RFR: 8303680 Virtual Flow freezes after calling scrollTo and scrollPixels in succession

[Florian Kirmaier]

On Mon, 6 Mar 2023 21:02:43 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> Possible fix for VirtualFlow freeze.
>> 
>> I encountered the problem when experimenting with VirtualFlow.
>> 
>> Guess @johanvos should take a look.
>> All tests are still green, so with some luck, this doesn't break anything but fixes some known and unknown bugs.
>
> modules/javafx.controls/src/main/java/javafx/scene/control/skin/VirtualFlow.java line 1718:
> 
>> 1716:         // Finally, update the scroll bars
>> 1717:         updateScrollBarsAndCells(false);
>> 1718:         lastPosition = getPosition();
> 
> This is not a formal review -- I'll let Andy and Johan do that -- but can you explain why this is the right fix? Presumably there was at least some reasoning behind updating `lastPosition`. Are there any side effects of not doing that?

I've written more about the explanation below. Actually, it's a good question whether there is reasoning behind updating lastPosition. Wouldn't be surprised, if it is just an artifact of some bug-fixing attempt.

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PR: https://git.openjdk.org/jfx/pull/1052