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time: panic in release when timer polled after completing #3681

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time: panic in release when timer polled after completing #3681

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time: panic in release when timer polled after completing
davidpdrsn Apr 6, 2021
cebf39a
use `compare_exchange_weak` as its called in a loop
davidpdrsn Apr 6, 2021
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15 changes: 9 additions & 6 deletions tokio/src/time/driver/entry.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -164,20 +164,23 @@ impl StateCell {
///
/// SAFETY: Must hold the driver lock.
unsafe fn mark_pending(&self, not_after: u64) -> Result<(), u64> {
// Quick initial debug check to see if the timer is already fired. Since
// firing the timer can only happen with the driver lock held, we know
// we shouldn't be able to "miss" a transition to a fired state, even
// with relaxed ordering.
let mut cur_state = self.state.load(Ordering::Relaxed);

loop {
debug_assert!(cur_state < STATE_MIN_VALUE);
// Check to see if the timer is already fired. Since firing the
// timer can only happen with the driver lock held, we know we
// shouldn't be able to "miss" a transition to a fired state, even
// with relaxed ordering.
//
// In part also to improve the error message for things like
// https://github.com/tokio-rs/tokio/issues/3675
assert!(cur_state < STATE_MIN_VALUE, "timer polled after completing");
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Is this the right error message here? Can it actually happen if it is polled after completion too, or does this require moving a pinned Sleep?


if cur_state > not_after {
break Err(cur_state);
}

match self.state.compare_exchange(
match self.state.compare_exchange_weak(
cur_state,
STATE_PENDING_FIRE,
Ordering::AcqRel,
Expand Down