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在我的程序中CountDownLatch的await()方法会继续阻塞程序，CountDownLatch正如它所写，是一个倒计时锁存器，当count到0时触发三个Thread执行，并证明当cdAnswer减为0时三个Thread已经被执行，那么主线程执行，但在我的程序中，三个线程只完成了两个主线程，谁可以帮助我，我将非常感激。底部是我的程序。

public class CountdownLatchTest {
    public static void main(String[] args) {
        ExecutorService service = Executors.newCachedThreadPool();
        final CountDownLatch cdOrder = new CountDownLatch(1);
        final CountDownLatch cdAnswer = new CountDownLatch(3);

        for (int i = 0; i < 3; i++) {
            Runnable runnable = new Runnable() {
                @Override
                public void run() {
                    try {
                        System.out.println("Thread" + Thread.currentThread().getName()
                                + "Wait for the command");

                        cdOrder.await();
                        System.out.println("Thread" + Thread.currentThread().getName()
                                + "received command");
                        Thread.sleep((long) (Math.random() * 10000));
                        System.out.println("Thread" + Thread.currentThread().getName()
                                + "Feedback the results");
                        cdAnswer.countDown();
                    } catch (Exception e) {
                        e.printStackTrace();
                    } finally {
                        System.out.println("To complete the order");
                        cdAnswer.countDown();

                    }
                }
            };
            service.execute(runnable);
        }
        try {
            Thread.sleep((long) (Math.random() * 10000));

            System.out.println("Thread" + Thread.currentThread().getName()
                    + "The upcoming orders");
            cdOrder.countDown();
            System.out.println("Thread" + Thread.currentThread().getName()
                    + "Sent the command, are waiting for the result");
            cdAnswer.await();
            System.out.println("Thread" + Thread.currentThread().getName()
                    + "Have received all the response. "
                    + "The results of this task has been completed");
        } catch (Exception e) {
            e.printStackTrace();
        }
        service.shutdown();

    }
}

问题补充：这个结果不是我所期望的，我以为这句话'已经收到了所有的回应。此任务的结果已经完成'将在最终打印中

图片显示了我的程序的结果。 在此处输入图像描述

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1 回答 1

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这是因为如果您看到 runnable 的 run 方法

            public void run() {
                try {
                    System.out.println("Thread"
                            + Thread.currentThread().getName()
                            + "Wait for the command");

                    cdOrder.await();
                    System.out.println("Thread"
                            + Thread.currentThread().getName()
                            + "received command");
                    Thread.sleep((long) (Math.random() * 10000));
                    System.out.println("Thread"
                            + Thread.currentThread().getName()
                            + "Feedback the results");
                    cdAnswer.countDown(); -- countdown on latch cdAnswer
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    System.out.println("To complete the order");
                    cdAnswer.countDown(); -- countdown on latch cdAnswer

                }
            }

cdAnswer.countDown(); 在 finally 和 catch 子句之前的每个可运行的一个中调用两次。因此，对于三个线程，倒计时被调用六次，结果主线程在 3 个倒计时后启动。

删除 cdAnswer.countDown(); 就在 catch 语句之上，它按预期工作

于 2015-09-02T10:25:19.123 回答