Revert "Use pselect(2) not select(2), if available, to wait in postmaster's loop."

This reverts commit b9515b62879722e3497236f6e0d6783c3fc059a2.

Buildfarm results suggest that some platforms have versions of pselect(2)
that are not merely non-atomic, but flat out non-functional.  Revert the
use-pselect patch to confirm this diagnosis (and exclude the no-SA_RESTART
patch as the source of trouble).  If it's so, we should probably look into
blacklisting specific platforms that have broken pselect.

Discussion: https://postgr.es/m/9696.1493072081@sss.pgh.pa.us

3 files changed, 17 insertions, 52 deletions

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index cd793886f83..5a609958896 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -606,9 +606,9 @@ PostmasterMain(int argc, char *argv[])
 	 * In the postmaster, we want to install non-ignored handlers *without*
 	 * SA_RESTART.  This is because they'll be blocked at all times except
 	 * when ServerLoop is waiting for something to happen, and during that
-	 * window, we want signals to exit the pselect(2) wait so that ServerLoop
+	 * window, we want signals to exit the select(2) wait so that ServerLoop
 	 * can respond if anything interesting happened.  On some platforms,
-	 * signals marked SA_RESTART would not cause the pselect() wait to end.
+	 * signals marked SA_RESTART would not cause the select() wait to end.
 	 * Child processes will generally want SA_RESTART, but we expect them to
 	 * set up their own handlers before unblocking signals.
 	 *
@@ -1642,8 +1642,6 @@ ServerLoop(void)
 	for (;;)
 	{
 		fd_set		rmask;
-		fd_set	   *rmask_p;
-		struct timeval timeout;
 		int			selres;
 		time_t		now;
 
@@ -1653,64 +1651,37 @@ ServerLoop(void)
 		 * We block all signals except while sleeping. That makes it safe for
 		 * signal handlers, which again block all signals while executing, to
 		 * do nontrivial work.
+		 *
+		 * If we are in PM_WAIT_DEAD_END state, then we don't want to accept
+		 * any new connections, so we don't call select(), and just sleep.
 		 */
+		memcpy((char *) &rmask, (char *) &readmask, sizeof(fd_set));
+
 		if (pmState == PM_WAIT_DEAD_END)
 		{
-			/*
-			 * If we are in PM_WAIT_DEAD_END state, then we don't want to
-			 * accept any new connections, so pass a null rmask.
-			 */
-			rmask_p = NULL;
-			timeout.tv_sec = 0;
-			timeout.tv_usec = 100000;	/* 100 msec seems reasonable */
+			PG_SETMASK(&UnBlockSig);
+
+			pg_usleep(100000L); /* 100 msec seems reasonable */
+			selres = 0;
+
+			PG_SETMASK(&BlockSig);
 		}
 		else
 		{
-			/* Normal case: check sockets, and compute a suitable timeout */
-			memcpy(&rmask, &readmask, sizeof(fd_set));
-			rmask_p = &rmask;
+			/* must set timeout each time; some OSes change it! */
+			struct timeval timeout;
 
 			/* Needs to run with blocked signals! */
 			DetermineSleepTime(&timeout);
-		}
 
-		/*
-		 * We prefer to wait with pselect(2) if available, as using that,
-		 * together with *not* using SA_RESTART for signals, guarantees that
-		 * we will get kicked off the wait if a signal occurs.
-		 *
-		 * If we lack pselect(2), fake it with select(2).  This has a race
-		 * condition: a signal that was already pending will be delivered
-		 * before we reach the select(), and therefore the select() will wait,
-		 * even though we might wish to do something in response.  Therefore,
-		 * beware of putting any time-critical signal response logic into
-		 * ServerLoop rather than into the signal handler itself.  It will run
-		 * eventually, but maybe not till after a timeout delay.
-		 *
-		 * Some implementations of pselect() are reportedly not atomic, making
-		 * the first alternative here functionally equivalent to the second.
-		 * Not much we can do about that though.
-		 */
-		{
-#ifdef HAVE_PSELECT
-			/* pselect uses a randomly different timeout API, sigh */
-			struct timespec ptimeout;
-
-			ptimeout.tv_sec = timeout.tv_sec;
-			ptimeout.tv_nsec = timeout.tv_usec * 1000;
-
-			selres = pselect(nSockets, rmask_p, NULL, NULL,
-							 &ptimeout, &UnBlockSig);
-#else
 			PG_SETMASK(&UnBlockSig);
 
-			selres = select(nSockets, rmask_p, NULL, NULL, &timeout);
+			selres = select(nSockets, &rmask, NULL, NULL, &timeout);
 
 			PG_SETMASK(&BlockSig);
-#endif
 		}
 
-		/* Now check the select()/pselect() result */
+		/* Now check the select() result */
 		if (selres < 0)
 		{
 			if (errno != EINTR && errno != EWOULDBLOCK)
diff --git a/src/include/pg_config.h.in b/src/include/pg_config.h.in
index 5eabcce5da4..7dbfa90bf49 100644
--- a/src/include/pg_config.h.in
+++ b/src/include/pg_config.h.in
@@ -397,9 +397,6 @@
 /* Define to 1 if the assembler supports PPC's LWARX mutex hint bit. */
 #undef HAVE_PPC_LWARX_MUTEX_HINT
 
-/* Define to 1 if you have the `pselect' function. */
-#undef HAVE_PSELECT
-
 /* Define to 1 if you have the `pstat' function. */
 #undef HAVE_PSTAT
 
diff --git a/src/include/pg_config.h.win32 b/src/include/pg_config.h.win32
index 9288e05e07b..21631870828 100644
--- a/src/include/pg_config.h.win32
+++ b/src/include/pg_config.h.win32
@@ -264,9 +264,6 @@
 /* Define to 1 if you have the <poll.h> header file. */
 /* #undef HAVE_POLL_H */
 
-/* Define to 1 if you have the `pselect' function. */
-/* #undef HAVE_PSELECT */
-
 /* Define to 1 if you have the `pstat' function. */
 /* #undef HAVE_PSTAT */