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I try to communicate with a PLC through a DLL (C API interface distributed by the manufacturer of the PLC). I'm using Python 3.1.4 who is embedded as a scripting environment in an other software (x64 - Windows 7).

The callback function bellow doesn't work in this embedded scripting environment (nothing happen). I the trigger for the callback function is generated after that the script has been started and stopped, then the software with the embedded python crashes completely.

The code works fine in a standalone python (3.1.4 MSC v1500 64bit AMD as well)

I have successfully implemented other function of the DLL that doesn't use callbacks in the embedded Python.

Does anyone have I idea what it could be ? 

def callback_func(amsaddr,notifHeader,huser):
    print('do something')
    pass

CMPFUNC = WINFUNCTYPE(None,POINTER(AmsAddr),POINTER(AdsNotificationHeader),c_ulong)
cmp_func = CMPFUNC(callback_func) 


netId =  AmsNetId((c_ubyte*6)(5,18,18,27,1,1))
plcAddress = AmsAddr(netId,801)
nIndexGroup = c_ulong(0xF021)
nIndexOffset = c_ulong(0x0)
adsNotif = AdsNotificationAttrib(1,4,1000000,1000000)
handle = c_ulong()
huser = c_ulong(10)

ADS_DLL = WinDLL("C:/Program Files/TwinCAT/Ads Api/TcAdsDll/x64/TcAdsDll.dll")
ADS_DLL.AdsSyncAddDeviceNotificationReq.argtypes=[POINTER(AmsAddr),c_ulong,c_ulong,POINTER(AdsNotificationAttrib),CMPFUNC,c_ulong,POINTER(c_ulong)]
ADS_DLL.AdsSyncAddDeviceNotificationReq.restype=c_long

#Function in the DLL with the callback
errCode = ADS_DLL.AdsSyncAddDeviceNotificationReq(pointer(plcAddress),nIndexGroup,nIndexOffset,pointer(adsNotif),cmp_func,huser,pointer(handle))
print('Device Notification error Code : %s' %errCode)

EDIT ^2

I tried a simple ctypes callback and it failed miserably in the embedded python version...The software just hangs and I have to kill it in the taskmanager. I tried the following code (from the docs):

from ctypes import *
IntArray5 = c_int * 5
ia = IntArray5(5, 1, 7, 33, 99)

libc = cdll.msvcrt #or libc = cdll.msvcr90  --> same problem
qsort = libc.qsort
qsort.restype = None

CMPFUNC = CFUNCTYPE(c_int, POINTER(c_int), POINTER(c_int))
def py_cmp_func(a, b):
    print("py_cmp_func", a[0], b[0])
    return 0
cmp_func = CMPFUNC(py_cmp_func)

qsort(ia, len(ia), sizeof(c_int), cmp_func)

EDIT ^3

Managed to get some improvements with the use of threading. Only the print() function doesn't print anything in the callback... An other function as os.system('c:/windows/notepad.exe') doesn't work either for example. 

from ctypes import *
import threading, queue
import os
IntArray5 = c_int * 5
ia = IntArray5(5, 1, 7, 33, 99)
libc = cdll.msvcrt
qsort = libc.qsort
qsort.restype = None

q = queue.Queue()

CMPFUNC = CFUNCTYPE(None,POINTER(c_int), POINTER(c_int))
def py_cmp_func(a, b):
    print("py_cmp_func", a[0], b[0]) #--> doesn't print anything
    print('Callback, in thread %s' % threading.current_thread().name) #--> doesn't print anything
    q.put('something')

cmp_func = CMPFUNC(py_cmp_func)
t = threading.Thread(target=qsort, args=(ia, len(ia), sizeof(c_int), cmp_func))
t.start()
print(threading.enumerate()) #--> prints [<Thread(Thread-1, started 2068)>, <_MainThread(MainThread, started 2956)>] 
t.join()
print(threading.enumerate()) # --> prints [<_MainThread(MainThread, started 2956)>]
print(q.get()) #--> prints 'something'
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