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Subject: RE: OSGi Binding
Date: Fri, 10 Nov 2006 10:53:00 -0500
Message-ID: 
 <EF62E58A8B80AC46A06F68DC173DE34E0115E7D5@nasa-dtw-ex003.nasa.cpwr.corp>
Thread-Topic: OSGi Binding
Thread-Index: AccETNM10G+dOSPMRHCL3zzN/4LTOgATrPdQAA4YCrA=
From: "Hawkins, Joel" <Joel.Hawkins@compuware.com>
To: <tuscany-dev@ws.apache.org>

Hi guys,

I'm EST (just barely). Like Nicole, I'm stuck behind a corporate
firewall.=20
Today's looking problematic for me. I'm game for either Monday (I'll
just work from home) or possibly sometime this weekend.

Some questions in the meantime:

A runtime can have multiple root system composites, each isolated from
another, and each system composite may have multiple root application
composites. Do I (finally) have it right?

Is it sufficient for the root system composites to be isolated with
respect to wiring (in other words, based on visibility of components
available within the root system composite), or must they be isolated
based on class loaders as well. I'd like to make sure that the fragment
bundle solution is insufficient before we go off and re-invent fragment
bundles. ;-)

Thanks,
Joel=20

-----Original Message-----
From: Wengatz, Nicole [mailto:nicole.wengatz@siemens.com]=20
Sent: Friday, November 10, 2006 2:48 AM
To: tuscany-dev@ws.apache.org
Subject: RE: OSGi Binding

>Sure. I could be available. Nicole, what Timezone are you in? I'm PST,
Joel, I believe you are CST.
I'm CET (Germany). Having the IRC in the evening (e.g. 19:00 CET or
later) would be fine for me.=20
I assume it's anyway easier for me to attend from home (due to the
companies firewall).

Best regards
Nicole
-----Original Message-----
From: Jim Marino [mailto:jmarino@myromatours.com]=20
Sent: Thursday, November 09, 2006 11:14 PM
To: tuscany-dev@ws.apache.org
Subject: Re: OSGi Binding


On Nov 9, 2006, at 6:44 AM, Hawkins, Joel wrote:

> I think an IRC might be helpful.  Comments below:
Sure. I could be available. Nicole, what Timezone are you in? I'm PST,
Joel, I believe you are CST.

>
> -----Original Message-----
> From: Jim Marino [mailto:jmarino@myromatours.com]
> Sent: Thursday, November 09, 2006 1:12 AM
> To: tuscany-dev@ws.apache.org
> 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 =20=

> I'm
> being dense. Are you referring to support for an optimized wire?
>
Yes basically an optimized wire so we don't need to proxy.

>> 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
>            /=09
> Root Application Composite
>
> Why only one root application composite? The code I have today =20
> hosts one
> root system composite and multiple root application composites
> (applications pretty much correspond to bundles).
Sorry, I'm ASCII-art challenged. The above tree could be extended to =20
include multiple leaves. The root application composite can contain =20
0..n composite children, which would correspond to application =20
deployed in the runtime. I just tried t simplify it here to highlight =20=

that there are two sides of the runtime tree.
> 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 =20
> applications,
> which makes sense in the context of a web-app deployment, but not as
> much under OSGi.
Yes agreed. We don't have the Highlander model here. App composites =20
would be deployed as children of the root app composite (or children =20
of those children).

> 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 =20
> 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 =20
> 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 =20
> 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.
For system extensions, I would like to have a uniform packaging =20
scheme that works across different host environments. Specifically, =20
we would have a jar that is contributed to the runtime. That jar =20
would be the same (e.g. Axis2 extension) and could be deployed in  a =20
war, to the standalone or to the OSGi container. The mechanism for =20
how that jar is contributed to the runtime may vary. So, for example, =20=

in a war, it may go in the /lib directory. For OSGi bindle fragments, =20=

is there a deployment API/mechanism where I can take a plain jar =20
(i.e. no OSGi manifest entries), hand it to the OSGI container and =20
declare that it is a fragment (maybe it is something specific to =20
Equinox)?
>
> 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 :-).
>
Yes we need extensions to be hidden from the application. However, we =20=

may need some classes from the extension to be visible. For example, =20
an extension may hide its StAX parser implementation but wish to =20
expose an API for applications to use that is also used by some =20
internal code (Spring does this with ApplicationContext). In =20
standalone we would load these classes in a classloader that was the =20
parent to the extension classloader. This parent would then also =20
become a parent to the application composite classloader, which would =20=

have multiple parents. In OSGi I  was thinking we would take a =20
slightly different approach. Instead of creating a parent classloader =20=

that was shared, we would programmatically export those shared =20
classes in the extension bundle. The application bundle would then =20
import them.
>> 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 =20
> remove
> - it was placed in as part of a demo I did at EclipseWorld that =20
> showed a
> sample WSDM integration using a management annotation. Sorry for the
> delay on that - swarms of distractions here.
>
NP I'm the same way. If possible it would be great to see/hear about =20
what you did.
>
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