On 08/12/12 00:03, Claude Warren wrote:
I am looking at a case where I need to register a listener to the
model. The default implementation then converts that to a graph
listener, so my question applies to both.
I don't have a way to detect when my class will be garbage collected
(OK, I could use finalize() but that is not guaranteed to be called).
My plan was to have a listener registered with the model that would
modify my class instance as appropriate. But when my class instance
goes out of scope I want both it and the listener to be garbage
collected.
This got me wondering if the listener implementation in model (and
graph) shouldn't have weak references to the listening entities (e.g.
anything registered as a listener).
I suppose I can make my listening implementation weakly referred and
clean itself up but shouldn't the base implementation of listener do
this by default?
-- Claude
So there does need to be a weak reference between the listener and your
class if your class is going to be a candidate for GC.
There is a sort-of related case where there are huge numbers of
listeners and you want them to be deregistered. The problem here is to
not have a massive list of listeners.
The event mechanism is only supposed to be a base level piece of
machinery where other things can be built on top.
How about a separate ModelListenerAdapter2 that keeps a weak reference
to the ModelChangedListener (and model m)?
What I'm not sure about is whether building in the WeakReferences into
the core system is right for everyone. Plus reported experience with
WeakReference in the first place (from Jeremy). If it's general, and
stable, then fine - an indirection ModelListenerAdapter2 should also work.
If a Weakreference goes null, the listener would deregister itself I
presume? This would clearout the underlying listener tracking (a list?)
so good for long running systems not accumulating dead listeners.
Andy
