Re: [ecf-dev] Remote service API

[Jeff McAffer <Jeff_McAffer@xxxxxxxxxx>]

Sounds like fun!  I have not been
following the ins and outs of ECF much so please excuse any ignorant questions...

- do you see a path to this being integrated
with declarative services and/or Spring and whatever Spring does for remoting?

- do you see integrating with/using
concurrency constructs like Futures whith remove services?  

- can I assume that under the covers
you can use any transport to contact the remote service?

- do you know where I can find some
spare time to play with all the great things people are creating these
days? ;-)

Jeff

slewis <slewis@xxxxxxxxxxxxx>
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08/04/2006 12:02 PM

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Subject	[ecf-dev] Remote service API

Hi Folks,

Although not completed, a 'signs of life' ECF remote service API is now
functioning with test code.  The intention of this API is to provide
access to remote services similar to the manner in which OSGI provides
access to local services via OSGi service registry.

The remoteservice API, however, is *not* the same as the OSGi service 
API,  in recognition/acknowledgment of the problems introduced by
approaches that attempt network transparency.   The remoteservice
API  
exposes a distinct API and underlying service registry, similar in 
structure to the OSGi services API, but with modifications to account 
for 1) the use of asynchronous messaging; 2) partial failure.

The three plugins in CVS are:

plugins/org.eclipse.ecf.remoteservice (API)
plugins/org.eclipse.ecf.provider.remoteservice (exampleprovider)
plugins/org.eclipse.ecf.test.remoteservice (JUnit Plugin test code)

As a brief example, here's how a remote service is registered/made 
available for remotes to access.  This is done on the client that
is the 
server for this particular service

// First get IRemoteServiceContainer adapter
IRemoteServiceContainer rsc = (IRemoteServiceContainer) 
container.getAdapter(IRemoteServiceContainer);
// Then register remote service
rsc.registerRemoteService(new String [] { IMyService.class.getName() },
service, null);

Note that the 'service' object must implement the IMyService.  Assume
that IMyService has a single method "exec()".  For those
familiar with 
the OSGI service interface, this looks very much like the 
BundleContext.registerService method.

Then, on the client that wishes to use the service:

IRemoteServiceReference [] refs = rsc.getRemoteServiceReferences(null,
IMyService.class.getName(),null);
// Assume we want the first one
IRemoteService remoteService = rsc.getRemoteService(refs[0]);
// Now call service with one of methods on IRemoteService:  callSynch,
callAsynch, fireAsynch, getProxy()

Note the getRemoteServiceReferences(...) and getRemoteService(...) are
similar to the OSGI BundleContext.getServiceReferences(...) and 
getService(...) methods.

The methods on IRemoteService allow the client to invoke the service in
several different ways...i.e. synchronously (callSynch) or 
asynchronously (callAsynch...with a listener callback for results, and
fireAsynch which fires a remote method asynchronously with no return 
value).  Note also the 'getProxy()' call, which will return an Object
*that is guaranteed to implement the IMyService interface*.  Meaning
that one can do this:

IMyService proxy = (IMyService) remoteService.getProxy();
proxy.exec();

And the remote 'exec()' method will be remotely invoked.

So the point of the IRemoteService interface is to allow the client to
control how the remote service invocation is done...synchronously with
return value, synchronously via proxy, or asynchronously with 
(callAsynch)/without (fireAsynch) return value.

There's test code in the org.eclipse.ecf.test.remoteservice test plugin
that uses these methods on IRemoteService interface.  I've made put
project set files for committer and anonymous cvs access here: 
http://wiki.eclipse.org/index.php/Remote_OSGI_Services

Any comments/criticisms/flames welcome.  This is just an initial "signs
of life" attempt, and the API and implementation will likely go through
many changes. 

Thanks,

Scott
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