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/******************************************************************************
*
* $Id$
*
* Copyright (C) 1997-2006 by Dimitri van Heesch.
*
* Permission to use, copy, modify, and distribute this software and its
* documentation under the terms of the GNU General Public License is hereby
* granted. No representations are made about the suitability of this software
* for any purpose. It is provided "as is" without express or implied warranty.
* See the GNU General Public License for more details.
*
* Documents produced by Doxygen are derivative works derived from the
* input used in their production; they are not affected by this license.
*
*/
#ifndef OBJCACHE_H
#define OBJCACHE_H
//#define CACHE_TEST
//#define CACHE_DEBUG
#define CACHE_STATS
/** @brief Cache for objects.
*
* This cache is used to decide which objects should remain in
* memory. It uses a least recently used policy (LRU) to decide
* which object should make room for a new object when the cache
* is full. An object should be added using add(), and then use()
* should be called when the object is used.
*/
class ObjCache
{
private:
struct CacheNode
{
CacheNode() : next(-1), prev(-1), obj(0) {}
int next;
int prev;
void *obj;
};
struct HashNode
{
HashNode() : head(-1), nextHash(-1), index(-1), obj(0) {}
int head;
int nextHash;
int index;
void *obj;
};
public:
/*! Creates the cache. The number of elements in the cache is 2 to
* the power of \a logSize.
*/
ObjCache(unsigned int logSize);
/*! Deletes the cache and free all internal data-structures used. */
~ObjCache();
/*! Adds \a obj to the cache. When victim is not null, this object is
* removed from the cache to make room for \a obj.
* Returns a handle to the object, which can be used by the use()
* function, each time the object is used.
*/
int add(void *obj,void **victim);
/*! Indicates that this object is used. This will move the object
* to the front of the internal LRU list to make sure it is removed last.
* The parameter \a handle is returned when called add().
*/
void use(int handle)
{
hits++;
if (handle==m_lastHandle) return;
m_lastHandle = handle;
moveToFront(handle);
}
/*! Removes the item identified by \a handle from the cache.
* @see add()
*/
void del(int handle);
/*! Debug function. Prints the LRU list */
void printLRU();
/*! Print miss/hits statistics */
void printStats();
private:
void moveToFront(int index);
unsigned int hash(void *addr);
HashNode *hashFind(void *obj);
HashNode *hashInsert(void *obj);
void hashRemove(void *obj);
CacheNode *m_cache;
HashNode *m_hash;
int m_head;
int m_tail;
int m_size;
int m_freeHashNodes;
int m_freeCacheNodes;
int m_lastHandle;
#ifdef CACHE_STATS
static int misses;
static int hits;
#endif
};
#endif // OBJCACHE_H
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