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 queue 2011-12-18 23:12:39.843 INFO net.spy.memcached.MemcachedConnection: Connection state changed for sun.nio.ch.SelectionKeyImpl@b09e89 Non-CAS 2: Michael Non-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, "Love"); CASValue casValue1 = cache.gets("y"); CASValue casValue2 = cache.gets("y"); cache.cas("y", casValue2.getCas(), casValue2.getValue()); 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 queue 2011-12-18 23:07:14.541 INFO net.spy.memcached.MemcachedConnection: Connection state changed for sun.nio.ch.SelectionKeyImpl@1621e42 CAS 2: 11 Value 2: Love CAS 1: 11 Value 1: Love