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fix(runtime): use Weak to break reference cycle #490

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Merged
merged 1 commit into from
Oct 19, 2025
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fix(runtime): use Weak to break reference cycle #490

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31 changes: 12 additions & 19 deletions compio-runtime/src/runtime/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -202,11 +202,19 @@ impl Runtime {
///
/// The caller should ensure the captured lifetime long enough.
pub unsafe fn spawn_unchecked<F: Future>(&self, future: F) -> Task<F::Output> {
let runnables = self.runnables.clone();
let handle = self.driver.borrow().handle();
let schedule = move |runnable| {
runnables.schedule(runnable, &handle);
let schedule = {
// Use `Weak` to break reference cycle.
// `RunnableQueue` -> `Runnable` -> `RunnableQueue`
let runnables = Arc::downgrade(&self.runnables);
let handle = self.driver.borrow().handle();

move |runnable| {
if let Some(runnables) = runnables.upgrade() {
runnables.schedule(runnable, &handle);
}
}
};

let (runnable, task) = async_task::spawn_unchecked(future, schedule);
runnable.schedule();
task
Expand Down Expand Up @@ -418,21 +426,6 @@ impl Runtime {
}
}

impl Drop for Runtime {
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@Berrysoft Berrysoft Oct 27, 2025

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Oh, no. This change may make the runtime panic on drop. The runnables should be dropped in self.enter, or they cannot find the right runtime to cancel the time futures.

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@Paraworker Paraworker Oct 27, 2025

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Also, I recently discovered that if a Waker is dropped in another thread and the Weak upgrade fails inside schedule, the Runnable end up being dropped in that other thread. I’m currently looking into how async-executor implements this.

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@Berrysoft Berrysoft Oct 27, 2025

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We might want to forget the runnable in that case...

fn drop(&mut self) {
self.enter(|| {
while self.runnables.sync_runnables.pop().is_some() {}
let local_runnables = unsafe { self.runnables.local_runnables.get_unchecked() };
loop {
let runnable = local_runnables.borrow_mut().pop_front();
if runnable.is_none() {
break;
}
}
})
}
}

impl AsRawFd for Runtime {
fn as_raw_fd(&self) -> RawFd {
self.driver.borrow().as_raw_fd()
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