1/*-
2 * See the file LICENSE for redistribution information.
3 *
4 * Copyright (c) 1996, 1997, 1998
5 *	Sleepycat Software.  All rights reserved.
6 */
7
8#include "config.h"
9
10#ifndef lint
11static const char sccsid[] = "@(#)lock_util.c	10.10 (Sleepycat) 9/20/98";
12#endif /* not lint */
13
14#ifndef NO_SYSTEM_INCLUDES
15#include <sys/types.h>
16
17#include <string.h>
18#endif
19
20#include "db_int.h"
21#include "shqueue.h"
22#include "db_page.h"
23#include "db_shash.h"
24#include "hash.h"
25#include "lock.h"
26
27/*
28 * __lock_cmp --
29 *	This function is used to compare a DBT that is about to be entered
30 *	into a hash table with an object already in the hash table.  Note
31 *	that it just returns true on equal and 0 on not-equal.  Therefore
32 *	this function cannot be used as a sort function; its purpose is to
33 *	be used as a hash comparison function.
34 *
35 * PUBLIC: int __lock_cmp __P((const DBT *, DB_LOCKOBJ *));
36 */
37int
38__lock_cmp(dbt, lock_obj)
39	const DBT *dbt;
40	DB_LOCKOBJ *lock_obj;
41{
42	void *obj_data;
43
44	if (lock_obj->type != DB_LOCK_OBJTYPE)
45		return (0);
46
47	obj_data = SH_DBT_PTR(&lock_obj->lockobj);
48	return (dbt->size == lock_obj->lockobj.size &&
49		memcmp(dbt->data, obj_data, dbt->size) == 0);
50}
51
52/*
53 * PUBLIC: int __lock_locker_cmp __P((u_int32_t, DB_LOCKOBJ *));
54 */
55int
56__lock_locker_cmp(locker, lock_obj)
57	u_int32_t locker;
58	DB_LOCKOBJ *lock_obj;
59{
60	void *obj_data;
61
62	if (lock_obj->type != DB_LOCK_LOCKER)
63		return (0);
64
65	obj_data = SH_DBT_PTR(&lock_obj->lockobj);
66	return (memcmp(&locker, obj_data, sizeof(u_int32_t)) == 0);
67}
68
69/*
70 * The next two functions are the hash functions used to store objects in the
71 * lock hash table.  They are hashing the same items, but one (__lock_ohash)
72 * takes a DBT (used for hashing a parameter passed from the user) and the
73 * other (__lock_lhash) takes a DB_LOCKOBJ (used for hashing something that is
74 * already in the lock manager).  In both cases, we have a special check to
75 * fast path the case where we think we are doing a hash on a DB page/fileid
76 * pair.  If the size is right, then we do the fast hash.
77 *
78 * We know that DB uses DB_LOCK_ILOCK types for its lock objects.  The first
79 * four bytes are the 4-byte page number and the next DB_FILE_ID_LEN bytes
80 * are a unique file id, where the first 4 bytes on UNIX systems are the file
81 * inode number, and the first 4 bytes on Windows systems are the FileIndexLow
82 * bytes.  So, we use the XOR of the page number and the first four bytes of
83 * the file id to produce a 32-bit hash value.
84 *
85 * We have no particular reason to believe that this algorithm will produce
86 * a good hash, but we want a fast hash more than we want a good one, when
87 * we're coming through this code path.
88 */
89#define FAST_HASH(P) {			\
90	u_int32_t __h;			\
91	u_int8_t *__cp, *__hp;		\
92	__hp = (u_int8_t *)&__h;	\
93	__cp = (u_int8_t *)(P);		\
94	__hp[0] = __cp[0] ^ __cp[4];	\
95	__hp[1] = __cp[1] ^ __cp[5];	\
96	__hp[2] = __cp[2] ^ __cp[6];	\
97	__hp[3] = __cp[3] ^ __cp[7];	\
98	return (__h);			\
99}
100
101/*
102 * __lock_ohash --
103 *
104 * PUBLIC: u_int32_t __lock_ohash __P((const DBT *));
105 */
106u_int32_t
107__lock_ohash(dbt)
108	const DBT *dbt;
109{
110	if (dbt->size == sizeof(DB_LOCK_ILOCK))
111		FAST_HASH(dbt->data);
112
113	return (__ham_func5(dbt->data, dbt->size));
114}
115
116/*
117 * __lock_lhash --
118 *
119 * PUBLIC: u_int32_t __lock_lhash __P((DB_LOCKOBJ *));
120 */
121u_int32_t
122__lock_lhash(lock_obj)
123	DB_LOCKOBJ *lock_obj;
124{
125	u_int32_t tmp;
126	void *obj_data;
127
128	obj_data = SH_DBT_PTR(&lock_obj->lockobj);
129	if (lock_obj->type == DB_LOCK_LOCKER) {
130		memcpy(&tmp, obj_data, sizeof(u_int32_t));
131		return (tmp);
132	}
133
134	if (lock_obj->lockobj.size == sizeof(DB_LOCK_ILOCK))
135		FAST_HASH(obj_data);
136
137	return (__ham_func5(obj_data, lock_obj->lockobj.size));
138}
139
140/*
141 * __lock_locker_hash --
142 *	Hash function for entering lockers into the hash table.  Since these
143 *	are simply 32-bit unsigned integers, just return the locker value.
144 *
145 * PUBLIC: u_int32_t __lock_locker_hash __P((u_int32_t));
146 */
147u_int32_t
148__lock_locker_hash(locker)
149	u_int32_t locker;
150{
151	return (locker);
152}
153