SQLite

  int (*xDelete)(const char*);
  int (*xFileExists)(const char*);
  char *(*xFullPathname)(const char*);
  int (*xIsDirWritable)(char*);
  int (*xSyncDirectory)(const char*);
  int (*xTempFileName)(char*);

  int (*xRandomSeed)(char*);
  int (*xSleep)(int ms);
  int (*xCurrentTime)(double*);

  void (*xEnterMutex)(void);
  void (*xLeaveMutex)(void);
  int (*xInMutex)(void);
  void *(*xThreadSpecificData)(int);

  void *(*xMalloc)(int);
  void *(*xRealloc)(void *, int);
  void (*xFree)(void *);
  int (*xAllocationSize)(void *);
} sqlite3Os;


/*
** The semi-published API for setting and getting methods from the 
** global sqlite3OsVtbl structure. Neither sqlite3_os_routine_XXX() function
** is intriniscally thread-safe.
**
** External get/set access is only provided to the routines identified 
** by the following SQLITE_OS_ROUTINE symbols:
*/
#define SQLITE_OS_ROUTINE_OPENREADWRITE   1
#define SQLITE_OS_ROUTINE_OPENREADONLY    2
#define SQLITE_OS_ROUTINE_OPENEXCLUSIVE   3
#define SQLITE_OS_ROUTINE_DELETE          4
#define SQLITE_OS_ROUTINE_FILEEXISTS      5
#define SQLITE_OS_ROUTINE_SYNCDIRECTORY   6

static void unixLeaveMutex(){
  assert( inMutex );
  inMutex = 0;
#ifdef SQLITE_UNIX_THREADS
  pthread_mutex_unlock(&mutex);
#endif
}

/*
** Return TRUE if we are currently within the mutex and FALSE if not.
** This routine is intended for sanity checking only.  It is designed
** for use in an assert() to verify that the mutex is held or not held
** in certain routines.
*/
static int unixInMutex(){
  return inMutex;
}

/*
** This function is called automatically when a thread exists to delete
** the threads SqliteTsd structure. 
**
** Because the SqliteTsd structure is required by higher level routines
** such as sqliteMalloc() we use OsFree() and OsMalloc() directly to

  IF_DISKIO( unixSyncDirectory ),
  IF_DISKIO( unixTempFileName ),
  unixRandomSeed,
  unixSleep,
  unixCurrentTime,
  unixEnterMutex,
  unixLeaveMutex,
  unixInMutex,
  unixThreadSpecificData,
  genericMalloc,
  genericRealloc,
  genericFree,
  genericAllocationSize
};



#endif /* OS_UNIX */

static void winLeaveMutex(){
  assert( inMutex );
  inMutex = 0;
#ifdef SQLITE_W32_THREADS
  LeaveCriticalSection(&cs);
#endif
}

/*
** Return TRUE if we are currently within the mutex and FALSE if not.
** This routine is intended for sanity checking only.  It is designed
** for use in an assert() to verify that the mutex is held or not held
** in certain routines.
*/
static int winInMutex(){
  return inMutex;
}


/*
** The following variable, if set to a non-zero value, becomes the result
** returned from sqlite3OsCurrentTime().  This is used for testing.
*/
#ifdef SQLITE_TEST
int sqlite3_current_time = 0;

  IF_DISKIO( winSyncDirectory ),
  IF_DISKIO( winTempFileName ),
  winRandomSeed,
  winSleep,
  winCurrentTime,
  winEnterMutex,
  winLeaveMutex,
  winInMutex,
  winThreadSpecificData,
  genericMalloc,
  genericRealloc,
  genericFree,
  genericAllocationSize
};

#endif /* OS_WIN */