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Message-ID: <7.0.0.16.2.20051208210843.059ef560@zend.com>
Date: Thu, 08 Dec 2005 21:10:56 -0800
To: Alan Pinstein <apinstein@mac.com>,internals@lists.php.net
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Subject: Re: [PHP-DEV] $this->this and avoiding circular references
From: andi@zend.com (Andi Gutmans)

Hi Alan,

Generally speaking, if you create a circular reference (whether by 
reference or by value), then you will have a "memory leak" until the 
end of the request. This is not only true for objects (and circular 
references might be indirect) but also for arrays.
This is a side-effect of reference counting systems, but within the 
way PHP is used within a request/response paradigm, it shouldn't be a 
real limiting factor in real-life usage. On the contrary, for these 
kind of apps, garbage collecting systems have potential to be 
significantly slower.

Andi

At 08:15 PM 12/7/2005, Alan Pinstein wrote:
>My question is closely related to the one discussed on this php-dev
>thread:
>
>http://thread.gmane.org/gmane.comp.php.devel/32430
>
>Someone just sent me this link, which I didn't find myself when
>searching b/c the searches strip "this" from queries.
>
>Anyway, the question is related to reference counting of objects when
>assigned by value and by reference. It is a very important OO topic
>as the ability to have a non-ref-counted object "handle" is basically
>requisite to prevent circular reference deadlocks in OO projects.
>
>If the way I have proposed doesn't work, then what is the official
>way? And there *must* be one, otherwise, there is no way to avoid
>huge memory leaks (deferred release until end-of-script, I know, but
>it's a memory leak in the context of the script while it's running)
>with this kind of OO arrangement.
>
>In particular what confuses me is, why does, at least on PHP 5.0.4,
>this:
>
>$obj = &$this->this;    // doesn't seem to increment the refcount of the
>object
>
>behaves differently from:
>
>$obj = &$this;          // does seem to increment the refcount to the object
>
>References to $this should not only be valid, but are pretty much
>required for proper memory management in an OO environment, unless
>there is some other sanctioned way to get a weak reference... now I
>am not sure if the fact that making a & reference to an object
>doesn't increment the refcount is intended behavior, or an unintended
>side effect that may change. This is one of my major questions.
>
>Also, in regards to the thread linked above, I'd say that making & 
>$this an error is not desirable behavior; but maybe changing the
>value of $this should be (ie in C terms, $this is not an lvalue).
>Although, in C++/Obj-C you *can* even change this/self... in fact
>it's common in Obj-C:
>
>- (id) init
>{
>     if (self = [super init]) { /* etc */ }
>     return self;
>}
>
>Of course PHP is not Obj-C, but it's OO and garbage collected in a
>similar way, so PHP has the same need for manipulating $this; that
>is, creating weak references.
>
>Alan
>
>
>On Dec 7, 2005, at 11:27 AM, Antony Dovgal wrote:
>
>>On 07.12.2005 18:40, Alan Pinstein wrote:
>>>Hi all-
>><skip>
>>
>>Please use php-general@lists.php.net for questions regarding
>>development *in* PHP.
>>--
>>Wbr, Antony Dovgal
>
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