title: How to get Executor for main thread on API level < 28
body: <p>On API level 28(Pie) a new method is introduced in the <code>Context</code> class to get Executor for the main thread <a href="https://developer.android.com/reference/android/content/Context#getMainExecutor()" rel="noreferrer"><code>getMainExecutor()</code></a>.</p>
  
  <p>How to get this executor on API level below 28?</p>