Hello, We are looking at implementing a reference implementation for Distributed-OSGi based on SCA metadata using Tuscany. In the long term, this support is expected to be based on pure SCA dynamic wiring at the domain level. But since this support requires changes to SCA to enable property matching for wires, auto-promotion and domain-level autowiring which are being debated at the moment, we would like to propose a temporary solution based on wiredByImpl where the wiring is done by implementation.osgi. This is a tactical solution which will be eventually replaced by proper SCA wiring, and as far as possible, we will try to minimize SPI changes required to implement this.
Here is an example of what we would like to get working for the SCA-based reference implementation of RFC-119 (based on the example from RFC 119 for Distributed-OSGi). <composite ... targetNamespace="http://beer.org"; name="BeerOrderComposite"> <component name="BeerOrderComponent"> <tuscany:implementation.osgi bundleSymbolicName=" org.beer.BeerOrderComponent" > <properties reference="warehouse"> <property name="location">London</property> </properties> </tuscany:implementation.osgi> <service name="BeerOrderService" /> <reference name="warehouse" wiredByImpl="true" requires="authentication"> <binding.ws/> </reference> </component> </composite> <composite ... targetNamespace="http://beer.org"; name="BeerWarehouseComposite"> <component name="BeerWarehouseComponent"> <tuscany:implementation.osgi bundleSymbolicName=" org.beer.BeerWarehouseComponent"> <properties service="BeerWarehouseService"> <property name="location">London</property> </properties> </tuscany:implementation.osgi> <service name="BeerWarehouseService" requires="authentication"> <binding.ws/> </service> </component> </composite> The reference BeerOrderComponent/warehouse is autowired to BeerWarehouseService when the BeerWarehouseComposite is contributed to the domain. But rather than use domain level autowiring, we would like to implement this initially by wiring this from implementation.osgi. The reference is marked wiredByImpl to avoid SCA wiring. The wires are recalculated by implementation.osgi whenever there are changes to matching services for references marked wiredByImpl. wiredByImpl in implementation.osgi enables 1. Property matching for wires using OSGi properties which dont currently have an equivalent in SCA 2. Domain-level autowiring required for Distributed-OSGi, but still being debated for SCA 3. The use of a RFC 119 compatible discovery service for OSGi services which are outside of an SCA domain. This can be prototyped inside implementation.osgi without impacting the rest of SCA. 4. Rewireable proxies required for Distributed-OSGi can be prototyped inside implementation.osgi The implementation of wiredByImpl requires 1. implementation.osgi provider to be notified whenever matching services for a wiredByImpl reference are added or removed from the SCA domain. This could be done by the node by starting and stopping the component. 2. implementation.osgi needs to find a list of matching target services in the domain. Since this matching includes interface/binding/policy matching, it is best for Simon's new DomainWireBuilder to do the matching. The code could then be reused for autowiring.The easiest way for implementation.osgi to obtain the list of matching services would be using the target field of the reference. So the domain would fill in the list of matching services in the target field, and implementation.osgi would choose from the matching services taking into account OSGi-specific properties. At the moment, the primary purpose of this work is to produce a proof-of-concept SCA-based solution for Distributed-OSGi and in particular to demonstrate that this solution will interoperate with non-SCA based Distributed-OSGi software based on RFC 119. It will be our goal to refactor most of this into core Tuscany once the requirements are clearer. Suggestions? Objections? Thank you... Regards, Rajini
