Adding upstream version 86.0.1.upstream/86.0.1upstream

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

11 files changed, 1740 insertions, 0 deletions

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..18beb1bdbb
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/cfg.rs
@@ -0,0 +1,322 @@
+#![allow(unused_macros)]
+
+macro_rules! cfg_resource_drivers {
+    ($($item:item)*) => {
+        $(
+            #[cfg(any(feature = "io-driver", feature = "time"))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_blocking {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "blocking")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "blocking")))]
+            $item
+        )*
+    }
+}
+
+/// Enables blocking API internals
+macro_rules! cfg_blocking_impl {
+    ($($item:item)*) => {
+        $(
+            #[cfg(any(
+                    feature = "blocking",
+                    feature = "fs",
+                    feature = "dns",
+                    feature = "io-std",
+                    feature = "rt-threaded",
+                    ))]
+            $item
+        )*
+    }
+}
+
+/// Enables blocking API internals
+macro_rules! cfg_not_blocking_impl {
+    ($($item:item)*) => {
+        $(
+            #[cfg(not(any(
+                        feature = "blocking",
+                        feature = "fs",
+                        feature = "dns",
+                        feature = "io-std",
+                        feature = "rt-threaded",
+                        )))]
+            $item
+        )*
+    }
+}
+
+/// Enables internal `AtomicWaker` impl
+macro_rules! cfg_atomic_waker_impl {
+    ($($item:item)*) => {
+        $(
+            #[cfg(any(
+                feature = "io-driver",
+                feature = "time",
+                all(feature = "rt-core", feature = "rt-util")
+            ))]
+            #[cfg(not(loom))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_dns {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "dns")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "dns")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_fs {
+    ($($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(feature = "io-driver")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "io-driver")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_not_io_driver {
+    ($($item:item)*) => {
+        $(
+            #[cfg(not(feature = "io-driver"))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_io_std {
+    ($($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")))]
+            #[doc(inline)]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_process {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "process")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "process")))]
+            #[cfg(not(loom))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_signal {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "signal")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "signal")))]
+            #[cfg(not(loom))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_stream {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "stream")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "stream")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_sync {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "sync")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "sync")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_not_sync {
+    ($($item:item)*) => {
+        $( #[cfg(not(feature = "sync"))] $item )*
+    }
+}
+
+macro_rules! cfg_rt_core {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "rt-core")]
+            $item
+        )*
+    }
+}
+
+macro_rules! doc_rt_core {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "rt-core")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "rt-core")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_not_rt_core {
+    ($($item:item)*) => {
+        $( #[cfg(not(feature = "rt-core"))] $item )*
+    }
+}
+
+macro_rules! cfg_rt_threaded {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "rt-threaded")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "rt-threaded")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_rt_util {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "rt-util")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "rt-util")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_not_rt_threaded {
+    ($($item:item)*) => {
+        $( #[cfg(not(feature = "rt-threaded"))] $item )*
+    }
+}
+
+macro_rules! cfg_tcp {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "tcp")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "tcp")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_test_util {
+    ($($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"))] $item )*
+    }
+}
+
+macro_rules! cfg_udp {
+    ($($item:item)*) => {
+        $(
+            #[cfg(feature = "udp")]
+            #[cfg_attr(docsrs, doc(cfg(feature = "udp")))]
+            $item
+        )*
+    }
+}
+
+macro_rules! cfg_uds {
+    ($($item:item)*) => {
+        $(
+            #[cfg(all(unix, feature = "uds"))]
+            #[cfg_attr(docsrs, doc(cfg(feature = "uds")))]
+            $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..5f37af510d
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/join.rs
@@ -0,0 +1,119 @@
+/// Wait 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..2643c36018
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/mod.rs
@@ -0,0 +1,35 @@
+#![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;
+
+#[macro_use]
+#[cfg(feature = "rt-core")]
+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..33d8499e10
--- /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`]: https://doc.rust-lang.org/std/future/trait.Future.html
+/// [`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, 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 $e {
+            std::task::Poll::Ready(t) => t,
+            std::task::Poll::Pending => return std::task::Poll::Pending,
+        }
+    };
+}
diff --git a/third_party/rust/tokio/src/macros/scoped_tls.rs b/third_party/rust/tokio/src/macros/scoped_tls.rs
new file mode 100644
index 0000000000..666f382b28
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/scoped_tls.rs
@@ -0,0 +1,80 @@
+use crate::loom::thread::LocalKey;
+
+use std::cell::Cell;
+use std::marker;
+
+/// Set a reference as a thread-local
+#[macro_export]
+macro_rules! scoped_thread_local {
+    ($(#[$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> {
+    #[doc(hidden)]
+    pub(crate) inner: &'static LocalKey<Cell<*const ()>>,
+    #[doc(hidden)]
+    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..51b6fcd608
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/select.rs
@@ -0,0 +1,876 @@
+/// Wait 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. This
+/// precondition is evaluated **before** the `<async expression>`. If the
+/// precondition returns `false`, the branch is entirely disabled. This
+/// capability is useful when using `select!` within a loop.
+///
+/// The complete lifecycle of a `select!` expression is as follows:
+///
+/// 1. Evaluate all provded `<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 none
+///    is provided, panic.
+///
+/// # Notes
+///
+/// ### 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
+///
+/// ### 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 `delay` with `if`. The objective
+/// is to repeatedly run an asynchronous task for up to 50 milliseconds.
+/// However, there is a potential for the `delay` completion to be missed.
+///
+/// ```no_run
+/// use tokio::time::{self, Duration};
+///
+/// async fn some_async_work() {
+///     // do work
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let mut delay = time::delay_for(Duration::from_millis(50));
+///
+///     while !delay.is_elapsed() {
+///         tokio::select! {
+///             _ = &mut delay, if !delay.is_elapsed() => {
+///                 println!("operation timed out");
+///             }
+///             _ = some_async_work() => {
+///                 println!("operation completed");
+///             }
+///         }
+///     }
+/// }
+/// ```
+///
+/// In the above example, `delay.is_elapsed()` may return `true` even if
+/// `delay.poll()` never returned `Ready`. This opens up a potential race
+/// condition where `delay` expires between the `while !delay.is_elapsed()`
+/// check and the call to `select!` resulting in the `some_async_work()` call to
+/// run uninterrupted despite the delay 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::delay_for(Duration::from_millis(10)).await;
+///     // do work
+/// }
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let mut delay = time::delay_for(Duration::from_millis(50));
+///
+///     loop {
+///         tokio::select! {
+///             _ = &mut delay => {
+///                 println!("operation timed out");
+///                 break;
+///             }
+///             _ = some_async_work() => {
+///                 println!("operation completed");
+///             }
+///         }
+///     }
+/// }
+/// ```
+///
+/// ### Fairness
+///
+/// `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.
+///
+/// # Panics
+///
+/// `select!` 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>.
+///
+/// # 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, 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, 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, StreamExt};
+/// use tokio::time::{self, Duration};
+///
+/// #[tokio::main]
+/// async fn main() {
+///     let mut stream = stream::iter(vec![1, 2, 3]);
+///     let mut delay = time::delay_for(Duration::from_secs(1));
+///
+///     loop {
+///         tokio::select! {
+///             maybe_v = stream.next() => {
+///                 if let Some(v) = maybe_v {
+///                     println!("got = {}", v);
+///                 } else {
+///                     break;
+///                 }
+///             }
+///             _ = &mut delay => {
+///                 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");
+/// }
+/// ```
+#[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.
+    (@ {
+        // 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 = 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;
+
+                // Randomly generate a starting point. This makes `select!` a
+                // bit more fair and avoids always polling the first future.
+                let start = $crate::macros::support::thread_rng_n(BRANCHES);
+
+                for i in 0..BRANCHES {
+                    let branch = (start + i) % BRANCHES;
+
+                    match branch {
+                        $(
+                            $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 fut.poll(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)]
+                                match &out {
+                                    $bind => {}
+                                    _ => continue,
+                                }
+
+                                // The select is complete, return the value
+                                return Ready($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.
+
+    (@ { $($t:tt)* } ) => {
+        // No `else` branch
+        $crate::select!(@{ $($t)*; unreachable!() })
+    };
+    (@ { $($t:tt)* } else => $else:expr $(,)?) => {
+        $crate::select!(@{ $($t)*; $else })
+    };
+    (@ { ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr, if $c:expr => $h:block, $($r:tt)* ) => {
+        $crate::select!(@{ ($($s)* _) $($t)* ($($s)*) $p = $f, if $c => $h, } $($r)*)
+    };
+    (@ { ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr => $h:block, $($r:tt)* ) => {
+        $crate::select!(@{ ($($s)* _) $($t)* ($($s)*) $p = $f, if true => $h, } $($r)*)
+    };
+    (@ { ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr, if $c:expr => $h:block $($r:tt)* ) => {
+        $crate::select!(@{ ($($s)* _) $($t)* ($($s)*) $p = $f, if $c => $h, } $($r)*)
+    };
+    (@ { ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr => $h:block $($r:tt)* ) => {
+        $crate::select!(@{ ($($s)* _) $($t)* ($($s)*) $p = $f, if true => $h, } $($r)*)
+    };
+    (@ { ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr, if $c:expr => $h:expr ) => {
+        $crate::select!(@{ ($($s)* _) $($t)* ($($s)*) $p = $f, if $c => $h, })
+    };
+    (@ { ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr => $h:expr ) => {
+        $crate::select!(@{ ($($s)* _) $($t)* ($($s)*) $p = $f, if true => $h, })
+    };
+    (@ { ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr, if $c:expr => $h:expr, $($r:tt)* ) => {
+        $crate::select!(@{ ($($s)* _) $($t)* ($($s)*) $p = $f, if $c => $h, } $($r)*)
+    };
+    (@ { ( $($s:tt)* ) $($t:tt)* } $p:pat = $f:expr => $h:expr, $($r:tt)* ) => {
+        $crate::select!(@{ ($($s)* _) $($t)* ($($s)*) $p = $f, if true => $h, } $($r)*)
+    };
+
+    // ===== Entry point =====
+
+    ( $p:pat = $($t:tt)* ) => {
+        $crate::select!(@{ () } $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..fc1cdfcfa0
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/support.rs
@@ -0,0 +1,8 @@
+cfg_macros! {
+    pub use crate::future::{maybe_done, poll_fn};
+    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/try_join.rs b/third_party/rust/tokio/src/macros/try_join.rs
new file mode 100644
index 0000000000..fa5850ef0e
--- /dev/null
+++ b/third_party/rust/tokio/src/macros/try_join.rs
@@ -0,0 +1,132 @@
+/// Wait 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);
+///          }
+///     }
+/// }
+/// ```
+#[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,)*)
+    };
+}