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Bug #62468 SimpleXML memory leak, if circular references are removed by Garbage Collector
Submitted: 2012-07-02 20:13 UTC Modified: -
Votes:8
Avg. Score:3.9 ± 1.4
Reproduced:7 of 8 (87.5%)
Same Version:2 (28.6%)
Same OS:4 (57.1%)
From: zerkyn at gmail dot com Assigned:
Status: Open Package: SimpleXML related
PHP Version: 5.3.14 OS: Windows 7, Linux
Private report: No CVE-ID:
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 [2012-07-02 20:13 UTC] zerkyn at gmail dot com
Description:
------------
The SimpleXMLElement memory leaks, when:
1) An object holds reference to a SimpleXMLElement, and
2) The object is involved in a circular references net, and
3) All external references to that net are cleared, so Garbage Collector finds that net, correctly sees it as a garbage cycle, and cleans all its objects

After the Garbage Collector finishes its work, the memory, consumed by SimpleXMLElement is not freed, thus producing a memory leak.

The issue is reproduced both at Windows and Linux platforms.

Full version for the test script is there: https://dl.dropbox.com/u/17950262/php/issues/simplexml_memory_leak.zip


Test script:
---------------
<?php
class SelfLinked
{
    public $xml;
    public $me;

    public function __construct()
    {
        $this->xml = simplexml_load_file('pretty_big_file_of_1mb_size.xml');
        $this->me = $this;
    }
}

echo "Sys memory usage before: ", SystemMemoryUsage(), "\n";

for ($i = 0; $i < 1000; $i++) {
    $a = new SelfLinked();
    unset($a);
    gc_collect_cycles();
}

echo "Sys memory usage after: ", SystemMemoryUsage(), "\n";

/** ----------------------------------------------------- */
function SystemMemoryUsage() 
{
    ... 
    // Return memory consumption by executing system tool - tasklist, ps or anything else
    // See https://bugs.php.net/bug.php?id=62467 on proper memory profiling of SimpleXML functions
}
}

Expected result:
----------------
Memory consumption does not change.

Actual result:
--------------
Huge increase of memory consumption is reported.

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 [2012-07-05 11:16 UTC] Sjon at hortensius dot net
I can confirm this, but it has already been fixed in PHP 5.4. I assume this is 
because of the circular references that were fixed then.

http://3v4l.org/JICRi
 
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