title: How to lock several objects?
body: <p>I want to lock on two objects at the same time.
  Why can't I write like such code?</p>
  <pre><code>lock (obj1, obj2)
  </code></pre>
  <p>Should I always write like that?</p>
  <pre><code>lock (obj1)
  {
      lock (obj2)
      {
      }
  }
  </code></pre>
  <p>Probably this could be made simpler?
  Likely it would be better to introduce special private object, and use it for a lock...</p>