浅析Java中CountDownLatch用法

廉价感情. 提交于 2020-03-29 20:15:43
/**
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         }     } }



 
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