1 /*
2 ** 2008 October 07
3 **
4 ** The author disclaims copyright to this source code. In place of
5 ** a legal notice, here is a blessing:
6 **
7 ** May you do good and not evil.
8 ** May you find forgiveness for yourself and forgive others.
9 ** May you share freely, never taking more than you give.
10 **
11 *************************************************************************
12 ** This file contains the C functions that implement mutexes.
13 **
14 ** This implementation in this file does not provide any mutual
15 ** exclusion and is thus suitable for use only in applications
16 ** that use SQLite in a single thread. The routines defined
17 ** here are place-holders. Applications can substitute working
18 ** mutex routines at start-time using the
19 **
20 ** sqlite3_config(SQLITE_CONFIG_MUTEX,...)
21 **
22 ** interface.
23 **
24 ** If compiled with SQLITE_DEBUG, then additional logic is inserted
25 ** that does error checking on mutexes to make sure they are being
26 ** called correctly.
27 */
28 #include "sqliteInt.h"
29
30 #ifndef SQLITE_MUTEX_OMIT
31
32 #ifndef SQLITE_DEBUG
33 /*
34 ** Stub routines for all mutex methods.
35 **
36 ** This routines provide no mutual exclusion or error checking.
37 */
noopMutexInit(void)38 static int noopMutexInit(void){ return SQLITE_OK; }
noopMutexEnd(void)39 static int noopMutexEnd(void){ return SQLITE_OK; }
noopMutexAlloc(int id)40 static sqlite3_mutex *noopMutexAlloc(int id){
41 UNUSED_PARAMETER(id);
42 return (sqlite3_mutex*)8;
43 }
noopMutexFree(sqlite3_mutex * p)44 static void noopMutexFree(sqlite3_mutex *p){ UNUSED_PARAMETER(p); return; }
noopMutexEnter(sqlite3_mutex * p)45 static void noopMutexEnter(sqlite3_mutex *p){ UNUSED_PARAMETER(p); return; }
noopMutexTry(sqlite3_mutex * p)46 static int noopMutexTry(sqlite3_mutex *p){
47 UNUSED_PARAMETER(p);
48 return SQLITE_OK;
49 }
noopMutexLeave(sqlite3_mutex * p)50 static void noopMutexLeave(sqlite3_mutex *p){ UNUSED_PARAMETER(p); return; }
51
sqlite3NoopMutex(void)52 sqlite3_mutex_methods const *sqlite3NoopMutex(void){
53 static const sqlite3_mutex_methods sMutex = {
54 noopMutexInit,
55 noopMutexEnd,
56 noopMutexAlloc,
57 noopMutexFree,
58 noopMutexEnter,
59 noopMutexTry,
60 noopMutexLeave,
61
62 0,
63 0,
64 };
65
66 return &sMutex;
67 }
68 #endif /* !SQLITE_DEBUG */
69
70 #ifdef SQLITE_DEBUG
71 /*
72 ** In this implementation, error checking is provided for testing
73 ** and debugging purposes. The mutexes still do not provide any
74 ** mutual exclusion.
75 */
76
77 /*
78 ** The mutex object
79 */
80 typedef struct sqlite3_debug_mutex {
81 int id; /* The mutex type */
82 int cnt; /* Number of entries without a matching leave */
83 } sqlite3_debug_mutex;
84
85 /*
86 ** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
87 ** intended for use inside assert() statements.
88 */
debugMutexHeld(sqlite3_mutex * pX)89 static int debugMutexHeld(sqlite3_mutex *pX){
90 sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
91 return p==0 || p->cnt>0;
92 }
debugMutexNotheld(sqlite3_mutex * pX)93 static int debugMutexNotheld(sqlite3_mutex *pX){
94 sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
95 return p==0 || p->cnt==0;
96 }
97
98 /*
99 ** Initialize and deinitialize the mutex subsystem.
100 */
debugMutexInit(void)101 static int debugMutexInit(void){ return SQLITE_OK; }
debugMutexEnd(void)102 static int debugMutexEnd(void){ return SQLITE_OK; }
103
104 /*
105 ** The sqlite3_mutex_alloc() routine allocates a new
106 ** mutex and returns a pointer to it. If it returns NULL
107 ** that means that a mutex could not be allocated.
108 */
debugMutexAlloc(int id)109 static sqlite3_mutex *debugMutexAlloc(int id){
110 static sqlite3_debug_mutex aStatic[SQLITE_MUTEX_STATIC_VFS3 - 1];
111 sqlite3_debug_mutex *pNew = 0;
112 switch( id ){
113 case SQLITE_MUTEX_FAST:
114 case SQLITE_MUTEX_RECURSIVE: {
115 pNew = sqlite3Malloc(sizeof(*pNew));
116 if( pNew ){
117 pNew->id = id;
118 pNew->cnt = 0;
119 }
120 break;
121 }
122 default: {
123 #ifdef SQLITE_ENABLE_API_ARMOR
124 if( id-2<0 || id-2>=ArraySize(aStatic) ){
125 (void)SQLITE_MISUSE_BKPT;
126 return 0;
127 }
128 #endif
129 pNew = &aStatic[id-2];
130 pNew->id = id;
131 break;
132 }
133 }
134 return (sqlite3_mutex*)pNew;
135 }
136
137 /*
138 ** This routine deallocates a previously allocated mutex.
139 */
debugMutexFree(sqlite3_mutex * pX)140 static void debugMutexFree(sqlite3_mutex *pX){
141 sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
142 assert( p->cnt==0 );
143 if( p->id==SQLITE_MUTEX_RECURSIVE || p->id==SQLITE_MUTEX_FAST ){
144 sqlite3_free(p);
145 }else{
146 #ifdef SQLITE_ENABLE_API_ARMOR
147 (void)SQLITE_MISUSE_BKPT;
148 #endif
149 }
150 }
151
152 /*
153 ** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
154 ** to enter a mutex. If another thread is already within the mutex,
155 ** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
156 ** SQLITE_BUSY. The sqlite3_mutex_try() interface returns SQLITE_OK
157 ** upon successful entry. Mutexes created using SQLITE_MUTEX_RECURSIVE can
158 ** be entered multiple times by the same thread. In such cases the,
159 ** mutex must be exited an equal number of times before another thread
160 ** can enter. If the same thread tries to enter any other kind of mutex
161 ** more than once, the behavior is undefined.
162 */
debugMutexEnter(sqlite3_mutex * pX)163 static void debugMutexEnter(sqlite3_mutex *pX){
164 sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
165 assert( p->id==SQLITE_MUTEX_RECURSIVE || debugMutexNotheld(pX) );
166 p->cnt++;
167 }
debugMutexTry(sqlite3_mutex * pX)168 static int debugMutexTry(sqlite3_mutex *pX){
169 sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
170 assert( p->id==SQLITE_MUTEX_RECURSIVE || debugMutexNotheld(pX) );
171 p->cnt++;
172 return SQLITE_OK;
173 }
174
175 /*
176 ** The sqlite3_mutex_leave() routine exits a mutex that was
177 ** previously entered by the same thread. The behavior
178 ** is undefined if the mutex is not currently entered or
179 ** is not currently allocated. SQLite will never do either.
180 */
debugMutexLeave(sqlite3_mutex * pX)181 static void debugMutexLeave(sqlite3_mutex *pX){
182 sqlite3_debug_mutex *p = (sqlite3_debug_mutex*)pX;
183 assert( debugMutexHeld(pX) );
184 p->cnt--;
185 assert( p->id==SQLITE_MUTEX_RECURSIVE || debugMutexNotheld(pX) );
186 }
187
sqlite3NoopMutex(void)188 sqlite3_mutex_methods const *sqlite3NoopMutex(void){
189 static const sqlite3_mutex_methods sMutex = {
190 debugMutexInit,
191 debugMutexEnd,
192 debugMutexAlloc,
193 debugMutexFree,
194 debugMutexEnter,
195 debugMutexTry,
196 debugMutexLeave,
197
198 debugMutexHeld,
199 debugMutexNotheld
200 };
201
202 return &sMutex;
203 }
204 #endif /* SQLITE_DEBUG */
205
206 /*
207 ** If compiled with SQLITE_MUTEX_NOOP, then the no-op mutex implementation
208 ** is used regardless of the run-time threadsafety setting.
209 */
210 #ifdef SQLITE_MUTEX_NOOP
sqlite3DefaultMutex(void)211 sqlite3_mutex_methods const *sqlite3DefaultMutex(void){
212 return sqlite3NoopMutex();
213 }
214 #endif /* defined(SQLITE_MUTEX_NOOP) */
215 #endif /* !defined(SQLITE_MUTEX_OMIT) */
216