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

[Kevin Rushforth]

On Thu, 16 Feb 2023 21:48:08 GMT, Marius Hanl <mhanl at openjdk.org> wrote:

>> This PR adds the last missing method for dealing with nested event loops.
>> As also written in the ticket, there is currently no (public) way to find out whether it is safe to start an event loop now or not.
>> Classes like `Dialog` check via `Toolkit.getToolkit().canStartNestedEventLoop()` (sun api), if it safe to start a nested event loop before doing so.
>
> Marius Hanl has updated the pull request incrementally with one additional commit since the last revision:
> 
>   JDK-8302355: checkFxUserThread(), adjusted javadoc accordingly. Added Tests

I left a couple suggestions on the docs, but otherwise it looks ready to me.

The implementation changes and the new test look good.

modules/javafx.graphics/src/main/java/javafx/application/Platform.java line 396:

> 394:     /**
> 395:      * Indicates whether a nested event loop can be started from the current thread in the current state.
> 396:      * Note that a nested event loop is not allowed outside an event handler.

I would either remove this sentence (probably cleanest), or else change it to a positive statement (say when it is allowed, not when it isn't) and also add that it's ok when called from a Runnable passed to `Platform.runLater`. Maybe something like this:


A nested event loop can be started from an event handler or from a `Runnable` passed
to `Platform.runLater(Runnable)`.

modules/javafx.graphics/src/main/java/javafx/application/Platform.java line 399:

> 397:      * This method must be called on the JavaFX Application thread.
> 398:      *
> 399:      * @return true if a nested event loop can be started, and false otherwise.

I recommend code case here: `{@code true}` and `{@code false}`.

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