[deal.II] Broadcasting packed objects

[Maurice Rohracker]

Dear deal.II community,

For a distributed implementation, we would like to broadcast packed data 
objects.

For the beginning, we would like to understand how the serialize function 
for packing an object is working in the sense of the deal.II way, before it 
is getting more complicated.

I created a small test with a class, which should be broadcasted. As a 
comparison, I took the dealii:Point<dim>, which can obviously be packed and 
broadcasted without any issues.

Unfortunately, the broadcast for our class does not work. We assume that 
our serialize function is not in the correct manner. Is it possible to pack 
own objects using the dealii::Utilities:pack() function? What is the proper 
way defining the serialize function?

Attached you'll find our small example code. We are using deal.II 9.0.1.

Thank you very much in advance.

Best regards,
Maurice Rohracker
Master Student Computational Engineering
FAU Erlange-Nürnberg

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cmake_minimum_required(VERSION 3.10)
set(CMAKE_BUILD_TYPE Release)

find_package(MPI)
include_directories(SYSTEM ${MPI_INCLUDE_PATH})

# Ensure dealii is present
SET(DEAL_II_DIR /usr/local/bin/dealii/)
FIND_PACKAGE(deal.II 9.0.0 QUIET
        HINTS ${deal.II_DIR} ${DEAL_II_DIR} $ENV{DEAL_II_DIR}
        )
IF(NOT ${deal.II_FOUND})
    MESSAGE(FATAL_ERROR "\n"
            "*** Could not locate a (sufficiently recent) version of deal.II. 
***\n\n"
            "You may want to either pass a flag -DDEAL_II_DIR=/path/to/deal.II 
to cmake\n"
            "or set an environment variable \"DEAL_II_DIR\" that contains this 
path."
            )
ENDIF()
SET(CMAKE_CXX_COMPILER mpicxx)

add_executable(serializationTest serializationTestMain.cpp)

target_link_libraries(serializationTest ${MPI_CPP_LIBRARIES})
DEAL_II_SETUP_TARGET(serializationTest)

//
// Created by Maurice on 04.06.2020.
//

#ifndef SERIALIZATIONTEST_ROOM_H
#define SERIALIZATIONTEST_ROOM_H

#include <string>

class Room {
private:
    int nWindows;
    int nDoors;

public:
    Room() : nWindows(0), nDoors(0) { }

    Room(int nW, int nD) : nWindows(nW), nDoors(nD) { }

    ~Room() { }

    Room(const Room &other) : nWindows(other.nWindows), nDoors(other.nDoors) { }

    Room& operator=(const Room &other) {
        if (this != &other) {
            nWindows = other.nWindows;
            nDoors = other.nDoors;
        }
        return *this;
    }

    void setWindows(int n) {
        nWindows = n;
    }

    void setDoors(int n) {
        nDoors = n;
    }

    std::string print() const {
        return "number of windows: " + std::to_string(nWindows) + " | number of doors: " + std::to_string(nDoors);
    }

    template<class Archive>
    void serialize(Archive &ar, const unsigned int version);
};

template<class Archive>
inline
void
Room::serialize(Archive & ar, const unsigned int version) {
    ar & nWindows;
    ar & nDoors;
}

#endif //SERIALIZATIONTEST_ROOM_H

//
// Created by Maurice on 03.06.2020.
//

#include "mpi.h"
#include <deal.II/base/point.h>
#include <deal.II/base/mpi.h>
#include <string>
#include <iostream>
#include "Room.h"


int main(int argc, char *argv[]) {
  dealii::Utilities::MPI::MPI_InitFinalize mpi_initialization(argc, argv, 1);
  MPI_Comm const &                         mpi_communicator(MPI_COMM_WORLD);

  Room r1;
  const unsigned dim = 5;
  dealii::Point<dim> p1;
  if (dealii::Utilities::MPI::this_mpi_process(mpi_communicator) == 0) {
      r1.setWindows(4);
      r1.setDoors(6);
      for(int i = 0; i < dim; ++i)
          p1[i] = i + 2;
    }

  // pack objects
  auto buffer = dealii::Utilities::pack(r1);
  auto bufferPoint = dealii::Utilities::pack(p1);

  // broadcast objects
  MPI_Bcast(&buffer[0], buffer.size(), MPI_CHAR, 0, mpi_communicator); // with commenting this line the code works without errors
  MPI_Bcast(&bufferPoint[0], bufferPoint.size(), MPI_CHAR, 0, mpi_communicator);


  // unpack objects (if not root process)
  if (dealii::Utilities::MPI::this_mpi_process(mpi_communicator) != 0) {
      r1 = dealii::Utilities::unpack<Room>(buffer);
      p1 = dealii::Utilities::unpack<dealii::Point<5> >(bufferPoint);
    }

  // print to see, if all worked
  std::cout << "Hello form "
            << dealii::Utilities::MPI::this_mpi_process(mpi_communicator)
            << " of "
            << dealii::Utilities::MPI::n_mpi_processes(mpi_communicator)
            << std::endl;
  std::cout << "Process: "
            << dealii::Utilities::MPI::this_mpi_process(mpi_communicator) << " "
            << r1.print() << std::endl;
  std::cout << "Process: "
            << dealii::Utilities::MPI::this_mpi_process(mpi_communicator) << std::endl;
  for(int i = 0; i < dim; ++i)
           std::cout << p1[i] << " ";
  std::cout << std::endl;
}