pool: don't trample upon users of localtime().

The function is not thread safe -- and even in single-threaded code, the
user might be using the value with a library call in between.

src/core/util.c

@@ -395,14 +395,24 @@ util_concat_str(const char *s1, const char *s2)
  * in such cases.
  */
 struct tm *
-util_localtime(const time_t *timep)
+util_localtime(const time_t *timep, struct tm *tm)
 {
+#ifdef _WIN32
+	/* C11 has localtime_s(), but Microsoft's version reverses the args */
+	int err = localtime_s(tm, timep);
+	if (err) {
+		errno = err;
+		return NULL;
+	} else {
+		return tm;
+	}
+#else
 	int oerrno = errno;
-	struct tm *tm = localtime(timep);
+	tm = localtime_r(timep, tm);
 	if (tm != NULL)
 		errno = oerrno;
-
 	return tm;
+#endif
 }
 
 /*

src/core/util.h

@@ -95,7 +95,7 @@ char *util_part_realpath(const char *path);
 int util_compare_file_inodes(const char *path1, const char *path2);
 void *util_aligned_malloc(size_t alignment, size_t size);
 void util_aligned_free(void *ptr);
-struct tm *util_localtime(const time_t *timep);
+struct tm *util_localtime(const time_t *timep, struct tm *tm);
 int util_safe_strcpy(char *dst, const char *src, size_t max_length);
 void util_emit_log(const char *lib, const char *func, int order);
 char *util_readline(FILE *fh);

src/libpmempool/check_util.c

@@ -628,10 +628,10 @@ const char *
 check_get_time_str(time_t time)
 {
 	static char str_buff[STR_MAX] = {0, };
-	struct tm *tm = util_localtime(&time);
+	struct tm tm;
 
-	if (tm)
-		strftime(str_buff, STR_MAX, TIME_STR_FMT, tm);
+	if (util_localtime(&time, &tm))
+		strftime(str_buff, STR_MAX, TIME_STR_FMT, &tm);
 	else {
 		int ret = util_snprintf(str_buff, STR_MAX, "unknown");
 		if (ret < 0) {

src/tools/pmempool/output.c

@@ -348,10 +348,10 @@ const char *
 out_get_time_str(time_t time)
 {
 	static char str_buff[STR_MAX] = {0, };
-	struct tm *tm = util_localtime(&time);
+	struct tm tm;
 
-	if (tm) {
-		strftime(str_buff, STR_MAX, TIME_STR_FMT, tm);
+	if (util_localtime(&time, &tm)) {
+		strftime(str_buff, STR_MAX, TIME_STR_FMT, &tm);
 	} else {
 		int ret = util_snprintf(str_buff, STR_MAX, "unknown");
 		if (ret < 0)