RFR: JDK-8269921 Text in Textflow and listeners on bounds can cause endless loop/crash and other performance issues [v4]

[danielpeintner]

On Mon, 22 Aug 2022 09:46:24 GMT, Florian Kirmaier <fkirmaier at openjdk.org> wrote:

>> It's "a bit" complicated.
>> In some situations, getRuns get's called because listeners on bounds are set.
>> This causes TextFlow to layout to compute the runs.
>> Afterward, the bounds of the parents get updated. 
>> This triggers a call to compute bounds - which cascades up to the children.
>> When the geometry of the previous Text gets computed in this big stack - it throws an nullpointer.
>> The Text doesn't have its runs, and calling TextFlow.layout is now a noop (it detects repeated calls in the same stack)
>> 
>> In the case it happened - it didn't repair and the application kinda crashed.
>> This bug most likely can also be triggered by ScenicView or similar tools, which sets listeners to the bounds.
>> It also can cause unpredictable performance issues.
>> 
>> Unit test and example stacktrace are in the ticket.
>> 
>> The suggested fix makes sure that recomputing the geometry of the Text, doesn't trigger the layout of the TextFlow. 
>> The Textflow should be layouting by the Parent.
>> This might change the behavior in some cases, but as far as I've tested it works without issues in TextFlow Heavy applications.
>> 
>> Benefits:
>>  * Better Tooling Support For ScenicView etc.
>>  * Fixes complicated but reproducible crashes
>>  * Might fix some rare crashes, which are hard to reproduce
>>  * Likely improves performance - might fix some edge cases with unpredictable bad performance
>
> Florian Kirmaier has updated the pull request incrementally with one additional commit since the last revision:
> 
>   JDK-8269921
>   Reverted the change to the layout, so we can fix the main-bug without further discussions.

FYI: in the near past we have also many of those "crashes" when the UI gets heavily restructured. Crashes in our case means that on Windows for example you get the loading circle but the UI freezes endlessly. I assume it might be related. 

Question: does the simple `null` check help in such a case?

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PR: https://git.openjdk.org/jfx/pull/564