This was well written and informative, but I think I still see a bug in this code. After closing the file and opening it for read/write access but before putting the exclusive lock on it, someone else could swoop in and read the file...which would be minus your current entry, as it hasn't been added yet. After adding your entry, the previous persons then add theirs, minus yours. So the file is corrupted. Two alternatives: Append to the file instead of clearing it out OR open it for read/write from the very beginning with exclusive control. Thoughts?