Line data Source code
1 : /*--------------------------------------------------------------------
2 : * bgworker.c
3 : * POSTGRES pluggable background workers implementation
4 : *
5 : * Portions Copyright (c) 1996-2021, 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/interrupt.h"
22 : #include "postmaster/postmaster.h"
23 : #include "replication/logicallauncher.h"
24 : #include "replication/logicalworker.h"
25 : #include "storage/dsm.h"
26 : #include "storage/ipc.h"
27 : #include "storage/latch.h"
28 : #include "storage/lwlock.h"
29 : #include "storage/pg_shmem.h"
30 : #include "storage/pmsignal.h"
31 : #include "storage/proc.h"
32 : #include "storage/procsignal.h"
33 : #include "storage/shmem.h"
34 : #include "tcop/tcopprot.h"
35 : #include "utils/ascii.h"
36 : #include "utils/ps_status.h"
37 : #include "utils/timeout.h"
38 :
39 : /*
40 : * The postmaster's list of registered background workers, in private memory.
41 : */
42 : slist_head BackgroundWorkerList = SLIST_STATIC_INIT(BackgroundWorkerList);
43 :
44 : /*
45 : * BackgroundWorkerSlots exist in shared memory and can be accessed (via
46 : * the BackgroundWorkerArray) by both the postmaster and by regular backends.
47 : * However, the postmaster cannot take locks, even spinlocks, because this
48 : * might allow it to crash or become wedged if shared memory gets corrupted.
49 : * Such an outcome is intolerable. Therefore, we need a lockless protocol
50 : * for coordinating access to this data.
51 : *
52 : * The 'in_use' flag is used to hand off responsibility for the slot between
53 : * the postmaster and the rest of the system. When 'in_use' is false,
54 : * the postmaster will ignore the slot entirely, except for the 'in_use' flag
55 : * itself, which it may read. In this state, regular backends may modify the
56 : * slot. Once a backend sets 'in_use' to true, the slot becomes the
57 : * responsibility of the postmaster. Regular backends may no longer modify it,
58 : * but the postmaster may examine it. Thus, a backend initializing a slot
59 : * must fully initialize the slot - and insert a write memory barrier - before
60 : * marking it as in use.
61 : *
62 : * As an exception, however, even when the slot is in use, regular backends
63 : * may set the 'terminate' flag for a slot, telling the postmaster not
64 : * to restart it. Once the background worker is no longer running, the slot
65 : * will be released for reuse.
66 : *
67 : * In addition to coordinating with the postmaster, backends modifying this
68 : * data structure must coordinate with each other. Since they can take locks,
69 : * this is straightforward: any backend wishing to manipulate a slot must
70 : * take BackgroundWorkerLock in exclusive mode. Backends wishing to read
71 : * data that might get concurrently modified by other backends should take
72 : * this lock in shared mode. No matter what, backends reading this data
73 : * structure must be able to tolerate concurrent modifications by the
74 : * postmaster.
75 : */
76 : typedef struct BackgroundWorkerSlot
77 : {
78 : bool in_use;
79 : bool terminate;
80 : pid_t pid; /* InvalidPid = not started yet; 0 = dead */
81 : uint64 generation; /* incremented when slot is recycled */
82 : BackgroundWorker worker;
83 : } BackgroundWorkerSlot;
84 :
85 : /*
86 : * In order to limit the total number of parallel workers (according to
87 : * max_parallel_workers GUC), we maintain the number of active parallel
88 : * workers. Since the postmaster cannot take locks, two variables are used for
89 : * this purpose: the number of registered parallel workers (modified by the
90 : * backends, protected by BackgroundWorkerLock) and the number of terminated
91 : * parallel workers (modified only by the postmaster, lockless). The active
92 : * number of parallel workers is the number of registered workers minus the
93 : * terminated ones. These counters can of course overflow, but it's not
94 : * important here since the subtraction will still give the right number.
95 : */
96 : typedef struct BackgroundWorkerArray
97 : {
98 : int total_slots;
99 : uint32 parallel_register_count;
100 : uint32 parallel_terminate_count;
101 : BackgroundWorkerSlot slot[FLEXIBLE_ARRAY_MEMBER];
102 : } BackgroundWorkerArray;
103 :
104 : struct BackgroundWorkerHandle
105 : {
106 : int slot;
107 : uint64 generation;
108 : };
109 :
110 : static BackgroundWorkerArray *BackgroundWorkerData;
111 :
112 : /*
113 : * List of internal background worker entry points. We need this for
114 : * reasons explained in LookupBackgroundWorkerFunction(), below.
115 : */
116 : static const struct
117 : {
118 : const char *fn_name;
119 : bgworker_main_type fn_addr;
120 : } InternalBGWorkers[] =
121 :
122 : {
123 : {
124 : "ParallelWorkerMain", ParallelWorkerMain
125 : },
126 : {
127 : "ApplyLauncherMain", ApplyLauncherMain
128 : },
129 : {
130 : "ApplyWorkerMain", ApplyWorkerMain
131 : }
132 : };
133 :
134 : /* Private functions. */
135 : static bgworker_main_type LookupBackgroundWorkerFunction(const char *libraryname, const char *funcname);
136 :
137 :
138 : /*
139 : * Calculate shared memory needed.
140 : */
141 : Size
142 6736 : BackgroundWorkerShmemSize(void)
143 : {
144 : Size size;
145 :
146 : /* Array of workers is variably sized. */
147 6736 : size = offsetof(BackgroundWorkerArray, slot);
148 6736 : size = add_size(size, mul_size(max_worker_processes,
149 : sizeof(BackgroundWorkerSlot)));
150 :
151 6736 : return size;
152 : }
153 :
154 : /*
155 : * Initialize shared memory.
156 : */
157 : void
158 2894 : BackgroundWorkerShmemInit(void)
159 : {
160 : bool found;
161 :
162 2894 : BackgroundWorkerData = ShmemInitStruct("Background Worker Data",
163 : BackgroundWorkerShmemSize(),
164 : &found);
165 2894 : if (!IsUnderPostmaster)
166 : {
167 : slist_iter siter;
168 2894 : int slotno = 0;
169 :
170 2894 : BackgroundWorkerData->total_slots = max_worker_processes;
171 2894 : BackgroundWorkerData->parallel_register_count = 0;
172 2894 : BackgroundWorkerData->parallel_terminate_count = 0;
173 :
174 : /*
175 : * Copy contents of worker list into shared memory. Record the shared
176 : * memory slot assigned to each worker. This ensures a 1-to-1
177 : * correspondence between the postmaster's private list and the array
178 : * in shared memory.
179 : */
180 3846 : slist_foreach(siter, &BackgroundWorkerList)
181 : {
182 952 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
183 : RegisteredBgWorker *rw;
184 :
185 952 : rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur);
186 : Assert(slotno < max_worker_processes);
187 952 : slot->in_use = true;
188 952 : slot->terminate = false;
189 952 : slot->pid = InvalidPid;
190 952 : slot->generation = 0;
191 952 : rw->rw_shmem_slot = slotno;
192 952 : rw->rw_worker.bgw_notify_pid = 0; /* might be reinit after crash */
193 952 : memcpy(&slot->worker, &rw->rw_worker, sizeof(BackgroundWorker));
194 952 : ++slotno;
195 : }
196 :
197 : /*
198 : * Mark any remaining slots as not in use.
199 : */
200 25094 : while (slotno < max_worker_processes)
201 : {
202 22200 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
203 :
204 22200 : slot->in_use = false;
205 22200 : ++slotno;
206 : }
207 : }
208 : else
209 : Assert(found);
210 2894 : }
211 :
212 : /*
213 : * Search the postmaster's backend-private list of RegisteredBgWorker objects
214 : * for the one that maps to the given slot number.
215 : */
216 : static RegisteredBgWorker *
217 3788 : FindRegisteredWorkerBySlotNumber(int slotno)
218 : {
219 : slist_iter siter;
220 :
221 9326 : slist_foreach(siter, &BackgroundWorkerList)
222 : {
223 : RegisteredBgWorker *rw;
224 :
225 7294 : rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur);
226 7294 : if (rw->rw_shmem_slot == slotno)
227 1756 : return rw;
228 : }
229 :
230 2032 : return NULL;
231 : }
232 :
233 : /*
234 : * Notice changes to shared memory made by other backends.
235 : * Accept new worker requests only if allow_new_workers is true.
236 : *
237 : * This code runs in the postmaster, so we must be very careful not to assume
238 : * that shared memory contents are sane. Otherwise, a rogue backend could
239 : * take out the postmaster.
240 : */
241 : void
242 1114 : BackgroundWorkerStateChange(bool allow_new_workers)
243 : {
244 : int slotno;
245 :
246 : /*
247 : * The total number of slots stored in shared memory should match our
248 : * notion of max_worker_processes. If it does not, something is very
249 : * wrong. Further down, we always refer to this value as
250 : * max_worker_processes, in case shared memory gets corrupted while we're
251 : * looping.
252 : */
253 1114 : if (max_worker_processes != BackgroundWorkerData->total_slots)
254 : {
255 0 : ereport(LOG,
256 : (errmsg("inconsistent background worker state (max_worker_processes=%d, total_slots=%d)",
257 : max_worker_processes,
258 : BackgroundWorkerData->total_slots)));
259 0 : return;
260 : }
261 :
262 : /*
263 : * Iterate through slots, looking for newly-registered workers or workers
264 : * who must die.
265 : */
266 10026 : for (slotno = 0; slotno < max_worker_processes; ++slotno)
267 : {
268 8912 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
269 : RegisteredBgWorker *rw;
270 :
271 8912 : if (!slot->in_use)
272 5124 : continue;
273 :
274 : /*
275 : * Make sure we don't see the in_use flag before the updated slot
276 : * contents.
277 : */
278 3788 : pg_read_barrier();
279 :
280 : /* See whether we already know about this worker. */
281 3788 : rw = FindRegisteredWorkerBySlotNumber(slotno);
282 3788 : if (rw != NULL)
283 : {
284 : /*
285 : * In general, the worker data can't change after it's initially
286 : * registered. However, someone can set the terminate flag.
287 : */
288 1756 : if (slot->terminate && !rw->rw_terminate)
289 : {
290 4 : rw->rw_terminate = true;
291 4 : if (rw->rw_pid != 0)
292 4 : kill(rw->rw_pid, SIGTERM);
293 : else
294 : {
295 : /* Report never-started, now-terminated worker as dead. */
296 0 : ReportBackgroundWorkerPID(rw);
297 : }
298 : }
299 1756 : continue;
300 : }
301 :
302 : /*
303 : * If we aren't allowing new workers, then immediately mark it for
304 : * termination; the next stanza will take care of cleaning it up.
305 : * Doing this ensures that any process waiting for the worker will get
306 : * awoken, even though the worker will never be allowed to run.
307 : */
308 2032 : if (!allow_new_workers)
309 0 : slot->terminate = true;
310 :
311 : /*
312 : * If the worker is marked for termination, we don't need to add it to
313 : * the registered workers list; we can just free the slot. However, if
314 : * bgw_notify_pid is set, the process that registered the worker may
315 : * need to know that we've processed the terminate request, so be sure
316 : * to signal it.
317 : */
318 2032 : if (slot->terminate)
319 : {
320 : int notify_pid;
321 :
322 : /*
323 : * We need a memory barrier here to make sure that the load of
324 : * bgw_notify_pid and the update of parallel_terminate_count
325 : * complete before the store to in_use.
326 : */
327 0 : notify_pid = slot->worker.bgw_notify_pid;
328 0 : if ((slot->worker.bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
329 0 : BackgroundWorkerData->parallel_terminate_count++;
330 0 : slot->pid = 0;
331 :
332 0 : pg_memory_barrier();
333 0 : slot->in_use = false;
334 :
335 0 : if (notify_pid != 0)
336 0 : kill(notify_pid, SIGUSR1);
337 :
338 0 : continue;
339 : }
340 :
341 : /*
342 : * Copy the registration data into the registered workers list.
343 : */
344 2032 : rw = malloc(sizeof(RegisteredBgWorker));
345 2032 : if (rw == NULL)
346 : {
347 0 : ereport(LOG,
348 : (errcode(ERRCODE_OUT_OF_MEMORY),
349 : errmsg("out of memory")));
350 0 : return;
351 : }
352 :
353 : /*
354 : * Copy strings in a paranoid way. If shared memory is corrupted, the
355 : * source data might not even be NUL-terminated.
356 : */
357 2032 : ascii_safe_strlcpy(rw->rw_worker.bgw_name,
358 2032 : slot->worker.bgw_name, BGW_MAXLEN);
359 2032 : ascii_safe_strlcpy(rw->rw_worker.bgw_type,
360 2032 : slot->worker.bgw_type, BGW_MAXLEN);
361 2032 : ascii_safe_strlcpy(rw->rw_worker.bgw_library_name,
362 2032 : slot->worker.bgw_library_name, BGW_MAXLEN);
363 2032 : ascii_safe_strlcpy(rw->rw_worker.bgw_function_name,
364 2032 : slot->worker.bgw_function_name, BGW_MAXLEN);
365 :
366 : /*
367 : * Copy various fixed-size fields.
368 : *
369 : * flags, start_time, and restart_time are examined by the postmaster,
370 : * but nothing too bad will happen if they are corrupted. The
371 : * remaining fields will only be examined by the child process. It
372 : * might crash, but we won't.
373 : */
374 2032 : rw->rw_worker.bgw_flags = slot->worker.bgw_flags;
375 2032 : rw->rw_worker.bgw_start_time = slot->worker.bgw_start_time;
376 2032 : rw->rw_worker.bgw_restart_time = slot->worker.bgw_restart_time;
377 2032 : rw->rw_worker.bgw_main_arg = slot->worker.bgw_main_arg;
378 2032 : memcpy(rw->rw_worker.bgw_extra, slot->worker.bgw_extra, BGW_EXTRALEN);
379 :
380 : /*
381 : * Copy the PID to be notified about state changes, but only if the
382 : * postmaster knows about a backend with that PID. It isn't an error
383 : * if the postmaster doesn't know about the PID, because the backend
384 : * that requested the worker could have died (or been killed) just
385 : * after doing so. Nonetheless, at least until we get some experience
386 : * with how this plays out in the wild, log a message at a relative
387 : * high debug level.
388 : */
389 2032 : rw->rw_worker.bgw_notify_pid = slot->worker.bgw_notify_pid;
390 2032 : if (!PostmasterMarkPIDForWorkerNotify(rw->rw_worker.bgw_notify_pid))
391 : {
392 0 : elog(DEBUG1, "worker notification PID %ld is not valid",
393 : (long) rw->rw_worker.bgw_notify_pid);
394 0 : rw->rw_worker.bgw_notify_pid = 0;
395 : }
396 :
397 : /* Initialize postmaster bookkeeping. */
398 2032 : rw->rw_backend = NULL;
399 2032 : rw->rw_pid = 0;
400 2032 : rw->rw_child_slot = 0;
401 2032 : rw->rw_crashed_at = 0;
402 2032 : rw->rw_shmem_slot = slotno;
403 2032 : rw->rw_terminate = false;
404 :
405 : /* Log it! */
406 2032 : ereport(DEBUG1,
407 : (errmsg_internal("registering background worker \"%s\"",
408 : rw->rw_worker.bgw_name)));
409 :
410 2032 : slist_push_head(&BackgroundWorkerList, &rw->rw_lnode);
411 : }
412 : }
413 :
414 : /*
415 : * Forget about a background worker that's no longer needed.
416 : *
417 : * The worker must be identified by passing an slist_mutable_iter that
418 : * points to it. This convention allows deletion of workers during
419 : * searches of the worker list, and saves having to search the list again.
420 : *
421 : * Caller is responsible for notifying bgw_notify_pid, if appropriate.
422 : *
423 : * This function must be invoked only in the postmaster.
424 : */
425 : void
426 2036 : ForgetBackgroundWorker(slist_mutable_iter *cur)
427 : {
428 : RegisteredBgWorker *rw;
429 : BackgroundWorkerSlot *slot;
430 :
431 2036 : rw = slist_container(RegisteredBgWorker, rw_lnode, cur->cur);
432 :
433 : Assert(rw->rw_shmem_slot < max_worker_processes);
434 2036 : slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
435 : Assert(slot->in_use);
436 :
437 : /*
438 : * We need a memory barrier here to make sure that the update of
439 : * parallel_terminate_count completes before the store to in_use.
440 : */
441 2036 : if ((rw->rw_worker.bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
442 1690 : BackgroundWorkerData->parallel_terminate_count++;
443 :
444 2036 : pg_memory_barrier();
445 2036 : slot->in_use = false;
446 :
447 2036 : ereport(DEBUG1,
448 : (errmsg_internal("unregistering background worker \"%s\"",
449 : rw->rw_worker.bgw_name)));
450 :
451 2036 : slist_delete_current(cur);
452 2036 : free(rw);
453 2036 : }
454 :
455 : /*
456 : * Report the PID of a newly-launched background worker in shared memory.
457 : *
458 : * This function should only be called from the postmaster.
459 : */
460 : void
461 2858 : ReportBackgroundWorkerPID(RegisteredBgWorker *rw)
462 : {
463 : BackgroundWorkerSlot *slot;
464 :
465 : Assert(rw->rw_shmem_slot < max_worker_processes);
466 2858 : slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
467 2858 : slot->pid = rw->rw_pid;
468 :
469 2858 : if (rw->rw_worker.bgw_notify_pid != 0)
470 2032 : kill(rw->rw_worker.bgw_notify_pid, SIGUSR1);
471 2858 : }
472 :
473 : /*
474 : * Report that the PID of a background worker is now zero because a
475 : * previously-running background worker has exited.
476 : *
477 : * This function should only be called from the postmaster.
478 : */
479 : void
480 2524 : ReportBackgroundWorkerExit(slist_mutable_iter *cur)
481 : {
482 : RegisteredBgWorker *rw;
483 : BackgroundWorkerSlot *slot;
484 : int notify_pid;
485 :
486 2524 : rw = slist_container(RegisteredBgWorker, rw_lnode, cur->cur);
487 :
488 : Assert(rw->rw_shmem_slot < max_worker_processes);
489 2524 : slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
490 2524 : slot->pid = rw->rw_pid;
491 2524 : notify_pid = rw->rw_worker.bgw_notify_pid;
492 :
493 : /*
494 : * If this worker is slated for deregistration, do that before notifying
495 : * the process which started it. Otherwise, if that process tries to
496 : * reuse the slot immediately, it might not be available yet. In theory
497 : * that could happen anyway if the process checks slot->pid at just the
498 : * wrong moment, but this makes the window narrower.
499 : */
500 2524 : if (rw->rw_terminate ||
501 638 : rw->rw_worker.bgw_restart_time == BGW_NEVER_RESTART)
502 2026 : ForgetBackgroundWorker(cur);
503 :
504 2524 : if (notify_pid != 0)
505 1992 : kill(notify_pid, SIGUSR1);
506 2524 : }
507 :
508 : /*
509 : * Cancel SIGUSR1 notifications for a PID belonging to an exiting backend.
510 : *
511 : * This function should only be called from the postmaster.
512 : */
513 : void
514 220 : BackgroundWorkerStopNotifications(pid_t pid)
515 : {
516 : slist_iter siter;
517 :
518 616 : slist_foreach(siter, &BackgroundWorkerList)
519 : {
520 : RegisteredBgWorker *rw;
521 :
522 396 : rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur);
523 396 : if (rw->rw_worker.bgw_notify_pid == pid)
524 30 : rw->rw_worker.bgw_notify_pid = 0;
525 : }
526 220 : }
527 :
528 : /*
529 : * Cancel any not-yet-started worker requests that have waiting processes.
530 : *
531 : * This is called during a normal ("smart" or "fast") database shutdown.
532 : * After this point, no new background workers will be started, so anything
533 : * that might be waiting for them needs to be kicked off its wait. We do
534 : * that by cancelling the bgworker registration entirely, which is perhaps
535 : * overkill, but since we're shutting down it does not matter whether the
536 : * registration record sticks around.
537 : *
538 : * This function should only be called from the postmaster.
539 : */
540 : void
541 544 : ForgetUnstartedBackgroundWorkers(void)
542 : {
543 : slist_mutable_iter iter;
544 :
545 1118 : slist_foreach_modify(iter, &BackgroundWorkerList)
546 : {
547 : RegisteredBgWorker *rw;
548 : BackgroundWorkerSlot *slot;
549 :
550 574 : rw = slist_container(RegisteredBgWorker, rw_lnode, iter.cur);
551 : Assert(rw->rw_shmem_slot < max_worker_processes);
552 574 : slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
553 :
554 : /* If it's not yet started, and there's someone waiting ... */
555 574 : if (slot->pid == InvalidPid &&
556 46 : rw->rw_worker.bgw_notify_pid != 0)
557 : {
558 : /* ... then zap it, and notify the waiter */
559 0 : int notify_pid = rw->rw_worker.bgw_notify_pid;
560 :
561 0 : ForgetBackgroundWorker(&iter);
562 0 : if (notify_pid != 0)
563 0 : kill(notify_pid, SIGUSR1);
564 : }
565 : }
566 544 : }
567 :
568 : /*
569 : * Reset background worker crash state.
570 : *
571 : * We assume that, after a crash-and-restart cycle, background workers without
572 : * the never-restart flag should be restarted immediately, instead of waiting
573 : * for bgw_restart_time to elapse. On the other hand, workers with that flag
574 : * should be forgotten immediately, since we won't ever restart them.
575 : *
576 : * This function should only be called from the postmaster.
577 : */
578 : void
579 8 : ResetBackgroundWorkerCrashTimes(void)
580 : {
581 : slist_mutable_iter iter;
582 :
583 16 : slist_foreach_modify(iter, &BackgroundWorkerList)
584 : {
585 : RegisteredBgWorker *rw;
586 :
587 8 : rw = slist_container(RegisteredBgWorker, rw_lnode, iter.cur);
588 :
589 8 : if (rw->rw_worker.bgw_restart_time == BGW_NEVER_RESTART)
590 : {
591 : /*
592 : * Workers marked BGW_NEVER_RESTART shouldn't get relaunched after
593 : * the crash, so forget about them. (If we wait until after the
594 : * crash to forget about them, and they are parallel workers,
595 : * parallel_terminate_count will get incremented after we've
596 : * already zeroed parallel_register_count, which would be bad.)
597 : */
598 0 : ForgetBackgroundWorker(&iter);
599 : }
600 : else
601 : {
602 : /*
603 : * The accounting which we do via parallel_register_count and
604 : * parallel_terminate_count would get messed up if a worker marked
605 : * parallel could survive a crash and restart cycle. All such
606 : * workers should be marked BGW_NEVER_RESTART, and thus control
607 : * should never reach this branch.
608 : */
609 : Assert((rw->rw_worker.bgw_flags & BGWORKER_CLASS_PARALLEL) == 0);
610 :
611 : /*
612 : * Allow this worker to be restarted immediately after we finish
613 : * resetting.
614 : */
615 8 : rw->rw_crashed_at = 0;
616 :
617 : /*
618 : * If there was anyone waiting for it, they're history.
619 : */
620 8 : rw->rw_worker.bgw_notify_pid = 0;
621 : }
622 : }
623 8 : }
624 :
625 : #ifdef EXEC_BACKEND
626 : /*
627 : * In EXEC_BACKEND mode, workers use this to retrieve their details from
628 : * shared memory.
629 : */
630 : BackgroundWorker *
631 : BackgroundWorkerEntry(int slotno)
632 : {
633 : static BackgroundWorker myEntry;
634 : BackgroundWorkerSlot *slot;
635 :
636 : Assert(slotno < BackgroundWorkerData->total_slots);
637 : slot = &BackgroundWorkerData->slot[slotno];
638 : Assert(slot->in_use);
639 :
640 : /* must copy this in case we don't intend to retain shmem access */
641 : memcpy(&myEntry, &slot->worker, sizeof myEntry);
642 : return &myEntry;
643 : }
644 : #endif
645 :
646 : /*
647 : * Complain about the BackgroundWorker definition using error level elevel.
648 : * Return true if it looks ok, false if not (unless elevel >= ERROR, in
649 : * which case we won't return at all in the not-OK case).
650 : */
651 : static bool
652 2954 : SanityCheckBackgroundWorker(BackgroundWorker *worker, int elevel)
653 : {
654 : /* sanity check for flags */
655 :
656 : /*
657 : * We used to support workers not connected to shared memory, but don't
658 : * anymore. Thus this is a required flag now. We're not removing the flag
659 : * for compatibility reasons and because the flag still provides some
660 : * signal when reading code.
661 : */
662 2954 : if (!(worker->bgw_flags & BGWORKER_SHMEM_ACCESS))
663 : {
664 0 : ereport(elevel,
665 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
666 : errmsg("background worker \"%s\": background worker without shared memory access are not supported",
667 : worker->bgw_name)));
668 0 : return false;
669 : }
670 :
671 2954 : if (worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION)
672 : {
673 2940 : if (worker->bgw_start_time == BgWorkerStart_PostmasterStart)
674 : {
675 0 : ereport(elevel,
676 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
677 : errmsg("background worker \"%s\": cannot request database access if starting at postmaster start",
678 : worker->bgw_name)));
679 0 : return false;
680 : }
681 :
682 : /* XXX other checks? */
683 : }
684 :
685 2954 : if ((worker->bgw_restart_time < 0 &&
686 2004 : worker->bgw_restart_time != BGW_NEVER_RESTART) ||
687 2954 : (worker->bgw_restart_time > USECS_PER_DAY / 1000))
688 : {
689 0 : ereport(elevel,
690 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
691 : errmsg("background worker \"%s\": invalid restart interval",
692 : worker->bgw_name)));
693 0 : return false;
694 : }
695 :
696 : /*
697 : * Parallel workers may not be configured for restart, because the
698 : * parallel_register_count/parallel_terminate_count accounting can't
699 : * handle parallel workers lasting through a crash-and-restart cycle.
700 : */
701 2954 : if (worker->bgw_restart_time != BGW_NEVER_RESTART &&
702 950 : (worker->bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
703 : {
704 0 : ereport(elevel,
705 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
706 : errmsg("background worker \"%s\": parallel workers may not be configured for restart",
707 : worker->bgw_name)));
708 0 : return false;
709 : }
710 :
711 : /*
712 : * If bgw_type is not filled in, use bgw_name.
713 : */
714 2954 : if (strcmp(worker->bgw_type, "") == 0)
715 0 : strcpy(worker->bgw_type, worker->bgw_name);
716 :
717 2954 : return true;
718 : }
719 :
720 : /*
721 : * Standard SIGTERM handler for background workers
722 : */
723 : static void
724 0 : bgworker_die(SIGNAL_ARGS)
725 : {
726 0 : PG_SETMASK(&BlockSig);
727 :
728 0 : ereport(FATAL,
729 : (errcode(ERRCODE_ADMIN_SHUTDOWN),
730 : errmsg("terminating background worker \"%s\" due to administrator command",
731 : MyBgworkerEntry->bgw_type)));
732 : }
733 :
734 : /*
735 : * Start a new background worker
736 : *
737 : * This is the main entry point for background worker, to be called from
738 : * postmaster.
739 : */
740 : void
741 2530 : StartBackgroundWorker(void)
742 : {
743 : sigjmp_buf local_sigjmp_buf;
744 2530 : BackgroundWorker *worker = MyBgworkerEntry;
745 : bgworker_main_type entrypt;
746 :
747 2530 : if (worker == NULL)
748 0 : elog(FATAL, "unable to find bgworker entry");
749 :
750 2530 : IsBackgroundWorker = true;
751 :
752 2530 : MyBackendType = B_BG_WORKER;
753 2530 : init_ps_display(worker->bgw_name);
754 :
755 2530 : SetProcessingMode(InitProcessing);
756 :
757 : /* Apply PostAuthDelay */
758 2530 : if (PostAuthDelay > 0)
759 0 : pg_usleep(PostAuthDelay * 1000000L);
760 :
761 : /*
762 : * Set up signal handlers.
763 : */
764 2530 : if (worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION)
765 : {
766 : /*
767 : * SIGINT is used to signal canceling the current action
768 : */
769 2516 : pqsignal(SIGINT, StatementCancelHandler);
770 2516 : pqsignal(SIGUSR1, procsignal_sigusr1_handler);
771 2516 : pqsignal(SIGFPE, FloatExceptionHandler);
772 :
773 : /* XXX Any other handlers needed here? */
774 : }
775 : else
776 : {
777 14 : pqsignal(SIGINT, SIG_IGN);
778 14 : pqsignal(SIGUSR1, SIG_IGN);
779 14 : pqsignal(SIGFPE, SIG_IGN);
780 : }
781 2530 : pqsignal(SIGTERM, bgworker_die);
782 : /* SIGQUIT handler was already set up by InitPostmasterChild */
783 2530 : pqsignal(SIGHUP, SIG_IGN);
784 :
785 2530 : InitializeTimeouts(); /* establishes SIGALRM handler */
786 :
787 2530 : pqsignal(SIGPIPE, SIG_IGN);
788 2530 : pqsignal(SIGUSR2, SIG_IGN);
789 2530 : pqsignal(SIGCHLD, SIG_DFL);
790 :
791 : /*
792 : * If an exception is encountered, processing resumes here.
793 : *
794 : * We just need to clean up, report the error, and go away.
795 : */
796 2530 : if (sigsetjmp(local_sigjmp_buf, 1) != 0)
797 : {
798 : /* Since not using PG_TRY, must reset error stack by hand */
799 56 : error_context_stack = NULL;
800 :
801 : /* Prevent interrupts while cleaning up */
802 56 : HOLD_INTERRUPTS();
803 :
804 : /*
805 : * sigsetjmp will have blocked all signals, but we may need to accept
806 : * signals while communicating with our parallel leader. Once we've
807 : * done HOLD_INTERRUPTS() it should be safe to unblock signals.
808 : */
809 56 : BackgroundWorkerUnblockSignals();
810 :
811 : /* Report the error to the parallel leader and the server log */
812 56 : EmitErrorReport();
813 :
814 : /*
815 : * Do we need more cleanup here? For shmem-connected bgworkers, we
816 : * will call InitProcess below, which will install ProcKill as exit
817 : * callback. That will take care of releasing locks, etc.
818 : */
819 :
820 : /* and go away */
821 56 : proc_exit(1);
822 : }
823 :
824 : /* We can now handle ereport(ERROR) */
825 2530 : PG_exception_stack = &local_sigjmp_buf;
826 :
827 : /*
828 : * Create a per-backend PGPROC struct in shared memory, except in the
829 : * EXEC_BACKEND case where this was done in SubPostmasterMain. We must
830 : * do this before we can use LWLocks (and in the EXEC_BACKEND case we
831 : * already had to do some stuff with LWLocks).
832 : */
833 : #ifndef EXEC_BACKEND
834 2530 : InitProcess();
835 : #endif
836 :
837 : /*
838 : * Early initialization.
839 : */
840 2530 : BaseInit();
841 :
842 : /*
843 : * Look up the entry point function, loading its library if necessary.
844 : */
845 5060 : entrypt = LookupBackgroundWorkerFunction(worker->bgw_library_name,
846 2530 : worker->bgw_function_name);
847 :
848 : /*
849 : * Note that in normal processes, we would call InitPostgres here. For a
850 : * worker, however, we don't know what database to connect to, yet; so we
851 : * need to wait until the user code does it via
852 : * BackgroundWorkerInitializeConnection().
853 : */
854 :
855 : /*
856 : * Now invoke the user-defined worker code
857 : */
858 2530 : entrypt(worker->bgw_main_arg);
859 :
860 : /* ... and if it returns, we're done */
861 1686 : proc_exit(0);
862 : }
863 :
864 : /*
865 : * Register a new static background worker.
866 : *
867 : * This can only be called directly from postmaster or in the _PG_init
868 : * function of a module library that's loaded by shared_preload_libraries;
869 : * otherwise it will have no effect.
870 : */
871 : void
872 954 : RegisterBackgroundWorker(BackgroundWorker *worker)
873 : {
874 : RegisteredBgWorker *rw;
875 : static int numworkers = 0;
876 :
877 954 : if (!IsUnderPostmaster)
878 954 : ereport(DEBUG1,
879 : (errmsg_internal("registering background worker \"%s\"", worker->bgw_name)));
880 :
881 954 : if (!process_shared_preload_libraries_in_progress &&
882 950 : strcmp(worker->bgw_library_name, "postgres") != 0)
883 : {
884 0 : if (!IsUnderPostmaster)
885 0 : ereport(LOG,
886 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
887 : errmsg("background worker \"%s\": must be registered in shared_preload_libraries",
888 : worker->bgw_name)));
889 0 : return;
890 : }
891 :
892 954 : if (!SanityCheckBackgroundWorker(worker, LOG))
893 0 : return;
894 :
895 954 : if (worker->bgw_notify_pid != 0)
896 : {
897 0 : ereport(LOG,
898 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
899 : errmsg("background worker \"%s\": only dynamic background workers can request notification",
900 : worker->bgw_name)));
901 0 : return;
902 : }
903 :
904 : /*
905 : * Enforce maximum number of workers. Note this is overly restrictive: we
906 : * could allow more non-shmem-connected workers, because these don't count
907 : * towards the MAX_BACKENDS limit elsewhere. For now, it doesn't seem
908 : * important to relax this restriction.
909 : */
910 954 : if (++numworkers > max_worker_processes)
911 : {
912 0 : ereport(LOG,
913 : (errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
914 : errmsg("too many background workers"),
915 : errdetail_plural("Up to %d background worker can be registered with the current settings.",
916 : "Up to %d background workers can be registered with the current settings.",
917 : max_worker_processes,
918 : max_worker_processes),
919 : errhint("Consider increasing the configuration parameter \"max_worker_processes\".")));
920 0 : return;
921 : }
922 :
923 : /*
924 : * Copy the registration data into the registered workers list.
925 : */
926 954 : rw = malloc(sizeof(RegisteredBgWorker));
927 954 : if (rw == NULL)
928 : {
929 0 : ereport(LOG,
930 : (errcode(ERRCODE_OUT_OF_MEMORY),
931 : errmsg("out of memory")));
932 0 : return;
933 : }
934 :
935 954 : rw->rw_worker = *worker;
936 954 : rw->rw_backend = NULL;
937 954 : rw->rw_pid = 0;
938 954 : rw->rw_child_slot = 0;
939 954 : rw->rw_crashed_at = 0;
940 954 : rw->rw_terminate = false;
941 :
942 954 : slist_push_head(&BackgroundWorkerList, &rw->rw_lnode);
943 : }
944 :
945 : /*
946 : * Register a new background worker from a regular backend.
947 : *
948 : * Returns true on success and false on failure. Failure typically indicates
949 : * that no background worker slots are currently available.
950 : *
951 : * If handle != NULL, we'll set *handle to a pointer that can subsequently
952 : * be used as an argument to GetBackgroundWorkerPid(). The caller can
953 : * free this pointer using pfree(), if desired.
954 : */
955 : bool
956 2000 : RegisterDynamicBackgroundWorker(BackgroundWorker *worker,
957 : BackgroundWorkerHandle **handle)
958 : {
959 : int slotno;
960 2000 : bool success = false;
961 : bool parallel;
962 2000 : uint64 generation = 0;
963 :
964 : /*
965 : * We can't register dynamic background workers from the postmaster. If
966 : * this is a standalone backend, we're the only process and can't start
967 : * any more. In a multi-process environment, it might be theoretically
968 : * possible, but we don't currently support it due to locking
969 : * considerations; see comments on the BackgroundWorkerSlot data
970 : * structure.
971 : */
972 2000 : if (!IsUnderPostmaster)
973 0 : return false;
974 :
975 2000 : if (!SanityCheckBackgroundWorker(worker, ERROR))
976 0 : return false;
977 :
978 2000 : parallel = (worker->bgw_flags & BGWORKER_CLASS_PARALLEL) != 0;
979 :
980 2000 : LWLockAcquire(BackgroundWorkerLock, LW_EXCLUSIVE);
981 :
982 : /*
983 : * If this is a parallel worker, check whether there are already too many
984 : * parallel workers; if so, don't register another one. Our view of
985 : * parallel_terminate_count may be slightly stale, but that doesn't really
986 : * matter: we would have gotten the same result if we'd arrived here
987 : * slightly earlier anyway. There's no help for it, either, since the
988 : * postmaster must not take locks; a memory barrier wouldn't guarantee
989 : * anything useful.
990 : */
991 2000 : if (parallel && (BackgroundWorkerData->parallel_register_count -
992 1704 : BackgroundWorkerData->parallel_terminate_count) >=
993 : max_parallel_workers)
994 : {
995 : Assert(BackgroundWorkerData->parallel_register_count -
996 : BackgroundWorkerData->parallel_terminate_count <=
997 : MAX_PARALLEL_WORKER_LIMIT);
998 12 : LWLockRelease(BackgroundWorkerLock);
999 12 : return false;
1000 : }
1001 :
1002 : /*
1003 : * Look for an unused slot. If we find one, grab it.
1004 : */
1005 6226 : for (slotno = 0; slotno < BackgroundWorkerData->total_slots; ++slotno)
1006 : {
1007 6224 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
1008 :
1009 6224 : if (!slot->in_use)
1010 : {
1011 1986 : memcpy(&slot->worker, worker, sizeof(BackgroundWorker));
1012 1986 : slot->pid = InvalidPid; /* indicates not started yet */
1013 1986 : slot->generation++;
1014 1986 : slot->terminate = false;
1015 1986 : generation = slot->generation;
1016 1986 : if (parallel)
1017 1690 : BackgroundWorkerData->parallel_register_count++;
1018 :
1019 : /*
1020 : * Make sure postmaster doesn't see the slot as in use before it
1021 : * sees the new contents.
1022 : */
1023 1986 : pg_write_barrier();
1024 :
1025 1986 : slot->in_use = true;
1026 1986 : success = true;
1027 1986 : break;
1028 : }
1029 : }
1030 :
1031 1988 : LWLockRelease(BackgroundWorkerLock);
1032 :
1033 : /* If we found a slot, tell the postmaster to notice the change. */
1034 1988 : if (success)
1035 1986 : SendPostmasterSignal(PMSIGNAL_BACKGROUND_WORKER_CHANGE);
1036 :
1037 : /*
1038 : * If we found a slot and the user has provided a handle, initialize it.
1039 : */
1040 1988 : if (success && handle)
1041 : {
1042 1986 : *handle = palloc(sizeof(BackgroundWorkerHandle));
1043 1986 : (*handle)->slot = slotno;
1044 1986 : (*handle)->generation = generation;
1045 : }
1046 :
1047 1988 : return success;
1048 : }
1049 :
1050 : /*
1051 : * Get the PID of a dynamically-registered background worker.
1052 : *
1053 : * If the worker is determined to be running, the return value will be
1054 : * BGWH_STARTED and *pidp will get the PID of the worker process. If the
1055 : * postmaster has not yet attempted to start the worker, the return value will
1056 : * be BGWH_NOT_YET_STARTED. Otherwise, the return value is BGWH_STOPPED.
1057 : *
1058 : * BGWH_STOPPED can indicate either that the worker is temporarily stopped
1059 : * (because it is configured for automatic restart and exited non-zero),
1060 : * or that the worker is permanently stopped (because it exited with exit
1061 : * code 0, or was not configured for automatic restart), or even that the
1062 : * worker was unregistered without ever starting (either because startup
1063 : * failed and the worker is not configured for automatic restart, or because
1064 : * TerminateBackgroundWorker was used before the worker was successfully
1065 : * started).
1066 : */
1067 : BgwHandleStatus
1068 13756790 : GetBackgroundWorkerPid(BackgroundWorkerHandle *handle, pid_t *pidp)
1069 : {
1070 : BackgroundWorkerSlot *slot;
1071 : pid_t pid;
1072 :
1073 : Assert(handle->slot < max_worker_processes);
1074 13756790 : slot = &BackgroundWorkerData->slot[handle->slot];
1075 :
1076 : /*
1077 : * We could probably arrange to synchronize access to data using memory
1078 : * barriers only, but for now, let's just keep it simple and grab the
1079 : * lock. It seems unlikely that there will be enough traffic here to
1080 : * result in meaningful contention.
1081 : */
1082 13756790 : LWLockAcquire(BackgroundWorkerLock, LW_SHARED);
1083 :
1084 : /*
1085 : * The generation number can't be concurrently changed while we hold the
1086 : * lock. The pid, which is updated by the postmaster, can change at any
1087 : * time, but we assume such changes are atomic. So the value we read
1088 : * won't be garbage, but it might be out of date by the time the caller
1089 : * examines it (but that's unavoidable anyway).
1090 : *
1091 : * The in_use flag could be in the process of changing from true to false,
1092 : * but if it is already false then it can't change further.
1093 : */
1094 13756790 : if (handle->generation != slot->generation || !slot->in_use)
1095 1690 : pid = 0;
1096 : else
1097 13755100 : pid = slot->pid;
1098 :
1099 : /* All done. */
1100 13756790 : LWLockRelease(BackgroundWorkerLock);
1101 :
1102 13756790 : if (pid == 0)
1103 1690 : return BGWH_STOPPED;
1104 13755100 : else if (pid == InvalidPid)
1105 3342438 : return BGWH_NOT_YET_STARTED;
1106 10412662 : *pidp = pid;
1107 10412662 : return BGWH_STARTED;
1108 : }
1109 :
1110 : /*
1111 : * Wait for a background worker to start up.
1112 : *
1113 : * This is like GetBackgroundWorkerPid(), except that if the worker has not
1114 : * yet started, we wait for it to do so; thus, BGWH_NOT_YET_STARTED is never
1115 : * returned. However, if the postmaster has died, we give up and return
1116 : * BGWH_POSTMASTER_DIED, since it that case we know that startup will not
1117 : * take place.
1118 : *
1119 : * The caller *must* have set our PID as the worker's bgw_notify_pid,
1120 : * else we will not be awoken promptly when the worker's state changes.
1121 : */
1122 : BgwHandleStatus
1123 4 : WaitForBackgroundWorkerStartup(BackgroundWorkerHandle *handle, pid_t *pidp)
1124 : {
1125 : BgwHandleStatus status;
1126 : int rc;
1127 :
1128 : for (;;)
1129 2 : {
1130 : pid_t pid;
1131 :
1132 4 : CHECK_FOR_INTERRUPTS();
1133 :
1134 4 : status = GetBackgroundWorkerPid(handle, &pid);
1135 4 : if (status == BGWH_STARTED)
1136 2 : *pidp = pid;
1137 4 : if (status != BGWH_NOT_YET_STARTED)
1138 2 : break;
1139 :
1140 2 : rc = WaitLatch(MyLatch,
1141 : WL_LATCH_SET | WL_POSTMASTER_DEATH, 0,
1142 : WAIT_EVENT_BGWORKER_STARTUP);
1143 :
1144 2 : if (rc & WL_POSTMASTER_DEATH)
1145 : {
1146 0 : status = BGWH_POSTMASTER_DIED;
1147 0 : break;
1148 : }
1149 :
1150 2 : ResetLatch(MyLatch);
1151 : }
1152 :
1153 2 : return status;
1154 : }
1155 :
1156 : /*
1157 : * Wait for a background worker to stop.
1158 : *
1159 : * If the worker hasn't yet started, or is running, we wait for it to stop
1160 : * and then return BGWH_STOPPED. However, if the postmaster has died, we give
1161 : * up and return BGWH_POSTMASTER_DIED, because it's the postmaster that
1162 : * notifies us when a worker's state changes.
1163 : *
1164 : * The caller *must* have set our PID as the worker's bgw_notify_pid,
1165 : * else we will not be awoken promptly when the worker's state changes.
1166 : */
1167 : BgwHandleStatus
1168 3404 : WaitForBackgroundWorkerShutdown(BackgroundWorkerHandle *handle)
1169 : {
1170 : BgwHandleStatus status;
1171 : int rc;
1172 :
1173 : for (;;)
1174 1714 : {
1175 : pid_t pid;
1176 :
1177 3404 : CHECK_FOR_INTERRUPTS();
1178 :
1179 3404 : status = GetBackgroundWorkerPid(handle, &pid);
1180 3404 : if (status == BGWH_STOPPED)
1181 1690 : break;
1182 :
1183 1714 : rc = WaitLatch(MyLatch,
1184 : WL_LATCH_SET | WL_POSTMASTER_DEATH, 0,
1185 : WAIT_EVENT_BGWORKER_SHUTDOWN);
1186 :
1187 1714 : if (rc & WL_POSTMASTER_DEATH)
1188 : {
1189 0 : status = BGWH_POSTMASTER_DIED;
1190 0 : break;
1191 : }
1192 :
1193 1714 : ResetLatch(MyLatch);
1194 : }
1195 :
1196 1690 : return status;
1197 : }
1198 :
1199 : /*
1200 : * Instruct the postmaster to terminate a background worker.
1201 : *
1202 : * Note that it's safe to do this without regard to whether the worker is
1203 : * still running, or even if the worker may already have exited and been
1204 : * unregistered.
1205 : */
1206 : void
1207 4 : TerminateBackgroundWorker(BackgroundWorkerHandle *handle)
1208 : {
1209 : BackgroundWorkerSlot *slot;
1210 4 : bool signal_postmaster = false;
1211 :
1212 : Assert(handle->slot < max_worker_processes);
1213 4 : slot = &BackgroundWorkerData->slot[handle->slot];
1214 :
1215 : /* Set terminate flag in shared memory, unless slot has been reused. */
1216 4 : LWLockAcquire(BackgroundWorkerLock, LW_EXCLUSIVE);
1217 4 : if (handle->generation == slot->generation)
1218 : {
1219 4 : slot->terminate = true;
1220 4 : signal_postmaster = true;
1221 : }
1222 4 : LWLockRelease(BackgroundWorkerLock);
1223 :
1224 : /* Make sure the postmaster notices the change to shared memory. */
1225 4 : if (signal_postmaster)
1226 4 : SendPostmasterSignal(PMSIGNAL_BACKGROUND_WORKER_CHANGE);
1227 4 : }
1228 :
1229 : /*
1230 : * Look up (and possibly load) a bgworker entry point function.
1231 : *
1232 : * For functions contained in the core code, we use library name "postgres"
1233 : * and consult the InternalBGWorkers array. External functions are
1234 : * looked up, and loaded if necessary, using load_external_function().
1235 : *
1236 : * The point of this is to pass function names as strings across process
1237 : * boundaries. We can't pass actual function addresses because of the
1238 : * possibility that the function has been loaded at a different address
1239 : * in a different process. This is obviously a hazard for functions in
1240 : * loadable libraries, but it can happen even for functions in the core code
1241 : * on platforms using EXEC_BACKEND (e.g., Windows).
1242 : *
1243 : * At some point it might be worthwhile to get rid of InternalBGWorkers[]
1244 : * in favor of applying load_external_function() for core functions too;
1245 : * but that raises portability issues that are not worth addressing now.
1246 : */
1247 : static bgworker_main_type
1248 2530 : LookupBackgroundWorkerFunction(const char *libraryname, const char *funcname)
1249 : {
1250 : /*
1251 : * If the function is to be loaded from postgres itself, search the
1252 : * InternalBGWorkers array.
1253 : */
1254 2530 : if (strcmp(libraryname, "postgres") == 0)
1255 : {
1256 : int i;
1257 :
1258 3646 : for (i = 0; i < lengthof(InternalBGWorkers); i++)
1259 : {
1260 3646 : if (strcmp(InternalBGWorkers[i].fn_name, funcname) == 0)
1261 2510 : return InternalBGWorkers[i].fn_addr;
1262 : }
1263 :
1264 : /* We can only reach this by programming error. */
1265 0 : elog(ERROR, "internal function \"%s\" not found", funcname);
1266 : }
1267 :
1268 : /* Otherwise load from external library. */
1269 20 : return (bgworker_main_type)
1270 20 : load_external_function(libraryname, funcname, true, NULL);
1271 : }
1272 :
1273 : /*
1274 : * Given a PID, get the bgw_type of the background worker. Returns NULL if
1275 : * not a valid background worker.
1276 : *
1277 : * The return value is in static memory belonging to this function, so it has
1278 : * to be used before calling this function again. This is so that the caller
1279 : * doesn't have to worry about the background worker locking protocol.
1280 : */
1281 : const char *
1282 1034 : GetBackgroundWorkerTypeByPid(pid_t pid)
1283 : {
1284 : int slotno;
1285 1034 : bool found = false;
1286 : static char result[BGW_MAXLEN];
1287 :
1288 1034 : LWLockAcquire(BackgroundWorkerLock, LW_SHARED);
1289 :
1290 1106 : for (slotno = 0; slotno < BackgroundWorkerData->total_slots; slotno++)
1291 : {
1292 1106 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
1293 :
1294 1106 : if (slot->pid > 0 && slot->pid == pid)
1295 : {
1296 1034 : strcpy(result, slot->worker.bgw_type);
1297 1034 : found = true;
1298 1034 : break;
1299 : }
1300 : }
1301 :
1302 1034 : LWLockRelease(BackgroundWorkerLock);
1303 :
1304 1034 : if (!found)
1305 0 : return NULL;
1306 :
1307 1034 : return result;
1308 : }
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