[Hawkular-dev] WF9 requires us to change our agent subsystem extension classes

[John Mazzitelli]

Here's what the error looks like:

https://travis-ci.org/hawkular/hawkular-agent/builds/63771085

And here's the changes that would need to be made for it to compile with WildFly 9 but introduces the circular constructor problem (this is just to workaround that issue with this.attributes changed to "final"):

https://github.com/hawkular/hawkular-agent/commit/84fbfb3354f2eba4524fd4fd1849ef11eca45fd3

As the comment says,  I tried passing Array.asList(XYZDefinition.ATTRIBUTES) in the constructor, as well as what you see here (XYZDefinition.INSTANCE.getAttributes()) but both have this circular problem and breaks.

----- Original Message -----
> The quick summary of this email: the Hawkular Wildfly Monitor Agent will not
> be able to run on WildFly 9 in its current state. It must be refactored due
> to changes that were made in the WildFly 9 subsystem extension API.
> 
> Details:
> 
> After staring at this for a while, I found that our currently WildFly8 code
> layout of the subsystem extensions in the agent needs to change for this to
> run in WF9 - I don't think I used this approach in the bus or nest subsystem
> extensions so nothing needs to change there.
> 
> The design pattern here is to use PersistentResourceDefinition subclasses for
> our the subsystem resource definitions (called the Definition classes). In
> here you define static members for all attributes and operations as well as
> an INSTANCE object of the definition itself, among other things.
> 
> The problem is, that same Definition class needs to grab (and thus create) an
> instance of the AddStepHandler within the Definition class' constructor. And
> THAT AddStepHandler needs to refer back to the Definition object for the
> attributes. Today, it does so in the populateModel() overloaded method,
> which isn't a problem. However, we needed to access a parent class' data
> field (this.attributes) to set our attributes in that populateModel()
> method. Unfortunately, that parent class in WF9 has changed that
> this.attributes data field to final. So we can't do that anymore. Instead,
> it appears the only way to set the attributes now is to pass them in via the
> AddStepHandler class' constructor (calling the superclass's
> "super(Collection<?> attributes")).
> 
> But this introduces an ugly circular dependency in the Definition and
> AddStepHandler constructors - it bombs with an NPE.
> 
> So this means in order for us to move the agent to WF9, I would need to
> refactor the subsystem definition classes - I would probably have to extract
> out all of the attribute/operation definitions into some independent class
> that can be shared between the *Definition and *Add classes to avoid this
> constructor-circularity dependency. It probably won't be hard to do this,
> just a hour or two hopefully. But as it is now, it can't run on WF9.
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