In the context of ASP.NET, why doesn't Task.Run(…).Result deadlock when calling an async method?

Question

I created a simple WebApi project with a single controller and a single method:

public static class DoIt
{
    public static async Task GetStrAsync         


        

Answer 1

I'll give you as short answer the other way around: how to produce a deadlock:

Lets start in a Click handler that is executing synchronous and offloading some async call to a separate Task, then waiting for the result

private void MenuItem_Click(object sender, RoutedEventArgs e)
{
    var t = Task.Run(() => DeadlockProducer(sender as MenuItem));
    var result = t.Result;
}

private async Task DeadlockProducer(MenuItem sender)
{
    await Task.Delay(1);
    Dispatcher.Invoke(() => sender.Header = "Life sucks");
    return 0;
}

The async method is doing another bad thing: it tries to bring some UI change synchronously, but the UI thread is still waiting for the task result...

So basically, Task.Run is half way out and will work for a lot of well formed async code, but there are ways to break it, so its not a reliable solution.

This sample code was written in context of WPF, but I guess ASP.Net could be abused to produce similar behavior.