<AWT Dev> <Swing Dev> [9] Review request for JDK-8039383: NPE when changing Windows Theme

Alexey Ivanov alexey.ivanov at oracle.com
Thu Apr 24 12:23:14 UTC 2014

Hi Anthony, AWT and Swing teams,

Here's the updated fix:

In the new version of the fix, I use a new xpstyleEnabled field of 
AtomicBoolean in WToolkit to track the current value of 
"win.xpstyle.themeActive" desktop property. Its value is updated in 
windowsSettingChange() and in updateProperties().
XPStyle.getXP() checks its cached value in themeActive and the current 
value in WToolkit; if the value changes, it schedules updateAllUIs and 
invalidates the current style right away, so that components would not 
access data from the theme that became unavailable.
Two functions in ThemeReader also check this special field from WToolkit 
which prevents throwing InternalError when paint is called before theme 
change is fully handled.

Before updateAllUIs is invoked, it's possible that application will 
paint with some values cached from the previous theme. Usually it 
happens before "Theme change" dialog disappears from the screen, at 
least I noticed no UI glitches during normal theme change.

Regression test:
No regression test is provided due to its complexity. Additionally, 
whether NullPointerException or InternalError are thrown depends on the 
order of event handling, sometimes exceptions do not occur when changing 
theme of visual styles enabled theme to a classic theme.

Thank you,

On 18.04.2014 18:52, Anthony Petrov wrote:
> Hi Alexey,
> No, unfortunately I don't have any suggestions right now.
> As for allowing executing user code on the toolkit thread, we can't 
> accept such a fix. Sorry about that.
> -- 
> best regards,
> Anthony
> On 4/18/2014 6:48 PM, Alexey Ivanov wrote:
>> Hi Anthony,
>> Thank you for your review.
>> Yes, user code can install a property change listener... It was my
>> concern too, that's why I explicitly noted about this.
>> Do you have any suggestion how this situation can be handled?
>> Is it a general rule that all desktop property change listeners must be
>> called on EDT?
>> Thanks,
>> Alexey.
>> On 18.04.2014 16:02, Anthony Petrov wrote:
>>> Hi Alexey,
>>>> With this change, property "win.xpstyle.themeActive" change is fired
>>>> on the toolkit thread
>>> Is it possible to install a change listener for this property from
>>> user code, and hence eventually allow executing some user code on the
>>> toolkit thread with your fix?
>>> -- 
>>> best regards,
>>> Anthony
>>> On 4/18/2014 12:09 PM, Alexey Ivanov wrote:
>>>> Hello Swing and AWT teams,
>>>> Could you please review the fix for jdk9:
>>>>      bug: https://bugs.openjdk.java.net/browse/JDK-8039383
>>>>      webrev: 
>>>> http://cr.openjdk.java.net/~dmarkov/8039383/jdk9/webrev.00/
>>>> Problem description:
>>>> When changing Windows themes from a theme with visual styles (Windows
>>>> Aero or Windows Basic) to a classic one, NullPointerException could be
>>>> thrown from Swing code during component tree validation, or
>>>> InternalError could be thrown during component painting.
>>>> Root cause:
>>>> Windows theme data are "cached" in XPStyle object. When the theme is
>>>> switched to a classic one, HTHEME handle becomes unavailable and data
>>>> cannot be accessed from the theme any more. The change in theme in
>>>> posted to EDT via invokeLater. At the same time, the UI needs to 
>>>> repaint
>>>> itself as soon as Windows changed the theme, and paint code is often
>>>> called before the theme change is handled in Java. This leads to 
>>>> NPE and
>>>> InternalError as the code tries to access the data that has become
>>>> unavailable.
>>>> The fix:
>>>> Update "win.xpstyle.themeActive" desktop property and invalidate the
>>>> cached XPStyle as soon as windowsSettingChange() is called from native
>>>> code. Thus when Swing code needs to access theme data, it will see no
>>>> theme is available and will fallback to classic painting.
>>>> Note: Before the fix, PropertyChangeEvents for desktop properties in
>>>> Windows were fired on the Event Dispatch Thread. With this change,
>>>> property "win.xpstyle.themeActive" change is fired on the toolkit
>>>> thread; all other properties are changed on the EDT as before.
>>>> Regards,
>>>> Alexey.

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