'static) {
+    #[cfg(loom)]
+    loom::model(f);
+
+    #[cfg(not(loom))]
+    f();
+}
+
+#[test]
+fn single_timer() {
+    model(|| {
+        let clock = crate::time::clock::Clock::new(true, false);
+        let time_source = super::ClockTime::new(clock.clone());
+
+        let inner = super::Inner::new(time_source.clone(), MockUnpark::mock());
+        let handle = Handle::new(Arc::new(inner));
+
+        let handle_ = handle.clone();
+        let jh = thread::spawn(move || {
+            let entry = TimerEntry::new(&handle_, clock.now() + Duration::from_secs(1));
+            pin!(entry);
+
+            block_on(futures::future::poll_fn(|cx| {
+                entry.as_mut().poll_elapsed(cx)
+            }))
+            .unwrap();
+        });
+
+        thread::yield_now();
+
+        // This may or may not return Some (depending on how it races with the
+        // thread). If it does return None, however, the timer should complete
+        // synchronously.
+        handle.process_at_time(time_source.now() + 2_000_000_000);
+
+        jh.join().unwrap();
+    })
+}
+
+#[test]
+fn drop_timer() {
+    model(|| {
+        let clock = crate::time::clock::Clock::new(true, false);
+        let time_source = super::ClockTime::new(clock.clone());
+
+        let inner = super::Inner::new(time_source.clone(), MockUnpark::mock());
+        let handle = Handle::new(Arc::new(inner));
+
+        let handle_ = handle.clone();
+        let jh = thread::spawn(move || {
+            let entry = TimerEntry::new(&handle_, clock.now() + Duration::from_secs(1));
+            pin!(entry);
+
+            let _ = entry
+                .as_mut()
+                .poll_elapsed(&mut Context::from_waker(futures::task::noop_waker_ref()));
+            let _ = entry
+                .as_mut()
+                .poll_elapsed(&mut Context::from_waker(futures::task::noop_waker_ref()));
+        });
+
+        thread::yield_now();
+
+        // advance 2s in the future.
+        handle.process_at_time(time_source.now() + 2_000_000_000);
+
+        jh.join().unwrap();
+    })
+}
+
+#[test]
+fn change_waker() {
+    model(|| {
+        let clock = crate::time::clock::Clock::new(true, false);
+        let time_source = super::ClockTime::new(clock.clone());
+
+        let inner = super::Inner::new(time_source.clone(), MockUnpark::mock());
+        let handle = Handle::new(Arc::new(inner));
+
+        let handle_ = handle.clone();
+        let jh = thread::spawn(move || {
+            let entry = TimerEntry::new(&handle_, clock.now() + Duration::from_secs(1));
+            pin!(entry);
+
+            let _ = entry
+                .as_mut()
+                .poll_elapsed(&mut Context::from_waker(futures::task::noop_waker_ref()));
+
+            block_on(futures::future::poll_fn(|cx| {
+                entry.as_mut().poll_elapsed(cx)
+            }))
+            .unwrap();
+        });
+
+        thread::yield_now();
+
+        // advance 2s
+        handle.process_at_time(time_source.now() + 2_000_000_000);
+
+        jh.join().unwrap();
+    })
+}
+
+#[test]
+fn reset_future() {
+    model(|| {
+        let finished_early = Arc::new(AtomicBool::new(false));
+
+        let clock = crate::time::clock::Clock::new(true, false);
+        let time_source = super::ClockTime::new(clock.clone());
+
+        let inner = super::Inner::new(time_source.clone(), MockUnpark::mock());
+        let handle = Handle::new(Arc::new(inner));
+
+        let handle_ = handle.clone();
+        let finished_early_ = finished_early.clone();
+        let start = clock.now();
+
+        let jh = thread::spawn(move || {
+            let entry = TimerEntry::new(&handle_, start + Duration::from_secs(1));
+            pin!(entry);
+
+            let _ = entry
+                .as_mut()
+                .poll_elapsed(&mut Context::from_waker(futures::task::noop_waker_ref()));
+
+            entry.as_mut().reset(start + Duration::from_secs(2));
+
+            // shouldn't complete before 2s
+            block_on(futures::future::poll_fn(|cx| {
+                entry.as_mut().poll_elapsed(cx)
+            }))
+            .unwrap();
+
+            finished_early_.store(true, Ordering::Relaxed);
+        });
+
+        thread::yield_now();
+
+        // This may or may not return a wakeup time.
+        handle.process_at_time(time_source.instant_to_tick(start + Duration::from_millis(1500)));
+
+        assert!(!finished_early.load(Ordering::Relaxed));
+
+        handle.process_at_time(time_source.instant_to_tick(start + Duration::from_millis(2500)));
+
+        jh.join().unwrap();
+
+        assert!(finished_early.load(Ordering::Relaxed));
+    })
+}
+
+#[cfg(not(loom))]
+fn normal_or_miri<T>(normal: T, miri: T) -> T {
+    if cfg!(miri) {
+        miri
+    } else {
+        normal
+    }
+}
+
+#[test]
+#[cfg(not(loom))]
+fn poll_process_levels() {
+    let clock = crate::time::clock::Clock::new(true, false);
+    clock.pause();
+
+    let time_source = super::ClockTime::new(clock.clone());
+
+    let inner = super::Inner::new(time_source, MockUnpark::mock());
+    let handle = Handle::new(Arc::new(inner));
+
+    let mut entries = vec![];
+
+    for i in 0..normal_or_miri(1024, 64) {
+        let mut entry = Box::pin(TimerEntry::new(
+            &handle,
+            clock.now() + Duration::from_millis(i),
+        ));
+
+        let _ = entry
+            .as_mut()
+            .poll_elapsed(&mut Context::from_waker(noop_waker_ref()));
+
+        entries.push(entry);
+    }
+
+    for t in 1..normal_or_miri(1024, 64) {
+        handle.process_at_time(t as u64);
+        for (deadline, future) in entries.iter_mut().enumerate() {
+            let mut context = Context::from_waker(noop_waker_ref());
+            if deadline <= t {
+                assert!(future.as_mut().poll_elapsed(&mut context).is_ready());
+            } else {
+                assert!(future.as_mut().poll_elapsed(&mut context).is_pending());
+            }
+        }
+    }
+}
+
+#[test]
+#[cfg(not(loom))]
+fn poll_process_levels_targeted() {
+    let mut context = Context::from_waker(noop_waker_ref());
+
+    let clock = crate::time::clock::Clock::new(true, false);
+    clock.pause();
+
+    let time_source = super::ClockTime::new(clock.clone());
+
+    let inner = super::Inner::new(time_source, MockUnpark::mock());
+    let handle = Handle::new(Arc::new(inner));
+
+    let e1 = TimerEntry::new(&handle, clock.now() + Duration::from_millis(193));
+    pin!(e1);
+
+    handle.process_at_time(62);
+    assert!(e1.as_mut().poll_elapsed(&mut context).is_pending());
+    handle.process_at_time(192);
+    handle.process_at_time(192);
+}
+
+/*
+#[test]
+fn balanced_incr_and_decr() {
+    const OPS: usize = 5;
+
+    fn incr(inner: Arc<Inner>) {
+        for _ in 0..OPS {
+            inner.increment().expect("increment should not have failed");
+            thread::yield_now();
+        }
+    }
+
+    fn decr(inner: Arc<Inner>) {
+        let mut ops_performed = 0;
+        while ops_performed < OPS {
+            if inner.num(Ordering::Relaxed) > 0 {
+                ops_performed += 1;
+                inner.decrement();
+            }
+            thread::yield_now();
+        }
+    }
+
+    loom::model(|| {
+        let unpark = Box::new(MockUnpark);
+        let instant = Instant::now();
+
+        let inner = Arc::new(Inner::new(instant, unpark));
+
+        let incr_inner = inner.clone();
+        let decr_inner = inner.clone();
+
+        let incr_hndle = thread::spawn(move || incr(incr_inner));
+        let decr_hndle = thread::spawn(move || decr(decr_inner));
+
+        incr_hndle.join().expect("should never fail");
+        decr_hndle.join().expect("should never fail");
+
+        assert_eq!(inner.num(Ordering::SeqCst), 0);
+    })
+}
+*/
diff --git a/third_party/rust/tokio/src/time/driver/wheel/level.rs b/third_party/rust/tokio/src/time/driver/wheel/level.rs
new file mode 100644
index 0000000000..878754177b
--- /dev/null
+++ b/third_party/rust/tokio/src/time/driver/wheel/level.rs
@@ -0,0 +1,276 @@
+use crate::time::driver::TimerHandle;
+
+use crate::time::driver::{EntryList, TimerShared};
+
+use std::{fmt, ptr::NonNull};
+
+/// Wheel for a single level in the timer. This wheel contains 64 slots.
+pub(crate) struct Level {
+    level: usize,
+
+    /// Bit field tracking which slots currently contain entries.
+    ///
+    /// Using a bit field to track slots that contain entries allows avoiding a
+    /// scan to find entries. This field is updated when entries are added or
+    /// removed from a slot.
+    ///
+    /// The least-significant bit represents slot zero.
+    occupied: u64,
+
+    /// Slots. We access these via the EntryInner `current_list` as well, so this needs to be an UnsafeCell.
+    slot: [EntryList; LEVEL_MULT],
+}
+
+/// Indicates when a slot must be processed next.
+#[derive(Debug)]
+pub(crate) struct Expiration {
+    /// The level containing the slot.
+    pub(crate) level: usize,
+
+    /// The slot index.
+    pub(crate) slot: usize,
+
+    /// The instant at which the slot needs to be processed.
+    pub(crate) deadline: u64,
+}
+
+/// Level multiplier.
+///
+/// Being a power of 2 is very important.
+const LEVEL_MULT: usize = 64;
+
+impl Level {
+    pub(crate) fn new(level: usize) -> Level {
+        // A value has to be Copy in order to use syntax like:
+        //     let stack = Stack::default();
+        //     ...
+        //     slots: [stack; 64],
+        //
+        // Alternatively, since Stack is Default one can
+        // use syntax like:
+        //     let slots: [Stack; 64] = Default::default();
+        //
+        // However, that is only supported for arrays of size
+        // 32 or fewer.  So in our case we have to explicitly
+        // invoke the constructor for each array element.
+        let ctor = EntryList::default;
+
+        Level {
+            level,
+            occupied: 0,
+            slot: [
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+                ctor(),
+            ],
+        }
+    }
+
+    /// Finds the slot that needs to be processed next and returns the slot and
+    /// `Instant` at which this slot must be processed.
+    pub(crate) fn next_expiration(&self, now: u64) -> Option<Expiration> {
+        // Use the `occupied` bit field to get the index of the next slot that
+        // needs to be processed.
+        let slot = match self.next_occupied_slot(now) {
+            Some(slot) => slot,
+            None => return None,
+        };
+
+        // From the slot index, calculate the `Instant` at which it needs to be
+        // processed. This value *must* be in the future with respect to `now`.
+
+        let level_range = level_range(self.level);
+        let slot_range = slot_range(self.level);
+
+        // Compute the start date of the current level by masking the low bits
+        // of `now` (`level_range` is a power of 2).
+        let level_start = now & !(level_range - 1);
+        let mut deadline = level_start + slot as u64 * slot_range;
+
+        if deadline <= now {
+            // A timer is in a slot "prior" to the current time. This can occur
+            // because we do not have an infinite hierarchy of timer levels, and
+            // eventually a timer scheduled for a very distant time might end up
+            // being placed in a slot that is beyond the end of all of the
+            // arrays.
+            //
+            // To deal with this, we first limit timers to being scheduled no
+            // more than MAX_DURATION ticks in the future; that is, they're at
+            // most one rotation of the top level away. Then, we force timers
+            // that logically would go into the top+1 level, to instead go into
+            // the top level's slots.
+            //
+            // What this means is that the top level's slots act as a
+            // pseudo-ring buffer, and we rotate around them indefinitely. If we
+            // compute a deadline before now, and it's the top level, it
+            // therefore means we're actually looking at a slot in the future.
+            debug_assert_eq!(self.level, super::NUM_LEVELS - 1);
+
+            deadline += level_range;
+        }
+
+        debug_assert!(
+            deadline >= now,
+            "deadline={:016X}; now={:016X}; level={}; lr={:016X}, sr={:016X}, slot={}; occupied={:b}",
+            deadline,
+            now,
+            self.level,
+            level_range,
+            slot_range,
+            slot,
+            self.occupied
+        );
+
+        Some(Expiration {
+            level: self.level,
+            slot,
+            deadline,
+        })
+    }
+
+    fn next_occupied_slot(&self, now: u64) -> Option<usize> {
+        if self.occupied == 0 {
+            return None;
+        }
+
+        // Get the slot for now using Maths
+        let now_slot = (now / slot_range(self.level)) as usize;
+        let occupied = self.occupied.rotate_right(now_slot as u32);
+        let zeros = occupied.trailing_zeros() as usize;
+        let slot = (zeros + now_slot) % 64;
+
+        Some(slot)
+    }
+
+    pub(crate) unsafe fn add_entry(&mut self, item: TimerHandle) {
+        let slot = slot_for(item.cached_when(), self.level);
+
+        self.slot[slot].push_front(item);
+
+        self.occupied |= occupied_bit(slot);
+    }
+
+    pub(crate) unsafe fn remove_entry(&mut self, item: NonNull<TimerShared>) {
+        let slot = slot_for(unsafe { item.as_ref().cached_when() }, self.level);
+
+        unsafe { self.slot[slot].remove(item) };
+        if self.slot[slot].is_empty() {
+            // The bit is currently set
+            debug_assert!(self.occupied & occupied_bit(slot) != 0);
+
+            // Unset the bit
+            self.occupied ^= occupied_bit(slot);
+        }
+    }
+
+    pub(crate) fn take_slot(&mut self, slot: usize) -> EntryList {
+        self.occupied &= !occupied_bit(slot);
+
+        std::mem::take(&mut self.slot[slot])
+    }
+}
+
+impl fmt::Debug for Level {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt.debug_struct("Level")
+            .field("occupied", &self.occupied)
+            .finish()
+    }
+}
+
+fn occupied_bit(slot: usize) -> u64 {
+    1 << slot
+}
+
+fn slot_range(level: usize) -> u64 {
+    LEVEL_MULT.pow(level as u32) as u64
+}
+
+fn level_range(level: usize) -> u64 {
+    LEVEL_MULT as u64 * slot_range(level)
+}
+
+/// Converts a duration (milliseconds) and a level to a slot position.
+fn slot_for(duration: u64, level: usize) -> usize {
+    ((duration >> (level * 6)) % LEVEL_MULT as u64) as usize
+}
+
+#[cfg(all(test, not(loom)))]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_slot_for() {
+        for pos in 0..64 {
+            assert_eq!(pos as usize, slot_for(pos, 0));
+        }
+
+        for level in 1..5 {
+            for pos in level..64 {
+                let a = pos * 64_usize.pow(level as u32);
+                assert_eq!(pos as usize, slot_for(a as u64, level));
+            }
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/time/driver/wheel/mod.rs b/third_party/rust/tokio/src/time/driver/wheel/mod.rs
new file mode 100644
index 0000000000..f088f2cfd6
--- /dev/null
+++ b/third_party/rust/tokio/src/time/driver/wheel/mod.rs
@@ -0,0 +1,359 @@
+use crate::time::driver::{TimerHandle, TimerShared};
+use crate::time::error::InsertError;
+
+mod level;
+pub(crate) use self::level::Expiration;
+use self::level::Level;
+
+use std::ptr::NonNull;
+
+use super::EntryList;
+
+/// Timing wheel implementation.
+///
+/// This type provides the hashed timing wheel implementation that backs `Timer`
+/// and `DelayQueue`.
+///
+/// The structure is generic over `T: Stack`. This allows handling timeout data
+/// being stored on the heap or in a slab. In order to support the latter case,
+/// the slab must be passed into each function allowing the implementation to
+/// lookup timer entries.
+///
+/// See `Timer` documentation for some implementation notes.
+#[derive(Debug)]
+pub(crate) struct Wheel {
+    /// The number of milliseconds elapsed since the wheel started.
+    elapsed: u64,
+
+    /// Timer wheel.
+    ///
+    /// Levels:
+    ///
+    /// * 1 ms slots / 64 ms range
+    /// * 64 ms slots / ~ 4 sec range
+    /// * ~ 4 sec slots / ~ 4 min range
+    /// * ~ 4 min slots / ~ 4 hr range
+    /// * ~ 4 hr slots / ~ 12 day range
+    /// * ~ 12 day slots / ~ 2 yr range
+    levels: Vec<Level>,
+
+    /// Entries queued for firing
+    pending: EntryList,
+}
+
+/// Number of levels. Each level has 64 slots. By using 6 levels with 64 slots
+/// each, the timer is able to track time up to 2 years into the future with a
+/// precision of 1 millisecond.
+const NUM_LEVELS: usize = 6;
+
+/// The maximum duration of a `Sleep`.
+pub(super) const MAX_DURATION: u64 = (1 << (6 * NUM_LEVELS)) - 1;
+
+impl Wheel {
+    /// Creates a new timing wheel.
+    pub(crate) fn new() -> Wheel {
+        let levels = (0..NUM_LEVELS).map(Level::new).collect();
+
+        Wheel {
+            elapsed: 0,
+            levels,
+            pending: EntryList::new(),
+        }
+    }
+
+    /// Returns the number of milliseconds that have elapsed since the timing
+    /// wheel's creation.
+    pub(crate) fn elapsed(&self) -> u64 {
+        self.elapsed
+    }
+
+    /// Inserts an entry into the timing wheel.
+    ///
+    /// # Arguments
+    ///
+    /// * `item`: The item to insert into the wheel.
+    ///
+    /// # Return
+    ///
+    /// Returns `Ok` when the item is successfully inserted, `Err` otherwise.
+    ///
+    /// `Err(Elapsed)` indicates that `when` represents an instant that has
+    /// already passed. In this case, the caller should fire the timeout
+    /// immediately.
+    ///
+    /// `Err(Invalid)` indicates an invalid `when` argument as been supplied.
+    ///
+    /// # Safety
+    ///
+    /// This function registers item into an intrusive linked list. The caller
+    /// must ensure that `item` is pinned and will not be dropped without first
+    /// being deregistered.
+    pub(crate) unsafe fn insert(
+        &mut self,
+        item: TimerHandle,
+    ) -> Result<u64, (TimerHandle, InsertError)> {
+        let when = item.sync_when();
+
+        if when <= self.elapsed {
+            return Err((item, InsertError::Elapsed));
+        }
+
+        // Get the level at which the entry should be stored
+        let level = self.level_for(when);
+
+        unsafe {
+            self.levels[level].add_entry(item);
+        }
+
+        debug_assert!({
+            self.levels[level]
+                .next_expiration(self.elapsed)
+                .map(|e| e.deadline >= self.elapsed)
+                .unwrap_or(true)
+        });
+
+        Ok(when)
+    }
+
+    /// Removes `item` from the timing wheel.
+    pub(crate) unsafe fn remove(&mut self, item: NonNull<TimerShared>) {
+        unsafe {
+            let when = item.as_ref().cached_when();
+            if when == u64::MAX {
+                self.pending.remove(item);
+            } else {
+                debug_assert!(
+                    self.elapsed <= when,
+                    "elapsed={}; when={}",
+                    self.elapsed,
+                    when
+                );
+
+                let level = self.level_for(when);
+
+                self.levels[level].remove_entry(item);
+            }
+        }
+    }
+
+    /// Instant at which to poll.
+    pub(crate) fn poll_at(&self) -> Option<u64> {
+        self.next_expiration().map(|expiration| expiration.deadline)
+    }
+
+    /// Advances the timer up to the instant represented by `now`.
+    pub(crate) fn poll(&mut self, now: u64) -> Option<TimerHandle> {
+        loop {
+            if let Some(handle) = self.pending.pop_back() {
+                return Some(handle);
+            }
+
+            // under what circumstances is poll.expiration Some vs. None?
+            let expiration = self.next_expiration().and_then(|expiration| {
+                if expiration.deadline > now {
+                    None
+                } else {
+                    Some(expiration)
+                }
+            });
+
+            match expiration {
+                Some(ref expiration) if expiration.deadline > now => return None,
+                Some(ref expiration) => {
+                    self.process_expiration(expiration);
+
+                    self.set_elapsed(expiration.deadline);
+                }
+                None => {
+                    // in this case the poll did not indicate an expiration
+                    // _and_ we were not able to find a next expiration in
+                    // the current list of timers.  advance to the poll's
+                    // current time and do nothing else.
+                    self.set_elapsed(now);
+                    break;
+                }
+            }
+        }
+
+        self.pending.pop_back()
+    }
+
+    /// Returns the instant at which the next timeout expires.
+    fn next_expiration(&self) -> Option<Expiration> {
+        if !self.pending.is_empty() {
+            // Expire immediately as we have things pending firing
+            return Some(Expiration {
+                level: 0,
+                slot: 0,
+                deadline: self.elapsed,
+            });
+        }
+
+        // Check all levels
+        for level in 0..NUM_LEVELS {
+            if let Some(expiration) = self.levels[level].next_expiration(self.elapsed) {
+                // There cannot be any expirations at a higher level that happen
+                // before this one.
+                debug_assert!(self.no_expirations_before(level + 1, expiration.deadline));
+
+                return Some(expiration);
+            }
+        }
+
+        None
+    }
+
+    /// Returns the tick at which this timer wheel next needs to perform some
+    /// processing, or None if there are no timers registered.
+    pub(super) fn next_expiration_time(&self) -> Option<u64> {
+        self.next_expiration().map(|ex| ex.deadline)
+    }
+
+    /// Used for debug assertions
+    fn no_expirations_before(&self, start_level: usize, before: u64) -> bool {
+        let mut res = true;
+
+        for l2 in start_level..NUM_LEVELS {
+            if let Some(e2) = self.levels[l2].next_expiration(self.elapsed) {
+                if e2.deadline < before {
+                    res = false;
+                }
+            }
+        }
+
+        res
+    }
+
+    /// iteratively find entries that are between the wheel's current
+    /// time and the expiration time.  for each in that population either
+    /// queue it for notification (in the case of the last level) or tier
+    /// it down to the next level (in all other cases).
+    pub(crate) fn process_expiration(&mut self, expiration: &Expiration) {
+        // Note that we need to take _all_ of the entries off the list before
+        // processing any of them. This is important because it's possible that
+        // those entries might need to be reinserted into the same slot.
+        //
+        // This happens only on the highest level, when an entry is inserted
+        // more than MAX_DURATION into the future. When this happens, we wrap
+        // around, and process some entries a multiple of MAX_DURATION before
+        // they actually need to be dropped down a level. We then reinsert them
+        // back into the same position; we must make sure we don't then process
+        // those entries again or we'll end up in an infinite loop.
+        let mut entries = self.take_entries(expiration);
+
+        while let Some(item) = entries.pop_back() {
+            if expiration.level == 0 {
+                debug_assert_eq!(unsafe { item.cached_when() }, expiration.deadline);
+            }
+
+            // Try to expire the entry; this is cheap (doesn't synchronize) if
+            // the timer is not expired, and updates cached_when.
+            match unsafe { item.mark_pending(expiration.deadline) } {
+                Ok(()) => {
+                    // Item was expired
+                    self.pending.push_front(item);
+                }
+                Err(expiration_tick) => {
+                    let level = level_for(expiration.deadline, expiration_tick);
+                    unsafe {
+                        self.levels[level].add_entry(item);
+                    }
+                }
+            }
+        }
+    }
+
+    fn set_elapsed(&mut self, when: u64) {
+        assert!(
+            self.elapsed <= when,
+            "elapsed={:?}; when={:?}",
+            self.elapsed,
+            when
+        );
+
+        if when > self.elapsed {
+            self.elapsed = when;
+        }
+    }
+
+    /// Obtains the list of entries that need processing for the given expiration.
+    ///
+    fn take_entries(&mut self, expiration: &Expiration) -> EntryList {
+        self.levels[expiration.level].take_slot(expiration.slot)
+    }
+
+    fn level_for(&self, when: u64) -> usize {
+        level_for(self.elapsed, when)
+    }
+}
+
+fn level_for(elapsed: u64, when: u64) -> usize {
+    const SLOT_MASK: u64 = (1 << 6) - 1;
+
+    // Mask in the trailing bits ignored by the level calculation in order to cap
+    // the possible leading zeros
+    let mut masked = elapsed ^ when | SLOT_MASK;
+
+    if masked >= MAX_DURATION {
+        // Fudge the timer into the top level
+        masked = MAX_DURATION - 1;
+    }
+
+    let leading_zeros = masked.leading_zeros() as usize;
+    let significant = 63 - leading_zeros;
+
+    significant / 6
+}
+
+#[cfg(all(test, not(loom)))]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_level_for() {
+        for pos in 0..64 {
+            assert_eq!(
+                0,
+                level_for(0, pos),
+                "level_for({}) -- binary = {:b}",
+                pos,
+                pos
+            );
+        }
+
+        for level in 1..5 {
+            for pos in level..64 {
+                let a = pos * 64_usize.pow(level as u32);
+                assert_eq!(
+                    level,
+                    level_for(0, a as u64),
+                    "level_for({}) -- binary = {:b}",
+                    a,
+                    a
+                );
+
+                if pos > level {
+                    let a = a - 1;
+                    assert_eq!(
+                        level,
+                        level_for(0, a as u64),
+                        "level_for({}) -- binary = {:b}",
+                        a,
+                        a
+                    );
+                }
+
+                if pos < 64 {
+                    let a = a + 1;
+                    assert_eq!(
+                        level,
+                        level_for(0, a as u64),
+                        "level_for({}) -- binary = {:b}",
+                        a,
+                        a
+                    );
+                }
+            }
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/time/driver/wheel/stack.rs b/third_party/rust/tokio/src/time/driver/wheel/stack.rs
new file mode 100644
index 0000000000..80651c309e
--- /dev/null
+++ b/third_party/rust/tokio/src/time/driver/wheel/stack.rs
@@ -0,0 +1,112 @@
+use super::{Item, OwnedItem};
+use crate::time::driver::Entry;
+
+use std::ptr;
+
+/// A doubly linked stack.
+#[derive(Debug)]
+pub(crate) struct Stack {
+    head: Option<OwnedItem>,
+}
+
+impl Default for Stack {
+    fn default() -> Stack {
+        Stack { head: None }
+    }
+}
+
+impl Stack {
+    pub(crate) fn is_empty(&self) -> bool {
+        self.head.is_none()
+    }
+
+    pub(crate) fn push(&mut self, entry: OwnedItem) {
+        // Get a pointer to the entry to for the prev link
+        let ptr: *const Entry = &*entry as *const _;
+
+        // Remove the old head entry
+        let old = self.head.take();
+
+        unsafe {
+            // Ensure the entry is not already in a stack.
+            debug_assert!((*entry.next_stack.get()).is_none());
+            debug_assert!((*entry.prev_stack.get()).is_null());
+
+            if let Some(ref entry) = old.as_ref() {
+                debug_assert!({
+                    // The head is not already set to the entry
+                    ptr != &***entry as *const _
+                });
+
+                // Set the previous link on the old head
+                *entry.prev_stack.get() = ptr;
+            }
+
+            // Set this entry's next pointer
+            *entry.next_stack.get() = old;
+        }
+
+        // Update the head pointer
+        self.head = Some(entry);
+    }
+
+    /// Pops an item from the stack.
+    pub(crate) fn pop(&mut self) -> Option<OwnedItem> {
+        let entry = self.head.take();
+
+        unsafe {
+            if let Some(entry) = entry.as_ref() {
+                self.head = (*entry.next_stack.get()).take();
+
+                if let Some(entry) = self.head.as_ref() {
+                    *entry.prev_stack.get() = ptr::null();
+                }
+
+                *entry.prev_stack.get() = ptr::null();
+            }
+        }
+
+        entry
+    }
+
+    pub(crate) fn remove(&mut self, entry: &Item) {
+        unsafe {
+            // Ensure that the entry is in fact contained by the stack
+            debug_assert!({
+                // This walks the full linked list even if an entry is found.
+                let mut next = self.head.as_ref();
+                let mut contains = false;
+
+                while let Some(n) = next {
+                    if entry as *const _ == &**n as *const _ {
+                        debug_assert!(!contains);
+                        contains = true;
+                    }
+
+                    next = (*n.next_stack.get()).as_ref();
+                }
+
+                contains
+            });
+
+            // Unlink `entry` from the next node
+            let next = (*entry.next_stack.get()).take();
+
+            if let Some(next) = next.as_ref() {
+                (*next.prev_stack.get()) = *entry.prev_stack.get();
+            }
+
+            // Unlink `entry` from the prev node
+
+            if let Some(prev) = (*entry.prev_stack.get()).as_ref() {
+                *prev.next_stack.get() = next;
+            } else {
+                // It is the head
+                self.head = next;
+            }
+
+            // Unset the prev pointer
+            *entry.prev_stack.get() = ptr::null();
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/time/error.rs b/third_party/rust/tokio/src/time/error.rs
new file mode 100644
index 0000000000..63f0a3b0bd
--- /dev/null
+++ b/third_party/rust/tokio/src/time/error.rs
@@ -0,0 +1,120 @@
+//! Time error types.
+
+use self::Kind::*;
+use std::error;
+use std::fmt;
+
+/// Errors encountered by the timer implementation.
+///
+/// Currently, there are two different errors that can occur:
+///
+/// * `shutdown` occurs when a timer operation is attempted, but the timer
+///   instance has been dropped. In this case, the operation will never be able
+///   to complete and the `shutdown` error is returned. This is a permanent
+///   error, i.e., once this error is observed, timer operations will never
+///   succeed in the future.
+///
+/// * `at_capacity` occurs when a timer operation is attempted, but the timer
+///   instance is currently handling its maximum number of outstanding sleep instances.
+///   In this case, the operation is not able to be performed at the current
+///   moment, and `at_capacity` is returned. This is a transient error, i.e., at
+///   some point in the future, if the operation is attempted again, it might
+///   succeed. Callers that observe this error should attempt to [shed load]. One
+///   way to do this would be dropping the future that issued the timer operation.
+///
+/// [shed load]: https://en.wikipedia.org/wiki/Load_Shedding
+#[derive(Debug, Copy, Clone)]
+pub struct Error(Kind);
+
+#[derive(Debug, Clone, Copy, Eq, PartialEq)]
+#[repr(u8)]
+pub(crate) enum Kind {
+    Shutdown = 1,
+    AtCapacity = 2,
+    Invalid = 3,
+}
+
+impl From<Kind> for Error {
+    fn from(k: Kind) -> Self {
+        Error(k)
+    }
+}
+
+/// Errors returned by `Timeout`.
+#[derive(Debug, PartialEq)]
+pub struct Elapsed(());
+
+#[derive(Debug)]
+pub(crate) enum InsertError {
+    Elapsed,
+}
+
+// ===== impl Error =====
+
+impl Error {
+    /// Creates an error representing a shutdown timer.
+    pub fn shutdown() -> Error {
+        Error(Shutdown)
+    }
+
+    /// Returns `true` if the error was caused by the timer being shutdown.
+    pub fn is_shutdown(&self) -> bool {
+        matches!(self.0, Kind::Shutdown)
+    }
+
+    /// Creates an error representing a timer at capacity.
+    pub fn at_capacity() -> Error {
+        Error(AtCapacity)
+    }
+
+    /// Returns `true` if the error was caused by the timer being at capacity.
+    pub fn is_at_capacity(&self) -> bool {
+        matches!(self.0, Kind::AtCapacity)
+    }
+
+    /// Creates an error representing a misconfigured timer.
+    pub fn invalid() -> Error {
+        Error(Invalid)
+    }
+
+    /// Returns `true` if the error was caused by the timer being misconfigured.
+    pub fn is_invalid(&self) -> bool {
+        matches!(self.0, Kind::Invalid)
+    }
+}
+
+impl error::Error for Error {}
+
+impl fmt::Display for Error {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use self::Kind::*;
+        let descr = match self.0 {
+            Shutdown => "the timer is shutdown, must be called from the context of Tokio runtime",
+            AtCapacity => "timer is at capacity and cannot create a new entry",
+            Invalid => "timer duration exceeds maximum duration",
+        };
+        write!(fmt, "{}", descr)
+    }
+}
+
+// ===== impl Elapsed =====
+
+impl Elapsed {
+    pub(crate) fn new() -> Self {
+        Elapsed(())
+    }
+}
+
+impl fmt::Display for Elapsed {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        "deadline has elapsed".fmt(fmt)
+    }
+}
+
+impl std::error::Error for Elapsed {}
+
+impl From<Elapsed> for std::io::Error {
+    fn from(_err: Elapsed) -> std::io::Error {
+        std::io::ErrorKind::TimedOut.into()
+    }
+}
diff --git a/third_party/rust/tokio/src/time/instant.rs b/third_party/rust/tokio/src/time/instant.rs
new file mode 100644
index 0000000000..f18492930a
--- /dev/null
+++ b/third_party/rust/tokio/src/time/instant.rs
@@ -0,0 +1,223 @@
+#![allow(clippy::trivially_copy_pass_by_ref)]
+
+use std::fmt;
+use std::ops;
+use std::time::Duration;
+
+/// A measurement of a monotonically nondecreasing clock.
+/// Opaque and useful only with `Duration`.
+///
+/// Instants are always guaranteed to be no less than any previously measured
+/// instant when created, and are often useful for tasks such as measuring
+/// benchmarks or timing how long an operation takes.
+///
+/// Note, however, that instants are not guaranteed to be **steady**. In other
+/// words, each tick of the underlying clock may not be the same length (e.g.
+/// some seconds may be longer than others). An instant may jump forwards or
+/// experience time dilation (slow down or speed up), but it will never go
+/// backwards.
+///
+/// Instants are opaque types that can only be compared to one another. There is
+/// no method to get "the number of seconds" from an instant. Instead, it only
+/// allows measuring the duration between two instants (or comparing two
+/// instants).
+///
+/// The size of an `Instant` struct may vary depending on the target operating
+/// system.
+///
+/// # Note
+///
+/// This type wraps the inner `std` variant and is used to align the Tokio
+/// clock for uses of `now()`. This can be useful for testing where you can
+/// take advantage of `time::pause()` and `time::advance()`.
+#[derive(Clone, Copy, Eq, PartialEq, PartialOrd, Ord, Hash)]
+pub struct Instant {
+    std: std::time::Instant,
+}
+
+impl Instant {
+    /// Returns an instant corresponding to "now".
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::time::Instant;
+    ///
+    /// let now = Instant::now();
+    /// ```
+    pub fn now() -> Instant {
+        variant::now()
+    }
+
+    /// Create a `tokio::time::Instant` from a `std::time::Instant`.
+    pub fn from_std(std: std::time::Instant) -> Instant {
+        Instant { std }
+    }
+
+    pub(crate) fn far_future() -> Instant {
+        // Roughly 30 years from now.
+        // API does not provide a way to obtain max `Instant`
+        // or convert specific date in the future to instant.
+        // 1000 years overflows on macOS, 100 years overflows on FreeBSD.
+        Self::now() + Duration::from_secs(86400 * 365 * 30)
+    }
+
+    /// Convert the value into a `std::time::Instant`.
+    pub fn into_std(self) -> std::time::Instant {
+        self.std
+    }
+
+    /// Returns the amount of time elapsed from another instant to this one, or
+    /// zero duration if that instant is later than this one.
+    pub fn duration_since(&self, earlier: Instant) -> Duration {
+        self.std.saturating_duration_since(earlier.std)
+    }
+
+    /// Returns the amount of time elapsed from another instant to this one, or
+    /// None if that instant is later than this one.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::time::{Duration, Instant, sleep};
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let now = Instant::now();
+    ///     sleep(Duration::new(1, 0)).await;
+    ///     let new_now = Instant::now();
+    ///     println!("{:?}", new_now.checked_duration_since(now));
+    ///     println!("{:?}", now.checked_duration_since(new_now)); // None
+    /// }
+    /// ```
+    pub fn checked_duration_since(&self, earlier: Instant) -> Option<Duration> {
+        self.std.checked_duration_since(earlier.std)
+    }
+
+    /// Returns the amount of time elapsed from another instant to this one, or
+    /// zero duration if that instant is later than this one.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::time::{Duration, Instant, sleep};
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let now = Instant::now();
+    ///     sleep(Duration::new(1, 0)).await;
+    ///     let new_now = Instant::now();
+    ///     println!("{:?}", new_now.saturating_duration_since(now));
+    ///     println!("{:?}", now.saturating_duration_since(new_now)); // 0ns
+    /// }
+    /// ```
+    pub fn saturating_duration_since(&self, earlier: Instant) -> Duration {
+        self.std.saturating_duration_since(earlier.std)
+    }
+
+    /// Returns the amount of time elapsed since this instant was created,
+    /// or zero duration if that this instant is in the future.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::time::{Duration, Instant, sleep};
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let instant = Instant::now();
+    ///     let three_secs = Duration::from_secs(3);
+    ///     sleep(three_secs).await;
+    ///     assert!(instant.elapsed() >= three_secs);
+    /// }
+    /// ```
+    pub fn elapsed(&self) -> Duration {
+        Instant::now().saturating_duration_since(*self)
+    }
+
+    /// Returns `Some(t)` where `t` is the time `self + duration` if `t` can be
+    /// represented as `Instant` (which means it's inside the bounds of the
+    /// underlying data structure), `None` otherwise.
+    pub fn checked_add(&self, duration: Duration) -> Option<Instant> {
+        self.std.checked_add(duration).map(Instant::from_std)
+    }
+
+    /// Returns `Some(t)` where `t` is the time `self - duration` if `t` can be
+    /// represented as `Instant` (which means it's inside the bounds of the
+    /// underlying data structure), `None` otherwise.
+    pub fn checked_sub(&self, duration: Duration) -> Option<Instant> {
+        self.std.checked_sub(duration).map(Instant::from_std)
+    }
+}
+
+impl From<std::time::Instant> for Instant {
+    fn from(time: std::time::Instant) -> Instant {
+        Instant::from_std(time)
+    }
+}
+
+impl From<Instant> for std::time::Instant {
+    fn from(time: Instant) -> std::time::Instant {
+        time.into_std()
+    }
+}
+
+impl ops::Add<Duration> for Instant {
+    type Output = Instant;
+
+    fn add(self, other: Duration) -> Instant {
+        Instant::from_std(self.std + other)
+    }
+}
+
+impl ops::AddAssign<Duration> for Instant {
+    fn add_assign(&mut self, rhs: Duration) {
+        *self = *self + rhs;
+    }
+}
+
+impl ops::Sub for Instant {
+    type Output = Duration;
+
+    fn sub(self, rhs: Instant) -> Duration {
+        self.std.saturating_duration_since(rhs.std)
+    }
+}
+
+impl ops::Sub<Duration> for Instant {
+    type Output = Instant;
+
+    fn sub(self, rhs: Duration) -> Instant {
+        Instant::from_std(self.std - rhs)
+    }
+}
+
+impl ops::SubAssign<Duration> for Instant {
+    fn sub_assign(&mut self, rhs: Duration) {
+        *self = *self - rhs;
+    }
+}
+
+impl fmt::Debug for Instant {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.std.fmt(fmt)
+    }
+}
+
+#[cfg(not(feature = "test-util"))]
+mod variant {
+    use super::Instant;
+
+    pub(super) fn now() -> Instant {
+        Instant::from_std(std::time::Instant::now())
+    }
+}
+
+#[cfg(feature = "test-util")]
+mod variant {
+    use super::Instant;
+
+    pub(super) fn now() -> Instant {
+        crate::time::clock::now()
+    }
+}
diff --git a/third_party/rust/tokio/src/time/interval.rs b/third_party/rust/tokio/src/time/interval.rs
new file mode 100644
index 0000000000..8ecb15b389
--- /dev/null
+++ b/third_party/rust/tokio/src/time/interval.rs
@@ -0,0 +1,531 @@
+use crate::future::poll_fn;
+use crate::time::{sleep_until, Duration, Instant, Sleep};
+use crate::util::trace;
+
+use std::panic::Location;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+use std::{convert::TryInto, future::Future};
+
+/// Creates new [`Interval`] that yields with interval of `period`. The first
+/// tick completes immediately. The default [`MissedTickBehavior`] is
+/// [`Burst`](MissedTickBehavior::Burst), but this can be configured
+/// by calling [`set_missed_tick_behavior`](Interval::set_missed_tick_behavior).
+///
+/// An interval will tick indefinitely. At any time, the [`Interval`] value can
+/// be dropped. This cancels the interval.
+///
+/// This function is equivalent to
+/// [`interval_at(Instant::now(), period)`](interval_at).
+///
+/// # Panics
+///
+/// This function panics if `period` is zero.
+///
+/// # Examples
+///
+/// ```
+/// use tokio::time::{self, Duration};
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let mut interval = time::interval(Duration::from_millis(10));
+///
+///     interval.tick().await; // ticks immediately
+///     interval.tick().await; // ticks after 10ms
+///     interval.tick().await; // ticks after 10ms
+///
+///     // approximately 20ms have elapsed.
+/// }
+/// ```
+///
+/// A simple example using `interval` to execute a task every two seconds.
+///
+/// The difference between `interval` and [`sleep`] is that an [`Interval`]
+/// measures the time since the last tick, which means that [`.tick().await`]
+/// may wait for a shorter time than the duration specified for the interval
+/// if some time has passed between calls to [`.tick().await`].
+///
+/// If the tick in the example below was replaced with [`sleep`], the task
+/// would only be executed once every three seconds, and not every two
+/// seconds.
+///
+/// ```
+/// use tokio::time;
+///
+/// async fn task_that_takes_a_second() {
+///     println!("hello");
+///     time::sleep(time::Duration::from_secs(1)).await
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let mut interval = time::interval(time::Duration::from_secs(2));
+///     for _i in 0..5 {
+///         interval.tick().await;
+///         task_that_takes_a_second().await;
+///     }
+/// }
+/// ```
+///
+/// [`sleep`]: crate::time::sleep()
+/// [`.tick().await`]: Interval::tick
+#[track_caller]
+pub fn interval(period: Duration) -> Interval {
+    assert!(period > Duration::new(0, 0), "`period` must be non-zero.");
+    internal_interval_at(Instant::now(), period, trace::caller_location())
+}
+
+/// Creates new [`Interval`] that yields with interval of `period` with the
+/// first tick completing at `start`. The default [`MissedTickBehavior`] is
+/// [`Burst`](MissedTickBehavior::Burst), but this can be configured
+/// by calling [`set_missed_tick_behavior`](Interval::set_missed_tick_behavior).
+///
+/// An interval will tick indefinitely. At any time, the [`Interval`] value can
+/// be dropped. This cancels the interval.
+///
+/// # Panics
+///
+/// This function panics if `period` is zero.
+///
+/// # Examples
+///
+/// ```
+/// use tokio::time::{interval_at, Duration, Instant};
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let start = Instant::now() + Duration::from_millis(50);
+///     let mut interval = interval_at(start, Duration::from_millis(10));
+///
+///     interval.tick().await; // ticks after 50ms
+///     interval.tick().await; // ticks after 10ms
+///     interval.tick().await; // ticks after 10ms
+///
+///     // approximately 70ms have elapsed.
+/// }
+/// ```
+#[track_caller]
+pub fn interval_at(start: Instant, period: Duration) -> Interval {
+    assert!(period > Duration::new(0, 0), "`period` must be non-zero.");
+    internal_interval_at(start, period, trace::caller_location())
+}
+
+#[cfg_attr(not(all(tokio_unstable, feature = "tracing")), allow(unused_variables))]
+fn internal_interval_at(
+    start: Instant,
+    period: Duration,
+    location: Option<&'static Location<'static>>,
+) -> Interval {
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    let resource_span = {
+        let location = location.expect("should have location if tracing");
+
+        tracing::trace_span!(
+            "runtime.resource",
+            concrete_type = "Interval",
+            kind = "timer",
+            loc.file = location.file(),
+            loc.line = location.line(),
+            loc.col = location.column(),
+        )
+    };
+
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    let delay = resource_span.in_scope(|| Box::pin(sleep_until(start)));
+
+    #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+    let delay = Box::pin(sleep_until(start));
+
+    Interval {
+        delay,
+        period,
+        missed_tick_behavior: Default::default(),
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        resource_span,
+    }
+}
+
+/// Defines the behavior of an [`Interval`] when it misses a tick.
+///
+/// Sometimes, an [`Interval`]'s tick is missed. For example, consider the
+/// following:
+///
+/// ```
+/// use tokio::time::{self, Duration};
+/// # async fn task_that_takes_one_to_three_millis() {}
+///
+/// #[tokio::main]
+/// async fn main() {
+///     // ticks every 2 milliseconds
+///     let mut interval = time::interval(Duration::from_millis(2));
+///     for _ in 0..5 {
+///         interval.tick().await;
+///         // if this takes more than 2 milliseconds, a tick will be delayed
+///         task_that_takes_one_to_three_millis().await;
+///     }
+/// }
+/// ```
+///
+/// Generally, a tick is missed if too much time is spent without calling
+/// [`Interval::tick()`].
+///
+/// By default, when a tick is missed, [`Interval`] fires ticks as quickly as it
+/// can until it is "caught up" in time to where it should be.
+/// `MissedTickBehavior` can be used to specify a different behavior for
+/// [`Interval`] to exhibit. Each variant represents a different strategy.
+///
+/// Note that because the executor cannot guarantee exact precision with timers,
+/// these strategies will only apply when the delay is greater than 5
+/// milliseconds.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum MissedTickBehavior {
+    /// Ticks as fast as possible until caught up.
+    ///
+    /// When this strategy is used, [`Interval`] schedules ticks "normally" (the
+    /// same as it would have if the ticks hadn't been delayed), which results
+    /// in it firing ticks as fast as possible until it is caught up in time to
+    /// where it should be. Unlike [`Delay`] and [`Skip`], the ticks yielded
+    /// when `Burst` is used (the [`Instant`]s that [`tick`](Interval::tick)
+    /// yields) aren't different than they would have been if a tick had not
+    /// been missed. Like [`Skip`], and unlike [`Delay`], the ticks may be
+    /// shortened.
+    ///
+    /// This looks something like this:
+    /// ```text
+    /// Expected ticks: |     1     |     2     |     3     |     4     |     5     |     6     |
+    /// Actual ticks:   | work -----|          delay          | work | work | work -| work -----|
+    /// ```
+    ///
+    /// In code:
+    ///
+    /// ```
+    /// use tokio::time::{interval, Duration};
+    /// # async fn task_that_takes_200_millis() {}
+    ///
+    /// # #[tokio::main(flavor = "current_thread")]
+    /// # async fn main() {
+    /// let mut interval = interval(Duration::from_millis(50));
+    ///
+    /// task_that_takes_200_millis().await;
+    /// // The `Interval` has missed a tick
+    ///
+    /// // Since we have exceeded our timeout, this will resolve immediately
+    /// interval.tick().await;
+    ///
+    /// // Since we are more than 100ms after the start of `interval`, this will
+    /// // also resolve immediately.
+    /// interval.tick().await;
+    ///
+    /// // Also resolves immediately, because it was supposed to resolve at
+    /// // 150ms after the start of `interval`
+    /// interval.tick().await;
+    ///
+    /// // Resolves immediately
+    /// interval.tick().await;
+    ///
+    /// // Since we have gotten to 200ms after the start of `interval`, this
+    /// // will resolve after 50ms
+    /// interval.tick().await;
+    /// # }
+    /// ```
+    ///
+    /// This is the default behavior when [`Interval`] is created with
+    /// [`interval`] and [`interval_at`].
+    ///
+    /// [`Delay`]: MissedTickBehavior::Delay
+    /// [`Skip`]: MissedTickBehavior::Skip
+    Burst,
+
+    /// Tick at multiples of `period` from when [`tick`] was called, rather than
+    /// from `start`.
+    ///
+    /// When this strategy is used and [`Interval`] has missed a tick, instead
+    /// of scheduling ticks to fire at multiples of `period` from `start` (the
+    /// time when the first tick was fired), it schedules all future ticks to
+    /// happen at a regular `period` from the point when [`tick`] was called.
+    /// Unlike [`Burst`] and [`Skip`], ticks are not shortened, and they aren't
+    /// guaranteed to happen at a multiple of `period` from `start` any longer.
+    ///
+    /// This looks something like this:
+    /// ```text
+    /// Expected ticks: |     1     |     2     |     3     |     4     |     5     |     6     |
+    /// Actual ticks:   | work -----|          delay          | work -----| work -----| work -----|
+    /// ```
+    ///
+    /// In code:
+    ///
+    /// ```
+    /// use tokio::time::{interval, Duration, MissedTickBehavior};
+    /// # async fn task_that_takes_more_than_50_millis() {}
+    ///
+    /// # #[tokio::main(flavor = "current_thread")]
+    /// # async fn main() {
+    /// let mut interval = interval(Duration::from_millis(50));
+    /// interval.set_missed_tick_behavior(MissedTickBehavior::Delay);
+    ///
+    /// task_that_takes_more_than_50_millis().await;
+    /// // The `Interval` has missed a tick
+    ///
+    /// // Since we have exceeded our timeout, this will resolve immediately
+    /// interval.tick().await;
+    ///
+    /// // But this one, rather than also resolving immediately, as might happen
+    /// // with the `Burst` or `Skip` behaviors, will not resolve until
+    /// // 50ms after the call to `tick` up above. That is, in `tick`, when we
+    /// // recognize that we missed a tick, we schedule the next tick to happen
+    /// // 50ms (or whatever the `period` is) from right then, not from when
+    /// // were were *supposed* to tick
+    /// interval.tick().await;
+    /// # }
+    /// ```
+    ///
+    /// [`Burst`]: MissedTickBehavior::Burst
+    /// [`Skip`]: MissedTickBehavior::Skip
+    /// [`tick`]: Interval::tick
+    Delay,
+
+    /// Skips missed ticks and tick on the next multiple of `period` from
+    /// `start`.
+    ///
+    /// When this strategy is used, [`Interval`] schedules the next tick to fire
+    /// at the next-closest tick that is a multiple of `period` away from
+    /// `start` (the point where [`Interval`] first ticked). Like [`Burst`], all
+    /// ticks remain multiples of `period` away from `start`, but unlike
+    /// [`Burst`], the ticks may not be *one* multiple of `period` away from the
+    /// last tick. Like [`Delay`], the ticks are no longer the same as they
+    /// would have been if ticks had not been missed, but unlike [`Delay`], and
+    /// like [`Burst`], the ticks may be shortened to be less than one `period`
+    /// away from each other.
+    ///
+    /// This looks something like this:
+    /// ```text
+    /// Expected ticks: |     1     |     2     |     3     |     4     |     5     |     6     |
+    /// Actual ticks:   | work -----|          delay          | work ---| work -----| work -----|
+    /// ```
+    ///
+    /// In code:
+    ///
+    /// ```
+    /// use tokio::time::{interval, Duration, MissedTickBehavior};
+    /// # async fn task_that_takes_75_millis() {}
+    ///
+    /// # #[tokio::main(flavor = "current_thread")]
+    /// # async fn main() {
+    /// let mut interval = interval(Duration::from_millis(50));
+    /// interval.set_missed_tick_behavior(MissedTickBehavior::Skip);
+    ///
+    /// task_that_takes_75_millis().await;
+    /// // The `Interval` has missed a tick
+    ///
+    /// // Since we have exceeded our timeout, this will resolve immediately
+    /// interval.tick().await;
+    ///
+    /// // This one will resolve after 25ms, 100ms after the start of
+    /// // `interval`, which is the closest multiple of `period` from the start
+    /// // of `interval` after the call to `tick` up above.
+    /// interval.tick().await;
+    /// # }
+    /// ```
+    ///
+    /// [`Burst`]: MissedTickBehavior::Burst
+    /// [`Delay`]: MissedTickBehavior::Delay
+    Skip,
+}
+
+impl MissedTickBehavior {
+    /// If a tick is missed, this method is called to determine when the next tick should happen.
+    fn next_timeout(&self, timeout: Instant, now: Instant, period: Duration) -> Instant {
+        match self {
+            Self::Burst => timeout + period,
+            Self::Delay => now + period,
+            Self::Skip => {
+                now + period
+                    - Duration::from_nanos(
+                        ((now - timeout).as_nanos() % period.as_nanos())
+                            .try_into()
+                            // This operation is practically guaranteed not to
+                            // fail, as in order for it to fail, `period` would
+                            // have to be longer than `now - timeout`, and both
+                            // would have to be longer than 584 years.
+                            //
+                            // If it did fail, there's not a good way to pass
+                            // the error along to the user, so we just panic.
+                            .expect(
+                                "too much time has elapsed since the interval was supposed to tick",
+                            ),
+                    )
+            }
+        }
+    }
+}
+
+impl Default for MissedTickBehavior {
+    /// Returns [`MissedTickBehavior::Burst`].
+    ///
+    /// For most usecases, the [`Burst`] strategy is what is desired.
+    /// Additionally, to preserve backwards compatibility, the [`Burst`]
+    /// strategy must be the default. For these reasons,
+    /// [`MissedTickBehavior::Burst`] is the default for [`MissedTickBehavior`].
+    /// See [`Burst`] for more details.
+    ///
+    /// [`Burst`]: MissedTickBehavior::Burst
+    fn default() -> Self {
+        Self::Burst
+    }
+}
+
+/// Interval returned by [`interval`] and [`interval_at`].
+///
+/// This type allows you to wait on a sequence of instants with a certain
+/// duration between each instant. Unlike calling [`sleep`] in a loop, this lets
+/// you count the time spent between the calls to [`sleep`] as well.
+///
+/// An `Interval` can be turned into a `Stream` with [`IntervalStream`].
+///
+/// [`IntervalStream`]: https://docs.rs/tokio-stream/latest/tokio_stream/wrappers/struct.IntervalStream.html
+/// [`sleep`]: crate::time::sleep
+#[derive(Debug)]
+pub struct Interval {
+    /// Future that completes the next time the `Interval` yields a value.
+    delay: Pin<Box<Sleep>>,
+
+    /// The duration between values yielded by `Interval`.
+    period: Duration,
+
+    /// The strategy `Interval` should use when a tick is missed.
+    missed_tick_behavior: MissedTickBehavior,
+
+    #[cfg(all(tokio_unstable, feature = "tracing"))]
+    resource_span: tracing::Span,
+}
+
+impl Interval {
+    /// Completes when the next instant in the interval has been reached.
+    ///
+    /// # Cancel safety
+    ///
+    /// This method is cancellation safe. If `tick` is used as the branch in a `tokio::select!` and
+    /// another branch completes first, then no tick has been consumed.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::time;
+    ///
+    /// use std::time::Duration;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let mut interval = time::interval(Duration::from_millis(10));
+    ///
+    ///     interval.tick().await;
+    ///     interval.tick().await;
+    ///     interval.tick().await;
+    ///
+    ///     // approximately 20ms have elapsed.
+    /// }
+    /// ```
+    pub async fn tick(&mut self) -> Instant {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let resource_span = self.resource_span.clone();
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        let instant = trace::async_op(
+            || poll_fn(|cx| self.poll_tick(cx)),
+            resource_span,
+            "Interval::tick",
+            "poll_tick",
+            false,
+        );
+        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+        let instant = poll_fn(|cx| self.poll_tick(cx));
+
+        instant.await
+    }
+
+    /// Polls for the next instant in the interval to be reached.
+    ///
+    /// This method can return the following values:
+    ///
+    ///  * `Poll::Pending` if the next instant has not yet been reached.
+    ///  * `Poll::Ready(instant)` if the next instant has been reached.
+    ///
+    /// When this method returns `Poll::Pending`, the current task is scheduled
+    /// to receive a wakeup when the instant has elapsed. Note that on multiple
+    /// calls to `poll_tick`, only the [`Waker`](std::task::Waker) from the
+    /// [`Context`] passed to the most recent call is scheduled to receive a
+    /// wakeup.
+    pub fn poll_tick(&mut self, cx: &mut Context<'_>) -> Poll<Instant> {
+        // Wait for the delay to be done
+        ready!(Pin::new(&mut self.delay).poll(cx));
+
+        // Get the time when we were scheduled to tick
+        let timeout = self.delay.deadline();
+
+        let now = Instant::now();
+
+        // If a tick was not missed, and thus we are being called before the
+        // next tick is due, just schedule the next tick normally, one `period`
+        // after `timeout`
+        //
+        // However, if a tick took excessively long and we are now behind,
+        // schedule the next tick according to how the user specified with
+        // `MissedTickBehavior`
+        let next = if now > timeout + Duration::from_millis(5) {
+            self.missed_tick_behavior
+                .next_timeout(timeout, now, self.period)
+        } else {
+            timeout + self.period
+        };
+
+        self.delay.as_mut().reset(next);
+
+        // Return the time when we were scheduled to tick
+        Poll::Ready(timeout)
+    }
+
+    /// Resets the interval to complete one period after the current time.
+    ///
+    /// This method ignores [`MissedTickBehavior`] strategy.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use tokio::time;
+    ///
+    /// use std::time::Duration;
+    ///
+    /// #[tokio::main]
+    /// async fn main() {
+    ///     let mut interval = time::interval(Duration::from_millis(100));
+    ///
+    ///     interval.tick().await;
+    ///
+    ///     time::sleep(Duration::from_millis(50)).await;
+    ///     interval.reset();
+    ///
+    ///     interval.tick().await;
+    ///     interval.tick().await;
+    ///
+    ///     // approximately 250ms have elapsed.
+    /// }
+    /// ```
+    pub fn reset(&mut self) {
+        self.delay.as_mut().reset(Instant::now() + self.period);
+    }
+
+    /// Returns the [`MissedTickBehavior`] strategy currently being used.
+    pub fn missed_tick_behavior(&self) -> MissedTickBehavior {
+        self.missed_tick_behavior
+    }
+
+    /// Sets the [`MissedTickBehavior`] strategy that should be used.
+    pub fn set_missed_tick_behavior(&mut self, behavior: MissedTickBehavior) {
+        self.missed_tick_behavior = behavior;
+    }
+
+    /// Returns the period of the interval.
+    pub fn period(&self) -> Duration {
+        self.period
+    }
+}
diff --git a/third_party/rust/tokio/src/time/mod.rs b/third_party/rust/tokio/src/time/mod.rs
new file mode 100644
index 0000000000..281990ef9a
--- /dev/null
+++ b/third_party/rust/tokio/src/time/mod.rs
@@ -0,0 +1,114 @@
+//! Utilities for tracking time.
+//!
+//! This module provides a number of types for executing code after a set period
+//! of time.
+//!
+//! * [`Sleep`] is a future that does no work and completes at a specific [`Instant`]
+//!   in time.
+//!
+//! * [`Interval`] is a stream yielding a value at a fixed period. It is
+//!   initialized with a [`Duration`] and repeatedly yields each time the duration
+//!   elapses.
+//!
+//! * [`Timeout`]: Wraps a future or stream, setting an upper bound to the amount
+//!   of time it is allowed to execute. If the future or stream does not
+//!   complete in time, then it is canceled and an error is returned.
+//!
+//! These types are sufficient for handling a large number of scenarios
+//! involving time.
+//!
+//! These types must be used from within the context of the [`Runtime`](crate::runtime::Runtime).
+//!
+//! # Examples
+//!
+//! Wait 100ms and print "100 ms have elapsed"
+//!
+//! ```
+//! use std::time::Duration;
+//! use tokio::time::sleep;
+//!
+//! #[tokio::main]
+//! async fn main() {
+//!     sleep(Duration::from_millis(100)).await;
+//!     println!("100 ms have elapsed");
+//! }
+//! ```
+//!
+//! Require that an operation takes no more than 1s.
+//!
+//! ```
+//! use tokio::time::{timeout, Duration};
+//!
+//! async fn long_future() {
+//!     // do work here
+//! }
+//!
+//! # async fn dox() {
+//! let res = timeout(Duration::from_secs(1), long_future()).await;
+//!
+//! if res.is_err() {
+//!     println!("operation timed out");
+//! }
+//! # }
+//! ```
+//!
+//! A simple example using [`interval`] to execute a task every two seconds.
+//!
+//! The difference between [`interval`] and [`sleep`] is that an [`interval`]
+//! measures the time since the last tick, which means that `.tick().await` may
+//! wait for a shorter time than the duration specified for the interval
+//! if some time has passed between calls to `.tick().await`.
+//!
+//! If the tick in the example below was replaced with [`sleep`], the task
+//! would only be executed once every three seconds, and not every two
+//! seconds.
+//!
+//! ```
+//! use tokio::time;
+//!
+//! async fn task_that_takes_a_second() {
+//!     println!("hello");
+//!     time::sleep(time::Duration::from_secs(1)).await
+//! }
+//!
+//! #[tokio::main]
+//! async fn main() {
+//!     let mut interval = time::interval(time::Duration::from_secs(2));
+//!     for _i in 0..5 {
+//!         interval.tick().await;
+//!         task_that_takes_a_second().await;
+//!     }
+//! }
+//! ```
+//!
+//! [`interval`]: crate::time::interval()
+
+mod clock;
+pub(crate) use self::clock::Clock;
+#[cfg(feature = "test-util")]
+pub use clock::{advance, pause, resume};
+
+pub(crate) mod driver;
+
+#[doc(inline)]
+pub use driver::sleep::{sleep, sleep_until, Sleep};
+
+pub mod error;
+
+mod instant;
+pub use self::instant::Instant;
+
+mod interval;
+pub use interval::{interval, interval_at, Interval, MissedTickBehavior};
+
+mod timeout;
+#[doc(inline)]
+pub use timeout::{timeout, timeout_at, Timeout};
+
+#[cfg(test)]
+#[cfg(not(loom))]
+mod tests;
+
+// Re-export for convenience
+#[doc(no_inline)]
+pub use std::time::Duration;
diff --git a/third_party/rust/tokio/src/time/tests/mod.rs b/third_party/rust/tokio/src/time/tests/mod.rs
new file mode 100644
index 0000000000..35e1060aca
--- /dev/null
+++ b/third_party/rust/tokio/src/time/tests/mod.rs
@@ -0,0 +1,22 @@
+mod test_sleep;
+
+use crate::time::{self, Instant};
+use std::time::Duration;
+
+fn assert_send<T: Send>() {}
+fn assert_sync<T: Sync>() {}
+
+#[test]
+fn registration_is_send_and_sync() {
+    use crate::time::Sleep;
+
+    assert_send::<Sleep>();
+    assert_sync::<Sleep>();
+}
+
+#[test]
+#[should_panic]
+fn sleep_is_eager() {
+    let when = Instant::now() + Duration::from_millis(100);
+    let _ = time::sleep_until(when);
+}
diff --git a/third_party/rust/tokio/src/time/tests/test_sleep.rs b/third_party/rust/tokio/src/time/tests/test_sleep.rs
new file mode 100644
index 0000000000..77ca07e319
--- /dev/null
+++ b/third_party/rust/tokio/src/time/tests/test_sleep.rs
@@ -0,0 +1,443 @@
+//use crate::time::driver::{Driver, Entry, Handle};
+
+/*
+macro_rules! poll {
+    ($e:expr) => {
+        $e.enter(|cx, e| e.poll_elapsed(cx))
+    };
+}
+
+#[test]
+fn frozen_utility_returns_correct_advanced_duration() {
+    let clock = Clock::new();
+    clock.pause();
+    let start = clock.now();
+
+    clock.advance(ms(10));
+    assert_eq!(clock.now() - start, ms(10));
+}
+
+#[test]
+fn immediate_sleep() {
+    let (mut driver, clock, handle) = setup();
+    let start = clock.now();
+
+    let when = clock.now();
+    let mut e = task::spawn(sleep_until(&handle, when));
+
+    assert_ready_ok!(poll!(e));
+
+    assert_ok!(driver.park_timeout(Duration::from_millis(1000)));
+
+    // The time has not advanced. The `turn` completed immediately.
+    assert_eq!(clock.now() - start, ms(1000));
+}
+
+#[test]
+fn delayed_sleep_level_0() {
+    let (mut driver, clock, handle) = setup();
+    let start = clock.now();
+
+    for &i in &[1, 10, 60] {
+        // Create a `Sleep` that elapses in the future
+        let mut e = task::spawn(sleep_until(&handle, start + ms(i)));
+
+        // The sleep instance has not elapsed.
+        assert_pending!(poll!(e));
+
+        assert_ok!(driver.park());
+        assert_eq!(clock.now() - start, ms(i));
+
+        assert_ready_ok!(poll!(e));
+    }
+}
+
+#[test]
+fn sub_ms_delayed_sleep() {
+    let (mut driver, clock, handle) = setup();
+
+    for _ in 0..5 {
+        let deadline = clock.now() + ms(1) + Duration::new(0, 1);
+
+        let mut e = task::spawn(sleep_until(&handle, deadline));
+
+        assert_pending!(poll!(e));
+
+        assert_ok!(driver.park());
+        assert_ready_ok!(poll!(e));
+
+        assert!(clock.now() >= deadline);
+
+        clock.advance(Duration::new(0, 1));
+    }
+}
+
+#[test]
+fn delayed_sleep_wrapping_level_0() {
+    let (mut driver, clock, handle) = setup();
+    let start = clock.now();
+
+    assert_ok!(driver.park_timeout(ms(5)));
+    assert_eq!(clock.now() - start, ms(5));
+
+    let mut e = task::spawn(sleep_until(&handle, clock.now() + ms(60)));
+
+    assert_pending!(poll!(e));
+
+    assert_ok!(driver.park());
+    assert_eq!(clock.now() - start, ms(64));
+    assert_pending!(poll!(e));
+
+    assert_ok!(driver.park());
+    assert_eq!(clock.now() - start, ms(65));
+
+    assert_ready_ok!(poll!(e));
+}
+
+#[test]
+fn timer_wrapping_with_higher_levels() {
+    let (mut driver, clock, handle) = setup();
+    let start = clock.now();
+
+    // Set sleep to hit level 1
+    let mut e1 = task::spawn(sleep_until(&handle, clock.now() + ms(64)));
+    assert_pending!(poll!(e1));
+
+    // Turn a bit
+    assert_ok!(driver.park_timeout(ms(5)));
+
+    // Set timeout such that it will hit level 0, but wrap
+    let mut e2 = task::spawn(sleep_until(&handle, clock.now() + ms(60)));
+    assert_pending!(poll!(e2));
+
+    // This should result in s1 firing
+    assert_ok!(driver.park());
+    assert_eq!(clock.now() - start, ms(64));
+
+    assert_ready_ok!(poll!(e1));
+    assert_pending!(poll!(e2));
+
+    assert_ok!(driver.park());
+    assert_eq!(clock.now() - start, ms(65));
+
+    assert_ready_ok!(poll!(e1));
+}
+
+#[test]
+fn sleep_with_deadline_in_past() {
+    let (mut driver, clock, handle) = setup();
+    let start = clock.now();
+
+    // Create `Sleep` that elapsed immediately.
+    let mut e = task::spawn(sleep_until(&handle, clock.now() - ms(100)));
+
+    // Even though the `Sleep` expires in the past, it is not ready yet
+    // because the timer must observe it.
+    assert_ready_ok!(poll!(e));
+
+    // Turn the timer, it runs for the elapsed time
+    assert_ok!(driver.park_timeout(ms(1000)));
+
+    // The time has not advanced. The `turn` completed immediately.
+    assert_eq!(clock.now() - start, ms(1000));
+}
+
+#[test]
+fn delayed_sleep_level_1() {
+    let (mut driver, clock, handle) = setup();
+    let start = clock.now();
+
+    // Create a `Sleep` that elapses in the future
+    let mut e = task::spawn(sleep_until(&handle, clock.now() + ms(234)));
+
+    // The sleep has not elapsed.
+    assert_pending!(poll!(e));
+
+    // Turn the timer, this will wake up to cascade the timer down.
+    assert_ok!(driver.park_timeout(ms(1000)));
+    assert_eq!(clock.now() - start, ms(192));
+
+    // The sleep has not elapsed.
+    assert_pending!(poll!(e));
+
+    // Turn the timer again
+    assert_ok!(driver.park_timeout(ms(1000)));
+    assert_eq!(clock.now() - start, ms(234));
+
+    // The sleep has elapsed.
+    assert_ready_ok!(poll!(e));
+
+    let (mut driver, clock, handle) = setup();
+    let start = clock.now();
+
+    // Create a `Sleep` that elapses in the future
+    let mut e = task::spawn(sleep_until(&handle, clock.now() + ms(234)));
+
+    // The sleep has not elapsed.
+    assert_pending!(poll!(e));
+
+    // Turn the timer with a smaller timeout than the cascade.
+    assert_ok!(driver.park_timeout(ms(100)));
+    assert_eq!(clock.now() - start, ms(100));
+
+    assert_pending!(poll!(e));
+
+    // Turn the timer, this will wake up to cascade the timer down.
+    assert_ok!(driver.park_timeout(ms(1000)));
+    assert_eq!(clock.now() - start, ms(192));
+
+    // The sleep has not elapsed.
+    assert_pending!(poll!(e));
+
+    // Turn the timer again
+    assert_ok!(driver.park_timeout(ms(1000)));
+    assert_eq!(clock.now() - start, ms(234));
+
+    // The sleep has elapsed.
+    assert_ready_ok!(poll!(e));
+}
+
+#[test]
+fn concurrently_set_two_timers_second_one_shorter() {
+    let (mut driver, clock, handle) = setup();
+    let start = clock.now();
+
+    let mut e1 = task::spawn(sleep_until(&handle, clock.now() + ms(500)));
+    let mut e2 = task::spawn(sleep_until(&handle, clock.now() + ms(200)));
+
+    // The sleep has not elapsed
+    assert_pending!(poll!(e1));
+    assert_pending!(poll!(e2));
+
+    // Sleep until a cascade
+    assert_ok!(driver.park());
+    assert_eq!(clock.now() - start, ms(192));
+
+    // Sleep until the second timer.
+    assert_ok!(driver.park());
+    assert_eq!(clock.now() - start, ms(200));
+
+    // The shorter sleep fires
+    assert_ready_ok!(poll!(e2));
+    assert_pending!(poll!(e1));
+
+    assert_ok!(driver.park());
+    assert_eq!(clock.now() - start, ms(448));
+
+    assert_pending!(poll!(e1));
+
+    // Turn again, this time the time will advance to the second sleep
+    assert_ok!(driver.park());
+    assert_eq!(clock.now() - start, ms(500));
+
+    assert_ready_ok!(poll!(e1));
+}
+
+#[test]
+fn short_sleep() {
+    let (mut driver, clock, handle) = setup();
+    let start = clock.now();
+
+    // Create a `Sleep` that elapses in the future
+    let mut e = task::spawn(sleep_until(&handle, clock.now() + ms(1)));
+
+    // The sleep has not elapsed.
+    assert_pending!(poll!(e));
+
+    // Turn the timer, but not enough time will go by.
+    assert_ok!(driver.park());
+
+    // The sleep has elapsed.
+    assert_ready_ok!(poll!(e));
+
+    // The time has advanced to the point of the sleep elapsing.
+    assert_eq!(clock.now() - start, ms(1));
+}
+
+#[test]
+fn sorta_long_sleep_until() {
+    const MIN_5: u64 = 5 * 60 * 1000;
+
+    let (mut driver, clock, handle) = setup();
+    let start = clock.now();
+
+    // Create a `Sleep` that elapses in the future
+    let mut e = task::spawn(sleep_until(&handle, clock.now() + ms(MIN_5)));
+
+    // The sleep has not elapsed.
+    assert_pending!(poll!(e));
+
+    let cascades = &[262_144, 262_144 + 9 * 4096, 262_144 + 9 * 4096 + 15 * 64];
+
+    for &elapsed in cascades {
+        assert_ok!(driver.park());
+        assert_eq!(clock.now() - start, ms(elapsed));
+
+        assert_pending!(poll!(e));
+    }
+
+    assert_ok!(driver.park());
+    assert_eq!(clock.now() - start, ms(MIN_5));
+
+    // The sleep has elapsed.
+    assert_ready_ok!(poll!(e));
+}
+
+#[test]
+fn very_long_sleep() {
+    const MO_5: u64 = 5 * 30 * 24 * 60 * 60 * 1000;
+
+    let (mut driver, clock, handle) = setup();
+    let start = clock.now();
+
+    // Create a `Sleep` that elapses in the future
+    let mut e = task::spawn(sleep_until(&handle, clock.now() + ms(MO_5)));
+
+    // The sleep has not elapsed.
+    assert_pending!(poll!(e));
+
+    let cascades = &[
+        12_884_901_888,
+        12_952_010_752,
+        12_959_875_072,
+        12_959_997_952,
+    ];
+
+    for &elapsed in cascades {
+        assert_ok!(driver.park());
+        assert_eq!(clock.now() - start, ms(elapsed));
+
+        assert_pending!(poll!(e));
+    }
+
+    // Turn the timer, but not enough time will go by.
+    assert_ok!(driver.park());
+
+    // The time has advanced to the point of the sleep elapsing.
+    assert_eq!(clock.now() - start, ms(MO_5));
+
+    // The sleep has elapsed.
+    assert_ready_ok!(poll!(e));
+}
+
+#[test]
+fn unpark_is_delayed() {
+    // A special park that will take much longer than the requested duration
+    struct MockPark(Clock);
+
+    struct MockUnpark;
+
+    impl Park for MockPark {
+        type Unpark = MockUnpark;
+        type Error = ();
+
+        fn unpark(&self) -> Self::Unpark {
+            MockUnpark
+        }
+
+        fn park(&mut self) -> Result<(), Self::Error> {
+            panic!("parking forever");
+        }
+
+        fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
+            assert_eq!(duration, ms(0));
+            self.0.advance(ms(436));
+            Ok(())
+        }
+
+        fn shutdown(&mut self) {}
+    }
+
+    impl Unpark for MockUnpark {
+        fn unpark(&self) {}
+    }
+
+    let clock = Clock::new();
+    clock.pause();
+    let start = clock.now();
+    let mut driver = Driver::new(MockPark(clock.clone()), clock.clone());
+    let handle = driver.handle();
+
+    let mut e1 = task::spawn(sleep_until(&handle, clock.now() + ms(100)));
+    let mut e2 = task::spawn(sleep_until(&handle, clock.now() + ms(101)));
+    let mut e3 = task::spawn(sleep_until(&handle, clock.now() + ms(200)));
+
+    assert_pending!(poll!(e1));
+    assert_pending!(poll!(e2));
+    assert_pending!(poll!(e3));
+
+    assert_ok!(driver.park());
+
+    assert_eq!(clock.now() - start, ms(500));
+
+    assert_ready_ok!(poll!(e1));
+    assert_ready_ok!(poll!(e2));
+    assert_ready_ok!(poll!(e3));
+}
+
+#[test]
+fn set_timeout_at_deadline_greater_than_max_timer() {
+    const YR_1: u64 = 365 * 24 * 60 * 60 * 1000;
+    const YR_5: u64 = 5 * YR_1;
+
+    let (mut driver, clock, handle) = setup();
+    let start = clock.now();
+
+    for _ in 0..5 {
+        assert_ok!(driver.park_timeout(ms(YR_1)));
+    }
+
+    let mut e = task::spawn(sleep_until(&handle, clock.now() + ms(1)));
+    assert_pending!(poll!(e));
+
+    assert_ok!(driver.park_timeout(ms(1000)));
+    assert_eq!(clock.now() - start, ms(YR_5) + ms(1));
+
+    assert_ready_ok!(poll!(e));
+}
+
+fn setup() -> (Driver<MockPark>, Clock, Handle) {
+    let clock = Clock::new();
+    clock.pause();
+    let driver = Driver::new(MockPark(clock.clone()), clock.clone());
+    let handle = driver.handle();
+
+    (driver, clock, handle)
+}
+
+fn sleep_until(handle: &Handle, when: Instant) -> Arc<Entry> {
+    Entry::new(&handle, when, ms(0))
+}
+
+struct MockPark(Clock);
+
+struct MockUnpark;
+
+impl Park for MockPark {
+    type Unpark = MockUnpark;
+    type Error = ();
+
+    fn unpark(&self) -> Self::Unpark {
+        MockUnpark
+    }
+
+    fn park(&mut self) -> Result<(), Self::Error> {
+        panic!("parking forever");
+    }
+
+    fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> {
+        self.0.advance(duration);
+        Ok(())
+    }
+
+    fn shutdown(&mut self) {}
+}
+
+impl Unpark for MockUnpark {
+    fn unpark(&self) {}
+}
+
+fn ms(n: u64) -> Duration {
+    Duration::from_millis(n)
+}
+*/
diff --git a/third_party/rust/tokio/src/time/timeout.rs b/third_party/rust/tokio/src/time/timeout.rs
new file mode 100644
index 0000000000..4a93089e8e
--- /dev/null
+++ b/third_party/rust/tokio/src/time/timeout.rs
@@ -0,0 +1,202 @@
+//! Allows a future to execute for a maximum amount of time.
+//!
+//! See [`Timeout`] documentation for more details.
+//!
+//! [`Timeout`]: struct@Timeout
+
+use crate::{
+    coop,
+    time::{error::Elapsed, sleep_until, Duration, Instant, Sleep},
+    util::trace,
+};
+
+use pin_project_lite::pin_project;
+use std::future::Future;
+use std::pin::Pin;
+use std::task::{self, Poll};
+
+/// Requires a `Future` to complete before the specified duration has elapsed.
+///
+/// If the future completes before the duration has elapsed, then the completed
+/// value is returned. Otherwise, an error is returned and the future is
+/// canceled.
+///
+/// # Cancelation
+///
+/// Cancelling a timeout is done by dropping the future. No additional cleanup
+/// or other work is required.
+///
+/// The original future may be obtained by calling [`Timeout::into_inner`]. This
+/// consumes the `Timeout`.
+///
+/// # Examples
+///
+/// Create a new `Timeout` set to expire in 10 milliseconds.
+///
+/// ```rust
+/// use tokio::time::timeout;
+/// use tokio::sync::oneshot;
+///
+/// use std::time::Duration;
+///
+/// # async fn dox() {
+/// let (tx, rx) = oneshot::channel();
+/// # tx.send(()).unwrap();
+///
+/// // Wrap the future with a `Timeout` set to expire in 10 milliseconds.
+/// if let Err(_) = timeout(Duration::from_millis(10), rx).await {
+///     println!("did not receive value within 10 ms");
+/// }
+/// # }
+/// ```
+///
+/// # Panics
+///
+/// This function panics if there is no current timer set.
+///
+/// It can be triggered when [`Builder::enable_time`] or
+/// [`Builder::enable_all`] are not included in the builder.
+///
+/// It can also panic whenever a timer is created outside of a
+/// Tokio runtime. That is why `rt.block_on(sleep(...))` will panic,
+/// since the function is executed outside of the runtime.
+/// Whereas `rt.block_on(async {sleep(...).await})` doesn't panic.
+/// And this is because wrapping the function on an async makes it lazy,
+/// and so gets executed inside the runtime successfully without
+/// panicking.
+///
+/// [`Builder::enable_time`]: crate::runtime::Builder::enable_time
+/// [`Builder::enable_all`]: crate::runtime::Builder::enable_all
+#[track_caller]
+pub fn timeout<T>(duration: Duration, future: T) -> Timeout<T>
+where
+    T: Future,
+{
+    let location = trace::caller_location();
+
+    let deadline = Instant::now().checked_add(duration);
+    let delay = match deadline {
+        Some(deadline) => Sleep::new_timeout(deadline, location),
+        None => Sleep::far_future(location),
+    };
+    Timeout::new_with_delay(future, delay)
+}
+
+/// Requires a `Future` to complete before the specified instant in time.
+///
+/// If the future completes before the instant is reached, then the completed
+/// value is returned. Otherwise, an error is returned.
+///
+/// # Cancelation
+///
+/// Cancelling a timeout is done by dropping the future. No additional cleanup
+/// or other work is required.
+///
+/// The original future may be obtained by calling [`Timeout::into_inner`]. This
+/// consumes the `Timeout`.
+///
+/// # Examples
+///
+/// Create a new `Timeout` set to expire in 10 milliseconds.
+///
+/// ```rust
+/// use tokio::time::{Instant, timeout_at};
+/// use tokio::sync::oneshot;
+///
+/// use std::time::Duration;
+///
+/// # async fn dox() {
+/// let (tx, rx) = oneshot::channel();
+/// # tx.send(()).unwrap();
+///
+/// // Wrap the future with a `Timeout` set to expire 10 milliseconds into the
+/// // future.
+/// if let Err(_) = timeout_at(Instant::now() + Duration::from_millis(10), rx).await {
+///     println!("did not receive value within 10 ms");
+/// }
+/// # }
+/// ```
+pub fn timeout_at<T>(deadline: Instant, future: T) -> Timeout<T>
+where
+    T: Future,
+{
+    let delay = sleep_until(deadline);
+
+    Timeout {
+        value: future,
+        delay,
+    }
+}
+
+pin_project! {
+    /// Future returned by [`timeout`](timeout) and [`timeout_at`](timeout_at).
+    #[must_use = "futures do nothing unless you `.await` or poll them"]
+    #[derive(Debug)]
+    pub struct Timeout<T> {
+        #[pin]
+        value: T,
+        #[pin]
+        delay: Sleep,
+    }
+}
+
+impl<T> Timeout<T> {
+    pub(crate) fn new_with_delay(value: T, delay: Sleep) -> Timeout<T> {
+        Timeout { value, delay }
+    }
+
+    /// Gets a reference to the underlying value in this timeout.
+    pub fn get_ref(&self) -> &T {
+        &self.value
+    }
+
+    /// Gets a mutable reference to the underlying value in this timeout.
+    pub fn get_mut(&mut self) -> &mut T {
+        &mut self.value
+    }
+
+    /// Consumes this timeout, returning the underlying value.
+    pub fn into_inner(self) -> T {
+        self.value
+    }
+}
+
+impl<T> Future for Timeout<T>
+where
+    T: Future,
+{
+    type Output = Result<T::Output, Elapsed>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut task::Context<'_>) -> Poll<Self::Output> {
+        let me = self.project();
+
+        let had_budget_before = coop::has_budget_remaining();
+
+        // First, try polling the future
+        if let Poll::Ready(v) = me.value.poll(cx) {
+            return Poll::Ready(Ok(v));
+        }
+
+        let has_budget_now = coop::has_budget_remaining();
+
+        let delay = me.delay;
+
+        let poll_delay = || -> Poll<Self::Output> {
+            match delay.poll(cx) {
+                Poll::Ready(()) => Poll::Ready(Err(Elapsed::new())),
+                Poll::Pending => Poll::Pending,
+            }
+        };
+
+        if let (true, false) = (had_budget_before, has_budget_now) {
+            // if it is the underlying future that exhausted the budget, we poll
+            // the `delay` with an unconstrained one. This prevents pathological
+            // cases where the underlying future always exhausts the budget and
+            // we never get a chance to evaluate whether the timeout was hit or
+            // not.
+            coop::with_unconstrained(poll_delay)
+        } else {
+            poll_delay()
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/util/atomic_cell.rs b/third_party/rust/tokio/src/util/atomic_cell.rs
new file mode 100644
index 0000000000..07e37303a7
--- /dev/null
+++ b/third_party/rust/tokio/src/util/atomic_cell.rs
@@ -0,0 +1,51 @@
+use crate::loom::sync::atomic::AtomicPtr;
+
+use std::ptr;
+use std::sync::atomic::Ordering::AcqRel;
+
+pub(crate) struct AtomicCell<T> {
+    data: AtomicPtr<T>,
+}
+
+unsafe impl<T: Send> Send for AtomicCell<T> {}
+unsafe impl<T: Send> Sync for AtomicCell<T> {}
+
+impl<T> AtomicCell<T> {
+    pub(crate) fn new(data: Option<Box<T>>) -> AtomicCell<T> {
+        AtomicCell {
+            data: AtomicPtr::new(to_raw(data)),
+        }
+    }
+
+    pub(crate) fn swap(&self, val: Option<Box<T>>) -> Option<Box<T>> {
+        let old = self.data.swap(to_raw(val), AcqRel);
+        from_raw(old)
+    }
+
+    pub(crate) fn set(&self, val: Box<T>) {
+        let _ = self.swap(Some(val));
+    }
+
+    pub(crate) fn take(&self) -> Option<Box<T>> {
+        self.swap(None)
+    }
+}
+
+fn to_raw<T>(data: Option<Box<T>>) -> *mut T {
+    data.map(Box::into_raw).unwrap_or(ptr::null_mut())
+}
+
+fn from_raw<T>(val: *mut T) -> Option<Box<T>> {
+    if val.is_null() {
+        None
+    } else {
+        Some(unsafe { Box::from_raw(val) })
+    }
+}
+
+impl<T> Drop for AtomicCell<T> {
+    fn drop(&mut self) {
+        // Free any data still held by the cell
+        let _ = self.take();
+    }
+}
diff --git a/third_party/rust/tokio/src/util/bit.rs b/third_party/rust/tokio/src/util/bit.rs
new file mode 100644
index 0000000000..a43c2c2d36
--- /dev/null
+++ b/third_party/rust/tokio/src/util/bit.rs
@@ -0,0 +1,77 @@
+use std::fmt;
+
+#[derive(Clone, Copy, PartialEq)]
+pub(crate) struct Pack {
+    mask: usize,
+    shift: u32,
+}
+
+impl Pack {
+    /// Value is packed in the `width` least-significant bits.
+    pub(crate) const fn least_significant(width: u32) -> Pack {
+        let mask = mask_for(width);
+
+        Pack { mask, shift: 0 }
+    }
+
+    /// Value is packed in the `width` more-significant bits.
+    pub(crate) const fn then(&self, width: u32) -> Pack {
+        let shift = pointer_width() - self.mask.leading_zeros();
+        let mask = mask_for(width) << shift;
+
+        Pack { mask, shift }
+    }
+
+    /// Width, in bits, dedicated to storing the value.
+    pub(crate) const fn width(&self) -> u32 {
+        pointer_width() - (self.mask >> self.shift).leading_zeros()
+    }
+
+    /// Max representable value.
+    pub(crate) const fn max_value(&self) -> usize {
+        (1 << self.width()) - 1
+    }
+
+    pub(crate) fn pack(&self, value: usize, base: usize) -> usize {
+        assert!(value <= self.max_value());
+        (base & !self.mask) | (value << self.shift)
+    }
+
+    /// Packs the value with `base`, losing any bits of `value` that fit.
+    ///
+    /// If `value` is larger than the max value that can be represented by the
+    /// allotted width, the most significant bits are truncated.
+    pub(crate) fn pack_lossy(&self, value: usize, base: usize) -> usize {
+        self.pack(value & self.max_value(), base)
+    }
+
+    pub(crate) fn unpack(&self, src: usize) -> usize {
+        unpack(src, self.mask, self.shift)
+    }
+}
+
+impl fmt::Debug for Pack {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(
+            fmt,
+            "Pack {{ mask: {:b}, shift: {} }}",
+            self.mask, self.shift
+        )
+    }
+}
+
+/// Returns the width of a pointer in bits.
+pub(crate) const fn pointer_width() -> u32 {
+    std::mem::size_of::<usize>() as u32 * 8
+}
+
+/// Returns a `usize` with the right-most `n` bits set.
+pub(crate) const fn mask_for(n: u32) -> usize {
+    let shift = 1usize.wrapping_shl(n - 1);
+    shift | (shift - 1)
+}
+
+/// Unpacks a value using a mask & shift.
+pub(crate) const fn unpack(src: usize, mask: usize, shift: u32) -> usize {
+    (src & mask) >> shift
+}
diff --git a/third_party/rust/tokio/src/util/error.rs b/third_party/rust/tokio/src/util/error.rs
new file mode 100644
index 0000000000..8f252c0c91
--- /dev/null
+++ b/third_party/rust/tokio/src/util/error.rs
@@ -0,0 +1,17 @@
+/// Error string explaining that the Tokio context hasn't been instantiated.
+pub(crate) const CONTEXT_MISSING_ERROR: &str =
+    "there is no reactor running, must be called from the context of a Tokio 1.x runtime";
+
+// some combinations of features might not use this
+#[allow(dead_code)]
+/// Error string explaining that the Tokio context is shutting down and cannot drive timers.
+pub(crate) const RUNTIME_SHUTTING_DOWN_ERROR: &str =
+    "A Tokio 1.x context was found, but it is being shutdown.";
+
+// some combinations of features might not use this
+#[allow(dead_code)]
+/// Error string explaining that the Tokio context is not available because the
+/// thread-local storing it has been destroyed. This usually only happens during
+/// destructors of other thread-locals.
+pub(crate) const THREAD_LOCAL_DESTROYED_ERROR: &str =
+    "The Tokio context thread-local variable has been destroyed.";
diff --git a/third_party/rust/tokio/src/util/idle_notified_set.rs b/third_party/rust/tokio/src/util/idle_notified_set.rs
new file mode 100644
index 0000000000..71f3a32a85
--- /dev/null
+++ b/third_party/rust/tokio/src/util/idle_notified_set.rs
@@ -0,0 +1,463 @@
+//! This module defines an `IdleNotifiedSet`, which is a collection of elements.
+//! Each element is intended to correspond to a task, and the collection will
+//! keep track of which tasks have had their waker notified, and which have not.
+//!
+//! Each entry in the set holds some user-specified value. The value's type is
+//! specified using the `T` parameter. It will usually be a `JoinHandle` or
+//! similar.
+
+use std::marker::PhantomPinned;
+use std::mem::ManuallyDrop;
+use std::ptr::NonNull;
+use std::task::{Context, Waker};
+
+use crate::loom::cell::UnsafeCell;
+use crate::loom::sync::{Arc, Mutex};
+use crate::util::linked_list::{self, Link};
+use crate::util::{waker_ref, Wake};
+
+type LinkedList<T> =
+    linked_list::LinkedList<ListEntry<T>, <ListEntry<T> as linked_list::Link>::Target>;
+
+/// This is the main handle to the collection.
+pub(crate) struct IdleNotifiedSet<T> {
+    lists: Arc<Lists<T>>,
+    length: usize,
+}
+
+/// A handle to an entry that is guaranteed to be stored in the idle or notified
+/// list of its `IdleNotifiedSet`. This value borrows the `IdleNotifiedSet`
+/// mutably to prevent the entry from being moved to the `Neither` list, which
+/// only the `IdleNotifiedSet` may do.
+///
+/// The main consequence of being stored in one of the lists is that the `value`
+/// field has not yet been consumed.
+///
+/// Note: This entry can be moved from the idle to the notified list while this
+/// object exists by waking its waker.
+pub(crate) struct EntryInOneOfTheLists<'a, T> {
+    entry: Arc<ListEntry<T>>,
+    set: &'a mut IdleNotifiedSet<T>,
+}
+
+type Lists<T> = Mutex<ListsInner<T>>;
+
+/// The linked lists hold strong references to the ListEntry items, and the
+/// ListEntry items also hold a strong reference back to the Lists object, but
+/// the destructor of the `IdleNotifiedSet` will clear the two lists, so once
+/// that object is destroyed, no ref-cycles will remain.
+struct ListsInner<T> {
+    notified: LinkedList<T>,
+    idle: LinkedList<T>,
+    /// Whenever an element in the `notified` list is woken, this waker will be
+    /// notified and consumed, if it exists.
+    waker: Option<Waker>,
+}
+
+/// Which of the two lists in the shared Lists object is this entry stored in?
+///
+/// If the value is `Idle`, then an entry's waker may move it to the notified
+/// list. Otherwise, only the `IdleNotifiedSet` may move it.
+///
+/// If the value is `Neither`, then it is still possible that the entry is in
+/// some third external list (this happens in `drain`).
+#[derive(Copy, Clone, Eq, PartialEq)]
+enum List {
+    Notified,
+    Idle,
+    Neither,
+}
+
+/// An entry in the list.
+///
+/// # Safety
+///
+/// The `my_list` field must only be accessed while holding the mutex in
+/// `parent`. It is an invariant that the value of `my_list` corresponds to
+/// which linked list in the `parent` holds this entry. Once this field takes
+/// the value `Neither`, then it may never be modified again.
+///
+/// If the value of `my_list` is `Notified` or `Idle`, then the `pointers` field
+/// must only be accessed while holding the mutex. If the value of `my_list` is
+/// `Neither`, then the `pointers` field may be accessed by the
+/// `IdleNotifiedSet` (this happens inside `drain`).
+///
+/// The `value` field is owned by the `IdleNotifiedSet` and may only be accessed
+/// by the `IdleNotifiedSet`. The operation that sets the value of `my_list` to
+/// `Neither` assumes ownership of the `value`, and it must either drop it or
+/// move it out from this entry to prevent it from getting leaked. (Since the
+/// two linked lists are emptied in the destructor of `IdleNotifiedSet`, the
+/// value should not be leaked.)
+///
+/// This type is `#[repr(C)]` because its `linked_list::Link` implementation
+/// requires that `pointers` is the first field.
+#[repr(C)]
+struct ListEntry<T> {
+    /// The linked list pointers of the list this entry is in.
+    pointers: linked_list::Pointers<ListEntry<T>>,
+    /// Pointer to the shared `Lists` struct.
+    parent: Arc<Lists<T>>,
+    /// The value stored in this entry.
+    value: UnsafeCell<ManuallyDrop<T>>,
+    /// Used to remember which list this entry is in.
+    my_list: UnsafeCell<List>,
+    /// Required by the `linked_list::Pointers` field.
+    _pin: PhantomPinned,
+}
+
+// With mutable access to the `IdleNotifiedSet`, you can get mutable access to
+// the values.
+unsafe impl<T: Send> Send for IdleNotifiedSet<T> {}
+// With the current API we strictly speaking don't even need `T: Sync`, but we
+// require it anyway to support adding &self APIs that access the values in the
+// future.
+unsafe impl<T: Sync> Sync for IdleNotifiedSet<T> {}
+
+// These impls control when it is safe to create a Waker. Since the waker does
+// not allow access to the value in any way (including its destructor), it is
+// not necessary for `T` to be Send or Sync.
+unsafe impl<T> Send for ListEntry<T> {}
+unsafe impl<T> Sync for ListEntry<T> {}
+
+impl<T> IdleNotifiedSet<T> {
+    /// Create a new IdleNotifiedSet.
+    pub(crate) fn new() -> Self {
+        let lists = Mutex::new(ListsInner {
+            notified: LinkedList::new(),
+            idle: LinkedList::new(),
+            waker: None,
+        });
+
+        IdleNotifiedSet {
+            lists: Arc::new(lists),
+            length: 0,
+        }
+    }
+
+    pub(crate) fn len(&self) -> usize {
+        self.length
+    }
+
+    pub(crate) fn is_empty(&self) -> bool {
+        self.length == 0
+    }
+
+    /// Insert the given value into the `idle` list.
+    pub(crate) fn insert_idle(&mut self, value: T) -> EntryInOneOfTheLists<'_, T> {
+        self.length += 1;
+
+        let entry = Arc::new(ListEntry {
+            parent: self.lists.clone(),
+            value: UnsafeCell::new(ManuallyDrop::new(value)),
+            my_list: UnsafeCell::new(List::Idle),
+            pointers: linked_list::Pointers::new(),
+            _pin: PhantomPinned,
+        });
+
+        {
+            let mut lock = self.lists.lock();
+            lock.idle.push_front(entry.clone());
+        }
+
+        // Safety: We just put the entry in the idle list, so it is in one of the lists.
+        EntryInOneOfTheLists { entry, set: self }
+    }
+
+    /// Pop an entry from the notified list to poll it. The entry is moved to
+    /// the idle list atomically.
+    pub(crate) fn pop_notified(&mut self, waker: &Waker) -> Option<EntryInOneOfTheLists<'_, T>> {
+        // We don't decrement the length because this call moves the entry to
+        // the idle list rather than removing it.
+        if self.length == 0 {
+            // Fast path.
+            return None;
+        }
+
+        let mut lock = self.lists.lock();
+
+        let should_update_waker = match lock.waker.as_mut() {
+            Some(cur_waker) => !waker.will_wake(cur_waker),
+            None => true,
+        };
+        if should_update_waker {
+            lock.waker = Some(waker.clone());
+        }
+
+        // Pop the entry, returning None if empty.
+        let entry = lock.notified.pop_back()?;
+
+        lock.idle.push_front(entry.clone());
+
+        // Safety: We are holding the lock.
+        entry.my_list.with_mut(|ptr| unsafe {
+            *ptr = List::Idle;
+        });
+
+        drop(lock);
+
+        // Safety: We just put the entry in the idle list, so it is in one of the lists.
+        Some(EntryInOneOfTheLists { entry, set: self })
+    }
+
+    /// Call a function on every element in this list.
+    pub(crate) fn for_each<F: FnMut(&mut T)>(&mut self, mut func: F) {
+        fn get_ptrs<T>(list: &mut LinkedList<T>, ptrs: &mut Vec<*mut T>) {
+            let mut node = list.last();
+
+            while let Some(entry) = node {
+                ptrs.push(entry.value.with_mut(|ptr| {
+                    let ptr: *mut ManuallyDrop<T> = ptr;
+                    let ptr: *mut T = ptr.cast();
+                    ptr
+                }));
+
+                let prev = entry.pointers.get_prev();
+                node = prev.map(|prev| unsafe { &*prev.as_ptr() });
+            }
+        }
+
+        // Atomically get a raw pointer to the value of every entry.
+        //
+        // Since this only locks the mutex once, it is not possible for a value
+        // to get moved from the idle list to the notified list during the
+        // operation, which would otherwise result in some value being listed
+        // twice.
+        let mut ptrs = Vec::with_capacity(self.len());
+        {
+            let mut lock = self.lists.lock();
+
+            get_ptrs(&mut lock.idle, &mut ptrs);
+            get_ptrs(&mut lock.notified, &mut ptrs);
+        }
+        debug_assert_eq!(ptrs.len(), ptrs.capacity());
+
+        for ptr in ptrs {
+            // Safety: When we grabbed the pointers, the entries were in one of
+            // the two lists. This means that their value was valid at the time,
+            // and it must still be valid because we are the IdleNotifiedSet,
+            // and only we can remove an entry from the two lists. (It's
+            // possible that an entry is moved from one list to the other during
+            // this loop, but that is ok.)
+            func(unsafe { &mut *ptr });
+        }
+    }
+
+    /// Remove all entries in both lists, applying some function to each element.
+    ///
+    /// The closure is called on all elements even if it panics. Having it panic
+    /// twice is a double-panic, and will abort the application.
+    pub(crate) fn drain<F: FnMut(T)>(&mut self, func: F) {
+        if self.length == 0 {
+            // Fast path.
+            return;
+        }
+        self.length = 0;
+
+        // The LinkedList is not cleared on panic, so we use a bomb to clear it.
+        //
+        // This value has the invariant that any entry in its `all_entries` list
+        // has `my_list` set to `Neither` and that the value has not yet been
+        // dropped.
+        struct AllEntries<T, F: FnMut(T)> {
+            all_entries: LinkedList<T>,
+            func: F,
+        }
+
+        impl<T, F: FnMut(T)> AllEntries<T, F> {
+            fn pop_next(&mut self) -> bool {
+                if let Some(entry) = self.all_entries.pop_back() {
+                    // Safety: We just took this value from the list, so we can
+                    // destroy the value in the entry.
+                    entry
+                        .value
+                        .with_mut(|ptr| unsafe { (self.func)(ManuallyDrop::take(&mut *ptr)) });
+                    true
+                } else {
+                    false
+                }
+            }
+        }
+
+        impl<T, F: FnMut(T)> Drop for AllEntries<T, F> {
+            fn drop(&mut self) {
+                while self.pop_next() {}
+            }
+        }
+
+        let mut all_entries = AllEntries {
+            all_entries: LinkedList::new(),
+            func,
+        };
+
+        // Atomically move all entries to the new linked list in the AllEntries
+        // object.
+        {
+            let mut lock = self.lists.lock();
+            unsafe {
+                // Safety: We are holding the lock and `all_entries` is a new
+                // LinkedList.
+                move_to_new_list(&mut lock.idle, &mut all_entries.all_entries);
+                move_to_new_list(&mut lock.notified, &mut all_entries.all_entries);
+            }
+        }
+
+        // Keep destroying entries in the list until it is empty.
+        //
+        // If the closure panics, then the destructor of the `AllEntries` bomb
+        // ensures that we keep running the destructor on the remaining values.
+        // A second panic will abort the program.
+        while all_entries.pop_next() {}
+    }
+}
+
+/// # Safety
+///
+/// The mutex for the entries must be held, and the target list must be such
+/// that setting `my_list` to `Neither` is ok.
+unsafe fn move_to_new_list<T>(from: &mut LinkedList<T>, to: &mut LinkedList<T>) {
+    while let Some(entry) = from.pop_back() {
+        entry.my_list.with_mut(|ptr| {
+            *ptr = List::Neither;
+        });
+        to.push_front(entry);
+    }
+}
+
+impl<'a, T> EntryInOneOfTheLists<'a, T> {
+    /// Remove this entry from the list it is in, returning the value associated
+    /// with the entry.
+    ///
+    /// This consumes the value, since it is no longer guaranteed to be in a
+    /// list.
+    pub(crate) fn remove(self) -> T {
+        self.set.length -= 1;
+
+        {
+            let mut lock = self.set.lists.lock();
+
+            // Safety: We are holding the lock so there is no race, and we will
+            // remove the entry afterwards to uphold invariants.
+            let old_my_list = self.entry.my_list.with_mut(|ptr| unsafe {
+                let old_my_list = *ptr;
+                *ptr = List::Neither;
+                old_my_list
+            });
+
+            let list = match old_my_list {
+                List::Idle => &mut lock.idle,
+                List::Notified => &mut lock.notified,
+                // An entry in one of the lists is in one of the lists.
+                List::Neither => unreachable!(),
+            };
+
+            unsafe {
+                // Safety: We just checked that the entry is in this particular
+                // list.
+                list.remove(ListEntry::as_raw(&self.entry)).unwrap();
+            }
+        }
+
+        // By setting `my_list` to `Neither`, we have taken ownership of the
+        // value. We return it to the caller.
+        //
+        // Safety: We have a mutable reference to the `IdleNotifiedSet` that
+        // owns this entry, so we can use its permission to access the value.
+        self.entry
+            .value
+            .with_mut(|ptr| unsafe { ManuallyDrop::take(&mut *ptr) })
+    }
+
+    /// Access the value in this entry together with a context for its waker.
+    pub(crate) fn with_value_and_context<F, U>(&mut self, func: F) -> U
+    where
+        F: FnOnce(&mut T, &mut Context<'_>) -> U,
+        T: 'static,
+    {
+        let waker = waker_ref(&self.entry);
+
+        let mut context = Context::from_waker(&waker);
+
+        // Safety: We have a mutable reference to the `IdleNotifiedSet` that
+        // owns this entry, so we can use its permission to access the value.
+        self.entry
+            .value
+            .with_mut(|ptr| unsafe { func(&mut *ptr, &mut context) })
+    }
+}
+
+impl<T> Drop for IdleNotifiedSet<T> {
+    fn drop(&mut self) {
+        // Clear both lists.
+        self.drain(drop);
+
+        #[cfg(debug_assertions)]
+        if !std::thread::panicking() {
+            let lock = self.lists.lock();
+            assert!(lock.idle.is_empty());
+            assert!(lock.notified.is_empty());
+        }
+    }
+}
+
+impl<T: 'static> Wake for ListEntry<T> {
+    fn wake_by_ref(me: &Arc<Self>) {
+        let mut lock = me.parent.lock();
+
+        // Safety: We are holding the lock and we will update the lists to
+        // maintain invariants.
+        let old_my_list = me.my_list.with_mut(|ptr| unsafe {
+            let old_my_list = *ptr;
+            if old_my_list == List::Idle {
+                *ptr = List::Notified;
+            }
+            old_my_list
+        });
+
+        if old_my_list == List::Idle {
+            // We move ourself to the notified list.
+            let me = unsafe {
+                // Safety: We just checked that we are in this particular list.
+                lock.idle.remove(NonNull::from(&**me)).unwrap()
+            };
+            lock.notified.push_front(me);
+
+            if let Some(waker) = lock.waker.take() {
+                drop(lock);
+                waker.wake();
+            }
+        }
+    }
+
+    fn wake(me: Arc<Self>) {
+        Self::wake_by_ref(&me)
+    }
+}
+
+/// # Safety
+///
+/// `ListEntry` is forced to be !Unpin.
+unsafe impl<T> linked_list::Link for ListEntry<T> {
+    type Handle = Arc<ListEntry<T>>;
+    type Target = ListEntry<T>;
+
+    fn as_raw(handle: &Self::Handle) -> NonNull<ListEntry<T>> {
+        let ptr: *const ListEntry<T> = Arc::as_ptr(handle);
+        // Safety: We can't get a null pointer from `Arc::as_ptr`.
+        unsafe { NonNull::new_unchecked(ptr as *mut ListEntry<T>) }
+    }
+
+    unsafe fn from_raw(ptr: NonNull<ListEntry<T>>) -> Arc<ListEntry<T>> {
+        Arc::from_raw(ptr.as_ptr())
+    }
+
+    unsafe fn pointers(
+        target: NonNull<ListEntry<T>>,
+    ) -> NonNull<linked_list::Pointers<ListEntry<T>>> {
+        // Safety: The pointers struct is the first field and ListEntry is
+        // `#[repr(C)]` so this cast is safe.
+        //
+        // We do this rather than doing a field access since `std::ptr::addr_of`
+        // is too new for our MSRV.
+        target.cast()
+    }
+}
diff --git a/third_party/rust/tokio/src/util/linked_list.rs b/third_party/rust/tokio/src/util/linked_list.rs
new file mode 100644
index 0000000000..e6bdde68c7
--- /dev/null
+++ b/third_party/rust/tokio/src/util/linked_list.rs
@@ -0,0 +1,693 @@
+#![cfg_attr(not(feature = "full"), allow(dead_code))]
+
+//! An intrusive double linked list of data.
+//!
+//! The data structure supports tracking pinned nodes. Most of the data
+//! structure's APIs are `unsafe` as they require the caller to ensure the
+//! specified node is actually contained by the list.
+
+use core::cell::UnsafeCell;
+use core::fmt;
+use core::marker::{PhantomData, PhantomPinned};
+use core::mem::ManuallyDrop;
+use core::ptr::{self, NonNull};
+
+/// An intrusive linked list.
+///
+/// Currently, the list is not emptied on drop. It is the caller's
+/// responsibility to ensure the list is empty before dropping it.
+pub(crate) struct LinkedList<L, T> {
+    /// Linked list head
+    head: Option<NonNull<T>>,
+
+    /// Linked list tail
+    tail: Option<NonNull<T>>,
+
+    /// Node type marker.
+    _marker: PhantomData<*const L>,
+}
+
+unsafe impl<L: Link> Send for LinkedList<L, L::Target> where L::Target: Send {}
+unsafe impl<L: Link> Sync for LinkedList<L, L::Target> where L::Target: Sync {}
+
+/// Defines how a type is tracked within a linked list.
+///
+/// In order to support storing a single type within multiple lists, accessing
+/// the list pointers is decoupled from the entry type.
+///
+/// # Safety
+///
+/// Implementations must guarantee that `Target` types are pinned in memory. In
+/// other words, when a node is inserted, the value will not be moved as long as
+/// it is stored in the list.
+pub(crate) unsafe trait Link {
+    /// Handle to the list entry.
+    ///
+    /// This is usually a pointer-ish type.
+    type Handle;
+
+    /// Node type.
+    type Target;
+
+    /// Convert the handle to a raw pointer without consuming the handle.
+    #[allow(clippy::wrong_self_convention)]
+    fn as_raw(handle: &Self::Handle) -> NonNull<Self::Target>;
+
+    /// Convert the raw pointer to a handle
+    unsafe fn from_raw(ptr: NonNull<Self::Target>) -> Self::Handle;
+
+    /// Return the pointers for a node
+    ///
+    /// # Safety
+    ///
+    /// The resulting pointer should have the same tag in the stacked-borrows
+    /// stack as the argument. In particular, the method may not create an
+    /// intermediate reference in the process of creating the resulting raw
+    /// pointer.
+    unsafe fn pointers(target: NonNull<Self::Target>) -> NonNull<Pointers<Self::Target>>;
+}
+
+/// Previous / next pointers.
+pub(crate) struct Pointers<T> {
+    inner: UnsafeCell<PointersInner<T>>,
+}
+/// We do not want the compiler to put the `noalias` attribute on mutable
+/// references to this type, so the type has been made `!Unpin` with a
+/// `PhantomPinned` field.
+///
+/// Additionally, we never access the `prev` or `next` fields directly, as any
+/// such access would implicitly involve the creation of a reference to the
+/// field, which we want to avoid since the fields are not `!Unpin`, and would
+/// hence be given the `noalias` attribute if we were to do such an access.
+/// As an alternative to accessing the fields directly, the `Pointers` type
+/// provides getters and setters for the two fields, and those are implemented
+/// using raw pointer casts and offsets, which is valid since the struct is
+/// #[repr(C)].
+///
+/// See this link for more information:
+/// <https://github.com/rust-lang/rust/pull/82834>
+#[repr(C)]
+struct PointersInner<T> {
+    /// The previous node in the list. null if there is no previous node.
+    ///
+    /// This field is accessed through pointer manipulation, so it is not dead code.
+    #[allow(dead_code)]
+    prev: Option<NonNull<T>>,
+
+    /// The next node in the list. null if there is no previous node.
+    ///
+    /// This field is accessed through pointer manipulation, so it is not dead code.
+    #[allow(dead_code)]
+    next: Option<NonNull<T>>,
+
+    /// This type is !Unpin due to the heuristic from:
+    /// <https://github.com/rust-lang/rust/pull/82834>
+    _pin: PhantomPinned,
+}
+
+unsafe impl<T: Send> Send for Pointers<T> {}
+unsafe impl<T: Sync> Sync for Pointers<T> {}
+
+// ===== impl LinkedList =====
+
+impl<L, T> LinkedList<L, T> {
+    /// Creates an empty linked list.
+    pub(crate) const fn new() -> LinkedList<L, T> {
+        LinkedList {
+            head: None,
+            tail: None,
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl<L: Link> LinkedList<L, L::Target> {
+    /// Adds an element first in the list.
+    pub(crate) fn push_front(&mut self, val: L::Handle) {
+        // The value should not be dropped, it is being inserted into the list
+        let val = ManuallyDrop::new(val);
+        let ptr = L::as_raw(&*val);
+        assert_ne!(self.head, Some(ptr));
+        unsafe {
+            L::pointers(ptr).as_mut().set_next(self.head);
+            L::pointers(ptr).as_mut().set_prev(None);
+
+            if let Some(head) = self.head {
+                L::pointers(head).as_mut().set_prev(Some(ptr));
+            }
+
+            self.head = Some(ptr);
+
+            if self.tail.is_none() {
+                self.tail = Some(ptr);
+            }
+        }
+    }
+
+    /// Removes the last element from a list and returns it, or None if it is
+    /// empty.
+    pub(crate) fn pop_back(&mut self) -> Option<L::Handle> {
+        unsafe {
+            let last = self.tail?;
+            self.tail = L::pointers(last).as_ref().get_prev();
+
+            if let Some(prev) = L::pointers(last).as_ref().get_prev() {
+                L::pointers(prev).as_mut().set_next(None);
+            } else {
+                self.head = None
+            }
+
+            L::pointers(last).as_mut().set_prev(None);
+            L::pointers(last).as_mut().set_next(None);
+
+            Some(L::from_raw(last))
+        }
+    }
+
+    /// Returns whether the linked list does not contain any node
+    pub(crate) fn is_empty(&self) -> bool {
+        if self.head.is_some() {
+            return false;
+        }
+
+        assert!(self.tail.is_none());
+        true
+    }
+
+    /// Removes the specified node from the list
+    ///
+    /// # Safety
+    ///
+    /// The caller **must** ensure that `node` is currently contained by
+    /// `self` or not contained by any other list.
+    pub(crate) unsafe fn remove(&mut self, node: NonNull<L::Target>) -> Option<L::Handle> {
+        if let Some(prev) = L::pointers(node).as_ref().get_prev() {
+            debug_assert_eq!(L::pointers(prev).as_ref().get_next(), Some(node));
+            L::pointers(prev)
+                .as_mut()
+                .set_next(L::pointers(node).as_ref().get_next());
+        } else {
+            if self.head != Some(node) {
+                return None;
+            }
+
+            self.head = L::pointers(node).as_ref().get_next();
+        }
+
+        if let Some(next) = L::pointers(node).as_ref().get_next() {
+            debug_assert_eq!(L::pointers(next).as_ref().get_prev(), Some(node));
+            L::pointers(next)
+                .as_mut()
+                .set_prev(L::pointers(node).as_ref().get_prev());
+        } else {
+            // This might be the last item in the list
+            if self.tail != Some(node) {
+                return None;
+            }
+
+            self.tail = L::pointers(node).as_ref().get_prev();
+        }
+
+        L::pointers(node).as_mut().set_next(None);
+        L::pointers(node).as_mut().set_prev(None);
+
+        Some(L::from_raw(node))
+    }
+}
+
+impl<L: Link> fmt::Debug for LinkedList<L, L::Target> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("LinkedList")
+            .field("head", &self.head)
+            .field("tail", &self.tail)
+            .finish()
+    }
+}
+
+#[cfg(any(
+    feature = "fs",
+    feature = "rt",
+    all(unix, feature = "process"),
+    feature = "signal",
+    feature = "sync",
+))]
+impl<L: Link> LinkedList<L, L::Target> {
+    pub(crate) fn last(&self) -> Option<&L::Target> {
+        let tail = self.tail.as_ref()?;
+        unsafe { Some(&*tail.as_ptr()) }
+    }
+}
+
+impl<L: Link> Default for LinkedList<L, L::Target> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+// ===== impl DrainFilter =====
+
+cfg_io_readiness! {
+    pub(crate) struct DrainFilter<'a, T: Link, F> {
+        list: &'a mut LinkedList<T, T::Target>,
+        filter: F,
+        curr: Option<NonNull<T::Target>>,
+    }
+
+    impl<T: Link> LinkedList<T, T::Target> {
+        pub(crate) fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F>
+        where
+            F: FnMut(&mut T::Target) -> bool,
+        {
+            let curr = self.head;
+            DrainFilter {
+                curr,
+                filter,
+                list: self,
+            }
+        }
+    }
+
+    impl<'a, T, F> Iterator for DrainFilter<'a, T, F>
+    where
+        T: Link,
+        F: FnMut(&mut T::Target) -> bool,
+    {
+        type Item = T::Handle;
+
+        fn next(&mut self) -> Option<Self::Item> {
+            while let Some(curr) = self.curr {
+                // safety: the pointer references data contained by the list
+                self.curr = unsafe { T::pointers(curr).as_ref() }.get_next();
+
+                // safety: the value is still owned by the linked list.
+                if (self.filter)(unsafe { &mut *curr.as_ptr() }) {
+                    return unsafe { self.list.remove(curr) };
+                }
+            }
+
+            None
+        }
+    }
+}
+
+// ===== impl Pointers =====
+
+impl<T> Pointers<T> {
+    /// Create a new set of empty pointers
+    pub(crate) fn new() -> Pointers<T> {
+        Pointers {
+            inner: UnsafeCell::new(PointersInner {
+                prev: None,
+                next: None,
+                _pin: PhantomPinned,
+            }),
+        }
+    }
+
+    pub(crate) fn get_prev(&self) -> Option<NonNull<T>> {
+        // SAFETY: prev is the first field in PointersInner, which is #[repr(C)].
+        unsafe {
+            let inner = self.inner.get();
+            let prev = inner as *const Option<NonNull<T>>;
+            ptr::read(prev)
+        }
+    }
+    pub(crate) fn get_next(&self) -> Option<NonNull<T>> {
+        // SAFETY: next is the second field in PointersInner, which is #[repr(C)].
+        unsafe {
+            let inner = self.inner.get();
+            let prev = inner as *const Option<NonNull<T>>;
+            let next = prev.add(1);
+            ptr::read(next)
+        }
+    }
+
+    fn set_prev(&mut self, value: Option<NonNull<T>>) {
+        // SAFETY: prev is the first field in PointersInner, which is #[repr(C)].
+        unsafe {
+            let inner = self.inner.get();
+            let prev = inner as *mut Option<NonNull<T>>;
+            ptr::write(prev, value);
+        }
+    }
+    fn set_next(&mut self, value: Option<NonNull<T>>) {
+        // SAFETY: next is the second field in PointersInner, which is #[repr(C)].
+        unsafe {
+            let inner = self.inner.get();
+            let prev = inner as *mut Option<NonNull<T>>;
+            let next = prev.add(1);
+            ptr::write(next, value);
+        }
+    }
+}
+
+impl<T> fmt::Debug for Pointers<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let prev = self.get_prev();
+        let next = self.get_next();
+        f.debug_struct("Pointers")
+            .field("prev", &prev)
+            .field("next", &next)
+            .finish()
+    }
+}
+
+#[cfg(test)]
+#[cfg(not(loom))]
+mod tests {
+    use super::*;
+
+    use std::pin::Pin;
+
+    #[derive(Debug)]
+    #[repr(C)]
+    struct Entry {
+        pointers: Pointers<Entry>,
+        val: i32,
+    }
+
+    unsafe impl<'a> Link for &'a Entry {
+        type Handle = Pin<&'a Entry>;
+        type Target = Entry;
+
+        fn as_raw(handle: &Pin<&'_ Entry>) -> NonNull<Entry> {
+            NonNull::from(handle.get_ref())
+        }
+
+        unsafe fn from_raw(ptr: NonNull<Entry>) -> Pin<&'a Entry> {
+            Pin::new_unchecked(&*ptr.as_ptr())
+        }
+
+        unsafe fn pointers(target: NonNull<Entry>) -> NonNull<Pointers<Entry>> {
+            target.cast()
+        }
+    }
+
+    fn entry(val: i32) -> Pin<Box<Entry>> {
+        Box::pin(Entry {
+            pointers: Pointers::new(),
+            val,
+        })
+    }
+
+    fn ptr(r: &Pin<Box<Entry>>) -> NonNull<Entry> {
+        r.as_ref().get_ref().into()
+    }
+
+    fn collect_list(list: &mut LinkedList<&'_ Entry, <&'_ Entry as Link>::Target>) -> Vec<i32> {
+        let mut ret = vec![];
+
+        while let Some(entry) = list.pop_back() {
+            ret.push(entry.val);
+        }
+
+        ret
+    }
+
+    fn push_all<'a>(
+        list: &mut LinkedList<&'a Entry, <&'_ Entry as Link>::Target>,
+        entries: &[Pin<&'a Entry>],
+    ) {
+        for entry in entries.iter() {
+            list.push_front(*entry);
+        }
+    }
+
+    macro_rules! assert_clean {
+        ($e:ident) => {{
+            assert!($e.pointers.get_next().is_none());
+            assert!($e.pointers.get_prev().is_none());
+        }};
+    }
+
+    macro_rules! assert_ptr_eq {
+        ($a:expr, $b:expr) => {{
+            // Deal with mapping a Pin<&mut T> -> Option<NonNull<T>>
+            assert_eq!(Some($a.as_ref().get_ref().into()), $b)
+        }};
+    }
+
+    #[test]
+    fn const_new() {
+        const _: LinkedList<&Entry, <&Entry as Link>::Target> = LinkedList::new();
+    }
+
+    #[test]
+    fn push_and_drain() {
+        let a = entry(5);
+        let b = entry(7);
+        let c = entry(31);
+
+        let mut list = LinkedList::new();
+        assert!(list.is_empty());
+
+        list.push_front(a.as_ref());
+        assert!(!list.is_empty());
+        list.push_front(b.as_ref());
+        list.push_front(c.as_ref());
+
+        let items: Vec<i32> = collect_list(&mut list);
+        assert_eq!([5, 7, 31].to_vec(), items);
+
+        assert!(list.is_empty());
+    }
+
+    #[test]
+    fn push_pop_push_pop() {
+        let a = entry(5);
+        let b = entry(7);
+
+        let mut list = LinkedList::<&Entry, <&Entry as Link>::Target>::new();
+
+        list.push_front(a.as_ref());
+
+        let entry = list.pop_back().unwrap();
+        assert_eq!(5, entry.val);
+        assert!(list.is_empty());
+
+        list.push_front(b.as_ref());
+
+        let entry = list.pop_back().unwrap();
+        assert_eq!(7, entry.val);
+
+        assert!(list.is_empty());
+        assert!(list.pop_back().is_none());
+    }
+
+    #[test]
+    fn remove_by_address() {
+        let a = entry(5);
+        let b = entry(7);
+        let c = entry(31);
+
+        unsafe {
+            // Remove first
+            let mut list = LinkedList::new();
+
+            push_all(&mut list, &[c.as_ref(), b.as_ref(), a.as_ref()]);
+            assert!(list.remove(ptr(&a)).is_some());
+            assert_clean!(a);
+            // `a` should be no longer there and can't be removed twice
+            assert!(list.remove(ptr(&a)).is_none());
+            assert!(!list.is_empty());
+
+            assert!(list.remove(ptr(&b)).is_some());
+            assert_clean!(b);
+            // `b` should be no longer there and can't be removed twice
+            assert!(list.remove(ptr(&b)).is_none());
+            assert!(!list.is_empty());
+
+            assert!(list.remove(ptr(&c)).is_some());
+            assert_clean!(c);
+            // `b` should be no longer there and can't be removed twice
+            assert!(list.remove(ptr(&c)).is_none());
+            assert!(list.is_empty());
+        }
+
+        unsafe {
+            // Remove middle
+            let mut list = LinkedList::new();
+
+            push_all(&mut list, &[c.as_ref(), b.as_ref(), a.as_ref()]);
+
+            assert!(list.remove(ptr(&a)).is_some());
+            assert_clean!(a);
+
+            assert_ptr_eq!(b, list.head);
+            assert_ptr_eq!(c, b.pointers.get_next());
+            assert_ptr_eq!(b, c.pointers.get_prev());
+
+            let items = collect_list(&mut list);
+            assert_eq!([31, 7].to_vec(), items);
+        }
+
+        unsafe {
+            // Remove middle
+            let mut list = LinkedList::new();
+
+            push_all(&mut list, &[c.as_ref(), b.as_ref(), a.as_ref()]);
+
+            assert!(list.remove(ptr(&b)).is_some());
+            assert_clean!(b);
+
+            assert_ptr_eq!(c, a.pointers.get_next());
+            assert_ptr_eq!(a, c.pointers.get_prev());
+
+            let items = collect_list(&mut list);
+            assert_eq!([31, 5].to_vec(), items);
+        }
+
+        unsafe {
+            // Remove last
+            // Remove middle
+            let mut list = LinkedList::new();
+
+            push_all(&mut list, &[c.as_ref(), b.as_ref(), a.as_ref()]);
+
+            assert!(list.remove(ptr(&c)).is_some());
+            assert_clean!(c);
+
+            assert!(b.pointers.get_next().is_none());
+            assert_ptr_eq!(b, list.tail);
+
+            let items = collect_list(&mut list);
+            assert_eq!([7, 5].to_vec(), items);
+        }
+
+        unsafe {
+            // Remove first of two
+            let mut list = LinkedList::new();
+
+            push_all(&mut list, &[b.as_ref(), a.as_ref()]);
+
+            assert!(list.remove(ptr(&a)).is_some());
+
+            assert_clean!(a);
+
+            // a should be no longer there and can't be removed twice
+            assert!(list.remove(ptr(&a)).is_none());
+
+            assert_ptr_eq!(b, list.head);
+            assert_ptr_eq!(b, list.tail);
+
+            assert!(b.pointers.get_next().is_none());
+            assert!(b.pointers.get_prev().is_none());
+
+            let items = collect_list(&mut list);
+            assert_eq!([7].to_vec(), items);
+        }
+
+        unsafe {
+            // Remove last of two
+            let mut list = LinkedList::new();
+
+            push_all(&mut list, &[b.as_ref(), a.as_ref()]);
+
+            assert!(list.remove(ptr(&b)).is_some());
+
+            assert_clean!(b);
+
+            assert_ptr_eq!(a, list.head);
+            assert_ptr_eq!(a, list.tail);
+
+            assert!(a.pointers.get_next().is_none());
+            assert!(a.pointers.get_prev().is_none());
+
+            let items = collect_list(&mut list);
+            assert_eq!([5].to_vec(), items);
+        }
+
+        unsafe {
+            // Remove last item
+            let mut list = LinkedList::new();
+
+            push_all(&mut list, &[a.as_ref()]);
+
+            assert!(list.remove(ptr(&a)).is_some());
+            assert_clean!(a);
+
+            assert!(list.head.is_none());
+            assert!(list.tail.is_none());
+            let items = collect_list(&mut list);
+            assert!(items.is_empty());
+        }
+
+        unsafe {
+            // Remove missing
+            let mut list = LinkedList::<&Entry, <&Entry as Link>::Target>::new();
+
+            list.push_front(b.as_ref());
+            list.push_front(a.as_ref());
+
+            assert!(list.remove(ptr(&c)).is_none());
+        }
+    }
+
+    #[cfg(not(target_arch = "wasm32"))]
+    proptest::proptest! {
+        #[test]
+        fn fuzz_linked_list(ops: Vec<usize>) {
+            run_fuzz(ops);
+        }
+    }
+
+    fn run_fuzz(ops: Vec<usize>) {
+        use std::collections::VecDeque;
+
+        #[derive(Debug)]
+        enum Op {
+            Push,
+            Pop,
+            Remove(usize),
+        }
+
+        let ops = ops
+            .iter()
+            .map(|i| match i % 3 {
+                0 => Op::Push,
+                1 => Op::Pop,
+                2 => Op::Remove(i / 3),
+                _ => unreachable!(),
+            })
+            .collect::<Vec<_>>();
+
+        let mut ll = LinkedList::<&Entry, <&Entry as Link>::Target>::new();
+        let mut reference = VecDeque::new();
+
+        let entries: Vec<_> = (0..ops.len()).map(|i| entry(i as i32)).collect();
+
+        for (i, op) in ops.iter().enumerate() {
+            match op {
+                Op::Push => {
+                    reference.push_front(i as i32);
+                    assert_eq!(entries[i].val, i as i32);
+
+                    ll.push_front(entries[i].as_ref());
+                }
+                Op::Pop => {
+                    if reference.is_empty() {
+                        assert!(ll.is_empty());
+                        continue;
+                    }
+
+                    let v = reference.pop_back();
+                    assert_eq!(v, ll.pop_back().map(|v| v.val));
+                }
+                Op::Remove(n) => {
+                    if reference.is_empty() {
+                        assert!(ll.is_empty());
+                        continue;
+                    }
+
+                    let idx = n % reference.len();
+                    let expect = reference.remove(idx).unwrap();
+
+                    unsafe {
+                        let entry = ll.remove(ptr(&entries[expect as usize])).unwrap();
+                        assert_eq!(expect, entry.val);
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/util/mod.rs b/third_party/rust/tokio/src/util/mod.rs
new file mode 100644
index 0000000000..618f554380
--- /dev/null
+++ b/third_party/rust/tokio/src/util/mod.rs
@@ -0,0 +1,83 @@
+cfg_io_driver! {
+    pub(crate) mod bit;
+    pub(crate) mod slab;
+}
+
+#[cfg(feature = "rt")]
+pub(crate) mod atomic_cell;
+
+#[cfg(any(
+    // io driver uses `WakeList` directly
+    feature = "net",
+    feature = "process",
+    // `sync` enables `Notify` and `batch_semaphore`, which require `WakeList`.
+    feature = "sync",
+    // `fs` uses `batch_semaphore`, which requires `WakeList`.
+    feature = "fs",
+    // rt and signal use `Notify`, which requires `WakeList`.
+    feature = "rt",
+    feature = "signal",
+))]
+mod wake_list;
+#[cfg(any(
+    feature = "net",
+    feature = "process",
+    feature = "sync",
+    feature = "fs",
+    feature = "rt",
+    feature = "signal",
+))]
+pub(crate) use wake_list::WakeList;
+
+#[cfg(any(
+    feature = "fs",
+    feature = "net",
+    feature = "process",
+    feature = "rt",
+    feature = "sync",
+    feature = "signal",
+    feature = "time",
+))]
+pub(crate) mod linked_list;
+
+#[cfg(any(feature = "rt-multi-thread", feature = "macros"))]
+mod rand;
+
+cfg_rt! {
+    cfg_unstable! {
+        mod idle_notified_set;
+        pub(crate) use idle_notified_set::IdleNotifiedSet;
+    }
+
+    mod wake;
+    pub(crate) use wake::WakerRef;
+    pub(crate) use wake::{waker_ref, Wake};
+
+    mod sync_wrapper;
+    pub(crate) use sync_wrapper::SyncWrapper;
+
+    mod vec_deque_cell;
+    pub(crate) use vec_deque_cell::VecDequeCell;
+}
+
+cfg_rt_multi_thread! {
+    pub(crate) use self::rand::FastRand;
+
+    mod try_lock;
+    pub(crate) use try_lock::TryLock;
+}
+
+pub(crate) mod trace;
+
+#[cfg(any(feature = "macros"))]
+#[cfg_attr(not(feature = "macros"), allow(unreachable_pub))]
+pub use self::rand::thread_rng_n;
+
+#[cfg(any(
+    feature = "rt",
+    feature = "time",
+    feature = "net",
+    feature = "process",
+    all(unix, feature = "signal")
+))]
+pub(crate) mod error;
diff --git a/third_party/rust/tokio/src/util/pad.rs b/third_party/rust/tokio/src/util/pad.rs
new file mode 100644
index 0000000000..bf0913ca85
--- /dev/null
+++ b/third_party/rust/tokio/src/util/pad.rs
@@ -0,0 +1,52 @@
+use core::fmt;
+use core::ops::{Deref, DerefMut};
+
+#[derive(Clone, Copy, Default, Hash, PartialEq, Eq)]
+// Starting from Intel's Sandy Bridge, spatial prefetcher is now pulling pairs of 64-byte cache
+// lines at a time, so we have to align to 128 bytes rather than 64.
+//
+// Sources:
+// - https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-optimization-manual.pdf
+// - https://github.com/facebook/folly/blob/1b5288e6eea6df074758f877c849b6e73bbb9fbb/folly/lang/Align.h#L107
+#[cfg_attr(target_arch = "x86_64", repr(align(128)))]
+#[cfg_attr(not(target_arch = "x86_64"), repr(align(64)))]
+pub(crate) struct CachePadded<T> {
+    value: T,
+}
+
+unsafe impl<T: Send> Send for CachePadded<T> {}
+unsafe impl<T: Sync> Sync for CachePadded<T> {}
+
+impl<T> CachePadded<T> {
+    pub(crate) fn new(t: T) -> CachePadded<T> {
+        CachePadded::<T> { value: t }
+    }
+}
+
+impl<T> Deref for CachePadded<T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        &self.value
+    }
+}
+
+impl<T> DerefMut for CachePadded<T> {
+    fn deref_mut(&mut self) -> &mut T {
+        &mut self.value
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for CachePadded<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("CachePadded")
+            .field("value", &self.value)
+            .finish()
+    }
+}
+
+impl<T> From<T> for CachePadded<T> {
+    fn from(t: T) -> Self {
+        CachePadded::new(t)
+    }
+}
diff --git a/third_party/rust/tokio/src/util/rand.rs b/third_party/rust/tokio/src/util/rand.rs
new file mode 100644
index 0000000000..6b19c8be95
--- /dev/null
+++ b/third_party/rust/tokio/src/util/rand.rs
@@ -0,0 +1,64 @@
+use std::cell::Cell;
+
+/// Fast random number generate.
+///
+/// Implement xorshift64+: 2 32-bit xorshift sequences added together.
+/// Shift triplet `[17,7,16]` was calculated as indicated in Marsaglia's
+/// Xorshift paper: <https://www.jstatsoft.org/article/view/v008i14/xorshift.pdf>
+/// This generator passes the SmallCrush suite, part of TestU01 framework:
+/// <http://simul.iro.umontreal.ca/testu01/tu01.html>
+#[derive(Debug)]
+pub(crate) struct FastRand {
+    one: Cell<u32>,
+    two: Cell<u32>,
+}
+
+impl FastRand {
+    /// Initializes a new, thread-local, fast random number generator.
+    pub(crate) fn new(seed: u64) -> FastRand {
+        let one = (seed >> 32) as u32;
+        let mut two = seed as u32;
+
+        if two == 0 {
+            // This value cannot be zero
+            two = 1;
+        }
+
+        FastRand {
+            one: Cell::new(one),
+            two: Cell::new(two),
+        }
+    }
+
+    pub(crate) fn fastrand_n(&self, n: u32) -> u32 {
+        // This is similar to fastrand() % n, but faster.
+        // See https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
+        let mul = (self.fastrand() as u64).wrapping_mul(n as u64);
+        (mul >> 32) as u32
+    }
+
+    fn fastrand(&self) -> u32 {
+        let mut s1 = self.one.get();
+        let s0 = self.two.get();
+
+        s1 ^= s1 << 17;
+        s1 = s1 ^ s0 ^ s1 >> 7 ^ s0 >> 16;
+
+        self.one.set(s0);
+        self.two.set(s1);
+
+        s0.wrapping_add(s1)
+    }
+}
+
+// Used by the select macro and `StreamMap`
+#[cfg(any(feature = "macros"))]
+#[doc(hidden)]
+#[cfg_attr(not(feature = "macros"), allow(unreachable_pub))]
+pub fn thread_rng_n(n: u32) -> u32 {
+    thread_local! {
+        static THREAD_RNG: FastRand = FastRand::new(crate::loom::rand::seed());
+    }
+
+    THREAD_RNG.with(|rng| rng.fastrand_n(n))
+}
diff --git a/third_party/rust/tokio/src/util/slab.rs b/third_party/rust/tokio/src/util/slab.rs
new file mode 100644
index 0000000000..214fa08dc8
--- /dev/null
+++ b/third_party/rust/tokio/src/util/slab.rs
@@ -0,0 +1,855 @@
+#![cfg_attr(not(feature = "rt"), allow(dead_code))]
+
+use crate::loom::cell::UnsafeCell;
+use crate::loom::sync::atomic::{AtomicBool, AtomicUsize};
+use crate::loom::sync::{Arc, Mutex};
+use crate::util::bit;
+use std::fmt;
+use std::mem;
+use std::ops;
+use std::ptr;
+use std::sync::atomic::Ordering::Relaxed;
+
+/// Amortized allocation for homogeneous data types.
+///
+/// The slab pre-allocates chunks of memory to store values. It uses a similar
+/// growing strategy as `Vec`. When new capacity is needed, the slab grows by
+/// 2x.
+///
+/// # Pages
+///
+/// Unlike `Vec`, growing does not require moving existing elements. Instead of
+/// being a continuous chunk of memory for all elements, `Slab` is an array of
+/// arrays. The top-level array is an array of pages. Each page is 2x bigger
+/// than the previous one. When the slab grows, a new page is allocated.
+///
+/// Pages are lazily initialized.
+///
+/// # Allocating
+///
+/// When allocating an object, first previously used slots are reused. If no
+/// previously used slot is available, a new slot is initialized in an existing
+/// page. If all pages are full, then a new page is allocated.
+///
+/// When an allocated object is released, it is pushed into it's page's free
+/// list. Allocating scans all pages for a free slot.
+///
+/// # Indexing
+///
+/// The slab is able to index values using an address. Even when the indexed
+/// object has been released, it is still safe to index. This is a key ability
+/// for using the slab with the I/O driver. Addresses are registered with the
+/// OS's selector and I/O resources can be released without synchronizing with
+/// the OS.
+///
+/// # Compaction
+///
+/// `Slab::compact` will release pages that have been allocated but are no
+/// longer used. This is done by scanning the pages and finding pages with no
+/// allocated objects. These pages are then freed.
+///
+/// # Synchronization
+///
+/// The `Slab` structure is able to provide (mostly) unsynchronized reads to
+/// values stored in the slab. Insertions and removals are synchronized. Reading
+/// objects via `Ref` is fully unsynchronized. Indexing objects uses amortized
+/// synchronization.
+///
+pub(crate) struct Slab<T> {
+    /// Array of pages. Each page is synchronized.
+    pages: [Arc<Page<T>>; NUM_PAGES],
+
+    /// Caches the array pointer & number of initialized slots.
+    cached: [CachedPage<T>; NUM_PAGES],
+}
+
+/// Allocate values in the associated slab.
+pub(crate) struct Allocator<T> {
+    /// Pages in the slab. The first page has a capacity of 16 elements. Each
+    /// following page has double the capacity of the previous page.
+    ///
+    /// Each returned `Ref` holds a reference count to this `Arc`.
+    pages: [Arc<Page<T>>; NUM_PAGES],
+}
+
+/// References a slot in the slab. Indexing a slot using an `Address` is memory
+/// safe even if the slot has been released or the page has been deallocated.
+/// However, it is not guaranteed that the slot has not been reused and is now
+/// represents a different value.
+///
+/// The I/O driver uses a counter to track the slot's generation. Once accessing
+/// the slot, the generations are compared. If they match, the value matches the
+/// address.
+#[derive(Debug, Copy, Clone, PartialEq, Eq)]
+pub(crate) struct Address(usize);
+
+/// An entry in the slab.
+pub(crate) trait Entry: Default {
+    /// Resets the entry's value and track the generation.
+    fn reset(&self);
+}
+
+/// A reference to a value stored in the slab.
+pub(crate) struct Ref<T> {
+    value: *const Value<T>,
+}
+
+/// Maximum number of pages a slab can contain.
+const NUM_PAGES: usize = 19;
+
+/// Minimum number of slots a page can contain.
+const PAGE_INITIAL_SIZE: usize = 32;
+const PAGE_INDEX_SHIFT: u32 = PAGE_INITIAL_SIZE.trailing_zeros() + 1;
+
+/// A page in the slab.
+struct Page<T> {
+    /// Slots.
+    slots: Mutex<Slots<T>>,
+
+    // Number of slots currently being used. This is not guaranteed to be up to
+    // date and should only be used as a hint.
+    used: AtomicUsize,
+
+    // Set to `true` when the page has been allocated.
+    allocated: AtomicBool,
+
+    // The number of slots the page can hold.
+    len: usize,
+
+    // Length of all previous pages combined.
+    prev_len: usize,
+}
+
+struct CachedPage<T> {
+    /// Pointer to the page's slots.
+    slots: *const Slot<T>,
+
+    /// Number of initialized slots.
+    init: usize,
+}
+
+/// Page state.
+struct Slots<T> {
+    /// Slots.
+    slots: Vec<Slot<T>>,
+
+    head: usize,
+
+    /// Number of slots currently in use.
+    used: usize,
+}
+
+unsafe impl<T: Sync> Sync for Page<T> {}
+unsafe impl<T: Sync> Send for Page<T> {}
+unsafe impl<T: Sync> Sync for CachedPage<T> {}
+unsafe impl<T: Sync> Send for CachedPage<T> {}
+unsafe impl<T: Sync> Sync for Ref<T> {}
+unsafe impl<T: Sync> Send for Ref<T> {}
+
+/// A slot in the slab. Contains slot-specific metadata.
+///
+/// `#[repr(C)]` guarantees that the struct starts w/ `value`. We use pointer
+/// math to map a value pointer to an index in the page.
+#[repr(C)]
+struct Slot<T> {
+    /// Pointed to by `Ref`.
+    value: UnsafeCell<Value<T>>,
+
+    /// Next entry in the free list.
+    next: u32,
+
+    /// Makes miri happy by making mutable references not take exclusive access.
+    ///
+    /// Could probably also be fixed by replacing `slots` with a raw-pointer
+    /// based equivalent.
+    _pin: std::marker::PhantomPinned,
+}
+
+/// Value paired with a reference to the page.
+struct Value<T> {
+    /// Value stored in the value.
+    value: T,
+
+    /// Pointer to the page containing the slot.
+    ///
+    /// A raw pointer is used as this creates a ref cycle.
+    page: *const Page<T>,
+}
+
+impl<T> Slab<T> {
+    /// Create a new, empty, slab.
+    pub(crate) fn new() -> Slab<T> {
+        // Initializing arrays is a bit annoying. Instead of manually writing
+        // out an array and every single entry, `Default::default()` is used to
+        // initialize the array, then the array is iterated and each value is
+        // initialized.
+        let mut slab = Slab {
+            pages: Default::default(),
+            cached: Default::default(),
+        };
+
+        let mut len = PAGE_INITIAL_SIZE;
+        let mut prev_len: usize = 0;
+
+        for page in &mut slab.pages {
+            let page = Arc::get_mut(page).unwrap();
+            page.len = len;
+            page.prev_len = prev_len;
+            len *= 2;
+            prev_len += page.len;
+
+            // Ensure we don't exceed the max address space.
+            debug_assert!(
+                page.len - 1 + page.prev_len < (1 << 24),
+                "max = {:b}",
+                page.len - 1 + page.prev_len
+            );
+        }
+
+        slab
+    }
+
+    /// Returns a new `Allocator`.
+    ///
+    /// The `Allocator` supports concurrent allocation of objects.
+    pub(crate) fn allocator(&self) -> Allocator<T> {
+        Allocator {
+            pages: self.pages.clone(),
+        }
+    }
+
+    /// Returns a reference to the value stored at the given address.
+    ///
+    /// `&mut self` is used as the call may update internal cached state.
+    pub(crate) fn get(&mut self, addr: Address) -> Option<&T> {
+        let page_idx = addr.page();
+        let slot_idx = self.pages[page_idx].slot(addr);
+
+        // If the address references a slot that was last seen as uninitialized,
+        // the `CachedPage` is updated. This requires acquiring the page lock
+        // and updating the slot pointer and initialized offset.
+        if self.cached[page_idx].init <= slot_idx {
+            self.cached[page_idx].refresh(&self.pages[page_idx]);
+        }
+
+        // If the address **still** references an uninitialized slot, then the
+        // address is invalid and `None` is returned.
+        if self.cached[page_idx].init <= slot_idx {
+            return None;
+        }
+
+        // Get a reference to the value. The lifetime of the returned reference
+        // is bound to `&self`. The only way to invalidate the underlying memory
+        // is to call `compact()`. The lifetimes prevent calling `compact()`
+        // while references to values are outstanding.
+        //
+        // The referenced data is never mutated. Only `&self` references are
+        // used and the data is `Sync`.
+        Some(self.cached[page_idx].get(slot_idx))
+    }
+
+    /// Calls the given function with a reference to each slot in the slab. The
+    /// slot may not be in-use.
+    ///
+    /// This is used by the I/O driver during the shutdown process to notify
+    /// each pending task.
+    pub(crate) fn for_each(&mut self, mut f: impl FnMut(&T)) {
+        for page_idx in 0..self.pages.len() {
+            // It is required to avoid holding the lock when calling the
+            // provided function. The function may attempt to acquire the lock
+            // itself. If we hold the lock here while calling `f`, a deadlock
+            // situation is possible.
+            //
+            // Instead of iterating the slots directly in `page`, which would
+            // require holding the lock, the cache is updated and the slots are
+            // iterated from the cache.
+            self.cached[page_idx].refresh(&self.pages[page_idx]);
+
+            for slot_idx in 0..self.cached[page_idx].init {
+                f(self.cached[page_idx].get(slot_idx));
+            }
+        }
+    }
+
+    // Release memory back to the allocator.
+    //
+    // If pages are empty, the underlying memory is released back to the
+    // allocator.
+    pub(crate) fn compact(&mut self) {
+        // Iterate each page except the very first one. The very first page is
+        // never freed.
+        for (idx, page) in self.pages.iter().enumerate().skip(1) {
+            if page.used.load(Relaxed) != 0 || !page.allocated.load(Relaxed) {
+                // If the page has slots in use or the memory has not been
+                // allocated then it cannot be compacted.
+                continue;
+            }
+
+            let mut slots = match page.slots.try_lock() {
+                Some(slots) => slots,
+                // If the lock cannot be acquired due to being held by another
+                // thread, don't try to compact the page.
+                _ => continue,
+            };
+
+            if slots.used > 0 || slots.slots.capacity() == 0 {
+                // The page is in use or it has not yet been allocated. Either
+                // way, there is no more work to do.
+                continue;
+            }
+
+            page.allocated.store(false, Relaxed);
+
+            // Remove the slots vector from the page. This is done so that the
+            // freeing process is done outside of the lock's critical section.
+            let vec = mem::take(&mut slots.slots);
+            slots.head = 0;
+
+            // Drop the lock so we can drop the vector outside the lock below.
+            drop(slots);
+
+            debug_assert!(
+                self.cached[idx].slots.is_null() || self.cached[idx].slots == vec.as_ptr(),
+                "cached = {:?}; actual = {:?}",
+                self.cached[idx].slots,
+                vec.as_ptr(),
+            );
+
+            // Clear cache
+            self.cached[idx].slots = ptr::null();
+            self.cached[idx].init = 0;
+
+            drop(vec);
+        }
+    }
+}
+
+impl<T> fmt::Debug for Slab<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        debug(fmt, "Slab", &self.pages[..])
+    }
+}
+
+impl<T: Entry> Allocator<T> {
+    /// Allocate a new entry and return a handle to the entry.
+    ///
+    /// Scans pages from smallest to biggest, stopping when a slot is found.
+    /// Pages are allocated if necessary.
+    ///
+    /// Returns `None` if the slab is full.
+    pub(crate) fn allocate(&self) -> Option<(Address, Ref<T>)> {
+        // Find the first available slot.
+        for page in &self.pages[..] {
+            if let Some((addr, val)) = Page::allocate(page) {
+                return Some((addr, val));
+            }
+        }
+
+        None
+    }
+}
+
+impl<T> fmt::Debug for Allocator<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        debug(fmt, "slab::Allocator", &self.pages[..])
+    }
+}
+
+impl<T> ops::Deref for Ref<T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        // Safety: `&mut` is never handed out to the underlying value. The page
+        // is not freed until all `Ref` values are dropped.
+        unsafe { &(*self.value).value }
+    }
+}
+
+impl<T> Drop for Ref<T> {
+    fn drop(&mut self) {
+        // Safety: `&mut` is never handed out to the underlying value. The page
+        // is not freed until all `Ref` values are dropped.
+        let _ = unsafe { (*self.value).release() };
+    }
+}
+
+impl<T: fmt::Debug> fmt::Debug for Ref<T> {
+    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
+        (**self).fmt(fmt)
+    }
+}
+
+impl<T: Entry> Page<T> {
+    // Allocates an object, returns the ref and address.
+    //
+    // `self: &Arc<Page<T>>` is avoided here as this would not work with the
+    // loom `Arc`.
+    fn allocate(me: &Arc<Page<T>>) -> Option<(Address, Ref<T>)> {
+        // Before acquiring the lock, use the `used` hint.
+        if me.used.load(Relaxed) == me.len {
+            return None;
+        }
+
+        // Allocating objects requires synchronization
+        let mut locked = me.slots.lock();
+
+        if locked.head < locked.slots.len() {
+            // Re-use an already initialized slot.
+            //
+            // Help out the borrow checker
+            let locked = &mut *locked;
+
+            // Get the index of the slot at the head of the free stack. This is
+            // the slot that will be reused.
+            let idx = locked.head;
+            let slot = &locked.slots[idx];
+
+            // Update the free stack head to point to the next slot.
+            locked.head = slot.next as usize;
+
+            // Increment the number of used slots
+            locked.used += 1;
+            me.used.store(locked.used, Relaxed);
+
+            // Reset the slot
+            slot.value.with(|ptr| unsafe { (*ptr).value.reset() });
+
+            // Return a reference to the slot
+            Some((me.addr(idx), locked.gen_ref(idx, me)))
+        } else if me.len == locked.slots.len() {
+            // The page is full
+            None
+        } else {
+            // No initialized slots are available, but the page has more
+            // capacity. Initialize a new slot.
+            let idx = locked.slots.len();
+
+            if idx == 0 {
+                // The page has not yet been allocated. Allocate the storage for
+                // all page slots.
+                locked.slots.reserve_exact(me.len);
+            }
+
+            // Initialize a new slot
+            locked.slots.push(Slot {
+                value: UnsafeCell::new(Value {
+                    value: Default::default(),
+                    page: Arc::as_ptr(me),
+                }),
+                next: 0,
+                _pin: std::marker::PhantomPinned,
+            });
+
+            // Increment the head to indicate the free stack is empty
+            locked.head += 1;
+
+            // Increment the number of used slots
+            locked.used += 1;
+            me.used.store(locked.used, Relaxed);
+            me.allocated.store(true, Relaxed);
+
+            debug_assert_eq!(locked.slots.len(), locked.head);
+
+            Some((me.addr(idx), locked.gen_ref(idx, me)))
+        }
+    }
+}
+
+impl<T> Page<T> {
+    /// Returns the slot index within the current page referenced by the given
+    /// address.
+    fn slot(&self, addr: Address) -> usize {
+        addr.0 - self.prev_len
+    }
+
+    /// Returns the address for the given slot.
+    fn addr(&self, slot: usize) -> Address {
+        Address(slot + self.prev_len)
+    }
+}
+
+impl<T> Default for Page<T> {
+    fn default() -> Page<T> {
+        Page {
+            used: AtomicUsize::new(0),
+            allocated: AtomicBool::new(false),
+            slots: Mutex::new(Slots {
+                slots: Vec::new(),
+                head: 0,
+                used: 0,
+            }),
+            len: 0,
+            prev_len: 0,
+        }
+    }
+}
+
+impl<T> Page<T> {
+    /// Release a slot into the page's free list.
+    fn release(&self, value: *const Value<T>) {
+        let mut locked = self.slots.lock();
+
+        let idx = locked.index_for(value);
+        locked.slots[idx].next = locked.head as u32;
+        locked.head = idx;
+        locked.used -= 1;
+
+        self.used.store(locked.used, Relaxed);
+    }
+}
+
+impl<T> CachedPage<T> {
+    /// Refreshes the cache.
+    fn refresh(&mut self, page: &Page<T>) {
+        let slots = page.slots.lock();
+
+        if !slots.slots.is_empty() {
+            self.slots = slots.slots.as_ptr();
+            self.init = slots.slots.len();
+        }
+    }
+
+    /// Gets a value by index.
+    fn get(&self, idx: usize) -> &T {
+        assert!(idx < self.init);
+
+        // Safety: Pages are allocated concurrently, but are only ever
+        // **deallocated** by `Slab`. `Slab` will always have a more
+        // conservative view on the state of the slot array. Once `CachedPage`
+        // sees a slot pointer and initialized offset, it will remain valid
+        // until `compact()` is called. The `compact()` function also updates
+        // `CachedPage`.
+        unsafe {
+            let slot = self.slots.add(idx);
+            let value = slot as *const Value<T>;
+
+            &(*value).value
+        }
+    }
+}
+
+impl<T> Default for CachedPage<T> {
+    fn default() -> CachedPage<T> {
+        CachedPage {
+            slots: ptr::null(),
+            init: 0,
+        }
+    }
+}
+
+impl<T> Slots<T> {
+    /// Maps a slot pointer to an offset within the current page.
+    ///
+    /// The pointer math removes the `usize` index from the `Ref` struct,
+    /// shrinking the struct to a single pointer size. The contents of the
+    /// function is safe, the resulting `usize` is bounds checked before being
+    /// used.
+    ///
+    /// # Panics
+    ///
+    /// panics if the provided slot pointer is not contained by the page.
+    fn index_for(&self, slot: *const Value<T>) -> usize {
+        use std::mem;
+
+        let base = &self.slots[0] as *const _ as usize;
+
+        assert!(base != 0, "page is unallocated");
+
+        let slot = slot as usize;
+        let width = mem::size_of::<Slot<T>>();
+
+        assert!(slot >= base, "unexpected pointer");
+
+        let idx = (slot - base) / width;
+        assert!(idx < self.slots.len() as usize);
+
+        idx
+    }
+
+    /// Generates a `Ref` for the slot at the given index. This involves bumping the page's ref count.
+    fn gen_ref(&self, idx: usize, page: &Arc<Page<T>>) -> Ref<T> {
+        assert!(idx < self.slots.len());
+        mem::forget(page.clone());
+
+        let vec_ptr = self.slots.as_ptr();
+        let slot: *const Slot<T> = unsafe { vec_ptr.add(idx) };
+        let value: *const Value<T> = slot as *const Value<T>;
+
+        Ref { value }
+    }
+}
+
+impl<T> Value<T> {
+    /// Releases the slot, returning the `Arc<Page<T>>` logically owned by the ref.
+    fn release(&self) -> Arc<Page<T>> {
+        // Safety: called by `Ref`, which owns an `Arc<Page<T>>` instance.
+        let page = unsafe { Arc::from_raw(self.page) };
+        page.release(self as *const _);
+        page
+    }
+}
+
+impl Address {
+    fn page(self) -> usize {
+        // Since every page is twice as large as the previous page, and all page
+        // sizes are powers of two, we can determine the page index that
+        // contains a given address by shifting the address down by the smallest
+        // page size and looking at how many twos places necessary to represent
+        // that number, telling us what power of two page size it fits inside
+        // of. We can determine the number of twos places by counting the number
+        // of leading zeros (unused twos places) in the number's binary
+        // representation, and subtracting that count from the total number of
+        // bits in a word.
+        let slot_shifted = (self.0 + PAGE_INITIAL_SIZE) >> PAGE_INDEX_SHIFT;
+        (bit::pointer_width() - slot_shifted.leading_zeros()) as usize
+    }
+
+    pub(crate) const fn as_usize(self) -> usize {
+        self.0
+    }
+
+    pub(crate) fn from_usize(src: usize) -> Address {
+        Address(src)
+    }
+}
+
+fn debug<T>(fmt: &mut fmt::Formatter<'_>, name: &str, pages: &[Arc<Page<T>>]) -> fmt::Result {
+    let mut capacity = 0;
+    let mut len = 0;
+
+    for page in pages {
+        if page.allocated.load(Relaxed) {
+            capacity += page.len;
+            len += page.used.load(Relaxed);
+        }
+    }
+
+    fmt.debug_struct(name)
+        .field("len", &len)
+        .field("capacity", &capacity)
+        .finish()
+}
+
+#[cfg(all(test, not(loom)))]
+mod test {
+    use super::*;
+    use std::sync::atomic::AtomicUsize;
+    use std::sync::atomic::Ordering::SeqCst;
+
+    struct Foo {
+        cnt: AtomicUsize,
+        id: AtomicUsize,
+    }
+
+    impl Default for Foo {
+        fn default() -> Foo {
+            Foo {
+                cnt: AtomicUsize::new(0),
+                id: AtomicUsize::new(0),
+            }
+        }
+    }
+
+    impl Entry for Foo {
+        fn reset(&self) {
+            self.cnt.fetch_add(1, SeqCst);
+        }
+    }
+
+    #[test]
+    fn insert_remove() {
+        let mut slab = Slab::<Foo>::new();
+        let alloc = slab.allocator();
+
+        let (addr1, foo1) = alloc.allocate().unwrap();
+        foo1.id.store(1, SeqCst);
+        assert_eq!(0, foo1.cnt.load(SeqCst));
+
+        let (addr2, foo2) = alloc.allocate().unwrap();
+        foo2.id.store(2, SeqCst);
+        assert_eq!(0, foo2.cnt.load(SeqCst));
+
+        assert_eq!(1, slab.get(addr1).unwrap().id.load(SeqCst));
+        assert_eq!(2, slab.get(addr2).unwrap().id.load(SeqCst));
+
+        drop(foo1);
+
+        assert_eq!(1, slab.get(addr1).unwrap().id.load(SeqCst));
+
+        let (addr3, foo3) = alloc.allocate().unwrap();
+        assert_eq!(addr3, addr1);
+        assert_eq!(1, foo3.cnt.load(SeqCst));
+        foo3.id.store(3, SeqCst);
+        assert_eq!(3, slab.get(addr3).unwrap().id.load(SeqCst));
+
+        drop(foo2);
+        drop(foo3);
+
+        slab.compact();
+
+        // The first page is never released
+        assert!(slab.get(addr1).is_some());
+        assert!(slab.get(addr2).is_some());
+        assert!(slab.get(addr3).is_some());
+    }
+
+    #[test]
+    fn insert_many() {
+        const MANY: usize = normal_or_miri(10_000, 50);
+
+        let mut slab = Slab::<Foo>::new();
+        let alloc = slab.allocator();
+        let mut entries = vec![];
+
+        for i in 0..MANY {
+            let (addr, val) = alloc.allocate().unwrap();
+            val.id.store(i, SeqCst);
+            entries.push((addr, val));
+        }
+
+        for (i, (addr, v)) in entries.iter().enumerate() {
+            assert_eq!(i, v.id.load(SeqCst));
+            assert_eq!(i, slab.get(*addr).unwrap().id.load(SeqCst));
+        }
+
+        entries.clear();
+
+        for i in 0..MANY {
+            let (addr, val) = alloc.allocate().unwrap();
+            val.id.store(MANY - i, SeqCst);
+            entries.push((addr, val));
+        }
+
+        for (i, (addr, v)) in entries.iter().enumerate() {
+            assert_eq!(MANY - i, v.id.load(SeqCst));
+            assert_eq!(MANY - i, slab.get(*addr).unwrap().id.load(SeqCst));
+        }
+    }
+
+    #[test]
+    fn insert_drop_reverse() {
+        let mut slab = Slab::<Foo>::new();
+        let alloc = slab.allocator();
+        let mut entries = vec![];
+
+        for i in 0..normal_or_miri(10_000, 100) {
+            let (addr, val) = alloc.allocate().unwrap();
+            val.id.store(i, SeqCst);
+            entries.push((addr, val));
+        }
+
+        for _ in 0..10 {
+            // Drop 1000 in reverse
+            for _ in 0..normal_or_miri(1_000, 10) {
+                entries.pop();
+            }
+
+            // Check remaining
+            for (i, (addr, v)) in entries.iter().enumerate() {
+                assert_eq!(i, v.id.load(SeqCst));
+                assert_eq!(i, slab.get(*addr).unwrap().id.load(SeqCst));
+            }
+        }
+    }
+
+    #[test]
+    fn no_compaction_if_page_still_in_use() {
+        let mut slab = Slab::<Foo>::new();
+        let alloc = slab.allocator();
+        let mut entries1 = vec![];
+        let mut entries2 = vec![];
+
+        for i in 0..normal_or_miri(10_000, 100) {
+            let (addr, val) = alloc.allocate().unwrap();
+            val.id.store(i, SeqCst);
+
+            if i % 2 == 0 {
+                entries1.push((addr, val, i));
+            } else {
+                entries2.push(val);
+            }
+        }
+
+        drop(entries2);
+
+        for (addr, _, i) in &entries1 {
+            assert_eq!(*i, slab.get(*addr).unwrap().id.load(SeqCst));
+        }
+    }
+
+    const fn normal_or_miri(normal: usize, miri: usize) -> usize {
+        if cfg!(miri) {
+            miri
+        } else {
+            normal
+        }
+    }
+
+    #[test]
+    fn compact_all() {
+        let mut slab = Slab::<Foo>::new();
+        let alloc = slab.allocator();
+        let mut entries = vec![];
+
+        for _ in 0..2 {
+            entries.clear();
+
+            for i in 0..normal_or_miri(10_000, 100) {
+                let (addr, val) = alloc.allocate().unwrap();
+                val.id.store(i, SeqCst);
+
+                entries.push((addr, val));
+            }
+
+            let mut addrs = vec![];
+
+            for (addr, _) in entries.drain(..) {
+                addrs.push(addr);
+            }
+
+            slab.compact();
+
+            // The first page is never freed
+            for addr in &addrs[PAGE_INITIAL_SIZE..] {
+                assert!(slab.get(*addr).is_none());
+            }
+        }
+    }
+
+    #[test]
+    fn issue_3014() {
+        let mut slab = Slab::<Foo>::new();
+        let alloc = slab.allocator();
+        let mut entries = vec![];
+
+        for _ in 0..normal_or_miri(5, 2) {
+            entries.clear();
+
+            // Allocate a few pages + 1
+            for i in 0..(32 + 64 + 128 + 1) {
+                let (addr, val) = alloc.allocate().unwrap();
+                val.id.store(i, SeqCst);
+
+                entries.push((addr, val, i));
+            }
+
+            for (addr, val, i) in &entries {
+                assert_eq!(*i, val.id.load(SeqCst));
+                assert_eq!(*i, slab.get(*addr).unwrap().id.load(SeqCst));
+            }
+
+            // Release the last entry
+            entries.pop();
+
+            // Compact
+            slab.compact();
+
+            // Check all the addresses
+
+            for (addr, val, i) in &entries {
+                assert_eq!(*i, val.id.load(SeqCst));
+                assert_eq!(*i, slab.get(*addr).unwrap().id.load(SeqCst));
+            }
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/util/sync_wrapper.rs b/third_party/rust/tokio/src/util/sync_wrapper.rs
new file mode 100644
index 0000000000..5ffc8f96b1
--- /dev/null
+++ b/third_party/rust/tokio/src/util/sync_wrapper.rs
@@ -0,0 +1,26 @@
+//! This module contains a type that can make `Send + !Sync` types `Sync` by
+//! disallowing all immutable access to the value.
+//!
+//! A similar primitive is provided in the `sync_wrapper` crate.
+
+pub(crate) struct SyncWrapper<T> {
+    value: T,
+}
+
+// safety: The SyncWrapper being send allows you to send the inner value across
+// thread boundaries.
+unsafe impl<T: Send> Send for SyncWrapper<T> {}
+
+// safety: An immutable reference to a SyncWrapper is useless, so moving such an
+// immutable reference across threads is safe.
+unsafe impl<T> Sync for SyncWrapper<T> {}
+
+impl<T> SyncWrapper<T> {
+    pub(crate) fn new(value: T) -> Self {
+        Self { value }
+    }
+
+    pub(crate) fn into_inner(self) -> T {
+        self.value
+    }
+}
diff --git a/third_party/rust/tokio/src/util/trace.rs b/third_party/rust/tokio/src/util/trace.rs
new file mode 100644
index 0000000000..6080e2358a
--- /dev/null
+++ b/third_party/rust/tokio/src/util/trace.rs
@@ -0,0 +1,99 @@
+cfg_trace! {
+    cfg_rt! {
+        use core::{
+            pin::Pin,
+            task::{Context, Poll},
+        };
+        use pin_project_lite::pin_project;
+        use std::future::Future;
+        pub(crate) use tracing::instrument::Instrumented;
+
+        #[inline]
+        #[track_caller]
+        pub(crate) fn task<F>(task: F, kind: &'static str, name: Option<&str>) -> Instrumented<F> {
+            use tracing::instrument::Instrument;
+            let location = std::panic::Location::caller();
+            let span = tracing::trace_span!(
+                target: "tokio::task",
+                "runtime.spawn",
+                %kind,
+                task.name = %name.unwrap_or_default(),
+                loc.file = location.file(),
+                loc.line = location.line(),
+                loc.col = location.column(),
+            );
+            task.instrument(span)
+        }
+
+        pub(crate) fn async_op<P,F>(inner: P, resource_span: tracing::Span, source: &str, poll_op_name: &'static str, inherits_child_attrs: bool) -> InstrumentedAsyncOp<F>
+        where P: FnOnce() -> F {
+            resource_span.in_scope(|| {
+                let async_op_span = tracing::trace_span!("runtime.resource.async_op", source = source, inherits_child_attrs = inherits_child_attrs);
+                let enter = async_op_span.enter();
+                let async_op_poll_span = tracing::trace_span!("runtime.resource.async_op.poll");
+                let inner = inner();
+                drop(enter);
+                let tracing_ctx = AsyncOpTracingCtx {
+                    async_op_span,
+                    async_op_poll_span,
+                    resource_span: resource_span.clone(),
+                };
+                InstrumentedAsyncOp {
+                    inner,
+                    tracing_ctx,
+                    poll_op_name,
+                }
+            })
+        }
+
+        #[derive(Debug, Clone)]
+        pub(crate) struct AsyncOpTracingCtx {
+            pub(crate) async_op_span: tracing::Span,
+            pub(crate) async_op_poll_span: tracing::Span,
+            pub(crate) resource_span: tracing::Span,
+        }
+
+
+        pin_project! {
+            #[derive(Debug, Clone)]
+            pub(crate) struct InstrumentedAsyncOp<F> {
+                #[pin]
+                pub(crate) inner: F,
+                pub(crate) tracing_ctx: AsyncOpTracingCtx,
+                pub(crate) poll_op_name: &'static str
+            }
+        }
+
+        impl<F: Future> Future for InstrumentedAsyncOp<F> {
+            type Output = F::Output;
+
+            fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+                let this = self.project();
+                let poll_op_name = &*this.poll_op_name;
+                let _res_enter = this.tracing_ctx.resource_span.enter();
+                let _async_op_enter = this.tracing_ctx.async_op_span.enter();
+                let _async_op_poll_enter = this.tracing_ctx.async_op_poll_span.enter();
+                trace_poll_op!(poll_op_name, this.inner.poll(cx))
+            }
+        }
+    }
+}
+cfg_time! {
+    #[track_caller]
+    pub(crate) fn caller_location() -> Option<&'static std::panic::Location<'static>> {
+        #[cfg(all(tokio_unstable, feature = "tracing"))]
+        return Some(std::panic::Location::caller());
+        #[cfg(not(all(tokio_unstable, feature = "tracing")))]
+        None
+    }
+}
+
+cfg_not_trace! {
+    cfg_rt! {
+        #[inline]
+        pub(crate) fn task<F>(task: F, _: &'static str, _name: Option<&str>) -> F {
+            // nop
+            task
+        }
+    }
+}
diff --git a/third_party/rust/tokio/src/util/try_lock.rs b/third_party/rust/tokio/src/util/try_lock.rs
new file mode 100644
index 0000000000..8b0edb4a87
--- /dev/null
+++ b/third_party/rust/tokio/src/util/try_lock.rs
@@ -0,0 +1,80 @@
+use crate::loom::sync::atomic::AtomicBool;
+
+use std::cell::UnsafeCell;
+use std::marker::PhantomData;
+use std::ops::{Deref, DerefMut};
+use std::sync::atomic::Ordering::SeqCst;
+
+pub(crate) struct TryLock<T> {
+    locked: AtomicBool,
+    data: UnsafeCell<T>,
+}
+
+pub(crate) struct LockGuard<'a, T> {
+    lock: &'a TryLock<T>,
+    _p: PhantomData<std::rc::Rc<()>>,
+}
+
+unsafe impl<T: Send> Send for TryLock<T> {}
+unsafe impl<T: Send> Sync for TryLock<T> {}
+
+unsafe impl<T: Sync> Sync for LockGuard<'_, T> {}
+
+macro_rules! new {
+    ($data:ident) => {
+        TryLock {
+            locked: AtomicBool::new(false),
+            data: UnsafeCell::new($data),
+        }
+    };
+}
+
+impl<T> TryLock<T> {
+    #[cfg(not(loom))]
+    /// Create a new `TryLock`
+    pub(crate) const fn new(data: T) -> TryLock<T> {
+        new!(data)
+    }
+
+    #[cfg(loom)]
+    /// Create a new `TryLock`
+    pub(crate) fn new(data: T) -> TryLock<T> {
+        new!(data)
+    }
+
+    /// Attempt to acquire lock
+    pub(crate) fn try_lock(&self) -> Option<LockGuard<'_, T>> {
+        if self
+            .locked
+            .compare_exchange(false, true, SeqCst, SeqCst)
+            .is_err()
+        {
+            return None;
+        }
+
+        Some(LockGuard {
+            lock: self,
+            _p: PhantomData,
+        })
+    }
+}
+
+impl<T> Deref for LockGuard<'_, T> {
+    type Target = T;
+
+    fn deref(&self) -> &T {
+        unsafe { &*self.lock.data.get() }
+    }
+}
+
+impl<T> DerefMut for LockGuard<'_, T> {
+    fn deref_mut(&mut self) -> &mut T {
+        unsafe { &mut *self.lock.data.get() }
+    }
+}
+
+impl<T> Drop for LockGuard<'_, T> {
+    fn drop(&mut self) {
+        self.lock.locked.store(false, SeqCst);
+    }
+}
diff --git a/third_party/rust/tokio/src/util/vec_deque_cell.rs b/third_party/rust/tokio/src/util/vec_deque_cell.rs
new file mode 100644
index 0000000000..b4e124c151
--- /dev/null
+++ b/third_party/rust/tokio/src/util/vec_deque_cell.rs
@@ -0,0 +1,53 @@
+use crate::loom::cell::UnsafeCell;
+
+use std::collections::VecDeque;
+use std::marker::PhantomData;
+
+/// This type is like VecDeque, except that it is not Sync and can be modified
+/// through immutable references.
+pub(crate) struct VecDequeCell<T> {
+    inner: UnsafeCell<VecDeque<T>>,
+    _not_sync: PhantomData<*const ()>,
+}
+
+// This is Send for the same reasons that RefCell<VecDeque<T>> is Send.
+unsafe impl<T: Send> Send for VecDequeCell<T> {}
+
+impl<T> VecDequeCell<T> {
+    pub(crate) fn with_capacity(cap: usize) -> Self {
+        Self {
+            inner: UnsafeCell::new(VecDeque::with_capacity(cap)),
+            _not_sync: PhantomData,
+        }
+    }
+
+    /// Safety: This method may not be called recursively.
+    #[inline]
+    unsafe fn with_inner<F, R>(&self, f: F) -> R
+    where
+        F: FnOnce(&mut VecDeque<T>) -> R,
+    {
+        // safety: This type is not Sync, so concurrent calls of this method
+        // cannot happen. Furthermore, the caller guarantees that the method is
+        // not called recursively. Finally, this is the only place that can
+        // create mutable references to the inner VecDeque. This ensures that
+        // any mutable references created here are exclusive.
+        self.inner.with_mut(|ptr| f(&mut *ptr))
+    }
+
+    pub(crate) fn pop_front(&self) -> Option<T> {
+        unsafe { self.with_inner(VecDeque::pop_front) }
+    }
+
+    pub(crate) fn push_back(&self, item: T) {
+        unsafe {
+            self.with_inner(|inner| inner.push_back(item));
+        }
+    }
+
+    /// Replaces the inner VecDeque with an empty VecDeque and return the current
+    /// contents.
+    pub(crate) fn take(&self) -> VecDeque<T> {
+        unsafe { self.with_inner(|inner| std::mem::take(inner)) }
+    }
+}
diff --git a/third_party/rust/tokio/src/util/wake.rs b/third_party/rust/tokio/src/util/wake.rs
new file mode 100644
index 0000000000..5526cbc63a
--- /dev/null
+++ b/third_party/rust/tokio/src/util/wake.rs
@@ -0,0 +1,80 @@
+use crate::loom::sync::Arc;
+
+use std::marker::PhantomData;
+use std::mem::ManuallyDrop;
+use std::ops::Deref;
+use std::task::{RawWaker, RawWakerVTable, Waker};
+
+/// Simplified waking interface based on Arcs.
+pub(crate) trait Wake: Send + Sync + Sized + 'static {
+    /// Wake by value.
+    fn wake(arc_self: Arc<Self>);
+
+    /// Wake by reference.
+    fn wake_by_ref(arc_self: &Arc<Self>);
+}
+
+/// A `Waker` that is only valid for a given lifetime.
+#[derive(Debug)]
+pub(crate) struct WakerRef<'a> {
+    waker: ManuallyDrop<Waker>,
+    _p: PhantomData<&'a ()>,
+}
+
+impl Deref for WakerRef<'_> {
+    type Target = Waker;
+
+    fn deref(&self) -> &Waker {
+        &self.waker
+    }
+}
+
+/// Creates a reference to a `Waker` from a reference to `Arc<impl Wake>`.
+pub(crate) fn waker_ref<W: Wake>(wake: &Arc<W>) -> WakerRef<'_> {
+    let ptr = Arc::as_ptr(wake) as *const ();
+
+    let waker = unsafe { Waker::from_raw(RawWaker::new(ptr, waker_vtable::<W>())) };
+
+    WakerRef {
+        waker: ManuallyDrop::new(waker),
+        _p: PhantomData,
+    }
+}
+
+fn waker_vtable<W: Wake>() -> &'static RawWakerVTable {
+    &RawWakerVTable::new(
+        clone_arc_raw::<W>,
+        wake_arc_raw::<W>,
+        wake_by_ref_arc_raw::<W>,
+        drop_arc_raw::<W>,
+    )
+}
+
+unsafe fn inc_ref_count<T: Wake>(data: *const ()) {
+    // Retain Arc, but don't touch refcount by wrapping in ManuallyDrop
+    let arc = ManuallyDrop::new(Arc::<T>::from_raw(data as *const T));
+
+    // Now increase refcount, but don't drop new refcount either
+    let _arc_clone: ManuallyDrop<_> = arc.clone();
+}
+
+unsafe fn clone_arc_raw<T: Wake>(data: *const ()) -> RawWaker {
+    inc_ref_count::<T>(data);
+    RawWaker::new(data, waker_vtable::<T>())
+}
+
+unsafe fn wake_arc_raw<T: Wake>(data: *const ()) {
+    let arc: Arc<T> = Arc::from_raw(data as *const T);
+    Wake::wake(arc);
+}
+
+// used by `waker_ref`
+unsafe fn wake_by_ref_arc_raw<T: Wake>(data: *const ()) {
+    // Retain Arc, but don't touch refcount by wrapping in ManuallyDrop
+    let arc = ManuallyDrop::new(Arc::<T>::from_raw(data as *const T));
+    Wake::wake_by_ref(&arc);
+}
+
+unsafe fn drop_arc_raw<T: Wake>(data: *const ()) {
+    drop(Arc::<T>::from_raw(data as *const T))
+}
diff --git a/third_party/rust/tokio/src/util/wake_list.rs b/third_party/rust/tokio/src/util/wake_list.rs
new file mode 100644
index 0000000000..aa569dd17b
--- /dev/null
+++ b/third_party/rust/tokio/src/util/wake_list.rs
@@ -0,0 +1,53 @@
+use core::mem::MaybeUninit;
+use core::ptr;
+use std::task::Waker;
+
+const NUM_WAKERS: usize = 32;
+
+pub(crate) struct WakeList {
+    inner: [MaybeUninit<Waker>; NUM_WAKERS],
+    curr: usize,
+}
+
+impl WakeList {
+    pub(crate) fn new() -> Self {
+        Self {
+            inner: unsafe {
+                // safety: Create an uninitialized array of `MaybeUninit`. The
+                // `assume_init` is safe because the type we are claiming to
+                // have initialized here is a bunch of `MaybeUninit`s, which do
+                // not require initialization.
+                MaybeUninit::uninit().assume_init()
+            },
+            curr: 0,
+        }
+    }
+
+    #[inline]
+    pub(crate) fn can_push(&self) -> bool {
+        self.curr < NUM_WAKERS
+    }
+
+    pub(crate) fn push(&mut self, val: Waker) {
+        debug_assert!(self.can_push());
+
+        self.inner[self.curr] = MaybeUninit::new(val);
+        self.curr += 1;
+    }
+
+    pub(crate) fn wake_all(&mut self) {
+        assert!(self.curr <= NUM_WAKERS);
+        while self.curr > 0 {
+            self.curr -= 1;
+            let waker = unsafe { ptr::read(self.inner[self.curr].as_mut_ptr()) };
+            waker.wake();
+        }
+    }
+}
+
+impl Drop for WakeList {
+    fn drop(&mut self) {
+        let slice = ptr::slice_from_raw_parts_mut(self.inner.as_mut_ptr() as *mut Waker, self.curr);
+        unsafe { ptr::drop_in_place(slice) };
+    }
+}