code: func (q *execQueue) quit() {
  	q.mu.Lock()
  	if !q.isClosed() {
  		q.closeWait = make(chan struct{})
  		q.cond.Signal()
  	}
  	q.mu.Unlock()
  	<-q.closeWait
  }
docs: // quit stops the exec queue.
  // quit waits for the current execution to finish before returning.