You are correct.

Execute the following on both Perl 5.8.8 and Perl 5.10.0 and I get different results.

Under Perl 5.8.8, I leak no memory and everything runs fine.

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

Uses 200Mb of RAM.

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

Uses 2,476Kb RAM.

Please Note that I did as many folks right here have recommended and compiled my Perl 5.10.0 from the source on CPAN, without threads.

Perhaps we'll see some discussion on that here as well.

For reference, this is the exact code I am running:

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 );
}
[download]