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LibPthread: Fix ordering

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It would be enough to use relaxed ordering here if it weren't for
the mutex, which we also need to store and retrieve. To ensure the
pthread_cond_broadcast() call sees the store, use release and acquire
as appropriate. Thankfully, both of these are on the slow paths.
This commit is contained in:
Sergey Bugaev 2021-07-06 14:36:51 +03:00 committed by Andreas Kling
parent 30caa33f7e
commit 78f5c4a4c2
Notes: sideshowbarker 2024-07-18 10:17:29 +09:00 
Author: https://github.com/bugaevc
Commit: https://github.com/SerenityOS/serenity/commit/78f5c4a4c29
Pull-request: https://github.com/SerenityOS/serenity/pull/8495
1 changed files with 2 additions and 2 deletions
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4
Userland/Libraries/LibPthread/pthread_cond.cpp
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@ -73,7 +73,7 @@ int pthread_cond_timedwait(pthread_cond_t* cond, pthread_mutex_t* mutex, const s
// Fetch the current value, and record that we're about to wait. Fetching
// the current value has to be done while we hold the mutex, because the
// value might change as soon as we unlock it.
u32 value = AK::atomic_fetch_or(&cond->value, NEED_TO_WAKE_ONE | NEED_TO_WAKE_ALL, AK::memory_order_relaxed) | NEED_TO_WAKE_ONE | NEED_TO_WAKE_ALL;
u32 value = AK::atomic_fetch_or(&cond->value, NEED_TO_WAKE_ONE | NEED_TO_WAKE_ALL, AK::memory_order_release) | NEED_TO_WAKE_ONE | NEED_TO_WAKE_ALL;
pthread_mutex_unlock(mutex);
int rc = futex_wait(&cond->value, value, abstime, cond->clockid);
if (rc < 0 && errno != EAGAIN)
@ -122,7 +122,7 @@ int pthread_cond_broadcast(pthread_cond_t* cond)
if (!(value & NEED_TO_WAKE_ALL)) [[likely]]
return 0;
AK::atomic_fetch_and(&cond->value, ~(NEED_TO_WAKE_ONE | NEED_TO_WAKE_ALL), AK::memory_order_relaxed);
AK::atomic_fetch_and(&cond->value, ~(NEED_TO_WAKE_ONE | NEED_TO_WAKE_ALL), AK::memory_order_acquire);
pthread_mutex_t* mutex = AK::atomic_load(&cond->mutex, AK::memory_order_relaxed);
VERIFY(mutex);