RFR: 8369306: Implement invokeAndWait and finishTerminating on headless platform [v4]

[Jose Pereda]

On Mon, 13 Oct 2025 18:22:07 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> As I said in my previous comment, I don't see this as a showstopper for this PR, but since it might help in general, I keep thinking about approaches to remove the sleep.
>> Wouldn't it be an option here to obtain the JavaFX Application Thread after the `assertTrue(Platform.isFxApplicationThread());` and assign it to e.g. `Thread fxThread` so that instead of the `Util.sleep` we can do `fxThread.join(10)` ? (I might be missing something though)
>
> Yes, something like what you describe might work in this case.
> 
> As for the more general problem, which goes well beyond this PR, there are many places in our tests where we do need sleeps. They fall into two cases
> 
> 1. Lack of a feature that provides a deterministic way to know when something has occurred. Implementing the missing functionality could allow us to replace sleeps with something more deterministic.
> 2. Inherent limitations where there cannot be a deterministic way to know when something has occurred.
> 
> Many, if not most, of the instances of 1 could be addressed with an implementation of `Robot::waitForIdle`. It's a long-standing feature request. It's not rocket science to implement, but isn't trivial either.
> 
> Most of the instances of 2 are due to either A) platform delay in realizing certain window system operations (show/hide/minimize/maximize/to-front/etc); or B) inherent GC non-determinism.

I've replaced `Util.sleep(10)` with `fxThread.join(10)`

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PR Review Comment: https://git.openjdk.org/jfx/pull/1934#discussion_r2428320801