使用ConcurrentDictionary实现轻量缓存

项目中需要用到一个轻量缓存，存储重复使用的数据。
在设计中需要考虑：
1.做成通用组件，为未来其他模块方法操作结果做准备。
2.缓存模块需要接口化，为未来替换使用外部缓存做准备。
3.使用默认缓存过期时间，单个Key的过期时间可以*配置。

使用ConcurrentDictionary来作为我们的缓存容器，并能保证线程安全。

     public interface IDataCache
     {
         TimeSpan Ttl
         {
             get;
         }

         void Set(string key, object value);

         void Set(string key, object value, TimeSpan ttl);

         object Get(string key);

         void PurgeExpiredEntries();
     }

     /// <summary>
     /// An implementation of <see cref="IDataCache"/> which uses a dictionary to cache values in memory.
     /// </summary>
     public class InMemDataCache:IDataCache
     {
         private static readonly TimeSpan DefaultTtl = TimeSpan.FromMinutes(10);

         private readonly TimeSpan _ttl;
         private readonly ConcurrentDictionary<string, CacheEntry> _cache = new ConcurrentDictionary<string, CacheEntry>();

         /// <summary>
         /// Initialize a new instance of <see cref="InMemDataCache"/> using the default TTL.
         /// </summary>
         public InMemDataCache()
             : this(DefaultTtl)
         {

         }

         /// <summary>
         /// Initialize a new instance of <see cref="InMemDataCache"/> using a specified TTL.
         /// </summary>
         /// <param name="ttl">
         /// The time-to-live (TTL) of value saved into the cache. Zero or negative value indicates that values shall never expire.
         /// </param>
         public InMemDataCache(TimeSpan ttl)
         {
             _ttl = ttl;
         }

         /// <summary>
         /// The time-to-live (TTL) of value saved into the cache.
         /// </summary>
         public TimeSpan Ttl
         {
             get
             {
                 return _ttl;
             }
         }

         /// <summary>
         /// Save a key-value pair into the cache using the global TTL settings.
         /// Existed value associated with the specified key shall be overwritten.
         /// </summary>
         /// <param name="key"></param>
         /// <param name="value"></param>
         public void Set(string key, object value)
         {
             Set(key, value, _ttl);
         }

         /// <summary>
         /// Save a key-value pair into the cache using the global TTL settings.
         /// Existed value associated with the specified key shall be overwritten.
         /// </summary>
         /// <param name="key"></param>
         /// <param name="value"></param>
         /// <param name="ttl">
         /// The time-to-live (TTL) of value saved into the cache. Zero or negative value indicates that values shall never expire.
         /// </param>
         public void Set(string key, object value, TimeSpan ttl)
         {
             var expirationTime = ttl <= TimeSpan.Zero ? DateTime.MinValue : DateTime.Now.Add(ttl);
             var result = new CacheEntry(value, expirationTime);
             _cache.AddOrUpdate(key, result, (k, o) => result);
         }

         public object Get(string key)
         {
             CacheEntry entry;
             if (!_cache.TryGetValue(key, out entry))
             {
                 return null;
             }

             if (entry.ExpirationTime == DateTime.MinValue || DateTime.Now < entry.ExpirationTime)
             {
                 return entry.Value;
             }

             CacheEntry old;
             _cache.TryRemove(key, out old);
             return null;
         }

         public void PurgeExpiredEntries()
         {
             foreach (var key in _cache.Keys)
             {
                 Get(key);
             }
         }

         private class CacheEntry
         {
             public readonly object Value;
             public readonly DateTime ExpirationTime;

             public CacheEntry(object value, DateTime expirationTime)
             {
                 // TODO: Complete member initialization
                 Value = value;
                 ExpirationTime = expirationTime;
             }
         }
     }

完整demo路径:http://files.cnblogs.com/files/Nicolas-wang/Examples.Cache.zip