Re: [ecf-dev] Re: pub sub example and distributed OSGI service registry

[Scott Lewis <slewis@xxxxxxxxxxxxx>]

Hi Ken,

Ken Gilmer wrote:
> > > Personally, I feel much safer about model replication along w/ 
> > > MDD/MVC style applications rather than code calling code in a 
> > > distributed fashion.
> >
> > I don't understand what you mean with this Ken.  Do you mean that 
> > with model replication the service is meant to transparently look to 
> > clients as if it's 'local'?
> > e.g. a client could get a local reference and cast to appropriate type:
>
> I mean, rather than using the OSGi Service" functionality (service 
> discovery, advertising, and consumption) as a way to bind isolated 
> runtime environments together, using a passive model (ie, no 
> application-level remote code calling) by which operations are 
> performed against a domain model, which is then replicated across 
> peers using something like Datashare.  

OK, I see. 

> So I would have some sort of model bundle that hosted a model.  The 
> model would be exposed to my other local bundles via a traditional 
> OSGi service interface.  However no ECF related functionality would be 
> exposed.  The model bundle would internally use ECF to perform 
> replication and change notification.  Of course, as said in previous 
> emails, the "distributed OSGi services" approach has been developed 
> before (flowOSGI.pdf).  I would be curious to play around with 
> distributed OSGi services, but would be inclined to avoid them in 
> general, mainly due to the issues described in the "A Note on 
> Distributed Computing".

OK.  I don't disagree with you Ken...as I have similar concerns (based 
upon ANODC and other papers critical about transparency) about RPC-based 
systems in general...including RPC for remote OSGi services.  Believe it 
or not, ANODC and other such papers critical of network transparency is 
really one of the major reasons why ECF is replication/asynch messaging 
based to begin with.

But I/we have gotten input that a remote OSGi services API is desireable 
for some and perhaps many, and of course a model like ECF's can support 
the creation of RPC APIs (e.g. through 'trivial replications'...i.e. 
proxies).  So I would at least like to see if there is something useful 
ECF could do here...and what/whether people would be interested in ECF 
doing such a thing.

Thanks for clarification/explanation,

Scott




> -Ken
>
>
> On Jul 18, 2006, at 5:56 PM, Scott Lewis wrote:
>
> > Hi Ken,
> >
> > Ken Gilmer wrote:
> > > > with the remote service:  1) IRemoteService.callSynch(...): which 
> > > > would provide blocking call/return semantics; 2) 
> > > > IRemoteService.callAsynch(...) (either one) which sends a message 
> > > > to remote service, and either uses polling (AsynchResult) or 
> > > > notification to receive a return value; and 3) 
> > > > IRemoteService.fire(...): which would simply send a one-way message 
> > > > to invoke the remote service but not expect or wait for a return 
> > > > value.
> > >
> > > So there would be no explicit Java interface binding?
> >
> > There could be explicit java interface binding as well (i.e. 
> > proxies).  The IRemoteService API could have a method Object 
> > IRemoteService.getService() that by contract would expose an Object 
> > that implemented the interfaces specified in the 
> > registerRemoteService(...) call.
> > The methods currently listed on IRemoteService is intended to allow 
> > explicit support for one-way (fire) and asych invocation 
> > (callAsynch).  I probably should have already made this clear and 
> > added getService().
> >
> > > How would complex types as parameters be handled?
> >
> > Through Object [] parameters...using/assuming autoboxing for 
> > primitive types.
> >
> > > Personally, I feel much safer about model replication along w/ 
> > > MDD/MVC style applications rather than code calling code in a 
> > > distributed fashion.
> >
> > I don't understand what you mean with this Ken.  Do you mean that 
> > with model replication the service is meant to transparently look to 
> > clients as if it's 'local'?
> > e.g. a client could get a local reference and cast to appropriate type:
> >
> > IMyServiceInterface service = (IMyServiceInterface) 
> > container.getRemoteService(remoteReference).getService();
> > // call it...hiding the fact that the model is actually replicated 
> > locally
> > int result = service.getMyValue("foo");
> >
> > Is this what you mean or am I misinterpreting?
> >
> > Thanks,
> >
> > Scott
> >
> >
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>
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