Signal handler calling Py_Finalize() when child processes being killed.
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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
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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