[ctypes-users] python, ctypes, callbacks -- access violation when calling callback

[resurtm r. <re...@gm...>]

Hello.

I'm trying to pass to the C function pointer to callback function from
python. But when i'm trying to do this i get access violation within
the DLL file when calling python callback.

Here is the python side code:

from ctypes import *

# ...

class NewtonBody(Structure):
   def __init__(self, pointer = 0):
      self.pointer = pointer

# ...

class Newton:
   def __init__(self):
      self._cdll = CDLL('newton.dll')
      self.world = NewtonWorld()

# ...

   # NewtonBodySetForceAndTorqueCallback
   def bodySetForceAndTorqueCallback(self, body):
      CALLBACK = CFUNCTYPE(c_int, POINTER(NewtonBody), c_float, c_int)
      def callback(a, b, c):
         print '1'
         return 0
      self._cdll.NewtonBodySetForceAndTorqueCallback(body.pointer,
CALLBACK(callback))
      return None

Traceback:

Traceback (most recent call last):
  File "Newton.py", line 119, in <module>
    newton.update(10.5)
  File "Newton.py", line 42, in update
    self._cdll.NewtonUpdate(self.world.pointer, c_float(timestep))
WindowsError: exception: access violation reading 0x3C888899

And finally prototype of function which i'm trying to call and
callback function type declarations:

typedef void (*NewtonApplyForceAndTorque) (const NewtonBody* body,
dFloat timestep, int threadIndex);

// ...

NEWTON_API void  NewtonBodySetForceAndTorqueCallback (const
NewtonBody* body, NewtonApplyForceAndTorque callback);

Can anybody explain my errors when trying to pass callback to DLL function?

Thanks!
Best regards,
Timur.