mcs/class/System.Web.Mvc2/System.Web.Mvc/ReaderWriterCache`2.cs

   1 /* ****************************************************************************\r
   2  *\r
   3  * Copyright (c) Microsoft Corporation. All rights reserved.\r
   4  *\r
   5  * This software is subject to the Microsoft Public License (Ms-PL). \r
   6  * A copy of the license can be found in the license.htm file included \r
   7  * in this distribution.\r
   8  *\r
   9  * You must not remove this notice, or any other, from this software.\r
  10  *\r
  11  * ***************************************************************************/\r
  12 \r
  13 namespace System.Web.Mvc {\r
  14     using System;\r
  15     using System.Collections.Generic;\r
  16     using System.Diagnostics.CodeAnalysis;\r
  17     using System.Threading;\r
  18 \r
  19     [SuppressMessage("Microsoft.Design", "CA1001:TypesThatOwnDisposableFieldsShouldBeDisposable",\r
  20         Justification = "Instances of this type are meant to be singletons.")]\r
  21     internal abstract class ReaderWriterCache<TKey, TValue> {\r
  22 \r
  23         private readonly Dictionary<TKey, TValue> _cache;\r
  24         private readonly ReaderWriterLockSlim _rwLock = new ReaderWriterLockSlim();\r
  25 \r
  26         protected ReaderWriterCache()\r
  27             : this(null) {\r
  28         }\r
  29 \r
  30         protected ReaderWriterCache(IEqualityComparer<TKey> comparer) {\r
  31             _cache = new Dictionary<TKey, TValue>(comparer);\r
  32         }\r
  33 \r
  34         protected Dictionary<TKey, TValue> Cache {\r
  35             get {\r
  36                 return _cache;\r
  37             }\r
  38         }\r
  39 \r
  40         protected TValue FetchOrCreateItem(TKey key, Func<TValue> creator) {\r
  41             // first, see if the item already exists in the cache\r
  42             _rwLock.EnterReadLock();\r
  43             try {\r
  44                 TValue existingEntry;\r
  45                 if (_cache.TryGetValue(key, out existingEntry)) {\r
  46                     return existingEntry;\r
  47                 }\r
  48             }\r
  49             finally {\r
  50                 _rwLock.ExitReadLock();\r
  51             }\r
  52 \r
  53             // insert the new item into the cache\r
  54             TValue newEntry = creator();\r
  55             _rwLock.EnterWriteLock();\r
  56             try {\r
  57                 TValue existingEntry;\r
  58                 if (_cache.TryGetValue(key, out existingEntry)) {\r
  59                     // another thread already inserted an item, so use that one\r
  60                     return existingEntry;\r
  61                 }\r
  62 \r
  63                 _cache[key] = newEntry;\r
  64                 return newEntry;\r
  65             }\r
  66             finally {\r
  67                 _rwLock.ExitWriteLock();\r
  68             }\r
  69         }\r
  70 \r
  71     }\r
  72 }\r