RFR: 8252936: Optimize removal of listeners from ExpressionHelper.Generic

[dannygonzalez]

On Fri, 17 Apr 2020 10:46:51 GMT, dannygonzalez <github.com+6702882+dannygonzalez at openjdk.org> wrote:

>> The problem is that there are usually many nodes, but only very few scenes and windows, so registering a listener for each node on a scene or window is pretty bad design (also consider the amount of notifications that a scene change would trigger in such scenarios).  As far as I can see, this is the only such listener and only needed for two very limited cases, and its addition in the past may have slipped through the cracks.
>> 
>> Adding a performance unit test that specifically checks add/remove performance of nodes may prevent such future regressions.
>
> @hjohn, agreed regards the issues of adding a listener to each node.
> 
> Would it be worth doing the additional work of updating PopupWindow and ProgressIndicatorSkin to add their own listeners to make this a pull request that can be reviewed officially?
> 
> I await any further comments from @kevinrushforth et al.

I have attached a code sample. If you use OpenJFX 16-ea+1 and run visual VM and look at the hotspots in the JavaFX thread, you can see that about 45% of the time in the JavaFX thread is spent in removeListener calls.

Note: In CPU settings of VisualVM, I removed all packages from the "Do not profile packages section".

[JavaFXSluggish.java.zip](https://github.com/openjdk/jfx/files/5130298/JavaFXSluggish.java.zip)

-------------

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