Merge three existing ways of signaling postmaster from child processes,

so that only one signal number is used not three.  Flags in shared
memory tell the reason(s) for the current signal.  This method is
extensible to handle more signal reasons without chewing up even more
signal numbers, but the immediate reason is to keep pg_pwd reloads
separate from SIGHUP processing in the postmaster.
Also clean up some problems in the postmaster with delayed response to
checkpoint status changes --- basically, it wouldn't schedule a checkpoint
if it wasn't getting connection requests on a regular basis.

src/backend/storage/ipc/Makefile

@@ -1,7 +1,7 @@
 #
 # Makefile for storage/ipc
 #
-# $Header: /cvsroot/pgsql/src/backend/storage/ipc/Makefile,v 1.16 2001/09/27 19:10:02 tgl Exp $
+# $Header: /cvsroot/pgsql/src/backend/storage/ipc/Makefile,v 1.17 2001/11/04 19:55:31 tgl Exp $
 #
 
 subdir = src/backend/storage/ipc
@@ -15,7 +15,7 @@ override CFLAGS+= -fno-inline
 endif
 endif
 
-OBJS = ipc.o ipci.o shmem.o shmqueue.o sinval.o sinvaladt.o
+OBJS = ipc.o ipci.o pmsignal.o shmem.o shmqueue.o sinval.o sinvaladt.o
 
 all: SUBSYS.o
 

src/backend/storage/ipc/ipci.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/ipc/ipci.c,v 1.44 2001/10/25 05:49:42 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/ipc/ipci.c,v 1.45 2001/11/04 19:55:31 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -23,6 +23,7 @@
 #include "storage/freespace.h"
 #include "storage/lmgr.h"
 #include "storage/lwlock.h"
+#include "storage/pmsignal.h"
 #include "storage/proc.h"
 #include "storage/sinval.h"
 #include "storage/spin.h"
@@ -121,4 +122,9 @@ CreateSharedMemoryAndSemaphores(bool makePrivate, int maxBackends)
 	 * Set up free-space map
 	 */
 	InitFreeSpaceMap();
+
+	/*
+	 * Set up child-to-postmaster signaling mechanism
+	 */
+	PMSignalInit();
 }

src/backend/storage/ipc/pmsignal.c

@@ -0,0 +1,86 @@
+/*-------------------------------------------------------------------------
+ *
+ * pmsignal.c
+ *	  routines for signaling the postmaster from its child processes
+ *
+ *
+ * Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/ipc/pmsignal.c,v 1.1 2001/11/04 19:55:31 tgl Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <signal.h>
+#include <unistd.h>
+
+#include "miscadmin.h"
+#include "storage/pmsignal.h"
+#include "storage/shmem.h"
+
+
+/*
+ * The postmaster is signaled by its children by sending SIGUSR1.  The
+ * specific reason is communicated via flags in shared memory.  We keep
+ * a boolean flag for each possible "reason", so that different reasons
+ * can be signaled by different backends at the same time.  (However,
+ * if the same reason is signaled more than once simultaneously, the
+ * postmaster will observe it only once.)
+ *
+ * The flags are actually declared as "volatile sig_atomic_t" for maximum
+ * portability.  This should ensure that loads and stores of the flag
+ * values are atomic, allowing us to dispense with any explicit locking.
+ */
+
+static volatile sig_atomic_t * PMSignalFlags;
+
+
+/*
+ * PMSignalInit - initialize during shared-memory creation
+ */
+void
+PMSignalInit(void)
+{
+	/* Should be called only once */
+	Assert(!PMSignalFlags);
+
+	PMSignalFlags = (sig_atomic_t *)
+		ShmemAlloc(NUM_PMSIGNALS * sizeof(sig_atomic_t));
+
+	MemSet(PMSignalFlags, 0, NUM_PMSIGNALS * sizeof(sig_atomic_t));
+}
+
+/*
+ * SendPostmasterSignal - signal the postmaster from a child process
+ */
+void
+SendPostmasterSignal(PMSignalReason reason)
+{
+	/* If called in a standalone backend, do nothing */
+	if (!IsUnderPostmaster)
+		return;
+	/* Atomically set the proper flag */
+	PMSignalFlags[reason] = true;
+	/* Send signal to postmaster (assume it is our direct parent) */
+	kill(getppid(), SIGUSR1);
+}
+
+/*
+ * CheckPostmasterSignal - check to see if a particular reason has been
+ * signaled, and clear the signal flag.  Should be called by postmaster
+ * after receiving SIGUSR1.
+ */
+bool
+CheckPostmasterSignal(PMSignalReason reason)
+{
+	/* Careful here --- don't clear flag if we haven't seen it set */
+	if (PMSignalFlags[reason])
+	{
+		PMSignalFlags[reason] = false;
+		return true;
+	}
+	return false;
+}

src/backend/storage/ipc/sinvaladt.c

@@ -8,17 +8,15 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/storage/ipc/sinvaladt.c,v 1.41 2001/09/29 04:02:24 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/storage/ipc/sinvaladt.c,v 1.42 2001/11/04 19:55:31 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
 #include "postgres.h"
 
-#include <signal.h>
-#include <unistd.h>
-
 #include "miscadmin.h"
 #include "storage/backendid.h"
+#include "storage/pmsignal.h"
 #include "storage/proc.h"
 #include "storage/sinvaladt.h"
 
@@ -205,11 +203,11 @@ SIInsertDataEntry(SISeg *segP, SharedInvalidationMessage *data)
 
 	/*
 	 * Try to prevent table overflow.  When the table is 70% full send a
-	 * SIGUSR2 (ordinarily a NOTIFY signal) to the postmaster, which will
-	 * send it back to all the backends.  This will force idle backends to
-	 * execute a transaction to look through pg_listener for NOTIFY
-	 * messages, and as a byproduct of the transaction start they will
-	 * read SI entries.
+	 * WAKEN_CHILDREN request to the postmaster.  The postmaster will send
+	 * a SIGUSR2 signal (ordinarily a NOTIFY signal) to all the backends.
+	 * This will force idle backends to execute a transaction to look through
+	 * pg_listener for NOTIFY messages, and as a byproduct of the transaction
+	 * start they will read SI entries.
 	 *
 	 * This should never happen if all the backends are actively executing
 	 * queries, but if a backend is sitting idle then it won't be starting
@@ -222,7 +220,7 @@ SIInsertDataEntry(SISeg *segP, SharedInvalidationMessage *data)
 	{
 		if (DebugLvl >= 1)
 			elog(DEBUG, "SIInsertDataEntry: table is 70%% full, signaling postmaster");
-		kill(getppid(), SIGUSR2);
+		SendPostmasterSignal(PMSIGNAL_WAKEN_CHILDREN);
 	}
 
 	/*