[development] sess_write() and PHP processes

Nic Ivy nji at njivy.org
Thu May 18 00:38:04 UTC 2006

Thanks for the clarification.  The sequence of the log entries was a  
red herring, a distraction.

It still bothers me that sess_write() is called twice for one page  
request.  I suspect there's a drupal_goto() involved, courtesy of the  
FAPI, which introduces a race condition between the first sess_write 
() and the second sess_read().

It seems like sess_write() should always win, though, unless the  
database is heavily optimized for reading at the expense of writing.

Any thoughts?


On May 17, 2006, at 6:55 PM, John VanDyk wrote:

> I think you may be confusing two things.
> $_SESSION = 'foo';
> this statement simply assigns a value to the $_SESSION superglobal.  
> The superglobal is in memory at this point.
> sess_write() is called by PHP's built-in session handling code. It  
> is the very last thing called before PHP exits. Within this  
> function, Drupal updates the appropriate database row with the  
> value of $_SESSION.
> So the sequence you gave is correct.
>> Is sess_write() called by the same PHP process that handles page  
>> requests?
>> I'm working with dado to debug node_import.module (see http:// 
>> drupal.org/node/63581).  node_import.module uses a $_SESSION  
>> variable to control the workflow state, which is something I've  
>> not seen often.
>> Simply put, the workflow progresses normally for some people (e.g.  
>> dado) and not for others (e.g. me).  For me, some variables in  
>> $_SESSION are effectively not updated.  I say "effectively"  
>> because $_SESSION is written twice.  The second write uses old  
>> values.
>> At one point, I have the following debugging statements:
>> <?php
>> watchdog('debug', 'Before');
>> $_SESSION['node_import'] = $edit; // NOTE: sess_write() calls  
>> watchdog('debug', 'Writing').
>> watchdog('debug', 'After');
>> ?>
>> The logs consistently show, in reverse chronological order:
>> Writing
>> After
>> Before
>> What's going on?
>> Nic

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