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88 lines
2.7 KiB
C
88 lines
2.7 KiB
C
/*
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* $Id$
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*
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* Caches of pointers to user structs in which the least-recently-used
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* element is replaced in the event of a cache miss after the cache has
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* reached a given size.
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*
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* John Ellson (ellson@lucent.com) Oct 31, 1997
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*
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* Test this with:
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* gcc -o gdcache -g -Wall -DTEST gdcache.c
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*
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* The cache is implemented by a singly-linked list of elements
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* each containing a pointer to a user struct that is being managed by
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* the cache.
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*
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* The head structure has a pointer to the most-recently-used
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* element, and elements are moved to this position in the list each
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* time they are used. The head also contains pointers to three
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* user defined functions:
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* - a function to test if a cached userdata matches some keydata
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* - a function to provide a new userdata struct to the cache
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* if there has been a cache miss.
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* - a function to release a userdata struct when it is
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* no longer being managed by the cache
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*
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* In the event of a cache miss the cache is allowed to grow up to
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* a specified maximum size. After the maximum size is reached then
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* the least-recently-used element is discarded to make room for the
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* new. The most-recently-returned value is always left at the
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* beginning of the list after retrieval.
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*
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* In the current implementation the cache is traversed by a linear
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* search from most-recent to least-recent. This linear search
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* probably limits the usefulness of this implementation to cache
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* sizes of a few tens of elements.
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*/
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/*********************************************************/
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/* header */
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/*********************************************************/
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#ifndef _OSD_POSIX
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#include <malloc.h>
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#else
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#include <stdlib.h> /* BS2000/OSD defines malloc() & friends in stdlib.h */
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#endif
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#ifndef NULL
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#define NULL (void *)0
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#endif
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/* user defined function templates */
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typedef int (*gdCacheTestFn_t)(void *userdata, void *keydata);
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typedef void *(*gdCacheFetchFn_t)(char **error, void *keydata);
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typedef void (*gdCacheReleaseFn_t)(void *userdata);
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/* element structure */
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typedef struct gdCache_element_s gdCache_element_t;
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struct gdCache_element_s {
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gdCache_element_t *next;
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void *userdata;
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};
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/* head structure */
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typedef struct gdCache_head_s gdCache_head_t;
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struct gdCache_head_s {
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gdCache_element_t *mru;
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int size;
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char *error;
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gdCacheTestFn_t gdCacheTest;
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gdCacheFetchFn_t gdCacheFetch;
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gdCacheReleaseFn_t gdCacheRelease;
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};
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/* function templates */
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gdCache_head_t *
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gdCacheCreate(
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int size,
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gdCacheTestFn_t gdCacheTest,
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gdCacheFetchFn_t gdCacheFetch,
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gdCacheReleaseFn_t gdCacheRelease );
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void
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gdCacheDelete( gdCache_head_t *head );
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void *
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gdCacheGet( gdCache_head_t *head, void *keydata );
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