Function Initialize_without_split

Src/Base/AMReX_MPMD.cpp:44–95

Initialize_without_split function assigns and checks the required AMReX_MPMD variables. This function is internally leveraged by Initialize function. This function needs to be used EXPLICITLY ONLY with pyAMReX (python) so that the communication split can be performed using a python library, for example, mpi4py. */

library, for example, mpi4py.
*/
void Initialize_without_split (int argc, char* argv[])
{
    initialized = true;
    int flag;
    MPI_Initialized(&flag);
    if (!flag) {
        MPI_Init(&argc, &argv);
        mpi_initialized_by_us = true;
    }

    MPI_Comm_rank(MPI_COMM_WORLD, &myproc);
    MPI_Comm_size(MPI_COMM_WORLD, &nprocs);

    int* p = nullptr;
    MPI_Comm_get_attr(MPI_COMM_WORLD, MPI_APPNUM, &p, &flag);
    appnum = (flag && p) ? *p : -1;

    std::vector<int> all_appnum(nprocs);
    MPI_Allgather(&appnum, 1, MPI_INT, all_appnum.data(), 1, MPI_INT, MPI_COMM_WORLD);
    int napps = num_unique_elements(all_appnum);

    // MPI_APPNUM does not appear to work with slurm on some systems.
    if (napps != 2) {
        std::vector<int> all_argc(nprocs);
        MPI_Allgather(&argc, 1, MPI_INT, all_argc.data(), 1, MPI_INT, MPI_COMM_WORLD);
        napps = num_unique_elements(all_argc);
        if (napps == 2) {
            appnum = static_cast<int>(argc != all_argc[0]);
        }
    }

    if (napps != 2) {
        std::string exename;
        if (argc > 0) {
            exename = std::string(argv[0]);
        }
        unsigned long long hexe = std::hash<std::string>{}(exename);
        std::vector<unsigned long long> all_hexe(nprocs);
        MPI_Allgather(&hexe, 1, MPI_UNSIGNED_LONG_LONG,
                      all_hexe.data(), 1, MPI_UNSIGNED_LONG_LONG, MPI_COMM_WORLD);
        napps = num_unique_elements(all_hexe);
        if (napps == 2) {
            appnum = static_cast<int>(hexe != all_hexe[0]);
        }
    }

    if (napps != 2) {
        std::cout << "amrex::MPMD only supports two programs." << '\n';
        MPI_Abort(MPI_COMM_WORLD, 1);
    }

}

MPI_Comm Initialize (int argc, char* argv[])
{