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.