CounDownLatchDemo

1package com.my.demo;
2import java.util.concurrent.CountDownLatch;
3import java.util.concurrent.ExecutorService;
4import java.util.concurrent.Executors;
5
6/**
7 * 用CountDownLatch来模拟运动员赛跑的Demmo.
8 */
9public class CountDownLatchDemo {
10    /** 参与比赛的人数（并发线程数） */
11    private static int PLAYER_NUM = 8;
12    
13    public static void main(String[] args) throws Exception {
14        //用于让主线程（裁判）等待所有子线程（运动员）就绪
15        final CountDownLatch readySignal = new CountDownLatch(PLAYER_NUM);
16        //用于让子线程（运动员）等待主线程（裁判）发号施令
17        final CountDownLatch beginSignal = new CountDownLatch(1);
18        //用于让主线程（裁判）等待所有子线程（运动员）执行（比赛）完成
19        final CountDownLatch endSignal = new CountDownLatch(PLAYER_NUM);
20        ExecutorService executorService = Executors.newFixedThreadPool(PLAYER_NUM);
21        
22        for(int i = 0; i < PLAYER_NUM; i++){
23            final int num = i + 1;
24            Runnable player = new Runnable(){
25                @Override
26                public void run() {
27                    System.out.println("No." + num + " is ready");
28                    //一个任务就绪后，减少readySignal上的等待
29                    readySignal.countDown();
30                    try {
31                        //等待主线程比赛开始的命令
32                        beginSignal.await();
33                        System.out.println("No." + num + " is running");
34                        Thread.sleep((long) (Math.random() * 5000));
35                        System.out.println("No.-----" + num + " arrived");
36                    } catch (InterruptedException e) {
37                        e.printStackTrace();
38                    } finally {
39                        //每个线程执行完成后，调用countDown减少在endSignal上的等待线程数
40                        endSignal.countDown();
41                    }
42                }
43            };
44            executorService.execute(player);
45        }
46        
47        //这里让主线程等待，确保所有子线程已开始执行并调用了await进入等待状态
48        readySignal.await();
49        System.out.println("Game Start!");
50        //所有等待在beginSignal上的线程（运动员）开始执行（比赛）
51        beginSignal.countDown();
52        try {
53            //等待所有在endSignal上的线程（运动员）执行（比赛）完成
54            endSignal.await();
55        } catch (InterruptedException e) {
56            e.printStackTrace();
57        } finally {
58            System.out.println("Game Over!");
59            executorService.shutdown();
60        }
61    }
62}