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Links

• http://stackoverflow.com/questions/10359985/is-in-python-thread-safe
• http://effbot.org/pyfaq/what-kinds-of-global-value-mutation-are-thread-safe.htm
• PyPy: STM update: back to threads?
• Threading and Import locks
  • HN comment: Simple example of import deadlock with threading
  • Comment on python bug report
    • Though the bug is about mod_wsgi issues, the comment highlights the problem in general, and points out that the PyImport_ImportModuleNoBlock function makes it worse for the cases where there wouldn't be a deadlock by assuming that there might be and throwing an exception.
• Forking and Threading
  • From reddit comment
    • If the application has more than one thread and you can't control the "library" code that runs in your new child, then the safest bet is to prefork a child that'll fork new children on your behalf.
    • The multiprocessing module has support for this:
      • start a new child prior to any threads being started.
    • When you want to start a new process, ask that child to start the process on your behalf.
    • The child consisting of only a single thread, forks and starts the process, then (optionally) passes the new child's stdio pipe fds back to the parent (this is the bit multiprocessing has magic support for).
    • At that point, your main process can safely interact with the new cihld, requiring only the exit status to be passed back via the proxy child (since it is the new child's parent).

Gotchas

• Calling .join() from the main thread without a timeout is uninterruptable. This means that signal handers won't be invoked either. To work around it, add a timeout to .join().
  • Ref: http://bugs.python.org/issue1167930