Line data Source code
1 : /*--------------------------------------------------------------------
2 : * bgworker.c
3 : * POSTGRES pluggable background workers implementation
4 : *
5 : * Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
6 : *
7 : * IDENTIFICATION
8 : * src/backend/postmaster/bgworker.c
9 : *
10 : *-------------------------------------------------------------------------
11 : */
12 :
13 : #include "postgres.h"
14 :
15 : #include <unistd.h>
16 :
17 : #include "libpq/pqsignal.h"
18 : #include "access/parallel.h"
19 : #include "miscadmin.h"
20 : #include "pgstat.h"
21 : #include "port/atomics.h"
22 : #include "postmaster/bgworker_internals.h"
23 : #include "postmaster/postmaster.h"
24 : #include "replication/logicallauncher.h"
25 : #include "replication/logicalworker.h"
26 : #include "storage/dsm.h"
27 : #include "storage/ipc.h"
28 : #include "storage/latch.h"
29 : #include "storage/lwlock.h"
30 : #include "storage/pg_shmem.h"
31 : #include "storage/pmsignal.h"
32 : #include "storage/proc.h"
33 : #include "storage/procsignal.h"
34 : #include "storage/shmem.h"
35 : #include "tcop/tcopprot.h"
36 : #include "utils/ascii.h"
37 : #include "utils/ps_status.h"
38 : #include "utils/timeout.h"
39 :
40 : /*
41 : * The postmaster's list of registered background workers, in private memory.
42 : */
43 : slist_head BackgroundWorkerList = SLIST_STATIC_INIT(BackgroundWorkerList);
44 :
45 : /*
46 : * BackgroundWorkerSlots exist in shared memory and can be accessed (via
47 : * the BackgroundWorkerArray) by both the postmaster and by regular backends.
48 : * However, the postmaster cannot take locks, even spinlocks, because this
49 : * might allow it to crash or become wedged if shared memory gets corrupted.
50 : * Such an outcome is intolerable. Therefore, we need a lockless protocol
51 : * for coordinating access to this data.
52 : *
53 : * The 'in_use' flag is used to hand off responsibility for the slot between
54 : * the postmaster and the rest of the system. When 'in_use' is false,
55 : * the postmaster will ignore the slot entirely, except for the 'in_use' flag
56 : * itself, which it may read. In this state, regular backends may modify the
57 : * slot. Once a backend sets 'in_use' to true, the slot becomes the
58 : * responsibility of the postmaster. Regular backends may no longer modify it,
59 : * but the postmaster may examine it. Thus, a backend initializing a slot
60 : * must fully initialize the slot - and insert a write memory barrier - before
61 : * marking it as in use.
62 : *
63 : * As an exception, however, even when the slot is in use, regular backends
64 : * may set the 'terminate' flag for a slot, telling the postmaster not
65 : * to restart it. Once the background worker is no longer running, the slot
66 : * will be released for reuse.
67 : *
68 : * In addition to coordinating with the postmaster, backends modifying this
69 : * data structure must coordinate with each other. Since they can take locks,
70 : * this is straightforward: any backend wishing to manipulate a slot must
71 : * take BackgroundWorkerLock in exclusive mode. Backends wishing to read
72 : * data that might get concurrently modified by other backends should take
73 : * this lock in shared mode. No matter what, backends reading this data
74 : * structure must be able to tolerate concurrent modifications by the
75 : * postmaster.
76 : */
77 : typedef struct BackgroundWorkerSlot
78 : {
79 : bool in_use;
80 : bool terminate;
81 : pid_t pid; /* InvalidPid = not started yet; 0 = dead */
82 : uint64 generation; /* incremented when slot is recycled */
83 : BackgroundWorker worker;
84 : } BackgroundWorkerSlot;
85 :
86 : /*
87 : * In order to limit the total number of parallel workers (according to
88 : * max_parallel_workers GUC), we maintain the number of active parallel
89 : * workers. Since the postmaster cannot take locks, two variables are used for
90 : * this purpose: the number of registered parallel workers (modified by the
91 : * backends, protected by BackgroundWorkerLock) and the number of terminated
92 : * parallel workers (modified only by the postmaster, lockless). The active
93 : * number of parallel workers is the number of registered workers minus the
94 : * terminated ones. These counters can of course overflow, but it's not
95 : * important here since the subtraction will still give the right number.
96 : */
97 : typedef struct BackgroundWorkerArray
98 : {
99 : int total_slots;
100 : uint32 parallel_register_count;
101 : uint32 parallel_terminate_count;
102 : BackgroundWorkerSlot slot[FLEXIBLE_ARRAY_MEMBER];
103 : } BackgroundWorkerArray;
104 :
105 : struct BackgroundWorkerHandle
106 : {
107 : int slot;
108 : uint64 generation;
109 : };
110 :
111 : static BackgroundWorkerArray *BackgroundWorkerData;
112 :
113 : /*
114 : * List of internal background worker entry points. We need this for
115 : * reasons explained in LookupBackgroundWorkerFunction(), below.
116 : */
117 : static const struct
118 : {
119 : const char *fn_name;
120 : bgworker_main_type fn_addr;
121 : } InternalBGWorkers[] =
122 :
123 : {
124 : {
125 : "ParallelWorkerMain", ParallelWorkerMain
126 : },
127 : {
128 : "ApplyLauncherMain", ApplyLauncherMain
129 : },
130 : {
131 : "ApplyWorkerMain", ApplyWorkerMain
132 : }
133 : };
134 :
135 : /* Private functions. */
136 : static bgworker_main_type LookupBackgroundWorkerFunction(const char *libraryname, const char *funcname);
137 :
138 :
139 : /*
140 : * Calculate shared memory needed.
141 : */
142 : Size
143 3720 : BackgroundWorkerShmemSize(void)
144 : {
145 : Size size;
146 :
147 : /* Array of workers is variably sized. */
148 3720 : size = offsetof(BackgroundWorkerArray, slot);
149 3720 : size = add_size(size, mul_size(max_worker_processes,
150 : sizeof(BackgroundWorkerSlot)));
151 :
152 3720 : return size;
153 : }
154 :
155 : /*
156 : * Initialize shared memory.
157 : */
158 : void
159 1858 : BackgroundWorkerShmemInit(void)
160 : {
161 : bool found;
162 :
163 1858 : BackgroundWorkerData = ShmemInitStruct("Background Worker Data",
164 : BackgroundWorkerShmemSize(),
165 : &found);
166 1858 : if (!IsUnderPostmaster)
167 : {
168 : slist_iter siter;
169 1858 : int slotno = 0;
170 :
171 1858 : BackgroundWorkerData->total_slots = max_worker_processes;
172 1858 : BackgroundWorkerData->parallel_register_count = 0;
173 1858 : BackgroundWorkerData->parallel_terminate_count = 0;
174 :
175 : /*
176 : * Copy contents of worker list into shared memory. Record the shared
177 : * memory slot assigned to each worker. This ensures a 1-to-1
178 : * correspondence between the postmaster's private list and the array
179 : * in shared memory.
180 : */
181 2440 : slist_foreach(siter, &BackgroundWorkerList)
182 : {
183 582 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
184 : RegisteredBgWorker *rw;
185 :
186 582 : rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur);
187 : Assert(slotno < max_worker_processes);
188 582 : slot->in_use = true;
189 582 : slot->terminate = false;
190 582 : slot->pid = InvalidPid;
191 582 : slot->generation = 0;
192 582 : rw->rw_shmem_slot = slotno;
193 582 : rw->rw_worker.bgw_notify_pid = 0; /* might be reinit after crash */
194 582 : memcpy(&slot->worker, &rw->rw_worker, sizeof(BackgroundWorker));
195 582 : ++slotno;
196 : }
197 :
198 : /*
199 : * Mark any remaining slots as not in use.
200 : */
201 17998 : while (slotno < max_worker_processes)
202 : {
203 14282 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
204 :
205 14282 : slot->in_use = false;
206 14282 : ++slotno;
207 : }
208 : }
209 : else
210 : Assert(found);
211 1858 : }
212 :
213 : /*
214 : * Search the postmaster's backend-private list of RegisteredBgWorker objects
215 : * for the one that maps to the given slot number.
216 : */
217 : static RegisteredBgWorker *
218 3042 : FindRegisteredWorkerBySlotNumber(int slotno)
219 : {
220 : slist_iter siter;
221 :
222 7664 : slist_foreach(siter, &BackgroundWorkerList)
223 : {
224 : RegisteredBgWorker *rw;
225 :
226 5894 : rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur);
227 5894 : if (rw->rw_shmem_slot == slotno)
228 1272 : return rw;
229 : }
230 :
231 1770 : return NULL;
232 : }
233 :
234 : /*
235 : * Notice changes to shared memory made by other backends. This code
236 : * runs in the postmaster, so we must be very careful not to assume that
237 : * shared memory contents are sane. Otherwise, a rogue backend could take
238 : * out the postmaster.
239 : */
240 : void
241 872 : BackgroundWorkerStateChange(void)
242 : {
243 : int slotno;
244 :
245 : /*
246 : * The total number of slots stored in shared memory should match our
247 : * notion of max_worker_processes. If it does not, something is very
248 : * wrong. Further down, we always refer to this value as
249 : * max_worker_processes, in case shared memory gets corrupted while we're
250 : * looping.
251 : */
252 872 : if (max_worker_processes != BackgroundWorkerData->total_slots)
253 : {
254 0 : elog(LOG,
255 : "inconsistent background worker state (max_worker_processes=%d, total_slots=%d",
256 : max_worker_processes,
257 : BackgroundWorkerData->total_slots);
258 0 : return;
259 : }
260 :
261 : /*
262 : * Iterate through slots, looking for newly-registered workers or workers
263 : * who must die.
264 : */
265 7848 : for (slotno = 0; slotno < max_worker_processes; ++slotno)
266 : {
267 6976 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
268 : RegisteredBgWorker *rw;
269 :
270 6976 : if (!slot->in_use)
271 3934 : continue;
272 :
273 : /*
274 : * Make sure we don't see the in_use flag before the updated slot
275 : * contents.
276 : */
277 3042 : pg_read_barrier();
278 :
279 : /* See whether we already know about this worker. */
280 3042 : rw = FindRegisteredWorkerBySlotNumber(slotno);
281 3042 : if (rw != NULL)
282 : {
283 : /*
284 : * In general, the worker data can't change after it's initially
285 : * registered. However, someone can set the terminate flag.
286 : */
287 1272 : if (slot->terminate && !rw->rw_terminate)
288 : {
289 4 : rw->rw_terminate = true;
290 4 : if (rw->rw_pid != 0)
291 4 : kill(rw->rw_pid, SIGTERM);
292 : else
293 : {
294 : /* Report never-started, now-terminated worker as dead. */
295 0 : ReportBackgroundWorkerPID(rw);
296 : }
297 : }
298 1272 : continue;
299 : }
300 :
301 : /*
302 : * If the worker is marked for termination, we don't need to add it to
303 : * the registered workers list; we can just free the slot. However, if
304 : * bgw_notify_pid is set, the process that registered the worker may
305 : * need to know that we've processed the terminate request, so be sure
306 : * to signal it.
307 : */
308 1770 : if (slot->terminate)
309 : {
310 : int notify_pid;
311 :
312 : /*
313 : * We need a memory barrier here to make sure that the load of
314 : * bgw_notify_pid and the update of parallel_terminate_count
315 : * complete before the store to in_use.
316 : */
317 0 : notify_pid = slot->worker.bgw_notify_pid;
318 0 : if ((slot->worker.bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
319 0 : BackgroundWorkerData->parallel_terminate_count++;
320 0 : pg_memory_barrier();
321 0 : slot->pid = 0;
322 0 : slot->in_use = false;
323 0 : if (notify_pid != 0)
324 0 : kill(notify_pid, SIGUSR1);
325 :
326 0 : continue;
327 : }
328 :
329 : /*
330 : * Copy the registration data into the registered workers list.
331 : */
332 1770 : rw = malloc(sizeof(RegisteredBgWorker));
333 1770 : if (rw == NULL)
334 : {
335 0 : ereport(LOG,
336 : (errcode(ERRCODE_OUT_OF_MEMORY),
337 : errmsg("out of memory")));
338 0 : return;
339 : }
340 :
341 : /*
342 : * Copy strings in a paranoid way. If shared memory is corrupted, the
343 : * source data might not even be NUL-terminated.
344 : */
345 1770 : ascii_safe_strlcpy(rw->rw_worker.bgw_name,
346 1770 : slot->worker.bgw_name, BGW_MAXLEN);
347 1770 : ascii_safe_strlcpy(rw->rw_worker.bgw_type,
348 1770 : slot->worker.bgw_type, BGW_MAXLEN);
349 1770 : ascii_safe_strlcpy(rw->rw_worker.bgw_library_name,
350 1770 : slot->worker.bgw_library_name, BGW_MAXLEN);
351 1770 : ascii_safe_strlcpy(rw->rw_worker.bgw_function_name,
352 1770 : slot->worker.bgw_function_name, BGW_MAXLEN);
353 :
354 : /*
355 : * Copy various fixed-size fields.
356 : *
357 : * flags, start_time, and restart_time are examined by the postmaster,
358 : * but nothing too bad will happen if they are corrupted. The
359 : * remaining fields will only be examined by the child process. It
360 : * might crash, but we won't.
361 : */
362 1770 : rw->rw_worker.bgw_flags = slot->worker.bgw_flags;
363 1770 : rw->rw_worker.bgw_start_time = slot->worker.bgw_start_time;
364 1770 : rw->rw_worker.bgw_restart_time = slot->worker.bgw_restart_time;
365 1770 : rw->rw_worker.bgw_main_arg = slot->worker.bgw_main_arg;
366 1770 : memcpy(rw->rw_worker.bgw_extra, slot->worker.bgw_extra, BGW_EXTRALEN);
367 :
368 : /*
369 : * Copy the PID to be notified about state changes, but only if the
370 : * postmaster knows about a backend with that PID. It isn't an error
371 : * if the postmaster doesn't know about the PID, because the backend
372 : * that requested the worker could have died (or been killed) just
373 : * after doing so. Nonetheless, at least until we get some experience
374 : * with how this plays out in the wild, log a message at a relative
375 : * high debug level.
376 : */
377 1770 : rw->rw_worker.bgw_notify_pid = slot->worker.bgw_notify_pid;
378 1770 : if (!PostmasterMarkPIDForWorkerNotify(rw->rw_worker.bgw_notify_pid))
379 : {
380 0 : elog(DEBUG1, "worker notification PID %lu is not valid",
381 : (long) rw->rw_worker.bgw_notify_pid);
382 0 : rw->rw_worker.bgw_notify_pid = 0;
383 : }
384 :
385 : /* Initialize postmaster bookkeeping. */
386 1770 : rw->rw_backend = NULL;
387 1770 : rw->rw_pid = 0;
388 1770 : rw->rw_child_slot = 0;
389 1770 : rw->rw_crashed_at = 0;
390 1770 : rw->rw_shmem_slot = slotno;
391 1770 : rw->rw_terminate = false;
392 :
393 : /* Log it! */
394 1770 : ereport(DEBUG1,
395 : (errmsg("registering background worker \"%s\"",
396 : rw->rw_worker.bgw_name)));
397 :
398 1770 : slist_push_head(&BackgroundWorkerList, &rw->rw_lnode);
399 : }
400 : }
401 :
402 : /*
403 : * Forget about a background worker that's no longer needed.
404 : *
405 : * The worker must be identified by passing an slist_mutable_iter that
406 : * points to it. This convention allows deletion of workers during
407 : * searches of the worker list, and saves having to search the list again.
408 : *
409 : * This function must be invoked only in the postmaster.
410 : */
411 : void
412 1774 : ForgetBackgroundWorker(slist_mutable_iter *cur)
413 : {
414 : RegisteredBgWorker *rw;
415 : BackgroundWorkerSlot *slot;
416 :
417 1774 : rw = slist_container(RegisteredBgWorker, rw_lnode, cur->cur);
418 :
419 : Assert(rw->rw_shmem_slot < max_worker_processes);
420 1774 : slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
421 1774 : if ((rw->rw_worker.bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
422 1630 : BackgroundWorkerData->parallel_terminate_count++;
423 :
424 1774 : slot->in_use = false;
425 :
426 1774 : ereport(DEBUG1,
427 : (errmsg("unregistering background worker \"%s\"",
428 : rw->rw_worker.bgw_name)));
429 :
430 1774 : slist_delete_current(cur);
431 1774 : free(rw);
432 1774 : }
433 :
434 : /*
435 : * Report the PID of a newly-launched background worker in shared memory.
436 : *
437 : * This function should only be called from the postmaster.
438 : */
439 : void
440 2272 : ReportBackgroundWorkerPID(RegisteredBgWorker *rw)
441 : {
442 : BackgroundWorkerSlot *slot;
443 :
444 : Assert(rw->rw_shmem_slot < max_worker_processes);
445 2272 : slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
446 2272 : slot->pid = rw->rw_pid;
447 :
448 2272 : if (rw->rw_worker.bgw_notify_pid != 0)
449 1770 : kill(rw->rw_worker.bgw_notify_pid, SIGUSR1);
450 2272 : }
451 :
452 : /*
453 : * Report that the PID of a background worker is now zero because a
454 : * previously-running background worker has exited.
455 : *
456 : * This function should only be called from the postmaster.
457 : */
458 : void
459 2130 : ReportBackgroundWorkerExit(slist_mutable_iter *cur)
460 : {
461 : RegisteredBgWorker *rw;
462 : BackgroundWorkerSlot *slot;
463 : int notify_pid;
464 :
465 2130 : rw = slist_container(RegisteredBgWorker, rw_lnode, cur->cur);
466 :
467 : Assert(rw->rw_shmem_slot < max_worker_processes);
468 2130 : slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
469 2130 : slot->pid = rw->rw_pid;
470 2130 : notify_pid = rw->rw_worker.bgw_notify_pid;
471 :
472 : /*
473 : * If this worker is slated for deregistration, do that before notifying
474 : * the process which started it. Otherwise, if that process tries to
475 : * reuse the slot immediately, it might not be available yet. In theory
476 : * that could happen anyway if the process checks slot->pid at just the
477 : * wrong moment, but this makes the window narrower.
478 : */
479 2554 : if (rw->rw_terminate ||
480 424 : rw->rw_worker.bgw_restart_time == BGW_NEVER_RESTART)
481 1774 : ForgetBackgroundWorker(cur);
482 :
483 2130 : if (notify_pid != 0)
484 1762 : kill(notify_pid, SIGUSR1);
485 2130 : }
486 :
487 : /*
488 : * Cancel SIGUSR1 notifications for a PID belonging to an exiting backend.
489 : *
490 : * This function should only be called from the postmaster.
491 : */
492 : void
493 88 : BackgroundWorkerStopNotifications(pid_t pid)
494 : {
495 : slist_iter siter;
496 :
497 232 : slist_foreach(siter, &BackgroundWorkerList)
498 : {
499 : RegisteredBgWorker *rw;
500 :
501 144 : rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur);
502 144 : if (rw->rw_worker.bgw_notify_pid == pid)
503 8 : rw->rw_worker.bgw_notify_pid = 0;
504 : }
505 88 : }
506 :
507 : /*
508 : * Reset background worker crash state.
509 : *
510 : * We assume that, after a crash-and-restart cycle, background workers without
511 : * the never-restart flag should be restarted immediately, instead of waiting
512 : * for bgw_restart_time to elapse.
513 : */
514 : void
515 4 : ResetBackgroundWorkerCrashTimes(void)
516 : {
517 : slist_mutable_iter iter;
518 :
519 8 : slist_foreach_modify(iter, &BackgroundWorkerList)
520 : {
521 : RegisteredBgWorker *rw;
522 :
523 4 : rw = slist_container(RegisteredBgWorker, rw_lnode, iter.cur);
524 :
525 4 : if (rw->rw_worker.bgw_restart_time == BGW_NEVER_RESTART)
526 : {
527 : /*
528 : * Workers marked BGW_NEVER_RESTART shouldn't get relaunched after
529 : * the crash, so forget about them. (If we wait until after the
530 : * crash to forget about them, and they are parallel workers,
531 : * parallel_terminate_count will get incremented after we've
532 : * already zeroed parallel_register_count, which would be bad.)
533 : */
534 0 : ForgetBackgroundWorker(&iter);
535 : }
536 : else
537 : {
538 : /*
539 : * The accounting which we do via parallel_register_count and
540 : * parallel_terminate_count would get messed up if a worker marked
541 : * parallel could survive a crash and restart cycle. All such
542 : * workers should be marked BGW_NEVER_RESTART, and thus control
543 : * should never reach this branch.
544 : */
545 : Assert((rw->rw_worker.bgw_flags & BGWORKER_CLASS_PARALLEL) == 0);
546 :
547 : /*
548 : * Allow this worker to be restarted immediately after we finish
549 : * resetting.
550 : */
551 4 : rw->rw_crashed_at = 0;
552 : }
553 : }
554 4 : }
555 :
556 : #ifdef EXEC_BACKEND
557 : /*
558 : * In EXEC_BACKEND mode, workers use this to retrieve their details from
559 : * shared memory.
560 : */
561 : BackgroundWorker *
562 : BackgroundWorkerEntry(int slotno)
563 : {
564 : static BackgroundWorker myEntry;
565 : BackgroundWorkerSlot *slot;
566 :
567 : Assert(slotno < BackgroundWorkerData->total_slots);
568 : slot = &BackgroundWorkerData->slot[slotno];
569 : Assert(slot->in_use);
570 :
571 : /* must copy this in case we don't intend to retain shmem access */
572 : memcpy(&myEntry, &slot->worker, sizeof myEntry);
573 : return &myEntry;
574 : }
575 : #endif
576 :
577 : /*
578 : * Complain about the BackgroundWorker definition using error level elevel.
579 : * Return true if it looks ok, false if not (unless elevel >= ERROR, in
580 : * which case we won't return at all in the not-OK case).
581 : */
582 : static bool
583 2350 : SanityCheckBackgroundWorker(BackgroundWorker *worker, int elevel)
584 : {
585 : /* sanity check for flags */
586 2350 : if (worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION)
587 : {
588 2336 : if (!(worker->bgw_flags & BGWORKER_SHMEM_ACCESS))
589 : {
590 0 : ereport(elevel,
591 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
592 : errmsg("background worker \"%s\": must attach to shared memory in order to request a database connection",
593 : worker->bgw_name)));
594 0 : return false;
595 : }
596 :
597 2336 : if (worker->bgw_start_time == BgWorkerStart_PostmasterStart)
598 : {
599 0 : ereport(elevel,
600 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
601 : errmsg("background worker \"%s\": cannot request database access if starting at postmaster start",
602 : worker->bgw_name)));
603 0 : return false;
604 : }
605 :
606 : /* XXX other checks? */
607 : }
608 :
609 4124 : if ((worker->bgw_restart_time < 0 &&
610 4124 : worker->bgw_restart_time != BGW_NEVER_RESTART) ||
611 2350 : (worker->bgw_restart_time > USECS_PER_DAY / 1000))
612 : {
613 0 : ereport(elevel,
614 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
615 : errmsg("background worker \"%s\": invalid restart interval",
616 : worker->bgw_name)));
617 0 : return false;
618 : }
619 :
620 : /*
621 : * Parallel workers may not be configured for restart, because the
622 : * parallel_register_count/parallel_terminate_count accounting can't
623 : * handle parallel workers lasting through a crash-and-restart cycle.
624 : */
625 2926 : if (worker->bgw_restart_time != BGW_NEVER_RESTART &&
626 576 : (worker->bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
627 : {
628 0 : ereport(elevel,
629 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
630 : errmsg("background worker \"%s\": parallel workers may not be configured for restart",
631 : worker->bgw_name)));
632 0 : return false;
633 : }
634 :
635 : /*
636 : * If bgw_type is not filled in, use bgw_name.
637 : */
638 2350 : if (strcmp(worker->bgw_type, "") == 0)
639 0 : strcpy(worker->bgw_type, worker->bgw_name);
640 :
641 2350 : return true;
642 : }
643 :
644 : static void
645 0 : bgworker_quickdie(SIGNAL_ARGS)
646 : {
647 : /*
648 : * We DO NOT want to run proc_exit() or atexit() callbacks -- we're here
649 : * because shared memory may be corrupted, so we don't want to try to
650 : * clean up our transaction. Just nail the windows shut and get out of
651 : * town. The callbacks wouldn't be safe to run from a signal handler,
652 : * anyway.
653 : *
654 : * Note we do _exit(2) not _exit(0). This is to force the postmaster into
655 : * a system reset cycle if someone sends a manual SIGQUIT to a random
656 : * backend. This is necessary precisely because we don't clean up our
657 : * shared memory state. (The "dead man switch" mechanism in pmsignal.c
658 : * should ensure the postmaster sees this as a crash, too, but no harm in
659 : * being doubly sure.)
660 : */
661 0 : _exit(2);
662 : }
663 :
664 : /*
665 : * Standard SIGTERM handler for background workers
666 : */
667 : static void
668 0 : bgworker_die(SIGNAL_ARGS)
669 : {
670 0 : PG_SETMASK(&BlockSig);
671 :
672 0 : ereport(FATAL,
673 : (errcode(ERRCODE_ADMIN_SHUTDOWN),
674 : errmsg("terminating background worker \"%s\" due to administrator command",
675 : MyBgworkerEntry->bgw_type)));
676 : }
677 :
678 : /*
679 : * Standard SIGUSR1 handler for unconnected workers
680 : *
681 : * Here, we want to make sure an unconnected worker will at least heed
682 : * latch activity.
683 : */
684 : static void
685 213604 : bgworker_sigusr1_handler(SIGNAL_ARGS)
686 : {
687 213604 : int save_errno = errno;
688 :
689 213604 : latch_sigusr1_handler();
690 :
691 213604 : errno = save_errno;
692 213604 : }
693 :
694 : /*
695 : * Start a new background worker
696 : *
697 : * This is the main entry point for background worker, to be called from
698 : * postmaster.
699 : */
700 : void
701 2134 : StartBackgroundWorker(void)
702 : {
703 : sigjmp_buf local_sigjmp_buf;
704 2134 : BackgroundWorker *worker = MyBgworkerEntry;
705 : bgworker_main_type entrypt;
706 :
707 2134 : if (worker == NULL)
708 0 : elog(FATAL, "unable to find bgworker entry");
709 :
710 2134 : IsBackgroundWorker = true;
711 :
712 : /* Identify myself via ps */
713 2134 : init_ps_display(worker->bgw_name, "", "", "");
714 :
715 : /*
716 : * If we're not supposed to have shared memory access, then detach from
717 : * shared memory. If we didn't request shared memory access, the
718 : * postmaster won't force a cluster-wide restart if we exit unexpectedly,
719 : * so we'd better make sure that we don't mess anything up that would
720 : * require that sort of cleanup.
721 : */
722 2134 : if ((worker->bgw_flags & BGWORKER_SHMEM_ACCESS) == 0)
723 : {
724 0 : dsm_detach_all();
725 0 : PGSharedMemoryDetach();
726 : }
727 :
728 2134 : SetProcessingMode(InitProcessing);
729 :
730 : /* Apply PostAuthDelay */
731 2134 : if (PostAuthDelay > 0)
732 0 : pg_usleep(PostAuthDelay * 1000000L);
733 :
734 : /*
735 : * Set up signal handlers.
736 : */
737 2134 : if (worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION)
738 : {
739 : /*
740 : * SIGINT is used to signal canceling the current action
741 : */
742 2120 : pqsignal(SIGINT, StatementCancelHandler);
743 2120 : pqsignal(SIGUSR1, procsignal_sigusr1_handler);
744 2120 : pqsignal(SIGFPE, FloatExceptionHandler);
745 :
746 : /* XXX Any other handlers needed here? */
747 : }
748 : else
749 : {
750 14 : pqsignal(SIGINT, SIG_IGN);
751 14 : pqsignal(SIGUSR1, bgworker_sigusr1_handler);
752 14 : pqsignal(SIGFPE, SIG_IGN);
753 : }
754 2134 : pqsignal(SIGTERM, bgworker_die);
755 2134 : pqsignal(SIGHUP, SIG_IGN);
756 :
757 2134 : pqsignal(SIGQUIT, bgworker_quickdie);
758 2134 : InitializeTimeouts(); /* establishes SIGALRM handler */
759 :
760 2134 : pqsignal(SIGPIPE, SIG_IGN);
761 2134 : pqsignal(SIGUSR2, SIG_IGN);
762 2134 : pqsignal(SIGCHLD, SIG_DFL);
763 :
764 : /*
765 : * If an exception is encountered, processing resumes here.
766 : *
767 : * See notes in postgres.c about the design of this coding.
768 : */
769 2160 : if (sigsetjmp(local_sigjmp_buf, 1) != 0)
770 : {
771 : /* Since not using PG_TRY, must reset error stack by hand */
772 26 : error_context_stack = NULL;
773 :
774 : /* Prevent interrupts while cleaning up */
775 26 : HOLD_INTERRUPTS();
776 :
777 : /* Report the error to the server log */
778 26 : EmitErrorReport();
779 :
780 : /*
781 : * Do we need more cleanup here? For shmem-connected bgworkers, we
782 : * will call InitProcess below, which will install ProcKill as exit
783 : * callback. That will take care of releasing locks, etc.
784 : */
785 :
786 : /* and go away */
787 26 : proc_exit(1);
788 : }
789 :
790 : /* We can now handle ereport(ERROR) */
791 2134 : PG_exception_stack = &local_sigjmp_buf;
792 :
793 : /*
794 : * If the background worker request shared memory access, set that up now;
795 : * else, detach all shared memory segments.
796 : */
797 2134 : if (worker->bgw_flags & BGWORKER_SHMEM_ACCESS)
798 : {
799 : /*
800 : * Early initialization. Some of this could be useful even for
801 : * background workers that aren't using shared memory, but they can
802 : * call the individual startup routines for those subsystems if
803 : * needed.
804 : */
805 2134 : BaseInit();
806 :
807 : /*
808 : * Create a per-backend PGPROC struct in shared memory, except in the
809 : * EXEC_BACKEND case where this was done in SubPostmasterMain. We must
810 : * do this before we can use LWLocks (and in the EXEC_BACKEND case we
811 : * already had to do some stuff with LWLocks).
812 : */
813 : #ifndef EXEC_BACKEND
814 2134 : InitProcess();
815 : #endif
816 : }
817 :
818 : /*
819 : * Look up the entry point function, loading its library if necessary.
820 : */
821 2134 : entrypt = LookupBackgroundWorkerFunction(worker->bgw_library_name,
822 2134 : worker->bgw_function_name);
823 :
824 : /*
825 : * Note that in normal processes, we would call InitPostgres here. For a
826 : * worker, however, we don't know what database to connect to, yet; so we
827 : * need to wait until the user code does it via
828 : * BackgroundWorkerInitializeConnection().
829 : */
830 :
831 : /*
832 : * Now invoke the user-defined worker code
833 : */
834 2134 : entrypt(worker->bgw_main_arg);
835 :
836 : /* ... and if it returns, we're done */
837 1626 : proc_exit(0);
838 : }
839 :
840 : /*
841 : * Register a new static background worker.
842 : *
843 : * This can only be called directly from postmaster or in the _PG_init
844 : * function of a module library that's loaded by shared_preload_libraries;
845 : * otherwise it will have no effect.
846 : */
847 : void
848 580 : RegisterBackgroundWorker(BackgroundWorker *worker)
849 : {
850 : RegisteredBgWorker *rw;
851 : static int numworkers = 0;
852 :
853 580 : if (!IsUnderPostmaster)
854 580 : ereport(DEBUG1,
855 : (errmsg("registering background worker \"%s\"", worker->bgw_name)));
856 :
857 1156 : if (!process_shared_preload_libraries_in_progress &&
858 576 : strcmp(worker->bgw_library_name, "postgres") != 0)
859 : {
860 0 : if (!IsUnderPostmaster)
861 0 : ereport(LOG,
862 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
863 : errmsg("background worker \"%s\": must be registered in shared_preload_libraries",
864 : worker->bgw_name)));
865 0 : return;
866 : }
867 :
868 580 : if (!SanityCheckBackgroundWorker(worker, LOG))
869 0 : return;
870 :
871 580 : if (worker->bgw_notify_pid != 0)
872 : {
873 0 : ereport(LOG,
874 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
875 : errmsg("background worker \"%s\": only dynamic background workers can request notification",
876 : worker->bgw_name)));
877 0 : return;
878 : }
879 :
880 : /*
881 : * Enforce maximum number of workers. Note this is overly restrictive: we
882 : * could allow more non-shmem-connected workers, because these don't count
883 : * towards the MAX_BACKENDS limit elsewhere. For now, it doesn't seem
884 : * important to relax this restriction.
885 : */
886 580 : if (++numworkers > max_worker_processes)
887 : {
888 0 : ereport(LOG,
889 : (errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
890 : errmsg("too many background workers"),
891 : errdetail_plural("Up to %d background worker can be registered with the current settings.",
892 : "Up to %d background workers can be registered with the current settings.",
893 : max_worker_processes,
894 : max_worker_processes),
895 : errhint("Consider increasing the configuration parameter \"max_worker_processes\".")));
896 0 : return;
897 : }
898 :
899 : /*
900 : * Copy the registration data into the registered workers list.
901 : */
902 580 : rw = malloc(sizeof(RegisteredBgWorker));
903 580 : if (rw == NULL)
904 : {
905 0 : ereport(LOG,
906 : (errcode(ERRCODE_OUT_OF_MEMORY),
907 : errmsg("out of memory")));
908 0 : return;
909 : }
910 :
911 580 : rw->rw_worker = *worker;
912 580 : rw->rw_backend = NULL;
913 580 : rw->rw_pid = 0;
914 580 : rw->rw_child_slot = 0;
915 580 : rw->rw_crashed_at = 0;
916 580 : rw->rw_terminate = false;
917 :
918 580 : slist_push_head(&BackgroundWorkerList, &rw->rw_lnode);
919 : }
920 :
921 : /*
922 : * Register a new background worker from a regular backend.
923 : *
924 : * Returns true on success and false on failure. Failure typically indicates
925 : * that no background worker slots are currently available.
926 : *
927 : * If handle != NULL, we'll set *handle to a pointer that can subsequently
928 : * be used as an argument to GetBackgroundWorkerPid(). The caller can
929 : * free this pointer using pfree(), if desired.
930 : */
931 : bool
932 1770 : RegisterDynamicBackgroundWorker(BackgroundWorker *worker,
933 : BackgroundWorkerHandle **handle)
934 : {
935 : int slotno;
936 1770 : bool success = false;
937 : bool parallel;
938 1770 : uint64 generation = 0;
939 :
940 : /*
941 : * We can't register dynamic background workers from the postmaster. If
942 : * this is a standalone backend, we're the only process and can't start
943 : * any more. In a multi-process environment, it might be theoretically
944 : * possible, but we don't currently support it due to locking
945 : * considerations; see comments on the BackgroundWorkerSlot data
946 : * structure.
947 : */
948 1770 : if (!IsUnderPostmaster)
949 0 : return false;
950 :
951 1770 : if (!SanityCheckBackgroundWorker(worker, ERROR))
952 0 : return false;
953 :
954 1770 : parallel = (worker->bgw_flags & BGWORKER_CLASS_PARALLEL) != 0;
955 :
956 1770 : LWLockAcquire(BackgroundWorkerLock, LW_EXCLUSIVE);
957 :
958 : /*
959 : * If this is a parallel worker, check whether there are already too many
960 : * parallel workers; if so, don't register another one. Our view of
961 : * parallel_terminate_count may be slightly stale, but that doesn't really
962 : * matter: we would have gotten the same result if we'd arrived here
963 : * slightly earlier anyway. There's no help for it, either, since the
964 : * postmaster must not take locks; a memory barrier wouldn't guarantee
965 : * anything useful.
966 : */
967 5054 : if (parallel && (BackgroundWorkerData->parallel_register_count -
968 3284 : BackgroundWorkerData->parallel_terminate_count) >=
969 : max_parallel_workers)
970 : {
971 : Assert(BackgroundWorkerData->parallel_register_count -
972 : BackgroundWorkerData->parallel_terminate_count <=
973 : MAX_PARALLEL_WORKER_LIMIT);
974 12 : LWLockRelease(BackgroundWorkerLock);
975 12 : return false;
976 : }
977 :
978 : /*
979 : * Look for an unused slot. If we find one, grab it.
980 : */
981 5508 : for (slotno = 0; slotno < BackgroundWorkerData->total_slots; ++slotno)
982 : {
983 5508 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
984 :
985 5508 : if (!slot->in_use)
986 : {
987 1758 : memcpy(&slot->worker, worker, sizeof(BackgroundWorker));
988 1758 : slot->pid = InvalidPid; /* indicates not started yet */
989 1758 : slot->generation++;
990 1758 : slot->terminate = false;
991 1758 : generation = slot->generation;
992 1758 : if (parallel)
993 1630 : BackgroundWorkerData->parallel_register_count++;
994 :
995 : /*
996 : * Make sure postmaster doesn't see the slot as in use before it
997 : * sees the new contents.
998 : */
999 1758 : pg_write_barrier();
1000 :
1001 1758 : slot->in_use = true;
1002 1758 : success = true;
1003 1758 : break;
1004 : }
1005 : }
1006 :
1007 1758 : LWLockRelease(BackgroundWorkerLock);
1008 :
1009 : /* If we found a slot, tell the postmaster to notice the change. */
1010 1758 : if (success)
1011 1758 : SendPostmasterSignal(PMSIGNAL_BACKGROUND_WORKER_CHANGE);
1012 :
1013 : /*
1014 : * If we found a slot and the user has provided a handle, initialize it.
1015 : */
1016 1758 : if (success && handle)
1017 : {
1018 1758 : *handle = palloc(sizeof(BackgroundWorkerHandle));
1019 1758 : (*handle)->slot = slotno;
1020 1758 : (*handle)->generation = generation;
1021 : }
1022 :
1023 1758 : return success;
1024 : }
1025 :
1026 : /*
1027 : * Get the PID of a dynamically-registered background worker.
1028 : *
1029 : * If the worker is determined to be running, the return value will be
1030 : * BGWH_STARTED and *pidp will get the PID of the worker process. If the
1031 : * postmaster has not yet attempted to start the worker, the return value will
1032 : * be BGWH_NOT_YET_STARTED. Otherwise, the return value is BGWH_STOPPED.
1033 : *
1034 : * BGWH_STOPPED can indicate either that the worker is temporarily stopped
1035 : * (because it is configured for automatic restart and exited non-zero),
1036 : * or that the worker is permanently stopped (because it exited with exit
1037 : * code 0, or was not configured for automatic restart), or even that the
1038 : * worker was unregistered without ever starting (either because startup
1039 : * failed and the worker is not configured for automatic restart, or because
1040 : * TerminateBackgroundWorker was used before the worker was successfully
1041 : * started).
1042 : */
1043 : BgwHandleStatus
1044 9028566 : GetBackgroundWorkerPid(BackgroundWorkerHandle *handle, pid_t *pidp)
1045 : {
1046 : BackgroundWorkerSlot *slot;
1047 : pid_t pid;
1048 :
1049 : Assert(handle->slot < max_worker_processes);
1050 9028566 : slot = &BackgroundWorkerData->slot[handle->slot];
1051 :
1052 : /*
1053 : * We could probably arrange to synchronize access to data using memory
1054 : * barriers only, but for now, let's just keep it simple and grab the
1055 : * lock. It seems unlikely that there will be enough traffic here to
1056 : * result in meaningful contention.
1057 : */
1058 9028566 : LWLockAcquire(BackgroundWorkerLock, LW_SHARED);
1059 :
1060 : /*
1061 : * The generation number can't be concurrently changed while we hold the
1062 : * lock. The pid, which is updated by the postmaster, can change at any
1063 : * time, but we assume such changes are atomic. So the value we read
1064 : * won't be garbage, but it might be out of date by the time the caller
1065 : * examines it (but that's unavoidable anyway).
1066 : *
1067 : * The in_use flag could be in the process of changing from true to false,
1068 : * but if it is already false then it can't change further.
1069 : */
1070 9028566 : if (handle->generation != slot->generation || !slot->in_use)
1071 1630 : pid = 0;
1072 : else
1073 9026936 : pid = slot->pid;
1074 :
1075 : /* All done. */
1076 9028566 : LWLockRelease(BackgroundWorkerLock);
1077 :
1078 9028566 : if (pid == 0)
1079 1630 : return BGWH_STOPPED;
1080 9026936 : else if (pid == InvalidPid)
1081 3446714 : return BGWH_NOT_YET_STARTED;
1082 5580222 : *pidp = pid;
1083 5580222 : return BGWH_STARTED;
1084 : }
1085 :
1086 : /*
1087 : * Wait for a background worker to start up.
1088 : *
1089 : * This is like GetBackgroundWorkerPid(), except that if the worker has not
1090 : * yet started, we wait for it to do so; thus, BGWH_NOT_YET_STARTED is never
1091 : * returned. However, if the postmaster has died, we give up and return
1092 : * BGWH_POSTMASTER_DIED, since it that case we know that startup will not
1093 : * take place.
1094 : */
1095 : BgwHandleStatus
1096 6 : WaitForBackgroundWorkerStartup(BackgroundWorkerHandle *handle, pid_t *pidp)
1097 : {
1098 : BgwHandleStatus status;
1099 : int rc;
1100 :
1101 : for (;;)
1102 4 : {
1103 : pid_t pid;
1104 :
1105 6 : CHECK_FOR_INTERRUPTS();
1106 :
1107 6 : status = GetBackgroundWorkerPid(handle, &pid);
1108 6 : if (status == BGWH_STARTED)
1109 2 : *pidp = pid;
1110 6 : if (status != BGWH_NOT_YET_STARTED)
1111 4 : break;
1112 :
1113 4 : rc = WaitLatch(MyLatch,
1114 : WL_LATCH_SET | WL_POSTMASTER_DEATH, 0,
1115 : WAIT_EVENT_BGWORKER_STARTUP);
1116 :
1117 4 : if (rc & WL_POSTMASTER_DEATH)
1118 : {
1119 0 : status = BGWH_POSTMASTER_DIED;
1120 0 : break;
1121 : }
1122 :
1123 4 : ResetLatch(MyLatch);
1124 : }
1125 :
1126 2 : return status;
1127 : }
1128 :
1129 : /*
1130 : * Wait for a background worker to stop.
1131 : *
1132 : * If the worker hasn't yet started, or is running, we wait for it to stop
1133 : * and then return BGWH_STOPPED. However, if the postmaster has died, we give
1134 : * up and return BGWH_POSTMASTER_DIED, because it's the postmaster that
1135 : * notifies us when a worker's state changes.
1136 : */
1137 : BgwHandleStatus
1138 3504 : WaitForBackgroundWorkerShutdown(BackgroundWorkerHandle *handle)
1139 : {
1140 : BgwHandleStatus status;
1141 : int rc;
1142 :
1143 : for (;;)
1144 1874 : {
1145 : pid_t pid;
1146 :
1147 3504 : CHECK_FOR_INTERRUPTS();
1148 :
1149 3504 : status = GetBackgroundWorkerPid(handle, &pid);
1150 3504 : if (status == BGWH_STOPPED)
1151 3260 : break;
1152 :
1153 1874 : rc = WaitLatch(MyLatch,
1154 : WL_LATCH_SET | WL_POSTMASTER_DEATH, 0,
1155 : WAIT_EVENT_BGWORKER_SHUTDOWN);
1156 :
1157 1874 : if (rc & WL_POSTMASTER_DEATH)
1158 : {
1159 0 : status = BGWH_POSTMASTER_DIED;
1160 0 : break;
1161 : }
1162 :
1163 1874 : ResetLatch(MyLatch);
1164 : }
1165 :
1166 1630 : return status;
1167 : }
1168 :
1169 : /*
1170 : * Instruct the postmaster to terminate a background worker.
1171 : *
1172 : * Note that it's safe to do this without regard to whether the worker is
1173 : * still running, or even if the worker may already have existed and been
1174 : * unregistered.
1175 : */
1176 : void
1177 4 : TerminateBackgroundWorker(BackgroundWorkerHandle *handle)
1178 : {
1179 : BackgroundWorkerSlot *slot;
1180 4 : bool signal_postmaster = false;
1181 :
1182 : Assert(handle->slot < max_worker_processes);
1183 4 : slot = &BackgroundWorkerData->slot[handle->slot];
1184 :
1185 : /* Set terminate flag in shared memory, unless slot has been reused. */
1186 4 : LWLockAcquire(BackgroundWorkerLock, LW_EXCLUSIVE);
1187 4 : if (handle->generation == slot->generation)
1188 : {
1189 4 : slot->terminate = true;
1190 4 : signal_postmaster = true;
1191 : }
1192 4 : LWLockRelease(BackgroundWorkerLock);
1193 :
1194 : /* Make sure the postmaster notices the change to shared memory. */
1195 4 : if (signal_postmaster)
1196 4 : SendPostmasterSignal(PMSIGNAL_BACKGROUND_WORKER_CHANGE);
1197 4 : }
1198 :
1199 : /*
1200 : * Look up (and possibly load) a bgworker entry point function.
1201 : *
1202 : * For functions contained in the core code, we use library name "postgres"
1203 : * and consult the InternalBGWorkers array. External functions are
1204 : * looked up, and loaded if necessary, using load_external_function().
1205 : *
1206 : * The point of this is to pass function names as strings across process
1207 : * boundaries. We can't pass actual function addresses because of the
1208 : * possibility that the function has been loaded at a different address
1209 : * in a different process. This is obviously a hazard for functions in
1210 : * loadable libraries, but it can happen even for functions in the core code
1211 : * on platforms using EXEC_BACKEND (e.g., Windows).
1212 : *
1213 : * At some point it might be worthwhile to get rid of InternalBGWorkers[]
1214 : * in favor of applying load_external_function() for core functions too;
1215 : * but that raises portability issues that are not worth addressing now.
1216 : */
1217 : static bgworker_main_type
1218 2134 : LookupBackgroundWorkerFunction(const char *libraryname, const char *funcname)
1219 : {
1220 : /*
1221 : * If the function is to be loaded from postgres itself, search the
1222 : * InternalBGWorkers array.
1223 : */
1224 2134 : if (strcmp(libraryname, "postgres") == 0)
1225 : {
1226 : int i;
1227 :
1228 2722 : for (i = 0; i < lengthof(InternalBGWorkers); i++)
1229 : {
1230 2722 : if (strcmp(InternalBGWorkers[i].fn_name, funcname) == 0)
1231 2114 : return InternalBGWorkers[i].fn_addr;
1232 : }
1233 :
1234 : /* We can only reach this by programming error. */
1235 0 : elog(ERROR, "internal function \"%s\" not found", funcname);
1236 : }
1237 :
1238 : /* Otherwise load from external library. */
1239 20 : return (bgworker_main_type)
1240 : load_external_function(libraryname, funcname, true, NULL);
1241 : }
1242 :
1243 : /*
1244 : * Given a PID, get the bgw_type of the background worker. Returns NULL if
1245 : * not a valid background worker.
1246 : *
1247 : * The return value is in static memory belonging to this function, so it has
1248 : * to be used before calling this function again. This is so that the caller
1249 : * doesn't have to worry about the background worker locking protocol.
1250 : */
1251 : const char *
1252 194 : GetBackgroundWorkerTypeByPid(pid_t pid)
1253 : {
1254 : int slotno;
1255 194 : bool found = false;
1256 : static char result[BGW_MAXLEN];
1257 :
1258 194 : LWLockAcquire(BackgroundWorkerLock, LW_SHARED);
1259 :
1260 194 : for (slotno = 0; slotno < BackgroundWorkerData->total_slots; slotno++)
1261 : {
1262 194 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
1263 :
1264 194 : if (slot->pid > 0 && slot->pid == pid)
1265 : {
1266 194 : strcpy(result, slot->worker.bgw_type);
1267 194 : found = true;
1268 194 : break;
1269 : }
1270 : }
1271 :
1272 194 : LWLockRelease(BackgroundWorkerLock);
1273 :
1274 194 : if (!found)
1275 0 : return NULL;
1276 :
1277 194 : return result;
1278 : }
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