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Date: Fri, 06 Mar 2009 10:16:38 +0300
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To: Igor Feghali <igor.feghali@gmail.com>
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Subject: Re: [PHP-DEV] Memory Leaks with Objects (no circular reference)
From: dmitry@zend.com (Dmitry Stogov)

Hi Igor,

It's definitely not a memory leak. The memory manager in php-5.2 was 
changed so it behaves little bit different. BTW: both 5.1 and 5.2 use 
some caches of the chunks with most useful sizes. They allow to 
eliminate annecessury free()/malloc() calls and speedup the whole 
system. memory_get_usage() returns allocated memory including these 
caches, so you can think that memory lost however it's just preallocated 
and ready for next emalloc()s.

Thanks. Dmitry.

Igor Feghali wrote:
> Hi,
> 
> I am facing some memory leaks with php 5.1.6 that has been fixed in
> 5.2.0. So I suppose the fix should be somewhere between those
> versions, but I couldn't find exactly which line in the NEWS file is
> that.
> 
> <?php
> 
> class foo
> {
>    var $a1;
>    var $a2;
>    var $a3;
>    var $a4;
>    var $a5;
>    var $a6;
>    var $a7;
>    var $a8;
>    var $a9;
> }
> 
> class bar
> {
>    var $a1;
>    var $a2;
>    var $a3;
>    var $a4;
>    var $a5;
>    var $a6;
>    var $a7;
>    var $a8;
> }
> 
> echo "--- 9 ---\n";
> for ($i = 0; $i < 5; $i++){
>    $u =& new foo();
>    unset($u);
>    echo memory_get_usage()."\n";
> }
> 
> echo "--- 8 ---\n";
> for ($i = 0; $i < 5; $i++){
>    $u =& new bar();
>    unset($u);
>    echo memory_get_usage()."\n";
> }
> 
> ?>
> 
> Output for 5.1.6:
> --- 9 ---
> 44712
> 44784
> 44848
> 44912
> 44976
> --- 8 ---
> 45008
> 45008
> 45008
> 45008
> 45008
> 
> Conclusion: memory consumption keeps constant for the class with 8
> properties. unset() doesnt frees all the memory up for the class with
> 9 properties.
> 
> Output for 5.2.0:
> --- 9 ---
> 66784
> 66828
> 66828
> 66828
> 66828
> --- 8 ---
> 66896
> 66896
> 66896
> 66896
> 66896
> 
> Conclusion: memory consumption constant along the whole code, as expected.
> 
> I have seen that reported many times in the bugs system, but in all
> the cases it ended up being something related to circular references
> which is not the case here. Some people also reported that replacing
> "unset($obj)" with "$obj = null" would help but I tried it and the
> problem remains.
> 
> Any help on how to workaround that in userland would be very
> appreciated. Surely upgrading will fix that, but I am trying to keep
> compatibility with prior versions as much as possible.
> 
> Best,
> ~IF.
>