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To: Nikita Popov <nikita.ppv@gmail.com>
Cc: PHP Internals <internals@lists.php.net>
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Date: Tue, 30 May 2017 11:06:08 +0200
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Subject: Re: [PHP-DEV] Get variable refcount
From: php@list.imperialat.at (Martijn van Duren)

On 05/30/17 10:23, Nikita Popov wrote:
> On Tue, May 30, 2017 at 9:11 AM, Martijn van Duren <php@list.imperialat.at>
> wrote:
> 
>> Hello internals@,
>>
>> I'm new to this list, so let me first introduce myself.
>> My name is Martijn van Duren and I work for a webhosting company in the
>> Netherlands. Apart from that I'm also an OpenBSD h^Hslacker.
>>
>> tl;dr:
>> How do I properly use Z_REFCOUNT on a zval?
>>
>> I'm faced with the following issue:
>> I've build a framework which allows to talk to a remote interface over
>> a persistent connection. This interface can return variables of
>> arbitrary types. When an object is returned it is stored locally in an
>> array accompanied by its id. This way I can ensure that the same object
>> (and not an identical object) is returned on multiple requests.
>>
>> The problem I'm facing is that because this interface holds a reference
>> of the object it's never truly released and thus a memory leak. For the
>> application I use it for this is not an issue, but that might change in
>> the future.
>>
>> To solve this I was thinking of creating a small extension which exports
>> a function that gives me the active reference count. This way I could
>> check in certain parts of the code if there's more than 1 variables
>> linked to the object and if not, remove it from the internal array.
>> This would not give a 100% result, but it's still better than hanging on
>> to everything all the time.
>>
>> When playing with the extension I made the following function:
>> PHP_FUNCTION(refcount)
>> {
>>     zval var;
>>     zend_long refcount;
>>
>>     if (zend_parse_parameters(ZEND_NUM_ARGS(), "z", &var) == FAILURE) {
>>         return;
>>     }
>>
>>     refcount = (zend_long) Z_REFCOUNT(var);
>>
>>     RETURN_LONG(refcount);
>> }
>>
>> Which didn't returned what I expected:
>> $ php -r 'dl("refcount.so"); for ($a = 0; $a < 4; $a++)
>>     echo refcount($a)."\n";'
>> 0
>> 1
>> 2
>> 3
>>
>> Could someone point me to what I'm doing wrong with Z_REFCOUNT?
>> If there is a better way to solve my actual problem I would be all ears
>> of course.
>>
>> Sincerely,
>>
>> Martijn van Duren
>>
> 
> Since PHP 7 not all zval types are refcounted. Before accessing Z_REFCOUNT
> you should first use Z_REFCOUNTED to check if a refcount exists. You are
> testing with integers, which is one of the not reference counted types.
> (Objects are always reference counted.)

Thanks for the explanation.
> 
> From your description, it sounds like you might be looking for the weakref
> PECL extension.

That's even better than my original concept. Thanks.
> 
> Nikita
>