/*

** 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.

**

** The implementation in this file does not provide any mutual

** exclusion and is thus suitable for use only in applications

** that use SQLite in a single thread.  But this implementation

** does do a lot of error checking on mutexes to make sure they

** are called correctly and at appropriate times.  Hence, this

** implementation is suitable for testing.

** debugging purposes

**

** $Id: mutex.c,v 1.27 2008/06/19 08:51:24 danielk1977 Exp $

*/

#include "sqliteInt.h"

#ifndef SQLITE_MUTEX_NOOP

/*

** Initialize the mutex system.

*/

int sqlite3MutexInit(void){ 

  int rc = SQLITE_OK;

  if( sqlite3Config.bCoreMutex ){

    if( !sqlite3Config.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 sqlite3Config 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 sqlite3Config 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( sqlite3Config.mutex.xMutexAlloc==0 

             || sqlite3Config.mutex.xMutexAlloc==p->xMutexAlloc

        );

        if( !sqlite3Config.mutex.xMutexAlloc ){

          sqlite3Config.mutex = *p;

        }

        p->xMutexLeave(pMaster);

      }

    }else{

      rc = sqlite3Config.mutex.xMutexInit();

    }

  }

  return rc;

}

/*

** Shutdown the mutex system. This call frees resources allocated by

** sqlite3MutexInit().

*/

int sqlite3MutexEnd(void){

  int rc = SQLITE_OK;

  rc = sqlite3Config.mutex.xMutexEnd();

  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( sqlite3_initialize() ) return 0;

#endif

  return sqlite3Config.mutex.xMutexAlloc(id);

}

sqlite3_mutex *sqlite3MutexAlloc(int id){

  if( !sqlite3Config.bCoreMutex ){

    return 0;

  }

  return sqlite3Config.mutex.xMutexAlloc(id);

}

/*

** Free a dynamic mutex.

*/

void sqlite3_mutex_free(sqlite3_mutex *p){

  if( p ){

    sqlite3Config.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 ){

    sqlite3Config.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 ){

    return sqlite3Config.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 ){

    sqlite3Config.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){

  return p==0 || sqlite3Config.mutex.xMutexHeld(p);

}

int sqlite3_mutex_notheld(sqlite3_mutex *p){

  return p==0 || sqlite3Config.mutex.xMutexNotheld(p);

}

#endif

#endif

#ifdef SQLITE_MUTEX_NOOP_DEBUG

/*

** In this implementation, mutexes do not provide any mutual exclusion.

** But the error checking is provided.  This implementation is useful

** for test purposes.

*/

/*

** The mutex object

*/

struct sqlite3_mutex {

  int id;     /* The mutex type */

  int cnt;    /* Number of entries without a matching leave */

};

/*

** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are

** intended for use inside assert() statements.

*/

static int noopMutexHeld(sqlite3_mutex *p){

  return p==0 || p->cnt>0;

}

static int noopMutexNotheld(sqlite3_mutex *p){

  return p==0 || p->cnt==0;

}

/*

** Initialize and deinitialize the mutex subsystem.

*/

static int noopMutexInit(void){ return SQLITE_OK; }

static int noopMutexEnd(void){ return SQLITE_OK; }

/*

** The sqlite3_mutex_alloc() routine allocates a new

** mutex and returns a pointer to it.  If it returns NULL

** that means that a mutex could not be allocated. 

*/

static sqlite3_mutex *noopMutexAlloc(int id){

  static sqlite3_mutex aStatic[6];

  sqlite3_mutex *pNew = 0;

  switch( id ){

    case SQLITE_MUTEX_FAST:

    case SQLITE_MUTEX_RECURSIVE: {

      pNew = sqlite3Malloc(sizeof(*pNew));

      if( pNew ){

        pNew->id = id;

        pNew->cnt = 0;

      }

      break;

    }

    default: {

      assert( id-2 >= 0 );

      assert( id-2 < sizeof(aStatic)/sizeof(aStatic[0]) );

      pNew = &aStatic[id-2];

      pNew->id = id;

      break;

    }

  }

  return pNew;

}

/*

** This routine deallocates a previously allocated mutex.

*/

static void noopMutexFree(sqlite3_mutex *p){

  assert( p->cnt==0 );

  assert( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE );

  sqlite3_free(p);

}

/*

** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt

** to enter a mutex.  If another thread is already within the mutex,

** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return

** SQLITE_BUSY.  The sqlite3_mutex_try() interface returns SQLITE_OK

** upon successful entry.  Mutexes created using SQLITE_MUTEX_RECURSIVE can

** be entered multiple times by the same thread.  In such cases the,

** mutex must be exited an equal number of times before another thread

** can enter.  If the same thread tries to enter any other kind of mutex

** more than once, the behavior is undefined.

*/

static void noopMutexEnter(sqlite3_mutex *p){

  assert( p->id==SQLITE_MUTEX_RECURSIVE || noopMutexNotheld(p) );

  p->cnt++;

}

static int noopMutexTry(sqlite3_mutex *p){

  assert( p->id==SQLITE_MUTEX_RECURSIVE || noopMutexNotheld(p) );

  p->cnt++;

  return SQLITE_OK;

}

/*

** 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 or

** is not currently allocated.  SQLite will never do either.

*/

static void noopMutexLeave(sqlite3_mutex *p){

  assert( noopMutexHeld(p) );

  p->cnt--;

  assert( p->id==SQLITE_MUTEX_RECURSIVE || noopMutexNotheld(p) );

}

sqlite3_mutex_methods *sqlite3DefaultMutex(void){

  static sqlite3_mutex_methods sMutex = {

    noopMutexInit,

    noopMutexEnd,

    noopMutexAlloc,

    noopMutexFree,

    noopMutexEnter,

    noopMutexTry,

    noopMutexLeave,

    noopMutexHeld,

    noopMutexNotheld

  };

  return &sMutex;

}

#endif /* SQLITE_MUTEX_NOOP_DEBUG */