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;
 }