lockfuncs.c

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/*-------------------------------------------------------------------------
 *
 * lockfuncs.c
 *      Functions for SQL access to various lock-manager capabilities.
 *
 * Copyright (c) 2002-2013, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *      src/backend/utils/adt/lockfuncs.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

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


/* This must match enum LockTagType! */
static const char *const LockTagTypeNames[] = {
    "relation",
    "extend",
    "page",
    "tuple",
    "transactionid",
    "virtualxid",
    "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 pg_locks view in system_views.sql */
        tupdesc = CreateTemplateTupleDesc(NUM_LOCK_STATUS_COLUMNS, false);
        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);
}


/*
 * 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();
}