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Posted by Curt Zirzow on 12/08/05 09:34
On Wed, Dec 07, 2005 at 09:30:36PM -0500, Alan Pinstein wrote:
>
> On Dec 7, 2005, at 12:36 AM, Curt Zirzow wrote:
> >
> >I'm not sure how you mean a weak reference, and well a refcount is
> >rather meaning less in php userland.
>
> So, this gets interesting. I don't know if you're familiar with the
> circular-reference problem. But if you have two instances that have
> references to each other, even once you remove all references to the
> objects, they will not be GC'd since they have a mutual deadlock on
> each other:
>
> $a = new MyObj;
> $b = new MyObj;
> $a->setB($b); // does $this->b = $b;
> $b->setA($a); // does $this->a = $a;
>
> $a = NULL;
> $b = NULL;
>
> The actual instances pointed to by $a and $b WILL NOT GET FREED HERE
> as you would *wish*. However this is expected behavior.
I would have to disagree with the 'as you would *wish*' part.
if I pass something to a function/method via copy (vs reference) i
would hardly expect code outside the function/method to affect
their existance.
>
> Only by changing MyObj to store "weak references", that is references
> to the objects that are NOT reference-counted, can you get the GC to
> free the instances.
>
> function setB(&$B) { $this->b = &$a; }
> function setA(&$B) { $this->a = &$b; }
>
> Now, the instances will be freed when the $a and $b are null'd out.
I think you meant to type:
function setB(&$a) { $this->b = &$a; }
function setA(&$b) { $this->a = &$b; }
And consider the definition written as:
function setB(&$a) { $this->b = $a; }
function setA(&$b) { $this->a = $b; }
does the $a = null; and $b = null; outside the class cause the
objects to get null'd inside the class as well?
> So, while I now feel more confident of how references act with
> respect to objects (which is, they act the same as they do for any
> variable), I still am not sure what "$this->this" is and why it
> worked so magically.
You lost me on your $this->this statement.
Curt.
--
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