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1 CountDownLatch 用法

CountDownLatch是java.util.concurrent包中一个类，CountDownLatch只要提供的机制是多个（具体数量等于初始化CountDownLatch时count的值）线程都达到了预期状态或者完成了预期工作时触发事件，其他线程可以等待这个事件来触发自己后续的工作。等待的线程可以是多个，即CountDownLatch可以唤醒多个等待的线程。到达自己预期状态的线程会调用CountDownLatch的countDown方法，而等待的线程会调用CountDownLatch的await方法。

什么情况下可以用这个cdl呢？我平常约朋友们打英雄联盟（5V5竞技游戏），然后总有那么一个人要在大家都上号了之后他才上号，这个情形就可以使用CDL来表示，废话不说直接上demo！

Player类作为我们提前上号的好队友，因为tx这垃圾服务器的存在，所以上号需要一定时间，这里随机数设置为等待0-10s~

/** * @author ：ChenHao86 * @date ：Created in 2021/12/31 14:49 * @description： * @modified By： * @version: $ */public class Player implements Runnable {
       private CountDownLatch downLatch;    private String name;    public Player(CountDownLatch downLatch, String name) {
           this.downLatch = downLatch;        this.name = name;    }    public void run() {
           this.doWork();        try {
               TimeUnit.SECONDS.sleep(new Random().nextInt(10));        } catch (Exception e) {
           }        System.out.println(this.name + "已经上号了！");        this.downLatch.countDown();    }    private void doWork() {
           System.out.println(this.name + "正在上号!");    }}

BadPlayer作为等大家都上了号以后，才上号那个拖延症坏队友

/** * @author ：ChenHao86 * @date ：Created in 2021/12/31 14:49 * @description： * @modified By： * @version: $ */public class BadPlayer implements Runnable {
       private CountDownLatch downLatch;    public BadPlayer(CountDownLatch downLatch){
           this.downLatch = downLatch;    }    public void run() {
           System.out.println("拖延症玩家等其他队友都上号.....");        try {
               this.downLatch.await();        } catch (Exception e) {
           }        System.out.println("其他队友都上号了,他终于上号了~!!");    }}

主方法

/** * @author ：ChenHao86 * @date ：Created in 2021/12/31 14:50 * @description： * @modified By： * @version: $ */public class CountDownLatchDemo {
       public static void main(String[] args) {
           ThreadPoolExecutor executor = new ThreadPoolExecutor(5, 5, 5, TimeUnit.SECONDS, new ArrayBlockingQueue(16));        CountDownLatch latch = new CountDownLatch(3);        Player p1 = new Player(latch, "盖伦");        Player p2 = new Player(latch, "瑞兹");        Player p3 = new Player(latch, "娑娜");        Player p4 = new Player(latch, "赵信");        BadPlayer badPlayer = new BadPlayer(latch);        executor.execute(p3);        executor.execute(p2);        executor.execute(p1);        executor.execute(p4);        executor.execute(badPlayer);        executor.shutdown();    }}

shift+F10执行方法

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