Cannot call synchronous C# methods for Blazor Web App and WasmEnableThreads

[nealles]

1. Create Blazor Web App wth InteractiveWebAssembly rendering
2. Added to Program.cs for the Client:

builder.Services.AddBlazorJSRuntime();
await builder.Build().BlazorJSRunAsync();

4. Modify Counter.razor like this:

@page "/counter"
@using SpawnDev.BlazorJS
@using SpawnDev.BlazorJS.JSObjects

@rendermode @(new InteractiveWebAssemblyRenderMode(false))

<PageTitle>Counter</PageTitle>

<h1>Counter</h1>

<p role="status">Current count: @currentCount</p>
<button class="btn btn-primary" @onclick="IncrementCount">Click me</button>
<p>@message</p>

@code {
    private string message = "Not clicked yet";
    private int currentCount = 0;

    private string status = "";

    [Inject]
    BlazorJSRuntime JS { get; init; }

    private void IncrementCount()
    {
        var numbers = new object[] { 5, 15, 25 };
        var max = JS.CallApply<int>("Math.max", numbers);
        Console.WriteLine($"Max: {max}");
        currentCount++;
        message = $"Clicked! Thread: {Environment.CurrentManagedThreadId}";
        Console.WriteLine($"Button clicked on thread: {Environment.CurrentManagedThreadId}");
    }
}

4. Run it and try to change a page to Counter ASAP and click a button "Click me".
5. You'll see an error in the console:

Uncaught Error: Cannot call synchronous C# methods.
    at Dn (managed-exports.ts:308:23)
    at Object.<anonymous> (invoke-cs.ts:327:17)
    at Vr.St._internal.updateRootComponents (blazor.web.b9228eflpl.js:1:175568)
    at blazor.web.b9228eflpl.js:1:194816
    at Pi.updateWebAssemblyRootComponents (blazor.web.b9228eflpl.js:1:195013)
    at Pi.refreshRootComponents (blazor.web.b9228eflpl.js:1:194498)
    at blazor.web.b9228eflpl.js:1:192714

• It does not happen if WasmEnableThreads = false
• Sometimes it is enough to click a link Counter, sometimes the issue happens after one click, sometimes I need to click several times
• The issue itself does not bother me because it happens once and var max = JS.CallApply<int>("Math.max", numbers); calculates after this issue correctly but I can not use Shared Worker because of this issue. I see that CallApply is used when I inject the WebWorkerService.
• It seems to me it is connected to the server prerender

[LostBeard]

It does not happen if WasmEnableThreads = false

I have done zero testing with Workers with WasmEnableThreads enabled, so I will need to look into that.

but I can not use Shared Worker because of this issue

I am failing to see what this has to do with Shared Workers, which are not even used on this page... how is it related?

I will say this even though it does not seem to be the problem here, but you may come across it using threads.

• You cannot use Javascript interop inside threads (WasmEnableThreads threads) other than the main thread. You will get an exception.

[LostBeard]

And just an FYI... The fastest way for me to help you is for YOU to make it easy for me to reproduce YOUR issue. In other words... if you want it fixed fast, create a minimal project repo that reproduces the issue and share it with me. When I have to write an entire test project to help YOU and I am guessing at what you did for most of the setup... It wastes my time and leads to miscommunication or failure to reproduce the issue. You are asking for my help, and I am glad to help, but don't put the entire burden of me helping you, ON ME. I love to help but I have a finite amount of time. Thank you for reporting issues you find. 🖖

[nealles]

I have added a demo project to your WebWorkers repository because my demo project contains webworkers and it is much easier to reproduce the issue with webworkers than to reproduce the issue without workers.
If you have questions or problems to get my demo project or other questions please let me know.
LostBeard/SpawnDev.BlazorJS.WebWorkers#27 (comment)