More precisely, every 1000ms send_request() function sends request to the server (see setInterval line in polling_start() function). ajax-progress-bar.php returns XML and request_handler() processes received XML. Progress value from XML has meaning of percentage completion of a job.
Here you can see the source of ajax-progress-bar.php (how is job progress emulated). In your case you will have to calculate percentage of completion and return it in XML format. Caching for ajax-progress-bar.php should be disabled. Many proxies and clients can be forced to disable caching with “header” lines pragma, cache-control and expires.
Download source code: redips6.tar.gz
11/21/2010 – Code tested with JSLint & enabled source download
06/10/2011 – Added limit of how many times to request the server (automatic demo stop)