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

[Scott Marlow]

On 10/27/2016 08:42 AM, Gunnar Morling wrote:
> 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.

We have been talking about wanting to pass the "hibernate.jandex_index" 
into Hibernate ORM, from Jipijapa but haven't been able to yet since 
there are no safe guards to ensure the "hibernate.jandex_index" 
reference is cleared after application deployment completes.

If an IndexView could be closed, versus just be garbage collected when 
there are zero references, it would probably be closed by something 
higher up the (deployment) call stack in WildFly, than the JPA container 
(or Jipijapa integration code).

However, if there are references to the Jandex (partially) loaded class 
definitions, those probably also need to be cleared, for us to benefit 
from this idea.  Just clearing the top down IndexView reference is 
probably not enough to reduce memory usage.

>
> 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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