| Graham Dumpleton (JIRA) 2006-01-07, 7:46 am |
| 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 SIGTERM signal to the child processes. This causes a signal handler registered by Apache to be run. That si
gnal 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/...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.
|