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Commitc1772ad

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Change the way that LWLocks for extensions are allocated.
The previous RequestAddinLWLocks() method had several disadvantages.First, the locks would be in the main tranche; we've recently decidedthat it's useful for LWLocks used for separate purposes to haveseparate tranche IDs. Second, there wasn't any correlation betweenwhat code called RequestAddinLWLocks() and what code calledLWLockAssign(); when multiple modules are in use, it could becomequite difficult to troubleshoot problems where LWLockAssign() ran outof locks. To fix, create a concept of named LWLock tranches whichcan be used either by extension or by core code.Amit Kapila and Robert Haas
1 parent5ef244a commitc1772ad

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7 files changed

+210
-50
lines changed

7 files changed

+210
-50
lines changed

‎contrib/pg_stat_statements/pg_stat_statements.c‎

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -404,7 +404,7 @@ _PG_init(void)
404404
* resources in pgss_shmem_startup().
405405
*/
406406
RequestAddinShmemSpace(pgss_memsize());
407-
RequestAddinLWLocks(1);
407+
RequestNamedLWLockTranche("pg_stat_statements",1);
408408

409409
/*
410410
* Install hooks.
@@ -480,7 +480,7 @@ pgss_shmem_startup(void)
480480
if (!found)
481481
{
482482
/* First time through ... */
483-
pgss->lock=LWLockAssign();
483+
pgss->lock=&(GetNamedLWLockTranche("pg_stat_statements"))->lock;
484484
pgss->cur_median_usage=ASSUMED_MEDIAN_INIT;
485485
pgss->mean_query_len=ASSUMED_LENGTH_INIT;
486486
SpinLockInit(&pgss->mutex);

‎doc/src/sgml/xfunc.sgml‎

Lines changed: 6 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -3335,9 +3335,12 @@ void RequestAddinShmemSpace(int size)
33353335
<para>
33363336
LWLocks are reserved by calling:
33373337
<programlisting>
3338-
voidRequestAddinLWLocks(intn)
3338+
voidRequestNamedLWLockTranche(const char *tranche_name,intnum_lwlocks)
33393339
</programlisting>
3340-
from <function>_PG_init</>.
3340+
from <function>_PG_init</>. This will ensure that an array of
3341+
<literal>num_lwlocks</> LWLocks is available under the name
3342+
<literal>tranche_name</>. Use <function>GetNamedLWLockTranche</>
3343+
to get a pointer to this array.
33413344
</para>
33423345
<para>
33433346
To avoid possible race-conditions, each backend should use the LWLock
@@ -3356,7 +3359,7 @@ if (!ptr)
33563359
{
33573360
initialize contents of shmem area;
33583361
acquire any requested LWLocks using:
3359-
ptr->mylockid =LWLockAssign();
3362+
ptr->locks =GetNamedLWLockTranche("my tranche name");
33603363
}
33613364
LWLockRelease(AddinShmemInitLock);
33623365
}

‎src/backend/postmaster/postmaster.c‎

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -485,6 +485,8 @@ typedef struct
485485
#ifndefHAVE_SPINLOCKS
486486
PGSemaphoreSpinlockSemaArray;
487487
#endif
488+
intNamedLWLockTrancheRequests;
489+
NamedLWLockTranche*NamedLWLockTrancheArray;
488490
LWLockPadded*MainLWLockArray;
489491
slock_t*ProcStructLock;
490492
PROC_HDR*ProcGlobal;
@@ -5800,6 +5802,8 @@ save_backend_variables(BackendParameters *param, Port *port,
58005802
#ifndefHAVE_SPINLOCKS
58015803
param->SpinlockSemaArray=SpinlockSemaArray;
58025804
#endif
5805+
param->NamedLWLockTrancheRequests=NamedLWLockTrancheRequests;
5806+
param->NamedLWLockTrancheArray=NamedLWLockTrancheArray;
58035807
param->MainLWLockArray=MainLWLockArray;
58045808
param->ProcStructLock=ProcStructLock;
58055809
param->ProcGlobal=ProcGlobal;
@@ -6031,6 +6035,8 @@ restore_backend_variables(BackendParameters *param, Port *port)
60316035
#ifndefHAVE_SPINLOCKS
60326036
SpinlockSemaArray=param->SpinlockSemaArray;
60336037
#endif
6038+
NamedLWLockTrancheRequests=param->NamedLWLockTrancheRequests;
6039+
NamedLWLockTrancheArray=param->NamedLWLockTrancheArray;
60346040
MainLWLockArray=param->MainLWLockArray;
60356041
ProcStructLock=param->ProcStructLock;
60366042
ProcGlobal=param->ProcGlobal;

‎src/backend/storage/lmgr/lwlock.c‎

Lines changed: 177 additions & 35 deletions
Original file line numberDiff line numberDiff line change
@@ -144,8 +144,20 @@ typedef struct LWLockHandle
144144
staticintnum_held_lwlocks=0;
145145
staticLWLockHandleheld_lwlocks[MAX_SIMUL_LWLOCKS];
146146

147-
staticintlock_addin_request=0;
148-
staticboollock_addin_request_allowed= true;
147+
/* struct representing the LWLock tranche request for named tranche */
148+
typedefstructNamedLWLockTrancheRequest
149+
{
150+
chartranche_name[NAMEDATALEN];
151+
intnum_lwlocks;
152+
}NamedLWLockTrancheRequest;
153+
154+
NamedLWLockTrancheRequest*NamedLWLockTrancheRequestArray=NULL;
155+
staticintNamedLWLockTrancheRequestsAllocated=0;
156+
intNamedLWLockTrancheRequests=0;
157+
158+
NamedLWLockTranche*NamedLWLockTrancheArray=NULL;
159+
160+
staticboollock_named_request_allowed= true;
149161

150162
#ifdefLWLOCK_STATS
151163
typedefstructlwlock_stats_key
@@ -335,6 +347,22 @@ get_lwlock_stats_entry(LWLock *lock)
335347
#endif/* LWLOCK_STATS */
336348

337349

350+
/*
351+
* Compute number of LWLocks required by named tranches. These will be
352+
* allocated in the main array.
353+
*/
354+
staticint
355+
NumLWLocksByNamedTranches(void)
356+
{
357+
intnumLocks=0;
358+
inti;
359+
360+
for (i=0;i<NamedLWLockTrancheRequests;i++)
361+
numLocks+=NamedLWLockTrancheRequestArray[i].num_lwlocks;
362+
363+
returnnumLocks;
364+
}
365+
338366
/*
339367
* Compute number of LWLocks to allocate in the main array.
340368
*/
@@ -353,64 +381,49 @@ NumLWLocks(void)
353381
/* Predefined LWLocks */
354382
numLocks=NUM_FIXED_LWLOCKS;
355383

356-
/*
357-
* Add any requested by loadable modules; for backwards-compatibility
358-
* reasons, allocate at least NUM_USER_DEFINED_LWLOCKS of them even if
359-
* there are no explicit requests.
360-
*/
361-
lock_addin_request_allowed= false;
362-
numLocks+=Max(lock_addin_request,NUM_USER_DEFINED_LWLOCKS);
384+
/* Disallow named LWLocks' requests after startup */
385+
lock_named_request_allowed= false;
363386

364387
returnnumLocks;
365388
}
366389

367-
368-
/*
369-
* RequestAddinLWLocks
370-
*Request that extra LWLocks be allocated for use by
371-
*a loadable module.
372-
*
373-
* This is only useful if called from the _PG_init hook of a library that
374-
* is loaded into the postmaster via shared_preload_libraries. Once
375-
* shared memory has been allocated, calls will be ignored. (We could
376-
* raise an error, but it seems better to make it a no-op, so that
377-
* libraries containing such calls can be reloaded if needed.)
378-
*/
379-
void
380-
RequestAddinLWLocks(intn)
381-
{
382-
if (IsUnderPostmaster|| !lock_addin_request_allowed)
383-
return;/* too late */
384-
lock_addin_request+=n;
385-
}
386-
387-
388390
/*
389-
* Compute shmem space needed for LWLocks.
391+
* Compute shmem space needed for LWLocks and named tranches.
390392
*/
391393
Size
392394
LWLockShmemSize(void)
393395
{
394396
Sizesize;
397+
inti;
395398
intnumLocks=NumLWLocks();
396399

400+
numLocks+=NumLWLocksByNamedTranches();
401+
397402
/* Space for the LWLock array. */
398403
size=mul_size(numLocks,sizeof(LWLockPadded));
399404

400405
/* Space for dynamic allocation counter, plus room for alignment. */
401406
size=add_size(size,3*sizeof(int)+LWLOCK_PADDED_SIZE);
402407

408+
/* space for named tranches. */
409+
size=add_size(size,mul_size(NamedLWLockTrancheRequests,sizeof(NamedLWLockTranche)));
410+
411+
/* space for name of each tranche. */
412+
for (i=0;i<NamedLWLockTrancheRequests;i++)
413+
size=add_size(size,strlen(NamedLWLockTrancheRequestArray[i].tranche_name)+1);
414+
403415
returnsize;
404416
}
405417

406-
407418
/*
408-
* Allocate shmem space for the main LWLock array andinitialize it. We also
409-
* register the maintranch here.
419+
* Allocate shmem space for the main LWLock array andnamed tranches and
420+
*initialize it. We alsoregister the mainand named tranche here.
410421
*/
411422
void
412423
CreateLWLocks(void)
413424
{
425+
inti;
426+
414427
StaticAssertExpr(LW_VAL_EXCLUSIVE> (uint32)MAX_BACKENDS,
415428
"MAX_BACKENDS too big for lwlock.c");
416429

@@ -421,11 +434,13 @@ CreateLWLocks(void)
421434
if (!IsUnderPostmaster)
422435
{
423436
intnumLocks=NumLWLocks();
437+
intnumNamedLocks=NumLWLocksByNamedTranches();
424438
SizespaceLocks=LWLockShmemSize();
425439
LWLockPadded*lock;
426440
int*LWLockCounter;
427441
char*ptr;
428442
intid;
443+
intj;
429444

430445
/* Allocate space */
431446
ptr= (char*)ShmemAlloc(spaceLocks);
@@ -438,7 +453,7 @@ CreateLWLocks(void)
438453

439454
MainLWLockArray= (LWLockPadded*)ptr;
440455

441-
/* Initialize all LWLocks in main array */
456+
/* Initialize allfixedLWLocks in main array */
442457
for (id=0,lock=MainLWLockArray;id<numLocks;id++,lock++)
443458
LWLockInitialize(&lock->lock,LWTRANCHE_MAIN);
444459

@@ -453,6 +468,40 @@ CreateLWLocks(void)
453468
LWLockCounter[0]=NUM_FIXED_LWLOCKS;
454469
LWLockCounter[1]=numLocks;
455470
LWLockCounter[2]=LWTRANCHE_FIRST_USER_DEFINED;
471+
472+
/* Initialize named tranches. */
473+
if (NamedLWLockTrancheRequests>0)
474+
{
475+
char*trancheNames;
476+
477+
NamedLWLockTrancheArray= (NamedLWLockTranche*)
478+
&MainLWLockArray[numLocks+numNamedLocks];
479+
480+
trancheNames= (char*)NamedLWLockTrancheArray+
481+
(NamedLWLockTrancheRequests*sizeof(NamedLWLockTranche));
482+
lock=&MainLWLockArray[numLocks];
483+
484+
for (i=0;i<NamedLWLockTrancheRequests;i++)
485+
{
486+
NamedLWLockTrancheRequest*request;
487+
NamedLWLockTranche*tranche;
488+
char*name;
489+
490+
request=&NamedLWLockTrancheRequestArray[i];
491+
tranche=&NamedLWLockTrancheArray[i];
492+
493+
name=trancheNames;
494+
trancheNames+=strlen(request->tranche_name)+1;
495+
strcpy(name,request->tranche_name);
496+
tranche->lwLockTranche.name=name;
497+
tranche->trancheId=LWLockNewTrancheId();
498+
tranche->lwLockTranche.array_base=lock;
499+
tranche->lwLockTranche.array_stride=sizeof(LWLockPadded);
500+
501+
for (j=0;j<request->num_lwlocks;j++,lock++)
502+
LWLockInitialize(&lock->lock,tranche->trancheId);
503+
}
504+
}
456505
}
457506

458507
if (LWLockTrancheArray==NULL)
@@ -468,6 +517,11 @@ CreateLWLocks(void)
468517
MainLWLockTranche.array_base=MainLWLockArray;
469518
MainLWLockTranche.array_stride=sizeof(LWLockPadded);
470519
LWLockRegisterTranche(LWTRANCHE_MAIN,&MainLWLockTranche);
520+
521+
/* Register named tranches. */
522+
for (i=0;i<NamedLWLockTrancheRequests;i++)
523+
LWLockRegisterTranche(NamedLWLockTrancheArray[i].trancheId,
524+
&NamedLWLockTrancheArray[i].lwLockTranche);
471525
}
472526

473527
/*
@@ -507,6 +561,45 @@ LWLockAssign(void)
507561
returnresult;
508562
}
509563

564+
/*
565+
* GetNamedLWLockTranche - returns the base address of LWLock from the
566+
*specified tranche.
567+
*
568+
* Caller needs to retrieve the requested number of LWLocks starting from
569+
* the base lock address returned by this API. This can be used for
570+
* tranches that are requested by using RequestNamedLWLockTranche() API.
571+
*/
572+
LWLockPadded*
573+
GetNamedLWLockTranche(constchar*tranche_name)
574+
{
575+
intlock_pos;
576+
inti;
577+
int*LWLockCounter;
578+
579+
LWLockCounter= (int*) ((char*)MainLWLockArray-3*sizeof(int));
580+
581+
/*
582+
* Obtain the position of base address of LWLock belonging to requested
583+
* tranche_name in MainLWLockArray. LWLocks for named tranches are placed
584+
* in MainLWLockArray after LWLocks specified by LWLockCounter[1].
585+
*/
586+
lock_pos=LWLockCounter[1];
587+
for (i=0;i<NamedLWLockTrancheRequests;i++)
588+
{
589+
if (strcmp(NamedLWLockTrancheRequestArray[i].tranche_name,
590+
tranche_name)==0)
591+
return&MainLWLockArray[lock_pos];
592+
593+
lock_pos+=NamedLWLockTrancheRequestArray[i].num_lwlocks;
594+
}
595+
596+
if (i >=NamedLWLockTrancheRequests)
597+
elog(ERROR,"requested tranche is not registered");
598+
599+
/* just to keep compiler quiet */
600+
returnNULL;
601+
}
602+
510603
/*
511604
* Allocate a new tranche ID.
512605
*/
@@ -551,6 +644,55 @@ LWLockRegisterTranche(int tranche_id, LWLockTranche *tranche)
551644
LWLockTrancheArray[tranche_id]=tranche;
552645
}
553646

647+
/*
648+
* RequestNamedLWLockTranche
649+
*Request that extra LWLocks be allocated during postmaster
650+
*startup.
651+
*
652+
* This is only useful for extensions if called from the _PG_init hook
653+
* of a library that is loaded into the postmaster via
654+
* shared_preload_libraries. Once shared memory has been allocated, calls
655+
* will be ignored. (We could raise an error, but it seems better to make
656+
* it a no-op, so that libraries containing such calls can be reloaded if
657+
* needed.)
658+
*/
659+
void
660+
RequestNamedLWLockTranche(constchar*tranche_name,intnum_lwlocks)
661+
{
662+
NamedLWLockTrancheRequest*request;
663+
664+
if (IsUnderPostmaster|| !lock_named_request_allowed)
665+
return;/* too late */
666+
667+
if (NamedLWLockTrancheRequestArray==NULL)
668+
{
669+
NamedLWLockTrancheRequestsAllocated=16;
670+
NamedLWLockTrancheRequestArray= (NamedLWLockTrancheRequest*)
671+
MemoryContextAlloc(TopMemoryContext,
672+
NamedLWLockTrancheRequestsAllocated
673+
*sizeof(NamedLWLockTrancheRequest));
674+
}
675+
676+
if (NamedLWLockTrancheRequests >=NamedLWLockTrancheRequestsAllocated)
677+
{
678+
inti=NamedLWLockTrancheRequestsAllocated;
679+
680+
while (i <=NamedLWLockTrancheRequests)
681+
i *=2;
682+
683+
NamedLWLockTrancheRequestArray= (NamedLWLockTrancheRequest*)
684+
repalloc(NamedLWLockTrancheRequestArray,
685+
i*sizeof(NamedLWLockTrancheRequest));
686+
NamedLWLockTrancheRequestsAllocated=i;
687+
}
688+
689+
request=&NamedLWLockTrancheRequestArray[NamedLWLockTrancheRequests];
690+
Assert(strlen(tranche_name)+1<NAMEDATALEN);
691+
StrNCpy(request->tranche_name,tranche_name,NAMEDATALEN);
692+
request->num_lwlocks=num_lwlocks;
693+
NamedLWLockTrancheRequests++;
694+
}
695+
554696
/*
555697
* LWLockInitialize - initialize a new lwlock; it's initially unlocked
556698
*/

‎src/include/pg_config_manual.h‎

Lines changed: 0 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -51,11 +51,6 @@
5151
#defineSEQ_MAXVALUEPG_INT64_MAX
5252
#defineSEQ_MINVALUE(-SEQ_MAXVALUE)
5353

54-
/*
55-
* Number of spare LWLocks to allocate for user-defined add-on code.
56-
*/
57-
#defineNUM_USER_DEFINED_LWLOCKS4
58-
5954
/*
6055
* When we don't have native spinlocks, we use semaphores to simulate them.
6156
* Decreasing this value reduces consumption of OS resources; increasing it

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