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sync: drop wakers after unlocking the mutex in Notify (#5471)

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Alice Ryhl 2023-02-19 22:16:24 +01:00 committed by GitHub
parent d07027f5bc
commit ee09e04c31
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1 changed files with 19 additions and 4 deletions
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23
tokio/src/sync/notify.rs
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@ -917,10 +917,14 @@ impl Notified<'_> {
}
}
let mut old_waker = None;
if waker.is_some() {
// Safety: called while locked.
//
// The use of `old_waiter` here is not necessary, as the field is always
// None when we reach this line.
unsafe {
(*waiter.get()).waker = waker;
old_waker = std::mem::replace(&mut (*waiter.get()).waker, waker);
}
}
@ -931,6 +935,9 @@ impl Notified<'_> {
*state = Waiting;
drop(waiters);
drop(old_waker);
return Poll::Pending;
}
Waiting => {
@ -945,12 +952,13 @@ impl Notified<'_> {
// Safety: called while locked
let w = unsafe { &mut *waiter.get() };
let mut old_waker = None;
if w.notified.is_some() {
// Our waker has been notified and our waiter is already removed from
// the list. Reset the notification and convert to `Done`.
old_waker = std::mem::take(&mut w.waker);
w.notified = None;
w.waker = None;
*state = Done;
} else if get_num_notify_waiters_calls(curr) != *notify_waiters_calls {
// Before we add a waiter to the list we check if these numbers are
@ -960,7 +968,7 @@ impl Notified<'_> {
// We can treat the waiter as notified and remove it from the list, as
// it would have been notified in the `notify_waiters` call anyways.
w.waker = None;
old_waker = std::mem::take(&mut w.waker);
// Safety: we hold the lock, so we have an exclusive access to the list.
// The list is used in `notify_waiters`, so it must be guarded.
@ -975,10 +983,14 @@ impl Notified<'_> {
None => true,
};
if should_update {
w.waker = Some(waker.clone());
old_waker = std::mem::replace(&mut w.waker, Some(waker.clone()));
}
}
// Drop the old waker after releasing the lock.
drop(waiters);
drop(old_waker);
return Poll::Pending;
}
@ -988,6 +1000,9 @@ impl Notified<'_> {
// is helpful to visualize the scope of the critical
// section.
drop(waiters);
// Drop the old waker after releasing the lock.
drop(old_waker);
}
Done => {
return Poll::Ready(());