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Subject: Re: [sca-j] ASSEMBLY-218: Review Interface Compatibility logic toaccomodate @Remotable attribute in the SCDL - proposal


The links to issues are incorrect. They should be:


IMO, the @remotable attribute in SCDL is tricky because it is the first case that component configuration starts to alter the interface remotability in the componentType. There are basically two use cases:

* A java component implements a "local" java interface and we want to expose such service to a remote binding.
* A java component with a reference of a "local" java interface and we want to use it to access a remote service.

Did we consider the case that more than one component uses the same Java implementation class, for example:

Component C1 exposing S1 as web service.

<component name="C1">
        <implementation.java class="test.TestServiceImpl"/>
        <service name="S1">
                <interface.java interface="test.TestService" remotable="true"/> <!-- test.TestService interface doesn't have @Remotable -->
                <binding.ws .../>

Component C2 exposing S1 as a local service for binding.sca.

<component name="C2">
        <implementation.java class="test.TestServiceImpl"/>
        <service name="S1">
                <interface.java interface="test.TestService"/>

Is this allowed? If so, do we expect test.TestServiceImpl to support both the local pass-by-reference or remote pass-by-value semantics depending on the components that use the impl class?

A few crazy thoughts:

1) Based on the original use case, should we only allow the SCA componentType to set the interface.java to be remotable instead of the component, for example:

<componentType ...>
        <service name="S1">
                <interface.java interface="test.TestService" remotable="true"/>

(Please note that componentType can be just an in-memory model. The XML is for illustration purpose.)

In fact, when we (Tuscany) implement OSGi remote services using SCA, we generate the componentType from the OSGi properties (service.exported.interfaces) so that the java interface is remotable.

2) For the direct use of "local" java interfaces as remotable in Java components, can we just have a subinterface so that:

public interface RemotableJavaInterface extends LocalJavaInterface {


Raymond Feng
Senior Software Engineer, Apache Tuscany PMC Member & Committer

IBM Bay Area Lab, 1001 E Hillsdale Blvd, Suite 400, Foster City, CA 94404, USA
rfeng@us.ibm.com, Notes: Raymond Feng/Burlingame/IBM, Tel: 650-645-8117, T/L: 367-8117
Personal Web Site
Apache Tuscany
Co-author of Tuscany In Action:

From: David Booz/Poughkeepsie/IBM@IBMUS
To: sca-assembly@lists.oasis-open.org
Cc: sca-j@lists.oasis-open.org
Date: 02/16/2010 09:38 AM
Subject: [sca-j] ASSEMBLY-218: Review Interface Compatibility logic to accomodate @Remotable attribute in the SCDL - proposal

Following discussion of Assembly-218 [1] on the Assembly TC telecon today,
I took a closer look at the Assembly, Java CAA and Java POJO specs. I've
copied the Java TC on this email for awareness.

The assembly spec rule for matching interfaces based on remotability is
fundamentally important, so I don't think we can change that.  The Java CAA
spec is the one that defines @remotable for <interface.java/>.  The Java
POJO spec contains the componentType introspection rules and describes the
use of Java POJOs for component implementations.

IMHO, if there is any spec text in error or at the very least that we
should consider updating, it is the Java POJO spec [2]. Issue Java-125 [3]
and Java-153 [4] introduced the @remotable attribute but did not address
the trip hazard that is described in Assembly-218.

In the Java POJO spec [2], see section 2.2 (toward the end) and section
2.3.  At both points the spec makes some very specific statements about
interface remotability but leaves out any mention that the determination of
remotability could be further altered by the introduction of @remotable on
a component definition.  Interestingly, section 2.2 was heavily updated
when Java issues 125 and 153 were resolved.  Those were the Java issues
that introduced @remotable on <interface.java/> in the first place.  The
Java POJO spec is (in general) maniacally focused on the componentType of a
Java component (I'm sure that's what was in all of the Java TC minds when
it resolved 125 and 153).  This trip hazard [1] comes along with the
combination of a component definition which seems to have the ability to
assert remotability into an underlying componentType and an introspected
componentType which says local.

Let's see if others buy this analysis before I suggest moving the issue to
the Java TC.


Dave Booz
STSM, BPM and SCA Architecture
Co-Chair OASIS SCA-Policy TC and SCA-J TC
"Distributed objects first, then world hunger"
Poughkeepsie, NY (845)-435-6093  or  8-295-6093

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