RFR: 8255248: NullPointerException in JFXPanel due to race condition in HostContainer [v2]

[Andy Goryachev]

On Tue, 11 Nov 2025 03:02:01 GMT, Prasanta Sadhukhan <psadhukhan at openjdk.org> wrote:

>> NPE is seen while accessing transient "scenePeer" variable between reads..
>> Fix is made to store it in a temp variable rather than reading it twice since the value can change between successive reads in many places it is accessed.
>> Also some debug logs added to be enabled via `jfxpanel.debug` property
>
> Prasanta Sadhukhan has updated the pull request incrementally with one additional commit since the last revision:
> 
>   debug fix

Changes requested by angorya (Reviewer).

modules/javafx.swing/src/main/java/javafx/embed/swing/JFXPanel.java line 212:

> 210: 
> 211:     private static void debug_println(String str) {
> 212:         if (DEBUG) {

I am sorry, I was not sufficiently clear.
This method does not need the conditional.  The conditionals are needed in **every** place that calls here.
In other words, we don't want to incur the string concatenation overhead if **DEBUG** is false.

modules/javafx.swing/src/main/java/javafx/embed/swing/JFXPanel.java line 286:

> 284:         super();
> 285: 
> 286:         debug_println("JFXPanel Thread " + Thread.currentThread().getName() + " isFXUserThread " + Toolkit.getToolkit().isFxUserThread());

Basically, here (and elsewhere debug_println() is called) we should have

if(DEBUG) {
          debug_println("JFXPanel Thread " + Thread.currentThread().getName() + " isFXUserThread " + Toolkit.getToolkit().isFxUserThread());
}


As a separate note, you may want to consider removing some noise from debugging output and only print when "unexpected" condition occurs, such as (thread != fx), right?

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

PR Review: https://git.openjdk.org/jfx/pull/1968#pullrequestreview-3454498726
PR Review Comment: https://git.openjdk.org/jfx/pull/1968#discussion_r2519095341
PR Review Comment: https://git.openjdk.org/jfx/pull/1968#discussion_r2519105890