Performance issue - Subscribing\Unsubscribing to events

[alexserov]

Describe the bug
When profiling our test application, we've seen that every event subscription takes a noticeable time.
In our case, this slows down the application startup for about 200ms.

I made a small sample that shows the issue. I've also prepared the WPF test application so you can compare performance.

Steps to reproduce the bug

Steps to reproduce the behavior:

1. Download from the attachments and open the FrameworkEventsTest solution;
2. Set the following solution properties:
   • Configuration - "Release"
   • Platform - "x64"
   • Startup Project - "FrameworkEventsTest (Package)"
3. Run the application
4. Click on the "Click Me" button
5. Wait until the result is shown in the text editor (this may take up to 40 seconds)
6. Repeat steps 4 and 5 for more accurate results

In the table below, you can see the difference between WPF and WinUI performance when subscribing\unsibscribing to the IsEnabledChanged event.
I've also tried the Loaded and the KeyDown event and got the same results.

Case #	Description	WPF	WinUI pre-2	WinUI pre-3
1	Subscribe to 1 button event with 1 method 1000 times	0	0	0
2	Subscribe and Unsubscribe to 1 button event with 1 method 1000 times	0	26	7
3	Subscribe to 1 button event with 1000 methods 1 time	406	269	341
4	Subscribe and Unsubscribe to 1 button event with 1000 methods 1 time	170	23365	5685
5	Subscribe to 1000 buttons event with 1 method 1 time	0	336	217
6	Subscribe and Unsubscribe to 1000 buttons event with 1 method 1 time	0	326	217

Expected behavior
I expect that cases 5 and 6 should be instant (like in WPF) since this is very close to a real scenario: in our app, we have lots of controls with subscriptions to such events as Loaded, Unloaded, IsEnabledChanged, LayoutUpdated.

I'm also surprised at the poor performance of scenario 4; however, I understand that this is synthetic and may not exist in the real application.

Version Info

NuGet package version:
[Microsoft.WinUI 3.0.0-preview2.200713.0]
[Microsoft.WinUI 3.0.0-preview3.201113.0]

Windows app type:

UWP	Win32
	Yes

Windows 10 version	Saw the problem?
Insider Build (xxxxx)
May 2020 Update (19041)	Yes
November 2019 Update (18363)
May 2019 Update (18362)
October 2018 Update (17763)
April 2018 Update (17134)
Fall Creators Update (16299)
Creators Update (15063)

Device form factor	Saw the problem?
Desktop	Yes
Xbox
Surface Hub
IoT

Additional context

FrameworkEventsTest.zip

[chrisglein]

@alexserov WinUI3 is more similar to UWP XAML than WPF. Are you seeing similar behavior in an app built off of inbox XAML?
@Austin-Lamb Here someone is looking at performance of subscribe/unsubscribe of events of WinUI3. Is this something you or @bartekk8 have looked into?

[alexserov]

Hello @chrisglein , I've just measured my tests for UWP XAML and WinUI3 (Preview2) for UWP, and here are the results:

Case #	Description	UWP XAML	WinUI for UWP
1	Subscribe to 1 button event with 1 method 1000 times	2	2
2	Subscribe and Unsubscribe to 1 button event with 1 method 1000 times	27	23
3	Subscribe to 1 button event with 1000 methods 1 time	44834	49764
4	Subscribe and Unsubscribe to 1 button event with 1000 methods 1 time	7264	7448
5	Subscribe to 1000 buttons event with 1 method 1 time	5	5
6	Subscribe and Unsubscribe to 1000 buttons event with 1 method 1 time	35	34

The code is the same for every project. You can find it in my attachment to the original post.

As I mentioned earlier, my main interest is in cases 5 and 6 (WinUI for Win32) since we experience the same performance issue in our application.

upd: we have our custom controls in the app; they mostly derive from Microsoft.UI.Xaml.Controls.Control. The ctor looks like follows:

public BaseControl() {
    LayoutUpdated += OnLayoutUpdated;
    Loaded += OnLoaded;
    Unloaded += OnUnloaded;
    IsEnabledChanged += OnIsEnabledChanged;
}

Since we reuse our code from our UWP project, I expect the performance should be the same or even better. Unfortunately, it is not.

[alexserov]

I've updated my initial post with the measurements for the WinUI3 Preview3. I see the progress; however, the issue still exists.

Case #	Description	WinUI 3 pre-3
1	Subscribe to 1 button event with 1 method 1000 times	0
2	Subscribe and Unsubscribe to 1 button event with 1 method 1000 times	7
3	Subscribe to 1 button event with 1000 methods 1 time	341
4	Subscribe and Unsubscribe to 1 button event with 1000 methods 1 time	5685
5	Subscribe to 1000 buttons event with 1 method 1 time	217
6	Subscribe and Unsubscribe to 1000 buttons event with 1 method 1 time	217

[chrisglein]

Thanks for the extra data, we really appreciate it.

For what it's worth this isn't necessarily true:

I expect the performance should be the same or even better

WinUI3 isn't guaranteed to have the same performance profile as UWP XAML. There are places where it may be better, places where it'll be worse, and places where it is the same. But moving the platform out of the OS into separate infrastructure will cause changes. We're working on measuring this and working to make those differences minimal/positive, but it will take time.

[chrisglein]

One addition to the stack in this case is going to be CsWinRT. There's still analysis of that happening elsewhere, which could uncover potential improvements with events specifically (e.g. this issue)

[github-actions]

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