We have a Perl utility (let's call it utility.pl
) that is supposed to avoid starting if another instance of itself is already running. The way we've implemented this requirement is to check for the existence of a semaphore file, semaphore.txt
, in a particular directory. If the semaphore file exists, the utility program dies with a message saying
Either another instance of utility.pl is already running, or the file semaphore.txt needs to be deleted.
If the semaphore file doesn't exist, the utility first writes it, then does its work (which can take minutes), then unlinks it.
Is this the best way to do this, or can somebody suggest a better way?
Thank you, LanX, for the link to the thread from 2006.
What I meant by "better" was "not theoretically constituting a race condition". Also not leaving its semaphore file lying around when it crashes, which has happened. The solution that opens and locks $0
is my favorite so far, but I'm on Windows, so the second running instance dies silently without divulging my error.