實戰Memcached快取系統（5）Memcached的CAS程式例項

尊重知識，轉載請註明本文來自：程式設計藝術家Poechant的CSDN部落格 http://blog.csdn.net/poechant

1. 非CAS

首先看一個不是CAS的Memcached程式例項。例項的問題原型，見上一篇博文。

程式例項：

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);
	}
}

執行結果：

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

可見在多個Client操作時，一定會引起寫不一致性的問題。

2. CAS

程式例項：

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());
	}
}

執行結果：

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