java CyclicBarrier

import java.io.IOException;
import java.util.Random;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

 public class R {  

    public static void main(String[] args) throws IOException, InterruptedException {
        //如果将参数改为4，但是下面只加入了3个选手，这永远等待下去
        //Waits until all parties have invoked await on this barrier.
        CyclicBarrier barrier = new CyclicBarrier();  

        ExecutorService executor = Executors.newFixedThreadPool();
        executor.submit(new Thread(new Runner(barrier, "1号选手")));
        executor.submit(new Thread(new Runner(barrier, "2号选手")));
        executor.submit(new Thread(new Runner(barrier, "3号选手")));  

        executor.shutdown();
    }
}  

class Runner implements Runnable {
    // 一个同步辅助类，它允许一组线程互相等待，直到到达某个公共屏障点 (common barrier point)
    private CyclicBarrier barrier;  

    private String name;  

    public Runner(CyclicBarrier barrier, String name) {
        super();
        this.barrier = barrier;
        this.name = name;
    }  

    @Override
    public void run() {
        try {
            Thread.sleep( * (new Random()).nextInt());
            System.out.println(name + " 准备好了...");  //
            // barrier的await方法，在所有参与者都已经在此 barrier 上调用 await 方法之前，将一直等待。
            //barrier.await();  关闭此处，所有线程各自执行会不影响

            //让barrier中所有线程 做完 barrier.await()之前的任务，
            //比如 "System.out.println(name + " 准备好了..."); "   然后才继续下面的任务
            barrier.await(); 

        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (BrokenBarrierException e) {
            e.printStackTrace();
         }
        System.out.println(name + " 起跑！");
    }
}