granicus.if.org Git - postgresql/blob - src/backend/postmaster/bgworker.c

   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 BackgroundWorkerShmemSize(void)
 144 {
 145         Size            size;
 146
 147         /* Array of workers is variably sized. */
 148         size = offsetof(BackgroundWorkerArray, slot);
 149         size = add_size(size, mul_size(max_worker_processes,
 150                                                                    sizeof(BackgroundWorkerSlot)));
 151
 152         return size;
 153 }
 154
 155 /*
 156  * Initialize shared memory.
 157  */
 158 void
 159 BackgroundWorkerShmemInit(void)
 160 {
 161         bool            found;
 162
 163         BackgroundWorkerData = ShmemInitStruct("Background Worker Data",
 164                                                                                    BackgroundWorkerShmemSize(),
 165                                                                                    &found);
 166         if (!IsUnderPostmaster)
 167         {
 168                 slist_iter      siter;
 169                 int                     slotno = 0;
 170
 171                 BackgroundWorkerData->total_slots = max_worker_processes;
 172                 BackgroundWorkerData->parallel_register_count = 0;
 173                 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                 slist_foreach(siter, &BackgroundWorkerList)
 182                 {
 183                         BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
 184                         RegisteredBgWorker *rw;
 185
 186                         rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur);
 187                         Assert(slotno < max_worker_processes);
 188                         slot->in_use = true;
 189                         slot->terminate = false;
 190                         slot->pid = InvalidPid;
 191                         slot->generation = 0;
 192                         rw->rw_shmem_slot = slotno;
 193                         rw->rw_worker.bgw_notify_pid = 0;       /* might be reinit after crash */
 194                         memcpy(&slot->worker, &rw->rw_worker, sizeof(BackgroundWorker));
 195                         ++slotno;
 196                 }
 197
 198                 /*
 199                  * Mark any remaining slots as not in use.
 200                  */
 201                 while (slotno < max_worker_processes)
 202                 {
 203                         BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
 204
 205                         slot->in_use = false;
 206                         ++slotno;
 207                 }
 208         }
 209         else
 210                 Assert(found);
 211 }
 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 FindRegisteredWorkerBySlotNumber(int slotno)
 219 {
 220         slist_iter      siter;
 221
 222         slist_foreach(siter, &BackgroundWorkerList)
 223         {
 224                 RegisteredBgWorker *rw;
 225
 226                 rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur);
 227                 if (rw->rw_shmem_slot == slotno)
 228                         return rw;
 229         }
 230
 231         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 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         if (max_worker_processes != BackgroundWorkerData->total_slots)
 253         {
 254                 elog(LOG,
 255                          "inconsistent background worker state (max_worker_processes=%d, total_slots=%d",
 256                          max_worker_processes,
 257                          BackgroundWorkerData->total_slots);
 258                 return;
 259         }
 260
 261         /*
 262          * Iterate through slots, looking for newly-registered workers or workers
 263          * who must die.
 264          */
 265         for (slotno = 0; slotno < max_worker_processes; ++slotno)
 266         {
 267                 BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
 268                 RegisteredBgWorker *rw;
 269
 270                 if (!slot->in_use)
 271                         continue;
 272
 273                 /*
 274                  * Make sure we don't see the in_use flag before the updated slot
 275                  * contents.
 276                  */
 277                 pg_read_barrier();
 278
 279                 /* See whether we already know about this worker. */
 280                 rw = FindRegisteredWorkerBySlotNumber(slotno);
 281                 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                         if (slot->terminate && !rw->rw_terminate)
 288                         {
 289                                 rw->rw_terminate = true;
 290                                 if (rw->rw_pid != 0)
 291                                         kill(rw->rw_pid, SIGTERM);
 292                                 else
 293                                 {
 294                                         /* Report never-started, now-terminated worker as dead. */
 295                                         ReportBackgroundWorkerPID(rw);
 296                                 }
 297                         }
 298                         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                 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                         notify_pid = slot->worker.bgw_notify_pid;
 318                         if ((slot->worker.bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
 319                                 BackgroundWorkerData->parallel_terminate_count++;
 320                         pg_memory_barrier();
 321                         slot->pid = 0;
 322                         slot->in_use = false;
 323                         if (notify_pid != 0)
 324                                 kill(notify_pid, SIGUSR1);
 325
 326                         continue;
 327                 }
 328
 329                 /*
 330                  * Copy the registration data into the registered workers list.
 331                  */
 332                 rw = malloc(sizeof(RegisteredBgWorker));
 333                 if (rw == NULL)
 334                 {
 335                         ereport(LOG,
 336                                         (errcode(ERRCODE_OUT_OF_MEMORY),
 337                                          errmsg("out of memory")));
 338                         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                 ascii_safe_strlcpy(rw->rw_worker.bgw_name,
 346                                                    slot->worker.bgw_name, BGW_MAXLEN);
 347                 ascii_safe_strlcpy(rw->rw_worker.bgw_type,
 348                                                    slot->worker.bgw_type, BGW_MAXLEN);
 349                 ascii_safe_strlcpy(rw->rw_worker.bgw_library_name,
 350                                                    slot->worker.bgw_library_name, BGW_MAXLEN);
 351                 ascii_safe_strlcpy(rw->rw_worker.bgw_function_name,
 352                                                    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                 rw->rw_worker.bgw_flags = slot->worker.bgw_flags;
 363                 rw->rw_worker.bgw_start_time = slot->worker.bgw_start_time;
 364                 rw->rw_worker.bgw_restart_time = slot->worker.bgw_restart_time;
 365                 rw->rw_worker.bgw_main_arg = slot->worker.bgw_main_arg;
 366                 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                 rw->rw_worker.bgw_notify_pid = slot->worker.bgw_notify_pid;
 378                 if (!PostmasterMarkPIDForWorkerNotify(rw->rw_worker.bgw_notify_pid))
 379                 {
 380                         elog(DEBUG1, "worker notification PID %lu is not valid",
 381                                  (long) rw->rw_worker.bgw_notify_pid);
 382                         rw->rw_worker.bgw_notify_pid = 0;
 383                 }
 384
 385                 /* Initialize postmaster bookkeeping. */
 386                 rw->rw_backend = NULL;
 387                 rw->rw_pid = 0;
 388                 rw->rw_child_slot = 0;
 389                 rw->rw_crashed_at = 0;
 390                 rw->rw_shmem_slot = slotno;
 391                 rw->rw_terminate = false;
 392
 393                 /* Log it! */
 394                 ereport(DEBUG1,
 395                                 (errmsg("registering background worker \"%s\"",
 396                                                 rw->rw_worker.bgw_name)));
 397
 398                 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 ForgetBackgroundWorker(slist_mutable_iter *cur)
 413 {
 414         RegisteredBgWorker *rw;
 415         BackgroundWorkerSlot *slot;
 416
 417         rw = slist_container(RegisteredBgWorker, rw_lnode, cur->cur);
 418
 419         Assert(rw->rw_shmem_slot < max_worker_processes);
 420         slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
 421         if ((rw->rw_worker.bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
 422                 BackgroundWorkerData->parallel_terminate_count++;
 423
 424         slot->in_use = false;
 425
 426         ereport(DEBUG1,
 427                         (errmsg("unregistering background worker \"%s\"",
 428                                         rw->rw_worker.bgw_name)));
 429
 430         slist_delete_current(cur);
 431         free(rw);
 432 }
 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 ReportBackgroundWorkerPID(RegisteredBgWorker *rw)
 441 {
 442         BackgroundWorkerSlot *slot;
 443
 444         Assert(rw->rw_shmem_slot < max_worker_processes);
 445         slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
 446         slot->pid = rw->rw_pid;
 447
 448         if (rw->rw_worker.bgw_notify_pid != 0)
 449                 kill(rw->rw_worker.bgw_notify_pid, SIGUSR1);
 450 }
 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 ReportBackgroundWorkerExit(slist_mutable_iter *cur)
 460 {
 461         RegisteredBgWorker *rw;
 462         BackgroundWorkerSlot *slot;
 463         int                     notify_pid;
 464
 465         rw = slist_container(RegisteredBgWorker, rw_lnode, cur->cur);
 466
 467         Assert(rw->rw_shmem_slot < max_worker_processes);
 468         slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot];
 469         slot->pid = rw->rw_pid;
 470         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         if (rw->rw_terminate ||
 480                 rw->rw_worker.bgw_restart_time == BGW_NEVER_RESTART)
 481                 ForgetBackgroundWorker(cur);
 482
 483         if (notify_pid != 0)
 484                 kill(notify_pid, SIGUSR1);
 485 }
 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 BackgroundWorkerStopNotifications(pid_t pid)
 494 {
 495         slist_iter      siter;
 496
 497         slist_foreach(siter, &BackgroundWorkerList)
 498         {
 499                 RegisteredBgWorker *rw;
 500
 501                 rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur);
 502                 if (rw->rw_worker.bgw_notify_pid == pid)
 503                         rw->rw_worker.bgw_notify_pid = 0;
 504         }
 505 }
 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 ResetBackgroundWorkerCrashTimes(void)
 516 {
 517         slist_mutable_iter iter;
 518
 519         slist_foreach_modify(iter, &BackgroundWorkerList)
 520         {
 521                 RegisteredBgWorker *rw;
 522
 523                 rw = slist_container(RegisteredBgWorker, rw_lnode, iter.cur);
 524
 525                 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                         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                         rw->rw_crashed_at = 0;
 552                 }
 553         }
 554 }
 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 SanityCheckBackgroundWorker(BackgroundWorker *worker, int elevel)
 584 {
 585         /* sanity check for flags */
 586         if (worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION)
 587         {
 588                 if (!(worker->bgw_flags & BGWORKER_SHMEM_ACCESS))
 589                 {
 590                         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                         return false;
 595                 }
 596
 597                 if (worker->bgw_start_time == BgWorkerStart_PostmasterStart)
 598                 {
 599                         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                         return false;
 604                 }
 605
 606                 /* XXX other checks? */
 607         }
 608
 609         if ((worker->bgw_restart_time < 0 &&
 610                  worker->bgw_restart_time != BGW_NEVER_RESTART) ||
 611                 (worker->bgw_restart_time > USECS_PER_DAY / 1000))
 612         {
 613                 ereport(elevel,
 614                                 (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 615                                  errmsg("background worker \"%s\": invalid restart interval",
 616                                                 worker->bgw_name)));
 617                 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         if (worker->bgw_restart_time != BGW_NEVER_RESTART &&
 626                 (worker->bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
 627         {
 628                 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                 return false;
 633         }
 634
 635         /*
 636          * If bgw_type is not filled in, use bgw_name.
 637          */
 638         if (strcmp(worker->bgw_type, "") == 0)
 639                 strcpy(worker->bgw_type, worker->bgw_name);
 640
 641         return true;
 642 }
 643
 644 static void
 645 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         _exit(2);
 662 }
 663
 664 /*
 665  * Standard SIGTERM handler for background workers
 666  */
 667 static void
 668 bgworker_die(SIGNAL_ARGS)
 669 {
 670         PG_SETMASK(&BlockSig);
 671
 672         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 bgworker_sigusr1_handler(SIGNAL_ARGS)
 686 {
 687         int                     save_errno = errno;
 688
 689         latch_sigusr1_handler();
 690
 691         errno = save_errno;
 692 }
 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 StartBackgroundWorker(void)
 702 {
 703         sigjmp_buf      local_sigjmp_buf;
 704         BackgroundWorker *worker = MyBgworkerEntry;
 705         bgworker_main_type entrypt;
 706
 707         if (worker == NULL)
 708                 elog(FATAL, "unable to find bgworker entry");
 709
 710         IsBackgroundWorker = true;
 711
 712         /* Identify myself via ps */
 713         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         if ((worker->bgw_flags & BGWORKER_SHMEM_ACCESS) == 0)
 723         {
 724                 dsm_detach_all();
 725                 PGSharedMemoryDetach();
 726         }
 727
 728         SetProcessingMode(InitProcessing);
 729
 730         /* Apply PostAuthDelay */
 731         if (PostAuthDelay > 0)
 732                 pg_usleep(PostAuthDelay * 1000000L);
 733
 734         /*
 735          * Set up signal handlers.
 736          */
 737         if (worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION)
 738         {
 739                 /*
 740                  * SIGINT is used to signal canceling the current action
 741                  */
 742                 pqsignal(SIGINT, StatementCancelHandler);
 743                 pqsignal(SIGUSR1, procsignal_sigusr1_handler);
 744                 pqsignal(SIGFPE, FloatExceptionHandler);
 745
 746                 /* XXX Any other handlers needed here? */
 747         }
 748         else
 749         {
 750                 pqsignal(SIGINT, SIG_IGN);
 751                 pqsignal(SIGUSR1, bgworker_sigusr1_handler);
 752                 pqsignal(SIGFPE, SIG_IGN);
 753         }
 754         pqsignal(SIGTERM, bgworker_die);
 755         pqsignal(SIGHUP, SIG_IGN);
 756
 757         pqsignal(SIGQUIT, bgworker_quickdie);
 758         InitializeTimeouts();           /* establishes SIGALRM handler */
 759
 760         pqsignal(SIGPIPE, SIG_IGN);
 761         pqsignal(SIGUSR2, SIG_IGN);
 762         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         if (sigsetjmp(local_sigjmp_buf, 1) != 0)
 770         {
 771                 /* Since not using PG_TRY, must reset error stack by hand */
 772                 error_context_stack = NULL;
 773
 774                 /* Prevent interrupts while cleaning up */
 775                 HOLD_INTERRUPTS();
 776
 777                 /* Report the error to the server log */
 778                 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                 proc_exit(1);
 788         }
 789
 790         /* We can now handle ereport(ERROR) */
 791         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         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                 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                 InitProcess();
 815 #endif
 816         }
 817
 818         /*
 819          * Look up the entry point function, loading its library if necessary.
 820          */
 821         entrypt = LookupBackgroundWorkerFunction(worker->bgw_library_name,
 822                                                                                          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         entrypt(worker->bgw_main_arg);
 835
 836         /* ... and if it returns, we're done */
 837         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 RegisterBackgroundWorker(BackgroundWorker *worker)
 849 {
 850         RegisteredBgWorker *rw;
 851         static int      numworkers = 0;
 852
 853         if (!IsUnderPostmaster)
 854                 ereport(DEBUG1,
 855                                 (errmsg("registering background worker \"%s\"", worker->bgw_name)));
 856
 857         if (!process_shared_preload_libraries_in_progress &&
 858                 strcmp(worker->bgw_library_name, "postgres") != 0)
 859         {
 860                 if (!IsUnderPostmaster)
 861                         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                 return;
 866         }
 867
 868         if (!SanityCheckBackgroundWorker(worker, LOG))
 869                 return;
 870
 871         if (worker->bgw_notify_pid != 0)
 872         {
 873                 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                 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         if (++numworkers > max_worker_processes)
 887         {
 888                 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                 return;
 897         }
 898
 899         /*
 900          * Copy the registration data into the registered workers list.
 901          */
 902         rw = malloc(sizeof(RegisteredBgWorker));
 903         if (rw == NULL)
 904         {
 905                 ereport(LOG,
 906                                 (errcode(ERRCODE_OUT_OF_MEMORY),
 907                                  errmsg("out of memory")));
 908                 return;
 909         }
 910
 911         rw->rw_worker = *worker;
 912         rw->rw_backend = NULL;
 913         rw->rw_pid = 0;
 914         rw->rw_child_slot = 0;
 915         rw->rw_crashed_at = 0;
 916         rw->rw_terminate = false;
 917
 918         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 RegisterDynamicBackgroundWorker(BackgroundWorker *worker,
 933                                                                 BackgroundWorkerHandle **handle)
 934 {
 935         int                     slotno;
 936         bool            success = false;
 937         bool            parallel;
 938         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         if (!IsUnderPostmaster)
 949                 return false;
 950
 951         if (!SanityCheckBackgroundWorker(worker, ERROR))
 952                 return false;
 953
 954         parallel = (worker->bgw_flags & BGWORKER_CLASS_PARALLEL) != 0;
 955
 956         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         if (parallel && (BackgroundWorkerData->parallel_register_count -
 968                                          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                 LWLockRelease(BackgroundWorkerLock);
 975                 return false;
 976         }
 977
 978         /*
 979          * Look for an unused slot.  If we find one, grab it.
 980          */
 981         for (slotno = 0; slotno < BackgroundWorkerData->total_slots; ++slotno)
 982         {
 983                 BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
 984
 985                 if (!slot->in_use)
 986                 {
 987                         memcpy(&slot->worker, worker, sizeof(BackgroundWorker));
 988                         slot->pid = InvalidPid; /* indicates not started yet */
 989                         slot->generation++;
 990                         slot->terminate = false;
 991                         generation = slot->generation;
 992                         if (parallel)
 993                                 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                         pg_write_barrier();
1000
1001                         slot->in_use = true;
1002                         success = true;
1003                         break;
1004                 }
1005         }
1006
1007         LWLockRelease(BackgroundWorkerLock);
1008
1009         /* If we found a slot, tell the postmaster to notice the change. */
1010         if (success)
1011                 SendPostmasterSignal(PMSIGNAL_BACKGROUND_WORKER_CHANGE);
1012
1013         /*
1014          * If we found a slot and the user has provided a handle, initialize it.
1015          */
1016         if (success && handle)
1017         {
1018                 *handle = palloc(sizeof(BackgroundWorkerHandle));
1019                 (*handle)->slot = slotno;
1020                 (*handle)->generation = generation;
1021         }
1022
1023         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 GetBackgroundWorkerPid(BackgroundWorkerHandle *handle, pid_t *pidp)
1045 {
1046         BackgroundWorkerSlot *slot;
1047         pid_t           pid;
1048
1049         Assert(handle->slot < max_worker_processes);
1050         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         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         if (handle->generation != slot->generation || !slot->in_use)
1071                 pid = 0;
1072         else
1073                 pid = slot->pid;
1074
1075         /* All done. */
1076         LWLockRelease(BackgroundWorkerLock);
1077
1078         if (pid == 0)
1079                 return BGWH_STOPPED;
1080         else if (pid == InvalidPid)
1081                 return BGWH_NOT_YET_STARTED;
1082         *pidp = pid;
1083         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 WaitForBackgroundWorkerStartup(BackgroundWorkerHandle *handle, pid_t *pidp)
1097 {
1098         BgwHandleStatus status;
1099         int                     rc;
1100
1101         for (;;)
1102         {
1103                 pid_t           pid;
1104
1105                 CHECK_FOR_INTERRUPTS();
1106
1107                 status = GetBackgroundWorkerPid(handle, &pid);
1108                 if (status == BGWH_STARTED)
1109                         *pidp = pid;
1110                 if (status != BGWH_NOT_YET_STARTED)
1111                         break;
1112
1113                 rc = WaitLatch(MyLatch,
1114                                            WL_LATCH_SET | WL_POSTMASTER_DEATH, 0,
1115                                            WAIT_EVENT_BGWORKER_STARTUP);
1116
1117                 if (rc & WL_POSTMASTER_DEATH)
1118                 {
1119                         status = BGWH_POSTMASTER_DIED;
1120                         break;
1121                 }
1122
1123                 ResetLatch(MyLatch);
1124         }
1125
1126         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 WaitForBackgroundWorkerShutdown(BackgroundWorkerHandle *handle)
1139 {
1140         BgwHandleStatus status;
1141         int                     rc;
1142
1143         for (;;)
1144         {
1145                 pid_t           pid;
1146
1147                 CHECK_FOR_INTERRUPTS();
1148
1149                 status = GetBackgroundWorkerPid(handle, &pid);
1150                 if (status == BGWH_STOPPED)
1151                         break;
1152
1153                 rc = WaitLatch(MyLatch,
1154                                            WL_LATCH_SET | WL_POSTMASTER_DEATH, 0,
1155                                            WAIT_EVENT_BGWORKER_SHUTDOWN);
1156
1157                 if (rc & WL_POSTMASTER_DEATH)
1158                 {
1159                         status = BGWH_POSTMASTER_DIED;
1160                         break;
1161                 }
1162
1163                 ResetLatch(MyLatch);
1164         }
1165
1166         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 TerminateBackgroundWorker(BackgroundWorkerHandle *handle)
1178 {
1179         BackgroundWorkerSlot *slot;
1180         bool            signal_postmaster = false;
1181
1182         Assert(handle->slot < max_worker_processes);
1183         slot = &BackgroundWorkerData->slot[handle->slot];
1184
1185         /* Set terminate flag in shared memory, unless slot has been reused. */
1186         LWLockAcquire(BackgroundWorkerLock, LW_EXCLUSIVE);
1187         if (handle->generation == slot->generation)
1188         {
1189                 slot->terminate = true;
1190                 signal_postmaster = true;
1191         }
1192         LWLockRelease(BackgroundWorkerLock);
1193
1194         /* Make sure the postmaster notices the change to shared memory. */
1195         if (signal_postmaster)
1196                 SendPostmasterSignal(PMSIGNAL_BACKGROUND_WORKER_CHANGE);
1197 }
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 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         if (strcmp(libraryname, "postgres") == 0)
1225         {
1226                 int                     i;
1227
1228                 for (i = 0; i < lengthof(InternalBGWorkers); i++)
1229                 {
1230                         if (strcmp(InternalBGWorkers[i].fn_name, funcname) == 0)
1231                                 return InternalBGWorkers[i].fn_addr;
1232                 }
1233
1234                 /* We can only reach this by programming error. */
1235                 elog(ERROR, "internal function \"%s\" not found", funcname);
1236         }
1237
1238         /* Otherwise load from external library. */
1239         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 GetBackgroundWorkerTypeByPid(pid_t pid)
1253 {
1254         int                     slotno;
1255         bool            found = false;
1256         static char result[BGW_MAXLEN];
1257
1258         LWLockAcquire(BackgroundWorkerLock, LW_SHARED);
1259
1260         for (slotno = 0; slotno < BackgroundWorkerData->total_slots; slotno++)
1261         {
1262                 BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno];
1263
1264                 if (slot->pid > 0 && slot->pid == pid)
1265                 {
1266                         strcpy(result, slot->worker.bgw_type);
1267                         found = true;
1268                         break;
1269                 }
1270         }
1271
1272         LWLockRelease(BackgroundWorkerLock);
1273
1274         if (!found)
1275                 return NULL;
1276
1277         return result;
1278 }