title: What is Main Thread Checker in Xcode
body: <p>I checked what's new in Xcode 9 documentation and I found this </p>
  
  <p><a href="https://i.stack.imgur.com/UaLQD.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/UaLQD.png" alt="enter image description here"></a></p>
  
  <p>But i didn't understand what is that how I can use this with new Xcode 9.</p>