HI Mike,
That's very interesting question. I think for that use
case injecting a dead reference (or invalidating somehow the old working
reference) is more consistent with the resolution that was made
as ASSEMBLY-6 :
...
A reference with multiplicity 1..1 or 1..n MUST have at least one
target service defined.
Where it is
detected that the above rules have been violated, either at deployment
or at execution time, an SCA Runtime MUST
generate an error no later than
when the
reference is invoked by the component implementation.
So that would lead to having "dead references" and
saying that the "null representation" rule is not applied for domain level
wires.
Btw, another way of thinking would be to require
from the deployment tooling to detect such invalid deployment operations
that lead to unwired references with multiplicity 1 and reject them.
I.e. a good implementation could show a dialog - " You are
trying to undeploy a wire from A to B, however component A is using the wire
with multiplicity 1 and the operation can not be performed, do you want to
- undeploy A as well
- abort undeployment.
- redeploy A with changed multiplicity to
0
Just thinking aloud.
Best Regards
Peter
From: Mike Edwards
[mailto:]
Sent: Tuesday, 8. January 2008
12:22
To: OASIS Java
Subject: RE: [sca-j] ISSUE 4 -
Dependency reinjection
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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