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

[Kevin Rushforth]

On Mon, 6 Mar 2023 16:04:02 GMT, Florian Kirmaier <fkirmaier 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.

I'll let others do the formal review of this, but I would like to see an evaluation of what the root cause is, why this is the right fix, and whether there are any side effects. As it is, all I see is a removed line with no explanation of the problem or the solution.

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?

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