/*
** Initialize the mutex system.
*/
int sqlite3MutexInit(void){
int rc = SQLITE_OK;
if( !sqlite3GlobalConfig.mutex.xMutexAlloc ){
/* If the xMutexAlloc method has not been set, then the user did not
** install a mutex implementation via sqlite3_config() prior to
** sqlite3_initialize() being called. This block copies pointers to
** the default implementation into the sqlite3GlobalConfig structure.
*/
sqlite3_mutex_methods const *pFrom;
sqlite3_mutex_methods *pTo = &sqlite3GlobalConfig.mutex;
if( sqlite3GlobalConfig.bCoreMutex ){
pFrom = sqlite3DefaultMutex();
}else{
pFrom = sqlite3NoopMutex();
}
memcpy(pTo, pFrom, offsetof(sqlite3_mutex_methods, xMutexAlloc));
memcpy(&pTo->xMutexFree, &pFrom->xMutexFree,
sizeof(*pTo) - offsetof(sqlite3_mutex_methods, xMutexFree));
pTo->xMutexAlloc = pFrom->xMutexAlloc;
}
rc = sqlite3GlobalConfig.mutex.xMutexInit();
#ifdef SQLITE_DEBUG
GLOBAL(int, mutexIsInit) = 1;
#endif
return rc;
}
/*
** Initialize the mutex system.
*/
int sqlite3MutexInit(void){
int rc = SQLITE_OK;
if( !sqlite3GlobalConfig.mutex.xMutexAlloc ){
/* If the xMutexAlloc method has not been set, then the user did not
** install a mutex implementation via sqlite3_config() prior to
** sqlite3_initialize() being called. This block copies pointers to
** the default implementation into the sqlite3GlobalConfig structure.
*/
// ** the default implementation into the sqlite3GlobalConfig structure.
// **如果xMutexAlloc 函数没设置，
// ** 这段复制指针向sqlite3GlobalConfig默认实现结构。
// */
//////////////////////////////////////////////////////////////////////////
/************************************************************************/
/* 我是华丽的分割线 */
//这段内容讲sqliteInt.h" 中sqlite3_mutex_methods结构体中 mutex 的xMutexAlloc无定义，则从sqlite3_mutex_methods 复制一个
/************************************************************************/
//majin78 xMutexAlloc未设置，定义于"sqliteInt.h" 前提是系统不支持可写静态数据
//内容为 #define sqlite3GlobalConfig GLOBAL(struct Sqlite3Config, sqlite3Config) 宏定义为Sqlite3Config结构体，后一参数为结构体size
//majin78 sqlite3GlobalConfig.mutex 属性为sqlite3_mem_methods 定义于sqlite3.h 内容为 typedef struct sqlite3_mutex_methods sqlite3_mutex_methods;
//struct sqlite3_mutex_methods 定义于sqlite3.h 为一些函数指针
sqlite3_mutex_methods const *pFrom;
sqlite3_mutex_methods *pTo = &sqlite3GlobalConfig.mutex;
if( sqlite3GlobalConfig.bCoreMutex ){// 定义于"sqliteInt.h" 内容为 int bCoreMutex; /* True to enable core mutexing */
pFrom = sqlite3DefaultMutex();//定义于"sqliteInt.h" sqlite3_mutex_methods const *类型 需先定义SQLITE_MUTEX_OMIT
}else{
pFrom = sqlite3NoopMutex();// 定义于"sqliteInt.h" sqlite3_mutex_methods const *类型 需先定义SQLITE_MUTEX_OMIT
}
memcpy(pTo, pFrom, offsetof(sqlite3_mutex_methods, xMutexAlloc));//offsetof该宏用于求结构体中一个成员在该结构体中的偏移量。
memcpy(&pTo->xMutexFree, &pFrom->xMutexFree,
sizeof(*pTo) - offsetof(sqlite3_mutex_methods, xMutexFree));
pTo->xMutexAlloc = pFrom->xMutexAlloc;
}
rc = sqlite3GlobalConfig.mutex.xMutexInit();
#ifdef SQLITE_DEBUG//调试时支持支持可写静态数据
GLOBAL(int, mutexIsInit) = 1;//mutexIsInit赋值1
#endif
return rc;
}
/*
** Initialize the mutex system.
*/
int sqlite3MutexInit(void){
int rc = SQLITE_OK;
if( sqlite3GlobalConfig.bCoreMutex ){
if( !sqlite3GlobalConfig.mutex.xMutexAlloc ){
/* If the xMutexAlloc method has not been set, then the user did not
** install a mutex implementation via sqlite3_config() prior to
** sqlite3_initialize() being called. This block copies pointers to
** the default implementation into the sqlite3GlobalConfig structure.
**
** The danger is that although sqlite3_config() is not a threadsafe
** API, sqlite3_initialize() is, and so multiple threads may be
** attempting to run this function simultaneously. To guard write
** access to the sqlite3GlobalConfig structure, the 'MASTER' static mutex
** is obtained before modifying it.
*/
sqlite3_mutex_methods *p = sqlite3DefaultMutex();
sqlite3_mutex *pMaster = 0;
rc = p->xMutexInit();
if( rc==SQLITE_OK ){
pMaster = p->xMutexAlloc(SQLITE_MUTEX_STATIC_MASTER);
assert(pMaster);
p->xMutexEnter(pMaster);
assert( sqlite3GlobalConfig.mutex.xMutexAlloc==0
|| sqlite3GlobalConfig.mutex.xMutexAlloc==p->xMutexAlloc
);
if( !sqlite3GlobalConfig.mutex.xMutexAlloc ){
sqlite3GlobalConfig.mutex = *p;
}
p->xMutexLeave(pMaster);
}
}else{
rc = sqlite3GlobalConfig.mutex.xMutexInit();
}
}
return rc;
}
