#ifdef __cplusplus

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extern "C" {

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#endif

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/*

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* gdcache.h

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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@graphviz.org) 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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#include <stdlib.h>

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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 *gdCacheCreate(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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);

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void gdCacheDelete(gdCache_head_t *head);

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

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#ifdef __cplusplus

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}

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#endif

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