thread_utils: release mutex before signaling
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.
@@ -217,8 +217,12 @@ static THREADFN ThreadLoop(void* ptr) {
done = 1;
}
// 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_cond_signal(&impl->condition_);
}
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
if (new_status != OK) {
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_);
+ return;
}
}
pthread_mutex_unlock(&impl->mutex_);
