Inspiration or Hallucination? A proposal to resolve issues 25, 46 and 10

[Simon Nash <NASH@uk.ibm.com>]

Jetlag can have interesting effects,
such as waking up early in the morning with the mind racing at full speed
and ideas coming faster than I can capture them.

Here's a proposal to resolve issue 25,
along the lines of the action that I took at the F2F yesterday.  The
thought process behind this also leads to conclusions on how issues 46
and 10 should be resolved, and suggests a simpler approach for handling
conversational state.

1. Remove ServiceReference and retain
CallableReference.
2. CallableReference instances are immutable.
3. A CallableReference instance contains
a service destination (endpoint), an optional callback destination (endpoint),
and an identity that can be compared using equals().
4. Each type-safe proxy has an associated
CallableReference instance.  ComponentContext.cast() can be used on
a proxy to obtain its CallableReference instance.  CallableReference.getService()
can be used to obtain a type-safe proxy for the service destination of
the CallableReference.  CallableReference.getCallback() can be used
to obtain a type-safe proxy for the callback destination of the CallableReference,
if it has a callback destination.  The same CallableReference state
is shared between the results of all these methods.
5. When making a forward call across
a bi-directional interface, the CallableReference that made the forward
call is passed by the infrastructure and is available to the service business
method by injection of a CallableReference or a type-safe callback proxy,
or from the RequestContext.
6. When making a callback across a bi-directional
interface, the CallableReference that made the forward call is passed by
the infrastructure and is available to the callback business method by
injection of a CallableReference, or from the RequestContext.
7. The client can correlate between
the forward call and any callbacks made on behalf of that call by an equals()
comparison of the CallableReference used to make the forward call and the
CallableReference received by the callback.
8. If the client wants to associate
distinct identities with different forward calls, it does this by creating
and using a new CallableReference for each distinct identity that is needed.
 This is done by calling CallableReference.createCallableReference().
 The result of this method has the same service and callback destinations
and a different identity for equality comparison purposes.
9. The same mechanism is used to identify
conversations.  All calls made by a client on behalf of the same conversation
use the same CallableReference instance.  A new conversation is started
by creating and using a new CallableReference instance.
10. A CONVERSATION-scoped implementation
uses the CallableReference passed with a call to automatically locate the
instance to be used to dispatch the business method.  For COMPOSITE
and STATELESS scopes, the CallableReference is available to business logic
so that it can perform its own correlation.
11a. There is no need to mark interfaces
as conversational, as all SCA calls pass a CallableReference that may be
used to provide conversational semantics.  (Alternative option 11b:
retain the conversational marking of interfaces and only pass the client's
CallableReference identity if the interface is marked as bidirectional
or conversational.)

The following can be eliminated from
the Java APIs with no loss of capability:
a. The ServiceReference interface.
b. The getCallbackReference() method
of RequestContext.
c. The isConversational(), getConversation()
and getCallbackID() methods of CallableReference.
d. The Conversation interface.
e. The @Conversational annotation (if
option 11a is chosen).
f. The @ConversationID annotation.
g. The @EndsConversation annotation.


The following should be added:
h. CallableReference.getCallback()
i. CallableReference.createCallableReference
j. An @CallableReference annotation
to inject the CallableReference that was passed with the forward call or
callback (replaces @ConverationID).


And then I woke up :-)  What do
you think... was this inspiration or hallucination?

    Simon

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

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