主线程等待子线程操作完成

摘要

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

 

例子

1. public class CountDownLatchDemo {  

2.     final static SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");  

3.     public static void main(String[] args) throws InterruptedException {  

4.         CountDownLatch latch=new CountDownLatch(2);//两个工人的协作  

5.         Worker worker1=new Worker("zhang san", 5000, latch);  

6.         Worker worker2=new Worker("li si", 8000, latch);  

7.         worker1.start();//  

8.         worker2.start();//  

9.         latch.await();//等待所有工人完成工作  

10.         System.out.println("all work done at "+sdf.format(new Date()));  

11.     }  

12.       

13.       

14.     static class Worker extends Thread{  

15.         String workerName;   

16.         int workTime;  

17.         CountDownLatch latch;  

18.         public Worker(String workerName ,int workTime ,CountDownLatch latch){  

19.              this.workerName=workerName;  

20.              this.workTime=workTime;  

21.              this.latch=latch;  

22.         }  

23.         public void run(){  

24.             System.out.println("Worker "+workerName+" do work begin at "+sdf.format(new Date()));  

25.             doWork();//工作了  

26.             System.out.println("Worker "+workerName+" do work complete at "+sdf.format(new Date()));  

27.             latch.countDown();//工人完成工作，计数器减一  

28.   

29.         }  

30.           

31.         private void doWork(){  

32.             try {  

33.                 Thread.sleep(workTime);  

34.             } catch (InterruptedException e) {  

35.                 e.printStackTrace();  

36.             }  

37.         }  

38.     }  

39.       

40.        

41. }  

 

输出：

Worker zhang san do work begin at 2011-04-14 11:05:11
Worker li si do work begin at 2011-04-14 11:05:11
Worker zhang san do work complete at 2011-04-14 11:05:16
Worker li si do work complete at 2011-04-14 11:05:19
all work done at 2011-04-14 11:05:19