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Date: Fri, 09 Dec 2005 17:37:43 +0100
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To: Andi Gutmans <andi@zend.com>
Cc: Alan Pinstein <apinstein@mac.com>, internals@lists.php.net
References: <AC5F3B0F-49B6-4CB7-87D1-45767F8D9DD5@mac.com>	<43970D54.1040206@zend.com>	<63053C31-56D1-49A3-8D24-4FC41188A92A@mac.com> <7.0.0.16.2.20051208210843.059ef560@zend.com>
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Subject: Re: [PHP-DEV] $this->this and avoiding circular references
From: jochem@iamjochem.com (Jochem Maas)

Andi - your email client seems to be leaking :-)

Andi Gutmans wrote:
> 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
>>
>>
>> -- 
>> PHP Internals - PHP Runtime Development Mailing List
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> 
>