Make pg_ctl stop/restart/promote recheck postmaster aliveness.

"pg_ctl stop/restart" checked that the postmaster PID is valid just
once, as a side-effect of sending the stop signal, and then would
wait-till-timeout for the postmaster.pid file to go away.  This
neglects the case wherein the postmaster dies uncleanly after we
signal it.  Similarly, once "pg_ctl promote" has sent the signal,
it'd wait for the corresponding on-disk state change to occur
even if the postmaster dies.

I'm not sure how we've managed not to notice this problem, but it
seems to explain slow execution of the 017_shm.pl test script on AIX
since commit 4fdbf9af5, which added a speculative "pg_ctl stop" with
the idea of making real sure that the postmaster isn't there.  In the
test steps that kill-9 and then restart the postmaster, it's possible
to get past the initial signal attempt before kill() stops working
for the doomed postmaster.  If that happens, pg_ctl waited till
PGCTLTIMEOUT before giving up ... and the buildfarm's AIX members
have that set very high.

To fix, include a "kill(pid, 0)" test (similar to what
postmaster_is_alive uses) in these wait loops, so that we'll
give up immediately if the postmaster PID disappears.

While here, I chose to refactor those loops out of where they were.
do_stop() and do_restart() can perfectly well share one copy of the
wait-for-stop loop, and it seems desirable to put a similar function
beside that for wait-for-promote.

Back-patch to all supported versions, since pg_ctl's wait logic
is substantially identical in all, and we're seeing the slow test
behavior in all branches.

Discussion: https://postgr.es/m/20220210023537.GA3222837@rfd.leadboat.com

src/bin/pg_ctl/pg_ctl.c

@@ -155,7 +155,9 @@ static void free_readfile(char **optlines);
 static pgpid_t start_postmaster(void);
 static void read_post_opts(void);
 
-static WaitPMResult wait_for_postmaster(pgpid_t pm_pid, bool do_checkpoint);
+static WaitPMResult wait_for_postmaster_start(pgpid_t pm_pid, bool do_checkpoint);
+static bool wait_for_postmaster_stop(void);
+static bool wait_for_postmaster_promote(void);
 static bool postmaster_is_alive(pid_t pid);
 
 #if defined(HAVE_GETRLIMIT) && defined(RLIMIT_CORE)
@@ -590,7 +592,7 @@ start_postmaster(void)
  * manager checkpoint, it's got nothing to do with database checkpoints!!
  */
 static WaitPMResult
-wait_for_postmaster(pgpid_t pm_pid, bool do_checkpoint)
+wait_for_postmaster_start(pgpid_t pm_pid, bool do_checkpoint)
 {
 	int			i;
 
@@ -700,6 +702,76 @@ wait_for_postmaster(pgpid_t pm_pid, bool do_checkpoint)
 }
 
 
+/*
+ * Wait for the postmaster to stop.
+ *
+ * Returns true if the postmaster stopped cleanly (i.e., removed its pidfile).
+ * Returns false if the postmaster dies uncleanly, or if we time out.
+ */
+static bool
+wait_for_postmaster_stop(void)
+{
+	int			cnt;
+
+	for (cnt = 0; cnt < wait_seconds * WAITS_PER_SEC; cnt++)
+	{
+		pgpid_t		pid;
+
+		if ((pid = get_pgpid(false)) == 0)
+			return true;		/* pid file is gone */
+
+		if (kill((pid_t) pid, 0) != 0)
+		{
+			/*
+			 * Postmaster seems to have died.  Check the pid file once more to
+			 * avoid a race condition, but give up waiting.
+			 */
+			if (get_pgpid(false) == 0)
+				return true;	/* pid file is gone */
+			return false;		/* postmaster died untimely */
+		}
+
+		if (cnt % WAITS_PER_SEC == 0)
+			print_msg(".");
+		pg_usleep(USEC_PER_SEC / WAITS_PER_SEC);
+	}
+	return false;				/* timeout reached */
+}
+
+
+/*
+ * Wait for the postmaster to promote.
+ *
+ * Returns true on success, else false.
+ * To avoid waiting uselessly, we check for postmaster death here too.
+ */
+static bool
+wait_for_postmaster_promote(void)
+{
+	int			cnt;
+
+	for (cnt = 0; cnt < wait_seconds * WAITS_PER_SEC; cnt++)
+	{
+		pgpid_t		pid;
+		DBState		state;
+
+		if ((pid = get_pgpid(false)) == 0)
+			return false;		/* pid file is gone */
+		if (kill((pid_t) pid, 0) != 0)
+			return false;		/* postmaster died */
+
+		state = get_control_dbstate();
+		if (state == DB_IN_PRODUCTION)
+			return true;		/* successful promotion */
+
+		if (cnt % WAITS_PER_SEC == 0)
+			print_msg(".");
+		pg_usleep(USEC_PER_SEC / WAITS_PER_SEC);
+	}
+	return false;				/* timeout reached */
+}
+
+
 #if defined(HAVE_GETRLIMIT) && defined(RLIMIT_CORE)
 static void
 unlimit_core_size(void)
@@ -913,7 +985,7 @@ do_start(void)
 
 		print_msg(_("waiting for server to start..."));
 
-		switch (wait_for_postmaster(pm_pid, false))
+		switch (wait_for_postmaster_start(pm_pid, false))
 		{
 			case POSTMASTER_READY:
 				print_msg(_(" done\n"));
@@ -948,7 +1020,6 @@ do_start(void)
 static void
 do_stop(void)
 {
-	int			cnt;
 	pgpid_t		pid;
 	struct stat statbuf;
 
@@ -999,19 +1070,7 @@ do_stop(void)
 
 		print_msg(_("waiting for server to shut down..."));
 
-		for (cnt = 0; cnt < wait_seconds * WAITS_PER_SEC; cnt++)
-		{
-			if ((pid = get_pgpid(false)) != 0)
-			{
-				if (cnt % WAITS_PER_SEC == 0)
-					print_msg(".");
-				pg_usleep(USEC_PER_SEC / WAITS_PER_SEC);
-			}
-			else
-				break;
-		}
-
-		if (pid != 0)			/* pid file still exists */
+		if (!wait_for_postmaster_stop())
 		{
 			print_msg(_(" failed\n"));
 
@@ -1035,7 +1094,6 @@ do_stop(void)
 static void
 do_restart(void)
 {
-	int			cnt;
 	pgpid_t		pid;
 	struct stat statbuf;
 
@@ -1089,20 +1147,7 @@ do_restart(void)
 		print_msg(_("waiting for server to shut down..."));
 
 		/* always wait for restart */
-
-		for (cnt = 0; cnt < wait_seconds * WAITS_PER_SEC; cnt++)
-		{
-			if ((pid = get_pgpid(false)) != 0)
-			{
-				if (cnt % WAITS_PER_SEC == 0)
-					print_msg(".");
-				pg_usleep(USEC_PER_SEC / WAITS_PER_SEC);
-			}
-			else
-				break;
-		}
-
-		if (pid != 0)			/* pid file still exists */
+		if (!wait_for_postmaster_stop())
 		{
 			print_msg(_(" failed\n"));
 
@@ -1222,21 +1267,8 @@ do_promote(void)
 
 	if (do_wait)
 	{
-		DBState		state = DB_STARTUP;
-		int			cnt;
-
 		print_msg(_("waiting for server to promote..."));
-		for (cnt = 0; cnt < wait_seconds * WAITS_PER_SEC; cnt++)
-		{
-			state = get_control_dbstate();
-			if (state == DB_IN_PRODUCTION)
-				break;
-
-			if (cnt % WAITS_PER_SEC == 0)
-				print_msg(".");
-			pg_usleep(USEC_PER_SEC / WAITS_PER_SEC);
-		}
-		if (state == DB_IN_PRODUCTION)
+		if (wait_for_postmaster_promote())
 		{
 			print_msg(_(" done\n"));
 			print_msg(_("server promoted\n"));
@@ -1655,7 +1687,7 @@ pgwin32_ServiceMain(DWORD argc, LPTSTR *argv)
 	if (do_wait)
 	{
 		write_eventlog(EVENTLOG_INFORMATION_TYPE, _("Waiting for server startup...\n"));
-		if (wait_for_postmaster(postmasterPID, true) != POSTMASTER_READY)
+		if (wait_for_postmaster_start(postmasterPID, true) != POSTMASTER_READY)
 		{
 			write_eventlog(EVENTLOG_ERROR_TYPE, _("Timed out waiting for server startup\n"));
 			pgwin32_SetServiceStatus(SERVICE_STOPPED);
@@ -1676,7 +1708,7 @@ pgwin32_ServiceMain(DWORD argc, LPTSTR *argv)
 			{
 				/*
 				 * status.dwCheckPoint can be incremented by
-				 * wait_for_postmaster(), so it might not start from 0.
+				 * wait_for_postmaster_start(), so it might not start from 0.
 				 */
 				int			maxShutdownCheckPoint = status.dwCheckPoint + 12;