Peter,
I'd be happy keeping the use of null
for unwired references for 0..x multiplicity cases. This gives the
implementation
code a very simple way of checking whether
the reference is wired or not. Note in your table below, reinjection
may give a null reference, an empty
collection or simply a reduced size collection (for 0..n cases with multiple
targets present).
The more interesting question is what
to do in the case of 1..x multiplicity cases where the wiring is supplied
"externally"
- ie not in the direct configuration
of the reference itself, at domain level. So, I'm thinking of
a) reference is marked with autowire
& targets arrive from other contributions
b) reference is wired with explicit
<wire/> elements supplied in a separate contribution
If the multiplicity constraints are
not honoured at some time, what is supposed to happen? Is it valid
to inject a null
reference object in this case? If
not, what DOES the runtime inject when the wiring changes so that there
is no wire
present any longer.....
I don't have a clear view of this at
the moment. The consistent thing to do is to inject a null reference.
However, for
a component declaring the reference
1..x, this should not happen. An alternative is to inject a "dead"
reference -
one which can only ever generate an
exception if any of its business methods are invoked.
Yours, Mike.
Strategist - Emerging Technologies, SCA & SDO.
Co Chair OASIS SCA Assembly TC.
IBM Hursley Park, Mail Point 146, Winchester, SO21 2JN, Great Britain.
Phone & FAX: +44-1962-818014 Mobile: +44-7802-467431
Email:
"Peshev, Peter"
<>
07/01/2008 18:18
To
"Blohm, Henning" <>,
Mike Edwards/UK/IBM@IBMGB, "OASIS Java" <>
cc
Subject
RE: [sca-j] ISSUE 4 - Dependency reinjection
HI,
Just to comment on " Targeted Service Undeployed " usecase.
According to the OSOA errata submitted in OASIS, unwired references should
have the following representation :
"An unwired reference with a multiplicity of 0..1 must be null. An
unwired reference with a multiplicity of 0..N must be an empty array or
collection"
So perhaps the following representation looks more consistent to that decision
:
Effect on
Change Event
Reference
Existing ServiceReference
Object
Subsequent Invocations of
ComponentContext.
getServiceReference()
Targeted Service Undeployed
Reinjection with null /empty collection MAY
occur
Business methods SHOULD throw ServiceUnavialbleException.
Returns null or empty collection
I would personally would be happy to revisit that decision and say that
the "null representation" is not valid for domain level wiring
that is subject to change and keep the exception throwing as defined by
Reza.
Best Regards
Peter
________________________________
From: Blohm, Henning [mailto:]
Sent: Monday, 7. January 2008 19:43
To: Mike Edwards; OASIS Java
Subject: AW: [sca-j] ISSUE 4 - Dependency reinjection
Hi Reza, Mike,
I am sure that table helps a lot. I believe the component context
should always reflect the most current wiring situation (independent of
whether re-injection occured or not). That is easiest to understand and
implement and otherwise there would be no way of getting to the current
wiring (while hoilding on to a service reference is always possible).
It seems that less re-injection is probably safer than more re-injection,
so designating an annotation attribute looks like a smart move.
Thanks,
Henning
________________________________
Von: Mike Edwards [mailto:]
Gesendet: Montag, 7. Januar 2008 10:27
An: OASIS Java
Betreff: Re: [sca-j] ISSUE 4 - Dependency reinjection
Reza,
This is a good contribution to settling this item of work.
I suggest one addition to the table - "Target Service Undeployed"
is OK for services within the SCA Domain - to deal with services elsewhere,
"Target Service becomes Unavailable" is a better description
(we don't know anything about HOW it became unavailable), but the effects
are the same.
Effect on
Change Event
Reference
Existing ServiceReference Object
Subsequent Invocations of ComponentContext.
getServiceReference() or
cast()
Change to the Target of a Reference MAY be reinjected (if
other conditions apply).
If not reinjected, then it MUST continue to work as if the reference target
was not changed. MUST continue to work as if the reference
target was not changed. Result corresponds to the
injected
reference (i.e. changed only if
reinjection occurred).
Targeted Service Undeployed
Target Service becomes Unavailable Business methods
SHOULD throw InvalidServiceException. Business methods SHOULD throw
InvalidServiceException. Result SHOULD be a reference to the undeployed
service. Business methods SHOULD throw InvalidServiceException.
Targeted Service Changed MAY continue to work,
depending on the runtime and the type of change that was made. If it doesn't
work, the exception thrown will depend on the runtime and the cause of
the failure. MAY continue to work, depending on the runtime and the
type of change that was made. If it doesn't work, the exception thrown
will depend on the runtime and the cause of the failure. Result SHOULD
be a reference to the changed service.
Now, I'd like to propose the following, which I realize changes some of
the decisions we made previously, but I am getting concerned about complexity:
1. No reinjection of references occurs by default for any component of
any scope
2. Any component of any scope can declare that it requires reinjection.
My suggestion is to provide a parameter to the @Reference
annotation reinject="true", which only has meaning for References
which are a) Fields b) accessible via a setter method (ie it cannot apply
to a
reference injected via the constructor).
This I believe is much simpler and it gives the component writer a chance
to decide for themselves whether they want to be concerned about
wiring changes occurring dynamically during the lifetime of a component.
It will also make it simpler for us to give a good description of
the
kinds of circumstance in which it might be good to react to wiring changes.
Yours, Mike.
Strategist - Emerging Technologies, SCA & SDO.
Co Chair OASIS SCA Assembly TC.
IBM Hursley Park, Mail Point 146, Winchester, SO21 2JN, Great Britain.
Phone & FAX: +44-1962-818014 Mobile: +44-7802-467431
Email:
"Reza Shafii" <>
04/01/2008 22:19
To
<>
cc
Subject
[sca-j] ISSUE 4 - Dependency reinjection
Hi All,
In an effort to try to put more structure around a potential solution to
issue 4, Michael and I put together the attached table. Most of the content
is derived from conlusions reached by the TC's past discussions. A matrix
such as this might help us better focus future discussions.
Looking forward to your feedback,
Reza
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