Edit report at http://bugs.php.net/bug.php?id=48781&edit=1
ID: 48781
Updated by: j...@php.net
Reported by: nate at frickenate dot com
Summary: Cyclical garbage collector memory leak
Status: Assigned
Type: Bug
Package: Scripting Engine problem
Operating System: Debian 5.0 kernel 2.6.24-23-xen
PHP Version: 5.3.0
Assigned To: dmitry
New Comment:
I am unable to duplicate this behaviour using 5.3.2. The code given
below consistently uses 0.65 MB even up to 10 million iterations - I
pasted the output of up to 6 million, with the extended GC reporting
turned on:
<?php
class User {
protected $profile;
public function __construct () {
$this->profile = new UserProfile($this);
}
public function dispose() {
$this->profile->dispose();
$this->profile = null;
}
}
class UserProfile {
private $user;
public function __construct ($user) {
$this->user = $user;
}
public function dispose() {
$this->user = null;
}
}
for ($userid = 1; ; $userid++) {
if(isset($user)) {
$user->dispose();
}
$user = new User;
if ($userid % 100000 == 0)
printf("memory usage after %s users: %s MB.\n",
number_format($userid), number_format(memory_get_usage() / 1024 / 1024,
2));
continue;
}
?>
memory usage after 100,000 users: 0.65 MB.
memory usage after 200,000 users: 0.65 MB.
memory usage after 300,000 users: 0.65 MB.
[snip]
memory usage after 5,700,000 users: 0.65 MB.
memory usage after 5,800,000 users: 0.65 MB.
memory usage after 5,900,000 users: 0.65 MB.
GC Statistics
-------------
Runs: 0
Collected: 0
Root buffer length: 0
Root buffer peak: 9
Possible Remove from Marked
Root Buffered buffer grey
-------- -------- ----------- ------
ZVAL 16 7 7 0
ZOBJ 77999984 11999998 11999998 0
Previous Comments:
------------------------------------------------------------------------
[2010-01-05 19:31:01] nightstorm at tlen dot pl
I confirm, there is a true memory leak. Consider the following script,
where the references are unmounted manually with an extra dispose()
method:
~~~~
<?php
/*
How to use:
a) run test 1 by running code as-is
b) run test 2 by commenting out test 1, uncomment test 2
c) run test 3 by commenting out test 1 & 2, uncomment test 3
*/
class User {
protected
$profile;
public function __construct () {
$this->profile = new UserProfile($this);
}
public function dispose()
{
$this->profile->dispose();
$this->profile = null;
} // end dispose();
}
class UserProfile {
private
$user;
public function __construct ($user) {
$this->user = $user;
}
public function dispose()
{
$this->user = null;
} // end dispose();
}
for ($userid = 1; ; $userid++) {
if(isset($user))
{
$user->dispose();
}
$user = new User;
if ($userid % 100000 == 0)
printf("memory usage after %s users: %s MB.\n",
number_format($userid), number_format(memory_get_usage() / 1024 / 1024,
2));
continue;
}
~~~~~
In this case the result is still the same (PHP 5.3.1):
~~~~
memory usage after 100,000 users: 0.61 MB.
memory usage after 200,000 users: 0.61 MB.
memory usage after 300,000 users: 0.61 MB.
memory usage after 400,000 users: 0.61 MB.
memory usage after 500,000 users: 0.61 MB.
memory usage after 600,000 users: 0.61 MB.
memory usage after 700,000 users: 0.61 MB.
memory usage after 800,000 users: 0.61 MB.
memory usage after 900,000 users: 0.61 MB.
memory usage after 1,000,000 users: 0.61 MB.
memory usage after 1,100,000 users: 0.61 MB.
memory usage after 1,200,000 users: 0.61 MB.
~~~~
If we enable the garbage collector and remove the dispose() method, the
used memory level begins to increase, and if we call gc_collect_cycles()
after creating a new object, the used memory increases even much faster.
On my PC, it is not able to perform display even a single control
message after 100000 iterations. It stopped after approx. 33000 users:
~~~~
memory usage after 30,000 users: 25.37 MB.
memory usage after 31,000 users: 26.07 MB.
memory usage after 32,000 users: 26.76 MB.
memory usage after 33,000 users: 31.46 MB.
Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to
allocate 89 bytes) in /home/me/test/memleak.php on line 17
~~~~
------------------------------------------------------------------------
[2009-12-15 01:00:00] php-bugs at lists dot php dot net
No feedback was provided for this bug for over a week, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".
------------------------------------------------------------------------
[2009-12-08 15:23:16] nate at frickenate dot com
No change, same problem. Considering this bug hasn't even been looked at
or assigned, no surprise there.
------------------------------------------------------------------------
[2009-12-07 09:12:35] j...@php.net
Please try using this snapshot:
http://snaps.php.net/php5.3-latest.tar.gz
For Windows:
http://windows.php.net/snapshots/
------------------------------------------------------------------------
[2009-07-02 18:35:42] nate at frickenate dot com
Description:
------------
The new cyclical garbage collector isn't collecting everything it should
be - somewhere there is a memory leak. The issue I am bringing up is not
about delayed collection - this is a true memory leak with memory that
is never reclaimed.
When a variable (in this example, $user) contains an object with a
cyclical reference, there is a small amount of memory that is leaked/not
reclaimed when you set $user to another object (of any class). If you
set $user to an int/string/boolean/null before setting $user to another
object, all memory is collected properly.
I came to the conclusion that this must be a problem with the garbage
collector, since if you replace the "$this->user = $user;" with
"$this->user = new StdClass;" (thus preventing the creation of a
cyclical reference), the leak goes away.
So basically right now:
<?php
while ($user = get_next_user()) {
// do stuff with $user
// php bug: have to unset before next iteration
// to prevent memory leak caused by buggy gc
unset($user);
}
?>
Reproduce code:
---------------
<?php
/*
How to use:
a) run test 1 by running code as-is
b) run test 2 by commenting out test 1, uncomment test 2
c) run test 3 by commenting out test 1 & 2, uncomment test 3
*/
class User {
protected
$profile;
public function __construct () {
$this->profile = new UserProfile($this);
}
}
class UserProfile {
private
$user;
public function __construct ($user) {
$this->user = $user;
}
}
for ($userid = 1; ; $userid++) {
$user = new User;
if ($userid % 100000 == 0)
printf("memory usage after %s users: %s MB.\n",
number_format($userid), number_format(memory_get_usage() / 1024 / 1024,
2));
// TEST 1 - do nothing before we set the
// new User on next iteration of the loop).
// RESULT: leaks memory (see "Actual result" section)
continue;
// TEST 2 - set $user to an empty object, before
// we set the new User on next iteration
// RESULT: leaks memory (see "Actual result" section)
//$user = new StdClass; continue;
// TEST 3 - set $user to anything other than an object,
// before we set the new User on next iteration.
// RESULT: does NOT leak memory (see "Expected result" section)
//$user = 'not an object'; continue;
}
?>
Expected result:
----------------
memory usage after 100,000 users: 1.54 MB.
memory usage after 200,000 users: 1.54 MB.
memory usage after 300,000 users: 1.54 MB.
memory usage after 400,000 users: 1.54 MB.
memory usage after 500,000 users: 1.54 MB.
memory usage after 600,000 users: 1.54 MB.
memory usage after 700,000 users: 1.54 MB.
memory usage after 800,000 users: 1.54 MB.
memory usage after 900,000 users: 1.54 MB.
memory usage after 1,000,000 users: 1.54 MB.
[snip]
memory usage after 99,000,000 users: 1.54 MB.
memory usage after 99,100,000 users: 1.54 MB.
memory usage after 99,200,000 users: 1.54 MB.
memory usage after 99,300,000 users: 1.54 MB.
memory usage after 99,400,000 users: 1.54 MB.
memory usage after 99,500,000 users: 1.54 MB.
memory usage after 99,600,000 users: 1.54 MB.
memory usage after 99,700,000 users: 1.54 MB.
memory usage after 99,800,000 users: 1.54 MB.
memory usage after 99,900,000 users: 1.54 MB.
memory usage after 100,000,000 users: 1.54 MB.
Actual result:
--------------
memory usage after 100,000 users: 1.55 MB.
memory usage after 200,000 users: 1.57 MB.
memory usage after 300,000 users: 1.58 MB.
memory usage after 400,000 users: 1.59 MB.
memory usage after 500,000 users: 1.61 MB.
memory usage after 600,000 users: 1.62 MB.
memory usage after 700,000 users: 1.64 MB.
memory usage after 800,000 users: 1.65 MB.
memory usage after 900,000 users: 1.66 MB.
memory usage after 1,000,000 users: 1.68 MB.
[snip]
memory usage after 99,000,000 users: 18.43 MB.
memory usage after 99,100,000 users: 18.44 MB.
memory usage after 99,200,000 users: 18.46 MB.
memory usage after 99,300,000 users: 18.47 MB.
memory usage after 99,400,000 users: 18.48 MB.
memory usage after 99,500,000 users: 18.50 MB.
memory usage after 99,600,000 users: 18.51 MB.
memory usage after 99,700,000 users: 18.53 MB.
memory usage after 99,800,000 users: 18.54 MB.
memory usage after 99,900,000 users: 18.55 MB.
memory usage after 100,000,000 users: 18.57 MB.
------------------------------------------------------------------------
--
Edit this bug report at http://bugs.php.net/bug.php?id=48781&edit=1
