Usually this is due to the unload order of extensions.

This was up for discussion recently &  but has been on the wiki[1] for a bit of time with no takers :)

So when session gets unloaded after APC, it causes cleanup ordering issues. The easiest way to resolve this is to add a php.auto_append_file with 

<?php
session_write_close();

just to close out all the pending session data before APC starts unloading functions from memory.

[1] - https://wiki.php.net/ideas/dependencyinterfaceapi#initial_brainstorming_and_design

Okay, I did that but know I get another exception :-( i get the feeling that APC does not like me...

ModLoad: ...
(1758.1184): Break instruction exception - code 80000003 (first chance)
ntdll!DbgBreakPoint:
00000000`774d0530 cc              int     3
0:004> g
ModLoad: 00000000`70f90000 00000000`71010000   C:\Windows\SysWOW64\uxtheme.dll
ModLoad: 00000000`71040000 00000000`71053000   C:\Windows\SysWOW64\dwmapi.dll
(1758.b50): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
php5ts!_zend_mm_alloc_int+0x59:
73deab59 8b03            mov     eax,dword ptr [ebx]  ds:002b:371abf0e=????????

Backtrace:
php5ts!_zend_mm_alloc_int(struct _zend_mm_heap * heap = 0x01138788, unsigned int size = 0x2d)+0x59
php5ts!_emalloc(unsigned int size = 0x2d)+0x34
php5ts!_zend_hash_add_or_update(struct _hashtable * ht = <Memory access error>, char * arKey = <Memory access error>, unsigned int nKeyLength = <Memory access error>, void * pData = <Memory access error>, unsigned int nDataSize = <Memory access error>, void ** pDest = <Memory access error>, int flag = <Memory access error>)+0x13a
php5ts!php_var_serialize_intern(struct smart_str * buf = 0x00000000, struct _zval_struct * struc = 0x00000000, struct _hashtable * var_hash = 0x00000000, void *** tsrm_ls = 0x00000000)+0x19a
MSWSOCK!WSPSend+0x375

I forgot to mention the output that I get from the built-in webserver in the cmd:
[Tue Nov 13 10:29:05 2012] 127.0.0.1:3053 [200]: /index.php/admin/system_config/edit/section/intraship/key/a0628cd73a5a9d7c55a17c7ed5e75230/ - include(): Cannot redeclare class mage_adminhtml_block_widget_form in C:\projects\projectname\magento\lib\Varien\Autoload.php on line 93

Also drop that xdebug. It can create bad side effects, also rather pointless to 
have a debugger and an opcode cache loaded at the same time, from a perf point of 
view :)

Hi,

still fails for you? The second BT is not very informative, not sure it's APC related.

Hi. Thanks for your feedback.

@pajoye@php.net: Yes, it is just because of debugging, on my local machine ;-) and to test a caching module. But I have disabled xdebug for my tests now.

@ab@php.net: I have tested it again and the issue still exists. But it seems like I have not copied the whole BT...

I have started built-in server and before the exception occurs I get the warning on CLI:
[Mon Dec 10 08:45:03 2012] 127.0.0.1:13418 [200]: /index.php/admin/system_config/edit/section/intraship/key/baf7484082345fe06f81b914d20cb490/ - include(): Cannot redeclare class mage_adminhtml_block_widget_form in C:\projects\kosmetikzentrum\magento\lib\Varien\Autoload.php on line 95

Although there is nothing special in this class. Just some usual methods and properties.
Here's the whole BT:

php5ts!_zend_mm_alloc_int(struct _zend_mm_heap * heap = 0x02738928, unsigned int size = 0x2c)+0x59
php5ts!_emalloc(unsigned int size = 0x2c)+0x34
php5ts!_zend_hash_add_or_update(struct _hashtable * ht = <Memory access error>, char * arKey = <Memory access error>, unsigned int nKeyLength = <Memory access error>, void * pData = <Memory access error>, unsigned int nDataSize = <Memory access error>, void ** pDest = <Memory access error>, int flag = <Memory access error>)+0x13a
php5ts!php_var_serialize_intern(struct smart_str * buf = 0x00000000, struct _zval_struct * struc = 0x00000000, struct _hashtable * var_hash = 0x00000000, void *** tsrm_ls = 0x00000000)+0x19a
MSWSOCK!WSPSend+0x1bf
php!php_cli_server_client_send_through(struct php_cli_server_client * client = 0x00000038, char * str = 0x00000009 "--- memory read error at address 0x00000009 ---", unsigned int str_len = 0x6e68c31)+0x25
php5ts!_emalloc(unsigned int size = <Memory access error>)+0x34
php5ts!_zend_hash_add_or_update(struct _hashtable * ht = <Memory access error>, char * arKey = <Memory access error>, unsigned int nKeyLength = <Memory access error>, void * pData = <Memory access error>, unsigned int nDataSize = <Memory access error>, void ** pDest = <Memory access error>, int flag = <Memory access error>)+0x15d
php5ts!php_var_serialize_intern(struct smart_str * buf = 0x00000001, struct _zval_struct * struc = 0x00000000, struct _hashtable * var_hash = 0x00000001, void *** tsrm_ls = 0x00000000)+0x19a
MSWSOCK!WSPSend+0x375
php5ts!php_session_encode(int * newlen = 0x00b6e474, void *** tsrm_ls = 0x0000002c)+0x41
php5ts!php_session_save_current_state(void *** tsrm_ls = 0x02738928)+0x3b
php5ts!zm_deactivate_session(int type = 0n1, int module_number = 0n17, void *** tsrm_ls = 0x02732f30)+0xae
php5ts!zend_deactivate_modules(void *** tsrm_ls = 0x02732f30)+0x7a
php5ts!php_request_shutdown(void * dummy = 0x00000000)+0x1f3
php!php_cli_server_request_shutdown(struct php_cli_server * server = 0x00000188, struct php_cli_server_client * client = 0x0327f728, void *** tsrm_ls = 0x02738928)+0x8
php!php_cli_server_dispatch(struct php_cli_server * server = 0x00000005, struct php_cli_server_client * client = 0x00000188, void *** tsrm_ls = 0x06e68c29)+0xf1
php!php_cli_server_recv_event_read_request(struct php_cli_server * server = <Memory access error>, struct php_cli_server_client * client = <Memory access error>, void *** tsrm_ls = <Memory access error>)+0xa7
php!php_cli_server_do_event_for_each_fd_callback(void * _params = <Memory access error>, int fd = <Memory access error>, int event = <Memory access error>)+0xdc
php!php_cli_server_poller_iter_on_active(struct php_cli_server_poller * poller = 0x0000002c, void * opaque = <Memory access error>, <function> * callback = <Memory access error>)+0xb4
php!php_cli_server_do_event_loop(struct php_cli_server * server = 0x08088a8b, void *** tsrm_ls = 0x06e68c31)+0x94
php!do_cli_server(int argc = 0n1473983318, char ** argv = 0x00000005, void *** tsrm_ls = 0x14245c89)+0x1f5
ntdll_775e0000!RtlpLowFragHeapAllocFromContext+0xaec
ntdll_775e0000!RtlAllocateHeap+0x206
WARNING: Frame IP not in any known module. Following frames may be wrong.
0xff8b9090
0x5077f80
icudt49!icudt49_dat+0x8b740f
0x78b0006
0xeec1f78b
0x33f03303
0x6e00a435
0xfc7d8977
0x468bf133
0xf4458904
0x800747c6
0x647c6
0x8b085e8b
0x5d890c4e
0x1c383e0
0x83e44d89
0xe38101d1

The BT shows the session ext is still not happy. Anyway could you please tell where you've added your session_write_close() call? Please also try to move the session close call around, may be you'll find a more suitable place to close the session (i'm just not a big magento specialist :)).

I've tried with magento version 1.7.0.2 (pure), APC 3.1.14-dev (same build as for the bug #63445) and the latest 5.4 snap. No crash but magento just hangs forever on the first request.

Sorry, I have done something wrong with the session_write_close() call. Now the BT has changed.

I have done some further tests and have noticed something.
The exception occurs only on one particular page (Magento Backend Configuration of the DHL Intraship Module).

When I start the built-in server, clean the file cache, visit some other pages and then go to the above named page, I only get the error Message "Fatal error: include(): Cannot redeclare class mage_adminhtml_block_widget_form in C:\projects\xyz\magento\lib\Varien\Autoload.php on line 102" but WITHOUT the exception in the core of PHP.

Now, if I clean Magento's file cache, start the server (plus WinDbg) and reload the page (without calling another page) I get the exception in PHP.

First the debugger says:

(8f4.520): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
php5ts!_zend_mm_alloc_int+0x59:
5797ab59 8b03            mov     eax,dword ptr [ebx]  ds:002b:297cb2a0=????????

With this BT:
php5ts!_zend_mm_alloc_int(struct _zend_mm_heap * heap = 0x01188788, unsigned int size = 0x2d)+0x59
php5ts!_emalloc(unsigned int size = 0x2d)+0x34
php5ts!_zend_hash_add_or_update(struct _hashtable * ht = <Memory access error>, char * arKey = <Memory access error>, unsigned int nKeyLength = <Memory access error>, void * pData = <Memory access error>, unsigned int nDataSize = <Memory access error>, void ** pDest = <Memory access error>, int flag = <Memory access error>)+0x13a
php5ts!php_var_serialize_intern(struct smart_str * buf = 0x00505536, struct _zval_struct * struc = 0x00000031, struct _hashtable * var_hash = 0x00000039, void *** tsrm_ls = 0x0000000a)+0x19a
MSWSOCK!WSPSend+0x375


Then when I click "GO (F5)" on WinDbg, the debugger says:

0:000:x86> g
(8f4.520): Access violation - code c0000005 (!!! second chance !!!)
ntdll_77a40000!ZwRaiseException+0x12:
77a615de 83c404          add     esp,4

With this BT:
ntdll_77a40000!ZwRaiseException+0x12
ntdll_77a40000!KiUserExceptionDispatcher+0x29
WARNING: Frame IP not in any known module. Following frames may be wrong.
0xc0000005
php5ts!_emalloc(unsigned int size = 0x2d)+0x34
php5ts!_zend_hash_add_or_update(struct _hashtable * ht = <Memory access error>, char * arKey = <Memory access error>, unsigned int nKeyLength = <Memory access error>, void * pData = <Memory access error>, unsigned int nDataSize = <Memory access error>, void ** pDest = <Memory access error>, int flag = <Memory access error>)+0x13a
php5ts!php_var_serialize_intern(struct smart_str * buf = 0x00505536, struct _zval_struct * struc = 0x00000031, struct _hashtable * var_hash = 0x00000039, void *** tsrm_ls = 0x0000000a)+0x19a
MSWSOCK!WSPSend+0x375

So where do I have to put session_write_close() now to get such a trace? What 
further testing was it?

In php.ini I have added:
auto_append_file = "auto_append.php"

And this file is in the include_path and just contains
<?php
session_write_close();

But I found out that this distroys sessions in Symfony 2.1. They are always empty after a page load.


My "further testing" was just clicking around on different pages and finding out that the problem occurs only on the particular page I have mentioned.

One question though - testing with apache was you using the official PHP 
binaries? If not, could you please retry the test using the official PHP binaries 
(including the apache SAPI dll). If you use apache 2.2, you can find that dll in 
any 5.4 release package. If you use apache 2.4, you can fetch the php module from 
one of the latest snaps here http://windows.php.net/downloads/snaps/php-5.4/ . 
Please be sure you're using apache built with VC9/openssl 0.9.8x - this way we 
can reduce the incompatibility errors.

Another idea here - would it be possible you to provide your complete install with the test data? That might be the way to reproduce and debug.

I have installed Apache 2.4 built with VC9/openssl 0.9.8x and the corresponding Apache PHP module from the latest snaps, now. But the error still occurs.

It is not possible to provide the complete install with the data, because it is a customer project with many customer data... sorry for that.
But I have tried to reproduce this bug with a fresh Magento 1.7.0.2 installation and with the DHL module and there I do not get this exception. So this does not seem to be a generall problem.

Do you have any other ideas?

We have tried many ways to reproduce the problem. We failed.

So basically, no, not other idea. If you can find a way to get us the data and 
code to reproduce it, we can then try to fix it. But right now we are shooting in 
the dark.

Initial reporter can't reproduce it anymore.