greenplumn bgworker 源码
greenplumn bgworker 代码
文件路径：/src/backend/postmaster/bgworker.c
/*--------------------------------------------------------------------
* bgworker.c
* POSTGRES pluggable background workers implementation
*
* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
*
* IDENTIFICATION
* src/backend/postmaster/bgworker.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include <unistd.h>
#include "cdb/ic_proxy_bgworker.h"
#include "libpq/pqsignal.h"
#include "access/parallel.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "port/atomics.h"
#include "postmaster/bgworker_internals.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"
#include "postmaster/backoff.h"
#include "postmaster/fts.h"
#include "utils/gdd.h"
extern bool isAuxiliaryBgWorker(BackgroundWorker *worker);
/*
* 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
}
/* GPDB additions */
,
{
"FtsProbeMain", FtsProbeMain
},
{
"GlobalDeadLockDetectorMain", GlobalDeadLockDetectorMain
},
{
"DtxRecoveryMain", DtxRecoveryMain
},
{
"BackoffSweeperMain", BackoffSweeperMain
},
#ifdef ENABLE_IC_PROXY
{
"ICProxyMain", ICProxyMain
},
#endif /* ENABLE_IC_PROXY */
};
/* 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. 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(void)
{
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)
{
elog(LOG,
"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 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++;
pg_memory_barrier();
slot->pid = 0;
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 %lu is not valid",
(long) 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("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.
*
* 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];
if ((rw->rw_worker.bgw_flags & BGWORKER_CLASS_PARALLEL) != 0)
BackgroundWorkerData->parallel_terminate_count++;
slot->in_use = false;
ereport(DEBUG1,
(errmsg("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;
}
}
/*
* 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.
*/
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;
}
}
}
#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 */
if (worker->bgw_flags & BGWORKER_BACKEND_DATABASE_CONNECTION)
{
if (!(worker->bgw_flags & BGWORKER_SHMEM_ACCESS))
{
ereport(elevel,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("background worker \"%s\": must attach to shared memory in order to request a database connection",
worker->bgw_name)));
return false;
}
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;
}
/*
* it's unsafe to allow custom workers to accessing database if distributed
* transactions are not recovered yet.
*
* Built-in auxiliary workers like FTS are fine because we know what
* they do and they can work even dtx are not recovered.
*/
if (worker->bgw_start_time == BgWorkerStart_DtxRecovering &&
!isAuxiliaryBgWorker(worker))
{
ereport(elevel,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("background worker \"%s\": cannot request database access if starting at distributed transactions recovering",
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;
}
static void
bgworker_quickdie(SIGNAL_ARGS)
{
/*
* We DO NOT want to run proc_exit() or atexit() callbacks -- we're here
* because shared memory may be corrupted, so we don't want to try to
* clean up our transaction. Just nail the windows shut and get out of
* town. The callbacks wouldn't be safe to run from a signal handler,
* anyway.
*
* Note we do _exit(2) not _exit(0). This is to force the postmaster into
* a system reset cycle if someone sends a manual SIGQUIT to a random
* backend. This is necessary precisely because we don't clean up our
* shared memory state. (The "dead man switch" mechanism in pmsignal.c
* should ensure the postmaster sees this as a crash, too, but no harm in
* being doubly sure.)
*/
_exit(2);
}
/*
* Standard SIGTERM handler for background workers
*/
static void
bgworker_die(SIGNAL_ARGS)
{
PG_SETMASK(&BlockSig);
ereport(FATAL,
(errcode(ERRCODE_ADMIN_SHUTDOWN),
errmsg("terminating background worker \"%s\" due to administrator command",
MyBgworkerEntry->bgw_type)));
}
/*
* Standard SIGUSR1 handler for unconnected workers
*
* Here, we want to make sure an unconnected worker will at least heed
* latch activity.
*/
static void
bgworker_sigusr1_handler(SIGNAL_ARGS)
{
int save_errno = errno;
latch_sigusr1_handler();
errno = save_errno;
}
/*
* 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;
/* Identify myself via ps */
init_ps_display(worker->bgw_name, "", "", "");
/*
* If we're not supposed to have shared memory access, then detach from
* shared memory. If we didn't request shared memory access, the
* postmaster won't force a cluster-wide restart if we exit unexpectedly,
* so we'd better make sure that we don't mess anything up that would
* require that sort of cleanup.
*/
if ((worker->bgw_flags & BGWORKER_SHMEM_ACCESS) == 0)
{
dsm_detach_all();
PGSharedMemoryDetach();
}
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, bgworker_sigusr1_handler);
pqsignal(SIGFPE, SIG_IGN);
}
pqsignal(SIGTERM, bgworker_die);
pqsignal(SIGHUP, SIG_IGN);
pqsignal(SIGQUIT, bgworker_quickdie);
InitializeTimeouts(); /* establishes SIGALRM handler */
pqsignal(SIGPIPE, SIG_IGN);
pqsignal(SIGUSR2, SIG_IGN);
pqsignal(SIGCHLD, SIG_DFL);
/*
* If an exception is encountered, processing resumes here.
*
* See notes in postgres.c about the design of this coding.
*/
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();
/* Report the error to 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;
/*
* If the background worker request shared memory access, set that up now;
* else, detach all shared memory segments.
*/
if (worker->bgw_flags & BGWORKER_SHMEM_ACCESS)
{
/*
* Early initialization. Some of this could be useful even for
* background workers that aren't using shared memory, but they can
* call the individual startup routines for those subsystems if
* needed.
*/
BaseInit();
/*
* 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
}
/*
* 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;
bool auxworker = false;
static int numworkers = 0;
if (!IsUnderPostmaster)
ereport(DEBUG1,
(errmsg("registering background worker \"%s\"", worker->bgw_name)));
auxworker = isAuxiliaryBgWorker(worker);
if (!process_shared_preload_libraries_in_progress && !auxworker
&& 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 (!auxworker && ++numworkers > max_worker_processes - MaxPMAuxProc)
{
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.
*/
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.
*/
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 existed 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;
}
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