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
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