(转)java多线程CountDownLatch用法-优快云博客

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