khtml/imload/tilecache.h

   1 /*
   2     Large image displaying library.
   3
   4     Copyright (C) 2004,2005 Maks Orlovich (maksim@kde.org)
   5
   6     Permission is hereby granted, free of charge, to any person obtaining a copy
   7     of this software and associated documentation files (the "Software"), to deal
   8     in the Software without restriction, including without limitation the rights
   9     to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  10     copies of the Software, and to permit persons to whom the Software is
  11     furnished to do so, subject to the following conditions:
  12
  13     The above copyright notice and this permission notice shall be included in
  14     all copies or substantial portions of the Software.
  15
  16     THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  17     IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  18     FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
  19     AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
  20     AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
  21     CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  22
  23 */
  24
  25 #ifndef TILE_CACHE_H
  26 #define TILE_CACHE_H
  27
  28 #include <assert.h>
  29
  30 #include "tile.h"
  31
  32 namespace khtmlImLoad {
  33
  34
  35 class TileCacheNode
  36 {
  37 public:
  38     //Interface to the cache LRU chains
  39     TileCacheNode* cacheNext;
  40     TileCacheNode* cachePrev;
  41
  42     void unlink()
  43     {
  44         cacheNext->cachePrev = cachePrev;
  45         cachePrev->cacheNext = cacheNext;
  46         cacheNext = 0;
  47         cachePrev = 0;
  48     }
  49
  50     void linkBefore(TileCacheNode* node)
  51     {
  52         this->cacheNext = node;
  53         this->cachePrev = node->cachePrev;
  54
  55         node->cachePrev = this;
  56         this->cachePrev->cacheNext = this;
  57     }
  58
  59     Tile* tile;
  60
  61     TileCacheNode(): cacheNext(0), cachePrev(0), tile(0)
  62     {}
  63 };
  64
  65
  66 /**
  67  An LRU-replacement cache for tiles.
  68 */
  69 class TileCache
  70 {
  71 public:
  72     typedef TileCacheNode Node;
  73
  74
  75     Node* poolHead;
  76
  77     //### TODO: consider smarter allocation for these?.
  78     Node* create()
  79     {
  80         if (poolHead)
  81         {
  82             Node* toRet = poolHead;
  83             poolHead    = poolHead->cacheNext;
  84             return toRet;
  85         }
  86         else
  87             return new Node();
  88     }
  89
  90     void release(Node* entry)
  91     {
  92         //### TODO: Limit ??
  93         entry->cacheNext = poolHead;
  94         poolHead         = entry;
  95     }
  96
  97 private:
  98     int sizeLimit;
  99     int size;
 100
 101     /**
 102      We keep tiles in a double-linked list, with the most recent one being at the rear
 103     */
 104     Node* front;
 105     Node* rear;
 106
 107     /**
 108      Discard the node, and removes it from the list. Does not free the node.
 109     */
 110     void doDiscard(Node* node)
 111     {
 112         assert(node->tile->cacheNode == node);
 113         node->tile->discard();
 114         node->tile->cacheNode = 0;
 115         node->unlink();
 116         --size;
 117         assert(size >= 0);
 118     }
 119 public:
 120
 121     TileCache(int _sizeLimit):sizeLimit(_sizeLimit), size(0)
 122     {
 123         front = new Node;
 124         rear  = new Node;
 125
 126         front->cacheNext = rear;
 127         rear ->cachePrev = front;
 128
 129         poolHead = 0;
 130     }
 131
 132     /**
 133      Add an entry to the cache.
 134      */
 135     void addEntry(Tile* tile)
 136     {
 137         assert (tile->cacheNode == 0);
 138
 139         Node* node;
 140
 141         //Must have room
 142         if (size >= sizeLimit)
 143         {
 144             //Remove the front entry, reuse it
 145             //for the new node
 146             node = front->cacheNext;
 147             doDiscard(node);
 148         }
 149         else
 150             node = create();
 151
 152         //Link in before the end sentinel, i.e. at the very last spot, increment usage count
 153         node->tile            = tile;
 154         tile->cacheNode       = node;
 155         node->linkBefore(rear);
 156         size++;
 157     }
 158
 159
 160     /**
 161      "Touches" the entry, making it the most recent
 162      (i.e. moves the entry to the rear of the chain)
 163      */
 164     void touchEntry(Tile* tile)
 165     {
 166         Node* node = tile->cacheNode;
 167         node->unlink();
 168         node->linkBefore(rear);
 169     }
 170
 171     /**
 172      Removes the entry from the cache, discards it.
 173      */
 174     void removeEntry(Tile* tile)
 175     {
 176         Node* node = tile->cacheNode;
 177         doDiscard(node);
 178
 179         release(node);
 180     }
 181 };
 182
 183 }
 184
 185 #endif
 186 // kate: indent-width 4; replace-tabs on; tab-width 4; space-indent on;