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From "Farr, Aaron" <Aaron.F...@am.sony.com>
Subject RE: [meta+merlin] runtime service dependencies
Date Sat, 30 Aug 2003 21:05:36 GMT

> -----Original Message-----
> From: Stephen McConnell [mailto:mcconnell@apache.org]
> >While I understand dependency resolution is important, we need to have a
> way to support runtime dependencies.
> >
> Just so that we are on the same page - I'm interpriting what your saying
> as "we need to have a mechanism through which a component can declare to
> a container that it has a dependency on a service discovery service" and
> by implication, (a) the container should be providing this service
> independently of the containment context, and (b) for compatibility
> reasons, the functionality of a such a service should be exposed using
> the service manager lookup operation.


What I'm looking for is a service discovery service.  My component/extension
would be (structurally) dependent on the discovery service, not the services
subsequently looked up. 

I can also see at least two discovery use cases:

  1. Arbitrary:
     looking up a service by key only

  2. Service Providers:
     looking up ALL service providers for a given service

The ServiceSelector and [] or {} service lookup methods provided for this
second use case.

Perhaps the semantics for this in Merlin would look something like this (?);

@avalon.dependency type="org.apache.avalon.framework.service.ServiceManager"

Where the provided ServiceManager would actually be a special discovery
service.  That seems to jive better with Merlin's structure.

Of course, we're still stuck with the mix of dependencies vs discovery.

> >
> >Even something like a wildcard would be nice:
> >
> >@avalon.dependency type="org.proj.MyService" key="*"
> >
> What is the problem with:
>   @avalon.dependency type="org.proj.MyService"

Nothing.  I thought about that after I sent my email.



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