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From "Dominique Gallot (JIRA)" <j...@apache.org>
Subject [jira] Commented: (BEEHIVE-1100) page flow shared by two threads can be destroyed by one but isn't reinitialized by the other
Date Thu, 17 Apr 2008 12:23:21 GMT

    [ https://issues.apache.org/jira/browse/BEEHIVE-1100?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12589998#action_12589998
] 

Dominique Gallot commented on BEEHIVE-1100:
-------------------------------------------

I ran into this issue as well.
It is a common issue, if you have page that take some time to load before sending the data
to the client.
Example 
  we have Two controller Upload and List 
  We go to Upload
  Then go to List Page ( this distroy the current Upload controller, but does not change the
current ), this take time, page Upload is still show.
  So the user, which does not like to wait, click on a button page page upload, the PageFlowRequestProcessor.getFlowController
is called, a current Upload Flow controller is already set, so it is reused.   
  But since it is destroyed all beehive control are null -> NPE.

The solution ( or workaround ? ) is to replace the lines ( PageFlowRequestProcessor:598 in
the method getFlowController( RequestContext requestContext, String fcClassName )  )

            PageFlowController current = PageFlowUtils.getCurrentPageFlow( request, getServletContext()
);
            if ( current != null && current.getClass().equals( fcClass )) 
            {
by 
            PageFlowController current = PageFlowUtils.getCurrentPageFlow( request, getServletContext()
);
            if ( current != null && current.getClass().equals( fcClass ) &&
(!current.isDestroyed())) 
            {

which does not reuse a current flow controller if it has already be destroyed.

Hope this can be usefull.
Dominique
  

> page flow shared by two threads can be destroyed by one but isn't reinitialized by the
other
> --------------------------------------------------------------------------------------------
>
>                 Key: BEEHIVE-1100
>                 URL: https://issues.apache.org/jira/browse/BEEHIVE-1100
>             Project: Beehive
>          Issue Type: Bug
>          Components: NetUI
>    Affects Versions: 1.0, 1.0.1, 1.0.2
>            Reporter: Eddie O'Neil
>
> This is a JPF threading issue where two threads can start off sharing the same Page Flow.
 When one thread destroys that JPF, the second thread continues to reuse the destroyed instance.
 This can cause problems when re-running the destroyed JPF because any Controls or other fields
cleared in the "onDestroy" lifecycle handler can cause unexpected exceptions / behavior. 
For example:
> Thread 1:  current page flow is /a/A.jpf
> 1: reference /a/A.jpf
> 2: execute action "step 2"
> 5: attempt to execute action "step 3" -- strange behavior because
> internal state has been whacked by "destroy".
> Thread 2: current page flow is /a/A.jpf
> 3: reference /a/A.jpf
> 4: forward to /b/B.jpf -- causes onDestroy to be called on A.jpf
> I believe that the fix is to have the Thread1 re-create the JPF mid-request.  This means
that Thread1 will lose the state /a/A.jpf, but in the current architecture, that makes sense
because the JPF was destroyed.  When the JPF is re-created, it will attempt to run action
"step2" which could work but might also fail with an error or redirect to the beginning of
a wizard (for example).  Fortunately, this scenario is the same as the case where the user
types this into their browser window:
>   http://localhost:8080/fooWeb/somewizard/step2.do
> and the action either works or fails.  It's just like starting a JPF over again in the
middle of the request.

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