title: How to make only one instance of the same script running at any time
body: <p>Let's suppose we have a long script: Foo.pyx<br>
  If I execute it two times, they are going to run simultaneously.</p>
  
  <p>How can I terminate the first one if I execute it two times?</p>
  
  <p>Edit: terminating the later ones can also work, I just want only one instance to run at any time.</p>