Re: [xml] [PATCH] Python bindings: DOM casts everything to xmlNode

[Daniel Veillard <veillard redhat com>]

On Fri, Feb 22, 2013 at 12:11:33AM -0800, Alexey Neyman wrote:
> [Adding back the list - I accidentally hit "reply" instead of "reply all" in 
> previous email]
>
> On Friday, February 22, 2013 01:38:51 PM Daniel Veillard wrote:
> > [sending again since mail was apparently lost]
> >
> > On Thu, Feb 21, 2013 at 10:21:18AM -0800, Alexey Neyman wrote:
> > > On Thursday, February 21, 2013 04:01:45 PM you wrote:
> > > > On Wed, Feb 20, 2013 at 06:28:25PM -0800, Alexey Neyman wrote:
> > > > > Hi libxml developers,
> > > > >
> > > > > [BTW, is this list alive?]
> > > >   yes, why ?
> > >
> > > I've sent another patch 3 days ago, and there was no response at all. Here
> > > it is:
> > >
> > > https://mail.gnome.org/archives/xml/2013-February/msg00013.html
> >
> >   yep, I saw it, but it's more complex, I'm worried about what happens
> > if there is some kind of deallocation like calling popInputCallbacks()
> > from the python bindings themselves, while said input is still in use
> > by a parser, I smell some reference counting would have to be added to
> > take care of this, i.e. the single
> >   Py_INCREF(pythonInputOpenCallbackObject);
> > on registration may not be sufficient to cover that case. The problem
> > is that the new use is done directly from C and there is no mechanism we
> > can use to increment/decrement the counter when a parser creates an
> > input based on those callbacks.
>
> I see your point... If I understand it correctly, I need to increment the 
> refcount each time open callback succeeds (i.e. in pythonInputOpenCallback(), 
> when the return value is not Py_None) and decrement it whenever the close 
> callback is called (i.e., wrap xmlPythonFileCloseRaw() into a new function, 
> pythonInputCloseCallback()).

  yes, that's it basically, we need to catch new open and closes and
adjust ref counts accordingly.

> Am I missing anything?

  no, hopefully that will be sufficient :-)

> > So i'm afraid we are stuck with a known
> > problem we can't fix, unless we never release the python reference,
> > which creates a leak (but a leak is better than a crash)
> >
> >   in any case tests suite addition would be welcome, yes :-)
>
> Yes, I just wanted to first settle on the API for the binding :)

  Having a test which exercise the above refcount small problem would
be a good thing too,

  thanks a lot !

Daniel

-- 
Daniel Veillard      | Open Source and Standards, Red Hat
veillard redhat com  | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
http://veillard.com/ | virtualization library  http://libvirt.org/