实战Memcached缓存系统（5）Memcached的CAS程序实例

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1. 非CAS

首先看一个不是CAS的Memcached程序实例。实例的问题原型，见上一篇博文。

程序实例：

package com.sinosuperman.memcached;import java.io.IOException;import java.net.InetSocketAddress;import net.spy.memcached.MemcachedClient;public class Test {public static void main(String[] args) throws IOException {MemcachedClient cache = new MemcachedClient(new InetSocketAddress("127.0.0.1", 11211));cache.set("x", 1800, "Love");String obj1 = (String) cache.get("x");String obj2 = (String) cache.get("x");obj2 = "Michael";cache.set("x", 1800, obj2);System.out.println("Non-CAS 2:\t" + obj2);System.out.println("Non-CAS 1:\t" + obj1);}}

运行结果：

2011-12-18 23:12:39.836 INFO net.spy.memcached.MemcachedConnection:  Added {QA sa=/127.0.0.1:11211, #Rops=0, #Wops=0, #iq=0, topRop=null, topWop=null, toWrite=0, interested=0} to connect queue2011-12-18 23:12:39.843 INFO net.spy.memcached.MemcachedConnection:  Connection state changed for sun.nio.ch.SelectionKeyImpl@b09e89Non-CAS 2:MichaelNon-CAS 1:Love

可见在多个Client操作时，一定会引起写不一致性的问题。

2. CAS

程序实例：

package com.sinosuperman.memcached;import java.io.IOException;import java.net.InetSocketAddress;import net.spy.memcached.CASValue;import net.spy.memcached.MemcachedClient;public class Test {@SuppressWarnings("unchecked")public static void main(String[] args) throws IOException {MemcachedClient cache = new MemcachedClient(new InetSocketAddress("127.0.0.1", 11211));cache.set("y", 1800, "Michael");CASValue casValue1 = cache.gets("y");CASValue casValue2 = cache.gets("y");cache.cas("y", casValue2.getCas(), "Love");System.out.println("CAS 2:\t" + casValue2.getCas());System.out.println("Value 2:\t" + casValue2.getValue());System.out.println("CAS 1:\t" + casValue1.getCas());System.out.println("Value 1:\t" + casValue1.getValue());}}

运行结果：

2011-12-18 23:07:14.528 INFO net.spy.memcached.MemcachedConnection:  Added {QA sa=/127.0.0.1:11211, #Rops=0, #Wops=0, #iq=0, topRop=null, topWop=null, toWrite=0, interested=0} to connect queue2011-12-18 23:07:14.541 INFO net.spy.memcached.MemcachedConnection:  Connection state changed for sun.nio.ch.SelectionKeyImpl@1621e42CAS 2:11Value 2:LoveCAS 1:11Value 1:Love