lwlock.c File Reference

#include "postgres.h"
#include "miscadmin.h"
#include "pg_trace.h"
#include "pgstat.h"
#include "postmaster/postmaster.h"
#include "replication/slot.h"
#include "storage/ipc.h"
#include "storage/predicate.h"
#include "storage/proc.h"
#include "storage/proclist.h"
#include "storage/spin.h"
#include "utils/memutils.h"

Include dependency graph for lwlock.c:

Go to the source code of this file.

Data Structures
struct	LWLockHandle
struct	NamedLWLockTrancheRequest

Macros
#define	LW_FLAG_HAS_WAITERS   ((uint32) 1 << 30)
#define	LW_FLAG_RELEASE_OK   ((uint32) 1 << 29)
#define	LW_FLAG_LOCKED   ((uint32) 1 << 28)
#define	LW_VAL_EXCLUSIVE   ((uint32) 1 << 24)
#define	LW_VAL_SHARED   1
#define	LW_LOCK_MASK   ((uint32) ((1 << 25)-1))
#define	LW_SHARED_MASK   ((uint32) ((1 << 24)-1))
#define	T_NAME(lock)   (LWLockTrancheArray[(lock)->tranche])
#define	MAX_SIMUL_LWLOCKS   200
#define	PRINT_LWDEBUG(a, b, c)   ((void)0)
#define	LOG_LWDEBUG(a, b, c)   ((void)0)

Typedefs
typedef struct LWLockHandle	LWLockHandle
typedef struct NamedLWLockTrancheRequest	NamedLWLockTrancheRequest

Functions
static void	InitializeLWLocks (void)
static void	RegisterLWLockTranches (void)
static void	LWLockReportWaitStart (LWLock *lock)
static void	LWLockReportWaitEnd (void)
static int	NumLWLocksByNamedTranches (void)
Size	LWLockShmemSize (void)
void	CreateLWLocks (void)
void	InitLWLockAccess (void)
LWLockPadded *	GetNamedLWLockTranche (const char *tranche_name)
int	LWLockNewTrancheId (void)
void	LWLockRegisterTranche (int tranche_id, const char *tranche_name)
void	RequestNamedLWLockTranche (const char *tranche_name, int num_lwlocks)
void	LWLockInitialize (LWLock *lock, int tranche_id)
const char *	GetLWLockIdentifier (uint32 classId, uint16 eventId)
static bool	LWLockAttemptLock (LWLock *lock, LWLockMode mode)
static void	LWLockWaitListLock (LWLock *lock)
static void	LWLockWaitListUnlock (LWLock *lock)
static void	LWLockWakeup (LWLock *lock)
static void	LWLockQueueSelf (LWLock *lock, LWLockMode mode)
static void	LWLockDequeueSelf (LWLock *lock)
bool	LWLockAcquire (LWLock *lock, LWLockMode mode)
bool	LWLockConditionalAcquire (LWLock *lock, LWLockMode mode)
bool	LWLockAcquireOrWait (LWLock *lock, LWLockMode mode)
static bool	LWLockConflictsWithVar (LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval, bool *result)
bool	LWLockWaitForVar (LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval)
void	LWLockUpdateVar (LWLock *lock, uint64 *valptr, uint64 val)
void	LWLockRelease (LWLock *lock)
void	LWLockReleaseClearVar (LWLock *lock, uint64 *valptr, uint64 val)
void	LWLockReleaseAll (void)
bool	LWLockHeldByMe (LWLock *l)
bool	LWLockHeldByMeInMode (LWLock *l, LWLockMode mode)

Variables
slock_t *	ShmemLock
static const char **	LWLockTrancheArray = NULL
static int	LWLockTranchesAllocated = 0
LWLockPadded *	MainLWLockArray = NULL
static int	num_held_lwlocks = 0
static LWLockHandle	held_lwlocks [MAX_SIMUL_LWLOCKS]
NamedLWLockTrancheRequest *	NamedLWLockTrancheRequestArray = NULL
static int	NamedLWLockTrancheRequestsAllocated = 0
int	NamedLWLockTrancheRequests = 0
NamedLWLockTranche *	NamedLWLockTrancheArray = NULL
static bool	lock_named_request_allowed = true

Macro Definition Documentation

LOG_LWDEBUG

#define LOG_LWDEBUG	(		a,
			b,
			c
	)		((void)0)

Definition at line 228 of file lwlock.c.

Referenced by LWLockAcquire(), LWLockAcquireOrWait(), LWLockConditionalAcquire(), LWLockRelease(), LWLockWaitForVar(), and LWLockWakeup().

LW_FLAG_HAS_WAITERS

#define LW_FLAG_HAS_WAITERS   ((uint32) 1 << 30)

Definition at line 99 of file lwlock.c.

Referenced by LWLockDequeueSelf(), LWLockQueueSelf(), LWLockRelease(), and LWLockWakeup().

LW_FLAG_LOCKED

#define LW_FLAG_LOCKED   ((uint32) 1 << 28)

Definition at line 101 of file lwlock.c.

Referenced by LWLockWaitListLock(), LWLockWaitListUnlock(), and LWLockWakeup().

LW_FLAG_RELEASE_OK

#define LW_FLAG_RELEASE_OK   ((uint32) 1 << 29)

Definition at line 100 of file lwlock.c.

Referenced by LWLockAcquire(), LWLockDequeueSelf(), LWLockInitialize(), LWLockRelease(), LWLockWaitForVar(), and LWLockWakeup().

LW_LOCK_MASK

#define LW_LOCK_MASK   ((uint32) ((1 << 25)-1))

Definition at line 106 of file lwlock.c.

Referenced by LWLockAttemptLock(), and LWLockRelease().

LW_SHARED_MASK

#define LW_SHARED_MASK   ((uint32) ((1 << 24)-1))

Definition at line 108 of file lwlock.c.

LW_VAL_EXCLUSIVE

#define LW_VAL_EXCLUSIVE   ((uint32) 1 << 24)

Definition at line 103 of file lwlock.c.

Referenced by CreateLWLocks(), LWLockAttemptLock(), LWLockConflictsWithVar(), LWLockRelease(), and LWLockUpdateVar().

LW_VAL_SHARED

#define LW_VAL_SHARED   1

Definition at line 104 of file lwlock.c.

Referenced by LWLockAttemptLock(), and LWLockRelease().

MAX_SIMUL_LWLOCKS

#define MAX_SIMUL_LWLOCKS   200

Definition at line 133 of file lwlock.c.

Referenced by LWLockAcquire(), LWLockAcquireOrWait(), and LWLockConditionalAcquire().

PRINT_LWDEBUG

#define PRINT_LWDEBUG	(		a,
			b,
			c
	)		((void)0)

Definition at line 227 of file lwlock.c.

Referenced by LWLockAcquire(), LWLockAcquireOrWait(), LWLockConditionalAcquire(), LWLockRelease(), LWLockUpdateVar(), and LWLockWaitForVar().

T_NAME

#define T_NAME

(

lock

)

(LWLockTrancheArray[(lock)->tranche])

Definition at line 117 of file lwlock.c.

Referenced by LWLockAcquire(), LWLockAcquireOrWait(), LWLockConditionalAcquire(), LWLockRelease(), and LWLockWaitForVar().

Typedef Documentation

LWLockHandle

typedef struct LWLockHandle LWLockHandle

NamedLWLockTrancheRequest

typedef struct NamedLWLockTrancheRequest NamedLWLockTrancheRequest

Function Documentation

CreateLWLocks()

void CreateLWLocks

(

void

)

Definition at line 381 of file lwlock.c.

References InitializeLWLocks(), IsUnderPostmaster, LW_VAL_EXCLUSIVE, LWLOCK_MINIMAL_SIZE, LWLOCK_PADDED_SIZE, LWLockShmemSize(), LWTRANCHE_FIRST_USER_DEFINED, MAX_BACKENDS, RegisterLWLockTranches(), ShmemAlloc(), and StaticAssertStmt.

Referenced by CreateSharedMemoryAndSemaphores().

{
    StaticAssertStmt(LW_VAL_EXCLUSIVE > (uint32) MAX_BACKENDS,
                     "MAX_BACKENDS too big for lwlock.c");

    StaticAssertStmt(sizeof(LWLock) <= LWLOCK_MINIMAL_SIZE &&
                     sizeof(LWLock) <= LWLOCK_PADDED_SIZE,
                     "Miscalculated LWLock padding");

    if (!IsUnderPostmaster)
    {
        Size        spaceLocks = LWLockShmemSize();
        int        *LWLockCounter;
        char       *ptr;

        /* Allocate space */
        ptr = (char *) ShmemAlloc(spaceLocks);

        /* Leave room for dynamic allocation of tranches */
        ptr += sizeof(int);

        /* Ensure desired alignment of LWLock array */
        ptr += LWLOCK_PADDED_SIZE - ((uintptr_t) ptr) % LWLOCK_PADDED_SIZE;

        MainLWLockArray = (LWLockPadded *) ptr;

        /*
         * Initialize the dynamic-allocation counter for tranches, which is
         * stored just before the first LWLock.
         */
        LWLockCounter = (int *) ((char *) MainLWLockArray - sizeof(int));
        *LWLockCounter = LWTRANCHE_FIRST_USER_DEFINED;

        /* Initialize all LWLocks */
        InitializeLWLocks();
    }

    /* Register all LWLock tranches */
    RegisterLWLockTranches();
}

GetLWLockIdentifier()

const char* GetLWLockIdentifier	(	uint32	classId,
		uint16	eventId
	)

Definition at line 714 of file lwlock.c.

References Assert, LWLockTrancheArray, LWLockTranchesAllocated, and PG_WAIT_LWLOCK.

Referenced by pgstat_get_wait_event().

{
    Assert(classId == PG_WAIT_LWLOCK);

    /*
     * It is quite possible that user has registered tranche in one of the
     * backends (e.g. by allocating lwlocks in dynamic shared memory) but not
     * all of them, so we can't assume the tranche is registered here.
     */
    if (eventId >= LWLockTranchesAllocated ||
        LWLockTrancheArray[eventId] == NULL)
        return "extension";

    return LWLockTrancheArray[eventId];
}

GetNamedLWLockTranche()

LWLockPadded* GetNamedLWLockTranche

(

const char *

tranche_name

)

Definition at line 552 of file lwlock.c.

References elog, ERROR, i, NamedLWLockTrancheRequests, NUM_FIXED_LWLOCKS, and NamedLWLockTrancheRequest::num_lwlocks.

Referenced by pgss_shmem_startup().

{
    int         lock_pos;
    int         i;

    /*
     * Obtain the position of base address of LWLock belonging to requested
     * tranche_name in MainLWLockArray.  LWLocks for named tranches are placed
     * in MainLWLockArray after fixed locks.
     */
    lock_pos = NUM_FIXED_LWLOCKS;
    for (i = 0; i < NamedLWLockTrancheRequests; i++)
    {
        if (strcmp(NamedLWLockTrancheRequestArray[i].tranche_name,
                   tranche_name) == 0)
            return &MainLWLockArray[lock_pos];

        lock_pos += NamedLWLockTrancheRequestArray[i].num_lwlocks;
    }

    if (i >= NamedLWLockTrancheRequests)
        elog(ERROR, "requested tranche is not registered");

    /* just to keep compiler quiet */
    return NULL;
}

InitializeLWLocks()

static void InitializeLWLocks ( void  )

static

Definition at line 426 of file lwlock.c.

References i, LWLockPadded::lock, LWLockHandle::lock, LWLockInitialize(), LWLockNewTrancheId(), LWTRANCHE_BUFFER_MAPPING, LWTRANCHE_LOCK_MANAGER, LWTRANCHE_PREDICATE_LOCK_MANAGER, name, NamedLWLockTrancheRequests, NUM_BUFFER_PARTITIONS, NUM_FIXED_LWLOCKS, NUM_LOCK_PARTITIONS, NamedLWLockTrancheRequest::num_lwlocks, NUM_PREDICATELOCK_PARTITIONS, NumLWLocksByNamedTranches(), NamedLWLockTrancheRequest::tranche_name, NamedLWLockTranche::trancheId, and NamedLWLockTranche::trancheName.

Referenced by CreateLWLocks().

{
    int         numNamedLocks = NumLWLocksByNamedTranches();
    int         id;
    int         i;
    int         j;
    LWLockPadded *lock;

    /* Initialize all individual LWLocks in main array */
    for (id = 0, lock = MainLWLockArray; id < NUM_INDIVIDUAL_LWLOCKS; id++, lock++)
        LWLockInitialize(&lock->lock, id);

    /* Initialize buffer mapping LWLocks in main array */
    lock = MainLWLockArray + NUM_INDIVIDUAL_LWLOCKS;
    for (id = 0; id < NUM_BUFFER_PARTITIONS; id++, lock++)
        LWLockInitialize(&lock->lock, LWTRANCHE_BUFFER_MAPPING);

    /* Initialize lmgrs' LWLocks in main array */
    lock = MainLWLockArray + NUM_INDIVIDUAL_LWLOCKS + NUM_BUFFER_PARTITIONS;
    for (id = 0; id < NUM_LOCK_PARTITIONS; id++, lock++)
        LWLockInitialize(&lock->lock, LWTRANCHE_LOCK_MANAGER);

    /* Initialize predicate lmgrs' LWLocks in main array */
    lock = MainLWLockArray + NUM_INDIVIDUAL_LWLOCKS +
        NUM_BUFFER_PARTITIONS + NUM_LOCK_PARTITIONS;
    for (id = 0; id < NUM_PREDICATELOCK_PARTITIONS; id++, lock++)
        LWLockInitialize(&lock->lock, LWTRANCHE_PREDICATE_LOCK_MANAGER);

    /* Initialize named tranches. */
    if (NamedLWLockTrancheRequests > 0)
    {
        char       *trancheNames;

        NamedLWLockTrancheArray = (NamedLWLockTranche *)
            &MainLWLockArray[NUM_FIXED_LWLOCKS + numNamedLocks];

        trancheNames = (char *) NamedLWLockTrancheArray +
            (NamedLWLockTrancheRequests * sizeof(NamedLWLockTranche));
        lock = &MainLWLockArray[NUM_FIXED_LWLOCKS];

        for (i = 0; i < NamedLWLockTrancheRequests; i++)
        {
            NamedLWLockTrancheRequest *request;
            NamedLWLockTranche *tranche;
            char       *name;

            request = &NamedLWLockTrancheRequestArray[i];
            tranche = &NamedLWLockTrancheArray[i];

            name = trancheNames;
            trancheNames += strlen(request->tranche_name) + 1;
            strcpy(name, request->tranche_name);
            tranche->trancheId = LWLockNewTrancheId();
            tranche->trancheName = name;

            for (j = 0; j < request->num_lwlocks; j++, lock++)
                LWLockInitialize(&lock->lock, tranche->trancheId);
        }
    }
}

InitLWLockAccess()

void InitLWLockAccess

(

void

)

Definition at line 536 of file lwlock.c.

Referenced by InitProcess().

{
#ifdef LWLOCK_STATS
    init_lwlock_stats();
#endif
}

LWLockAcquire()

bool LWLockAcquire	(	LWLock *	lock,
		LWLockMode	mode
	)

Definition at line 1122 of file lwlock.c.

References Assert, AssertArg, elog, ERROR, HOLD_INTERRUPTS, IsUnderPostmaster, LWLockHandle::lock, LOG_LWDEBUG, LW_EXCLUSIVE, LW_FLAG_RELEASE_OK, LW_SHARED, LWLockAttemptLock(), LWLockDequeueSelf(), LWLockQueueSelf(), LWLockReportWaitEnd(), LWLockReportWaitStart(), PGPROC::lwWaiting, MAX_BACKENDS, MAX_SIMUL_LWLOCKS, LWLockHandle::mode, MyProc, num_held_lwlocks, pg_atomic_fetch_or_u32(), pg_atomic_fetch_sub_u32(), PG_USED_FOR_ASSERTS_ONLY, PGSemaphoreLock(), PGSemaphoreUnlock(), PRINT_LWDEBUG, PGPROC::sem, LWLock::state, and T_NAME.

Referenced by _bt_end_vacuum(), _bt_start_vacuum(), _bt_vacuum_cycleid(), AbortBufferIO(), AbsorbSyncRequests(), ActivateCommitTs(), AdvanceNextFullTransactionIdPastXid(), AdvanceOldestClogXid(), AdvanceOldestCommitTsXid(), AdvanceXLInsertBuffer(), alloc_object(), AlterSystemSetConfigFile(), analyze_rel(), ApplyLauncherMain(), apw_detach_shmem(), apw_dump_now(), apw_init_shmem(), apw_load_buffers(), asyncQueueAddEntries(), asyncQueueAdvanceTail(), asyncQueueReadAllNotifications(), asyncQueueUnregister(), AsyncShmemInit(), AtAbort_Twophase(), AtPrepare_PredicateLocks(), attach_internal(), autoprewarm_main(), autoprewarm_start_worker(), AutoVacLauncherMain(), AutoVacuumRequestWork(), AutoVacWorkerMain(), BackendIdGetProc(), BackendIdGetTransactionIds(), BackendPidGetProc(), BackendXidGetPid(), BecomeLockGroupLeader(), BecomeLockGroupMember(), BootStrapCLOG(), BootStrapMultiXact(), BootStrapSUBTRANS(), BufferAlloc(), CancelDBBackends(), CancelVirtualTransaction(), check_for_freed_segments(), CheckDeadLock(), CheckForSerializableConflictOut(), CheckPointPredicate(), CheckPointRelationMap(), CheckPointReplicationOrigin(), CheckPointReplicationSlots(), CheckPointTwoPhase(), CheckRecoveryConsistency(), CheckTableForSerializableConflictIn(), CheckTargetForConflictsIn(), choose_next_subplan_for_leader(), choose_next_subplan_for_worker(), CleanupInvalidationState(), ClearOldPredicateLocks(), clog_redo(), commit_ts_redo(), copy_replication_slot(), CountDBBackends(), CountDBConnections(), CountOtherDBBackends(), CountUserBackends(), CreateCheckPoint(), CreateEndOfRecoveryRecord(), CreateInitDecodingContext(), CreatePredicateLock(), CreateRestartPoint(), DeactivateCommitTs(), DeleteChildTargetLocks(), DeleteLockTarget(), destroy_superblock(), do_autovacuum(), do_pg_start_backup(), do_pg_stop_backup(), do_start_worker(), DropAllPredicateLocksFromTable(), DropSubscription(), DropTableSpace(), dsa_allocate_extended(), dsa_dump(), dsa_free(), dsa_pin(), dsa_release_in_place(), dsa_set_size_limit(), dsa_trim(), dsa_unpin(), dshash_delete_key(), dshash_dump(), dshash_find(), dshash_find_or_insert(), dsm_attach(), dsm_create(), dsm_detach(), dsm_pin_segment(), dsm_unpin_segment(), ensure_active_superblock(), entry_reset(), Exec_ListenPreCommit(), ExecParallelHashMergeCounters(), ExecParallelHashPopChunkQueue(), ExecParallelHashTupleAlloc(), ExecParallelHashTuplePrealloc(), ExpireAllKnownAssignedTransactionIds(), ExpireOldKnownAssignedTransactionIds(), ExpireTreeKnownAssignedTransactionIds(), ExtendCLOG(), ExtendCommitTs(), ExtendMultiXactMember(), ExtendMultiXactOffset(), ExtendSUBTRANS(), FastPathGetRelationLockEntry(), FastPathTransferRelationLocks(), FinishPreparedTransaction(), FlushDatabaseBuffers(), FlushRelationBuffers(), ForceTransactionIdLimitUpdate(), ForwardSyncRequest(), FreeWorkerInfo(), GetBackgroundWorkerPid(), GetBackgroundWorkerTypeByPid(), GetBlockerStatusData(), GetConflictingVirtualXIDs(), GetCurrentVirtualXIDs(), GetLastImportantRecPtr(), GetLastSegSwitchData(), GetLatestCommitTsData(), GetLockConflicts(), GetLockStatusData(), GetMultiXactIdMembers(), GetNewMultiXactId(), GetNewObjectId(), GetNewTransactionId(), GetOldestActiveTransactionId(), GetOldestMultiXactId(), GetOldestRestartPoint(), GetOldestSafeDecodingTransactionId(), GetOldestXmin(), GetPredicateLockStatusData(), GetPreparedTransactionList(), GetRunningTransactionData(), GetRunningTransactionLocks(), GetSafeSnapshot(), GetSafeSnapshotBlockingPids(), GetSerializableTransactionSnapshotInt(), GetSnapshotData(), GetVirtualXIDsDelayingChkpt(), HandleAutoVacLauncherInterrupts(), HaveVirtualXIDsDelayingChkpt(), InstallXLogFileSegment(), InvalidateBuffer(), KnownAssignedXidsAdd(), KnownAssignedXidsReset(), lock_twophase_recover(), LockAcquireExtended(), LockBuffer(), LockErrorCleanup(), LockGXact(), LockHasWaiters(), LockRefindAndRelease(), LockRelease(), LockReleaseAll(), LockWaiterCount(), logicalrep_worker_attach(), logicalrep_worker_detach(), logicalrep_worker_launch(), logicalrep_worker_stop(), logicalrep_worker_wakeup(), MaintainOldSnapshotTimeMapping(), MarkAsPrepared(), MarkAsPreparing(), MaybeExtendOffsetSlru(), multixact_redo(), MultiXactAdvanceNextMXact(), MultiXactGetCheckptMulti(), MultiXactIdSetOldestMember(), MultiXactIdSetOldestVisible(), MultiXactSetNextMXact(), OldSerXidAdd(), OldSerXidGetMinConflictCommitSeqNo(), OldSerXidSetActiveSerXmin(), PageIsPredicateLocked(), perform_relmap_update(), pg_get_replication_slots(), pg_get_shmem_allocations(), pg_notification_queue_usage(), pg_show_replication_origin_status(), pg_stat_get_subscription(), pg_stat_get_wal_senders(), pg_stat_statements_internal(), pgss_shmem_startup(), pgss_store(), PostPrepare_Locks(), PostPrepare_MultiXact(), PostPrepare_Twophase(), PreCommit_CheckForSerializationFailure(), PreCommit_Notify(), predicatelock_twophase_recover(), PredicateLockPageSplit(), PredicateLockTwoPhaseFinish(), PrefetchBuffer(), PrescanPreparedTransactions(), ProcArrayAdd(), ProcArrayApplyRecoveryInfo(), ProcArrayApplyXidAssignment(), ProcArrayGetReplicationSlotXmin(), ProcArrayGroupClearXid(), ProcArrayInstallImportedXmin(), ProcArrayInstallRestoredXmin(), ProcArrayRemove(), ProcArraySetReplicationSlotXmin(), process_syncing_tables_for_apply(), ProcKill(), ProcSleep(), ReadBuffer_common(), ReadMultiXactCounts(), ReadNextFullTransactionId(), ReadNextMultiXactId(), ReadRecord(), RecordNewMultiXact(), RecoverPreparedTransactions(), RegisterDynamicBackgroundWorker(), RegisterPredicateLockingXid(), RelationCacheInitFilePreInvalidate(), ReleaseOneSerializableXact(), ReleasePredicateLocks(), RemoveScratchTarget(), ReplicationOriginExitCleanup(), ReplicationSlotAcquire(), ReplicationSlotCleanup(), ReplicationSlotCreate(), ReplicationSlotDropPtr(), ReplicationSlotRelease(), ReplicationSlotsComputeLogicalRestartLSN(), ReplicationSlotsComputeRequiredLSN(), ReplicationSlotsComputeRequiredXmin(), ReplicationSlotsCountDBSlots(), ReplicationSlotsDropDBSlots(), replorigin_advance(), replorigin_drop(), replorigin_get_progress(), replorigin_session_advance(), replorigin_session_get_progress(), replorigin_session_reset(), replorigin_session_setup(), resize(), RestoreScratchTarget(), restoreTwoPhaseData(), SaveSlotToPath(), SetCommitTsLimit(), SetMultiXactIdLimit(), SetOffsetVacuumLimit(), SetTransactionIdLimit(), SetXidCommitTsInPage(), SharedInvalBackendInit(), ShmemInitStruct(), SICleanupQueue(), SIGetDataEntries(), SignalBackends(), SIInsertDataEntries(), SimpleLruFlush(), SimpleLruReadPage(), SimpleLruReadPage_ReadOnly(), SimpleLruTruncate(), SimpleLruWaitIO(), SlruDeleteSegment(), SlruInternalWritePage(), SnapBuildInitialSnapshot(), ss_get_location(), StandbyRecoverPreparedTransactions(), StartBufferIO(), StartupCLOG(), StartupDecodingContext(), StartupSUBTRANS(), StartupXLOG(), sts_parallel_scan_next(), SubTransSetParent(), SummarizeOldestCommittedSxact(), SyncOneBuffer(), SyncRepCancelWait(), SyncRepCleanupAtProcExit(), SyncRepInitConfig(), SyncRepReleaseWaiters(), SyncRepUpdateSyncStandbysDefined(), SyncRepWaitForLSN(), TablespaceCreateDbspace(), tbm_shared_iterate(), TerminateBackgroundWorker(), TerminateOtherDBBackends(), TransactionGroupUpdateXidStatus(), TransactionIdGetCommitTsData(), TransactionIdIsActive(), TransactionIdIsInProgress(), TransactionIdLimitedForOldSnapshots(), TransactionIdSetPageStatus(), TransactionTreeSetCommitTsData(), TransferPredicateLocksToNewTarget(), TrimCLOG(), TrimMultiXact(), TruncateMultiXact(), TwoPhaseGetGXact(), txid_status(), UpdateMinRecoveryPoint(), vacuum_rel(), VirtualXactLock(), VirtualXactLockTableCleanup(), VirtualXactLockTableInsert(), wait_for_relation_state_change(), wait_for_worker_state_change(), WaitForReplicationWorkerAttach(), WaitIO(), WALInsertLockAcquire(), WALInsertLockAcquireExclusive(), write_relcache_init_file(), xact_redo(), XidCacheRemoveRunningXids(), xlog_redo(), and XLogBackgroundFlush().

{
    PGPROC     *proc = MyProc;
    bool        result = true;
    int         extraWaits = 0;
#ifdef LWLOCK_STATS
    lwlock_stats *lwstats;

    lwstats = get_lwlock_stats_entry(lock);
#endif

    AssertArg(mode == LW_SHARED || mode == LW_EXCLUSIVE);

    PRINT_LWDEBUG("LWLockAcquire", lock, mode);

#ifdef LWLOCK_STATS
    /* Count lock acquisition attempts */
    if (mode == LW_EXCLUSIVE)
        lwstats->ex_acquire_count++;
    else
        lwstats->sh_acquire_count++;
#endif                          /* LWLOCK_STATS */

    /*
     * We can't wait if we haven't got a PGPROC.  This should only occur
     * during bootstrap or shared memory initialization.  Put an Assert here
     * to catch unsafe coding practices.
     */
    Assert(!(proc == NULL && IsUnderPostmaster));

    /* Ensure we will have room to remember the lock */
    if (num_held_lwlocks >= MAX_SIMUL_LWLOCKS)
        elog(ERROR, "too many LWLocks taken");

    /*
     * Lock out cancel/die interrupts until we exit the code section protected
     * by the LWLock.  This ensures that interrupts will not interfere with
     * manipulations of data structures in shared memory.
     */
    HOLD_INTERRUPTS();

    /*
     * Loop here to try to acquire lock after each time we are signaled by
     * LWLockRelease.
     *
     * NOTE: it might seem better to have LWLockRelease actually grant us the
     * lock, rather than retrying and possibly having to go back to sleep. But
     * in practice that is no good because it means a process swap for every
     * lock acquisition when two or more processes are contending for the same
     * lock.  Since LWLocks are normally used to protect not-very-long
     * sections of computation, a process needs to be able to acquire and
     * release the same lock many times during a single CPU time slice, even
     * in the presence of contention.  The efficiency of being able to do that
     * outweighs the inefficiency of sometimes wasting a process dispatch
     * cycle because the lock is not free when a released waiter finally gets
     * to run.  See pgsql-hackers archives for 29-Dec-01.
     */
    for (;;)
    {
        bool        mustwait;

        /*
         * Try to grab the lock the first time, we're not in the waitqueue
         * yet/anymore.
         */
        mustwait = LWLockAttemptLock(lock, mode);

        if (!mustwait)
        {
            LOG_LWDEBUG("LWLockAcquire", lock, "immediately acquired lock");
            break;              /* got the lock */
        }

        /*
         * Ok, at this point we couldn't grab the lock on the first try. We
         * cannot simply queue ourselves to the end of the list and wait to be
         * woken up because by now the lock could long have been released.
         * Instead add us to the queue and try to grab the lock again. If we
         * succeed we need to revert the queuing and be happy, otherwise we
         * recheck the lock. If we still couldn't grab it, we know that the
         * other locker will see our queue entries when releasing since they
         * existed before we checked for the lock.
         */

        /* add to the queue */
        LWLockQueueSelf(lock, mode);

        /* we're now guaranteed to be woken up if necessary */
        mustwait = LWLockAttemptLock(lock, mode);

        /* ok, grabbed the lock the second time round, need to undo queueing */
        if (!mustwait)
        {
            LOG_LWDEBUG("LWLockAcquire", lock, "acquired, undoing queue");

            LWLockDequeueSelf(lock);
            break;
        }

        /*
         * Wait until awakened.
         *
         * Since we share the process wait semaphore with the regular lock
         * manager and ProcWaitForSignal, and we may need to acquire an LWLock
         * while one of those is pending, it is possible that we get awakened
         * for a reason other than being signaled by LWLockRelease. If so,
         * loop back and wait again.  Once we've gotten the LWLock,
         * re-increment the sema by the number of additional signals received,
         * so that the lock manager or signal manager will see the received
         * signal when it next waits.
         */
        LOG_LWDEBUG("LWLockAcquire", lock, "waiting");

#ifdef LWLOCK_STATS
        lwstats->block_count++;
#endif

        LWLockReportWaitStart(lock);
        TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), mode);

        for (;;)
        {
            PGSemaphoreLock(proc->sem);
            if (!proc->lwWaiting)
                break;
            extraWaits++;
        }

        /* Retrying, allow LWLockRelease to release waiters again. */
        pg_atomic_fetch_or_u32(&lock->state, LW_FLAG_RELEASE_OK);

#ifdef LOCK_DEBUG
        {
            /* not waiting anymore */
            uint32      nwaiters PG_USED_FOR_ASSERTS_ONLY = pg_atomic_fetch_sub_u32(&lock->nwaiters, 1);

            Assert(nwaiters < MAX_BACKENDS);
        }
#endif

        TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), mode);
        LWLockReportWaitEnd();

        LOG_LWDEBUG("LWLockAcquire", lock, "awakened");

        /* Now loop back and try to acquire lock again. */
        result = false;
    }

    TRACE_POSTGRESQL_LWLOCK_ACQUIRE(T_NAME(lock), mode);

    /* Add lock to list of locks held by this backend */
    held_lwlocks[num_held_lwlocks].lock = lock;
    held_lwlocks[num_held_lwlocks++].mode = mode;

    /*
     * Fix the process wait semaphore's count for any absorbed wakeups.
     */
    while (extraWaits-- > 0)
        PGSemaphoreUnlock(proc->sem);

    return result;
}

LWLockAcquireOrWait()

bool LWLockAcquireOrWait	(	LWLock *	lock,
		LWLockMode	mode
	)

Definition at line 1349 of file lwlock.c.

References Assert, elog, ERROR, HOLD_INTERRUPTS, LWLockHandle::lock, LOG_LWDEBUG, LW_EXCLUSIVE, LW_SHARED, LW_WAIT_UNTIL_FREE, LWLockAttemptLock(), LWLockDequeueSelf(), LWLockQueueSelf(), LWLockReportWaitEnd(), LWLockReportWaitStart(), PGPROC::lwWaiting, MAX_BACKENDS, MAX_SIMUL_LWLOCKS, LWLockHandle::mode, MyProc, num_held_lwlocks, pg_atomic_fetch_sub_u32(), PG_USED_FOR_ASSERTS_ONLY, PGSemaphoreLock(), PGSemaphoreUnlock(), PRINT_LWDEBUG, RESUME_INTERRUPTS, PGPROC::sem, and T_NAME.

Referenced by XLogFlush().

{
    PGPROC     *proc = MyProc;
    bool        mustwait;
    int         extraWaits = 0;
#ifdef LWLOCK_STATS
    lwlock_stats *lwstats;

    lwstats = get_lwlock_stats_entry(lock);
#endif

    Assert(mode == LW_SHARED || mode == LW_EXCLUSIVE);

    PRINT_LWDEBUG("LWLockAcquireOrWait", lock, mode);

    /* Ensure we will have room to remember the lock */
    if (num_held_lwlocks >= MAX_SIMUL_LWLOCKS)
        elog(ERROR, "too many LWLocks taken");

    /*
     * Lock out cancel/die interrupts until we exit the code section protected
     * by the LWLock.  This ensures that interrupts will not interfere with
     * manipulations of data structures in shared memory.
     */
    HOLD_INTERRUPTS();

    /*
     * NB: We're using nearly the same twice-in-a-row lock acquisition
     * protocol as LWLockAcquire(). Check its comments for details.
     */
    mustwait = LWLockAttemptLock(lock, mode);

    if (mustwait)
    {
        LWLockQueueSelf(lock, LW_WAIT_UNTIL_FREE);

        mustwait = LWLockAttemptLock(lock, mode);

        if (mustwait)
        {
            /*
             * Wait until awakened.  Like in LWLockAcquire, be prepared for
             * bogus wakeups, because we share the semaphore with
             * ProcWaitForSignal.
             */
            LOG_LWDEBUG("LWLockAcquireOrWait", lock, "waiting");

#ifdef LWLOCK_STATS
            lwstats->block_count++;
#endif

            LWLockReportWaitStart(lock);
            TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), mode);

            for (;;)
            {
                PGSemaphoreLock(proc->sem);
                if (!proc->lwWaiting)
                    break;
                extraWaits++;
            }

#ifdef LOCK_DEBUG
            {
                /* not waiting anymore */
                uint32      nwaiters PG_USED_FOR_ASSERTS_ONLY = pg_atomic_fetch_sub_u32(&lock->nwaiters, 1);

                Assert(nwaiters < MAX_BACKENDS);
            }
#endif
            TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), mode);
            LWLockReportWaitEnd();

            LOG_LWDEBUG("LWLockAcquireOrWait", lock, "awakened");
        }
        else
        {
            LOG_LWDEBUG("LWLockAcquireOrWait", lock, "acquired, undoing queue");

            /*
             * Got lock in the second attempt, undo queueing. We need to treat
             * this as having successfully acquired the lock, otherwise we'd
             * not necessarily wake up people we've prevented from acquiring
             * the lock.
             */
            LWLockDequeueSelf(lock);
        }
    }

    /*
     * Fix the process wait semaphore's count for any absorbed wakeups.
     */
    while (extraWaits-- > 0)
        PGSemaphoreUnlock(proc->sem);

    if (mustwait)
    {
        /* Failed to get lock, so release interrupt holdoff */
        RESUME_INTERRUPTS();
        LOG_LWDEBUG("LWLockAcquireOrWait", lock, "failed");
        TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT_FAIL(T_NAME(lock), mode);
    }
    else
    {
        LOG_LWDEBUG("LWLockAcquireOrWait", lock, "succeeded");
        /* Add lock to list of locks held by this backend */
        held_lwlocks[num_held_lwlocks].lock = lock;
        held_lwlocks[num_held_lwlocks++].mode = mode;
        TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT(T_NAME(lock), mode);
    }

    return !mustwait;
}

LWLockAttemptLock()

static bool LWLockAttemptLock ( LWLock *  lock, LWLockMode  mode  )

static

Definition at line 740 of file lwlock.c.

References AssertArg, LW_EXCLUSIVE, LW_LOCK_MASK, LW_SHARED, LW_VAL_EXCLUSIVE, LW_VAL_SHARED, MyProc, pg_atomic_compare_exchange_u32(), pg_atomic_read_u32(), pg_unreachable, and LWLock::state.

Referenced by LWLockAcquire(), LWLockAcquireOrWait(), and LWLockConditionalAcquire().

{
    uint32      old_state;

    AssertArg(mode == LW_EXCLUSIVE || mode == LW_SHARED);

    /*
     * Read once outside the loop, later iterations will get the newer value
     * via compare & exchange.
     */
    old_state = pg_atomic_read_u32(&lock->state);

    /* loop until we've determined whether we could acquire the lock or not */
    while (true)
    {
        uint32      desired_state;
        bool        lock_free;

        desired_state = old_state;

        if (mode == LW_EXCLUSIVE)
        {
            lock_free = (old_state & LW_LOCK_MASK) == 0;
            if (lock_free)
                desired_state += LW_VAL_EXCLUSIVE;
        }
        else
        {
            lock_free = (old_state & LW_VAL_EXCLUSIVE) == 0;
            if (lock_free)
                desired_state += LW_VAL_SHARED;
        }

        /*
         * Attempt to swap in the state we are expecting. If we didn't see
         * lock to be free, that's just the old value. If we saw it as free,
         * we'll attempt to mark it acquired. The reason that we always swap
         * in the value is that this doubles as a memory barrier. We could try
         * to be smarter and only swap in values if we saw the lock as free,
         * but benchmark haven't shown it as beneficial so far.
         *
         * Retry if the value changed since we last looked at it.
         */
        if (pg_atomic_compare_exchange_u32(&lock->state,
                                           &old_state, desired_state))
        {
            if (lock_free)
            {
                /* Great! Got the lock. */
#ifdef LOCK_DEBUG
                if (mode == LW_EXCLUSIVE)
                    lock->owner = MyProc;
#endif
                return false;
            }
            else
                return true;    /* somebody else has the lock */
        }
    }
    pg_unreachable();
}

LWLockConditionalAcquire()

bool LWLockConditionalAcquire	(	LWLock *	lock,
		LWLockMode	mode
	)

Definition at line 1294 of file lwlock.c.

References AssertArg, elog, ERROR, HOLD_INTERRUPTS, LWLockHandle::lock, LOG_LWDEBUG, LW_EXCLUSIVE, LW_SHARED, LWLockAttemptLock(), MAX_SIMUL_LWLOCKS, LWLockHandle::mode, num_held_lwlocks, PRINT_LWDEBUG, RESUME_INTERRUPTS, and T_NAME.

Referenced by BufferAlloc(), ConditionalLockBuffer(), ProcArrayEndTransaction(), SimpleLruWaitIO(), ss_report_location(), TransactionIdSetPageStatus(), and XLogNeedsFlush().

{
    bool        mustwait;

    AssertArg(mode == LW_SHARED || mode == LW_EXCLUSIVE);

    PRINT_LWDEBUG("LWLockConditionalAcquire", lock, mode);

    /* Ensure we will have room to remember the lock */
    if (num_held_lwlocks >= MAX_SIMUL_LWLOCKS)
        elog(ERROR, "too many LWLocks taken");

    /*
     * Lock out cancel/die interrupts until we exit the code section protected
     * by the LWLock.  This ensures that interrupts will not interfere with
     * manipulations of data structures in shared memory.
     */
    HOLD_INTERRUPTS();

    /* Check for the lock */
    mustwait = LWLockAttemptLock(lock, mode);

    if (mustwait)
    {
        /* Failed to get lock, so release interrupt holdoff */
        RESUME_INTERRUPTS();

        LOG_LWDEBUG("LWLockConditionalAcquire", lock, "failed");
        TRACE_POSTGRESQL_LWLOCK_CONDACQUIRE_FAIL(T_NAME(lock), mode);
    }
    else
    {
        /* Add lock to list of locks held by this backend */
        held_lwlocks[num_held_lwlocks].lock = lock;
        held_lwlocks[num_held_lwlocks++].mode = mode;
        TRACE_POSTGRESQL_LWLOCK_CONDACQUIRE(T_NAME(lock), mode);
    }
    return !mustwait;
}

LWLockConflictsWithVar()

static bool LWLockConflictsWithVar ( LWLock *  lock, uint64 *  valptr, uint64  oldval, uint64 *  newval, bool *  result  )

static

Definition at line 1473 of file lwlock.c.

References LW_VAL_EXCLUSIVE, LWLockWaitListLock(), LWLockWaitListUnlock(), pg_atomic_read_u32(), LWLock::state, and value.

Referenced by LWLockWaitForVar().

{
    bool        mustwait;
    uint64      value;

    /*
     * Test first to see if it the slot is free right now.
     *
     * XXX: the caller uses a spinlock before this, so we don't need a memory
     * barrier here as far as the current usage is concerned.  But that might
     * not be safe in general.
     */
    mustwait = (pg_atomic_read_u32(&lock->state) & LW_VAL_EXCLUSIVE) != 0;

    if (!mustwait)
    {
        *result = true;
        return false;
    }

    *result = false;

    /*
     * Read value using the lwlock's wait list lock, as we can't generally
     * rely on atomic 64 bit reads/stores.  TODO: On platforms with a way to
     * do atomic 64 bit reads/writes the spinlock should be optimized away.
     */
    LWLockWaitListLock(lock);
    value = *valptr;
    LWLockWaitListUnlock(lock);

    if (value != oldval)
    {
        mustwait = false;
        *newval = value;
    }
    else
    {
        mustwait = true;
    }

    return mustwait;
}

LWLockDequeueSelf()

static void LWLockDequeueSelf ( LWLock *  lock )

static

Definition at line 1027 of file lwlock.c.

References Assert, proclist_mutable_iter::cur, LW_FLAG_HAS_WAITERS, LW_FLAG_RELEASE_OK, LWLockWaitListLock(), LWLockWaitListUnlock(), PGPROC::lwWaiting, MAX_BACKENDS, MyProc, pg_atomic_fetch_and_u32(), pg_atomic_fetch_or_u32(), pg_atomic_fetch_sub_u32(), pg_atomic_read_u32(), PG_USED_FOR_ASSERTS_ONLY, PGPROC::pgprocno, PGSemaphoreLock(), PGSemaphoreUnlock(), proclist_delete, proclist_foreach_modify, proclist_is_empty(), PGPROC::sem, LWLock::state, and LWLock::waiters.

Referenced by LWLockAcquire(), LWLockAcquireOrWait(), and LWLockWaitForVar().

{
    bool        found = false;
    proclist_mutable_iter iter;

#ifdef LWLOCK_STATS
    lwlock_stats *lwstats;

    lwstats = get_lwlock_stats_entry(lock);

    lwstats->dequeue_self_count++;
#endif

    LWLockWaitListLock(lock);

    /*
     * Can't just remove ourselves from the list, but we need to iterate over
     * all entries as somebody else could have dequeued us.
     */
    proclist_foreach_modify(iter, &lock->waiters, lwWaitLink)
    {
        if (iter.cur == MyProc->pgprocno)
        {
            found = true;
            proclist_delete(&lock->waiters, iter.cur, lwWaitLink);
            break;
        }
    }

    if (proclist_is_empty(&lock->waiters) &&
        (pg_atomic_read_u32(&lock->state) & LW_FLAG_HAS_WAITERS) != 0)
    {
        pg_atomic_fetch_and_u32(&lock->state, ~LW_FLAG_HAS_WAITERS);
    }

    /* XXX: combine with fetch_and above? */
    LWLockWaitListUnlock(lock);

    /* clear waiting state again, nice for debugging */
    if (found)
        MyProc->lwWaiting = false;
    else
    {
        int         extraWaits = 0;

        /*
         * Somebody else dequeued us and has or will wake us up. Deal with the
         * superfluous absorption of a wakeup.
         */

        /*
         * Reset RELEASE_OK flag if somebody woke us before we removed
         * ourselves - they'll have set it to false.
         */
        pg_atomic_fetch_or_u32(&lock->state, LW_FLAG_RELEASE_OK);

        /*
         * Now wait for the scheduled wakeup, otherwise our ->lwWaiting would
         * get reset at some inconvenient point later. Most of the time this
         * will immediately return.
         */
        for (;;)
        {
            PGSemaphoreLock(MyProc->sem);
            if (!MyProc->lwWaiting)
                break;
            extraWaits++;
        }

        /*
         * Fix the process wait semaphore's count for any absorbed wakeups.
         */
        while (extraWaits-- > 0)
            PGSemaphoreUnlock(MyProc->sem);
    }

#ifdef LOCK_DEBUG
    {
        /* not waiting anymore */
        uint32      nwaiters PG_USED_FOR_ASSERTS_ONLY = pg_atomic_fetch_sub_u32(&lock->nwaiters, 1);

        Assert(nwaiters < MAX_BACKENDS);
    }
#endif
}

LWLockHeldByMe()

bool LWLockHeldByMe

(

LWLock *

l

)

Definition at line 1842 of file lwlock.c.

References i, and num_held_lwlocks.

Referenced by alloc_object(), check_for_freed_segments_locked(), CompactCheckpointerRequestQueue(), delete_item(), DeleteLockTarget(), dshash_dump(), ensure_active_superblock(), FlushOneBuffer(), get_best_segment(), GetOldestSafeDecodingTransactionId(), init_span(), logicalrep_sync_worker_count(), logicalrep_worker_find(), logicalrep_worker_wakeup_ptr(), logicalrep_workers_find(), make_new_segment(), MarkBufferDirtyHint(), OnConflict_CheckForSerializationFailure(), ProcArraySetReplicationSlotXmin(), ReleaseOneSerializableXact(), RemoveScratchTarget(), RemoveTargetIfNoLongerUsed(), resize(), RestoreScratchTarget(), SetNewSxactGlobalXmin(), SyncRepGetSyncRecPtr(), SyncRepGetSyncStandbys(), TransactionIdInRecentPast(), TwoPhaseGetGXact(), and UnpinBuffer().

{
    int         i;

    for (i = 0; i < num_held_lwlocks; i++)
    {
        if (held_lwlocks[i].lock == l)
            return true;
    }
    return false;
}

LWLockHeldByMeInMode()

bool LWLockHeldByMeInMode	(	LWLock *	l,
		LWLockMode	mode
	)

Definition at line 1860 of file lwlock.c.

References i, and num_held_lwlocks.

Referenced by DeleteLockTarget(), dshash_delete_entry(), dshash_release_lock(), IsBufferCleanupOK(), logicalrep_worker_cleanup(), MarkAsPreparingGuts(), MarkBufferDirty(), PrepareRedoAdd(), PrepareRedoRemove(), ProcessTwoPhaseBuffer(), RemoveGXact(), SyncRepWakeQueue(), TransactionIdSetPageStatusInternal(), and TransferPredicateLocksToNewTarget().

{
    int         i;

    for (i = 0; i < num_held_lwlocks; i++)
    {
        if (held_lwlocks[i].lock == l && held_lwlocks[i].mode == mode)
            return true;
    }
    return false;
}

LWLockInitialize()

void LWLockInitialize	(	LWLock *	lock,
		int	tranche_id
	)

Definition at line 678 of file lwlock.c.

References LW_FLAG_RELEASE_OK, pg_atomic_init_u32(), proclist_init(), LWLock::state, LWLock::tranche, and LWLock::waiters.

Referenced by apw_init_shmem(), create_internal(), dshash_create(), ExecAppendInitializeDSM(), ExecHashJoinInitializeDSM(), InitBufferPool(), InitializeLWLocks(), InitPredicateLocks(), InitProcGlobal(), ReplicationOriginShmemInit(), ReplicationSlotsShmemInit(), SimpleLruInit(), sts_initialize(), tbm_prepare_shared_iterate(), and XLOGShmemInit().

{
    pg_atomic_init_u32(&lock->state, LW_FLAG_RELEASE_OK);
#ifdef LOCK_DEBUG
    pg_atomic_init_u32(&lock->nwaiters, 0);
#endif
    lock->tranche = tranche_id;
    proclist_init(&lock->waiters);
}

LWLockNewTrancheId()

int LWLockNewTrancheId

(

void

)

Definition at line 583 of file lwlock.c.

References ShmemLock, SpinLockAcquire, and SpinLockRelease.

Referenced by apw_init_shmem(), and InitializeLWLocks().

{
    int         result;
    int        *LWLockCounter;

    LWLockCounter = (int *) ((char *) MainLWLockArray - sizeof(int));
    SpinLockAcquire(ShmemLock);
    result = (*LWLockCounter)++;
    SpinLockRelease(ShmemLock);

    return result;
}

LWLockQueueSelf()

static void LWLockQueueSelf ( LWLock *  lock, LWLockMode  mode  )

static

Definition at line 983 of file lwlock.c.

References elog, LW_FLAG_HAS_WAITERS, LW_WAIT_UNTIL_FREE, LWLockWaitListLock(), LWLockWaitListUnlock(), PGPROC::lwWaiting, PGPROC::lwWaitMode, LWLockHandle::mode, MyProc, PANIC, pg_atomic_fetch_add_u32(), pg_atomic_fetch_or_u32(), PGPROC::pgprocno, proclist_push_head, proclist_push_tail, LWLock::state, and LWLock::waiters.

Referenced by LWLockAcquire(), LWLockAcquireOrWait(), and LWLockWaitForVar().

{
    /*
     * If we don't have a PGPROC structure, there's no way to wait. This
     * should never occur, since MyProc should only be null during shared
     * memory initialization.
     */
    if (MyProc == NULL)
        elog(PANIC, "cannot wait without a PGPROC structure");

    if (MyProc->lwWaiting)
        elog(PANIC, "queueing for lock while waiting on another one");

    LWLockWaitListLock(lock);

    /* setting the flag is protected by the spinlock */
    pg_atomic_fetch_or_u32(&lock->state, LW_FLAG_HAS_WAITERS);

    MyProc->lwWaiting = true;
    MyProc->lwWaitMode = mode;

    /* LW_WAIT_UNTIL_FREE waiters are always at the front of the queue */
    if (mode == LW_WAIT_UNTIL_FREE)
        proclist_push_head(&lock->waiters, MyProc->pgprocno, lwWaitLink);
    else
        proclist_push_tail(&lock->waiters, MyProc->pgprocno, lwWaitLink);

    /* Can release the mutex now */
    LWLockWaitListUnlock(lock);

#ifdef LOCK_DEBUG
    pg_atomic_fetch_add_u32(&lock->nwaiters, 1);
#endif

}

LWLockRegisterTranche()

void LWLockRegisterTranche	(	int	tranche_id,
		const char *	tranche_name
	)

Definition at line 603 of file lwlock.c.

References Assert, i, LWLockTrancheArray, LWLockTranchesAllocated, and repalloc().

Referenced by apw_init_shmem(), CreateSharedProcArray(), InitBufferPool(), RegisterLWLockTranches(), ReplicationOriginShmemInit(), ReplicationSlotsShmemInit(), SimpleLruInit(), and XLOGShmemInit().

{
    Assert(LWLockTrancheArray != NULL);

    if (tranche_id >= LWLockTranchesAllocated)
    {
        int         i = LWLockTranchesAllocated;
        int         j = LWLockTranchesAllocated;

        while (i <= tranche_id)
            i *= 2;

        LWLockTrancheArray = (const char **)
            repalloc(LWLockTrancheArray, i * sizeof(char *));
        LWLockTranchesAllocated = i;
        while (j < LWLockTranchesAllocated)
            LWLockTrancheArray[j++] = NULL;
    }

    LWLockTrancheArray[tranche_id] = tranche_name;
}

LWLockRelease()

void LWLockRelease

(

LWLock *

lock

)

Definition at line 1726 of file lwlock.c.

References Assert, elog, ERROR, i, LOG_LWDEBUG, LW_EXCLUSIVE, LW_FLAG_HAS_WAITERS, LW_FLAG_RELEASE_OK, LW_LOCK_MASK, LW_VAL_EXCLUSIVE, LW_VAL_SHARED, LWLockWakeup(), LWLockHandle::mode, num_held_lwlocks, pg_atomic_sub_fetch_u32(), PRINT_LWDEBUG, RESUME_INTERRUPTS, and T_NAME.

Referenced by _bt_end_vacuum(), _bt_start_vacuum(), _bt_vacuum_cycleid(), AbsorbSyncRequests(), ActivateCommitTs(), AdvanceNextFullTransactionIdPastXid(), AdvanceOldestClogXid(), AdvanceOldestCommitTsXid(), AdvanceXLInsertBuffer(), alloc_object(), AlterSystemSetConfigFile(), analyze_rel(), ApplyLauncherMain(), apw_detach_shmem(), apw_dump_now(), apw_init_shmem(), apw_load_buffers(), asyncQueueAddEntries(), asyncQueueAdvanceTail(), asyncQueueReadAllNotifications(), asyncQueueUnregister(), AsyncShmemInit(), AtAbort_Twophase(), AtPrepare_PredicateLocks(), attach_internal(), autoprewarm_main(), autoprewarm_start_worker(), AutoVacLauncherMain(), AutoVacuumRequestWork(), AutoVacWorkerMain(), BackendIdGetProc(), BackendIdGetTransactionIds(), BackendPidGetProc(), BackendXidGetPid(), BecomeLockGroupLeader(), BecomeLockGroupMember(), BootStrapCLOG(), BootStrapMultiXact(), BootStrapSUBTRANS(), BufferAlloc(), CancelDBBackends(), CancelVirtualTransaction(), check_for_freed_segments(), CheckDeadLock(), CheckForSerializableConflictOut(), CheckPointPredicate(), CheckPointRelationMap(), CheckPointReplicationOrigin(), CheckPointReplicationSlots(), CheckPointTwoPhase(), CheckRecoveryConsistency(), CheckTableForSerializableConflictIn(), CheckTargetForConflictsIn(), choose_next_subplan_for_leader(), choose_next_subplan_for_worker(), CleanupInvalidationState(), ClearOldPredicateLocks(), clog_redo(), commit_ts_redo(), copy_replication_slot(), CountDBBackends(), CountDBConnections(), CountOtherDBBackends(), CountUserBackends(), CreateCheckPoint(), CreateEndOfRecoveryRecord(), CreateInitDecodingContext(), CreatePredicateLock(), CreateRestartPoint(), DeactivateCommitTs(), DeleteChildTargetLocks(), DeleteLockTarget(), destroy_superblock(), do_autovacuum(), do_pg_start_backup(), do_pg_stop_backup(), do_start_worker(), DropAllPredicateLocksFromTable(), DropSubscription(), DropTableSpace(), dsa_allocate_extended(), dsa_dump(), dsa_free(), dsa_pin(), dsa_release_in_place(), dsa_set_size_limit(), dsa_trim(), dsa_unpin(), dshash_delete_entry(), dshash_delete_key(), dshash_dump(), dshash_find(), dshash_find_or_insert(), dshash_release_lock(), dsm_attach(), dsm_create(), dsm_detach(), dsm_pin_segment(), dsm_unpin_segment(), ensure_active_superblock(), entry_reset(), Exec_ListenPreCommit(), ExecParallelHashMergeCounters(), ExecParallelHashPopChunkQueue(), ExecParallelHashTupleAlloc(), ExecParallelHashTuplePrealloc(), ExpireAllKnownAssignedTransactionIds(), ExpireOldKnownAssignedTransactionIds(), ExpireTreeKnownAssignedTransactionIds(), ExtendCLOG(), ExtendCommitTs(), ExtendMultiXactMember(), ExtendMultiXactOffset(), ExtendSUBTRANS(), FastPathGetRelationLockEntry(), FastPathTransferRelationLocks(), find_multixact_start(), FinishPreparedTransaction(), FlushDatabaseBuffers(), FlushRelationBuffers(), ForceTransactionIdLimitUpdate(), ForwardSyncRequest(), FreeWorkerInfo(), GetBackgroundWorkerPid(), GetBackgroundWorkerTypeByPid(), GetBlockerStatusData(), GetConflictingVirtualXIDs(), GetCurrentVirtualXIDs(), GetLastImportantRecPtr(), GetLastSegSwitchData(), GetLatestCommitTsData(), GetLockConflicts(), GetLockStatusData(), GetMultiXactIdMembers(), GetNewMultiXactId(), GetNewObjectId(), GetNewTransactionId(), GetOldestActiveTransactionId(), GetOldestMultiXactId(), GetOldestRestartPoint(), GetOldestSafeDecodingTransactionId(), GetOldestXmin(), GetPredicateLockStatusData(), GetPreparedTransactionList(), GetRunningTransactionLocks(), GetSafeSnapshot(), GetSafeSnapshotBlockingPids(), GetSerializableTransactionSnapshotInt(), GetSnapshotData(), GetVirtualXIDsDelayingChkpt(), HandleAutoVacLauncherInterrupts(), HaveVirtualXIDsDelayingChkpt(), InstallXLogFileSegment(), InvalidateBuffer(), KnownAssignedXidsAdd(), KnownAssignedXidsReset(), lock_twophase_recover(), LockAcquireExtended(), LockBuffer(), LockErrorCleanup(), LockGXact(), LockHasWaiters(), LockRefindAndRelease(), LockRelease(), LockReleaseAll(), LockWaiterCount(), logicalrep_worker_attach(), logicalrep_worker_detach(), logicalrep_worker_launch(), logicalrep_worker_stop(), logicalrep_worker_wakeup(), LogStandbySnapshot(), LWLockReleaseAll(), LWLockReleaseClearVar(), MaintainOldSnapshotTimeMapping(), MarkAsPrepared(), MarkAsPreparing(), MaybeExtendOffsetSlru(), multixact_redo(), MultiXactAdvanceNextMXact(), MultiXactGetCheckptMulti(), MultiXactIdSetOldestMember(), MultiXactIdSetOldestVisible(), MultiXactSetNextMXact(), OldSerXidAdd(), OldSerXidGetMinConflictCommitSeqNo(), OldSerXidSetActiveSerXmin(), OnConflict_CheckForSerializationFailure(), PageIsPredicateLocked(), perform_relmap_update(), pg_get_replication_slots(), pg_get_shmem_allocations(), pg_notification_queue_usage(), pg_show_replication_origin_status(), pg_stat_get_subscription(), pg_stat_get_wal_senders(), pg_stat_statements_internal(), pgss_shmem_startup(), pgss_store(), PostPrepare_Locks(), PostPrepare_MultiXact(), PostPrepare_Twophase(), PreCommit_CheckForSerializationFailure(), PreCommit_Notify(), predicatelock_twophase_recover(), PredicateLockPageSplit(), PredicateLockTwoPhaseFinish(), PrefetchBuffer(), PrescanPreparedTransactions(), ProcArrayAdd(), ProcArrayApplyRecoveryInfo(), ProcArrayApplyXidAssignment(), ProcArrayEndTransaction(), ProcArrayGetReplicationSlotXmin(), ProcArrayGroupClearXid(), ProcArrayInstallImportedXmin(), ProcArrayInstallRestoredXmin(), ProcArrayRemove(), ProcArraySetReplicationSlotXmin(), process_syncing_tables_for_apply(), ProcKill(), ProcSleep(), ReadMultiXactCounts(), ReadNextFullTransactionId(), ReadNextMultiXactId(), ReadRecord(), RecordNewMultiXact(), RecoverPreparedTransactions(), RegisterDynamicBackgroundWorker(), RegisterPredicateLockingXid(), RelationCacheInitFilePostInvalidate(), ReleaseOneSerializableXact(), ReleasePredicateLocks(), RemoveScratchTarget(), ReplicationOriginExitCleanup(), ReplicationSlotAcquire(), ReplicationSlotCleanup(), ReplicationSlotCreate(), ReplicationSlotDropPtr(), ReplicationSlotRelease(), ReplicationSlotsComputeLogicalRestartLSN(), ReplicationSlotsComputeRequiredLSN(), ReplicationSlotsComputeRequiredXmin(), ReplicationSlotsCountDBSlots(), ReplicationSlotsDropDBSlots(), replorigin_advance(), replorigin_drop(), replorigin_get_progress(), replorigin_session_advance(), replorigin_session_get_progress(), replorigin_session_reset(), replorigin_session_setup(), resize(), RestoreScratchTarget(), restoreTwoPhaseData(), SaveSlotToPath(), SetCommitTsLimit(), SetMultiXactIdLimit(), SetOffsetVacuumLimit(), SetTransactionIdLimit(), SetXidCommitTsInPage(), SharedInvalBackendInit(), ShmemInitStruct(), SICleanupQueue(), SIGetDataEntries(), SignalBackends(), SIInsertDataEntries(), SimpleLruFlush(), SimpleLruReadPage(), SimpleLruReadPage_ReadOnly(), SimpleLruTruncate(), SimpleLruWaitIO(), SlruDeleteSegment(), SlruInternalWritePage(), SnapBuildInitialSnapshot(), ss_get_location(), ss_report_location(), StandbyRecoverPreparedTransactions(), StartBufferIO(), StartupCLOG(), StartupDecodingContext(), StartupSUBTRANS(), StartupXLOG(), sts_parallel_scan_next(), SubTransGetParent(), SubTransSetParent(), SummarizeOldestCommittedSxact(), SyncOneBuffer(), SyncRepCancelWait(), SyncRepCleanupAtProcExit(), SyncRepInitConfig(), SyncRepReleaseWaiters(), SyncRepUpdateSyncStandbysDefined(), SyncRepWaitForLSN(), TablespaceCreateDbspace(), tbm_shared_iterate(), TerminateBackgroundWorker(), TerminateBufferIO(), TerminateOtherDBBackends(), TransactionGroupUpdateXidStatus(), TransactionIdGetCommitTsData(), TransactionIdGetStatus(), TransactionIdIsActive(), TransactionIdIsInProgress(), TransactionIdLimitedForOldSnapshots(), TransactionIdSetPageStatus(), TransactionTreeSetCommitTsData(), TransferPredicateLocksToNewTarget(), TrimCLOG(), TrimMultiXact(), TruncateMultiXact(), TwoPhaseGetGXact(), txid_status(), UpdateMinRecoveryPoint(), vacuum_rel(), VirtualXactLock(), VirtualXactLockTableCleanup(), VirtualXactLockTableInsert(), wait_for_relation_state_change(), wait_for_worker_state_change(), WaitForReplicationWorkerAttach(), WaitIO(), WaitOnLock(), write_relcache_init_file(), xact_redo(), XidCacheRemoveRunningXids(), xlog_redo(), XLogBackgroundFlush(), XLogFlush(), and XLogNeedsFlush().

{
    LWLockMode  mode;
    uint32      oldstate;
    bool        check_waiters;
    int         i;

    /*
     * Remove lock from list of locks held.  Usually, but not always, it will
     * be the latest-acquired lock; so search array backwards.
     */
    for (i = num_held_lwlocks; --i >= 0;)
        if (lock == held_lwlocks[i].lock)
            break;

    if (i < 0)
        elog(ERROR, "lock %s is not held", T_NAME(lock));

    mode = held_lwlocks[i].mode;

    num_held_lwlocks--;
    for (; i < num_held_lwlocks; i++)
        held_lwlocks[i] = held_lwlocks[i + 1];

    PRINT_LWDEBUG("LWLockRelease", lock, mode);

    /*
     * Release my hold on lock, after that it can immediately be acquired by
     * others, even if we still have to wakeup other waiters.
     */
    if (mode == LW_EXCLUSIVE)
        oldstate = pg_atomic_sub_fetch_u32(&lock->state, LW_VAL_EXCLUSIVE);
    else
        oldstate = pg_atomic_sub_fetch_u32(&lock->state, LW_VAL_SHARED);

    /* nobody else can have that kind of lock */
    Assert(!(oldstate & LW_VAL_EXCLUSIVE));


    /*
     * We're still waiting for backends to get scheduled, don't wake them up
     * again.
     */
    if ((oldstate & (LW_FLAG_HAS_WAITERS | LW_FLAG_RELEASE_OK)) ==
        (LW_FLAG_HAS_WAITERS | LW_FLAG_RELEASE_OK) &&
        (oldstate & LW_LOCK_MASK) == 0)
        check_waiters = true;
    else
        check_waiters = false;

    /*
     * As waking up waiters requires the spinlock to be acquired, only do so
     * if necessary.
     */
    if (check_waiters)
    {
        /* XXX: remove before commit? */
        LOG_LWDEBUG("LWLockRelease", lock, "releasing waiters");
        LWLockWakeup(lock);
    }

    TRACE_POSTGRESQL_LWLOCK_RELEASE(T_NAME(lock));

    /*
     * Now okay to allow cancel/die interrupts.
     */
    RESUME_INTERRUPTS();
}

LWLockReleaseAll()

void LWLockReleaseAll

(

void

)

Definition at line 1825 of file lwlock.c.

References HOLD_INTERRUPTS, LWLockRelease(), and num_held_lwlocks.

Referenced by AbortSubTransaction(), AbortTransaction(), AutoVacLauncherMain(), AuxiliaryProcKill(), BackgroundWriterMain(), CheckpointerMain(), ProcKill(), ShutdownAuxiliaryProcess(), WalSndErrorCleanup(), and WalWriterMain().

{
    while (num_held_lwlocks > 0)
    {
        HOLD_INTERRUPTS();      /* match the upcoming RESUME_INTERRUPTS */

        LWLockRelease(held_lwlocks[num_held_lwlocks - 1].lock);
    }
}

LWLockReleaseClearVar()

void LWLockReleaseClearVar	(	LWLock *	lock,
		uint64 *	valptr,
		uint64	val
	)

Definition at line 1799 of file lwlock.c.

References LWLockRelease(), LWLockWaitListLock(), LWLockWaitListUnlock(), and val.

Referenced by WALInsertLockRelease().

{
    LWLockWaitListLock(lock);

    /*
     * Set the variable's value before releasing the lock, that prevents race
     * a race condition wherein a new locker acquires the lock, but hasn't yet
     * set the variables value.
     */
    *valptr = val;
    LWLockWaitListUnlock(lock);

    LWLockRelease(lock);
}

LWLockReportWaitEnd()

static void LWLockReportWaitEnd ( void  )

inlinestatic

Definition at line 705 of file lwlock.c.

References pgstat_report_wait_end().

Referenced by LWLockAcquire(), LWLockAcquireOrWait(), and LWLockWaitForVar().

{
    pgstat_report_wait_end();
}

LWLockReportWaitStart()

static void LWLockReportWaitStart ( LWLock *  lock )

inlinestatic

Definition at line 696 of file lwlock.c.

References PG_WAIT_LWLOCK, pgstat_report_wait_start(), and LWLock::tranche.

Referenced by LWLockAcquire(), LWLockAcquireOrWait(), and LWLockWaitForVar().

{
    pgstat_report_wait_start(PG_WAIT_LWLOCK | lock->tranche);
}

LWLockShmemSize()

Size LWLockShmemSize

(

void

)

Definition at line 349 of file lwlock.c.

References add_size(), i, lock_named_request_allowed, LWLOCK_PADDED_SIZE, mul_size(), NamedLWLockTrancheRequests, NUM_FIXED_LWLOCKS, and NumLWLocksByNamedTranches().

Referenced by CreateLWLocks(), and CreateSharedMemoryAndSemaphores().

{
    Size        size;
    int         i;
    int         numLocks = NUM_FIXED_LWLOCKS;

    numLocks += NumLWLocksByNamedTranches();

    /* Space for the LWLock array. */
    size = mul_size(numLocks, sizeof(LWLockPadded));

    /* Space for dynamic allocation counter, plus room for alignment. */
    size = add_size(size, sizeof(int) + LWLOCK_PADDED_SIZE);

    /* space for named tranches. */
    size = add_size(size, mul_size(NamedLWLockTrancheRequests, sizeof(NamedLWLockTranche)));

    /* space for name of each tranche. */
    for (i = 0; i < NamedLWLockTrancheRequests; i++)
        size = add_size(size, strlen(NamedLWLockTrancheRequestArray[i].tranche_name) + 1);

    /* Disallow named LWLocks' requests after startup */
    lock_named_request_allowed = false;

    return size;
}

LWLockUpdateVar()

void LWLockUpdateVar	(	LWLock *	lock,
		uint64 *	valptr,
		uint64	val
	)

Definition at line 1672 of file lwlock.c.

References Assert, proclist_mutable_iter::cur, GetPGProcByNumber, LW_EXCLUSIVE, LW_VAL_EXCLUSIVE, LW_WAIT_UNTIL_FREE, LWLockWaitListLock(), LWLockWaitListUnlock(), PGPROC::lwWaiting, PGPROC::lwWaitMode, pg_atomic_read_u32(), pg_write_barrier, PGSemaphoreUnlock(), PRINT_LWDEBUG, proclist_delete, proclist_foreach_modify, proclist_init(), proclist_push_tail, PGPROC::sem, LWLock::state, val, and LWLock::waiters.

Referenced by WALInsertLockAcquireExclusive(), and WALInsertLockUpdateInsertingAt().

{
    proclist_head wakeup;
    proclist_mutable_iter iter;

    PRINT_LWDEBUG("LWLockUpdateVar", lock, LW_EXCLUSIVE);

    proclist_init(&wakeup);

    LWLockWaitListLock(lock);

    Assert(pg_atomic_read_u32(&lock->state) & LW_VAL_EXCLUSIVE);

    /* Update the lock's value */
    *valptr = val;

    /*
     * See if there are any LW_WAIT_UNTIL_FREE waiters that need to be woken
     * up. They are always in the front of the queue.
     */
    proclist_foreach_modify(iter, &lock->waiters, lwWaitLink)
    {
        PGPROC     *waiter = GetPGProcByNumber(iter.cur);

        if (waiter->lwWaitMode != LW_WAIT_UNTIL_FREE)
            break;

        proclist_delete(&lock->waiters, iter.cur, lwWaitLink);
        proclist_push_tail(&wakeup, iter.cur, lwWaitLink);
    }

    /* We are done updating shared state of the lock itself. */
    LWLockWaitListUnlock(lock);

    /*
     * Awaken any waiters I removed from the queue.
     */
    proclist_foreach_modify(iter, &wakeup, lwWaitLink)
    {
        PGPROC     *waiter = GetPGProcByNumber(iter.cur);

        proclist_delete(&wakeup, iter.cur, lwWaitLink);
        /* check comment in LWLockWakeup() about this barrier */
        pg_write_barrier();
        waiter->lwWaiting = false;
        PGSemaphoreUnlock(waiter->sem);
    }
}

LWLockWaitForVar()

bool LWLockWaitForVar	(	LWLock *	lock,
		uint64 *	valptr,
		uint64	oldval,
		uint64 *	newval
	)

Definition at line 1533 of file lwlock.c.

References Assert, HOLD_INTERRUPTS, LOG_LWDEBUG, LW_EXCLUSIVE, LW_FLAG_RELEASE_OK, LW_WAIT_UNTIL_FREE, LWLockConflictsWithVar(), LWLockDequeueSelf(), LWLockQueueSelf(), LWLockReportWaitEnd(), LWLockReportWaitStart(), PGPROC::lwWaiting, MAX_BACKENDS, MyProc, pg_atomic_fetch_or_u32(), pg_atomic_fetch_sub_u32(), PG_USED_FOR_ASSERTS_ONLY, PGSemaphoreLock(), PGSemaphoreUnlock(), PRINT_LWDEBUG, RESUME_INTERRUPTS, PGPROC::sem, LWLock::state, and T_NAME.

Referenced by WaitXLogInsertionsToFinish().

{
    PGPROC     *proc = MyProc;
    int         extraWaits = 0;
    bool        result = false;
#ifdef LWLOCK_STATS
    lwlock_stats *lwstats;

    lwstats = get_lwlock_stats_entry(lock);
#endif

    PRINT_LWDEBUG("LWLockWaitForVar", lock, LW_WAIT_UNTIL_FREE);

    /*
     * Lock out cancel/die interrupts while we sleep on the lock.  There is no
     * cleanup mechanism to remove us from the wait queue if we got
     * interrupted.
     */
    HOLD_INTERRUPTS();

    /*
     * Loop here to check the lock's status after each time we are signaled.
     */
    for (;;)
    {
        bool        mustwait;

        mustwait = LWLockConflictsWithVar(lock, valptr, oldval, newval,
                                          &result);

        if (!mustwait)
            break;              /* the lock was free or value didn't match */

        /*
         * Add myself to wait queue. Note that this is racy, somebody else
         * could wakeup before we're finished queuing. NB: We're using nearly
         * the same twice-in-a-row lock acquisition protocol as
         * LWLockAcquire(). Check its comments for details. The only
         * difference is that we also have to check the variable's values when
         * checking the state of the lock.
         */
        LWLockQueueSelf(lock, LW_WAIT_UNTIL_FREE);

        /*
         * Set RELEASE_OK flag, to make sure we get woken up as soon as the
         * lock is released.
         */
        pg_atomic_fetch_or_u32(&lock->state, LW_FLAG_RELEASE_OK);

        /*
         * We're now guaranteed to be woken up if necessary. Recheck the lock
         * and variables state.
         */
        mustwait = LWLockConflictsWithVar(lock, valptr, oldval, newval,
                                          &result);

        /* Ok, no conflict after we queued ourselves. Undo queueing. */
        if (!mustwait)
        {
            LOG_LWDEBUG("LWLockWaitForVar", lock, "free, undoing queue");

            LWLockDequeueSelf(lock);
            break;
        }

        /*
         * Wait until awakened.
         *
         * Since we share the process wait semaphore with the regular lock
         * manager and ProcWaitForSignal, and we may need to acquire an LWLock
         * while one of those is pending, it is possible that we get awakened
         * for a reason other than being signaled by LWLockRelease. If so,
         * loop back and wait again.  Once we've gotten the LWLock,
         * re-increment the sema by the number of additional signals received,
         * so that the lock manager or signal manager will see the received
         * signal when it next waits.
         */
        LOG_LWDEBUG("LWLockWaitForVar", lock, "waiting");

#ifdef LWLOCK_STATS
        lwstats->block_count++;
#endif

        LWLockReportWaitStart(lock);
        TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), LW_EXCLUSIVE);

        for (;;)
        {
            PGSemaphoreLock(proc->sem);
            if (!proc->lwWaiting)
                break;
            extraWaits++;
        }

#ifdef LOCK_DEBUG
        {
            /* not waiting anymore */
            uint32      nwaiters PG_USED_FOR_ASSERTS_ONLY = pg_atomic_fetch_sub_u32(&lock->nwaiters, 1);

            Assert(nwaiters < MAX_BACKENDS);
        }
#endif

        TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), LW_EXCLUSIVE);
        LWLockReportWaitEnd();

        LOG_LWDEBUG("LWLockWaitForVar", lock, "awakened");

        /* Now loop back and check the status of the lock again. */
    }

    TRACE_POSTGRESQL_LWLOCK_ACQUIRE(T_NAME(lock), LW_EXCLUSIVE);

    /*
     * Fix the process wait semaphore's count for any absorbed wakeups.
     */
    while (extraWaits-- > 0)
        PGSemaphoreUnlock(proc->sem);

    /*
     * Now okay to allow cancel/die interrupts.
     */
    RESUME_INTERRUPTS();

    return result;
}

LWLockWaitListLock()

static void LWLockWaitListLock ( LWLock *  lock )

static

Definition at line 811 of file lwlock.c.

References SpinDelayStatus::delays, finish_spin_delay(), init_local_spin_delay, LW_FLAG_LOCKED, perform_spin_delay(), pg_atomic_fetch_or_u32(), pg_atomic_read_u32(), and LWLock::state.

Referenced by LWLockConflictsWithVar(), LWLockDequeueSelf(), LWLockQueueSelf(), LWLockReleaseClearVar(), LWLockUpdateVar(), and LWLockWakeup().

{
    uint32      old_state;
#ifdef LWLOCK_STATS
    lwlock_stats *lwstats;
    uint32      delays = 0;

    lwstats = get_lwlock_stats_entry(lock);
#endif

    while (true)
    {
        /* always try once to acquire lock directly */
        old_state = pg_atomic_fetch_or_u32(&lock->state, LW_FLAG_LOCKED);
        if (!(old_state & LW_FLAG_LOCKED))
            break;              /* got lock */

        /* and then spin without atomic operations until lock is released */
        {
            SpinDelayStatus delayStatus;

            init_local_spin_delay(&delayStatus);

            while (old_state & LW_FLAG_LOCKED)
            {
                perform_spin_delay(&delayStatus);
                old_state = pg_atomic_read_u32(&lock->state);
            }
#ifdef LWLOCK_STATS
            delays += delayStatus.delays;
#endif
            finish_spin_delay(&delayStatus);
        }

        /*
         * Retry. The lock might obviously already be re-acquired by the time
         * we're attempting to get it again.
         */
    }

#ifdef LWLOCK_STATS
    lwstats->spin_delay_count += delays;
#endif
}

LWLockWaitListUnlock()

static void LWLockWaitListUnlock ( LWLock *  lock )

static

Definition at line 863 of file lwlock.c.

References Assert, LW_FLAG_LOCKED, pg_atomic_fetch_and_u32(), PG_USED_FOR_ASSERTS_ONLY, and LWLock::state.

Referenced by LWLockConflictsWithVar(), LWLockDequeueSelf(), LWLockQueueSelf(), LWLockReleaseClearVar(), and LWLockUpdateVar().

{
    uint32      old_state PG_USED_FOR_ASSERTS_ONLY;

    old_state = pg_atomic_fetch_and_u32(&lock->state, ~LW_FLAG_LOCKED);

    Assert(old_state & LW_FLAG_LOCKED);
}

LWLockWakeup()

static void LWLockWakeup ( LWLock *  lock )

static

Definition at line 876 of file lwlock.c.

References Assert, proclist_mutable_iter::cur, GetPGProcByNumber, LOG_LWDEBUG, LW_EXCLUSIVE, LW_FLAG_HAS_WAITERS, LW_FLAG_LOCKED, LW_FLAG_RELEASE_OK, LW_WAIT_UNTIL_FREE, LWLockWaitListLock(), PGPROC::lwWaiting, PGPROC::lwWaitMode, pg_atomic_compare_exchange_u32(), pg_atomic_read_u32(), pg_write_barrier, PGSemaphoreUnlock(), proclist_delete, proclist_foreach_modify, proclist_init(), proclist_is_empty(), proclist_push_tail, PGPROC::sem, LWLock::state, and LWLock::waiters.

Referenced by LWLockRelease().

{
    bool        new_release_ok;
    bool        wokeup_somebody = false;
    proclist_head wakeup;
    proclist_mutable_iter iter;

    proclist_init(&wakeup);

    new_release_ok = true;

    /* lock wait list while collecting backends to wake up */
    LWLockWaitListLock(lock);

    proclist_foreach_modify(iter, &lock->waiters, lwWaitLink)
    {
        PGPROC     *waiter = GetPGProcByNumber(iter.cur);

        if (wokeup_somebody && waiter->lwWaitMode == LW_EXCLUSIVE)
            continue;

        proclist_delete(&lock->waiters, iter.cur, lwWaitLink);
        proclist_push_tail(&wakeup, iter.cur, lwWaitLink);

        if (waiter->lwWaitMode != LW_WAIT_UNTIL_FREE)
        {
            /*
             * Prevent additional wakeups until retryer gets to run. Backends
             * that are just waiting for the lock to become free don't retry
             * automatically.
             */
            new_release_ok = false;

            /*
             * Don't wakeup (further) exclusive locks.
             */
            wokeup_somebody = true;
        }

        /*
         * Once we've woken up an exclusive lock, there's no point in waking
         * up anybody else.
         */
        if (waiter->lwWaitMode == LW_EXCLUSIVE)
            break;
    }

    Assert(proclist_is_empty(&wakeup) || pg_atomic_read_u32(&lock->state) & LW_FLAG_HAS_WAITERS);

    /* unset required flags, and release lock, in one fell swoop */
    {
        uint32      old_state;
        uint32      desired_state;

        old_state = pg_atomic_read_u32(&lock->state);
        while (true)
        {
            desired_state = old_state;

            /* compute desired flags */

            if (new_release_ok)
                desired_state |= LW_FLAG_RELEASE_OK;
            else
                desired_state &= ~LW_FLAG_RELEASE_OK;

            if (proclist_is_empty(&wakeup))
                desired_state &= ~LW_FLAG_HAS_WAITERS;

            desired_state &= ~LW_FLAG_LOCKED;   /* release lock */

            if (pg_atomic_compare_exchange_u32(&lock->state, &old_state,
                                               desired_state))
                break;
        }
    }

    /* Awaken any waiters I removed from the queue. */
    proclist_foreach_modify(iter, &wakeup, lwWaitLink)
    {
        PGPROC     *waiter = GetPGProcByNumber(iter.cur);

        LOG_LWDEBUG("LWLockRelease", lock, "release waiter");
        proclist_delete(&wakeup, iter.cur, lwWaitLink);

        /*
         * Guarantee that lwWaiting being unset only becomes visible once the
         * unlink from the link has completed. Otherwise the target backend
         * could be woken up for other reason and enqueue for a new lock - if
         * that happens before the list unlink happens, the list would end up
         * being corrupted.
         *
         * The barrier pairs with the LWLockWaitListLock() when enqueuing for
         * another lock.
         */
        pg_write_barrier();
        waiter->lwWaiting = false;
        PGSemaphoreUnlock(waiter->sem);
    }
}

NumLWLocksByNamedTranches()

static int NumLWLocksByNamedTranches ( void  )

static

Definition at line 334 of file lwlock.c.

References i, and NamedLWLockTrancheRequests.

Referenced by InitializeLWLocks(), and LWLockShmemSize().

{
    int         numLocks = 0;
    int         i;

    for (i = 0; i < NamedLWLockTrancheRequests; i++)
        numLocks += NamedLWLockTrancheRequestArray[i].num_lwlocks;

    return numLocks;
}

RegisterLWLockTranches()

static void RegisterLWLockTranches ( void  )

static

Definition at line 491 of file lwlock.c.

References Assert, i, LWLockRegisterTranche(), LWLockTrancheArray, LWLockTranchesAllocated, LWTRANCHE_BUFFER_MAPPING, LWTRANCHE_FIRST_USER_DEFINED, LWTRANCHE_LOCK_MANAGER, LWTRANCHE_PARALLEL_APPEND, LWTRANCHE_PARALLEL_HASH_JOIN, LWTRANCHE_PARALLEL_QUERY_DSA, LWTRANCHE_PREDICATE_LOCK_MANAGER, LWTRANCHE_SESSION_DSA, LWTRANCHE_SESSION_RECORD_TABLE, LWTRANCHE_SESSION_TYPMOD_TABLE, LWTRANCHE_SHARED_TUPLESTORE, LWTRANCHE_SXACT, LWTRANCHE_TBM, MainLWLockNames, MemoryContextAllocZero(), NamedLWLockTrancheRequests, and TopMemoryContext.

Referenced by CreateLWLocks().

{
    int         i;

    if (LWLockTrancheArray == NULL)
    {
        LWLockTranchesAllocated = 128;
        LWLockTrancheArray = (const char **)
            MemoryContextAllocZero(TopMemoryContext,
                                   LWLockTranchesAllocated * sizeof(char *));
        Assert(LWLockTranchesAllocated >= LWTRANCHE_FIRST_USER_DEFINED);
    }

    for (i = 0; i < NUM_INDIVIDUAL_LWLOCKS; ++i)
        LWLockRegisterTranche(i, MainLWLockNames[i]);

    LWLockRegisterTranche(LWTRANCHE_BUFFER_MAPPING, "buffer_mapping");
    LWLockRegisterTranche(LWTRANCHE_LOCK_MANAGER, "lock_manager");
    LWLockRegisterTranche(LWTRANCHE_PREDICATE_LOCK_MANAGER,
                          "predicate_lock_manager");
    LWLockRegisterTranche(LWTRANCHE_PARALLEL_QUERY_DSA,
                          "parallel_query_dsa");
    LWLockRegisterTranche(LWTRANCHE_SESSION_DSA,
                          "session_dsa");
    LWLockRegisterTranche(LWTRANCHE_SESSION_RECORD_TABLE,
                          "session_record_table");
    LWLockRegisterTranche(LWTRANCHE_SESSION_TYPMOD_TABLE,
                          "session_typmod_table");
    LWLockRegisterTranche(LWTRANCHE_SHARED_TUPLESTORE,
                          "shared_tuplestore");
    LWLockRegisterTranche(LWTRANCHE_TBM, "tbm");
    LWLockRegisterTranche(LWTRANCHE_PARALLEL_APPEND, "parallel_append");
    LWLockRegisterTranche(LWTRANCHE_PARALLEL_HASH_JOIN, "parallel_hash_join");
    LWLockRegisterTranche(LWTRANCHE_SXACT, "serializable_xact");

    /* Register named tranches. */
    for (i = 0; i < NamedLWLockTrancheRequests; i++)
        LWLockRegisterTranche(NamedLWLockTrancheArray[i].trancheId,
                              NamedLWLockTrancheArray[i].trancheName);
}

RequestNamedLWLockTranche()

void RequestNamedLWLockTranche	(	const char *	tranche_name,
		int	num_lwlocks
	)

Definition at line 638 of file lwlock.c.

References Assert, i, IsUnderPostmaster, lock_named_request_allowed, MemoryContextAlloc(), NAMEDATALEN, NamedLWLockTrancheRequests, NamedLWLockTrancheRequestsAllocated, NamedLWLockTrancheRequest::num_lwlocks, repalloc(), StrNCpy, TopMemoryContext, and NamedLWLockTrancheRequest::tranche_name.

Referenced by _PG_init().

{
    NamedLWLockTrancheRequest *request;

    if (IsUnderPostmaster || !lock_named_request_allowed)
        return;                 /* too late */

    if (NamedLWLockTrancheRequestArray == NULL)
    {
        NamedLWLockTrancheRequestsAllocated = 16;
        NamedLWLockTrancheRequestArray = (NamedLWLockTrancheRequest *)
            MemoryContextAlloc(TopMemoryContext,
                               NamedLWLockTrancheRequestsAllocated
                               * sizeof(NamedLWLockTrancheRequest));
    }

    if (NamedLWLockTrancheRequests >= NamedLWLockTrancheRequestsAllocated)
    {
        int         i = NamedLWLockTrancheRequestsAllocated;

        while (i <= NamedLWLockTrancheRequests)
            i *= 2;

        NamedLWLockTrancheRequestArray = (NamedLWLockTrancheRequest *)
            repalloc(NamedLWLockTrancheRequestArray,
                     i * sizeof(NamedLWLockTrancheRequest));
        NamedLWLockTrancheRequestsAllocated = i;
    }

    request = &NamedLWLockTrancheRequestArray[NamedLWLockTrancheRequests];
    Assert(strlen(tranche_name) + 1 < NAMEDATALEN);
    StrNCpy(request->tranche_name, tranche_name, NAMEDATALEN);
    request->num_lwlocks = num_lwlocks;
    NamedLWLockTrancheRequests++;
}

Variable Documentation

held_lwlocks

LWLockHandle held_lwlocks[MAX_SIMUL_LWLOCKS]

static

Definition at line 143 of file lwlock.c.

lock_named_request_allowed

bool lock_named_request_allowed = true

static

Definition at line 158 of file lwlock.c.

Referenced by LWLockShmemSize(), and RequestNamedLWLockTranche().

LWLockTrancheArray

const char** LWLockTrancheArray = NULL

static

Definition at line 114 of file lwlock.c.

Referenced by GetLWLockIdentifier(), LWLockRegisterTranche(), and RegisterLWLockTranches().

LWLockTranchesAllocated

int LWLockTranchesAllocated = 0

static

Definition at line 115 of file lwlock.c.

Referenced by GetLWLockIdentifier(), LWLockRegisterTranche(), and RegisterLWLockTranches().

MainLWLockArray

LWLockPadded* MainLWLockArray = NULL

Definition at line 125 of file lwlock.c.

Referenced by PostmasterMarkPIDForWorkerNotify().

NamedLWLockTrancheArray

NamedLWLockTranche* NamedLWLockTrancheArray = NULL

Definition at line 156 of file lwlock.c.

Referenced by PostmasterMarkPIDForWorkerNotify().

NamedLWLockTrancheRequestArray

NamedLWLockTrancheRequest* NamedLWLockTrancheRequestArray = NULL

Definition at line 152 of file lwlock.c.

NamedLWLockTrancheRequests

int NamedLWLockTrancheRequests = 0

Definition at line 154 of file lwlock.c.

Referenced by GetNamedLWLockTranche(), InitializeLWLocks(), LWLockShmemSize(), NumLWLocksByNamedTranches(), PostmasterMarkPIDForWorkerNotify(), RegisterLWLockTranches(), and RequestNamedLWLockTranche().

NamedLWLockTrancheRequestsAllocated

int NamedLWLockTrancheRequestsAllocated = 0

static

Definition at line 153 of file lwlock.c.

Referenced by RequestNamedLWLockTranche().

num_held_lwlocks

int num_held_lwlocks = 0

static

Definition at line 142 of file lwlock.c.

Referenced by LWLockAcquire(), LWLockAcquireOrWait(), LWLockConditionalAcquire(), LWLockHeldByMe(), LWLockHeldByMeInMode(), LWLockRelease(), and LWLockReleaseAll().

ShmemLock

slock_t* ShmemLock

Definition at line 88 of file shmem.c.

Referenced by InitShmemAllocation(), LWLockNewTrancheId(), PostmasterMarkPIDForWorkerNotify(), and ShmemAllocRaw().