For this sort of problem my preferred solution is to simply take an exclusive non blocking lock on a file with flock. Then the operating system does the checking for me. For nice error messages I usually let the process that takes the lock write its pid in the file (or another file if I need it to work on Windows) so that a program that fails to take the lock can just read the pid from the lockfile and mention that in a warning message.

Don't delete the lockfile when you are done by the way. That can lead to subtle races.

In reply to Re: Easiest way to protect process from duplication. by thospel
in thread [Solved]Easiest way to protect process from duplication. by kazak

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