On 25/09/06, Jon Anderson <[EMAIL PROTECTED]> wrote:
I posted this to php-general several days ago, and the only response suggested that perhaps I should forward the question to PHP internals. If what's below isn't expected behavior, I'd be glad to dedicate a few days to helping track down the problem.I've tried what's below on the server cluster in the office, running Debian Sarge i386 (with an x86-64 kernel), PHP 5.0.16, and Apache 2.0.54. I've also tried at home on a Gentoo box (Athlon-MPs) running PHP 5.0.16 and Apache 2.2. Both produce similar results. (If compiled-in/shared module lists, compile options, or any other information would help, I can provide those too.) What's below this sentence is the original text of the message sent to php-general. Sorry folks, this is a long one...I've re-read a bunch of the documentation, and I can't find a solution. In debugging an out of memory condition, I found that PHP doesn't seem to garbage collect unreferenced objects. It seems to work fine for anything other than objects. (Arrays, strings, integers, etc.) Here's a simple example: define a class, create 3 instances, destroy them in reverse order. I would expect that after each unset and/or NULL, the memory usage would go down, they don't. See the output below. <?php class Tester { protected $test1; protected $test2; protected $test3; protected $test4; public function __construct() { $test1 = rand(); $test2 = rand(); $test3 = rand(); $test4 = rand(); } } echo memory_get_usage() . "\n"; $t1 = new Tester(); echo memory_get_usage() . "\n"; $t2 = new Tester(); echo memory_get_usage() . "\n"; $t3 = new Tester(); echo memory_get_usage() . "\n"; unset($t3); $t3 = NULL; echo memory_get_usage() . "\n"; $t2 = NULL; echo memory_get_usage() . "\n"; unset($t1); echo memory_get_usage() . "\n"; This outputs: 43344 43928 44232 44568 44640 44640 44640 Note: the memory usage remains constant after the objects are allocated, even when they're unset/NULL'ed. Some of the user contributed notes on the PHP documentation suggest that the memory is actually freed and available for use by other variables/objects even though memory_get_usage() says otherwise. Another little test seems to disprove that too... The idea here is to allocate close to 8 MB, then free it to show that it can allocate that data within the memory limit. Then allocate enough class instances and free them again such that the memory usage increases enough that the same data allocated and freed initially doesn't fit anymore. If PHP did indeed free the objects, the data would fit the second time too... <?php ini_set('memory_limit','8m'); class Tester { protected $test; public function __construct() { $this->test = rand(); } } echo "Initial Memory Usage: " . memory_get_usage() . "\n"; $mb = 6 * 1024 * 1024; echo "Allocating 7 MB of data..."; $dat = ""; for ($x=0;$x<$mb;$x++) { $dat .= "x"; } echo "Memory Usage: " . memory_get_usage() . "\n"; unset($dat,$x,$mb); echo "Unset Usage: " . memory_get_usage() . "\n"; $num = 32767; $objects = array(); echo "Initial Memory Usage (2): " . memory_get_usage() . "\n"; echo "Allocating $num objects..."; for ($x=0;$x<$num;$x++) { $objects[$x] = new Tester(); } echo "Done. Memory Usage: " . memory_get_usage() . "\n"; echo "Freeing $num objects..."; for ($x=0;$x<$num;$x++) { unset($objects[$x]); $objects[$x] = NULL; } echo "Done. Memory Usage: " . memory_get_usage() . "\n"; $mb = 6 * 1024 * 1024; echo "Allocating 7 MB of data..."; $dat = ""; for ($x=0;$x<$mb;$x++) { $dat .= "x"; } This gives: Initial Memory Usage: 44248 Allocating 7 MB of data...Memory Usage: 6335888 Unset Usage: 44448 Initial Memory Usage (2): 44504 Allocating 32767 objects...Done. Memory Usage: 7752920 Freeing 32767 objects...Done. Memory Usage: 2807080 Allocating 7 MB of data... Fatal error: Allowed memory size of 8388608 bytes exhausted (tried to allocate 1 bytes) in /home/janderson/svn/memtest.php on line 44 Am I missing something? (Is there a force_garbage_collection() function somewhere that I'm missing?) Any suggestions/workarounds/anything would be most appreciated. Cheers, jon
Using PHP 5.2.0RC5-dev (cli) (built: Sep 18 2006 08:20:52) on Windows (which has no memory_get_usage() functions), the scripts work fine. Allocating 7 MB of data...Allocating 32767 objects...Freeing 32767 objects...Allocating 7 MB of data... Using System Internals Process Explorer, you can see the memory increase and decrease as expected. Using the same script via ISAPI also worked as expected. Not much help in answering the issue, so maybe this is an issue that has been fixed already? -- ----- Richard Quadling Zend Certified Engineer : http://zend.com/zce.php?c=ZEND002498&r=213474731 "Standing on the shoulders of some very clever giants!" -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
