Simon,
I am certainly willing to give up any
automatic correlation when there may be multiple simultaneous outstanding
callbacks. In that case, use business data.
However, for the common case where there
is only one outstanding callback for a specific client, then your approach
already allows the client to know what the callback is talking about without
passing any correlation information in the business data. This is because
your approach routes the callback to the right client instance.
I think this is good. We should
encourage it. However, in the unfortunate event that someone can’t
use a conversational-scoped client, they should still be able to use the
bi-directional service without having to ask the service provider to change its
interface. Admittedly, the stateless client will have to implement many
of the steps that you list below, but that is the price for being non-conversational.
I also believe that if we followed your
suggestion, then no matter what we say, people just won’t send unneeded
correlation information as business data when they know that the callback is
going to be sent to the right place. They won’t think: “Oh,
just in case I ever have a stateless client, I better put this extra data into
the business data.” Instead, they will just leave out the data,
with the unintended consequence being that they’ve limited their clients
to being only those that use a conversational scope. That would be bad.
Michael
From: Simon
Nash [mailto:NASH@uk.ibm.com]
Sent: Thursday, April 03, 2008
12:13 PM
To: Michael Rowley
Cc: sca-j@lists.oasis-open.org
Subject: RE: [sca-j] ISSUE 25 -
Callback Simplification
There's a basic problem with this approach. Whether
or not B has conversational scope depends on its interactions with A. In
a single A to B conversation, the same conversational instance of B might place
5 orders with C. Using the A to B conversation ID to identify the order
that was placed is therefore never safe, even if B is conversational.
The
only way this approach could work is if B were to generate a new "callback
conversation ID" for every request that it sends to C. This would be
different from any regular conversation ID that B may be sending to C as part
of a B to C conversation. Here are the steps that would need to be
followed.
1.
B generates a new "callback conversation ID" and associates it with
its reference for C. This needs to happen before any calls to C are made.
2.
An API needs to be defined to allow B to get this "callback conversation
ID" before it makes the placeOrder() call to C. B stores the
"callback conversation ID" and associates it with the order it is
placing.
3.
B makes a placeOrder() call to C.
4.
The SCA infrastructure transmits the "callback conversation ID" from
B to C with the placeOrder() call.
5.
C stores the "callback conversation ID" in the callback reference so
that it can be returned to B in any callbacks.
6.
C makes a callback to B.
7.
The SCA infrastructure transmits the "callback conversation ID" from
C to B with the callback.
8.
An API needs to be defined to allow B to get this "callback conversation
ID" when the callback is executing. This ID is different from the
conversation ID that's active for the A to B conversation.
All
of the above are not needed if the correlation information is passed as
business data, which is a much simpler approach.
I
considered this approach when I was trying to come up with a good definition of
conversational callback interfaces between the 3/20 and 3/27 calls, but I
rejected it because I did not believe that the value justified the complexity.
Simon
Simon C. Nash, IBM Distinguished Engineer
Member of the IBM
Academy of Technology
Tel. +44-1962-815156 Fax +44-1962-818999
"Michael Rowley"
<mnrowley@gmail.com>
03/04/2008 15:40
Please
respond to
mrowley@bea.com
|
|
To
|
Simon Nash/UK/IBM@IBMGB,
sca-j@lists.oasis-open.org
|
cc
|
|
Subject
|
RE: [sca-j] ISSUE 25 - Callback
Simplification
|
|
I like the fact that, in
Simon's model, callbacks always go back to the instance that made the outbound
call. However, it looks like he does not take advantage of that fact in
the interfaces of the examples that he created. For example, he has the
following:
@Callback(OrderCallback.class)
public interface Order {
void
placeOrder(String orderID, String orderData);
}
public interface OrderCallback {
void
confirm(String orderID);
void
update(String orderID, String status);
}
However, since you know
that the order callback goes back to the right instance, you should be able to
define the callback interface as follows:
public interface OrderCallback {
void
confirm();
void
update(String status);
}
In Simon's model this
should be possible, but there is a catch. If the callback interface is
defined this way, the client has to use a conversational scope. If the
client is stateless or composite scoped, then the routing of the callback to
the right instance doesn't say anything useful about what is being confirmed.
I would like to enable
this style of callback interface irrespective of the scope of the client.
As with Simon's approach, if the client is conversational scoped, then
the client is especially simple and does not have to do any correlation at all.
However, if the client needs to use some other scope, for whatever
reason, then the service with the callback can still be used. However, it
just needs to get the callback ID (or conversation ID) that is associated with
the callback in order to determine what the callback is talking about.
Michael
From: Simon
Nash [mailto:NASH@uk.ibm.com]
Sent: Thursday, March 27, 2008 11:47 AM
To: sca-j@lists.oasis-open.org
Subject: Re: [sca-j] ISSUE 25 - Callback Simplification
There's an update to this proposal at
http://www.oasis-open.org/apps/org/workgroup/sca-j/download.php/27733/JAVA-25-Proposal-2.doc
This version removes conversational callbacks as all my attempts to define
these involve more complexity than is justified by the functional value of this
capability.
Simon
Simon C. Nash, IBM Distinguished Engineer
Member of the IBM
Academy of Technology
Tel. +44-1962-815156 Fax +44-1962-818999
Simon Nash/UK/IBM@IBMGB
20/03/2008
11:01
|
|
Last week I took an action to produce a written up proposal for callback
simplification by today. I have uploaded this to the document repository
as
http://www.oasis-open.org/apps/org/workgroup/sca-j/download.php/27649/JAVA-25-Proposal.doc.
The content of this proposal corresponds to the "Callback
Simplification" section of the proposal sent out by Michael R, and does
not address the changes proposed in the "API Simplification" section.
I think it is best to have these discussions separately.
This proposal corresponds to what I was describing at the sca-j F2F with two
changes / additions:
1. Outstanding callbacks don't pin conversational objects after the
conversation's creator has ended the conversation.
2. In all cases, the caller of a bidirectional interface creates the callback
EPR that will be used (including any reference parameters needed).
I believe the issues that still need to be discussed and resolved are as
follows:
a) Should all 4 combinations of conversational and non-conversational forward
and callback interfaces be allowed, or only 2 of these?
b) Should the callback interface used to make callbacks to a conversation-scoped
component be marked as conversational?
c) Should each forward request within a conversation generate a unique ID that
is not part of business data and is returned with the callback?
Simon
Simon C. Nash, IBM Distinguished Engineer
Member of the IBM
Academy of Technology
Tel. +44-1962-815156 Fax +44-1962-818999
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
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