katui-rt 0.0.3

//! Termination requests from outside: a signal sets a flag, and the loop
//! leaves through its normal restore path.

use std::io;
use std::sync::Arc;
use std::sync::atomic::{AtomicBool, Ordering};

use signal_hook::SigId;
use signal_hook::consts::{SIGHUP, SIGINT, SIGQUIT, SIGTERM};
use signal_hook::flag;

const STOPPING: [i32; 4] = [SIGTERM, SIGHUP, SIGINT, SIGQUIT];

/// Set once the process was asked to stop. Dropping it gives the signals
/// their usual meaning back.
#[derive(Debug, Default)]
pub(crate) struct StopRequest {
    requested: Arc<AtomicBool>,
    handlers: Vec<SigId>,
}

impl StopRequest {
    /// Watch the signals that end a program. A second signal while we
    /// restore the terminal ends the process at once, so a hung restore
    /// never traps the user.
    pub(crate) fn watch() -> io::Result<Self> {
        let mut stop = Self::default();
        for signal in STOPPING {
            let shutdown =
                flag::register_conditional_shutdown(signal, 1, Arc::clone(&stop.requested))?;
            stop.handlers.push(shutdown);
            stop.handlers
                .push(flag::register(signal, Arc::clone(&stop.requested))?);
        }
        Ok(stop)
    }

    pub(crate) fn requested(&self) -> bool {
        self.requested.load(Ordering::Relaxed)
    }
}

impl Drop for StopRequest {
    fn drop(&mut self) {
        for handler in self.handlers.drain(..) {
            signal_hook::low_level::unregister(handler);
        }
    }
}

#[cfg(test)]
mod tests {
    use super::StopRequest;

    /// One test only: signal handlers are process-wide, so a second test
    /// running alongside would see this one's signals.
    #[test]
    fn a_signal_sets_the_request_and_a_later_watch_starts_fresh() {
        let earlier = StopRequest::watch().expect("signal handlers register");
        assert!(!earlier.requested());
        signal_hook::low_level::raise(signal_hook::consts::SIGQUIT).expect("raise works");
        assert!(
            earlier.requested(),
            "the signal set the flag and the process lives"
        );
        drop(earlier);
        let later = StopRequest::watch().expect("signal handlers register");
        assert!(!later.requested());
        // with the earlier handlers still installed, its set flag would
        // end this test process here instead of setting the new flag
        signal_hook::low_level::raise(signal_hook::consts::SIGQUIT).expect("raise works");
        assert!(later.requested());
    }
}