jwilm / chan-signal

Respond to OS signals with channels.

This crate provies experimental support for responding to OS signals using channels. Currently, this only works on Unix based systems, but I'd appreciate help adding Windows support.

Dual-licensed under MIT or the UNLICENSE.

Documentation

http://burntsushi.net/rustdoc/chan_signal/.

Example

Use is really simple. Just ask the chan_signal crate to create a channel subscribed to a set of signals. When a signal is sent to the process it will be delivered to the channel.

use chan_signal::Signal;

let signal = chan_signal::notify(&[Signal::INT, Signal::TERM]);

// Blocks until this process is sent an INT or TERM signal.
// Since the channel is never closed, we can unwrap the received value.
signal.recv().unwrap();

A realer example

When combined with chan_select! from the chan crate, one can easily integrate signals with the rest of your program. For example, consider a main function that waits for either normal completion of work (which is done in a separate thread) or for a signal to be delivered:

#[macro_use]
extern crate chan;
extern crate chan_signal;

use chan_signal::Signal;

fn main() {
    // Signal gets a value when the OS sent a INT or TERM signal.
    let signal = chan_signal::notify(&[Signal::INT, Signal::TERM]);
    // When our work is complete, send a sentinel value on `sdone`.
    let (sdone, rdone) = chan::sync(0);
    // Run work.
    ::std::thread::spawn(move || run(sdone));

    // Wait for a signal or for work to be done.
    chan_select! {
        signal.recv() -> signal => {
            println!("received signal: {:?}", signal)
        },
        rdone.recv() => {
            println!("Program completed normally.");
        }
    }
}

fn run(_sdone: chan::Sender<()>) {
    println!("Running work for 5 seconds.");
    println!("Can you send a signal quickly enough?");
    // Do some work.
    ::std::thread::sleep_ms(5000);

    // _sdone gets dropped which closes the channel and causes `rdone`
    // to unblock.
}

This is much easier than registering a signal handler because:

1. Signal handlers run asynchronously.
2. The code you're permitted to execute in a signal handler is extremely constrained (e.g., no allocation), so it is difficult to integrate it with the rest of your program.

Using channels, you can invent whatever flow you like and handle OS signals just like anything else.

How it works

TL;DR - Spawn a thread, block on sigwait, deliver signals, repeat.

It's explained a bit more in the docs.