Documentation/describe: improve one-line summary
[git.git] / commit-slab.h
blobf37ec3831f60cb9072d6cbf4f3d0126bc0681bf1
1 #ifndef COMMIT_SLAB_H
2 #define COMMIT_SLAB_H
4 /*
5 * define_commit_slab(slabname, elemtype) creates boilerplate code to define
6 * a new struct (struct slabname) that is used to associate a piece of data
7 * of elemtype to commits, and a few functions to use that struct.
9 * After including this header file, using:
11 * define_commit_slab(indegee, int);
13 * will let you call the following functions:
15 * - int *indegree_at(struct indegree *, struct commit *);
17 * This function locates the data associated with the given commit in
18 * the indegree slab, and returns the pointer to it.
20 * - void init_indegree(struct indegree *);
21 * void init_indegree_with_stride(struct indegree *, int);
23 * Initializes the indegree slab that associates an array of integers
24 * to each commit. 'stride' specifies how big each array is. The slab
25 * that is initialized by the variant without "_with_stride" associates
26 * each commit with an array of one integer.
28 * - void clear_indegree(struct indegree *);
30 * Empties the slab. The slab can be reused with the same stride
31 * without calling init_indegree() again or can be reconfigured to a
32 * different stride by calling init_indegree_with_stride().
34 * Call this function before the slab falls out of scope to avoid
35 * leaking memory.
38 /* allocate ~512kB at once, allowing for malloc overhead */
39 #ifndef COMMIT_SLAB_SIZE
40 #define COMMIT_SLAB_SIZE (512*1024-32)
41 #endif
43 #define MAYBE_UNUSED __attribute__((__unused__))
45 #define define_commit_slab(slabname, elemtype) \
47 struct slabname { \
48 unsigned slab_size; \
49 unsigned stride; \
50 unsigned slab_count; \
51 elemtype **slab; \
52 }; \
53 static int stat_ ##slabname## realloc; \
55 static MAYBE_UNUSED void init_ ##slabname## _with_stride(struct slabname *s, \
56 unsigned stride) \
57 { \
58 unsigned int elem_size; \
59 if (!stride) \
60 stride = 1; \
61 s->stride = stride; \
62 elem_size = sizeof(elemtype) * stride; \
63 s->slab_size = COMMIT_SLAB_SIZE / elem_size; \
64 s->slab_count = 0; \
65 s->slab = NULL; \
66 } \
68 static MAYBE_UNUSED void init_ ##slabname(struct slabname *s) \
69 { \
70 init_ ##slabname## _with_stride(s, 1); \
71 } \
73 static MAYBE_UNUSED void clear_ ##slabname(struct slabname *s) \
74 { \
75 int i; \
76 for (i = 0; i < s->slab_count; i++) \
77 free(s->slab[i]); \
78 s->slab_count = 0; \
79 free(s->slab); \
80 s->slab = NULL; \
81 } \
83 static MAYBE_UNUSED elemtype *slabname## _at(struct slabname *s, \
84 const struct commit *c) \
85 { \
86 int nth_slab, nth_slot; \
88 nth_slab = c->index / s->slab_size; \
89 nth_slot = c->index % s->slab_size; \
91 if (s->slab_count <= nth_slab) { \
92 int i; \
93 REALLOC_ARRAY(s->slab, nth_slab + 1); \
94 stat_ ##slabname## realloc++; \
95 for (i = s->slab_count; i <= nth_slab; i++) \
96 s->slab[i] = NULL; \
97 s->slab_count = nth_slab + 1; \
98 } \
99 if (!s->slab[nth_slab]) \
100 s->slab[nth_slab] = xcalloc(s->slab_size, \
101 sizeof(**s->slab) * s->stride); \
102 return &s->slab[nth_slab][nth_slot * s->stride]; \
105 static int stat_ ##slabname## realloc
108 * Note that this seemingly redundant second declaration is required
109 * to allow a terminating semicolon, which makes instantiations look
110 * like function declarations. I.e., the expansion of
112 * define_commit_slab(indegree, int);
114 * ends in 'static int stat_indegreerealloc;'. This would otherwise
115 * be a syntax error according (at least) to ISO C. It's hard to
116 * catch because GCC silently parses it by default.
120 * Statically initialize a commit slab named "var". Note that this
121 * evaluates "stride" multiple times! Example:
123 * struct indegree indegrees = COMMIT_SLAB_INIT(1, indegrees);
126 #define COMMIT_SLAB_INIT(stride, var) { \
127 COMMIT_SLAB_SIZE / sizeof(**((var).slab)) / (stride), \
128 (stride), 0, NULL \
131 #endif /* COMMIT_SLAB_H */