I asked this question here a few days ago, and someone suggested I ask again, providing all the code, so that it can be actually tried. So here it is, and I’m still stumped.

Original post: 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 code looks like this: // fetimer.cpp : Defines the exported functions for timer function. #define_WIN32_WINNT 0x502

#include"stdafx.h" #include"mmsystem.h" #include"python.h"

#defineTARGET_RESOLUTION 1

UINT wTimerRes,fooval;

BOOL LEDflag,timeFlag; BOOL timerActive = FALSE; BOOL timerSet = FALSE; BOOL funcsetFlag = FALSE; BOOL modsetFlag = FALSE; BOOL attrsetFlag = FALSE; UINT wTimerID,timeval,setVal = 2000; HANDLE porthandle; TIMECAPS tc;

UINT userval,*pVal;

PyObject *mod, *attr, *pargs, *pres;

UINT SetTimerCallback( UINT wTimrID, UINT msInterval ); staticvoid CALLBACK PeriodicTimer(UINT wTimerID, UINT msg, DWORD dwUser, DWORD dw1, DWORD dw2); PyObject *ProcessTimer( void ); PyObject *pymod; PyObject *pattr; PyObject *foop; staticvoid (*pFunc)(UINT wTimerID, UINT msg, DWORD dwUser, DWORD dw1, DWORD dw2);

staticPyObject *timer_setup( PyObject *pSelf, PyObject *pArgs ) {

  if (timeGetDevCaps(&tc, sizeof(TIMECAPS)) != TIMERR_NOERROR) {
  }

  wTimerRes = min(max(tc.wPeriodMin, TARGET_RESOLUTION), tc.wPeriodMax);
  timeBeginPeriod(wTimerRes); 

  LEDflag = FALSE;
  timeFlag = FALSE;
  timerActive = FALSE;
  userval = 123;
  pVal = &userval;
  Py_Initialize();
  fooval = 0;
  return Py_None;

}

staticPyObject *timer_start( PyObject *pSelf, PyObject *pArgs ) { int tval = 2000; if( timerActive ){ timeKillEvent( wTimerID ); } if( timerSet ){ tval = setVal; } UINT retval = SetTimerCallback( wTimerID, tval ); timerActive = TRUE; return Py_None; }

UINT SetTimerCallback(UINT wTimrID, // sequencer data UINT msInterval) // event interval { wTimerID = timeSetEvent( msInterval, // delay wTimerRes, // resolution (global variable) (LPTIMECALLBACK)PeriodicTimer, // callback function wTimrID, // user data TIME_PERIODIC|TIME_CALLBACK_FUNCTION );
if(!wTimerID) { return 999; } else{ return 0; } }

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 );

}

staticPyObject *timer_kill( PyObject *pSelf, PyObject *pArgs ) { timeKillEvent( wTimerID ); timerSet = FALSE; timerActive = FALSE; return Py_None; }

staticPyObject *timer_settime( PyObject *pSelf, PyObject *pArgs ) { UINT t; PyArg_ParseTuple( pArgs, "i", &t ); setVal = t; timerSet = TRUE; return Py_None; }

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; }

staticPyMethodDef fetimer_methods[] = { {"timer", timer_setup, METH_VARARGS, "blah"}, {"start", timer_start, METH_VARARGS, "start timer" }, {"kill", timer_kill, METH_VARARGS, "kill timer" }, {"settime", timer_settime, METH_VARARGS, "set timer" }, {"setmodname", timer_setmodname, METH_VARARGS, "set module name" }, {"setprocname", timer_setprocname, METH_VARARGS, "set procedure name" }, {NULL, NULL} };

PyMODINIT_FUNC initfetimer(void) { Py_InitModule("fetimer", fetimer_methods); } The Python code (Timetest3.py) that sets this up looks like this: #Time Test 3.py

import fetimer #import feserial import time

Hit = 0 L = 0

fetimer.timer()

fetimer.settime(30)

fetimer.setmodname("Timeslice3")

fetimer.setprocname("Timetester")

#feserial.open(4)

#feserial.dtr(0)

print "\n Program Waiting for Time Slice"

fetimer.start()

while True: time.sleep(0.010)

and the module Timeslice3.py looks like this:

#Timeslice3.py def Timetester(): pass

The application should run by entering "python timetest3.py" at the command prompt.

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.