title: iOS - Ensure execution on main thread
body: <p>I want to know how to call my <code>function</code> on the <em>main thread</em>.</p>
  
  <p>How do I make sure my <code>function</code> is called on the <em>main thread</em>?</p>
  
  <p><em>(this follows a previous <a href="https://stackoverflow.com/questions/11054457/ios-concurrent-access-to-memory-resources">question</a> of mine).</em></p>