title: Maintaining state between browser tabs in PHP
body: <p>I'm building a web application that allows users to run a query against one of two databases. They are only allowed to submit 1 query to each database at a time. Currently, I'm setting $_SESSION['runningAdvancedQuery'] (for instance) to let me know if they're running a query. This is to prevent someone from opening up a 2nd browser tab and hitting the resource again. It works great except...</p>
  
  <p>If I start a query in a tab, then close that tab before it finishes, the flag does not get unset. Therefore, if I reopen the page, I cannot run any queries because it thinks I have one still running. Anyone have advice for getting around this?</p>