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string-list: use QSORT_S in string_list_sort()

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Pass the comparison function to cmp_items() via the context parameter of
qsort_s() instead of using a global variable.  That allows calling
string_list_sort() from multiple parallel threads.

Our qsort_s() in compat/ is slightly slower than qsort(1) from glibc
2.24 for sorting lots of lines:

Test                         HEAD^             HEAD
---------------------------------------------------------------------
0071.2: sort(1)              0.10(0.22+0.01)   0.09(0.21+0.00) -10.0%
0071.3: string_list_sort()   0.16(0.15+0.01)   0.17(0.15+0.00) +6.3%

GNU sort(1) version 8.26 is significantly faster because it uses
multiple parallel threads; with the unportable option --parallel=1 it
becomes slower:

Test                         HEAD^             HEAD
--------------------------------------------------------------------
0071.2: sort(1)              0.21(0.18+0.01)   0.20(0.18+0.01) -4.8%
0071.3: string_list_sort()   0.16(0.13+0.02)   0.17(0.15+0.01) +6.3%

There is some instability -- the numbers for the sort(1) check shouldn't
be affected by this patch.  Anyway, the performance of our qsort_s()
implementation is apparently good enough, at least for this test.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
René Scharfe 2017-01-22 18:57:09 +01:00 committed by Junio C Hamano
parent 564e94e619
commit 5ebd9472a4
1 changed files with 5 additions and 8 deletions
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13
string-list.c
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@ -211,21 +211,18 @@ struct string_list_item *string_list_append(struct string_list *list,
list->strdup_strings ? xstrdup(string) : (char *)string);
}
/* Yuck */
static compare_strings_fn compare_for_qsort;
/* Only call this from inside string_list_sort! */
static int cmp_items(const void *a, const void *b)
static int cmp_items(const void *a, const void *b, void *ctx)
{
compare_strings_fn cmp = ctx;
const struct string_list_item *one = a;
const struct string_list_item *two = b;
return compare_for_qsort(one->string, two->string);
return cmp(one->string, two->string);
}
void string_list_sort(struct string_list *list)
{
compare_for_qsort = list->cmp ? list->cmp : strcmp;
QSORT(list->items, list->nr, cmp_items);
QSORT_S(list->items, list->nr, cmp_items,
list->cmp ? list->cmp : strcmp);
}
struct string_list_item *unsorted_string_list_lookup(struct string_list *list,