How can I ensure I have only one instance of a PHP script running via Apache?

Question

I have an index.php script that I use as a post-commit URL on a Google Code site. This script clones a directory and builds a project that may take some work.

Answer 1

Only if you save the state of the running script and check when the script starts if an other script is currently active.

For example to save if a script is running you could do something like this:

$state = file_get_contents('state.txt');

if (!$state) {
   file_put_contents('state.txt', 'RUNNING, started at '.time());

   // Do your stuff here...

   // When your stuff is finished, empty file
   file_put_contents('state.txt', '');
}