使用Exchanger实现线程间的数据交换

从JDK 1.5之后，在java.util.concurrent包下引入了好多的处理多线程的工具类，本文介绍Exchanger工具类, 然后采用Exchanger给出一个两个线程交换数值的简单实例。

Exchanger介绍

Exchanger描述

代码语言：javascript复制

/**
 * A synchronization point at which two threads can exchange objects.
 * Each thread presents some object on entry to the {@link #exchange
 * exchange} method, and receives the object presented by the other
 * thread on return.
*/

从上面的注释中可以看出：Exchanger提供了一个同步点，在这个同步点，两个线程可以交换数据。每个线程通过exchange()方法的入口提供数据给另外的线程，并接收其它线程提供的数据，并返回。

Exchanger相关类图

Exchanger通过Lock和Condition来完成功能，Exchanger的一个重要的public方法是exchange方法，用于线程的数据交换, 相关的类图以及详细的Exchanger类内容如下：

Exchanger工具类的使用案例

案例描述

完成一个简单的例子，实现两个线程之间交换数据，用Exchanger来做非常简单。

代码及测试

代码语言：javascript复制

import java.util.concurrent.Exchanger;
import java.util.concurrent.atomic.AtomicReference;

public class ThreadA implements Runnable {

  private final Exchanger<Integer> exchanger;

  private final AtomicReference<Integer> last = new AtomicReference<Integer>(
      5);

  public ThreadA(Exchanger<Integer> exchanger) {
    this.exchanger = exchanger;
  }

  public void run() {
    try {
      while (true) {
        last.set(exchanger.exchange(last.get()));
        System.out
            .println(" After calling exchange. Thread A has value: "
                  last.get());
        Thread.sleep(2000);
      }
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }

}

代码语言：javascript复制

import java.util.concurrent.Exchanger;
import java.util.concurrent.atomic.AtomicReference;

public class ThreadB implements Runnable {

  private Exchanger<Integer> exchanger;

  private final AtomicReference<Integer> last = new AtomicReference<Integer>(
      10);

  public ThreadB(Exchanger<Integer> exchanger) {
    this.exchanger = exchanger;
  }

  public void run() {
    try {
      while (true) {
        last.set(exchanger.exchange(last.get()));
        System.out
            .println(" After calling exchange. Thread B has value: "
                  last.get());
        Thread.sleep(2000);
      }
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }

}

代码语言：javascript复制

import java.util.concurrent.Exchanger;

public class Main {

  public static void main(String[] args) {
    Exchanger<Integer> exchanger = new Exchanger<Integer>();
    new Thread(new ThreadA(exchanger)).start();
    new Thread(new ThreadB(exchanger)).start();
  }
}

某次运行的结果

代码语言：javascript复制

 After calling exchange. Thread A has value: 10
 After calling exchange. Thread B has value: 5
 After calling exchange. Thread B has value: 10
 After calling exchange. Thread A has value: 5
 After calling exchange. Thread A has value: 10
 After calling exchange. Thread B has value: 5
 After calling exchange. Thread B has value: 10
 After calling exchange. Thread A has value: 5
 After calling exchange. Thread A has value: 10
 After calling exchange. Thread B has value: 5
 After calling exchange. Thread B has value: 10
 After calling exchange. Thread A has value: 5
 After calling exchange. Thread A has value: 10
 After calling exchange. Thread B has value: 5
 After calling exchange. Thread B has value: 10
 After calling exchange. Thread A has value: 5
 After calling exchange. Thread A has value: 10
 After calling exchange. Thread B has value: 5

//省略其它的
... ...

可以看出：两个线程的数据一直都在相互交换。

java jdk lock public 工具类

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