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In a current project, I have the need to make sure that a script can only run a single copy at a time. I'd like to hear comments on the sub routine below, which gets called at the beginning of a script. I'm hoping to 'solidify' it enough for reuse in my workplace (across our Unix and Win32 environments).

The latest tweak I've been contemplating is whether calling flock() on PID_FILE would gain me anything. Perhaps preventing a race condition if 2 processes were launched simultaneously?

sub single_instance{ $SIG{INT} = sub {exit()}; my ($prog) = $0 =~ m|(?:.*[/\\])?(.*)$|; my $tmp_dir = $^O =~ "MSWin32" ? "C:/Windows/Temp" : "/tmp"; my $lockfile = "$tmp_dir/$prog.pid"; local *PID_FILE; if (-e $lockfile){ open(PID_FILE, "<$lockfile") or die("single_instance(): Can't +open $lockfile: $!\n"); my $running_pid = <PID_FILE>; close(PID_FILE); chomp($running_pid); if (kill 0, $running_pid){ die("Already running as pid $running_pid\n"); } } open(PID_FILE, "+>$lockfile") or die("single_instance(): Can't ope +n $lockfile: $!\n"); print PID_FILE "$$\n"; close(PID_FILE); chmod(0666, $lockfile); eval "END {unlink '$lockfile'}"; die("single_instance(): $@\n") if($@); }

-Nitrox


In reply to Determine if script is already running by Nitrox

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