date: make DATE_MODE thread-safe

date_mode_from_type() modifies a static variable and returns a pointer
to it.  This is not thread-safe.  Most callers of date_mode_from_type()
use it via the macro DATE_MODE and pass its result on to functions like
show_date(), which take a const pointer and don't modify the struct.

Avoid the static storage by putting the variable on the stack and
returning the whole struct date_mode.  Change functions that take a
constant pointer to expect the whole struct instead.

Reduce the cost of passing struct date_mode around on 64-bit systems
by reordering its members to close the hole between the 32-bit wide
.type and the 64-bit aligned .strftime_fmt as well as the alignment
hole at the end.  sizeof reports 24 before and 16 with this change
on x64.  Keep .type at the top to still allow initialization without
designator -- though that's only done in a single location, in
builtin/blame.c.

Signed-off-by: René Scharfe <l.s.r@web.de>
Acked-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 18 insertions, 18 deletions

diff --git a/date.c b/date.c
index 44cf2221d8..7365a4ad24 100644
--- a/date.c
+++ b/date.c
@@ -207,13 +207,13 @@ void show_date_relative(timestamp_t time, struct strbuf *timebuf)
 		 (diff + 183) / 365);
 }
 
-struct date_mode *date_mode_from_type(enum date_mode_type type)
+struct date_mode date_mode_from_type(enum date_mode_type type)
 {
-	static struct date_mode mode = DATE_MODE_INIT;
+	struct date_mode mode = DATE_MODE_INIT;
 	if (type == DATE_STRFTIME)
 		BUG("cannot create anonymous strftime date_mode struct");
 	mode.type = type;
-	return &mode;
+	return mode;
 }
 
 static void show_date_normal(struct strbuf *buf, timestamp_t time, struct tm *tm, int tz, struct tm *human_tm, int human_tz, int local)
@@ -283,7 +283,7 @@ static void show_date_normal(struct strbuf *buf, timestamp_t time, struct tm *tm
 		strbuf_addf(buf, " %+05d", tz);
 }
 
-const char *show_date(timestamp_t time, int tz, const struct date_mode *mode)
+const char *show_date(timestamp_t time, int tz, struct date_mode mode)
 {
 	struct tm *tm;
 	struct tm tmbuf = { 0 };
@@ -291,13 +291,13 @@ const char *show_date(timestamp_t time, int tz, const struct date_mode *mode)
 	int human_tz = -1;
 	static struct strbuf timebuf = STRBUF_INIT;
 
-	if (mode->type == DATE_UNIX) {
+	if (mode.type == DATE_UNIX) {
 		strbuf_reset(&timebuf);
 		strbuf_addf(&timebuf, "%"PRItime, time);
 		return timebuf.buf;
 	}
 
-	if (mode->type == DATE_HUMAN) {
+	if (mode.type == DATE_HUMAN) {
 		struct timeval now;
 
 		get_time(&now);
@@ -306,22 +306,22 @@ const char *show_date(timestamp_t time, int tz, const struct date_mode *mode)
 		human_tz = local_time_tzoffset(now.tv_sec, &human_tm);
 	}
 
-	if (mode->local)
+	if (mode.local)
 		tz = local_tzoffset(time);
 
-	if (mode->type == DATE_RAW) {
+	if (mode.type == DATE_RAW) {
 		strbuf_reset(&timebuf);
 		strbuf_addf(&timebuf, "%"PRItime" %+05d", time, tz);
 		return timebuf.buf;
 	}
 
-	if (mode->type == DATE_RELATIVE) {
+	if (mode.type == DATE_RELATIVE) {
 		strbuf_reset(&timebuf);
 		show_date_relative(time, &timebuf);
 		return timebuf.buf;
 	}
 
-	if (mode->local)
+	if (mode.local)
 		tm = time_to_tm_local(time, &tmbuf);
 	else
 		tm = time_to_tm(time, tz, &tmbuf);
@@ -331,17 +331,17 @@ const char *show_date(timestamp_t time, int tz, const struct date_mode *mode)
 	}
 
 	strbuf_reset(&timebuf);
-	if (mode->type == DATE_SHORT)
+	if (mode.type == DATE_SHORT)
 		strbuf_addf(&timebuf, "%04d-%02d-%02d", tm->tm_year + 1900,
 				tm->tm_mon + 1, tm->tm_mday);
-	else if (mode->type == DATE_ISO8601)
+	else if (mode.type == DATE_ISO8601)
 		strbuf_addf(&timebuf, "%04d-%02d-%02d %02d:%02d:%02d %+05d",
 				tm->tm_year + 1900,
 				tm->tm_mon + 1,
 				tm->tm_mday,
 				tm->tm_hour, tm->tm_min, tm->tm_sec,
 				tz);
-	else if (mode->type == DATE_ISO8601_STRICT) {
+	else if (mode.type == DATE_ISO8601_STRICT) {
 		strbuf_addf(&timebuf, "%04d-%02d-%02dT%02d:%02d:%02d",
 				tm->tm_year + 1900,
 				tm->tm_mon + 1,
@@ -354,16 +354,16 @@ const char *show_date(timestamp_t time, int tz, const struct date_mode *mode)
 			tz = abs(tz);
 			strbuf_addf(&timebuf, "%02d:%02d", tz / 100, tz % 100);
 		}
-	} else if (mode->type == DATE_RFC2822)
+	} else if (mode.type == DATE_RFC2822)
 		strbuf_addf(&timebuf, "%.3s, %d %.3s %d %02d:%02d:%02d %+05d",
 			weekday_names[tm->tm_wday], tm->tm_mday,
 			month_names[tm->tm_mon], tm->tm_year + 1900,
 			tm->tm_hour, tm->tm_min, tm->tm_sec, tz);
-	else if (mode->type == DATE_STRFTIME)
-		strbuf_addftime(&timebuf, mode->strftime_fmt, tm, tz,
-				!mode->local);
+	else if (mode.type == DATE_STRFTIME)
+		strbuf_addftime(&timebuf, mode.strftime_fmt, tm, tz,
+				!mode.local);
 	else
-		show_date_normal(&timebuf, time, tm, tz, &human_tm, human_tz, mode->local);
+		show_date_normal(&timebuf, time, tm, tz, &human_tm, human_tz, mode.local);
 	return timebuf.buf;
 }