| Graham Dumpleton (JIRA) 2006-02-28, 7:46 am |
| [ 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 "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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