title: How to have only one instance of program run scheduled task?
body: <p>My software runs on multiple machines against a single database.</p>
  
  <p>I would like a task to be performed within the software on a daily basis - eg. at midday.</p>
  
  <p>How can I ensure this task is:</p>
  
  <ul>
  <li>performed only once per day,</li>
  <li>performed no matter which machine/user happens to be running the software that day, and</li>
  <li>not performed simultaneously with any other instances of the software?</li>
  </ul>