Merge branch 'rs/qsort-s'

A few codepaths had to rely on a global variable when sorting
elements of an array because sort(3) API does not allow extra data
to be passed to the comparison function.  Use qsort_s() when
natively available, and a fallback implementation of it when not,
to eliminate the need, which is a prerequisite for making the
codepath reentrant.

* rs/qsort-s:
  ref-filter: use QSORT_S in ref_array_sort()
  string-list: use QSORT_S in string_list_sort()
  perf: add basic sort performance test
  add QSORT_S
  compat: add qsort_s()

t/helper/test-string-list.c

@@ -97,6 +97,31 @@ int cmd_main(int argc, const char **argv)
 		return 0;
 	}
 
+	if (argc == 2 && !strcmp(argv[1], "sort")) {
+		struct string_list list = STRING_LIST_INIT_NODUP;
+		struct strbuf sb = STRBUF_INIT;
+		struct string_list_item *item;
+
+		strbuf_read(&sb, 0, 0);
+
+		/*
+		 * Split by newline, but don't create a string_list item
+		 * for the empty string after the last separator.
+		 */
+		if (sb.buf[sb.len - 1] == '\n')
+			strbuf_setlen(&sb, sb.len - 1);
+		string_list_split_in_place(&list, sb.buf, '\n', -1);
+
+		string_list_sort(&list);
+
+		for_each_string_list_item(item, &list)
+			puts(item->string);
+
+		string_list_clear(&list, 0);
+		strbuf_release(&sb);
+		return 0;
+	}
+
 	fprintf(stderr, "%s: unknown function name: %s\n", argv[0],
 		argv[1] ? argv[1] : "(there was none)");
 	return 1;

t/perf/p0071-sort.sh

@@ -0,0 +1,26 @@
+#!/bin/sh
+
+test_description='Basic sort performance tests'
+. ./perf-lib.sh
+
+test_perf_default_repo
+
+test_expect_success 'setup' '
+	git ls-files --stage "*.[ch]" "*.sh" |
+	cut -f2 -d" " |
+	git cat-file --batch >unsorted
+'
+
+test_perf 'sort(1)' '
+	sort <unsorted >expect
+'
+
+test_perf 'string_list_sort()' '
+	test-string-list sort <unsorted >actual
+'
+
+test_expect_success 'string_list_sort() sorts like sort(1)' '
+	test_cmp_bin expect actual
+'
+
+test_done