Re: Circular Reference cleanup

Chris, I think this would be better posted to phpdev as they decide stuff like this. They will give you reasons why it is done the way it is! David. ----- Original Message ----- From: Chris Monson <ckmonson@burgoyne.com> To: <php-general@lists.php.net> Sent: Monday, July 10, 2000 6:25 PM Subject: [PHP] Circular Reference cleanup > Since PHP is a reference counted language, it has trouble with circular > references (of course). Now that PHP 4 supports references to > variables, it is possible to create structures that were difficult or > impossible to represent before, like n-trees, etc. > > I have created such a structure, where each node in the tree has as one > of its memebers a reference to its parent node. This is very useful for > reverse traversal, and it would be painful (possible, but painful) to > have to get rid of the parent references in each node. > > The reason that having a reference to a parent node from a child node is > a problem is this: PHP is reference counted. That means that data > elements that have circular references like this will not be destroyed > until the script exits, at which point the Zend code dumps out a bunch > of memory leak information. > > There are a few ways of addressing this issue: > > 1) Implement true garbage collection (likely not an option) > 2) Allow for "soft" references (allow a reference variable to exist > without incrementing the reference count, thus allowing an object to be > destroyed even though other variables refer to it) > 3) Have a destructor in PHP that allows the class creator to go and > clean up the circular references when some container object is destroyed. > > The first option is probably not an option at all, so I won't bother > addressing it here. > > The second is actually very appealing, in that it would allow for self- > referential data structures and it would simultaneously allow reference > counting to work. The downside is that it would require a special sort > of syntax to differentiate between reference types, and it would confuse > the issue of references just a bit. > > The third is my favorite because it seems that it should be easy to > implement some sort of destructor mechanism in PHP without breaking the > existing code and without confusing the language with obscure features > like soft references. It has always been a bit disturbing to me that > there is no (documented) destructor mechanism for PHP objects. Even if > PHP is great at cleaning stuff up, it is very nice to have a destructor > mechanism so that file handles, queries, and contained self-referential > structures can be cleaned up. > > At any rate, if anyone knows of a destructor mechanism in PHP that has > simply not been documented yet, please let me know. Otherwise, let's > discuss this shortcoming in PHP and see if there are other solutions or > workarounds. > > Chris > > > -- > PHP General Mailing List (http://www.php.net/) > To unsubscribe, e-mail: php-general-unsubscribe@lists.php.net > For additional commands, e-mail: php-general-help@lists.php.net > To contact the list administrators, e-mail: php-list-admin@lists.php.net >