JAVA之Exchanger

如果两个线程在运行过程中需要交换彼此的信息，比如一个数据或者使用的空间，就需要用到Exchanger这个类，Exchanger为线程交换信息提供了非常方便的途径，它可以作为两个线程交换对象的同步点，只有当每个线程都在进入 exchange ()方法并给出对象时，才能接受其他线程返回时给出的对象。
      
       Exchanger的构造方法如下：
[java] 
Exchanger();  //创建一个新的 Exchanger。

Exchanger用到的主要方法有：
[java]
exchange(V x);  //等待另一个线程到达此交换点（除非它被中断），然后将给定的对象传送给该线程，并接收该线程的对象。 
exchange(V x, long timeout, TimeUnit unit)；   // 等待另一个线程到达此交换点（除非它被中断，或者超出了指定的等待时间），然后将给定的对象传送给该线程，同时接收该线程的对象。

下面是demo代码：

 package com.xt.thinks21_7;

 import java.util.ArrayList;
 import java.util.List;
 import java.util.Random;
 import java.util.concurrent.Exchanger;
 import java.util.concurrent.TimeUnit;

 public class ThreadLocalTest {

     public static void main(String[] args) {
         Exchanger<List<Integer>> exchanger = new Exchanger<List<Integer>>();
         new Thread1(exchanger).start();
         new Thread2(exchanger).start();
     }

 }

 class Thread1 extends Thread {
     List<Integer> list = new ArrayList<Integer>();
     Exchanger<List<Integer>> exchanger = null;

     public Thread1(Exchanger<List<Integer>> exchanger) {
         this.exchanger = exchanger;
     }

     @Override
     public void run() {
         Random rand = new Random();
         list.add(rand.nextInt(10000));
         list.add(rand.nextInt(10000));
         list.add(rand.nextInt(10000));
         list.add(rand.nextInt(10000));
         list.add(rand.nextInt(10000));
         System.out.println("\nThread1:list-->" + list.size() + "\n" + list);
         for (int i = 0; i < 10; i++) {
             try {
                 list = exchanger.exchange(list);
                 System.out.println("\nThread1:sizeoflist-->" + list.size()
                         + "\n" + list);
             } catch (InterruptedException e) {
                 // TODO Auto-generated catch block
                 e.printStackTrace();
             }
         }
     }
 }

 class Thread2 extends Thread {
     List<Integer> list = new ArrayList<Integer>();
     Exchanger<List<Integer>> exchanger = null;

     public Thread2(Exchanger<List<Integer>> exchanger) {
         this.exchanger = exchanger;
     }

     @Override
     public void run() {
         try {
             TimeUnit.MILLISECONDS.sleep(10);
         } catch (InterruptedException e1) {
             // TODO Auto-generated catch block
             e1.printStackTrace();
         }
         Random rand = new Random();
         list.add(rand.nextInt(10000));
         list.add(rand.nextInt(10000));
         list.add(rand.nextInt(10000));
         list.add(rand.nextInt(10000));
         list.add(rand.nextInt(10000));
         System.out.println("\nThread2:list-->" + list.size() + "\n" + list);
         for (int i = 0; i < 10; i++) {
             try {
                 list = exchanger.exchange(list);
             } catch (InterruptedException e) {
                 // TODO Auto-generated catch block
                 e.printStackTrace();
             }
             System.out.println("\nThread2:sizeoflist-->" + list.size() + "\n"
                     + list);
         }
     }
 }

输出结果：

Thread1:list-->5

[5943, 3873, 5422, 2297, 3070]

Thread2:list-->5

[2774, 3676, 2137, 1446, 9944]

Thread2:sizeoflist-->5

[5943, 3873, 5422, 2297, 3070]

Thread1:sizeoflist-->5

[2774, 3676, 2137, 1446, 9944]

Thread2:sizeoflist-->5

[2774, 3676, 2137, 1446, 9944]

Thread1:sizeoflist-->5

[5943, 3873, 5422, 2297, 3070]

Thread1:sizeoflist-->5

[2774, 3676, 2137, 1446, 9944]

Thread2:sizeoflist-->5

[5943, 3873, 5422, 2297, 3070]

Thread2:sizeoflist-->5

[2774, 3676, 2137, 1446, 9944]

Thread1:sizeoflist-->5

[5943, 3873, 5422, 2297, 3070]

Thread2:sizeoflist-->5

[5943, 3873, 5422, 2297, 3070]

Thread1:sizeoflist-->5

[2774, 3676, 2137, 1446, 9944]

Thread1:sizeoflist-->5

[5943, 3873, 5422, 2297, 3070]

Thread2:sizeoflist-->5

[2774, 3676, 2137, 1446, 9944]

Thread2:sizeoflist-->5

[5943, 3873, 5422, 2297, 3070]

Thread1:sizeoflist-->5

[2774, 3676, 2137, 1446, 9944]

Thread1:sizeoflist-->5

[5943, 3873, 5422, 2297, 3070]

Thread2:sizeoflist-->5

[2774, 3676, 2137, 1446, 9944]

Thread2:sizeoflist-->5

[5943, 3873, 5422, 2297, 3070]

Thread1:sizeoflist-->5

[2774, 3676, 2137, 1446, 9944]

Thread1:sizeoflist-->5

[5943, 3873, 5422, 2297, 3070]

Thread2:sizeoflist-->5

[2774, 3676, 2137, 1446, 9944]

从输出结果中可以看出两个线程互相交换数据，直到循环结束。