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

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