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：

 1 package com.xt.thinks21_7;
 2 
 3 import java.util.ArrayList;
 4 import java.util.List;
 5 import java.util.Random;
 6 import java.util.concurrent.Exchanger;
 7 import java.util.concurrent.TimeUnit;
 8 
 9 public class ThreadLocalTest {
10 
11     public static void main(String[] args) {
12         Exchanger<List<Integer>> exchanger = new Exchanger<List<Integer>>();
13         new Thread1(exchanger).start();
14         new Thread2(exchanger).start();
15     }
16 
17 }
18 
19 class Thread1 extends Thread {
20     List<Integer> list = new ArrayList<Integer>();
21     Exchanger<List<Integer>> exchanger = null;
22 
23     public Thread1(Exchanger<List<Integer>> exchanger) {
24         this.exchanger = exchanger;
25     }
26 
27     @Override
28     public void run() {
29         Random rand = new Random();
30         list.add(rand.nextInt(10000));
31         list.add(rand.nextInt(10000));
32         list.add(rand.nextInt(10000));
33         list.add(rand.nextInt(10000));
34         list.add(rand.nextInt(10000));
35         System.out.println("
Thread1:list-->" + list.size() + "
" + list);
36         for (int i = 0; i < 10; i++) {
37             try {
38                 list = exchanger.exchange(list);
39                 System.out.println("
Thread1:sizeoflist-->" + list.size()
40                         + "
" + list);
41             } catch (InterruptedException e) {
42                 // TODO Auto-generated catch block
43                 e.printStackTrace();
44             }
45         }
46     }
47 }
48 
49 class Thread2 extends Thread {
50     List<Integer> list = new ArrayList<Integer>();
51     Exchanger<List<Integer>> exchanger = null;
52 
53     public Thread2(Exchanger<List<Integer>> exchanger) {
54         this.exchanger = exchanger;
55     }
56 
57     @Override
58     public void run() {
59         try {
60             TimeUnit.MILLISECONDS.sleep(10);
61         } catch (InterruptedException e1) {
62             // TODO Auto-generated catch block
63             e1.printStackTrace();
64         }
65         Random rand = new Random();
66         list.add(rand.nextInt(10000));
67         list.add(rand.nextInt(10000));
68         list.add(rand.nextInt(10000));
69         list.add(rand.nextInt(10000));
70         list.add(rand.nextInt(10000));
71         System.out.println("
Thread2:list-->" + list.size() + "
" + list);
72         for (int i = 0; i < 10; i++) {
73             try {
74                 list = exchanger.exchange(list);
75             } catch (InterruptedException e) {
76                 // TODO Auto-generated catch block
77                 e.printStackTrace();
78             }
79             System.out.println("
Thread2:sizeoflist-->" + list.size() + "
"
80                     + list);
81         }
82     }
83 }

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。