Amaury Forgeot d'Arc <amauryfa@gmail.com> added the comment:

ctypes performs the initializations in a way that break the threading.local functionality.

Not quite. ctypes (or more exactly: the PyGILState_Ensure() and PyGILState_Release() functions, which are the standard API to do this) is in a situation where it must call Python code from a thread which has no PyThreadState. So it creates a thread state, runs the code, and destroys the thread state; is this wrong? If you want to keep Python state during your C thread, there are 4 lines to add to your function: void *async_cb(void *dummy) { PyGILState_STATE gstate = PyGILState_Ensure(); Py_BEGIN_ALLOW_THREADS (*callback_fn)(); (*callback_fn)(); Py_END_ALLOW_THREADS PyGILState_Release(gstate); pthread_exit(NULL); } ---------- resolution: -> works for me status: open -> closed _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue6627> _______________________________________