Folks,

Here is my pennyworth:

1. I think it is simpler if the callbackID is ALWAYS present on both reference proxies and also on ServiceReference objects from the moment they are created.

so getCallbackID() always returns a valid callbackID

2. Regarding the case where the communication protocol forces the use of some specific form of the ID that can only be known at the time of first invocation, then I would suggest that a mapping is done from the application-level callbackID to a protocol specific ID, this mapping being done somewhere in the binding code (for both outward bound and return mesages)

3. For the question as to whether we need both a callbackID and a conversationID. I note that the usage of these two IDs is very similar. - callbackID is used to relate one or more messages received on the callback interface to a previous message sent out through a reference invocation - conversationID is used to relate subsequent messages received by a service provider and also the subsequent responses received by the client

The two IDs may interact since a conversation may be conducted through a callback style asynchronous interaction pattern.

Is it possible to combine these two IDs into one? I'm not sure that they can. My concern is over the potentially different lifetimes of these IDs:

a) callbackID logically can get changed for EACH invocation of a forward call on a reference - if this isn't done, then it is impossible to differentiate the responses received as a consequence of successive invocations on the reference

b) conversationID gets a new value whenever a new conversation starts. This point is vague - a conversation may be started by any one of the forward invocations on a reference. It is also be terminated by some other invocation on the reference. Logically, the conversationID can live across a whole series of requests, If asynchronous callbacks are used between client and provider there is also still the question of associating a given callback message with a particular request message - multiple requests may be part of the same conversation but the callback messages still may require some differentiation (I'm making the assumption that a given callback message may result from more than one request). It's this last case that seems to demand that conversationID is separate from callbackID.

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

"Peshev, Peter" To Simon Nash/UK/IBM@IBMGB, <pete...@sap.com> <sca...@lists.oasis-open.org> cc 16/01/2008 10:22 Subject RE: [sca-j] ISSUE 11: Semantics of getCallbackID() are underspecified

Hi Simon,

Some loud thinking on that issue:

In order for that scenario to work, the callbackId must be transported by the binding together with the parameters for the forward / backwards calls. Some binding offer extensibility (JMS message properties) however some other binding must try to map SCA system data (including callbackId) to its own concept and header fields. (Unless an implementation would wish to alter the interface and add the id as parameters). So far so good, but potentially some bindings/transport protocols may be able to generate such ID only after the first message sending (i.e. the forward call) , and not accept a general one generated before the invocation. Although when having only 3 official bindings I don't think such situation is present at the moment.

Not directly relevant to the issue, but when looking at that scenario and speaking for data correlation and emulating conversation by the client managing its own state, I admit I am not that sure whether callbackId and conversationId should be the same and should map to one and the same field in the underlying binding (if present). The spec says :

" .... the client may like to use a feature such as the conversationID to keep track of any state data relating to the conversation. "

If we say yes they are the same, as a consequence for bidirectional interfaces annotated with @conversational, the runtime is responsible for managing the state of the conversations as well as ensuring that ServiceReference.getConversationID () and ServiceReference.getCallbackID () is one and the same. If we say those two can be different, I guess we will need to think of two placeholders for that. (An issue for the binding tc, the JMS spec for example only defines scaConversationId, no callbackId )

Your thoughts ?

Best Regards Peter

-----Original Message----- From: Simon Nash [mailto:NA...@uk.ibm.com] Sent: Tuesday, 15. January 2008 23:45 To: sca...@lists.oasis-open.org Subject: RE: [sca-j] ISSUE 11: Semantics of getCallbackID() are underspecified

I recently had to write a component implementation that does this, and it turns out that returning null at point 4 and non-null at point 6 doesn't work.

Suppose I am going to use the callback ID to correlate some state within my component. After I make the forward call at point 5, the callback can arrive at any time (including before point 6), so I must have saved the callback ID (together with its associated state) corresponding to the call at point 5 before making the call (i.e., before point 5). This implies that the call at point 4 must return non-null.

Now consider the following sequence of events: 7) A type-safe reference (proxy) is created by injection. 8) A ServiceReference is created from the type-safe reference by ComponentContext.cast(). 9) getCallbackID() is called on the ServiceReference. 10) A service call is made through the type-safe reference.

For the same reason as above, the call at point 9 must return non-null. In this case, this call is made immediately after creating the ServiceReference. This seems to imply that a newly created ServiceReference should return a non-null callback ID from the first call to getCallbackID() that is made.

Having consistent rules for the two scenarios is desirable. This would mean that the call at point 2 in the original scenario would also return non-null.

Putting all this together, getCallbackID() would never return null.

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> 05/10/2007 14:23

To "Peshev, Peter" <pete...@sap.com>, <sca...@lists.oasis-open.org> cc

Subject RE: [sca-j] ISSUE 11: Semantics of getCallbackID() are underspecified

I was thinking that some bindings may have the client-side choose the ID, while others (where there is a synchronous exchange with the first message) may have the service provider provide the id. But looking at it more carefully, I see that both scenarios would result in the same client-visible behavior (null at 4, and non-null at 6).

Michael

-----Original Message----- From: Peshev, Peter [mailto:pete...@sap.com] Sent: Friday, October 05, 2007 2:30 AM To: sca...@lists.oasis-open.org Subject: RE: [sca-j] ISSUE 11: Semantics of getCallbackID() are underspecified

Hi,

I fully agree with the proposal, but I am not sure I understand the concern of Michael raised during the meeting that different bindings may behave differently. I would expect that the only interraction with the binding will happen at point 5 when the proxy will invoke it, and before that everything should be one and the same and there is no problem to specify the semantics.

@Michael - is there something that I am missing ?

Best Regards Peter

-----Original Message----- From: Barack, Ron [mailto:ron....@sap.com] Sent: Thursday, 4. October 2007 21:03 To: sca...@lists.oasis-open.org Subject: [sca-j] ISSUE 11: Semantics of getCallbackID() are underspecified

http://www.osoa.org/jira/browse/JAVA-11

-----Ursprüngliche Nachricht----- Von: Simon Nash [mailto:NA...@uk.ibm.com] Gesendet: Mittwoch, 26. September 2007 15:43 An: sca...@lists.oasis-open.org Betreff: [sca-j] NEW ISSUE: Semantics of getCallbackID() are underspecified

TARGET:

Java Common Annotations and APIs specification, section "Java API" / {"CallableReference"}

DESCRIPTION:

The getCallbackID() method description doesn't specify the initial state of the returned value and the events that cause this value to change.

Consider the following sequence of events: 1) A ServiceReference is created, either by injection or by ComponentContext.getServiceReference(). 2) getCallbackID() is called on the ServiceReference. 3) A type-safe reference (proxy) is created from the ServiceReference by CallableReference.getService(). 4) getCallbackID() is called on the ServiceReference. 5) A service call is made through the type-safe reference. 6) getCallbackID() is called on the ServiceReference.

It seems reasonably intuitive that call 2) will return null and call 6) will return the system-generated callback ID that was used for the service

call. It's less clear what call 4) will return. Does the system-generated callback ID get created and set into the ServiceReference

as part of event 3) or as part of event 5)?

The description of the getCallbackID() method should describe a "state model" for how the value returned would change based on other actions.

PROPOSAL:

At point 2) the value returned will be null. At point 4, it will still be

null, At point 6), it will be the system-generated callback ID that was used for the service call 5). This information should be stated explicitly in the description of getCallbackID().

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