java并发编程之CountDownLatch

CountDownLatch的一个有用特性是，它不要求调用countDown方法的线程等到计数到达零时才继续，而在所有线程都能通过之前，它只是阻止任何线程继续通过一个 await。

以下是一个简单的例子

演示了启动5个线程，等到所有线程执行完毕之后，打印出最后结果

package com.lala.shop;

import java.time.Duration;
import java.time.Instant;
import java.util.Random;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;

public class CountDownLatchDemo 
{
	/**
	 * 启动size个线程，等到所有线程执行完毕之后，打印出最后结果
	 * @param size
	 */
	public void demo(final int size)
	{
		CountDownLatch cdl = new CountDownLatch(size);
		
		Instant start = Instant.now();
		
		for(int i=1;i<=size;i++)
		{
			new Thread(() -> {
				try
				{
					long time = new Long(new Random().nextInt(10));
					TimeUnit.SECONDS.sleep(time);
					System.out.println(Thread.currentThread().getName() + " sleep " + time + " then finish ...");
					cdl.countDown();
				} catch (InterruptedException e)
				{
					e.printStackTrace();
				}
			}).start();
		}
		
		try 
		{
			cdl.await();
		} catch (InterruptedException e)
		{
			e.printStackTrace();
		}
		
		Instant end = Instant.now();
		Duration time = Duration.between(start, end);
		long seconds = time.getSeconds();//秒表示 
		
		System.out.println("finish this task ... spend time " + seconds + " seconds");
	}
	public static void main(String[] args)
	{
		new CountDownLatchDemo().demo(5);
	}
}

java并发编程之CountDownLatch

原文：http://blog.csdn.net/mn960mn/article/details/46655651