Fun with Akonadi Dataengine

[Sebastian Kügler]

On Monday 16 February 2009 19:42:03 David Baron wrote:
> On Monday 16 February 2009 19:08:03 Aaron J. Seigo wrote:
> > On Sunday 15 February 2009, David Baron wrote:
> > > 1. The ContactCollection-# loads all the contacts but they are not
> > > necessarily accessible at this point. I might have to try
> >
> > hm; this sounds rather inefficient for large address books. perhaps it's
> > a good idea to collect use cases for this part of the engine and build
> > specifically for those rather than build something too general purpose;
> > the engine doesn't need to be able to support building an entire address
> > book application around it (that's not the point of engines), so defining
> > what a widget should like to do with it is probably a good start point.
>
> It's a point. But I am dialing the phone. Here is how I do it now:
>
> 1. In init(), I start a QTimer with 1 second interval.

If you need to use a timer here, I think something's wrong. You should be able 
to just connect to dataUpdated() for that collection and

If it's necessary to use a timer, there's something wrong with the interface. 
It should be completely event-based, no?

> 2. At 1st timeout, I do the a query("ContactCollections")
> then if I find a suitable key, connectSource, i.e to ContentCollection-6.

You can just do that in or from init(). Why use a timer here?

> 3. After that, I connectAllSources at 1 second intervals until dataUpdated
> gets called. At this point, I stop the QTimer and am now receiving the
> contacts. Using these, I assemble my phone book into a QListWIdget.

You should query ContactCollections and then in dataUpdated(), you check if 
the source is 

Why in one-second intervals? Is it blocking for you otherwise?

If you're unsure how to do it, you can look at lionmail.cpp. There, it should 
be async and pretty similar to what you want. 

Well, what exactly is it that you actually want? :D

> This works nicely in the background without delaying the panel/desktop and
> the GUI stays live. Using a QThread was my 1st try but the dataengine did
> not like that. The QTimer looks like a thread but is done differently so
> this plays.
>
> The alternative of writing a dataengine tailored to this type of task such
> as was done in a birthday plasmoid could be considered, not using Akonadi.
> Unless these background daemons are tactfully niced, I think folks may
> uninstall them. Nepomuk and all the Akonadi children take a large bite of
> CPU, especially after login. They may quiet down a lot later on (after
> everything is sync'ed?).

Yeah, that is indeed a problem of all data-intensive services. It is also why 
it's all the more important to have display of data fully async, and not 
depending on complete initialization of all data on startup.
-- 
sebas

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