title: Are Android.App.Application activity life cycle callbacks invoked on the UI thread?
body: <p>I'm investigating performance degradation that started occurring after an update of a third party library we use (Xamarin.Insights). During my investigation, I stopped the application during a large pause that showed a mutex lock buried within <code>Android.App.Android.OnActivityDestroyed</code>.</p>
  
  <p>The call stack shows the library utilises a registered instance of the <a href="http://developer.android.com/reference/android/app/Application.ActivityLifecycleCallbacks.html" rel="nofollow"><code>ActivityLifecycleCallbacks</code></a> interface to track activity lifecycle events in our application. I'm trying to establish if these callbacks are invoked on the UI thread.</p>
  
  <p>Intuitively I think they are invoked on the UI thread but I can't find definitive proof that confirms this.</p>
  
  <ul>
  <li>Are <code>ActivityLifecycleCallbacks</code> invoked on the UI thread?</li>
  <li>Could I have a link that provides proof of this?</li>
  </ul>