4 ** The author disclaims copyright to this source code. In place of
5 ** a legal notice, here is a blessing:
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.
11 *************************************************************************
12 ** This file contains the C functions that implement mutexes.
14 ** This file contains code that is common across all mutex implementations.
17 ** $Id: mutex.c,v 1.29 2008/10/07 15:25:48 drh Exp $
19 #include "sqliteInt.h"
21 #ifndef SQLITE_MUTEX_OMIT
23 ** Initialize the mutex system.
25 int sqlite3MutexInit(void){
27 if( sqlite3GlobalConfig.bCoreMutex ){
28 if( !sqlite3GlobalConfig.mutex.xMutexAlloc ){
29 /* If the xMutexAlloc method has not been set, then the user did not
30 ** install a mutex implementation via sqlite3_config() prior to
31 ** sqlite3_initialize() being called. This block copies pointers to
32 ** the default implementation into the sqlite3GlobalConfig structure.
34 ** The danger is that although sqlite3_config() is not a threadsafe
35 ** API, sqlite3_initialize() is, and so multiple threads may be
36 ** attempting to run this function simultaneously. To guard write
37 ** access to the sqlite3GlobalConfig structure, the 'MASTER' static mutex
38 ** is obtained before modifying it.
40 sqlite3_mutex_methods *p = sqlite3DefaultMutex();
41 sqlite3_mutex *pMaster = 0;
45 pMaster = p->xMutexAlloc(SQLITE_MUTEX_STATIC_MASTER);
47 p->xMutexEnter(pMaster);
48 assert( sqlite3GlobalConfig.mutex.xMutexAlloc==0
49 || sqlite3GlobalConfig.mutex.xMutexAlloc==p->xMutexAlloc
51 if( !sqlite3GlobalConfig.mutex.xMutexAlloc ){
52 sqlite3GlobalConfig.mutex = *p;
54 p->xMutexLeave(pMaster);
57 rc = sqlite3GlobalConfig.mutex.xMutexInit();
65 ** Shutdown the mutex system. This call frees resources allocated by
66 ** sqlite3MutexInit().
68 int sqlite3MutexEnd(void){
70 if( sqlite3GlobalConfig.mutex.xMutexEnd ){
71 rc = sqlite3GlobalConfig.mutex.xMutexEnd();
77 ** Retrieve a pointer to a static mutex or allocate a new dynamic one.
79 sqlite3_mutex *sqlite3_mutex_alloc(int id){
80 #ifndef SQLITE_OMIT_AUTOINIT
81 if( sqlite3_initialize() ) return 0;
83 return sqlite3GlobalConfig.mutex.xMutexAlloc(id);
86 sqlite3_mutex *sqlite3MutexAlloc(int id){
87 if( !sqlite3GlobalConfig.bCoreMutex ){
90 return sqlite3GlobalConfig.mutex.xMutexAlloc(id);
94 ** Free a dynamic mutex.
96 void sqlite3_mutex_free(sqlite3_mutex *p){
98 sqlite3GlobalConfig.mutex.xMutexFree(p);
103 ** Obtain the mutex p. If some other thread already has the mutex, block
104 ** until it can be obtained.
106 void sqlite3_mutex_enter(sqlite3_mutex *p){
108 sqlite3GlobalConfig.mutex.xMutexEnter(p);
113 ** Obtain the mutex p. If successful, return SQLITE_OK. Otherwise, if another
114 ** thread holds the mutex and it cannot be obtained, return SQLITE_BUSY.
116 int sqlite3_mutex_try(sqlite3_mutex *p){
119 return sqlite3GlobalConfig.mutex.xMutexTry(p);
125 ** The sqlite3_mutex_leave() routine exits a mutex that was previously
126 ** entered by the same thread. The behavior is undefined if the mutex
127 ** is not currently entered. If a NULL pointer is passed as an argument
128 ** this function is a no-op.
130 void sqlite3_mutex_leave(sqlite3_mutex *p){
132 sqlite3GlobalConfig.mutex.xMutexLeave(p);
138 ** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
139 ** intended for use inside assert() statements.
141 int sqlite3_mutex_held(sqlite3_mutex *p){
142 return p==0 || sqlite3GlobalConfig.mutex.xMutexHeld(p);
144 int sqlite3_mutex_notheld(sqlite3_mutex *p){
145 return p==0 || sqlite3GlobalConfig.mutex.xMutexNotheld(p);
149 #endif /* SQLITE_OMIT_MUTEX */