Replace time_t with pg_time_t (same values, but always int64) in on-disk

data structures and backend internal APIs.  This solves problems we've seen
recently with inconsistent layout of pg_control between machines that have
32-bit time_t and those that have already migrated to 64-bit time_t.  Also,
we can get out from under the problem that Windows' Unix-API emulation is not
consistent about the width of time_t.

There are a few remaining places where local time_t variables are used to hold
the current or recent result of time(NULL).  I didn't bother changing these
since they do not affect any cross-module APIs and surely all platforms will
have 64-bit time_t before overflow becomes an actual risk.  time_t should
be avoided for anything visible to extension modules, however.

src/backend/utils/adt/date.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/date.c,v 1.138 2008/01/01 19:45:52 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/date.c,v 1.139 2008/02/17 02:09:28 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -945,8 +945,10 @@ tm2time(struct pg_tm * tm, fsec_t fsec, TimeADT *result)
 
 /* time2tm()
  * Convert time data type to POSIX time structure.
- * For dates within the system-supported time_t range, convert to the
- *	local time zone. If out of this range, leave as GMT. - tgl 97/05/27
+ *
+ * For dates within the range of pg_time_t, convert to the local time zone.
+ * If out of this range, leave as UTC (in practice that could only happen
+ * if pg_time_t is just 32 bits) - thomas 97/05/27
  */
 static int
 time2tm(TimeADT time, struct pg_tm * tm, fsec_t *fsec)
@@ -2466,10 +2468,9 @@ timetz_zone(PG_FUNCTION_ARGS)
 	if (tzp)
 	{
 		/* Get the offset-from-GMT that is valid today for the selected zone */
-		pg_time_t	now;
+		pg_time_t	now = (pg_time_t) time(NULL);
 		struct pg_tm *tm;
 
-		now = time(NULL);
 		tm = pg_localtime(&now, tzp);
 		tz = -tm->tm_gmtoff;
 	}

src/backend/utils/adt/datetime.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/datetime.c,v 1.184 2008/01/01 19:45:52 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/datetime.c,v 1.185 2008/02/17 02:09:28 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -650,9 +650,11 @@ ParseDateTime(const char *timestr, char *workbuf, size_t buflen,
  *				"20011225T040506.789-07"
  *
  * Use the system-provided functions to get the current time zone
- *	if not specified in the input string.
- * If the date is outside the time_t system-supported time range,
- *	then assume UTC time zone. - thomas 1997-05-27
+ * if not specified in the input string.
+ *
+ * If the date is outside the range of pg_time_t (in practice that could only
+ * happen if pg_time_t is just 32 bits), then assume UTC time zone - thomas
+ * 1997-05-27
  */
 int
 DecodeDateTime(char **field, int *ftype, int nf,

src/backend/utils/adt/nabstime.c

@@ -10,7 +10,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/nabstime.c,v 1.152 2008/01/01 19:45:52 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/nabstime.c,v 1.153 2008/02/17 02:09:28 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -86,6 +86,8 @@ static void parsetinterval(char *i_string,
  * GetCurrentAbsoluteTime()
  *
  * Get the current system time (relative to Unix epoch).
+ *
+ * NB: this will overflow in 2038; it should be gone long before that.
  */
 AbsoluteTime
 GetCurrentAbsoluteTime(void)
@@ -1029,12 +1031,7 @@ tintervalrel(PG_FUNCTION_ARGS)
 Datum
 timenow(PG_FUNCTION_ARGS)
 {
-	time_t		sec;
-
-	if (time(&sec) < 0)
-		PG_RETURN_ABSOLUTETIME(INVALID_ABSTIME);
-
-	PG_RETURN_ABSOLUTETIME((AbsoluteTime) sec);
+	PG_RETURN_ABSOLUTETIME(GetCurrentAbsoluteTime());
 }
 
 /*

src/backend/utils/adt/timestamp.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/timestamp.c,v 1.184 2008/01/01 19:45:52 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/timestamp.c,v 1.185 2008/02/17 02:09:28 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1264,9 +1264,14 @@ TimestampDifferenceExceeds(TimestampTz start_time,
  *
  * We do not use time_t internally in Postgres, but this is provided for use
  * by functions that need to interpret, say, a stat(2) result.
+ *
+ * To avoid having the function's ABI vary depending on the width of time_t,
+ * we declare the argument as pg_time_t, which is cast-compatible with
+ * time_t but always 64 bits wide (unless the platform has no 64-bit type).
+ * This detail should be invisible to callers, at least at source code level.
  */
 TimestampTz
-time_t_to_timestamptz(time_t tm)
+time_t_to_timestamptz(pg_time_t tm)
 {
 	TimestampTz result;
 
@@ -1284,17 +1289,22 @@ time_t_to_timestamptz(time_t tm)
  * Convert a TimestampTz to time_t.
  *
  * This too is just marginally useful, but some places need it.
+ *
+ * To avoid having the function's ABI vary depending on the width of time_t,
+ * we declare the result as pg_time_t, which is cast-compatible with
+ * time_t but always 64 bits wide (unless the platform has no 64-bit type).
+ * This detail should be invisible to callers, at least at source code level.
  */
-time_t
+pg_time_t
 timestamptz_to_time_t(TimestampTz t)
 {
-	time_t		result;
+	pg_time_t	result;
 
 #ifdef HAVE_INT64_TIMESTAMP
-	result = (time_t) (t / USECS_PER_SEC +
+	result = (pg_time_t) (t / USECS_PER_SEC +
 				 ((POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * SECS_PER_DAY));
 #else
-	result = (time_t) (t +
+	result = (pg_time_t) (t +
 				 ((POSTGRES_EPOCH_JDATE - UNIX_EPOCH_JDATE) * SECS_PER_DAY));
 #endif