title: handling concurrency in cron php
body: <p>I am setting up a cron job that executes a script page.php every minute
  I wanted to know about the concurrency.
  The script it self take 15 minutes to complete, so how the cron will run?</p>
  
  <pre><code>Lets take a time frame of 15 minutes, how many crons will run in that time? 1 or 15?
  
  will cron runs till its completion or it can be interrupted?
  
  Thanks.
  </code></pre>