code: public void stop(boolean afterQueueEmpty){
  		for (QueueConsumer<E> c: consumers.values()){
  			c.preStop(afterQueueEmpty);
  		}
  		for (QueueConsumer<E> c: consumers.values()){
  			c.stop(afterQueueEmpty);
  		}
  	}
docs: Stop all the working threads one by one;
  This method will not return until all threads are stopped.<br>
  逐个停止所工作线程，这个方法会等到所有工作线程结束才返回。
  
  @param afterQueueEmpty	true if working thread should keep processing until the queue is empty;<br>
  false if working thread should stop after finished current work;<br>
  如果为true，则工作线程要等到队列处理空了才结束；<br>
  如果为false，则工作线程处理完当前数据就结束。