[Qgis-developer] API changes

[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