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

[dannygonzalez]

On Wed, 26 Feb 2020 09:49:04 GMT, Jeanette Winzenburg <fastegal at openjdk.org> wrote:

> Hmm .. personally, I would consider changing such a basic (and probably highly optimized) implementation used all over the framework is a very high risk change that at the worst outcome would detoriate internal and external code. So before going that lane, I would try - as you probably have, just me not seeing it :) - to tackle the problem from the other end:
> 
> > I know that in our application, the **thousands of listeners** unregistering when using a TableView was stalling the JavaFX thread.
> 
> .. sounds like a lot. Any idea, where exactly they come into play?

I did start to look at why there were so many change listeners unregistering but felt that would take a deeper understanding of the architecture and design decisions of JavaFX scene graph and I didn't have that time to invest. 
I do know that there are thousands of them unregistering in a TableView and unregistering them is a bottleneck for the JavaFX thread.

There are multiple change listeners on a Node for example, so you can imagine with the number of nodes in a TableView this is going to be a problem if the unregistering is slow.

To get our application usable I profiled the code and saw this unregistering as a major bottleneck, hence why I looked at this more obvious solution.

I'm happy to look at the problem from the other angle and happy to listen to suggestions from people with more experience of the design and architecture but tackling the problem from the perspective of re-architecting the behaviour of listeners in the scene graph would be more work than I could feasibly take on.

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