/*
** 2007 August 14
**
** 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.
**
** This file contains code that is common across all mutex implementations.
*/
#include "sqliteInt.h"
#if defined(SQLITE_DEBUG) && !defined(SQLITE_MUTEX_OMIT)
/*
** For debugging purposes, record when the mutex subsystem is initialized
** and uninitialized so that we can assert() if there is an attempt to
** allocate a mutex while the system is uninitialized.
*/
static SQLITE_WSD int mutexIsInit = 0;
#endif /* SQLITE_DEBUG && !defined(SQLITE_MUTEX_OMIT) */
#ifndef SQLITE_MUTEX_OMIT
/*
** Copies a mutex implementation. Both arguments must point to valid
** memory.
*/
void sqlite3MutexCopy(
sqlite3_mutex_methods *pTo,
sqlite3_mutex_methods const *pFrom
){
pTo->xMutexInit = pFrom->xMutexInit;
pTo->xMutexEnd = pFrom->xMutexEnd;
pTo->xMutexFree = pFrom->xMutexFree;
pTo->xMutexEnter = pFrom->xMutexEnter;
pTo->xMutexTry = pFrom->xMutexTry;
pTo->xMutexLeave = pFrom->xMutexLeave;
pTo->xMutexHeld = pFrom->xMutexHeld;
pTo->xMutexNotheld = pFrom->xMutexNotheld;
pTo->xMutexAlloc = pFrom->xMutexAlloc;
}
/*
** Initialize the mutex system.
*/
int sqlite3MutexInit(void){
int rc;
sqlite3MemoryBarrier();
if( sqlite3CompareAndSwap(
(void * volatile *)&sqlite3GlobalConfig.mutex.xMutexAlloc,
0, sqlite3GlobalConfig.mutex.xMutexAlloc)==0 ){
/* 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;
if( sqlite3GlobalConfig.bCoreMutex ){
pFrom = sqlite3DefaultMutex();
}else{
pFrom = sqlite3NoopMutex();
}
sqlite3MutexCopy(&sqlite3GlobalConfig.mutex, pFrom);
sqlite3MemoryBarrier();
}
assert( sqlite3GlobalConfig.mutex.xMutexInit );
rc = sqlite3GlobalConfig.mutex.xMutexInit();
#ifdef SQLITE_DEBUG
GLOBAL(int, mutexIsInit) = 1;
#endif
return rc;
}
/*
** Shutdown the mutex system. This call frees resources allocated by
** sqlite3MutexInit().
*/
int sqlite3MutexEnd(void){
int rc = SQLITE_OK;
if( sqlite3GlobalConfig.mutex.xMutexEnd ){
rc = sqlite3GlobalConfig.mutex.xMutexEnd();
}
#ifdef SQLITE_DEBUG
GLOBAL(int, mutexIsInit) = 0;
#endif
return rc;
}
/*
** Retrieve a pointer to a static mutex or allocate a new dynamic one.
*/
sqlite3_mutex *sqlite3_mutex_alloc(int id){
#ifndef SQLITE_OMIT_AUTOINIT
if( id<=SQLITE_MUTEX_RECURSIVE && sqlite3_initialize() ) return 0;
if( id>SQLITE_MUTEX_RECURSIVE && sqlite3MutexInit() ) return 0;
#endif
assert( sqlite3GlobalConfig.mutex.xMutexAlloc );
return sqlite3GlobalConfig.mutex.xMutexAlloc(id);
}
sqlite3_mutex *sqlite3MutexAlloc(int id){
if( !sqlite3GlobalConfig.bCoreMutex ){
return 0;
}
assert( GLOBAL(int, mutexIsInit) );
assert( sqlite3GlobalConfig.mutex.xMutexAlloc );
return sqlite3GlobalConfig.mutex.xMutexAlloc(id);
}
/*
** Free a dynamic mutex.
*/
void sqlite3_mutex_free(sqlite3_mutex *p){
if( p ){
assert( sqlite3GlobalConfig.mutex.xMutexFree );
sqlite3GlobalConfig.mutex.xMutexFree(p);
}
}
/*
** Obtain the mutex p. If some other thread already has the mutex, block
** until it can be obtained.
*/
void sqlite3_mutex_enter(sqlite3_mutex *p){
if( p ){
assert( sqlite3GlobalConfig.mutex.xMutexEnter );
sqlite3GlobalConfig.mutex.xMutexEnter(p);
}
}
/*
** Obtain the mutex p. If successful, return SQLITE_OK. Otherwise, if another
** thread holds the mutex and it cannot be obtained, return SQLITE_BUSY.
*/
int sqlite3_mutex_try(sqlite3_mutex *p){
int rc = SQLITE_OK;
if( p ){
assert( sqlite3GlobalConfig.mutex.xMutexTry );
return sqlite3GlobalConfig.mutex.xMutexTry(p);
}
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. If a NULL pointer is passed as an argument
** this function is a no-op.
*/
void sqlite3_mutex_leave(sqlite3_mutex *p){
if( p ){
assert( sqlite3GlobalConfig.mutex.xMutexLeave );
sqlite3GlobalConfig.mutex.xMutexLeave(p);
}
}
#ifndef NDEBUG
/*
** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
** intended for use inside assert() statements.
*/
int sqlite3_mutex_held(sqlite3_mutex *p){
assert( p==0 || sqlite3GlobalConfig.mutex.xMutexHeld );
return p==0 || sqlite3GlobalConfig.mutex.xMutexHeld(p);
}
int sqlite3_mutex_notheld(sqlite3_mutex *p){
assert( p==0 || sqlite3GlobalConfig.mutex.xMutexNotheld );
return p==0 || sqlite3GlobalConfig.mutex.xMutexNotheld(p);
}
#endif
#endif /* !defined(SQLITE_MUTEX_OMIT) */
|