Re: Deadlock in DisplayImpl or ScalarMap?

On Fri, Jul 04, 2003 at 09:12:18AM -0500, Bill Hibbard wrote:
> > By tracing with the universal debugging tool (System.out.println()) I
> > can see that one VisAD thread is in, synchronized on
> > lockEnabled, and an AWT thread (presumably from
> > SwingUtilities.invokeLater()) is waiting to synchronize in the same
> > place.  The VisAD thread does not leave the synchronized block, it gets
> > to DisplayRenderer.prepareAction(), calls map.setRange(shadow) where map
> > is a ScalarMap (Time->DisplayAnimation) and hangs there.
> I can't find any deadlock by inspection. ScalarMap.setRange() for
> a ScalarMap (Time->DisplayAnimation) calls AnimationControl.setSet(),
> which calls AnimationSetControl.setSet(), which calls
> Control.changeControl(), which does 'synchronized (ListenerVector)',
> but it hard to see how your code in the AWT Thread can be holding
> a lock on ListenerVector in Control.

Found it.

We have a class elsewhere in the app that implements ControlListener,
and listens to AnimationControl events.  That class updates swing
components with invokeAndWait().  So we have a swing thread wanting to
do VisAD stuff and a VisAD thread wanting to do swing stuff.  Deadlock.

Now I have to think about some redesign in there.

> A very good way to find deadlocks is to run under jdb. When it hangs,
> do a 'suspend all' and then a 'where all', which will dump the call
> stack for all Threads. You should be able to spot the deadlock by
> examining the locks held by the two hung Threads. I'd be happy to
> take a look at the output of 'where all'.

Thanks for this advice, Bill.  jdb showed me exactly what was going on.


Russell Steicke

-- Fortune says:
Freedom from incrustation of grime is contiguous to rectitude.

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