[jboss-as7-dev] OSGi subsystem dependencies

[David M. Lloyd]

On 11/29/2010 12:07 PM, Jason T. Greene wrote:
> This was talked about briefly on the pull request list, but no
> resolution was made.
>
> The issue is that JBAS-8585 and JBAS-8599 both add module dependencies
> from some of the core subsystems on to the osgi subsystem (naming and
> transactions). In addition we already have a module dependency from
> domain to osgi.  So for all intents and purposes, we are moving towards
> AS7 having osgi as a required base level component. Before progressing
> much further in this direction we should evaluate whether this is the
> right thing to do, and how this solution compares to alternative
> approaches. I can think of three approaches right off the bat.
>
> 1. Continue as is, osgi is a core required component
>      Pros: OSGi subsystem module is simpler, no additional subsystems or
> modules needed
>      Cons: AS7 must always have OSGi binaries no matter the configuration
>
> 2. Change the osgi subsystem to use optional dependencies on all of the
> subsystems it maps.
>      Pros: No additional subsystems are needed
>            AS7 no longer requires OSGi binaries
>      Cons: osgi subsystem code will need to do a lot of conditional
> checking for handling different subsystems being available
>
> 3. Create an osgi subsystem per subsystem it wraps (e.g. osgi-naming,
> osgi-transactions, etc)
>       Pros: OSGi subsystem code is simpler
>             AS7 no longer requires OSGi binaries
>       Cons: More subsystems are introduced, almost one per functional
>             subsystem.

Either #2 or #3.  #1 is a non-option in my opinion.  Once we open this 
door we're going to lose any rational boundaries between our subsystems 
and end up with a mess.

We've used #2 to decent effect already in the Txn subsystem.  An 
additional advantage to this approach is that you don't need the 
configuration overhead - you just enable OSGi, and if you have Txn 
enabled, you get OSGi+Txn as well.  This is in line with user 
expectations in my opinion.

-- 
- DML