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(indegree, 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.  The location to
  19  *   store the data is allocated as necessary.
  20  *
  21  * - int *indegree_peek(struct indegree *, struct commit *);
  22  *
  23  *   This function is similar to indegree_at(), but it will return NULL
  24  *   until a call to indegree_at() was made for the commit.
  25  *
  26  * - void init_indegree(struct indegree *);
  27  *   void init_indegree_with_stride(struct indegree *, int);
  28  *
  29  *   Initializes the indegree slab that associates an array of integers
  30  *   to each commit. 'stride' specifies how big each array is.  The slab
  31  *   that is initialized by the variant without "_with_stride" associates
  32  *   each commit with an array of one integer.
  33  *
  34  * - void clear_indegree(struct indegree *);
  35  *
  36  *   Empties the slab.  The slab can be reused with the same stride
  37  *   without calling init_indegree() again or can be reconfigured to a
  38  *   different stride by calling init_indegree_with_stride().
  39  *
  40  *   Call this function before the slab falls out of scope to avoid
  41  *   leaking memory.
  42  */
  43
  44 /* allocate ~512kB at once, allowing for malloc overhead */
  45 #ifndef COMMIT_SLAB_SIZE
  46 #define COMMIT_SLAB_SIZE (512*1024-32)
  47 #endif
  48
  49 #define MAYBE_UNUSED __attribute__((__unused__))
  50
  51 #define define_commit_slab(slabname, elemtype)                          \
  52                                                                         \
  53 struct slabname {                                                       \
  54         unsigned slab_size;                                             \
  55         unsigned stride;                                                \
  56         unsigned slab_count;                                            \
  57         elemtype **slab;                                                \
  58 };                                                                      \
  59 static int stat_ ##slabname## realloc;                                  \
  60                                                                         \
  61 static MAYBE_UNUSED void init_ ##slabname## _with_stride(struct slabname *s, \
  62                                                    unsigned stride)     \
  63 {                                                                       \
  64         unsigned int elem_size;                                         \
  65         if (!stride)                                                    \
  66                 stride = 1;                                             \
  67         s->stride = stride;                                             \
  68         elem_size = sizeof(elemtype) * stride;                          \
  69         s->slab_size = COMMIT_SLAB_SIZE / elem_size;                    \
  70         s->slab_count = 0;                                              \
  71         s->slab = NULL;                                                 \
  72 }                                                                       \
  73                                                                         \
  74 static MAYBE_UNUSED void init_ ##slabname(struct slabname *s)           \
  75 {                                                                       \
  76         init_ ##slabname## _with_stride(s, 1);                          \
  77 }                                                                       \
  78                                                                         \
  79 static MAYBE_UNUSED void clear_ ##slabname(struct slabname *s)          \
  80 {                                                                       \
  81         int i;                                                          \
  82         for (i = 0; i < s->slab_count; i++)                             \
  83                 free(s->slab[i]);                                       \
  84         s->slab_count = 0;                                              \
  85         FREE_AND_NULL(s->slab);                                         \
  86 }                                                                       \
  87                                                                         \
  88 static MAYBE_UNUSED elemtype *slabname## _at_peek(struct slabname *s,   \
  89                                                   const struct commit *c, \
  90                                                   int add_if_missing)   \
  91 {                                                                       \
  92         int nth_slab, nth_slot;                                         \
  93                                                                         \
  94         nth_slab = c->index / s->slab_size;                             \
  95         nth_slot = c->index % s->slab_size;                             \
  96                                                                         \
  97         if (s->slab_count <= nth_slab) {                                \
  98                 int i;                                                  \
  99                 if (!add_if_missing)                                    \
 100                         return NULL;                                    \
 101                 REALLOC_ARRAY(s->slab, nth_slab + 1);                   \
 102                 stat_ ##slabname## realloc++;                           \
 103                 for (i = s->slab_count; i <= nth_slab; i++)             \
 104                         s->slab[i] = NULL;                              \
 105                 s->slab_count = nth_slab + 1;                           \
 106         }                                                               \
 107         if (!s->slab[nth_slab]) {                                       \
 108                 if (!add_if_missing)                                    \
 109                         return NULL;                                    \
 110                 s->slab[nth_slab] = xcalloc(s->slab_size,               \
 111                                             sizeof(**s->slab) * s->stride);             \
 112         }                                                               \
 113         return &s->slab[nth_slab][nth_slot * s->stride];                \
 114 }                                                                       \
 115                                                                         \
 116 static MAYBE_UNUSED elemtype *slabname## _at(struct slabname *s,        \
 117                                              const struct commit *c)    \
 118 {                                                                       \
 119         return slabname##_at_peek(s, c, 1);                             \
 120 }                                                                       \
 121                                                                         \
 122 static MAYBE_UNUSED elemtype *slabname## _peek(struct slabname *s,      \
 123                                              const struct commit *c)    \
 124 {                                                                       \
 125         return slabname##_at_peek(s, c, 0);                             \
 126 }                                                                       \
 127                                                                         \
 128 struct slabname
 129
 130 /*
 131  * Note that this redundant forward declaration is required
 132  * to allow a terminating semicolon, which makes instantiations look
 133  * like function declarations.  I.e., the expansion of
 134  *
 135  *    define_commit_slab(indegree, int);
 136  *
 137  * ends in 'struct indegree;'.  This would otherwise
 138  * be a syntax error according (at least) to ISO C.  It's hard to
 139  * catch because GCC silently parses it by default.
 140  */
 141
 142 /*
 143  * Statically initialize a commit slab named "var". Note that this
 144  * evaluates "stride" multiple times! Example:
 145  *
 146  *   struct indegree indegrees = COMMIT_SLAB_INIT(1, indegrees);
 147  *
 148  */
 149 #define COMMIT_SLAB_INIT(stride, var) { \
 150         COMMIT_SLAB_SIZE / sizeof(**((var).slab)) / (stride), \
 151         (stride), 0, NULL \
 152 }
 153
 154 #endif /* COMMIT_SLAB_H */