(转)java多线程CountDownLatch用法

本文介绍了一个使用 Java 并发工具类 CountDownLatch 的示例。CountDownLatch 允许一个或多个线程等待其他线程完成操作。示例展示了如何通过两个 Worker 线程模拟并发任务,并确保所有任务完成后才继续执行主线程。

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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);
Worker worker1 = new Worker("A", 15000, latch);
Worker worker2 = new Worker("B", 8000, latch);

worker1.start();
worker2.start();
latch.await();
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();
System.out.println("Worker "+workerName+" do work complete at "+sdf.format(new Date()));
latch.countDown();
}

private void doWork(){
try{
Thread.sleep(workTime);
}catch(InterruptedException e){
e.printStackTrace();
}
}
}
}


输出:

Worker A do work begin at 2014-04-01 15:19:23
Worker B do work begin at 2014-04-01 15:19:23
Worker B do work complete at 2014-04-01 15:19:31
Worker A do work complete at 2014-04-01 15:19:38
all work done at 2014-04-01 15:19:38
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