title: Perform requests with Retrofit inside custom Runnable
body: <p>I am migrating from <code>Volley</code> to a custom implementation using <code>Retrofit</code>, but I'm trying to add to my implementation some of the <code>Volley</code> features that I liked, for example</p>
  
  <p><strong>RequestQueue.cancel(String tag)</strong></p>
  
  <p>If the <code>Request</code> has the requested tag, then it's canceled by setting a <code>boolean</code> value, <code>mCanceled</code>, to true. The <code>run</code> method checks this value and returns if it's true.
  To be able to reproduce this with <code>Retrofit</code> I should be able to use my custom class implementing <code>Runnable</code> instead of the default one, where I have a <code>mTag</code> and a <code>mCanceled</code> field. 
  Moreover, <code>Volley</code> was also able to set such flag inside the active <code>Thread</code>s and immediately stop them. My <code>cancelAll</code> method, that I've already implemented, just drains the queue to another queue, but isn't able to access the active threads.
  Is it possible to achieve the same results with <code>Retrofit</code> and <code>ThreadPoolExecutor</code>?</p>