Initial commit
This commit is contained in:
commit
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github: stjepang
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|
||||||
|
name: Build and test
|
||||||
|
|
||||||
|
on:
|
||||||
|
push:
|
||||||
|
branches:
|
||||||
|
- master
|
||||||
|
pull_request:
|
||||||
|
|
||||||
|
jobs:
|
||||||
|
build_and_test:
|
||||||
|
runs-on: ${{ matrix.os }}
|
||||||
|
strategy:
|
||||||
|
fail-fast: false
|
||||||
|
matrix:
|
||||||
|
os: [ubuntu-latest]
|
||||||
|
rust: [nightly, beta, stable]
|
||||||
|
steps:
|
||||||
|
- uses: actions/checkout@v2
|
||||||
|
|
||||||
|
- name: Set current week of the year in environnement
|
||||||
|
if: startsWith(matrix.os, 'ubuntu') || startsWith(matrix.os, 'macOS')
|
||||||
|
run: echo "::set-env name=CURRENT_WEEK::$(date +%V)"
|
||||||
|
|
||||||
|
- name: Set current week of the year in environnement
|
||||||
|
if: startsWith(matrix.os, 'windows')
|
||||||
|
run: echo "::set-env name=CURRENT_WEEK::$(Get-Date -UFormat %V)"
|
||||||
|
|
||||||
|
- name: Install latest ${{ matrix.rust }}
|
||||||
|
uses: actions-rs/toolchain@v1
|
||||||
|
with:
|
||||||
|
toolchain: ${{ matrix.rust }}
|
||||||
|
profile: minimal
|
||||||
|
override: true
|
||||||
|
|
||||||
|
- name: Run cargo check
|
||||||
|
uses: actions-rs/cargo@v1
|
||||||
|
with:
|
||||||
|
command: check
|
||||||
|
args: --all --bins --examples --tests --all-features
|
||||||
|
|
||||||
|
- name: Run cargo check (without dev-dependencies to catch missing feature flags)
|
||||||
|
if: startsWith(matrix.rust, 'nightly')
|
||||||
|
uses: actions-rs/cargo@v1
|
||||||
|
with:
|
||||||
|
command: check
|
||||||
|
args: -Z features=dev_dep
|
||||||
|
|
||||||
|
- name: Run cargo test
|
||||||
|
uses: actions-rs/cargo@v1
|
||||||
|
with:
|
||||||
|
command: test
|
|
@ -0,0 +1,26 @@
|
||||||
|
name: Lint
|
||||||
|
|
||||||
|
on:
|
||||||
|
push:
|
||||||
|
branches:
|
||||||
|
- master
|
||||||
|
pull_request:
|
||||||
|
|
||||||
|
jobs:
|
||||||
|
clippy:
|
||||||
|
runs-on: ubuntu-latest
|
||||||
|
steps:
|
||||||
|
- uses: actions/checkout@v2
|
||||||
|
|
||||||
|
- name: Set current week of the year in environnement
|
||||||
|
run: echo "::set-env name=CURRENT_WEEK::$(date +%V)"
|
||||||
|
|
||||||
|
- uses: actions-rs/toolchain@v1
|
||||||
|
with:
|
||||||
|
toolchain: stable
|
||||||
|
profile: minimal
|
||||||
|
components: clippy
|
||||||
|
- uses: actions-rs/clippy-check@v1
|
||||||
|
with:
|
||||||
|
token: ${{ secrets.GITHUB_TOKEN }}
|
||||||
|
args: --all-features -- -W clippy::all
|
|
@ -0,0 +1,20 @@
|
||||||
|
name: Security audit
|
||||||
|
|
||||||
|
on:
|
||||||
|
push:
|
||||||
|
branches:
|
||||||
|
- master
|
||||||
|
pull_request:
|
||||||
|
|
||||||
|
jobs:
|
||||||
|
security_audit:
|
||||||
|
runs-on: ubuntu-latest
|
||||||
|
steps:
|
||||||
|
- uses: actions/checkout@v2
|
||||||
|
|
||||||
|
- name: Set current week of the year in environnement
|
||||||
|
run: echo "::set-env name=CURRENT_WEEK::$(date +%V)"
|
||||||
|
|
||||||
|
- uses: actions-rs/audit-check@v1
|
||||||
|
with:
|
||||||
|
token: ${{ secrets.GITHUB_TOKEN }}
|
|
@ -0,0 +1,2 @@
|
||||||
|
/target
|
||||||
|
Cargo.lock
|
|
@ -0,0 +1,3 @@
|
||||||
|
# Version 1.0.0
|
||||||
|
|
||||||
|
- Initial version
|
|
@ -0,0 +1,16 @@
|
||||||
|
[package]
|
||||||
|
name = "atomic-waker"
|
||||||
|
version = "1.0.0"
|
||||||
|
authors = ["Stjepan Glavina <stjepang@gmail.com>"]
|
||||||
|
edition = "2018"
|
||||||
|
description = "A synchronization primitive for task wakeup"
|
||||||
|
license = "Apache-2.0 OR MIT"
|
||||||
|
repository = "https://github.com/stjepang/futures-lite"
|
||||||
|
homepage = "https://github.com/stjepang/futures-lite"
|
||||||
|
documentation = "https://docs.rs/futures-lite"
|
||||||
|
keywords = ["waker", "notify", "wake", "futures", "async"]
|
||||||
|
categories = ["asynchronous", "concurrency"]
|
||||||
|
readme = "README.md"
|
||||||
|
|
||||||
|
[dev-dependencies]
|
||||||
|
futures = "0.3.5"
|
|
@ -0,0 +1,201 @@
|
||||||
|
Apache License
|
||||||
|
Version 2.0, January 2004
|
||||||
|
http://www.apache.org/licenses/
|
||||||
|
|
||||||
|
TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
|
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|
|
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|
1. Definitions.
|
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|
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|
"License" shall mean the terms and conditions for use, reproduction,
|
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|
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|
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APPENDIX: How to apply the Apache License to your work.
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To apply the Apache License to your work, attach the following
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@ -0,0 +1,23 @@
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Permission is hereby granted, free of charge, to any
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DEALINGS IN THE SOFTWARE.
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|
@ -0,0 +1,27 @@
|
||||||
|
# atomic-waker
|
||||||
|
|
||||||
|
[![Build](https://github.com/stjepang/atomic-waker/workflows/Build%20and%20test/badge.svg)](
|
||||||
|
https://github.com/stjepang/atomic-waker/actions)
|
||||||
|
[![License](https://img.shields.io/badge/license-MIT%2FApache--2.0-blue.svg)](
|
||||||
|
https://github.com/stjepang/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.
|
|
@ -0,0 +1,414 @@
|
||||||
|
//! `futures::task::AtomicWaker` extracted into its own crate.
|
||||||
|
|
||||||
|
use std::cell::UnsafeCell;
|
||||||
|
use std::fmt;
|
||||||
|
use std::sync::atomic::AtomicUsize;
|
||||||
|
use std::sync::atomic::Ordering::{Acquire, Release, AcqRel};
|
||||||
|
use std::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 {
|
||||||
|
/// 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<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 {}
|
||||||
|
|
||||||
|
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_and_swap(WAITING, REGISTERING, Acquire) {
|
||||||
|
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 {
|
||||||
|
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 {}
|
|
@ -0,0 +1,50 @@
|
||||||
|
use 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();
|
||||||
|
}
|
Loading…
Reference in New Issue