RFR: 8350048: Enforce threading restrictions for show and hide methods in Window, Control, and Skin [v4]

[Andy Goryachev]

On Fri, 28 Feb 2025 21:09:37 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> - enforced fx application thread
>> - clarify doc where an `IllegalStateException` can get thrown, such as hide() and show()
>> - clarified `ComboBoxBase::show`
>> - added a headful test `TestThreadingRestrictions`
>
> Andy Goryachev has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review comments

Created https://bugs.openjdk.org/browse/JDK-8350976 for the MenuBarSkin.

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PR Comment: https://git.openjdk.org/jfx/pull/1717#issuecomment-2691682516