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From "Sergey Beryozkin" <sergey.beryoz...@progress.com>
Subject Jetty Continuations in CXF
Date Fri, 24 Oct 2008 13:21:15 GMT
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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