kernal-api 0.1.21

Async OS HAL, profiling, symbolization, and allocator instrumentation
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//! `Notify` futures created before they wait, `Task::detach_on_drop`,
//! payload-agnostic channel `Debug`, and the blocking-lane thread cap.

use kernal_api::async_engine::{self, Notify, RuntimeBuilder};
use std::pin::pin;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::Arc;
use std::time::Duration;

const BOUND: Duration = Duration::from_secs(10);

#[tokio::test]
async fn an_enabled_notified_future_sees_a_later_broadcast() {
    let notify = Notify::new();
    let mut notified = pin!(notify.notified());
    assert!(!notified.as_mut().enable(), "nothing sent yet");
    // `notify_waiters` wakes only registered waiters and stores no permit:
    // registering through `enable` is what makes this broadcast count.
    notify.notify_waiters();
    async_engine::timeout(BOUND, notified)
        .await
        .expect("the registered waiter is woken");
}

#[tokio::test]
async fn enable_reports_a_stored_permit() {
    let notify = Notify::new();
    notify.notify_one();
    let mut notified = pin!(notify.notified());
    assert!(notified.as_mut().enable(), "the stored permit is received");
    async_engine::timeout(BOUND, notified)
        .await
        .expect("a received notification completes at once");
}

#[tokio::test]
async fn an_owned_notified_future_outlives_its_borrow() {
    let notify = Arc::new(Notify::new());
    let mut notified = Box::pin(Arc::clone(&notify).owned_notified());
    assert!(!notified.as_mut().enable());
    let waiter = async_engine::launch(notified);
    notify.notify_waiters();
    async_engine::timeout(BOUND, waiter)
        .await
        .expect("the owned waiter is woken")
        .unwrap();
    assert!(format!("{:?}", Arc::clone(&notify).owned_notified()).contains("OwnedNotified"));
}

#[tokio::test]
async fn a_detach_on_drop_task_survives_its_handle_and_stays_joinable() {
    let (release, released) = async_engine::oneshot_channel::<()>();
    let (done, mut finished) = async_engine::channel::<u32>(1);
    let task = async_engine::launch(async move {
        let _ = released.await;
        done.send(7).await.unwrap();
    })
    .detach_on_drop();
    drop(task);
    release.send(()).unwrap();
    let value = async_engine::timeout(BOUND, finished.recv())
        .await
        .expect("the dropped handle did not cancel the task");
    assert_eq!(value, Some(7));

    let joinable = async_engine::launch(async { 11 }).detach_on_drop();
    assert_eq!(joinable.await.unwrap(), 11);

    let cancellable = async_engine::launch(std::future::pending::<()>()).detach_on_drop();
    cancellable.cancel();
    assert!(cancellable.await.unwrap_err().is_cancelled());
}

#[test]
fn channel_handles_debug_without_a_debug_payload() {
    struct Opaque;
    let (sender, receiver) = async_engine::channel::<Opaque>(1);
    let (unbounded, unbounded_receiver) = async_engine::unbounded_channel::<Opaque>();
    let (oneshot, oneshot_receiver) = async_engine::oneshot_channel::<Opaque>();
    for (debug, name) in [
        (format!("{sender:?}"), "Sender"),
        (format!("{receiver:?}"), "Receiver"),
        (format!("{unbounded:?}"), "UnboundedSender"),
        (format!("{unbounded_receiver:?}"), "UnboundedReceiver"),
        (format!("{oneshot:?}"), "OneshotSender"),
        (format!("{oneshot_receiver:?}"), "OneshotReceiver"),
    ] {
        assert!(debug.starts_with(name), "{debug}");
    }
}

#[test]
fn max_blocking_threads_caps_the_blocking_lane() {
    let runtime = RuntimeBuilder::multi_thread()
        .worker_threads(1)
        .max_blocking_threads(1)
        .build()
        .unwrap();
    let running = Arc::new(AtomicUsize::new(0));
    let peak = Arc::new(AtomicUsize::new(0));
    runtime.run(async {
        let tasks: Vec<_> = (0..4)
            .map(|_| {
                let running = Arc::clone(&running);
                let peak = Arc::clone(&peak);
                async_engine::launch_blocking(move || {
                    let now = running.fetch_add(1, Ordering::SeqCst) + 1;
                    peak.fetch_max(now, Ordering::SeqCst);
                    std::thread::sleep(Duration::from_millis(20));
                    running.fetch_sub(1, Ordering::SeqCst);
                })
            })
            .collect();
        for task in tasks {
            task.await.unwrap();
        }
    });
    assert_eq!(
        peak.load(Ordering::SeqCst),
        1,
        "one blocking thread at a time"
    );
}

#[test]
#[should_panic(expected = "max_blocking_threads must be greater than zero")]
fn max_blocking_threads_rejects_zero() {
    let _ = RuntimeBuilder::multi_thread().max_blocking_threads(0);
}