procsignal.h File Reference

#include "storage/backendid.h"

Include dependency graph for procsignal.h:

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Go to the source code of this file.

Enumerations
enum	ProcSignalReason {   PROCSIG_CATCHUP_INTERRUPT , PROCSIG_NOTIFY_INTERRUPT , PROCSIG_PARALLEL_MESSAGE , PROCSIG_WALSND_INIT_STOPPING ,   PROCSIG_BARRIER , PROCSIG_LOG_MEMORY_CONTEXT , PROCSIG_PARALLEL_APPLY_MESSAGE , PROCSIG_RECOVERY_CONFLICT_FIRST ,   PROCSIG_RECOVERY_CONFLICT_DATABASE = PROCSIG_RECOVERY_CONFLICT_FIRST , PROCSIG_RECOVERY_CONFLICT_TABLESPACE , PROCSIG_RECOVERY_CONFLICT_LOCK , PROCSIG_RECOVERY_CONFLICT_SNAPSHOT ,   PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT , PROCSIG_RECOVERY_CONFLICT_BUFFERPIN , PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK , PROCSIG_RECOVERY_CONFLICT_LAST = PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK ,   NUM_PROCSIGNALS }
enum	ProcSignalBarrierType { PROCSIGNAL_BARRIER_SMGRRELEASE }

Functions
Size	ProcSignalShmemSize (void)
void	ProcSignalShmemInit (void)
void	ProcSignalInit (int pss_idx)
int	SendProcSignal (pid_t pid, ProcSignalReason reason, BackendId backendId)
uint64	EmitProcSignalBarrier (ProcSignalBarrierType type)
void	WaitForProcSignalBarrier (uint64 generation)
void	ProcessProcSignalBarrier (void)
void	procsignal_sigusr1_handler (SIGNAL_ARGS)

Enumeration Type Documentation

ProcSignalBarrierType

enum ProcSignalBarrierType

Enumerator
PROCSIGNAL_BARRIER_SMGRRELEASE

Definition at line 54 of file procsignal.h.

{
    PROCSIGNAL_BARRIER_SMGRRELEASE  /* ask smgr to close files */
} ProcSignalBarrierType;

ProcSignalReason

enum ProcSignalReason

Enumerator
PROCSIG_CATCHUP_INTERRUPT
PROCSIG_NOTIFY_INTERRUPT
PROCSIG_PARALLEL_MESSAGE
PROCSIG_WALSND_INIT_STOPPING
PROCSIG_BARRIER
PROCSIG_LOG_MEMORY_CONTEXT
PROCSIG_PARALLEL_APPLY_MESSAGE
PROCSIG_RECOVERY_CONFLICT_FIRST
PROCSIG_RECOVERY_CONFLICT_DATABASE
PROCSIG_RECOVERY_CONFLICT_TABLESPACE
PROCSIG_RECOVERY_CONFLICT_LOCK
PROCSIG_RECOVERY_CONFLICT_SNAPSHOT
PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT
PROCSIG_RECOVERY_CONFLICT_BUFFERPIN
PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK
PROCSIG_RECOVERY_CONFLICT_LAST
NUM_PROCSIGNALS

Definition at line 30 of file procsignal.h.

{
    PROCSIG_CATCHUP_INTERRUPT,  /* sinval catchup interrupt */
    PROCSIG_NOTIFY_INTERRUPT,   /* listen/notify interrupt */
    PROCSIG_PARALLEL_MESSAGE,   /* message from cooperating parallel backend */
    PROCSIG_WALSND_INIT_STOPPING,   /* ask walsenders to prepare for shutdown  */
    PROCSIG_BARRIER,            /* global barrier interrupt  */
    PROCSIG_LOG_MEMORY_CONTEXT, /* ask backend to log the memory contexts */
    PROCSIG_PARALLEL_APPLY_MESSAGE, /* Message from parallel apply workers */
 
    /* Recovery conflict reasons */
    PROCSIG_RECOVERY_CONFLICT_FIRST,
    PROCSIG_RECOVERY_CONFLICT_DATABASE = PROCSIG_RECOVERY_CONFLICT_FIRST,
    PROCSIG_RECOVERY_CONFLICT_TABLESPACE,
    PROCSIG_RECOVERY_CONFLICT_LOCK,
    PROCSIG_RECOVERY_CONFLICT_SNAPSHOT,
    PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT,
    PROCSIG_RECOVERY_CONFLICT_BUFFERPIN,
    PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
    PROCSIG_RECOVERY_CONFLICT_LAST = PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK,
 
    NUM_PROCSIGNALS             /* Must be last! */
} ProcSignalReason;

Function Documentation

EmitProcSignalBarrier()

uint64 EmitProcSignalBarrier

(

ProcSignalBarrierType

type

)

Definition at line 333 of file procsignal.c.

{
    uint32      flagbit = 1 << (uint32) type;
    uint64      generation;
 
    /*
     * Set all the flags.
     *
     * Note that pg_atomic_fetch_or_u32 has full barrier semantics, so this is
     * totally ordered with respect to anything the caller did before, and
     * anything that we do afterwards. (This is also true of the later call to
     * pg_atomic_add_fetch_u64.)
     */
    for (int i = 0; i < NumProcSignalSlots; i++)
    {
        volatile ProcSignalSlot *slot = &ProcSignal->psh_slot[i];
 
        pg_atomic_fetch_or_u32(&slot->pss_barrierCheckMask, flagbit);
    }
 
    /*
     * Increment the generation counter.
     */
    generation =
        pg_atomic_add_fetch_u64(&ProcSignal->psh_barrierGeneration, 1);
 
    /*
     * Signal all the processes, so that they update their advertised barrier
     * generation.
     *
     * Concurrency is not a problem here. Backends that have exited don't
     * matter, and new backends that have joined since we entered this
     * function must already have current state, since the caller is
     * responsible for making sure that the relevant state is entirely visible
     * before calling this function in the first place. We still have to wake
     * them up - because we can't distinguish between such backends and older
     * backends that need to update state - but they won't actually need to
     * change any state.
     */
    for (int i = NumProcSignalSlots - 1; i >= 0; i--)
    {
        volatile ProcSignalSlot *slot = &ProcSignal->psh_slot[i];
        pid_t       pid = slot->pss_pid;
 
        if (pid != 0)
        {
            /* see SendProcSignal for details */
            slot->pss_signalFlags[PROCSIG_BARRIER] = true;
            kill(pid, SIGUSR1);
        }
    }
 
    return generation;
}

References i, kill, NumProcSignalSlots, pg_atomic_add_fetch_u64(), pg_atomic_fetch_or_u32(), PROCSIG_BARRIER, ProcSignal, ProcSignalHeader::psh_barrierGeneration, ProcSignalHeader::psh_slot, ProcSignalSlot::pss_barrierCheckMask, ProcSignalSlot::pss_pid, ProcSignalSlot::pss_signalFlags, SIGUSR1, and type.

Referenced by dbase_redo(), dropdb(), DropTableSpace(), movedb(), and tblspc_redo().

ProcessProcSignalBarrier()

void ProcessProcSignalBarrier

(

void

)

Definition at line 468 of file procsignal.c.

{
    uint64      local_gen;
    uint64      shared_gen;
    volatile uint32 flags;
 
    Assert(MyProcSignalSlot);
 
    /* Exit quickly if there's no work to do. */
    if (!ProcSignalBarrierPending)
        return;
    ProcSignalBarrierPending = false;
 
    /*
     * It's not unlikely to process multiple barriers at once, before the
     * signals for all the barriers have arrived. To avoid unnecessary work in
     * response to subsequent signals, exit early if we already have processed
     * all of them.
     */
    local_gen = pg_atomic_read_u64(&MyProcSignalSlot->pss_barrierGeneration);
    shared_gen = pg_atomic_read_u64(&ProcSignal->psh_barrierGeneration);
 
    Assert(local_gen <= shared_gen);
 
    if (local_gen == shared_gen)
        return;
 
    /*
     * Get and clear the flags that are set for this backend. Note that
     * pg_atomic_exchange_u32 is a full barrier, so we're guaranteed that the
     * read of the barrier generation above happens before we atomically
     * extract the flags, and that any subsequent state changes happen
     * afterward.
     *
     * NB: In order to avoid race conditions, we must zero
     * pss_barrierCheckMask first and only afterwards try to do barrier
     * processing. If we did it in the other order, someone could send us
     * another barrier of some type right after we called the
     * barrier-processing function but before we cleared the bit. We would
     * have no way of knowing that the bit needs to stay set in that case, so
     * the need to call the barrier-processing function again would just get
     * forgotten. So instead, we tentatively clear all the bits and then put
     * back any for which we don't manage to successfully absorb the barrier.
     */
    flags = pg_atomic_exchange_u32(&MyProcSignalSlot->pss_barrierCheckMask, 0);
 
    /*
     * If there are no flags set, then we can skip doing any real work.
     * Otherwise, establish a PG_TRY block, so that we don't lose track of
     * which types of barrier processing are needed if an ERROR occurs.
     */
    if (flags != 0)
    {
        bool        success = true;
 
        PG_TRY();
        {
            /*
             * Process each type of barrier. The barrier-processing functions
             * should normally return true, but may return false if the
             * barrier can't be absorbed at the current time. This should be
             * rare, because it's pretty expensive.  Every single
             * CHECK_FOR_INTERRUPTS() will return here until we manage to
             * absorb the barrier, and that cost will add up in a hurry.
             *
             * NB: It ought to be OK to call the barrier-processing functions
             * unconditionally, but it's more efficient to call only the ones
             * that might need us to do something based on the flags.
             */
            while (flags != 0)
            {
                ProcSignalBarrierType type;
                bool        processed = true;
 
                type = (ProcSignalBarrierType) pg_rightmost_one_pos32(flags);
                switch (type)
                {
                    case PROCSIGNAL_BARRIER_SMGRRELEASE:
                        processed = ProcessBarrierSmgrRelease();
                        break;
                }
 
                /*
                 * To avoid an infinite loop, we must always unset the bit in
                 * flags.
                 */
                BARRIER_CLEAR_BIT(flags, type);
 
                /*
                 * If we failed to process the barrier, reset the shared bit
                 * so we try again later, and set a flag so that we don't bump
                 * our generation.
                 */
                if (!processed)
                {
                    ResetProcSignalBarrierBits(((uint32) 1) << type);
                    success = false;
                }
            }
        }
        PG_CATCH();
        {
            /*
             * If an ERROR occurred, we'll need to try again later to handle
             * that barrier type and any others that haven't been handled yet
             * or weren't successfully absorbed.
             */
            ResetProcSignalBarrierBits(flags);
            PG_RE_THROW();
        }
        PG_END_TRY();
 
        /*
         * If some barrier types were not successfully absorbed, we will have
         * to try again later.
         */
        if (!success)
            return;
    }
 
    /*
     * State changes related to all types of barriers that might have been
     * emitted have now been handled, so we can update our notion of the
     * generation to the one we observed before beginning the updates. If
     * things have changed further, it'll get fixed up when this function is
     * next called.
     */
    pg_atomic_write_u64(&MyProcSignalSlot->pss_barrierGeneration, shared_gen);
    ConditionVariableBroadcast(&MyProcSignalSlot->pss_barrierCV);
}

References Assert(), BARRIER_CLEAR_BIT, ConditionVariableBroadcast(), MyProcSignalSlot, pg_atomic_exchange_u32(), pg_atomic_read_u64(), pg_atomic_write_u64(), PG_CATCH, PG_END_TRY, PG_RE_THROW, pg_rightmost_one_pos32(), PG_TRY, ProcessBarrierSmgrRelease(), ProcSignal, PROCSIGNAL_BARRIER_SMGRRELEASE, ProcSignalBarrierPending, ProcSignalHeader::psh_barrierGeneration, ProcSignalSlot::pss_barrierCheckMask, ProcSignalSlot::pss_barrierCV, ProcSignalSlot::pss_barrierGeneration, ResetProcSignalBarrierBits(), success, and type.

Referenced by BufferSync(), CheckpointWriteDelay(), HandleAutoVacLauncherInterrupts(), HandleCheckpointerInterrupts(), HandleMainLoopInterrupts(), HandlePgArchInterrupts(), HandleStartupProcInterrupts(), HandleWalWriterInterrupts(), and ProcessInterrupts().

procsignal_sigusr1_handler()

void procsignal_sigusr1_handler

(

SIGNAL_ARGS

)

Definition at line 639 of file procsignal.c.

{
    int         save_errno = errno;
 
    if (CheckProcSignal(PROCSIG_CATCHUP_INTERRUPT))
        HandleCatchupInterrupt();
 
    if (CheckProcSignal(PROCSIG_NOTIFY_INTERRUPT))
        HandleNotifyInterrupt();
 
    if (CheckProcSignal(PROCSIG_PARALLEL_MESSAGE))
        HandleParallelMessageInterrupt();
 
    if (CheckProcSignal(PROCSIG_WALSND_INIT_STOPPING))
        HandleWalSndInitStopping();
 
    if (CheckProcSignal(PROCSIG_BARRIER))
        HandleProcSignalBarrierInterrupt();
 
    if (CheckProcSignal(PROCSIG_LOG_MEMORY_CONTEXT))
        HandleLogMemoryContextInterrupt();
 
    if (CheckProcSignal(PROCSIG_PARALLEL_APPLY_MESSAGE))
        HandleParallelApplyMessageInterrupt();
 
    if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_DATABASE))
        HandleRecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_DATABASE);
 
    if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_TABLESPACE))
        HandleRecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_TABLESPACE);
 
    if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_LOCK))
        HandleRecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_LOCK);
 
    if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_SNAPSHOT))
        HandleRecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_SNAPSHOT);
 
    if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT))
        HandleRecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT);
 
    if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK))
        HandleRecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK);
 
    if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
        HandleRecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
 
    SetLatch(MyLatch);
 
    errno = save_errno;
}

References CheckProcSignal(), HandleCatchupInterrupt(), HandleLogMemoryContextInterrupt(), HandleNotifyInterrupt(), HandleParallelApplyMessageInterrupt(), HandleParallelMessageInterrupt(), HandleProcSignalBarrierInterrupt(), HandleRecoveryConflictInterrupt(), HandleWalSndInitStopping(), MyLatch, PROCSIG_BARRIER, PROCSIG_CATCHUP_INTERRUPT, PROCSIG_LOG_MEMORY_CONTEXT, PROCSIG_NOTIFY_INTERRUPT, PROCSIG_PARALLEL_APPLY_MESSAGE, PROCSIG_PARALLEL_MESSAGE, PROCSIG_RECOVERY_CONFLICT_BUFFERPIN, PROCSIG_RECOVERY_CONFLICT_DATABASE, PROCSIG_RECOVERY_CONFLICT_LOCK, PROCSIG_RECOVERY_CONFLICT_LOGICALSLOT, PROCSIG_RECOVERY_CONFLICT_SNAPSHOT, PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK, PROCSIG_RECOVERY_CONFLICT_TABLESPACE, PROCSIG_WALSND_INIT_STOPPING, and SetLatch().

Referenced by autoprewarm_main(), AutoVacLauncherMain(), AutoVacWorkerMain(), BackgroundWriterMain(), CheckpointerMain(), PgArchiverMain(), PostgresMain(), StartBackgroundWorker(), StartupProcessMain(), WalReceiverMain(), WalSndSignals(), and WalWriterMain().

ProcSignalInit()

void ProcSignalInit

(

int

pss_idx

)

Definition at line 162 of file procsignal.c.

{
    ProcSignalSlot *slot;
    uint64      barrier_generation;
 
    Assert(pss_idx >= 1 && pss_idx <= NumProcSignalSlots);
 
    slot = &ProcSignal->psh_slot[pss_idx - 1];
 
    /* sanity check */
    if (slot->pss_pid != 0)
        elog(LOG, "process %d taking over ProcSignal slot %d, but it's not empty",
             MyProcPid, pss_idx);
 
    /* Clear out any leftover signal reasons */
    MemSet(slot->pss_signalFlags, 0, NUM_PROCSIGNALS * sizeof(sig_atomic_t));
 
    /*
     * Initialize barrier state. Since we're a brand-new process, there
     * shouldn't be any leftover backend-private state that needs to be
     * updated. Therefore, we can broadcast the latest barrier generation and
     * disregard any previously-set check bits.
     *
     * NB: This only works if this initialization happens early enough in the
     * startup sequence that we haven't yet cached any state that might need
     * to be invalidated. That's also why we have a memory barrier here, to be
     * sure that any later reads of memory happen strictly after this.
     */
    pg_atomic_write_u32(&slot->pss_barrierCheckMask, 0);
    barrier_generation =
        pg_atomic_read_u64(&ProcSignal->psh_barrierGeneration);
    pg_atomic_write_u64(&slot->pss_barrierGeneration, barrier_generation);
    pg_memory_barrier();
 
    /* Mark slot with my PID */
    slot->pss_pid = MyProcPid;
 
    /* Remember slot location for CheckProcSignal */
    MyProcSignalSlot = slot;
 
    /* Set up to release the slot on process exit */
    on_shmem_exit(CleanupProcSignalState, Int32GetDatum(pss_idx));
}

References Assert(), CleanupProcSignalState(), elog(), Int32GetDatum(), LOG, MemSet, MyProcPid, MyProcSignalSlot, NUM_PROCSIGNALS, NumProcSignalSlots, on_shmem_exit(), pg_atomic_read_u64(), pg_atomic_write_u32(), pg_atomic_write_u64(), pg_memory_barrier, ProcSignal, ProcSignalHeader::psh_barrierGeneration, ProcSignalHeader::psh_slot, ProcSignalSlot::pss_barrierCheckMask, ProcSignalSlot::pss_barrierGeneration, ProcSignalSlot::pss_pid, and ProcSignalSlot::pss_signalFlags.

Referenced by AuxiliaryProcessMain(), and InitPostgres().

ProcSignalShmemInit()

void ProcSignalShmemInit

(

void

)

Definition at line 126 of file procsignal.c.

{
    Size        size = ProcSignalShmemSize();
    bool        found;
 
    ProcSignal = (ProcSignalHeader *)
        ShmemInitStruct("ProcSignal", size, &found);
 
    /* If we're first, initialize. */
    if (!found)
    {
        int         i;
 
        pg_atomic_init_u64(&ProcSignal->psh_barrierGeneration, 0);
 
        for (i = 0; i < NumProcSignalSlots; ++i)
        {
            ProcSignalSlot *slot = &ProcSignal->psh_slot[i];
 
            slot->pss_pid = 0;
            MemSet(slot->pss_signalFlags, 0, sizeof(slot->pss_signalFlags));
            pg_atomic_init_u64(&slot->pss_barrierGeneration, PG_UINT64_MAX);
            pg_atomic_init_u32(&slot->pss_barrierCheckMask, 0);
            ConditionVariableInit(&slot->pss_barrierCV);
        }
    }
}

References ConditionVariableInit(), i, MemSet, NumProcSignalSlots, pg_atomic_init_u32(), pg_atomic_init_u64(), PG_UINT64_MAX, ProcSignal, ProcSignalShmemSize(), ProcSignalHeader::psh_barrierGeneration, ProcSignalHeader::psh_slot, ProcSignalSlot::pss_barrierCheckMask, ProcSignalSlot::pss_barrierCV, ProcSignalSlot::pss_barrierGeneration, ProcSignalSlot::pss_pid, ProcSignalSlot::pss_signalFlags, and ShmemInitStruct().

Referenced by CreateSharedMemoryAndSemaphores().

ProcSignalShmemSize()

Size ProcSignalShmemSize

(

void

)

Definition at line 112 of file procsignal.c.

{
    Size        size;
 
    size = mul_size(NumProcSignalSlots, sizeof(ProcSignalSlot));
    size = add_size(size, offsetof(ProcSignalHeader, psh_slot));
    return size;
}

References add_size(), mul_size(), and NumProcSignalSlots.

Referenced by CalculateShmemSize(), and ProcSignalShmemInit().

SendProcSignal()

int SendProcSignal	(	pid_t	pid,
		ProcSignalReason	reason,
		BackendId	backendId
	)

Definition at line 262 of file procsignal.c.

{
    volatile ProcSignalSlot *slot;
 
    if (backendId != InvalidBackendId)
    {
        slot = &ProcSignal->psh_slot[backendId - 1];
 
        /*
         * Note: Since there's no locking, it's possible that the target
         * process detaches from shared memory and exits right after this
         * test, before we set the flag and send signal. And the signal slot
         * might even be recycled by a new process, so it's remotely possible
         * that we set a flag for a wrong process. That's OK, all the signals
         * are such that no harm is done if they're mistakenly fired.
         */
        if (slot->pss_pid == pid)
        {
            /* Atomically set the proper flag */
            slot->pss_signalFlags[reason] = true;
            /* Send signal */
            return kill(pid, SIGUSR1);
        }
    }
    else
    {
        /*
         * BackendId not provided, so search the array using pid.  We search
         * the array back to front so as to reduce search overhead.  Passing
         * InvalidBackendId means that the target is most likely an auxiliary
         * process, which will have a slot near the end of the array.
         */
        int         i;
 
        for (i = NumProcSignalSlots - 1; i >= 0; i--)
        {
            slot = &ProcSignal->psh_slot[i];
 
            if (slot->pss_pid == pid)
            {
                /* the above note about race conditions applies here too */
 
                /* Atomically set the proper flag */
                slot->pss_signalFlags[reason] = true;
                /* Send signal */
                return kill(pid, SIGUSR1);
            }
        }
    }
 
    errno = ESRCH;
    return -1;
}

References i, InvalidBackendId, kill, NumProcSignalSlots, ProcSignal, ProcSignalHeader::psh_slot, ProcSignalSlot::pss_pid, ProcSignalSlot::pss_signalFlags, and SIGUSR1.

Referenced by CancelDBBackends(), InvalidatePossiblyObsoleteSlot(), mq_putmessage(), pa_shutdown(), ParallelWorkerShutdown(), pg_log_backend_memory_contexts(), SICleanupQueue(), SignalBackends(), SignalVirtualTransaction(), and WalSndInitStopping().

WaitForProcSignalBarrier()

void WaitForProcSignalBarrier

(

uint64

generation

)

Definition at line 393 of file procsignal.c.

{
    Assert(generation <= pg_atomic_read_u64(&ProcSignal->psh_barrierGeneration));
 
    elog(DEBUG1,
         "waiting for all backends to process ProcSignalBarrier generation "
         UINT64_FORMAT,
         generation);
 
    for (int i = NumProcSignalSlots - 1; i >= 0; i--)
    {
        ProcSignalSlot *slot = &ProcSignal->psh_slot[i];
        uint64      oldval;
 
        /*
         * It's important that we check only pss_barrierGeneration here and
         * not pss_barrierCheckMask. Bits in pss_barrierCheckMask get cleared
         * before the barrier is actually absorbed, but pss_barrierGeneration
         * is updated only afterward.
         */
        oldval = pg_atomic_read_u64(&slot->pss_barrierGeneration);
        while (oldval < generation)
        {
            if (ConditionVariableTimedSleep(&slot->pss_barrierCV,
                                            5000,
                                            WAIT_EVENT_PROC_SIGNAL_BARRIER))
                ereport(LOG,
                        (errmsg("still waiting for backend with PID %d to accept ProcSignalBarrier",
                                (int) slot->pss_pid)));
            oldval = pg_atomic_read_u64(&slot->pss_barrierGeneration);
        }
        ConditionVariableCancelSleep();
    }
 
    elog(DEBUG1,
         "finished waiting for all backends to process ProcSignalBarrier generation "
         UINT64_FORMAT,
         generation);
 
    /*
     * The caller is probably calling this function because it wants to read
     * the shared state or perform further writes to shared state once all
     * backends are known to have absorbed the barrier. However, the read of
     * pss_barrierGeneration was performed unlocked; insert a memory barrier
     * to separate it from whatever follows.
     */
    pg_memory_barrier();
}

References Assert(), ConditionVariableCancelSleep(), ConditionVariableTimedSleep(), DEBUG1, elog(), ereport, errmsg(), i, LOG, NumProcSignalSlots, pg_atomic_read_u64(), pg_memory_barrier, ProcSignal, ProcSignalHeader::psh_barrierGeneration, ProcSignalHeader::psh_slot, ProcSignalSlot::pss_barrierCV, ProcSignalSlot::pss_barrierGeneration, ProcSignalSlot::pss_pid, and UINT64_FORMAT.

Referenced by dbase_redo(), dropdb(), DropTableSpace(), movedb(), and tblspc_redo().