Debugger locks up the app when there are many threads/web requests

[mattleibow]

Type: Bug

Not sure who or what is to blame here, but something is causing my app to freeze and the debugger seems to just block on exceptions.

If you run this app with the debugger on Mac Catalyst it will freeze when scrolling quickly. But, if you launch without the debugger, it works fine. Also, if you scroll slow enough so that only 1 or 2 images scroll on screen at a time, then the images load - even with the debugger.

Swapping to labels also work fine.

Images in maui are downloaded using HttpClient, so something is happening when the app starts requesting many images and then cancelling them. I will try reproduce without UI controls as soon as I can.

• Maui: DebuggerTests.zip
• Mac Catalyst: DebuggerMacCatalystTests.zip

Extension version: 2.62.18
VS Code version: Code - Insiders 1.97.0-insider (Universal) (d226a2a497b928d78aa654f74c8af5317d3becfb, 2025-01-22T05:05:14.565Z)
OS version: Darwin arm64 23.6.0
Modes:

System Info

Item	Value
CPUs	Apple M1 Pro (8 x 2400)
GPU Status	2d_canvas: enabled canvas_oop_rasterization: enabled_on direct_rendering_display_compositor: disabled_off_ok gpu_compositing: enabled multiple_raster_threads: enabled_on opengl: enabled_on rasterization: enabled raw_draw: disabled_off_ok skia_graphite: disabled_off video_decode: enabled video_encode: enabled webgl: enabled webgl2: enabled webgpu: enabled webnn: disabled_off
Load (avg)	53, 49, 44
Memory (System)	32.00GB (0.25GB free)
Process Argv	--crash-reporter-id 6698d004-6faf-44a5-a725-f730c3f1de63
Screen Reader	no
VM	0%

A/B Experiments

vsliv368:30146709
vspor879:30202332
vspor708:30202333
vspor363:30204092
vscod805:30301674
vsaa593cf:30376535
py29gd2263:31024238
c4g48928:30535728
962ge761:30841072
9b8hh234:30694863
pythonnoceb:30776497
dsvsc014:30777825
dsvsc015:30821418
pythonmypyd1:30859725
2e7ec940:31000449
pythontbext0:30879054
cppperfnew:30980852
pythonait:30973460
dvdeprecation:31040973
dwnewjupytercf:31046870
2f103344:31071589
nativerepl1:31134653
pythonrstrctxt:31093868
nativeloc1:31118317
cf971741:31144450
e80f6927:31120813
iacca1:31150324
notype1:31143044
dwcopilot:31158714
h409b430:31177054
c3hdf307:31184662
6074i472:31201624
dwoutputs:31217127
8did9651:31218798
9064b325:31222308
copilot_t_ci:31222730

[mattleibow]

Source code for the lazy (after dotnet new maui):

<CollectionView x:Name="cv">
    <CollectionView.ItemTemplate>
        <DataTemplate>
            <Grid Padding="6">
                <Image
                    Source="{Binding Image}"
                    Aspect="AspectFill"
                    HeightRequest="100"
                    WidthRequest="100"/>
            </Grid>
        </DataTemplate>
    </CollectionView.ItemTemplate>
</CollectionView>

public partial class MainPage : ContentPage
{
	public MainPage()
	{
		InitializeComponent();

		var items = new List<Item>();

		for (var i = 0; i < 1085; i++)
		{
			items.Add(new Item
			{
				Image = $"https://picsum.photos/100/100?image={i}"
			});
		}

		cv.ItemsSource = items;
	}

	class Item
	{
		public string? Image { get; set; }
	}
}

[mattleibow]

Added a mac catalyst sample that also freezes.

[mattleibow]

I could simplify this in mac catalyst a bit more:

public async void DoWork()
{
	await Task.Delay(1000);

	Debug.WriteLine("Hello, World!");

	for (int i = 0; i < 1100; i++)
	{
		var cancel = (i % 100) != 0;

		Debug.WriteLine($"Starting {i} => cancel: {cancel}");

		_ = NewMethod(i, cancel);

		await Task.Delay(100);
	}

	Debug.WriteLine("Done");
}

static async Task NewMethod(int item, bool cancel)
{
	try
	{
		var cts = new CancellationTokenSource();

		if (cancel)
			cts.CancelAfter(250);

		await Task.Run(async () => {
			await Task.Delay(1000, cts.Token);
		}, cts.Token);

		Console.WriteLine($"{item} => done");
	}
	catch (Exception ex)
	{
		Debug.WriteLine($"{item} => {ex.Message}");
	}
}

[gregg-miskelly]

A few questions:

1. By "freeze" do you mean that it will pause for a while (say a second or two)? Or that it will hang and never recover?
2. What version of .NET are you targeting?
3. Do you have Just My Code enabled? (it is on by default)
4. If it is hanging completely, what happens if you hit the pause key?
5. If you look in the debug console, you should see a line for all the cancellation exceptions the code you included has. How many do you see?

The performance of .NET Exceptions under the debugger is several orders of magnitude worse than when a debugger is attached when it is not, especially if Just My Code isn't enabled. So, I am guessing that is what you are experiencing. But we will see.