package com.my.demo;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * 用CountDownLatch来模拟运动员赛跑的Demmo.
 */
public class CountDownLatchDemo {
    /** 参与比赛的人数（并发线程数） */
    private static int PLAYER_NUM = 8;
    
    public static void main(String[] args) throws Exception {
        //用于让主线程（裁判）等待所有子线程（运动员）就绪
        final CountDownLatch readySignal = new CountDownLatch(PLAYER_NUM);
        //用于让子线程（运动员）等待主线程（裁判）发号施令
        final CountDownLatch beginSignal = new CountDownLatch(1);
        //用于让主线程（裁判）等待所有子线程（运动员）执行（比赛）完成
        final CountDownLatch endSignal = new CountDownLatch(PLAYER_NUM);
        ExecutorService executorService = Executors.newFixedThreadPool(PLAYER_NUM);
        
        for(int i = 0; i < PLAYER_NUM; i++){
            final int num = i + 1;
            Runnable player = new Runnable(){
                @Override
                public void run() {
                    System.out.println("No." + num + " is ready");
                    //一个任务就绪后，减少readySignal上的等待
                    readySignal.countDown();
                    try {
                        //等待主线程比赛开始的命令
                        beginSignal.await();
                        System.out.println("No." + num + " is running");
                        Thread.sleep((long) (Math.random() * 5000));
                        System.out.println("No.-----" + num + " arrived");
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    } finally {
                        //每个线程执行完成后，调用countDown减少在endSignal上的等待线程数
                        endSignal.countDown();
                    }
                }
            };
            executorService.execute(player);
        }
        
        //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
        readySignal.await();
        System.out.println("Game Start!");
        //所有等待在beginSignal上的线程（运动员）开始执行（比赛）
        beginSignal.countDown();
        try {
            //等待所有在endSignal上的线程（运动员）执行（比赛）完成
            endSignal.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            System.out.println("Game Over!");
            executorService.shutdown();
        }
    }
}