Semaphore 和 CountDownLatch 组合使用，报异常

Question

CountDownLatch 单独使用

CountDownLatch 这样单独使用没有问题 - 做多线程的倒计时

private final static Integer count = 6;
public static void main(String[] args) throws InterruptedException {
        countDownLatchTest();
    }

    public static void countDownLatchTest() throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(count);
        for (int i = 0; i < count; i++) {
            new Thread(() -> {
                countDownLatch.countDown();
                System.out.println(Thread.currentThread().getName() + "~~~倒计时~~~count=" + countDownLatch.getCount());
            }, "Thread-Name-" + i).start();
        }
        countDownLatch.await();
        System.out.println(Thread.currentThread().getName() + "~~~OVER");
    }

Semaphore 单独使用

Semaphore 这样单独使用也没有问题，多线程多窗口

    private final static Integer count = 3;
    public static void main(String[] args) throws InterruptedException {
        Semaphore semaphore = new Semaphore(count);
        for (int i = 0; i < count * count; i++) {
            new Thread(() -> {
                try {
                    semaphore.acquire();
                    System.out.println(Thread.currentThread().getName() + "~~~抢到线程");
                    int rand = RandomUtils.getRandom(5);
                    TimeUnit.SECONDS.sleep(rand);
                    System.out.println(Thread.currentThread().getName()  + "~~~执行" +rand + "秒后，离开~~");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    semaphore.release();
                }
            }, "Thread-Name-" + i).start();
        }
        System.out.println(Thread.currentThread().getName() + "~~~OVER");
    }

但是当我想要组合使用时报错，如下写法

private final static Integer count = 3;

    public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(count * count);
        Semaphore semaphore = new Semaphore(count);
        for (int i = 0; i < count * count; i++) {
            new Thread(() -> {
                try {
                    semaphore.acquire();
                    System.out.println(Thread.currentThread().getName() + "~~~抢到线程");
                    int rand = RandomUtils.getRandom(15);
                    TimeUnit.SECONDS.sleep(rand);
                    System.out.println(Thread.currentThread().getName()  + "~~~执行" +rand + "秒后，离开~~");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    semaphore.release();
                    countDownLatch.countDown();
                }
            }, "Thread-Name-" + i).start();
        }
        countDownLatch.wait();
        System.out.println(Thread.currentThread().getName() + "~~~OVER");
    }

上述代码会在执行 countDownLatch.wait(); 语句的时候报错

Exception in thread "main" java.lang.IllegalMonitorStateException
    at java.lang.Object.wait(Native Method)
    at java.lang.Object.wait(Object.java:502)
    at com.ax.ieng.pmcallout.test.demo.SemaphoreDemo.main(SemaphoreDemo.java:32)

Answer 1

countDownLatch.wait(); 改为 countDownLatch.await();