From: herzog at online.de (Bernhard Herzog)
Date: 11 Apr 1999 14:40:26 +0200
Subject: _tkinter.c, threads and C-modules in 1.5.2
Message-ID: <m3aewfba9x.fsf@greebo.nodomain.de>
Content-Length: 1662
X-UID: 253                                                  


A few weeks ago, there was a bug report on c.l.py regarding an
incompatibility between Sketch and Python 1.5.2b2 on Linux/glibc2. It
seems to me that the cause for the problems is the new Tcl-lock in
1.5.2.

The tcl-lock was introduced for better thread support in Tkinter.
Whenever _tkinter calls the tcl interpreter, it releases the python-lock
and acquires the tcl-lock. Sketch defines some tcl-callbacks in C, which
in turn may call the python interpreter, but without releasing the
tcl-lock and acquiring the python-lock. I think that this is the cause,
because compiling just the _tkinter module without thread support cures
the problem, or so I'm told, I can't test this myself at the moment as
I'm still on libc5.

The question now is, how do I make Sketch work correctly with a
threadable _tkinter? AFAICT, Sketch would have to have access to some
static variables in _tkinter.c.

The best solution IMO would be to give third-party C-modules access to
the functionality of the macros ENTER_TCL, LEAVE_TCL, etc, via some
C-functions to access those variables and a _tkinter headerfile
installed with the other Python headerfiles.

As it's probably too late to get something like this into Python 1.5.2
final :(, the easiest solution for Sketch is to provide its own
non-threaded _tkinter module that is used instead of Python's if Sketch
runs with Python 1.5.2.

It's kind of funny that 1.5.2 make it both easier, with the new
interpaddr() method, and harder, with the tcl-lock, to extend tkinter
with C-modules.


    Bernhard


-- 
Bernhard Herzog	  | Sketch, a python based drawing program
herzog at online.de  | http://www.online.de/home/sketch/




