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
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
|
/*
** 2007 August 28
**
** The author disclaims copyright to this source code. In place of
** a legal notice, here is a blessing:
**
** May you do good and not evil.
** May you find forgiveness for yourself and forgive others.
** May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains the C functions that implement mutexes for pthreads
**
** $Id: mutex_unix.c,v 1.2 2007/08/28 22:24:35 drh Exp $
*/
#include "sqliteInt.h"
/*
** The code in this file is only used if we are compiling threadsafe
** under unix with pthreads.
**
** Note that this implementation requires a version of pthreads that
** supports recursive mutexes.
*/
#ifdef SQLITE_MUTEX_PTHREADS
#include <pthread.h>
/*
** Each recursive mutex is an instance of the following structure.
*/
struct sqlite3_mutex {
pthread_mutex_t mutex; /* Mutex controlling the lock */
int id; /* Mutex type */
int nRef; /* Number of entrances */
pthread_t owner; /* Thread that is within this mutex */
#ifdef SQLITE_DEBUG
int trace; /* True to trace changes */
#endif
};
/*
** The sqlite3_mutex_alloc() routine allocates a new
** mutex and returns a pointer to it. If it returns NULL
** that means that a mutex could not be allocated. SQLite
** will unwind its stack and return an error. The argument
** to sqlite3_mutex_alloc() is one of these integer constants:
**
** <ul>
** <li> SQLITE_MUTEX_FAST
** <li> SQLITE_MUTEX_RECURSIVE
** <li> SQLITE_MUTEX_STATIC_MASTER
** <li> SQLITE_MUTEX_STATIC_MEM
** <li> SQLITE_MUTEX_STATIC_MEM2
** <li> SQLITE_MUTEX_STATIC_PRNG
** <li> SQLITE_MUTEX_STATIC_LRU
** </ul>
**
** The first two constants cause sqlite3_mutex_alloc() to create
** a new mutex. The new mutex is recursive when SQLITE_MUTEX_RECURSIVE
** is used but not necessarily so when SQLITE_MUTEX_FAST is used.
** The mutex implementation does not need to make a distinction
** between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does
** not want to. But SQLite will only request a recursive mutex in
** cases where it really needs one. If a faster non-recursive mutex
** implementation is available on the host platform, the mutex subsystem
** might return such a mutex in response to SQLITE_MUTEX_FAST.
**
** The other allowed parameters to sqlite3_mutex_alloc() each return
** a pointer to a static preexisting mutex. Three static mutexes are
** used by the current version of SQLite. Future versions of SQLite
** may add additional static mutexes. Static mutexes are for internal
** use by SQLite only. Applications that use SQLite mutexes should
** use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or
** SQLITE_MUTEX_RECURSIVE.
**
** Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST
** or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc()
** returns a different mutex on every call. But for the static
** mutex types, the same mutex is returned on every call that has
** the same type number.
*/
sqlite3_mutex *sqlite3_mutex_alloc(int iType){
static sqlite3_mutex staticMutexes[] = {
{ PTHREAD_MUTEX_INITIALIZER, },
{ PTHREAD_MUTEX_INITIALIZER, },
{ PTHREAD_MUTEX_INITIALIZER, },
{ PTHREAD_MUTEX_INITIALIZER, },
{ PTHREAD_MUTEX_INITIALIZER, },
};
sqlite3_mutex *p;
switch( iType ){
case SQLITE_MUTEX_RECURSIVE: {
p = sqlite3MallocZero( sizeof(*p) );
if( p ){
pthread_mutexattr_t recursiveAttr;
pthread_mutexattr_init(&recursiveAttr);
pthread_mutexattr_settype(&recursiveAttr, PTHREAD_MUTEX_RECURSIVE);
pthread_mutex_init(&p->mutex, &recursiveAttr);
pthread_mutexattr_destroy(&recursiveAttr);
p->id = iType;
}
break;
}
case SQLITE_MUTEX_FAST: {
p = sqlite3MallocZero( sizeof(*p) );
if( p ){
p->id = iType;
pthread_mutex_init(&p->mutex, 0);
}
break;
}
default: {
assert( iType-2 >= 0 );
assert( iType-2 < sizeof(staticMutexes)/sizeof(staticMutexes[0]) );
p = &staticMutexes[iType-2];
p->id = iType;
break;
}
}
return p;
}
/*
** This routine deallocates a previously
** allocated mutex. SQLite is careful to deallocate every
** mutex that it allocates.
*/
void sqlite3_mutex_free(sqlite3_mutex *p){
assert( p );
assert( p->nRef==0 );
assert( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE );
pthread_mutex_destroy(&p->mutex);
sqlite3_free(p);
}
/*
** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
** to enter a mutex. If another thread is already within the mutex,
** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
** SQLITE_BUSY. The sqlite3_mutex_try() interface returns SQLITE_OK
** upon successful entry. Mutexes created using SQLITE_MUTEX_RECURSIVE can
** be entered multiple times by the same thread. In such cases the,
** mutex must be exited an equal number of times before another thread
** can enter. If the same thread tries to enter any other kind of mutex
** more than once, the behavior is undefined.
*/
void sqlite3_mutex_enter(sqlite3_mutex *p){
assert( p );
assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
pthread_mutex_lock(&p->mutex);
p->owner = pthread_self();
p->nRef++;
#ifdef SQLITE_DEBUG
if( p->trace ){
printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
}
#endif
}
int sqlite3_mutex_try(sqlite3_mutex *p){
int rc;
assert( p );
assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
if( pthread_mutex_trylock(&p->mutex)==0 ){
p->owner = pthread_self();
p->nRef++;
rc = SQLITE_OK;
#ifdef SQLITE_DEBUG
if( p->trace ){
printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
}
#endif
}else{
rc = SQLITE_BUSY;
}
return rc;
}
/*
** The sqlite3_mutex_leave() routine exits a mutex that was
** previously entered by the same thread. The behavior
** is undefined if the mutex is not currently entered or
** is not currently allocated. SQLite will never do either.
*/
void sqlite3_mutex_leave(sqlite3_mutex *p){
assert( p );
assert( sqlite3_mutex_held(p) );
p->nRef--;
assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );
#ifdef SQLITE_DEBUG
if( p->trace ){
printf("leave mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
}
#endif
pthread_mutex_unlock(&p->mutex);
}
/*
** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
** intended for use only inside assert() statements. On some platforms,
** there might be race conditions that can cause these routines to
** deliver incorrect results. In particular, if pthread_equal() is
** not an atomic operation, then these routines might delivery
** incorrect results. On most platforms, pthread_equal() is a
** comparison of two integers and is therefore atomic. But we are
** told that HPUX is not such a platform. If so, then these routines
** will not always work correctly on HPUX.
**
** On those platforms where pthread_equal() is not atomic, SQLite
** should be compiled without -DSQLITE_DEBUG and with -DNDEBUG to
** make sure no assert() statements are evaluated and hence these
** routines are never called.
*/
#ifndef NDEBUG
int sqlite3_mutex_held(sqlite3_mutex *p){
return p==0 || (p->nRef!=0 && pthread_equal(p->owner, pthread_self()));
}
int sqlite3_mutex_notheld(sqlite3_mutex *p){
return p==0 || p->nRef==0 || pthread_equal(p->owner, pthread_self())==0;
}
#endif
#endif /* SQLITE_MUTEX_PTHREAD */
|
