Synchronizing session-scope objects?

Question

          Hi,
          I have this problem, using Weblogic 5.1 SP8:
          In a JSP-file I use a java-object with the useBean-directive and
          session-scope.
          The problem occur when a user (for some strange reason) decides
          to double-click in his browser on a link pointing to this
          JSP-page.
          This makes the weblogic server start two separate request-threads to the same page
          in the same session. This will sometimes screw up tha data that the java-object holds
          since both threads at the same time uses the same object.
          The only solution that I have found is to put synchronized blocks in the JSP-file
          either synchronizing the java-object or the session-object.
          Does anyone have any similar problems or perhaps any opinions?
          regards/
          H Waller
          

Answer 1

          The problem we discussed (and fixed)was specifically in
          WLCS 3.2.
          If you are not using WLCS, you will not experience THAT problem.
          If you are using member servlet, member JSP variables or static
          variables, you will see a similar problem - don't.
          If it is data in the httpSession - you have to rethink your
          design.
          Mike
          "Ashutosh Khandelwal" <[email protected]> wrote:
          >
          >Hello Ture and Mike,
          >
          >I have been experiencing problems when a user decides to double-click
          >in the browser
          >pointing to a servlet. This makes the weblogic server start two seperate
          >request-thread
          >to the same page in the same session. This always screws up the data.
          >I am using
          >WLS 5.1 with SP8.
          >
          >According to your previous emails, this was only a problem with WLCS3.2,
          >which
          >uses PipelineSession. You have also indicated that this should not be
          >happening
          >with WLS 5.1 or 6.0 with SP8 or above.
          >
          >Well, I continue to have this problem with WLS5.1. Do you have any suggestions/opinion,
          >etc.
          >
          >regards,
          >
          >Ashu
          >
          >
          >
          >"Mike Reiche" <[email protected]> wrote:
          >>
          >>Thanks for the fast turn-around.
          >>
          >>- Mike
          >>
          >>Ture Hoefner <[email protected]> wrote:
          >>>Hello Mike,
          >>> As you know, a WLCS 3.2 (Commerce Server)
          >>>patch now exists for this problem. I thought
          >>>that I should post the details here to clear
          >>>up any confusion in the WebLogic user
          >>>community.
          >>> The problem that Mike experienced was that
          >>>the WLCS PipelineSession was keeping all
          >>>request-scoped attributes in a single bucket,
          >>>so concurrent requests from a single session
          >>>were experiencing naming collisions. Also,
          >>>one pipeline would empty the bucket when
          >>>finished, but other concurrent piplines may
          >>>have been using the bucket. This was not a
          >>>problem with WLS. It was a limitation of the
          >>>design of WLCS 3.2 PipelineSession, which is
          >>>not used in WLS 5.1 or 6.0.
          >>> Our engineering team has quickly responded:
          >>> they have designed and implemented a
          >>>PipelineSessionExtended that uses multiple buckets.
          >>> Each bucket is associated with a
          >>>request using a unique requestId.
          >>> A patch and details of the design fix and
          >>>use of the patch are available from support.
          >>>Please reference CR043462 when requesting the
          >>>patch.
          >>>
          >>>Mike Reiche wrote:
          >>>
          >>>> I don't mind that the HttpSession is shared,
          >>>my problem
          >>>> is that the PipelineSession is shared - because
          >>>that
          >>>> breaks <pipeline:getProperty > tags. When
          >>>I save a Pipeline
          >>>> propert as REQUEST_SCOPE, that's exactly what
          >>>I expect. But
          >>>> apparently, it's scope is beyond a request.
          >>>>
          >>>> What about a PageContext? That's not shared
          >>>between requests,
          >>>> is it? Maybe that's where REQUEST_SCOPE variables
          >>>should be
          >>>> stored.
          >>>>
          >>>> Mike
          >>>>
          >>>> Robert Patrick <[email protected]>
          >>>wrote:
          >>>> >Hmm...
          >>>> >
          >>>> >I always thought that it was browser specific
          >>>whether
          >>>> >the multiple browser windows
          >>>> >shared or did not share the same session
          >>>(and the Netscape
          >>>> >and IE do exactly the
          >>>> >opposite thing here). Regardless of the
          >>>multiple window
          >>>> >scenario, this can and will
          >>>> >happen if you have multiple frames in the
          >>>same window
          >>>> >making requests concurrently (or
          >>>> >possibly if you double-click on a link causing
          >>>the browser
          >>>> >to generate two requests to
          >>>> >WebLogic).
          >>>> >
          >>>> >Anyway, the crux of the matter is that your
          >>>servlets/JSPs
          >>>> >must be prepared to deal with
          >>>> >multiple requests from the same user accessing
          >>>the same
          >>>> >session. The servlet/JSP spec
          >>>> >doesn't, to my knowledge, address this issue.
          >>> You will
          >>>> >probably need to add
          >>>> >synchronization code somewhere, I would just
          >>>make sure
          >>>> >that you are synchronizing on an
          >>>> >object that is only used by one user (e.g.,
          >>>session) and
          >>>> >keep the synchronization
          >>>> >blocks as short as possible...
          >>>> >
          >>>> >Hope this helps,
          >>>> >Robert
          >>>> >
          >>>> >Michael Reiche wrote:
          >>>> >
          >>>> >> BEA says that's just your imagination....
          >>>> >>
          >>>> >> FR: nelson
          >>>> >>
          >>>> >> CASE_ID_NUM: 222714
          >>>> >> MESSAGE:
          >>>> >> Hi Michael,
          >>>> >>
          >>>> >> The Commerce Server is nothing more then
          >>>an application
          >>>> >riding
          >>>> >> on top of WebLogic Server.
          >>>> >> The HTTPSession is still being managed
          >>>by the WebLogic
          >>>> >Server,
          >>>> >> and not the Commerce Server.
          >>>> >> As I mentioned on my previous email, prior
          >>>to and including
          >>>> >SP6
          >>>> >> for WLS 5.1, the spawning of a child browser
          >>>window,
          >>>> >does create
          >>>> >> a shared HTTPSession, thus creating a shared
          >>>PipelineSession.
          >>>> >>
          >>>> >> If you have indeed upgraded to SP8 for
          >>>WLS 5.1, then
          >>>> >this should
          >>>> >> not be happening.
          >>>> >> Can you tell us exactly how you are spawning
          >>>the new
          >>>> >browser window,
          >>>> >> such that both requests are being sent
          >>>almost concurrently.
          >>>> >> Also, can you send us a copy of your "weblogic.log"
          >>>> >file from the
          >>>> >> Commerce Server as an attachment. If it
          >>>is large, please
          >>>> >zip it.
          >>>> >>
          >>>> >> Regards,
          >>>> >> Nelson Paiva
          >>>> >> WLCS DRE
          >>>> >>
          >>>> >> **********
          >>>> >> If you are replying to this email, please
          >>>DO NOT modify
          >>>> >the subject
          >>>> >> of
          >>>> >> this email in order to ensure that your
          >>>reply is processed
          >>>> >automatically.
          >>>> >>
          >>>> >> You can now "AskBEA" Customer Support questions
          >>>on the
          >>>> >web and
          >>>> >> get
          >>>> >> immediate responses. "AskBEA" is available
          >>>on http://www.bea.com/support/index.html
          >>>> >> **********
          >>>> >>
          >>>> >> "H Waller" <[email protected]>
          >>>wrote:
          >>>> >> >
          >>>> >> >Hi,
          >>>> >> >
          >>>> >> >I have this problem, using Weblogic 5.1
          >>>SP8:
          >>>> >> >
          >>>> >> >In a JSP-file I use a java-object with
          >>>the useBean-directive
          >>>> >> >and
          >>>> >> >session-scope.
          >>>> >> >The problem occur when a user (for some
          >>>strange reason)
          >>>> >> >decides
          >>>> >> >to double-click in his browser on a link
          >>>pointing to
          >>>> >this
          >>>> >> >
          >>>> >> >JSP-page.
          >>>> >> >This makes the weblogic server start two
          >>>separate request-threads
          >>>> >> >to the same page
          >>>> >> >in the same session. This will sometimes
          >>>screw up tha
          >>>> >> >data that the java-object holds
          >>>> >> >since both threads at the same time uses
          >>>the same object.
          >>>> >> >
          >>>> >> >The only solution that I have found is
          >>>to put synchronized
          >>>> >> >blocks in the JSP-file
          >>>> >> >either synchronizing the java-object or
          >>>the session-object.
          >>>> >> >
          >>>> >> >Does anyone have any similar problems
          >>>or perhaps any
          >>>> >opinions?
          >>>> >> >
          >>>> >> >regards/
          >>>> >> >H Waller
          >>>> >
          >>>
          >>>--
          >>>Ture Hoefner
          >>>BEA Systems, Inc.
          >>>2590 Pearl St.
          >>>Suite 110
          >>>Boulder, CO 80302
          >>>www.bea.com
          >>>
          >>>
          >>
          >