缓存

最新推荐文章于 2025-08-03 18:41:44 发布

转载最新推荐文章于 2025-08-03 18:41:44 发布 · 91 阅读

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原文链接：http://www.cnblogs.com/Spinoza/p/9992570.html

本文详细介绍了缓存机制的实现方式，包括静态字典作为缓存的基础，以及主动和被动过期策略的结合使用。通过具体代码示例，展示了如何在C#中实现缓存，并处理缓存项的过期问题。

1.缓存的机制就是静态字典

2. 使用缓存的时候，都是固定的套路给一个key，然后判断是否存在，存在怎么样不存在怎么样

3.过期问题,先上一个被动过期的例子,就是用户先查,查到过期就删除

  1 private static Dictionary<string, KeyValuePair<DateTime, object>> _CustomerCacheDictionary = new Dictionary<string, KeyValuePair<DateTime, object>>();
  2 
  3         static CustomerCache()
  4         {
  5             Task.Run(() =>
  6             {
  7                 while (true)
  8                 {
  9                     if (_CustomerCacheDictionary.Count > 0)
 10                     {
 11                         List<string> list = new List<string>();
 12                         foreach (var item in _CustomerCacheDictionary)
 13                         {
 14                             KeyValuePair<DateTime, object> keyValuePair = item.Value;
 15                             if (DateTime.Now > keyValuePair.Key)//过期了
 16                             {
 17                                 list.Add(item.Key);
 18                             }
 19                         }
 20                         foreach (var key in list)
 21                         {
 22                             _CustomerCacheDictionary.Remove(key);
 23                         }
 24                     }
 25                     Thread.Sleep(1000);
 26                 }
 27             });
 28         }
 29 
 30         /// <summary>
 31         /// 
 32         /// </summary>
 33         /// <param name="key"></param>
 34         /// <param name="data"></param>
 35         /// <param name="cacheTime">默认30分钟  单位分钟</param>
 36         public void Add(string key, object data, int cacheTime = 30)
 37         {
 38             if (_CustomerCacheDictionary.ContainsKey(key))
 39                 throw new Exception("相同的key");
 40             _CustomerCacheDictionary.Add(key, new KeyValuePair<DateTime, object>(DateTime.Now.AddMinutes(cacheTime), data));
 41         }
 42 
 43         /// <summary>
 44         /// 应该先检查，再get
 45         /// </summary>
 46         /// <typeparam name="T"></typeparam>
 47         /// <param name="key"></param>
 48         /// <returns></returns>
 49         public T Get<T>(string key)
 50         {
 51             return (T)_CustomerCacheDictionary[key].Value;
 52             //if (this.Contains(key))
 53             //{
 54             //    return (T)_CustomerCacheDictionary[key].Value;
 55             //}
 56             //else
 57             //{
 58             //    //return default(T);//T int  0  
 59             //    throw new Exception("not such key");
 60             //}
 61 
 62             //if (_CustomerCacheDictionary.ContainsKey(key))
 63             //{
 64             //    KeyValuePair<DateTime, object> keyValuePair = _CustomerCacheDictionary[key];
 65             //    if (DateTime.Now > keyValuePair.Key)//过期了
 66             //    {
 67             //        _CustomerCacheDictionary.Remove(key);
 68             //        return default(T);
 69             //    }
 70             //    else
 71             //    {
 72             //        return (T)keyValuePair.Value;
 73             //    }
 74             //}
 75             //else
 76             //{
 77             //    return default(T);
 78             //}
 79         }
 80         /// <summary>
 81         /// 
 82         /// </summary>
 83         /// <param name="key"></param>
 84         /// <returns></returns>
 85         public bool Contains(string key)
 86         {
 87             //完成清理  不能用
 88             //return _CustomerCacheDictionary.ContainsKey(key) && DateTime.Now <= _CustomerCacheDictionary[key].Key;
 89 
 90             if (_CustomerCacheDictionary.ContainsKey(key))
 91             {
 92                 KeyValuePair<DateTime, object> keyValuePair = _CustomerCacheDictionary[key];
 93                 if (DateTime.Now > keyValuePair.Key)//过期了
 94                 {
 95                     _CustomerCacheDictionary.Remove(key);
 96                     return false;
 97                 }
 98                 else
 99                     return true;
100             }
101             return false;
102         }

4.主动过期,利用异步线程技术实时查询缓存的过期时间

 1 static CustomerCache()
 2         {
 3             Task.Run(() =>
 4             {
 5                 while (true)
 6                 {
 7                     if (_CustomerCacheDictionary.Count > 0)
 8                     {
 9                         List<string> list = new List<string>();
10                         foreach (var item in _CustomerCacheDictionary)
11                         {
12                             KeyValuePair<DateTime, object> keyValuePair = item.Value;
13                             if (DateTime.Now > keyValuePair.Key)//过期了
14                             {
15                                 list.Add(item.Key);
16                             }
17                         }
18                         foreach (var key in list)
19                         {
20                             _CustomerCacheDictionary.Remove(key);
21                         }
22                     }
23                     Thread.Sleep(1000);
24                 }
25             });
26         }