title: Create new session which shares memory and variables of an existing session
body: <p>I already have a TensorFlow session initialized, with a couple of variables in it.</p>
  
  <p>I want to create a new session as cheaply as possible, and reuse the existing variables (such that I don't need to allocate new memory, and I don't need to initialize the variables again), and maybe also reuse the same memory allocator.</p>
  
  <p>Is that possible? How?</p>
  
  <p>(To answer the obligatory question, why I want to do this: Because of <a href="https://stackoverflow.com/questions/57707445/how-to-add-control-input-to-an-op-after-it-was-run-by-a-session">this</a>. Also because I just want to know.)</p>