RFR: JDK-8269921 TextFlow: listeners on bounds can throw NPE while computing text bounds [v6]

[Andy Goryachev]

On Mon, 30 Oct 2023 15:03:05 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:
> 
>   updated test to junit5
>   improved name for method onEveryNode -> addBoundsListener

As long as subsequent layout cycles fix the bounds (and apps like ScenicView show them correctly), I am ok with this fix.

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Marked as reviewed by angorya (Reviewer).

PR Review: https://git.openjdk.org/jfx/pull/564#pullrequestreview-1730205022