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From Göktürk Gezer <gokturk.ge...@gmail.com>
Subject Re: [API][ApacheDS][Studio] Status on the OSGI branch
Date Wed, 23 Nov 2011 16:36:36 GMT
On Wed, Nov 23, 2011 at 5:31 PM, Pierre-Arnaud Marcelot <pa@marcelot.net>wrote:

> Hi guys,
>
> I wanted to give you a little bit of feedback and ask for status from the
> other team members (especially Göktük) working on the OSGI branch.
>
>
> On the API side, Göktük introduced extensibility for the comparators and
> syntax checkers using Apache Felix iPojo.
> From what I've seen it works great both as OSGI bundles and plain old jars.
>

That's cool.


>
> On the Studio side, I'm still struggling with these modifications.
> Despite all my efforts and hacks (especially with the
> 'Bundle-ActivationPolicy' directive of the MANIFEST.MF file), I'm still
> unable to load extensible elements of the API within Studio.
>
> Here's a quick recap of the problems I encountered.
>
> At first, I noticed that in Equinox (Eclipse's OSGI container), the iPojo
> bundle and Shared's iPojo utilities bundle were not started and their
> activators not called when I was using the API
>
> I rebranded the iPojo bundle in Studio's projects to include the
> 'Bundle-ActivationPolicy' directive in its MANIFEST.MF file, and also
> included it in the 'ipojo-manager' of ApacheDS.
>
> This is already a bad hack, but it is still not enough…
>
> Now, both bundles are started at the first time one of their classes is
> accessed by another bundle, and their activators are getting called
> correctly.
>
> However I'm still getting an exception, a NullPointerException.
> This NPE occurs when we ask the bundle context for the service references
> related to iPojo.
> Here's a file containing the full stack trace of the exception: [1]
>
> At this point, there should be a service reference for iPojo ready to use,
> but we get nothing.
>
> This is how far I've managed to go… It is not enough, but I've tried every
> fix idea I had and I empty now…
> If someone has a clever idea… ;)
>

I just have ideas on why this is failing. The first thing to consider is,
something in eclipse equinox is preventing IPojo from actually
initializing. I mean it seems started but, actually it isn't. IPojo does
not have custom equinox console command, so that makes finding out what
happened harder. If we assume IPojo is initialized correctly, then the
problem is about the thread model of the equinox which leads Ipojo
annotated api elements(Comprators, etc...) to not registered with IPojo
before the code looks for them through IPojo. Starting them right after the
IPojo in equinox may solve the problem.

Actually there is no nice-looking solution to this problem, because we're
deploying osgi partially into the code, so we must manage these problems
somehow. I couldn't have a chance to look at what is wrong with the studio.
IPojo runs on equinox for sure. I'll try to set my environment for
debugging that problem.


>
> On the ApacheDS side, I am able to run a small part of ApacheDS using the
> 'apache-felix' module and its Eclipse launch configuration.
>
> At the end of the execution I hit this exception:
> org.apache.directory.server.config.ConfigurationException: Cannot
> initialize the
> org.apache.directory.server.core.normalization.NormalizationInterceptor,
> error : java.lang.ClassNotFoundException:
> org.apache.directory.server.core.normalization.NormalizationInterceptor not
> found by org.apache.directory.server.service.builder [44]
> Here's a file containing the full stack trace of the exception: [2]
>
> I think it is, at the moment, the intended behavior since a few things
> still remain to be set in ApacheDS to allow it to run successfully within
> an OSGI container.
>
> Göktük, can you confirm this is the intended behavior please?
>

Yeah, that's the same stacktrace with the one i get . Interceptors are not
even visible to service-osgi bundle, so NoClassDefFound is expected
exception when we try to classload them which is what we do right now.

More importantly, can you share with us the status of the OSGI-fication of
> ApacheDS? What is the purpose of the 'component-hub' you have been working
> on lately?
>

component-hub is the main extendibility layer i'm working on. This will
provide us as developers a facility to provide extendibility to any aspect
of the ApacheDS. It's almost done with the implementation. It needs testing
after that of course. It will be a standalone engine in ApacheDS, means you
won't have to use OSGI directly to provide extendibility. ComponentHub
provides facilities for, listening some type of components, creating
instance of them, configuring the instances through associated entries in
DIT, saving and loading those created/configured instances through java
property files.

So when we want to provide extendibility for interceptors lets say, we will
write 3 class(schema generator, instance generator and listener). Schema
generator is for generating custom schema elements to represent the
component's instances on DIT. Instance generator in the other hand must be
compatible with its schema generator, and its purpose is generating
instances with the default configuration which we'll extract from the
implementing class. When we register schema generator and instance
generator with the component-hub, our listener will start getting
information of all the interceptors in the system through callback methods
with ADSComponent argument. Through this ADSComponent reference we'll be
able to create manage,create.configure the component instances, easilly.
Each created instance will also be represented by ADSComponentInstance
reference which will provide facilities for hooking its configuration with
the some entry on DIT and so..I already wrote general purpose
schema-instance generators, but individual component types may need some
extra, hardcoded things in its schema and DIT entries, so that's why i make
generators extendible. I'll document the infrastructure after i finish and
test it completely. All i can say is after it finishes, making something in
ApacheDS extendible in all aspects will be really easy procedure.


>
>
> I hope we can move forward and find fixes to all the remaining issues
> quickly on OSGI.
> Even if we merge back the modifications from trunk to the OSGI branch very
> often, it's never a good idea for a branch to last too long… It usually
> make the last merge (when merging back to trunk) a nightmare.
>

With the component-hub working as standalone extendibility engine, there
won't be major changes in the code i guess. But OSGI-fication of ApacheDS
is some kind a incremental work, we'll face the problem and solve it, so i
can't accurately say when the ApacheDS will run on OSGI completely. I hope
the branch won't last longer than 2 month, but it's strongly needed right
now even if ApacheDS runs on OSGI tomorrow :)


>
> Regards,
> Pierre-Arnaud
>
> [1] - http://cl.ly/C3eB
> [2] - http://cl.ly/C3O s <http://cl.ly/C3Os>


Regards,
Göktürk

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