Adding upstream version 1.64.0+dfsg1.upstream/1.64.0+dfsg1

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

7 files changed, 800 insertions, 0 deletions

diff --git a/vendor/futures-core/src/future.rs b/vendor/futures-core/src/future.rs
new file mode 100644
index 000000000..7540cd027
--- /dev/null
+++ b/vendor/futures-core/src/future.rs
@@ -0,0 +1,103 @@
+//! Futures.
+
+use core::ops::DerefMut;
+use core::pin::Pin;
+use core::task::{Context, Poll};
+
+#[doc(no_inline)]
+pub use core::future::Future;
+
+/// An owned dynamically typed [`Future`] for use in cases where you can't
+/// statically type your result or need to add some indirection.
+#[cfg(feature = "alloc")]
+pub type BoxFuture<'a, T> = Pin<alloc::boxed::Box<dyn Future<Output = T> + Send + 'a>>;
+
+/// `BoxFuture`, but without the `Send` requirement.
+#[cfg(feature = "alloc")]
+pub type LocalBoxFuture<'a, T> = Pin<alloc::boxed::Box<dyn Future<Output = T> + 'a>>;
+
+/// A future which tracks whether or not the underlying future
+/// should no longer be polled.
+///
+/// `is_terminated` will return `true` if a future should no longer be polled.
+/// Usually, this state occurs after `poll` (or `try_poll`) returned
+/// `Poll::Ready`. However, `is_terminated` may also return `true` if a future
+/// has become inactive and can no longer make progress and should be ignored
+/// or dropped rather than being `poll`ed again.
+pub trait FusedFuture: Future {
+    /// Returns `true` if the underlying future should no longer be polled.
+    fn is_terminated(&self) -> bool;
+}
+
+impl<F: FusedFuture + ?Sized + Unpin> FusedFuture for &mut F {
+    fn is_terminated(&self) -> bool {
+        <F as FusedFuture>::is_terminated(&**self)
+    }
+}
+
+impl<P> FusedFuture for Pin<P>
+where
+    P: DerefMut + Unpin,
+    P::Target: FusedFuture,
+{
+    fn is_terminated(&self) -> bool {
+        <P::Target as FusedFuture>::is_terminated(&**self)
+    }
+}
+
+mod private_try_future {
+    use super::Future;
+
+    pub trait Sealed {}
+
+    impl<F, T, E> Sealed for F where F: ?Sized + Future<Output = Result<T, E>> {}
+}
+
+/// A convenience for futures that return `Result` values that includes
+/// a variety of adapters tailored to such futures.
+pub trait TryFuture: Future + private_try_future::Sealed {
+    /// The type of successful values yielded by this future
+    type Ok;
+
+    /// The type of failures yielded by this future
+    type Error;
+
+    /// Poll this `TryFuture` as if it were a `Future`.
+    ///
+    /// This method is a stopgap for a compiler limitation that prevents us from
+    /// directly inheriting from the `Future` trait; in the future it won't be
+    /// needed.
+    fn try_poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<Self::Ok, Self::Error>>;
+}
+
+impl<F, T, E> TryFuture for F
+where
+    F: ?Sized + Future<Output = Result<T, E>>,
+{
+    type Ok = T;
+    type Error = E;
+
+    #[inline]
+    fn try_poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        self.poll(cx)
+    }
+}
+
+#[cfg(feature = "alloc")]
+mod if_alloc {
+    use super::*;
+    use alloc::boxed::Box;
+
+    impl<F: FusedFuture + ?Sized + Unpin> FusedFuture for Box<F> {
+        fn is_terminated(&self) -> bool {
+            <F as FusedFuture>::is_terminated(&**self)
+        }
+    }
+
+    #[cfg(feature = "std")]
+    impl<F: FusedFuture> FusedFuture for std::panic::AssertUnwindSafe<F> {
+        fn is_terminated(&self) -> bool {
+            <F as FusedFuture>::is_terminated(&**self)
+        }
+    }
+}
diff --git a/vendor/futures-core/src/lib.rs b/vendor/futures-core/src/lib.rs
new file mode 100644
index 000000000..9c31d8d90
--- /dev/null
+++ b/vendor/futures-core/src/lib.rs
@@ -0,0 +1,27 @@
+//! Core traits and types for asynchronous operations in Rust.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+#![warn(missing_debug_implementations, missing_docs, rust_2018_idioms, unreachable_pub)]
+// It cannot be included in the published code because this lints have false positives in the minimum required version.
+#![cfg_attr(test, warn(single_use_lifetimes))]
+#![doc(test(
+    no_crate_inject,
+    attr(
+        deny(warnings, rust_2018_idioms, single_use_lifetimes),
+        allow(dead_code, unused_assignments, unused_variables)
+    )
+))]
+
+#[cfg(feature = "alloc")]
+extern crate alloc;
+
+pub mod future;
+#[doc(no_inline)]
+pub use self::future::{FusedFuture, Future, TryFuture};
+
+pub mod stream;
+#[doc(no_inline)]
+pub use self::stream::{FusedStream, Stream, TryStream};
+
+#[macro_use]
+pub mod task;
diff --git a/vendor/futures-core/src/stream.rs b/vendor/futures-core/src/stream.rs
new file mode 100644
index 000000000..ad5350b79
--- /dev/null
+++ b/vendor/futures-core/src/stream.rs
@@ -0,0 +1,235 @@
+//! Asynchronous streams.
+
+use core::ops::DerefMut;
+use core::pin::Pin;
+use core::task::{Context, Poll};
+
+/// An owned dynamically typed [`Stream`] for use in cases where you can't
+/// statically type your result or need to add some indirection.
+#[cfg(feature = "alloc")]
+pub type BoxStream<'a, T> = Pin<alloc::boxed::Box<dyn Stream<Item = T> + Send + 'a>>;
+
+/// `BoxStream`, but without the `Send` requirement.
+#[cfg(feature = "alloc")]
+pub type LocalBoxStream<'a, T> = Pin<alloc::boxed::Box<dyn Stream<Item = T> + 'a>>;
+
+/// A stream of values produced asynchronously.
+///
+/// If `Future<Output = T>` is an asynchronous version of `T`, then `Stream<Item
+/// = T>` is an asynchronous version of `Iterator<Item = T>`. A stream
+/// represents a sequence of value-producing events that occur asynchronously to
+/// the caller.
+///
+/// The trait is modeled after `Future`, but allows `poll_next` to be called
+/// even after a value has been produced, yielding `None` once the stream has
+/// been fully exhausted.
+#[must_use = "streams do nothing unless polled"]
+pub trait Stream {
+    /// Values yielded by the stream.
+    type Item;
+
+    /// Attempt to pull out the next value of this stream, registering the
+    /// current task for wakeup if the value is not yet available, and returning
+    /// `None` if the stream is exhausted.
+    ///
+    /// # Return value
+    ///
+    /// There are several possible return values, each indicating a distinct
+    /// stream state:
+    ///
+    /// - `Poll::Pending` means that this stream's next value is not ready
+    /// yet. Implementations will ensure that the current task will be notified
+    /// when the next value may be ready.
+    ///
+    /// - `Poll::Ready(Some(val))` means that the stream has successfully
+    /// produced a value, `val`, and may produce further values on subsequent
+    /// `poll_next` calls.
+    ///
+    /// - `Poll::Ready(None)` means that the stream has terminated, and
+    /// `poll_next` should not be invoked again.
+    ///
+    /// # Panics
+    ///
+    /// Once a stream has finished (returned `Ready(None)` from `poll_next`), calling its
+    /// `poll_next` method again may panic, block forever, or cause other kinds of
+    /// problems; the `Stream` trait places no requirements on the effects of
+    /// such a call. However, as the `poll_next` method is not marked `unsafe`,
+    /// Rust's usual rules apply: calls must never cause undefined behavior
+    /// (memory corruption, incorrect use of `unsafe` functions, or the like),
+    /// regardless of the stream's state.
+    ///
+    /// If this is difficult to guard against then the [`fuse`] adapter can be used
+    /// to ensure that `poll_next` always returns `Ready(None)` in subsequent
+    /// calls.
+    ///
+    /// [`fuse`]: https://docs.rs/futures/0.3/futures/stream/trait.StreamExt.html#method.fuse
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>>;
+
+    /// Returns the bounds on the remaining length of the stream.
+    ///
+    /// Specifically, `size_hint()` returns a tuple where the first element
+    /// is the lower bound, and the second element is the upper bound.
+    ///
+    /// The second half of the tuple that is returned is an [`Option`]`<`[`usize`]`>`.
+    /// A [`None`] here means that either there is no known upper bound, or the
+    /// upper bound is larger than [`usize`].
+    ///
+    /// # Implementation notes
+    ///
+    /// It is not enforced that a stream implementation yields the declared
+    /// number of elements. A buggy stream may yield less than the lower bound
+    /// or more than the upper bound of elements.
+    ///
+    /// `size_hint()` is primarily intended to be used for optimizations such as
+    /// reserving space for the elements of the stream, but must not be
+    /// trusted to e.g., omit bounds checks in unsafe code. An incorrect
+    /// implementation of `size_hint()` should not lead to memory safety
+    /// violations.
+    ///
+    /// That said, the implementation should provide a correct estimation,
+    /// because otherwise it would be a violation of the trait's protocol.
+    ///
+    /// The default implementation returns `(0, `[`None`]`)` which is correct for any
+    /// stream.
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (0, None)
+    }
+}
+
+impl<S: ?Sized + Stream + Unpin> Stream for &mut S {
+    type Item = S::Item;
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        S::poll_next(Pin::new(&mut **self), cx)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (**self).size_hint()
+    }
+}
+
+impl<P> Stream for Pin<P>
+where
+    P: DerefMut + Unpin,
+    P::Target: Stream,
+{
+    type Item = <P::Target as Stream>::Item;
+
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        self.get_mut().as_mut().poll_next(cx)
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (**self).size_hint()
+    }
+}
+
+/// A stream which tracks whether or not the underlying stream
+/// should no longer be polled.
+///
+/// `is_terminated` will return `true` if a future should no longer be polled.
+/// Usually, this state occurs after `poll_next` (or `try_poll_next`) returned
+/// `Poll::Ready(None)`. However, `is_terminated` may also return `true` if a
+/// stream has become inactive and can no longer make progress and should be
+/// ignored or dropped rather than being polled again.
+pub trait FusedStream: Stream {
+    /// Returns `true` if the stream should no longer be polled.
+    fn is_terminated(&self) -> bool;
+}
+
+impl<F: ?Sized + FusedStream + Unpin> FusedStream for &mut F {
+    fn is_terminated(&self) -> bool {
+        <F as FusedStream>::is_terminated(&**self)
+    }
+}
+
+impl<P> FusedStream for Pin<P>
+where
+    P: DerefMut + Unpin,
+    P::Target: FusedStream,
+{
+    fn is_terminated(&self) -> bool {
+        <P::Target as FusedStream>::is_terminated(&**self)
+    }
+}
+
+mod private_try_stream {
+    use super::Stream;
+
+    pub trait Sealed {}
+
+    impl<S, T, E> Sealed for S where S: ?Sized + Stream<Item = Result<T, E>> {}
+}
+
+/// A convenience for streams that return `Result` values that includes
+/// a variety of adapters tailored to such futures.
+pub trait TryStream: Stream + private_try_stream::Sealed {
+    /// The type of successful values yielded by this future
+    type Ok;
+
+    /// The type of failures yielded by this future
+    type Error;
+
+    /// Poll this `TryStream` as if it were a `Stream`.
+    ///
+    /// This method is a stopgap for a compiler limitation that prevents us from
+    /// directly inheriting from the `Stream` trait; in the future it won't be
+    /// needed.
+    fn try_poll_next(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<Self::Ok, Self::Error>>>;
+}
+
+impl<S, T, E> TryStream for S
+where
+    S: ?Sized + Stream<Item = Result<T, E>>,
+{
+    type Ok = T;
+    type Error = E;
+
+    fn try_poll_next(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<Self::Ok, Self::Error>>> {
+        self.poll_next(cx)
+    }
+}
+
+#[cfg(feature = "alloc")]
+mod if_alloc {
+    use super::*;
+    use alloc::boxed::Box;
+
+    impl<S: ?Sized + Stream + Unpin> Stream for Box<S> {
+        type Item = S::Item;
+
+        fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+            Pin::new(&mut **self).poll_next(cx)
+        }
+
+        fn size_hint(&self) -> (usize, Option<usize>) {
+            (**self).size_hint()
+        }
+    }
+
+    #[cfg(feature = "std")]
+    impl<S: Stream> Stream for std::panic::AssertUnwindSafe<S> {
+        type Item = S::Item;
+
+        fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<S::Item>> {
+            unsafe { self.map_unchecked_mut(|x| &mut x.0) }.poll_next(cx)
+        }
+
+        fn size_hint(&self) -> (usize, Option<usize>) {
+            self.0.size_hint()
+        }
+    }
+
+    impl<S: ?Sized + FusedStream + Unpin> FusedStream for Box<S> {
+        fn is_terminated(&self) -> bool {
+            <S as FusedStream>::is_terminated(&**self)
+        }
+    }
+}
diff --git a/vendor/futures-core/src/task/__internal/atomic_waker.rs b/vendor/futures-core/src/task/__internal/atomic_waker.rs
new file mode 100644
index 000000000..d49d04361
--- /dev/null
+++ b/vendor/futures-core/src/task/__internal/atomic_waker.rs
@@ -0,0 +1,409 @@
+use core::cell::UnsafeCell;
+use core::fmt;
+use core::sync::atomic::AtomicUsize;
+use core::sync::atomic::Ordering::{AcqRel, Acquire, Release};
+use core::task::Waker;
+
+/// A synchronization primitive for task wakeup.
+///
+/// Sometimes the task interested in a given event will change over time.
+/// An `AtomicWaker` can coordinate concurrent notifications with the consumer
+/// potentially "updating" the underlying task to wake up. This is useful in
+/// scenarios where a computation completes in another thread and wants to
+/// notify 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`.
+///
+/// # Memory ordering
+///
+/// Calling `register` "acquires" all memory "released" by calls to `wake`
+/// before the call to `register`.  Later calls to `wake` will wake the
+/// registered waker (on contention this wake might be triggered in `register`).
+///
+/// For concurrent calls to `register` (should be avoided) the ordering is only
+/// guaranteed for the winning call.
+///
+/// # Examples
+///
+/// Here is a simple example providing a `Flag` that can be signalled manually
+/// when it is ready.
+///
+/// ```
+/// use futures::future::Future;
+/// use futures::task::{Context, Poll, AtomicWaker};
+/// use std::sync::Arc;
+/// use std::sync::atomic::AtomicBool;
+/// use std::sync::atomic::Ordering::Relaxed;
+/// use std::pin::Pin;
+///
+/// struct Inner {
+///     waker: AtomicWaker,
+///     set: AtomicBool,
+/// }
+///
+/// #[derive(Clone)]
+/// struct Flag(Arc<Inner>);
+///
+/// impl Flag {
+///     pub fn new() -> Self {
+///         Self(Arc::new(Inner {
+///             waker: AtomicWaker::new(),
+///             set: AtomicBool::new(false),
+///         }))
+///     }
+///
+///     pub fn signal(&self) {
+///         self.0.set.store(true, Relaxed);
+///         self.0.waker.wake();
+///     }
+/// }
+///
+/// impl Future for Flag {
+///     type Output = ();
+///
+///     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
+///         // quick check to avoid registration if already done.
+///         if self.0.set.load(Relaxed) {
+///             return Poll::Ready(());
+///         }
+///
+///         self.0.waker.register(cx.waker());
+///
+///         // Need to check condition **after** `register` to avoid a race
+///         // condition that would result in lost notifications.
+///         if self.0.set.load(Relaxed) {
+///             Poll::Ready(())
+///         } else {
+///             Poll::Pending
+///         }
+///     }
+/// }
+/// ```
+pub struct AtomicWaker {
+    state: AtomicUsize,
+    waker: UnsafeCell<Option<Waker>>,
+}
+
+// `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 (to wake it) 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.  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 wake itself.
+//
+// If another thread is in the `wake` critical section, then it will handle
+// waking the 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 awoken. The wakers also change the application state before
+// calling wake.
+//
+// Because of this, the waker will do one of two things.
+//
+// 1) Observe the application state change that Thread B is woken for. 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 waker currently registered with the `AtomicWaker` cell is being woken.
+const WAKING: usize = 0b10;
+
+impl AtomicWaker {
+    /// Create an `AtomicWaker`.
+    pub const fn new() -> Self {
+        // Make sure that task is Sync
+        trait AssertSync: Sync {}
+        impl AssertSync for Waker {}
+
+        Self { state: AtomicUsize::new(WAITING), waker: UnsafeCell::new(None) }
+    }
+
+    /// Registers the waker to be notified on calls to `wake`.
+    ///
+    /// The new task will take place of any previous tasks 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
+    /// notify the `register` caller's task and deregister the waker from future
+    /// notifications. Because of this, callers should ensure `register` gets
+    /// invoked with a new `Waker` **each** time they require a wakeup.
+    ///
+    /// It is safe to call `register` with multiple other threads concurrently
+    /// calling `wake`. This will result in the `register` caller's current
+    /// task being notified 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 notified. One of the callers will win and have its task set,
+    /// but there is no guarantee as to which caller will succeed.
+    ///
+    /// # Examples
+    ///
+    /// Here is how `register` is used when implementing a flag.
+    ///
+    /// ```
+    /// use futures::future::Future;
+    /// use futures::task::{Context, Poll, AtomicWaker};
+    /// use std::sync::atomic::AtomicBool;
+    /// use std::sync::atomic::Ordering::Relaxed;
+    /// use std::pin::Pin;
+    ///
+    /// struct Flag {
+    ///     waker: AtomicWaker,
+    ///     set: AtomicBool,
+    /// }
+    ///
+    /// impl Future for Flag {
+    ///     type Output = ();
+    ///
+    ///     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
+    ///         // Register **before** checking `set` to avoid a race condition
+    ///         // that would result in lost notifications.
+    ///         self.waker.register(cx.waker());
+    ///
+    ///         if self.set.load(Relaxed) {
+    ///             Poll::Ready(())
+    ///         } else {
+    ///             Poll::Pending
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    pub fn register(&self, waker: &Waker) {
+        match self
+            .state
+            .compare_exchange(WAITING, REGISTERING, Acquire, Acquire)
+            .unwrap_or_else(|x| x)
+        {
+            WAITING => {
+                unsafe {
+                    // Locked acquired, update the waker cell
+                    *self.waker.get() = Some(waker.clone());
+
+                    // Release the lock. If the state transitioned to include
+                    // the `WAKING` bit, this means that at least one wake has
+                    // been called concurrently.
+                    //
+                    // Start by assuming that the state is `REGISTERING` as this
+                    // is what we just set it to. If this holds, we know that no
+                    // other writes were performed in the meantime, so there is
+                    // nothing to acquire, only release. In case of concurrent
+                    // wakers, we need to acquire their releases, so success needs
+                    // to do both.
+                    let res = self.state.compare_exchange(REGISTERING, WAITING, AcqRel, Acquire);
+
+                    match res {
+                        Ok(_) => {
+                            // memory ordering: acquired self.state during CAS
+                            // - if previous wakes went through it syncs with
+                            //   their final release (`fetch_and`)
+                            // - if there was no previous wake the next wake
+                            //   will wake us, no sync needed.
+                        }
+                        Err(actual) => {
+                            // This branch can only be reached if at least one
+                            // 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 waker = (*self.waker.get()).take().unwrap();
+
+                            // We need to return to WAITING state (clear our lock and
+                            // concurrent WAKING flag). This needs to acquire all
+                            // WAKING fetch_or releases and it needs to release our
+                            // update to self.waker, so we need a `swap` operation.
+                            self.state.swap(WAITING, AcqRel);
+
+                            // memory ordering: we acquired the state for all
+                            // concurrent wakes, but future wakes might still
+                            // need to wake us in case we can't make progress
+                            // from the pending wakes.
+                            //
+                            // So we simply schedule to come back later (we could
+                            // also simply leave the registration in place above).
+                            waker.wake();
+                        }
+                    }
+                }
+            }
+            WAKING => {
+                // Currently in the process of waking the task, i.e.,
+                // `wake` is currently being called on the old task handle.
+                //
+                // memory ordering: we acquired the state for all
+                // concurrent wakes, but future wakes might still
+                // need to wake us in case we can't make progress
+                // from the pending wakes.
+                //
+                // So we simply schedule to come back later (we
+                // could also spin here trying to acquire the lock
+                // to register).
+                waker.wake_by_ref();
+            }
+            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.
+                //
+                // memory ordering: don't care. a concurrent register() is going
+                // to succeed and provide proper memory ordering.
+                //
+                // We just want to maintain memory safety. It is ok to drop the
+                // call to `register`.
+                debug_assert!(state == REGISTERING || state == REGISTERING | WAKING);
+            }
+        }
+    }
+
+    /// Calls `wake` on the last `Waker` passed to `register`.
+    ///
+    /// If `register` has not been called yet, then this does nothing.
+    pub fn wake(&self) {
+        if let Some(waker) = self.take() {
+            waker.wake();
+        }
+    }
+
+    /// Returns the last `Waker` passed to `register`, so that the user can wake it.
+    ///
+    ///
+    /// Sometimes, just waking the AtomicWaker is not fine grained enough. This allows the user
+    /// to take the waker and then wake it separately, rather than performing both steps in one
+    /// atomic action.
+    ///
+    /// If a waker has not been registered, this returns `None`.
+    pub fn take(&self) -> Option<Waker> {
+        // AcqRel ordering is used in order to acquire the value of the `task`
+        // 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.get()).take() };
+
+                // Release the lock
+                self.state.fetch_and(!WAKING, Release);
+
+                waker
+            }
+            state => {
+                // There is a concurrent thread currently updating the
+                // associated task.
+                //
+                // 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 {
+        Self::new()
+    }
+}
+
+impl fmt::Debug for AtomicWaker {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "AtomicWaker")
+    }
+}
+
+unsafe impl Send for AtomicWaker {}
+unsafe impl Sync for AtomicWaker {}
diff --git a/vendor/futures-core/src/task/__internal/mod.rs b/vendor/futures-core/src/task/__internal/mod.rs
new file mode 100644
index 000000000..c902eb4bf
--- /dev/null
+++ b/vendor/futures-core/src/task/__internal/mod.rs
@@ -0,0 +1,4 @@
+#[cfg(not(futures_no_atomic_cas))]
+mod atomic_waker;
+#[cfg(not(futures_no_atomic_cas))]
+pub use self::atomic_waker::AtomicWaker;
diff --git a/vendor/futures-core/src/task/mod.rs b/vendor/futures-core/src/task/mod.rs
new file mode 100644
index 000000000..19e4eaecd
--- /dev/null
+++ b/vendor/futures-core/src/task/mod.rs
@@ -0,0 +1,10 @@
+//! Task notification.
+
+#[macro_use]
+mod poll;
+
+#[doc(hidden)]
+pub mod __internal;
+
+#[doc(no_inline)]
+pub use core::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
diff --git a/vendor/futures-core/src/task/poll.rs b/vendor/futures-core/src/task/poll.rs
new file mode 100644
index 000000000..607e78e06
--- /dev/null
+++ b/vendor/futures-core/src/task/poll.rs
@@ -0,0 +1,12 @@
+/// Extracts the successful type of a `Poll<T>`.
+///
+/// This macro bakes in propagation of `Pending` signals by returning early.
+#[macro_export]
+macro_rules! ready {
+    ($e:expr $(,)?) => {
+        match $e {
+            $crate::task::Poll::Ready(t) => t,
+            $crate::task::Poll::Pending => return $crate::task::Poll::Pending,
+        }
+    };
+}