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gd-libgd / src / gdcache.h

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#ifdef __cplusplus
extern "C" {
#endif

	/*
	 * gdcache.h
	 *
	 * Caches of pointers to user structs in which the least-recently-used
	 * element is replaced in the event of a cache miss after the cache has
	 * reached a given size.
	 *
	 * John Ellson  (ellson@graphviz.org)  Oct 31, 1997
	 *
	 * Test this with:
	 *		 gcc -o gdcache -g -Wall -DTEST gdcache.c
	 *
	 * The cache is implemented by a singly-linked list of elements
	 * each containing a pointer to a user struct that is being managed by
	 * the cache.
	 *
	 * The head structure has a pointer to the most-recently-used
	 * element, and elements are moved to this position in the list each
	 * time they are used.  The head also contains pointers to three
	 * user defined functions:
	 *		- a function to test if a cached userdata matches some keydata
	 *		- a function to provide a new userdata struct to the cache
	 *          if there has been a cache miss.
	 *		- a function to release a userdata struct when it is
	 *          no longer being managed by the cache
	 *
	 * In the event of a cache miss the cache is allowed to grow up to
	 * a specified maximum size.  After the maximum size is reached then
	 * the least-recently-used element is discarded to make room for the
	 * new.  The most-recently-returned value is always left at the
	 * beginning of the list after retrieval.
	 *
	 * In the current implementation the cache is traversed by a linear
	 * search from most-recent to least-recent.  This linear search
	 * probably limits the usefulness of this implementation to cache
	 * sizes of a few tens of elements.
	 */

	/*********************************************************/
	/* header                                                */
	/*********************************************************/

#include <stdlib.h>
#ifndef NULL
#	define NULL (void *)0
#endif

	/* user defined function templates */
	typedef int (*gdCacheTestFn_t)(void *userdata, void *keydata);
	typedef void *(*gdCacheFetchFn_t)(char **error, void *keydata);
	typedef void (*gdCacheReleaseFn_t)(void *userdata);

	/* element structure */
	typedef struct gdCache_element_s gdCache_element_t;
	struct gdCache_element_s {
		gdCache_element_t *next;
		void *userdata;
	};

	/* head structure */
	typedef struct gdCache_head_s gdCache_head_t;
	struct gdCache_head_s {
		gdCache_element_t *mru;
		int size;
		char *error;
		gdCacheTestFn_t gdCacheTest;
		gdCacheFetchFn_t gdCacheFetch;
		gdCacheReleaseFn_t gdCacheRelease;
	};

	/* function templates */
	gdCache_head_t *gdCacheCreate(int size,
	                              gdCacheTestFn_t gdCacheTest,
	                              gdCacheFetchFn_t gdCacheFetch,
	                              gdCacheReleaseFn_t gdCacheRelease
	                             );

	void gdCacheDelete(gdCache_head_t *head);

	void *gdCacheGet(gdCache_head_t *head, void *keydata);

#ifdef __cplusplus
}
#endif