Java 提升之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();

 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

package com.study.thread.concurrent;

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

/**
 * @author draem0507
 * @TODO 学下countdownLatch
 * @version 0.1
 * @create 2012 15:03:28
 * 
 */
public class CountDownLatchTest {
    /**
     * <p>
     * CountDownLatch类是一个同步计数器,构造时传入int参数,
     * </p>
     * <p>
     * 该参数就是计数器的初始值，每调用一次countDown()方法，计数器减1,
     * </p>
     * <p>
     * 计数器大于0 时，await()方法会阻塞程序继续执行
     * </p>
     */

    public static void main(String[] args) {

        CountDownLatch countDownLatch = new CountDownLatch(3);
        Worker worker1 = new Worker("小明", countDownLatch);
        Worker worker2 = new Worker("小红", countDownLatch);
        Worker worker3 = new Worker("小强", countDownLatch);
        Boss boss = new Boss(countDownLatch);
        ExecutorService service = Executors.newCachedThreadPool();
        service.execute(worker1);
        service.execute(worker2);
        service.execute(worker3);
        service.execute(boss);
        service.shutdown();

    }
}

class Worker implements Runnable {
    private String name;
    private CountDownLatch countDownLatch;

    public void run() {
        doWork();
        try {
            Thread.sleep((new Random().nextInt(10)) * 1000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println(name + "-->结束干活");
        countDownLatch.countDown();

    }

    public Worker(String name, CountDownLatch countDownLatch) {

        this.name = name;
        this.countDownLatch = countDownLatch;
    }

    private void doWork() {

        System.out.println(name + "-->正在干活");
    }
}

class Boss implements Runnable {
    private CountDownLatch countDownLatch;

    public Boss(CountDownLatch countDownLatch) {

        this.countDownLatch = countDownLatch;
    }

    public void run() {
        System.out.println("老板正在等待验工");

        try {
            countDownLatch.await();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        System.out.println("工人干活都结束,老板开始验工");
    }
}

结果:

小明-->正在干活
小红-->正在干活
老板正在等待验工
小强-->正在干活
小强-->结束干活
小明-->结束干活
小红-->结束干活
工人干活都结束,老板开始验工

不一定都按上述结果呈现，但是最后一句话肯定是最后执行

参考:

　　http://www.cnblogs.com/yezhenhan/archive/2012/01/07/2315652.html

　　http://www.iteye.com/topic/1002652