package Cron::AvoidMultipleRuns;

use strict;
use warnings;

use Cwd                   qw( realpath );
use Errno                 qw( EWOULDBLOCK );
use Fcntl                 qw( LOCK_EX LOCK_NB );
use File::Spec::Functions qw( rel2abs );

my $lock_file;
my $lock_fh;

{
    $lock_file = realpath(rel2abs($0)) . '.lock';

    open($lock_fh, '+>>', $lock_file)
        or die("Can't create lock file \"$lock_file\": $!\n");

    if (!flock($lock_fh, LOCK_EX|LOCK_NB)) {
        undef $lock_fh;

        if ($! == ($^O =~ /Win32/ ? 33 : EWOULDBLOCK)) {
            die("Another instance of this program is running. Exiting.\n");
        } else {
            die("Cannot lock lock file \"$lock_file\": $!\n");
        }
    }
}

END {
    if (defined($lock_fh)) {
        undef $lock_fh;  # Release lock
        unlink($lock_file)
            ;#or warn("Can't unlink lock file \"$lock_file\": $!\n");
    }
}

1;