string-list: use QSORT_S in string_list_sort()
authorRené Scharfe <l.s.r@web.de>
Sun, 22 Jan 2017 17:57:09 +0000 (18:57 +0100)
committerJunio C Hamano <gitster@pobox.com>
Mon, 23 Jan 2017 19:02:38 +0000 (11:02 -0800)
commit5ebd9472a490b12ff941b8085b1b0932a755ffcc
tree3251d2b6d21617441d73c28e06fd731820e68472
parent564e94e6190a1a41d8516eaf58b268785ed0a7a7
string-list: use QSORT_S in string_list_sort()

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>
string-list.c