event-listener

Notify async tasks or threads.

This is a synchronization primitive similar to eventcounts invented by Dmitry Vyukov.

You can use this crate to turn non-blocking data structures into async or blocking data structures. See a simple mutex implementation that exposes an async and a blocking interface for acquiring locks.

Examples

Wait until another thread sets a boolean flag:

use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;
use std::thread;
use std::time::Duration;
use event_listener::Event;

let flag = Arc::new(AtomicBool::new(false));
let event = Arc::new(Event::new());

// Spawn a thread that will set the flag after 1 second.
thread::spawn({
    let flag = flag.clone();
    let event = event.clone();
    move || {
        // Wait for a second.
        thread::sleep(Duration::from_secs(1));

        // Set the flag.
        flag.store(true, Ordering::SeqCst);

        // Notify all listeners that the flag has been set.
        event.notify(usize::MAX);
    }
});

// Wait until the flag is set.
loop {
    // Check the flag.
    if flag.load(Ordering::SeqCst) {
        break;
    }

    // Start listening for events.
    let listener = event.listen();

    // Check the flag again after creating the listener.
    if flag.load(Ordering::SeqCst) {
        break;
    }

    // Wait for a notification and continue the loop.
    listener.wait();
}

Features

• The std feature (enabled by default) enables the use of the Rust standard library. Disable it for no_std support.

• The critical-section feature enables usage of the critical-section crate to enable a more efficient implementation of event-listener for no_std platforms.

• The portable-atomic feature enables the use of the portable-atomic crate to provide atomic operations on platforms that don't support them.

In production environments, at least one of std or critical-section should be enabled. This ensures that the internal locking mechanism has a critical section of some kind to fall back on. Otherwise, it falls back to a spinlock implementation. This implementation is dangerous to rely on.

License

Licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or https://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or https://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.