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/*-
* See the file LICENSE for redistribution information.
*
* Copyright (c) 1996-2009 Oracle. All rights reserved.
*
* $Id$
*/
#include "db_config.h"
#include "db_int.h"
#include "dbinc/db_page.h"
#include "dbinc/hash.h"
#include "dbinc/lock.h"
/*
* The next two functions are the hash functions used to store objects in the
* lock hash tables. They are hashing the same items, but one (__lock_ohash)
* takes a DBT (used for hashing a parameter passed from the user) and the
* other (__lock_lhash) takes a DB_LOCKOBJ (used for hashing something that is
* already in the lock manager). In both cases, we have a special check to
* fast path the case where we think we are doing a hash on a DB page/fileid
* pair. If the size is right, then we do the fast hash.
*
* We know that DB uses DB_LOCK_ILOCK types for its lock objects. The first
* four bytes are the 4-byte page number and the next DB_FILE_ID_LEN bytes
* are a unique file id, where the first 4 bytes on UNIX systems are the file
* inode number, and the first 4 bytes on Windows systems are the FileIndexLow
* bytes. This is followed by a random number. The inode values tend
* to increment fairly slowly and are not good for hashing. So, we use
* the XOR of the page number and the four bytes of the file id randome
* number to produce a 32-bit hash value.
*
* We have no particular reason to believe that this algorithm will produce
* a good hash, but we want a fast hash more than we want a good one, when
* we're coming through this code path.
*/
#define FAST_HASH(P) { \
u_int32_t __h; \
u_int8_t *__cp, *__hp; \
__hp = (u_int8_t *)&__h; \
__cp = (u_int8_t *)(P); \
__hp[0] = __cp[0] ^ __cp[12]; \
__hp[1] = __cp[1] ^ __cp[13]; \
__hp[2] = __cp[2] ^ __cp[14]; \
__hp[3] = __cp[3] ^ __cp[15]; \
return (__h); \
}
/*
* __lock_ohash --
*
* PUBLIC: u_int32_t __lock_ohash __P((const DBT *));
*/
u_int32_t
__lock_ohash(dbt)
const DBT *dbt;
{
if (dbt->size == sizeof(DB_LOCK_ILOCK))
FAST_HASH(dbt->data);
return (__ham_func5(NULL, dbt->data, dbt->size));
}
/*
* __lock_lhash --
*
* PUBLIC: u_int32_t __lock_lhash __P((DB_LOCKOBJ *));
*/
u_int32_t
__lock_lhash(lock_obj)
DB_LOCKOBJ *lock_obj;
{
void *obj_data;
obj_data = SH_DBT_PTR(&lock_obj->lockobj);
if (lock_obj->lockobj.size == sizeof(DB_LOCK_ILOCK))
FAST_HASH(obj_data);
return (__ham_func5(NULL, obj_data, lock_obj->lockobj.size));
}
/*
* __lock_nomem --
* Report a lack of some resource.
*
* PUBLIC: int __lock_nomem __P((ENV *, const char *));
*/
int
__lock_nomem(env, res)
ENV *env;
const char *res;
{
__db_errx(env, "Lock table is out of available %s", res);
return (ENOMEM);
}
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