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From "Sergey Beryozkin" <sergey.beryoz...@progress.com>
Subject Re: Jetty Continuations in CXF
Date Fri, 24 Oct 2008 13:27:01 GMT
Forwarding to the right address

Hi

I'd like to continue the discussion on how to handle Jetty continuations[1] in CXF[2] here.

In short the requirement is for CXF to be able to handle the application code (ServiceMix
JBI consumers served by ServiceMix CXF 
BindingComponent in this case) doing explicit continuations.

Ex. CXF receives a request on a Jetty thread, creates an exchange and sends it further along
to the consumer. Consumer is about to 
do some work so it spawns some activity or checks for some event and then does continuation.suspend().
This results in a specific 
Runtime exception being thrown.

The challenge is how to 'suspend' the interception chain, let this exception propagate down
to the Jetty stack so that it can free 
the thread and put this pending request in its internal queue, and then resume it when a consumer
code decides to do 
continuation.resume().

See [3] for a more detailed description of the issues.

Dan, here're some comments :

1. "something would need to be done to allow the "suspend" exception thing to propogate up,
but without taking a jetty dependency into the core."

I guess the basic thing we can do is to check the class name of the exception (like exception.getClass().equals("JettyException")),

and if it matches the expected name then we can wrap up this exception in a SuspendedFault
exception, to be recognized by the rest 
of CXF runtime

2. Now, if the above can be figured out, the next problem arises: when
the "trigger" to wake up the continuation occurs

I think we can can do in JettyDestination omething similar to what is done in SMX. When getting
a SuspendedFault exception, we can 
extract from it the original continuation instance or else we can do ContinuationSupport.getContinuation(request)
which should 
return us the instance. At this point we can use it as a ket to store the current exchange
plus all the other info we may need.

When the user/application code does continuation.resume(), the Jetty thread will come back
and we will use the 
ContinuationSupport.getContinuation(request) to get us the active continuation and use it
to extract the suspended exchange and 
proceed from there, say we'll call PhaseInterceptorPhase.resume(), etc, something along the
lines you suggested


3. Basically, to do this "right", we'd need to audit pretty much everything to
make sure nothing is stored on the stack and is "resumable". Once that is
done, the rest is relatively easy.

Yea - probably can be the quite challenging


Thoughts ?

Cheers, Sergey




[1] http://docs.codehaus.org/display/JETTY/Continuations
[2] https://issues.apache.org/jira/browse/CXF-1835
[3] https://issues.apache.org/jira/browse/CXF-1835?focusedCommentId=12642361#action_12642361



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