1 /* 2 ** 2007 August 14 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 file contains code that is common across all mutex implementations. 15 */ 16 #include "sqliteInt.h" 17 18 #if defined(SQLITE_DEBUG) && !defined(SQLITE_MUTEX_OMIT) 19 /* 20 ** For debugging purposes, record when the mutex subsystem is initialized 21 ** and uninitialized so that we can assert() if there is an attempt to 22 ** allocate a mutex while the system is uninitialized. 23 */ 24 static SQLITE_WSD int mutexIsInit = 0; 25 #endif /* SQLITE_DEBUG */ 26 27 28 #ifndef SQLITE_MUTEX_OMIT 29 /* 30 ** Initialize the mutex system. 31 */ 32 int sqlite3MutexInit(void){ 33 int rc = SQLITE_OK; 34 if( !sqlite3GlobalConfig.mutex.xMutexAlloc ){ 35 /* If the xMutexAlloc method has not been set, then the user did not 36 ** install a mutex implementation via sqlite3_config() prior to 37 ** sqlite3_initialize() being called. This block copies pointers to 38 ** the default implementation into the sqlite3GlobalConfig structure. 39 */ 40 sqlite3_mutex_methods const *pFrom; 41 sqlite3_mutex_methods *pTo = &sqlite3GlobalConfig.mutex; 42 43 if( sqlite3GlobalConfig.bCoreMutex ){ 44 pFrom = sqlite3DefaultMutex(); 45 }else{ 46 pFrom = sqlite3NoopMutex(); 47 } 48 memcpy(pTo, pFrom, offsetof(sqlite3_mutex_methods, xMutexAlloc)); 49 memcpy(&pTo->xMutexFree, &pFrom->xMutexFree, 50 sizeof(*pTo) - offsetof(sqlite3_mutex_methods, xMutexFree)); 51 pTo->xMutexAlloc = pFrom->xMutexAlloc; 52 } 53 rc = sqlite3GlobalConfig.mutex.xMutexInit(); 54 55 #ifdef SQLITE_DEBUG 56 GLOBAL(int, mutexIsInit) = 1; 57 #endif 58 59 return rc; 60 } 61 62 /* 63 ** Shutdown the mutex system. This call frees resources allocated by 64 ** sqlite3MutexInit(). 65 */ 66 int sqlite3MutexEnd(void){ 67 int rc = SQLITE_OK; 68 if( sqlite3GlobalConfig.mutex.xMutexEnd ){ 69 rc = sqlite3GlobalConfig.mutex.xMutexEnd(); 70 } 71 72 #ifdef SQLITE_DEBUG 73 GLOBAL(int, mutexIsInit) = 0; 74 #endif 75 76 return rc; 77 } 78 79 /* 80 ** Retrieve a pointer to a static mutex or allocate a new dynamic one. 81 */ 82 sqlite3_mutex *sqlite3_mutex_alloc(int id){ 83 #ifndef SQLITE_OMIT_AUTOINIT 84 if( sqlite3_initialize() ) return 0; 85 #endif 86 return sqlite3GlobalConfig.mutex.xMutexAlloc(id); 87 } 88 89 sqlite3_mutex *sqlite3MutexAlloc(int id){ 90 if( !sqlite3GlobalConfig.bCoreMutex ){ 91 return 0; 92 } 93 assert( GLOBAL(int, mutexIsInit) ); 94 return sqlite3GlobalConfig.mutex.xMutexAlloc(id); 95 } 96 97 /* 98 ** Free a dynamic mutex. 99 */ 100 void sqlite3_mutex_free(sqlite3_mutex *p){ 101 if( p ){ 102 sqlite3GlobalConfig.mutex.xMutexFree(p); 103 } 104 } 105 106 /* 107 ** Obtain the mutex p. If some other thread already has the mutex, block 108 ** until it can be obtained. 109 */ 110 void sqlite3_mutex_enter(sqlite3_mutex *p){ 111 if( p ){ 112 sqlite3GlobalConfig.mutex.xMutexEnter(p); 113 } 114 } 115 116 /* 117 ** Obtain the mutex p. If successful, return SQLITE_OK. Otherwise, if another 118 ** thread holds the mutex and it cannot be obtained, return SQLITE_BUSY. 119 */ 120 int sqlite3_mutex_try(sqlite3_mutex *p){ 121 int rc = SQLITE_OK; 122 if( p ){ 123 return sqlite3GlobalConfig.mutex.xMutexTry(p); 124 } 125 return rc; 126 } 127 128 /* 129 ** The sqlite3_mutex_leave() routine exits a mutex that was previously 130 ** entered by the same thread. The behavior is undefined if the mutex 131 ** is not currently entered. If a NULL pointer is passed as an argument 132 ** this function is a no-op. 133 */ 134 void sqlite3_mutex_leave(sqlite3_mutex *p){ 135 if( p ){ 136 sqlite3GlobalConfig.mutex.xMutexLeave(p); 137 } 138 } 139 140 #ifndef NDEBUG 141 /* 142 ** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are 143 ** intended for use inside assert() statements. 144 */ 145 int sqlite3_mutex_held(sqlite3_mutex *p){ 146 return p==0 || sqlite3GlobalConfig.mutex.xMutexHeld(p); 147 } 148 int sqlite3_mutex_notheld(sqlite3_mutex *p){ 149 return p==0 || sqlite3GlobalConfig.mutex.xMutexNotheld(p); 150 } 151 #endif 152 153 #endif /* !defined(SQLITE_MUTEX_OMIT) */ 154