RFR: 8185886: Improve scrolling performance of TableView and TreeTableView

[dannygonzalez]

On Sun, 23 Feb 2020 04:20:55 GMT, Nir Lisker <nlisker at openjdk.org> wrote:

>> https://bugs.openjdk.java.net/browse/JDK-8185886
>> 
>> Optimisation to ExpressionHelper.Generic class to use Sets rather than Arrays to improve listener removal speed.
>> 
>> This was due to the removal of listeners in TableView taking up to 50% of CPU time on the JavaFX Application thread when scrolling/adding rows to TableViews.
>> 
>> This may alleviate some of the issues seen here:
>> 
>> TableView has a horrific performance with many columns #409
>> https://github.com/javafxports/openjdk-jfx/issues/409#event-2206515033
>> 
>> JDK-8088394 : Huge memory consumption in TableView with too many columns
>> JDK-8166956: JavaFX TreeTableView slow scroll performance
>> JDK-8185887: TableRowSkinBase fails to correctly virtualise cells in horizontal direction
>> 
>> OpenJFX mailing list thread: TableView slow vertical scrolling with 300+ columns
>> https://mail.openjdk.java.net/pipermail/openjfx-dev/2020-January/024780.html
> 
> modules/javafx.base/src/main/java/com/sun/javafx/binding/ExpressionHelper.java line 197:
> 
>> 196:         private int weakChangeListenerGcCount = 2;
>> 197:         private int weakInvalidationListenerGcCount = 2;
>> 198: 
> 
> Why are these set to 2 and why do you need them at all? The previous implementation needed to grow and shrink the array so it had to keep these, but `Map` takes care of this for you.

I agree, I kept these in as I wasn't sure if there was a need to manually force the garbage collection of weak listeners at the same rate as the original implementation.
Removing this would make sense to me also.

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PR: https://git.openjdk.java.net/jfx/pull/108