Investigate the CheckAccess pattern in Blazor

[rynowak]

See: #11930 (comment)

I suspect that this test isn't implemented correctly, and as a result it's possible to run work concurrently on the sync context.

[rynowak]

I don't think there's an issue here. I tested with the following code:

@code  { 

    protected override void OnInitialized()
    {
        Task.Run(() =>
        {
            Console.WriteLine($"SynchronizationContext.Current: {System.Threading.SynchronizationContext.Current}");

            _ = InvokeAsync(() =>
            {
                Console.WriteLine($"SynchronizationContext.Current: {System.Threading.SynchronizationContext.Current}");
                System.Threading.Interlocked.Increment(ref counter);
                for (var i = 0; i < 10; i++)
                {
                    Console.WriteLine($"A: {counter}");
                }
                System.Threading.Interlocked.Decrement(ref counter);
                Console.WriteLine($"SynchronizationContext.Current: {System.Threading.SynchronizationContext.Current}");
            });
        });

        System.Threading.Interlocked.Increment(ref counter);
        for (var i = 0; i < 10; i++)
        {
            Console.WriteLine($"A: {counter}");
        }
        System.Threading.Interlocked.Decrement(ref counter);
    }

    int counter = 0;
}

If the counter ever showed two, this would indicate a bug.

When you start a new task via Task.Run it won't inherit the sync context. Therefore when you call InvokeAsync inside it, it will do a proper dispatch.

So there is one way you could break our invariant, which would be to set the your current sync context to ours, and then call InvokeAsync. This doesn't seem like something that will happen in valid/reasonable code.