code: func (hook *GraylogHook) Flush() {
  	hook.mu.Lock() // claim the mutex as a Lock - we want exclusive access to it
  	defer hook.mu.Unlock()
  
  	hook.wg.Wait()
  }
docs: // Flush waits for the log queue to be empty.
  // This func is meant to be used when the hook was created with NewAsyncGraylogHook.