child_barriers.cpp

#include <mpi.h>
#include <iostream>


using namespace MPI;
using namespace std;

int main(int argc, char**argv) {

    //Initiate the MPI API
    Init(argc, argv);

    // Get the communicator and the Process API
    Intercomm parentComm = Comm::Get_parent();
    int rank = parentComm.Get_rank();
    int size = parentComm.Get_size();
    cout << "Started worker rank: " << rank << "/" << size <<endl;
    if(rank == 0)
        cout << "Root comm size: " << parentComm.Get_remote_size() << endl;

    parentComm.Barrier();
    cout << rank << " - Barrier1: ok" << endl;
    parentComm.Barrier();
    cout << rank << " - Barrier2: ok" << endl;
    parentComm.Barrier();
    cout << rank << " - Barrier3: ok" << endl;
    parentComm.Barrier();
    cout << rank << " - Barrier4: ok" << endl;
    parentComm.Barrier();
    cout << rank << " - Barrier5: ok" << endl;

    
    parentComm.Disconnect();
    Finalize();
    if(Is_finalized())
        return 0;
    return 1;
}

main_barriers.cpp

#include <mpi.h>
#include <iostream>

using namespace MPI;
using namespace std;

int main(int argc, char**argv) {
    Init(argc, argv);

    Intercomm comm = COMM_WORLD.Spawn(
        "./child_barriers", NULL, 2, INFO_NULL, 0);
    cout << "Remote size root: " << comm.Get_remote_size() << endl;

    cout << "Barrier" << endl;
    comm.Barrier();
    cout << "Barrier1: ok" << endl;
    comm.Barrier();
    cout << "Barrier2: ok" << endl;
    comm.Barrier();
    cout << "Barrier3: ok" << endl;
    comm.Barrier();
    cout << "Barrier4: ok" << endl;
    comm.Barrier();
    cout << "Barrier5: ok" << endl;

    comm.Disconnect();
    Finalize();
}

makefile

EXECS=child_barriers main_barriers

all: ${EXECS}


child_barriers:
	mpic++ -o child_barriers child_barriers.cpp

main_barriers:
	mpic++ -o main_barriers main_barriers.cpp