[ http://issues.apache.org/jira/brows...ON-109?page=all ]

Work on MODPYTHON-109 started 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
>     Reporter: Graham Dumpleton
>     Assignee: Graham Dumpleton

>
> When Apache is killing off child processes as part of actions taken when the "apac
hectl 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. Th
at
signal handler destroys the main child memory pool. That memory pool has though a cleanup ha
ndler 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 pr
oce
ss exiting due to the SIGTERM causing the Apache parent process to send it a SIGKILL to real
ly kill it.
> For a more detailed assessment of the problem and what lead to this conclu
sion 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_Finaliz
e() 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 call
ed in child processes. The full consequences of this is unknown, but on face value i
t would seem that it might be a reasonable thing to do. More research may be require
d.

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