2015-12 December MPI Forum slides: sessions

backwards-compat-1.c

void legacy_library_init(void) {
    MPI_Initialized(&init);
    MPI_Finalized(&finalized);
    if (init && !finalized) {
        MPI_Comm_dup(MPI_COMM_WORLD, &comm);
        // Do MPI things
    }
}

backwards-compat-2.c

void new_style_library_init(void) {
#if MPI_VERSION >= 4
    // MPI >= v4 allows Info/Errhandler before INIT
    MPI_Info_create(...);
    MPI_Errhandler_create(...);

    // If MPI_INIT was not already called, make me a
    // session and communicator.
    // Otherwise, dup MPI_COMM_WORLD.
    if (MPI_Session_create(..., &session) == MPI_SUCCESS) {
        MPI_Comm_create_from_session(session, &comm);
    } else {
        MPI_Comm_dup(MPI_COMM_WORLD, &comm);
    }
#else
    legacy_library_init();
#endif
    // Do MPI things with comm
}