Function ChangeState

libraries/webp/src/utils/thread_utils.c:231–257

main thread state control

// main thread state control
static void ChangeState(WebPWorker* const worker, WebPWorkerStatus new_status) {
  // No-op when attempting to change state on a thread that didn't come up.
  // Checking status_ without acquiring the lock first would result in a data
  // race.
  WebPWorkerImpl* const impl = (WebPWorkerImpl*)worker->impl_;
  if (impl == NULL) return;

  pthread_mutex_lock(&impl->mutex_);
  if (worker->status_ >= OK) {
    // wait for the worker to finish
    while (worker->status_ != OK) {
      pthread_cond_wait(&impl->condition_, &impl->mutex_);
    }
    // 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_);
}

#endif  // WEBP_USE_THREAD