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80cdaba569
Callers currently must use init_foo_slab() at runtime before accessing a slab. For global slabs, it's much nicer if we can initialize them in BSS, so that each user does not have to add code to check-and-initialize. Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>
132 lines
4 KiB
C
132 lines
4 KiB
C
#ifndef COMMIT_SLAB_H
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#define COMMIT_SLAB_H
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/*
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* define_commit_slab(slabname, elemtype) creates boilerplate code to define
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* a new struct (struct slabname) that is used to associate a piece of data
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* of elemtype to commits, and a few functions to use that struct.
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*
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* After including this header file, using:
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*
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* define_commit_slab(indegee, int);
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*
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* will let you call the following functions:
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*
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* - int *indegree_at(struct indegree *, struct commit *);
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*
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* This function locates the data associated with the given commit in
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* the indegree slab, and returns the pointer to it.
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*
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* - void init_indegree(struct indegree *);
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* void init_indegree_with_stride(struct indegree *, int);
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*
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* Initializes the indegree slab that associates an array of integers
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* to each commit. 'stride' specifies how big each array is. The slab
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* that is initialized by the variant without "_with_stride" associates
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* each commit with an array of one integer.
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*
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* - void clear_indegree(struct indegree *);
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*
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* Empties the slab. The slab can be reused with the same stride
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* without calling init_indegree() again or can be reconfigured to a
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* different stride by calling init_indegree_with_stride().
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*
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* Call this function before the slab falls out of scope to avoid
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* leaking memory.
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*/
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/* allocate ~512kB at once, allowing for malloc overhead */
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#ifndef COMMIT_SLAB_SIZE
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#define COMMIT_SLAB_SIZE (512*1024-32)
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#endif
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#define MAYBE_UNUSED __attribute__((__unused__))
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#define define_commit_slab(slabname, elemtype) \
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\
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struct slabname { \
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unsigned slab_size; \
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unsigned stride; \
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unsigned slab_count; \
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elemtype **slab; \
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}; \
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static int stat_ ##slabname## realloc; \
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\
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static MAYBE_UNUSED void init_ ##slabname## _with_stride(struct slabname *s, \
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unsigned stride) \
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{ \
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unsigned int elem_size; \
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if (!stride) \
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stride = 1; \
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s->stride = stride; \
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elem_size = sizeof(elemtype) * stride; \
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s->slab_size = COMMIT_SLAB_SIZE / elem_size; \
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s->slab_count = 0; \
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s->slab = NULL; \
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} \
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\
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static MAYBE_UNUSED void init_ ##slabname(struct slabname *s) \
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{ \
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init_ ##slabname## _with_stride(s, 1); \
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} \
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\
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static MAYBE_UNUSED void clear_ ##slabname(struct slabname *s) \
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{ \
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int i; \
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for (i = 0; i < s->slab_count; i++) \
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free(s->slab[i]); \
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s->slab_count = 0; \
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free(s->slab); \
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s->slab = NULL; \
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} \
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\
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static MAYBE_UNUSED elemtype *slabname## _at(struct slabname *s, \
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const struct commit *c) \
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{ \
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int nth_slab, nth_slot; \
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\
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nth_slab = c->index / s->slab_size; \
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nth_slot = c->index % s->slab_size; \
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\
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if (s->slab_count <= nth_slab) { \
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int i; \
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s->slab = xrealloc(s->slab, \
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(nth_slab + 1) * sizeof(*s->slab)); \
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stat_ ##slabname## realloc++; \
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for (i = s->slab_count; i <= nth_slab; i++) \
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s->slab[i] = NULL; \
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s->slab_count = nth_slab + 1; \
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} \
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if (!s->slab[nth_slab]) \
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s->slab[nth_slab] = xcalloc(s->slab_size, \
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sizeof(**s->slab) * s->stride); \
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return &s->slab[nth_slab][nth_slot * s->stride]; \
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} \
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\
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static int stat_ ##slabname## realloc
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/*
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* Note that this seemingly redundant second declaration is required
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* to allow a terminating semicolon, which makes instantiations look
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* like function declarations. I.e., the expansion of
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*
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* define_commit_slab(indegree, int);
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*
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* ends in 'static int stat_indegreerealloc;'. This would otherwise
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* be a syntax error according (at least) to ISO C. It's hard to
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* catch because GCC silently parses it by default.
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*/
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/*
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* Statically initialize a commit slab named "var". Note that this
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* evaluates "stride" multiple times! Example:
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*
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* struct indegree indegrees = COMMIT_SLAB_INIT(1, indegrees);
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*
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*/
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#define COMMIT_SLAB_INIT(stride, var) { \
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COMMIT_SLAB_SIZE / sizeof(**((var).slab)) / (stride), \
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(stride), 0, NULL \
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}
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#endif /* COMMIT_SLAB_H */
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