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/*-------------------------------------------------------------------------
*
* hashscan.c
* manage scans on hash tables
*
* Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/hash/hashscan.c,v 1.34 2004/07/01 00:49:29 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/hash.h"
typedef struct HashScanListData
{
IndexScanDesc hashsl_scan;
TransactionId hashsl_creatingXid;
struct HashScanListData *hashsl_next;
} HashScanListData;
typedef HashScanListData *HashScanList;
static HashScanList HashScans = NULL;
/*
* AtEOXact_hash() --- clean up hash subsystem at xact abort or commit.
*
* This is here because it needs to touch this module's static var HashScans.
*/
void
AtEOXact_hash(void)
{
/*
* Note: these actions should only be necessary during xact abort; but
* they can't hurt during a commit.
*/
/*
* Reset the active-scans list to empty. We do not need to free the
* list elements, because they're all palloc()'d, so they'll go away
* at end of transaction anyway.
*/
HashScans = NULL;
}
/*
* AtEOSubXact_hash() --- clean up hash subsystem at subxact abort or commit.
*
* This is here because it needs to touch this module's static var HashScans.
*/
void
AtEOSubXact_hash(TransactionId childXid)
{
HashScanList l;
HashScanList prev;
HashScanList next;
/*
* Note: these actions should only be necessary during xact abort; but
* they can't hurt during a commit.
*/
/*
* Forget active scans that were started in this subtransaction.
*/
prev = NULL;
for (l = HashScans; l != NULL; l = next)
{
next = l->hashsl_next;
if (l->hashsl_creatingXid == childXid)
{
if (prev == NULL)
HashScans = next;
else
prev->hashsl_next = next;
pfree(l);
/* prev does not change */
}
else
prev = l;
}
}
/*
* _Hash_regscan() -- register a new scan.
*/
void
_hash_regscan(IndexScanDesc scan)
{
HashScanList new_el;
new_el = (HashScanList) palloc(sizeof(HashScanListData));
new_el->hashsl_scan = scan;
new_el->hashsl_creatingXid = GetCurrentTransactionId();
new_el->hashsl_next = HashScans;
HashScans = new_el;
}
/*
* _hash_dropscan() -- drop a scan from the scan list
*/
void
_hash_dropscan(IndexScanDesc scan)
{
HashScanList chk,
last;
last = NULL;
for (chk = HashScans;
chk != NULL && chk->hashsl_scan != scan;
chk = chk->hashsl_next)
last = chk;
if (chk == NULL)
elog(ERROR, "hash scan list trashed; can't find 0x%p", (void *) scan);
if (last == NULL)
HashScans = chk->hashsl_next;
else
last->hashsl_next = chk->hashsl_next;
pfree(chk);
}
/*
* Is there an active scan in this bucket?
*/
bool
_hash_has_active_scan(Relation rel, Bucket bucket)
{
Oid relid = RelationGetRelid(rel);
HashScanList l;
for (l = HashScans; l != NULL; l = l->hashsl_next)
{
if (relid == l->hashsl_scan->indexRelation->rd_id)
{
HashScanOpaque so = (HashScanOpaque) l->hashsl_scan->opaque;
if (so->hashso_bucket_valid &&
so->hashso_bucket == bucket)
return true;
}
}
return false;
}
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