RFR: 8345348: CSS media feature queries [v21]

[Michael Strauß]

On Tue, 6 May 2025 18:51:47 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> `volatile` is not enough, because the different values are correlated (for example `foreground`, `background`, and `colorScheme`). All values need to be updated in a single transaction, as otherwise we could end up reading a transient combination of values.
>
> I see.  The I suggest we enforce single-threaded nature of it: everything must happen in the FX Application Thread.  I don't think it's a good idea to start synchronizing things in FX now all of a sudden.
> 
> Any code that wants to access FX from a background thread must do so using a combination of `runLater` and a `CountDownLatch`.
> 
> What do you think?

That would be okay, except that `Scene` is allowed to be created on a background thread (it's in the class documentation), so we can't completely enforce it to be single-threaded. Once a scene is created, a user can also request its preferences. This is when we need some way to get the current platform preferences on a background thread, as otherwise users would potentially see the scene preferences suddenly change once the scene is shown.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1655#discussion_r2076107914