cannot replicate deadlock on async await

Question

I expect deadlock occurs on below code:

static async Task<int> DelayAndReturnAsync(int val)
{
    await Task.Delay(TimeSpan.FromSeconds(val));
    return val;
}

static async Task<int> ProcessTaskAsync()
{
    var taskA = await DelayAndReturnAsync(3);
    int num = taskA++;
    return num;
}

static void Main(string[] arg)
{
    var testTask = ProcessTaskAsync();
    testTask.Wait();
    Console.WriteLine("Done");
}

As the main thread(current context) is put on wait after calling ProcessTaskAsync() and being blocked on teskTask.Wait(), it cannot go back to the method and continue the rest of the code when DelayAndReturnAsync() completed.The main thread will wait for ProcessTaskAsync to complete while ProcessTaskAsync is waiting for it(the original context) to continue with the rest of the code. Thus a deadlock.

Please let me know if there is anything wrong with my understanding. I was originally trying to replicate a deadlock and test the solution which uses ConfigureAwait(false) method on ProcessTaskAsync. e.g. ProcessTaslAsync.ConfigureAwait(false).

Answer 1

That deadlock can only happen in the presence of a SynchronizationContext which isn't present by default in console apps. Since there's no SynchronizationContext to begin with it's as if every await implicitly adds ConfigureAwait(false).

You can try it in a UI or asp.net application or even better add a SynchronizationContext to your test with Stephen Cleary's AsyncContext:

"The AsyncContext type provides a context for executing asynchronous operations. The await keyword requires a context to return back to; for most programs, this is a UI context, and you don't have to worry about it. ASP.NET also provides a proper context and you don't have to use your own.

However, Console applications and Win32 services do not have a suitable context, and AsyncContext or AsyncContextThread could be used in those situations."