diff options
Diffstat (limited to 'src/backend/postmaster/bgworker.c')
| -rw-r--r-- | src/backend/postmaster/bgworker.c | 1311 |
1 files changed, 1311 insertions, 0 deletions
diff --git a/src/backend/postmaster/bgworker.c b/src/backend/postmaster/bgworker.c new file mode 100644 index 0000000..0dd22b2 --- /dev/null +++ b/src/backend/postmaster/bgworker.c @@ -0,0 +1,1311 @@ +/*-------------------------------------------------------------------- + * bgworker.c + * POSTGRES pluggable background workers implementation + * + * Portions Copyright (c) 1996-2023, PostgreSQL Global Development Group + * + * IDENTIFICATION + * src/backend/postmaster/bgworker.c + * + *------------------------------------------------------------------------- + */ + +#include "postgres.h" + +#include "access/parallel.h" +#include "libpq/pqsignal.h" +#include "miscadmin.h" +#include "pgstat.h" +#include "port/atomics.h" +#include "postmaster/bgworker_internals.h" +#include "postmaster/interrupt.h" +#include "postmaster/postmaster.h" +#include "replication/logicallauncher.h" +#include "replication/logicalworker.h" +#include "storage/dsm.h" +#include "storage/ipc.h" +#include "storage/latch.h" +#include "storage/lwlock.h" +#include "storage/pg_shmem.h" +#include "storage/pmsignal.h" +#include "storage/proc.h" +#include "storage/procsignal.h" +#include "storage/shmem.h" +#include "tcop/tcopprot.h" +#include "utils/ascii.h" +#include "utils/ps_status.h" +#include "utils/timeout.h" + +/* + * The postmaster's list of registered background workers, in private memory. + */ +slist_head BackgroundWorkerList = SLIST_STATIC_INIT(BackgroundWorkerList); + +/* + * BackgroundWorkerSlots exist in shared memory and can be accessed (via + * the BackgroundWorkerArray) by both the postmaster and by regular backends. + * However, the postmaster cannot take locks, even spinlocks, because this + * might allow it to crash or become wedged if shared memory gets corrupted. + * Such an outcome is intolerable. Therefore, we need a lockless protocol + * for coordinating access to this data. + * + * The 'in_use' flag is used to hand off responsibility for the slot between + * the postmaster and the rest of the system. When 'in_use' is false, + * the postmaster will ignore the slot entirely, except for the 'in_use' flag + * itself, which it may read. In this state, regular backends may modify the + * slot. Once a backend sets 'in_use' to true, the slot becomes the + * responsibility of the postmaster. Regular backends may no longer modify it, + * but the postmaster may examine it. Thus, a backend initializing a slot + * must fully initialize the slot - and insert a write memory barrier - before + * marking it as in use. + * + * As an exception, however, even when the slot is in use, regular backends + * may set the 'terminate' flag for a slot, telling the postmaster not + * to restart it. Once the background worker is no longer running, the slot + * will be released for reuse. + * + * In addition to coordinating with the postmaster, backends modifying this + * data structure must coordinate with each other. Since they can take locks, + * this is straightforward: any backend wishing to manipulate a slot must + * take BackgroundWorkerLock in exclusive mode. Backends wishing to read + * data that might get concurrently modified by other backends should take + * this lock in shared mode. No matter what, backends reading this data + * structure must be able to tolerate concurrent modifications by the + * postmaster. + */ +typedef struct BackgroundWorkerSlot +{ + bool in_use; + bool terminate; + pid_t pid; /* InvalidPid = not started yet; 0 = dead */ + uint64 generation; /* incremented when slot is recycled */ + BackgroundWorker worker; +} BackgroundWorkerSlot; + +/* + * In order to limit the total number of parallel workers (according to + * max_parallel_workers GUC), we maintain the number of active parallel + * workers. Since the postmaster cannot take locks, two variables are used for + * this purpose: the number of registered parallel workers (modified by the + * backends, protected by BackgroundWorkerLock) and the number of terminated + * parallel workers (modified only by the postmaster, lockless). The active + * number of parallel workers is the number of registered workers minus the + * terminated ones. These counters can of course overflow, but it's not + * important here since the subtraction will still give the right number. + */ +typedef struct BackgroundWorkerArray +{ + int total_slots; + uint32 parallel_register_count; + uint32 parallel_terminate_count; + BackgroundWorkerSlot slot[FLEXIBLE_ARRAY_MEMBER]; +} BackgroundWorkerArray; + +struct BackgroundWorkerHandle +{ + int slot; + uint64 generation; +}; + +static BackgroundWorkerArray *BackgroundWorkerData; + +/* + * List of internal background worker entry points. We need this for + * reasons explained in LookupBackgroundWorkerFunction(), below. + */ +static const struct +{ + const char *fn_name; + bgworker_main_type fn_addr; +} InternalBGWorkers[] = + +{ + { + "ParallelWorkerMain", ParallelWorkerMain + }, + { + "ApplyLauncherMain", ApplyLauncherMain + }, + { + "ApplyWorkerMain", ApplyWorkerMain + }, + { + "ParallelApplyWorkerMain", ParallelApplyWorkerMain + } +}; + +/* Private functions. */ +static bgworker_main_type LookupBackgroundWorkerFunction(const char *libraryname, const char *funcname); + + +/* + * Calculate shared memory needed. + */ +Size +BackgroundWorkerShmemSize(void) +{ + Size size; + + /* Array of workers is variably sized. */ + size = offsetof(BackgroundWorkerArray, slot); + size = add_size(size, mul_size(max_worker_processes, + sizeof(BackgroundWorkerSlot))); + + return size; +} + +/* + * Initialize shared memory. + */ +void +BackgroundWorkerShmemInit(void) +{ + bool found; + + BackgroundWorkerData = ShmemInitStruct("Background Worker Data", + BackgroundWorkerShmemSize(), + &found); + if (!IsUnderPostmaster) + { + slist_iter siter; + int slotno = 0; + + BackgroundWorkerData->total_slots = max_worker_processes; + BackgroundWorkerData->parallel_register_count = 0; + BackgroundWorkerData->parallel_terminate_count = 0; + + /* + * Copy contents of worker list into shared memory. Record the shared + * memory slot assigned to each worker. This ensures a 1-to-1 + * correspondence between the postmaster's private list and the array + * in shared memory. + */ + slist_foreach(siter, &BackgroundWorkerList) + { + BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno]; + RegisteredBgWorker *rw; + + rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur); + Assert(slotno < max_worker_processes); + slot->in_use = true; + slot->terminate = false; + slot->pid = InvalidPid; + slot->generation = 0; + rw->rw_shmem_slot = slotno; + rw->rw_worker.bgw_notify_pid = 0; /* might be reinit after crash */ + memcpy(&slot->worker, &rw->rw_worker, sizeof(BackgroundWorker)); + ++slotno; + } + + /* + * Mark any remaining slots as not in use. + */ + while (slotno < max_worker_processes) + { + BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno]; + + slot->in_use = false; + ++slotno; + } + } + else + Assert(found); +} + +/* + * Search the postmaster's backend-private list of RegisteredBgWorker objects + * for the one that maps to the given slot number. + */ +static RegisteredBgWorker * +FindRegisteredWorkerBySlotNumber(int slotno) +{ + slist_iter siter; + + slist_foreach(siter, &BackgroundWorkerList) + { + RegisteredBgWorker *rw; + + rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur); + if (rw->rw_shmem_slot == slotno) + return rw; + } + + return NULL; +} + +/* + * Notice changes to shared memory made by other backends. + * Accept new worker requests only if allow_new_workers is true. + * + * This code runs in the postmaster, so we must be very careful not to assume + * that shared memory contents are sane. Otherwise, a rogue backend could + * take out the postmaster. + */ +void +BackgroundWorkerStateChange(bool allow_new_workers) +{ + int slotno; + + /* + * The total number of slots stored in shared memory should match our + * notion of max_worker_processes. If it does not, something is very + * wrong. Further down, we always refer to this value as + * max_worker_processes, in case shared memory gets corrupted while we're + * looping. + */ + if (max_worker_processes != BackgroundWorkerData->total_slots) + { + ereport(LOG, + (errmsg("inconsistent background worker state (max_worker_processes=%d, total_slots=%d)", + max_worker_processes, + BackgroundWorkerData->total_slots))); + return; + } + + /* + * Iterate through slots, looking for newly-registered workers or workers + * who must die. + */ + for (slotno = 0; slotno < max_worker_processes; ++slotno) + { + BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno]; + RegisteredBgWorker *rw; + + if (!slot->in_use) + continue; + + /* + * Make sure we don't see the in_use flag before the updated slot + * contents. + */ + pg_read_barrier(); + + /* See whether we already know about this worker. */ + rw = FindRegisteredWorkerBySlotNumber(slotno); + if (rw != NULL) + { + /* + * In general, the worker data can't change after it's initially + * registered. However, someone can set the terminate flag. + */ + if (slot->terminate && !rw->rw_terminate) + { + rw->rw_terminate = true; + if (rw->rw_pid != 0) + kill(rw->rw_pid, SIGTERM); + else + { + /* Report never-started, now-terminated worker as dead. */ + ReportBackgroundWorkerPID(rw); + } + } + continue; + } + + /* + * If we aren't allowing new workers, then immediately mark it for + * termination; the next stanza will take care of cleaning it up. + * Doing this ensures that any process waiting for the worker will get + * awoken, even though the worker will never be allowed to run. + */ + if (!allow_new_workers) + slot->terminate = true; + + /* + * If the worker is marked for termination, we don't need to add it to + * the registered workers list; we can just free the slot. However, if + * bgw_notify_pid is set, the process that registered the worker may + * need to know that we've processed the terminate request, so be sure + * to signal it. + */ + if (slot->terminate) + { + int notify_pid; + + /* + * We need a memory barrier here to make sure that the load of + * bgw_notify_pid and the update of parallel_terminate_count + * complete before the store to in_use. + */ + notify_pid = slot->worker.bgw_notify_pid; + if ((slot->worker.bgw_flags & BGWORKER_CLASS_PARALLEL) != 0) + BackgroundWorkerData->parallel_terminate_count++; + slot->pid = 0; + + pg_memory_barrier(); + slot->in_use = false; + + if (notify_pid != 0) + kill(notify_pid, SIGUSR1); + + continue; + } + + /* + * Copy the registration data into the registered workers list. + */ + rw = malloc(sizeof(RegisteredBgWorker)); + if (rw == NULL) + { + ereport(LOG, + (errcode(ERRCODE_OUT_OF_MEMORY), + errmsg("out of memory"))); + return; + } + + /* + * Copy strings in a paranoid way. If shared memory is corrupted, the + * source data might not even be NUL-terminated. + */ + ascii_safe_strlcpy(rw->rw_worker.bgw_name, + slot->worker.bgw_name, BGW_MAXLEN); + ascii_safe_strlcpy(rw->rw_worker.bgw_type, + slot->worker.bgw_type, BGW_MAXLEN); + ascii_safe_strlcpy(rw->rw_worker.bgw_library_name, + slot->worker.bgw_library_name, BGW_MAXLEN); + ascii_safe_strlcpy(rw->rw_worker.bgw_function_name, + slot->worker.bgw_function_name, BGW_MAXLEN); + + /* + * Copy various fixed-size fields. + * + * flags, start_time, and restart_time are examined by the postmaster, + * but nothing too bad will happen if they are corrupted. The + * remaining fields will only be examined by the child process. It + * might crash, but we won't. + */ + rw->rw_worker.bgw_flags = slot->worker.bgw_flags; + rw->rw_worker.bgw_start_time = slot->worker.bgw_start_time; + rw->rw_worker.bgw_restart_time = slot->worker.bgw_restart_time; + rw->rw_worker.bgw_main_arg = slot->worker.bgw_main_arg; + memcpy(rw->rw_worker.bgw_extra, slot->worker.bgw_extra, BGW_EXTRALEN); + + /* + * Copy the PID to be notified about state changes, but only if the + * postmaster knows about a backend with that PID. It isn't an error + * if the postmaster doesn't know about the PID, because the backend + * that requested the worker could have died (or been killed) just + * after doing so. Nonetheless, at least until we get some experience + * with how this plays out in the wild, log a message at a relative + * high debug level. + */ + rw->rw_worker.bgw_notify_pid = slot->worker.bgw_notify_pid; + if (!PostmasterMarkPIDForWorkerNotify(rw->rw_worker.bgw_notify_pid)) + { + elog(DEBUG1, "worker notification PID %d is not valid", + (int) rw->rw_worker.bgw_notify_pid); + rw->rw_worker.bgw_notify_pid = 0; + } + + /* Initialize postmaster bookkeeping. */ + rw->rw_backend = NULL; + rw->rw_pid = 0; + rw->rw_child_slot = 0; + rw->rw_crashed_at = 0; + rw->rw_shmem_slot = slotno; + rw->rw_terminate = false; + + /* Log it! */ + ereport(DEBUG1, + (errmsg_internal("registering background worker \"%s\"", + rw->rw_worker.bgw_name))); + + slist_push_head(&BackgroundWorkerList, &rw->rw_lnode); + } +} + +/* + * Forget about a background worker that's no longer needed. + * + * The worker must be identified by passing an slist_mutable_iter that + * points to it. This convention allows deletion of workers during + * searches of the worker list, and saves having to search the list again. + * + * Caller is responsible for notifying bgw_notify_pid, if appropriate. + * + * This function must be invoked only in the postmaster. + */ +void +ForgetBackgroundWorker(slist_mutable_iter *cur) +{ + RegisteredBgWorker *rw; + BackgroundWorkerSlot *slot; + + rw = slist_container(RegisteredBgWorker, rw_lnode, cur->cur); + + Assert(rw->rw_shmem_slot < max_worker_processes); + slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot]; + Assert(slot->in_use); + + /* + * We need a memory barrier here to make sure that the update of + * parallel_terminate_count completes before the store to in_use. + */ + if ((rw->rw_worker.bgw_flags & BGWORKER_CLASS_PARALLEL) != 0) + BackgroundWorkerData->parallel_terminate_count++; + + pg_memory_barrier(); + slot->in_use = false; + + ereport(DEBUG1, + (errmsg_internal("unregistering background worker \"%s\"", + rw->rw_worker.bgw_name))); + + slist_delete_current(cur); + free(rw); +} + +/* + * Report the PID of a newly-launched background worker in shared memory. + * + * This function should only be called from the postmaster. + */ +void +ReportBackgroundWorkerPID(RegisteredBgWorker *rw) +{ + BackgroundWorkerSlot *slot; + + Assert(rw->rw_shmem_slot < max_worker_processes); + slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot]; + slot->pid = rw->rw_pid; + + if (rw->rw_worker.bgw_notify_pid != 0) + kill(rw->rw_worker.bgw_notify_pid, SIGUSR1); +} + +/* + * Report that the PID of a background worker is now zero because a + * previously-running background worker has exited. + * + * This function should only be called from the postmaster. + */ +void +ReportBackgroundWorkerExit(slist_mutable_iter *cur) +{ + RegisteredBgWorker *rw; + BackgroundWorkerSlot *slot; + int notify_pid; + + rw = slist_container(RegisteredBgWorker, rw_lnode, cur->cur); + + Assert(rw->rw_shmem_slot < max_worker_processes); + slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot]; + slot->pid = rw->rw_pid; + notify_pid = rw->rw_worker.bgw_notify_pid; + + /* + * If this worker is slated for deregistration, do that before notifying + * the process which started it. Otherwise, if that process tries to + * reuse the slot immediately, it might not be available yet. In theory + * that could happen anyway if the process checks slot->pid at just the + * wrong moment, but this makes the window narrower. + */ + if (rw->rw_terminate || + rw->rw_worker.bgw_restart_time == BGW_NEVER_RESTART) + ForgetBackgroundWorker(cur); + + if (notify_pid != 0) + kill(notify_pid, SIGUSR1); +} + +/* + * Cancel SIGUSR1 notifications for a PID belonging to an exiting backend. + * + * This function should only be called from the postmaster. + */ +void +BackgroundWorkerStopNotifications(pid_t pid) +{ + slist_iter siter; + + slist_foreach(siter, &BackgroundWorkerList) + { + RegisteredBgWorker *rw; + + rw = slist_container(RegisteredBgWorker, rw_lnode, siter.cur); + if (rw->rw_worker.bgw_notify_pid == pid) + rw->rw_worker.bgw_notify_pid = 0; + } +} + +/* + * Cancel any not-yet-started worker requests that have waiting processes. + * + * This is called during a normal ("smart" or "fast") database shutdown. + * After this point, no new background workers will be started, so anything + * that might be waiting for them needs to be kicked off its wait. We do + * that by canceling the bgworker registration entirely, which is perhaps + * overkill, but since we're shutting down it does not matter whether the + * registration record sticks around. + * + * This function should only be called from the postmaster. + */ +void +ForgetUnstartedBackgroundWorkers(void) +{ + slist_mutable_iter iter; + + slist_foreach_modify(iter, &BackgroundWorkerList) + { + RegisteredBgWorker *rw; + BackgroundWorkerSlot *slot; + + rw = slist_container(RegisteredBgWorker, rw_lnode, iter.cur); + Assert(rw->rw_shmem_slot < max_worker_processes); + slot = &BackgroundWorkerData->slot[rw->rw_shmem_slot]; + + /* If it's not yet started, and there's someone waiting ... */ + if (slot->pid == InvalidPid && + rw->rw_worker.bgw_notify_pid != 0) + { + /* ... then zap it, and notify the waiter */ + int notify_pid = rw->rw_worker.bgw_notify_pid; + + ForgetBackgroundWorker(&iter); + if (notify_pid != 0) + kill(notify_pid, SIGUSR1); + } + } +} + +/* + * Reset background worker crash state. + * + * We assume that, after a crash-and-restart cycle, background workers without + * the never-restart flag should be restarted immediately, instead of waiting + * for bgw_restart_time to elapse. On the other hand, workers with that flag + * should be forgotten immediately, since we won't ever restart them. + * + * This function should only be called from the postmaster. + */ +void +ResetBackgroundWorkerCrashTimes(void) +{ + slist_mutable_iter iter; + + slist_foreach_modify(iter, &BackgroundWorkerList) + { + RegisteredBgWorker *rw; + + rw = slist_container(RegisteredBgWorker, rw_lnode, iter.cur); + + if (rw->rw_worker.bgw_restart_time == BGW_NEVER_RESTART) + { + /* + * Workers marked BGW_NEVER_RESTART shouldn't get relaunched after + * the crash, so forget about them. (If we wait until after the + * crash to forget about them, and they are parallel workers, + * parallel_terminate_count will get incremented after we've + * already zeroed parallel_register_count, which would be bad.) + */ + ForgetBackgroundWorker(&iter); + } + else + { + /* + * The accounting which we do via parallel_register_count and + * parallel_terminate_count would get messed up if a worker marked + * parallel could survive a crash and restart cycle. All such + * workers should be marked BGW_NEVER_RESTART, and thus control + * should never reach this branch. + */ + Assert((rw->rw_worker.bgw_flags & BGWORKER_CLASS_PARALLEL) == 0); + + /* + * Allow this worker to be restarted immediately after we finish + * resetting. + */ + rw->rw_crashed_at = 0; + + /* + * If there was anyone waiting for it, they're history. + */ + rw->rw_worker.bgw_notify_pid = 0; + } + } +} + +#ifdef EXEC_BACKEND +/* + * In EXEC_BACKEND mode, workers use this to retrieve their details from + * shared memory. + */ +BackgroundWorker * +BackgroundWorkerEntry(int slotno) +{ + static BackgroundWorker myEntry; + BackgroundWorkerSlot *slot; + + Assert(slotno < BackgroundWorkerData->total_slots); + slot = &BackgroundWorkerData->slot[slotno]; + Assert(slot->in_use); + + /* must copy this in case we don't intend to retain shmem access */ + memcpy(&myEntry, &slot->worker, sizeof myEntry); + return &myEntry; +} +#endif + +/* + * Complain about the BackgroundWorker definition using error level elevel. + * Return true if it looks ok, false if not (unless elevel >= ERROR, in + * which case we won't return at all in the not-OK case). + */ +static bool +SanityCheckBackgroundWorker(BackgroundWorker *worker, int elevel) +{ + /* sanity check for flags */ + + /* + * We used to support workers not connected to shared memory, but don't + * anymore. Thus this is a required flag now. We're not removing the flag + * for compatibility reasons and because the flag still provides some + * signal when reading code. + */ + if (!(worker->bgw_flags & BGWORKER_SHMEM_ACCESS)) + { + ereport(elevel, + (errcode(ERRCODE_INVALID_PARAMETER_VALUE), + errmsg("background worker \"%s\": background workers without shared memory access are not supported", + worker->bgw_name))); + return false; + } + + if (worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION) + { + if (worker->bgw_start_time == BgWorkerStart_PostmasterStart) + { + ereport(elevel, + (errcode(ERRCODE_INVALID_PARAMETER_VALUE), + errmsg("background worker \"%s\": cannot request database access if starting at postmaster start", + worker->bgw_name))); + return false; + } + + /* XXX other checks? */ + } + + if ((worker->bgw_restart_time < 0 && + worker->bgw_restart_time != BGW_NEVER_RESTART) || + (worker->bgw_restart_time > USECS_PER_DAY / 1000)) + { + ereport(elevel, + (errcode(ERRCODE_INVALID_PARAMETER_VALUE), + errmsg("background worker \"%s\": invalid restart interval", + worker->bgw_name))); + return false; + } + + /* + * Parallel workers may not be configured for restart, because the + * parallel_register_count/parallel_terminate_count accounting can't + * handle parallel workers lasting through a crash-and-restart cycle. + */ + if (worker->bgw_restart_time != BGW_NEVER_RESTART && + (worker->bgw_flags & BGWORKER_CLASS_PARALLEL) != 0) + { + ereport(elevel, + (errcode(ERRCODE_INVALID_PARAMETER_VALUE), + errmsg("background worker \"%s\": parallel workers may not be configured for restart", + worker->bgw_name))); + return false; + } + + /* + * If bgw_type is not filled in, use bgw_name. + */ + if (strcmp(worker->bgw_type, "") == 0) + strcpy(worker->bgw_type, worker->bgw_name); + + return true; +} + +/* + * Standard SIGTERM handler for background workers + */ +static void +bgworker_die(SIGNAL_ARGS) +{ + sigprocmask(SIG_SETMASK, &BlockSig, NULL); + + ereport(FATAL, + (errcode(ERRCODE_ADMIN_SHUTDOWN), + errmsg("terminating background worker \"%s\" due to administrator command", + MyBgworkerEntry->bgw_type))); +} + +/* + * Start a new background worker + * + * This is the main entry point for background worker, to be called from + * postmaster. + */ +void +StartBackgroundWorker(void) +{ + sigjmp_buf local_sigjmp_buf; + BackgroundWorker *worker = MyBgworkerEntry; + bgworker_main_type entrypt; + + if (worker == NULL) + elog(FATAL, "unable to find bgworker entry"); + + IsBackgroundWorker = true; + + MyBackendType = B_BG_WORKER; + init_ps_display(worker->bgw_name); + + SetProcessingMode(InitProcessing); + + /* Apply PostAuthDelay */ + if (PostAuthDelay > 0) + pg_usleep(PostAuthDelay * 1000000L); + + /* + * Set up signal handlers. + */ + if (worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION) + { + /* + * SIGINT is used to signal canceling the current action + */ + pqsignal(SIGINT, StatementCancelHandler); + pqsignal(SIGUSR1, procsignal_sigusr1_handler); + pqsignal(SIGFPE, FloatExceptionHandler); + + /* XXX Any other handlers needed here? */ + } + else + { + pqsignal(SIGINT, SIG_IGN); + pqsignal(SIGUSR1, SIG_IGN); + pqsignal(SIGFPE, SIG_IGN); + } + pqsignal(SIGTERM, bgworker_die); + /* SIGQUIT handler was already set up by InitPostmasterChild */ + pqsignal(SIGHUP, SIG_IGN); + + InitializeTimeouts(); /* establishes SIGALRM handler */ + + pqsignal(SIGPIPE, SIG_IGN); + pqsignal(SIGUSR2, SIG_IGN); + pqsignal(SIGCHLD, SIG_DFL); + + /* + * If an exception is encountered, processing resumes here. + * + * We just need to clean up, report the error, and go away. + */ + if (sigsetjmp(local_sigjmp_buf, 1) != 0) + { + /* Since not using PG_TRY, must reset error stack by hand */ + error_context_stack = NULL; + + /* Prevent interrupts while cleaning up */ + HOLD_INTERRUPTS(); + + /* + * sigsetjmp will have blocked all signals, but we may need to accept + * signals while communicating with our parallel leader. Once we've + * done HOLD_INTERRUPTS() it should be safe to unblock signals. + */ + BackgroundWorkerUnblockSignals(); + + /* Report the error to the parallel leader and the server log */ + EmitErrorReport(); + + /* + * Do we need more cleanup here? For shmem-connected bgworkers, we + * will call InitProcess below, which will install ProcKill as exit + * callback. That will take care of releasing locks, etc. + */ + + /* and go away */ + proc_exit(1); + } + + /* We can now handle ereport(ERROR) */ + PG_exception_stack = &local_sigjmp_buf; + + /* + * Create a per-backend PGPROC struct in shared memory, except in the + * EXEC_BACKEND case where this was done in SubPostmasterMain. We must do + * this before we can use LWLocks (and in the EXEC_BACKEND case we already + * had to do some stuff with LWLocks). + */ +#ifndef EXEC_BACKEND + InitProcess(); +#endif + + /* + * Early initialization. + */ + BaseInit(); + + /* + * Look up the entry point function, loading its library if necessary. + */ + entrypt = LookupBackgroundWorkerFunction(worker->bgw_library_name, + worker->bgw_function_name); + + /* + * Note that in normal processes, we would call InitPostgres here. For a + * worker, however, we don't know what database to connect to, yet; so we + * need to wait until the user code does it via + * BackgroundWorkerInitializeConnection(). + */ + + /* + * Now invoke the user-defined worker code + */ + entrypt(worker->bgw_main_arg); + + /* ... and if it returns, we're done */ + proc_exit(0); +} + +/* + * Register a new static background worker. + * + * This can only be called directly from postmaster or in the _PG_init + * function of a module library that's loaded by shared_preload_libraries; + * otherwise it will have no effect. + */ +void +RegisterBackgroundWorker(BackgroundWorker *worker) +{ + RegisteredBgWorker *rw; + static int numworkers = 0; + + if (!IsUnderPostmaster) + ereport(DEBUG1, + (errmsg_internal("registering background worker \"%s\"", worker->bgw_name))); + + if (!process_shared_preload_libraries_in_progress && + strcmp(worker->bgw_library_name, "postgres") != 0) + { + if (!IsUnderPostmaster) + ereport(LOG, + (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), + errmsg("background worker \"%s\": must be registered in shared_preload_libraries", + worker->bgw_name))); + return; + } + + if (!SanityCheckBackgroundWorker(worker, LOG)) + return; + + if (worker->bgw_notify_pid != 0) + { + ereport(LOG, + (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), + errmsg("background worker \"%s\": only dynamic background workers can request notification", + worker->bgw_name))); + return; + } + + /* + * Enforce maximum number of workers. Note this is overly restrictive: we + * could allow more non-shmem-connected workers, because these don't count + * towards the MAX_BACKENDS limit elsewhere. For now, it doesn't seem + * important to relax this restriction. + */ + if (++numworkers > max_worker_processes) + { + ereport(LOG, + (errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED), + errmsg("too many background workers"), + errdetail_plural("Up to %d background worker can be registered with the current settings.", + "Up to %d background workers can be registered with the current settings.", + max_worker_processes, + max_worker_processes), + errhint("Consider increasing the configuration parameter \"max_worker_processes\"."))); + return; + } + + /* + * Copy the registration data into the registered workers list. + */ + rw = malloc(sizeof(RegisteredBgWorker)); + if (rw == NULL) + { + ereport(LOG, + (errcode(ERRCODE_OUT_OF_MEMORY), + errmsg("out of memory"))); + return; + } + + rw->rw_worker = *worker; + rw->rw_backend = NULL; + rw->rw_pid = 0; + rw->rw_child_slot = 0; + rw->rw_crashed_at = 0; + rw->rw_terminate = false; + + slist_push_head(&BackgroundWorkerList, &rw->rw_lnode); +} + +/* + * Register a new background worker from a regular backend. + * + * Returns true on success and false on failure. Failure typically indicates + * that no background worker slots are currently available. + * + * If handle != NULL, we'll set *handle to a pointer that can subsequently + * be used as an argument to GetBackgroundWorkerPid(). The caller can + * free this pointer using pfree(), if desired. + */ +bool +RegisterDynamicBackgroundWorker(BackgroundWorker *worker, + BackgroundWorkerHandle **handle) +{ + int slotno; + bool success = false; + bool parallel; + uint64 generation = 0; + + /* + * We can't register dynamic background workers from the postmaster. If + * this is a standalone backend, we're the only process and can't start + * any more. In a multi-process environment, it might be theoretically + * possible, but we don't currently support it due to locking + * considerations; see comments on the BackgroundWorkerSlot data + * structure. + */ + if (!IsUnderPostmaster) + return false; + + if (!SanityCheckBackgroundWorker(worker, ERROR)) + return false; + + parallel = (worker->bgw_flags & BGWORKER_CLASS_PARALLEL) != 0; + + LWLockAcquire(BackgroundWorkerLock, LW_EXCLUSIVE); + + /* + * If this is a parallel worker, check whether there are already too many + * parallel workers; if so, don't register another one. Our view of + * parallel_terminate_count may be slightly stale, but that doesn't really + * matter: we would have gotten the same result if we'd arrived here + * slightly earlier anyway. There's no help for it, either, since the + * postmaster must not take locks; a memory barrier wouldn't guarantee + * anything useful. + */ + if (parallel && (BackgroundWorkerData->parallel_register_count - + BackgroundWorkerData->parallel_terminate_count) >= + max_parallel_workers) + { + Assert(BackgroundWorkerData->parallel_register_count - + BackgroundWorkerData->parallel_terminate_count <= + MAX_PARALLEL_WORKER_LIMIT); + LWLockRelease(BackgroundWorkerLock); + return false; + } + + /* + * Look for an unused slot. If we find one, grab it. + */ + for (slotno = 0; slotno < BackgroundWorkerData->total_slots; ++slotno) + { + BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno]; + + if (!slot->in_use) + { + memcpy(&slot->worker, worker, sizeof(BackgroundWorker)); + slot->pid = InvalidPid; /* indicates not started yet */ + slot->generation++; + slot->terminate = false; + generation = slot->generation; + if (parallel) + BackgroundWorkerData->parallel_register_count++; + + /* + * Make sure postmaster doesn't see the slot as in use before it + * sees the new contents. + */ + pg_write_barrier(); + + slot->in_use = true; + success = true; + break; + } + } + + LWLockRelease(BackgroundWorkerLock); + + /* If we found a slot, tell the postmaster to notice the change. */ + if (success) + SendPostmasterSignal(PMSIGNAL_BACKGROUND_WORKER_CHANGE); + + /* + * If we found a slot and the user has provided a handle, initialize it. + */ + if (success && handle) + { + *handle = palloc(sizeof(BackgroundWorkerHandle)); + (*handle)->slot = slotno; + (*handle)->generation = generation; + } + + return success; +} + +/* + * Get the PID of a dynamically-registered background worker. + * + * If the worker is determined to be running, the return value will be + * BGWH_STARTED and *pidp will get the PID of the worker process. If the + * postmaster has not yet attempted to start the worker, the return value will + * be BGWH_NOT_YET_STARTED. Otherwise, the return value is BGWH_STOPPED. + * + * BGWH_STOPPED can indicate either that the worker is temporarily stopped + * (because it is configured for automatic restart and exited non-zero), + * or that the worker is permanently stopped (because it exited with exit + * code 0, or was not configured for automatic restart), or even that the + * worker was unregistered without ever starting (either because startup + * failed and the worker is not configured for automatic restart, or because + * TerminateBackgroundWorker was used before the worker was successfully + * started). + */ +BgwHandleStatus +GetBackgroundWorkerPid(BackgroundWorkerHandle *handle, pid_t *pidp) +{ + BackgroundWorkerSlot *slot; + pid_t pid; + + Assert(handle->slot < max_worker_processes); + slot = &BackgroundWorkerData->slot[handle->slot]; + + /* + * We could probably arrange to synchronize access to data using memory + * barriers only, but for now, let's just keep it simple and grab the + * lock. It seems unlikely that there will be enough traffic here to + * result in meaningful contention. + */ + LWLockAcquire(BackgroundWorkerLock, LW_SHARED); + + /* + * The generation number can't be concurrently changed while we hold the + * lock. The pid, which is updated by the postmaster, can change at any + * time, but we assume such changes are atomic. So the value we read + * won't be garbage, but it might be out of date by the time the caller + * examines it (but that's unavoidable anyway). + * + * The in_use flag could be in the process of changing from true to false, + * but if it is already false then it can't change further. + */ + if (handle->generation != slot->generation || !slot->in_use) + pid = 0; + else + pid = slot->pid; + + /* All done. */ + LWLockRelease(BackgroundWorkerLock); + + if (pid == 0) + return BGWH_STOPPED; + else if (pid == InvalidPid) + return BGWH_NOT_YET_STARTED; + *pidp = pid; + return BGWH_STARTED; +} + +/* + * Wait for a background worker to start up. + * + * This is like GetBackgroundWorkerPid(), except that if the worker has not + * yet started, we wait for it to do so; thus, BGWH_NOT_YET_STARTED is never + * returned. However, if the postmaster has died, we give up and return + * BGWH_POSTMASTER_DIED, since it that case we know that startup will not + * take place. + * + * The caller *must* have set our PID as the worker's bgw_notify_pid, + * else we will not be awoken promptly when the worker's state changes. + */ +BgwHandleStatus +WaitForBackgroundWorkerStartup(BackgroundWorkerHandle *handle, pid_t *pidp) +{ + BgwHandleStatus status; + int rc; + + for (;;) + { + pid_t pid; + + CHECK_FOR_INTERRUPTS(); + + status = GetBackgroundWorkerPid(handle, &pid); + if (status == BGWH_STARTED) + *pidp = pid; + if (status != BGWH_NOT_YET_STARTED) + break; + + rc = WaitLatch(MyLatch, + WL_LATCH_SET | WL_POSTMASTER_DEATH, 0, + WAIT_EVENT_BGWORKER_STARTUP); + + if (rc & WL_POSTMASTER_DEATH) + { + status = BGWH_POSTMASTER_DIED; + break; + } + + ResetLatch(MyLatch); + } + + return status; +} + +/* + * Wait for a background worker to stop. + * + * If the worker hasn't yet started, or is running, we wait for it to stop + * and then return BGWH_STOPPED. However, if the postmaster has died, we give + * up and return BGWH_POSTMASTER_DIED, because it's the postmaster that + * notifies us when a worker's state changes. + * + * The caller *must* have set our PID as the worker's bgw_notify_pid, + * else we will not be awoken promptly when the worker's state changes. + */ +BgwHandleStatus +WaitForBackgroundWorkerShutdown(BackgroundWorkerHandle *handle) +{ + BgwHandleStatus status; + int rc; + + for (;;) + { + pid_t pid; + + CHECK_FOR_INTERRUPTS(); + + status = GetBackgroundWorkerPid(handle, &pid); + if (status == BGWH_STOPPED) + break; + + rc = WaitLatch(MyLatch, + WL_LATCH_SET | WL_POSTMASTER_DEATH, 0, + WAIT_EVENT_BGWORKER_SHUTDOWN); + + if (rc & WL_POSTMASTER_DEATH) + { + status = BGWH_POSTMASTER_DIED; + break; + } + + ResetLatch(MyLatch); + } + + return status; +} + +/* + * Instruct the postmaster to terminate a background worker. + * + * Note that it's safe to do this without regard to whether the worker is + * still running, or even if the worker may already have exited and been + * unregistered. + */ +void +TerminateBackgroundWorker(BackgroundWorkerHandle *handle) +{ + BackgroundWorkerSlot *slot; + bool signal_postmaster = false; + + Assert(handle->slot < max_worker_processes); + slot = &BackgroundWorkerData->slot[handle->slot]; + + /* Set terminate flag in shared memory, unless slot has been reused. */ + LWLockAcquire(BackgroundWorkerLock, LW_EXCLUSIVE); + if (handle->generation == slot->generation) + { + slot->terminate = true; + signal_postmaster = true; + } + LWLockRelease(BackgroundWorkerLock); + + /* Make sure the postmaster notices the change to shared memory. */ + if (signal_postmaster) + SendPostmasterSignal(PMSIGNAL_BACKGROUND_WORKER_CHANGE); +} + +/* + * Look up (and possibly load) a bgworker entry point function. + * + * For functions contained in the core code, we use library name "postgres" + * and consult the InternalBGWorkers array. External functions are + * looked up, and loaded if necessary, using load_external_function(). + * + * The point of this is to pass function names as strings across process + * boundaries. We can't pass actual function addresses because of the + * possibility that the function has been loaded at a different address + * in a different process. This is obviously a hazard for functions in + * loadable libraries, but it can happen even for functions in the core code + * on platforms using EXEC_BACKEND (e.g., Windows). + * + * At some point it might be worthwhile to get rid of InternalBGWorkers[] + * in favor of applying load_external_function() for core functions too; + * but that raises portability issues that are not worth addressing now. + */ +static bgworker_main_type +LookupBackgroundWorkerFunction(const char *libraryname, const char *funcname) +{ + /* + * If the function is to be loaded from postgres itself, search the + * InternalBGWorkers array. + */ + if (strcmp(libraryname, "postgres") == 0) + { + int i; + + for (i = 0; i < lengthof(InternalBGWorkers); i++) + { + if (strcmp(InternalBGWorkers[i].fn_name, funcname) == 0) + return InternalBGWorkers[i].fn_addr; + } + + /* We can only reach this by programming error. */ + elog(ERROR, "internal function \"%s\" not found", funcname); + } + + /* Otherwise load from external library. */ + return (bgworker_main_type) + load_external_function(libraryname, funcname, true, NULL); +} + +/* + * Given a PID, get the bgw_type of the background worker. Returns NULL if + * not a valid background worker. + * + * The return value is in static memory belonging to this function, so it has + * to be used before calling this function again. This is so that the caller + * doesn't have to worry about the background worker locking protocol. + */ +const char * +GetBackgroundWorkerTypeByPid(pid_t pid) +{ + int slotno; + bool found = false; + static char result[BGW_MAXLEN]; + + LWLockAcquire(BackgroundWorkerLock, LW_SHARED); + + for (slotno = 0; slotno < BackgroundWorkerData->total_slots; slotno++) + { + BackgroundWorkerSlot *slot = &BackgroundWorkerData->slot[slotno]; + + if (slot->pid > 0 && slot->pid == pid) + { + strcpy(result, slot->worker.bgw_type); + found = true; + break; + } + } + + LWLockRelease(BackgroundWorkerLock); + + if (!found) + return NULL; + + return result; +} |