Problem with using Wait() method in ASP.NET MVC.

The issue is clearly illustrated by this code:

public class TestCommand: IRequest
{ }

public class TestHandler : IAsyncRequestHandler<TestCommand>
{
    public Task Handle(TestCommand message)
    {
        return Task.Factory.StartNew(() =>
        {
            throw new ApplicationException();
        });
    }
}

public class HomeController : Controller
{
    private readonly IMediator _mediator;

    public HomeController(IMediator mediator)
    {
        _mediator = mediator;
    }

    public  ActionResult Index()
    {
        try
        {
            _mediator.Send(new TestCommand()).Wait();  // deadlock 
        }
        catch (Exception e)
        {
            // unreachable block 
        }

        return View();
    }
}

If i use await operator catch block is reachable:

try
{
   await _mediator.Send(new TestCommand());
}
catch (Exception e)
{
    // OK
}

but when use Wait() method i have a problem, because catch block is unreachable.

try
{
   _mediator.Send(new TestCommand()).Wait(); // deadlock 
}
catch (Exception e)
{
    // unreachable block 
}

[sq735]

Perhaps I found a lines of code which can cause problems, for example the deadlock. I think we needs to use ConfigureAwait(false).

RequestHandler.cs

RequestHandler.cs

RequestPostProcessorBehavior.cs

RequestPostProcessorBehavior.cs

RequestPreProcessorBehavior.cs

RequestPreProcessorBehavior.cs

P.S. This can be useful Don’t Block on Async Code

[mycroes]

I agree about the ConfigureAwait(false). MediatR doesn’t depend on the context, so there’s no need to have continuations run on the calling context. If a higher level does depend on context, that’ll still work as-is.