RFR: 8185886: Improve scrolling performance of TableView and TreeTableView

[John Hendrikx]

On Thu, 16 Apr 2020 07:11:58 GMT, John Hendrikx <jhendrikx at openjdk.org> wrote:

>> The patch proposed here does not share the case where the listener deletion performance becomes a bottleneck.
>> 
>> I think that it is necessary to reproduce it by testing first, but
>> 
>> If you just focus on improving listener removal performance,
>> 
>> If the lifespan of a large number of registered listeners is biased,
>> It seems like the next simple change can improve delete performance without changing the data structure.
>> 
>> * Change the search from the front of the list to the search from the back.
>> 
>> This will reduce the number of long-life listeners matching.
>
> Looking at the commit  https://github.com/openjdk/jfx/commit/e21606d3a1b73cd4b44383babc750a4b4721edfd
>  it seems that the long listener lists are actually part of the `Scene`'s `Window` property and the `Window`'s `Showing`
>  property.  Each `Node` registers itself on those and so the listener lists for those properties would scale with the
>  number of nodes.
> 
> A test case showing this problem would really be great as then the patch can also be verified to solve the problem, but
> I suppose it could be reproduced simply by having a large number of Nodes in a scene.  @dannygonzalez could you give us
> an idea how many Nodes we're talking about?  1000? 10.000?  It also means there might be other options, do Nodes really
> need to add these listeners and for which functionality and are there alternatives?  It would also be possible to
> target only these specific properties with an optimized listener list to reduce the impact of this change.

The listeners added by `Node` are apparently internally required for internal properties `TreeShowing` and
`TreeVisible`, and are used to take various decisions like whether to play/pause animations.  There is also a couple of
listeners registering on these properties in turn (in `PopupWindow`, `SwingNode`, `WebView` and `MediaView`).

A lot of the checks for visibility / showing could easily be done by using the `Scene` property and checking visibility
/ showing status from there.  No need for so many listeners.  The other classes mentioned might register their own
listener, instead of having `Node` do it for them (and thus impacting *every* node).

Alternatively, `Node` may lazily register the listeners for Scene.Window and Window.Showing only when needed (which
from what I can see is for pretty specific classes only, not classes that you'd see a lot in a TableView...)

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