I would go with the database if that is desirable since it might well make future reporting easier to manage. But you could always use the Benchmark module to test out different methods.

As for flock and INI files, I presume you mean a typical foo.ini file for config variables. I don't see why you would have any conflicts unless the file is remote mounted over a network. Some versions of flock might have problems with that. YMMV.

The main issue is to devise a decent semaphore scheme that removes any dependence upon sleep() to synchronize the various parts other than establishing a timing loop for polling the semaphore.