commit-slab.h

   1 #ifndef COMMIT_SLAB_H
   2 #define COMMIT_SLAB_H
   3
   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.
   8  *
   9  * After including this header file, using:
  10  *
  11  * define_commit_slab(indegee, int);
  12  *
  13  * will let you call the following functions:
  14  *
  15  * - int *indegree_at(struct indegree *, struct commit *);
  16  *
  17  *   This function locates the data associated with the given commit in
  18  *   the indegree slab, and returns the pointer to it.
  19  *
  20  * - void init_indegree(struct indegree *);
  21  *   void init_indegree_with_stride(struct indegree *, int);
  22  *
  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.
  27  *
  28  * - void clear_indegree(struct indegree *);
  29  *
  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().
  33  *
  34  *   Call this function before the slab falls out of scope to avoid
  35  *   leaking memory.
  36  */
  37
  38 /* allocate ~512kB at once, allowing for malloc overhead */
  39 #ifndef COMMIT_SLAB_SIZE
  40 #define COMMIT_SLAB_SIZE (512*1024-32)
  41 #endif
  42
  43 #define MAYBE_UNUSED __attribute__((__unused__))
  44
  45 #define define_commit_slab(slabname, elemtype)                          \
  46                                                                         \
  47 struct slabname {                                                       \
  48         unsigned slab_size;                                             \
  49         unsigned stride;                                                \
  50         unsigned slab_count;                                            \
  51         elemtype **slab;                                                \
  52 };                                                                      \
  53 static int stat_ ##slabname## realloc;                                  \
  54                                                                         \
  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 }                                                                       \
  67                                                                         \
  68 static MAYBE_UNUSED void init_ ##slabname(struct slabname *s)           \
  69 {                                                                       \
  70         init_ ##slabname## _with_stride(s, 1);                          \
  71 }                                                                       \
  72                                                                         \
  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 }                                                                       \
  82                                                                         \
  83 static MAYBE_UNUSED elemtype *slabname## _at(struct slabname *s,        \
  84                                        const struct commit *c)          \
  85 {                                                                       \
  86         int nth_slab, nth_slot;                                         \
  87                                                                         \
  88         nth_slab = c->index / s->slab_size;                             \
  89         nth_slot = c->index % s->slab_size;                             \
  90                                                                         \
  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];                                \
 103 }                                                                       \
 104                                                                         \
 105 static int stat_ ##slabname## realloc
 106
 107 /*
 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
 111  *
 112  *    define_commit_slab(indegree, int);
 113  *
 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.
 117  */
 118
 119 /*
 120  * Statically initialize a commit slab named "var". Note that this
 121  * evaluates "stride" multiple times! Example:
 122  *
 123  *   struct indegree indegrees = COMMIT_SLAB_INIT(1, indegrees);
 124  *
 125  */
 126 #define COMMIT_SLAB_INIT(stride, var) { \
 127         COMMIT_SLAB_SIZE / sizeof(**((var).slab)) / (stride), \
 128         (stride), 0, NULL \
 129 }
 130
 131 #endif /* COMMIT_SLAB_H */