On Tue, 28 Jul 2026 21:22:22 GMT, Michael Strauß <[email protected]> wrote:
> On Windows, changing a system preference such as the light/dark color mode
> can crash an application that embeds JavaFX in SWT using `FXCanvas`.
>
> `GlassApplication` receives the Java `WinApplication` instance as the local
> JNI reference `jrefThis`. It passes this reference to `PlatformSupport` and
> separately creates a global reference for `m_grefThis`:
>
> GlassApplication::GlassApplication(jobject jrefThis) : BaseWnd(),
> m_platformSupport(GetEnv(), jrefThis)
> {
> m_grefThis = GetEnv()->NewGlobalRef(jrefThis);
> ...
> }
>
>
> Creating `m_grefThis` does not promote the original reference. `NewGlobalRef`
> returns a new handle, while the copy retained by `PlatformSupport` remains a
> local JNI reference. That local reference becomes invalid when the native
> method invocation returns.
>
> Using an invalid JNI reference is undefined behavior. Depending on the state
> of the reused local-reference slot, the result can be a
> `NullPointerException` without Java frames or an access violation inside the
> JVM.
>
> This change stores the application reference as a `JGlobalRef<jobject>`,
> which creates an independent global JNI reference while the input local
> reference is still valid.
>
> ---------
> - [x] I confirm that I make this contribution in accordance with the [OpenJDK
> Interim AI Policy](https://openjdk.org/legal/ai).
LGTM, tested on my Windows 11 machine, usual tests also look good
-------------
Marked as reviewed by lkostyra (Reviewer).
PR Review: https://git.openjdk.org/jfx/pull/2226#pullrequestreview-4830380251
