Java 并发编程框架（三）

Java

这一节主要讲述CountDownLatch的用法，不废话，直接上代码
测试用例CountDownLatchDemo类

/**
CountDownLatch类是一个同步计数器,构造时传入int参数,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,计数器大于0 时，await()方法会阻塞程序继续执行
CountDownLatch如其所写，是一个倒计数的锁存器，当计数减至0时触发特定的事件。利用这种特性，可以让主线程等待子线程的结束。下面以一个模拟运动员比赛的例子加以说明。
*/
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class CountDownLatchDemo {
    private static final int PLAYER_AMOUNT = 5;
    public CountDownLatchDemo() {
    }
    public static void main(String[] args) {
     //对于每位运动员，CountDownLatch减1后即结束比赛
     CountDownLatch begin = new CountDownLatch(1);
     //对于整个比赛，所有运动员结束后才算结束
     CountDownLatch end = new CountDownLatch(PLAYER_AMOUNT);
     Player[] plays = new Player[PLAYER_AMOUNT];
     for(int i=0;i<PLAYER_AMOUNT;i++)
         plays[i] = new Player(i+1,begin,end);
     //设置特定的线程池，大小为5
     ExecutorService exe = Executors.newFixedThreadPool(PLAYER_AMOUNT);
     for(Player p:plays)
         exe.execute(p);            //分配线程
     System.out.println("Race begins!");
     begin.countDown();
     try{
         end.await();            //等待end状态变为0，即为比赛结束
     }catch (InterruptedException e) {
         e.printStackTrace();
     }finally{
         System.out.println("Race ends!");
     }
     exe.shutdown();
    }
}

接下来是Player类（worker线程）

import java.util.concurrent.CountDownLatch;
public class Player implements Runnable {
    private int id;
    private CountDownLatch begin;
    private CountDownLatch end;
    public Player(int i, CountDownLatch begin, CountDownLatch end) {
     super();
     this.id = i;
     this.begin = begin;
     this.end = end;
    }
    @Override
    public void run() {
         try{
             begin.await();        //等待begin的状态为0
             Thread.sleep((long)(Math.random()*100));    //随机分配时间，即运动员完成时间
             System.out.println("Play"+id+" arrived.");
         }catch (InterruptedException e) {
             // TODO: handle exception
             e.printStackTrace();
         }finally{
             end.countDown();    //使end状态减1，最终减至0
         }
    }
}

转载文章浅析Java中CountDownLatch用法