1 /* 2 * $Id$ 3 * 4 * Caches of pointers to user structs in which the least-recently-used 5 * element is replaced in the event of a cache miss after the cache has 6 * reached a given size. 7 * 8 * John Ellson (ellson@lucent.com) Oct 31, 1997 9 * 10 * Test this with: 11 * gcc -o gdcache -g -Wall -DTEST gdcache.c 12 * 13 * The cache is implemented by a singly-linked list of elements 14 * each containing a pointer to a user struct that is being managed by 15 * the cache. 16 * 17 * The head structure has a pointer to the most-recently-used 18 * element, and elements are moved to this position in the list each 19 * time they are used. The head also contains pointers to three 20 * user defined functions: 21 * - a function to test if a cached userdata matches some keydata 22 * - a function to provide a new userdata struct to the cache 23 * if there has been a cache miss. 24 * - a function to release a userdata struct when it is 25 * no longer being managed by the cache 26 * 27 * In the event of a cache miss the cache is allowed to grow up to 28 * a specified maximum size. After the maximum size is reached then 29 * the least-recently-used element is discarded to make room for the 30 * new. The most-recently-returned value is always left at the 31 * beginning of the list after retrieval. 32 * 33 * In the current implementation the cache is traversed by a linear 34 * search from most-recent to least-recent. This linear search 35 * probably limits the usefulness of this implementation to cache 36 * sizes of a few tens of elements. 37 */ 38 39 /*********************************************************/ 40 /* header */ 41 /*********************************************************/ 42 43 #if (!defined(_OSD_POSIX) && !defined(__FreeBSD__)) && HAVE_MALLOC_H 44 #include <malloc.h> 45 #else 46 #include <stdlib.h> /* BS2000/OSD defines malloc() & friends in stdlib.h */ 47 #endif 48 #ifndef NULL 49 #define NULL (void *)0 50 #endif 51 52 /* user defined function templates */ 53 typedef int (*gdCacheTestFn_t)(void *userdata, void *keydata); 54 typedef void *(*gdCacheFetchFn_t)(char **error, void *keydata); 55 typedef void (*gdCacheReleaseFn_t)(void *userdata); 56 57 /* element structure */ 58 typedef struct gdCache_element_s gdCache_element_t; 59 struct gdCache_element_s { 60 gdCache_element_t *next; 61 void *userdata; 62 }; 63 64 /* head structure */ 65 typedef struct gdCache_head_s gdCache_head_t; 66 struct gdCache_head_s { 67 gdCache_element_t *mru; 68 int size; 69 char *error; 70 gdCacheTestFn_t gdCacheTest; 71 gdCacheFetchFn_t gdCacheFetch; 72 gdCacheReleaseFn_t gdCacheRelease; 73 }; 74 75 /* function templates */ 76 gdCache_head_t * 77 gdCacheCreate( 78 int size, 79 gdCacheTestFn_t gdCacheTest, 80 gdCacheFetchFn_t gdCacheFetch, 81 gdCacheReleaseFn_t gdCacheRelease ); 82 83 void 84 gdCacheDelete( gdCache_head_t *head ); 85 86 void * 87 gdCacheGet( gdCache_head_t *head, void *keydata ); 88
