Memory leak when passing anonymous functions to lua interpreter

[ComaVN]

When passing anonymous PHP functions to LUA using assign or registerCallback, some memory is not reclaimed when the Lua object is unset.

See https://github.com/ComaVN/php-lua-memoryleak for a proof of concept.

[hvt]

I can affirm this behavior, also on older PHP and older php-lua versions:

$ php -v
PHP 5.6.30-1+deb.sury.org~trusty+1 (cli) 
Copyright (c) 1997-2016 The PHP Group
Zend Engine v2.6.0, Copyright (c) 1998-2016 Zend Technologies

$ dpkg -s liblua5.2-dev | grep Version
Version: 5.2.3-1

$ php -i | grep '^lua '
lua support => enabled
lua extension version => 1.1.0
lua release => Lua 5.2.3
lua copyright => Lua 5.2.3  Copyright (C) 1994-2013 Lua.org, PUC-Rio
lua authors => R. Ierusalimschy, L. H. de Figueiredo, W. Celes

$ php test-assign.php
Mem at start of test (real): 235000 (262144)
Mem at start of loop (real): 235184 (262144)
Mem at end of loop (real): 262520 (524288)
Mem at start of loop (real): 262520 (524288)
Mem at end of loop (real): 262960 (524288)
...
Mem at start of loop (real): 721288 (1048576)
Mem at end of loop (real): 721656 (1048576)
Mem at start of loop (real): 721656 (1048576)
Mem at end of loop (real): 722160 (1048576)
Mem at end of test (real): 695704 (1048576)

$ php test-registerCallback.php 
Mem at start of test (real): 235152 (262144)
Mem at start of loop (real): 235336 (262144)
Mem at end of loop (real): 262696 (524288)
Mem at start of loop (real): 262696 (524288)
Mem at end of loop (real): 263112 (524288)
...
Mem at start of loop (real): 721912 (1048576)
Mem at end of loop (real): 722360 (1048576)
Mem at start of loop (real): 722360 (1048576)
Mem at end of loop (real): 722824 (1048576)
Mem at end of test (real): 696344 (1048576)

[hvt]

Hey there, I was wondering whether I could somehow help fixing this problem. Does anyone have any pointers where to start investigating this?

[sgolemon]

#31 fixes this.

[laruence]

the problem is these callbacks are stashed as lua class's static properties.. which could only be reclaimed in request shutdown phase.

hmm, yeah it is better to reclaim it after object's destruction... but, need some work to do...

[ComaVN]

the PoC still shows the same memory leak, am I doing anything wrong here? I don't see a difference with the latest version:

$ cat /etc/issue
Ubuntu 16.04.3 LTS \n \l

$ php -v
PHP 7.0.22-0ubuntu0.16.04.1 (cli) ( NTS )
Copyright (c) 1997-2017 The PHP Group
Zend Engine v3.0.0, Copyright (c) 1998-2017 Zend Technologies
    with Zend OPcache v7.0.22-0ubuntu0.16.04.1, Copyright (c) 1999-2017, by Zend Technologies

$ dpkg -s liblua5.2-dev | grep Version
Version: 5.2.4-1ubuntu1

$ php -i | grep '^lua '
lua support => enabled
lua extension version => 2.0.5
lua release => Lua 5.2.4
lua copyright => Lua 5.2.4  Copyright (C) 1994-2015 Lua.org, PUC-Rio
lua authors => R. Ierusalimschy, L. H. de Figueiredo, W. Celes

$ php test-assign.php
Mem at start of test (real): 362960 (2097152)
Mem at start of loop (real): 362992 (2097152)
Mem at end of loop (real): 363752 (2097152)
Mem at start of loop (real): 363752 (2097152)
Mem at end of loop (real): 364072 (2097152)
(...)
Mem at start of loop (real): 719336 (2097152)
Mem at end of loop (real): 719656 (2097152)
Mem at start of loop (real): 719656 (2097152)
Mem at end of loop (real): 719976 (2097152)
Mem at end of test (real): 719928 (2097152)

$ php test-registerCallback.php 
Mem at start of test (real): 363120 (2097152)
Mem at start of loop (real): 363152 (2097152)
Mem at end of loop (real): 363912 (2097152)
Mem at start of loop (real): 363912 (2097152)
Mem at end of loop (real): 364232 (2097152)
(...)
Mem at start of loop (real): 719496 (2097152)
Mem at end of loop (real): 719816 (2097152)
Mem at start of loop (real): 719816 (2097152)
Mem at end of loop (real): 720136 (2097152)
Mem at end of test (real): 720088 (2097152)