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


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 SIGT
ERM signal to the child processes. This causes a signal handler registered b
y Apache to be run. That si
gnal handler destroys the main child memory pool. That memory pool has thoug
h a cleanup handler associated with it which was registered by mod_python. T
hat cleanup handler ultimately calls Py_Finalize().

The problem with this is that Py_Finalize() isn't safe to be called from a s
ignal handler and if a handler is still executing or there is a separate thr
ead running in the context of Python, a deadlock will likely ensue. This wil
l prevent the child process
exiting due to the SIGTERM causing the Apache parent process to send it a SI
GKILL to really kill it.

For a more detailed assessment of the problem and what lead to this conclusi
on 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 a
dd:

if (child_init_pool)
return APR_SUCCESS;

at the start of python_finalize(). This will mean that Py_Finalize() is neve
r called in child processes. The full consequences of this is unknown, but o
n face value it would seem that it might be a reasonable thing to do. More r
esearch may be required.

[ Post a follow-up to this message ]