summaryrefslogtreecommitdiffstats
path: root/src/backend/utils/adt/lockfuncs.c
blob: 5dc0a5882cf602356b04ed024d3a9e8db6a314bd (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
/*-------------------------------------------------------------------------
 *
 * lockfuncs.c
 *		Functions for SQL access to various lock-manager capabilities.
 *
 * Copyright (c) 2002-2021, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *		src/backend/utils/adt/lockfuncs.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/htup_details.h"
#include "access/xact.h"
#include "catalog/pg_type.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "storage/predicate_internals.h"
#include "utils/array.h"
#include "utils/builtins.h"


/*
 * This must match enum LockTagType!  Also, be sure to document any changes
 * in the docs for the pg_locks view and for wait event types.
 */
const char *const LockTagTypeNames[] = {
	"relation",
	"extend",
	"frozenid",
	"page",
	"tuple",
	"transactionid",
	"virtualxid",
	"spectoken",
	"object",
	"userlock",
	"advisory"
};

StaticAssertDecl(lengthof(LockTagTypeNames) == (LOCKTAG_ADVISORY + 1),
				 "array length mismatch");

/* This must match enum PredicateLockTargetType (predicate_internals.h) */
static const char *const PredicateLockTagTypeNames[] = {
	"relation",
	"page",
	"tuple"
};

StaticAssertDecl(lengthof(PredicateLockTagTypeNames) == (PREDLOCKTAG_TUPLE + 1),
				 "array length mismatch");

/* Working status for pg_lock_status */
typedef struct
{
	LockData   *lockData;		/* state data from lmgr */
	int			currIdx;		/* current PROCLOCK index */
	PredicateLockData *predLockData;	/* state data for pred locks */
	int			predLockIdx;	/* current index for pred lock */
} PG_Lock_Status;

/* Number of columns in pg_locks output */
#define NUM_LOCK_STATUS_COLUMNS		16

/*
 * VXIDGetDatum - Construct a text representation of a VXID
 *
 * This is currently only used in pg_lock_status, so we put it here.
 */
static Datum
VXIDGetDatum(BackendId bid, LocalTransactionId lxid)
{
	/*
	 * The representation is "<bid>/<lxid>", decimal and unsigned decimal
	 * respectively.  Note that elog.c also knows how to format a vxid.
	 */
	char		vxidstr[32];

	snprintf(vxidstr, sizeof(vxidstr), "%d/%u", bid, lxid);

	return CStringGetTextDatum(vxidstr);
}


/*
 * pg_lock_status - produce a view with one row per held or awaited lock mode
 */
Datum
pg_lock_status(PG_FUNCTION_ARGS)
{
	FuncCallContext *funcctx;
	PG_Lock_Status *mystatus;
	LockData   *lockData;
	PredicateLockData *predLockData;

	if (SRF_IS_FIRSTCALL())
	{
		TupleDesc	tupdesc;
		MemoryContext oldcontext;

		/* create a function context for cross-call persistence */
		funcctx = SRF_FIRSTCALL_INIT();

		/*
		 * switch to memory context appropriate for multiple function calls
		 */
		oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);

		/* build tupdesc for result tuples */
		/* this had better match function's declaration in pg_proc.h */
		tupdesc = CreateTemplateTupleDesc(NUM_LOCK_STATUS_COLUMNS);
		TupleDescInitEntry(tupdesc, (AttrNumber) 1, "locktype",
						   TEXTOID, -1, 0);
		TupleDescInitEntry(tupdesc, (AttrNumber) 2, "database",
						   OIDOID, -1, 0);
		TupleDescInitEntry(tupdesc, (AttrNumber) 3, "relation",
						   OIDOID, -1, 0);
		TupleDescInitEntry(tupdesc, (AttrNumber) 4, "page",
						   INT4OID, -1, 0);
		TupleDescInitEntry(tupdesc, (AttrNumber) 5, "tuple",
						   INT2OID, -1, 0);
		TupleDescInitEntry(tupdesc, (AttrNumber) 6, "virtualxid",
						   TEXTOID, -1, 0);
		TupleDescInitEntry(tupdesc, (AttrNumber) 7, "transactionid",
						   XIDOID, -1, 0);
		TupleDescInitEntry(tupdesc, (AttrNumber) 8, "classid",
						   OIDOID, -1, 0);
		TupleDescInitEntry(tupdesc, (AttrNumber) 9, "objid",
						   OIDOID, -1, 0);
		TupleDescInitEntry(tupdesc, (AttrNumber) 10, "objsubid",
						   INT2OID, -1, 0);
		TupleDescInitEntry(tupdesc, (AttrNumber) 11, "virtualtransaction",
						   TEXTOID, -1, 0);
		TupleDescInitEntry(tupdesc, (AttrNumber) 12, "pid",
						   INT4OID, -1, 0);
		TupleDescInitEntry(tupdesc, (AttrNumber) 13, "mode",
						   TEXTOID, -1, 0);
		TupleDescInitEntry(tupdesc, (AttrNumber) 14, "granted",
						   BOOLOID, -1, 0);
		TupleDescInitEntry(tupdesc, (AttrNumber) 15, "fastpath",
						   BOOLOID, -1, 0);
		TupleDescInitEntry(tupdesc, (AttrNumber) 16, "waitstart",
						   TIMESTAMPTZOID, -1, 0);

		funcctx->tuple_desc = BlessTupleDesc(tupdesc);

		/*
		 * Collect all the locking information that we will format and send
		 * out as a result set.
		 */
		mystatus = (PG_Lock_Status *) palloc(sizeof(PG_Lock_Status));
		funcctx->user_fctx = (void *) mystatus;

		mystatus->lockData = GetLockStatusData();
		mystatus->currIdx = 0;
		mystatus->predLockData = GetPredicateLockStatusData();
		mystatus->predLockIdx = 0;

		MemoryContextSwitchTo(oldcontext);
	}

	funcctx = SRF_PERCALL_SETUP();
	mystatus = (PG_Lock_Status *) funcctx->user_fctx;
	lockData = mystatus->lockData;

	while (mystatus->currIdx < lockData->nelements)
	{
		bool		granted;
		LOCKMODE	mode = 0;
		const char *locktypename;
		char		tnbuf[32];
		Datum		values[NUM_LOCK_STATUS_COLUMNS];
		bool		nulls[NUM_LOCK_STATUS_COLUMNS];
		HeapTuple	tuple;
		Datum		result;
		LockInstanceData *instance;

		instance = &(lockData->locks[mystatus->currIdx]);

		/*
		 * Look to see if there are any held lock modes in this PROCLOCK. If
		 * so, report, and destructively modify lockData so we don't report
		 * again.
		 */
		granted = false;
		if (instance->holdMask)
		{
			for (mode = 0; mode < MAX_LOCKMODES; mode++)
			{
				if (instance->holdMask & LOCKBIT_ON(mode))
				{
					granted = true;
					instance->holdMask &= LOCKBIT_OFF(mode);
					break;
				}
			}
		}

		/*
		 * If no (more) held modes to report, see if PROC is waiting for a
		 * lock on this lock.
		 */
		if (!granted)
		{
			if (instance->waitLockMode != NoLock)
			{
				/* Yes, so report it with proper mode */
				mode = instance->waitLockMode;

				/*
				 * We are now done with this PROCLOCK, so advance pointer to
				 * continue with next one on next call.
				 */
				mystatus->currIdx++;
			}
			else
			{
				/*
				 * Okay, we've displayed all the locks associated with this
				 * PROCLOCK, proceed to the next one.
				 */
				mystatus->currIdx++;
				continue;
			}
		}

		/*
		 * Form tuple with appropriate data.
		 */
		MemSet(values, 0, sizeof(values));
		MemSet(nulls, false, sizeof(nulls));

		if (instance->locktag.locktag_type <= LOCKTAG_LAST_TYPE)
			locktypename = LockTagTypeNames[instance->locktag.locktag_type];
		else
		{
			snprintf(tnbuf, sizeof(tnbuf), "unknown %d",
					 (int) instance->locktag.locktag_type);
			locktypename = tnbuf;
		}
		values[0] = CStringGetTextDatum(locktypename);

		switch ((LockTagType) instance->locktag.locktag_type)
		{
			case LOCKTAG_RELATION:
			case LOCKTAG_RELATION_EXTEND:
				values[1] = ObjectIdGetDatum(instance->locktag.locktag_field1);
				values[2] = ObjectIdGetDatum(instance->locktag.locktag_field2);
				nulls[3] = true;
				nulls[4] = true;
				nulls[5] = true;
				nulls[6] = true;
				nulls[7] = true;
				nulls[8] = true;
				nulls[9] = true;
				break;
			case LOCKTAG_DATABASE_FROZEN_IDS:
				values[1] = ObjectIdGetDatum(instance->locktag.locktag_field1);
				nulls[2] = true;
				nulls[3] = true;
				nulls[4] = true;
				nulls[5] = true;
				nulls[6] = true;
				nulls[7] = true;
				nulls[8] = true;
				nulls[9] = true;
				break;
			case LOCKTAG_PAGE:
				values[1] = ObjectIdGetDatum(instance->locktag.locktag_field1);
				values[2] = ObjectIdGetDatum(instance->locktag.locktag_field2);
				values[3] = UInt32GetDatum(instance->locktag.locktag_field3);
				nulls[4] = true;
				nulls[5] = true;
				nulls[6] = true;
				nulls[7] = true;
				nulls[8] = true;
				nulls[9] = true;
				break;
			case LOCKTAG_TUPLE:
				values[1] = ObjectIdGetDatum(instance->locktag.locktag_field1);
				values[2] = ObjectIdGetDatum(instance->locktag.locktag_field2);
				values[3] = UInt32GetDatum(instance->locktag.locktag_field3);
				values[4] = UInt16GetDatum(instance->locktag.locktag_field4);
				nulls[5] = true;
				nulls[6] = true;
				nulls[7] = true;
				nulls[8] = true;
				nulls[9] = true;
				break;
			case LOCKTAG_TRANSACTION:
				values[6] =
					TransactionIdGetDatum(instance->locktag.locktag_field1);
				nulls[1] = true;
				nulls[2] = true;
				nulls[3] = true;
				nulls[4] = true;
				nulls[5] = true;
				nulls[7] = true;
				nulls[8] = true;
				nulls[9] = true;
				break;
			case LOCKTAG_VIRTUALTRANSACTION:
				values[5] = VXIDGetDatum(instance->locktag.locktag_field1,
										 instance->locktag.locktag_field2);
				nulls[1] = true;
				nulls[2] = true;
				nulls[3] = true;
				nulls[4] = true;
				nulls[6] = true;
				nulls[7] = true;
				nulls[8] = true;
				nulls[9] = true;
				break;
			case LOCKTAG_OBJECT:
			case LOCKTAG_USERLOCK:
			case LOCKTAG_ADVISORY:
			default:			/* treat unknown locktags like OBJECT */
				values[1] = ObjectIdGetDatum(instance->locktag.locktag_field1);
				values[7] = ObjectIdGetDatum(instance->locktag.locktag_field2);
				values[8] = ObjectIdGetDatum(instance->locktag.locktag_field3);
				values[9] = Int16GetDatum(instance->locktag.locktag_field4);
				nulls[2] = true;
				nulls[3] = true;
				nulls[4] = true;
				nulls[5] = true;
				nulls[6] = true;
				break;
		}

		values[10] = VXIDGetDatum(instance->backend, instance->lxid);
		if (instance->pid != 0)
			values[11] = Int32GetDatum(instance->pid);
		else
			nulls[11] = true;
		values[12] = CStringGetTextDatum(GetLockmodeName(instance->locktag.locktag_lockmethodid, mode));
		values[13] = BoolGetDatum(granted);
		values[14] = BoolGetDatum(instance->fastpath);
		if (!granted && instance->waitStart != 0)
			values[15] = TimestampTzGetDatum(instance->waitStart);
		else
			nulls[15] = true;

		tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
		result = HeapTupleGetDatum(tuple);
		SRF_RETURN_NEXT(funcctx, result);
	}

	/*
	 * Have returned all regular locks. Now start on the SIREAD predicate
	 * locks.
	 */
	predLockData = mystatus->predLockData;
	if (mystatus->predLockIdx < predLockData->nelements)
	{
		PredicateLockTargetType lockType;

		PREDICATELOCKTARGETTAG *predTag = &(predLockData->locktags[mystatus->predLockIdx]);
		SERIALIZABLEXACT *xact = &(predLockData->xacts[mystatus->predLockIdx]);
		Datum		values[NUM_LOCK_STATUS_COLUMNS];
		bool		nulls[NUM_LOCK_STATUS_COLUMNS];
		HeapTuple	tuple;
		Datum		result;

		mystatus->predLockIdx++;

		/*
		 * Form tuple with appropriate data.
		 */
		MemSet(values, 0, sizeof(values));
		MemSet(nulls, false, sizeof(nulls));

		/* lock type */
		lockType = GET_PREDICATELOCKTARGETTAG_TYPE(*predTag);

		values[0] = CStringGetTextDatum(PredicateLockTagTypeNames[lockType]);

		/* lock target */
		values[1] = GET_PREDICATELOCKTARGETTAG_DB(*predTag);
		values[2] = GET_PREDICATELOCKTARGETTAG_RELATION(*predTag);
		if (lockType == PREDLOCKTAG_TUPLE)
			values[4] = GET_PREDICATELOCKTARGETTAG_OFFSET(*predTag);
		else
			nulls[4] = true;
		if ((lockType == PREDLOCKTAG_TUPLE) ||
			(lockType == PREDLOCKTAG_PAGE))
			values[3] = GET_PREDICATELOCKTARGETTAG_PAGE(*predTag);
		else
			nulls[3] = true;

		/* these fields are targets for other types of locks */
		nulls[5] = true;		/* virtualxid */
		nulls[6] = true;		/* transactionid */
		nulls[7] = true;		/* classid */
		nulls[8] = true;		/* objid */
		nulls[9] = true;		/* objsubid */

		/* lock holder */
		values[10] = VXIDGetDatum(xact->vxid.backendId,
								  xact->vxid.localTransactionId);
		if (xact->pid != 0)
			values[11] = Int32GetDatum(xact->pid);
		else
			nulls[11] = true;

		/*
		 * Lock mode. Currently all predicate locks are SIReadLocks, which are
		 * always held (never waiting) and have no fast path
		 */
		values[12] = CStringGetTextDatum("SIReadLock");
		values[13] = BoolGetDatum(true);
		values[14] = BoolGetDatum(false);
		nulls[15] = true;

		tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
		result = HeapTupleGetDatum(tuple);
		SRF_RETURN_NEXT(funcctx, result);
	}

	SRF_RETURN_DONE(funcctx);
}


/*
 * pg_blocking_pids - produce an array of the PIDs blocking given PID
 *
 * The reported PIDs are those that hold a lock conflicting with blocked_pid's
 * current request (hard block), or are requesting such a lock and are ahead
 * of blocked_pid in the lock's wait queue (soft block).
 *
 * In parallel-query cases, we report all PIDs blocking any member of the
 * given PID's lock group, and the reported PIDs are those of the blocking
 * PIDs' lock group leaders.  This allows callers to compare the result to
 * lists of clients' pg_backend_pid() results even during a parallel query.
 *
 * Parallel query makes it possible for there to be duplicate PIDs in the
 * result (either because multiple waiters are blocked by same PID, or
 * because multiple blockers have same group leader PID).  We do not bother
 * to eliminate such duplicates from the result.
 *
 * We need not consider predicate locks here, since those don't block anything.
 */
Datum
pg_blocking_pids(PG_FUNCTION_ARGS)
{
	int			blocked_pid = PG_GETARG_INT32(0);
	Datum	   *arrayelems;
	int			narrayelems;
	BlockedProcsData *lockData; /* state data from lmgr */
	int			i,
				j;

	/* Collect a snapshot of lock manager state */
	lockData = GetBlockerStatusData(blocked_pid);

	/* We can't need more output entries than there are reported PROCLOCKs */
	arrayelems = (Datum *) palloc(lockData->nlocks * sizeof(Datum));
	narrayelems = 0;

	/* For each blocked proc in the lock group ... */
	for (i = 0; i < lockData->nprocs; i++)
	{
		BlockedProcData *bproc = &lockData->procs[i];
		LockInstanceData *instances = &lockData->locks[bproc->first_lock];
		int		   *preceding_waiters = &lockData->waiter_pids[bproc->first_waiter];
		LockInstanceData *blocked_instance;
		LockMethod	lockMethodTable;
		int			conflictMask;

		/*
		 * Locate the blocked proc's own entry in the LockInstanceData array.
		 * There should be exactly one matching entry.
		 */
		blocked_instance = NULL;
		for (j = 0; j < bproc->num_locks; j++)
		{
			LockInstanceData *instance = &(instances[j]);

			if (instance->pid == bproc->pid)
			{
				Assert(blocked_instance == NULL);
				blocked_instance = instance;
			}
		}
		Assert(blocked_instance != NULL);

		lockMethodTable = GetLockTagsMethodTable(&(blocked_instance->locktag));
		conflictMask = lockMethodTable->conflictTab[blocked_instance->waitLockMode];

		/* Now scan the PROCLOCK data for conflicting procs */
		for (j = 0; j < bproc->num_locks; j++)
		{
			LockInstanceData *instance = &(instances[j]);

			/* A proc never blocks itself, so ignore that entry */
			if (instance == blocked_instance)
				continue;
			/* Members of same lock group never block each other, either */
			if (instance->leaderPid == blocked_instance->leaderPid)
				continue;

			if (conflictMask & instance->holdMask)
			{
				/* hard block: blocked by lock already held by this entry */
			}
			else if (instance->waitLockMode != NoLock &&
					 (conflictMask & LOCKBIT_ON(instance->waitLockMode)))
			{
				/* conflict in lock requests; who's in front in wait queue? */
				bool		ahead = false;
				int			k;

				for (k = 0; k < bproc->num_waiters; k++)
				{
					if (preceding_waiters[k] == instance->pid)
					{
						/* soft block: this entry is ahead of blocked proc */
						ahead = true;
						break;
					}
				}
				if (!ahead)
					continue;	/* not blocked by this entry */
			}
			else
			{
				/* not blocked by this entry */
				continue;
			}

			/* blocked by this entry, so emit a record */
			arrayelems[narrayelems++] = Int32GetDatum(instance->leaderPid);
		}
	}

	/* Assert we didn't overrun arrayelems[] */
	Assert(narrayelems <= lockData->nlocks);

	/* Construct array, using hardwired knowledge about int4 type */
	PG_RETURN_ARRAYTYPE_P(construct_array(arrayelems, narrayelems,
										  INT4OID,
										  sizeof(int32), true, TYPALIGN_INT));
}


/*
 * pg_safe_snapshot_blocking_pids - produce an array of the PIDs blocking
 * given PID from getting a safe snapshot
 *
 * XXX this does not consider parallel-query cases; not clear how big a
 * problem that is in practice
 */
Datum
pg_safe_snapshot_blocking_pids(PG_FUNCTION_ARGS)
{
	int			blocked_pid = PG_GETARG_INT32(0);
	int		   *blockers;
	int			num_blockers;
	Datum	   *blocker_datums;

	/* A buffer big enough for any possible blocker list without truncation */
	blockers = (int *) palloc(MaxBackends * sizeof(int));

	/* Collect a snapshot of processes waited for by GetSafeSnapshot */
	num_blockers =
		GetSafeSnapshotBlockingPids(blocked_pid, blockers, MaxBackends);

	/* Convert int array to Datum array */
	if (num_blockers > 0)
	{
		int			i;

		blocker_datums = (Datum *) palloc(num_blockers * sizeof(Datum));
		for (i = 0; i < num_blockers; ++i)
			blocker_datums[i] = Int32GetDatum(blockers[i]);
	}
	else
		blocker_datums = NULL;

	/* Construct array, using hardwired knowledge about int4 type */
	PG_RETURN_ARRAYTYPE_P(construct_array(blocker_datums, num_blockers,
										  INT4OID,
										  sizeof(int32), true, TYPALIGN_INT));
}


/*
 * pg_isolation_test_session_is_blocked - support function for isolationtester
 *
 * Check if specified PID is blocked by any of the PIDs listed in the second
 * argument.  Currently, this looks for blocking caused by waiting for
 * heavyweight locks or safe snapshots.  We ignore blockage caused by PIDs
 * not directly under the isolationtester's control, eg autovacuum.
 *
 * This is an undocumented function intended for use by the isolation tester,
 * and may change in future releases as required for testing purposes.
 */
Datum
pg_isolation_test_session_is_blocked(PG_FUNCTION_ARGS)
{
	int			blocked_pid = PG_GETARG_INT32(0);
	ArrayType  *interesting_pids_a = PG_GETARG_ARRAYTYPE_P(1);
	ArrayType  *blocking_pids_a;
	int32	   *interesting_pids;
	int32	   *blocking_pids;
	int			num_interesting_pids;
	int			num_blocking_pids;
	int			dummy;
	int			i,
				j;

	/* Validate the passed-in array */
	Assert(ARR_ELEMTYPE(interesting_pids_a) == INT4OID);
	if (array_contains_nulls(interesting_pids_a))
		elog(ERROR, "array must not contain nulls");
	interesting_pids = (int32 *) ARR_DATA_PTR(interesting_pids_a);
	num_interesting_pids = ArrayGetNItems(ARR_NDIM(interesting_pids_a),
										  ARR_DIMS(interesting_pids_a));

	/*
	 * Get the PIDs of all sessions blocking the given session's attempt to
	 * acquire heavyweight locks.
	 */
	blocking_pids_a =
		DatumGetArrayTypeP(DirectFunctionCall1(pg_blocking_pids, blocked_pid));

	Assert(ARR_ELEMTYPE(blocking_pids_a) == INT4OID);
	Assert(!array_contains_nulls(blocking_pids_a));
	blocking_pids = (int32 *) ARR_DATA_PTR(blocking_pids_a);
	num_blocking_pids = ArrayGetNItems(ARR_NDIM(blocking_pids_a),
									   ARR_DIMS(blocking_pids_a));

	/*
	 * Check if any of these are in the list of interesting PIDs, that being
	 * the sessions that the isolation tester is running.  We don't use
	 * "arrayoverlaps" here, because it would lead to cache lookups and one of
	 * our goals is to run quickly with debug_discard_caches > 0.  We expect
	 * blocking_pids to be usually empty and otherwise a very small number in
	 * isolation tester cases, so make that the outer loop of a naive search
	 * for a match.
	 */
	for (i = 0; i < num_blocking_pids; i++)
		for (j = 0; j < num_interesting_pids; j++)
		{
			if (blocking_pids[i] == interesting_pids[j])
				PG_RETURN_BOOL(true);
		}

	/*
	 * Check if blocked_pid is waiting for a safe snapshot.  We could in
	 * theory check the resulting array of blocker PIDs against the
	 * interesting PIDs list, but since there is no danger of autovacuum
	 * blocking GetSafeSnapshot there seems to be no point in expending cycles
	 * on allocating a buffer and searching for overlap; so it's presently
	 * sufficient for the isolation tester's purposes to use a single element
	 * buffer and check if the number of safe snapshot blockers is non-zero.
	 */
	if (GetSafeSnapshotBlockingPids(blocked_pid, &dummy, 1) > 0)
		PG_RETURN_BOOL(true);

	PG_RETURN_BOOL(false);
}


/*
 * Functions for manipulating advisory locks
 *
 * We make use of the locktag fields as follows:
 *
 *	field1: MyDatabaseId ... ensures locks are local to each database
 *	field2: first of 2 int4 keys, or high-order half of an int8 key
 *	field3: second of 2 int4 keys, or low-order half of an int8 key
 *	field4: 1 if using an int8 key, 2 if using 2 int4 keys
 */
#define SET_LOCKTAG_INT64(tag, key64) \
	SET_LOCKTAG_ADVISORY(tag, \
						 MyDatabaseId, \
						 (uint32) ((key64) >> 32), \
						 (uint32) (key64), \
						 1)
#define SET_LOCKTAG_INT32(tag, key1, key2) \
	SET_LOCKTAG_ADVISORY(tag, MyDatabaseId, key1, key2, 2)

/*
 * pg_advisory_lock(int8) - acquire exclusive lock on an int8 key
 */
Datum
pg_advisory_lock_int8(PG_FUNCTION_ARGS)
{
	int64		key = PG_GETARG_INT64(0);
	LOCKTAG		tag;

	SET_LOCKTAG_INT64(tag, key);

	(void) LockAcquire(&tag, ExclusiveLock, true, false);

	PG_RETURN_VOID();
}

/*
 * pg_advisory_xact_lock(int8) - acquire xact scoped
 * exclusive lock on an int8 key
 */
Datum
pg_advisory_xact_lock_int8(PG_FUNCTION_ARGS)
{
	int64		key = PG_GETARG_INT64(0);
	LOCKTAG		tag;

	SET_LOCKTAG_INT64(tag, key);

	(void) LockAcquire(&tag, ExclusiveLock, false, false);

	PG_RETURN_VOID();
}

/*
 * pg_advisory_lock_shared(int8) - acquire share lock on an int8 key
 */
Datum
pg_advisory_lock_shared_int8(PG_FUNCTION_ARGS)
{
	int64		key = PG_GETARG_INT64(0);
	LOCKTAG		tag;

	SET_LOCKTAG_INT64(tag, key);

	(void) LockAcquire(&tag, ShareLock, true, false);

	PG_RETURN_VOID();
}

/*
 * pg_advisory_xact_lock_shared(int8) - acquire xact scoped
 * share lock on an int8 key
 */
Datum
pg_advisory_xact_lock_shared_int8(PG_FUNCTION_ARGS)
{
	int64		key = PG_GETARG_INT64(0);
	LOCKTAG		tag;

	SET_LOCKTAG_INT64(tag, key);

	(void) LockAcquire(&tag, ShareLock, false, false);

	PG_RETURN_VOID();
}

/*
 * pg_try_advisory_lock(int8) - acquire exclusive lock on an int8 key, no wait
 *
 * Returns true if successful, false if lock not available
 */
Datum
pg_try_advisory_lock_int8(PG_FUNCTION_ARGS)
{
	int64		key = PG_GETARG_INT64(0);
	LOCKTAG		tag;
	LockAcquireResult res;

	SET_LOCKTAG_INT64(tag, key);

	res = LockAcquire(&tag, ExclusiveLock, true, true);

	PG_RETURN_BOOL(res != LOCKACQUIRE_NOT_AVAIL);
}

/*
 * pg_try_advisory_xact_lock(int8) - acquire xact scoped
 * exclusive lock on an int8 key, no wait
 *
 * Returns true if successful, false if lock not available
 */
Datum
pg_try_advisory_xact_lock_int8(PG_FUNCTION_ARGS)
{
	int64		key = PG_GETARG_INT64(0);
	LOCKTAG		tag;
	LockAcquireResult res;

	SET_LOCKTAG_INT64(tag, key);

	res = LockAcquire(&tag, ExclusiveLock, false, true);

	PG_RETURN_BOOL(res != LOCKACQUIRE_NOT_AVAIL);
}

/*
 * pg_try_advisory_lock_shared(int8) - acquire share lock on an int8 key, no wait
 *
 * Returns true if successful, false if lock not available
 */
Datum
pg_try_advisory_lock_shared_int8(PG_FUNCTION_ARGS)
{
	int64		key = PG_GETARG_INT64(0);
	LOCKTAG		tag;
	LockAcquireResult res;

	SET_LOCKTAG_INT64(tag, key);

	res = LockAcquire(&tag, ShareLock, true, true);

	PG_RETURN_BOOL(res != LOCKACQUIRE_NOT_AVAIL);
}

/*
 * pg_try_advisory_xact_lock_shared(int8) - acquire xact scoped
 * share lock on an int8 key, no wait
 *
 * Returns true if successful, false if lock not available
 */
Datum
pg_try_advisory_xact_lock_shared_int8(PG_FUNCTION_ARGS)
{
	int64		key = PG_GETARG_INT64(0);
	LOCKTAG		tag;
	LockAcquireResult res;

	SET_LOCKTAG_INT64(tag, key);

	res = LockAcquire(&tag, ShareLock, false, true);

	PG_RETURN_BOOL(res != LOCKACQUIRE_NOT_AVAIL);
}

/*
 * pg_advisory_unlock(int8) - release exclusive lock on an int8 key
 *
 * Returns true if successful, false if lock was not held
*/
Datum
pg_advisory_unlock_int8(PG_FUNCTION_ARGS)
{
	int64		key = PG_GETARG_INT64(0);
	LOCKTAG		tag;
	bool		res;

	SET_LOCKTAG_INT64(tag, key);

	res = LockRelease(&tag, ExclusiveLock, true);

	PG_RETURN_BOOL(res);
}

/*
 * pg_advisory_unlock_shared(int8) - release share lock on an int8 key
 *
 * Returns true if successful, false if lock was not held
 */
Datum
pg_advisory_unlock_shared_int8(PG_FUNCTION_ARGS)
{
	int64		key = PG_GETARG_INT64(0);
	LOCKTAG		tag;
	bool		res;

	SET_LOCKTAG_INT64(tag, key);

	res = LockRelease(&tag, ShareLock, true);

	PG_RETURN_BOOL(res);
}

/*
 * pg_advisory_lock(int4, int4) - acquire exclusive lock on 2 int4 keys
 */
Datum
pg_advisory_lock_int4(PG_FUNCTION_ARGS)
{
	int32		key1 = PG_GETARG_INT32(0);
	int32		key2 = PG_GETARG_INT32(1);
	LOCKTAG		tag;

	SET_LOCKTAG_INT32(tag, key1, key2);

	(void) LockAcquire(&tag, ExclusiveLock, true, false);

	PG_RETURN_VOID();
}

/*
 * pg_advisory_xact_lock(int4, int4) - acquire xact scoped
 * exclusive lock on 2 int4 keys
 */
Datum
pg_advisory_xact_lock_int4(PG_FUNCTION_ARGS)
{
	int32		key1 = PG_GETARG_INT32(0);
	int32		key2 = PG_GETARG_INT32(1);
	LOCKTAG		tag;

	SET_LOCKTAG_INT32(tag, key1, key2);

	(void) LockAcquire(&tag, ExclusiveLock, false, false);

	PG_RETURN_VOID();
}

/*
 * pg_advisory_lock_shared(int4, int4) - acquire share lock on 2 int4 keys
 */
Datum
pg_advisory_lock_shared_int4(PG_FUNCTION_ARGS)
{
	int32		key1 = PG_GETARG_INT32(0);
	int32		key2 = PG_GETARG_INT32(1);
	LOCKTAG		tag;

	SET_LOCKTAG_INT32(tag, key1, key2);

	(void) LockAcquire(&tag, ShareLock, true, false);

	PG_RETURN_VOID();
}

/*
 * pg_advisory_xact_lock_shared(int4, int4) - acquire xact scoped
 * share lock on 2 int4 keys
 */
Datum
pg_advisory_xact_lock_shared_int4(PG_FUNCTION_ARGS)
{
	int32		key1 = PG_GETARG_INT32(0);
	int32		key2 = PG_GETARG_INT32(1);
	LOCKTAG		tag;

	SET_LOCKTAG_INT32(tag, key1, key2);

	(void) LockAcquire(&tag, ShareLock, false, false);

	PG_RETURN_VOID();
}

/*
 * pg_try_advisory_lock(int4, int4) - acquire exclusive lock on 2 int4 keys, no wait
 *
 * Returns true if successful, false if lock not available
 */
Datum
pg_try_advisory_lock_int4(PG_FUNCTION_ARGS)
{
	int32		key1 = PG_GETARG_INT32(0);
	int32		key2 = PG_GETARG_INT32(1);
	LOCKTAG		tag;
	LockAcquireResult res;

	SET_LOCKTAG_INT32(tag, key1, key2);

	res = LockAcquire(&tag, ExclusiveLock, true, true);

	PG_RETURN_BOOL(res != LOCKACQUIRE_NOT_AVAIL);
}

/*
 * pg_try_advisory_xact_lock(int4, int4) - acquire xact scoped
 * exclusive lock on 2 int4 keys, no wait
 *
 * Returns true if successful, false if lock not available
 */
Datum
pg_try_advisory_xact_lock_int4(PG_FUNCTION_ARGS)
{
	int32		key1 = PG_GETARG_INT32(0);
	int32		key2 = PG_GETARG_INT32(1);
	LOCKTAG		tag;
	LockAcquireResult res;

	SET_LOCKTAG_INT32(tag, key1, key2);

	res = LockAcquire(&tag, ExclusiveLock, false, true);

	PG_RETURN_BOOL(res != LOCKACQUIRE_NOT_AVAIL);
}

/*
 * pg_try_advisory_lock_shared(int4, int4) - acquire share lock on 2 int4 keys, no wait
 *
 * Returns true if successful, false if lock not available
 */
Datum
pg_try_advisory_lock_shared_int4(PG_FUNCTION_ARGS)
{
	int32		key1 = PG_GETARG_INT32(0);
	int32		key2 = PG_GETARG_INT32(1);
	LOCKTAG		tag;
	LockAcquireResult res;

	SET_LOCKTAG_INT32(tag, key1, key2);

	res = LockAcquire(&tag, ShareLock, true, true);

	PG_RETURN_BOOL(res != LOCKACQUIRE_NOT_AVAIL);
}

/*
 * pg_try_advisory_xact_lock_shared(int4, int4) - acquire xact scoped
 * share lock on 2 int4 keys, no wait
 *
 * Returns true if successful, false if lock not available
 */
Datum
pg_try_advisory_xact_lock_shared_int4(PG_FUNCTION_ARGS)
{
	int32		key1 = PG_GETARG_INT32(0);
	int32		key2 = PG_GETARG_INT32(1);
	LOCKTAG		tag;
	LockAcquireResult res;

	SET_LOCKTAG_INT32(tag, key1, key2);

	res = LockAcquire(&tag, ShareLock, false, true);

	PG_RETURN_BOOL(res != LOCKACQUIRE_NOT_AVAIL);
}

/*
 * pg_advisory_unlock(int4, int4) - release exclusive lock on 2 int4 keys
 *
 * Returns true if successful, false if lock was not held
*/
Datum
pg_advisory_unlock_int4(PG_FUNCTION_ARGS)
{
	int32		key1 = PG_GETARG_INT32(0);
	int32		key2 = PG_GETARG_INT32(1);
	LOCKTAG		tag;
	bool		res;

	SET_LOCKTAG_INT32(tag, key1, key2);

	res = LockRelease(&tag, ExclusiveLock, true);

	PG_RETURN_BOOL(res);
}

/*
 * pg_advisory_unlock_shared(int4, int4) - release share lock on 2 int4 keys
 *
 * Returns true if successful, false if lock was not held
 */
Datum
pg_advisory_unlock_shared_int4(PG_FUNCTION_ARGS)
{
	int32		key1 = PG_GETARG_INT32(0);
	int32		key2 = PG_GETARG_INT32(1);
	LOCKTAG		tag;
	bool		res;

	SET_LOCKTAG_INT32(tag, key1, key2);

	res = LockRelease(&tag, ShareLock, true);

	PG_RETURN_BOOL(res);
}

/*
 * pg_advisory_unlock_all() - release all advisory locks
 */
Datum
pg_advisory_unlock_all(PG_FUNCTION_ARGS)
{
	LockReleaseSession(USER_LOCKMETHOD);

	PG_RETURN_VOID();
}