[Kde-bindings] Problem condition in Qyoto MethodCall

Arno Rehn arno at arnorehn.de
Mon Feb 12 17:13:17 UTC 2007

Am Montag, 12. Februar 2007 schrieb Richard Dale:
> On Monday 12 February 2007, Arno Rehn wrote:
> > > [ ... cut ... ]
> >
> > Well, I've hacked a lot around in qyoto.cpp and changed the way we check
> > if it's a contained instance or not: I've added a field to
> > smokeqyoto_object called 'contained' and it is set up when the
> > constructor was just called. This was necessary because sometimes the
> > instance was already destroyed and we still wanted to get the parent of
> > it. The new field is updated when the parent of the widget is changed
> > because it is added to a layout, too. It works better now and up to t10
> > every tutorial works well. But with t11 it keeps crashing and I can't
> > figure out why it does so. Since I've created quite a mess, I don't want
> > to check in what I have. I've attached a patch with all the changes, if
> > you could take a look at it and tell me what you think...
> I'm not sure if this is the best way to do it, as 'contained' seems to
> duplicate the function of 'allocated'. If an instance is 'owned' by another
> instance we can just set 'allocated' to false, and the Qyoto runtime won't
> delete it when the corresponding C# instance is garbage collected.
Yes, didn't think about that, but it's right. Setting allocated to false would 
be better.
Do I see that right: If allocated has to be true for a destructor to be 
called, we only want to call destructors for instances which have been 
created by a C# constructor? Then we'd just have to check if it's a 
destructor and if getPointerObject returns something other than 0.

> What problem does it solve that the current scheme with the
> IsContainedInstance() function doesn't do?
The problem is the following: We have a QLabel which is a child to a QWidget, 
for example. Now the QWidget is destroyed and with it the QLabel is gone. 
Nevertheless the Qyoto runtime wants to call the destructor for the QLabel as 
it still 'thinks' the QLabel exists. To check whether QLabel is a child to 
something and whether to call the destructor we call IsContainedInstance() 
which checks for any parents. Thus it will cause an error when trying to call 
QLabel->parent() as the QLabel is already destroyed. Therefore it's better to 
set this property up when the instance is created and when the parent is 

> I don't think there's any hurry to solve the problem straight away, and it's
> best to keep experimenting like you're doing, but not actually commiting
> anything.  
Yes, that's what I thought, too. 

> If we use the 'Transfer' data in the PyQt sip files we would need to change
> ownership when a method, or argument within a method was marked
> with 'Transfer'. So that data could either go into the smoke library
> runtime, as it would be useful for every language. Another way would be to
> add it as C# Attributes, in the 'SmokeMethod' one perhaps.
What exactly is this 'Transfer' data used in PyQt? Haven't heard of it 

> Qyoto seems a bit slow to me - I expected it to be faster than QtRuby, but
> it's actually slower at the moment. I tried running mono with the
> '--profile' option and there doesn't seem to be any obvious method that is
> hogging the time. The methodId caching scheme where the methodId was put
> inside the SmokeMethod didn't work, and so there seems to be something
> strange about how Attributes work. Now I've added caching of methodIds
> again, it didn't seem to make much difference to the speed.
I think all the marshalling functions make Qyoto so slow, because for a simple 
marshalling a whole bunch of C# methods is called from C++ and vice versa. 
But I only recognize a slowdown when I start an application up. The mono 
runtime itself needs some time to start and then then Qyoto runtime needs 
some little time. But when it finally runs it's quite fast from what I've 
seen so far.

Arno Rehn
arno at arnorehn.de

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