[cdi-dev] Hierarchy of ManageableContext and Context

[Matej Novotny]

Hi all,

here are my two cents on this (pretty much covered that in the PR comments, just didn't get much attention there):

* I am also standing behind the idea to keep ManageableContext (MC) in the current hierarchy. It should extend AlterableContext and obviously we will need to add activate/deactivate methods there.
 ** In short... Yes, I see this as a _Context_ :)
* As an entry point, BeanManager seems a good way.
 ** BM.getContext() can stay as it is now, therefore we won't break any compatibility. It will return the running context, throw exception otherwise
 ** We should add BM.getManageableContext (or something along those lines) which will give you an instance of ManageableContext which you can then activate
* As for people implementing this on their own (and registering via extension which was the argument against it)
 ** There might not really be any harm in it; or at least I see none, though I may be missing something
 ** And if you feel otherwise, we might still change the doc and say that this is forbidden
 ** Again, such doc change will not cause any backward compatibility because there are not apps which would have it now.

Matej

----- Original Message -----
> From: "Martin Kouba" <mkouba at redhat.com>
> To: cdi-dev at lists.jboss.org
> Sent: Tuesday, July 19, 2016 9:26:25 AM
> Subject: Re: [cdi-dev] Hierarchy of ManageableContext and Context
> 
> Hi John,
> 
> I don't see a problem if we introduce a ManageableContext interface
> (with activate/deactivate) and a custom context implements it. In other
> words, I don't think it has to be used only for built-in contexts.
> 
> Also the context definition is clear (6.2. The Context interface) and
> again, if these are two different things then we should not call it a
> context at all [1].
> 
> Martin
> 
> [1]
> https://github.com/cdi-spec/cdi/pull/296#issuecomment-229942823
> 
> 
> Dne 18.7.2016 v 13:19 John D. Ament napsal(a):
> > All,
> >
> > I'm starting a discussion thread outside of the PR to avoid folks on the
> > EG not receiving github notifications.  I want to drive to get the
> > opinions of the broader EG and use this as feedback on whether or not we
> > change the hierarchy.
> >
> > I've been against having ManageableContext (MC) extend
> > Context/AlterableContext (AC).  There's a few reasons.  First,
> > semantically I can register a context, but I shouldn't be able to
> > register a MC.  That means from an inheritance standpoint MC does not
> > pass the is-a check on AC.  MC may be a composition style, or nothing at
> > all since it may not be associated to any specific thread in the
> > future.  While we can put in spec verbiage and exceptions to cover the
> > cases where someone does implement MC and try to register it,
> > realistically if it's there as a compilation time option, I shouldn't
> > get an error if it passes.
> >
> > I can agree that the bulk of the methods on MC should match AC.  That's
> > where I introduced a new base class for the two and had MC extend that.
> > The base class provided no behavior, just method signatures.  The second
> > key thing for me is in this area.  AC is more like a definition, where
> > as MC is a running instance of that definition.  Since these are
> > different, it shows that MC doesn't inherit the use-case of the parent AC.
> >
> > Third issue I have with extending is that AC is meant to be implemented
> > by developers to create custom contexts.  Developers aren't intended to
> > implement MC.  The container should provide these instances, since they
> > are intended only for built in contexts.  We allow developers who
> > implement AC to control their activation, as a result we've already
> > provided a means to disassociate a custom AC from any thread.
> >
> > I want to get others opinions on whether these reasons make sense and if
> > they guide to the same conclusion about not extending AC.  For what its
> > worth, I've shown these classes to some of  my own developers to get
> > their feedback, who have had to do things like quartz integration or
> > responding to netty requests and activate contexts.  The concerns I
> > raise are based on questions they've asked me.
> >
> > John
> >
> >
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