Dave,
I don't think the proposal is a hack
- it expresses some capability in a way very familiar to Java
programmers.
I agree that there is still a bigger
problem - see my subsequent posting which muses about the
bigger problem.
Allowing reference reinjection has only
a small connection with the bigger issues.
So, to address the particular issue
you raise here - if a component has a reference and if it
cannot tolerate the loss of that reference
then:
a) you are then establishing a contract
between the component and the wider SCA runtime along
the lines that the runtime cannot undeploy
a target component instance that is "being used" by
this component. This may imply a process
of quiescing the target component when a change is
required, or the ability to run old
and new versions of the target in parallel. This is part of the
"bigger picture" question.
It may be indicated by an intent of some kind, although the target
of
the intent is a very curious one - it
is the runtime container of the target service component. We
haven't got one quite like that, although
it is close to some of the transaction intents.....
b) how do you deal with cases where
the loss is of a service that is external to the SCA domain
over which SCA has no control? I
suppose "serviceunavailable" fault is the likely response to
this occurrence. If this is so,
why would things be different for a target service WITHIN the SCA
domain?
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:
David Booz <>
05/12/2007 13:29
To
cc
Subject
RE: [sca-j] ISSUE 4 - Dependency reinjection
Seems like a hack to me. And it doesn't address
the larger problem where
the reference suddenly becomes unusable because the target was changed.
This is similar to a referential integrity problem. The component
wants to
state that it can't tolerate the loss of a valid reference part way through
it's processing.
Dave Booz
STSM, SCA and WebSphere Architecture
Co-Chair OASIS SCA-Policy TC
"Distributed objects first, then world hunger"
Poughkeepsie, NY (845)-435-6093 or 8-295-6093
e-mail:
http://washome.austin.ibm.com/xwiki/bin/view/SCA2Team/WebHome
Mike Edwards
<mike_edwards@uk.
ibm.com>
To
12/05/2007 04:28
cc
AM
Subject
RE: [sca-j]
ISSUE 4 - Dependency
reinjection
Folks,
Controlling whether reinjection is allowed AT ALL for a component is
relatively simple in
my opinion:
- if a component does not want reference reinjection to occur, ever, then
the implementation
simply declares the reference annotation on a constructor parameter and
does not
provide the reference via either a field or via a setter method. If
the
reference is only
injectable via the constructor then it can never be changed by the
container.
This simple design choice allows complete control by the developer of the
implementation.
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:
David Booz <>
05/12/2007 02:37
To
-open.o
rg
cc
Subject
RE: [sca-j] ISSUE 4 -
Dependency reinjection
It's simple, just not well expressed. I'm wondering if there are
cases
where a component implementation might want to delay or "opt out"
of
re-injection either permanently or temporarily. There might be cases
where
a particular component implementation really can't tolerate a re-injection.
I was thinking out loud about using concurrency control as a temporary
means to delay re-injection. There are other ways. Maybe a different
approach like an annotation @AllowsReinjection (or the opposite) is
sufficient.
I understand that what you are proposing is optional for a runtime to
support, but for those runtimes that do support it, each component
implementation might need to have a say in how it works. Still thinking
out loud....
Dave Booz
STSM, SCA and WebSphere Architecture
Co-Chair OASIS SCA-Policy TC
"Distributed objects first, then world hunger"
Poughkeepsie, NY (845)-435-6093 or 8-295-6093
e-mail:
http://washome.austin.ibm.com/xwiki/bin/view/SCA2Team/WebHome
"Michael Rowley"
<>
To
12/04/2007 08:11
David Booz/Poughkeepsie/IBM@IBMUS,
PM
<>
cc
Subject
RE: [sca-j]
ISSUE 4 - Dependency
reinjection
-----Original Message-----
From: David Booz [mailto:]
Sent: Tuesday, December 04, 2007 3:06 PM
To:
Subject: RE: [sca-j] ISSUE 4 - Dependency reinjection
Michael,
And tagging on a few more questions:
1) I presume that the use of setter based injection would
allow for]
concurrency serialization by the component implementation
so that it
could:
stabilize it's use of references. This brings up an
interesting
question;:
is there (or should there be) some linkage between the lifecycle
of
the
target service and these references? Just because
a ref target has
been
altered, does not mean that the target service is gone.
It's the
lifecycle
of that target service which will determine how long a reference
remains
usable after a wiring change occurs. Just raising
the question for
now
because it will affect all the component's whose references
can't be
re-injected.
[MR: I’m sorry, but I don’t follow you.]
2) I'm curious about your introduction of InvalidServiceException.
We
already have ServiceUnavailableException. I think
there's room to
clarify
the wording of SUE to make room for ISE..
[MR: I think that a service that has been correctly identified, but isn’t
currently available is quite different from a service that is incorrectly
identified (it isn’t in the logical domain). As such, I think it
deserves
a different exception.]
3) +1 to Mike E.
[MR: No objection from me.]
Michael
Dave Booz
STSM, SCA and WebSphere Architecture
Co-Chair OASIS SCA-Policy TC
"Distributed objects first, then world hunger"
Poughkeepsie, NY (845)-435-6093 or 8-295-6093
e-mail:
http://washome.austin.ibm.com/xwiki/bin/view/SCA2Team/WebHome
Mike Edwards
<mike_edwards@uk.
ibm.com>
To
"OASIS Java"
12/04/2007
10:22 <>
AM
cc
Subject
RE: [sca-j] ISSUE 4 -
Dependency
reinjection
Michael,
Thanks for the proposal. It is good to have something
concrete as it
help
crystallise the
issues.
Please help me understand the rationale for treating Composite-scoped
components
differently from Conversation scoped components.
Both types of component have an extended lifecycle. Both
may easily
have a
lifecycle
that spans changes in configuration that affects their references,
even
where those
references are not conversational and do not in themselves
involve
some
extended
lifetime. Why is it justified to change references
in the one case
and not
allow changes
in the other case?
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:
"Michael Rowley" <> wrote
on 29/11/2007 20:19:28:
>
> I took an action item to make a more specific proposal
for:
> dependency reinjection. Here it is:
>
> Reinjection
> -----------
>
> References MAY be reinjected after the initial creation
of a
> component due to a change in wiring that has occurred
since the
> component was initialized. In order for reinjection
to occur, the
> following MUST be true:
> - The component MUST be composite-scoped.
> - The reference MUST use either field-based injection
or setter
> injection. References that are injected through
constructor
> injection MUST NOT be changed.
> - If the reference has a conversational interface,
then a
> conversation MUST NOT be active at the time of the
reinjection.
>
> If processing in reaction to a change in a reference
is necessary,
> then setter injection should be used, with code in
the setter
method
> that does the proper processing in reaction to a change.
>
> Components with any scope other than the composite
scope MUST NOT
> have references reinjected. If an operation is
called on a
> reference where the target of that reference is no
longer valid,
> then InvalidServiceException MUST be thrown.
>
> In cases where changes to a reference are not valid,
the reference
> as accessed through the component context also MUST
NOT change.
> More precisely, the ComponentContext.getService() and
> getServiceReference() methods MUST return the same
reference target
> as would be accessed through injection. However,
the
> ServiceReference that is returned by getServiceReference()
never
> changes its target. If the wiring of a composite
component causes
a
> reference to be reinjected, any ServiceReference object
that was
> acquired before the reinjection will still correspond
to the target
> prior to the change. If the target service for
a ServiceReference
> ever becomes invalid, then attempts to call business
methods
through
> that ServiceReference MUST throw InvalidServiceException.
>
> The rules for reference reinjection also apply to references
with a
> 0..N or 1..N. This means that in the cases listed
above where
> reference reinjection is not allowed, the array or
Collection for
> the reference MUST NOT change their contents. In
cases where the
> contents of a reference collection MAY change, then
for references
> that use setter injection, the setter method MUST be
called for any
> change to the contents. The injected collection
MAY be the same
> collection object as is currently used by the component,
but with
> some change to its contents.
>
> Michael
Unless stated otherwise above:
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Registered office: PO Box 41, North Harbour, Portsmouth,
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Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
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