Detecting user_abort when using ob_start().

Hello there, I have a script which is called using ajax. This script can take a while executing. Now it sometimes happens that a user aborts a connection, like stop the ajax request. This won't stop the php script from executing. Now i need some way to detect if the user has stoped/aborted the connection. I tryed to use connection_aborted and/or connection_status. But this doesn't seem to work or something. I Tryed to search for a sollution, but not much luck. Also, i use ob_start() because of headers that needs to be sent and to compress etc.. Thx in advance.