atomic-waker-1.1.2/.cargo_vcs_info.json0000644000000001360000000000100134200ustar { "git": { "sha1": "9969a29ccd1fe298e2df7346849c0095ba303a64" }, "path_in_vcs": "" }atomic-waker-1.1.2/CHANGELOG.md000064400000000000000000000004001046102023000140130ustar 00000000000000# Version 1.1.2 - Add `smol-rs` logo to docs. (#16) # Version 1.1.1 - Use `will_wake()` to avoid unnecessary cloning. (#12) # Version 1.1.0 - Support `no_std` platforms. (#7) - Support `portable-atomic` crate. (#7) # Version 1.0.0 - Initial version atomic-waker-1.1.2/Cargo.toml0000644000000024210000000000100114150ustar # 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 = "atomic-waker" version = "1.1.2" authors = [ "Stjepan Glavina ", "Contributors to futures-rs", ] exclude = ["/.*"] description = "A synchronization primitive for task wakeup" readme = "README.md" keywords = [ "waker", "notify", "wake", "futures", "async", ] categories = [ "asynchronous", "concurrency", ] license = "Apache-2.0 OR MIT" repository = "https://github.com/smol-rs/atomic-waker" [[bench]] name = "waker" harness = false [dependencies.portable-atomic] version = "1" optional = true default-features = false [dev-dependencies.criterion] version = "0.4.0" features = ["cargo_bench_support"] default-features = false [dev-dependencies.futures] version = "0.3.5" [dev-dependencies.rayon] version = "1.7.0" atomic-waker-1.1.2/Cargo.toml.orig000064400000000000000000000015601046102023000151010ustar 00000000000000[package] name = "atomic-waker" # When publishing a new version: # - Update CHANGELOG.md # - Create "v1.x.y" git tag version = "1.1.2" authors = [ "Stjepan Glavina ", "Contributors to futures-rs", ] edition = "2018" rust-version = "1.36" description = "A synchronization primitive for task wakeup" license = "Apache-2.0 OR MIT" repository = "https://github.com/smol-rs/atomic-waker" keywords = ["waker", "notify", "wake", "futures", "async"] categories = ["asynchronous", "concurrency"] exclude = ["/.*"] [dependencies] # Uses portable-atomic polyfill atomics on targets without them portable-atomic = { version = "1", optional = true, default-features = false } [dev-dependencies] criterion = { version = "0.4.0", default-features = false, features = ["cargo_bench_support"] } futures = "0.3.5" rayon = "1.7.0" [[bench]] name = "waker" harness = false atomic-waker-1.1.2/LICENSE-APACHE000064400000000000000000000251371046102023000141440ustar 00000000000000 Apache License Version 2.0, January 2004 http://www.apache.org/licenses/ TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION 1. 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See the License for the specific language governing permissions and limitations under the License. atomic-waker-1.1.2/LICENSE-MIT000064400000000000000000000017771046102023000136600ustar 00000000000000Permission 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. atomic-waker-1.1.2/LICENSE-THIRD-PARTY000064400000000000000000000034711046102023000147670ustar 00000000000000=============================================================================== 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. =============================================================================== Copyright (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. 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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. atomic-waker-1.1.2/README.md000064400000000000000000000020041046102023000134630ustar 00000000000000# atomic-waker [![Build](https://github.com/smol-rs/atomic-waker/workflows/Build%20and%20test/badge.svg)]( https://github.com/smol-rs/atomic-waker/actions) [![License](https://img.shields.io/badge/license-Apache--2.0_OR_MIT-blue.svg)]( https://github.com/smol-rs/atomic-waker) [![Cargo](https://img.shields.io/crates/v/atomic-waker.svg)]( https://crates.io/crates/atomic-waker) [![Documentation](https://docs.rs/atomic-waker/badge.svg)]( https://docs.rs/atomic-waker) `futures::task::AtomicWaker` extracted into its own crate. ## License Licensed under either of * Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0) * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT) at your option. #### Contribution 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. atomic-waker-1.1.2/benches/waker.rs000064400000000000000000000045441046102023000153050ustar 00000000000000use atomic_waker::AtomicWaker; use criterion::{black_box, criterion_group, criterion_main, BenchmarkGroup, Criterion}; use std::sync::Arc; use std::task::{Wake, Waker}; enum Contention { Low, High, } impl Contention { fn bench( self, group: &mut BenchmarkGroup<'_, M>, f: impl Fn(&AtomicWaker) + Send + Sync + Clone, ) where M: criterion::measurement::Measurement, { let waker = AtomicWaker::new(); match self { Self::Low => { // Run the benchmark with low contention. group.bench_function("low contention", move |b| { b.iter(|| { for _ in 0..500 { f(&waker); } }) }); } Self::High => { // Run the benchmark with high contention. group.bench_function("high contention", move |b| { b.iter(|| { use rayon::prelude::*; (0..100_000).into_par_iter().for_each(|_| f(&waker)); }) }); } } } } fn run_lo_hi(c: &mut Criterion, name: &str, f: impl Fn(&AtomicWaker) + Send + Sync + Clone) { let mut group = c.benchmark_group(name); Contention::Low.bench(&mut group, f.clone()); Contention::High.bench(&mut group, f); group.finish(); } fn store_and_wake(c: &mut Criterion) { run_lo_hi(c, "store and wake", |waker| { let noop_waker = noop_waker(); waker.register(&noop_waker); waker.wake(); }); run_lo_hi(c, "store and take", |waker| { let noop_waker = noop_waker(); waker.register(&noop_waker); black_box(waker.take()); }); } fn wake_without_store(c: &mut Criterion) { run_lo_hi(c, "wake without store", |waker| { waker.wake(); }); run_lo_hi(c, "take without store", |waker| { black_box(waker.take()); }); } criterion_group!(benches, store_and_wake, wake_without_store); criterion_main!(benches); fn noop_waker() -> Waker { struct Noop; impl Wake for Noop { fn wake(self: Arc) { // Do nothing } fn wake_by_ref(self: &Arc) { // Do nothing } } Waker::from(Arc::new(Noop)) } atomic-waker-1.1.2/src/lib.rs000064400000000000000000000432501046102023000141170ustar 00000000000000//! `futures::task::AtomicWaker` extracted into its own crate. //! //! # Features //! //! This crate adds a feature, `portable-atomic`, which uses a polyfill //! from the [`portable-atomic`] crate in order to provide functionality //! to targets without atomics. See the [`README`] for the [`portable-atomic`] //! crate for more information on how to use it. //! //! [`portable-atomic`]: https://crates.io/crates/portable-atomic //! [`README`]: https://github.com/taiki-e/portable-atomic/blob/main/README.md#optional-cfg #![no_std] #![doc( html_favicon_url = "https://raw.githubusercontent.com/smol-rs/smol/master/assets/images/logo_fullsize_transparent.png" )] #![doc( html_logo_url = "https://raw.githubusercontent.com/smol-rs/smol/master/assets/images/logo_fullsize_transparent.png" )] use core::cell::UnsafeCell; use core::fmt; use core::sync::atomic::Ordering::{AcqRel, Acquire, Release}; use core::task::Waker; #[cfg(not(feature = "portable-atomic"))] use core::sync::atomic::AtomicUsize; #[cfg(feature = "portable-atomic")] use portable_atomic::AtomicUsize; /// 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 { /// Flag(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 {} AtomicWaker { 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 // Avoid cloning the waker if the old waker will awaken the same task. match &*self.waker.get() { Some(old_waker) if old_waker.will_wake(waker) => (), _ => *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 { AtomicWaker::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 {} atomic-waker-1.1.2/tests/basic.rs000064400000000000000000000024651046102023000150100ustar 00000000000000use std::sync::atomic::AtomicUsize; use std::sync::atomic::Ordering; use std::sync::Arc; use std::task::Poll; use std::thread; use atomic_waker::AtomicWaker; use futures::executor::block_on; use futures::future::poll_fn; #[test] fn basic() { let atomic_waker = Arc::new(AtomicWaker::new()); let atomic_waker_copy = atomic_waker.clone(); let returned_pending = Arc::new(AtomicUsize::new(0)); let returned_pending_copy = returned_pending.clone(); let woken = Arc::new(AtomicUsize::new(0)); let woken_copy = woken.clone(); let t = thread::spawn(move || { let mut pending_count = 0; block_on(poll_fn(move |cx| { if woken_copy.load(Ordering::Relaxed) == 1 { Poll::Ready(()) } else { // Assert we return pending exactly once assert_eq!(0, pending_count); pending_count += 1; atomic_waker_copy.register(cx.waker()); returned_pending_copy.store(1, Ordering::Relaxed); Poll::Pending } })) }); while returned_pending.load(Ordering::Relaxed) == 0 {} // give spawned thread some time to sleep in `block_on` thread::yield_now(); woken.store(1, Ordering::Relaxed); atomic_waker.wake(); t.join().unwrap(); }