如何中断在 take() 上阻塞的 BlockingQueue？

Question

我有一个类，它从BlockingQueue 获取对象并通过在连续循环中调用take() 来处理它们。在某个时候，我知道不会有更多的对象被添加到队列中。如何中断take() 方法使其停止阻塞？

这是处理对象的类：

public class MyObjHandler implements Runnable {

  private final BlockingQueue<MyObj> queue;

  public class MyObjHandler(BlockingQueue queue) {
    this.queue = queue;
  }

  public void run() {
    try {
      while (true) {
        MyObj obj = queue.take();
        // process obj here
        // ...
      }
    } catch (InterruptedException e) {
      Thread.currentThread().interrupt();
    }
  }
}

下面是使用这个类来处理对象的方法：

public void testHandler() {

  BlockingQueue<MyObj> queue = new ArrayBlockingQueue<MyObj>(100);  

  MyObjectHandler  handler = new MyObjectHandler(queue);
  new Thread(handler).start();

  // get objects for handler to process
  for (Iterator<MyObj> i = getMyObjIterator(); i.hasNext(); ) {
    queue.put(i.next());
  }

  // what code should go here to tell the handler
  // to stop waiting for more objects?
}

Answer 1

如果中断线程不是一种选择，另一种方法是在队列上放置一个“标记”或“命令”对象，MyObjHandler 将识别为这样并跳出循环。

Answer 2

BlockingQueue<MyObj> queue = new ArrayBlockingQueue<MyObj>(100);
MyObjectHandler handler = new MyObjectHandler(queue);
Thread thread = new Thread(handler);
thread.start();
for (Iterator<MyObj> i = getMyObjIterator(); i.hasNext(); ) {
  queue.put(i.next());
}
thread.interrupt();

但是，如果您这样做，线程可能会在队列中仍有项目等待处理时被中断。您可能需要考虑使用poll 而不是take，这将允许处理线程超时并在它等待一段时间没有新输入时终止。

Answer 3

很晚了，但希望这对其他人也有帮助我遇到了类似的问题，并使用了erickson above 建议的poll 方法，并进行了一些小改动，

class MyObjHandler implements Runnable 
{
    private final BlockingQueue<MyObj> queue;
    public volatile boolean Finished;  //VOLATILE GUARANTEES UPDATED VALUE VISIBLE TO ALL
    public MyObjHandler(BlockingQueue queue) 
    {
        this.queue = queue;
        Finished = false;
    }
    @Override
    public void run() 
    {        
        while (true) 
        {
            try 
            {
                MyObj obj = queue.poll(100, TimeUnit.MILLISECONDS);
                if(obj!= null)//Checking if job is to be processed then processing it first and then checking for return
                {
                    // process obj here
                    // ...
                }
                if(Finished && queue.isEmpty())
                    return;

            } 
            catch (InterruptedException e) 
            {                   
                return;
            }
        }
    }
}

public void testHandler() 
{
    BlockingQueue<MyObj> queue = new ArrayBlockingQueue<MyObj>(100); 

    MyObjHandler  handler = new MyObjHandler(queue);
    new Thread(handler).start();

    // get objects for handler to process
    for (Iterator<MyObj> i = getMyObjIterator(); i.hasNext(); )
    {
        queue.put(i.next());
    }

    // what code should go here to tell the handler to stop waiting for more objects?
    handler.Finished = true; //THIS TELLS HIM
    //If you need you can wait for the termination otherwise remove join
    myThread.join();
}

这两个问题都解决了

1. 标记了BlockingQueue，这样它就知道不必再等待元素了
2. 中间没有中断，因此仅当队列中的所有项目都已处理且没有剩余要添加的项目时，处理块才会终止

Answer 4

中断线程：

thread.interrupt()

Answer 5

还是别打断了，太恶心了。

    public class MyQueue<T> extends ArrayBlockingQueue<T> {

        private static final long serialVersionUID = 1L;
        private boolean done = false;

        public ParserQueue(int capacity) {  super(capacity); }

        public void done() { done = true; }

        public boolean isDone() { return done; }

        /**
         * May return null if producer ends the production after consumer 
         * has entered the element-await state.
         */
        public T take() throws InterruptedException {
            T el;
            while ((el = super.poll()) == null && !done) {
                synchronized (this) {
                    wait();
                }
            }

            return el;
        }
    }

1. 生产者将对象放入队列时，调用queue.notify()，如果结束，调用queue.done()
2. 循环 while (!queue.isDone() || !queue.isEmpty())
3. test take() 返回 null 值