RFR: JDK-8302355: Public API for Toolkit.canStartNestedEventLoop() [v2]

[Kevin Rushforth]

On Thu, 16 Feb 2023 18:25:23 GMT, Marius Hanl <mhanl at openjdk.org> wrote:

>> So someone is asking a question when they call this.
>> Throwing an Exception could be considered an unfriendly way of answering it.
>> It only makes sense if you think the programmer will have enough information to be sure that if S/HE does things correctly, it will always be the FxUserThread that is being used .. ie if we are in an event handler .. as is supposed to be the case .. and anything else is a blatant programming error that should be rewarded with an upfront response to that effect.
>> 
>> So
>> 1) programming error -> Exception
>> 2) Can't be sure -> return false.
>
> @prrace What is your preference here?
> Since `enterNestedEventLoop` and `exitNestedEventLoop` throw an exception when not on the fx user thread, I feel like it makes sense to also add it here as well.

Phil's comment got me thinking about this further. All other event loop methods, including `isNestedLoopRunning`, need to be called on the JavaFX thread. So I prefer option 1 as well for consistency.

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PR: https://git.openjdk.org/jfx/pull/1031