Question

我有几个使用ArrayBlockingQueue的工作者。

每个worker从队列中获取一个对象，处理它，结果可以得到几个对象，这些对象将被放入队列中进行进一步处理。所以，工人=生产者+消费者。

工人：

public class Worker implements Runnable
{
    private BlockingQueue<String> processQueue = null;

    public Worker(BlockingQueue<String> processQueue)
    {
        this.processQueue = processQueue;
    }

    public void run()
    {
        try
        {
            do
            {
                String item = this.processQueue.take();
                ArrayList<String> resultItems = this.processItem(item);

                for(String resultItem : resultItems)
                {
                    this.processQueue.put(resultItem);
                }
            }
            while(true);
        }
        catch(Exception)
        {
            ...
        }
    }

    private ArrayList<String> processItem(String item) throws Exception
    {
        ...
    }
}

主要

public class Test
{
    public static void main(String[] args) throws Exception
    {
        new Test().run();
    }

    private void run() throws Exception
    {
        BlockingQueue<String> processQueue = new ArrayBlockingQueue<>(10000);
        processQueue.put("lalala");

        Executor service = Executors.newFixedThreadPool(100);
        for(int i=0; i<100; ++i)
        {
            service.execute(new Worker(processQueue));
        }
    }
}

当没有工作时，什么是阻止工人的最好方法？

首先，我想到的是定期检查队列中有多少项目以及当前正在处理多少项目。如果两者都等于零，那么在ExecutorService上执行类似“shutdownNow（）”的操作。但我不确定这是最好的方式。

Answer 1

如果没有其他工作要做，请在队列中输入一条消息，然后让工作人员自行关闭。这是防止数据损坏的好方法。

如果您需要通知另一个线程所有工作人员已经回家，您可以使用CountDownLatch来执行此操作。

Answer 2

听起来你有自己的解决方案 - 使用一个单独的正在进行的队列，其大小将是当前正在处理的项目数。如果您使用访问任一队列的约定在synchronized(theArrayBlockingQueue)块中，那么一切都应该很好。特别是，当将项目移动到处理状态时，将其从ArrayBlockingQueue中移除并将其添加到相同同步块中的processingQueue。

Answer 3

我稍微修改了你的代码，不确定这是否是你所期望的，但至少它终止了！如果您使用shutdownNow而不是shutdown，您的工作人员将被中断，除非您将其重新投入工作，否则将退出而不保证队列为空。

public class Test {

    public static void main(String[] args) throws Exception {
        new Test().run();
    }

    private void run() throws Exception {
        BlockingQueue<String> processQueue = new ArrayBlockingQueue<>(10000);
        processQueue.put("lalalalalalalalalalalalala"); //a little longer to make sure there is enough to process

        ExecutorService service = Executors.newFixedThreadPool(100);
        for (int i = 0; i < 100; ++i) {
            service.execute(new Worker(processQueue));
        }
        service.shutdown(); //orderly shutdown = lets the tasks terminate what they are doing
        service.awaitTermination(1, TimeUnit.SECONDS); //blocks until all tasks have finished or throws TimeOutException if timeout is reached
    }

    public static class Worker implements Runnable {

        private BlockingQueue<String> processQueue = null;
        private int count = 0;

        public Worker(BlockingQueue<String> processQueue) {
            this.processQueue = processQueue;
        }

        @Override
        public void run() {
            try {
                do {
                    //tries to get something from the queue for 100ms and returns null if it could not get anything
                    String item = this.processQueue.poll(100, TimeUnit.MILLISECONDS);
                    if (item == null) break; //Ends the job because the queue was empty
                    count++;
                    List<String> resultItems = this.processItem(item);

                    for (String resultItem : resultItems) {
                        this.processQueue.put(resultItem);
                    }
                } while (true);
            } catch (InterruptedException e) {
                System.out.println("Interrupted");
                Thread.currentThread().interrupt();
            }
            if (count != 0) System.out.println(Thread.currentThread() + ": processed " + count + " entries");
        }

        private List<String> processItem(String item) { //let's put the string back less final character
            if (item.isEmpty()) {
                return Collections.<String> emptyList();
            } else {
                return Arrays.asList(item.substring(0, item.length() - 1));
            }
        }
    }
}

Java：Producer = Consumer，如何知道何时停止？

3 个答案: