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From "Carlin Rogers" <carlin.rog...@gmail.com>
Subject Deadlock with NetUI NameService
Date Wed, 27 Sep 2006 22:00:30 GMT
Eddie, Daryl,

Hey, there's a thread deadlock problem in the interaction between the
NetUI DeferredSessionStorageHandler (DSSH) and a page flow that uses
the NameService (either in an action calling the
NameService.instance() or rendering a JSP with the netui:tree tag
using the XHR support.

The problem occurs when two concurrent threads get the locks on the
session mutex object and page flow controller in reverse order. It can
occur in the following way:

Thread A, Step 1 - PageFlowRequestProcessor.process() completes the
execute of the action and calls DSSH.applyChanges().
Thread A, Step 2 - DSSH.applyChanges() gets a lock on the session mutex object.

Thread B, Step 1 - PFRP.process() starts the process to execute the
action of a page flow.
Thread B, Step 2 - FlowController.execute() gets a lock on the page
flow controller object.

Thread A, Step 3 - DSSH.applyChanges() tries to get lock on page flow
controller object (to apply changes from the request to the
session)... and waits.

Thread B, Step 3 - The PageFlow action calls NameService.instance()
which in turn tries to get a lock on the session mutex object (to
ensure that only a single NameService object is created within a
specific user session)... and waits.

...in a deadlock now.


I was wondering if there was another way we could get the NameService
instance in the session such that we did not need the session mutex
object. Maybe we create and add it within
HttpSessionMutexListener.sessionCreated() or create another listener?
Other ideas?

Thanks,
Carlin

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