/*

** 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

**

** $Id$

*/

#include "sqliteInt.h"

#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_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. 

*/

sqlite3_mutex *sqlite3_mutex_alloc(int id){

  static sqlite3_mutex aStatic[5];

  sqlite3_mutex *pNew = 0;

  switch( id ){

    case SQLITE_MUTEX_FAST:

    case SQLITE_MUTEX_RECURSIVE: {

      pNew = sqlite3_malloc(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.

*/

void sqlite3_mutex_free(sqlite3_mutex *p){

  assert( 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.

*/

void sqlite3_mutex_enter(sqlite3_mutex *p){

  assert( p );

  assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );

  p->cnt++;

}

int sqlite3_mutex_try(sqlite3_mutex *p){

  assert( p );

  assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(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.

*/

void sqlite3_mutex_leave(sqlite3_mutex *p){

  assert( p );

  assert( sqlite3_mutex_held(p) );

  p->cnt--;

  assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );

}

/*

** 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 || p->cnt>0;

}

int sqlite3_mutex_notheld(sqlite3_mutex *p){

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

}

#endif /* SQLITE_MUTEX_NOOP_DEBUG */