Title: PythonCmd in Modules/_tkinter.c should use the given "interp" parameter
Type: Stage:
Components: Tkinter Versions: Python 3.0, Python 3.1, Python 2.7, Python 2.6
Status: closed Resolution: fixed
Dependencies: Superseder:
Assigned To: Nosy List: gpolo
Priority: normal Keywords: patch

Created on 2008-12-31 15:29 by gpolo, last changed 2009-03-07 01:59 by gpolo. This issue is now closed.

File name Uploaded Description Edit
use_given_interp.diff gpolo, 2008-12-31 15:29
Messages (5)
msg78613 - (view) Author: Guilherme Polo (gpolo) * (Python committer) Date: 2008-12-31 15:29
Right now PythonCmd is using the Tcl interpreter stored in self->interp,
but this is unsafe and since it is a Tcl_CmdProc it already receives the
Tcl interpreter as a parameter. Using the interpreter in self->interp is
unsafe because Python might deallocate this TkappObject and then
PythonCmd could be invoked later, and using the interpreter given to the
Tcl_CmdProc is guaranteed to be safe by Tcl.

To reproduce this I needed a debug build and also needed to run the
example below in the interpreter:

>>> import tkFileDialog
>>> tkFileDialog.askdirectory() # here I both windows, then:
>>> Segmentation fault

There are other ways to reproduce this but I can't remember them
offhand, I know there are other ways because I've hit this same problem
in another python <-> tcl bridge by doing something else.

The patch could be expanded to remove the use of "self" in
PythonCmd_Clientdata, but given another wish I have -- to move to
Tcl_CreateObjCommand -- self would be needed again.
msg81329 - (view) Author: Guilherme Polo (gpolo) * (Python committer) Date: 2009-02-07 01:02
Another way to reproduce it (tested using debug build):

Python 2.7a0 (trunk:69375:69376M, Feb  6 2009, 20:27:09) 
[GCC 4.3.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import Tkinter
>>> Tkinter.Tk()
<Tkinter.Tk instance at 0xb79c8edc>
>>> Tkinter.Tk()
<Tkinter.Tk instance at 0xb79cb06c>

# close both windows now, get a segfault
msg83266 - (view) Author: Guilherme Polo (gpolo) * (Python committer) Date: 2009-03-07 01:37
I will be committing this but I'm afraid a test won't be added for it.
Several people told me that creating multiple tcl interpreters (even if
only one is active at some point) is problematic, specially in older tcl

So if someone can find another way to reproduce the problem you are
welcome to add a test. Ideally it would let the only tcl interpreter
created still alive (although as I see this bug you will only hit it if
a Tkapp is dealloced and then a callback created through Python is
invoked), otherwise the other existing tests will suffer.
msg83267 - (view) Author: Guilherme Polo (gpolo) * (Python committer) Date: 2009-03-07 01:48
Fixed in r70219.
msg83269 - (view) Author: Guilherme Polo (gpolo) * (Python committer) Date: 2009-03-07 01:59
Merges: r70220, r70221, r70222
Date User Action Args
2009-03-07 01:59:03gpolosetstatus: open -> closed
resolution: fixed
messages: + msg83269
2009-03-07 01:48:08gpolosetmessages: + msg83267
2009-03-07 01:37:49gpolosetmessages: + msg83266
2009-02-07 01:02:22gpolosetmessages: + msg81329
2008-12-31 15:29:57gpolocreate