classification
Title: Python 2 & 3 don't allow the user to disable ctypes SEH in windows
Type: enhancement Stage:
Components: ctypes Versions: Python 3.6
process
Status: open Resolution:
Dependencies: Superseder:
Assigned To: Nosy List: amaury.forgeotdarc, belopolsky, meador.inge, r.david.murray, tzickel
Priority: normal Keywords:

Created on 2015-11-05 21:49 by tzickel, last changed 2015-11-05 22:56 by r.david.murray.

Messages (2)
msg254143 - (view) Author: (tzickel) Date: 2015-11-05 21:49
In Windows, there is a mechanizm called SEH that allows C/C++ programs to catch OS Exceptions (such as divide by zero, page faults, etc..).

Python's ctypes module for some reason forces the user to wrap all ctypes FFI calls with a special SEH wrapper that converts those exceptions to Python exceptions.

For the UNIX people think about it that python installs a signal handler without you asking (or being able to remove it) when calling FFI functions.

The main issue with this, is that when you want to debug why a DLL behaves badly and you want a process dump (or catch the stack trace in the DLL) you can't without attaching a debugger and catching first-chance exceptions (because the ctypes SEH handling masks the issue).

My proposal is to have both in python 2 and in python 3 an option to call an FFI function with selectively using or not SEH.

Here is the SEH wrap (as you can see it's not optional in runtime):
https://github.com/python/cpython/blob/master/Modules/_ctypes/callproc.c#L806
msg254146 - (view) Author: R. David Murray (r.david.murray) * (Python committer) Date: 2015-11-05 22:56
This would be a new feature and so would not be acceptable for python2.7.

I wonder if cffi has such a switch.
History
Date User Action Args
2015-11-05 22:56:17r.david.murraysetversions: - Python 2.7
nosy: + r.david.murray

messages: + msg254146

type: behavior -> enhancement
2015-11-05 21:49:02tzickelcreate