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thread-safety: gmtime_r(), localtime_r()

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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
This commit is contained in:
Peter Eisentraut
2024-08-23 07:07:53 +02:00
parent 94a3373ac5
commit a2bbc58f74
7 changed files with 33 additions and 7 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
src/interfaces/ecpg/pgtypeslib/dt_common.c
View File

@@ -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)
{

3
src/interfaces/ecpg/pgtypeslib/timestamp.c
View File

@@ -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;

3
src/interfaces/libpq/fe-trace.c
View File

@@ -81,6 +81,7 @@ pqTraceFormatTimestamp(char *timestr, size_t ts_len)
{
struct timeval tval;
time_t now;
struct tm tmbuf;
gettimeofday(&tval, NULL);
@@ -93,7 +94,7 @@ pqTraceFormatTimestamp(char *timestr, size_t ts_len)
now = tval.tv_sec;
strftime(timestr, ts_len,
"%Y-%m-%d %H:%M:%S",
localtime(&now));
localtime_r(&now, &tmbuf));
/* append microseconds */
snprintf(timestr + strlen(timestr), ts_len - strlen(timestr),
".%06u", (unsigned int) (tval.tv_usec));