[slf4j-dev] [Bug 75] Cyclic dependency in OSGi

[bugzilla-daemon at pixie.qos.ch]

http://bugzilla.slf4j.org/show_bug.cgi?id=75





--- Comment #15 from Hugues Malphettes <hmalphettes at intalio.com>  2009-12-04 19:28:47 ---
(In reply to comment #14)
> FWIW, in the Eclipse Orbit repository we also provide an SLF4J API bundle. This
> bundle follows the fragment approach which a small difference. The SLF4J API
> bundle neither imports nor exports the "impl" package. The "impl" package has
> to be provided by a fragment. It's also not exported because it's not API.
> Others (except SLF4J) should not be able to import the "impl" package.
> 
> BTW, fragments can happily consume services simply by using FrameworkUtil to
> get access to the BundleContext of the SLF4J bundle. In Gyrex we provide a
> native SLF4J implementation which delegates to the OSGi LogService.
> 
> I also don't think that there will be a one-fits-all approach. I could imagine
> that there will be native OSGi SLF4J logger which doesn't delegate to the
> LogService but which extends SLF4J logger discover to use the OSGi service
> registry for discovering logger implementations. This might allow for the
> greatest flexibility (eg. switching logger implementations at runtime, maybe
> even use different logger implementations per thread/bundle, etc). However, I'm
> not sure if such flexibility is necessary for the majority of systems out there
> today.
> 

Hi Gunnar and thanks for the update.
I believe Ceki's goal is to choose the solution that fits as many as possible
so that eclipse and other consumers don't need to re-package slf4j.

Here is a fragment that supports pluggable slf4j implementations:
http://github.com/hmalphettes/slf4j/tree/osgi-binder/slf4j-api-osgi/src/main/java/org/slf4j/impl/

slf4j implementations would be packaged as bundles and slf4j-api would not
import the org.slf4j.impl package.

This was done as a small experiment:
http://github.com/hmalphettes/slf4j/blob/osgi-binder/README.txt

and we agree that pluggable implementations is really not a mainstream
production scenario.

But managing bundles is certainly nicer than managing fragments so maybe that
is a good approach?


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