procsignal.c File Reference

#include "postgres.h"
#include <signal.h>
#include <unistd.h>
#include "access/parallel.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)

Functions
static bool	CheckProcSignal (ProcSignalReason reason)
static void	CleanupProcSignalState (int status, Datum arg)
static void	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_SHOULD_CHECK

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

Definition at line 87 of file procsignal.c.

Referenced by ProcessProcSignalBarrier().

NumProcSignalSlots

#define NumProcSignalSlots   (MaxBackends + NUM_AUXPROCTYPES)

Definition at line 84 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 530 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 202 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 321 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 436 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 void ProcessBarrierPlaceholder ( void  )

static

Definition at line 512 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.
     */
}

ProcessProcSignalBarrier()

void ProcessProcSignalBarrier

(

void

)

Definition at line 452 of file procsignal.c.

References Assert, BARRIER_SHOULD_CHECK, pg_atomic_exchange_u32(), pg_atomic_read_u64(), pg_atomic_write_u64(), ProcessBarrierPlaceholder(), PROCSIGNAL_BARRIER_PLACEHOLDER, ProcSignalBarrierPending, ProcSignalHeader::psh_barrierGeneration, ProcSignalSlot::pss_barrierCheckMask, and ProcSignalSlot::pss_barrierGeneration.

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

{
    uint64      local_gen;
    uint64      shared_gen;
    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.
     */
    flags = pg_atomic_exchange_u32(&MyProcSignalSlot->pss_barrierCheckMask, 0);

    /*
     * Process each type of barrier. It's important that nothing we call from
     * here throws an error, because pss_barrierCheckMask has already been
     * cleared. If we jumped out of here before processing all barrier types,
     * then we'd forget about the need to do so later.
     *
     * 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.
     */
    if (BARRIER_SHOULD_CHECK(flags, PROCSIGNAL_BARRIER_PLACEHOLDER))
        ProcessBarrierPlaceholder();

    /*
     * 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 551 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 151 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 116 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 102 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;
}

SendProcSignal()

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

Definition at line 250 of file procsignal.c.

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

Referenced by CancelDBBackends(), CancelVirtualTransaction(), mq_putmessage(), ParallelWorkerShutdown(), SICleanupQueue(), SignalBackends(), 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 386 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;

        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 91 of file procsignal.c.

Referenced by CheckProcSignal().

ProcSignal

ProcSignalHeader* ProcSignal = NULL

static

Definition at line 90 of file procsignal.c.