title: Interrupt a reactive chunk in Shiny
body: <p>I have a Shiny app in which I have to run some lengthy calculations. These calculations use inputs from the user. I'm avoiding having a run button and would instead like to re-evaluate this chunk after the user hasn't changed the inputs for a certain duration. I'm able to accomplish this behaviour with <code>invalidate</code>.</p>
  
  <p>However, if the chunk's evaluation is already underway and the user changes inputs in the middle, then the evaluation still continues with the previous values. I'd like to interrupt and terminate the execution with old values. How can I accomplish this?</p>