Re: [g-a-devel] FocuCaretTracker issues

[Joseph Scheuhammer <clown alum mit edu>]

Hi Alejandro,

Thanks for your input.
> In any case, another pov for the same question would be: is there any
> advantage on each client having their own instance of the tracker?
> Because if there isn't any advantage, having this as a singleton have
> the memory advantage of maintaining just one reference. Probably that is
> a small advantage, but if having one instance per client have zero
> advantages, the singleton option is still winning 1-0.

The main advantage of each client having their own copy of the tracker 
is that there is no need to worry about accidentally deregistering the 
events with atspi.  With the singleton approach, the tracker has to note 
the number of clients connected to it, and (perhaps) deregister when no 
more clients are connected.  Put concretely, when a client is no longer 
interested in the tracker's signals, the client calls the tracker's 
disconnect() method.  When there are no more connections, then the 
tracker can safely dereigster with atspi.

On the non-singleton design, the tracker does not have to manage this 
since there is only one client connected to it.  The logic is somewhat 
simpler.  When the client is done, the deregistration for that client's 
instance of the tracker can be automatic.  I'm actually leaning towards 
this approach now, since the complexity associated with the singleton 
design may be an example of the anti-pattern you noted, "Accidental 
complexity".

On the other hand, with a singleton, the dbus traffic is limited to one 
atspi registration (well, actually three, but that's a detail). With 
mutliple trackers, there is one atspi registration per tracker.  How 
costly is that extra dbus traffic?  (Probably a Mike question).

Still thinking about the rest.  However:

>   In fact,
> doing that is a example of a well known anti-pattern: "Accidental
> complexity" [1]
>
> [1]http://en.wikipedia.org/wiki/Accidental_complexity

Thanks for the link.  :-)

--
;;;;joseph.


'A: After all, it isn't rocket science.'
'K: Right. It's merely computer science.'
             - J. D. Klaun -