smarm/tests/monitor.rs

//! Monitor tests: `monitor(pid)` delivers exactly one `Down` describing how
//! the target terminated, and `demonitor(&m)` tears a registration back down.
//!
//! A monitor is unidirectional and one-shot: it never propagates failure to
//! the watcher (that's a link), it just drops a `Down` into the returned
//! channel. These tests pin the three reasons — `Exit`, `Panic`, `NoProc` —
//! the fan-out case where several monitors watch the same target, and that
//! `demonitor` removes exactly the one registration it names.
//!
//! Scheduling note: under the default single-thread runtime the parent runs
//! until it parks, so every `monitor()` call below registers while the target
//! is still `Runnable` (it hasn't been resumed yet). Registration and
//! `finalize_actor` both serialize on the shared mutex, so a target that is
//! alive at registration time always produces a real `Down`, never a missed
//! one.

use smarm::{demonitor, monitor, run, spawn, DownReason};
use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
use std::sync::Arc;

#[test]
fn monitor_sees_normal_exit() {
    let ok = Arc::new(AtomicBool::new(false));
    let o = ok.clone();
    run(move || {
        let h = spawn(|| {});
        let pid = h.pid();
        let down = monitor(pid);
        let d = down.rx.recv().expect("monitor channel closed before Down");
        assert_eq!(d.pid, pid, "Down reported the wrong pid");
        if matches!(d.reason, DownReason::Exit) {
            o.store(true, Ordering::SeqCst);
        }
        let _ = h.join();
    });
    assert!(ok.load(Ordering::SeqCst), "expected DownReason::Exit");
}

#[test]
fn monitor_sees_panic() {
    let ok = Arc::new(AtomicBool::new(false));
    let o = ok.clone();
    run(move || {
        let h = spawn(|| panic!("boom"));
        let pid = h.pid();
        let down = monitor(pid);
        let d = down.rx.recv().expect("monitor channel closed before Down");
        assert_eq!(d.pid, pid);
        if matches!(d.reason, DownReason::Panic) {
            o.store(true, Ordering::SeqCst);
        }
        // Drain the panic outcome so the joiner path is exercised too; the
        // payload goes here, not to the monitor.
        let _ = h.join();
    });
    assert!(ok.load(Ordering::SeqCst), "expected DownReason::Panic");
}

#[test]
fn monitor_already_dead_target_is_noproc() {
    let ok = Arc::new(AtomicBool::new(false));
    let o = ok.clone();
    run(move || {
        let h = spawn(|| {});
        let pid = h.pid();
        // Consume the only handle on a finished child: the slot is reclaimed
        // and its generation bumped, so `pid` is now stale.
        h.join().unwrap();
        let down = monitor(pid);
        let d = down
            .rx
            .recv()
            .expect("NoProc Down should be delivered immediately");
        assert_eq!(d.pid, pid);
        if matches!(d.reason, DownReason::NoProc) {
            o.store(true, Ordering::SeqCst);
        }
    });
    assert!(ok.load(Ordering::SeqCst), "expected DownReason::NoProc");
}

#[test]
fn multiple_monitors_all_notified() {
    let count = Arc::new(AtomicUsize::new(0));
    let c = count.clone();
    run(move || {
        let h = spawn(|| {});
        let pid = h.pid();
        let monitors = [monitor(pid), monitor(pid), monitor(pid)];
        let _ = h.join();
        for m in monitors {
            if matches!(m.rx.recv().unwrap().reason, DownReason::Exit) {
                c.fetch_add(1, Ordering::SeqCst);
            }
        }
    });
    assert_eq!(
        count.load(Ordering::SeqCst),
        3,
        "every monitor should see the Down"
    );
}

#[test]
fn demonitor_stops_delivery() {
    // Demonitoring a live registration removes the slot's only sender for that
    // channel; the channel closes, so a later recv() observes Err rather than
    // a Down. demonitor reports the id it tore down.
    run(|| {
        let h = spawn(|| {});
        let pid = h.pid();
        let m = monitor(pid);
        assert_eq!(
            demonitor(&m),
            Some(m.id),
            "live registration should be removed"
        );
        assert!(
            m.rx.recv().is_err(),
            "no Down should arrive after demonitor"
        );
        let _ = h.join();
    });
}

#[test]
fn demonitor_one_of_many() {
    // Three monitors on one target; demonitor the middle. The other two still
    // fire; the demonitored channel is closed with no Down. Distinct ids mean
    // tearing one down never disturbs its siblings.
    run(|| {
        let h = spawn(|| {});
        let pid = h.pid();
        let ms = [monitor(pid), monitor(pid), monitor(pid)];
        assert_eq!(demonitor(&ms[1]), Some(ms[1].id));
        let _ = h.join();
        assert!(matches!(ms[0].rx.recv().unwrap().reason, DownReason::Exit));
        assert!(matches!(ms[2].rx.recv().unwrap().reason, DownReason::Exit));
        assert!(
            ms[1].rx.recv().is_err(),
            "demonitored channel should be closed"
        );
    });
}

#[test]
fn demonitor_after_fire_is_none() {
    // Once the Down has fired, the registration is already drained from the
    // slot, so demonitor finds nothing to remove and reports None.
    run(|| {
        let h = spawn(|| {});
        let pid = h.pid();
        let m = monitor(pid);
        let d = m.rx.recv().expect("Down before close");
        assert!(matches!(d.reason, DownReason::Exit));
        assert_eq!(
            demonitor(&m),
            None,
            "already-fired monitor has nothing to remove"
        );
        let _ = h.join();
    });
}