[Zope3-dev] EventService, references, and subscription semantics

[Casey Duncan]

On Monday 25 February 2002 10:24 am, Steve Alexander allegedly wrote:
[sniplets]
> So, transient (ie non persisted) subscription is kept distinct from
> subscription that persists between z3.py invocations.
> FS things are only allowed to use the FSEventService.
> Most code that wants to use the event service will get it by asking for
> an IEventService. The root ZODB event service will propagate events to
> the FSEventService.

Hmmm, I hadn't really considered an FSEventService, but the idea does have 
merit. I think we need to cook up some use cases, but I do think it could be 
a very useful CA addition, perhaps as a way to bind packages together or 
somesuch.

I do think we should punt on the persistent objects as FS EventService 
subscribers tho, I think it is more trouble then it is worth. I seems like 
too much mixing of levels, too much complexity and brittleness for my liking.

> Of course, it might turn out that we don't really need an
> FSEventService. Although, I can see it being useful for using the
> ComponentArchitecture outside of Zope3.

Maybe not, but my intuition says that it might solve some problems pretty 
elegantly...

> Then, we still have the issue of what to use for references.
> We can use object references provided we're happy to only allow
> persistent objects to be passed to subscribe().

This is the problem I tried to work on in my ExplicitObjectReferences 
proposal. The problem with using regular object references is that the 
subscriber looses its original context and the reference makes the object 
persist even if it is deleted from its original location.

So unless these two things aren't an issue, I don't think object references 
will work for this. I will definitely not mind being wrong, however.

/---------------------------------------------------\
  Casey Duncan, Sr. Web Developer
  National Legal Aid and Defender Association
  c.duncan@nlada.org
\---------------------------------------------------/