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Diffstat (limited to 'ext/gd/gdcache.h')
-rw-r--r-- | ext/gd/gdcache.h | 87 |
1 files changed, 87 insertions, 0 deletions
diff --git a/ext/gd/gdcache.h b/ext/gd/gdcache.h new file mode 100644 index 0000000..657eb18 --- /dev/null +++ b/ext/gd/gdcache.h @@ -0,0 +1,87 @@ +/* + * $Id$ + * + * 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 ); |