summaryrefslogtreecommitdiff
path: root/Build/source/libs/gd/libgd-src/src/gdcache.h
blob: 751a842154cd88b4f1cd4bc498fd1557c2c3ef1b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
#ifdef __cplusplus
extern "C" {
#endif

	/*
	 * gdcache.h
	 *
	 * 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@graphviz.org)  Oct 31, 1997
	 *
	 * Test this with:
	 *		 gcc -o gdcache -g -Wall -DTEST -DNEED_CACHE gdcache.c -lgd
   *		 or
	 *		 gcc -o gdcache -g -Wall -DTEST -DNEED_CACHE gdcache.c libgd.a
	 *
	 * 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                                                */
	/*********************************************************/

#include <stdlib.h>
#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);

#ifdef __cplusplus
}
#endif