Major Description
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.