主线程等待线程池所有任务完成

原文出处：http://blog.chenlb.com/2008/12/main-thread-wait-all-sub-thread-finish-task-in-thread-pool.html

用线程池编写多线程程序时，当所有任务完成时，要做一些统计的工作。而统计工作必须要在所有任务完成才能做。所以要让主线程等待所有任务完成。可以使用ThreadPoolExecutor.awaitTermination(long timeout, TimeUnit unit)。请看示例代码：

package com.chenlb;

import java.util.Random;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

/**
 * 线程池使用示例, 主线程等待所有任务完成再结束.
 *
 * @author chenlb 2008-12-2 上午10:31:03
 */
public class ThreadPoolUse {

    public static class MyTask implements Runnable {
        private static int id = 0;

        private String name = "task-"+(++id);
        private int sleep;

        public MyTask(int sleep) {
            super();
            this.sleep = sleep;
        }

        public void run() {
            System.out.println(name+" -----start-----");
            try {
                Thread.sleep(sleep);    //模拟任务执行.
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(name+" -----end "+sleep+"-----");
        }

    }

    public static void main(String[] args) {
        System.out.println("==================start==================");
        ThreadPoolExecutor executor = new ThreadPoolExecutor(5,5, 60, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>());
        int n = 10;
        int sleep = 10 * 1000;  //10s
        Random rm = new Random();
        for(int i=0; i<n; i++) {
            executor.execute(new MyTask(rm.nextInt(sleep)+1));
        }

        executor.shutdown();

        try {
            boolean loop = true;
            do {    //等待所有任务完成
                loop = !executor.awaitTermination(2, TimeUnit.SECONDS);
            } while(loop);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("==================end====================");
    }

}

当然还有其它方法。