线程：CountDownLatch同步工具

一个同步辅助类，在完成一组正在其他线程中执行的操作之前，它允许一个或多个线程一直等待。

类似计数器，当计数器的值为0时，继续往下执行。

package ch03;

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

public class CountDownLatchTest {

    public static void main(String[] args) {
        ExecutorService threadPool = Executors.newCachedThreadPool();
        //初始值设置为2
        final CountDownLatch latch = new CountDownLatch(2);
        for(int i=0; i<2; i++){
            Runnable runnable = new Runnable() {
                
                @Override
                public void run() {
                    try {
                        Thread.sleep(new Random().nextInt(6000));
                        System.out.println("子线程执行。。。");
                        //计数器自减
                        latch.countDown();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            };
            threadPool.execute(runnable);
        }
        
        try {
            //等待计数器自减到0，然后再往下执行。
            latch.await();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("主线程....");
    }

}