Collision detection not able to checkpoint

[KaiSzuttor]

see https://travis-ci.org/espressomd/espresso/jobs/364132063

[fweik]

Any ideas as to why that is?

…

On Tue, Apr 10, 2018, 08:59 Kai Szuttor ***@***.***> wrote: see https://travis-ci.org/espressomd/espresso/jobs/364132063 — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#1943>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AA2i38N_ejNuehX-M-whu__Fm02nZyIMks5tnFhJgaJpZM4TNs3y> .

[hmenke]

It might not be the case, but it is possible that you run into this problem at some point, so I wanted to make you aware of it.

Python 3 strings are not compatible with C++ std::string which leads to a loss of data when passing a string from Python to C++. This used to blow up our serialization in the pairinteraction project and here is how we fixed it (not Cython but SWIG). Also note our zero-copy approach to setstate.

// Make pickle work
// https://stackoverflow.com/questions/9310053/how-to-make-my-swig-extension-module-work-with-pickle
// remark: passing as std::stringstream does not work because swig calls the implicitly-deleted copy constructor of std::stringstream instead of the move constructor
%define %boost_picklable(cls...)
  %extend cls {
    PyObject* __getstate__() {
      std::stringstream ss;
      boost::archive::binary_oarchive ar(ss);
      ar << *($self);
      return PyBytes_FromStringAndSize(ss.str().data(), ss.str().length());
    }

    void __setstate_internal(PyObject* const sState) {
      char *buffer;
      Py_ssize_t len;
      PyBytes_AsStringAndSize(sState, &buffer, &len);
      boost::iostreams::array_source asource(buffer, static_cast<size_t>(len)); // prevents from copying
      boost::iostreams::stream<boost::iostreams::array_source> ss(asource);
      boost::archive::binary_iarchive ar(ss);
      ar >> *($self);
    }
  }
%enddef

[fweik]

Wouldn't you use bytes anyway in python 3? In my understanding the standard string class implies unicode. According to the cython docs std::string is convertible to and from bytes (== a char array), but not from str.

[RudolfWeeber]

This also depends on being able to control the order of restoring stuff, because the bonds used in the collision deteciton have to be present