title: What happens to an `awaiting` thread in C# Async CTP?
body: <p>I've been reading about the new async <code>await</code> keyword and it sounds awesome, but there is one key question I haven't been able to find the answer for in any of the intro videos I've watched so far (I also read the whitepaper a while back).</p>
  
  <p>Suppose I have a call to <code>await</code> in a nested function on the main UI thread. What happens to the thread at this point? Does control go back to the message loop and the UI thread is free to process other inputs?</p>
  
  <p>When the awaited task completes, does the entire stack get pushed onto a message queue, such that control will return through each of those nested functions, or is something else entirely happening here?</p>
  
  <p>And secondly (while I have your attention), I don't really understand why asynchronous methods need to be labeled with <code>async</code>. Can't any method be executed asynchronously? What if I want to execute a method asynchronously but it doesn't have an async keyword--is there a way to do that simply?</p>
  
  <p>Cheers. :)</p>
  
  <p><strong>Edit:</strong>
  Admittedly if I could get the sample code compiling I could probably just figure that out myself, but for one reason or another I'm running into a block there. What I really want to know is to what extent does a continuation continue... does it freeze the entire call stack, to resume it when the task completes, or does it only go back so far? Does a function itself need to be marked as async in order to support continuation, or (as I asked originally) does it continue the entire call stack?</p>
  
  <p>If it <em>doesn't</em> freeze the entire call stack, what happens when the async await hits a non-async calling function? Does it block there? Wouldn't that defeat the point of await? I hope you can see that I'm missing some understanding here that I hope someone can fill in so I can continue to learn this.</p>