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Subject: RE: [sca-j] ISSUE 4 - Dependency reinjection


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:  mike_edwards@uk.ibm.com

David Booz <booz@us.ibm.com>

05/12/2007 02:37

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

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

            "Michael Rowley"                                              
            12/04/2007 08:11          David Booz/Poughkeepsie/IBM@IBMUS,  
            PM                        <sca-j@lists.oasis-open.org>        
                                      RE: [sca-j] ISSUE 4 - Dependency    

     -----Original Message-----
     From: David Booz [mailto:booz@us.ibm.com]
     Sent: Tuesday, December 04, 2007 3:06 PM
     To: sca-j@lists.oasis-open.org
     Subject: RE: [sca-j] ISSUE 4 - Dependency reinjection


     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
     stabilize it's use of references.  This brings up an interesting
     is there (or should there be) some linkage between the lifecycle of
     target service and these references?  Just because a ref target has
     altered, does not mean that the target service is gone.  It's the
     of that target service which will determine how long a reference
     usable after a wiring change occurs.  Just raising the question for
     because it will affect all the component's whose references can't be

[MR: I’m sorry, but I don’t follow you.]

     2) I'm curious about your introduction of InvalidServiceException.
     already have ServiceUnavailableException.  I think there's room to
     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.]


     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

                  Mike Edwards
                                            "OASIS Java"
                  12/04/2007 10:22          <sca-j@lists.oasis-open.org>

                                            RE: [sca-j] ISSUE 4 -


     Thanks for the proposal.  It is good to have something concrete as it
     crystallise the

     Please help me understand the rationale for treating Composite-scoped
     differently from Conversation scoped components.

     Both types of component have an extended lifecycle.  Both may easily
     have a
     that spans changes in configuration that affects their references,
     where those
     references are not conversational and do not in themselves involve
     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
     Phone & FAX: +44-1962-818014    Mobile: +44-7802-467431
     Email:  mike_edwards@uk.ibm.com

     "Michael Rowley" <mrowley@bea.com> 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
     > 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
     > 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
     > 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

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