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/*-------------------------------------------------------------------------
*
* lockcmds.c
* LOCK command support code
*
* Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/commands/lockcmds.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/heapam.h"
#include "catalog/namespace.h"
#include "catalog/pg_inherits_fn.h"
#include "commands/lockcmds.h"
#include "miscadmin.h"
#include "parser/parse_clause.h"
#include "storage/lmgr.h"
#include "utils/acl.h"
#include "utils/lsyscache.h"
static void LockTableRecurse(Relation rel, LOCKMODE lockmode, bool nowait,
bool recurse);
/*
* LOCK TABLE
*/
void
LockTableCommand(LockStmt *lockstmt)
{
ListCell *p;
/*
* During recovery we only accept these variations: LOCK TABLE foo IN
* ACCESS SHARE MODE LOCK TABLE foo IN ROW SHARE MODE LOCK TABLE foo
* IN ROW EXCLUSIVE MODE This test must match the restrictions defined
* in LockAcquire()
*/
if (lockstmt->mode > RowExclusiveLock)
PreventCommandDuringRecovery("LOCK TABLE");
/*
* Iterate over the list and process the named relations one at a time
*/
foreach(p, lockstmt->relations)
{
RangeVar *rv = (RangeVar *) lfirst(p);
Relation rel;
bool recurse = interpretInhOption(rv->inhOpt);
Oid reloid;
reloid = RangeVarGetRelid(rv, lockstmt->mode, false, lockstmt->nowait);
rel = relation_open(reloid, NoLock);
LockTableRecurse(rel, lockstmt->mode, lockstmt->nowait, recurse);
}
}
/*
* Apply LOCK TABLE recursively over an inheritance tree
*/
static void
LockTableRecurse(Relation rel, LOCKMODE lockmode, bool nowait, bool recurse)
{
AclResult aclresult;
Oid reloid = RelationGetRelid(rel);
/* Verify adequate privilege */
if (lockmode == AccessShareLock)
aclresult = pg_class_aclcheck(reloid, GetUserId(),
ACL_SELECT);
else
aclresult = pg_class_aclcheck(reloid, GetUserId(),
ACL_UPDATE | ACL_DELETE | ACL_TRUNCATE);
if (aclresult != ACLCHECK_OK)
aclcheck_error(aclresult, ACL_KIND_CLASS,
RelationGetRelationName(rel));
/* Currently, we only allow plain tables to be locked */
if (rel->rd_rel->relkind != RELKIND_RELATION)
ereport(ERROR,
(errcode(ERRCODE_WRONG_OBJECT_TYPE),
errmsg("\"%s\" is not a table",
RelationGetRelationName(rel))));
/*
* If requested, recurse to children. We use find_inheritance_children
* not find_all_inheritors to avoid taking locks far in advance of
* checking privileges. This means we'll visit multiply-inheriting
* children more than once, but that's no problem.
*/
if (recurse)
{
List *children = find_inheritance_children(reloid, NoLock);
ListCell *lc;
Relation childrel;
foreach(lc, children)
{
Oid childreloid = lfirst_oid(lc);
/*
* Acquire the lock, to protect against concurrent drops. Note
* that a lock against an already-dropped relation's OID won't
* fail.
*/
if (!nowait)
LockRelationOid(childreloid, lockmode);
else if (!ConditionalLockRelationOid(childreloid, lockmode))
{
/* try to throw error by name; relation could be deleted... */
char *relname = get_rel_name(childreloid);
if (relname)
ereport(ERROR,
(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
errmsg("could not obtain lock on relation \"%s\"",
relname)));
else
ereport(ERROR,
(errcode(ERRCODE_LOCK_NOT_AVAILABLE),
errmsg("could not obtain lock on relation with OID %u",
reloid)));
}
/*
* Now that we have the lock, check to see if the relation really
* exists or not.
*/
childrel = try_relation_open(childreloid, NoLock);
if (!childrel)
{
/* Release useless lock */
UnlockRelationOid(childreloid, lockmode);
}
LockTableRecurse(childrel, lockmode, nowait, recurse);
}
}
relation_close(rel, NoLock); /* close rel, keep lock */
}
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