[Kde-bindings] Problem condition in Qyoto MethodCall

[Arno Rehn]

Am Samstag, 10. Februar 2007 schrieb Arno Rehn:
> Am Samstag, 10. Februar 2007 schrieb Richard Dale:
> > This is wrong, but I still haven't worked out what the correct version
> > should be:
> >
> > // We have to check here, if our target does still exists.
> > // If there is no entry in the weakRef Dictionary, the instance doesn't
> > exist anymore.
> > // There's also no entry, if the method is a constructor or the method is
> > static.
> > // If the target doesn't exist anymore, set _called to true so the method
> > won't be invoked.
> > // The other possibility is that the qApp was just destroyed and we want
> > to call a destructor.
> > // This could lead to a crash when we interfere with the destroying
> > mechanism of Q(Core)Application.
> > if ( ((getPointerObject(_current_object) == 0) && !_ctor && !(_tmp.flags
> > & Smoke::mf_static))
> >
> >         || ((_tmp.flags & Smoke::mf_dtor) && (qApp == 0)) )
> >
> >         _called = true;
> >
> > Not every instance has an entry in the weak reference map. For example, I
> > had a QVariant which was created in C++ code and it failed the condition
> > and '_called' was set to true. Try the qdbus/pingpong example - it
> > crashes when trying to access to QVariant returned.
>
> Oops, didn't know that not every instance is in the weakRef map.
>
> > We should only be looking at the 'o' and 'o->ptr' values and not call the
> > method if they are zero and it's not a static method or constructor. I
> > don't think we need to test for destructors at all because 'o->ptr' is
> > set to 0 once something has been deleted (or it should be anyway).
>
> Uhm, actually if we just test for o->ptr == 0 and the method not being a
> constructor it doesn't work. My code:
> 		if ((_current_object == 0) && !_ctor)
> 			_called = true;
> Result:
> *** glibc detected *** mono: free(): invalid pointer: 0xb6b94c9c ***
> at startup.
> As the problem with destructors just happens when the qApp is about to quit
> I think we shouldn't test for something being null at all, just if it is a
> destructor and if the qApp is about to quit. If so, don't call the
> destructor. If it still crashes somewhen else because the underlying C++
> instance doesn't exist anymore, the problem will probably have another
> cause.
Ok, that won't work, I didn't think about that it is possible to not have 
called QCoreApplication::exec and still can do something with Qt. But just 
checking for o->ptr being 0 won't work either, as I've already stated.

-- 
Arno Rehn
arno at arnorehn.de