/* * $Id$ * * 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@lucent.com) 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 */ /*********************************************************/ #if (!defined(_OSD_POSIX) && !defined(__FreeBSD__)) && HAVE_MALLOC_H #include <malloc.h> #else #include <stdlib.h> /* BS2000/OSD defines malloc() & friends in stdlib.h */ #endif #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 );