john@john-laptop:~/Projects/Cloud-T3n$ time perl refs.pl
1000000/1000000
real	0m53.021s
user	0m10.753s
sys	0m1.912s

##</code><code>##

john@john-laptop:~/Projects/Cloud-T3n$ time /usr/bin/perl refs.pl
1000000/1000000
real	0m58.048s
user	0m11.989s
sys	0m1.672s

##</code><code>##


package Top;

sub new {
  my $class = shift;
  my $s = bless { }, $class;
  $s->{bottom} = Bottom->new( $s );
  return $s;
}

#=====================================

package Bottom;
use Scalar::Util 'weaken';

sub new {
  my ($class, $top) = @_;
  my $s = bless { top => $top }, $class;
  weaken($s->{top});
  return $s;
}

#=====================================

package main;

use Devel::Cycle;

for( 1...1_000_000 )
{
  print "\r$_/1000000";

  my $top = Top->new();
  my $bottom = $top->{bottom} or die "NO BOTTOM!";
  $top = $bottom->{top} or die "NO TOP!";

  find_cycle( $top );
  find_cycle( $bottom );
}