CountDownLatch使用示例

public void countDown()

递减锁存器的计数，如果计数到达零，则释放所有等待的线程。如果当前计数大于零，则将计数减少.

public boolean await(long timeout,TimeUnit unit) throws InterruptedException

使当前线程在锁存器倒计数至零之前一直等待，除非线程被中断或超出了指定的等待时间。如果当前计数为零，则此方法立刻返回true值。

 /*
     * 主线程计数器只有1 countdown将计数器降为0，释放所有等待线程（MyRunable在run方法中执行了await方法）并且执行await方法等待子线程执行
     * 子线程开始执行 子线程每执行一次 计数器减1 直到计数器减为零，主线程又开始执行
     * */
    @Test
    void contextLoads() throws InterruptedException {

        CountDownLatch latch = new CountDownLatch(1);
        CountDownLatch await = new CountDownLatch(5);
        //创建五个线程
        for (int i = 0; i < 5; ++i) {
            new Thread(new MyRunable(latch, await)).start();
        }
        System.out.println("主线程开始执行");
        latch.countDown();//唤醒子线程
        System.out.println("随机");//唤醒了子线程但是主线程并没有沉睡 随意随机与子线程争抢
        await.await();//主线程等待子线程执行完成 必定是子线程全部执行完成后
        System.out.println("子线程执行结束主线程宣布end");
    }



    @Test
    void test2() throws InterruptedException {
        ThreadPoolExecutor threadPool = new ThreadPoolExecutor(5, 10, 100, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(5));
        final int count = 10;
        CountDownLatch latch = new CountDownLatch(count);
        System.out.println("hello我是:" + Thread.currentThread().getName() + "我确信我是老大，子线程都在我下面，都是弟弟");
        for (int i = 0; i < 10; i++) {
            threadPool.execute(new MyRunnable2(i, latch));
        }
        System.out.println("hello我是:" + Thread.currentThread().getName() + "我不确信我是老大，但是只要我给他们加上足够的休眠时间我还是那个西楚霸王");

        latch.await();//下面必定是线程池执行后才做的操作
        System.out.println("大道三千我悟了，我主线程应该为人民服务，在幕后为他们保驾护航");
        threadPool.shutdown();
    }

MyRunable类

package com.xi.thymeleaf;

import java.util.concurrent.CountDownLatch;

public class MyRunable implements Runnable{
    private CountDownLatch latch;
    private CountDownLatch await;

    public MyRunable(CountDownLatch latch, CountDownLatch await) {
        this.latch = latch;
        this.await = await;
    }

    @Override
    public void run() {
        try {
            latch.await();//等待线程 等待主线程执行完毕
            System.out.println("等待线程终于熬到头了，等待线程开始执行");
            await.countDown();//等待线程执行
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

MyRunable2

package com.xi.thymeleaf;

import java.util.concurrent.CountDownLatch;

public class MyRunnable2 implements Runnable{
    int i;
    CountDownLatch latch;

    public MyRunnable2(int i, CountDownLatch latch) {
        this.i = i;
        this.latch = latch;
    }

    @Override
    public void run() {

        try {
            Thread.currentThread();
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //上面的trycatch块注释掉 就不一定是西楚霸王了
        System.out.println("我是线程"+i+"正在执行任务");
        latch.countDown();
    }
}

test1的测试结果

test2的测试结果