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std: synchronize with all calls to unpark in id-based thread parker

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joboet 2023-08-07 19:13:34 +02:00
parent a6236fa460
commit fd9fcc580a
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GPG Key ID: 704E0149B0194B3C
1 changed files with 6 additions and 11 deletions
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17
library/std/src/sys_common/thread_parking/id.rs
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@ -56,18 +56,14 @@ impl Parker {
self.init_tid();
// Changes NOTIFIED to EMPTY and EMPTY to PARKED.
let mut state = self.state.fetch_sub(1, Acquire).wrapping_sub(1);
if state == PARKED {
let state = self.state.fetch_sub(1, Acquire);
if state == EMPTY {
// Loop to guard against spurious wakeups.
while state == PARKED {
// The state must be reset with acquire ordering to ensure that all
// calls to `unpark` synchronize with this thread.
while self.state.compare_exchange(NOTIFIED, EMPTY, Acquire, Relaxed).is_err() {
park(self.state.as_ptr().addr());
state = self.state.load(Acquire);
}
// Since the state change has already been observed with acquire
// ordering, the state can be reset with a relaxed store instead
// of a swap.
self.state.store(EMPTY, Relaxed);
}
}
@ -78,8 +74,7 @@ impl Parker {
if state == PARKED {
park_timeout(dur, self.state.as_ptr().addr());
// Swap to ensure that we observe all state changes with acquire
// ordering, even if the state has been changed after the timeout
// occurred.
// ordering.
self.state.swap(EMPTY, Acquire);
}
}