RFR: JDK-8322964 Optimize performance of CSS selector matching [v2]

[Marius Hanl]

On Thu, 11 Jan 2024 22:36:58 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

>> modules/javafx.graphics/src/main/java/com/sun/javafx/css/FixedCapacitySet.java line 94:
>> 
>>> 92:         return maximumCapacity == 0 ? empty()
>>> 93:              : maximumCapacity == 1 ? new Single<>()
>>> 94:              : maximumCapacity == 2 ? new Duo<>()
>> 
>> I can confirm that most of the code in my application uses 1-2 styleclasses.
>> Since all controls have one styleclass by default (some even more, think about `TextInputControl` with `text-input` -> `TextField` with `text-field`), does it make sense to also implement a specialized `Triple` class?
>> 
>> We also often add 2 more styleclasses, so 3 style classes seems like a usecase that happens quite often.
>> I also can confirm that 4 styleclasses or even more are very rare.
>> I only found one: (`.label` + 3 added from us)
>> ![image](https://github.com/openjdk/jfx/assets/66004280/2d80db3d-aca6-488e-a338-0759c82c35c8)
>
> Thanks for having a look, it's good to have some more use cases from other applications!  The sets are used both for the style classes on `Node`s but also the set of style classes in CSS selectors (multiple style classes in  selectors are even more rare I think than multiple style classes on `Node`s).
> 
> I think from a performance perspective, `Duo` and `Hashless` are likely very closely matched, but I can do some testing in that area.  The reason I say this is that I only got a very minor boost from including `Duo`, but kept it because it is a bit more memory efficient.
> 
> If you want, I'm also curious about how many styles are used in your application (you can see this by looking at the size of `StyleClassSet#styleClasses` after all styles are loaded).

I see, thanks for checking that out.

I checked the application, here is the result:
After starting the app:
![image](https://github.com/openjdk/jfx/assets/66004280/623049ac-c525-4854-8f06-b9712de5d746)

After using it a little bit:
![image](https://github.com/openjdk/jfx/assets/66004280/cca4df47-829a-4d9b-b937-705b6c058172)

---
I also checked out Scenebuilder after using it a little bit:
![image](https://github.com/openjdk/jfx/assets/66004280/0f8992b5-1073-4c77-b906-356b86c61389)

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PR Review Comment: https://git.openjdk.org/jfx/pull/1316#discussion_r1450360838