lock_util.c
上传用户:romrleung
上传日期:2022-05-23
资源大小:18897k
文件大小:4k
- /*-
- * See the file LICENSE for redistribution information.
- *
- * Copyright (c) 1996-2002
- * Sleepycat Software. All rights reserved.
- */
- #include "db_config.h"
- #ifndef lint
- static const char revid[] = "$Id: lock_util.c,v 11.8 2002/03/27 04:32:20 bostic Exp $";
- #endif /* not lint */
- #ifndef NO_SYSTEM_INCLUDES
- #include <sys/types.h>
- #include <string.h>
- #endif
- #include "db_int.h"
- #include "dbinc/db_page.h"
- #include "dbinc/db_shash.h"
- #include "dbinc/hash.h"
- #include "dbinc/lock.h"
- /*
- * __lock_cmp --
- * This function is used to compare a DBT that is about to be entered
- * into a hash table with an object already in the hash table. Note
- * that it just returns true on equal and 0 on not-equal. Therefore
- * this function cannot be used as a sort function; its purpose is to
- * be used as a hash comparison function.
- *
- * PUBLIC: int __lock_cmp __P((const DBT *, DB_LOCKOBJ *));
- */
- int
- __lock_cmp(dbt, lock_obj)
- const DBT *dbt;
- DB_LOCKOBJ *lock_obj;
- {
- void *obj_data;
- obj_data = SH_DBT_PTR(&lock_obj->lockobj);
- return (dbt->size == lock_obj->lockobj.size &&
- memcmp(dbt->data, obj_data, dbt->size) == 0);
- }
- /*
- * PUBLIC: int __lock_locker_cmp __P((u_int32_t, DB_LOCKER *));
- */
- int
- __lock_locker_cmp(locker, sh_locker)
- u_int32_t locker;
- DB_LOCKER *sh_locker;
- {
- return (locker == sh_locker->id);
- }
- /*
- * 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. So, we use the XOR of the page number and the first four bytes of
- * the file id 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[4];
- __hp[1] = __cp[1] ^ __cp[5];
- __hp[2] = __cp[2] ^ __cp[6];
- __hp[3] = __cp[3] ^ __cp[7];
- 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_locker_hash --
- * Hash function for entering lockers into the locker hash table.
- * Since these are simply 32-bit unsigned integers, just return
- * the locker value.
- *
- * PUBLIC: u_int32_t __lock_locker_hash __P((u_int32_t));
- */
- u_int32_t
- __lock_locker_hash(locker)
- u_int32_t locker;
- {
- return (locker);
- }