gmtime/localtime is considered unsafe in multithread environment.
git was started as single-thread application, but we have some multi-thread code, right now.
replace all usage of gmtime/localtime by their respective reentrant ones.
On most POSIX systems, we won't notice any differences in performance, since they implemented gmtime and gmtime_r mostly the same.
On Windows, we may be taxed, since gmtime_r and localtime_r is our compat functions, because we memcpy from returned data of gmtime/localtime.
To address that, I made patch #3 and included it together with this series. I'm not sure how much portable it is.
Doan Tran Cong Danh (3):
date.c: switch to reentrant {gm,local}time_r
archive-zip.c: switch to reentrant localtime_r
mingw: use {gm,local}time_s as backend for {gm,local}time_r archive-zip.c | 10 +++++-----
compat/mingw.c | 12 ++++++------
date.c | 18 ++++++++++--------
3 files changed, 21 insertions(+), 19 deletions(-)
Range-diff against v1:
1: 1e7e08b3c7 < -: ---------- date.c::datestamp: switch to reentrant localtime_r
2: 130eba77db ! 1: 71de738864 date.c::time_to_tm_local: use reentrant localtime_r(3)
@@ Metadata
Author: Doan Tran Cong Danh <congdanhqx@gmail.com>
## Commit message ##
- date.c::time_to_tm_local: use reentrant localtime_r(3)
+ date.c: switch to reentrant {gm,local}time_r
- Phase out `localtime(3)' in favour of reentrant `localtime_r(3)'
+ Originally, git was intended to be single-thread executable.
+ `gmtime(3)' and `localtime(3)' can be used in such codebase
+ for cleaner code.
+
+ Overtime, we're employing multithread in our code base.
+
+ Let's phase out `gmtime(3)' and `localtime(3)' in favour of
+ `gmtime_r(3)' and `localtime_r(3)'.
Signed-off-by: Doan Tran Cong Danh <congdanhqx@gmail.com>
## date.c ##
-@@ date.c: static struct tm *time_to_tm(timestamp_t time, int tz)
- return gmtime(&t);
+@@ date.c: static time_t gm_time_t(timestamp_t time, int tz)
+ * thing, which means that tz -0100 is passed in as the integer -100,
+ * even though it means "sixty minutes off"
+ */
+-static struct tm *time_to_tm(timestamp_t time, int tz)
++static struct tm *time_to_tm(timestamp_t time, int tz, struct tm *tm)
+ {
+ time_t t = gm_time_t(time, tz);
+- return gmtime(&t);
++ return gmtime_r(&t, tm);
}
-static struct tm *time_to_tm_local(timestamp_t time)
@@ date.c: const char *show_date(timestamp_t time, int tz, const struct date_mode *
- tm = time_to_tm_local(time);
+ tm = time_to_tm_local(time, &tmbuf);
else
- tm = time_to_tm(time, tz);
+- tm = time_to_tm(time, tz);
++ tm = time_to_tm(time, tz, &tmbuf);
if (!tm) {
+- tm = time_to_tm(0, 0);
++ tm = time_to_tm(0, 0, &tmbuf);
+ tz = 0;
+ }
+
+@@ date.c: void datestamp(struct strbuf *out)
+ {
+ time_t now;
+ int offset;
++ struct tm tm = { 0 };
+
+ time(&now);
+
+- offset = tm_to_time_t(localtime(&now)) - now;
++ offset = tm_to_time_t(localtime_r(&now, &tm)) - now;
+ offset /= 60;
+
+ date_string(now, offset, out);
3: ce7fe7bcf3 < -: ---------- date.c::time_to_tm: use reentrant gmtime_r(3)
4: f6fd89dfe1 ! 2: 77798f1773 archive-zip: use reentrant localtime_r(3)
@@ Metadata
Author: Doan Tran Cong Danh <congdanhqx@gmail.com>
## Commit message ##
- archive-zip: use reentrant localtime_r(3)
+ archive-zip.c: switch to reentrant localtime_r
+
+ Originally, git was intended to be single-thread executable.
+ `localtime(3)' can be used in such codebase for cleaner code.
+
+ Overtime, we're employing multithread in our code base.
+
+ Let's phase out `gmtime(3)' in favour of `localtime_r(3)'.
+
+ Signed-off-by: Doan Tran Cong Danh <congdanhqx@gmail.com>
## archive-zip.c ##
@@ archive-zip.c: static void write_zip_trailer(const struct object_id *oid)
5: 2c39f9a04f ! 3: 33a67eb377 mingw: use {gm,local}time_s as backend for {gm,local}time_r
@@ Commit message
Signed-off-by: Doan Tran Cong Danh <congdanhqx@gmail.com>
## compat/mingw.c ##
-@@
- #include "../git-compat-util.h"
- #include "win32.h"
- #include <conio.h>
-+#include <errno.h>
- #include <wchar.h>
- #include "../strbuf.h"
- #include "../run-command.h"
@@ compat/mingw.c: int pipe(int filedes[2])
struct tm *gmtime_r(const time_t *timep, struct tm *result)
Doan Tran Cong Danh
