Add a default local latch for use in signal handlers.

To do so, move InitializeLatchSupport() into the new common process
initialization functions, and add a new global variable MyLatch.

MyLatch is usable as soon InitPostmasterChild() has been called
(i.e. very early during startup). Initially it points to a process
local latch that exists in all processes. InitProcess/InitAuxiliaryProcess
then replaces that local latch with PGPROC->procLatch. During shutdown
the reverse happens.

This is primarily advantageous for two reasons: For one it simplifies
dealing with the shared process latch, especially in signal handlers,
because instead of having to check for MyProc, MyLatch can be used
unconditionally. For another, a later patch that makes FEs/BE
communication use latches, now can rely on the existence of a latch,
even before having gone through InitProcess.

Discussion: 20140927191243.GD5423@alap3.anarazel.de

src/backend/postmaster/autovacuum.c

@@ -589,11 +589,11 @@ AutoVacLauncherMain(int argc, char *argv[])
 		 * Wait until naptime expires or we get some type of signal (all the
 		 * signal handlers will wake us by calling SetLatch).
 		 */
-		rc = WaitLatch(&MyProc->procLatch,
+		rc = WaitLatch(MyLatch,
 					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
 					   (nap.tv_sec * 1000L) + (nap.tv_usec / 1000L));
 
-		ResetLatch(&MyProc->procLatch);
+		ResetLatch(MyLatch);
 
 		DisableCatchupInterrupt();
 
@@ -1341,8 +1341,7 @@ avl_sighup_handler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	got_SIGHUP = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -1354,8 +1353,7 @@ avl_sigusr2_handler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	got_SIGUSR2 = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -1367,8 +1365,7 @@ avl_sigterm_handler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	got_SIGTERM = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }

src/backend/postmaster/bgworker.c

@@ -942,7 +942,7 @@ WaitForBackgroundWorkerStartup(BackgroundWorkerHandle *handle, pid_t *pidp)
 			if (status != BGWH_NOT_YET_STARTED)
 				break;
 
-			rc = WaitLatch(&MyProc->procLatch,
+			rc = WaitLatch(MyLatch,
 						   WL_LATCH_SET | WL_POSTMASTER_DEATH, 0);
 
 			if (rc & WL_POSTMASTER_DEATH)
@@ -951,7 +951,7 @@ WaitForBackgroundWorkerStartup(BackgroundWorkerHandle *handle, pid_t *pidp)
 				break;
 			}
 
-			ResetLatch(&MyProc->procLatch);
+			ResetLatch(MyLatch);
 		}
 	}
 	PG_CATCH();

src/backend/postmaster/bgwriter.c

@@ -248,7 +248,7 @@ BackgroundWriterMain(void)
 		int			rc;
 
 		/* Clear any already-pending wakeups */
-		ResetLatch(&MyProc->procLatch);
+		ResetLatch(MyLatch);
 
 		if (got_SIGHUP)
 		{
@@ -336,7 +336,7 @@ BackgroundWriterMain(void)
 		 * down with latch events that are likely to happen frequently during
 		 * normal operation.
 		 */
-		rc = WaitLatch(&MyProc->procLatch,
+		rc = WaitLatch(MyLatch,
 					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
 					   BgWriterDelay /* ms */ );
 
@@ -363,7 +363,7 @@ BackgroundWriterMain(void)
 			/* Ask for notification at next buffer allocation */
 			StrategyNotifyBgWriter(MyProc->pgprocno);
 			/* Sleep ... */
-			rc = WaitLatch(&MyProc->procLatch,
+			rc = WaitLatch(MyLatch,
 						   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
 						   BgWriterDelay * HIBERNATE_FACTOR);
 			/* Reset the notification request in case we timed out */
@@ -426,8 +426,7 @@ BgSigHupHandler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	got_SIGHUP = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -439,8 +438,7 @@ ReqShutdownHandler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	shutdown_requested = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }

src/backend/postmaster/checkpointer.c

@@ -360,7 +360,7 @@ CheckpointerMain(void)
 		int			rc;
 
 		/* Clear any already-pending wakeups */
-		ResetLatch(&MyProc->procLatch);
+		ResetLatch(MyLatch);
 
 		/*
 		 * Process any requests or signals received recently.
@@ -559,7 +559,7 @@ CheckpointerMain(void)
 			cur_timeout = Min(cur_timeout, XLogArchiveTimeout - elapsed_secs);
 		}
 
-		rc = WaitLatch(&MyProc->procLatch,
+		rc = WaitLatch(MyLatch,
 					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
 					   cur_timeout * 1000L /* convert to ms */ );
 
@@ -832,8 +832,7 @@ ChkptSigHupHandler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	got_SIGHUP = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -845,8 +844,7 @@ ReqCheckpointHandler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	checkpoint_requested = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -869,8 +867,7 @@ ReqShutdownHandler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	shutdown_requested = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }

src/backend/postmaster/pgarch.c

@@ -78,11 +78,6 @@ static volatile sig_atomic_t got_SIGTERM = false;
 static volatile sig_atomic_t wakened = false;
 static volatile sig_atomic_t ready_to_stop = false;
 
-/*
- * Latch used by signal handlers to wake up the sleep in the main loop.
- */
-static Latch mainloop_latch;
-
 /* ----------
  * Local function forward declarations
  * ----------
@@ -220,10 +215,6 @@ pgarch_forkexec(void)
 NON_EXEC_STATIC void
 PgArchiverMain(int argc, char *argv[])
 {
-	InitializeLatchSupport();	/* needed for latch waits */
-
-	InitLatch(&mainloop_latch); /* initialize latch used in main loop */
-
 	/*
 	 * Ignore all signals usually bound to some action in the postmaster,
 	 * except for SIGHUP, SIGTERM, SIGUSR1, SIGUSR2, and SIGQUIT.
@@ -269,7 +260,7 @@ ArchSigHupHandler(SIGNAL_ARGS)
 
 	/* set flag to re-read config file at next convenient time */
 	got_SIGHUP = true;
-	SetLatch(&mainloop_latch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -287,7 +278,7 @@ ArchSigTermHandler(SIGNAL_ARGS)
 	 * archive commands.
 	 */
 	got_SIGTERM = true;
-	SetLatch(&mainloop_latch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -300,7 +291,7 @@ pgarch_waken(SIGNAL_ARGS)
 
 	/* set flag that there is work to be done */
 	wakened = true;
-	SetLatch(&mainloop_latch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -313,7 +304,7 @@ pgarch_waken_stop(SIGNAL_ARGS)
 
 	/* set flag to do a final cycle and shut down afterwards */
 	ready_to_stop = true;
-	SetLatch(&mainloop_latch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -344,7 +335,7 @@ pgarch_MainLoop(void)
 	 */
 	do
 	{
-		ResetLatch(&mainloop_latch);
+		ResetLatch(MyLatch);
 
 		/* When we get SIGUSR2, we do one more archive cycle, then exit */
 		time_to_stop = ready_to_stop;
@@ -397,7 +388,7 @@ pgarch_MainLoop(void)
 			{
 				int			rc;
 
-				rc = WaitLatch(&mainloop_latch,
+				rc = WaitLatch(MyLatch,
 							 WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
 							   timeout * 1000L);
 				if (rc & WL_TIMEOUT)

src/backend/postmaster/pgstat.c

@@ -130,8 +130,6 @@ PgStat_MsgBgWriter BgWriterStats;
  */
 NON_EXEC_STATIC pgsocket pgStatSock = PGINVALID_SOCKET;
 
-static Latch pgStatLatch;
-
 static struct sockaddr_storage pgStatAddr;
 
 static time_t last_pgstat_start_time;
@@ -3151,15 +3149,10 @@ PgstatCollectorMain(int argc, char *argv[])
 	PgStat_Msg	msg;
 	int			wr;
 
-	InitializeLatchSupport();	/* needed for latch waits */
-
-	/* Initialize private latch for use by signal handlers */
-	InitLatch(&pgStatLatch);
-
 	/*
 	 * Ignore all signals usually bound to some action in the postmaster,
 	 * except SIGHUP and SIGQUIT.  Note we don't need a SIGUSR1 handler to
-	 * support latch operations, because pgStatLatch is local not shared.
+	 * support latch operations, because we only use a local latch.
 	 */
 	pqsignal(SIGHUP, pgstat_sighup_handler);
 	pqsignal(SIGINT, SIG_IGN);
@@ -3205,7 +3198,7 @@ PgstatCollectorMain(int argc, char *argv[])
 	for (;;)
 	{
 		/* Clear any already-pending wakeups */
-		ResetLatch(&pgStatLatch);
+		ResetLatch(MyLatch);
 
 		/*
 		 * Quit if we get SIGQUIT from the postmaster.
@@ -3363,7 +3356,7 @@ PgstatCollectorMain(int argc, char *argv[])
 
 		/* Sleep until there's something to do */
 #ifndef WIN32
-		wr = WaitLatchOrSocket(&pgStatLatch,
+		wr = WaitLatchOrSocket(MyLatch,
 					 WL_LATCH_SET | WL_POSTMASTER_DEATH | WL_SOCKET_READABLE,
 							   pgStatSock,
 							   -1L);
@@ -3379,7 +3372,7 @@ PgstatCollectorMain(int argc, char *argv[])
 		 * to not provoke "pgstat wait timeout" complaints from
 		 * backend_read_statsfile.
 		 */
-		wr = WaitLatchOrSocket(&pgStatLatch,
+		wr = WaitLatchOrSocket(MyLatch,
 		WL_LATCH_SET | WL_POSTMASTER_DEATH | WL_SOCKET_READABLE | WL_TIMEOUT,
 							   pgStatSock,
 							   2 * 1000L /* msec */ );
@@ -3409,7 +3402,7 @@ pgstat_exit(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	need_exit = true;
-	SetLatch(&pgStatLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -3421,7 +3414,7 @@ pgstat_sighup_handler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	got_SIGHUP = true;
-	SetLatch(&pgStatLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }

src/backend/postmaster/syslogger.c

@@ -85,7 +85,6 @@ static FILE *csvlogFile = NULL;
 NON_EXEC_STATIC pg_time_t first_syslogger_file_time = 0;
 static char *last_file_name = NULL;
 static char *last_csv_file_name = NULL;
-static Latch sysLoggerLatch;
 
 /*
  * Buffers for saving partial messages from different backends.
@@ -231,12 +230,6 @@ SysLoggerMain(int argc, char *argv[])
 	syslogPipe[1] = 0;
 #endif
 
-	InitializeLatchSupport();		/* needed for latch waits */
-
-
-	/* Initialize private latch for use by signal handlers */
-	InitLatch(&sysLoggerLatch);
-
 	/*
 	 * Properly accept or ignore signals the postmaster might send us
 	 *
@@ -302,7 +295,7 @@ SysLoggerMain(int argc, char *argv[])
 #endif
 
 		/* Clear any already-pending wakeups */
-		ResetLatch(&sysLoggerLatch);
+		ResetLatch(MyLatch);
 
 		/*
 		 * Process any requests or signals received recently.
@@ -428,7 +421,7 @@ SysLoggerMain(int argc, char *argv[])
 		 * Sleep until there's something to do
 		 */
 #ifndef WIN32
-		rc = WaitLatchOrSocket(&sysLoggerLatch,
+		rc = WaitLatchOrSocket(MyLatch,
 							   WL_LATCH_SET | WL_SOCKET_READABLE | cur_flags,
 							   syslogPipe[0],
 							   cur_timeout);
@@ -480,7 +473,7 @@ SysLoggerMain(int argc, char *argv[])
 		 */
 		LeaveCriticalSection(&sysloggerSection);
 
-		(void) WaitLatch(&sysLoggerLatch,
+		(void) WaitLatch(MyLatch,
 						 WL_LATCH_SET | cur_flags,
 						 cur_timeout);
 
@@ -1061,7 +1054,7 @@ pipeThread(void *arg)
 		{
 			if (ftell(syslogFile) >= Log_RotationSize * 1024L ||
 				(csvlogFile != NULL && ftell(csvlogFile) >= Log_RotationSize * 1024L))
-				SetLatch(&sysLoggerLatch);
+				SetLatch(MyLatch);
 		}
 		LeaveCriticalSection(&sysloggerSection);
 	}
@@ -1073,7 +1066,7 @@ pipeThread(void *arg)
 	flush_pipe_input(logbuffer, &bytes_in_logbuffer);
 
 	/* set the latch to waken the main thread, which will quit */
-	SetLatch(&sysLoggerLatch);
+	SetLatch(MyLatch);
 
 	LeaveCriticalSection(&sysloggerSection);
 	_endthread();
@@ -1353,7 +1346,7 @@ sigHupHandler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	got_SIGHUP = true;
-	SetLatch(&sysLoggerLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -1365,7 +1358,7 @@ sigUsr1Handler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	rotation_requested = true;
-	SetLatch(&sysLoggerLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }

src/backend/postmaster/walwriter.c

@@ -252,7 +252,7 @@ WalWriterMain(void)
 		}
 
 		/* Clear any already-pending wakeups */
-		ResetLatch(&MyProc->procLatch);
+		ResetLatch(MyLatch);
 
 		/*
 		 * Process any requests or signals received recently.
@@ -287,7 +287,7 @@ WalWriterMain(void)
 		else
 			cur_timeout = WalWriterDelay * HIBERNATE_FACTOR;
 
-		rc = WaitLatch(&MyProc->procLatch,
+		rc = WaitLatch(MyLatch,
 					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
 					   cur_timeout);
 
@@ -345,8 +345,7 @@ WalSigHupHandler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	got_SIGHUP = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -358,8 +357,7 @@ WalShutdownHandler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	shutdown_requested = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }

src/backend/replication/syncrep.c

@@ -162,7 +162,7 @@ SyncRepWaitForLSN(XLogRecPtr XactCommitLSN)
 		int			syncRepState;
 
 		/* Must reset the latch before testing state. */
-		ResetLatch(&MyProc->procLatch);
+		ResetLatch(MyLatch);
 
 		/*
 		 * Try checking the state without the lock first.  There's no
@@ -235,7 +235,7 @@ SyncRepWaitForLSN(XLogRecPtr XactCommitLSN)
 		 * Wait on latch.  Any condition that should wake us up will set the
 		 * latch, so no need for timeout.
 		 */
-		WaitLatch(&MyProc->procLatch, WL_LATCH_SET | WL_POSTMASTER_DEATH, -1);
+		WaitLatch(MyLatch, WL_LATCH_SET | WL_POSTMASTER_DEATH, -1);
 	}
 
 	/*

src/backend/storage/ipc/procsignal.c

@@ -292,8 +292,8 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
 	if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
 		RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
-	if (set_latch_on_sigusr1 && MyProc != NULL)
-		SetLatch(&MyProc->procLatch);
+	if (set_latch_on_sigusr1)
+		SetLatch(MyLatch);
 
 	latch_sigusr1_handler();
 

src/backend/storage/ipc/shm_mq.c

@@ -827,13 +827,13 @@ shm_mq_send_bytes(shm_mq_handle *mqh, Size nbytes, const void *data,
 			 * at top of loop, because setting an already-set latch is much
 			 * cheaper than setting one that has been reset.
 			 */
-			WaitLatch(&MyProc->procLatch, WL_LATCH_SET, 0);
+			WaitLatch(MyLatch, WL_LATCH_SET, 0);
 
 			/* An interrupt may have occurred while we were waiting. */
 			CHECK_FOR_INTERRUPTS();
 
 			/* Reset the latch so we don't spin. */
-			ResetLatch(&MyProc->procLatch);
+			ResetLatch(MyLatch);
 		}
 		else
 		{
@@ -924,13 +924,13 @@ shm_mq_receive_bytes(shm_mq *mq, Size bytes_needed, bool nowait,
 		 * loop, because setting an already-set latch is much cheaper than
 		 * setting one that has been reset.
 		 */
-		WaitLatch(&MyProc->procLatch, WL_LATCH_SET, 0);
+		WaitLatch(MyLatch, WL_LATCH_SET, 0);
 
 		/* An interrupt may have occurred while we were waiting. */
 		CHECK_FOR_INTERRUPTS();
 
 		/* Reset the latch so we don't spin. */
-		ResetLatch(&MyProc->procLatch);
+		ResetLatch(MyLatch);
 	}
 }
 
@@ -991,13 +991,13 @@ shm_mq_wait_internal(volatile shm_mq *mq, PGPROC *volatile * ptr,
 			}
 
 			/* Wait to be signalled. */
-			WaitLatch(&MyProc->procLatch, WL_LATCH_SET, 0);
+			WaitLatch(MyLatch, WL_LATCH_SET, 0);
 
 			/* An interrupt may have occurred while we were waiting. */
 			CHECK_FOR_INTERRUPTS();
 
 			/* Reset the latch so we don't spin. */
-			ResetLatch(&MyProc->procLatch);
+			ResetLatch(MyLatch);
 		}
 	}
 	PG_CATCH();

src/backend/storage/lmgr/proc.c

@@ -290,13 +290,6 @@ InitProcess(void)
 	if (MyProc != NULL)
 		elog(ERROR, "you already exist");
 
-	/*
-	 * Initialize process-local latch support.  This could fail if the kernel
-	 * is low on resources, and if so we want to exit cleanly before acquiring
-	 * any shared-memory resources.
-	 */
-	InitializeLatchSupport();
-
 	/*
 	 * Try to get a proc struct from the free list.  If this fails, we must be
 	 * out of PGPROC structures (not to mention semaphores).
@@ -391,10 +384,12 @@ InitProcess(void)
 	SHMQueueElemInit(&(MyProc->syncRepLinks));
 
 	/*
-	 * Acquire ownership of the PGPROC's latch, so that we can use WaitLatch.
-	 * Note that there's no particular need to do ResetLatch here.
+	 * Acquire ownership of the PGPROC's latch, so that we can use WaitLatch
+	 * on it.  That allows us to repoint the process latch, which so far
+	 * points to process local one, to the shared one.
 	 */
 	OwnLatch(&MyProc->procLatch);
+	SwitchToSharedLatch();
 
 	/*
 	 * We might be reusing a semaphore that belonged to a failed process. So
@@ -474,13 +469,6 @@ InitAuxiliaryProcess(void)
 	if (MyProc != NULL)
 		elog(ERROR, "you already exist");
 
-	/*
-	 * Initialize process-local latch support.  This could fail if the kernel
-	 * is low on resources, and if so we want to exit cleanly before acquiring
-	 * any shared-memory resources.
-	 */
-	InitializeLatchSupport();
-
 	/*
 	 * We use the ProcStructLock to protect assignment and releasing of
 	 * AuxiliaryProcs entries.
@@ -547,10 +535,12 @@ InitAuxiliaryProcess(void)
 #endif
 
 	/*
-	 * Acquire ownership of the PGPROC's latch, so that we can use WaitLatch.
-	 * Note that there's no particular need to do ResetLatch here.
+	 * Acquire ownership of the PGPROC's latch, so that we can use WaitLatch
+	 * on it.  That allows us to repoint the process latch, which so far
+	 * points to process local one, to the shared one.
 	 */
 	OwnLatch(&MyProc->procLatch);
+	SwitchToSharedLatch();
 
 	/*
 	 * We might be reusing a semaphore that belonged to a failed process. So
@@ -800,10 +790,12 @@ ProcKill(int code, Datum arg)
 		ReplicationSlotRelease();
 
 	/*
-	 * Clear MyProc first; then disown the process latch.  This is so that
-	 * signal handlers won't try to clear the process latch after it's no
-	 * longer ours.
+	 * Reset MyLatch to the process local one.  This is so that signal
+	 * handlers et al can continue using the latch after the shared latch
+	 * isn't ours anymore. After that clear MyProc and disown the shared
+	 * latch.
 	 */
+	SwitchBackToLocalLatch();
 	proc = MyProc;
 	MyProc = NULL;
 	DisownLatch(&proc->procLatch);
@@ -867,10 +859,12 @@ AuxiliaryProcKill(int code, Datum arg)
 	LWLockReleaseAll();
 
 	/*
-	 * Clear MyProc first; then disown the process latch.  This is so that
-	 * signal handlers won't try to clear the process latch after it's no
-	 * longer ours.
+	 * Reset MyLatch to the process local one.  This is so that signal
+	 * handlers et al can continue using the latch after the shared latch
+	 * isn't ours anymore. After that clear MyProc and disown the shared
+	 * latch.
 	 */
+	SwitchBackToLocalLatch();
 	proc = MyProc;
 	MyProc = NULL;
 	DisownLatch(&proc->procLatch);

src/backend/tcop/postgres.c

@@ -2607,8 +2607,7 @@ die(SIGNAL_ARGS)
 	}
 
 	/* If we're still here, waken anything waiting on the process latch */
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -2649,8 +2648,7 @@ StatementCancelHandler(SIGNAL_ARGS)
 	}
 
 	/* If we're still here, waken anything waiting on the process latch */
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -2675,8 +2673,7 @@ SigHupHandler(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	got_SIGHUP = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -2814,8 +2811,7 @@ RecoveryConflictInterrupt(ProcSignalReason reason)
 	 * waiting on that latch, expecting to get interrupted by query cancels et
 	 * al., would also need to set set_latch_on_sigusr1.
 	 */
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }

src/backend/utils/adt/misc.c

@@ -413,10 +413,10 @@ pg_sleep(PG_FUNCTION_ARGS)
 		else
 			break;
 
-		(void) WaitLatch(&MyProc->procLatch,
+		(void) WaitLatch(MyLatch,
 						 WL_LATCH_SET | WL_TIMEOUT,
 						 delay_ms);
-		ResetLatch(&MyProc->procLatch);
+		ResetLatch(MyLatch);
 	}
 
 	PG_RETURN_VOID();

src/backend/utils/init/globals.c

@@ -40,6 +40,15 @@ struct Port *MyProcPort;
 long		MyCancelKey;
 int			MyPMChildSlot;
 
+/*
+ * MyLatch points to the latch that should be used for signal handling by the
+ * current process. It will either point to a process local latch if the
+ * current process does not have a PGPROC entry in that moment, or to
+ * PGPROC->procLatch if it has. Thus it can always be used in signal handlers,
+ * without checking for its existence.
+ */
+struct Latch *MyLatch;
+
 /*
  * DataDir is the absolute path to the top level of the PGDATA directory tree.
  * Except during early startup, this is also the server's working directory;

src/backend/utils/init/miscinit.c

@@ -39,6 +39,7 @@
 #include "postmaster/postmaster.h"
 #include "storage/fd.h"
 #include "storage/ipc.h"
+#include "storage/latch.h"
 #include "storage/pg_shmem.h"
 #include "storage/proc.h"
 #include "storage/procarray.h"
@@ -55,6 +56,7 @@ ProcessingMode Mode = InitProcessing;
 /* List of lock files to be removed at proc exit */
 static List *lock_files = NIL;
 
+static Latch LocalLatchData;
 
 /* ----------------------------------------------------------------
  *		ignoring system indexes support stuff
@@ -189,6 +191,11 @@ InitPostmasterChild(void)
 	/* We don't want the postmaster's proc_exit() handlers */
 	on_exit_reset();
 
+	/* Initialize process-local latch support */
+	InitializeLatchSupport();
+	MyLatch = &LocalLatchData;
+	InitLatch(MyLatch);
+
 	/*
 	 * If possible, make this process a group leader, so that the postmaster
 	 * can signal any child processes too. Not all processes will have
@@ -215,6 +222,11 @@ InitStandaloneProcess(const char *argv0)
 
 	MyStartTime = time(NULL);	/* set our start time in case we call elog */
 
+	/* Initialize process-local latch support */
+	InitializeLatchSupport();
+	MyLatch = &LocalLatchData;
+	InitLatch(MyLatch);
+
 	/* Compute paths, no postmaster to inherit from */
 	if (my_exec_path[0] == '\0')
 	{
@@ -227,6 +239,31 @@ InitStandaloneProcess(const char *argv0)
 		get_pkglib_path(my_exec_path, pkglib_path);
 }
 
+void
+SwitchToSharedLatch(void)
+{
+	Assert(MyLatch == &LocalLatchData);
+	Assert(MyProc != NULL);
+
+	MyLatch = &MyProc->procLatch;
+	/*
+	 * Set the shared latch as the local one might have been set. This
+	 * shouldn't normally be necessary as code is supposed to check the
+	 * condition before waiting for the latch, but a bit care can't hurt.
+	 */
+	SetLatch(MyLatch);
+}
+
+void
+SwitchBackToLocalLatch(void)
+{
+	Assert(MyLatch != &LocalLatchData);
+	Assert(MyProc != NULL && MyLatch == &MyProc->procLatch);
+
+	MyLatch = &LocalLatchData;
+	SetLatch(MyLatch);
+}
+
 /*
  * GetUserId - get the current effective user ID.
  *

src/backend/utils/misc/timeout.c

@@ -284,11 +284,9 @@ handle_sig_alarm(SIGNAL_ARGS)
 
 	/*
 	 * SIGALRM is always cause for waking anything waiting on the process
-	 * latch.  Cope with MyProc not being there, as the startup process also
-	 * uses this signal handler.
+	 * latch.
 	 */
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	/*
 	 * Fire any pending timeouts, but only if we're enabled to do so.

src/include/miscadmin.h

@@ -148,6 +148,7 @@ extern int	max_worker_processes;
 extern PGDLLIMPORT int MyProcPid;
 extern PGDLLIMPORT pg_time_t MyStartTime;
 extern PGDLLIMPORT struct Port *MyProcPort;
+extern PGDLLIMPORT struct Latch *MyLatch;
 extern long MyCancelKey;
 extern int	MyPMChildSlot;
 
@@ -302,6 +303,9 @@ extern void SetCurrentRoleId(Oid roleid, bool is_superuser);
 extern void SetDataDir(const char *dir);
 extern void ChangeToDataDir(void);
 
+extern void SwitchToSharedLatch(void);
+extern void SwitchBackToLocalLatch(void);
+
 /* in utils/misc/superuser.c */
 extern bool superuser(void);	/* current user is superuser */
 extern bool superuser_arg(Oid roleid);	/* given user is superuser */

src/include/storage/latch.h

@@ -85,7 +85,7 @@
  * the public functions. It is defined here to allow embedding Latches as
  * part of bigger structs.
  */
-typedef struct
+typedef struct Latch
 {
 	sig_atomic_t is_set;
 	bool		is_shared;

src/test/modules/test_shm_mq/setup.c

@@ -285,13 +285,13 @@ wait_for_workers_to_become_ready(worker_state *wstate,
 			}
 
 			/* Wait to be signalled. */
-			WaitLatch(&MyProc->procLatch, WL_LATCH_SET, 0);
+			WaitLatch(MyLatch, WL_LATCH_SET, 0);
 
 			/* An interrupt may have occurred while we were waiting. */
 			CHECK_FOR_INTERRUPTS();
 
 			/* Reset the latch so we don't spin. */
-			ResetLatch(&MyProc->procLatch);
+			ResetLatch(MyLatch);
 		}
 	}
 	PG_CATCH();

src/test/modules/test_shm_mq/test.c

@@ -230,9 +230,9 @@ test_shm_mq_pipelined(PG_FUNCTION_ARGS)
 			 * have read or written data and therefore there may now be work
 			 * for us to do.
 			 */
-			WaitLatch(&MyProc->procLatch, WL_LATCH_SET, 0);
+			WaitLatch(MyLatch, WL_LATCH_SET, 0);
 			CHECK_FOR_INTERRUPTS();
-			ResetLatch(&MyProc->procLatch);
+			ResetLatch(MyLatch);
 		}
 	}
 

src/test/modules/test_shm_mq/worker.c

@@ -211,8 +211,7 @@ handle_sigterm(SIGNAL_ARGS)
 {
 	int			save_errno = errno;
 
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	if (!proc_exit_inprogress)
 	{

src/test/modules/worker_spi/worker_spi.c

@@ -74,8 +74,7 @@ worker_spi_sigterm(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	got_sigterm = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -91,8 +90,7 @@ worker_spi_sighup(SIGNAL_ARGS)
 	int			save_errno = errno;
 
 	got_sighup = true;
-	if (MyProc)
-		SetLatch(&MyProc->procLatch);
+	SetLatch(MyLatch);
 
 	errno = save_errno;
 }
@@ -227,10 +225,10 @@ worker_spi_main(Datum main_arg)
 		 * necessary, but is awakened if postmaster dies.  That way the
 		 * background process goes away immediately in an emergency.
 		 */
-		rc = WaitLatch(&MyProc->procLatch,
+		rc = WaitLatch(MyLatch,
 					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
 					   worker_spi_naptime * 1000L);
-		ResetLatch(&MyProc->procLatch);
+		ResetLatch(MyLatch);
 
 		/* emergency bailout if postmaster has died */
 		if (rc & WL_POSTMASTER_DEATH)