After setting breakpoints and then debugging the Web Worker With Blazor WASM apps, the breakpoints are not hit

[EmilyFeng97]

REGRESSION INFO No, web worker is a new feature introduced in Preview 2. Also repro on 11.0 Preview 3

INSTALL STEPS

1. Clean Win11 x64 23h2 ENU
2. Install the latest VS 18.5 Insider 2
3. Install the latest .NET 11.0 preview 2 SDK

Platform

• Windows
• macOS
• Linux

Repro Steps

1. File > New Project > Select "Blazor WebAssembly Standalone App" > Give name "BlazorWasmApp" > Next > select ".NET 11.0" > Create

2. Right-click the Solution > Add > New Project > Select ".NET Web Worker" template > Give name "WorkerLib" > Create

3. Right-click the BlazorWasmApp project > Add > Project Reference > Check WorkerLib > OK

4. Open BlazorWasmApp.csproj and add inside :
   <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   Also add:

   <ItemGroup>
     <SupportedPlatform Include="browser" />
   </ItemGroup>
   

5. Create a new file Workers/MyWorkerMethods.cs with the following content:

   using System.Runtime.InteropServices.JavaScript;
   using System.Runtime.Versioning;
   using System.Text.Json;
   
   namespace BlazorWasmApp.Workers;
   
   [SupportedOSPlatform("browser")]
   public static partial class MyWorkerMethods
   {
       [JSExport]
       public static int Add(int a, int b) => a + b;
   
       [JSExport]
       public static string Greet(string name) => $"Hello, {name}!";
   
       [JSExport]
       public static string GetPersonJson()
           => JsonSerializer.Serialize(new { Name = "Alice", Age = 30 });
   }
   
   public record Person(string Name, int Age);
   

6. Open Pages/Home.razor and add the following code below the existing content:

   @using WorkerLib
   @using BlazorWasmApp.Workers
   @inject IJSRuntime JSRuntime
   @implements IAsyncDisposable
   
   <h3>WebWorker Demo</h3>
   <button @onclick="InitAndTest">Test WebWorker</button>
   <p>Status: @status</p>
   <p>Add result: @addResult</p>
   <p>Greet result: @greetResult</p>
   <p>JSON result: @jsonResult</p>
   
   @code {
       private WebWorkerClient? worker;
       private string status = "Not started";
       private string addResult = "", greetResult = "", jsonResult = "";
   
       private async Task InitAndTest()
       {
           status = "Initializing...";
           worker = await WebWorkerClient.CreateAsync(JSRuntime);
           status = "Ready";
   
           var sum = await worker.InvokeAsync<int>("BlazorWasmApp.Workers.MyWorkerMethods.Add", [5, 3]);
           addResult = sum.ToString();
   
           var greeting = await worker.InvokeAsync<string>("BlazorWasmApp.Workers.MyWorkerMethods.Greet", ["World"]);
           greetResult = greeting;
   
           var person = await worker.InvokeAsync<Person>("BlazorWasmApp.Workers.MyWorkerMethods.GetPersonJson", []);
           jsonResult = $"{person.Name}, Age {person.Age}";
       }
   
       public async ValueTask DisposeAsync()
       {
           if (worker != null) await worker.DisposeAsync();
       }
   }
   

7. Place a breakpoint at the addResult = sum.ToString(); line in Pages/Home.razor

8. Run the project (F5).

9. After the webpage loads successfully, click the Test WebWorker button

Note:

1. This issue also repro when place the breakpoint in MyWorkerMethods.cs file.
2. This issue does not repro when debugging if I don't set any breakpoints.
3. This issue does not repro when Ctrl + F5.

Actual Result
The WebWorker hang when debugging Blazor WASM apps in VS

Error Log

[github-actions]

Triage Summary

Area: area-blazor — Issue involves Blazor WebAssembly's WebWorkerClient API and the WASM debugging experience.
Type: bug — Reproducible behavior: WebWorkerClient.CreateAsync hangs during a debug session when any breakpoint is set. Works fine without breakpoints or without the debugger attached (Ctrl+F5).

Regression Info

• Previously working version: Not explicitly stated
• Broken since: .NET 11.0 Preview 2 (also confirmed on Preview 3)
• The reporter notes the issue under "REGRESSION INFO" and confirmed it reproduces on both .NET 11.0 Preview 2 and Preview 3. No earlier working version is mentioned, so it's unclear if this ever worked. The team may want to confirm if this was ever functional in a prior .NET version.

Potential Duplicates

• None found

Notes

• The hang appears to occur specifically during WebWorkerClient.CreateAsync() when the VS debugger is paused at a breakpoint. This could be a deadlock/synchronization issue between the main thread debugger pause and the Web Worker thread initialization.
• This may involve interaction between the VS debugger (VS 18.5 Insider) and the ASP.NET Core Blazor WASM runtime — a cross-team investigation with Visual Studio debugger team may be needed.
• Error log section appears empty in the report; requesting logs/browser console output might help diagnose further.

Generated by Issue Triage Agent for dotnet/aspnetcore for issue #65823 · ◷

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[ilonatommy]

@EmilyFeng97 the error picture nor log got saved.

[EmilyFeng97]

@EmilyFeng97 the error picture nor log got saved.

When the bug reproduce, I couldn't get any error messages in vs or the browser console, so I added a gif to help describe it.

This is a visualstudio-js-debugger file found in temp, hope it helps.
visualstudio-js-debugger.txt

[KristofferStrube]

I had a similar error in my WebWorker library that has the same fundamental structure as the new template. In my case the debugger was detached after the web worker has started.
KristofferStrube/Blazor.WebWorkers#2

[EmilyFeng97]

Verify this issue on the 18.5 Insider 3 and the latest .NET 11.0 Preview 3[11.0.100-preview.3.26174.112], it still reproduce.
@ilonatommy Could you please take a look?

[ilonatommy]

Verify this issue on the 18.5 Insider 3 and the latest .NET 11.0 Preview 3[11.0.100-preview.3.26174.112], it still reproduce. @ilonatommy Could you please take a look?

The fix that got merged was supposed to fix only the hang in the old debugger. Breakpoints still won't be hit correctly even with that fix. As a reproduction, do you refer to hanging or to being able to hit a breakpoint?