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http://www.cnblogs.com/davidwang456/p/4179488.html
Exchanger是自jdk1.5起开始提供的工具套件,一般用于两个工作线程之间交换数据。在本文中我将采取由浅入深的方式来介绍分析这个工具类。首先我们来看看官方的api文档中的叙述:
在以上的描述中,有几个要点:
接着看api文档,这个类提供对外的接口非常简洁,一个无参构造函数,两个重载的范型exchange方法:
public V exchange(V x) throws InterruptedException
public V exchange(V x, long timeout, TimeUnit unit) throws InterruptedException, TimeoutException
从官方的javadoc可以知道,当一个线程到达exchange调用点时,如果它的伙伴线程此前已经调用了此方法,那么它的伙伴会被调度唤醒并与之进行对象交换,然后各自返回。如果它的伙伴还没到达交换点,那么当前线程将会被挂起,直至伙伴线程到达——完成交换正常返回;或者当前线程被中断——抛出中断异常;又或者是等候超时——抛出超时异常。
注意的是,
线程1
obj1 = exchanger.exchange(obj1);
线程2
obj2= exchanger.exchange(obj2);
这样对调的结果就是obj1 = obj2, obj2= obj1
在java中都是引用的交换
在下面的例子中,ReadThread交换之后的buffList就指向了null
import java.util.LinkedList;import java.util.List;import java.util.concurrent.Exchanger; public class ExchangerTest { public static void main(String[] args) { Exchanger
> exchanger = new Exchanger
>(); new ReadThread(exchanger).start();// 启动读数据线程 new WriteThread(exchanger).start();// 启动写数据线程 } } class ReadThread extends Thread { private Exchanger
> exchanger; List bufferList = new LinkedList (); public static final Integer BUFFER_SIZE = 10; public ReadThread(Exchanger
> exchanger) { this.exchanger = exchanger; } @Override public void run() { System.out.println("ReadThread start"); for (int i = 0; i < BUFFER_SIZE; i++) { bufferList.add(String.valueOf( (char)( 'A' + i))); // 模拟读数据 } try { Thread.sleep(3000); bufferList = exchanger.exchange(bufferList); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("ReadThread end"); //System.out.println("buff size " + bufferList.size()); }} class WriteThread extends Thread { private Exchanger
> exchanger; List bufferList; public WriteThread(Exchanger
> exchanger) { this.exchanger = exchanger; } @Override public void run() { try { System.out.println("WriteThread start"); bufferList = exchanger.exchange(bufferList); // 从Exchanger获得缓存数据 } catch (InterruptedException e) { e.printStackTrace(); } for (String str : bufferList) { System.out.println(str); } System.out.println("WriteTread end"); }}