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From "Graham Dumpleton (JIRA)" <j...@apache.org>
Subject [jira] Work stopped: (MODPYTHON-109) Signal handler calling Py_Finalize() when child processes being killed.
Date Fri, 10 Mar 2006 10:42:39 GMT
     [ http://issues.apache.org/jira/browse/MODPYTHON-109?page=all ]

Work on MODPYTHON-109 stopped by Graham Dumpleton

> Signal handler calling Py_Finalize() when child processes being killed.
> -----------------------------------------------------------------------
>          Key: MODPYTHON-109
>          URL: http://issues.apache.org/jira/browse/MODPYTHON-109
>      Project: mod_python
>         Type: Bug
>   Components: core
>     Versions: 3.2.7
>     Reporter: Graham Dumpleton
>     Assignee: Graham Dumpleton
>  Attachments: MP109_20060308_grahamd_1.diff
> When Apache is killing off child processes as part of actions taken when the "apachectl
restart" or "apachectl graceful" command is run, it sends a SIGTERM signal to the child processes.
This causes a signal handler registered by Apache to be run. That signal handler destroys
the main child memory pool. That memory pool has though a cleanup handler associated with
it which was registered by mod_python. That cleanup handler ultimately calls Py_Finalize().
> The problem with this is that Py_Finalize() isn't safe to be called from a signal handler
and if a handler is still executing or there is a separate thread running in the context of
Python, a deadlock will likely ensue. This will prevent the child process exiting due to the
SIGTERM causing the Apache parent process to send it a SIGKILL to really kill it.
> For a more detailed assessment of the problem and what lead to this conclusion see:
>   http://www.modpython.org/pipermail/mod_python/2006-January/019865.html
>   http://www.modpython.org/pipermail/mod_python/2006-January/019866.html
>   http://www.modpython.org/pipermail/mod_python/2006-January/019870.html
> To avoid the problem, the only choice seems to be avoid calling Py_Finalize() from the
signal handler. The simplistic way of doing this seems to be to add:
>      if (child_init_pool)
>          return APR_SUCCESS;
> at the start of python_finalize(). This will mean that Py_Finalize() is never called
in child processes. The full consequences of this is unknown, but on face value it would seem
that it might be a reasonable thing to do. More research may be required.

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