sl@0: /*
sl@0: ** 2007 August 14
sl@0: **
sl@0: ** The author disclaims copyright to this source code.  In place of
sl@0: ** a legal notice, here is a blessing:
sl@0: **
sl@0: **    May you do good and not evil.
sl@0: **    May you find forgiveness for yourself and forgive others.
sl@0: **    May you share freely, never taking more than you give.
sl@0: **
sl@0: *************************************************************************
sl@0: ** This file contains the C functions that implement mutexes.
sl@0: **
sl@0: ** This file contains code that is common across all mutex implementations.
sl@0: 
sl@0: **
sl@0: ** $Id: mutex.c,v 1.29 2008/10/07 15:25:48 drh Exp $
sl@0: */
sl@0: #include "sqliteInt.h"
sl@0: 
sl@0: #ifndef SQLITE_MUTEX_OMIT
sl@0: /*
sl@0: ** Initialize the mutex system.
sl@0: */
sl@0: int sqlite3MutexInit(void){ 
sl@0:   int rc = SQLITE_OK;
sl@0:   if( sqlite3GlobalConfig.bCoreMutex ){
sl@0:     if( !sqlite3GlobalConfig.mutex.xMutexAlloc ){
sl@0:       /* If the xMutexAlloc method has not been set, then the user did not
sl@0:       ** install a mutex implementation via sqlite3_config() prior to 
sl@0:       ** sqlite3_initialize() being called. This block copies pointers to
sl@0:       ** the default implementation into the sqlite3GlobalConfig structure.
sl@0:       **
sl@0:       ** The danger is that although sqlite3_config() is not a threadsafe
sl@0:       ** API, sqlite3_initialize() is, and so multiple threads may be
sl@0:       ** attempting to run this function simultaneously. To guard write
sl@0:       ** access to the sqlite3GlobalConfig structure, the 'MASTER' static mutex
sl@0:       ** is obtained before modifying it.
sl@0:       */
sl@0:       sqlite3_mutex_methods *p = sqlite3DefaultMutex();
sl@0:       sqlite3_mutex *pMaster = 0;
sl@0:   
sl@0:       rc = p->xMutexInit();
sl@0:       if( rc==SQLITE_OK ){
sl@0:         pMaster = p->xMutexAlloc(SQLITE_MUTEX_STATIC_MASTER);
sl@0:         assert(pMaster);
sl@0:         p->xMutexEnter(pMaster);
sl@0:         assert( sqlite3GlobalConfig.mutex.xMutexAlloc==0 
sl@0:              || sqlite3GlobalConfig.mutex.xMutexAlloc==p->xMutexAlloc
sl@0:         );
sl@0:         if( !sqlite3GlobalConfig.mutex.xMutexAlloc ){
sl@0:           sqlite3GlobalConfig.mutex = *p;
sl@0:         }
sl@0:         p->xMutexLeave(pMaster);
sl@0:       }
sl@0:     }else{
sl@0:       rc = sqlite3GlobalConfig.mutex.xMutexInit();
sl@0:     }
sl@0:   }
sl@0: 
sl@0:   return rc;
sl@0: }
sl@0: 
sl@0: /*
sl@0: ** Shutdown the mutex system. This call frees resources allocated by
sl@0: ** sqlite3MutexInit().
sl@0: */
sl@0: int sqlite3MutexEnd(void){
sl@0:   int rc = SQLITE_OK;
sl@0:   if( sqlite3GlobalConfig.mutex.xMutexEnd ){
sl@0:     rc = sqlite3GlobalConfig.mutex.xMutexEnd();
sl@0:   }
sl@0:   return rc;
sl@0: }
sl@0: 
sl@0: /*
sl@0: ** Retrieve a pointer to a static mutex or allocate a new dynamic one.
sl@0: */
sl@0: sqlite3_mutex *sqlite3_mutex_alloc(int id){
sl@0: #ifndef SQLITE_OMIT_AUTOINIT
sl@0:   if( sqlite3_initialize() ) return 0;
sl@0: #endif
sl@0:   return sqlite3GlobalConfig.mutex.xMutexAlloc(id);
sl@0: }
sl@0: 
sl@0: sqlite3_mutex *sqlite3MutexAlloc(int id){
sl@0:   if( !sqlite3GlobalConfig.bCoreMutex ){
sl@0:     return 0;
sl@0:   }
sl@0:   return sqlite3GlobalConfig.mutex.xMutexAlloc(id);
sl@0: }
sl@0: 
sl@0: /*
sl@0: ** Free a dynamic mutex.
sl@0: */
sl@0: void sqlite3_mutex_free(sqlite3_mutex *p){
sl@0:   if( p ){
sl@0:     sqlite3GlobalConfig.mutex.xMutexFree(p);
sl@0:   }
sl@0: }
sl@0: 
sl@0: /*
sl@0: ** Obtain the mutex p. If some other thread already has the mutex, block
sl@0: ** until it can be obtained.
sl@0: */
sl@0: void sqlite3_mutex_enter(sqlite3_mutex *p){
sl@0:   if( p ){
sl@0:     sqlite3GlobalConfig.mutex.xMutexEnter(p);
sl@0:   }
sl@0: }
sl@0: 
sl@0: /*
sl@0: ** Obtain the mutex p. If successful, return SQLITE_OK. Otherwise, if another
sl@0: ** thread holds the mutex and it cannot be obtained, return SQLITE_BUSY.
sl@0: */
sl@0: int sqlite3_mutex_try(sqlite3_mutex *p){
sl@0:   int rc = SQLITE_OK;
sl@0:   if( p ){
sl@0:     return sqlite3GlobalConfig.mutex.xMutexTry(p);
sl@0:   }
sl@0:   return rc;
sl@0: }
sl@0: 
sl@0: /*
sl@0: ** The sqlite3_mutex_leave() routine exits a mutex that was previously
sl@0: ** entered by the same thread.  The behavior is undefined if the mutex 
sl@0: ** is not currently entered. If a NULL pointer is passed as an argument
sl@0: ** this function is a no-op.
sl@0: */
sl@0: void sqlite3_mutex_leave(sqlite3_mutex *p){
sl@0:   if( p ){
sl@0:     sqlite3GlobalConfig.mutex.xMutexLeave(p);
sl@0:   }
sl@0: }
sl@0: 
sl@0: #ifndef NDEBUG
sl@0: /*
sl@0: ** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
sl@0: ** intended for use inside assert() statements.
sl@0: */
sl@0: int sqlite3_mutex_held(sqlite3_mutex *p){
sl@0:   return p==0 || sqlite3GlobalConfig.mutex.xMutexHeld(p);
sl@0: }
sl@0: int sqlite3_mutex_notheld(sqlite3_mutex *p){
sl@0:   return p==0 || sqlite3GlobalConfig.mutex.xMutexNotheld(p);
sl@0: }
sl@0: #endif
sl@0: 
sl@0: #endif /* SQLITE_OMIT_MUTEX */