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From "Aaron Mulder" <ammul...@alumni.princeton.edu>
Subject Re: RTC PLEASE COMMENT Priority order for starting gbeans.
Date Mon, 06 Nov 2006 21:33:22 GMT
Well, if we go the class loader route, we could make it a feature of
the Configuration and the deployer could just set transformer classess
on the Configuration or Configuration Class Loader, and it could be
independent of the GBeans in the module.  It seems to me to be a
somewhat more straightforward approach than the GBean-ordering option
(though that feature probably has other advantages).

Thanks,
      Aaron

On 11/6/06, David Jencks <david_jencks@yahoo.com> wrote:
>
> On Nov 6, 2006, at 12:47 PM, Aaron Mulder wrote:
>
> > So for the JPA plugin, we just applied the transformer in the class
> > loader.  I'm not super-confident of the specific implementation -- but
> > is there a reason why this approach wouldn't work for us in Geronimo
> > (since we have a custom class loader already)?
> >
> > http://gplugins.svn.sourceforge.net/viewvc/gplugins/jpa/trunk/base/
> > common/src/java/org/gplugins/jpa/app/TransformingClassLoader.java?
> > revision=28&view=markup
>
> We could probably do something like that but I'd rather keep the code
> simple and use  the jvm facilities.  If someone else wants to
> experiment with this approach, fine.  In any case this doesn't really
> have a bearing on the gbean priority implementation:  no matter how
> the transformer is installed it still needs to be installed before we
> start loading classes.
>
> thanks
> david jencks
>
> >
> > Thanks,
> >     Aaron
> >
> > On 11/6/06, David Jencks <david_jencks@yahoo.com> wrote:
> >>
> >> On Nov 6, 2006, at 12:25 PM, Dain Sundstrom wrote:
> >>
> >> > So to be clear, I'm generally against adding destabilizing features
> >> > that aren't required to meet the features we have chosen for the
> >> > 1.2 release.  Does OpenJPA use a runtime class transformer?
> >>
> >> OpeneJPA can pre-enhance classes (using an ant task) or do runtime
> >> enhancement.  The jpa contracts require that we implement
> >> PersistenceUnitInfo.addTransformer which lets the persistence
> >> provider install a transformer.  The code I've written to make this
> >> work uses the java 5 java.lang.instrument facilities which
> >> unfortunately requires and elaborated command line like:
> >>
> >> java -javaagent:bin/jpa.jar -jar bin/server.jar
> >>
> >> to get the agent picked up.  If you just start the server you don't
> >> get errors, but you don't get runtime enhancement either.
> >>
> >> Currently runtime enhancement doesn't work if classes that need to be
> >> enhanced get loaded while gbean datas are deserialized.  So far I
> >> know this can happen with ejb web services that include methods that
> >> have enhanced classes as parameters.  It doesn't happen with ejbs
> >> that don't have enhanced classes as parameters.  I think that most
> >> users will want to work in eclipse or similar ide and not want to
> >> have to rebuild + pre-enhance their classes during development.
> >>
> >> Runtime enhancement is a required feature for full jpa support.  I
> >> think it's going to be pretty convenient when it works.  Therefore I
> >> think that if there aren't backwards compatibility problems with
> >> this stuff after gianny's fix we should keep it.
> >>
> >> thanks
> >> david jencks
> >>
> >>
> >> >
> >> > -dain
> >> >
> >> > On Nov 6, 2006, at 10:26 AM, Dain Sundstrom wrote:
> >> >
> >> >> As I mentioned on IRC, I would prefer if we keep changes like this
> >> >> out of 1.2.  From what I understand it is unnecessary since
> >> >> OpenJPA doesn't even use a transformer, so we are just
> >> >> destabilizing and breaking backwards compatibility.
> >> >>
> >> >> Can you explain how this works?  I don't see the code that is
> >> >> actually using this feature.
> >> >>
> >> >> -dain
> >> >>
> >> >> On Nov 5, 2006, at 12:54 AM, David Jencks wrote:
> >> >>
> >> >>> See GERONIMO-2541
> >> >>>
> >> >>> In order for runtime class enhancement for jpa to have any chance
> >> >>> of working, the persistence provider has to get started before
> >> >>> much of anything else happens so it can install the bytecode
> >> >>> transformer before any classes that need enhancement get loaded.
> >> >>>
> >> >>> To support this I wrote a priority order loading feature for
> >> >>> gbeans, see GERONIMO-2541.  This is pretty simple and appears to
> >> >>> work fine except it will prevent any pre-1.2 configurations from
> >> >>> running on 1.2 servers:  I have to write the priority for each
> >> >>> gbeandata in the serialized gbeanstate.  I don't know how to fix
> >> >>> this: if anyone else does please speak up.
> >> >>>
> >> >>> Runtime enhancement seems to work ok with this feature for simple
> >> >>> apps that use ejbs and web apps but there are some situations in
> >> >>> which I cannot get runtime enhancement to work because the
> >> >>> classes are loaded when some gbeans are loaded before any gbeans
> >> >>> are started.  So far this has occurred with web services that use
> >> >>> an enhanced class as a paramenter: I think that the axis 1
> >> >>> mapping info includes seriailzed class instances rather than the
> >> >>> names of the classes involved.
> >> >>>
> >> >>> So, is runtime enhancement for some jpa apps worth breaking
> >> >>> backwards compatibility for configs?  Can we do something to
> >> >>> recognize both old and new config formats?  If I don't hear
> >> >>> anything against this in a few days (about 3) I'm going to go
> >> >>> ahead and break backwards compatibility and commit this
> >> >>> patch..... you are warned.
> >> >>>
> >> >>> thanks
> >> >>> david jencks
> >> >
> >>
> >>
>
>

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