Line data Source code
1 : /*--------------------------------------------------------------------
2 : * bgworker.c
3 : * POSTGRES pluggable background workers implementation
4 : *
5 : * Portions Copyright (c) 1996-2025, 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 : dlist_head BackgroundWorkerList = DLIST_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 6150 : BackgroundWorkerShmemSize(void)
147 : {
148 : Size size;
149 :
150 : /* Array of workers is variably sized. */
151 6150 : size = offsetof(BackgroundWorkerArray, slot);
152 6150 : size = add_size(size, mul_size(max_worker_processes,
153 : sizeof(BackgroundWorkerSlot)));
154 :
155 6150 : return size;
156 : }
157 :
158 : /*
159 : * Initialize shared memory.
160 : */
161 : void
162 2152 : BackgroundWorkerShmemInit(void)
163 : {
164 : bool found;
165 :
166 2152 : BackgroundWorkerData = ShmemInitStruct("Background Worker Data",
167 : BackgroundWorkerShmemSize(),
168 : &found);
169 2152 : if (!IsUnderPostmaster)
170 : {
171 : dlist_iter iter;
172 2152 : int slotno = 0;
173 :
174 2152 : BackgroundWorkerData->total_slots = max_worker_processes;
175 2152 : BackgroundWorkerData->parallel_register_count = 0;
176 2152 : 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 3782 : dlist_foreach(iter, &BackgroundWorkerList)
185 : {
186 1630 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
187 : RegisteredBgWorker *rw;
188 :
189 1630 : rw = dlist_container(RegisteredBgWorker, rw_lnode, iter.cur);
190 : Assert(slotno < max_worker_processes);
191 1630 : slot->in_use = true;
192 1630 : slot->terminate = false;
193 1630 : slot->pid = InvalidPid;
194 1630 : slot->generation = 0;
195 1630 : rw->rw_shmem_slot = slotno;
196 1630 : rw->rw_worker.bgw_notify_pid = 0; /* might be reinit after crash */
197 1630 : memcpy(&slot->worker, &rw->rw_worker, sizeof(BackgroundWorker));
198 1630 : ++slotno;
199 : }
200 :
201 : /*
202 : * Mark any remaining slots as not in use.
203 : */
204 17734 : while (slotno < max_worker_processes)
205 : {
206 15582 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
207 :
208 15582 : slot->in_use = false;
209 15582 : ++slotno;
210 : }
211 : }
212 : else
213 : Assert(found);
214 2152 : }
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 8348 : FindRegisteredWorkerBySlotNumber(int slotno)
222 : {
223 : dlist_iter iter;
224 :
225 20734 : dlist_foreach(iter, &BackgroundWorkerList)
226 : {
227 : RegisteredBgWorker *rw;
228 :
229 16990 : rw = dlist_container(RegisteredBgWorker, rw_lnode, iter.cur);
230 16990 : if (rw->rw_shmem_slot == slotno)
231 4604 : return rw;
232 : }
233 :
234 3744 : 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 2492 : 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 2492 : 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 22716 : for (slotno = 0; slotno < max_worker_processes; ++slotno)
271 : {
272 20224 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
273 : RegisteredBgWorker *rw;
274 :
275 20224 : if (!slot->in_use)
276 11876 : continue;
277 :
278 : /*
279 : * Make sure we don't see the in_use flag before the updated slot
280 : * contents.
281 : */
282 8348 : pg_read_barrier();
283 :
284 : /* See whether we already know about this worker. */
285 8348 : rw = FindRegisteredWorkerBySlotNumber(slotno);
286 8348 : 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 4604 : if (slot->terminate && !rw->rw_terminate)
293 : {
294 12 : rw->rw_terminate = true;
295 12 : if (rw->rw_pid != 0)
296 12 : kill(rw->rw_pid, SIGTERM);
297 : else
298 : {
299 : /* Report never-started, now-terminated worker as dead. */
300 0 : ReportBackgroundWorkerPID(rw);
301 : }
302 : }
303 4604 : 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 3744 : if (!allow_new_workers)
313 0 : 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 3744 : if (slot->terminate)
323 0 : {
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 0 : notify_pid = slot->worker.bgw_notify_pid;
332 0 : if ((slot->worker.bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
333 0 : BackgroundWorkerData->parallel_terminate_count++;
334 0 : slot->pid = 0;
335 :
336 0 : pg_memory_barrier();
337 0 : slot->in_use = false;
338 :
339 0 : if (notify_pid != 0)
340 0 : kill(notify_pid, SIGUSR1);
341 :
342 0 : continue;
343 : }
344 :
345 : /*
346 : * Copy the registration data into the registered workers list.
347 : */
348 3744 : rw = MemoryContextAllocExtended(PostmasterContext,
349 : sizeof(RegisteredBgWorker),
350 : MCXT_ALLOC_NO_OOM | MCXT_ALLOC_ZERO);
351 3744 : 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 3744 : ascii_safe_strlcpy(rw->rw_worker.bgw_name,
364 3744 : slot->worker.bgw_name, BGW_MAXLEN);
365 3744 : ascii_safe_strlcpy(rw->rw_worker.bgw_type,
366 3744 : slot->worker.bgw_type, BGW_MAXLEN);
367 3744 : ascii_safe_strlcpy(rw->rw_worker.bgw_library_name,
368 3744 : slot->worker.bgw_library_name, MAXPGPATH);
369 3744 : ascii_safe_strlcpy(rw->rw_worker.bgw_function_name,
370 3744 : 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 3744 : rw->rw_worker.bgw_flags = slot->worker.bgw_flags;
381 3744 : rw->rw_worker.bgw_start_time = slot->worker.bgw_start_time;
382 3744 : rw->rw_worker.bgw_restart_time = slot->worker.bgw_restart_time;
383 3744 : rw->rw_worker.bgw_main_arg = slot->worker.bgw_main_arg;
384 3744 : 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 3744 : rw->rw_worker.bgw_notify_pid = slot->worker.bgw_notify_pid;
396 3744 : 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 3744 : rw->rw_pid = 0;
405 3744 : rw->rw_crashed_at = 0;
406 3744 : rw->rw_shmem_slot = slotno;
407 3744 : rw->rw_terminate = false;
408 :
409 : /* Log it! */
410 3744 : ereport(DEBUG1,
411 : (errmsg_internal("registering background worker \"%s\"",
412 : rw->rw_worker.bgw_name)));
413 :
414 3744 : dlist_push_head(&BackgroundWorkerList, &rw->rw_lnode);
415 : }
416 : }
417 :
418 : /*
419 : * Forget about a background worker that's no longer needed.
420 : *
421 : * NOTE: The entry is unlinked from BackgroundWorkerList. If the caller is
422 : * iterating through it, better use a mutable iterator!
423 : *
424 : * Caller is responsible for notifying bgw_notify_pid, if appropriate.
425 : *
426 : * This function must be invoked only in the postmaster.
427 : */
428 : void
429 3682 : ForgetBackgroundWorker(RegisteredBgWorker *rw)
430 : {
431 : BackgroundWorkerSlot *slot;
432 :
433 : Assert(rw->rw_shmem_slot < max_worker_processes);
434 3682 : 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 3682 : if ((rw->rw_worker.bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
442 2758 : BackgroundWorkerData->parallel_terminate_count++;
443 :
444 3682 : pg_memory_barrier();
445 3682 : slot->in_use = false;
446 :
447 3682 : ereport(DEBUG1,
448 : (errmsg_internal("unregistering background worker \"%s\"",
449 : rw->rw_worker.bgw_name)));
450 :
451 3682 : dlist_delete(&rw->rw_lnode);
452 3682 : pfree(rw);
453 3682 : }
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 5166 : ReportBackgroundWorkerPID(RegisteredBgWorker *rw)
462 : {
463 : BackgroundWorkerSlot *slot;
464 :
465 : Assert(rw->rw_shmem_slot < max_worker_processes);
466 5166 : slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
467 5166 : slot->pid = rw->rw_pid;
468 :
469 5166 : if (rw->rw_worker.bgw_notify_pid != 0)
470 3744 : kill(rw->rw_worker.bgw_notify_pid, SIGUSR1);
471 5166 : }
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 : * NOTE: The entry may be unlinked from BackgroundWorkerList. If the caller
478 : * is iterating through it, better use a mutable iterator!
479 : *
480 : * This function should only be called from the postmaster.
481 : */
482 : void
483 4498 : ReportBackgroundWorkerExit(RegisteredBgWorker *rw)
484 : {
485 : BackgroundWorkerSlot *slot;
486 : int notify_pid;
487 :
488 : Assert(rw->rw_shmem_slot < max_worker_processes);
489 4498 : slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
490 4498 : slot->pid = rw->rw_pid;
491 4498 : 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 4498 : if (rw->rw_terminate ||
501 1256 : rw->rw_worker.bgw_restart_time == BGW_NEVER_RESTART)
502 3682 : ForgetBackgroundWorker(rw);
503 :
504 4498 : if (notify_pid != 0)
505 3638 : kill(notify_pid, SIGUSR1);
506 4498 : }
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
514 484 : BackgroundWorkerStopNotifications(pid_t pid)
515 : {
516 : dlist_iter iter;
517 :
518 1536 : dlist_foreach(iter, &BackgroundWorkerList)
519 : {
520 : RegisteredBgWorker *rw;
521 :
522 1052 : rw = dlist_container(RegisteredBgWorker, rw_lnode, iter.cur);
523 1052 : if (rw->rw_worker.bgw_notify_pid == pid)
524 48 : rw->rw_worker.bgw_notify_pid = 0;
525 : }
526 484 : }
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 canceling 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 1030 : ForgetUnstartedBackgroundWorkers(void)
542 : {
543 : dlist_mutable_iter iter;
544 :
545 2040 : dlist_foreach_modify(iter, &BackgroundWorkerList)
546 : {
547 : RegisteredBgWorker *rw;
548 : BackgroundWorkerSlot *slot;
549 :
550 1010 : rw = dlist_container(RegisteredBgWorker, rw_lnode, iter.cur);
551 : Assert(rw->rw_shmem_slot < max_worker_processes);
552 1010 : slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
553 :
554 : /* If it's not yet started, and there's someone waiting ... */
555 1010 : if (slot->pid == InvalidPid &&
556 108 : 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(rw);
562 0 : if (notify_pid != 0)
563 0 : kill(notify_pid, SIGUSR1);
564 : }
565 : }
566 1030 : }
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 10 : ResetBackgroundWorkerCrashTimes(void)
580 : {
581 : dlist_mutable_iter iter;
582 :
583 20 : dlist_foreach_modify(iter, &BackgroundWorkerList)
584 : {
585 : RegisteredBgWorker *rw;
586 :
587 10 : rw = dlist_container(RegisteredBgWorker, rw_lnode, iter.cur);
588 :
589 10 : 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(rw);
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 10 : rw->rw_crashed_at = 0;
616 10 : rw->rw_pid = 0;
617 :
618 : /*
619 : * If there was anyone waiting for it, they're history.
620 : */
621 10 : rw->rw_worker.bgw_notify_pid = 0;
622 : }
623 : }
624 10 : }
625 :
626 : /*
627 : * Complain about the BackgroundWorker definition using error level elevel.
628 : * Return true if it looks ok, false if not (unless elevel >= ERROR, in
629 : * which case we won't return at all in the not-OK case).
630 : */
631 : static bool
632 5182 : SanityCheckBackgroundWorker(BackgroundWorker *worker, int elevel)
633 : {
634 : /* sanity check for flags */
635 :
636 : /*
637 : * We used to support workers not connected to shared memory, but don't
638 : * anymore. Thus this is a required flag now. We're not removing the flag
639 : * for compatibility reasons and because the flag still provides some
640 : * signal when reading code.
641 : */
642 5182 : if (!(worker->bgw_flags & BGWORKER_SHMEM_ACCESS))
643 : {
644 0 : ereport(elevel,
645 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
646 : errmsg("background worker \"%s\": background workers without shared memory access are not supported",
647 : worker->bgw_name)));
648 0 : return false;
649 : }
650 :
651 5182 : if (worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION)
652 : {
653 5164 : if (worker->bgw_start_time == BgWorkerStart_PostmasterStart)
654 : {
655 0 : ereport(elevel,
656 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
657 : errmsg("background worker \"%s\": cannot request database access if starting at postmaster start",
658 : worker->bgw_name)));
659 0 : return false;
660 : }
661 :
662 : /* XXX other checks? */
663 : }
664 :
665 5182 : if ((worker->bgw_restart_time < 0 &&
666 3554 : worker->bgw_restart_time != BGW_NEVER_RESTART) ||
667 5182 : (worker->bgw_restart_time > USECS_PER_DAY / 1000))
668 : {
669 0 : ereport(elevel,
670 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
671 : errmsg("background worker \"%s\": invalid restart interval",
672 : worker->bgw_name)));
673 0 : return false;
674 : }
675 :
676 : /*
677 : * Parallel workers may not be configured for restart, because the
678 : * parallel_register_count/parallel_terminate_count accounting can't
679 : * handle parallel workers lasting through a crash-and-restart cycle.
680 : */
681 5182 : if (worker->bgw_restart_time != BGW_NEVER_RESTART &&
682 1628 : (worker->bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
683 : {
684 0 : ereport(elevel,
685 : (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
686 : errmsg("background worker \"%s\": parallel workers may not be configured for restart",
687 : worker->bgw_name)));
688 0 : return false;
689 : }
690 :
691 : /*
692 : * If bgw_type is not filled in, use bgw_name.
693 : */
694 5182 : if (strcmp(worker->bgw_type, "") == 0)
695 0 : strcpy(worker->bgw_type, worker->bgw_name);
696 :
697 5182 : return true;
698 : }
699 :
700 : /*
701 : * Standard SIGTERM handler for background workers
702 : */
703 : static void
704 0 : bgworker_die(SIGNAL_ARGS)
705 : {
706 0 : sigprocmask(SIG_SETMASK, &BlockSig, NULL);
707 :
708 0 : ereport(FATAL,
709 : (errcode(ERRCODE_ADMIN_SHUTDOWN),
710 : errmsg("terminating background worker \"%s\" due to administrator command",
711 : MyBgworkerEntry->bgw_type)));
712 : }
713 :
714 : /*
715 : * Main entry point for background worker processes.
716 : */
717 : void
718 4538 : BackgroundWorkerMain(const void *startup_data, size_t startup_data_len)
719 : {
720 : sigjmp_buf local_sigjmp_buf;
721 : BackgroundWorker *worker;
722 : bgworker_main_type entrypt;
723 :
724 4538 : if (startup_data == NULL)
725 0 : elog(FATAL, "unable to find bgworker entry");
726 : Assert(startup_data_len == sizeof(BackgroundWorker));
727 4538 : worker = MemoryContextAlloc(TopMemoryContext, sizeof(BackgroundWorker));
728 4538 : memcpy(worker, startup_data, sizeof(BackgroundWorker));
729 :
730 : /*
731 : * Now that we're done reading the startup data, release postmaster's
732 : * working memory context.
733 : */
734 4538 : if (PostmasterContext)
735 : {
736 4538 : MemoryContextDelete(PostmasterContext);
737 4538 : PostmasterContext = NULL;
738 : }
739 :
740 4538 : MyBgworkerEntry = worker;
741 4538 : MyBackendType = B_BG_WORKER;
742 4538 : init_ps_display(worker->bgw_name);
743 :
744 : Assert(GetProcessingMode() == InitProcessing);
745 :
746 : /* Apply PostAuthDelay */
747 4538 : if (PostAuthDelay > 0)
748 0 : pg_usleep(PostAuthDelay * 1000000L);
749 :
750 : /*
751 : * Set up signal handlers.
752 : */
753 4538 : if (worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION)
754 : {
755 : /*
756 : * SIGINT is used to signal canceling the current action
757 : */
758 4520 : pqsignal(SIGINT, StatementCancelHandler);
759 4520 : pqsignal(SIGUSR1, procsignal_sigusr1_handler);
760 4520 : pqsignal(SIGFPE, FloatExceptionHandler);
761 :
762 : /* XXX Any other handlers needed here? */
763 : }
764 : else
765 : {
766 18 : pqsignal(SIGINT, SIG_IGN);
767 18 : pqsignal(SIGUSR1, SIG_IGN);
768 18 : pqsignal(SIGFPE, SIG_IGN);
769 : }
770 4538 : pqsignal(SIGTERM, bgworker_die);
771 : /* SIGQUIT handler was already set up by InitPostmasterChild */
772 4538 : pqsignal(SIGHUP, SIG_IGN);
773 :
774 4538 : InitializeTimeouts(); /* establishes SIGALRM handler */
775 :
776 4538 : pqsignal(SIGPIPE, SIG_IGN);
777 4538 : pqsignal(SIGUSR2, SIG_IGN);
778 4538 : pqsignal(SIGCHLD, SIG_DFL);
779 :
780 : /*
781 : * If an exception is encountered, processing resumes here.
782 : *
783 : * We just need to clean up, report the error, and go away.
784 : */
785 4538 : if (sigsetjmp(local_sigjmp_buf, 1) != 0)
786 : {
787 : /* Since not using PG_TRY, must reset error stack by hand */
788 262 : error_context_stack = NULL;
789 :
790 : /* Prevent interrupts while cleaning up */
791 262 : HOLD_INTERRUPTS();
792 :
793 : /*
794 : * sigsetjmp will have blocked all signals, but we may need to accept
795 : * signals while communicating with our parallel leader. Once we've
796 : * done HOLD_INTERRUPTS() it should be safe to unblock signals.
797 : */
798 262 : BackgroundWorkerUnblockSignals();
799 :
800 : /* Report the error to the parallel leader and the server log */
801 262 : EmitErrorReport();
802 :
803 : /*
804 : * Do we need more cleanup here? For shmem-connected bgworkers, we
805 : * will call InitProcess below, which will install ProcKill as exit
806 : * callback. That will take care of releasing locks, etc.
807 : */
808 :
809 : /* and go away */
810 262 : proc_exit(1);
811 : }
812 :
813 : /* We can now handle ereport(ERROR) */
814 4538 : PG_exception_stack = &local_sigjmp_buf;
815 :
816 : /*
817 : * Create a per-backend PGPROC struct in shared memory. We must do this
818 : * before we can use LWLocks or access any shared memory.
819 : */
820 4538 : InitProcess();
821 :
822 : /*
823 : * Early initialization.
824 : */
825 4538 : BaseInit();
826 :
827 : /*
828 : * Look up the entry point function, loading its library if necessary.
829 : */
830 9076 : entrypt = LookupBackgroundWorkerFunction(worker->bgw_library_name,
831 4538 : worker->bgw_function_name);
832 :
833 : /*
834 : * Note that in normal processes, we would call InitPostgres here. For a
835 : * worker, however, we don't know what database to connect to, yet; so we
836 : * need to wait until the user code does it via
837 : * BackgroundWorkerInitializeConnection().
838 : */
839 :
840 : /*
841 : * Now invoke the user-defined worker code
842 : */
843 4538 : entrypt(worker->bgw_main_arg);
844 :
845 : /* ... and if it returns, we're done */
846 2752 : proc_exit(0);
847 : }
848 :
849 : /*
850 : * Connect background worker to a database.
851 : */
852 : void
853 822 : BackgroundWorkerInitializeConnection(const char *dbname, const char *username, uint32 flags)
854 : {
855 822 : BackgroundWorker *worker = MyBgworkerEntry;
856 822 : bits32 init_flags = 0; /* never honor session_preload_libraries */
857 :
858 : /* ignore datallowconn and ACL_CONNECT? */
859 822 : if (flags & BGWORKER_BYPASS_ALLOWCONN)
860 0 : init_flags |= INIT_PG_OVERRIDE_ALLOW_CONNS;
861 : /* ignore rolcanlogin? */
862 822 : if (flags & BGWORKER_BYPASS_ROLELOGINCHECK)
863 0 : init_flags |= INIT_PG_OVERRIDE_ROLE_LOGIN;
864 :
865 : /* XXX is this the right errcode? */
866 822 : if (!(worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION))
867 0 : ereport(FATAL,
868 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
869 : errmsg("database connection requirement not indicated during registration")));
870 :
871 822 : InitPostgres(dbname, InvalidOid, /* database to connect to */
872 : username, InvalidOid, /* role to connect as */
873 : init_flags,
874 : NULL); /* no out_dbname */
875 :
876 : /* it had better not gotten out of "init" mode yet */
877 822 : if (!IsInitProcessingMode())
878 0 : ereport(ERROR,
879 : (errmsg("invalid processing mode in background worker")));
880 822 : SetProcessingMode(NormalProcessing);
881 822 : }
882 :
883 : /*
884 : * Connect background worker to a database using OIDs.
885 : */
886 : void
887 3698 : BackgroundWorkerInitializeConnectionByOid(Oid dboid, Oid useroid, uint32 flags)
888 : {
889 3698 : BackgroundWorker *worker = MyBgworkerEntry;
890 3698 : bits32 init_flags = 0; /* never honor session_preload_libraries */
891 :
892 : /* ignore datallowconn and ACL_CONNECT? */
893 3698 : if (flags & BGWORKER_BYPASS_ALLOWCONN)
894 2758 : init_flags |= INIT_PG_OVERRIDE_ALLOW_CONNS;
895 : /* ignore rolcanlogin? */
896 3698 : if (flags & BGWORKER_BYPASS_ROLELOGINCHECK)
897 2758 : init_flags |= INIT_PG_OVERRIDE_ROLE_LOGIN;
898 :
899 : /* XXX is this the right errcode? */
900 3698 : if (!(worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION))
901 0 : ereport(FATAL,
902 : (errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
903 : errmsg("database connection requirement not indicated during registration")));
904 :
905 3698 : InitPostgres(NULL, dboid, /* database to connect to */
906 : NULL, useroid, /* role to connect as */
907 : init_flags,
908 : NULL); /* no out_dbname */
909 :
910 : /* it had better not gotten out of "init" mode yet */
911 3686 : if (!IsInitProcessingMode())
912 0 : ereport(ERROR,
913 : (errmsg("invalid processing mode in background worker")));
914 3686 : SetProcessingMode(NormalProcessing);
915 3686 : }
916 :
917 : /*
918 : * Block/unblock signals in a background worker
919 : */
920 : void
921 0 : BackgroundWorkerBlockSignals(void)
922 : {
923 0 : sigprocmask(SIG_SETMASK, &BlockSig, NULL);
924 0 : }
925 :
926 : void
927 4800 : BackgroundWorkerUnblockSignals(void)
928 : {
929 4800 : sigprocmask(SIG_SETMASK, &UnBlockSig, NULL);
930 4800 : }
931 :
932 : /*
933 : * Register a new static background worker.
934 : *
935 : * This can only be called directly from postmaster or in the _PG_init
936 : * function of a module library that's loaded by shared_preload_libraries;
937 : * otherwise it will have no effect.
938 : */
939 : void
940 1634 : RegisterBackgroundWorker(BackgroundWorker *worker)
941 : {
942 : RegisteredBgWorker *rw;
943 : static int numworkers = 0;
944 :
945 : /*
946 : * Static background workers can only be registered in the postmaster
947 : * process.
948 : */
949 1634 : if (IsUnderPostmaster || !IsPostmasterEnvironment)
950 : {
951 : /*
952 : * In EXEC_BACKEND or single-user mode, we process
953 : * shared_preload_libraries in backend processes too. We cannot
954 : * register static background workers at that stage, but many
955 : * libraries' _PG_init() functions don't distinguish whether they're
956 : * being loaded in the postmaster or in a backend, they just check
957 : * process_shared_preload_libraries_in_progress. It's a bit sloppy,
958 : * but for historical reasons we tolerate it. In EXEC_BACKEND mode,
959 : * the background workers should already have been registered when the
960 : * library was loaded in postmaster.
961 : */
962 0 : if (process_shared_preload_libraries_in_progress)
963 0 : return;
964 0 : ereport(LOG,
965 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
966 : errmsg("background worker \"%s\": must be registered in \"shared_preload_libraries\"",
967 : worker->bgw_name)));
968 0 : return;
969 : }
970 :
971 : /*
972 : * Cannot register static background workers after calling
973 : * BackgroundWorkerShmemInit().
974 : */
975 1634 : if (BackgroundWorkerData != NULL)
976 0 : elog(ERROR, "cannot register background worker \"%s\" after shmem init",
977 : worker->bgw_name);
978 :
979 1634 : ereport(DEBUG1,
980 : (errmsg_internal("registering background worker \"%s\"", worker->bgw_name)));
981 :
982 1634 : if (!SanityCheckBackgroundWorker(worker, LOG))
983 0 : return;
984 :
985 1634 : if (worker->bgw_notify_pid != 0)
986 : {
987 0 : ereport(LOG,
988 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
989 : errmsg("background worker \"%s\": only dynamic background workers can request notification",
990 : worker->bgw_name)));
991 0 : return;
992 : }
993 :
994 : /*
995 : * Enforce maximum number of workers. Note this is overly restrictive: we
996 : * could allow more non-shmem-connected workers, because these don't count
997 : * towards the MAX_BACKENDS limit elsewhere. For now, it doesn't seem
998 : * important to relax this restriction.
999 : */
1000 1634 : if (++numworkers > max_worker_processes)
1001 : {
1002 0 : ereport(LOG,
1003 : (errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
1004 : errmsg("too many background workers"),
1005 : errdetail_plural("Up to %d background worker can be registered with the current settings.",
1006 : "Up to %d background workers can be registered with the current settings.",
1007 : max_worker_processes,
1008 : max_worker_processes),
1009 : errhint("Consider increasing the configuration parameter \"%s\".", "max_worker_processes")));
1010 0 : return;
1011 : }
1012 :
1013 : /*
1014 : * Copy the registration data into the registered workers list.
1015 : */
1016 1634 : rw = MemoryContextAllocExtended(PostmasterContext,
1017 : sizeof(RegisteredBgWorker),
1018 : MCXT_ALLOC_NO_OOM);
1019 1634 : if (rw == NULL)
1020 : {
1021 0 : ereport(LOG,
1022 : (errcode(ERRCODE_OUT_OF_MEMORY),
1023 : errmsg("out of memory")));
1024 0 : return;
1025 : }
1026 :
1027 1634 : rw->rw_worker = *worker;
1028 1634 : rw->rw_pid = 0;
1029 1634 : rw->rw_crashed_at = 0;
1030 1634 : rw->rw_terminate = false;
1031 :
1032 1634 : dlist_push_head(&BackgroundWorkerList, &rw->rw_lnode);
1033 : }
1034 :
1035 : /*
1036 : * Register a new background worker from a regular backend.
1037 : *
1038 : * Returns true on success and false on failure. Failure typically indicates
1039 : * that no background worker slots are currently available.
1040 : *
1041 : * If handle != NULL, we'll set *handle to a pointer that can subsequently
1042 : * be used as an argument to GetBackgroundWorkerPid(). The caller can
1043 : * free this pointer using pfree(), if desired.
1044 : */
1045 : bool
1046 3548 : RegisterDynamicBackgroundWorker(BackgroundWorker *worker,
1047 : BackgroundWorkerHandle **handle)
1048 : {
1049 : int slotno;
1050 3548 : bool success = false;
1051 : bool parallel;
1052 3548 : uint64 generation = 0;
1053 :
1054 : /*
1055 : * We can't register dynamic background workers from the postmaster. If
1056 : * this is a standalone backend, we're the only process and can't start
1057 : * any more. In a multi-process environment, it might be theoretically
1058 : * possible, but we don't currently support it due to locking
1059 : * considerations; see comments on the BackgroundWorkerSlot data
1060 : * structure.
1061 : */
1062 3548 : if (!IsUnderPostmaster)
1063 0 : return false;
1064 :
1065 3548 : if (!SanityCheckBackgroundWorker(worker, ERROR))
1066 0 : return false;
1067 :
1068 3548 : parallel = (worker->bgw_flags & BGWORKER_CLASS_PARALLEL) != 0;
1069 :
1070 3548 : LWLockAcquire(BackgroundWorkerLock, LW_EXCLUSIVE);
1071 :
1072 : /*
1073 : * If this is a parallel worker, check whether there are already too many
1074 : * parallel workers; if so, don't register another one. Our view of
1075 : * parallel_terminate_count may be slightly stale, but that doesn't really
1076 : * matter: we would have gotten the same result if we'd arrived here
1077 : * slightly earlier anyway. There's no help for it, either, since the
1078 : * postmaster must not take locks; a memory barrier wouldn't guarantee
1079 : * anything useful.
1080 : */
1081 3548 : if (parallel && (BackgroundWorkerData->parallel_register_count -
1082 2790 : BackgroundWorkerData->parallel_terminate_count) >=
1083 : max_parallel_workers)
1084 : {
1085 : Assert(BackgroundWorkerData->parallel_register_count -
1086 : BackgroundWorkerData->parallel_terminate_count <=
1087 : MAX_PARALLEL_WORKER_LIMIT);
1088 20 : LWLockRelease(BackgroundWorkerLock);
1089 20 : return false;
1090 : }
1091 :
1092 : /*
1093 : * Look for an unused slot. If we find one, grab it.
1094 : */
1095 11174 : for (slotno = 0; slotno < BackgroundWorkerData->total_slots; ++slotno)
1096 : {
1097 11162 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
1098 :
1099 11162 : if (!slot->in_use)
1100 : {
1101 3516 : memcpy(&slot->worker, worker, sizeof(BackgroundWorker));
1102 3516 : slot->pid = InvalidPid; /* indicates not started yet */
1103 3516 : slot->generation++;
1104 3516 : slot->terminate = false;
1105 3516 : generation = slot->generation;
1106 3516 : if (parallel)
1107 2758 : BackgroundWorkerData->parallel_register_count++;
1108 :
1109 : /*
1110 : * Make sure postmaster doesn't see the slot as in use before it
1111 : * sees the new contents.
1112 : */
1113 3516 : pg_write_barrier();
1114 :
1115 3516 : slot->in_use = true;
1116 3516 : success = true;
1117 3516 : break;
1118 : }
1119 : }
1120 :
1121 3528 : LWLockRelease(BackgroundWorkerLock);
1122 :
1123 : /* If we found a slot, tell the postmaster to notice the change. */
1124 3528 : if (success)
1125 3516 : SendPostmasterSignal(PMSIGNAL_BACKGROUND_WORKER_CHANGE);
1126 :
1127 : /*
1128 : * If we found a slot and the user has provided a handle, initialize it.
1129 : */
1130 3528 : if (success && handle)
1131 : {
1132 3516 : *handle = palloc(sizeof(BackgroundWorkerHandle));
1133 3516 : (*handle)->slot = slotno;
1134 3516 : (*handle)->generation = generation;
1135 : }
1136 :
1137 3528 : return success;
1138 : }
1139 :
1140 : /*
1141 : * Get the PID of a dynamically-registered background worker.
1142 : *
1143 : * If the worker is determined to be running, the return value will be
1144 : * BGWH_STARTED and *pidp will get the PID of the worker process. If the
1145 : * postmaster has not yet attempted to start the worker, the return value will
1146 : * be BGWH_NOT_YET_STARTED. Otherwise, the return value is BGWH_STOPPED.
1147 : *
1148 : * BGWH_STOPPED can indicate either that the worker is temporarily stopped
1149 : * (because it is configured for automatic restart and exited non-zero),
1150 : * or that the worker is permanently stopped (because it exited with exit
1151 : * code 0, or was not configured for automatic restart), or even that the
1152 : * worker was unregistered without ever starting (either because startup
1153 : * failed and the worker is not configured for automatic restart, or because
1154 : * TerminateBackgroundWorker was used before the worker was successfully
1155 : * started).
1156 : */
1157 : BgwHandleStatus
1158 18828304 : GetBackgroundWorkerPid(BackgroundWorkerHandle *handle, pid_t *pidp)
1159 : {
1160 : BackgroundWorkerSlot *slot;
1161 : pid_t pid;
1162 :
1163 : Assert(handle->slot < max_worker_processes);
1164 18828304 : slot = &BackgroundWorkerData->slot[handle->slot];
1165 :
1166 : /*
1167 : * We could probably arrange to synchronize access to data using memory
1168 : * barriers only, but for now, let's just keep it simple and grab the
1169 : * lock. It seems unlikely that there will be enough traffic here to
1170 : * result in meaningful contention.
1171 : */
1172 18828304 : LWLockAcquire(BackgroundWorkerLock, LW_SHARED);
1173 :
1174 : /*
1175 : * The generation number can't be concurrently changed while we hold the
1176 : * lock. The pid, which is updated by the postmaster, can change at any
1177 : * time, but we assume such changes are atomic. So the value we read
1178 : * won't be garbage, but it might be out of date by the time the caller
1179 : * examines it (but that's unavoidable anyway).
1180 : *
1181 : * The in_use flag could be in the process of changing from true to false,
1182 : * but if it is already false then it can't change further.
1183 : */
1184 18828304 : if (handle->generation != slot->generation || !slot->in_use)
1185 2760 : pid = 0;
1186 : else
1187 18825544 : pid = slot->pid;
1188 :
1189 : /* All done. */
1190 18828304 : LWLockRelease(BackgroundWorkerLock);
1191 :
1192 18828304 : if (pid == 0)
1193 2760 : return BGWH_STOPPED;
1194 18825544 : else if (pid == InvalidPid)
1195 902222 : return BGWH_NOT_YET_STARTED;
1196 17923322 : *pidp = pid;
1197 17923322 : return BGWH_STARTED;
1198 : }
1199 :
1200 : /*
1201 : * Wait for a background worker to start up.
1202 : *
1203 : * This is like GetBackgroundWorkerPid(), except that if the worker has not
1204 : * yet started, we wait for it to do so; thus, BGWH_NOT_YET_STARTED is never
1205 : * returned. However, if the postmaster has died, we give up and return
1206 : * BGWH_POSTMASTER_DIED, since it that case we know that startup will not
1207 : * take place.
1208 : *
1209 : * The caller *must* have set our PID as the worker's bgw_notify_pid,
1210 : * else we will not be awoken promptly when the worker's state changes.
1211 : */
1212 : BgwHandleStatus
1213 14 : WaitForBackgroundWorkerStartup(BackgroundWorkerHandle *handle, pid_t *pidp)
1214 : {
1215 : BgwHandleStatus status;
1216 : int rc;
1217 :
1218 : for (;;)
1219 0 : {
1220 : pid_t pid;
1221 :
1222 14 : CHECK_FOR_INTERRUPTS();
1223 :
1224 14 : status = GetBackgroundWorkerPid(handle, &pid);
1225 14 : if (status == BGWH_STARTED)
1226 14 : *pidp = pid;
1227 14 : if (status != BGWH_NOT_YET_STARTED)
1228 14 : break;
1229 :
1230 0 : rc = WaitLatch(MyLatch,
1231 : WL_LATCH_SET | WL_POSTMASTER_DEATH, 0,
1232 : WAIT_EVENT_BGWORKER_STARTUP);
1233 :
1234 0 : if (rc & WL_POSTMASTER_DEATH)
1235 : {
1236 0 : status = BGWH_POSTMASTER_DIED;
1237 0 : break;
1238 : }
1239 :
1240 0 : ResetLatch(MyLatch);
1241 : }
1242 :
1243 14 : return status;
1244 : }
1245 :
1246 : /*
1247 : * Wait for a background worker to stop.
1248 : *
1249 : * If the worker hasn't yet started, or is running, we wait for it to stop
1250 : * and then return BGWH_STOPPED. However, if the postmaster has died, we give
1251 : * up and return BGWH_POSTMASTER_DIED, because it's the postmaster that
1252 : * notifies us when a worker's state changes.
1253 : *
1254 : * The caller *must* have set our PID as the worker's bgw_notify_pid,
1255 : * else we will not be awoken promptly when the worker's state changes.
1256 : */
1257 : BgwHandleStatus
1258 2760 : WaitForBackgroundWorkerShutdown(BackgroundWorkerHandle *handle)
1259 : {
1260 : BgwHandleStatus status;
1261 : int rc;
1262 :
1263 : for (;;)
1264 3834 : {
1265 : pid_t pid;
1266 :
1267 6594 : CHECK_FOR_INTERRUPTS();
1268 :
1269 6594 : status = GetBackgroundWorkerPid(handle, &pid);
1270 6594 : if (status == BGWH_STOPPED)
1271 2760 : break;
1272 :
1273 3834 : rc = WaitLatch(MyLatch,
1274 : WL_LATCH_SET | WL_POSTMASTER_DEATH, 0,
1275 : WAIT_EVENT_BGWORKER_SHUTDOWN);
1276 :
1277 3834 : if (rc & WL_POSTMASTER_DEATH)
1278 : {
1279 0 : status = BGWH_POSTMASTER_DIED;
1280 0 : break;
1281 : }
1282 :
1283 3834 : ResetLatch(MyLatch);
1284 : }
1285 :
1286 2760 : return status;
1287 : }
1288 :
1289 : /*
1290 : * Instruct the postmaster to terminate a background worker.
1291 : *
1292 : * Note that it's safe to do this without regard to whether the worker is
1293 : * still running, or even if the worker may already have exited and been
1294 : * unregistered.
1295 : */
1296 : void
1297 12 : TerminateBackgroundWorker(BackgroundWorkerHandle *handle)
1298 : {
1299 : BackgroundWorkerSlot *slot;
1300 12 : bool signal_postmaster = false;
1301 :
1302 : Assert(handle->slot < max_worker_processes);
1303 12 : slot = &BackgroundWorkerData->slot[handle->slot];
1304 :
1305 : /* Set terminate flag in shared memory, unless slot has been reused. */
1306 12 : LWLockAcquire(BackgroundWorkerLock, LW_EXCLUSIVE);
1307 12 : if (handle->generation == slot->generation)
1308 : {
1309 12 : slot->terminate = true;
1310 12 : signal_postmaster = true;
1311 : }
1312 12 : LWLockRelease(BackgroundWorkerLock);
1313 :
1314 : /* Make sure the postmaster notices the change to shared memory. */
1315 12 : if (signal_postmaster)
1316 12 : SendPostmasterSignal(PMSIGNAL_BACKGROUND_WORKER_CHANGE);
1317 12 : }
1318 :
1319 : /*
1320 : * Look up (and possibly load) a bgworker entry point function.
1321 : *
1322 : * For functions contained in the core code, we use library name "postgres"
1323 : * and consult the InternalBGWorkers array. External functions are
1324 : * looked up, and loaded if necessary, using load_external_function().
1325 : *
1326 : * The point of this is to pass function names as strings across process
1327 : * boundaries. We can't pass actual function addresses because of the
1328 : * possibility that the function has been loaded at a different address
1329 : * in a different process. This is obviously a hazard for functions in
1330 : * loadable libraries, but it can happen even for functions in the core code
1331 : * on platforms using EXEC_BACKEND (e.g., Windows).
1332 : *
1333 : * At some point it might be worthwhile to get rid of InternalBGWorkers[]
1334 : * in favor of applying load_external_function() for core functions too;
1335 : * but that raises portability issues that are not worth addressing now.
1336 : */
1337 : static bgworker_main_type
1338 4538 : LookupBackgroundWorkerFunction(const char *libraryname, const char *funcname)
1339 : {
1340 : /*
1341 : * If the function is to be loaded from postgres itself, search the
1342 : * InternalBGWorkers array.
1343 : */
1344 4538 : if (strcmp(libraryname, "postgres") == 0)
1345 : {
1346 : int i;
1347 :
1348 7994 : for (i = 0; i < lengthof(InternalBGWorkers); i++)
1349 : {
1350 7994 : if (strcmp(InternalBGWorkers[i].fn_name, funcname) == 0)
1351 4512 : return InternalBGWorkers[i].fn_addr;
1352 : }
1353 :
1354 : /* We can only reach this by programming error. */
1355 0 : elog(ERROR, "internal function \"%s\" not found", funcname);
1356 : }
1357 :
1358 : /* Otherwise load from external library. */
1359 26 : return (bgworker_main_type)
1360 26 : load_external_function(libraryname, funcname, true, NULL);
1361 : }
1362 :
1363 : /*
1364 : * Given a PID, get the bgw_type of the background worker. Returns NULL if
1365 : * not a valid background worker.
1366 : *
1367 : * The return value is in static memory belonging to this function, so it has
1368 : * to be used before calling this function again. This is so that the caller
1369 : * doesn't have to worry about the background worker locking protocol.
1370 : */
1371 : const char *
1372 1926 : GetBackgroundWorkerTypeByPid(pid_t pid)
1373 : {
1374 : int slotno;
1375 1926 : bool found = false;
1376 : static char result[BGW_MAXLEN];
1377 :
1378 1926 : LWLockAcquire(BackgroundWorkerLock, LW_SHARED);
1379 :
1380 2240 : for (slotno = 0; slotno < BackgroundWorkerData->total_slots; slotno++)
1381 : {
1382 2240 : BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
1383 :
1384 2240 : if (slot->pid > 0 && slot->pid == pid)
1385 : {
1386 1926 : strcpy(result, slot->worker.bgw_type);
1387 1926 : found = true;
1388 1926 : break;
1389 : }
1390 : }
1391 :
1392 1926 : LWLockRelease(BackgroundWorkerLock);
1393 :
1394 1926 : if (!found)
1395 0 : return NULL;
1396 :
1397 1926 : return result;
1398 : }
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