java 多线程 CountDownLatch用法

最新推荐文章于 2022-03-29 23:51:51 发布

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最新推荐文章于 2022-03-29 23:51:51 发布

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文章标签： java

本文介绍如何利用CountDownLatch同步辅助类，在Java多线程环境下，实现一组线程之间的协作与等待机制。通过实例演示了如何在特定线程完成任务前，让其他线程进入等待状态，直至所有任务完成时解除等待。本文提供了具体的构造方法、方法调用及测试代码，展示了其在实际应用中的使用场景。

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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

测试例子：

package test.thread;

import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.CountDownLatch;

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 2012-03-01 10:04:58
Worker li si do work begin at 2012-03-01 10:04:58
Worker zhang san do work complete at 2012-03-01 10:05:03
Worker li si do work complete at 2012-03-01 10:05:06
all work done at 2012-03-01 10:05:06

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