resowner.c

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/*-------------------------------------------------------------------------
 *
 * resowner.c
 *    POSTGRES resource owner management code.
 *
 * Query-lifespan resources are tracked by associating them with
 * ResourceOwner objects.  This provides a simple mechanism for ensuring
 * that such resources are freed at the right time.
 * See utils/resowner/README for more info.
 *
 *
 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/resowner/resowner.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/hash.h"
#include "storage/predicate.h"
#include "storage/proc.h"
#include "utils/memutils.h"
#include "utils/rel.h"
#include "utils/resowner_private.h"
#include "utils/snapmgr.h"


/*
 * All resource IDs managed by this code are required to fit into a Datum,
 * which is fine since they are generally pointers or integers.
 *
 * Provide Datum conversion macros for a couple of things that are really
 * just "int".
 */
#define FileGetDatum(file) Int32GetDatum(file)
#define DatumGetFile(datum) ((File) DatumGetInt32(datum))
#define BufferGetDatum(buffer) Int32GetDatum(buffer)
#define DatumGetBuffer(datum) ((Buffer) DatumGetInt32(datum))

/*
 * ResourceArray is a common structure for storing all types of resource IDs.
 *
 * We manage small sets of resource IDs by keeping them in a simple array:
 * itemsarr[k] holds an ID, for 0 <= k < nitems <= maxitems = capacity.
 *
 * If a set grows large, we switch over to using open-addressing hashing.
 * Then, itemsarr[] is a hash table of "capacity" slots, with each
 * slot holding either an ID or "invalidval".  nitems is the number of valid
 * items present; if it would exceed maxitems, we enlarge the array and
 * re-hash.  In this mode, maxitems should be rather less than capacity so
 * that we don't waste too much time searching for empty slots.
 *
 * In either mode, lastidx remembers the location of the last item inserted
 * or returned by GetAny; this speeds up searches in ResourceArrayRemove.
 */
typedef struct ResourceArray
{
    Datum      *itemsarr;       /* buffer for storing values */
    Datum       invalidval;     /* value that is considered invalid */
    uint32      capacity;       /* allocated length of itemsarr[] */
    uint32      nitems;         /* how many items are stored in items array */
    uint32      maxitems;       /* current limit on nitems before enlarging */
    uint32      lastidx;        /* index of last item returned by GetAny */
} ResourceArray;

/*
 * Initially allocated size of a ResourceArray.  Must be power of two since
 * we'll use (arraysize - 1) as mask for hashing.
 */
#define RESARRAY_INIT_SIZE 16

/*
 * When to switch to hashing vs. simple array logic in a ResourceArray.
 */
#define RESARRAY_MAX_ARRAY 64
#define RESARRAY_IS_ARRAY(resarr) ((resarr)->capacity <= RESARRAY_MAX_ARRAY)

/*
 * How many items may be stored in a resource array of given capacity.
 * When this number is reached, we must resize.
 */
#define RESARRAY_MAX_ITEMS(capacity) \
    ((capacity) <= RESARRAY_MAX_ARRAY ? (capacity) : (capacity)/4 * 3)

/*
 * To speed up bulk releasing or reassigning locks from a resource owner to
 * its parent, each resource owner has a small cache of locks it owns. The
 * lock manager has the same information in its local lock hash table, and
 * we fall back on that if cache overflows, but traversing the hash table
 * is slower when there are a lot of locks belonging to other resource owners.
 *
 * MAX_RESOWNER_LOCKS is the size of the per-resource owner cache. It's
 * chosen based on some testing with pg_dump with a large schema. When the
 * tests were done (on 9.2), resource owners in a pg_dump run contained up
 * to 9 locks, regardless of the schema size, except for the top resource
 * owner which contained much more (overflowing the cache). 15 seems like a
 * nice round number that's somewhat higher than what pg_dump needs. Note that
 * making this number larger is not free - the bigger the cache, the slower
 * it is to release locks (in retail), when a resource owner holds many locks.
 */
#define MAX_RESOWNER_LOCKS 15

/*
 * ResourceOwner objects look like this
 */
typedef struct ResourceOwnerData
{
    ResourceOwner parent;       /* NULL if no parent (toplevel owner) */
    ResourceOwner firstchild;   /* head of linked list of children */
    ResourceOwner nextchild;    /* next child of same parent */
    const char *name;           /* name (just for debugging) */

    /* We have built-in support for remembering: */
    ResourceArray bufferarr;    /* owned buffers */
    ResourceArray catrefarr;    /* catcache references */
    ResourceArray catlistrefarr;    /* catcache-list pins */
    ResourceArray relrefarr;    /* relcache references */
    ResourceArray planrefarr;   /* plancache references */
    ResourceArray tupdescarr;   /* tupdesc references */
    ResourceArray snapshotarr;  /* snapshot references */
    ResourceArray filearr;      /* open temporary files */
    ResourceArray dsmarr;       /* dynamic shmem segments */

    /* We can remember up to MAX_RESOWNER_LOCKS references to local locks. */
    int         nlocks;         /* number of owned locks */
    LOCALLOCK  *locks[MAX_RESOWNER_LOCKS];  /* list of owned locks */
}           ResourceOwnerData;


/*****************************************************************************
 *    GLOBAL MEMORY                                                          *
 *****************************************************************************/

ResourceOwner CurrentResourceOwner = NULL;
ResourceOwner CurTransactionResourceOwner = NULL;
ResourceOwner TopTransactionResourceOwner = NULL;

/*
 * List of add-on callbacks for resource releasing
 */
typedef struct ResourceReleaseCallbackItem
{
    struct ResourceReleaseCallbackItem *next;
    ResourceReleaseCallback callback;
    void       *arg;
} ResourceReleaseCallbackItem;

static ResourceReleaseCallbackItem *ResourceRelease_callbacks = NULL;


/* Internal routines */
static void ResourceArrayInit(ResourceArray *resarr, Datum invalidval);
static void ResourceArrayEnlarge(ResourceArray *resarr);
static void ResourceArrayAdd(ResourceArray *resarr, Datum value);
static bool ResourceArrayRemove(ResourceArray *resarr, Datum value);
static bool ResourceArrayGetAny(ResourceArray *resarr, Datum *value);
static void ResourceArrayFree(ResourceArray *resarr);
static void ResourceOwnerReleaseInternal(ResourceOwner owner,
                             ResourceReleasePhase phase,
                             bool isCommit,
                             bool isTopLevel);
static void PrintRelCacheLeakWarning(Relation rel);
static void PrintPlanCacheLeakWarning(CachedPlan *plan);
static void PrintTupleDescLeakWarning(TupleDesc tupdesc);
static void PrintSnapshotLeakWarning(Snapshot snapshot);
static void PrintFileLeakWarning(File file);
static void PrintDSMLeakWarning(dsm_segment *seg);


/*****************************************************************************
 *    INTERNAL ROUTINES                                                      *
 *****************************************************************************/


/*
 * Initialize a ResourceArray
 */
static void
ResourceArrayInit(ResourceArray *resarr, Datum invalidval)
{
    /* Assert it's empty */
    Assert(resarr->itemsarr == NULL);
    Assert(resarr->capacity == 0);
    Assert(resarr->nitems == 0);
    Assert(resarr->maxitems == 0);
    /* Remember the appropriate "invalid" value */
    resarr->invalidval = invalidval;
    /* We don't allocate any storage until needed */
}

/*
 * Make sure there is room for at least one more resource in an array.
 *
 * This is separate from actually inserting a resource because if we run out
 * of memory, it's critical to do so *before* acquiring the resource.
 */
static void
ResourceArrayEnlarge(ResourceArray *resarr)
{
    uint32      i,
                oldcap,
                newcap;
    Datum      *olditemsarr;
    Datum      *newitemsarr;

    if (resarr->nitems < resarr->maxitems)
        return;                 /* no work needed */

    olditemsarr = resarr->itemsarr;
    oldcap = resarr->capacity;

    /* Double the capacity of the array (capacity must stay a power of 2!) */
    newcap = (oldcap > 0) ? oldcap * 2 : RESARRAY_INIT_SIZE;
    newitemsarr = (Datum *) MemoryContextAlloc(TopMemoryContext,
                                               newcap * sizeof(Datum));
    for (i = 0; i < newcap; i++)
        newitemsarr[i] = resarr->invalidval;

    /* We assume we can't fail below this point, so OK to scribble on resarr */
    resarr->itemsarr = newitemsarr;
    resarr->capacity = newcap;
    resarr->maxitems = RESARRAY_MAX_ITEMS(newcap);
    resarr->nitems = 0;

    if (olditemsarr != NULL)
    {
        /*
         * Transfer any pre-existing entries into the new array; they don't
         * necessarily go where they were before, so this simple logic is the
         * best way.  Note that if we were managing the set as a simple array,
         * the entries after nitems are garbage, but that shouldn't matter
         * because we won't get here unless nitems was equal to oldcap.
         */
        for (i = 0; i < oldcap; i++)
        {
            if (olditemsarr[i] != resarr->invalidval)
                ResourceArrayAdd(resarr, olditemsarr[i]);
        }

        /* And release old array. */
        pfree(olditemsarr);
    }

    Assert(resarr->nitems < resarr->maxitems);
}

/*
 * Add a resource to ResourceArray
 *
 * Caller must have previously done ResourceArrayEnlarge()
 */
static void
ResourceArrayAdd(ResourceArray *resarr, Datum value)
{
    uint32      idx;

    Assert(value != resarr->invalidval);
    Assert(resarr->nitems < resarr->maxitems);

    if (RESARRAY_IS_ARRAY(resarr))
    {
        /* Append to linear array. */
        idx = resarr->nitems;
    }
    else
    {
        /* Insert into first free slot at or after hash location. */
        uint32      mask = resarr->capacity - 1;

        idx = DatumGetUInt32(hash_any((void *) &value, sizeof(value))) & mask;
        for (;;)
        {
            if (resarr->itemsarr[idx] == resarr->invalidval)
                break;
            idx = (idx + 1) & mask;
        }
    }
    resarr->lastidx = idx;
    resarr->itemsarr[idx] = value;
    resarr->nitems++;
}

/*
 * Remove a resource from ResourceArray
 *
 * Returns true on success, false if resource was not found.
 *
 * Note: if same resource ID appears more than once, one instance is removed.
 */
static bool
ResourceArrayRemove(ResourceArray *resarr, Datum value)
{
    uint32      i,
                idx,
                lastidx = resarr->lastidx;

    Assert(value != resarr->invalidval);

    /* Search through all items, but try lastidx first. */
    if (RESARRAY_IS_ARRAY(resarr))
    {
        if (lastidx < resarr->nitems &&
            resarr->itemsarr[lastidx] == value)
        {
            resarr->itemsarr[lastidx] = resarr->itemsarr[resarr->nitems - 1];
            resarr->nitems--;
            /* Update lastidx to make reverse-order removals fast. */
            resarr->lastidx = resarr->nitems - 1;
            return true;
        }
        for (i = 0; i < resarr->nitems; i++)
        {
            if (resarr->itemsarr[i] == value)
            {
                resarr->itemsarr[i] = resarr->itemsarr[resarr->nitems - 1];
                resarr->nitems--;
                /* Update lastidx to make reverse-order removals fast. */
                resarr->lastidx = resarr->nitems - 1;
                return true;
            }
        }
    }
    else
    {
        uint32      mask = resarr->capacity - 1;

        if (lastidx < resarr->capacity &&
            resarr->itemsarr[lastidx] == value)
        {
            resarr->itemsarr[lastidx] = resarr->invalidval;
            resarr->nitems--;
            return true;
        }
        idx = DatumGetUInt32(hash_any((void *) &value, sizeof(value))) & mask;
        for (i = 0; i < resarr->capacity; i++)
        {
            if (resarr->itemsarr[idx] == value)
            {
                resarr->itemsarr[idx] = resarr->invalidval;
                resarr->nitems--;
                return true;
            }
            idx = (idx + 1) & mask;
        }
    }

    return false;
}

/*
 * Get any convenient entry in a ResourceArray.
 *
 * "Convenient" is defined as "easy for ResourceArrayRemove to remove";
 * we help that along by setting lastidx to match.  This avoids O(N^2) cost
 * when removing all ResourceArray items during ResourceOwner destruction.
 *
 * Returns true if we found an element, or false if the array is empty.
 */
static bool
ResourceArrayGetAny(ResourceArray *resarr, Datum *value)
{
    if (resarr->nitems == 0)
        return false;

    if (RESARRAY_IS_ARRAY(resarr))
    {
        /* Linear array: just return the first element. */
        resarr->lastidx = 0;
    }
    else
    {
        /* Hash: search forward from wherever we were last. */
        uint32      mask = resarr->capacity - 1;

        for (;;)
        {
            resarr->lastidx &= mask;
            if (resarr->itemsarr[resarr->lastidx] != resarr->invalidval)
                break;
            resarr->lastidx++;
        }
    }

    *value = resarr->itemsarr[resarr->lastidx];
    return true;
}

/*
 * Trash a ResourceArray (we don't care about its state after this)
 */
static void
ResourceArrayFree(ResourceArray *resarr)
{
    if (resarr->itemsarr)
        pfree(resarr->itemsarr);
}


/*****************************************************************************
 *    EXPORTED ROUTINES                                                      *
 *****************************************************************************/


/*
 * ResourceOwnerCreate
 *      Create an empty ResourceOwner.
 *
 * All ResourceOwner objects are kept in TopMemoryContext, since they should
 * only be freed explicitly.
 */
ResourceOwner
ResourceOwnerCreate(ResourceOwner parent, const char *name)
{
    ResourceOwner owner;

    owner = (ResourceOwner) MemoryContextAllocZero(TopMemoryContext,
                                                   sizeof(ResourceOwnerData));
    owner->name = name;

    if (parent)
    {
        owner->parent = parent;
        owner->nextchild = parent->firstchild;
        parent->firstchild = owner;
    }

    ResourceArrayInit(&(owner->bufferarr), BufferGetDatum(InvalidBuffer));
    ResourceArrayInit(&(owner->catrefarr), PointerGetDatum(NULL));
    ResourceArrayInit(&(owner->catlistrefarr), PointerGetDatum(NULL));
    ResourceArrayInit(&(owner->relrefarr), PointerGetDatum(NULL));
    ResourceArrayInit(&(owner->planrefarr), PointerGetDatum(NULL));
    ResourceArrayInit(&(owner->tupdescarr), PointerGetDatum(NULL));
    ResourceArrayInit(&(owner->snapshotarr), PointerGetDatum(NULL));
    ResourceArrayInit(&(owner->filearr), FileGetDatum(-1));
    ResourceArrayInit(&(owner->dsmarr), PointerGetDatum(NULL));

    return owner;
}

/*
 * ResourceOwnerRelease
 *      Release all resources owned by a ResourceOwner and its descendants,
 *      but don't delete the owner objects themselves.
 *
 * Note that this executes just one phase of release, and so typically
 * must be called three times.  We do it this way because (a) we want to
 * do all the recursion separately for each phase, thereby preserving
 * the needed order of operations; and (b) xact.c may have other operations
 * to do between the phases.
 *
 * phase: release phase to execute
 * isCommit: true for successful completion of a query or transaction,
 *          false for unsuccessful
 * isTopLevel: true if completing a main transaction, else false
 *
 * isCommit is passed because some modules may expect that their resources
 * were all released already if the transaction or portal finished normally.
 * If so it is reasonable to give a warning (NOT an error) should any
 * unreleased resources be present.  When isCommit is false, such warnings
 * are generally inappropriate.
 *
 * isTopLevel is passed when we are releasing TopTransactionResourceOwner
 * at completion of a main transaction.  This generally means that *all*
 * resources will be released, and so we can optimize things a bit.
 */
void
ResourceOwnerRelease(ResourceOwner owner,
                     ResourceReleasePhase phase,
                     bool isCommit,
                     bool isTopLevel)
{
    /* Rather than PG_TRY at every level of recursion, set it up once */
    ResourceOwner save;

    save = CurrentResourceOwner;
    PG_TRY();
    {
        ResourceOwnerReleaseInternal(owner, phase, isCommit, isTopLevel);
    }
    PG_CATCH();
    {
        CurrentResourceOwner = save;
        PG_RE_THROW();
    }
    PG_END_TRY();
    CurrentResourceOwner = save;
}

static void
ResourceOwnerReleaseInternal(ResourceOwner owner,
                             ResourceReleasePhase phase,
                             bool isCommit,
                             bool isTopLevel)
{
    ResourceOwner child;
    ResourceOwner save;
    ResourceReleaseCallbackItem *item;
    Datum       foundres;

    /* Recurse to handle descendants */
    for (child = owner->firstchild; child != NULL; child = child->nextchild)
        ResourceOwnerReleaseInternal(child, phase, isCommit, isTopLevel);

    /*
     * Make CurrentResourceOwner point to me, so that ReleaseBuffer etc don't
     * get confused.  We needn't PG_TRY here because the outermost level will
     * fix it on error abort.
     */
    save = CurrentResourceOwner;
    CurrentResourceOwner = owner;

    if (phase == RESOURCE_RELEASE_BEFORE_LOCKS)
    {
        /*
         * Release buffer pins.  Note that ReleaseBuffer will remove the
         * buffer entry from our array, so we just have to iterate till there
         * are none.
         *
         * During a commit, there shouldn't be any remaining pins --- that
         * would indicate failure to clean up the executor correctly --- so
         * issue warnings.  In the abort case, just clean up quietly.
         */
        while (ResourceArrayGetAny(&(owner->bufferarr), &foundres))
        {
            Buffer      res = DatumGetBuffer(foundres);

            if (isCommit)
                PrintBufferLeakWarning(res);
            ReleaseBuffer(res);
        }

        /* Ditto for relcache references */
        while (ResourceArrayGetAny(&(owner->relrefarr), &foundres))
        {
            Relation    res = (Relation) DatumGetPointer(foundres);

            if (isCommit)
                PrintRelCacheLeakWarning(res);
            RelationClose(res);
        }

        /* Ditto for dynamic shared memory segments */
        while (ResourceArrayGetAny(&(owner->dsmarr), &foundres))
        {
            dsm_segment *res = (dsm_segment *) DatumGetPointer(foundres);

            if (isCommit)
                PrintDSMLeakWarning(res);
            dsm_detach(res);
        }
    }
    else if (phase == RESOURCE_RELEASE_LOCKS)
    {
        if (isTopLevel)
        {
            /*
             * For a top-level xact we are going to release all locks (or at
             * least all non-session locks), so just do a single lmgr call at
             * the top of the recursion.
             */
            if (owner == TopTransactionResourceOwner)
            {
                ProcReleaseLocks(isCommit);
                ReleasePredicateLocks(isCommit);
            }
        }
        else
        {
            /*
             * Release locks retail.  Note that if we are committing a
             * subtransaction, we do NOT release its locks yet, but transfer
             * them to the parent.
             */
            LOCALLOCK **locks;
            int         nlocks;

            Assert(owner->parent != NULL);

            /*
             * Pass the list of locks owned by this resource owner to the lock
             * manager, unless it has overflowed.
             */
            if (owner->nlocks > MAX_RESOWNER_LOCKS)
            {
                locks = NULL;
                nlocks = 0;
            }
            else
            {
                locks = owner->locks;
                nlocks = owner->nlocks;
            }

            if (isCommit)
                LockReassignCurrentOwner(locks, nlocks);
            else
                LockReleaseCurrentOwner(locks, nlocks);
        }
    }
    else if (phase == RESOURCE_RELEASE_AFTER_LOCKS)
    {
        /*
         * Release catcache references.  Note that ReleaseCatCache will remove
         * the catref entry from our array, so we just have to iterate till
         * there are none.
         *
         * As with buffer pins, warn if any are left at commit time.
         */
        while (ResourceArrayGetAny(&(owner->catrefarr), &foundres))
        {
            HeapTuple   res = (HeapTuple) DatumGetPointer(foundres);

            if (isCommit)
                PrintCatCacheLeakWarning(res);
            ReleaseCatCache(res);
        }

        /* Ditto for catcache lists */
        while (ResourceArrayGetAny(&(owner->catlistrefarr), &foundres))
        {
            CatCList   *res = (CatCList *) DatumGetPointer(foundres);

            if (isCommit)
                PrintCatCacheListLeakWarning(res);
            ReleaseCatCacheList(res);
        }

        /* Ditto for plancache references */
        while (ResourceArrayGetAny(&(owner->planrefarr), &foundres))
        {
            CachedPlan *res = (CachedPlan *) DatumGetPointer(foundres);

            if (isCommit)
                PrintPlanCacheLeakWarning(res);
            ReleaseCachedPlan(res, true);
        }

        /* Ditto for tupdesc references */
        while (ResourceArrayGetAny(&(owner->tupdescarr), &foundres))
        {
            TupleDesc   res = (TupleDesc) DatumGetPointer(foundres);

            if (isCommit)
                PrintTupleDescLeakWarning(res);
            DecrTupleDescRefCount(res);
        }

        /* Ditto for snapshot references */
        while (ResourceArrayGetAny(&(owner->snapshotarr), &foundres))
        {
            Snapshot    res = (Snapshot) DatumGetPointer(foundres);

            if (isCommit)
                PrintSnapshotLeakWarning(res);
            UnregisterSnapshot(res);
        }

        /* Ditto for temporary files */
        while (ResourceArrayGetAny(&(owner->filearr), &foundres))
        {
            File        res = DatumGetFile(foundres);

            if (isCommit)
                PrintFileLeakWarning(res);
            FileClose(res);
        }
    }

    /* Let add-on modules get a chance too */
    for (item = ResourceRelease_callbacks; item; item = item->next)
        (*item->callback) (phase, isCommit, isTopLevel, item->arg);

    CurrentResourceOwner = save;
}

/*
 * ResourceOwnerDelete
 *      Delete an owner object and its descendants.
 *
 * The caller must have already released all resources in the object tree.
 */
void
ResourceOwnerDelete(ResourceOwner owner)
{
    /* We had better not be deleting CurrentResourceOwner ... */
    Assert(owner != CurrentResourceOwner);

    /* And it better not own any resources, either */
    Assert(owner->bufferarr.nitems == 0);
    Assert(owner->catrefarr.nitems == 0);
    Assert(owner->catlistrefarr.nitems == 0);
    Assert(owner->relrefarr.nitems == 0);
    Assert(owner->planrefarr.nitems == 0);
    Assert(owner->tupdescarr.nitems == 0);
    Assert(owner->snapshotarr.nitems == 0);
    Assert(owner->filearr.nitems == 0);
    Assert(owner->dsmarr.nitems == 0);
    Assert(owner->nlocks == 0 || owner->nlocks == MAX_RESOWNER_LOCKS + 1);

    /*
     * Delete children.  The recursive call will delink the child from me, so
     * just iterate as long as there is a child.
     */
    while (owner->firstchild != NULL)
        ResourceOwnerDelete(owner->firstchild);

    /*
     * We delink the owner from its parent before deleting it, so that if
     * there's an error we won't have deleted/busted owners still attached to
     * the owner tree.  Better a leak than a crash.
     */
    ResourceOwnerNewParent(owner, NULL);

    /* And free the object. */
    ResourceArrayFree(&(owner->bufferarr));
    ResourceArrayFree(&(owner->catrefarr));
    ResourceArrayFree(&(owner->catlistrefarr));
    ResourceArrayFree(&(owner->relrefarr));
    ResourceArrayFree(&(owner->planrefarr));
    ResourceArrayFree(&(owner->tupdescarr));
    ResourceArrayFree(&(owner->snapshotarr));
    ResourceArrayFree(&(owner->filearr));
    ResourceArrayFree(&(owner->dsmarr));

    pfree(owner);
}

/*
 * Fetch parent of a ResourceOwner (returns NULL if top-level owner)
 */
ResourceOwner
ResourceOwnerGetParent(ResourceOwner owner)
{
    return owner->parent;
}

/*
 * Reassign a ResourceOwner to have a new parent
 */
void
ResourceOwnerNewParent(ResourceOwner owner,
                       ResourceOwner newparent)
{
    ResourceOwner oldparent = owner->parent;

    if (oldparent)
    {
        if (owner == oldparent->firstchild)
            oldparent->firstchild = owner->nextchild;
        else
        {
            ResourceOwner child;

            for (child = oldparent->firstchild; child; child = child->nextchild)
            {
                if (owner == child->nextchild)
                {
                    child->nextchild = owner->nextchild;
                    break;
                }
            }
        }
    }

    if (newparent)
    {
        Assert(owner != newparent);
        owner->parent = newparent;
        owner->nextchild = newparent->firstchild;
        newparent->firstchild = owner;
    }
    else
    {
        owner->parent = NULL;
        owner->nextchild = NULL;
    }
}

/*
 * Register or deregister callback functions for resource cleanup
 *
 * These functions are intended for use by dynamically loaded modules.
 * For built-in modules we generally just hardwire the appropriate calls.
 *
 * Note that the callback occurs post-commit or post-abort, so the callback
 * functions can only do noncritical cleanup.
 */
void
RegisterResourceReleaseCallback(ResourceReleaseCallback callback, void *arg)
{
    ResourceReleaseCallbackItem *item;

    item = (ResourceReleaseCallbackItem *)
        MemoryContextAlloc(TopMemoryContext,
                           sizeof(ResourceReleaseCallbackItem));
    item->callback = callback;
    item->arg = arg;
    item->next = ResourceRelease_callbacks;
    ResourceRelease_callbacks = item;
}

void
UnregisterResourceReleaseCallback(ResourceReleaseCallback callback, void *arg)
{
    ResourceReleaseCallbackItem *item;
    ResourceReleaseCallbackItem *prev;

    prev = NULL;
    for (item = ResourceRelease_callbacks; item; prev = item, item = item->next)
    {
        if (item->callback == callback && item->arg == arg)
        {
            if (prev)
                prev->next = item->next;
            else
                ResourceRelease_callbacks = item->next;
            pfree(item);
            break;
        }
    }
}


/*
 * Make sure there is room for at least one more entry in a ResourceOwner's
 * buffer array.
 *
 * This is separate from actually inserting an entry because if we run out
 * of memory, it's critical to do so *before* acquiring the resource.
 *
 * We allow the case owner == NULL because the bufmgr is sometimes invoked
 * outside any transaction (for example, during WAL recovery).
 */
void
ResourceOwnerEnlargeBuffers(ResourceOwner owner)
{
    if (owner == NULL)
        return;
    ResourceArrayEnlarge(&(owner->bufferarr));
}

/*
 * Remember that a buffer pin is owned by a ResourceOwner
 *
 * Caller must have previously done ResourceOwnerEnlargeBuffers()
 *
 * We allow the case owner == NULL because the bufmgr is sometimes invoked
 * outside any transaction (for example, during WAL recovery).
 */
void
ResourceOwnerRememberBuffer(ResourceOwner owner, Buffer buffer)
{
    if (owner == NULL)
        return;
    ResourceArrayAdd(&(owner->bufferarr), BufferGetDatum(buffer));
}

/*
 * Forget that a buffer pin is owned by a ResourceOwner
 *
 * We allow the case owner == NULL because the bufmgr is sometimes invoked
 * outside any transaction (for example, during WAL recovery).
 */
void
ResourceOwnerForgetBuffer(ResourceOwner owner, Buffer buffer)
{
    if (owner == NULL)
        return;
    if (!ResourceArrayRemove(&(owner->bufferarr), BufferGetDatum(buffer)))
        elog(ERROR, "buffer %d is not owned by resource owner %s",
             buffer, owner->name);
}

/*
 * Remember that a Local Lock is owned by a ResourceOwner
 *
 * This is different from the other Remember functions in that the list of
 * locks is only a lossy cache. It can hold up to MAX_RESOWNER_LOCKS entries,
 * and when it overflows, we stop tracking locks. The point of only remembering
 * only up to MAX_RESOWNER_LOCKS entries is that if a lot of locks are held,
 * ResourceOwnerForgetLock doesn't need to scan through a large array to find
 * the entry.
 */
void
ResourceOwnerRememberLock(ResourceOwner owner, LOCALLOCK *locallock)
{
    Assert(locallock != NULL);

    if (owner->nlocks > MAX_RESOWNER_LOCKS)
        return;                 /* we have already overflowed */

    if (owner->nlocks < MAX_RESOWNER_LOCKS)
        owner->locks[owner->nlocks] = locallock;
    else
    {
        /* overflowed */
    }
    owner->nlocks++;
}

/*
 * Forget that a Local Lock is owned by a ResourceOwner
 */
void
ResourceOwnerForgetLock(ResourceOwner owner, LOCALLOCK *locallock)
{
    int         i;

    if (owner->nlocks > MAX_RESOWNER_LOCKS)
        return;                 /* we have overflowed */

    Assert(owner->nlocks > 0);
    for (i = owner->nlocks - 1; i >= 0; i--)
    {
        if (locallock == owner->locks[i])
        {
            owner->locks[i] = owner->locks[owner->nlocks - 1];
            owner->nlocks--;
            return;
        }
    }
    elog(ERROR, "lock reference %p is not owned by resource owner %s",
         locallock, owner->name);
}

/*
 * Make sure there is room for at least one more entry in a ResourceOwner's
 * catcache reference array.
 *
 * This is separate from actually inserting an entry because if we run out
 * of memory, it's critical to do so *before* acquiring the resource.
 */
void
ResourceOwnerEnlargeCatCacheRefs(ResourceOwner owner)
{
    ResourceArrayEnlarge(&(owner->catrefarr));
}

/*
 * Remember that a catcache reference is owned by a ResourceOwner
 *
 * Caller must have previously done ResourceOwnerEnlargeCatCacheRefs()
 */
void
ResourceOwnerRememberCatCacheRef(ResourceOwner owner, HeapTuple tuple)
{
    ResourceArrayAdd(&(owner->catrefarr), PointerGetDatum(tuple));
}

/*
 * Forget that a catcache reference is owned by a ResourceOwner
 */
void
ResourceOwnerForgetCatCacheRef(ResourceOwner owner, HeapTuple tuple)
{
    if (!ResourceArrayRemove(&(owner->catrefarr), PointerGetDatum(tuple)))
        elog(ERROR, "catcache reference %p is not owned by resource owner %s",
             tuple, owner->name);
}

/*
 * Make sure there is room for at least one more entry in a ResourceOwner's
 * catcache-list reference array.
 *
 * This is separate from actually inserting an entry because if we run out
 * of memory, it's critical to do so *before* acquiring the resource.
 */
void
ResourceOwnerEnlargeCatCacheListRefs(ResourceOwner owner)
{
    ResourceArrayEnlarge(&(owner->catlistrefarr));
}

/*
 * Remember that a catcache-list reference is owned by a ResourceOwner
 *
 * Caller must have previously done ResourceOwnerEnlargeCatCacheListRefs()
 */
void
ResourceOwnerRememberCatCacheListRef(ResourceOwner owner, CatCList *list)
{
    ResourceArrayAdd(&(owner->catlistrefarr), PointerGetDatum(list));
}

/*
 * Forget that a catcache-list reference is owned by a ResourceOwner
 */
void
ResourceOwnerForgetCatCacheListRef(ResourceOwner owner, CatCList *list)
{
    if (!ResourceArrayRemove(&(owner->catlistrefarr), PointerGetDatum(list)))
        elog(ERROR, "catcache list reference %p is not owned by resource owner %s",
             list, owner->name);
}

/*
 * Make sure there is room for at least one more entry in a ResourceOwner's
 * relcache reference array.
 *
 * This is separate from actually inserting an entry because if we run out
 * of memory, it's critical to do so *before* acquiring the resource.
 */
void
ResourceOwnerEnlargeRelationRefs(ResourceOwner owner)
{
    ResourceArrayEnlarge(&(owner->relrefarr));
}

/*
 * Remember that a relcache reference is owned by a ResourceOwner
 *
 * Caller must have previously done ResourceOwnerEnlargeRelationRefs()
 */
void
ResourceOwnerRememberRelationRef(ResourceOwner owner, Relation rel)
{
    ResourceArrayAdd(&(owner->relrefarr), PointerGetDatum(rel));
}

/*
 * Forget that a relcache reference is owned by a ResourceOwner
 */
void
ResourceOwnerForgetRelationRef(ResourceOwner owner, Relation rel)
{
    if (!ResourceArrayRemove(&(owner->relrefarr), PointerGetDatum(rel)))
        elog(ERROR, "relcache reference %s is not owned by resource owner %s",
             RelationGetRelationName(rel), owner->name);
}

/*
 * Debugging subroutine
 */
static void
PrintRelCacheLeakWarning(Relation rel)
{
    elog(WARNING, "relcache reference leak: relation \"%s\" not closed",
         RelationGetRelationName(rel));
}

/*
 * Make sure there is room for at least one more entry in a ResourceOwner's
 * plancache reference array.
 *
 * This is separate from actually inserting an entry because if we run out
 * of memory, it's critical to do so *before* acquiring the resource.
 */
void
ResourceOwnerEnlargePlanCacheRefs(ResourceOwner owner)
{
    ResourceArrayEnlarge(&(owner->planrefarr));
}

/*
 * Remember that a plancache reference is owned by a ResourceOwner
 *
 * Caller must have previously done ResourceOwnerEnlargePlanCacheRefs()
 */
void
ResourceOwnerRememberPlanCacheRef(ResourceOwner owner, CachedPlan *plan)
{
    ResourceArrayAdd(&(owner->planrefarr), PointerGetDatum(plan));
}

/*
 * Forget that a plancache reference is owned by a ResourceOwner
 */
void
ResourceOwnerForgetPlanCacheRef(ResourceOwner owner, CachedPlan *plan)
{
    if (!ResourceArrayRemove(&(owner->planrefarr), PointerGetDatum(plan)))
        elog(ERROR, "plancache reference %p is not owned by resource owner %s",
             plan, owner->name);
}

/*
 * Debugging subroutine
 */
static void
PrintPlanCacheLeakWarning(CachedPlan *plan)
{
    elog(WARNING, "plancache reference leak: plan %p not closed", plan);
}

/*
 * Make sure there is room for at least one more entry in a ResourceOwner's
 * tupdesc reference array.
 *
 * This is separate from actually inserting an entry because if we run out
 * of memory, it's critical to do so *before* acquiring the resource.
 */
void
ResourceOwnerEnlargeTupleDescs(ResourceOwner owner)
{
    ResourceArrayEnlarge(&(owner->tupdescarr));
}

/*
 * Remember that a tupdesc reference is owned by a ResourceOwner
 *
 * Caller must have previously done ResourceOwnerEnlargeTupleDescs()
 */
void
ResourceOwnerRememberTupleDesc(ResourceOwner owner, TupleDesc tupdesc)
{
    ResourceArrayAdd(&(owner->tupdescarr), PointerGetDatum(tupdesc));
}

/*
 * Forget that a tupdesc reference is owned by a ResourceOwner
 */
void
ResourceOwnerForgetTupleDesc(ResourceOwner owner, TupleDesc tupdesc)
{
    if (!ResourceArrayRemove(&(owner->tupdescarr), PointerGetDatum(tupdesc)))
        elog(ERROR, "tupdesc reference %p is not owned by resource owner %s",
             tupdesc, owner->name);
}

/*
 * Debugging subroutine
 */
static void
PrintTupleDescLeakWarning(TupleDesc tupdesc)
{
    elog(WARNING,
         "TupleDesc reference leak: TupleDesc %p (%u,%d) still referenced",
         tupdesc, tupdesc->tdtypeid, tupdesc->tdtypmod);
}

/*
 * Make sure there is room for at least one more entry in a ResourceOwner's
 * snapshot reference array.
 *
 * This is separate from actually inserting an entry because if we run out
 * of memory, it's critical to do so *before* acquiring the resource.
 */
void
ResourceOwnerEnlargeSnapshots(ResourceOwner owner)
{
    ResourceArrayEnlarge(&(owner->snapshotarr));
}

/*
 * Remember that a snapshot reference is owned by a ResourceOwner
 *
 * Caller must have previously done ResourceOwnerEnlargeSnapshots()
 */
void
ResourceOwnerRememberSnapshot(ResourceOwner owner, Snapshot snapshot)
{
    ResourceArrayAdd(&(owner->snapshotarr), PointerGetDatum(snapshot));
}

/*
 * Forget that a snapshot reference is owned by a ResourceOwner
 */
void
ResourceOwnerForgetSnapshot(ResourceOwner owner, Snapshot snapshot)
{
    if (!ResourceArrayRemove(&(owner->snapshotarr), PointerGetDatum(snapshot)))
        elog(ERROR, "snapshot reference %p is not owned by resource owner %s",
             snapshot, owner->name);
}

/*
 * Debugging subroutine
 */
static void
PrintSnapshotLeakWarning(Snapshot snapshot)
{
    elog(WARNING, "Snapshot reference leak: Snapshot %p still referenced",
         snapshot);
}


/*
 * Make sure there is room for at least one more entry in a ResourceOwner's
 * files reference array.
 *
 * This is separate from actually inserting an entry because if we run out
 * of memory, it's critical to do so *before* acquiring the resource.
 */
void
ResourceOwnerEnlargeFiles(ResourceOwner owner)
{
    ResourceArrayEnlarge(&(owner->filearr));
}

/*
 * Remember that a temporary file is owned by a ResourceOwner
 *
 * Caller must have previously done ResourceOwnerEnlargeFiles()
 */
void
ResourceOwnerRememberFile(ResourceOwner owner, File file)
{
    ResourceArrayAdd(&(owner->filearr), FileGetDatum(file));
}

/*
 * Forget that a temporary file is owned by a ResourceOwner
 */
void
ResourceOwnerForgetFile(ResourceOwner owner, File file)
{
    if (!ResourceArrayRemove(&(owner->filearr), FileGetDatum(file)))
        elog(ERROR, "temporary file %d is not owned by resource owner %s",
             file, owner->name);
}

/*
 * Debugging subroutine
 */
static void
PrintFileLeakWarning(File file)
{
    elog(WARNING, "temporary file leak: File %d still referenced",
         file);
}

/*
 * Make sure there is room for at least one more entry in a ResourceOwner's
 * dynamic shmem segment reference array.
 *
 * This is separate from actually inserting an entry because if we run out
 * of memory, it's critical to do so *before* acquiring the resource.
 */
void
ResourceOwnerEnlargeDSMs(ResourceOwner owner)
{
    ResourceArrayEnlarge(&(owner->dsmarr));
}

/*
 * Remember that a dynamic shmem segment is owned by a ResourceOwner
 *
 * Caller must have previously done ResourceOwnerEnlargeDSMs()
 */
void
ResourceOwnerRememberDSM(ResourceOwner owner, dsm_segment *seg)
{
    ResourceArrayAdd(&(owner->dsmarr), PointerGetDatum(seg));
}

/*
 * Forget that a dynamic shmem segment is owned by a ResourceOwner
 */
void
ResourceOwnerForgetDSM(ResourceOwner owner, dsm_segment *seg)
{
    if (!ResourceArrayRemove(&(owner->dsmarr), PointerGetDatum(seg)))
        elog(ERROR, "dynamic shared memory segment %u is not owned by resource owner %s",
             dsm_segment_handle(seg), owner->name);
}

/*
 * Debugging subroutine
 */
static void
PrintDSMLeakWarning(dsm_segment *seg)
{
    elog(WARNING, "dynamic shared memory leak: segment %u still referenced",
         dsm_segment_handle(seg));
}