Why does the Task.WhenAny not throw an expected TimeoutException?

Question

Please, observe the following trivial code:

class Program
{
    static void Main()
    {
        var sw = new Stopwatch();
        sw.Start();
        try
           


        

Answer 1

Task.WhenAny doesn't rethrow exceptions from the individual tasks (unlike Task.WhenAll):

"The returned task will complete when any of the supplied tasks has completed. The returned task will always end in the RanToCompletion state with its Result set to the first task to complete. This is true even if the first task to complete ended in the Canceled or Faulted state."

From Task.WhenAny

That means that it will complete successfully no matter what without any type of exceptions.

To actually rethrow the exception of the individual completed task you need to await the returned task itself:

var completedTask = await Task.WhenAny(tasks); // no exception
await completedTask; // possible exception

Or in your case:

Task.WhenAny(RunAsync()).GetAwaiter().GetResult().GetAwaiter().GetResult();