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From Sam Chance <sgcha...@gmail.com>
Subject Re: River & OSGi
Date Thu, 19 Nov 2009 01:14:31 GMT

I agree with the notion that Jini and OSGi both implement the publish,
find and bind interaction model/pattern/paradigm / whatever additional
related words one prefers. I've always described this construct as the
"operational model" of SOA. It is exceedingly obvious to even the most
casual observer that Jini and OSGi adhere to this. The essential
difference is - in general terms - OSGi implements "publish-find-bind"
in a local memory space (I.e. a JVM) and Jini implements this across
multiple memory spaces (I.e. distributed). In my view, it is precisely
this difference that yields the complimentary nature of the two [SOA]

Ironically, although contemporary mainstream SOA "deployments", which
are arguably Just a Bunch Of Web Services (JBOWS), prescribe 'publish,
find and bind', they rely little on a registry (e.g. UDDI) for the
'find' function. Instead, they achieve the 'find' function via a
highly distributed and decentralized mechanism called "WoM" (Word of
Mouth). :-)


On 11/18/09, Michael McGrady <mmcgrady@topiatechnology.com> wrote:
> Peter,
> Okay.  I see.  You are not using "pattern" in the sense of pattern brought
> into computer science by the Gang of Four.  You are using that term more in
> a plain English sense.  I think this is misleading in this venue and would
> suggest that you use another word to avoid the possible misunderstanding
> that you meant "design pattern" as it is used in computer science.
> On a more substantial note, I don't think the "pattern" you discuss is the
> same at all for Jini and OSGi.  The services for OSGi are not like the
> services for SOA.  SOA services may or may not be akin to the services for
> Jini.  I am very careful about abstracting or generalizing because, although
> my first and last love in computer science is architecture, the devil is in
> the detail.
> For my part, I think it would be worthwhile to determine the level of
> Ossification you want.  For example, there would be no harm at all in seeing
> whether you can modularize the jar files into bundles.  Once that is done,
> then you can begin seeing how the actual processes in OSGi match those in
> Jini.  As yet, you do not even know, as I understand it, what OSGi services
> you want.  That would need to be determined, since you will be customizing
> them.
> I hope this is helpful and thank you for stating what you were thinking.
> Mike
> On Nov 17, 2009, at 8:33 PM, Peter Firmstone wrote:
>> Mike McGrady wrote:
>>> I am presently the author of a framework called "Karma" (Kolona Automated
>>> Resource Management Architecture) that is open source with a management
>>> app under another open source framework AUM (Automated Universal
>>> Middleware).
>>> UM  (Universal Middleware) is a more current name for OSGi.
>>> We could have called it DUM (Distributed Universal Middleware) instead of
>>> AUM but thought better.
>>> Too bad we did not get on better when I asked you what you meant by
>>> "Service Pattern".  (I still have no idea what you mean.)
>> Here's a Clarification of what I meant by "Service Pattern", from Richards
>> Book, page 12, this should clear up any remaining confusion:
>> "the service-oriented publish, find, and bind interaction pattern: service
>> providers publish their services into a service registry, while service
>> clients search the
>> registry to find available services to use (see Figure 1.3)."
>> So there you go it's the "Publish, find and bind interaction pattern"
>> The point I was attempting to make in the beginning was that Jini, OSGi,
>> ServiceLoader and Netbeans Modules all use the "Publish, find and bind
>> interaction pattern" to solve different problems, I was trying to lay out
>> the understanding to avoid an argument and promote a discussion about how
>> to implement utilisation of OSGi within River and its applications.
>> I still haven't managed to achieve this discussion, hopefully the best way
>> forward will become more apparent during implementation.
>> Cheers,
>> Peter.
>>> Anyway, this does all you want to do and we have a plan to have it set as
>>> a standard with IEEE, where I am a member of the standards committee.  If
>>> you check there in a few months, you can see what I was hoping to talk to
>>> you about before your ego got in the way.
>>> Good luck with your endeavors.
>>> Mike
>>> On Nov 8, 2009, at 5:06 PM, Peter Firmstone wrote:
>>>> Yes that's the beauty of Services, they provide opportunity for
>>>> pluggable replacement implementations.  That's the "Service Pattern"  As
>>>> we have seen it is possible to use the Service Pattern to solve a number
>>>> of different problems.  Eg Netbean Plugins, SPI, OSGi, Jini.
>>>> I'm looking at OSGi to wire up services inside the JVM as you say.  When
>>>> I say package, I mean a java package residing in the local JVM it may or
>>>> may not be part of a Jini service, it may be a purely local JVM package,
>>>> eg a library dependency or local domain package.  For example, I have
>>>> package X, version 1 loaded in my local JVM, I need to have package X
>>>> version 2 loaded as version 1 isn't compatible with the new Objects
>>>> (domain data) I'm recieving in serialized form.  I need to share this
>>>> information locally with Package Y that currently has references to
>>>> objects in Package X version 1.  The Objects in Package X version 1 that
>>>> Package Y references need to have their class files upgraded.  Without
>>>> OSGi I can do this by persisting state, stopping the JVM, restarting and
>>>> loading package X version 2.
>>>> I'm not looking at distributed OSGi, but I can see a use case for
>>>> utilising a Jini Service, when a local OSGi bundle that performs some
>>>> task that could be done optimally if the processing can be moved to
>>>> where the data resides, this is just an example there are probably 10
>>>> other ways of doing this:
>>>> A local application bundle that provides an OSGi service locally queries
>>>> a remote database using JDBC and performs a considerable amount of
>>>> manipulation to that data prior to returning a subset.  The query and
>>>> its result are sent over the network using a database JDBC connection.
>>>> The processing for that data, if shifted to the machine that has the
>>>> database data, would consume significantly less network resources.  EG
>>>> the data transferred over the network is reduced by a factor of 100 by
>>>> processing the data on the database machine after querying.  A bundle
>>>> that provides a "local JVM application" an "OSGi service" could utilise
>>>> a "Jini Service" to request the data be processed at the Database
>>>> machine in a particular manner before receiving the result.  This
>>>> function could be locally available as an OSGi service to some other
>>>> local application, that application doesn't need to know about Jini, it
>>>> is an implementation detail that is abstracted.
>>>> My objectives are all based around codebase services (objects aren't
>>>> locked to their http codebase origin), in combination with OSGi or
>>>> something like it, to ensure compatible classes and packages are loaded
>>>> among separate JVM instances.  Yes Newton does something similar,
>>>> however it is AGPLv3 licensed.
>>>> I envision a distributed environment where nodes can have the majority
>>>> of their packages downloaded and upgraded via codebase servcies.
>>>> Providing an evolving cluster, that upgrades it's bundles incrementally,
>>>> while maintaining the maximum level of class and package compatibility.
>>>> Think Agile Cluster Running System component upgrades.
>>>> People, who are jumping in now because I've mentioned OSGi, are making
>>>> assumptions and haven't been following the discussions I've posted
>>>> previously about Versioned Classes, Classloader trees, Static Analysis
>>>> and Codebase Services, this is frustrating as I was hoping for some
>>>> participation.  It seems I can only get attention when I mention a
>>>> controversial subject.  What I want is attention to solving the problems
>>>> that will make River better.
>>>> In my note below when I'm referring to the "Service Pattern", I mean the
>>>> service pattern that OSGi implements, enables bundles to be upgraded by
>>>> loading the replacement bundle in a new classloader,  The service is a
>>>> common interface, the new upgraded service is discovered after it is
>>>> started.  The alternative is to use delegates to update references
>>>> between objects when the Classloader changes as per some of the other
>>>> patches I've uploaded.
>>>> Jini also utilises a "Service Pattern", but to solve a different
>>>> problem.
>>>> I knew this was going to be a difficult topic to present.
>>>> What we need are separate lists, where people who want to participate in
>>>> constructive development to solve problems can do so and another list
>>>> where people can pontificate about software ideals and have
>>>> disrespectful arguments with each other without holding up development.
>>>> While we're developing we can keep an eye on the argument list without
>>>> getting embroiled.
>>>> Anyway I've said enough, I'm going back to doing the things I need to
>>>> do, if someone who has been following my posts to date has
>>>> implementation ideas, but are afraid to mention it, please feel free to
>>>> contact me directly to discuss, I do need some input to gain confidence
>>>> that I'm approaching these problems in the right manner.
>>>> Peter.
>>>> Dennis Reedy wrote:
>>>>> On Nov 8, 2009, at 1251AM, Peter Firmstone wrote:
>>>>>> I had avoided OSGi purely due to the controversy it generates on
>>>>>> list, however without the Service Pattern one cannot upgrade a package
>>>>>> without first persisting everything and shutting down the entire
>>>>>> then restarting.  At least OSGi allows you to stop a bundle and any
>>>>>> dependents, persist what you need to then start with a later bundle
>>>>>> version if desired, without having to persist or shut down the entire
>>>>>> JVM.
>>>>> If thats all you want you dont need OSGi. Service lifecycles are
>>>>> supported with a variety of container approaches, from JEE, Spring to
>>>>> Rio. You also do not need to shutdown the JVM to load new service
>>>>> classes.
>>>>> Adopting OSGi as a micro-kernel architecture for wiring up services
>>>>> inside the JVM is a different thing. Looking at distributed OSGi is a
>>>>> totally different thing on top of that. IMO, if you want to consider
>>>>> OSGi for River, you focus on the former, not the latter.
>>> Mike McGrady
>>> Principal Investigator AF081-028 AFRL SBIR
>>> Senior Engineer
>>> Topia Technology, Inc.
>>> 1.253.720.3365
>>> mmcgrady@topiatechnology.com

Sent from my mobile device

Sam Chance
443-694-5293 (m)
410-694-0240 x108 (o)

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