From: xl269 at cam dot ac dot uk
Operating system: debian gnu/linux lenny
PHP version: 5.3CVS-2008-09-26 (CVS)
PHP Bug Type: Performance problem
Bug description: memory leak on garbage collecting function return values
Description:
------------
I have no idea if my explanation of this bug is correct, but here's a
guess anyway.
PHP does not seem to garbage collect return values from functions, when
they are operated-assigned (eg. $v = func() + 5; or $v = func()." ";) to a
variable in the caller. but this is fine for direct assignments (eg. $v =
func();)
It would seem from this that PHP is storing functions' return values
internally as if they were pointed to by a variable (that doesn't exist in
the script), and using copy-on-write to avoid copying this data when it's
assigned to an actual script variable. However copy-on-write, doesn't
trigger when there is an operation on this data before this assignment.
Reproduce code:
---------------
<?php
define('LF', chr(10));
// define('REALLY_LONG_STRING', str_repeat("really ", 65536)."long
string");
function generic($for, $title) {
mem('g+');
$data = '<abbr title="information for '.$for.'">'.$title.'</abbr>';
// $data = '<abbr title="information for
'.$for.'">'.$title.'</abbr>'.REALLY_LONG_STRING;
mem('g-');
return $data;
}
function lol1() {
mem('l1+');
$data = " ".generic("name", "test")." ";
mem('l1-');
return $data;
}
function lol2() {
mem('l2+');
$data = generic("name", "test");
mem('l2-');
return $data;
}
echo memory_get_usage().LF;
for ($i=0; $i<8; $i++) {
$a[] = lol2();
echo memory_get_usage().LF;
$a[] = lol1();
echo memory_get_usage().LF;
}
?>
Expected result:
----------------
see below
Actual result:
--------------
635168
635240 l2+
635496 g+
635672 g-
635672 l2- (no memory leak here)
635928
636024 l1+
636072 g+
636184 g-
636248 l1- (this value should only be 2 bytes larger than the previous)
636336
--
Edit bug report at http://bugs.php.net/?id=46181&edit=1
--
Try a CVS snapshot (PHP 5.2):
http://bugs.php.net/fix.php?id=46181&r=trysnapshot52
Try a CVS snapshot (PHP 5.3):
http://bugs.php.net/fix.php?id=46181&r=trysnapshot53
Try a CVS snapshot (PHP 6.0):
http://bugs.php.net/fix.php?id=46181&r=trysnapshot60
Fixed in CVS: http://bugs.php.net/fix.php?id=46181&r=fixedcvs
Fixed in release:
http://bugs.php.net/fix.php?id=46181&r=alreadyfixed
Need backtrace: http://bugs.php.net/fix.php?id=46181&r=needtrace
Need Reproduce Script: http://bugs.php.net/fix.php?id=46181&r=needscript
Try newer version: http://bugs.php.net/fix.php?id=46181&r=oldversion
Not developer issue: http://bugs.php.net/fix.php?id=46181&r=support
Expected behavior: http://bugs.php.net/fix.php?id=46181&r=notwrong
Not enough info:
http://bugs.php.net/fix.php?id=46181&r=notenoughinfo
Submitted twice:
http://bugs.php.net/fix.php?id=46181&r=submittedtwice
register_globals: http://bugs.php.net/fix.php?id=46181&r=globals
PHP 4 support discontinued: http://bugs.php.net/fix.php?id=46181&r=php4
Daylight Savings: http://bugs.php.net/fix.php?id=46181&r=dst
IIS Stability: http://bugs.php.net/fix.php?id=46181&r=isapi
Install GNU Sed: http://bugs.php.net/fix.php?id=46181&r=gnused
Floating point limitations: http://bugs.php.net/fix.php?id=46181&r=float
No Zend Extensions: http://bugs.php.net/fix.php?id=46181&r=nozend
MySQL Configuration Error: http://bugs.php.net/fix.php?id=46181&r=mysqlcfg
