One example he presented is suited to pre-PHP5. With PHP5, a reference to self could be kept inside the class as a static member. No need to use a global variable. Just wanted to bring this up for new comers to PHP references and global variables. Cheers. On 12/6/05, Ray Hauge <ray.hauge@xxxxxxxxxxxxxxxxxxxxxxx> wrote: > > I am uncertain on this, but I believe that the $this variable is already > just a reference to the class you are calling it from. Then passing the > reference by-reference to the addParent() method of the Child class > could be what is causing your issue. I'd be curious to see what would > happen if you took out the pass-by-reference and instead pass-by-value > for the addParent() method. Then again, that doesn't particularly sound > correct either. > > This link might help. They cover a lot of advanced reference usage for > PHP. > > http://www.onlamp.com/pub/a/php/2002/09/12/php_foundations.html > > Alan Pinstein wrote: > > > So.. I am having PHP5 memory management problems. > > > > They are similar to those described in this thread: > > > > http://aspn.activestate.com/ASPN/Mail/Message/php-Dev/1555640 > > > > (so maybe this question belongs on php-dev but I figured I'd try here > > first... seems like a userland question) > > > > Basically I have an object model to represent db objects, and I am > > bulk-loading the objects via some PHP scripts. Sadly the scripts > > consume unbounded memory because of this problem. > > > > I have done a lot of programming in C++ and Obj-C and the normal way > > to handle circular references is to have parents "retain" (keep ref- > > counted links) to their kids, and have the kids have "weak > > references" (non-ref-counted) links to their parents. This way, when > > the parent is no longer used, it will automatically 0-out the ref > > counts to all children it links too and things GC correctly. > > > > Now, how to do this in PHP? > > > > Well, there are no "documented" weak references. However, I figured > > out by trial that if you obtain a php-reference to an object, it > > doesn't bump the refcount. > > > > Question #1: Is the fact that references to objects in the form > > $objRef = &$obj don't bump the refcount of $obj an intended behavior > > that can be counted on? If so, cool! > > > > So, now that we have a way to do weak references, we should be able > > to implement a reasonable memory management scheme for parent-child > > objects. > > > > Normally from the client side the interface should look something like: > > > > $parent = new Parent(); > > $child = new Child(); > > $parent->addChild($child); > > > > Where parent can have 0,n children and child can have 0,1 parent. > > > > And all of parent's internal links to child should be refcounted, and > > the internal links from child to parent are weak (not ref-counted). > > > > So based on the above discovery about references, I tried to > > implement this as such: > > > > class Parent > > { > > public $children = array(); > > > > // add a child to our list. We want a ref-counted link here. > > function addChild($child) > > { > > $this->children[] = $child; // refCounted desired in > > parent->child link > > $child->setParent($this); > > } > > } > > > > class Child > > { > > public $parent; > > > > // set the parent object. We want a non-ref-counted link here. > > function setParent(&$parent) > > { > > // refCount NOT desired in child->parent link > > $this->parent = &$parent; > > } > > } > > > > Now, you'd expect this would work, but it doesn't. On a hunch, I > > changed the client code to: > > > > $parent = new Parent(); > > $child = new Child(); > > $parent->addChild($child); > > $child->setParent($child); // new line here - you can > > successfully create a reference to the object when not passed in as > > $this > > > > Now, this works! However, it's not practical. The setParent call > > should work from within the parent object.... > > > > So what I figured out is that $this is a "pseudo variable" according > > to the docs, but I don't know what that means. Empirically I have > > figured out that it means you cannot create a reference to it. > > > > Is this a feature or a bug? What's the workaround? > > > > This is a serious problem for PHP scripts that need to do things that > > require large amounts of memory. > > > > Please advise. > > > > Thanks, > > Alan > > > > -- > PHP General Mailing List (http://www.php.net/) > To unsubscribe, visit: http://www.php.net/unsub.php > > -- Anas Mughal
