mcs/class/System.Web/System.Web.Caching/CacheItemLRU.cs

   1 //
   2 // A simple LRU cache used for tracking the cache items
   3 //
   4 // Authors:
   5 //   Miguel de Icaza (miguel@gnome.org)
   6 //
   7 // Copyright 2010 Miguel de Icaza
   8 //
   9 // Permission is hereby granted, free of charge, to any person obtaining a copy
  10 // of this software and associated documentation files (the "Software"), to deal
  11 // in the Software without restriction, including without limitation the rights
  12 // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  13 // copies of the Software, and to permit persons to whom the Software is
  14 // furnished to do so, subject to the following conditions:
  15 //
  16 // The above copyright notice and this permission notice shall be included in
  17 // all copies or substantial portions of the Software.
  18 //
  19 // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  20 // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  21 // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  22 // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  23 // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  24 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  25 // THE SOFTWARE.
  26 //
  27 using System;
  28 using System.Collections.Generic;
  29
  30 namespace System.Web.Caching
  31 {
  32         sealed class CacheItemLRU
  33         {
  34                 public delegate bool SelectItemsQualifier (CacheItem item);
  35
  36                 Dictionary<string, LinkedListNode <CacheItem>> dict;
  37                 Dictionary<LinkedListNode<CacheItem>, string> revdict;
  38                 LinkedList<CacheItem> list;
  39                 Cache owner;
  40
  41                 // High/Low water mark is here to avoid situations when we hit a limit, evict an
  42                 // entry, add another one and have to evict again because the limit was hit. When we
  43                 // hit the high water limit, we evict until we reach the low water mark to avoid the
  44                 // situation.
  45                 int highWaterMark, lowWaterMark;
  46                 bool needsEviction;
  47
  48                 public int Count {
  49                         get { return dict.Count; }
  50                 }
  51
  52                 public CacheItemLRU (Cache owner, int highWaterMark, int lowWaterMark)
  53                 {
  54                         list = new LinkedList<CacheItem> ();
  55                         dict = new Dictionary<string, LinkedListNode<CacheItem>> (StringComparer.Ordinal);
  56                         revdict = new Dictionary<LinkedListNode<CacheItem>, string> ();
  57
  58                         this.highWaterMark = highWaterMark;
  59                         this.lowWaterMark = lowWaterMark;
  60                         this.owner = owner;
  61                 }
  62
  63                 public bool TryGetValue (string key, out CacheItem value)
  64                 {
  65                         LinkedListNode <CacheItem> item;
  66
  67                         if (dict.TryGetValue (key, out item)) {
  68                                 value = item.Value;
  69                                 return true;
  70                         }
  71                         value = null;
  72                         return false;
  73                 }
  74
  75                 // Must ALWAYS be called with the owner's write lock held
  76                 public void EvictIfNecessary ()
  77                 {
  78                         if (!needsEviction)
  79                                 return;
  80
  81                         for (int i = dict.Count; i > lowWaterMark; i--) {
  82                                 var key = revdict [list.Last];
  83
  84                                 owner.Remove (key, CacheItemRemovedReason.Underused, false, true);
  85                         }
  86                 }
  87
  88                 // Must ALWAYS be called with the owner's read lock held
  89                 public void InvokePrivateCallbacks ()
  90                 {
  91                         foreach (var de in dict) {
  92                                 CacheItem item = de.Value.Value;
  93                                 if (item == null || item.Disabled)
  94                                         continue;
  95
  96                                 if (item.OnRemoveCallback != null) {
  97                                         try {
  98                                                 item.OnRemoveCallback (de.Key, item.Value, CacheItemRemovedReason.Removed);
  99                                         } catch {
 100                                                 //TODO: anything to be done here?
 101                                         }
 102                                 }
 103                         }
 104                 }
 105
 106                 // Must ALWAYS be called with the owner's write lock held
 107                 public List <CacheItem> SelectItems (SelectItemsQualifier qualifier)
 108                 {
 109                         var ret = new List <CacheItem> ();
 110
 111                         foreach (LinkedListNode <CacheItem> node in dict.Values) {
 112                                 CacheItem item = node.Value;
 113
 114                                 if (qualifier (item))
 115                                         ret.Add (item);
 116                         }
 117
 118                         return ret;
 119                 }
 120
 121                 // Must ALWAYS be called with the owner's read lock held
 122                 public List <CacheItem> ToList ()
 123                 {
 124                         var ret = new List <CacheItem> ();
 125
 126                         if (dict.Count == 0)
 127                                 return ret;
 128
 129                         foreach (LinkedListNode <CacheItem> node in dict.Values)
 130                                 ret.Add (node.Value);
 131
 132                         return ret;
 133                 }
 134
 135                 public void Remove (string key)
 136                 {
 137                         if (key == null)
 138                                 return;
 139
 140                         LinkedListNode <CacheItem> node;
 141                         if (!dict.TryGetValue (key, out node))
 142                                 return;
 143
 144                         CacheItem item = node.Value;
 145                         dict.Remove (key);
 146
 147                         if (item == null || item.Priority != CacheItemPriority.NotRemovable) {
 148                                 revdict.Remove (node);
 149                                 list.Remove (node);
 150                         }
 151                 }
 152
 153                 public CacheItem this [string key] {
 154                         get {
 155                                 if (key == null)
 156                                         return null;
 157
 158                                 LinkedListNode<CacheItem> node;
 159                                 CacheItem item;
 160
 161                                 if (dict.TryGetValue (key, out node)){
 162                                         item = node.Value;
 163                                         if (item == null || item.Priority != CacheItemPriority.NotRemovable) {
 164                                                 list.Remove (node);
 165                                                 list.AddFirst (node);
 166                                         }
 167
 168                                         return item;
 169                                 }
 170
 171                                 return null;
 172                         }
 173
 174                         set {
 175                                 LinkedListNode<CacheItem> node;
 176
 177                                 if (dict.TryGetValue (key, out node)){
 178                                         // If we already have a key, move it to the front
 179                                         list.Remove (node);
 180                                         if (value == null || value.Priority != CacheItemPriority.NotRemovable)
 181                                                 list.AddFirst (node);
 182                                         else
 183                                                 revdict.Remove (node);
 184
 185                                         node.Value = value;
 186                                         return;
 187                                 }
 188                                 needsEviction = dict.Count >= highWaterMark;
 189
 190                                 // Adding new node
 191                                 node = new LinkedListNode<CacheItem> (value);
 192                                 if (value == null || value.Priority != CacheItemPriority.NotRemovable) {
 193                                         list.AddFirst (node);
 194                                         revdict [node] = key;
 195                                 }
 196
 197                                 dict [key] = node;
 198                         }
 199                 }
 200         }
 201 }