CountDownLatch

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();

对记数器减一

public void await() throws InterruptedException

上记数器到0之前一直等待
 

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

await()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

Java代码

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. }