| nbsp;
有了这个数据结构我们就可以将数据实现两份存储。再利用一些读写策略就可以实现上面我们讲的缓存方式。转
整个的缓存我们使用如下缓存类来控制：
/*
* http://www.cnblogs.com/chsword/
* chsword
* Date: 2009-3-31
* Time: 17:00
*
*/
using System;
using System.Collections;
using System.Collections.Generic;
using System.Threading;
namespace CHCache {
/// <summary>
/// 双存储的类
/// </summary>
public class DictionaryCache : IEnumerable {
/// <summary>
/// 在此缓存构造时初始化字典对象
/// </summary>
public DictionaryCache()
{
Store = new Dictionary<string, Medium>();
}
public void Add(string key,Func<object> func)
{
if (Store.ContainsKey(key)) {//修改，如果已经存在，再次添加时则采用其它线程
var elem = Store[key];
if (elem.IsUpdating)return; //正在写入未命中
var th = new ThreadHelper(elem, func);//ThreadHelper将在下文提及,是向其它线程传参用的
var td = new Thread(th.Doit);
td.Start();
}
else {//首次添加时可能也要读取，所以要本线程执行
Console.WriteLine("Begin first write");
Store.Add(key, new Medium {IsPrimary = true, Primary = func()});
Console.WriteLine("End first write");
}
}
/// <summary>
/// 读取时所用的索引
/// </summary>
/// <param name="key"></param>
/// <returns></returns>
public object this[string key] {
get {
if (!Store.ContainsKey(key))return null;
var elem = Store[key];
if (elem.IsUpdated) {//如果其它线程更新完毕，则将主次转置
elem.IsUpdated = false;
elem.IsPrimary = !elem.IsPrimary;
}
var ret = elem.IsPrimary ? elem.Primary : elem.Secondary;
var b = elem.IsPrimary ? " from 1" : " form 2";
return ret + b;
}
}
Dictionary<string, Medium> Store { get; set; }
public IEnumerator GetEnumerator() {
return ((IEnumerable)Store).GetEnumerator();
}
}
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