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LibC: Only set owner on recursive mutexes

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This lets us skip the gettid() calls on fast paths.

Also, verify that futex_wake() succeeds.
This commit is contained in:
Sergey Bugaev 2021-07-06 14:34:39 +03:00 • committed by Andreas Kling
parent d0447f23b8
commit 30caa33f7e
1 changed files with 15 additions and 10 deletions
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25
Userland/Libraries/LibC/pthread_integration.cpp
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@ -114,7 +114,8 @@ int __pthread_mutex_trylock(pthread_mutex_t* mutex)
bool exchanged = AK::atomic_compare_exchange_strong(&mutex->lock, expected, MUTEX_LOCKED_NO_NEED_TO_WAKE, AK::memory_order_acquire);
if (exchanged) [[likely]] {
AK::atomic_store(&mutex->owner, __pthread_self(), AK::memory_order_relaxed);
if (mutex->type == __PTHREAD_MUTEX_RECURSIVE)
AK::atomic_store(&mutex->owner, __pthread_self(), AK::memory_order_relaxed);
mutex->level = 0;
return 0;
} else if (mutex->type == __PTHREAD_MUTEX_RECURSIVE) {
@ -132,18 +133,17 @@ int pthread_mutex_trylock(pthread_mutex_t* mutex) __attribute__((weak, alias("__
int __pthread_mutex_lock(pthread_mutex_t* mutex)
{
pthread_t this_thread = __pthread_self();
// Fast path: attempt to claim the mutex without waiting.
u32 value = MUTEX_UNLOCKED;
bool exchanged = AK::atomic_compare_exchange_strong(&mutex->lock, value, MUTEX_LOCKED_NO_NEED_TO_WAKE, AK::memory_order_acquire);
if (exchanged) [[likely]] {
AK::atomic_store(&mutex->owner, this_thread, AK::memory_order_relaxed);
if (mutex->type == __PTHREAD_MUTEX_RECURSIVE)
AK::atomic_store(&mutex->owner, __pthread_self(), AK::memory_order_relaxed);
mutex->level = 0;
return 0;
} else if (mutex->type == __PTHREAD_MUTEX_RECURSIVE) {
pthread_t owner = AK::atomic_load(&mutex->owner, AK::memory_order_relaxed);
if (owner == this_thread) {
if (owner == __pthread_self()) {
// We already own the mutex!
mutex->level++;
return 0;
@ -160,7 +160,8 @@ int __pthread_mutex_lock(pthread_mutex_t* mutex)
value = AK::atomic_exchange(&mutex->lock, MUTEX_LOCKED_NEED_TO_WAKE, AK::memory_order_acquire);
}
AK::atomic_store(&mutex->owner, this_thread, AK::memory_order_relaxed);
if (mutex->type == __PTHREAD_MUTEX_RECURSIVE)
AK::atomic_store(&mutex->owner, __pthread_self(), AK::memory_order_relaxed);
mutex->level = 0;
return 0;
}
@ -178,7 +179,8 @@ int __pthread_mutex_lock_pessimistic_np(pthread_mutex_t* mutex)
value = AK::atomic_exchange(&mutex->lock, MUTEX_LOCKED_NEED_TO_WAKE, AK::memory_order_acquire);
}
AK::atomic_store(&mutex->owner, __pthread_self(), AK::memory_order_relaxed);
if (mutex->type == __PTHREAD_MUTEX_RECURSIVE)
AK::atomic_store(&mutex->owner, __pthread_self(), AK::memory_order_relaxed);
mutex->level = 0;
return 0;
}
@ -190,11 +192,14 @@ int __pthread_mutex_unlock(pthread_mutex_t* mutex)
return 0;
}
AK::atomic_store(&mutex->owner, 0, AK::memory_order_relaxed);
if (mutex->type == __PTHREAD_MUTEX_RECURSIVE)
AK::atomic_store(&mutex->owner, 0, AK::memory_order_relaxed);
u32 value = AK::atomic_exchange(&mutex->lock, MUTEX_UNLOCKED, AK::memory_order_release);
if (value == MUTEX_LOCKED_NEED_TO_WAKE) [[unlikely]]
futex_wake(&mutex->lock, 1);
if (value == MUTEX_LOCKED_NEED_TO_WAKE) [[unlikely]] {
int rc = futex_wake(&mutex->lock, 1);
VERIFY(rc >= 0);
}
return 0;
}