Question

如果我运行以下程序，JVM将不会在执行后终止。但是，如果我从代码中取消注释行（// newFixedThreadPool.execute(new Producer3());），程序将在执行后终止。我知道由于队列的阻塞性质，程序不会终止。在下面的代码的上下文中，代码的哪一部分阻止了JVM的终止？

public class LinkedBlockingQueueExample {

    public static void main(String[] args) {

      final BlockingQueue<String> blockingQueue = new LinkedBlockingQueue<String>(5);

      final class Producer implements Runnable {

        @Override
        public void run() {

            try {
                blockingQueue.put("Joshua");
                blockingQueue.put("Bloch");
                System.out.println("Put Joshua in the queue");
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }

      }

      final class Producer1 implements Runnable {

        @Override
        public void run() {

            try {
                blockingQueue.put("Martin");
                blockingQueue.put("Fowler");
                System.out.println("Put Mr Fowler in the Queue");
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }

      }

      final class Producer3 implements Runnable {

        @Override
        public void run() {

            try {
                blockingQueue.put("Malcom");
                blockingQueue.put("Gladwell");
                System.out.println("Put an Outlier in the Queue");
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }

    }

    final class Consumer implements Runnable {

        @Override
        public void run() {
            try {
                System.out.println(getClass() + " " + blockingQueue.take());
                System.out.println(getClass() + " " + blockingQueue.take());
                System.out.println(getClass() + " " + blockingQueue.take());
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

    }

    final class Consumer1 implements Runnable {

        @Override
        public void run() {
            try {
                System.out.println(getClass() + " " + blockingQueue.take());
                System.out.println(getClass() + " " + blockingQueue.take());
                System.out.println(getClass() + " " + blockingQueue.take());
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }

    }

    ExecutorService newFixedThreadPool = Executors.newFixedThreadPool(5);

    newFixedThreadPool.execute(new Producer());
    newFixedThreadPool.execute(new Producer1());
    // newFixedThreadPool.execute(new Producer3());
    newFixedThreadPool.execute(new Consumer());
    newFixedThreadPool.execute(new Consumer1());

    newFixedThreadPool.shutdown();

  }
}

Answer 1

Take()调用总是阻塞，直到元素可用。如果您不想阻止用户poll()

    poll()
Retrieves and removes the head of this queue, or returns null if this queue is empty.

参考：http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/LinkedBlockingQueue.html#poll()

Answer 2

额外的“接受”阻止终止。它阻止了额外的“采取”

LinkedBlockingQueue程序不会终止

2 个答案: