I think an IRC might be helpful. Comments below:
-----Original Message-----
From: Jim Marino [mailto:[EMAIL PROTECTED]
Sent: Thursday, November 09, 2006 1:12 AM
To: [email protected]
Subject: Re: OSGi Binding
>...services. I would also like to avoid proxying the OSGi services if
>possible.
Can you define what you mean by proxying the OSGi service? Sorry if I'm
being dense. Are you referring to support for an optimized wire?
>2. The OSGi container would isolate SCA application composites
>according to its classloader semantics.
>Currently, Tuscany has two composite trees, an application and system
>tree:
Runtime
|
/\
/ \
/ Root System Composite
/
Root Application Composite
Why only one root application composite? The code I have today hosts one
root system composite and multiple root application composites
(applications pretty much correspond to bundles). The reason I did this
was so that I could "name" the individual applications (for external
management, etc). My reading of the Host API was that there was a
Highlander model (there can only be one) when it comes to applications,
which makes sense in the context of a web-app deployment, but not as
much under OSGi. What made me think that was that the root application
composite had a name.
>The root composites may contain child composites. The system
>composite tree contains runtime extensions such as Axis. Each
>composite has its own classloader. This maintains isolation between
>application composites and runtime extensions.We plan on introducing
>a multi-parent classloader for system composites. This is arises from
>the need to support scenarios where application code may need to
>access dependencies associated with a system extension. For example,
>application code may need to access classes in Spring. These classes
>need to be shared with the application composite classloader. We were
>planning on loading dependencies that needed to be shared in a parent
>classloader of the system extension classloader. The former
>classloader would then also become a parent of the application
>classloader (which would have multiple parents).
Comments below at the end of the extension discussion.
>One issue is going to be reconciling this scheme with OSGi's
>classloading infrastructure. In relation to this, I was thinking we
>would want a common packaging mechanism for Tuscany extensions across
>host environments. For example, the Axis2 extension should not have
>to be repackaged or modified when deployed on Tomcat or Equinox.
>Application composites, however, could be bundles. I was thinking
>there would be one Tuscany runtime deployed to an OSGi container.
>This would get bootstrapped (as Joel mentioned) by a BundleActivator
>and would look similar to the web app launcher with one exception.
>Namely, while the web app launcher boots the runtime in a separate
>classloader, the BundleActivator would not need to do this and would
>instead boot Tuscany in the bundle classloader. The Tuscany runtime
>bundle would consequently have to export classes used by
>applications such as SCA API.
>Applications would be deployed as bundles as well. It would be nice
>if we could listen to bundles coming online and check for SCA scdl
>(configuration files). If one is found, we load the bundle as an
>application composite and stick it in the runtime application tree.
>The classloader for this composite would be the bundle's. The bundle
>itself would have to import certain SCA packages (i.e. the ones
>exported by the runtime bundle).
I think I've got this.
>The hard part is going to be figuring out how to deal with
>extensions. Specifically, in the case I mentioned above where
>application code needs to reference certain extension classes. I
>would like to avoid having special packaging for Tuscany extensions
>when deployed to an OSGi container versus the Servlet container. So,
>we could deploy the same Axis2 extension to Tuscany on an OSGi
>container and Tuscany on a Servlet container. This would mean the
>runtime would have to behave slightly differently depending on this
>host. In this respect, perhaps what we could do is instead of
>creating a parent classloader to the extension and also having it as
>a parent to the application, we could have OSGi manage this? One way
>to do this would be for a particular extension to use just the bundle
>classloader and programmatically export packages that need to be
>shared (is there an OSGi api to do this, I recall a "dynamic export/
>import")? One the application side, the bundle import those packages.
OSGi has a concept known as a Bundle Fragment. A fragment is packaged as
a separate bundle, but at runtime acts is if it were packaged directly
as part of the host bundle. My thought was to package runtime extensions
as fragments, and designate the sca kernel bundle as the bundle host.
Add to that a mechanism to populate the system composite tree with the
extensions, and you've got something that (to me) sounds very much like
what you've described above. Application bundles could specify a
dependency on the sca kernel bundle, at inherit classloader access to
all the extensions as a result.
What this doesn't do is allow you to hide extensions from particular
applications. Is this a requirement? From your diagram above (where
there's a single system composite tree) I'm assuming its not, but of
course I could be wrong :-).
>Do you guys think this makes sense? I have some skeletal code checked
>into the OSGi and Equinox projects.
>Also, I would like to try and get any code checked into the trunk
>since this will make things easier. Joel, when you get things synced
>back up submit a patch and I can apply it. Similarly, Nicole, if you
>have code that could benefit from being checked in, let me know.
I'll get back to the patch. There's some code in there I need to remove
- it was placed in as part of a demo I did at EclipseWorld that showed a
sample WSDM integration using a management annotation. Sorry for the
delay on that - swarms of distractions here.
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