<AWT Dev> hg: jdk8/awt/jdk: 6995769: occasion NPE thrown from SwingUtilities.computeIntersection()

[Roman Kennke]

Hi there,

> 2011/7/28  <pavel.porvatov at oracle.com>:
> > Changeset: 34fdcdb70d20
> > Author:    rupashka
> > Date:      2011-07-28 18:13 +0400
> > URL:       http://hg.openjdk.java.net/jdk8/awt/jdk/rev/34fdcdb70d20
> >
> > 6995769: occasion NPE thrown from SwingUtilities.computeIntersection()
> > Reviewed-by: alexp
> >
> > ! src/share/classes/javax/swing/RepaintManager.java
> 
> Hi Pavel,
> 
> I'm not very happy with this patch, what is the rationale behind it?
> 
> The bug report doesn't explain much, but from what I can see, I
> believe this could be related to the fact that the RepaintManager is
> not reentrant.

I agree with Mario. As one who suffered from this bug I can confirm that
it is (can be?) triggered when re-entering the RepaintManager. For
example, when you override paint() of a Swing component and inside there
bring up a modal dialog (I know I know), which launches a nested
dispatch loop, you may end up calling into the RM again. At this point
the internal datastructures goes crazy and throws the NPE. Catching null
there seems dangerous as it hides the problem, and may cause breakage
later. I propose to throw an IllegalStateException instead, for example
in java.awt.Dialog or when launching the nested dispatch loop, in the
case when we are coming from a RepaintManager call. This would increase
overall robustness.

If it helps, I can try to construct a testcase (should be something like
I outlined above).

Best regards, Roman