futures-core-0.3.17/.cargo_vcs_info.json0000644000000001120000000000100135410ustar { "git": { "sha1": "7caefa51304e78fd5018cd5d2a03f3b9089cc010" } } futures-core-0.3.17/Cargo.toml0000644000000020510000000000100115430ustar # 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" name = "futures-core" version = "0.3.17" authors = ["Alex Crichton "] description = "The core traits and types in for the `futures` library.\n" homepage = "https://rust-lang.github.io/futures-rs" documentation = "https://docs.rs/futures-core/0.3" 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 = [] futures-core-0.3.17/Cargo.toml.orig000064400000000000000000000013150072674642500152560ustar 00000000000000[package] name = "futures-core" edition = "2018" version = "0.3.17" authors = ["Alex Crichton "] license = "MIT OR Apache-2.0" repository = "https://github.com/rust-lang/futures-rs" homepage = "https://rust-lang.github.io/futures-rs" documentation = "https://docs.rs/futures-core/0.3" description = """ The core traits and types in for the `futures` library. """ [features] default = ["std"] std = ["alloc"] alloc = [] # These features are no longer used. # TODO: remove in the next major version. unstable = [] cfg-target-has-atomic = [] [dependencies] [dev-dependencies] futures = { path = "../futures" } [package.metadata.docs.rs] all-features = true rustdoc-args = ["--cfg", "docsrs"] futures-core-0.3.17/LICENSE-APACHE000064400000000000000000000251720072674642500143220ustar 00000000000000 Apache License Version 2.0, January 2004 http://www.apache.org/licenses/ TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 1. Definitions. "License" shall mean the terms and conditions for use, reproduction, and distribution as defined by Sections 1 through 9 of this document. "Licensor" shall mean the copyright owner or entity authorized by the copyright owner that is granting the License. "Legal Entity" shall mean the union of the acting entity and all other entities that control, are controlled by, or are under common control with that entity. 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We also recommend that a file or class name and description of purpose be included on the same "printed page" as the copyright notice for easier identification within third-party archives. Copyright (c) 2016 Alex Crichton Copyright (c) 2017 The Tokio Authors Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. futures-core-0.3.17/LICENSE-MIT000064400000000000000000000021060072674642500140220ustar 00000000000000Copyright (c) 2016 Alex Crichton Copyright (c) 2017 The Tokio Authors Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. futures-core-0.3.17/build.rs000064400000000000000000000030230072674642500140320ustar 00000000000000#![warn(rust_2018_idioms, single_use_lifetimes)] use std::env; include!("no_atomic_cas.rs"); // 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 strings below are // *not* public API. Please let us know by opening a GitHub issue if your build // environment requires some way to enable these cfgs other than by executing // our build script. 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_TARGETS.contains(&&*target) { println!("cargo:rustc-cfg=futures_no_atomic_cas"); } println!("cargo:rerun-if-changed=no_atomic_cas.rs"); } futures-core-0.3.17/no_atomic_cas.rs000064400000000000000000000005540072674642500155370ustar 00000000000000// This file is @generated by no_atomic_cas.sh. // It is not intended for manual editing. const NO_ATOMIC_CAS_TARGETS: &[&str] = &[ "avr-unknown-gnu-atmega328", "bpfeb-unknown-none", "bpfel-unknown-none", "msp430-none-elf", "riscv32i-unknown-none-elf", "riscv32imc-unknown-none-elf", "thumbv4t-none-eabi", "thumbv6m-none-eabi", ]; futures-core-0.3.17/src/future.rs000064400000000000000000000060220072674642500150360ustar 00000000000000//! 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 + Send + 'a>>; /// `BoxFuture`, but without the `Send` requirement. #[cfg(feature = "alloc")] pub type LocalBoxFuture<'a, T> = Pin + '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 FusedFuture for &mut F { fn is_terminated(&self) -> bool { ::is_terminated(&**self) } } impl

FusedFuture for Pin

where P: DerefMut + Unpin, P::Target: FusedFuture, { fn is_terminated(&self) -> bool { ::is_terminated(&**self) } } mod private_try_future { use super::Future; pub trait Sealed {} impl Sealed for F where F: ?Sized + Future> {} } /// 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>; } impl TryFuture for F where F: ?Sized + Future>, { type Ok = T; type Error = E; #[inline] fn try_poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll { self.poll(cx) } } #[cfg(feature = "alloc")] mod if_alloc { use super::*; use alloc::boxed::Box; impl FusedFuture for Box { fn is_terminated(&self) -> bool { ::is_terminated(&**self) } } #[cfg(feature = "std")] impl FusedFuture for std::panic::AssertUnwindSafe { fn is_terminated(&self) -> bool { ::is_terminated(&**self) } } } futures-core-0.3.17/src/lib.rs000064400000000000000000000014410072674642500142720ustar 00000000000000//! 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; futures-core-0.3.17/src/stream.rs000064400000000000000000000177070072674642500150330ustar 00000000000000//! 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 + Send + 'a>>; /// `BoxStream`, but without the `Send` requirement. #[cfg(feature = "alloc")] pub type LocalBoxStream<'a, T> = Pin + 'a>>; /// A stream of values produced asynchronously. /// /// If `Future` is an asynchronous version of `T`, then `Stream` is an asynchronous version of `Iterator`. 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>; /// 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) { (0, None) } } impl Stream for &mut S { type Item = S::Item; fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll> { S::poll_next(Pin::new(&mut **self), cx) } fn size_hint(&self) -> (usize, Option) { (**self).size_hint() } } impl

Stream for Pin

where P: DerefMut + Unpin, P::Target: Stream, { type Item = ::Item; fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll> { self.get_mut().as_mut().poll_next(cx) } fn size_hint(&self) -> (usize, Option) { (**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 FusedStream for &mut F { fn is_terminated(&self) -> bool { ::is_terminated(&**self) } } impl

FusedStream for Pin

where P: DerefMut + Unpin, P::Target: FusedStream, { fn is_terminated(&self) -> bool { ::is_terminated(&**self) } } mod private_try_stream { use super::Stream; pub trait Sealed {} impl Sealed for S where S: ?Sized + Stream> {} } /// 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>>; } impl TryStream for S where S: ?Sized + Stream>, { type Ok = T; type Error = E; fn try_poll_next( self: Pin<&mut Self>, cx: &mut Context<'_>, ) -> Poll>> { self.poll_next(cx) } } #[cfg(feature = "alloc")] mod if_alloc { use super::*; use alloc::boxed::Box; impl Stream for Box { type Item = S::Item; fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll> { Pin::new(&mut **self).poll_next(cx) } fn size_hint(&self) -> (usize, Option) { (**self).size_hint() } } #[cfg(feature = "std")] impl Stream for std::panic::AssertUnwindSafe { type Item = S::Item; fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll> { unsafe { self.map_unchecked_mut(|x| &mut x.0) }.poll_next(cx) } fn size_hint(&self) -> (usize, Option) { self.0.size_hint() } } impl FusedStream for Box { fn is_terminated(&self) -> bool { ::is_terminated(&**self) } } } futures-core-0.3.17/src/task/__internal/atomic_waker.rs000064400000000000000000000407010072674642500212470ustar 00000000000000use 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); /// /// 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>, } // `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 { // 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 {} futures-core-0.3.17/src/task/__internal/mod.rs000064400000000000000000000002010072674642500173500ustar 00000000000000#[cfg(not(futures_no_atomic_cas))] mod atomic_waker; #[cfg(not(futures_no_atomic_cas))] pub use self::atomic_waker::AtomicWaker; futures-core-0.3.17/src/task/mod.rs000064400000000000000000000002540072674642500152460ustar 00000000000000//! Task notification. #[macro_use] mod poll; #[doc(hidden)] pub mod __internal; #[doc(no_inline)] pub use core::task::{Context, Poll, RawWaker, RawWakerVTable, Waker}; futures-core-0.3.17/src/task/poll.rs000064400000000000000000000005440072674642500154370ustar 00000000000000/// Extracts the successful type of a `Poll`. /// /// 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, } }; }