Remove AvaloniaProperty.Initialized and PseudoClass static methods

[grokys]

What does the pull request do?

I'd like to get some thoughts on this, it's removing functionality in the pursuit of performance.

Every time an AvaloniaObject is constructed we fire an AvaloniaProperty.Initialized observable for each property registered on the object. This observable is used to automatically apply pseudoclasses to controls using the static PseudoClass() method calls. We've tried to optimize this process, but the performance hit is still quite large.

In this PR, I removed the AvaloniaProperty.Initialized observable and related machinery. I then tried to implement the PseudoClass functionality in what I hoped would be a more performant way - lets call this attempt PseudoClassEngine, you can see the code here. This did indeed improve performance a little, but there was still an overhead.

I then tried completely removing the static PseudoClass helper methods and managing pseudoclasses in code. Performance was much better. Here are some benchmarks:

master

|           Method |     Mean |     Error |    StdDev |  Gen 0 | Gen 1 | Gen 2 | Allocated |
|----------------- |---------:|----------:|----------:|-------:|------:|------:|----------:|
| InitializeButton | 2.545 us | 0.0135 us | 0.0120 us | 1.4534 |     - |     - |   1.37 KB |

PseudoclassEngine

|           Method |     Mean |    Error |   StdDev |  Gen 0 | Gen 1 | Gen 2 | Allocated |
|----------------- |---------:|---------:|---------:|-------:|------:|------:|----------:|
| InitializeButton | 915.4 ns | 1.783 ns | 1.581 ns | 1.1139 |     - |     - |   1.05 KB |

Pseudoclasses in code

|           Method |     Mean |     Error |    StdDev |  Gen 0 | Gen 1 | Gen 2 | Allocated |
|----------------- |---------:|----------:|----------:|-------:|------:|------:|----------:|
| InitializeButton | 246.7 ns | 0.8485 ns | 0.7937 ns | 0.9899 |     - |     - |     952 B |

As you can see, creating an instance of a Button is now 10x faster.

The question is: are we willing to remove functionality like this to get better performance?

Breaking changes

• AvaloniaProperty.Initialized removed
• Static PseudoClass methods removed

Note

Targets #3287

[JaggerJo]

Never needed AvaloniaProperty.Initialzed and 10x per control creation is a lot.

[MarchingCube]

I think that the benefit of dropping Initialized is huge since it also affects startup time of the app, when starting the app initialized property cache is invalidated and created again very often. Plus general simplification of our core codebase should make future optimizations easier to pull off.

[MarchingCube]

@grokys So what is the verdict here? Should we merge this in?

[grokys]

This targets #3287 and by extension #3255, so it's the last in a chain of quite large changes. I think we should decide when/whether to merge the others first. If we want this but not the others I can port this to target master.

[MarchingCube]

@grokys Since other PRs got merged are we planning to resume working on this?

[grokys]

Yeah I think this is worth doing, despite the breakage it will cause.

[grokys]

Ok, updated this to target master. Now ready for review.

[MarchingCube]

Generally LGTM, but one issue that I've found must be fixed.

[MarchingCube]

LGTM.