[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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