In .net 9 blazor wasm mode, unhandled exceptions in asynchronous methods will cause the Runtime to crash

[dashiell-zhang]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

In .net 9 blazor wasm mode, unhandled exceptions in asynchronous methods will cause the Runtime to crash

In .net 9, if the method is asynchronous and an unhandled exception is returned, the entire blazor wasm .net runtime will crash directly. After the crash, clicking on any interface will be invalid, and only error messages will continue to be output. And this crash cannot be captured by ErrorBoundary.

When an unhandled exception is generated in a non-asynchronous method, it will not crash.

As shown in the following two codes

@page "/counter"

<PageTitle>Counter</PageTitle>

<h1>Counter</h1>

<p role="status">Current count: @currentCount</p>

<button class="btn btn-primary" @onclick="IncrementCount">Click me</button>

<button class="btn btn-primary" @onclick="IncrementCountBug">Click me Bug</button>

@code {
    private int currentCount = 0;

    private  void IncrementCount()
    {
        currentCount++;

        if (currentCount == 3)
        {
            throw new Exception("NEW BUG");
        }
    }


    private async void IncrementCountBug()
    {
        await Task.Delay(1);

        currentCount++;

        if (currentCount == 3)
        {
            throw new Exception("NEW BUG");
        }
    }
}

1.mp4

2.mp4

When an exception occurs in the IncrementCount method, it will simply throw an exception, but this will not affect subsequent operations. However, when the IncrementCountBug throws an exception, it will directly cause the entire runtime to crash, and any subsequent button clicks will not work.

After switching to .net 6 .net 7 .net 8, the IncrementCountBug method will not cause a crash. This only happens in .net 9.

There is a test later that changes private async void IncrementCountBug() to private async Task IncrementCountBug() and the crash will not occur. So the conclusion is that if an unhandled exception is thrown in async void, it will directly cause the .net 9 wasm runtime to crash.

https://github.com/dashiell-zhang/BlazorAppTempIssues.git

Expected Behavior

No response

Steps To Reproduce

No response

Exceptions (if any)

No response

.NET Version

9.0.100

Anything else?

No response

[garrettlondon1]

And this crash cannot be captured by ErrorBoundary

#56413

• Have you tried the approach of WrappingComponent around all WASM components to see if that will work with Error Boundary?

Onclick handlers will not work with ErrorBoundary unless wrapped inside of another Interactive component

[javiercn]

@dashiell-zhang thanks for contacting us.

This is no different than any other .NET process. If you throw an exception from a background thread and goes unhandled it will tear down the process.

The example you provide is considered a bad practice (async void) precisely because the framework has no way to observe the result of the task, causing the entire process to go down in the event of an exception.

You should always use Task or ValueTask as a result of an async operation.

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