A ++ for thinking about lock deletion. This is a basic concurrency issue that many programmers I've known fail to grasp. Some just ignore the problem since it may not occur often and it didn't occur during their tests. I've seen others waste a lot of effort writing and rewriting their code trying to somehow eliminate this race condition by sheer force of will.
in reply to File Locking plus delete Lockfile question
In the general case you must know for sure that a lock cannot be accessed before you try to destroy it. As others have mentioned in general you need a higher level lock, or you need a special case (e.g. the machine is starting after a reboot and the app is known to have not started yet; the app is starting/completing and it knows it has no other threads running; etc). The special case may not work very well if your app is designed to run for weeks/months at a time.