CODEWITHSUNDEEP
pythonmultithreadingtkinter
Sandstone
Sandstone

Reputation: 148

Scanning for thread violations with Tkinter

We are just about to finish a very large update to our application which is built with python2.5 and Tkinter and the following error has crept in sadly:

alloc: invalid block: 06807CE7: 1 0 0

This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.

We've seen this before and it is usually a Tcl Interrupter error caused when a non GUI thread tries to access TK via Tkinter in anyway (TK not being thread safe). The error pops up on application close, after the python interrupter is finished with our code. This error is very hard to reproduce and I'm thinking I will have to scan all threads in the system to see if they access TK when they shouldn't.

I'm looking for a magic python trick to help with this. All Tkinter widgets we use are first subclassed and inherit from out own Widget base class.

With this in mind I'm looking for a way to add the following check to the beginning of every method in the widget sub classes:

import thread
if thread.get_ident() != TKINTER_GUI_THREAD_ID:
    assert 0, "Invalid thread accessing Tkinter!"

Decorators as a partial solution comes to mind. I do not want to add decorators manually to each method however. Is there a way I can add the decorator to all methods of a class that inherits from our Widget base class? Or is there a better way to do all this? Or does anyone have more info about this error?

enter code here

Upvotes: 1

Views: 1011

Answers (2)

Sandstone
Sandstone

Reputation: 148

I went with a slightly easier method. I used the __getattribute__ method. The code is as follows:

def __getattribute__(self, name):

    import ApplicationInfo
    import thread, traceback

    if ApplicationInfo.main_loop_thread_id != thread.get_ident():
        print "Thread GUI violation"
        traceback.print_stack()

    return object.__getattribute__(self, name)

And sure enough we found one obscure place where we were accessing state from within TK while not being in the main GUI thread.

Although I must admit I need to review my python, feeling noobish looking at your example.

Upvotes: 0

Petri Lehtinen
Petri Lehtinen

Reputation: 2145

I don't know if your approach is good, as I don't know Tkinter.

But here's a sample of how to decorate all class methods using a metaclass.

import functools

# This is the decorator
def my_decorator(func):
    @functools.wraps(func)
    def wrapper(*args, **kwargs):
        print 'calling', func.__name__, 'from decorator'
        return func(*args, **kwargs)

    return wrapper

# This is the metaclass
class DecorateMeta(type):
    def __new__(cls, name, bases, attrs):
        for key in attrs:
            # Skip special methods, e.g. __init__
            if not key.startswith('__') and callable(attrs[key]):
                attrs[key] = my_decorator(attrs[key])

        return super(DecorateMeta, cls).__new__(cls, name, bases, attrs)

# This is a sample class that uses the metaclass
class MyClass(object):
    __metaclass__ = DecorateMeta

    def __init__(self):
        print 'in __init__()'

    def test(self):
        print 'in test()'

obj = MyClass()
obj.test()

The metaclass overrides the class creation. It loops through all the attributes of the class being created and decorates all callable attributes that have a "regular" name with my_decorator.

Upvotes: 1

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