<AWT Dev> Bug 853079: focus problems with openjdk 1.7.0 under gnome3 when selcted keyboard is not the first in keyboard list

[Roman Kennke]

Am Donnerstag, den 08.11.2012, 18:00 +0100 schrieb Mario Torre:
> Hi all!
> 
> I would like to propose a fix for this bug:
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=853079
> 
> The root cause of the bug is an event being generated that sets the
> grabWindowRef on the window confusing the internal events state.
> 
> Usually, when a mouse press is detected the grabWindowRef is set.
> 
> However, in some cases (like the reproducer for bug in the report, but
> there are likely other conditions that have similar behaviour), the
> mouse events carry some flags that the actual code mistakenly interpret
> causing the grabWindowRef to not be unset.
> 
> The proposed patch address the code for the button event mapping:
> 
> http://cr.openjdk.java.net/~neugens/853079/webrev.01/
> 
> We have no easy way to automatically provide a test case for this bug
> unfortunately.
> 
> I could reproduce the bug with OpenJDK 6, 7 and 8 as well as Oracle JDK,
> so it's a long lasting bug. I'm not sure if it's worth to eventually
> backport to 7 as well if approved.

Let me add some little explanations (I worked with Mario on this
bugfix). The underlying problem is that the bitmask that we get in every
event (event-state) has 5 bits for button state (for the first 5
buttons). All other bits are used for other stuff. However, we get
number-of-buttons from X11 reported as 10, and hence look at 10 buttons
in that bitmask, which is wrong. In our particular case, the
KeymapStateMask was set (bit #14) and this lead to button-release
handler assuming not all buttons have been released and hence screwing
up the grab-state. However, the problem is more general: if we consider
more than 5 buttons in that mask, we risk to run into problems like
that. The fix limits to 5 buttons when dealing with the event-state
mask. (And, this is very reasonable: the other buttons are usually not
real buttons, but stuff like mouse-wheel or touch-scroll thingies.)

Kind regards,
Roman