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 <[email protected]>
Reviewed-by: Heikki Linnakangas <[email protected]>
Reviewed-by: Thomas Munro <[email protected]>
Discussion: https://www.postgresql.org/message-id/flat/eba1dc75-298e-4c46-8869-48ba8aad7d70@eisentraut.org

diff --git a/meson.build b/meson.build
index cd711c6d0188a7cc4a8b7e1815823d186f8926a0..ea07126f78e9ce2ee471c909a7503abc51e5dae0 100644 (file)
--- a/meson.build
+++ b/meson.build
@@ -268,6 +268,10 @@ elif host_system == 'windows'
   exesuffix = '.exe'
   dlsuffix = '.dll'
   library_path_var = ''
+  if cc.get_id() != 'msvc'
+    # define before including <time.h> for getting localtime_r() etc. on MinGW
+    cppflags += '-D_POSIX_C_SOURCE'
+  endif
 
   export_file_format = 'win'
   export_file_suffix = 'def'

diff --git a/src/backend/utils/adt/pg_locale.c b/src/backend/utils/adt/pg_locale.c
index 48b7e16d81bceacf1639ddca3ce159297c484cdb..643cca05d387800f3fcc2ef6ea824ba2038fb138 100644 (file)
--- a/src/backend/utils/adt/pg_locale.c
+++ b/src/backend/utils/adt/pg_locale.c
@@ -826,6 +826,7 @@ cache_locale_time(void)
    char       *bufptr;
    time_t      timenow;
    struct tm  *timeinfo;
+   struct tm   timeinfobuf;
    bool        strftimefail = false;
    int         encoding;
    int         i;
@@ -876,7 +877,7 @@ cache_locale_time(void)
 
    /* We use times close to current time as data for strftime(). */
    timenow = time(NULL);
-   timeinfo = localtime(&timenow);
+   timeinfo = gmtime_r(&timenow, &timeinfobuf);
 
    /* Store the strftime results in MAX_L10N_DATA-sized portions of buf[] */
    bufptr = buf;

diff --git a/src/include/port/win32_port.h b/src/include/port/win32_port.h
index 7ffe5891c69ac9b76b0f697ad75796b777140958..7789e0431aaa6599a0af6ec6b5dd4c84b5914ee8 100644 (file)
--- a/src/include/port/win32_port.h
+++ b/src/include/port/win32_port.h
@@ -420,6 +420,19 @@ extern int _pglstat64(const char *name, struct stat *buf);
  */
 #define strtok_r strtok_s
 
+/*
+ * Supplement to <time.h>.
+ */
+#ifdef _MSC_VER
+/*
+ * MinGW has these functions if _POSIX_C_SOURCE is defined.  Third-party
+ * libraries might do that, so to avoid clashes we get ahead of it and define
+ * it ourselves and use the system functions provided by MinGW.
+ */
+#define gmtime_r(clock, result) (gmtime_s(result, clock) ? NULL : (result))
+#define localtime_r(clock, result) (localtime_s(result, clock) ? NULL : (result))
+#endif
+
 /*
  * Locale stuff.
  *

diff --git a/src/interfaces/ecpg/pgtypeslib/dt_common.c b/src/interfaces/ecpg/pgtypeslib/dt_common.c
index ed08088bfe1320052aa87bc78f351a2e733aa245..0d63fe52c5bb382103b03a6f38d39d1b21d275f4 100644 (file)
--- 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 402fae6da679113bdd1cc91aa66b09d91033f608..7cf433266f45855bf5b491e4fe970658579f51d6 100644 (file)
--- 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;

diff --git a/src/interfaces/libpq/fe-trace.c b/src/interfaces/libpq/fe-trace.c
index bff7d919d570774af16e3f001acb6043391adf3b..19c5b8a89000488aef01247e1e9d21a2e62d1e40 100644 (file)
--- a/src/interfaces/libpq/fe-trace.c
+++ b/src/interfaces/libpq/fe-trace.c
@@ -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));

diff --git a/src/template/win32 b/src/template/win32
index 1895f067a889b52ac9b7fd9c23b548774b56dc72..4f8b0923fe0418290dcd8b0487e136fcd86660b1 100644 (file)
--- a/src/template/win32
+++ b/src/template/win32
@@ -1,5 +1,8 @@
 # src/template/win32
 
+# define before including <time.h> for getting localtime_r() etc. on MinGW
+CPPFLAGS="$CPPFLAGS -D_POSIX_C_SOURCE"
+
 # Extra CFLAGS for code that will go into a shared library
 CFLAGS_SL=""