If the async method is single, how can it be run in the background?

I am trying to understand async / await and have read a number of articles, but I am still confused about the synchronous / asynchronous nature.

I have the following test console application:

static void Main(string[] args)
{
    var test = FooAsync();
    Console.WriteLine("After FooAsync");

    for (int i = 0; i < 100; i++)
        Console.WriteLine("After that");

    Console.ReadKey();
}

private static async Task FooAsync()
{
    Console.WriteLine("Before delay");
    await Task.Delay(1);
    Console.WriteLine("After delay");
}

      

        
        
        
      

    

The code outputs line by line:

Before delay
After FooAsync
After that
After that
After that
After that
After delay
After that
.
.

      

        
        
        
      

    

I understand that async / await will not create a separate thread to process and that at the point a FooAsync

line appears await Task.Delay(1)

, it will Main

fall back to , since the task has not finished yet since we are only running on one thread, can anyone explain what causes the method FooAsync

to run in which -or an arbitrary point inside Main

before Main

can continue?

Update I am bringing it back and i3arnon and dariogriffo are correct. The code uses multiple threads (as I've seen before, looked in the debugger, or did the obvious as ha suggested). I was confused by the "Themes" section on the next page https://msdn.microsoft.com/en-us/library/hh191443.aspx#BKMK_Threads , not realizing that "continuation" actually refers to the continuation task scheduling starts as soon as the pending task ends.