Bug #53803 [NEW]: circular reference between SPL classes not collected by gc_collect_cycles()

From: Date: Fri, 21 Jan 2011 12:09:58 +0000
Subject: Bug #53803 [NEW]: circular reference between SPL classes not collected by gc_collect_cycles()
Groups: php.bugs 
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From:             
Operating system: FreeBSD
PHP version:      5.3.5
Package:          SPL related
Bug Type:         Bug
Bug description:circular reference between SPL classes not collected by gc_collect_cycles()

Description:
------------
Circular references between instances of SPL classes are not "cleaned up"
by gc_collect_cycles().

The code in the test script can be run from cli. It shows growing memory
usage because the circular references between the instances of an extended
ArrayObject class and instances of ArrayIterator are not cleaned up by
gc_collect_cycles.

The long code sample, downloadable from the url provided in "test script
section" shows:

Case1: SPL classes: expecting gc_collect_cycles to clean up circ
references
Case2: SPL classes: manual clearing of the circular reference
Case3: Userland classes: expecting gc_collect_cycles to clean up circ
references

This looks similar to http://bugs.php.net/53071 , BUT I am
running php5.3.5
which AFAIK includes r304723 and r304724 which were supposed to fix
#53071.




Test script:
---------------
Short code sample:

class Collection extends ArrayObject implements Serializable
{
  protected $iterator;

  public function getIterator()
  {
    $this->iterator = new ArrayIterator($this);
    return $this->iterator;
  }

  public function clearIterator()
  {
    $this->iterator = null;
  }
}

echo "Case 1: ArrayObject/ArrayIterator: expecting gc_collect_cycles() to
clean up...\n";

for ($i = 1; $i <= 100; $i++)
{
  $books = array('war and peace', 'crime and punishment');
  $book_collection = new Collection($books);
  $iterator = $book_collection->getIterator();

  echo gc_collect_cycles() . ":" . memory_get_peak_usage() . "\n";
}


full code sample:

http://www.realtsp.com/download/php_circular_reference_test_code_sample.txt


Expected result:
----------------
Expect all test cases (Case1, Case2, Case3) to have constant peak memory
usage. 



Actual result:
--------------
Only Case2 and Case3 have constant memory usage.

In Case1 memory usage grows linearly with loops iterations. 

This shows that gc_collect_cycles is not collecting circular references
between SPL classes. Also shown because it returns "0 cycles collected". In
Case 3 (Userland classes) gc_collect_cycles shows "5 cycles collected" each
iteration.





-- 
Edit bug report at http://bugs.php.net/bug.php?id=53803&edit=1
-- 
Try a snapshot (PHP 5.2):            http://bugs.php.net/fix.php?id=53803&r=trysnapshot52
Try a snapshot (PHP 5.3):            http://bugs.php.net/fix.php?id=53803&r=trysnapshot53
Try a snapshot (trunk):              http://bugs.php.net/fix.php?id=53803&r=trysnapshottrunk
Fixed in SVN:                        http://bugs.php.net/fix.php?id=53803&r=fixed
Fixed in SVN and need be documented: http://bugs.php.net/fix.php?id=53803&r=needdocs
Fixed in release:                    http://bugs.php.net/fix.php?id=53803&r=alreadyfixed
Need backtrace:                      http://bugs.php.net/fix.php?id=53803&r=needtrace
Need Reproduce Script:               http://bugs.php.net/fix.php?id=53803&r=needscript
Try newer version:                   http://bugs.php.net/fix.php?id=53803&r=oldversion
Not developer issue:                 http://bugs.php.net/fix.php?id=53803&r=support
Expected behavior:                   http://bugs.php.net/fix.php?id=53803&r=notwrong
Not enough info:                     http://bugs.php.net/fix.php?id=53803&r=notenoughinfo
Submitted twice:                     http://bugs.php.net/fix.php?id=53803&r=submittedtwice
register_globals:                    http://bugs.php.net/fix.php?id=53803&r=globals
PHP 4 support discontinued:          http://bugs.php.net/fix.php?id=53803&r=php4
Daylight Savings:                    http://bugs.php.net/fix.php?id=53803&r=dst
IIS Stability:                       http://bugs.php.net/fix.php?id=53803&r=isapi
Install GNU Sed:                     http://bugs.php.net/fix.php?id=53803&r=gnused
Floating point limitations:          http://bugs.php.net/fix.php?id=53803&r=float
No Zend Extensions:                  http://bugs.php.net/fix.php?id=53803&r=nozend
MySQL Configuration Error:           http://bugs.php.net/fix.php?id=53803&r=mysqlcfg

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