实战Memcached缓存系统（5）Memcached的CAS程序实例

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