lockfuncs.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * lockfuncs.c
 *      Functions for SQL access to various lock-manager capabilities.
 *
 * Copyright (c) 2002-2019, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *      src/backend/utils/adt/lockfuncs.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/htup_details.h"
#include "access/xact.h"
#include "catalog/pg_type.h"
#include "funcapi.h"
#include "miscadmin.h"
#include "storage/predicate_internals.h"
#include "utils/array.h"
#include "utils/builtins.h"


/* This must match enum LockTagType! */
const char *const LockTagTypeNames[] = {
    "relation",
    "extend",
    "page",
    "tuple",
    "transactionid",
    "virtualxid",
    "speculative token",
    "object",
    "userlock",
    "advisory"
};

/* This must match enum PredicateLockTargetType (predicate_internals.h) */
static const char *const PredicateLockTagTypeNames[] = {
    "relation",
    "page",
    "tuple"
};

/* Working status for pg_lock_status */
typedef struct
{
    LockData   *lockData;       /* state data from lmgr */
    int         currIdx;        /* current PROCLOCK index */
    PredicateLockData *predLockData;    /* state data for pred locks */
    int         predLockIdx;    /* current index for pred lock */
} PG_Lock_Status;

/* Number of columns in pg_locks output */
#define NUM_LOCK_STATUS_COLUMNS     15

/*
 * VXIDGetDatum - Construct a text representation of a VXID
 *
 * This is currently only used in pg_lock_status, so we put it here.
 */
static Datum
VXIDGetDatum(BackendId bid, LocalTransactionId lxid)
{
    /*
     * The representation is "<bid>/<lxid>", decimal and unsigned decimal
     * respectively.  Note that elog.c also knows how to format a vxid.
     */
    char        vxidstr[32];

    snprintf(vxidstr, sizeof(vxidstr), "%d/%u", bid, lxid);

    return CStringGetTextDatum(vxidstr);
}


/*
 * pg_lock_status - produce a view with one row per held or awaited lock mode
 */
Datum
pg_lock_status(PG_FUNCTION_ARGS)
{
    FuncCallContext *funcctx;
    PG_Lock_Status *mystatus;
    LockData   *lockData;
    PredicateLockData *predLockData;

    if (SRF_IS_FIRSTCALL())
    {
        TupleDesc   tupdesc;
        MemoryContext oldcontext;

        /* create a function context for cross-call persistence */
        funcctx = SRF_FIRSTCALL_INIT();

        /*
         * switch to memory context appropriate for multiple function calls
         */
        oldcontext = MemoryContextSwitchTo(funcctx->multi_call_memory_ctx);

        /* build tupdesc for result tuples */
        /* this had better match function's declaration in pg_proc.h */
        tupdesc = CreateTemplateTupleDesc(NUM_LOCK_STATUS_COLUMNS);
        TupleDescInitEntry(tupdesc, (AttrNumber) 1, "locktype",
                           TEXTOID, -1, 0);
        TupleDescInitEntry(tupdesc, (AttrNumber) 2, "database",
                           OIDOID, -1, 0);
        TupleDescInitEntry(tupdesc, (AttrNumber) 3, "relation",
                           OIDOID, -1, 0);
        TupleDescInitEntry(tupdesc, (AttrNumber) 4, "page",
                           INT4OID, -1, 0);
        TupleDescInitEntry(tupdesc, (AttrNumber) 5, "tuple",
                           INT2OID, -1, 0);
        TupleDescInitEntry(tupdesc, (AttrNumber) 6, "virtualxid",
                           TEXTOID, -1, 0);
        TupleDescInitEntry(tupdesc, (AttrNumber) 7, "transactionid",
                           XIDOID, -1, 0);
        TupleDescInitEntry(tupdesc, (AttrNumber) 8, "classid",
                           OIDOID, -1, 0);
        TupleDescInitEntry(tupdesc, (AttrNumber) 9, "objid",
                           OIDOID, -1, 0);
        TupleDescInitEntry(tupdesc, (AttrNumber) 10, "objsubid",
                           INT2OID, -1, 0);
        TupleDescInitEntry(tupdesc, (AttrNumber) 11, "virtualtransaction",
                           TEXTOID, -1, 0);
        TupleDescInitEntry(tupdesc, (AttrNumber) 12, "pid",
                           INT4OID, -1, 0);
        TupleDescInitEntry(tupdesc, (AttrNumber) 13, "mode",
                           TEXTOID, -1, 0);
        TupleDescInitEntry(tupdesc, (AttrNumber) 14, "granted",
                           BOOLOID, -1, 0);
        TupleDescInitEntry(tupdesc, (AttrNumber) 15, "fastpath",
                           BOOLOID, -1, 0);

        funcctx->tuple_desc = BlessTupleDesc(tupdesc);

        /*
         * Collect all the locking information that we will format and send
         * out as a result set.
         */
        mystatus = (PG_Lock_Status *) palloc(sizeof(PG_Lock_Status));
        funcctx->user_fctx = (void *) mystatus;

        mystatus->lockData = GetLockStatusData();
        mystatus->currIdx = 0;
        mystatus->predLockData = GetPredicateLockStatusData();
        mystatus->predLockIdx = 0;

        MemoryContextSwitchTo(oldcontext);
    }

    funcctx = SRF_PERCALL_SETUP();
    mystatus = (PG_Lock_Status *) funcctx->user_fctx;
    lockData = mystatus->lockData;

    while (mystatus->currIdx < lockData->nelements)
    {
        bool        granted;
        LOCKMODE    mode = 0;
        const char *locktypename;
        char        tnbuf[32];
        Datum       values[NUM_LOCK_STATUS_COLUMNS];
        bool        nulls[NUM_LOCK_STATUS_COLUMNS];
        HeapTuple   tuple;
        Datum       result;
        LockInstanceData *instance;

        instance = &(lockData->locks[mystatus->currIdx]);

        /*
         * Look to see if there are any held lock modes in this PROCLOCK. If
         * so, report, and destructively modify lockData so we don't report
         * again.
         */
        granted = false;
        if (instance->holdMask)
        {
            for (mode = 0; mode < MAX_LOCKMODES; mode++)
            {
                if (instance->holdMask & LOCKBIT_ON(mode))
                {
                    granted = true;
                    instance->holdMask &= LOCKBIT_OFF(mode);
                    break;
                }
            }
        }

        /*
         * If no (more) held modes to report, see if PROC is waiting for a
         * lock on this lock.
         */
        if (!granted)
        {
            if (instance->waitLockMode != NoLock)
            {
                /* Yes, so report it with proper mode */
                mode = instance->waitLockMode;

                /*
                 * We are now done with this PROCLOCK, so advance pointer to
                 * continue with next one on next call.
                 */
                mystatus->currIdx++;
            }
            else
            {
                /*
                 * Okay, we've displayed all the locks associated with this
                 * PROCLOCK, proceed to the next one.
                 */
                mystatus->currIdx++;
                continue;
            }
        }

        /*
         * Form tuple with appropriate data.
         */
        MemSet(values, 0, sizeof(values));
        MemSet(nulls, false, sizeof(nulls));

        if (instance->locktag.locktag_type <= LOCKTAG_LAST_TYPE)
            locktypename = LockTagTypeNames[instance->locktag.locktag_type];
        else
        {
            snprintf(tnbuf, sizeof(tnbuf), "unknown %d",
                     (int) instance->locktag.locktag_type);
            locktypename = tnbuf;
        }
        values[0] = CStringGetTextDatum(locktypename);

        switch ((LockTagType) instance->locktag.locktag_type)
        {
            case LOCKTAG_RELATION:
            case LOCKTAG_RELATION_EXTEND:
                values[1] = ObjectIdGetDatum(instance->locktag.locktag_field1);
                values[2] = ObjectIdGetDatum(instance->locktag.locktag_field2);
                nulls[3] = true;
                nulls[4] = true;
                nulls[5] = true;
                nulls[6] = true;
                nulls[7] = true;
                nulls[8] = true;
                nulls[9] = true;
                break;
            case LOCKTAG_PAGE:
                values[1] = ObjectIdGetDatum(instance->locktag.locktag_field1);
                values[2] = ObjectIdGetDatum(instance->locktag.locktag_field2);
                values[3] = UInt32GetDatum(instance->locktag.locktag_field3);
                nulls[4] = true;
                nulls[5] = true;
                nulls[6] = true;
                nulls[7] = true;
                nulls[8] = true;
                nulls[9] = true;
                break;
            case LOCKTAG_TUPLE:
                values[1] = ObjectIdGetDatum(instance->locktag.locktag_field1);
                values[2] = ObjectIdGetDatum(instance->locktag.locktag_field2);
                values[3] = UInt32GetDatum(instance->locktag.locktag_field3);
                values[4] = UInt16GetDatum(instance->locktag.locktag_field4);
                nulls[5] = true;
                nulls[6] = true;
                nulls[7] = true;
                nulls[8] = true;
                nulls[9] = true;
                break;
            case LOCKTAG_TRANSACTION:
                values[6] =
                    TransactionIdGetDatum(instance->locktag.locktag_field1);
                nulls[1] = true;
                nulls[2] = true;
                nulls[3] = true;
                nulls[4] = true;
                nulls[5] = true;
                nulls[7] = true;
                nulls[8] = true;
                nulls[9] = true;
                break;
            case LOCKTAG_VIRTUALTRANSACTION:
                values[5] = VXIDGetDatum(instance->locktag.locktag_field1,
                                         instance->locktag.locktag_field2);
                nulls[1] = true;
                nulls[2] = true;
                nulls[3] = true;
                nulls[4] = true;
                nulls[6] = true;
                nulls[7] = true;
                nulls[8] = true;
                nulls[9] = true;
                break;
            case LOCKTAG_OBJECT:
            case LOCKTAG_USERLOCK:
            case LOCKTAG_ADVISORY:
            default:            /* treat unknown locktags like OBJECT */
                values[1] = ObjectIdGetDatum(instance->locktag.locktag_field1);
                values[7] = ObjectIdGetDatum(instance->locktag.locktag_field2);
                values[8] = ObjectIdGetDatum(instance->locktag.locktag_field3);
                values[9] = Int16GetDatum(instance->locktag.locktag_field4);
                nulls[2] = true;
                nulls[3] = true;
                nulls[4] = true;
                nulls[5] = true;
                nulls[6] = true;
                break;
        }

        values[10] = VXIDGetDatum(instance->backend, instance->lxid);
        if (instance->pid != 0)
            values[11] = Int32GetDatum(instance->pid);
        else
            nulls[11] = true;
        values[12] = CStringGetTextDatum(GetLockmodeName(instance->locktag.locktag_lockmethodid, mode));
        values[13] = BoolGetDatum(granted);
        values[14] = BoolGetDatum(instance->fastpath);

        tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
        result = HeapTupleGetDatum(tuple);
        SRF_RETURN_NEXT(funcctx, result);
    }

    /*
     * Have returned all regular locks. Now start on the SIREAD predicate
     * locks.
     */
    predLockData = mystatus->predLockData;
    if (mystatus->predLockIdx < predLockData->nelements)
    {
        PredicateLockTargetType lockType;

        PREDICATELOCKTARGETTAG *predTag = &(predLockData->locktags[mystatus->predLockIdx]);
        SERIALIZABLEXACT *xact = &(predLockData->xacts[mystatus->predLockIdx]);
        Datum       values[NUM_LOCK_STATUS_COLUMNS];
        bool        nulls[NUM_LOCK_STATUS_COLUMNS];
        HeapTuple   tuple;
        Datum       result;

        mystatus->predLockIdx++;

        /*
         * Form tuple with appropriate data.
         */
        MemSet(values, 0, sizeof(values));
        MemSet(nulls, false, sizeof(nulls));

        /* lock type */
        lockType = GET_PREDICATELOCKTARGETTAG_TYPE(*predTag);

        values[0] = CStringGetTextDatum(PredicateLockTagTypeNames[lockType]);

        /* lock target */
        values[1] = GET_PREDICATELOCKTARGETTAG_DB(*predTag);
        values[2] = GET_PREDICATELOCKTARGETTAG_RELATION(*predTag);
        if (lockType == PREDLOCKTAG_TUPLE)
            values[4] = GET_PREDICATELOCKTARGETTAG_OFFSET(*predTag);
        else
            nulls[4] = true;
        if ((lockType == PREDLOCKTAG_TUPLE) ||
            (lockType == PREDLOCKTAG_PAGE))
            values[3] = GET_PREDICATELOCKTARGETTAG_PAGE(*predTag);
        else
            nulls[3] = true;

        /* these fields are targets for other types of locks */
        nulls[5] = true;        /* virtualxid */
        nulls[6] = true;        /* transactionid */
        nulls[7] = true;        /* classid */
        nulls[8] = true;        /* objid */
        nulls[9] = true;        /* objsubid */

        /* lock holder */
        values[10] = VXIDGetDatum(xact->vxid.backendId,
                                  xact->vxid.localTransactionId);
        if (xact->pid != 0)
            values[11] = Int32GetDatum(xact->pid);
        else
            nulls[11] = true;

        /*
         * Lock mode. Currently all predicate locks are SIReadLocks, which are
         * always held (never waiting) and have no fast path
         */
        values[12] = CStringGetTextDatum("SIReadLock");
        values[13] = BoolGetDatum(true);
        values[14] = BoolGetDatum(false);

        tuple = heap_form_tuple(funcctx->tuple_desc, values, nulls);
        result = HeapTupleGetDatum(tuple);
        SRF_RETURN_NEXT(funcctx, result);
    }

    SRF_RETURN_DONE(funcctx);
}


/*
 * pg_blocking_pids - produce an array of the PIDs blocking given PID
 *
 * The reported PIDs are those that hold a lock conflicting with blocked_pid's
 * current request (hard block), or are requesting such a lock and are ahead
 * of blocked_pid in the lock's wait queue (soft block).
 *
 * In parallel-query cases, we report all PIDs blocking any member of the
 * given PID's lock group, and the reported PIDs are those of the blocking
 * PIDs' lock group leaders.  This allows callers to compare the result to
 * lists of clients' pg_backend_pid() results even during a parallel query.
 *
 * Parallel query makes it possible for there to be duplicate PIDs in the
 * result (either because multiple waiters are blocked by same PID, or
 * because multiple blockers have same group leader PID).  We do not bother
 * to eliminate such duplicates from the result.
 *
 * We need not consider predicate locks here, since those don't block anything.
 */
Datum
pg_blocking_pids(PG_FUNCTION_ARGS)
{
    int         blocked_pid = PG_GETARG_INT32(0);
    Datum      *arrayelems;
    int         narrayelems;
    BlockedProcsData *lockData; /* state data from lmgr */
    int         i,
                j;

    /* Collect a snapshot of lock manager state */
    lockData = GetBlockerStatusData(blocked_pid);

    /* We can't need more output entries than there are reported PROCLOCKs */
    arrayelems = (Datum *) palloc(lockData->nlocks * sizeof(Datum));
    narrayelems = 0;

    /* For each blocked proc in the lock group ... */
    for (i = 0; i < lockData->nprocs; i++)
    {
        BlockedProcData *bproc = &lockData->procs[i];
        LockInstanceData *instances = &lockData->locks[bproc->first_lock];
        int        *preceding_waiters = &lockData->waiter_pids[bproc->first_waiter];
        LockInstanceData *blocked_instance;
        LockMethod  lockMethodTable;
        int         conflictMask;

        /*
         * Locate the blocked proc's own entry in the LockInstanceData array.
         * There should be exactly one matching entry.
         */
        blocked_instance = NULL;
        for (j = 0; j < bproc->num_locks; j++)
        {
            LockInstanceData *instance = &(instances[j]);

            if (instance->pid == bproc->pid)
            {
                Assert(blocked_instance == NULL);
                blocked_instance = instance;
            }
        }
        Assert(blocked_instance != NULL);

        lockMethodTable = GetLockTagsMethodTable(&(blocked_instance->locktag));
        conflictMask = lockMethodTable->conflictTab[blocked_instance->waitLockMode];

        /* Now scan the PROCLOCK data for conflicting procs */
        for (j = 0; j < bproc->num_locks; j++)
        {
            LockInstanceData *instance = &(instances[j]);

            /* A proc never blocks itself, so ignore that entry */
            if (instance == blocked_instance)
                continue;
            /* Members of same lock group never block each other, either */
            if (instance->leaderPid == blocked_instance->leaderPid)
                continue;

            if (conflictMask & instance->holdMask)
            {
                /* hard block: blocked by lock already held by this entry */
            }
            else if (instance->waitLockMode != NoLock &&
                     (conflictMask & LOCKBIT_ON(instance->waitLockMode)))
            {
                /* conflict in lock requests; who's in front in wait queue? */
                bool        ahead = false;
                int         k;

                for (k = 0; k < bproc->num_waiters; k++)
                {
                    if (preceding_waiters[k] == instance->pid)
                    {
                        /* soft block: this entry is ahead of blocked proc */
                        ahead = true;
                        break;
                    }
                }
                if (!ahead)
                    continue;   /* not blocked by this entry */
            }
            else
            {
                /* not blocked by this entry */
                continue;
            }

            /* blocked by this entry, so emit a record */
            arrayelems[narrayelems++] = Int32GetDatum(instance->leaderPid);
        }
    }

    /* Assert we didn't overrun arrayelems[] */
    Assert(narrayelems <= lockData->nlocks);

    /* Construct array, using hardwired knowledge about int4 type */
    PG_RETURN_ARRAYTYPE_P(construct_array(arrayelems, narrayelems,
                                          INT4OID,
                                          sizeof(int32), true, 'i'));
}


/*
 * pg_safe_snapshot_blocking_pids - produce an array of the PIDs blocking
 * given PID from getting a safe snapshot
 *
 * XXX this does not consider parallel-query cases; not clear how big a
 * problem that is in practice
 */
Datum
pg_safe_snapshot_blocking_pids(PG_FUNCTION_ARGS)
{
    int         blocked_pid = PG_GETARG_INT32(0);
    int        *blockers;
    int         num_blockers;
    Datum      *blocker_datums;

    /* A buffer big enough for any possible blocker list without truncation */
    blockers = (int *) palloc(MaxBackends * sizeof(int));

    /* Collect a snapshot of processes waited for by GetSafeSnapshot */
    num_blockers =
        GetSafeSnapshotBlockingPids(blocked_pid, blockers, MaxBackends);

    /* Convert int array to Datum array */
    if (num_blockers > 0)
    {
        int         i;

        blocker_datums = (Datum *) palloc(num_blockers * sizeof(Datum));
        for (i = 0; i < num_blockers; ++i)
            blocker_datums[i] = Int32GetDatum(blockers[i]);
    }
    else
        blocker_datums = NULL;

    /* Construct array, using hardwired knowledge about int4 type */
    PG_RETURN_ARRAYTYPE_P(construct_array(blocker_datums, num_blockers,
                                          INT4OID,
                                          sizeof(int32), true, 'i'));
}


/*
 * pg_isolation_test_session_is_blocked - support function for isolationtester
 *
 * Check if specified PID is blocked by any of the PIDs listed in the second
 * argument.  Currently, this looks for blocking caused by waiting for
 * heavyweight locks or safe snapshots.  We ignore blockage caused by PIDs
 * not directly under the isolationtester's control, eg autovacuum.
 *
 * This is an undocumented function intended for use by the isolation tester,
 * and may change in future releases as required for testing purposes.
 */
Datum
pg_isolation_test_session_is_blocked(PG_FUNCTION_ARGS)
{
    int         blocked_pid = PG_GETARG_INT32(0);
    ArrayType  *interesting_pids_a = PG_GETARG_ARRAYTYPE_P(1);
    ArrayType  *blocking_pids_a;
    int32      *interesting_pids;
    int32      *blocking_pids;
    int         num_interesting_pids;
    int         num_blocking_pids;
    int         dummy;
    int         i,
                j;

    /* Validate the passed-in array */
    Assert(ARR_ELEMTYPE(interesting_pids_a) == INT4OID);
    if (array_contains_nulls(interesting_pids_a))
        elog(ERROR, "array must not contain nulls");
    interesting_pids = (int32 *) ARR_DATA_PTR(interesting_pids_a);
    num_interesting_pids = ArrayGetNItems(ARR_NDIM(interesting_pids_a),
                                          ARR_DIMS(interesting_pids_a));

    /*
     * Get the PIDs of all sessions blocking the given session's attempt to
     * acquire heavyweight locks.
     */
    blocking_pids_a =
        DatumGetArrayTypeP(DirectFunctionCall1(pg_blocking_pids, blocked_pid));

    Assert(ARR_ELEMTYPE(blocking_pids_a) == INT4OID);
    Assert(!array_contains_nulls(blocking_pids_a));
    blocking_pids = (int32 *) ARR_DATA_PTR(blocking_pids_a);
    num_blocking_pids = ArrayGetNItems(ARR_NDIM(blocking_pids_a),
                                       ARR_DIMS(blocking_pids_a));

    /*
     * Check if any of these are in the list of interesting PIDs, that being
     * the sessions that the isolation tester is running.  We don't use
     * "arrayoverlaps" here, because it would lead to cache lookups and one of
     * our goals is to run quickly under CLOBBER_CACHE_ALWAYS.  We expect
     * blocking_pids to be usually empty and otherwise a very small number in
     * isolation tester cases, so make that the outer loop of a naive search
     * for a match.
     */
    for (i = 0; i < num_blocking_pids; i++)
        for (j = 0; j < num_interesting_pids; j++)
        {
            if (blocking_pids[i] == interesting_pids[j])
                PG_RETURN_BOOL(true);
        }

    /*
     * Check if blocked_pid is waiting for a safe snapshot.  We could in
     * theory check the resulting array of blocker PIDs against the
     * interesting PIDs whitelist, but since there is no danger of autovacuum
     * blocking GetSafeSnapshot there seems to be no point in expending cycles
     * on allocating a buffer and searching for overlap; so it's presently
     * sufficient for the isolation tester's purposes to use a single element
     * buffer and check if the number of safe snapshot blockers is non-zero.
     */
    if (GetSafeSnapshotBlockingPids(blocked_pid, &dummy, 1) > 0)
        PG_RETURN_BOOL(true);

    PG_RETURN_BOOL(false);
}


/*
 * Functions for manipulating advisory locks
 *
 * We make use of the locktag fields as follows:
 *
 *  field1: MyDatabaseId ... ensures locks are local to each database
 *  field2: first of 2 int4 keys, or high-order half of an int8 key
 *  field3: second of 2 int4 keys, or low-order half of an int8 key
 *  field4: 1 if using an int8 key, 2 if using 2 int4 keys
 */
#define SET_LOCKTAG_INT64(tag, key64) \
    SET_LOCKTAG_ADVISORY(tag, \
                         MyDatabaseId, \
                         (uint32) ((key64) >> 32), \
                         (uint32) (key64), \
                         1)
#define SET_LOCKTAG_INT32(tag, key1, key2) \
    SET_LOCKTAG_ADVISORY(tag, MyDatabaseId, key1, key2, 2)

/*
 * pg_advisory_lock(int8) - acquire exclusive lock on an int8 key
 */
Datum
pg_advisory_lock_int8(PG_FUNCTION_ARGS)
{
    int64       key = PG_GETARG_INT64(0);
    LOCKTAG     tag;

    SET_LOCKTAG_INT64(tag, key);

    (void) LockAcquire(&tag, ExclusiveLock, true, false);

    PG_RETURN_VOID();
}

/*
 * pg_advisory_xact_lock(int8) - acquire xact scoped
 * exclusive lock on an int8 key
 */
Datum
pg_advisory_xact_lock_int8(PG_FUNCTION_ARGS)
{
    int64       key = PG_GETARG_INT64(0);
    LOCKTAG     tag;

    SET_LOCKTAG_INT64(tag, key);

    (void) LockAcquire(&tag, ExclusiveLock, false, false);

    PG_RETURN_VOID();
}

/*
 * pg_advisory_lock_shared(int8) - acquire share lock on an int8 key
 */
Datum
pg_advisory_lock_shared_int8(PG_FUNCTION_ARGS)
{
    int64       key = PG_GETARG_INT64(0);
    LOCKTAG     tag;

    SET_LOCKTAG_INT64(tag, key);

    (void) LockAcquire(&tag, ShareLock, true, false);

    PG_RETURN_VOID();
}

/*
 * pg_advisory_xact_lock_shared(int8) - acquire xact scoped
 * share lock on an int8 key
 */
Datum
pg_advisory_xact_lock_shared_int8(PG_FUNCTION_ARGS)
{
    int64       key = PG_GETARG_INT64(0);
    LOCKTAG     tag;

    SET_LOCKTAG_INT64(tag, key);

    (void) LockAcquire(&tag, ShareLock, false, false);

    PG_RETURN_VOID();
}

/*
 * pg_try_advisory_lock(int8) - acquire exclusive lock on an int8 key, no wait
 *
 * Returns true if successful, false if lock not available
 */
Datum
pg_try_advisory_lock_int8(PG_FUNCTION_ARGS)
{
    int64       key = PG_GETARG_INT64(0);
    LOCKTAG     tag;
    LockAcquireResult res;

    SET_LOCKTAG_INT64(tag, key);

    res = LockAcquire(&tag, ExclusiveLock, true, true);

    PG_RETURN_BOOL(res != LOCKACQUIRE_NOT_AVAIL);
}

/*
 * pg_try_advisory_xact_lock(int8) - acquire xact scoped
 * exclusive lock on an int8 key, no wait
 *
 * Returns true if successful, false if lock not available
 */
Datum
pg_try_advisory_xact_lock_int8(PG_FUNCTION_ARGS)
{
    int64       key = PG_GETARG_INT64(0);
    LOCKTAG     tag;
    LockAcquireResult res;

    SET_LOCKTAG_INT64(tag, key);

    res = LockAcquire(&tag, ExclusiveLock, false, true);

    PG_RETURN_BOOL(res != LOCKACQUIRE_NOT_AVAIL);
}

/*
 * pg_try_advisory_lock_shared(int8) - acquire share lock on an int8 key, no wait
 *
 * Returns true if successful, false if lock not available
 */
Datum
pg_try_advisory_lock_shared_int8(PG_FUNCTION_ARGS)
{
    int64       key = PG_GETARG_INT64(0);
    LOCKTAG     tag;
    LockAcquireResult res;

    SET_LOCKTAG_INT64(tag, key);

    res = LockAcquire(&tag, ShareLock, true, true);

    PG_RETURN_BOOL(res != LOCKACQUIRE_NOT_AVAIL);
}

/*
 * pg_try_advisory_xact_lock_shared(int8) - acquire xact scoped
 * share lock on an int8 key, no wait
 *
 * Returns true if successful, false if lock not available
 */
Datum
pg_try_advisory_xact_lock_shared_int8(PG_FUNCTION_ARGS)
{
    int64       key = PG_GETARG_INT64(0);
    LOCKTAG     tag;
    LockAcquireResult res;

    SET_LOCKTAG_INT64(tag, key);

    res = LockAcquire(&tag, ShareLock, false, true);

    PG_RETURN_BOOL(res != LOCKACQUIRE_NOT_AVAIL);
}

/*
 * pg_advisory_unlock(int8) - release exclusive lock on an int8 key
 *
 * Returns true if successful, false if lock was not held
*/
Datum
pg_advisory_unlock_int8(PG_FUNCTION_ARGS)
{
    int64       key = PG_GETARG_INT64(0);
    LOCKTAG     tag;
    bool        res;

    SET_LOCKTAG_INT64(tag, key);

    res = LockRelease(&tag, ExclusiveLock, true);

    PG_RETURN_BOOL(res);
}

/*
 * pg_advisory_unlock_shared(int8) - release share lock on an int8 key
 *
 * Returns true if successful, false if lock was not held
 */
Datum
pg_advisory_unlock_shared_int8(PG_FUNCTION_ARGS)
{
    int64       key = PG_GETARG_INT64(0);
    LOCKTAG     tag;
    bool        res;

    SET_LOCKTAG_INT64(tag, key);

    res = LockRelease(&tag, ShareLock, true);

    PG_RETURN_BOOL(res);
}

/*
 * pg_advisory_lock(int4, int4) - acquire exclusive lock on 2 int4 keys
 */
Datum
pg_advisory_lock_int4(PG_FUNCTION_ARGS)
{
    int32       key1 = PG_GETARG_INT32(0);
    int32       key2 = PG_GETARG_INT32(1);
    LOCKTAG     tag;

    SET_LOCKTAG_INT32(tag, key1, key2);

    (void) LockAcquire(&tag, ExclusiveLock, true, false);

    PG_RETURN_VOID();
}

/*
 * pg_advisory_xact_lock(int4, int4) - acquire xact scoped
 * exclusive lock on 2 int4 keys
 */
Datum
pg_advisory_xact_lock_int4(PG_FUNCTION_ARGS)
{
    int32       key1 = PG_GETARG_INT32(0);
    int32       key2 = PG_GETARG_INT32(1);
    LOCKTAG     tag;

    SET_LOCKTAG_INT32(tag, key1, key2);

    (void) LockAcquire(&tag, ExclusiveLock, false, false);

    PG_RETURN_VOID();
}

/*
 * pg_advisory_lock_shared(int4, int4) - acquire share lock on 2 int4 keys
 */
Datum
pg_advisory_lock_shared_int4(PG_FUNCTION_ARGS)
{
    int32       key1 = PG_GETARG_INT32(0);
    int32       key2 = PG_GETARG_INT32(1);
    LOCKTAG     tag;

    SET_LOCKTAG_INT32(tag, key1, key2);

    (void) LockAcquire(&tag, ShareLock, true, false);

    PG_RETURN_VOID();
}

/*
 * pg_advisory_xact_lock_shared(int4, int4) - acquire xact scoped
 * share lock on 2 int4 keys
 */
Datum
pg_advisory_xact_lock_shared_int4(PG_FUNCTION_ARGS)
{
    int32       key1 = PG_GETARG_INT32(0);
    int32       key2 = PG_GETARG_INT32(1);
    LOCKTAG     tag;

    SET_LOCKTAG_INT32(tag, key1, key2);

    (void) LockAcquire(&tag, ShareLock, false, false);

    PG_RETURN_VOID();
}

/*
 * pg_try_advisory_lock(int4, int4) - acquire exclusive lock on 2 int4 keys, no wait
 *
 * Returns true if successful, false if lock not available
 */
Datum
pg_try_advisory_lock_int4(PG_FUNCTION_ARGS)
{
    int32       key1 = PG_GETARG_INT32(0);
    int32       key2 = PG_GETARG_INT32(1);
    LOCKTAG     tag;
    LockAcquireResult res;

    SET_LOCKTAG_INT32(tag, key1, key2);

    res = LockAcquire(&tag, ExclusiveLock, true, true);

    PG_RETURN_BOOL(res != LOCKACQUIRE_NOT_AVAIL);
}

/*
 * pg_try_advisory_xact_lock(int4, int4) - acquire xact scoped
 * exclusive lock on 2 int4 keys, no wait
 *
 * Returns true if successful, false if lock not available
 */
Datum
pg_try_advisory_xact_lock_int4(PG_FUNCTION_ARGS)
{
    int32       key1 = PG_GETARG_INT32(0);
    int32       key2 = PG_GETARG_INT32(1);
    LOCKTAG     tag;
    LockAcquireResult res;

    SET_LOCKTAG_INT32(tag, key1, key2);

    res = LockAcquire(&tag, ExclusiveLock, false, true);

    PG_RETURN_BOOL(res != LOCKACQUIRE_NOT_AVAIL);
}

/*
 * pg_try_advisory_lock_shared(int4, int4) - acquire share lock on 2 int4 keys, no wait
 *
 * Returns true if successful, false if lock not available
 */
Datum
pg_try_advisory_lock_shared_int4(PG_FUNCTION_ARGS)
{
    int32       key1 = PG_GETARG_INT32(0);
    int32       key2 = PG_GETARG_INT32(1);
    LOCKTAG     tag;
    LockAcquireResult res;

    SET_LOCKTAG_INT32(tag, key1, key2);

    res = LockAcquire(&tag, ShareLock, true, true);

    PG_RETURN_BOOL(res != LOCKACQUIRE_NOT_AVAIL);
}

/*
 * pg_try_advisory_xact_lock_shared(int4, int4) - acquire xact scoped
 * share lock on 2 int4 keys, no wait
 *
 * Returns true if successful, false if lock not available
 */
Datum
pg_try_advisory_xact_lock_shared_int4(PG_FUNCTION_ARGS)
{
    int32       key1 = PG_GETARG_INT32(0);
    int32       key2 = PG_GETARG_INT32(1);
    LOCKTAG     tag;
    LockAcquireResult res;

    SET_LOCKTAG_INT32(tag, key1, key2);

    res = LockAcquire(&tag, ShareLock, false, true);

    PG_RETURN_BOOL(res != LOCKACQUIRE_NOT_AVAIL);
}

/*
 * pg_advisory_unlock(int4, int4) - release exclusive lock on 2 int4 keys
 *
 * Returns true if successful, false if lock was not held
*/
Datum
pg_advisory_unlock_int4(PG_FUNCTION_ARGS)
{
    int32       key1 = PG_GETARG_INT32(0);
    int32       key2 = PG_GETARG_INT32(1);
    LOCKTAG     tag;
    bool        res;

    SET_LOCKTAG_INT32(tag, key1, key2);

    res = LockRelease(&tag, ExclusiveLock, true);

    PG_RETURN_BOOL(res);
}

/*
 * pg_advisory_unlock_shared(int4, int4) - release share lock on 2 int4 keys
 *
 * Returns true if successful, false if lock was not held
 */
Datum
pg_advisory_unlock_shared_int4(PG_FUNCTION_ARGS)
{
    int32       key1 = PG_GETARG_INT32(0);
    int32       key2 = PG_GETARG_INT32(1);
    LOCKTAG     tag;
    bool        res;

    SET_LOCKTAG_INT32(tag, key1, key2);

    res = LockRelease(&tag, ShareLock, true);

    PG_RETURN_BOOL(res);
}

/*
 * pg_advisory_unlock_all() - release all advisory locks
 */
Datum
pg_advisory_unlock_all(PG_FUNCTION_ARGS)
{
    LockReleaseSession(USER_LOCKMETHOD);

    PG_RETURN_VOID();
}