Line data Source code
1 : /*--------------------------------------------------------------------
2 : * bgworker.c
3 : * POSTGRES pluggable background workers implementation
4 : *
5 : * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
6 : *
7 : * IDENTIFICATION
8 : * src/backend/postmaster/bgworker.c
9 : *
10 : *-------------------------------------------------------------------------
11 : */
12 :
13 : #include "postgres.h"
14 :
15 : #include "access/parallel.h"
16 : #include "libpq/pqsignal.h"
17 : #include "miscadmin.h"
18 : #include "pgstat.h"
19 : #include "port/atomics.h"
20 : #include "postmaster/bgworker_internals.h"
21 : #include "postmaster/postmaster.h"
22 : #include "replication/logicallauncher.h"
23 : #include "replication/logicalworker.h"
24 : #include "storage/ipc.h"
25 : #include "storage/latch.h"
26 : #include "storage/lwlock.h"
27 : #include "storage/pmsignal.h"
28 : #include "storage/proc.h"
29 : #include "storage/procsignal.h"
30 : #include "storage/shmem.h"
31 : #include "tcop/tcopprot.h"
32 : #include "utils/ascii.h"
33 : #include "utils/memutils.h"
34 : #include "utils/ps_status.h"
35 : #include "utils/timeout.h"
36 :
37 : /*
38 : * The postmaster's list of registered background workers, in private memory.
39 : */
40 : slist_head BackgroundWorkerList = SLIST_STATIC_INIT(BackgroundWorkerList);
41 :
42 : /*
43 : * BackgroundWorkerSlots exist in shared memory and can be accessed (via
44 : * the BackgroundWorkerArray) by both the postmaster and by regular backends.
45 : * However, the postmaster cannot take locks, even spinlocks, because this
46 : * might allow it to crash or become wedged if shared memory gets corrupted.
47 : * Such an outcome is intolerable. Therefore, we need a lockless protocol
48 : * for coordinating access to this data.
49 : *
50 : * The 'in_use' flag is used to hand off responsibility for the slot between
51 : * the postmaster and the rest of the system. When 'in_use' is false,
52 : * the postmaster will ignore the slot entirely, except for the 'in_use' flag
53 : * itself, which it may read. In this state, regular backends may modify the
54 : * slot. Once a backend sets 'in_use' to true, the slot becomes the
55 : * responsibility of the postmaster. Regular backends may no longer modify it,
56 : * but the postmaster may examine it. Thus, a backend initializing a slot
57 : * must fully initialize the slot - and insert a write memory barrier - before
58 : * marking it as in use.
59 : *
60 : * As an exception, however, even when the slot is in use, regular backends
61 : * may set the 'terminate' flag for a slot, telling the postmaster not
62 : * to restart it. Once the background worker is no longer running, the slot
63 : * will be released for reuse.
64 : *
65 : * In addition to coordinating with the postmaster, backends modifying this
66 : * data structure must coordinate with each other. Since they can take locks,
67 : * this is straightforward: any backend wishing to manipulate a slot must
68 : * take BackgroundWorkerLock in exclusive mode. Backends wishing to read
69 : * data that might get concurrently modified by other backends should take
70 : * this lock in shared mode. No matter what, backends reading this data
71 : * structure must be able to tolerate concurrent modifications by the
72 : * postmaster.
73 : */
74 : typedef struct BackgroundWorkerSlot
75 : {
76 : bool in_use;
77 : bool terminate;
78 : pid_t pid; /* InvalidPid = not started yet; 0 = dead */
79 : uint64 generation; /* incremented when slot is recycled */
80 : BackgroundWorker worker;
81 : } BackgroundWorkerSlot;
82 :
83 : /*
84 : * In order to limit the total number of parallel workers (according to
85 : * max_parallel_workers GUC), we maintain the number of active parallel
86 : * workers. Since the postmaster cannot take locks, two variables are used for
87 : * this purpose: the number of registered parallel workers (modified by the
88 : * backends, protected by BackgroundWorkerLock) and the number of terminated
89 : * parallel workers (modified only by the postmaster, lockless). The active
90 : * number of parallel workers is the number of registered workers minus the
91 : * terminated ones. These counters can of course overflow, but it's not
92 : * important here since the subtraction will still give the right number.
93 : */
94 : typedef struct BackgroundWorkerArray
95 : {
96 : int total_slots;
97 : uint32 parallel_register_count;
98 : uint32 parallel_terminate_count;
99 : BackgroundWorkerSlot slot[FLEXIBLE_ARRAY_MEMBER];
100 : } BackgroundWorkerArray;
101 :
102 : struct BackgroundWorkerHandle
103 : {
104 : int slot;
105 : uint64 generation;
106 : };
107 :
108 : static BackgroundWorkerArray *BackgroundWorkerData;
109 :
110 : /*
111 : * List of internal background worker entry points. We need this for
112 : * reasons explained in LookupBackgroundWorkerFunction(), below.
113 : */
114 : static const struct
115 : {
116 : const char *fn_name;
117 : bgworker_main_type fn_addr;
118 : } InternalBGWorkers[] =
119 :
120 : {
121 : {
122 : "ParallelWorkerMain", ParallelWorkerMain
123 : },
124 : {
125 : "ApplyLauncherMain", ApplyLauncherMain
126 : },
127 : {
128 : "ApplyWorkerMain", ApplyWorkerMain
129 : },
130 : {
131 : "ParallelApplyWorkerMain", ParallelApplyWorkerMain
132 : },
133 : {
134 : "TablesyncWorkerMain", TablesyncWorkerMain
135 : }
136 : };
137 :
138 : /* Private functions. */
139 : static bgworker_main_type LookupBackgroundWorkerFunction(const char *libraryname, const char *funcname);
140 :
141 :
142 : /*
143 : * Calculate shared memory needed.
144 : */
145 : Size
146 5066 : BackgroundWorkerShmemSize(void)
147 : {
148 : Size size;
149 :
150 : /* Array of workers is variably sized. */
151 5066 : size = offsetof(BackgroundWorkerArray, slot);
152 5066 : size = add_size(size, mul_size(max_worker_processes,
153 : sizeof(BackgroundWorkerSlot)));
154 :
155 5066 : return size;
156 : }
157 :
158 : /*
159 : * Initialize shared memory.
160 : */
161 : void
162 1768 : BackgroundWorkerShmemInit(void)
163 : {
164 : bool found;
165 :
166 1768 : BackgroundWorkerData = ShmemInitStruct("Background Worker Data",
167 : BackgroundWorkerShmemSize(),
168 : &found);
169 1768 : if (!IsUnderPostmaster)
170 : {
171 : slist_iter siter;
172 1768 : int slotno = 0;
173 :
174 1768 : BackgroundWorkerData->total_slots = max_worker_processes;
175 1768 : BackgroundWorkerData->parallel_register_count = 0;
176 1768 : BackgroundWorkerData->parallel_terminate_count = 0;
177 :
178 : /*
179 : * Copy contents of worker list into shared memory. Record the shared
180 : * memory slot assigned to each worker. This ensures a 1-to-1
181 : * correspondence between the postmaster's private list and the array
182 : * in shared memory.
183 : */
184 3160 : slist_foreach(siter, &BackgroundWorkerList)
185 : {
186 1392 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
187 : RegisteredBgWorker *rw;
188 :
189 1392 : rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur);
190 : Assert(slotno < max_worker_processes);
191 1392 : slot->in_use = true;
192 1392 : slot->terminate = false;
193 1392 : slot->pid = InvalidPid;
194 1392 : slot->generation = 0;
195 1392 : rw->rw_shmem_slot = slotno;
196 1392 : rw->rw_worker.bgw_notify_pid = 0; /* might be reinit after crash */
197 1392 : memcpy(&slot->worker, &rw->rw_worker, sizeof(BackgroundWorker));
198 1392 : ++slotno;
199 : }
200 :
201 : /*
202 : * Mark any remaining slots as not in use.
203 : */
204 14544 : while (slotno < max_worker_processes)
205 : {
206 12776 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
207 :
208 12776 : slot->in_use = false;
209 12776 : ++slotno;
210 : }
211 : }
212 : else
213 : Assert(found);
214 1768 : }
215 :
216 : /*
217 : * Search the postmaster's backend-private list of RegisteredBgWorker objects
218 : * for the one that maps to the given slot number.
219 : */
220 : static RegisteredBgWorker *
221 6560 : FindRegisteredWorkerBySlotNumber(int slotno)
222 : {
223 : slist_iter siter;
224 :
225 15734 : slist_foreach(siter, &BackgroundWorkerList)
226 : {
227 : RegisteredBgWorker *rw;
228 :
229 12304 : rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur);
230 12304 : if (rw->rw_shmem_slot == slotno)
231 3130 : return rw;
232 : }
233 :
234 3430 : return NULL;
235 : }
236 :
237 : /*
238 : * Notice changes to shared memory made by other backends.
239 : * Accept new worker requests only if allow_new_workers is true.
240 : *
241 : * This code runs in the postmaster, so we must be very careful not to assume
242 : * that shared memory contents are sane. Otherwise, a rogue backend could
243 : * take out the postmaster.
244 : */
245 : void
246 1984 : BackgroundWorkerStateChange(bool allow_new_workers)
247 : {
248 : int slotno;
249 :
250 : /*
251 : * The total number of slots stored in shared memory should match our
252 : * notion of max_worker_processes. If it does not, something is very
253 : * wrong. Further down, we always refer to this value as
254 : * max_worker_processes, in case shared memory gets corrupted while we're
255 : * looping.
256 : */
257 1984 : if (max_worker_processes != BackgroundWorkerData->total_slots)
258 : {
259 0 : ereport(LOG,
260 : (errmsg("inconsistent background worker state (max_worker_processes=%d, total_slots=%d)",
261 : max_worker_processes,
262 : BackgroundWorkerData->total_slots)));
263 0 : return;
264 : }
265 :
266 : /*
267 : * Iterate through slots, looking for newly-registered workers or workers
268 : * who must die.
269 : */
270 18144 : for (slotno = 0; slotno < max_worker_processes; ++slotno)
271 : {
272 16160 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
273 : RegisteredBgWorker *rw;
274 :
275 16160 : if (!slot->in_use)
276 9600 : continue;
277 :
278 : /*
279 : * Make sure we don't see the in_use flag before the updated slot
280 : * contents.
281 : */
282 6560 : pg_read_barrier();
283 :
284 : /* See whether we already know about this worker. */
285 6560 : rw = FindRegisteredWorkerBySlotNumber(slotno);
286 6560 : if (rw != NULL)
287 : {
288 : /*
289 : * In general, the worker data can't change after it's initially
290 : * registered. However, someone can set the terminate flag.
291 : */
292 3130 : if (slot->terminate && !rw->rw_terminate)
293 : {
294 6 : rw->rw_terminate = true;
295 6 : if (rw->rw_pid != 0)
296 6 : kill(rw->rw_pid, SIGTERM);
297 : else
298 : {
299 : /* Report never-started, now-terminated worker as dead. */
300 0 : ReportBackgroundWorkerPID(rw);
301 : }
302 : }
303 3130 : continue;
304 : }
305 :
306 : /*
307 : * If we aren't allowing new workers, then immediately mark it for
308 : * termination; the next stanza will take care of cleaning it up.
309 : * Doing this ensures that any process waiting for the worker will get
310 : * awoken, even though the worker will never be allowed to run.
311 : */
312 3430 : if (!allow_new_workers)
313 2 : slot->terminate = true;
314 :
315 : /*
316 : * If the worker is marked for termination, we don't need to add it to
317 : * the registered workers list; we can just free the slot. However, if
318 : * bgw_notify_pid is set, the process that registered the worker may
319 : * need to know that we've processed the terminate request, so be sure
320 : * to signal it.
321 : */
322 3430 : if (slot->terminate)
323 : {
324 : int notify_pid;
325 :
326 : /*
327 : * We need a memory barrier here to make sure that the load of
328 : * bgw_notify_pid and the update of parallel_terminate_count
329 : * complete before the store to in_use.
330 : */
331 2 : notify_pid = slot->worker.bgw_notify_pid;
332 2 : if ((slot->worker.bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
333 0 : BackgroundWorkerData->parallel_terminate_count++;
334 2 : slot->pid = 0;
335 :
336 2 : pg_memory_barrier();
337 2 : slot->in_use = false;
338 :
339 2 : if (notify_pid != 0)
340 2 : kill(notify_pid, SIGUSR1);
341 :
342 2 : continue;
343 : }
344 :
345 : /*
346 : * Copy the registration data into the registered workers list.
347 : */
348 3428 : rw = MemoryContextAllocExtended(PostmasterContext,
349 : sizeof(RegisteredBgWorker),
350 : MCXT_ALLOC_NO_OOM | MCXT_ALLOC_ZERO);
351 3428 : if (rw == NULL)
352 : {
353 0 : ereport(LOG,
354 : (errcode(ERRCODE_OUT_OF_MEMORY),
355 : errmsg("out of memory")));
356 0 : return;
357 : }
358 :
359 : /*
360 : * Copy strings in a paranoid way. If shared memory is corrupted, the
361 : * source data might not even be NUL-terminated.
362 : */
363 3428 : ascii_safe_strlcpy(rw->rw_worker.bgw_name,
364 3428 : slot->worker.bgw_name, BGW_MAXLEN);
365 3428 : ascii_safe_strlcpy(rw->rw_worker.bgw_type,
366 3428 : slot->worker.bgw_type, BGW_MAXLEN);
367 3428 : ascii_safe_strlcpy(rw->rw_worker.bgw_library_name,
368 3428 : slot->worker.bgw_library_name, MAXPGPATH);
369 3428 : ascii_safe_strlcpy(rw->rw_worker.bgw_function_name,
370 3428 : slot->worker.bgw_function_name, BGW_MAXLEN);
371 :
372 : /*
373 : * Copy various fixed-size fields.
374 : *
375 : * flags, start_time, and restart_time are examined by the postmaster,
376 : * but nothing too bad will happen if they are corrupted. The
377 : * remaining fields will only be examined by the child process. It
378 : * might crash, but we won't.
379 : */
380 3428 : rw->rw_worker.bgw_flags = slot->worker.bgw_flags;
381 3428 : rw->rw_worker.bgw_start_time = slot->worker.bgw_start_time;
382 3428 : rw->rw_worker.bgw_restart_time = slot->worker.bgw_restart_time;
383 3428 : rw->rw_worker.bgw_main_arg = slot->worker.bgw_main_arg;
384 3428 : memcpy(rw->rw_worker.bgw_extra, slot->worker.bgw_extra, BGW_EXTRALEN);
385 :
386 : /*
387 : * Copy the PID to be notified about state changes, but only if the
388 : * postmaster knows about a backend with that PID. It isn't an error
389 : * if the postmaster doesn't know about the PID, because the backend
390 : * that requested the worker could have died (or been killed) just
391 : * after doing so. Nonetheless, at least until we get some experience
392 : * with how this plays out in the wild, log a message at a relative
393 : * high debug level.
394 : */
395 3428 : rw->rw_worker.bgw_notify_pid = slot->worker.bgw_notify_pid;
396 3428 : if (!PostmasterMarkPIDForWorkerNotify(rw->rw_worker.bgw_notify_pid))
397 : {
398 0 : elog(DEBUG1, "worker notification PID %d is not valid",
399 : (int) rw->rw_worker.bgw_notify_pid);
400 0 : rw->rw_worker.bgw_notify_pid = 0;
401 : }
402 :
403 : /* Initialize postmaster bookkeeping. */
404 3428 : rw->rw_backend = NULL;
405 3428 : rw->rw_pid = 0;
406 3428 : rw->rw_child_slot = 0;
407 3428 : rw->rw_crashed_at = 0;
408 3428 : rw->rw_shmem_slot = slotno;
409 3428 : rw->rw_terminate = false;
410 :
411 : /* Log it! */
412 3428 : ereport(DEBUG1,
413 : (errmsg_internal("registering background worker \"%s\"",
414 : rw->rw_worker.bgw_name)));
415 :
416 3428 : slist_push_head(&BackgroundWorkerList, &rw->rw_lnode);
417 : }
418 : }
419 :
420 : /*
421 : * Forget about a background worker that's no longer needed.
422 : *
423 : * The worker must be identified by passing an slist_mutable_iter that
424 : * points to it. This convention allows deletion of workers during
425 : * searches of the worker list, and saves having to search the list again.
426 : *
427 : * Caller is responsible for notifying bgw_notify_pid, if appropriate.
428 : *
429 : * This function must be invoked only in the postmaster.
430 : */
431 : void
432 3428 : ForgetBackgroundWorker(slist_mutable_iter *cur)
433 : {
434 : RegisteredBgWorker *rw;
435 : BackgroundWorkerSlot *slot;
436 :
437 3428 : rw = slist_container(RegisteredBgWorker, rw_lnode, cur->cur);
438 :
439 : Assert(rw->rw_shmem_slot < max_worker_processes);
440 3428 : slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
441 : Assert(slot->in_use);
442 :
443 : /*
444 : * We need a memory barrier here to make sure that the update of
445 : * parallel_terminate_count completes before the store to in_use.
446 : */
447 3428 : if ((rw->rw_worker.bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
448 2642 : BackgroundWorkerData->parallel_terminate_count++;
449 :
450 3428 : pg_memory_barrier();
451 3428 : slot->in_use = false;
452 :
453 3428 : ereport(DEBUG1,
454 : (errmsg_internal("unregistering background worker \"%s\"",
455 : rw->rw_worker.bgw_name)));
456 :
457 3428 : slist_delete_current(cur);
458 3428 : pfree(rw);
459 3428 : }
460 :
461 : /*
462 : * Report the PID of a newly-launched background worker in shared memory.
463 : *
464 : * This function should only be called from the postmaster.
465 : */
466 : void
467 4628 : ReportBackgroundWorkerPID(RegisteredBgWorker *rw)
468 : {
469 : BackgroundWorkerSlot *slot;
470 :
471 : Assert(rw->rw_shmem_slot < max_worker_processes);
472 4628 : slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
473 4628 : slot->pid = rw->rw_pid;
474 :
475 4628 : if (rw->rw_worker.bgw_notify_pid != 0)
476 3428 : kill(rw->rw_worker.bgw_notify_pid, SIGUSR1);
477 4628 : }
478 :
479 : /*
480 : * Report that the PID of a background worker is now zero because a
481 : * previously-running background worker has exited.
482 : *
483 : * This function should only be called from the postmaster.
484 : */
485 : void
486 4084 : ReportBackgroundWorkerExit(slist_mutable_iter *cur)
487 : {
488 : RegisteredBgWorker *rw;
489 : BackgroundWorkerSlot *slot;
490 : int notify_pid;
491 :
492 4084 : rw = slist_container(RegisteredBgWorker, rw_lnode, cur->cur);
493 :
494 : Assert(rw->rw_shmem_slot < max_worker_processes);
495 4084 : slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
496 4084 : slot->pid = rw->rw_pid;
497 4084 : notify_pid = rw->rw_worker.bgw_notify_pid;
498 :
499 : /*
500 : * If this worker is slated for deregistration, do that before notifying
501 : * the process which started it. Otherwise, if that process tries to
502 : * reuse the slot immediately, it might not be available yet. In theory
503 : * that could happen anyway if the process checks slot->pid at just the
504 : * wrong moment, but this makes the window narrower.
505 : */
506 4084 : if (rw->rw_terminate ||
507 1024 : rw->rw_worker.bgw_restart_time == BGW_NEVER_RESTART)
508 3404 : ForgetBackgroundWorker(cur);
509 :
510 4084 : if (notify_pid != 0)
511 3356 : kill(notify_pid, SIGUSR1);
512 4084 : }
513 :
514 : /*
515 : * Cancel SIGUSR1 notifications for a PID belonging to an exiting backend.
516 : *
517 : * This function should only be called from the postmaster.
518 : */
519 : void
520 424 : BackgroundWorkerStopNotifications(pid_t pid)
521 : {
522 : slist_iter siter;
523 :
524 1284 : slist_foreach(siter, &BackgroundWorkerList)
525 : {
526 : RegisteredBgWorker *rw;
527 :
528 860 : rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur);
529 860 : if (rw->rw_worker.bgw_notify_pid == pid)
530 52 : rw->rw_worker.bgw_notify_pid = 0;
531 : }
532 424 : }
533 :
534 : /*
535 : * Cancel any not-yet-started worker requests that have waiting processes.
536 : *
537 : * This is called during a normal ("smart" or "fast") database shutdown.
538 : * After this point, no new background workers will be started, so anything
539 : * that might be waiting for them needs to be kicked off its wait. We do
540 : * that by canceling the bgworker registration entirely, which is perhaps
541 : * overkill, but since we're shutting down it does not matter whether the
542 : * registration record sticks around.
543 : *
544 : * This function should only be called from the postmaster.
545 : */
546 : void
547 822 : ForgetUnstartedBackgroundWorkers(void)
548 : {
549 : slist_mutable_iter iter;
550 :
551 1662 : slist_foreach_modify(iter, &BackgroundWorkerList)
552 : {
553 : RegisteredBgWorker *rw;
554 : BackgroundWorkerSlot *slot;
555 :
556 840 : rw = slist_container(RegisteredBgWorker, rw_lnode, iter.cur);
557 : Assert(rw->rw_shmem_slot < max_worker_processes);
558 840 : slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
559 :
560 : /* If it's not yet started, and there's someone waiting ... */
561 840 : if (slot->pid == InvalidPid &&
562 94 : rw->rw_worker.bgw_notify_pid != 0)
563 : {
564 : /* ... then zap it, and notify the waiter */
565 0 : int notify_pid = rw->rw_worker.bgw_notify_pid;
566 :
567 0 : ForgetBackgroundWorker(&iter);
568 0 : if (notify_pid != 0)
569 0 : kill(notify_pid, SIGUSR1);
570 : }
571 : }
572 822 : }
573 :
574 : /*
575 : * Reset background worker crash state.
576 : *
577 : * We assume that, after a crash-and-restart cycle, background workers without
578 : * the never-restart flag should be restarted immediately, instead of waiting
579 : * for bgw_restart_time to elapse. On the other hand, workers with that flag
580 : * should be forgotten immediately, since we won't ever restart them.
581 : *
582 : * This function should only be called from the postmaster.
583 : */
584 : void
585 8 : ResetBackgroundWorkerCrashTimes(void)
586 : {
587 : slist_mutable_iter iter;
588 :
589 16 : slist_foreach_modify(iter, &BackgroundWorkerList)
590 : {
591 : RegisteredBgWorker *rw;
592 :
593 8 : rw = slist_container(RegisteredBgWorker, rw_lnode, iter.cur);
594 :
595 8 : if (rw->rw_worker.bgw_restart_time == BGW_NEVER_RESTART)
596 : {
597 : /*
598 : * Workers marked BGW_NEVER_RESTART shouldn't get relaunched after
599 : * the crash, so forget about them. (If we wait until after the
600 : * crash to forget about them, and they are parallel workers,
601 : * parallel_terminate_count will get incremented after we've
602 : * already zeroed parallel_register_count, which would be bad.)
603 : */
604 0 : ForgetBackgroundWorker(&iter);
605 : }
606 : else
607 : {
608 : /*
609 : * The accounting which we do via parallel_register_count and
610 : * parallel_terminate_count would get messed up if a worker marked
611 : * parallel could survive a crash and restart cycle. All such
612 : * workers should be marked BGW_NEVER_RESTART, and thus control
613 : * should never reach this branch.
614 : */
615 : Assert((rw->rw_worker.bgw_flags & BGWORKER_CLASS_PARALLEL) == 0);
616 :
617 : /*
618 : * Allow this worker to be restarted immediately after we finish
619 : * resetting.
620 : */
621 8 : rw->rw_crashed_at = 0;
622 :
623 : /*
624 : * If there was anyone waiting for it, they're history.
625 : */
626 8 : rw->rw_worker.bgw_notify_pid = 0;
627 : }
628 : }
629 8 : }
630 :
631 : /*
632 : * Complain about the BackgroundWorker definition using error level elevel.
633 : * Return true if it looks ok, false if not (unless elevel >= ERROR, in
634 : * which case we won't return at all in the not-OK case).
635 : */
636 : static bool
637 4692 : SanityCheckBackgroundWorker(BackgroundWorker *worker, int elevel)
638 : {
639 : /* sanity check for flags */
640 :
641 : /*
642 : * We used to support workers not connected to shared memory, but don't
643 : * anymore. Thus this is a required flag now. We're not removing the flag
644 : * for compatibility reasons and because the flag still provides some
645 : * signal when reading code.
646 : */
647 4692 : if (!(worker->bgw_flags & BGWORKER_SHMEM_ACCESS))
648 : {
649 0 : ereport(elevel,
650 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
651 : errmsg("background worker \"%s\": background workers without shared memory access are not supported",
652 : worker->bgw_name)));
653 0 : return false;
654 : }
655 :
656 4692 : if (worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION)
657 : {
658 4674 : if (worker->bgw_start_time == BgWorkerStart_PostmasterStart)
659 : {
660 0 : ereport(elevel,
661 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
662 : errmsg("background worker \"%s\": cannot request database access if starting at postmaster start",
663 : worker->bgw_name)));
664 0 : return false;
665 : }
666 :
667 : /* XXX other checks? */
668 : }
669 :
670 4692 : if ((worker->bgw_restart_time < 0 &&
671 3304 : worker->bgw_restart_time != BGW_NEVER_RESTART) ||
672 4692 : (worker->bgw_restart_time > USECS_PER_DAY / 1000))
673 : {
674 0 : ereport(elevel,
675 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
676 : errmsg("background worker \"%s\": invalid restart interval",
677 : worker->bgw_name)));
678 0 : return false;
679 : }
680 :
681 : /*
682 : * Parallel workers may not be configured for restart, because the
683 : * parallel_register_count/parallel_terminate_count accounting can't
684 : * handle parallel workers lasting through a crash-and-restart cycle.
685 : */
686 4692 : if (worker->bgw_restart_time != BGW_NEVER_RESTART &&
687 1388 : (worker->bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
688 : {
689 0 : ereport(elevel,
690 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
691 : errmsg("background worker \"%s\": parallel workers may not be configured for restart",
692 : worker->bgw_name)));
693 0 : return false;
694 : }
695 :
696 : /*
697 : * If bgw_type is not filled in, use bgw_name.
698 : */
699 4692 : if (strcmp(worker->bgw_type, "") == 0)
700 0 : strcpy(worker->bgw_type, worker->bgw_name);
701 :
702 4692 : return true;
703 : }
704 :
705 : /*
706 : * Standard SIGTERM handler for background workers
707 : */
708 : static void
709 0 : bgworker_die(SIGNAL_ARGS)
710 : {
711 0 : sigprocmask(SIG_SETMASK, &BlockSig, NULL);
712 :
713 0 : ereport(FATAL,
714 : (errcode(ERRCODE_ADMIN_SHUTDOWN),
715 : errmsg("terminating background worker \"%s\" due to administrator command",
716 : MyBgworkerEntry->bgw_type)));
717 : }
718 :
719 : /*
720 : * Main entry point for background worker processes.
721 : */
722 : void
723 4092 : BackgroundWorkerMain(char *startup_data, size_t startup_data_len)
724 : {
725 : sigjmp_buf local_sigjmp_buf;
726 : BackgroundWorker *worker;
727 : bgworker_main_type entrypt;
728 :
729 4092 : if (startup_data == NULL)
730 0 : elog(FATAL, "unable to find bgworker entry");
731 : Assert(startup_data_len == sizeof(BackgroundWorker));
732 4092 : worker = MemoryContextAlloc(TopMemoryContext, sizeof(BackgroundWorker));
733 4092 : memcpy(worker, startup_data, sizeof(BackgroundWorker));
734 :
735 : /*
736 : * Now that we're done reading the startup data, release postmaster's
737 : * working memory context.
738 : */
739 4092 : if (PostmasterContext)
740 : {
741 4092 : MemoryContextDelete(PostmasterContext);
742 4092 : PostmasterContext = NULL;
743 : }
744 :
745 4092 : MyBgworkerEntry = worker;
746 4092 : MyBackendType = B_BG_WORKER;
747 4092 : init_ps_display(worker->bgw_name);
748 :
749 4092 : SetProcessingMode(InitProcessing);
750 :
751 : /* Apply PostAuthDelay */
752 4092 : if (PostAuthDelay > 0)
753 0 : pg_usleep(PostAuthDelay * 1000000L);
754 :
755 : /*
756 : * Set up signal handlers.
757 : */
758 4092 : if (worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION)
759 : {
760 : /*
761 : * SIGINT is used to signal canceling the current action
762 : */
763 4074 : pqsignal(SIGINT, StatementCancelHandler);
764 4074 : pqsignal(SIGUSR1, procsignal_sigusr1_handler);
765 4074 : pqsignal(SIGFPE, FloatExceptionHandler);
766 :
767 : /* XXX Any other handlers needed here? */
768 : }
769 : else
770 : {
771 18 : pqsignal(SIGINT, SIG_IGN);
772 18 : pqsignal(SIGUSR1, SIG_IGN);
773 18 : pqsignal(SIGFPE, SIG_IGN);
774 : }
775 4092 : pqsignal(SIGTERM, bgworker_die);
776 : /* SIGQUIT handler was already set up by InitPostmasterChild */
777 4092 : pqsignal(SIGHUP, SIG_IGN);
778 :
779 4092 : InitializeTimeouts(); /* establishes SIGALRM handler */
780 :
781 4092 : pqsignal(SIGPIPE, SIG_IGN);
782 4092 : pqsignal(SIGUSR2, SIG_IGN);
783 4092 : pqsignal(SIGCHLD, SIG_DFL);
784 :
785 : /*
786 : * If an exception is encountered, processing resumes here.
787 : *
788 : * We just need to clean up, report the error, and go away.
789 : */
790 4092 : if (sigsetjmp(local_sigjmp_buf, 1) != 0)
791 : {
792 : /* Since not using PG_TRY, must reset error stack by hand */
793 164 : error_context_stack = NULL;
794 :
795 : /* Prevent interrupts while cleaning up */
796 164 : HOLD_INTERRUPTS();
797 :
798 : /*
799 : * sigsetjmp will have blocked all signals, but we may need to accept
800 : * signals while communicating with our parallel leader. Once we've
801 : * done HOLD_INTERRUPTS() it should be safe to unblock signals.
802 : */
803 164 : BackgroundWorkerUnblockSignals();
804 :
805 : /* Report the error to the parallel leader and the server log */
806 164 : EmitErrorReport();
807 :
808 : /*
809 : * Do we need more cleanup here? For shmem-connected bgworkers, we
810 : * will call InitProcess below, which will install ProcKill as exit
811 : * callback. That will take care of releasing locks, etc.
812 : */
813 :
814 : /* and go away */
815 164 : proc_exit(1);
816 : }
817 :
818 : /* We can now handle ereport(ERROR) */
819 4092 : PG_exception_stack = &local_sigjmp_buf;
820 :
821 : /*
822 : * Create a per-backend PGPROC struct in shared memory. We must do this
823 : * before we can use LWLocks or access any shared memory.
824 : */
825 4092 : InitProcess();
826 :
827 : /*
828 : * Early initialization.
829 : */
830 4092 : BaseInit();
831 :
832 : /*
833 : * Look up the entry point function, loading its library if necessary.
834 : */
835 8184 : entrypt = LookupBackgroundWorkerFunction(worker->bgw_library_name,
836 4092 : worker->bgw_function_name);
837 :
838 : /*
839 : * Note that in normal processes, we would call InitPostgres here. For a
840 : * worker, however, we don't know what database to connect to, yet; so we
841 : * need to wait until the user code does it via
842 : * BackgroundWorkerInitializeConnection().
843 : */
844 :
845 : /*
846 : * Now invoke the user-defined worker code
847 : */
848 4092 : entrypt(worker->bgw_main_arg);
849 :
850 : /* ... and if it returns, we're done */
851 2642 : proc_exit(0);
852 : }
853 :
854 : /*
855 : * Register a new static background worker.
856 : *
857 : * This can only be called directly from postmaster or in the _PG_init
858 : * function of a module library that's loaded by shared_preload_libraries;
859 : * otherwise it will have no effect.
860 : */
861 : void
862 1394 : RegisterBackgroundWorker(BackgroundWorker *worker)
863 : {
864 : RegisteredBgWorker *rw;
865 : static int numworkers = 0;
866 :
867 : /*
868 : * Static background workers can only be registered in the postmaster
869 : * process.
870 : */
871 1394 : if (IsUnderPostmaster || !IsPostmasterEnvironment)
872 : {
873 : /*
874 : * In EXEC_BACKEND or single-user mode, we process
875 : * shared_preload_libraries in backend processes too. We cannot
876 : * register static background workers at that stage, but many
877 : * libraries' _PG_init() functions don't distinguish whether they're
878 : * being loaded in the postmaster or in a backend, they just check
879 : * process_shared_preload_libraries_in_progress. It's a bit sloppy,
880 : * but for historical reasons we tolerate it. In EXEC_BACKEND mode,
881 : * the background workers should already have been registered when the
882 : * library was loaded in postmaster.
883 : */
884 0 : if (process_shared_preload_libraries_in_progress)
885 0 : return;
886 0 : ereport(LOG,
887 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
888 : errmsg("background worker \"%s\": must be registered in shared_preload_libraries",
889 : worker->bgw_name)));
890 0 : return;
891 : }
892 :
893 : /*
894 : * Cannot register static background workers after calling
895 : * BackgroundWorkerShmemInit().
896 : */
897 1394 : if (BackgroundWorkerData != NULL)
898 0 : elog(ERROR, "cannot register background worker \"%s\" after shmem init",
899 : worker->bgw_name);
900 :
901 1394 : ereport(DEBUG1,
902 : (errmsg_internal("registering background worker \"%s\"", worker->bgw_name)));
903 :
904 1394 : if (!SanityCheckBackgroundWorker(worker, LOG))
905 0 : return;
906 :
907 1394 : if (worker->bgw_notify_pid != 0)
908 : {
909 0 : ereport(LOG,
910 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
911 : errmsg("background worker \"%s\": only dynamic background workers can request notification",
912 : worker->bgw_name)));
913 0 : return;
914 : }
915 :
916 : /*
917 : * Enforce maximum number of workers. Note this is overly restrictive: we
918 : * could allow more non-shmem-connected workers, because these don't count
919 : * towards the MAX_BACKENDS limit elsewhere. For now, it doesn't seem
920 : * important to relax this restriction.
921 : */
922 1394 : if (++numworkers > max_worker_processes)
923 : {
924 0 : ereport(LOG,
925 : (errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
926 : errmsg("too many background workers"),
927 : errdetail_plural("Up to %d background worker can be registered with the current settings.",
928 : "Up to %d background workers can be registered with the current settings.",
929 : max_worker_processes,
930 : max_worker_processes),
931 : errhint("Consider increasing the configuration parameter max_worker_processes.")));
932 0 : return;
933 : }
934 :
935 : /*
936 : * Copy the registration data into the registered workers list.
937 : */
938 1394 : rw = MemoryContextAllocExtended(PostmasterContext,
939 : sizeof(RegisteredBgWorker),
940 : MCXT_ALLOC_NO_OOM);
941 1394 : if (rw == NULL)
942 : {
943 0 : ereport(LOG,
944 : (errcode(ERRCODE_OUT_OF_MEMORY),
945 : errmsg("out of memory")));
946 0 : return;
947 : }
948 :
949 1394 : rw->rw_worker = *worker;
950 1394 : rw->rw_backend = NULL;
951 1394 : rw->rw_pid = 0;
952 1394 : rw->rw_child_slot = 0;
953 1394 : rw->rw_crashed_at = 0;
954 1394 : rw->rw_terminate = false;
955 :
956 1394 : slist_push_head(&BackgroundWorkerList, &rw->rw_lnode);
957 : }
958 :
959 : /*
960 : * Register a new background worker from a regular backend.
961 : *
962 : * Returns true on success and false on failure. Failure typically indicates
963 : * that no background worker slots are currently available.
964 : *
965 : * If handle != NULL, we'll set *handle to a pointer that can subsequently
966 : * be used as an argument to GetBackgroundWorkerPid(). The caller can
967 : * free this pointer using pfree(), if desired.
968 : */
969 : bool
970 3298 : RegisterDynamicBackgroundWorker(BackgroundWorker *worker,
971 : BackgroundWorkerHandle **handle)
972 : {
973 : int slotno;
974 3298 : bool success = false;
975 : bool parallel;
976 3298 : uint64 generation = 0;
977 :
978 : /*
979 : * We can't register dynamic background workers from the postmaster. If
980 : * this is a standalone backend, we're the only process and can't start
981 : * any more. In a multi-process environment, it might be theoretically
982 : * possible, but we don't currently support it due to locking
983 : * considerations; see comments on the BackgroundWorkerSlot data
984 : * structure.
985 : */
986 3298 : if (!IsUnderPostmaster)
987 0 : return false;
988 :
989 3298 : if (!SanityCheckBackgroundWorker(worker, ERROR))
990 0 : return false;
991 :
992 3298 : parallel = (worker->bgw_flags & BGWORKER_CLASS_PARALLEL) != 0;
993 :
994 3298 : LWLockAcquire(BackgroundWorkerLock, LW_EXCLUSIVE);
995 :
996 : /*
997 : * If this is a parallel worker, check whether there are already too many
998 : * parallel workers; if so, don't register another one. Our view of
999 : * parallel_terminate_count may be slightly stale, but that doesn't really
1000 : * matter: we would have gotten the same result if we'd arrived here
1001 : * slightly earlier anyway. There's no help for it, either, since the
1002 : * postmaster must not take locks; a memory barrier wouldn't guarantee
1003 : * anything useful.
1004 : */
1005 3298 : if (parallel && (BackgroundWorkerData->parallel_register_count -
1006 2664 : BackgroundWorkerData->parallel_terminate_count) >=
1007 : max_parallel_workers)
1008 : {
1009 : Assert(BackgroundWorkerData->parallel_register_count -
1010 : BackgroundWorkerData->parallel_terminate_count <=
1011 : MAX_PARALLEL_WORKER_LIMIT);
1012 20 : LWLockRelease(BackgroundWorkerLock);
1013 20 : return false;
1014 : }
1015 :
1016 : /*
1017 : * Look for an unused slot. If we find one, grab it.
1018 : */
1019 10200 : for (slotno = 0; slotno < BackgroundWorkerData->total_slots; ++slotno)
1020 : {
1021 10198 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
1022 :
1023 10198 : if (!slot->in_use)
1024 : {
1025 3276 : memcpy(&slot->worker, worker, sizeof(BackgroundWorker));
1026 3276 : slot->pid = InvalidPid; /* indicates not started yet */
1027 3276 : slot->generation++;
1028 3276 : slot->terminate = false;
1029 3276 : generation = slot->generation;
1030 3276 : if (parallel)
1031 2642 : BackgroundWorkerData->parallel_register_count++;
1032 :
1033 : /*
1034 : * Make sure postmaster doesn't see the slot as in use before it
1035 : * sees the new contents.
1036 : */
1037 3276 : pg_write_barrier();
1038 :
1039 3276 : slot->in_use = true;
1040 3276 : success = true;
1041 3276 : break;
1042 : }
1043 : }
1044 :
1045 3278 : LWLockRelease(BackgroundWorkerLock);
1046 :
1047 : /* If we found a slot, tell the postmaster to notice the change. */
1048 3278 : if (success)
1049 3276 : SendPostmasterSignal(PMSIGNAL_BACKGROUND_WORKER_CHANGE);
1050 :
1051 : /*
1052 : * If we found a slot and the user has provided a handle, initialize it.
1053 : */
1054 3278 : if (success && handle)
1055 : {
1056 3276 : *handle = palloc(sizeof(BackgroundWorkerHandle));
1057 3276 : (*handle)->slot = slotno;
1058 3276 : (*handle)->generation = generation;
1059 : }
1060 :
1061 3278 : return success;
1062 : }
1063 :
1064 : /*
1065 : * Get the PID of a dynamically-registered background worker.
1066 : *
1067 : * If the worker is determined to be running, the return value will be
1068 : * BGWH_STARTED and *pidp will get the PID of the worker process. If the
1069 : * postmaster has not yet attempted to start the worker, the return value will
1070 : * be BGWH_NOT_YET_STARTED. Otherwise, the return value is BGWH_STOPPED.
1071 : *
1072 : * BGWH_STOPPED can indicate either that the worker is temporarily stopped
1073 : * (because it is configured for automatic restart and exited non-zero),
1074 : * or that the worker is permanently stopped (because it exited with exit
1075 : * code 0, or was not configured for automatic restart), or even that the
1076 : * worker was unregistered without ever starting (either because startup
1077 : * failed and the worker is not configured for automatic restart, or because
1078 : * TerminateBackgroundWorker was used before the worker was successfully
1079 : * started).
1080 : */
1081 : BgwHandleStatus
1082 16029964 : GetBackgroundWorkerPid(BackgroundWorkerHandle *handle, pid_t *pidp)
1083 : {
1084 : BackgroundWorkerSlot *slot;
1085 : pid_t pid;
1086 :
1087 : Assert(handle->slot < max_worker_processes);
1088 16029964 : slot = &BackgroundWorkerData->slot[handle->slot];
1089 :
1090 : /*
1091 : * We could probably arrange to synchronize access to data using memory
1092 : * barriers only, but for now, let's just keep it simple and grab the
1093 : * lock. It seems unlikely that there will be enough traffic here to
1094 : * result in meaningful contention.
1095 : */
1096 16029964 : LWLockAcquire(BackgroundWorkerLock, LW_SHARED);
1097 :
1098 : /*
1099 : * The generation number can't be concurrently changed while we hold the
1100 : * lock. The pid, which is updated by the postmaster, can change at any
1101 : * time, but we assume such changes are atomic. So the value we read
1102 : * won't be garbage, but it might be out of date by the time the caller
1103 : * examines it (but that's unavoidable anyway).
1104 : *
1105 : * The in_use flag could be in the process of changing from true to false,
1106 : * but if it is already false then it can't change further.
1107 : */
1108 16029964 : if (handle->generation != slot->generation || !slot->in_use)
1109 2644 : pid = 0;
1110 : else
1111 16027320 : pid = slot->pid;
1112 :
1113 : /* All done. */
1114 16029964 : LWLockRelease(BackgroundWorkerLock);
1115 :
1116 16029964 : if (pid == 0)
1117 2644 : return BGWH_STOPPED;
1118 16027320 : else if (pid == InvalidPid)
1119 5185506 : return BGWH_NOT_YET_STARTED;
1120 10841814 : *pidp = pid;
1121 10841814 : return BGWH_STARTED;
1122 : }
1123 :
1124 : /*
1125 : * Wait for a background worker to start up.
1126 : *
1127 : * This is like GetBackgroundWorkerPid(), except that if the worker has not
1128 : * yet started, we wait for it to do so; thus, BGWH_NOT_YET_STARTED is never
1129 : * returned. However, if the postmaster has died, we give up and return
1130 : * BGWH_POSTMASTER_DIED, since it that case we know that startup will not
1131 : * take place.
1132 : *
1133 : * The caller *must* have set our PID as the worker's bgw_notify_pid,
1134 : * else we will not be awoken promptly when the worker's state changes.
1135 : */
1136 : BgwHandleStatus
1137 34 : WaitForBackgroundWorkerStartup(BackgroundWorkerHandle *handle, pid_t *pidp)
1138 : {
1139 : BgwHandleStatus status;
1140 : int rc;
1141 :
1142 : for (;;)
1143 20 : {
1144 : pid_t pid;
1145 :
1146 34 : CHECK_FOR_INTERRUPTS();
1147 :
1148 34 : status = GetBackgroundWorkerPid(handle, &pid);
1149 34 : if (status == BGWH_STARTED)
1150 14 : *pidp = pid;
1151 34 : if (status != BGWH_NOT_YET_STARTED)
1152 14 : break;
1153 :
1154 20 : rc = WaitLatch(MyLatch,
1155 : WL_LATCH_SET | WL_POSTMASTER_DEATH, 0,
1156 : WAIT_EVENT_BGWORKER_STARTUP);
1157 :
1158 20 : if (rc & WL_POSTMASTER_DEATH)
1159 : {
1160 0 : status = BGWH_POSTMASTER_DIED;
1161 0 : break;
1162 : }
1163 :
1164 20 : ResetLatch(MyLatch);
1165 : }
1166 :
1167 14 : return status;
1168 : }
1169 :
1170 : /*
1171 : * Wait for a background worker to stop.
1172 : *
1173 : * If the worker hasn't yet started, or is running, we wait for it to stop
1174 : * and then return BGWH_STOPPED. However, if the postmaster has died, we give
1175 : * up and return BGWH_POSTMASTER_DIED, because it's the postmaster that
1176 : * notifies us when a worker's state changes.
1177 : *
1178 : * The caller *must* have set our PID as the worker's bgw_notify_pid,
1179 : * else we will not be awoken promptly when the worker's state changes.
1180 : */
1181 : BgwHandleStatus
1182 5002 : WaitForBackgroundWorkerShutdown(BackgroundWorkerHandle *handle)
1183 : {
1184 : BgwHandleStatus status;
1185 : int rc;
1186 :
1187 : for (;;)
1188 2358 : {
1189 : pid_t pid;
1190 :
1191 5002 : CHECK_FOR_INTERRUPTS();
1192 :
1193 5002 : status = GetBackgroundWorkerPid(handle, &pid);
1194 5002 : if (status == BGWH_STOPPED)
1195 2644 : break;
1196 :
1197 2358 : rc = WaitLatch(MyLatch,
1198 : WL_LATCH_SET | WL_POSTMASTER_DEATH, 0,
1199 : WAIT_EVENT_BGWORKER_SHUTDOWN);
1200 :
1201 2358 : if (rc & WL_POSTMASTER_DEATH)
1202 : {
1203 0 : status = BGWH_POSTMASTER_DIED;
1204 0 : break;
1205 : }
1206 :
1207 2358 : ResetLatch(MyLatch);
1208 : }
1209 :
1210 2644 : return status;
1211 : }
1212 :
1213 : /*
1214 : * Instruct the postmaster to terminate a background worker.
1215 : *
1216 : * Note that it's safe to do this without regard to whether the worker is
1217 : * still running, or even if the worker may already have exited and been
1218 : * unregistered.
1219 : */
1220 : void
1221 6 : TerminateBackgroundWorker(BackgroundWorkerHandle *handle)
1222 : {
1223 : BackgroundWorkerSlot *slot;
1224 6 : bool signal_postmaster = false;
1225 :
1226 : Assert(handle->slot < max_worker_processes);
1227 6 : slot = &BackgroundWorkerData->slot[handle->slot];
1228 :
1229 : /* Set terminate flag in shared memory, unless slot has been reused. */
1230 6 : LWLockAcquire(BackgroundWorkerLock, LW_EXCLUSIVE);
1231 6 : if (handle->generation == slot->generation)
1232 : {
1233 6 : slot->terminate = true;
1234 6 : signal_postmaster = true;
1235 : }
1236 6 : LWLockRelease(BackgroundWorkerLock);
1237 :
1238 : /* Make sure the postmaster notices the change to shared memory. */
1239 6 : if (signal_postmaster)
1240 6 : SendPostmasterSignal(PMSIGNAL_BACKGROUND_WORKER_CHANGE);
1241 6 : }
1242 :
1243 : /*
1244 : * Look up (and possibly load) a bgworker entry point function.
1245 : *
1246 : * For functions contained in the core code, we use library name "postgres"
1247 : * and consult the InternalBGWorkers array. External functions are
1248 : * looked up, and loaded if necessary, using load_external_function().
1249 : *
1250 : * The point of this is to pass function names as strings across process
1251 : * boundaries. We can't pass actual function addresses because of the
1252 : * possibility that the function has been loaded at a different address
1253 : * in a different process. This is obviously a hazard for functions in
1254 : * loadable libraries, but it can happen even for functions in the core code
1255 : * on platforms using EXEC_BACKEND (e.g., Windows).
1256 : *
1257 : * At some point it might be worthwhile to get rid of InternalBGWorkers[]
1258 : * in favor of applying load_external_function() for core functions too;
1259 : * but that raises portability issues that are not worth addressing now.
1260 : */
1261 : static bgworker_main_type
1262 4092 : LookupBackgroundWorkerFunction(const char *libraryname, const char *funcname)
1263 : {
1264 : /*
1265 : * If the function is to be loaded from postgres itself, search the
1266 : * InternalBGWorkers array.
1267 : */
1268 4092 : if (strcmp(libraryname, "postgres") == 0)
1269 : {
1270 : int i;
1271 :
1272 6932 : for (i = 0; i < lengthof(InternalBGWorkers); i++)
1273 : {
1274 6932 : if (strcmp(InternalBGWorkers[i].fn_name, funcname) == 0)
1275 4066 : return InternalBGWorkers[i].fn_addr;
1276 : }
1277 :
1278 : /* We can only reach this by programming error. */
1279 0 : elog(ERROR, "internal function \"%s\" not found", funcname);
1280 : }
1281 :
1282 : /* Otherwise load from external library. */
1283 26 : return (bgworker_main_type)
1284 26 : load_external_function(libraryname, funcname, true, NULL);
1285 : }
1286 :
1287 : /*
1288 : * Given a PID, get the bgw_type of the background worker. Returns NULL if
1289 : * not a valid background worker.
1290 : *
1291 : * The return value is in static memory belonging to this function, so it has
1292 : * to be used before calling this function again. This is so that the caller
1293 : * doesn't have to worry about the background worker locking protocol.
1294 : */
1295 : const char *
1296 1318 : GetBackgroundWorkerTypeByPid(pid_t pid)
1297 : {
1298 : int slotno;
1299 1318 : bool found = false;
1300 : static char result[BGW_MAXLEN];
1301 :
1302 1318 : LWLockAcquire(BackgroundWorkerLock, LW_SHARED);
1303 :
1304 1546 : for (slotno = 0; slotno < BackgroundWorkerData->total_slots; slotno++)
1305 : {
1306 1546 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
1307 :
1308 1546 : if (slot->pid > 0 && slot->pid == pid)
1309 : {
1310 1318 : strcpy(result, slot->worker.bgw_type);
1311 1318 : found = true;
1312 1318 : break;
1313 : }
1314 : }
1315 :
1316 1318 : LWLockRelease(BackgroundWorkerLock);
1317 :
1318 1318 : if (!found)
1319 0 : return NULL;
1320 :
1321 1318 : return result;
1322 : }
|
