[cdi-dev] Hierarchy of ManageableContext and Context

Martin Kouba mkouba at redhat.com
Tue Jul 19 03:26:25 EDT 2016

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].



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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