[PyKDE] Threading, PyQt and SIP

[Claus, Richard]

> -----Original Message-----
> From: Phil Thompson [mailto:phil at riverbankcomputing.co.uk] 
> Sent: Sunday, March 21, 2004 10:30 PM
> To: pykde at mats.imk.fraunhofer.de
> Cc: Claus, Richard
> Subject: Re: [PyKDE] Threading, PyQt and SIP
> 
> On Monday 22 March 2004 02:19, Claus, Richard wrote:
> >  I've written a library in C++ that takes a buffer of data 
> and calls 
> > back application resolved virtual methods based on the 
> contents of the buffer.
> > All the work is done in place, so there is no memory 
> management other 
> > than temporaries created on the stack.  It would be very 
> useful for us 
> > if this library were also available from Python, so I've used SIP 
> > 3.10.1 (snapshot
> > 20040313-194) to expose its interface.  I haven't tried to 
> do anything 
> > tricky with %MethodCode or anything like that.
> >
> > The results on Windows XP (Python 2.3.3, MSVS .Net 7.1) so far:
> >
> > - With a pure C++ application dynamically linked against 
> this library, 
> > I have seen no problems and everything works as expected. - With 
> > single and multi-threaded, non-PyQt applications, I have seen no 
> > problems and everything works as expected. - With PyQt 
> applications, I 
> > see no problems when I use the library from the Qt GUI 
> thread (the one 
> > running QApplication.exec_loop()).
> 
> > - With PyQt applications, there are problems when I use the library 
> > from a non-GUI thread.  Often Python crashes with "Fatal 
> Python error: 
> > GC object already tracked".  With Python 2.2, the message was 
> > something like "...GC object already on linked list".  
> Other crashes 
> > are access violations in seemingly random locations.  Once, I saw a 
> > Python traceback involving libqtc.sipCallCtor(204,self,args) ->
> > AttributeError: sipThis  before getting the GC error 
> (sorry, I can't 
> > paste it in right now).  This appeared to happen when the 
> GUI thread 
> > decided to update the screen.  The amount of time things 
> appear to run 
> > correctly before crashing seems to be random.
> 
> How are the threads being created?

Through a derived class from Thread for which the run() method is supplied.

> 
> > There are no intentional interactions between the usage of 
> my library 
> > and the rest of the PyQt application, e.g., the library's methods 
> > aren't trying to update the screen.
> 
> Problems like this are usually related to unintentional 
> interactions :)
> 
> > Can someone please describe for me how to keep two SIP applications 
> > running in two threads of the same process from tangling?
> 
> The first thing I'd try is SIP v4. The thread handling is 
> much more forgiving because it uses Python's new thread API.

Okay, I'll give that a whirl.

> 
> > Or is the rule of the game that there can be only one 
> thread using SIP 
> > generated code?  If so, can I solve this by going to one of 
> the other 
> > C/C++ to Python interface packages, e.g., SWIG or Boost?  Can these 
> > coexist with SIP?
> 
> I don't know about SWIG. Boost ignored threads and the GIL 
> completely, I don't know if this has changed recently.
> 
> Phil
>