8:06 p.m.
I agree in theory, but disagree in practice, sort of.
If we had a theoretical service container which had "perfect" scalability
characteristics (in other words, fully graph-based, so starting one service
requires only visiting its dependents and dependencies one time), and a
simple plain-Java way to declare services (e.g. a "Service" interface with
stop/start methods and a simple callback-based injection system), then
there is absolutely no reason why we wouldn't want every last thing to be
dependency-managed, because it would essentially eliminate start-order bugs
and would actually vastly simplify everything.
The reason that it doesn't work in practice is that (a) the internal MC
dependency resolution mechanisms and state machine is really complex, and
doesn't scale linearly and (b) it's much harder to use than it should be.
And (c) the core system has too many features, making (a) and (b) really
hard to solve. I firmly believe that a simple concurrent dependency graph
system with two basic states - UP and DOWN - is all that's needed -
everything else, including autowiring, the reflective POJO stuff, the JMX
magic, the existing notion of service controller states, etc. are not
required but could all be rebuilt on top of this basic system and would
work much more efficiently for it, possibly retaining some or maybe even
full compatibility with the current implementation.
The reason everyone wants to use MC is because of the above theory - that
if we do, everything will work as smoothly and efficiently as possible, and
rather than working out a very complex startup process, we can instead
define our startup process delcaratively (which will produce a far faster
and more efficient startup sequence than mere humans can figure out, with a
fraction of the effort). However I don't see that being the case today.
The situation is not hopeless - Ales, Kabir & team have been really digging
into it - but it seems pretty discouraging at the moment. We're never
going to get there from here without some major critical rethinking of
basic ideas.
- DML
On 02/17/2010 08:20 AM, Bill Burke wrote:
IoC can be done in plain Java. Using the MC to manage every nut and
bolt is just plain ridiculous.
IMO, you will only ever need this flexibility between releases. You
will never be asking a customer to change these things. Therefore, IMO,
plain Java IoC and delegation are good enough for the majority of the
ridiculous amount of EJB and Web Services internals that are exposed
currently within XML scripting. Coarse grain "wrapper" components will
both hide complexity from users and boost performance, without
disrupting flexibility.
For example, when I did Embedded EJB the first time, I created a *very*
coarse grain bean for datasources that manually created the JCA
components I needed to deploy. With this type of wrapper bean,
configuration is just calling constructors and setter methods. For
start/stop you either delegate or manually register with the MC,
although delegation, IMO, is better.
Carlo de Wolf wrote:
> Although I agree that we have user configuration and internal
> configuration mixed up in a lot of places, I don't agree on using other
> IoC constructs to resolve internal concerns. We want flexibility on
> every level and I would need an IoC construct anyway. So we should be
> able to use MC for all scenarios and fix the scalability issue where it
> lies.
>
> Carlo
>
> On 02/12/2010 02:34 PM, Dimitris Andreadis wrote:
>> I had seen something similar long time ago when measuring the memory footprint of
an MBean,
>> it was quite significant.
>>
>> It would be interesting to measure the memory overhead of a POJO (metadata and
all), but as
>> Bill suggest, having more coarse grained POJOs is better than many fine grained
ones.
>>
>> Bill Burke wrote:
>>
>>> Brian Stansberry wrote:
>>>
>>>>> * How about making our bean.xml files more coarse grain? Meaning *A
>>>>> LOT* less implementation details exposed through XML. You can do IoC
in
>>>>> Java you know. The vast majority of details within all our
beans.xml
>>>>> files will never ever change, nor will we want to support users
changing
>>>>> this stuff. If our beans.xml file are reduced to a few bean
definitions
>>>>> and classes, would make parsing and creating bean metadata much much
faster.
>>>>>
>>>>>
>>>> Semi-related, the ServiceBindingManager config needs a schema and a
>>>> parser. I create a lot of MC beans for SBM, most of which the MC has no
>>>> need to know anything about.
>>>>
>>>>
>>> EJB and Webservices create an insane amount of beans that can probably
>>> be collapsed into a few beans.
>>>
>>>
>>>
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