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From David Jencks <>
Subject Re: [DISCUSS] plugingroups - another idea
Date Thu, 11 Sep 2008 22:07:05 GMT
Maybe I don't understand your proposal.  If I do, you are arguing that  
the one new feature of plugin groups- that they do not define a  
classloader for the dependencies -- should be removed (or not  
implemented -- I'm not sure if it actually works yet) -- and we should  
use only plugins for all purposes.

I think the new alleged capability is a good idea.  I see the  
archetypical use case for plugin groups as installing a bunch of  
functions that you might want to use at the same time but have no  
classloading relationships between them.  For instance, I think of a  
"complete" jetty server as having jetty, jetty deployer, jasper  
deployer, and the basic jetty console.  (I don't know if we have this  
profile right now).  Jetty deployer and jetty console both pull in  
jetty so the dependency list wouldn't need jetty in it.  Now, why  
exactly should we supply a classloader containing these parents to  
everyone who happens to install this profile?  Note that anyone who  
wants to bundle a bunch of apps together into one classloader can  
already do that with a normal plugin.

david jencks

On Sep 11, 2008, at 5:26 PM, Joe Bohn wrote:

> I've been thinking about plugingroups and I'm wondering why we need  
> to make them very much different than regular plugins.
> We've been primarily focused on plugingroups as a way of simplifying  
> the creation of a custom server assembly.  That's a good use of  
> plugingroups.  However, perhaps it isn't the only use.   Because  
> we've been primarily thinking of them as server assembly bits we've  
> been looking to remove some of the regular plugin functions from  
> them ... like the classloaders they create and their entries in  
> config.xml.
> So the question is; can plugingroups be used in other ways and would  
> the classloaders, etc... be useful in those other scenarios?
> Perhaps a user or solution provider has a need to create a core set  
> of plugins and then "bundle" them together into higher function  
> plugingroups (just as we want to do with the server bits).  Their  
> customers could then create their own applications and include  
> dependencies on these plugingroups.  These plugingroups might also  
> be of value for a user to install on a server independently.  I  
> think our users could also benefit from this by creating  
> dependencies on our plugingroups rather than individual plugins.  A  
> user could create an application that requires tomcat, web services  
> with cxf, and jms.  It would be nice if they could reference the  
> plugingroups as dependencies when building a plugin via maven rather  
> than having to reference the individual plugins.
> IIUC, our current direction is that a user would deal with one set  
> of components (plugingroups) when building a server ... but a  
> different set of components (plugins) when creating their own  
> application plugin (at least I think that would be the case).  Also,  
> I suspect we would have to include additional capabilities in  
> Geronimo to protect against a user attempting to add a dependency on  
> a plugingroup.  I'm concerned that making the plugingroups too  
> specialized results in more work for us and less capability for the  
> end user.
> If we just let the regular processing occur for plugins that  
> aggregate other plugins (plugingroups), then I think the user could  
> leverage the plugin groups in many different ways and we'd have  
> fewer issues.
> How we actually work the internal details to construct classloaders  
> could still be enhanced to eventually "skip" the aggregate objects  
> and drill to the next level for plugingroups ... but I think that's  
> really an independent issue and an optimization.
> So, the proposal I was thinking of was simply this:
> 1) Create plugin groups as any other plugin and let our current  
> processing deal with them as any other plugin.  The classloader that  
> is created might actually be useful.  The config.xml entry probably  
> is not, but is it really causing any problems?
> 2) Use the plugin group attribute more as a way of classification  
> rather than function enhancement (at least for now).  We can always  
> decide to leverage this knowledge more completely to optimize  
> classloader construction or for other purposes such as organization.
> 3) Leave the assembly construction GUI/commandline and plugin  
> install GUI/commandline to work with plugins only ... no  
> differentiation with plugingroups.
> 4) To help clear the clutter from those GUIs/commandlines (one of  
> the primary motivations in the recent effort) we could create  
> different plugin catalogs.   The default catalog could primarily  
> include the plugingroups and perhaps a few specific plugins that  
> don't merit further aggregation.  An expert catalog would be the  
> complete catalog with all plugins included.  These same catalogs  
> would be used when installing plugins and constructing server  
> assemblies so there would be some consistency for the user.
> 5) The same set of plugins and plugingroups would be available as  
> dependencies when a user builds their own plugin via maven.
> I think this would broaden the usefulness of plugin groups.
> thoughts?
> BTW, why are the current plugingroups jars rather than cars ... and  
> why don't they appear in the geronimo-plugins.xml?
> Joe

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