CountDownLatch的用法/等待多线程执行结果

在前面一篇博文http://guoba6688-sina-com.iteye.com/blog/724536中提出如何更方便的等待多线程执行结果，该篇博文的做法是

//等待线程执行完毕   
        while(threadPool.getActiveCount() > 0){   
            try{   
                Thread.sleep(1000);   
            }catch(Exception e){   
                e.printStackTrace();   
            }   
        }   

 

今天发现java类库中的CountDownLatch可以很方便的完成这个工作

 

CountDownLatch的原理时

1、先设一个线程数，通过构造函数。

2、启动线程后，调用await()方法等待内部保持的线程数归零

3、每个线程在完成后调用countDown()，将活动的线程数减1

4、当活动线程数归零后，执行下面的代码

 

 

附上代码

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

/**
 * 
 * CountDownLatch  的用法
 *
 * @author 锅巴
 * @version 1.0 2010-8-9
 */
public class Main {

    private ExecutorService pool;
    private int threadCount = 10;
    private CountDownLatch countDownLatch;
    
    public static void main(String[] args) throws InterruptedException {
        
        Main main = new Main();
        main.execute();
       
        System.out.println("Main is end ");
        
//        System.exit(0);
    }
    
    public Main(){
        threadCount = 10;
        pool = Executors.newFixedThreadPool(threadCount);
        //初始化线程数
        countDownLatch = new CountDownLatch(threadCount);
    }
    
    public void execute() throws InterruptedException{
        for(int i=0; i<threadCount; i++){
            pool.execute(new Handler(10,countDownLatch));
        }
        pool.shutdown();
        //等待线程执行完成
        //实现上是等待count变成0
        countDownLatch.await();
       
    }
    
    
    class Handler implements Runnable {
       
        private int count;
        
        private CountDownLatch countDownLatch;

        public Handler(int count,CountDownLatch countDownLatch) {
            this.count = count;
            this.countDownLatch = countDownLatch;
        }

        public void run() {
            // read and service request
            for(int i=0; i<count; i++){
                System.out.println(Thread.currentThread().getName() + " : " + i);
                try {
                    Thread.sleep(100);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            //当本线程完成就减1
            countDownLatch.countDown();
        }
    }
}

 

评论

1 楼 mercyblitz 2010-08-09  

CountDownLatch并不是用户等待线程执行结束的，它是控制一定数量的线程执行。

要想得到结果，当线程运行完毕，要利用Future,或者ExecutorCompletionService。