mcs/class/System.Web.Mvc3/Mvc/ReaderWriterCache`2.cs

   1 namespace System.Web.Mvc {
   2     using System;
   3     using System.Collections.Generic;
   4     using System.Diagnostics.CodeAnalysis;
   5     using System.Threading;
   6
   7     [SuppressMessage("Microsoft.Design", "CA1001:TypesThatOwnDisposableFieldsShouldBeDisposable", Justification = "Instances of this type are meant to be singletons.")]
   8     internal abstract class ReaderWriterCache<TKey, TValue> {
   9
  10         private readonly Dictionary<TKey, TValue> _cache;
  11         private readonly ReaderWriterLockSlim _rwLock = new ReaderWriterLockSlim();
  12
  13         protected ReaderWriterCache()
  14             : this(null) {
  15         }
  16
  17         protected ReaderWriterCache(IEqualityComparer<TKey> comparer) {
  18             _cache = new Dictionary<TKey, TValue>(comparer);
  19         }
  20
  21         protected Dictionary<TKey, TValue> Cache {
  22             get {
  23                 return _cache;
  24             }
  25         }
  26
  27         protected TValue FetchOrCreateItem(TKey key, Func<TValue> creator) {
  28             // first, see if the item already exists in the cache
  29             _rwLock.EnterReadLock();
  30             try {
  31                 TValue existingEntry;
  32                 if (_cache.TryGetValue(key, out existingEntry)) {
  33                     return existingEntry;
  34                 }
  35             }
  36             finally {
  37                 _rwLock.ExitReadLock();
  38             }
  39
  40             // insert the new item into the cache
  41             TValue newEntry = creator();
  42             _rwLock.EnterWriteLock();
  43             try {
  44                 TValue existingEntry;
  45                 if (_cache.TryGetValue(key, out existingEntry)) {
  46                     // another thread already inserted an item, so use that one
  47                     return existingEntry;
  48                 }
  49
  50                 _cache[key] = newEntry;
  51                 return newEntry;
  52             }
  53             finally {
  54                 _rwLock.ExitWriteLock();
  55             }
  56         }
  57
  58     }
  59 }