title: how to use async and await in timer
body: <p>My windows app's requirement are:</p>
  
  <ol>
  <li><p>Using HttpWebRequest get web request/response every 3 seconds in one thread.(total is about 10 threads for doing this web request/response.)</p></li>
  <li><p>Each thread use some global variables.</p></li>
  </ol>
  
  <p>I want to use a System.Timers.Timer and async and await. But I don't know that is a best way for high performance. And then how to test them. I am a green in C#.</p>