Java中CountDownLatch用法解析

Java中CountDownLatch用法解析

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 sthttp://ub

}

/**

* @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

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

}

}

}

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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