When trace_lwlocks is used, identify individual lwlocks by name.

Naming the individual lwlocks seems like something that may be useful
for other types of debugging, monitoring, or instrumentation output,
but this commit just implements it for the specific case of
trace_lwlocks.

Patch by me, reviewed by Amit Kapila and Kyotaro Horiguchi

src/backend/storage/lmgr/.gitignore

@@ -0,0 +1,2 @@
+/lwlocknames.c
+/lwlocknames.h

src/backend/storage/lmgr/Makefile

@@ -24,8 +24,17 @@ s_lock_test: s_lock.c $(top_builddir)/src/port/libpgport.a
 	$(CC) $(CPPFLAGS) $(CFLAGS) -DS_LOCK_TEST=1 $(srcdir)/s_lock.c \
 		$(TASPATH) -L $(top_builddir)/src/port -lpgport -o s_lock_test
 
+# see explanation in ../../parser/Makefile
+lwlocknames.c: lwlocknames.h ;
+
+lwlocknames.h: $(top_srcdir)/src/backend/storage/lmgr/lwlocknames.txt generate-lwlocknames.pl
+	$(PERL) $(srcdir)/generate-lwlocknames.pl $<
+
 check: s_lock_test
 	./s_lock_test
 
-clean distclean maintainer-clean:
+clean distclean:
 	rm -f s_lock_test
+
+maintainer-clean: clean
+	rm -f lwlocknames.h lwlocknames.c

src/backend/storage/lmgr/generate-lwlocknames.pl

@@ -0,0 +1,67 @@
+#!/usr/bin/perl
+#
+# Generate lwlocknames.h and lwlocknames.c from lwlocknames.txt
+# Copyright (c) 2000-2015, PostgreSQL Global Development Group
+
+use warnings;
+use strict;
+
+my $lastlockidx = -1;
+my $continue = "\n";
+
+open my $lwlocknames, $ARGV[0] or die;
+
+# Include PID in suffix in case parallel make runs this multiple times.
+my $htmp = "lwlocknames.h.tmp$$";
+my $ctmp = "lwlocknames.c.tmp$$";
+open H, '>', $htmp or die "Could not open $htmp: $!";
+open C, '>', $ctmp or die "Could not open $ctmp: $!";
+
+my $autogen =
+	"/* autogenerated from src/backend/storage/lmgr/lwlocknames.txt, do not edit */\n";
+print H $autogen;
+print H "/* there is deliberately not an #ifndef LWLOCKNAMES_H here */\n\n";
+print C $autogen, "\n";
+
+print C "static char *MainLWLockNames[] = {";
+
+while (<$lwlocknames>)
+{
+	chomp;
+
+	# Skip comments
+	next if /^#/;
+	next if /^\s*$/;
+
+	die "unable to parse lwlocknames.txt"
+	  unless /^(\w+)\s+(\d+)$/;
+
+	(my $lockname, my $lockidx) = ($1, $2);
+
+	die "lwlocknames.txt not in order" if $lockidx < $lastlockidx;
+	die "lwlocknames.txt has duplicates" if $lockidx == $lastlockidx;
+
+	while ($lastlockidx < $lockidx - 1)
+	{
+		++$lastlockidx;
+		printf C "%s	\"<unassigned:%d>\"", $continue, $lastlockidx;
+		$continue = ",\n";
+	}
+	printf C "%s	\"%s\"", $continue, $lockname;
+	$lastlockidx = $lockidx;
+	$continue = ",\n";
+
+	print H "#define $lockname (&MainLWLockArray[$lockidx].lock)\n";
+}
+
+printf C "\n};\n";
+print H "\n";
+printf H "#define NUM_INDIVIDUAL_LWLOCKS		%s\n", $lastlockidx + 1;
+
+close H;
+close C;
+
+rename($htmp, 'lwlocknames.h') || die "rename: $htmp: $!";
+rename($ctmp, 'lwlocknames.c') || die "rename: $ctmp: $!";
+
+close $lwlocknames;

src/backend/storage/lmgr/lwlock.c

@@ -95,6 +95,9 @@
 #include "utils/hsearch.h"
 #endif
 
+/* Constants for lwlock names */
+#include "lwlocknames.c"
+
 
 /* We use the ShmemLock spinlock to protect LWLockAssign */
 extern slock_t *ShmemLock;
@@ -183,18 +186,32 @@ PRINT_LWDEBUG(const char *where, LWLock *lock, LWLockMode mode)
 	if (Trace_lwlocks)
 	{
 		uint32		state = pg_atomic_read_u32(&lock->state);
+		int			id = T_ID(lock);
 
-		ereport(LOG,
-				(errhidestmt(true),
-				 errhidecontext(true),
-				 errmsg("%d: %s(%s %d): excl %u shared %u haswaiters %u waiters %u rOK %d",
-						MyProcPid,
-						where, T_NAME(lock), T_ID(lock),
-						!!(state & LW_VAL_EXCLUSIVE),
-						state & LW_SHARED_MASK,
-						!!(state & LW_FLAG_HAS_WAITERS),
-						pg_atomic_read_u32(&lock->nwaiters),
-						!!(state & LW_FLAG_RELEASE_OK))));
+		if (lock->tranche == 0 && id < NUM_INDIVIDUAL_LWLOCKS)
+			ereport(LOG,
+					(errhidestmt(true),
+					 errhidecontext(true),
+					 errmsg("%d: %s(%s): excl %u shared %u haswaiters %u waiters %u rOK %d",
+							MyProcPid,
+							where, MainLWLockNames[id],
+							!!(state & LW_VAL_EXCLUSIVE),
+							state & LW_SHARED_MASK,
+							!!(state & LW_FLAG_HAS_WAITERS),
+							pg_atomic_read_u32(&lock->nwaiters),
+							!!(state & LW_FLAG_RELEASE_OK))));
+		else
+			ereport(LOG,
+					(errhidestmt(true),
+					 errhidecontext(true),
+					 errmsg("%d: %s(%s %d): excl %u shared %u haswaiters %u waiters %u rOK %d",
+							MyProcPid,
+							where, T_NAME(lock), id,
+							!!(state & LW_VAL_EXCLUSIVE),
+							state & LW_SHARED_MASK,
+							!!(state & LW_FLAG_HAS_WAITERS),
+							pg_atomic_read_u32(&lock->nwaiters),
+							!!(state & LW_FLAG_RELEASE_OK))));
 	}
 }
 
@@ -204,11 +221,20 @@ LOG_LWDEBUG(const char *where, LWLock *lock, const char *msg)
 	/* hide statement & context here, otherwise the log is just too verbose */
 	if (Trace_lwlocks)
 	{
-		ereport(LOG,
-				(errhidestmt(true),
-				 errhidecontext(true),
-				 errmsg("%s(%s %d): %s", where,
-						T_NAME(lock), T_ID(lock), msg)));
+		int			id = T_ID(lock);
+
+		if (lock->tranche == 0 && id < NUM_INDIVIDUAL_LWLOCKS)
+			ereport(LOG,
+					(errhidestmt(true),
+					 errhidecontext(true),
+					 errmsg("%s(%s): %s", where,
+							MainLWLockNames[id], msg)));
+		else
+			ereport(LOG,
+					(errhidestmt(true),
+					 errhidecontext(true),
+					 errmsg("%s(%s %d): %s", where,
+							T_NAME(lock), id, msg)));
 	}
 }
 

src/backend/storage/lmgr/lwlocknames.txt

@@ -0,0 +1,47 @@
+# Some commonly-used locks have predefined positions within MainLWLockArray;
+# these are defined here.  If you add a lock, add it to the end to avoid
+# renumbering the existing locks; if you remove a lock, consider leaving a gap
+# in the numbering sequence for the benefit of DTrace and other external
+# debugging scripts.
+
+# 0 is available; was formerly BufFreelistLock
+ShmemIndexLock						1
+OidGenLock							2
+XidGenLock							3
+ProcArrayLock						4
+SInvalReadLock						5
+SInvalWriteLock						6
+WALBufMappingLock					7
+WALWriteLock						8
+ControlFileLock						9
+CheckpointLock						10
+CLogControlLock						11
+SubtransControlLock					12
+MultiXactGenLock					13
+MultiXactOffsetControlLock			14
+MultiXactMemberControlLock			15
+RelCacheInitLock					16
+CheckpointerCommLock				17
+TwoPhaseStateLock					18
+TablespaceCreateLock				19
+BtreeVacuumLock						20
+AddinShmemInitLock					21
+AutovacuumLock						22
+AutovacuumScheduleLock				23
+SyncScanLock						24
+RelationMappingLock					25
+AsyncCtlLock						26
+AsyncQueueLock						27
+SerializableXactHashLock			28
+SerializableFinishedListLock		29
+SerializablePredicateLockListLock	30
+OldSerXidLock						31
+SyncRepLock							32
+BackgroundWorkerLock				33
+DynamicSharedMemoryControlLock		34
+AutoFileLock						35
+ReplicationSlotAllocationLock		36
+ReplicationSlotControlLock			37
+CommitTsControlLock					38
+CommitTsLock						39
+ReplicationOriginLock				40