[jira] [Commented] (CXF-7575) @Suspended race condition

["Sergey Beryozkin (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CXF-7575?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16343634#comment-16343634 ] 

Sergey Beryozkin commented on CXF-7575:
---------------------------------------

Sorry for a delay. I'm having problems reproducing it. I've updated existing test

https://github.com/apache/cxf/blob/master/systests/jaxrs/src/test/java/org/apache/cxf/systest/jaxrs/BookContinuationStore.java#L73

as per you patch (removed sleep()) and the client to do it 5000 times, it is just running, quite slow, not sure why, but no any failures.

It's quite hard to see where the problem might be, if the application code has called 'resume()' before JAXRSInvoker tries to really suspend (and hence return the current thread to the pool) then the async response (or rather its object) is returned on the original thread immediately without even interacting with the Continuation.

How do you set up the server, is it Jetty, Tomcat. etc ?

Sergey


  


> @Suspended race condition
> -------------------------
>
>                 Key: CXF-7575
>                 URL: https://issues.apache.org/jira/browse/CXF-7575
>             Project: CXF
>          Issue Type: Bug
>          Components: JAX-RS
>    Affects Versions: 3.1.14
>            Reporter: John Bellassai
>            Priority: Major
>         Attachments: CXF-7575.patch
>
>
> There appears to be a race condition with the use of AsyncResponseImpl where my user thread can invoke resume() before initialSuspend is set to false by suspendContinuationIfNeeded() and therefore the resume() call does not actually resume the Continuation _and returns true_, indicating that the resume was successful even though it wasn't.
> I've spent all day trying to make sense of this problem and my understanding of how all of this works together is still a bit spotty, but it seems to me that AsyncResponseImpl.suspendContinuationIfNeeded() (or something similar) should be called _before_ invoking the JAXRS method. Right now, that method is only called after the JAXRS method is invoked by JAXRSInvoker so the instance of AsyncResponse passed into the JAXRS method appears to not actually get suspended (or perhaps _marked_ internally as suspended) until after the JAXRS method returns.  If my async task happens to get finished very quickly and calls resume() before that happens, it fails silently.
> I seem to be able to circumvent this problem by running the following at the start of my JAXRS method (pseudo code):
> {code}
> @POST
> @Path(....)
> void myJaxrsMethod(@Suspended AsyncResponse asyncResponse, ...) {
>     if(asyncResponse instanceof AsyncResponseImpl) {
>         ((AsyncResponseImpl)asyncResponse).suspendContinuationIfNeeded()
>     }
>     Runnable asyncTask = createAsyncTask(asyncResponse)
>     submitAsyncTask(asyncTask)
> }
> {code}
> which is why I suspect suspendContinuationIfNeeded() should be called before JAXRSInvoker invokes the JAXRS method.
> One of the things that made this really difficult to track down was that AsyncResponseImpl.resume() returns true even if the Continuation was not resumed! If you make it into doResumeFinal(), like was happening in my case, the return is always true even if cont.resume() is not called. So from user code, it looks like everything is ok, but the response never gets sent to the client.
> This seems somewhat related to the problems reported in CXF-7037



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