// 一个CountDouwnLatch实例是不能重复使用的，也就是说它是一次性的，锁一经被打开就不能再关闭使用了，如果想重复使用，请考虑使用CyclicBarrier。
public class CountDownLatchTest {// 模拟了100米赛跑，10名选手已经准备就绪，只等裁判一声令下。当所有人都到达终点时，比赛结束。public static void main(String[] args) throws InterruptedException {// 开始的倒数锁 final CountDownLatch begin = new CountDownLatch(1);  // 结束的倒数锁 final CountDownLatch end = new CountDownLatch(10);  // 十名选手 final ExecutorService exec = Executors.newFixedThreadPool(10);  for (int index = 0; index < 10; index++) {final int NO = index + 1;  Runnable run = new Runnable() {public void run() {  try {  // 如果当前计数为零，则此方法立即返回。// 等待
                        begin.await();  Thread.sleep((long) (Math.random() * 10000));  System.out.println("No." + NO + " arrived");  } catch (InterruptedException e) {  } finally {  // 每个选手到达终点时，end就减一
                        end.countDown();}  }  };  exec.submit(run);}  System.out.println("Game Start");  // begin减一，开始游戏
        begin.countDown();  // 等待end变为0，即所有选手到达终点
        end.await();  System.out.println("Game Over");  exec.shutdown();  }
}

public class TestCyclicBarrier {private static final int THREAD_NUM = 5;    public static class WorkerThread implements Runnable{CyclicBarrier barrier;public WorkerThread(CyclicBarrier b){this.barrier = b;}public void run() {try{System.out.println("Worker's waiting");//线程在这里等待，直到所有线程都到达barrier。
                barrier.await();System.out.println("ID:"+Thread.currentThread().getId()+" Working");}catch(Exception e){e.printStackTrace();}}}public static void main(String[] args) {CyclicBarrier cb = new CyclicBarrier(THREAD_NUM, new Runnable() {//当所有线程到达barrier时执行public void run() {System.out.println("Inside Barrier");}});for(int i=0;i){new Thread(new WorkerThread(cb)).start();}}}
/*
以下是输出：
Worker's waiting
Worker's waiting
Worker's waiting
Worker's waiting
Worker's waiting
Inside Barrier
ID:12 Working
ID:8 Working
ID:11 Working
ID:9 Working
ID:10 Working
*/