1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
|
/*-
* See the file LICENSE for redistribution information.
*
* Copyright (c) 1996, 1997, 1998, 1999
* Sleepycat Software. All rights reserved.
*/
#include "db_config.h"
#ifdef HAVE_MUTEX_FCNTL
#ifndef lint
static const char sccsid[] = "@(#)mut_fcntl.c 11.1 (Sleepycat) 7/25/99";
#endif /* not lint */
#ifndef NO_SYSTEM_INCLUDES
#include <sys/types.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#endif
#include "db_int.h"
/*
* CDB___db_fcntl_mutex_init --
* Initialize a DB mutex structure.
*
* PUBLIC: int CDB___db_fcntl_mutex_init __P((DB_ENV *, MUTEX *, u_int32_t));
*/
int
CDB___db_fcntl_mutex_init(dbenv, mutexp, offset)
DB_ENV *dbenv;
MUTEX *mutexp;
u_int32_t offset;
{
memset(mutexp, 0, sizeof(*mutexp));
/*
* This is where we decide to ignore locks we don't need to set -- if
* the application is private, we don't need any locks.
*/
if (F_ISSET(dbenv, DB_ENV_PRIVATE)) {
F_SET(mutexp, MUTEX_IGNORE);
return (0);
}
mutexp->off = offset;
return (0);
}
/*
* CDB___db_fcntl_mutex_lock
* Lock on a mutex, blocking if necessary.
*
* PUBLIC: int CDB___db_fcntl_mutex_lock __P((MUTEX *, DB_FH *));
*/
int
CDB___db_fcntl_mutex_lock(mutexp, fhp)
MUTEX *mutexp;
DB_FH *fhp;
{
struct flock k_lock;
int locked, ms, waited;
if (!DB_GLOBAL(db_mutexlocks))
return (0);
/* Initialize the lock. */
k_lock.l_whence = SEEK_SET;
k_lock.l_start = mutexp->off;
k_lock.l_len = 1;
for (locked = waited = 0;;) {
/*
* Wait for the lock to become available; wait 1ms initially,
* up to 1 second.
*/
for (ms = 1; mutexp->pid != 0;) {
waited = 1;
CDB___os_yield(ms * USEC_PER_MS);
if ((ms <<= 1) > MS_PER_SEC)
ms = MS_PER_SEC;
}
/* Acquire an exclusive kernel lock. */
k_lock.l_type = F_WRLCK;
if (fcntl(fhp->fd, F_SETLKW, &k_lock))
return (CDB___os_get_errno());
/* If the resource is still available, it's ours. */
if (mutexp->pid == 0) {
locked = 1;
mutexp->pid = (u_int32_t)getpid();
}
/* Release the kernel lock. */
k_lock.l_type = F_UNLCK;
if (fcntl(fhp->fd, F_SETLK, &k_lock))
return (CDB___os_get_errno());
/*
* If we got the resource lock we're done.
*
* !!!
* We can't check to see if the lock is ours, because we may
* be trying to block ourselves in the lock manager, and so
* the holder of the lock that's preventing us from getting
* the lock may be us! (Seriously.)
*/
if (locked)
break;
}
if (waited)
++mutexp->mutex_set_wait;
else
++mutexp->mutex_set_nowait;
return (0);
}
/*
* CDB___db_fcntl_mutex_unlock --
* Release a lock.
*
* PUBLIC: int CDB___db_fcntl_mutex_unlock __P((MUTEX *));
*/
int
CDB___db_fcntl_mutex_unlock(mutexp)
MUTEX *mutexp;
{
if (!DB_GLOBAL(db_mutexlocks))
return (0);
#ifdef DIAGNOSTIC
#define MSG "mutex_unlock: ERROR: released lock that was unlocked\n"
#ifndef STDERR_FILENO
#define STDERR_FILENO 2
#endif
if (mutexp->pid == 0)
write(STDERR_FILENO, MSG, sizeof(MSG) - 1);
#endif
/*
* Release the resource. We don't have to acquire any locks because
* processes trying to acquire the lock are checking for a pid set to
* 0/non-0, not to any specific value.
*/
mutexp->pid = 0;
return (0);
}
#endif /* HAVE_MUTEX_FCNTL */
|
