[C++-sig] boost::python and threads

[Paul Scruby]

I am having some problems using boost::python with boost::thread.  I'm using 
threads because I want to run some tasks in the background when I'm using 
the Python's interactive shell.  However, when I use get_override() to call 
a Python method from  another boost::thread it crashes internally.  For 
example:

    #include <boost/python.hpp>
    #include <boost/thread/thread.hpp>
    #include <boost/thread/xtime.hpp>

    using namespace boost::python;

    class Ticker
        :    public wrapper<Ticker>
    {
    private:
        bool run_;
        volatile bool * running_;
        boost::thread * thread_;
        boost::xtime xt_;
    public:
        Ticker() : running_(&run_) { *running_ = false; }

        void operator()()
        {
            while (*running_)
            {
                boost::xtime_get(&xt_, boost::TIME_UTC);
                ++xt_.sec;
                boost::thread::sleep(xt_);
                onTick();
            }
        }

        void run()
        {
            if (*running_ == false)
            {
                *running_ = true;
                thread_ = new boost::thread(*this);
            }
        }

        void stop()
        {
            if (*running_ == true)
            {
                *running_ = false;
                thread_->join();
                delete thread_;
            }
        }

        virtual void onTick() { get_override("onTick")(); }
        void default_onTick() {}
    };

    BOOST_PYTHON_MODULE(tick)
    {
        class_<Ticker, boost::noncopyable> ("Ticker")
            .def("run", &Ticker::run)
            .def("stop", &Ticker::stop)
            .def("onTick", &Ticker::default_onTick);
    }

Here is a test script that which will crash when you import it into Python's 
interactive shell.

    from tick import Ticker

    class MyTicker(Ticker):
        def onTick(self):
        print "Each second"

    myticker = MyTicker()
    myticker.run()

I ran this test initially on Python 2.4.4 with the Sun C++ 5.9 compiler on 
Solaris and I also tested it using Python 2.6.2 with Visual Studio 2008 on 
Windows XP.

The call-stack in dbx on Solaris:

    >>> t at 2 (l at 2) signal SEGV (no mapping at the fault address) in 
PyErr_Restore at 0xfef38fa1
    0xfef38fa1: PyErr_Restore+0x0031:       movl     0x00000028(%edi),%ecx
    Current function is boost::python::override::operator()
       99           detail::method_result x(

    (dbx) where
    current thread: t at 2
      [1] PyErr_Restore(0x80652fc, 0x80f1220, 0x0, 0xfe77ee90, 0xfef3951e, 
0x80652fc), at 0xfef38fa1
      [2] PyErr_SetObject(0x80652fc, 0x80f1220), at 0xfef3901e
      [3] PyErr_Format(0x80652fc, 0xfef5c2d8, 0xfef7902c), at 0xfef3951e
      [4] PyObject_Call(0xfef88768, 0x806102c, 0x0), at 0xfeee291a
      [5] PyEval_CallObjectWithKeywords(0xfef88768, 0x806102c, 0x0), at 
0xfef2bf02
      [6] PyEval_CallFunction(0xfef88768, 0xfeb02004), at 0xfef434c5
    =>[7] boost::python::override::operator()(this = 0xfe77ef30), line 99 in 
"override.hpp"
      [8] Ticker::onTick(this = 0x810a304), line 48 in "ticker.cc"
      [9] Ticker::operator()(this = 0x810a304), line 25 in "ticker.cc"
      [10] boost::detail::thread_data<Ticker>::run(this = 0x810a288), line 
56 in "thread.hpp"
      [11] thread_proxy(0x810a288), at 0xfea78ce4
      [12] _thr_setup(0xfe670200), at 0xfee159b9
      [13] _lwp_start(0xfe77ef54, 0x80f1220, 0xfe77ee7c, 0xfef3901e, 
0x80652fc, 0x80f1220), at 0xfee15ca0

The call-stack in Visual Studio 2008:

    python26.dll!1e013595()
    [Frames below may be incorrect and/or missing, no symbols loaded for 
python26.dll]
    python26.dll!1e09ee7d()
  > tick.pyd!boost::python::override::operator()()  Line 103 + 0x16 bytes 
C++
    00f3fd64()
    tick.pyd!Ticker::operator()()  Line 27 + 0xe bytes C++
    tick.pyd!boost::detail::thread_data<Ticker>::run()  Line 57 C++
    tick.pyd!boost::`anonymous namespace'::thread_start_function(void * 
param=0x00245f30)  Line 168 C++
    msvcr90d.dll!_callthreadstartex()  Line 348 + 0xf bytes C
    msvcr90d.dll!_threadstartex(void * ptd=0x00d46938)  Line 331 C
    kernel32.dll!7c80b729()


Have a missed a trick using the wrapper, or does boost::python not support 
threading?

Many thanks,

Paul