RFR: 8255248: NullPointerException in JFXPanel due to race condition in HostContainer [v5]

[Prasanta Sadhukhan]

On Tue, 18 Nov 2025 17:03:49 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> Prasanta Sadhukhan has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   temp-var handling in few other methods
>
> modules/javafx.swing/src/main/java/javafx/embed/swing/JFXPanel.java line 156:
> 
>> 154:     private transient volatile EmbeddedWindow stage;
>> 155: 
>> 156:     private transient volatile Scene scene;
> 
> Minor: I would remove the blank line between these two declarations to make it clear that the comment applies to both.

I intentionally added the blank line to separate it out as `stage` is set in `setSceneImpl `in FX thread and accessed in `paintComponent `in EDT thread whereas `scene` is set in `setSceneImpl ` in FX thread and never accessed in EDT thread

> modules/javafx.swing/src/main/java/javafx/embed/swing/JFXPanel.java line 974:
> 
>> 972:                         getScene().getFocusOwner() != null &&
>> 973:                         getScene().getFocusOwner().isFocused()) {
>> 974:                     hStagePeer.focusUngrab();
> 
> This can be reverted. `stagePeer` is only accessed on the FX thread.

`stagePeer` is accessed in `processMouseEvent`, `sendResizeEventToFX`, `sendMoveEventToFX`, `sendFocusEventToFX `in EDT so I did that.
But it seems in this particular method, it is only accessed in FX thread as is mentioned so reverted..

> modules/javafx.swing/src/main/java/javafx/embed/swing/JFXPanel.java line 1023:
> 
>> 1021:             }
>> 1022:         });
>> 1023:         sendMoveEventToFX();
> 
> This is not an equivalent change, since `sendMoveEventToFX()` can now happen before `stage.show()` and will also happen unconditionally even if the stage is null or already showing. Rather than moving it out of the runOnFxThread block, leave it where it is and call `runOnEDT` like this:
> 
> 
>         SwingNodeHelper.runOnFxThread(() -> {
>             if ((stage != null) && !stage.isShowing()) {
>                 stage.show();
>                 SwingNodeHelper.runOnEDT(() -> sendMoveEventToFX());
>             }
>         });

ok

> modules/javafx.swing/src/main/java/javafx/embed/swing/JFXPanel.java line 1078:
> 
>> 1076:             stagePeer = embeddedStage;
>> 1077:             var hStagePeer = stagePeer;
>> 1078:             if (hStagePeer == null) {
> 
> If this is always invoked from the FX thread, you don't need to locally capture the peers.

but down below it is accessed in EDT so I did the local capture

> tests/system/src/test/java/test/javafx/embed/swing/JFXPanelNPETest.java line 105:
> 
>> 103:             Thread.sleep(100);
>> 104:         }
>> 105:         System.out.println("failure = " + failure.get());
> 
> This print can be removed.

ok

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

PR Review Comment: https://git.openjdk.org/jfx/pull/1968#discussion_r2541819249
PR Review Comment: https://git.openjdk.org/jfx/pull/1968#discussion_r2541821731
PR Review Comment: https://git.openjdk.org/jfx/pull/1968#discussion_r2541822284
PR Review Comment: https://git.openjdk.org/jfx/pull/1968#discussion_r2541822543
PR Review Comment: https://git.openjdk.org/jfx/pull/1968#discussion_r2541822916