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