procsignal.c File Reference

#include "postgres.h"
#include <signal.h>
#include <unistd.h>
#include "access/parallel.h"
#include "port/pg_bitutils.h"
#include "commands/async.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "replication/walsender.h"
#include "storage/ipc.h"
#include "storage/latch.h"
#include "storage/proc.h"
#include "storage/shmem.h"
#include "storage/sinval.h"
#include "tcop/tcopprot.h"

Include dependency graph for procsignal.c:

Go to the source code of this file.

Data Structures
struct	ProcSignalSlot
struct	ProcSignalHeader

Macros
#define	NumProcSignalSlots   (MaxBackends + NUM_AUXPROCTYPES)
#define	BARRIER_SHOULD_CHECK(flags, type)   (((flags) & (((uint32) 1) << (uint32) (type))) != 0)
#define	BARRIER_CLEAR_BIT(flags, type)   ((flags) &= ~(((uint32) 1) << (uint32) (type)))

Functions
static bool	CheckProcSignal (ProcSignalReason reason)
static void	CleanupProcSignalState (int status, Datum arg)
static void	ResetProcSignalBarrierBits (uint32 flags)
static bool	ProcessBarrierPlaceholder (void)
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)
static void	HandleProcSignalBarrierInterrupt (void)
void	ProcessProcSignalBarrier (void)
void	procsignal_sigusr1_handler (SIGNAL_ARGS)

Variables
static ProcSignalHeader *	ProcSignal = NULL
static volatile ProcSignalSlot *	MyProcSignalSlot = NULL

Macro Definition Documentation

BARRIER_CLEAR_BIT

#define BARRIER_CLEAR_BIT	(		flags,
			type
	)		((flags) &= ~(((uint32) 1) << (uint32) (type)))

Definition at line 92 of file procsignal.c.

Referenced by ProcessProcSignalBarrier().

BARRIER_SHOULD_CHECK

#define BARRIER_SHOULD_CHECK	(		flags,
			type
	)		(((flags) & (((uint32) 1) << (uint32) (type))) != 0)

Definition at line 88 of file procsignal.c.

NumProcSignalSlots

#define NumProcSignalSlots   (MaxBackends + NUM_AUXPROCTYPES)

Definition at line 85 of file procsignal.c.

Referenced by EmitProcSignalBarrier(), ProcSignalInit(), ProcSignalShmemInit(), ProcSignalShmemSize(), SendProcSignal(), and WaitForProcSignalBarrier().

Function Documentation

CheckProcSignal()

static bool CheckProcSignal ( ProcSignalReason  reason )

static

Definition at line 631 of file procsignal.c.

References MyProcSignalSlot, and ProcSignalSlot::pss_signalFlags.

Referenced by procsignal_sigusr1_handler().

{
    volatile ProcSignalSlot *slot = MyProcSignalSlot;

    if (slot != NULL)
    {
        /* Careful here --- don't clear flag if we haven't seen it set */
        if (slot->pss_signalFlags[reason])
        {
            slot->pss_signalFlags[reason] = false;
            return true;
        }
    }

    return false;
}

CleanupProcSignalState()

static void CleanupProcSignalState ( int  status, Datum  arg  )

static

Definition at line 208 of file procsignal.c.

References Assert, DatumGetInt32, elog, LOG, MyProcPid, pg_atomic_write_u64(), PG_UINT64_MAX, ProcSignalHeader::psh_slot, ProcSignalSlot::pss_barrierGeneration, and ProcSignalSlot::pss_pid.

Referenced by ProcSignalInit().

{
    int         pss_idx = DatumGetInt32(arg);
    volatile ProcSignalSlot *slot;

    slot = &ProcSignal->psh_slot[pss_idx - 1];
    Assert(slot == MyProcSignalSlot);

    /*
     * Clear MyProcSignalSlot, so that a SIGUSR1 received after this point
     * won't try to access it after it's no longer ours (and perhaps even
     * after we've unmapped the shared memory segment).
     */
    MyProcSignalSlot = NULL;

    /* sanity check */
    if (slot->pss_pid != MyProcPid)
    {
        /*
         * don't ERROR here. We're exiting anyway, and don't want to get into
         * infinite loop trying to exit
         */
        elog(LOG, "process %d releasing ProcSignal slot %d, but it contains %d",
             MyProcPid, pss_idx, (int) slot->pss_pid);
        return;                 /* XXX better to zero the slot anyway? */
    }

    /*
     * Make this slot look like it's absorbed all possible barriers, so that
     * no barrier waits block on it.
     */
    pg_atomic_write_u64(&slot->pss_barrierGeneration, PG_UINT64_MAX);

    slot->pss_pid = 0;
}

EmitProcSignalBarrier()

uint64 EmitProcSignalBarrier

(

ProcSignalBarrierType

type

)

Definition at line 327 of file procsignal.c.

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

{
    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;
}

HandleProcSignalBarrierInterrupt()

static void HandleProcSignalBarrierInterrupt ( void  )

static

Definition at line 448 of file procsignal.c.

References InterruptPending, and ProcSignalBarrierPending.

Referenced by procsignal_sigusr1_handler().

{
    InterruptPending = true;
    ProcSignalBarrierPending = true;
    /* latch will be set by procsignal_sigusr1_handler */
}

ProcessBarrierPlaceholder()

static bool ProcessBarrierPlaceholder ( void  )

static

Definition at line 608 of file procsignal.c.

Referenced by ProcessProcSignalBarrier().

{
    /*
     * XXX. This is just a placeholder until the first real user of this
     * machinery gets committed. Rename PROCSIGNAL_BARRIER_PLACEHOLDER to
     * PROCSIGNAL_BARRIER_SOMETHING_ELSE where SOMETHING_ELSE is something
     * appropriately descriptive. Get rid of this function and instead have
     * ProcessBarrierSomethingElse. Most likely, that function should live in
     * the file pertaining to that subsystem, rather than here.
     *
     * The return value should be 'true' if the barrier was successfully
     * absorbed and 'false' if not. Note that returning 'false' can lead to
     * very frequent retries, so try hard to make that an uncommon case.
     */
    return true;
}

ProcessProcSignalBarrier()

void ProcessProcSignalBarrier

(

void

)

Definition at line 464 of file procsignal.c.

References Assert, BARRIER_CLEAR_BIT, 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, ProcessBarrierPlaceholder(), PROCSIGNAL_BARRIER_PLACEHOLDER, ProcSignalBarrierPending, ProcSignalHeader::psh_barrierGeneration, ProcSignalSlot::pss_barrierCheckMask, ProcSignalSlot::pss_barrierGeneration, ResetProcSignalBarrierBits(), success, and generate_unaccent_rules::type.

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

{
    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_PLACEHOLDER:
                        processed = ProcessBarrierPlaceholder();
                        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);
}

procsignal_sigusr1_handler()

void procsignal_sigusr1_handler

(

SIGNAL_ARGS

)

Definition at line 652 of file procsignal.c.

References CheckProcSignal(), HandleCatchupInterrupt(), HandleNotifyInterrupt(), HandleParallelMessageInterrupt(), HandleProcSignalBarrierInterrupt(), HandleWalSndInitStopping(), latch_sigusr1_handler(), MyLatch, PROCSIG_BARRIER, PROCSIG_CATCHUP_INTERRUPT, PROCSIG_NOTIFY_INTERRUPT, PROCSIG_PARALLEL_MESSAGE, PROCSIG_RECOVERY_CONFLICT_BUFFERPIN, PROCSIG_RECOVERY_CONFLICT_DATABASE, PROCSIG_RECOVERY_CONFLICT_LOCK, PROCSIG_RECOVERY_CONFLICT_SNAPSHOT, PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK, PROCSIG_RECOVERY_CONFLICT_TABLESPACE, PROCSIG_WALSND_INIT_STOPPING, RecoveryConflictInterrupt(), and SetLatch().

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

{
    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_RECOVERY_CONFLICT_DATABASE))
        RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_DATABASE);

    if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_TABLESPACE))
        RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_TABLESPACE);

    if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_LOCK))
        RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_LOCK);

    if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_SNAPSHOT))
        RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_SNAPSHOT);

    if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK))
        RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_STARTUP_DEADLOCK);

    if (CheckProcSignal(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN))
        RecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);

    SetLatch(MyLatch);

    latch_sigusr1_handler();

    errno = save_errno;
}

ProcSignalInit()

void ProcSignalInit

(

int

pss_idx

)

Definition at line 157 of file procsignal.c.

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

Referenced by AuxiliaryProcessMain(), and InitPostgres().

{
    volatile 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));
}

ProcSignalShmemInit()

void ProcSignalShmemInit

(

void

)

Definition at line 122 of file procsignal.c.

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

Referenced by CreateSharedMemoryAndSemaphores().

{
    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);
        }
    }
}

ProcSignalShmemSize()

Size ProcSignalShmemSize

(

void

)

Definition at line 108 of file procsignal.c.

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

Referenced by CreateSharedMemoryAndSemaphores(), and ProcSignalShmemInit().

{
    Size        size;

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

ResetProcSignalBarrierBits()

static void ResetProcSignalBarrierBits ( uint32  flags )

static

Definition at line 600 of file procsignal.c.

References InterruptPending, pg_atomic_fetch_or_u32(), ProcSignalBarrierPending, and ProcSignalSlot::pss_barrierCheckMask.

Referenced by ProcessProcSignalBarrier().

{
    pg_atomic_fetch_or_u32(&MyProcSignalSlot->pss_barrierCheckMask, flags);
    ProcSignalBarrierPending = true;
    InterruptPending = true;
}

SendProcSignal()

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

Definition at line 256 of file procsignal.c.

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

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

{
    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;
}

WaitForProcSignalBarrier()

void WaitForProcSignalBarrier

(

uint64

generation

)

Definition at line 392 of file procsignal.c.

References Assert, CHECK_FOR_INTERRUPTS, i, Min, MyLatch, NumProcSignalSlots, pg_atomic_read_u64(), pg_memory_barrier, ProcSignalHeader::psh_barrierGeneration, ProcSignalHeader::psh_slot, ProcSignalSlot::pss_barrierGeneration, ResetLatch(), WAIT_EVENT_PROC_SIGNAL_BARRIER, WaitLatch(), WL_EXIT_ON_PM_DEATH, WL_LATCH_SET, and WL_TIMEOUT.

{
    long        timeout = 125L;

    Assert(generation <= pg_atomic_read_u64(&ProcSignal->psh_barrierGeneration));

    for (int i = NumProcSignalSlots - 1; i >= 0; i--)
    {
        volatile 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)
        {
            int         events;

            CHECK_FOR_INTERRUPTS();

            events =
                WaitLatch(MyLatch,
                          WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
                          timeout, WAIT_EVENT_PROC_SIGNAL_BARRIER);
            ResetLatch(MyLatch);

            oldval = pg_atomic_read_u64(&slot->pss_barrierGeneration);
            if (events & WL_TIMEOUT)
                timeout = Min(timeout * 2, 1000L);
        }
    }

    /*
     * 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();
}

Variable Documentation

MyProcSignalSlot

volatile ProcSignalSlot* MyProcSignalSlot = NULL

static

Definition at line 96 of file procsignal.c.

Referenced by CheckProcSignal().

ProcSignal

ProcSignalHeader* ProcSignal = NULL

static

Definition at line 95 of file procsignal.c.