CountDownLatch是一种通过计数实现的线程安全：只有当CountDownLatch的值变为0的时候，await线程才会执行。其他线程调用countDown方法之后并不会阻塞，可以执行其他业务。

package com.vincent.juc;import java.util.Random;import java.util.concurrent.CountDownLatch;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.TimeUnit;/** * Vincent 创建于 2016/6/1. */public class CountDownLatchDemo {    public static void main(String[] args) throws InterruptedException {        final CountDownLatch countDownLatch=new CountDownLatch(5);        final Random random=new Random();        ExecutorService threadPool = Executors.newCachedThreadPool();        for(int i=0;i<5;i++){            threadPool.execute(new Runnable() {                @Override                public void run() {                    try {                        int t = random.nextInt(10);                        TimeUnit.SECONDS.sleep(t+1);                        long id = Thread.currentThread().getId();                        System.out.println("线程"+id+"执行结束");                        countDownLatch.countDown();                        System.out.println(id+"做别的事去了");                    } catch (Exception e) {                        e.printStackTrace();                    }                }            });        }        System.out.println("主线程开始阻塞");        countDownLatch.await();        System.out.println("主线程开始执行");    }}

输出如下：

主线程开始阻塞线程16执行结束16做别的事去了线程14执行结束14做别的事去了线程13执行结束13做别的事去了线程12执行结束12做别的事去了线程15执行结束15做别的事去了主线程开始执行