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{"files":{"Cargo.toml":"0b01b731df784083fc25c37db0b517ba5a1e88b020bad53a120d07f22092c7cb","LICENSE-APACHE":"275c491d6d1160553c32fd6127061d7f9606c3ea25abfad6ca3f6ed088785427","LICENSE-MIT":"6652c868f35dfe5e8ef636810a4e576b9d663f3a17fb0f5613ad73583e1b88fd","README.md":"e8258273fed6f1796485777655118f2369fd3f000191e9d8cdbd10bf052946a9","build.rs":"5b263bd2bd587511a9c8daef580b05e0613c15a6c5f800b1e5bc145fa013d99e","no_atomic_cas.rs":"7ae747b83b08dd926c1696faf4ecab9399c652ae77d5179221258c73b8eecb6f","src/future.rs":"0cb559fad0d43566dab959e929c4631c25cf749e2e29a5444fbcad464c9262ae","src/lib.rs":"eacd5816fbb914ca061d49ff6203723ebbe639eb7c45ebfa8a0613069d174111","src/stream.rs":"f1c7ab84161c5d5b424655b257fc3183eb6f2ed5324ba4006a70f9a4b0dc8872","src/task/__internal/atomic_waker.rs":"4ca94b25d3bcf4db863f008224cc4797dbbe7c93495a1abb232048846694a716","src/task/__internal/mod.rs":"7d0d297f58987b05ffa152605feb78ddc9b6e5168e7d621ec36dfbee558e4bec","src/task/mod.rs":"e213602a2fe5ae78ad5f1ca20e6d32dcbab17aba5b6b072fb927a72da99b4a11","src/task/poll.rs":"74c2717c1f9a37587a367da1b690d1cd2312e95dbaffca42be4755f1cd164bb8"},"package":"04909a7a7e4633ae6c4a9ab280aeb86da1236243a77b694a49eacd659a4bd3ac"}

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# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
#
# When uploading crates to the registry Cargo will automatically
# "normalize" Cargo.toml files for maximal compatibility
# with all versions of Cargo and also rewrite `path` dependencies
# to registry (e.g., crates.io) dependencies.
#
# If you are reading this file be aware that the original Cargo.toml
# will likely look very different (and much more reasonable).
# See Cargo.toml.orig for the original contents.
[package]
edition = "2018"
rust-version = "1.36"
name = "futures-core"
version = "0.3.25"
description = """
The core traits and types in for the `futures` library.
"""
homepage = "https://rust-lang.github.io/futures-rs"
readme = "README.md"
license = "MIT OR Apache-2.0"
repository = "https://github.com/rust-lang/futures-rs"
[package.metadata.docs.rs]
all-features = true
rustdoc-args = [
"--cfg",
"docsrs",
]
[dependencies]
[dev-dependencies]
[features]
alloc = []
cfg-target-has-atomic = []
default = ["std"]
std = ["alloc"]
unstable = []

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Copyright (c) 2016 Alex Crichton
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Copyright (c) 2016 Alex Crichton
Copyright (c) 2017 The Tokio Authors
Permission is hereby granted, free of charge, to any
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The above copyright notice and this permission notice
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
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SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.

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# futures-core
The core traits and types in for the `futures` library.
## Usage
Add this to your `Cargo.toml`:
```toml
[dependencies]
futures-core = "0.3"
```
The current `futures-core` requires Rust 1.36 or later.
## License
Licensed under either of [Apache License, Version 2.0](LICENSE-APACHE) or
[MIT license](LICENSE-MIT) at your option.
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall
be dual licensed as above, without any additional terms or conditions.

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// The rustc-cfg listed below are considered public API, but it is *unstable*
// and outside of the normal semver guarantees:
//
// - `futures_no_atomic_cas`
// Assume the target does *not* support atomic CAS operations.
// This is usually detected automatically by the build script, but you may
// need to enable it manually when building for custom targets or using
// non-cargo build systems that don't run the build script.
//
// With the exceptions mentioned above, the rustc-cfg emitted by the build
// script are *not* public API.
#![warn(rust_2018_idioms, single_use_lifetimes)]
use std::env;
include!("no_atomic_cas.rs");
fn main() {
let target = match env::var("TARGET") {
Ok(target) => target,
Err(e) => {
println!(
"cargo:warning={}: unable to get TARGET environment variable: {}",
env!("CARGO_PKG_NAME"),
e
);
return;
}
};
// Note that this is `no_*`, not `has_*`. This allows treating
// `cfg(target_has_atomic = "ptr")` as true when the build script doesn't
// run. This is needed for compatibility with non-cargo build systems that
// don't run the build script.
if NO_ATOMIC_CAS.contains(&&*target) {
println!("cargo:rustc-cfg=futures_no_atomic_cas");
}
println!("cargo:rerun-if-changed=no_atomic_cas.rs");
}

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// This file is @generated by no_atomic_cas.sh.
// It is not intended for manual editing.
const NO_ATOMIC_CAS: &[&str] = &[
"armv4t-none-eabi",
"armv5te-none-eabi",
"avr-unknown-gnu-atmega328",
"bpfeb-unknown-none",
"bpfel-unknown-none",
"msp430-none-elf",
"riscv32i-unknown-none-elf",
"riscv32im-unknown-none-elf",
"riscv32imc-unknown-none-elf",
"thumbv4t-none-eabi",
"thumbv5te-none-eabi",
"thumbv6m-none-eabi",
];

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//! 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)
}
}
}

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//! 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;

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//! 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)
}
}
}

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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 {}

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#[cfg(not(futures_no_atomic_cas))]
mod atomic_waker;
#[cfg(not(futures_no_atomic_cas))]
pub use self::atomic_waker::AtomicWaker;

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//! Task notification.
#[macro_use]
mod poll;
#[doc(hidden)]
pub mod __internal;
#[doc(no_inline)]
pub use core::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};

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/// 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,
}
};
}