RFR: 8371128: NullPointerException occurs due to double cleanup of SwingNode [v2]

[Kevin Rushforth]

On Wed, 5 Nov 2025 03:01:50 GMT, Prasanta Sadhukhan <psadhukhan at openjdk.org> wrote:

>> Good catch. Other than being another possible source of an NPE, that one seems unrelated, so might be better handled as a follow-up. This one isn't a threading issue whereas the one you pointed out is.
>> 
>> @prsadhuk Can you at least take a look at it and see whether there is any relation to the bug you are fixing? If not, let's file a follow-up bug. The fix is to also check for null on the EDT before calling createUngrabEvent (as is done in disposeLwFrame -- even if you test lwFrame for null in the FX thread (to short-circuit creating the call on the EDT), you still need to check before use once you actually are on the EDT.
>
> I don't quite understand..In 
> 
> 
> private final EventHandler<FocusUngrabEvent> ungrabHandler = event -> {
>     556         if (!skipBackwardUnrgabNotification) {
>     557             if (lwFrame != null) {
>     558                 postAWTEvent(
>     559                     swNodeIOP.createUngrabEvent(lwFrame));
>     560             }
>     561         }
>     562     };
> 
> we are checking for null lwFrame in FX thread and there's no thread switching so how can we have again null lwFrame?
> In disposeLwFrame, we are checking for null lwFrame inside `SwingNodeHelper.runOnEDT` due to context switch but here no such thing is happening and is running in same thread, so I am not sure why and where to `check for null on the EDT before calling createUngrabEvent`

@prsadhuk You are correct. There is no thread switching in that block (it's all on the FX app thread, which creates an event and then sends that created event to the EDT).

Go ahead and integrate this PR.

-------------

PR Review Comment: https://git.openjdk.org/jfx/pull/1960#discussion_r2494323128