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lwlock.c
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1 /*-------------------------------------------------------------------------
2  *
3  * lwlock.c
4  * Lightweight lock manager
5  *
6  * Lightweight locks are intended primarily to provide mutual exclusion of
7  * access to shared-memory data structures. Therefore, they offer both
8  * exclusive and shared lock modes (to support read/write and read-only
9  * access to a shared object). There are few other frammishes. User-level
10  * locking should be done with the full lock manager --- which depends on
11  * LWLocks to protect its shared state.
12  *
13  * In addition to exclusive and shared modes, lightweight locks can be used to
14  * wait until a variable changes value. The variable is initially not set
15  * when the lock is acquired with LWLockAcquire, i.e. it remains set to the
16  * value it was set to when the lock was released last, and can be updated
17  * without releasing the lock by calling LWLockUpdateVar. LWLockWaitForVar
18  * waits for the variable to be updated, or until the lock is free. When
19  * releasing the lock with LWLockReleaseClearVar() the value can be set to an
20  * appropriate value for a free lock. The meaning of the variable is up to
21  * the caller, the lightweight lock code just assigns and compares it.
22  *
23  * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group
24  * Portions Copyright (c) 1994, Regents of the University of California
25  *
26  * IDENTIFICATION
27  * src/backend/storage/lmgr/lwlock.c
28  *
29  * NOTES:
30  *
31  * This used to be a pretty straight forward reader-writer lock
32  * implementation, in which the internal state was protected by a
33  * spinlock. Unfortunately the overhead of taking the spinlock proved to be
34  * too high for workloads/locks that were taken in shared mode very
35  * frequently. Often we were spinning in the (obviously exclusive) spinlock,
36  * while trying to acquire a shared lock that was actually free.
37  *
38  * Thus a new implementation was devised that provides wait-free shared lock
39  * acquisition for locks that aren't exclusively locked.
40  *
41  * The basic idea is to have a single atomic variable 'lockcount' instead of
42  * the formerly separate shared and exclusive counters and to use atomic
43  * operations to acquire the lock. That's fairly easy to do for plain
44  * rw-spinlocks, but a lot harder for something like LWLocks that want to wait
45  * in the OS.
46  *
47  * For lock acquisition we use an atomic compare-and-exchange on the lockcount
48  * variable. For exclusive lock we swap in a sentinel value
49  * (LW_VAL_EXCLUSIVE), for shared locks we count the number of holders.
50  *
51  * To release the lock we use an atomic decrement to release the lock. If the
52  * new value is zero (we get that atomically), we know we can/have to release
53  * waiters.
54  *
55  * Obviously it is important that the sentinel value for exclusive locks
56  * doesn't conflict with the maximum number of possible share lockers -
57  * luckily MAX_BACKENDS makes that easily possible.
58  *
59  *
60  * The attentive reader might have noticed that naively doing the above has a
61  * glaring race condition: We try to lock using the atomic operations and
62  * notice that we have to wait. Unfortunately by the time we have finished
63  * queuing, the former locker very well might have already finished it's
64  * work. That's problematic because we're now stuck waiting inside the OS.
65 
66  * To mitigate those races we use a two phased attempt at locking:
67  * Phase 1: Try to do it atomically, if we succeed, nice
68  * Phase 2: Add ourselves to the waitqueue of the lock
69  * Phase 3: Try to grab the lock again, if we succeed, remove ourselves from
70  * the queue
71  * Phase 4: Sleep till wake-up, goto Phase 1
72  *
73  * This protects us against the problem from above as nobody can release too
74  * quick, before we're queued, since after Phase 2 we're already queued.
75  * -------------------------------------------------------------------------
76  */
77 #include "postgres.h"
78 
79 #include "miscadmin.h"
80 #include "pg_trace.h"
81 #include "pgstat.h"
82 #include "port/pg_bitutils.h"
83 #include "postmaster/postmaster.h"
84 #include "replication/slot.h"
85 #include "storage/ipc.h"
86 #include "storage/predicate.h"
87 #include "storage/proc.h"
88 #include "storage/proclist.h"
89 #include "storage/spin.h"
90 #include "utils/memutils.h"
91 
92 #ifdef LWLOCK_STATS
93 #include "utils/hsearch.h"
94 #endif
95 
96 
97 /* We use the ShmemLock spinlock to protect LWLockCounter */
98 extern slock_t *ShmemLock;
99 
100 #define LW_FLAG_HAS_WAITERS ((uint32) 1 << 30)
101 #define LW_FLAG_RELEASE_OK ((uint32) 1 << 29)
102 #define LW_FLAG_LOCKED ((uint32) 1 << 28)
103 
104 #define LW_VAL_EXCLUSIVE ((uint32) 1 << 24)
105 #define LW_VAL_SHARED 1
106 
107 #define LW_LOCK_MASK ((uint32) ((1 << 25)-1))
108 /* Must be greater than MAX_BACKENDS - which is 2^23-1, so we're fine. */
109 #define LW_SHARED_MASK ((uint32) ((1 << 24)-1))
110 
112  "MAX_BACKENDS too big for lwlock.c");
113 
114 /*
115  * There are three sorts of LWLock "tranches":
116  *
117  * 1. The individually-named locks defined in lwlocknames.h each have their
118  * own tranche. The names of these tranches appear in IndividualLWLockNames[]
119  * in lwlocknames.c.
120  *
121  * 2. There are some predefined tranches for built-in groups of locks.
122  * These are listed in enum BuiltinTrancheIds in lwlock.h, and their names
123  * appear in BuiltinTrancheNames[] below.
124  *
125  * 3. Extensions can create new tranches, via either RequestNamedLWLockTranche
126  * or LWLockRegisterTranche. The names of these that are known in the current
127  * process appear in LWLockTrancheNames[].
128  *
129  * All these names are user-visible as wait event names, so choose with care
130  * ... and do not forget to update the documentation's list of wait events.
131  */
132 extern const char *const IndividualLWLockNames[]; /* in lwlocknames.c */
133 
134 static const char *const BuiltinTrancheNames[] = {
135  /* LWTRANCHE_XACT_BUFFER: */
136  "XactBuffer",
137  /* LWTRANCHE_COMMITTS_BUFFER: */
138  "CommitTsBuffer",
139  /* LWTRANCHE_SUBTRANS_BUFFER: */
140  "SubtransBuffer",
141  /* LWTRANCHE_MULTIXACTOFFSET_BUFFER: */
142  "MultiXactOffsetBuffer",
143  /* LWTRANCHE_MULTIXACTMEMBER_BUFFER: */
144  "MultiXactMemberBuffer",
145  /* LWTRANCHE_NOTIFY_BUFFER: */
146  "NotifyBuffer",
147  /* LWTRANCHE_SERIAL_BUFFER: */
148  "SerialBuffer",
149  /* LWTRANCHE_WAL_INSERT: */
150  "WALInsert",
151  /* LWTRANCHE_BUFFER_CONTENT: */
152  "BufferContent",
153  /* LWTRANCHE_REPLICATION_ORIGIN_STATE: */
154  "ReplicationOriginState",
155  /* LWTRANCHE_REPLICATION_SLOT_IO: */
156  "ReplicationSlotIO",
157  /* LWTRANCHE_LOCK_FASTPATH: */
158  "LockFastPath",
159  /* LWTRANCHE_BUFFER_MAPPING: */
160  "BufferMapping",
161  /* LWTRANCHE_LOCK_MANAGER: */
162  "LockManager",
163  /* LWTRANCHE_PREDICATE_LOCK_MANAGER: */
164  "PredicateLockManager",
165  /* LWTRANCHE_PARALLEL_HASH_JOIN: */
166  "ParallelHashJoin",
167  /* LWTRANCHE_PARALLEL_QUERY_DSA: */
168  "ParallelQueryDSA",
169  /* LWTRANCHE_PER_SESSION_DSA: */
170  "PerSessionDSA",
171  /* LWTRANCHE_PER_SESSION_RECORD_TYPE: */
172  "PerSessionRecordType",
173  /* LWTRANCHE_PER_SESSION_RECORD_TYPMOD: */
174  "PerSessionRecordTypmod",
175  /* LWTRANCHE_SHARED_TUPLESTORE: */
176  "SharedTupleStore",
177  /* LWTRANCHE_SHARED_TIDBITMAP: */
178  "SharedTidBitmap",
179  /* LWTRANCHE_PARALLEL_APPEND: */
180  "ParallelAppend",
181  /* LWTRANCHE_PER_XACT_PREDICATE_LIST: */
182  "PerXactPredicateList",
183  /* LWTRANCHE_PGSTATS_DSA: */
184  "PgStatsDSA",
185  /* LWTRANCHE_PGSTATS_HASH: */
186  "PgStatsHash",
187  /* LWTRANCHE_PGSTATS_DATA: */
188  "PgStatsData",
189  /* LWTRANCHE_LAUNCHER_DSA: */
190  "LogicalRepLauncherDSA",
191  /* LWTRANCHE_LAUNCHER_HASH: */
192  "LogicalRepLauncherHash",
193 };
194 
196  LWTRANCHE_FIRST_USER_DEFINED - NUM_INDIVIDUAL_LWLOCKS,
197  "missing entries in BuiltinTrancheNames[]");
198 
199 /*
200  * This is indexed by tranche ID minus LWTRANCHE_FIRST_USER_DEFINED, and
201  * stores the names of all dynamically-created tranches known to the current
202  * process. Any unused entries in the array will contain NULL.
203  */
204 static const char **LWLockTrancheNames = NULL;
206 
207 /*
208  * This points to the main array of LWLocks in shared memory. Backends inherit
209  * the pointer by fork from the postmaster (except in the EXEC_BACKEND case,
210  * where we have special measures to pass it down).
211  */
213 
214 /*
215  * We use this structure to keep track of locked LWLocks for release
216  * during error recovery. Normally, only a few will be held at once, but
217  * occasionally the number can be much higher; for example, the pg_buffercache
218  * extension locks all buffer partitions simultaneously.
219  */
220 #define MAX_SIMUL_LWLOCKS 200
221 
222 /* struct representing the LWLocks we're holding */
223 typedef struct LWLockHandle
224 {
228 
229 static int num_held_lwlocks = 0;
231 
232 /* struct representing the LWLock tranche request for named tranche */
234 {
238 
241 
242 /*
243  * NamedLWLockTrancheRequests is both the valid length of the request array,
244  * and the length of the shared-memory NamedLWLockTrancheArray later on.
245  * This variable and NamedLWLockTrancheArray are non-static so that
246  * postmaster.c can copy them to child processes in EXEC_BACKEND builds.
247  */
249 
250 /* points to data in shared memory: */
252 
253 static void InitializeLWLocks(void);
254 static inline void LWLockReportWaitStart(LWLock *lock);
255 static inline void LWLockReportWaitEnd(void);
256 static const char *GetLWTrancheName(uint16 trancheId);
257 
258 #define T_NAME(lock) \
259  GetLWTrancheName((lock)->tranche)
260 
261 #ifdef LWLOCK_STATS
262 typedef struct lwlock_stats_key
263 {
264  int tranche;
265  void *instance;
266 } lwlock_stats_key;
267 
268 typedef struct lwlock_stats
269 {
270  lwlock_stats_key key;
271  int sh_acquire_count;
272  int ex_acquire_count;
273  int block_count;
274  int dequeue_self_count;
275  int spin_delay_count;
276 } lwlock_stats;
277 
278 static HTAB *lwlock_stats_htab;
279 static lwlock_stats lwlock_stats_dummy;
280 #endif
281 
282 #ifdef LOCK_DEBUG
283 bool Trace_lwlocks = false;
284 
285 inline static void
286 PRINT_LWDEBUG(const char *where, LWLock *lock, LWLockMode mode)
287 {
288  /* hide statement & context here, otherwise the log is just too verbose */
289  if (Trace_lwlocks)
290  {
292 
293  ereport(LOG,
294  (errhidestmt(true),
295  errhidecontext(true),
296  errmsg_internal("%d: %s(%s %p): excl %u shared %u haswaiters %u waiters %u rOK %d",
297  MyProcPid,
298  where, T_NAME(lock), lock,
299  (state & LW_VAL_EXCLUSIVE) != 0,
301  (state & LW_FLAG_HAS_WAITERS) != 0,
302  pg_atomic_read_u32(&lock->nwaiters),
303  (state & LW_FLAG_RELEASE_OK) != 0)));
304  }
305 }
306 
307 inline static void
308 LOG_LWDEBUG(const char *where, LWLock *lock, const char *msg)
309 {
310  /* hide statement & context here, otherwise the log is just too verbose */
311  if (Trace_lwlocks)
312  {
313  ereport(LOG,
314  (errhidestmt(true),
315  errhidecontext(true),
316  errmsg_internal("%s(%s %p): %s", where,
317  T_NAME(lock), lock, msg)));
318  }
319 }
320 
321 #else /* not LOCK_DEBUG */
322 #define PRINT_LWDEBUG(a,b,c) ((void)0)
323 #define LOG_LWDEBUG(a,b,c) ((void)0)
324 #endif /* LOCK_DEBUG */
325 
326 #ifdef LWLOCK_STATS
327 
328 static void init_lwlock_stats(void);
329 static void print_lwlock_stats(int code, Datum arg);
330 static lwlock_stats * get_lwlock_stats_entry(LWLock *lock);
331 
332 static void
333 init_lwlock_stats(void)
334 {
335  HASHCTL ctl;
336  static MemoryContext lwlock_stats_cxt = NULL;
337  static bool exit_registered = false;
338 
339  if (lwlock_stats_cxt != NULL)
340  MemoryContextDelete(lwlock_stats_cxt);
341 
342  /*
343  * The LWLock stats will be updated within a critical section, which
344  * requires allocating new hash entries. Allocations within a critical
345  * section are normally not allowed because running out of memory would
346  * lead to a PANIC, but LWLOCK_STATS is debugging code that's not normally
347  * turned on in production, so that's an acceptable risk. The hash entries
348  * are small, so the risk of running out of memory is minimal in practice.
349  */
350  lwlock_stats_cxt = AllocSetContextCreate(TopMemoryContext,
351  "LWLock stats",
353  MemoryContextAllowInCriticalSection(lwlock_stats_cxt, true);
354 
355  ctl.keysize = sizeof(lwlock_stats_key);
356  ctl.entrysize = sizeof(lwlock_stats);
357  ctl.hcxt = lwlock_stats_cxt;
358  lwlock_stats_htab = hash_create("lwlock stats", 16384, &ctl,
360  if (!exit_registered)
361  {
362  on_shmem_exit(print_lwlock_stats, 0);
363  exit_registered = true;
364  }
365 }
366 
367 static void
368 print_lwlock_stats(int code, Datum arg)
369 {
370  HASH_SEQ_STATUS scan;
371  lwlock_stats *lwstats;
372 
373  hash_seq_init(&scan, lwlock_stats_htab);
374 
375  /* Grab an LWLock to keep different backends from mixing reports */
377 
378  while ((lwstats = (lwlock_stats *) hash_seq_search(&scan)) != NULL)
379  {
380  fprintf(stderr,
381  "PID %d lwlock %s %p: shacq %u exacq %u blk %u spindelay %u dequeue self %u\n",
382  MyProcPid, GetLWTrancheName(lwstats->key.tranche),
383  lwstats->key.instance, lwstats->sh_acquire_count,
384  lwstats->ex_acquire_count, lwstats->block_count,
385  lwstats->spin_delay_count, lwstats->dequeue_self_count);
386  }
387 
388  LWLockRelease(&MainLWLockArray[0].lock);
389 }
390 
391 static lwlock_stats *
392 get_lwlock_stats_entry(LWLock *lock)
393 {
394  lwlock_stats_key key;
395  lwlock_stats *lwstats;
396  bool found;
397 
398  /*
399  * During shared memory initialization, the hash table doesn't exist yet.
400  * Stats of that phase aren't very interesting, so just collect operations
401  * on all locks in a single dummy entry.
402  */
403  if (lwlock_stats_htab == NULL)
404  return &lwlock_stats_dummy;
405 
406  /* Fetch or create the entry. */
407  MemSet(&key, 0, sizeof(key));
408  key.tranche = lock->tranche;
409  key.instance = lock;
410  lwstats = hash_search(lwlock_stats_htab, &key, HASH_ENTER, &found);
411  if (!found)
412  {
413  lwstats->sh_acquire_count = 0;
414  lwstats->ex_acquire_count = 0;
415  lwstats->block_count = 0;
416  lwstats->dequeue_self_count = 0;
417  lwstats->spin_delay_count = 0;
418  }
419  return lwstats;
420 }
421 #endif /* LWLOCK_STATS */
422 
423 
424 /*
425  * Compute number of LWLocks required by named tranches. These will be
426  * allocated in the main array.
427  */
428 static int
430 {
431  int numLocks = 0;
432  int i;
433 
434  for (i = 0; i < NamedLWLockTrancheRequests; i++)
435  numLocks += NamedLWLockTrancheRequestArray[i].num_lwlocks;
436 
437  return numLocks;
438 }
439 
440 /*
441  * Compute shmem space needed for LWLocks and named tranches.
442  */
443 Size
445 {
446  Size size;
447  int i;
448  int numLocks = NUM_FIXED_LWLOCKS;
449 
450  /* Calculate total number of locks needed in the main array. */
451  numLocks += NumLWLocksForNamedTranches();
452 
453  /* Space for the LWLock array. */
454  size = mul_size(numLocks, sizeof(LWLockPadded));
455 
456  /* Space for dynamic allocation counter, plus room for alignment. */
457  size = add_size(size, sizeof(int) + LWLOCK_PADDED_SIZE);
458 
459  /* space for named tranches. */
461 
462  /* space for name of each tranche. */
463  for (i = 0; i < NamedLWLockTrancheRequests; i++)
464  size = add_size(size, strlen(NamedLWLockTrancheRequestArray[i].tranche_name) + 1);
465 
466  return size;
467 }
468 
469 /*
470  * Allocate shmem space for the main LWLock array and all tranches and
471  * initialize it. We also register extension LWLock tranches here.
472  */
473 void
475 {
476  if (!IsUnderPostmaster)
477  {
478  Size spaceLocks = LWLockShmemSize();
479  int *LWLockCounter;
480  char *ptr;
481 
482  /* Allocate space */
483  ptr = (char *) ShmemAlloc(spaceLocks);
484 
485  /* Leave room for dynamic allocation of tranches */
486  ptr += sizeof(int);
487 
488  /* Ensure desired alignment of LWLock array */
489  ptr += LWLOCK_PADDED_SIZE - ((uintptr_t) ptr) % LWLOCK_PADDED_SIZE;
490 
491  MainLWLockArray = (LWLockPadded *) ptr;
492 
493  /*
494  * Initialize the dynamic-allocation counter for tranches, which is
495  * stored just before the first LWLock.
496  */
497  LWLockCounter = (int *) ((char *) MainLWLockArray - sizeof(int));
498  *LWLockCounter = LWTRANCHE_FIRST_USER_DEFINED;
499 
500  /* Initialize all LWLocks */
502  }
503 
504  /* Register named extension LWLock tranches in the current process. */
505  for (int i = 0; i < NamedLWLockTrancheRequests; i++)
507  NamedLWLockTrancheArray[i].trancheName);
508 }
509 
510 /*
511  * Initialize LWLocks that are fixed and those belonging to named tranches.
512  */
513 static void
515 {
516  int numNamedLocks = NumLWLocksForNamedTranches();
517  int id;
518  int i;
519  int j;
520  LWLockPadded *lock;
521 
522  /* Initialize all individual LWLocks in main array */
523  for (id = 0, lock = MainLWLockArray; id < NUM_INDIVIDUAL_LWLOCKS; id++, lock++)
524  LWLockInitialize(&lock->lock, id);
525 
526  /* Initialize buffer mapping LWLocks in main array */
528  for (id = 0; id < NUM_BUFFER_PARTITIONS; id++, lock++)
530 
531  /* Initialize lmgrs' LWLocks in main array */
533  for (id = 0; id < NUM_LOCK_PARTITIONS; id++, lock++)
535 
536  /* Initialize predicate lmgrs' LWLocks in main array */
538  for (id = 0; id < NUM_PREDICATELOCK_PARTITIONS; id++, lock++)
540 
541  /*
542  * Copy the info about any named tranches into shared memory (so that
543  * other processes can see it), and initialize the requested LWLocks.
544  */
546  {
547  char *trancheNames;
548 
550  &MainLWLockArray[NUM_FIXED_LWLOCKS + numNamedLocks];
551 
552  trancheNames = (char *) NamedLWLockTrancheArray +
555 
556  for (i = 0; i < NamedLWLockTrancheRequests; i++)
557  {
558  NamedLWLockTrancheRequest *request;
559  NamedLWLockTranche *tranche;
560  char *name;
561 
562  request = &NamedLWLockTrancheRequestArray[i];
563  tranche = &NamedLWLockTrancheArray[i];
564 
565  name = trancheNames;
566  trancheNames += strlen(request->tranche_name) + 1;
567  strcpy(name, request->tranche_name);
568  tranche->trancheId = LWLockNewTrancheId();
569  tranche->trancheName = name;
570 
571  for (j = 0; j < request->num_lwlocks; j++, lock++)
572  LWLockInitialize(&lock->lock, tranche->trancheId);
573  }
574  }
575 }
576 
577 /*
578  * InitLWLockAccess - initialize backend-local state needed to hold LWLocks
579  */
580 void
582 {
583 #ifdef LWLOCK_STATS
584  init_lwlock_stats();
585 #endif
586 }
587 
588 /*
589  * GetNamedLWLockTranche - returns the base address of LWLock from the
590  * specified tranche.
591  *
592  * Caller needs to retrieve the requested number of LWLocks starting from
593  * the base lock address returned by this API. This can be used for
594  * tranches that are requested by using RequestNamedLWLockTranche() API.
595  */
596 LWLockPadded *
597 GetNamedLWLockTranche(const char *tranche_name)
598 {
599  int lock_pos;
600  int i;
601 
602  /*
603  * Obtain the position of base address of LWLock belonging to requested
604  * tranche_name in MainLWLockArray. LWLocks for named tranches are placed
605  * in MainLWLockArray after fixed locks.
606  */
607  lock_pos = NUM_FIXED_LWLOCKS;
608  for (i = 0; i < NamedLWLockTrancheRequests; i++)
609  {
610  if (strcmp(NamedLWLockTrancheRequestArray[i].tranche_name,
611  tranche_name) == 0)
612  return &MainLWLockArray[lock_pos];
613 
615  }
616 
617  elog(ERROR, "requested tranche is not registered");
618 
619  /* just to keep compiler quiet */
620  return NULL;
621 }
622 
623 /*
624  * Allocate a new tranche ID.
625  */
626 int
628 {
629  int result;
630  int *LWLockCounter;
631 
632  LWLockCounter = (int *) ((char *) MainLWLockArray - sizeof(int));
634  result = (*LWLockCounter)++;
636 
637  return result;
638 }
639 
640 /*
641  * Register a dynamic tranche name in the lookup table of the current process.
642  *
643  * This routine will save a pointer to the tranche name passed as an argument,
644  * so the name should be allocated in a backend-lifetime context
645  * (shared memory, TopMemoryContext, static constant, or similar).
646  *
647  * The tranche name will be user-visible as a wait event name, so try to
648  * use a name that fits the style for those.
649  */
650 void
651 LWLockRegisterTranche(int tranche_id, const char *tranche_name)
652 {
653  /* This should only be called for user-defined tranches. */
654  if (tranche_id < LWTRANCHE_FIRST_USER_DEFINED)
655  return;
656 
657  /* Convert to array index. */
658  tranche_id -= LWTRANCHE_FIRST_USER_DEFINED;
659 
660  /* If necessary, create or enlarge array. */
661  if (tranche_id >= LWLockTrancheNamesAllocated)
662  {
663  int newalloc;
664 
665  newalloc = pg_nextpower2_32(Max(8, tranche_id + 1));
666 
667  if (LWLockTrancheNames == NULL)
668  LWLockTrancheNames = (const char **)
670  newalloc * sizeof(char *));
671  else
674  LWLockTrancheNamesAllocated = newalloc;
675  }
676 
677  LWLockTrancheNames[tranche_id] = tranche_name;
678 }
679 
680 /*
681  * RequestNamedLWLockTranche
682  * Request that extra LWLocks be allocated during postmaster
683  * startup.
684  *
685  * This may only be called via the shmem_request_hook of a library that is
686  * loaded into the postmaster via shared_preload_libraries. Calls from
687  * elsewhere will fail.
688  *
689  * The tranche name will be user-visible as a wait event name, so try to
690  * use a name that fits the style for those.
691  */
692 void
693 RequestNamedLWLockTranche(const char *tranche_name, int num_lwlocks)
694 {
695  NamedLWLockTrancheRequest *request;
696 
698  elog(FATAL, "cannot request additional LWLocks outside shmem_request_hook");
699 
700  if (NamedLWLockTrancheRequestArray == NULL)
701  {
706  * sizeof(NamedLWLockTrancheRequest));
707  }
708 
710  {
712 
715  i * sizeof(NamedLWLockTrancheRequest));
717  }
718 
720  Assert(strlen(tranche_name) + 1 <= NAMEDATALEN);
721  strlcpy(request->tranche_name, tranche_name, NAMEDATALEN);
722  request->num_lwlocks = num_lwlocks;
724 }
725 
726 /*
727  * LWLockInitialize - initialize a new lwlock; it's initially unlocked
728  */
729 void
730 LWLockInitialize(LWLock *lock, int tranche_id)
731 {
733 #ifdef LOCK_DEBUG
734  pg_atomic_init_u32(&lock->nwaiters, 0);
735 #endif
736  lock->tranche = tranche_id;
737  proclist_init(&lock->waiters);
738 }
739 
740 /*
741  * Report start of wait event for light-weight locks.
742  *
743  * This function will be used by all the light-weight lock calls which
744  * needs to wait to acquire the lock. This function distinguishes wait
745  * event based on tranche and lock id.
746  */
747 static inline void
749 {
751 }
752 
753 /*
754  * Report end of wait event for light-weight locks.
755  */
756 static inline void
758 {
760 }
761 
762 /*
763  * Return the name of an LWLock tranche.
764  */
765 static const char *
767 {
768  /* Individual LWLock? */
769  if (trancheId < NUM_INDIVIDUAL_LWLOCKS)
770  return IndividualLWLockNames[trancheId];
771 
772  /* Built-in tranche? */
773  if (trancheId < LWTRANCHE_FIRST_USER_DEFINED)
774  return BuiltinTrancheNames[trancheId - NUM_INDIVIDUAL_LWLOCKS];
775 
776  /*
777  * It's an extension tranche, so look in LWLockTrancheNames[]. However,
778  * it's possible that the tranche has never been registered in the current
779  * process, in which case give up and return "extension".
780  */
781  trancheId -= LWTRANCHE_FIRST_USER_DEFINED;
782 
783  if (trancheId >= LWLockTrancheNamesAllocated ||
784  LWLockTrancheNames[trancheId] == NULL)
785  return "extension";
786 
787  return LWLockTrancheNames[trancheId];
788 }
789 
790 /*
791  * Return an identifier for an LWLock based on the wait class and event.
792  */
793 const char *
795 {
796  Assert(classId == PG_WAIT_LWLOCK);
797  /* The event IDs are just tranche numbers. */
798  return GetLWTrancheName(eventId);
799 }
800 
801 /*
802  * Internal function that tries to atomically acquire the lwlock in the passed
803  * in mode.
804  *
805  * This function will not block waiting for a lock to become free - that's the
806  * callers job.
807  *
808  * Returns true if the lock isn't free and we need to wait.
809  */
810 static bool
812 {
813  uint32 old_state;
814 
816 
817  /*
818  * Read once outside the loop, later iterations will get the newer value
819  * via compare & exchange.
820  */
821  old_state = pg_atomic_read_u32(&lock->state);
822 
823  /* loop until we've determined whether we could acquire the lock or not */
824  while (true)
825  {
826  uint32 desired_state;
827  bool lock_free;
828 
829  desired_state = old_state;
830 
831  if (mode == LW_EXCLUSIVE)
832  {
833  lock_free = (old_state & LW_LOCK_MASK) == 0;
834  if (lock_free)
835  desired_state += LW_VAL_EXCLUSIVE;
836  }
837  else
838  {
839  lock_free = (old_state & LW_VAL_EXCLUSIVE) == 0;
840  if (lock_free)
841  desired_state += LW_VAL_SHARED;
842  }
843 
844  /*
845  * Attempt to swap in the state we are expecting. If we didn't see
846  * lock to be free, that's just the old value. If we saw it as free,
847  * we'll attempt to mark it acquired. The reason that we always swap
848  * in the value is that this doubles as a memory barrier. We could try
849  * to be smarter and only swap in values if we saw the lock as free,
850  * but benchmark haven't shown it as beneficial so far.
851  *
852  * Retry if the value changed since we last looked at it.
853  */
855  &old_state, desired_state))
856  {
857  if (lock_free)
858  {
859  /* Great! Got the lock. */
860 #ifdef LOCK_DEBUG
861  if (mode == LW_EXCLUSIVE)
862  lock->owner = MyProc;
863 #endif
864  return false;
865  }
866  else
867  return true; /* somebody else has the lock */
868  }
869  }
870  pg_unreachable();
871 }
872 
873 /*
874  * Lock the LWLock's wait list against concurrent activity.
875  *
876  * NB: even though the wait list is locked, non-conflicting lock operations
877  * may still happen concurrently.
878  *
879  * Time spent holding mutex should be short!
880  */
881 static void
883 {
884  uint32 old_state;
885 #ifdef LWLOCK_STATS
886  lwlock_stats *lwstats;
887  uint32 delays = 0;
888 
889  lwstats = get_lwlock_stats_entry(lock);
890 #endif
891 
892  while (true)
893  {
894  /* always try once to acquire lock directly */
895  old_state = pg_atomic_fetch_or_u32(&lock->state, LW_FLAG_LOCKED);
896  if (!(old_state & LW_FLAG_LOCKED))
897  break; /* got lock */
898 
899  /* and then spin without atomic operations until lock is released */
900  {
901  SpinDelayStatus delayStatus;
902 
903  init_local_spin_delay(&delayStatus);
904 
905  while (old_state & LW_FLAG_LOCKED)
906  {
907  perform_spin_delay(&delayStatus);
908  old_state = pg_atomic_read_u32(&lock->state);
909  }
910 #ifdef LWLOCK_STATS
911  delays += delayStatus.delays;
912 #endif
913  finish_spin_delay(&delayStatus);
914  }
915 
916  /*
917  * Retry. The lock might obviously already be re-acquired by the time
918  * we're attempting to get it again.
919  */
920  }
921 
922 #ifdef LWLOCK_STATS
923  lwstats->spin_delay_count += delays;
924 #endif
925 }
926 
927 /*
928  * Unlock the LWLock's wait list.
929  *
930  * Note that it can be more efficient to manipulate flags and release the
931  * locks in a single atomic operation.
932  */
933 static void
935 {
937 
938  old_state = pg_atomic_fetch_and_u32(&lock->state, ~LW_FLAG_LOCKED);
939 
940  Assert(old_state & LW_FLAG_LOCKED);
941 }
942 
943 /*
944  * Wakeup all the lockers that currently have a chance to acquire the lock.
945  */
946 static void
948 {
949  bool new_release_ok;
950  bool wokeup_somebody = false;
953 
955 
956  new_release_ok = true;
957 
958  /* lock wait list while collecting backends to wake up */
959  LWLockWaitListLock(lock);
960 
961  proclist_foreach_modify(iter, &lock->waiters, lwWaitLink)
962  {
963  PGPROC *waiter = GetPGProcByNumber(iter.cur);
964 
965  if (wokeup_somebody && waiter->lwWaitMode == LW_EXCLUSIVE)
966  continue;
967 
968  proclist_delete(&lock->waiters, iter.cur, lwWaitLink);
969  proclist_push_tail(&wakeup, iter.cur, lwWaitLink);
970 
971  if (waiter->lwWaitMode != LW_WAIT_UNTIL_FREE)
972  {
973  /*
974  * Prevent additional wakeups until retryer gets to run. Backends
975  * that are just waiting for the lock to become free don't retry
976  * automatically.
977  */
978  new_release_ok = false;
979 
980  /*
981  * Don't wakeup (further) exclusive locks.
982  */
983  wokeup_somebody = true;
984  }
985 
986  /*
987  * Signal that the process isn't on the wait list anymore. This allows
988  * LWLockDequeueSelf() to remove itself of the waitlist with a
989  * proclist_delete(), rather than having to check if it has been
990  * removed from the list.
991  */
992  Assert(waiter->lwWaiting == LW_WS_WAITING);
994 
995  /*
996  * Once we've woken up an exclusive lock, there's no point in waking
997  * up anybody else.
998  */
999  if (waiter->lwWaitMode == LW_EXCLUSIVE)
1000  break;
1001  }
1002 
1004 
1005  /* unset required flags, and release lock, in one fell swoop */
1006  {
1007  uint32 old_state;
1008  uint32 desired_state;
1009 
1010  old_state = pg_atomic_read_u32(&lock->state);
1011  while (true)
1012  {
1013  desired_state = old_state;
1014 
1015  /* compute desired flags */
1016 
1017  if (new_release_ok)
1018  desired_state |= LW_FLAG_RELEASE_OK;
1019  else
1020  desired_state &= ~LW_FLAG_RELEASE_OK;
1021 
1022  if (proclist_is_empty(&wakeup))
1023  desired_state &= ~LW_FLAG_HAS_WAITERS;
1024 
1025  desired_state &= ~LW_FLAG_LOCKED; /* release lock */
1026 
1027  if (pg_atomic_compare_exchange_u32(&lock->state, &old_state,
1028  desired_state))
1029  break;
1030  }
1031  }
1032 
1033  /* Awaken any waiters I removed from the queue. */
1034  proclist_foreach_modify(iter, &wakeup, lwWaitLink)
1035  {
1036  PGPROC *waiter = GetPGProcByNumber(iter.cur);
1037 
1038  LOG_LWDEBUG("LWLockRelease", lock, "release waiter");
1039  proclist_delete(&wakeup, iter.cur, lwWaitLink);
1040 
1041  /*
1042  * Guarantee that lwWaiting being unset only becomes visible once the
1043  * unlink from the link has completed. Otherwise the target backend
1044  * could be woken up for other reason and enqueue for a new lock - if
1045  * that happens before the list unlink happens, the list would end up
1046  * being corrupted.
1047  *
1048  * The barrier pairs with the LWLockWaitListLock() when enqueuing for
1049  * another lock.
1050  */
1051  pg_write_barrier();
1052  waiter->lwWaiting = LW_WS_NOT_WAITING;
1053  PGSemaphoreUnlock(waiter->sem);
1054  }
1055 }
1056 
1057 /*
1058  * Add ourselves to the end of the queue.
1059  *
1060  * NB: Mode can be LW_WAIT_UNTIL_FREE here!
1061  */
1062 static void
1064 {
1065  /*
1066  * If we don't have a PGPROC structure, there's no way to wait. This
1067  * should never occur, since MyProc should only be null during shared
1068  * memory initialization.
1069  */
1070  if (MyProc == NULL)
1071  elog(PANIC, "cannot wait without a PGPROC structure");
1072 
1074  elog(PANIC, "queueing for lock while waiting on another one");
1075 
1076  LWLockWaitListLock(lock);
1077 
1078  /* setting the flag is protected by the spinlock */
1080 
1082  MyProc->lwWaitMode = mode;
1083 
1084  /* LW_WAIT_UNTIL_FREE waiters are always at the front of the queue */
1085  if (mode == LW_WAIT_UNTIL_FREE)
1086  proclist_push_head(&lock->waiters, MyProc->pgprocno, lwWaitLink);
1087  else
1088  proclist_push_tail(&lock->waiters, MyProc->pgprocno, lwWaitLink);
1089 
1090  /* Can release the mutex now */
1091  LWLockWaitListUnlock(lock);
1092 
1093 #ifdef LOCK_DEBUG
1094  pg_atomic_fetch_add_u32(&lock->nwaiters, 1);
1095 #endif
1096 }
1097 
1098 /*
1099  * Remove ourselves from the waitlist.
1100  *
1101  * This is used if we queued ourselves because we thought we needed to sleep
1102  * but, after further checking, we discovered that we don't actually need to
1103  * do so.
1104  */
1105 static void
1107 {
1108  bool on_waitlist;
1109 
1110 #ifdef LWLOCK_STATS
1111  lwlock_stats *lwstats;
1112 
1113  lwstats = get_lwlock_stats_entry(lock);
1114 
1115  lwstats->dequeue_self_count++;
1116 #endif
1117 
1118  LWLockWaitListLock(lock);
1119 
1120  /*
1121  * Remove ourselves from the waitlist, unless we've already been removed.
1122  * The removal happens with the wait list lock held, so there's no race in
1123  * this check.
1124  */
1125  on_waitlist = MyProc->lwWaiting == LW_WS_WAITING;
1126  if (on_waitlist)
1127  proclist_delete(&lock->waiters, MyProc->pgprocno, lwWaitLink);
1128 
1129  if (proclist_is_empty(&lock->waiters) &&
1130  (pg_atomic_read_u32(&lock->state) & LW_FLAG_HAS_WAITERS) != 0)
1131  {
1133  }
1134 
1135  /* XXX: combine with fetch_and above? */
1136  LWLockWaitListUnlock(lock);
1137 
1138  /* clear waiting state again, nice for debugging */
1139  if (on_waitlist)
1141  else
1142  {
1143  int extraWaits = 0;
1144 
1145  /*
1146  * Somebody else dequeued us and has or will wake us up. Deal with the
1147  * superfluous absorption of a wakeup.
1148  */
1149 
1150  /*
1151  * Reset RELEASE_OK flag if somebody woke us before we removed
1152  * ourselves - they'll have set it to false.
1153  */
1155 
1156  /*
1157  * Now wait for the scheduled wakeup, otherwise our ->lwWaiting would
1158  * get reset at some inconvenient point later. Most of the time this
1159  * will immediately return.
1160  */
1161  for (;;)
1162  {
1165  break;
1166  extraWaits++;
1167  }
1168 
1169  /*
1170  * Fix the process wait semaphore's count for any absorbed wakeups.
1171  */
1172  while (extraWaits-- > 0)
1174  }
1175 
1176 #ifdef LOCK_DEBUG
1177  {
1178  /* not waiting anymore */
1179  uint32 nwaiters PG_USED_FOR_ASSERTS_ONLY = pg_atomic_fetch_sub_u32(&lock->nwaiters, 1);
1180 
1181  Assert(nwaiters < MAX_BACKENDS);
1182  }
1183 #endif
1184 }
1185 
1186 /*
1187  * LWLockAcquire - acquire a lightweight lock in the specified mode
1188  *
1189  * If the lock is not available, sleep until it is. Returns true if the lock
1190  * was available immediately, false if we had to sleep.
1191  *
1192  * Side effect: cancel/die interrupts are held off until lock release.
1193  */
1194 bool
1196 {
1197  PGPROC *proc = MyProc;
1198  bool result = true;
1199  int extraWaits = 0;
1200 #ifdef LWLOCK_STATS
1201  lwlock_stats *lwstats;
1202 
1203  lwstats = get_lwlock_stats_entry(lock);
1204 #endif
1205 
1207 
1208  PRINT_LWDEBUG("LWLockAcquire", lock, mode);
1209 
1210 #ifdef LWLOCK_STATS
1211  /* Count lock acquisition attempts */
1212  if (mode == LW_EXCLUSIVE)
1213  lwstats->ex_acquire_count++;
1214  else
1215  lwstats->sh_acquire_count++;
1216 #endif /* LWLOCK_STATS */
1217 
1218  /*
1219  * We can't wait if we haven't got a PGPROC. This should only occur
1220  * during bootstrap or shared memory initialization. Put an Assert here
1221  * to catch unsafe coding practices.
1222  */
1223  Assert(!(proc == NULL && IsUnderPostmaster));
1224 
1225  /* Ensure we will have room to remember the lock */
1227  elog(ERROR, "too many LWLocks taken");
1228 
1229  /*
1230  * Lock out cancel/die interrupts until we exit the code section protected
1231  * by the LWLock. This ensures that interrupts will not interfere with
1232  * manipulations of data structures in shared memory.
1233  */
1234  HOLD_INTERRUPTS();
1235 
1236  /*
1237  * Loop here to try to acquire lock after each time we are signaled by
1238  * LWLockRelease.
1239  *
1240  * NOTE: it might seem better to have LWLockRelease actually grant us the
1241  * lock, rather than retrying and possibly having to go back to sleep. But
1242  * in practice that is no good because it means a process swap for every
1243  * lock acquisition when two or more processes are contending for the same
1244  * lock. Since LWLocks are normally used to protect not-very-long
1245  * sections of computation, a process needs to be able to acquire and
1246  * release the same lock many times during a single CPU time slice, even
1247  * in the presence of contention. The efficiency of being able to do that
1248  * outweighs the inefficiency of sometimes wasting a process dispatch
1249  * cycle because the lock is not free when a released waiter finally gets
1250  * to run. See pgsql-hackers archives for 29-Dec-01.
1251  */
1252  for (;;)
1253  {
1254  bool mustwait;
1255 
1256  /*
1257  * Try to grab the lock the first time, we're not in the waitqueue
1258  * yet/anymore.
1259  */
1260  mustwait = LWLockAttemptLock(lock, mode);
1261 
1262  if (!mustwait)
1263  {
1264  LOG_LWDEBUG("LWLockAcquire", lock, "immediately acquired lock");
1265  break; /* got the lock */
1266  }
1267 
1268  /*
1269  * Ok, at this point we couldn't grab the lock on the first try. We
1270  * cannot simply queue ourselves to the end of the list and wait to be
1271  * woken up because by now the lock could long have been released.
1272  * Instead add us to the queue and try to grab the lock again. If we
1273  * succeed we need to revert the queuing and be happy, otherwise we
1274  * recheck the lock. If we still couldn't grab it, we know that the
1275  * other locker will see our queue entries when releasing since they
1276  * existed before we checked for the lock.
1277  */
1278 
1279  /* add to the queue */
1280  LWLockQueueSelf(lock, mode);
1281 
1282  /* we're now guaranteed to be woken up if necessary */
1283  mustwait = LWLockAttemptLock(lock, mode);
1284 
1285  /* ok, grabbed the lock the second time round, need to undo queueing */
1286  if (!mustwait)
1287  {
1288  LOG_LWDEBUG("LWLockAcquire", lock, "acquired, undoing queue");
1289 
1290  LWLockDequeueSelf(lock);
1291  break;
1292  }
1293 
1294  /*
1295  * Wait until awakened.
1296  *
1297  * It is possible that we get awakened for a reason other than being
1298  * signaled by LWLockRelease. If so, loop back and wait again. Once
1299  * we've gotten the LWLock, re-increment the sema by the number of
1300  * additional signals received.
1301  */
1302  LOG_LWDEBUG("LWLockAcquire", lock, "waiting");
1303 
1304 #ifdef LWLOCK_STATS
1305  lwstats->block_count++;
1306 #endif
1307 
1308  LWLockReportWaitStart(lock);
1309  if (TRACE_POSTGRESQL_LWLOCK_WAIT_START_ENABLED())
1310  TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), mode);
1311 
1312  for (;;)
1313  {
1314  PGSemaphoreLock(proc->sem);
1315  if (proc->lwWaiting == LW_WS_NOT_WAITING)
1316  break;
1317  extraWaits++;
1318  }
1319 
1320  /* Retrying, allow LWLockRelease to release waiters again. */
1322 
1323 #ifdef LOCK_DEBUG
1324  {
1325  /* not waiting anymore */
1326  uint32 nwaiters PG_USED_FOR_ASSERTS_ONLY = pg_atomic_fetch_sub_u32(&lock->nwaiters, 1);
1327 
1328  Assert(nwaiters < MAX_BACKENDS);
1329  }
1330 #endif
1331 
1332  if (TRACE_POSTGRESQL_LWLOCK_WAIT_DONE_ENABLED())
1333  TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), mode);
1335 
1336  LOG_LWDEBUG("LWLockAcquire", lock, "awakened");
1337 
1338  /* Now loop back and try to acquire lock again. */
1339  result = false;
1340  }
1341 
1342  if (TRACE_POSTGRESQL_LWLOCK_ACQUIRE_ENABLED())
1343  TRACE_POSTGRESQL_LWLOCK_ACQUIRE(T_NAME(lock), mode);
1344 
1345  /* Add lock to list of locks held by this backend */
1348 
1349  /*
1350  * Fix the process wait semaphore's count for any absorbed wakeups.
1351  */
1352  while (extraWaits-- > 0)
1353  PGSemaphoreUnlock(proc->sem);
1354 
1355  return result;
1356 }
1357 
1358 /*
1359  * LWLockConditionalAcquire - acquire a lightweight lock in the specified mode
1360  *
1361  * If the lock is not available, return false with no side-effects.
1362  *
1363  * If successful, cancel/die interrupts are held off until lock release.
1364  */
1365 bool
1367 {
1368  bool mustwait;
1369 
1371 
1372  PRINT_LWDEBUG("LWLockConditionalAcquire", lock, mode);
1373 
1374  /* Ensure we will have room to remember the lock */
1376  elog(ERROR, "too many LWLocks taken");
1377 
1378  /*
1379  * Lock out cancel/die interrupts until we exit the code section protected
1380  * by the LWLock. This ensures that interrupts will not interfere with
1381  * manipulations of data structures in shared memory.
1382  */
1383  HOLD_INTERRUPTS();
1384 
1385  /* Check for the lock */
1386  mustwait = LWLockAttemptLock(lock, mode);
1387 
1388  if (mustwait)
1389  {
1390  /* Failed to get lock, so release interrupt holdoff */
1392 
1393  LOG_LWDEBUG("LWLockConditionalAcquire", lock, "failed");
1394  if (TRACE_POSTGRESQL_LWLOCK_CONDACQUIRE_FAIL_ENABLED())
1395  TRACE_POSTGRESQL_LWLOCK_CONDACQUIRE_FAIL(T_NAME(lock), mode);
1396  }
1397  else
1398  {
1399  /* Add lock to list of locks held by this backend */
1402  if (TRACE_POSTGRESQL_LWLOCK_CONDACQUIRE_ENABLED())
1403  TRACE_POSTGRESQL_LWLOCK_CONDACQUIRE(T_NAME(lock), mode);
1404  }
1405  return !mustwait;
1406 }
1407 
1408 /*
1409  * LWLockAcquireOrWait - Acquire lock, or wait until it's free
1410  *
1411  * The semantics of this function are a bit funky. If the lock is currently
1412  * free, it is acquired in the given mode, and the function returns true. If
1413  * the lock isn't immediately free, the function waits until it is released
1414  * and returns false, but does not acquire the lock.
1415  *
1416  * This is currently used for WALWriteLock: when a backend flushes the WAL,
1417  * holding WALWriteLock, it can flush the commit records of many other
1418  * backends as a side-effect. Those other backends need to wait until the
1419  * flush finishes, but don't need to acquire the lock anymore. They can just
1420  * wake up, observe that their records have already been flushed, and return.
1421  */
1422 bool
1424 {
1425  PGPROC *proc = MyProc;
1426  bool mustwait;
1427  int extraWaits = 0;
1428 #ifdef LWLOCK_STATS
1429  lwlock_stats *lwstats;
1430 
1431  lwstats = get_lwlock_stats_entry(lock);
1432 #endif
1433 
1435 
1436  PRINT_LWDEBUG("LWLockAcquireOrWait", lock, mode);
1437 
1438  /* Ensure we will have room to remember the lock */
1440  elog(ERROR, "too many LWLocks taken");
1441 
1442  /*
1443  * Lock out cancel/die interrupts until we exit the code section protected
1444  * by the LWLock. This ensures that interrupts will not interfere with
1445  * manipulations of data structures in shared memory.
1446  */
1447  HOLD_INTERRUPTS();
1448 
1449  /*
1450  * NB: We're using nearly the same twice-in-a-row lock acquisition
1451  * protocol as LWLockAcquire(). Check its comments for details.
1452  */
1453  mustwait = LWLockAttemptLock(lock, mode);
1454 
1455  if (mustwait)
1456  {
1458 
1459  mustwait = LWLockAttemptLock(lock, mode);
1460 
1461  if (mustwait)
1462  {
1463  /*
1464  * Wait until awakened. Like in LWLockAcquire, be prepared for
1465  * bogus wakeups.
1466  */
1467  LOG_LWDEBUG("LWLockAcquireOrWait", lock, "waiting");
1468 
1469 #ifdef LWLOCK_STATS
1470  lwstats->block_count++;
1471 #endif
1472 
1473  LWLockReportWaitStart(lock);
1474  if (TRACE_POSTGRESQL_LWLOCK_WAIT_START_ENABLED())
1475  TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), mode);
1476 
1477  for (;;)
1478  {
1479  PGSemaphoreLock(proc->sem);
1480  if (proc->lwWaiting == LW_WS_NOT_WAITING)
1481  break;
1482  extraWaits++;
1483  }
1484 
1485 #ifdef LOCK_DEBUG
1486  {
1487  /* not waiting anymore */
1488  uint32 nwaiters PG_USED_FOR_ASSERTS_ONLY = pg_atomic_fetch_sub_u32(&lock->nwaiters, 1);
1489 
1490  Assert(nwaiters < MAX_BACKENDS);
1491  }
1492 #endif
1493  if (TRACE_POSTGRESQL_LWLOCK_WAIT_DONE_ENABLED())
1494  TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), mode);
1496 
1497  LOG_LWDEBUG("LWLockAcquireOrWait", lock, "awakened");
1498  }
1499  else
1500  {
1501  LOG_LWDEBUG("LWLockAcquireOrWait", lock, "acquired, undoing queue");
1502 
1503  /*
1504  * Got lock in the second attempt, undo queueing. We need to treat
1505  * this as having successfully acquired the lock, otherwise we'd
1506  * not necessarily wake up people we've prevented from acquiring
1507  * the lock.
1508  */
1509  LWLockDequeueSelf(lock);
1510  }
1511  }
1512 
1513  /*
1514  * Fix the process wait semaphore's count for any absorbed wakeups.
1515  */
1516  while (extraWaits-- > 0)
1517  PGSemaphoreUnlock(proc->sem);
1518 
1519  if (mustwait)
1520  {
1521  /* Failed to get lock, so release interrupt holdoff */
1523  LOG_LWDEBUG("LWLockAcquireOrWait", lock, "failed");
1524  if (TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT_FAIL_ENABLED())
1525  TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT_FAIL(T_NAME(lock), mode);
1526  }
1527  else
1528  {
1529  LOG_LWDEBUG("LWLockAcquireOrWait", lock, "succeeded");
1530  /* Add lock to list of locks held by this backend */
1533  if (TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT_ENABLED())
1534  TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT(T_NAME(lock), mode);
1535  }
1536 
1537  return !mustwait;
1538 }
1539 
1540 /*
1541  * Does the lwlock in its current state need to wait for the variable value to
1542  * change?
1543  *
1544  * If we don't need to wait, and it's because the value of the variable has
1545  * changed, store the current value in newval.
1546  *
1547  * *result is set to true if the lock was free, and false otherwise.
1548  */
1549 static bool
1550 LWLockConflictsWithVar(LWLock *lock, pg_atomic_uint64 *valptr, uint64 oldval,
1551  uint64 *newval, bool *result)
1552 {
1553  bool mustwait;
1554  uint64 value;
1555 
1556  /*
1557  * Test first to see if it the slot is free right now.
1558  *
1559  * XXX: the unique caller of this routine, WaitXLogInsertionsToFinish()
1560  * via LWLockWaitForVar(), uses an implied barrier with a spinlock before
1561  * this, so we don't need a memory barrier here as far as the current
1562  * usage is concerned. But that might not be safe in general.
1563  */
1564  mustwait = (pg_atomic_read_u32(&lock->state) & LW_VAL_EXCLUSIVE) != 0;
1565 
1566  if (!mustwait)
1567  {
1568  *result = true;
1569  return false;
1570  }
1571 
1572  *result = false;
1573 
1574  /*
1575  * Reading this value atomically is safe even on platforms where uint64
1576  * cannot be read without observing a torn value.
1577  */
1578  value = pg_atomic_read_u64(valptr);
1579 
1580  if (value != oldval)
1581  {
1582  mustwait = false;
1583  *newval = value;
1584  }
1585  else
1586  {
1587  mustwait = true;
1588  }
1589 
1590  return mustwait;
1591 }
1592 
1593 /*
1594  * LWLockWaitForVar - Wait until lock is free, or a variable is updated.
1595  *
1596  * If the lock is held and *valptr equals oldval, waits until the lock is
1597  * either freed, or the lock holder updates *valptr by calling
1598  * LWLockUpdateVar. If the lock is free on exit (immediately or after
1599  * waiting), returns true. If the lock is still held, but *valptr no longer
1600  * matches oldval, returns false and sets *newval to the current value in
1601  * *valptr.
1602  *
1603  * Note: this function ignores shared lock holders; if the lock is held
1604  * in shared mode, returns 'true'.
1605  *
1606  * Be aware that LWLockConflictsWithVar() does not include a memory barrier,
1607  * hence the caller of this function may want to rely on an explicit barrier or
1608  * an implied barrier via spinlock or LWLock to avoid memory ordering issues.
1609  */
1610 bool
1611 LWLockWaitForVar(LWLock *lock, pg_atomic_uint64 *valptr, uint64 oldval,
1612  uint64 *newval)
1613 {
1614  PGPROC *proc = MyProc;
1615  int extraWaits = 0;
1616  bool result = false;
1617 #ifdef LWLOCK_STATS
1618  lwlock_stats *lwstats;
1619 
1620  lwstats = get_lwlock_stats_entry(lock);
1621 #endif
1622 
1623  PRINT_LWDEBUG("LWLockWaitForVar", lock, LW_WAIT_UNTIL_FREE);
1624 
1625  /*
1626  * Lock out cancel/die interrupts while we sleep on the lock. There is no
1627  * cleanup mechanism to remove us from the wait queue if we got
1628  * interrupted.
1629  */
1630  HOLD_INTERRUPTS();
1631 
1632  /*
1633  * Loop here to check the lock's status after each time we are signaled.
1634  */
1635  for (;;)
1636  {
1637  bool mustwait;
1638 
1639  mustwait = LWLockConflictsWithVar(lock, valptr, oldval, newval,
1640  &result);
1641 
1642  if (!mustwait)
1643  break; /* the lock was free or value didn't match */
1644 
1645  /*
1646  * Add myself to wait queue. Note that this is racy, somebody else
1647  * could wakeup before we're finished queuing. NB: We're using nearly
1648  * the same twice-in-a-row lock acquisition protocol as
1649  * LWLockAcquire(). Check its comments for details. The only
1650  * difference is that we also have to check the variable's values when
1651  * checking the state of the lock.
1652  */
1654 
1655  /*
1656  * Set RELEASE_OK flag, to make sure we get woken up as soon as the
1657  * lock is released.
1658  */
1660 
1661  /*
1662  * We're now guaranteed to be woken up if necessary. Recheck the lock
1663  * and variables state.
1664  */
1665  mustwait = LWLockConflictsWithVar(lock, valptr, oldval, newval,
1666  &result);
1667 
1668  /* Ok, no conflict after we queued ourselves. Undo queueing. */
1669  if (!mustwait)
1670  {
1671  LOG_LWDEBUG("LWLockWaitForVar", lock, "free, undoing queue");
1672 
1673  LWLockDequeueSelf(lock);
1674  break;
1675  }
1676 
1677  /*
1678  * Wait until awakened.
1679  *
1680  * It is possible that we get awakened for a reason other than being
1681  * signaled by LWLockRelease. If so, loop back and wait again. Once
1682  * we've gotten the LWLock, re-increment the sema by the number of
1683  * additional signals received.
1684  */
1685  LOG_LWDEBUG("LWLockWaitForVar", lock, "waiting");
1686 
1687 #ifdef LWLOCK_STATS
1688  lwstats->block_count++;
1689 #endif
1690 
1691  LWLockReportWaitStart(lock);
1692  if (TRACE_POSTGRESQL_LWLOCK_WAIT_START_ENABLED())
1693  TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), LW_EXCLUSIVE);
1694 
1695  for (;;)
1696  {
1697  PGSemaphoreLock(proc->sem);
1698  if (proc->lwWaiting == LW_WS_NOT_WAITING)
1699  break;
1700  extraWaits++;
1701  }
1702 
1703 #ifdef LOCK_DEBUG
1704  {
1705  /* not waiting anymore */
1706  uint32 nwaiters PG_USED_FOR_ASSERTS_ONLY = pg_atomic_fetch_sub_u32(&lock->nwaiters, 1);
1707 
1708  Assert(nwaiters < MAX_BACKENDS);
1709  }
1710 #endif
1711 
1712  if (TRACE_POSTGRESQL_LWLOCK_WAIT_DONE_ENABLED())
1713  TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), LW_EXCLUSIVE);
1715 
1716  LOG_LWDEBUG("LWLockWaitForVar", lock, "awakened");
1717 
1718  /* Now loop back and check the status of the lock again. */
1719  }
1720 
1721  /*
1722  * Fix the process wait semaphore's count for any absorbed wakeups.
1723  */
1724  while (extraWaits-- > 0)
1725  PGSemaphoreUnlock(proc->sem);
1726 
1727  /*
1728  * Now okay to allow cancel/die interrupts.
1729  */
1731 
1732  return result;
1733 }
1734 
1735 
1736 /*
1737  * LWLockUpdateVar - Update a variable and wake up waiters atomically
1738  *
1739  * Sets *valptr to 'val', and wakes up all processes waiting for us with
1740  * LWLockWaitForVar(). It first sets the value atomically and then wakes up
1741  * waiting processes so that any process calling LWLockWaitForVar() on the same
1742  * lock is guaranteed to see the new value, and act accordingly.
1743  *
1744  * The caller must be holding the lock in exclusive mode.
1745  */
1746 void
1748 {
1750  proclist_mutable_iter iter;
1751 
1752  PRINT_LWDEBUG("LWLockUpdateVar", lock, LW_EXCLUSIVE);
1753 
1754  /*
1755  * Note that pg_atomic_exchange_u64 is a full barrier, so we're guaranteed
1756  * that the variable is updated before waking up waiters.
1757  */
1758  pg_atomic_exchange_u64(valptr, val);
1759 
1761 
1762  LWLockWaitListLock(lock);
1763 
1765 
1766  /*
1767  * See if there are any LW_WAIT_UNTIL_FREE waiters that need to be woken
1768  * up. They are always in the front of the queue.
1769  */
1770  proclist_foreach_modify(iter, &lock->waiters, lwWaitLink)
1771  {
1772  PGPROC *waiter = GetPGProcByNumber(iter.cur);
1773 
1774  if (waiter->lwWaitMode != LW_WAIT_UNTIL_FREE)
1775  break;
1776 
1777  proclist_delete(&lock->waiters, iter.cur, lwWaitLink);
1778  proclist_push_tail(&wakeup, iter.cur, lwWaitLink);
1779 
1780  /* see LWLockWakeup() */
1781  Assert(waiter->lwWaiting == LW_WS_WAITING);
1782  waiter->lwWaiting = LW_WS_PENDING_WAKEUP;
1783  }
1784 
1785  /* We are done updating shared state of the lock itself. */
1786  LWLockWaitListUnlock(lock);
1787 
1788  /*
1789  * Awaken any waiters I removed from the queue.
1790  */
1791  proclist_foreach_modify(iter, &wakeup, lwWaitLink)
1792  {
1793  PGPROC *waiter = GetPGProcByNumber(iter.cur);
1794 
1795  proclist_delete(&wakeup, iter.cur, lwWaitLink);
1796  /* check comment in LWLockWakeup() about this barrier */
1797  pg_write_barrier();
1798  waiter->lwWaiting = LW_WS_NOT_WAITING;
1799  PGSemaphoreUnlock(waiter->sem);
1800  }
1801 }
1802 
1803 
1804 /*
1805  * LWLockRelease - release a previously acquired lock
1806  */
1807 void
1809 {
1810  LWLockMode mode;
1811  uint32 oldstate;
1812  bool check_waiters;
1813  int i;
1814 
1815  /*
1816  * Remove lock from list of locks held. Usually, but not always, it will
1817  * be the latest-acquired lock; so search array backwards.
1818  */
1819  for (i = num_held_lwlocks; --i >= 0;)
1820  if (lock == held_lwlocks[i].lock)
1821  break;
1822 
1823  if (i < 0)
1824  elog(ERROR, "lock %s is not held", T_NAME(lock));
1825 
1826  mode = held_lwlocks[i].mode;
1827 
1828  num_held_lwlocks--;
1829  for (; i < num_held_lwlocks; i++)
1830  held_lwlocks[i] = held_lwlocks[i + 1];
1831 
1832  PRINT_LWDEBUG("LWLockRelease", lock, mode);
1833 
1834  /*
1835  * Release my hold on lock, after that it can immediately be acquired by
1836  * others, even if we still have to wakeup other waiters.
1837  */
1838  if (mode == LW_EXCLUSIVE)
1839  oldstate = pg_atomic_sub_fetch_u32(&lock->state, LW_VAL_EXCLUSIVE);
1840  else
1841  oldstate = pg_atomic_sub_fetch_u32(&lock->state, LW_VAL_SHARED);
1842 
1843  /* nobody else can have that kind of lock */
1844  Assert(!(oldstate & LW_VAL_EXCLUSIVE));
1845 
1846  if (TRACE_POSTGRESQL_LWLOCK_RELEASE_ENABLED())
1847  TRACE_POSTGRESQL_LWLOCK_RELEASE(T_NAME(lock));
1848 
1849  /*
1850  * We're still waiting for backends to get scheduled, don't wake them up
1851  * again.
1852  */
1853  if ((oldstate & (LW_FLAG_HAS_WAITERS | LW_FLAG_RELEASE_OK)) ==
1855  (oldstate & LW_LOCK_MASK) == 0)
1856  check_waiters = true;
1857  else
1858  check_waiters = false;
1859 
1860  /*
1861  * As waking up waiters requires the spinlock to be acquired, only do so
1862  * if necessary.
1863  */
1864  if (check_waiters)
1865  {
1866  /* XXX: remove before commit? */
1867  LOG_LWDEBUG("LWLockRelease", lock, "releasing waiters");
1868  LWLockWakeup(lock);
1869  }
1870 
1871  /*
1872  * Now okay to allow cancel/die interrupts.
1873  */
1875 }
1876 
1877 /*
1878  * LWLockReleaseClearVar - release a previously acquired lock, reset variable
1879  */
1880 void
1882 {
1883  /*
1884  * Note that pg_atomic_exchange_u64 is a full barrier, so we're guaranteed
1885  * that the variable is updated before releasing the lock.
1886  */
1887  pg_atomic_exchange_u64(valptr, val);
1888 
1889  LWLockRelease(lock);
1890 }
1891 
1892 
1893 /*
1894  * LWLockReleaseAll - release all currently-held locks
1895  *
1896  * Used to clean up after ereport(ERROR). An important difference between this
1897  * function and retail LWLockRelease calls is that InterruptHoldoffCount is
1898  * unchanged by this operation. This is necessary since InterruptHoldoffCount
1899  * has been set to an appropriate level earlier in error recovery. We could
1900  * decrement it below zero if we allow it to drop for each released lock!
1901  */
1902 void
1904 {
1905  while (num_held_lwlocks > 0)
1906  {
1907  HOLD_INTERRUPTS(); /* match the upcoming RESUME_INTERRUPTS */
1908 
1910  }
1911 }
1912 
1913 
1914 /*
1915  * LWLockHeldByMe - test whether my process holds a lock in any mode
1916  *
1917  * This is meant as debug support only.
1918  */
1919 bool
1921 {
1922  int i;
1923 
1924  for (i = 0; i < num_held_lwlocks; i++)
1925  {
1926  if (held_lwlocks[i].lock == lock)
1927  return true;
1928  }
1929  return false;
1930 }
1931 
1932 /*
1933  * LWLockHeldByMe - test whether my process holds any of an array of locks
1934  *
1935  * This is meant as debug support only.
1936  */
1937 bool
1938 LWLockAnyHeldByMe(LWLock *lock, int nlocks, size_t stride)
1939 {
1940  char *held_lock_addr;
1941  char *begin;
1942  char *end;
1943  int i;
1944 
1945  begin = (char *) lock;
1946  end = begin + nlocks * stride;
1947  for (i = 0; i < num_held_lwlocks; i++)
1948  {
1949  held_lock_addr = (char *) held_lwlocks[i].lock;
1950  if (held_lock_addr >= begin &&
1951  held_lock_addr < end &&
1952  (held_lock_addr - begin) % stride == 0)
1953  return true;
1954  }
1955  return false;
1956 }
1957 
1958 /*
1959  * LWLockHeldByMeInMode - test whether my process holds a lock in given mode
1960  *
1961  * This is meant as debug support only.
1962  */
1963 bool
1965 {
1966  int i;
1967 
1968  for (i = 0; i < num_held_lwlocks; i++)
1969  {
1970  if (held_lwlocks[i].lock == lock && held_lwlocks[i].mode == mode)
1971  return true;
1972  }
1973  return false;
1974 }
static uint32 pg_atomic_fetch_and_u32(volatile pg_atomic_uint32 *ptr, uint32 and_)
Definition: atomics.h:353
static bool pg_atomic_compare_exchange_u32(volatile pg_atomic_uint32 *ptr, uint32 *expected, uint32 newval)
Definition: atomics.h:306
static uint32 pg_atomic_fetch_or_u32(volatile pg_atomic_uint32 *ptr, uint32 or_)
Definition: atomics.h:367
static uint32 pg_atomic_sub_fetch_u32(volatile pg_atomic_uint32 *ptr, int32 sub_)
Definition: atomics.h:396
static uint32 pg_atomic_fetch_sub_u32(volatile pg_atomic_uint32 *ptr, int32 sub_)
Definition: atomics.h:338
static void pg_atomic_init_u32(volatile pg_atomic_uint32 *ptr, uint32 val)
Definition: atomics.h:218
#define pg_write_barrier()
Definition: atomics.h:154
static uint32 pg_atomic_fetch_add_u32(volatile pg_atomic_uint32 *ptr, int32 add_)
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static uint32 pg_atomic_read_u32(volatile pg_atomic_uint32 *ptr)
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static uint64 pg_atomic_read_u64(volatile pg_atomic_uint64 *ptr)
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static uint64 pg_atomic_exchange_u64(volatile pg_atomic_uint64 *ptr, uint64 newval)
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unsigned short uint16
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unsigned int uint32
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#define PG_USED_FOR_ASSERTS_ONLY
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#define Max(x, y)
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#define pg_unreachable()
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#define lengthof(array)
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#define MemSet(start, val, len)
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size_t Size
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void * hash_search(HTAB *hashp, const void *keyPtr, HASHACTION action, bool *foundPtr)
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HTAB * hash_create(const char *tabname, long nelem, const HASHCTL *info, int flags)
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int errhidestmt(bool hide_stmt)
Definition: elog.c:1410
int errhidecontext(bool hide_ctx)
Definition: elog.c:1429
#define LOG
Definition: elog.h:31
#define FATAL
Definition: elog.h:41
#define PANIC
Definition: elog.h:42
#define ERROR
Definition: elog.h:39
#define ereport(elevel,...)
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int MyProcPid
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bool IsUnderPostmaster
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#define newval
@ HASH_ENTER
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#define HASH_CONTEXT
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#define HASH_ELEM
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#define HASH_BLOBS
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long val
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static struct @148 value
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int j
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int i
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Assert(fmt[strlen(fmt) - 1] !='\n')
#define LW_VAL_EXCLUSIVE
Definition: lwlock.c:104
void LWLockUpdateVar(LWLock *lock, pg_atomic_uint64 *valptr, uint64 val)
Definition: lwlock.c:1747
StaticAssertDecl(LW_VAL_EXCLUSIVE >(uint32) MAX_BACKENDS, "MAX_BACKENDS too big for lwlock.c")
static void LWLockWakeup(LWLock *lock)
Definition: lwlock.c:947
#define LW_FLAG_LOCKED
Definition: lwlock.c:102
bool LWLockHeldByMe(LWLock *lock)
Definition: lwlock.c:1920
const char * GetLWLockIdentifier(uint32 classId, uint16 eventId)
Definition: lwlock.c:794
LWLockPadded * GetNamedLWLockTranche(const char *tranche_name)
Definition: lwlock.c:597
static LWLockHandle held_lwlocks[MAX_SIMUL_LWLOCKS]
Definition: lwlock.c:230
static int LWLockTrancheNamesAllocated
Definition: lwlock.c:205
void LWLockReleaseClearVar(LWLock *lock, pg_atomic_uint64 *valptr, uint64 val)
Definition: lwlock.c:1881
const char *const IndividualLWLockNames[]
bool LWLockAcquire(LWLock *lock, LWLockMode mode)
Definition: lwlock.c:1195
void CreateLWLocks(void)
Definition: lwlock.c:474
NamedLWLockTranche * NamedLWLockTrancheArray
Definition: lwlock.c:251
#define LW_VAL_SHARED
Definition: lwlock.c:105
static bool LWLockAttemptLock(LWLock *lock, LWLockMode mode)
Definition: lwlock.c:811
static void LWLockWaitListLock(LWLock *lock)
Definition: lwlock.c:882
void LWLockRegisterTranche(int tranche_id, const char *tranche_name)
Definition: lwlock.c:651
bool LWLockHeldByMeInMode(LWLock *lock, LWLockMode mode)
Definition: lwlock.c:1964
static void LWLockReportWaitEnd(void)
Definition: lwlock.c:757
struct LWLockHandle LWLockHandle
bool LWLockWaitForVar(LWLock *lock, pg_atomic_uint64 *valptr, uint64 oldval, uint64 *newval)
Definition: lwlock.c:1611
int LWLockNewTrancheId(void)
Definition: lwlock.c:627
slock_t * ShmemLock
Definition: shmem.c:88
static const char * GetLWTrancheName(uint16 trancheId)
Definition: lwlock.c:766
#define LW_LOCK_MASK
Definition: lwlock.c:107
int NamedLWLockTrancheRequests
Definition: lwlock.c:248
void RequestNamedLWLockTranche(const char *tranche_name, int num_lwlocks)
Definition: lwlock.c:693
#define LW_FLAG_RELEASE_OK
Definition: lwlock.c:101
#define LW_FLAG_HAS_WAITERS
Definition: lwlock.c:100
#define MAX_SIMUL_LWLOCKS
Definition: lwlock.c:220
struct NamedLWLockTrancheRequest NamedLWLockTrancheRequest
static int NumLWLocksForNamedTranches(void)
Definition: lwlock.c:429
void LWLockRelease(LWLock *lock)
Definition: lwlock.c:1808
#define T_NAME(lock)
Definition: lwlock.c:258
static int num_held_lwlocks
Definition: lwlock.c:229
void LWLockReleaseAll(void)
Definition: lwlock.c:1903
static void InitializeLWLocks(void)
Definition: lwlock.c:514
void LWLockInitialize(LWLock *lock, int tranche_id)
Definition: lwlock.c:730
static int NamedLWLockTrancheRequestsAllocated
Definition: lwlock.c:240
static const char *const BuiltinTrancheNames[]
Definition: lwlock.c:134
static NamedLWLockTrancheRequest * NamedLWLockTrancheRequestArray
Definition: lwlock.c:239
static void LWLockWaitListUnlock(LWLock *lock)
Definition: lwlock.c:934
static const char ** LWLockTrancheNames
Definition: lwlock.c:204
#define LOG_LWDEBUG(a, b, c)
Definition: lwlock.c:323
bool LWLockConditionalAcquire(LWLock *lock, LWLockMode mode)
Definition: lwlock.c:1366
bool LWLockAcquireOrWait(LWLock *lock, LWLockMode mode)
Definition: lwlock.c:1423
static void LWLockQueueSelf(LWLock *lock, LWLockMode mode)
Definition: lwlock.c:1063
#define PRINT_LWDEBUG(a, b, c)
Definition: lwlock.c:322
static void LWLockReportWaitStart(LWLock *lock)
Definition: lwlock.c:748
LWLockPadded * MainLWLockArray
Definition: lwlock.c:212
static void LWLockDequeueSelf(LWLock *lock)
Definition: lwlock.c:1106
Size LWLockShmemSize(void)
Definition: lwlock.c:444
bool LWLockAnyHeldByMe(LWLock *lock, int nlocks, size_t stride)
Definition: lwlock.c:1938
#define LW_SHARED_MASK
Definition: lwlock.c:109
static bool LWLockConflictsWithVar(LWLock *lock, pg_atomic_uint64 *valptr, uint64 oldval, uint64 *newval, bool *result)
Definition: lwlock.c:1550
void InitLWLockAccess(void)
Definition: lwlock.c:581
@ LW_WS_NOT_WAITING
Definition: lwlock.h:29
@ LW_WS_WAITING
Definition: lwlock.h:30
@ LW_WS_PENDING_WAKEUP
Definition: lwlock.h:31
#define LWLOCK_PADDED_SIZE
Definition: lwlock.h:61
#define BUFFER_MAPPING_LWLOCK_OFFSET
Definition: lwlock.h:106
#define NUM_LOCK_PARTITIONS
Definition: lwlock.h:99
@ LWTRANCHE_FIRST_USER_DEFINED
Definition: lwlock.h:210
@ LWTRANCHE_PREDICATE_LOCK_MANAGER
Definition: lwlock.h:195
@ LWTRANCHE_BUFFER_MAPPING
Definition: lwlock.h:193
@ LWTRANCHE_LOCK_MANAGER
Definition: lwlock.h:194
#define LOCK_MANAGER_LWLOCK_OFFSET
Definition: lwlock.h:107
#define NUM_BUFFER_PARTITIONS
Definition: lwlock.h:95
#define PREDICATELOCK_MANAGER_LWLOCK_OFFSET
Definition: lwlock.h:109
#define NUM_FIXED_LWLOCKS
Definition: lwlock.h:111
LWLockMode
Definition: lwlock.h:115
@ LW_SHARED
Definition: lwlock.h:117
@ LW_WAIT_UNTIL_FREE
Definition: lwlock.h:118
@ LW_EXCLUSIVE
Definition: lwlock.h:116
#define NUM_PREDICATELOCK_PARTITIONS
Definition: lwlock.h:103
MemoryContext TopMemoryContext
Definition: mcxt.c:141
void * MemoryContextAllocZero(MemoryContext context, Size size)
Definition: mcxt.c:1064
void * repalloc(void *pointer, Size size)
Definition: mcxt.c:1476
void * MemoryContextAlloc(MemoryContext context, Size size)
Definition: mcxt.c:1021
void MemoryContextDelete(MemoryContext context)
Definition: mcxt.c:403
void MemoryContextAllowInCriticalSection(MemoryContext context, bool allow)
Definition: mcxt.c:603
#define AllocSetContextCreate
Definition: memutils.h:129
#define ALLOCSET_DEFAULT_SIZES
Definition: memutils.h:153
#define RESUME_INTERRUPTS()
Definition: miscadmin.h:134
#define HOLD_INTERRUPTS()
Definition: miscadmin.h:132
bool process_shmem_requests_in_progress
Definition: miscinit.c:1768
#define repalloc0_array(pointer, type, oldcount, count)
Definition: palloc.h:110
void * arg
static uint32 pg_nextpower2_32(uint32 num)
Definition: pg_bitutils.h:189
static PgChecksumMode mode
Definition: pg_checksums.c:56
#define NAMEDATALEN
#define fprintf
Definition: port.h:242
size_t strlcpy(char *dst, const char *src, size_t siz)
Definition: strlcpy.c:45
void PGSemaphoreUnlock(PGSemaphore sema)
Definition: posix_sema.c:340
void PGSemaphoreLock(PGSemaphore sema)
Definition: posix_sema.c:320
uintptr_t Datum
Definition: postgres.h:64
#define MAX_BACKENDS
Definition: postmaster.h:78
#define GetPGProcByNumber(n)
Definition: proc.h:408
#define proclist_delete(list, procno, link_member)
Definition: proclist.h:187
static void proclist_init(proclist_head *list)
Definition: proclist.h:29
#define proclist_push_tail(list, procno, link_member)
Definition: proclist.h:191
#define proclist_push_head(list, procno, link_member)
Definition: proclist.h:189
#define proclist_foreach_modify(iter, lhead, link_member)
Definition: proclist.h:206
static bool proclist_is_empty(const proclist_head *list)
Definition: proclist.h:38
void perform_spin_delay(SpinDelayStatus *status)
Definition: s_lock.c:126
void finish_spin_delay(SpinDelayStatus *status)
Definition: s_lock.c:186
#define init_local_spin_delay(status)
Definition: s_lock.h:863
int slock_t
Definition: s_lock.h:754
void * ShmemAlloc(Size size)
Definition: shmem.c:161
Size add_size(Size s1, Size s2)
Definition: shmem.c:502
Size mul_size(Size s1, Size s2)
Definition: shmem.c:519
#define SpinLockRelease(lock)
Definition: spin.h:64
#define SpinLockAcquire(lock)
Definition: spin.h:62
PGPROC * MyProc
Definition: proc.c:66
Size keysize
Definition: hsearch.h:75
Size entrysize
Definition: hsearch.h:76
MemoryContext hcxt
Definition: hsearch.h:86
Definition: dynahash.c:220
LWLockMode mode
Definition: lwlock.c:226
LWLock * lock
Definition: lwlock.c:225
Definition: lwlock.h:41
pg_atomic_uint32 state
Definition: lwlock.h:43
uint16 tranche
Definition: lwlock.h:42
proclist_head waiters
Definition: lwlock.h:44
char tranche_name[NAMEDATALEN]
Definition: lwlock.c:235
char * trancheName
Definition: lwlock.h:79
Definition: proc.h:162
uint8 lwWaitMode
Definition: proc.h:215
int pgprocno
Definition: proc.h:191
PGSemaphore sem
Definition: proc.h:167
uint8 lwWaiting
Definition: proc.h:214
Definition: regguts.h:323
LWLock lock
Definition: lwlock.h:69
#define PG_WAIT_LWLOCK
Definition: wait_event.h:18
static void pgstat_report_wait_start(uint32 wait_event_info)
Definition: wait_event.h:88
static void pgstat_report_wait_end(void)
Definition: wait_event.h:104
const char * name
static TimestampTz wakeup[NUM_WALRCV_WAKEUPS]
Definition: walreceiver.c:132