ID: 48781
Comment by: nate at frickenate dot com
Reported By: nate at frickenate dot com
Status: Open
Bug Type: Performance problem
Operating System: Debian 5.0 kernel 2.6.24-23-xen
PHP Version: 5.3.0
New Comment:
Anyone? :)
Previous Comments:
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[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.
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Edit this bug report at http://bugs.php.net/?id=48781&edit=1
