just wanted to say that you will most likely fail if you use a separate lock file together with register_shutdown_function.
my script did some different actions... resizing pictures, rotating them and this stuff. it needed a "database" file to get the correct file locations. this database file also stored some flags. and of course the script had to save that file when it was done.
because of my script exited on many different points depending on the action i used register_shutdown_function to save the file. it wanted to use a locking system to be sure the script doesn't overwrite the data another process had written into it some microseconds before. i was running on windows 2000 and apache2 on my developing machine, and flock always returned true for some reason... so i used a separate lock file. the script looked for it at the beginning and exited if it was found. otherwise it created it. but this file had to be deleted at the end. i put the unlink command into the registered shutdown-function but it never deleted the file. i tried clearstatcache and some other stuff but it didn't help.
maybe this helps someone.
