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();     } }

接下来是Player类

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) {         // TODO Auto-generated constructor stub         super();         this.id = i;         this.begin = begin;         this.end = end;     }

     @Override     public void run() {         // TODO Auto-generated method stub         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         }     } }