CountDownLatch的用法

1. CountDownLatch定义

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。
2.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值（count）实际上就是闭锁需要等待的线程数量
countDown方法，当前线程调用此方法，则计数减一
await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

3.例子

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 11:05:11
Worker li si do work begin at 2011-04-14 11:05:11
Worker zhang san do work complete at 2011-04-14 11:05:16
Worker li si do work complete at 2011-04-14 11:05:19
all work done at 2011-04-14 11:05:19

原文链接