Simon,

A dose of <mje>Edwards commentary</mje> 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...@uk.ibm.com

Simon Nash/UK/IBM@IBMGB To "OASIS Java" <sca...@lists.oasis-open.org> cc 30/01/2008 15:29 Subject RE: [sca-j] ISSUE 4 - Dependency reinjection

Now that we have agreed to permit reinjection into conversational-scoped instances, this (re)raises the question of callback reinjection.

We had decided not to permit this at all, based on the earlier decisions to limit reinjection to composite-scoped instances only, and to prohibit callback injection into composite-scoped instances. The reversal of the first of these decisions means that we need to consider the case of a conversational-scoped instance with a bidirectional interface that is invoked by two different callers using the same application-generated conversationID. Section 6.6.1 gives some hints that it is possible, without saying so explicitly.

We could address this in (at least) four ways: 1. Prohibit callback injection for conversation-scoped components, as we have done for composite-scoped components. This seems bad because it penalises a common case (calls from one client per conversational instance) in favour of a rare case (calls from multiple clients per conversational instance). 2. Say that in this case, callback reinjection MUST be done. This goes against the "big MAY" for other types of reinjection. It can also lead to non-deterministic behavior in multithreaded scenarios. 3. Say that in this case, callback reinjection MUST NOT be done. This puts the burden on developers to know that they should avoid using injected callbacks if there is a possibilty that the component will be invoked by multiple clients within the same conversation. 4. Say that in this case, callback reinjection MAY be done. This has a similar effect to option 3.

To start the ball rolling, I suggest that we adopt option 3. What do others think? <mje>The simple case for a conversation scoped component with a callback is that it has exactly one client. This will be the 99% case, in my opinion. This is dealt with by a simple injection of the callback at the start of the conversation.

Any case which might imply the need for reinjection is going to be a rare case - ie where the client in the same conversation changes during the conversation. I'm in favour of not doing anything to support this. No reinjection. If the component wants to do anything about it, it can use the (more complex) context calls to discover if the client has changed and then act accordingly.

This corresponds to your option 3.</mje>

<mje>I note that the default behaviour of most conversation scoped components will thus be to ignore a change of client during the progress of a single conversation. The implication of this is that it will not be possible to change the client in reality, since the service will always call back to the original client.</mje>

Simon

Simon C. Nash, IBM Distinguished Engineer Member of the IBM Academy of Technology Tel. +44-1962-815156 Fax +44-1962-818999

Simon Nash/UK/IBM@IBMGB 15/01/2008 22:32

To "OASIS Java" <sca...@lists.oasis-open.org> cc

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

Two approved motions from last week's call were not incorporated into the v3 version of the table. These were:

1. ComponentContext.getServiceReference() should be always in sync with the current configuration of the domain

2. no objections to dropping the column, as long as long as the text typed

by Michael is present

I have made these changes in the v4 version (attached).

Simon

Simon C. Nash, IBM Distinguished Engineer Member of the IBM Academy of Technology Tel. +44-1962-815156 Fax +44-1962-818999

"Michael Rowley" <mrow...@bea.com> 10/01/2008 21:19

To "OASIS Java" <sca...@lists.oasis-open.org> cc

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

Here is an updated table, based on the last TC meeting.

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