Java并发编程之代码实现两玩家交换装备

1 Exchanger 是什么

JDK 1.5 开始 JUC 包下提供的 Exchanger 类可用于两个线程之间交换信息。Exchanger 对象可理解为一个包含2个格子的容器,通过调用 exchanger 方法向其中的格子填充信息,当两个格子中的均被填充信息时,自动交换两个格子中的信息,然后将交换的信息返回给调用线程,从而实现两个线程的信息交换。

功能看似简单,但这在某些场景下是很有用处的,例如游戏中两个玩家交换装备;交友软件男女心仪对象匹配。

下面简单模拟下两个玩家交换装备的场景。

package com.chenpi;

import java.util.concurrent.Exchanger;

/**
 * @Description
 * @Author 陈皮
 * @Date 2021/7/11
 * @Version 1.0
 */
public class ChenPiMain {

  public static void main(String[] args) throws InterruptedException {

    Exchanger<String> exchanger = new Exchanger<>();

    new Thread(() -> {
      String str = null;
      try {
        str = exchanger.exchange("屠龙刀");
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
      System.out.println("交易成功," + Thread.currentThread().getName() + "获得" + str);
    }, "周芷若").start();

    new Thread(() -> {
      String str = null;
      try {
        str = exchanger.exchange("倚天剑");
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
      System.out.println("交易成功," + Thread.currentThread().getName() + "获得" + str);
    }, "张无忌").start();
  }
}

// 输出结果如下
交易成功,张无忌获得屠龙刀
交易成功,周芷若获得倚天剑
2 Exchanger 详解

Exchager 类可用于两个线程之间交换信息,如果一个线程调用了 Exchanger 对象的 exchange 方法之后,会一直阻塞直到另一个线程来和它交换信息,交换之后的信息返回给调用线程,从而实现两个线程的信息交换。

Exchager 底层也是使用到了自旋和 cas 机制。

注意,如果超过两个线程调用同一个 Exchanger 对象 exchange 方法时,结果是不可预计的,只要有2个线程满足条件了,就认为匹配成功并交换信息。而剩下的未能得到配对的线程,则会被阻塞一直等待直到有另一个线程能与它匹配与之配对。

package com.chenpi;

import java.util.concurrent.Exchanger;

/**
 * @Description
 * @Author 陈皮
 * @Date 2021/7/11
 * @Version 1.0
 */
public class ChenPiMain {

  public static void main(String[] args) {

    Exchanger<String> exchanger = new Exchanger<>();

    new Thread(() -> {
      String str = null;
      try {
        str = exchanger.exchange("屠龙刀");
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
      System.out.println("交易成功," + Thread.currentThread().getName() + "获得" + str);
    }, "周芷若").start();

    new Thread(() -> {
      String str = null;
      try {
        str = exchanger.exchange("倚天剑");
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
      System.out.println("交易成功," + Thread.currentThread().getName() + "获得" + str);
    }, "张无忌").start();

    new Thread(() -> {
      String str = null;
      try {
        str = exchanger.exchange("假的倚天剑");
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
      System.out.println("交易成功," + Thread.currentThread().getName() + "获得" + str);
    }, "成昆").start();
  }
}

// 输出结果如下
交易成功,周芷若获得假的倚天剑
交易成功,成昆获得屠龙刀

当然,在等待交换信息的线程是可以被中断的,就比如玩家在等待交易过程中,突然玩家下线了,那就应该中断线程等待。

package com.chenpi;

import java.lang.Thread.State;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Exchanger;

/**
 * @Description
 * @Author 陈皮
 * @Date 2021/7/11
 * @Version 1.0
 */
public class ChenPiMain {

  public static void main(String[] args) throws InterruptedException {

    Exchanger<String> exchanger = new Exchanger<>();

    List<Thread> threads = new ArrayList<>(3);

    Thread thread1 = new Thread(() -> {
      String str = null;
      try {
        str = exchanger.exchange("屠龙刀");
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
      System.out.println("交易成功," + Thread.currentThread().getName() + "获得" + str);
    }, "周芷若");
    threads.add(thread1);

    Thread thread2 = new Thread(() -> {
      String str = null;
      try {
        str = exchanger.exchange("倚天剑");
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
      System.out.println("交易成功," + Thread.currentThread().getName() + "获得" + str);
    }, "张无忌");
    threads.add(thread2);

    Thread thread3 = new Thread(() -> {
      String str = null;
      try {
        str = exchanger.exchange("假的屠龙刀");
      } catch (InterruptedException e) {
        e.printStackTrace();
      }
      System.out.println("交易成功," + Thread.currentThread().getName() + "获得" + str);
    }, "成昆");
    threads.add(thread3);

    for (Thread thread : threads) {
      thread.start();
    }

    // 等待5秒
    Thread.sleep(5000);

    for (Thread thread : threads) {
      System.out.println(thread.getName() + ":" + thread.getState());
      // 如果还在阻塞等待则中断线程
      if (thread.getState() == State.WAITING) {
        thread.interrupt();
      }
    }
  }
}

// 输出结果如下
交易成功,张无忌获得屠龙刀
交易成功,周芷若获得倚天剑
周芷若:TERMINATED
张无忌:TERMINATED
成昆:WAITING
交易成功,成昆获得null
java.lang.InterruptedException
	at java.util.concurrent.Exchanger.exchange(Exchanger.java:568)
	at com.chenpi.ChenPiMain.lambda$main$2(ChenPiMain.java:47)
	at java.lang.Thread.run(Thread.java:748)

上面演示的是线程如果等不到另一个线程和它交换信息,则会一直等待下去。其实 Exchanger 还可以设置等待指定时间。比如系统设置玩家交换装备匹配时间为60秒,如果超出时间则终止交易。

package com.chenpi;

import java.util.concurrent.Exchanger;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/**
 * @Description
 * @Author 陈皮
 * @Date 2021/7/11
 * @Version 1.0
 */
public class ChenPiMain {

  public static void main(String[] args) {

    Exchanger<String> exchanger = new Exchanger<>();

    new Thread(() -> {
      try {
        // 超时时间设置为5秒
        String str = exchanger.exchange("屠龙刀", 5, TimeUnit.SECONDS);
        System.out.println("交易成功," + Thread.currentThread().getName() + "获得" + str);
      } catch (TimeoutException e) {
        System.out.println("交易超时!");
        e.printStackTrace();
      } catch (InterruptedException e) {
        System.out.println("交易异常终止");
        e.printStackTrace();
      }
    }, "周芷若").start();
  }
}

// 输出结果如下
交易超时!
java.util.concurrent.TimeoutException
	at java.util.concurrent.Exchanger.exchange(Exchanger.java:626)
	at com.chenpi.ChenPiMain.lambda$main$0(ChenPiMain.java:22)
	at java.lang.Thread.run(Thread.java:748)
3 Exchanger 应用

Exchager 在遗传算法和管道设计等应用中是非常有用的。比如两个线程之间交换缓冲区,填充缓冲区的线程在需要时从另一个线程获得一个刚清空的缓冲区,并将填充的缓冲区传递给清空缓冲区的线程。

package com.chenpi;

import java.awt.image.DataBuffer;
import java.util.concurrent.Exchanger;

/**
 * @Description
 * @Author 陈皮
 * @Date 2021/7/11
 * @Version 1.0
 */
public class ChenPiMain {

  Exchanger<DataBuffer> exchanger = new Exchanger<DataBuffer>();
  DataBuffer initialEmptyBuffer = ... a made-up type
  DataBuffer initialFullBuffer = ...

  class FillingLoop implements Runnable {

    public void run() {
      DataBuffer currentBuffer = initialEmptyBuffer;
      try {
        while (currentBuffer != null) {
          addToBuffer(currentBuffer);
          if (currentBuffer.isFull()) {
            currentBuffer = exchanger.exchange(currentBuffer);
          }
        }
      } catch (InterruptedException ex) { ...handle ...}
    }
  }

  class EmptyingLoop implements Runnable {

    public void run() {
      DataBuffer currentBuffer = initialFullBuffer;
      try {
        while (currentBuffer != null) {
          takeFromBuffer(currentBuffer);
          if (currentBuffer.isEmpty()) {
            currentBuffer = exchanger.exchange(currentBuffer);
          }
        }
      } catch (InterruptedException ex) { ...handle ...}
    }
  }

  void start() {
    new Thread(new FillingLoop()).start();
    new Thread(new EmptyingLoop()).start();
  }
}
 
收藏 (0)
评论列表
正在载入评论列表...
我是有底线的
为您推荐
    暂时没有数据