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waker: Fix weak memory issue in wake_by_ref() #7622

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Merged
merged 1 commit into from
Sep 18, 2025
Merged

waker: Fix weak memory issue in wake_by_ref() #7622

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10 changes: 8 additions & 2 deletions tokio/src/runtime/task/state.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -252,9 +252,15 @@ impl State {
/// Transitions the state to `NOTIFIED`.
pub(super) fn transition_to_notified_by_ref(&self) -> TransitionToNotifiedByRef {
self.fetch_update_action(|mut snapshot| {
if snapshot.is_complete() || snapshot.is_notified() {
// There is nothing to do in this case.
if snapshot.is_complete() {
// The complete state is final
(TransitionToNotifiedByRef::DoNothing, None)
} else if snapshot.is_notified() {
// Even hough we have nothing to do in this branch,
// wake_by_ref() should synchronize-with the task starting execution,
// therefore we must use an Release store (with the same value),
// to pair with the Acquire in transition_to_running.
(TransitionToNotifiedByRef::DoNothing, Some(snapshot))
} else if snapshot.is_running() {
// If the task is running, we mark it as notified, but we should
// not submit as the thread currently running the future is
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