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The gigantic define_commit_slab() macro repeats the definition of a static variable that occurs earlier in the macro text. The purpose of the repeated definition at the end of the macro is that it takes the semicolon that occurs where the macro is used. We cannot just remove the first definition of the variable because it is referenced elsewhere in the macro text, and defining the macro later would produce undefined identifier errors. We cannot have a "forward" declaration, either. (This works only with "extern" global variables.) The solution is to use a declaration of a struct that is already defined earlier. This language construct can serve the same purpose as the duplicated static variable definition, but without the confusion. Signed-off-by: Johannes Sixt <j6t@kdbg.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>
132 lines
4.0 KiB
C
132 lines
4.0 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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REALLOC_ARRAY(s->slab, nth_slab + 1); \
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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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struct slabname
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/*
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* Note that this redundant forward 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 'struct indegree;'. 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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