I have a problem with threading using the Python/C API. I have an extension that implements a timer, and the C++ timer callback function calls a Python function. The relevant code looks like this: staticPyObject *timer_setmodname( PyObject *pSelf, PyObject *pArgs ) {

  char *b;
  PyArg_ParseTuple( pArgs, "s", &b );
  mod = PyImport_ImportModule(b);
  if( mod == NULL )
  {
        printf("Could not import %s\n",b);
        return Py_None;
  }
  modsetFlag = TRUE;
  return Py_None;

}

staticPyObject *timer_setprocname( PyObject *pSelf, PyObject *pArgs ) { char *b; if( !modsetFlag )return Py_None; PyArg_ParseTuple( pArgs, "s", &b ); attr = PyObject_GetAttrString(mod,b); if( attr == NULL ) { printf("Could not import %s\n",b); return Py_None; } attrsetFlag = TRUE; return Py_None; } staticvoid CALLBACK PeriodicTimer(UINT wTimerID, UINT msg, DWORD dwUser, DWORD dw1, DWORD dw2) { PyGILState_STATE pgs;

  pgs = PyGILState_Ensure();
  if(attrsetFlag)
  {
        pres = PyObject_CallFunction(attr,NULL);
        if( pres == NULL )printf("CallFunction failed!\n");
  }
  PyGILState_Release( pgs );

}

The Python code that sets this up looks like this:

fetimer.setmodname("Timeslice3") fetimer.setprocname("Timetester") print "\n Program Waiting for Time Slice" while True: time.sleep(0.010)

and the module Timeslice3.py looks like this:

#Timeslice3.py def Timetester(): pass

When I run this stuff, it works fine for hundreds, often even thousands, of timer ticks (I’ve been testing with about thirty ticks per second, but it doesn’t matter – it still crashes at ten or fewer ticks per second). Sometimes it runs for only a few seconds, sometimes for ten minutes or so. But it always eventually crashes Python. Usually it gives no error message. Sometimes, though, it does give an error message, but not always the same one. I’ve noted three that it has given in my testing so far:

Fatal Python Error: This thread state must be current when releasing

Fatal Python Error: PyThreadState_DeleteCurrent: no current tstate

Fatal Python Error: PyEval_SaveThread: NULL tstate

Can anybody help me make this code stable, so that it works all the time? I’m using Python 2.6.5 under Windows Vista, but it crashes under Windows XP as well.