Re: Problems keeping references to HttpServletRequest, HttpServletResponse and HttpSession

[Darrell Esau <da...@gmail.com>]

Makes perfect sense.

Unfortunately, I'm using tomcat 6 / JBoss 4.  Updating to J2EE 6 is
probably going to be a huge task.

I think I'll have to strip out my use of the request/response/session from
my async code.

Thanks Mark!

-d



On Sat, Aug 31, 2013 at 2:50 PM, Mark Thomas <ma...@apache.org> wrote:

> Darrell Esau <da...@gmail.com> wrote:
> >Hi all,
> >
> >I'm running into a problem with tomcat, which I believe is
> >self-inflicted.
> > Mostly I just want to confirm my suspicions.
> >
> >I'm doing some fairly high-rate polling (using
> >JavaScript/XmlHttpRequest/DWR).  I'm polling, which is just calling the
> >DWR
> >servlet once every second (using setTimeout on the response callback).
> >
> >Now.. So far nothing should seem out of the ordinary.  And indeed many
> >of
> >these polling cycles do run and complete successfully.  However after a
> >number of cycles (somewhere around 60), I start to get
> >NullPointerExceptions from the apache tomcat code.  Looks like from the
> >Response.recycle method, etc.  Full stack trace below.
> >
> >Now.. I don't think there's anything wrong with tomcat here.. I've been
> >using tomcat for years, and it's pretty rock solid.  I suspect the
> >problem
> >is in my lack of understanding of the life cycle of the
> >request/response
> >objects.  Here's the details in what I'm doing, and what I suspect I'm
> >doing wrong:
> >
> >This poll has the job of batching up "data requests" from the client
> >JavaScript code and passing them off to the server.  On the server,
> >each
> >data request is spawned off to a new thread using a thread pool.  After
> >the
> >threads are posted to the thread pool, the originating servlet request
> >returns.  However, before the response is committed, when the thread is
> >created for the thread pool, I'm assigning the HttpServletRequest and
> >Response (and the HttpSession) as local thread variables.  Once the
> >thread
> >is finished, I remove the references by assigning the local variables
> >to
> >null.
> >
> >So.. When I'm trying to preserve the request, response and session
> >objects
> >in a thread, knowing that the response will be committed before the
> >thread
> >dies, am I breaking a cardinal rule?
>
> Yes.
>
> > Should I expect that tomcat will
> >throw NullPointerExceptions because of this?
>
> Yes.
>
> However, there is some good news. If you use the async API, the app can
> stay pretty much as is.
>
> The short version is:
> - use startAsync and pass the async context to your threads
> - have those threads write to the response (make sure you don't write
> concurrently)
> - call complete once all the threads have completed
>
> Mark
>
>
> >
> >Full stack trace:Aug 30, 2013 9:50:51 PM
> >org.apache.coyote.http11.Http11Processor process
> >SEVERE: Error finishing response
> >java.lang.NullPointerException
> >at
> >org.apache.tomcat.util.http.MimeHeaders.setValue(MimeHeaders.java:302)
> >at
>
> >org.apache.coyote.http11.Http11Processor.prepareResponse(Http11Processor.java:1558)
> >at
> >org.apache.coyote.http11.Http11Processor.action(Http11Processor.java:958)
> >at org.apache.coyote.Response.action(Response.java:181)
> >at
>
> >org.apache.coyote.http11.InternalOutputBuffer.endRequest(InternalOutputBuffer.java:403)
> >at
> >org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:903)
> >at
>
> >org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606)
> >at
> >org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
> >at java.lang.Thread.run(Thread.java:680)
> >Aug 30, 2013 9:50:51 PM
> >org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler process
> >SEVERE: Error reading request, ignored
> >java.lang.NullPointerException
> >at org.apache.tomcat.util.http.MimeHeaders.clear(MimeHeaders.java:152)
> >at org.apache.coyote.Response.recycle(Response.java:579)
> >at
>
> >org.apache.coyote.http11.InternalOutputBuffer.nextRequest(InternalOutputBuffer.java:373)
> >at
> >org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:925)
> >at
>
> >org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606)
> >at
> >org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
> >at java.lang.Thread.run(Thread.java:680)
>
>
>
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