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

["Peshev, Peter" <peter.peshev@sap.com>]

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:NASH@uk.ibm.com] 
Sent: Tuesday, 15. January 2008 23:45
To: sca-j@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" <mrowley@bea.com> 
05/10/2007 14:23

To
"Peshev, Peter" <peter.peshev@sap.com>, <sca-j@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:peter.peshev@sap.com] 
Sent: Friday, October 05, 2007 2:30 AM
To: sca-j@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.barack@sap.com] 
Sent: Thursday, 4. October 2007 21:03
To: sca-j@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:NASH@uk.ibm.com] 
Gesendet: Mittwoch, 26. September 2007 15:43
An: sca-j@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().






Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU













Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU







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