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thread_utils: release mutex before signaling

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holding the associated mutex while signaling a condition variable isn't
necessary and in some implementations will reduce performance as the
woken thread may test the mutex, fail and go back to sleep.

Change-Id: Id685a47b0c76fc4a1c5acedcb6623e8c55056415
This commit is contained in:
James Zern 2019-06-10 20:58:30 -07:00
parent 9acf18ba46
commit 6682f2c415
1 changed files with 11 additions and 1 deletions
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12
src/utils/thread_utils.c
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@ -217,8 +217,12 @@ static THREADFN ThreadLoop(void* ptr) {
done = 1; done = 1;
} }
// signal to the main thread that we're done (for Sync()) // signal to the main thread that we're done (for Sync())
pthread_cond_signal(&impl->condition_); // Note the associated mutex does not need to be held when signaling the
// condition. Unlocking the mutex first may improve performance in some
// implementations, avoiding the case where the waiting thread can't
// reacquire the mutex when woken.
pthread_mutex_unlock(&impl->mutex_); pthread_mutex_unlock(&impl->mutex_);
pthread_cond_signal(&impl->condition_);
} }
return THREAD_RETURN(NULL); // Thread is finished return THREAD_RETURN(NULL); // Thread is finished
} }
@ -240,7 +244,13 @@ static void ChangeState(WebPWorker* const worker, WebPWorkerStatus new_status) {
// assign new status and release the working thread if needed // assign new status and release the working thread if needed
if (new_status != OK) { if (new_status != OK) {
worker->status_ = new_status; worker->status_ = new_status;
// Note the associated mutex does not need to be held when signaling the
// condition. Unlocking the mutex first may improve performance in some
// implementations, avoiding the case where the waiting thread can't
// reacquire the mutex when woken.
pthread_mutex_unlock(&impl->mutex_);
pthread_cond_signal(&impl->condition_); pthread_cond_signal(&impl->condition_);
return;
} }
} }
pthread_mutex_unlock(&impl->mutex_); pthread_mutex_unlock(&impl->mutex_);