thread-safety: gmtime_r(), localtime_r()

Use gmtime_r() and localtime_r() instead of gmtime() and localtime(),
for thread-safety.

There are a few affected calls in libpq and ecpg's libpgtypes, which
are probably effectively bugs, because those libraries already claim
to be thread-safe.

There is one affected call in the backend.  Most of the backend
otherwise uses the custom functions pg_gmtime() and pg_localtime(),
which are implemented differently.

While we're here, change the call in the backend to gmtime*() instead
of localtime*(), since for that use time zone behavior is irrelevant,
and this side-steps any questions about when time zones are
initialized by localtime_r() vs localtime().

Portability: gmtime_r() and localtime_r() are in POSIX but are not
available on Windows.  Windows has functions gmtime_s() and
localtime_s() that can fulfill the same purpose, so we add some small
wrappers around them.  (Note that these *_s() functions are also
different from the *_s() functions in the bounds-checking extension of
C11.  We are not using those here.)

On MinGW, you can get the POSIX-style *_r() functions by defining
_POSIX_C_SOURCE appropriately before including <time.h>.  This leads
to a conflict at least in plpython because apparently _POSIX_C_SOURCE
gets defined in some header there, and then our replacement
definitions conflict with the system definitions.  To avoid that sort
of thing, we now always define _POSIX_C_SOURCE on MinGW and use the
POSIX-style functions here.

Reviewed-by: Stepan Neretin <sncfmgg@gmail.com>
Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/eba1dc75-298e-4c46-8869-48ba8aad7d70@eisentraut.org

2 files changed, 9 insertions, 5 deletions

diff --git a/src/interfaces/ecpg/pgtypeslib/dt_common.c b/src/interfaces/ecpg/pgtypeslib/dt_common.c
index ed08088bfe1..0d63fe52c5b 100644
--- a/src/interfaces/ecpg/pgtypeslib/dt_common.c
+++ b/src/interfaces/ecpg/pgtypeslib/dt_common.c
@@ -949,9 +949,10 @@ int
 GetEpochTime(struct tm *tm)
 {
 	struct tm  *t0;
+	struct tm	tmbuf;
 	time_t		epoch = 0;
 
-	t0 = gmtime(&epoch);
+	t0 = gmtime_r(&epoch, &tmbuf);
 
 	if (t0)
 	{
@@ -973,12 +974,13 @@ abstime2tm(AbsoluteTime _time, int *tzp, struct tm *tm, char **tzn)
 {
 	time_t		time = (time_t) _time;
 	struct tm  *tx;
+	struct tm	tmbuf;
 
 	errno = 0;
 	if (tzp != NULL)
-		tx = localtime((time_t *) &time);
+		tx = localtime_r(&time, &tmbuf);
 	else
-		tx = gmtime((time_t *) &time);
+		tx = gmtime_r(&time, &tmbuf);
 
 	if (!tx)
 	{
@@ -2810,9 +2812,10 @@ PGTYPEStimestamp_defmt_scan(char **str, char *fmt, timestamp * d,
 				/* number of seconds in scan_val.luint_val */
 				{
 					struct tm  *tms;
+					struct tm	tmbuf;
 					time_t		et = (time_t) scan_val.luint_val;
 
-					tms = gmtime(&et);
+					tms = gmtime_r(&et, &tmbuf);
 
 					if (tms)
 					{
diff --git a/src/interfaces/ecpg/pgtypeslib/timestamp.c b/src/interfaces/ecpg/pgtypeslib/timestamp.c
index 402fae6da67..7cf433266f4 100644
--- a/src/interfaces/ecpg/pgtypeslib/timestamp.c
+++ b/src/interfaces/ecpg/pgtypeslib/timestamp.c
@@ -129,11 +129,12 @@ timestamp2tm(timestamp dt, int *tzp, struct tm *tm, fsec_t *fsec, const char **t
 		if (IS_VALID_UTIME(tm->tm_year, tm->tm_mon, tm->tm_mday))
 		{
 #if defined(HAVE_STRUCT_TM_TM_ZONE) || defined(HAVE_INT_TIMEZONE)
+			struct tm	tmbuf;
 
 			utime = dt / USECS_PER_SEC +
 				((date0 - date2j(1970, 1, 1)) * INT64CONST(86400));
 
-			tx = localtime(&utime);
+			tx = localtime_r(&utime, &tmbuf);
 			tm->tm_year = tx->tm_year + 1900;
 			tm->tm_mon = tx->tm_mon + 1;
 			tm->tm_mday = tx->tm_mday;