CountDownLatch

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

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