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Java中CountDownLatch用法解析

更新時間：2017年01月14日 13:05:37 作者：Java開發(fā)-擱淺

這篇文章主要為大家詳細(xì)介紹了Java中CountDownLatch用法，具有一定的參考價值，感興趣的小伙伴們可以參考一下

CountDownLatch類是一個同步計數(shù)器,構(gòu)造時傳入int參數(shù),該參數(shù)就是計數(shù)器的初始值，每調(diào)用一次countDown()方法，計數(shù)器減1,計數(shù)器大于0 時，await()方法會阻塞程序繼續(xù)執(zhí)行

CountDownLatch如其所寫，是一個倒計數(shù)的鎖存器，當(dāng)計數(shù)減至0時觸發(fā)特定的事件。利用這種特性，可以讓主線程等待子線程的結(jié)束。下面以一個模擬運動員比賽的例子加以說明。

 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
     //對于每位運動員，CountDownLatch減1后即結(jié)束比賽
     CountDownLatch begin = new CountDownLatch(1);
     //對于整個比賽，所有運動員結(jié)束后才算結(jié)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);
     
     //設(shè)置特定的線程池，大小為5
     ExecutorService exe = Executors.newFixedThreadPool(PLAYER_AMOUNT);
     for(Player p:plays)
       exe.execute(p);      //分配線程
     System.out.println("Race begins!");
     begin.countDown();
     try{
       end.await();      //等待end狀態(tài)變?yōu)?，即為比賽結(jié)束
     }catch (InterruptedException e) {
       // TODO: handle exception
       e.printStackTrace();
     }finally{
       System.out.println("Race ends!");
     }
     exe.shutdown();
   }
 }

接下來是Player類

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的狀態(tài)為0
       Thread.sleep((long)(Math.random()*100));  //隨機分配時間，即運動員完成時間
       System.out.println("Play"+id+" arrived.");
     }catch (InterruptedException e) {
       // TODO: handle exception
       e.printStackTrace();
     }finally{
       end.countDown();  //使end狀態(tài)減1，最終減至0
     }
   }
 }

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