Crate atomic_wait

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Expand description

Cross platform atomic wait and wake (aka futex) functionality.

This crate only supports functionality that’s available on all of Linux, FreeBSD, Windows, and macOS. That is:

  • Only AtomicU32 is supported. (Linux currently only supports 32-bit futexes.)
  • Only the “wait”, “wake one”, and “wake all” operations are supported. (Linux supports more operations, but Windows and macOS don’t.)
  • No timeouts. (macOS doesn’t have a stable/public API for timeouts.)
  • The wake operations don’t return the number of threads woken up. (Only Linux supports this.)

Supported platforms: Linux 2.6.22+, FreeBSD 11+, Windows 8+, Windows Server 2012+, macOS 11+, iOS 14+, watchOS 7+.


use std::sync::atomic::AtomicU32;
use atomic_wait::{wait, wake_one, wake_all};

let a = AtomicU32::new(0);

wait(&a, 1); // If the value is 1, wait.

wake_one(&a); // Wake one waiting thread.

wake_all(&a); // Wake all waiting threads.


On Linux, this uses the SYS_futex syscall.

On FreeBSD, this uses the _umtx_op syscall.

On Windows, this uses the WaitOnAddress and WakeByAddress APIs.

On macOS (and iOS and watchOS), this uses libc++, making use of the same (ABI-stable) functions behind C++20’s atomic_wait and atomic_notify functions.


If the value is value, wait until woken up.
Wake all threads that are waiting on this atomic.
Wake one thread that is waiting on this atomic.