[wildfly-dev] Making Jandex annotation index available to components

[Gunnar Morling]

Hi,

---
TL,DR: Hibernate components would like to receive the Jandex index during
deployment. A new method IndexView#close() may help to address concerns
about long-living index view references
---

Different projects from the Hibernate umbrella (e.g. ORM, Validator and
Search) rely heavily on meta-data given via annotations. In order to speed
up annotation retrieval, we are looking into using the Jandex index created
for deployments by the container.

This would require subsystems like JipiJapa or the one for Bean Validation
to pass the IndexView for the deployment to the bootstrapped component. The
change itself should be easy, I hope. But Scott expressed concerns about
components keeping references to the index after the deployment phase has
succeeded. As indexes can be large, this may potentially block a big chunk
of memory for as long as the deployment is running.

Of course we can promise that Hibernate components wouldn't keep such
references ;) But if that's not enough, could this concern be mitigated by
adding a new method IndexView#close()?

This method would free all resources of the index and would be called by
the container after the deployment has finished. Any operation on a closed
index view would throw an exception indicating that the view has been
closed. Then, even if a component accidentally kept a reference to an
IndexView, it wouldn't retain much memory (of course the index view
wouldn't be of much use to the component in that state).

Would that be an acceptable way forward? If so, I could send a pull request
towards Jandex. In a next step WF would have to make use of that new
version and invoke close() on a deployment's index at a suitable time
during the deployment lifecycle and eventually pass the index to ORM et al.

In a subsequent step we may consider to address use cases such as dynamic
reconfiguration which would require to access the index *after* deployment
time. One way for addressing this may be to allow for passing in some kind
of executor which would expect e.g. a Lambda doing work on an IndexView
passed in by the executor. That way components could access the index at
runtime, while not keeping a reference to it themselves and thus allowing
the container to manage the index and e.g. close or re-open it upon
execution. But I think this could be done as a follow-up.

Any thoughts?

Thanks,

--Gunnar

PS: As a side note, Hibernate Validator currently reads annotations lazily
at runtime (when first validating a specific bean type). When using Jandex,
we'd have to change this to eagerly build up all the meta-data for the
types listed in the index passed during bootstrap. A bit of work, but as
said we hope to gain a nice performance improvement from it.
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