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Date: Sun, 11 Apr 2010 17:42:22 +0200
Message-ID: <g2vb54d0abe1004110842z15cda3fcrc47555c3ff05a17b@mail.gmail.com>
To: Frederik Banke <frederik@tigermedia.dk>
Cc: internals@lists.php.net
Content-Type: multipart/alternative; boundary=0016e6da7de1d74cfc0483f7df18
Subject: Re: [PHP-DEV] PHP hangning on futex wait
From: tyra3l@gmail.com (Ferenc Kovacs)

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On Sun, Apr 11, 2010 at 3:43 PM, Frederik Banke <frederik@tigermedia.dk>wrote:

> Hi
>
> I have a problem with my php, once in a while an apache process will hang.
> In apache's /server-status it looks like:
> *11-1*111941/3/588*W* 0.20213490179.30.2227.03 xxx.xxx.xxx.xxx
> localhostGET xxx.php?xxx=xxxAs you can see from this line the process has
> been working for 21349sec and the status is W (Sending Reply). I can se
> from
> top that the process uses 0% cpu.
>
> I have been unable to find out what causes some of the processes to behave
> like this. When I try the same request as a process that stalls it finishes
> with no problem. The problem is that the request uses alot of memory and it
> is never released so when there is many stalled processes the server
> crashes. The stalled processes only occours on a few specific requests of
> large searches so the page generation time is large for the request (30sec+
> range).
>
> I have tried to setup another server with the same configuration to debug
> but I'm unable to reproduce the problem. I suspect it to be related to some
> kind of deadlock that only occours in special cases, because of the futex
> wait mentioned below.
>
> With strace and gdb on the process i get:
>
> strace -p 11194
> futex(0x7f9fefee3a00, FUTEX_WAIT_PRIVATE, 2, NULL
>
> (gdb) where
> #0  0x00007f9fefc6a6de in ?? () from /lib/libc.so.6
> #1  0x00007f9fefbf4025 in ?? () from /lib/libc.so.6
> #2  0x00007f9fefbf026b in free () from /lib/libc.so.6
> #3  0x00007f9fefb9fb6d in setlocale () from /lib/libc.so.6
> #4  0x00007f9fe95d8e61 in zm_deactivate_basic () from
> /usr/lib/apache2/modules/libphp5.so
> #5  0x00007f9fe969d4ac in module_registry_cleanup () from
> /usr/lib/apache2/modules/libphp5.so
> #6  0x00007f9fe96a698b in zend_hash_apply () from
> /usr/lib/apache2/modules/libphp5.so
> #7  0x00007f9fe969bdad in zend_deactivate_modules () from
> /usr/lib/apache2/modules/libphp5.so
> #8  0x00007f9fe9656085 in php_request_shutdown () from
> /usr/lib/apache2/modules/libphp5.so
> #9  0x00007f9fe9711123 in ?? () from /usr/lib/apache2/modules/libphp5.so
> #10 0x00007f9ff09e72d3 in ap_run_handler () from /usr/sbin/apache2
> #11 0x00007f9ff09eaa6f in ap_invoke_handler () from /usr/sbin/apache2
> #12 0x00007f9ff09f8430 in ap_internal_redirect () from /usr/sbin/apache2
> #13 0x00007f9fe8c47bd5 in ?? () from
> /usr/lib/apache2/modules/mod_rewrite.so
> #14 0x00007f9ff09e72d3 in ap_run_handler () from /usr/sbin/apache2
> #15 0x00007f9ff09eaa6f in ap_invoke_handler () from /usr/sbin/apache2
> #16 0x00007f9ff09f860e in ap_process_request () from /usr/sbin/apache2
> #17 0x00007f9ff09f5448 in ?? () from /usr/sbin/apache2
> #18 0x00007f9ff09eeca3 in ap_run_process_connection () from
> /usr/sbin/apache2
> #19 0x00007f9ff09fcf76 in ?? () from /usr/sbin/apache2
> #20 0x00007f9ff09fd2ea in ?? () from /usr/sbin/apache2
> #21 0x00007f9ff09fde1a in ap_mpm_run () from /usr/sbin/apache2
> #22 0x00007f9ff09d360d in main () from /usr/sbin/apache2
>
>
>
> So it looks like php hangs waiting for some futex. I have tried to
> find the zm_deactivate_basic function but i have only found a macro
> "#define ZEND_MODULE_DEACTIVATE_N(module) zm_deactivate_##module"
>
> This seems to point to the module basic, but i can't find this module
> anywhere so i suspect it to be some kind of internal/core "module".
>
> Any ideas on how to proceed to find a solution?
>
> /Frederik Banke
>
I can't help you, but in the past I did see apache processes got stuck for
some ajax requests, and because it was a third party application and I
didn't had the time to debug it properly, I ended up writing a simple
process which killed the long-running apache workers which stucked with the
W status.

Tyrael

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