Nested CallbackFilterIterator is leaking memory

[mvorisek]

Description

The following code:

https://3v4l.org/3nIOH

https://3v4l.org/YQIVJ/rfc#vgit.master

is expected to output:

 -- c 1
 Array
 (
     [0] => a
     [1] => b
 )
 -- d 1
 -- c 1
 Array
 (
     [0] => a
     [1] => b
 )
 -- d 1
 -- c 1
 Array
 (
     [0] => a
 )
+ -- d 1
 ----------------
- -- d 1

PHP Version

8.0.14, 8.1.1, master (all tested)

Operating System

linux

[mvorisek]

Can anyone from PHP team confirm this issue? It is probably related to afab9eb , the issue with CallbackFilterIterator is however fixed, thanks @nikic

[iluuu1994]

Doesn't seem like this is caused by afab9eb. In fact, it fixes the second iteration in your example, which also leaked.

Here's a somewhat condensed example:

class Action
{
    public \Iterator $iterator;

    public function __construct(array $data)
    {
        $this->iterator = new ArrayIterator($data);
        echo '-- c ' . spl_object_id($this) . "\n";
    }

    public function __destruct()
    {
        echo '-- d ' . spl_object_id($this) . "\n";
    }

    public function filter()
    {
        $this->iterator = new \CallbackFilterIterator($this->iterator, fn() => true);
        $this->iterator->rewind();
    }
}

$action = new Action(['a', 'b']);
$action->filter();
$action->filter();
print_r(iterator_to_array($action->iterator));
$action = null;
gc_collect_cycles();

-- c 1
Array
(
    [0] => a
    [1] => b
)
===DONE===
-- d 1
[Thu Feb  3 15:51:02 2022]  Script:  './ext/spl/tests/bug-gh7958.php'
./Zend/zend_closures.c(505) :  Freeing 0x00007f5edee6b900 (328 bytes), script=./ext/spl/tests/bug-gh7958.php
[Thu Feb  3 15:51:02 2022]  Script:  './ext/spl/tests/bug-gh7958.php'
./Zend/zend_objects_API.h(92) :  Freeing 0x00007f5edee84540 (176 bytes), script=./ext/spl/tests/bug-gh7958.php
[Thu Feb  3 15:51:02 2022]  Script:  './ext/spl/tests/bug-gh7958.php'
./Zend/zend_interfaces.c(206) :  Freeing 0x00007f5edee87280 (112 bytes), script=./ext/spl/tests/bug-gh7958.php
=== Total 3 memory leaks detected ===

It's caused by the reference to $this from the CallbackFilterIterator closure. Making the closure static solves the issue. It only happens for nested CallbackFilterIterator iterators.

[mvorisek]

It's caused by the reference to $this from the CallbackFilterIterator closure. Making the closure static solves the issue. It only happens for nested CallbackFilterIterator iterators.

Yes, it seems ref count is not properly decremented during GC cycle when CallbackFilterIterator is nested - https://3v4l.org/mNt0C/rfc#vgit.master

Can you please mark this issue as verified and do you think it can be fixed in PHP v8.0 or at least v8.1?