Canceling JSHost.ImportAsync fails because dynamic_import in invoke-js.ts is not cancelable

[nikonthethird]

Description

TLDR:

The cancellation token given to JSHost.ImportAsync does not work because the underlying JS function called by ImportAsync does not return a Promise that is "controllable" (outfitted with a special symbol).

// Repro here: https://github.com/nikonthethird/ImportAsyncError, or paste this code into an InitializeAsync  of a page in Blazor WASM:
var cts = new CancellationTokenSource();
cts.Cancel();
await JSHost.ImportAsync("hello", "world.js", cts.Token);

The code above fails with an exception because dynamic_import is not controllable (the promise generated by the function is not wrapped using wrap_as_cancelable_promise like for example http_wasm_fetch is).

Description

After upgrading to .NET 7, an application of mine has been throwing the following error messages in the log:

"Microsoft.AspNetCore.Components.WebAssembly.Rendering.WebAssemblyRenderer"]: Unhandled exception rendering component: "Error: Assert failed: Promise is not controllable"
at System.Runtime.InteropServices.JavaScript.CancelablePromise._CancelPromise(IntPtr )
   at System.Runtime.InteropServices.JavaScript.CancelablePromise.CancelPromise(Task )
   at System.Net.Http.BrowserHttpInterop.<>c__DisplayClass13_0`1[[System.Int32, System.Private.CoreLib, Version=7.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].<CancelationHelper>b__0()
   at System.Threading.CancellationToken.<>c.<Register>b__12_0(Object )
   at System.Threading.CancellationTokenSource.Invoke(Delegate , Object , CancellationTokenSource )
   at System.Threading.CancellationTokenSource.CallbackNode.<>c.<ExecuteCallback>b__9_0(Object )
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext , ContextCallback , Object )
--- End of stack trace from previous location ---

This is what I discovered:

• JSHost.ImportAsync calls JavaScriptImports.DynamicImport, then uses the CancelationHelper function to call CancelablePromise.CancelPromise when the cancellation token fires.
• CancelPromise calls mono_wasm_cancel_promise which throws the error above when the promise is not controllable, meaning when it does not have the promise control symbol.
• However, the promise returned by JavaScriptImports.DynamicImport is directly from the async function dynamic_import, which is NOT wrapped with wrap_as_cancelable_promise like all the others that use CancelationHelper are.

Since .NET 7 uses the [JSImport] source generator internally, I suspect the exceptions I am experiencing also come from some internal JSHost.ImportAsync calls.

Reproduction Steps

@page "/"
@using System.Runtime.InteropServices.JavaScript

<h1>Hello, world!</h1>

@if (error is not null) {
    <p>@error</p>
}

@code {
    private String? error;

    protected override async Task OnInitializedAsync() {
        var cts = new CancellationTokenSource();
        cts.Cancel();

        try {
            await JSHost.ImportAsync("hello", "world.js", cts.Token);
        } catch (Exception ex) {
            error = ex.ToString();
        }
        
    }
}

A reproduction can also be found here.

Expected behavior

The import should be cancelled.

Actual behavior

Error: Assert failed: Promise is not controllable

Regression?

Yes, no problem with my code in .NET 6.
Note that I do not even use JSHost.ImportAsync in my code directly, but .NET 7 itself uses the new [JSImport] source generated, and this is where I expect the error to occur.

Known Workarounds

None so far.

Configuration

.NET 7.0.1
Ubuntu 20.04 / Firefox
Windows 10 22H2 / Chromium
x64
It happens in all cases, I don't know why I even provided this info...

Other information

No response

[ghost]

Tagging subscribers to 'arch-wasm': @lewing
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Issue Details

---

Description

TLDR:

The cancellation token given to JSHost.ImportAsync does not work because the underlying JS function called by ImportAsync does not return a Promise that is "controllable" (outfitted with a special symbol).

// Repro here: https://github.com/nikonthethird/ImportAsyncError, or paste this code into an InitializeAsync  of a page in Blazor WASM:
var cts = new CancellationTokenSource();
cts.Cancel();
await JSHost.ImportAsync("hello", "world.js", cts.Token);

The code above fails with an exception because dynamic_import is not controllable (the promise generated by the function is not wrapped using wrap_as_cancelable_promise like for example http_wasm_fetch is).

Description

After upgrading to .NET 7, an application of mine has been throwing the following error messages in the log:

"Microsoft.AspNetCore.Components.WebAssembly.Rendering.WebAssemblyRenderer"]: Unhandled exception rendering component: "Error: Assert failed: Promise is not controllable"
at System.Runtime.InteropServices.JavaScript.CancelablePromise._CancelPromise(IntPtr )
   at System.Runtime.InteropServices.JavaScript.CancelablePromise.CancelPromise(Task )
   at System.Net.Http.BrowserHttpInterop.<>c__DisplayClass13_0`1[[System.Int32, System.Private.CoreLib, Version=7.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].<CancelationHelper>b__0()
   at System.Threading.CancellationToken.<>c.<Register>b__12_0(Object )
   at System.Threading.CancellationTokenSource.Invoke(Delegate , Object , CancellationTokenSource )
   at System.Threading.CancellationTokenSource.CallbackNode.<>c.<ExecuteCallback>b__9_0(Object )
   at System.Threading.ExecutionContext.RunInternal(ExecutionContext , ContextCallback , Object )
--- End of stack trace from previous location ---

This is what I discovered:

• JSHost.ImportAsync calls JavaScriptImports.DynamicImport, then uses the CancelationHelper function to call CancelablePromise.CancelPromise when the cancellation token fires.
• CancelPromise calls mono_wasm_cancel_promise which throws the error above when the promise is not controllable, meaning when it does not have the promise control symbol.
• However, the promise returned by JavaScriptImports.DynamicImport is directly from the async function dynamic_import, which is NOT wrapped with wrap_as_cancelable_promise like all the others that use CancelationHelper are.

Since .NET 7 uses the [JSImport] source generator internally, I suspect the exceptions I am experiencing also come from some internal JSHost.ImportAsync calls.

Reproduction Steps

@page "/"
@using System.Runtime.InteropServices.JavaScript

<h1>Hello, world!</h1>

@if (error is not null) {
    <p>@error</p>
}

@code {
    private String? error;

    protected override async Task OnInitializedAsync() {
        var cts = new CancellationTokenSource();
        cts.Cancel();

        try {
            await JSHost.ImportAsync("hello", "world.js", cts.Token);
        } catch (Exception ex) {
            error = ex.ToString();
        }
        
    }
}

A reproduction can also be found here.

Expected behavior

The import should be cancelled.

Actual behavior

Error: Assert failed: Promise is not controllable

Regression?

Yes, no problem with my code in .NET 6.
Note that I do not even use JSHost.ImportAsync in my code directly, but .NET 7 itself uses the new [JSImport] source generated, and this is where I expect the error to occur.

Known Workarounds

None so far.

Configuration

.NET 7.0.1
Ubuntu 20.04 / Firefox
Windows 10 22H2 / Chromium
x64
It happens in all cases, I don't know why I even provided this info...

Other information

No response

Author:	nikonthethird
Assignees:	-
Labels:	arch-wasm, untriaged, area-System.Runtime.InteropServices.JavaScript
Milestone:	-

[radical]

/cc @pavelsavara @maraf

[pavelsavara]

thanks @nikonthethird , your explanation is perfect :)