[Qgis-developer] API changes

Marco Hugentobler marco.hugentobler at karto.baug.ethz.ch
Mon Apr 2 03:56:09 EDT 2007

Ok, I changed the provider interface of the functions 'select' 
and 'getNextFeature' and also the related code of the qgis core and the 
individual providers.

I suggest to merge the branch back soon. This still leaves some time to test 
for new bugs.


Am Freitag, 30. März 2007 18:02 schrieb Martin Dobias:
> On 3/30/07, Marco Hugentobler <marco.hugentobler at karto.baug.ethz.ch> wrote:
> > Hi Martin,
> >
> > The interface looks good.
> >
> > It would be nice if getNextFeature could be const, but that would
> > probably require some members of providers declared as 'mutable'.
> I don't think this is possible: with every getNextFeature() provider
> changes its internal state as it must increase the counter (or
> delegate that to backend).
> > > Also it might be good to think about enabling concurrency as currently
> > > it's not possible to do more data retreivals at once with one
> > > provider. Iterator design pattern could solve this situation, the
> > > question is whether also provider backends support concurrency (e.g.
> > > OGR).
> >
> > This would be a very clean solution. However, it is probably a bit too
> > much for now. What are the use cases you have in mind for concurrency?
> > Something like multiple canvases sharing one data provider (and possibly
> > multithreaded)?
> One such scenario is a server application that does some processing
> (or rendering) in several threads. Another case is the one you've
> mentioned - in future we should do canvas rendering in a thread so
> that GUI won't freeze every render. And with more canvases we would
> get into troubles.
> But you're true that this would need some more time.
> Martin

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