Mike,
In case (1) below, are you imagining that
the ServiceReference object would be shared between threads, but that the callbackID
would be thread local?
Michael
From: Mike
Edwards [mailto:]
Sent: Friday, February 22, 2008
9:31 AM
To: OASIS Java
Subject: Re: [sca-j] AW: ISSUE 8:
Concurrency model for Service Reference instances
Folks,
I
said in a previous note that I'd get around to the question of Callbacks. This
note deals with the Callbacks.
Callbacks
are different from conversations today. (Yes, I realize that there are
proposals to change this)
The
principal difference is the need for a client to be able to distinguish each
invocation it makes on an
operation
of a service reference. ie logically, the client needs to impose a
callback ID on each invocation
of
the reference and be able to access this callbackID when it receives an
invocation on the callback
interface.
This
clearly gives a problem if multiple threads are allowed to make forward calls
on the service reference
object
held by the client. There is a time window between setting the callbackID
and invoking the reference
method
- and this allows one thread to potentially interfere with another.
There
seem to be two approaches to this:
1)
Have the callbackID set as a thread local variable.
2)
Change the design of callback interfaces so that there is a version of each
operation which includes the
callbackID
as an additional parameter on each method, allowing the client to set the
callbackID directly onto
each
invocation. The precedent for this approach is the existing JAX-WS
approach to the asynchronous client
API,
which is generated by formula from the standard call-and-return API for a
service.
Either
of these approaches means that any given forward request can have a correct
callbackID available on
a
per-invocation basis to the binding code that packages the request for
tranmisssion form the client to the
service.
Problem
solved.
Yours, Mike.
Strategist - Emerging Technologies, SCA & SDO.
Co Chair OASIS SCA Assembly TC.
IBM Hursley
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