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, 2 insertions, 2 deletions

diff --git a/reflog-walk.c b/reflog-walk.c
index d216f6f966..66484f4f32 100644
--- a/reflog-walk.c
+++ b/reflog-walk.c
@@ -223,7 +223,7 @@ int add_reflog_for_walk(struct reflog_walk_info *info,
 
 void get_reflog_selector(struct strbuf *sb,
 			 struct reflog_walk_info *reflog_info,
-			 const struct date_mode *dmode, int force_date,
+			 struct date_mode dmode, int force_date,
 			 int shorten)
 {
 	struct commit_reflog *commit_reflog = reflog_info->last_commit_reflog;
@@ -297,7 +297,7 @@ timestamp_t get_reflog_timestamp(struct reflog_walk_info *reflog_info)
 }
 
 void show_reflog_message(struct reflog_walk_info *reflog_info, int oneline,
-			 const struct date_mode *dmode, int force_date)
+			 struct date_mode dmode, int force_date)
 {
 	if (reflog_info && reflog_info->last_commit_reflog) {
 		struct commit_reflog *commit_reflog = reflog_info->last_commit_reflog;