How to catch signals in Rust

Question

I'm trying to write some code that will catch a signal like SIGTERM.

I found this and I also found How to handle blocking i/o in Rust, or long running external function calls in general.

But in the current Rust version (0.12 nightly) it seems like that std::io::signal::Listener was removed. Did it get put somewhere else? If so can someone point me to how to catch a signal?

Answer 1

It seems that it's now fairly trivial to implement this. The Signal handling section of Command Line Applications in Rust goes over the concept, and mentions the ctrlc crate to handle that specific signal, and the signal-hook crate to handle signals in general.

Via the guide, with signal-hook it should be as simple as:

use std::{error::Error, thread};
use signal_hook::{iterator::Signals, SIGTERM};

fn main() -> Result<(), Box<Error>> {
    let signals = Signals::new(&[SIGTERM])?;

    thread::spawn(move || {
        for sig in signals.forever() {
            println!("Received signal {:?}", sig);
        }
    });

    Ok(())
}

Answer 2

I believe that std::io::signal module was removed in this pull request. It is claimed that proper signals handling was never implemented properly for native runtime, so you likely wouldn't be able to use it now anyway. This seems to be a tracking issue for this problem.

In the meantime, I think, you will have to drop down to the lowest-level unsafe functions from libc.

Answer 3

At the time of writing this answer, there is an RFC for built-in signals.

I have had some success using the chan-signal crate:

#[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.
}