23.倒计时器CountDownLatch

import java.util.Random;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * 倒计时器：CountDownLatch
 * 通常用来控制线程等待，可以让某一个线程等待直到倒计时结束，再开始执行
 */
public class CountDownLatchDemo implements Runnable{
    static final CountDownLatch end = new CountDownLatch(10);//当前计算器的计数个数10
    static final CountDownLatchDemo demo = new CountDownLatchDemo();
    @Override
    public void run() {
        try {
            //模拟检查任务
            Thread.sleep(new Random().nextInt(10)*1000);
            System.out.println("check complete");
            end.countDown();//通知CountDownLatch一个线程完成任务，倒计时器减1
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    public static void main(String[] args) throws InterruptedException{
        ExecutorService exec = Executors.newFixedThreadPool(10);
        for (int i = 0; i < 10; i++) {
            exec.submit(demo);
        }
        //等待检查
        end.await();//主线程等待所有检查任务全部完成
        System.out.println("ok");
        exec.shutdown();
    }
}