RFR: 8285893: Hiding dialog and showing new one causes dialog to be frozen

[Kevin Rushforth]

On Sat, 4 May 2024 22:55:13 GMT, Martin Fox <mfox at openjdk.org> wrote:

> This PR is based on a discussion that happened over in PR #1324. Some of this explanation is copied from that thread.
> 
> When `exitNestedEventLoop` is called on the innermost loop the invokeLaterDispatcher suspends operation until the loop finishes. But if you immediately start a new event loop the previous one won't finish and the dispatcher will jam up and stop dispatching indefinitely.
> 
> When the invokeLaterDispatcher is told that the innermost loop is exiting it sets `leavingNestedEventLoop` to true expecting it to be set to false when the loop actually exits. When the dispatcher is told that a new event loop has started it is not clearing `leavingNestedEventLoop` which is causing the jam. Basically it should follow the same logic used in glass; leaving the innermost loop updates a boolean indicating that the loop should exit but if a new loop is started the boolean is set back to a running state since it now applies to the new loop, not the previous one.
> 
> I suspect the invokeLaterDispatcher exists in part to deal with the specifics of how deferred runnables are handled on the Mac. I investigated this a bit and wrote up some comments in the Mac glass code.

I get the following internal assertion failure when running the test on Linux:


NestedEventLoopTest > testCanExitAndThenEnterNewLoop FAILED
    java.lang.AssertionError: Internal inconsistency - wrong EventLoop
        at javafx.graphics at 23-ea/com.sun.glass.ui.EventLoop.enter(EventLoop.java:108)
        at javafx.graphics at 23-ea/com.sun.javafx.tk.quantum.QuantumToolkit.enterNestedEventLoop(QuantumToolkit.java:656)
        at javafx.graphics at 23-ea/javafx.application.Platform.enterNestedEventLoop(Platform.java:310)
        at test.javafx.stage.NestedEventLoopTest.lambda$testCanExitAndThenEnterNewLoop$29(NestedEventLoopTest.java:326


It ran cleanly on Mac and Windows.

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PR Comment: https://git.openjdk.org/jfx/pull/1449#issuecomment-2096641134