浅析Java中CountDownLatch用法

/**

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() {

         // TODO Auto-generated constructor stub   

      }

     /**

      * @param args

      */

     public static void main(String[] args) {

         // TODO Auto-generated method stub

         //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) {

             // TODO: handle exception

             e.printStackTrace();

         }finally{

             System.out.println("Race ends!");

         }

         exe.shutdown();

     }

 }