Uploaded image for project: 'mod_python'
  1. mod_python
  2. MODPYTHON-109

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



    • Bug
    • Status: Reopened
    • Major
    • Resolution: Unresolved
    • 3.2.7
    • None
    • core
    • None


      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:


      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.


        1. MP109_20060308_grahamd_1.diff
          5 kB
          Graham Phillip Dumpleton



            grahamd Graham Phillip Dumpleton
            grahamd Graham Phillip Dumpleton
            0 Vote for this issue
            0 Start watching this issue