| Graham Dumpleton (JIRA) 2007-04-11, 7:12 am |
|
[ https://issues.apache.org/jira/brow...action_12487986 ]
Graham Dumpleton commented on MODPYTHON-109:
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In Python 2.5.1c1 they have changed how the 'threading' module makes use of the atexit module to shutdown threading. Instead of using the atexit module, the C code Python main routine now explicitly calls 'threading._shutdown()' instead. Any changes to mo
d_python will thus have to call 'threading._shutdown()' if it exists and then call 'sys.exitfunc()'.
> Signal handler calling Py_Finalize() when child processes being killed.
> -----------------------------------------------------------------------
>
> Key: MODPYTHON-109
> URL: https://issues.apache.org/jira/browse/MODPYTHON-109
> Project: mod_python
> Issue Type: Bug
> Components: core
> Affects Versions: 3.2.7
> Reporter: Graham Dumpleton
> Assigned To: Graham Dumpleton
> Fix For: 3.3
>
> 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 proce
ss 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/...ary/019865.html
> http://www.modpython.org/pipermail/...ary/019866.html
> http://www.modpython.org/pipermail/...ary/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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