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    <p>If the problem is in the Perl code, you might have a reference that points to itself, or a parent node.</p> <p>Usually it comes in the form of an object, that reference a parent object.</p> <pre><code>{ package parent; sub new{ bless { 'name' =&gt; $_[1] }, $_[0] } sub add_child{ my($self,$child_name) = @_; my $child = child-&gt;new($child_name,$self); $self-&gt;{$child_name} = $child; # saves a reference to the child return $child; } } { package child; sub new{ my($class,$name,$parent) = @_; my $self = bless { 'name' =&gt; $name, 'parent' =&gt; $parent # saves a reference to the parent }, $class; return $self; } } { my $parent = parent-&gt;new('Dad'); my $child = parent-&gt;add_child('Son'); # At this point both of these are true # $parent-&gt;{Son}{parent} == $parent # $child-&gt;{parent}{Son} == $child # Both of the objects **would** be destroyed upon leaving # the current scope, except that the object is self-referential } # Both objects still exist here, but there is no way to access either of them. </code></pre> <p>The best way to fix this is to use <a href="http://search.cpan.org/perldoc/Scalar::Util#weaken" rel="noreferrer">Scalar::Util::weaken</a>.</p> <pre><code>use Scalar::Util qw'weaken'; { package child; sub new{ my($class,$name,$parent) = @_; my $self = bless { 'name' =&gt; $name, 'parent' =&gt; $parent }, $class; weaken ${$self-&gt;{parent}}; return $self; } } </code></pre> <p>I would recommend dropping the reference to the parent object, from the child, if at all possible.</p>
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    1. COIt's worth mentioning that with objects, you can also use a destructor to break any circular references. Your Child class could have `sub DESTROY { $_[0]->{parent} = undef; }`, or even `sub DESTROY { $_[0] = undef; }` and there is no need for weak references. Weak refs are a better way to handle things, they make correct behavior automatic. It is also worth noting that Moose features automatic reference weakening for attributes: http://search.cpan.org/dist/Moose/lib/Moose/Manual/Attributes.pod#Weak_references It's yet another way Moose makes OO Perl better.
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    2. CO@daotoad: You can't use a destructor to break circular references, because the destructor doesn't get called until the reference count drops to zero. If the destructor gets called, you don't have a circular reference problem. If you have circular references, you either need to use weak refs or manually call a destructor method when you're done with an object (which is error prone).
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    3. CO@cjm, you are right. It's been a while. `weaken` is really the way to go. You have to create a container object to hold the circular reference and let the container's destructor break the cycle. The other option is to have an explicit method call that clears a widget and breaks any cycles. For example, Perl Tk's `Widget::destroy()` method.
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