[Python-Dev] pystate.c changes for Python 2.4.2 (original) (raw)

Michael Hudson mwh at python.net
Fri Jan 13 11:07:53 CET 2006

Gabriel Becedillas <gabriel.becedillas at corest.com> writes:

Hi, At the company I work for, we've embedded Python in C++ application we develop. Since our upgrade to Python 2.4.2 from 2.4.1 we started hitting PyFatalError("Invalid thread state for this thread") when using debug builds. We use both multiple interpreters and thread states.

I know you've said this to me in email already, but I have no idea how you managed to get this to work with 2.4.1 :)

I think the problem is that PyThreadStateDelete (which is used when I destroy thread states and interpreters) is not making the same clean up that PyThreadStateDeleteCurrent is doing (which is used when we create threads from python code). If a thread id is reused (obviously not between two running threads), and the previous thread used PyThreadStateDelete instead of PyThreadStateDeleteCurrent, then an old and invalid value for autoTLSkey is still stored, and that is triggering the PyFatalError when a call to PyThreadStateSwap is made. If I add this code at the end of PyThreadStateDelete:

if (autoTLSkey && PyThreadgetkeyvalue(autoTLSkey) == tstate) PyThreaddeletekeyvalue(autoTLSkey); then everything works fine.

I think I begin to understand the problem... but this is still fragile: it relies on the fact that you delete a thread state from the OS level thread that created it, but while a thread belonging to a different interpreter state has the GIL (or at least: the interpreter state of the thread state being deleted doesn't hold the GIL). Can you guarantee that?

It seems to me that to be robust, you need a way of saying "delete the thread local value of autoTLSKey from thread $FOO". But this is all very confusing...

Could you please confirm if this is a bug ?

Yes, I think it's a bug.

Cheers, mwh

-- Jokes around here tend to get followed by implementations. -- from Twisted.Quotes

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