package My::ThereCanBeOnlyOne;
use strict;
use LockFile::Simple;

my $Lock;

sub import {
  my $self  = shift;
  my $name  = shift || 'therecanbeonlyone';
  my %args  = @_;

  # Using /tmp allows an internal denial of service attack.
  my $lockfile    = "/tmp/$name.pid";
  my $locker = LockFile::Simple->make(-autoclean => 0, %args);
  $Lock = $locker->lock($lockfile, '%f')
    and return 1;

  open(LOCKFILE, "< $lockfile")
    or die __PACKAGE__."Unable to open $lockfile: $!";
  my $other_pid = <LOCKFILE>;
  close(LOCKFILE);
  chomp($other_pid);
  die __PACKAGE__.": $name: $other_pid still running. $$ exiting\n";
}

END {
  $Lock->release();
}

1;

##</code><code>##

use My::ThereCanBeOnlyOne 'myprogram';

##</code><code>##

use My::ThereCanBeOnlyOne 'myprogram',
                          -hold  => 0,
                          -stale => 1,
                          -max   => 1;

##</code><code>##

use My::ThereCanBeOnlyOne 'myprogram'.int(rand(6));