并行中的顺序执行——CountDownLatch

? ? java.util.concurrent.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。--《JDK API 1.6.0》

? ? 换句话说，你可以并行的执行一段代码，并设置等待所有的线程都执行完的点，然后再一起开始执行

? ? 举例说，五个个人一起(并行)包饺子，只有等所有的饺子都包好以后才一起下锅，得，就这个意思咯。

其API相对来说比较简单：

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实例：

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);//两个线程并行
    	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点
        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();
			}
    	}
    }
         
}

实例输出：

Worker zhang san do work begin at 2015-01-03 21:26:38
Worker li si do work begin at 2015-01-03 21:26:38
Worker zhang san do work complete at 2015-01-03 21:26:43
Worker li si do work complete at 2015-01-03 21:26:46
all work done at 2015-01-03 21:26:46

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并行中的顺序执行——CountDownLatch

原文：http://java--hhf.iteye.com/blog/2172227