Extension Cleanup

Is there a set of functions within an extension that is called automatically by the ZEND engine framework to "initialize" and "deinitailize" the extension? In a particular PHP script, a user may call a method that sets up an environment. I cannot always rely on the user to call the cleanup API method at the end of the script. In that event, I would like my extension to automatically cleanup after itself when the script completes. Is there anyway to do this?