Task wakeup timer is overwritten

[m-mueller678]

In the following example, "Hello, world!" is printed after ten seconds, rather than 200ms.

fn main() {
    let cores = std::thread::available_parallelism().unwrap().get();
    for _ in 0..cores {
        std::thread::spawn(|| {
            std::thread::sleep(Duration::from_secs(10));
        });
    }
    std::thread::sleep(Duration::from_millis(200));
    println!("Hello, world!");
}

I believe this is because the oneshot timer is overwritten unconditionally in src/scheduler/task/mod.rs:

while let Some(node) = cursor.current() {
	let node_wakeup_time = node.wakeup_time;
	if node_wakeup_time.is_none() || wt < node_wakeup_time.unwrap() {
		cursor.insert_before(new_node);

		set_oneshot_timer();
		return;
	}

	cursor.move_next();
}

set_oneshot_timer();

[m-mueller678]

This seems to fix it for me. My fork is pretty diverged from hermit right now, so I probably won't get around to testing this in upstream and opening a PR before the end of the week. If you want to fix it sooner, feel free to use this.

if let Some(wt) = wakeup_time {
	for x in &self.list {
		info!(
			"task in list: {:?}: {:?}",
			x.wakeup_time,
			x.task.borrow_mut().id
		);
	}
	let mut cursor = self.list.cursor_front_mut();
	let any_earlier_timers = Cell::new(false);
	let set_oneshot_timer = || {
		if any_earlier_timers.get() {
			return;
		}
		#[cfg(not(feature = "net"))]
		arch::set_oneshot_timer(wakeup_time);
		#[cfg(feature = "net")]
		match self.network_wakeup_time {
			Some(time) => {
				if time > wt {
					arch::set_oneshot_timer(wakeup_time);
				} else {
					arch::set_oneshot_timer(self.network_wakeup_time);
				}
			}
			_ => arch::set_oneshot_timer(wakeup_time),
		}
	};

	while let Some(node) = cursor.current() {
		let node_wakeup_time = node.wakeup_time;
		let is_none_or = node_wakeup_time.is_none_or(|nwt| wt < nwt);
		info!("node_wakeup_time: {node_wakeup_time:?}, {is_none_or}");
		if is_none_or {
			cursor.insert_before(new_node);

			set_oneshot_timer();
			return;
		} else {
			any_earlier_timers.set(true);
		}

		cursor.move_next();
	}

	set_oneshot_timer();
}

I also saw other wake up functions in the same file that might have the same problem, did not look too closely.

There seems to be some ordering invariant on the blocked task queue, but I don't know for sure what it is. Seems to be ordered ascending by wake-up time, and tasks without a wake-up time come last? Would be great to have documentation attached to the definition of BlockedTaskQueue.