CountDownLatch，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。
主要方法
public CountDownLatch(int count);
public void countDown();
public void await() throws InterruptedException
构造方法参数指定了计数的次数
countDown方法，当前线程调用此方法，则计数减一
awaint方法，调用此方法会一直阻塞当前线程，直到计时器的值为0
例子
java代码
public class CountDownLatchDemo { final static SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); public static void main(String[] args) throws InterruptedException { CountDownLatch latch=new CountDownLatch(2);//两个工人的协作 Worker worker1=new Worker("zhang san", 5000, latch); Worker worker2=new Worker("li si", 8000, latch); worker1.start();// worker2.start();// latch.await();//等待所有工人完成工作 System.out.PRintln("all work done at "+sdf.format(new Date())); } static class Worker extends Thread{ String workerName; int workTime; CountDownLatch latch; public Worker(String workerName ,int workTime ,CountDownLatch latch){ this.workerName=workerName; this.workTime=workTime; this.latch=latch; } public void run(){ System.out.println("Worker "+workerName+" do work begin at "+sdf.format(new Date())); doWork();//工作了 System.out.println("Worker "+workerName+" do work complete at "+sdf.format(new Date())); latch.countDown();//工人完成工作，计数器减一 } private void doWork(){ try { Thread.sleep(workTime); } catch (InterruptedException e) { e.printStackTrace(); } } } }
输出：
Worker zhang san do work begin at 2011-04-14 11:05:11Worker li si do work begin at 2011-04-14 11:05:11Worker zhang san do work complete at 2011-04-14 11:05:16Worker li si do work complete at 2011-04-14 11:05:19all work done at 2011-04-14 11:05:19
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