Problem in _tkinter.c with extending both tk and python with C++

[Bernhard Herzog]

Jyrki Alakuijala <Jyrki.Alakuijala at mail.dosetek.varian.com> writes:

> I have an old python/tkinter application that used to work fine
> with Python 1.4 and 1.5. Roughly one year ago it got
> broken. The application is mostly C++ and Python with some
> "embedded" tcl. Now, with 1.5.2 the program crashes
> similarly in both Windows NT and Linux environments.
> 
> The problem occurs with the following pattern:
> First, I load a (self-made) tk widget as a dynamic library.
> 
> Second, I load the (self-made) python extensions as dynamic
> libraries.
> 
> Third, I make an operation in the user interface that
> starts as a Tk-event, going to python. Python updates
> my widget, which calls C++ code, which calls
> (Tcl_VarEval) which tries to visit Python code.
> This is when the program crashes.
> 
> The error message it gives before termination is:
> Fatal Python error: PyEval_RestoreThread: NULL tstate
> 
> I believe this has something to do with the thread
> safety of tkinter (ENTER_PYTHON and
> LEAVE_PYTHON). Perhaps I should take these
> macros into my code for visiting Tcl code from C++.
> However, I cannot get access the Tcl-lock declared in
> _tkinter.c, because it is static.

That's exactly what happens in _tkinter in Python 1.5.2. 

My drawing program Sketch was broken by this change when 1.5.2 came out
last year, too. Unfortunately, by the time I figured out what was
happening it was too late to make any more changes to Python.

> What should I do to get the code working with
> newer releases of Python? Should I give up with
> Tk and move to one of the newer UI libraries?
> Should I write my own _tkinter.c?

My solution was to distribute a modified _tkinter with Sketch and import
it instead of the standard one.


-- 
Bernhard Herzog   | Sketch, a drawing program for Unix
herzog at online.de  | http://sketch.sourceforge.net/