#include <mpi.h>
  #include <thread>
  #include <chrono>
  #include <stdlib.h>
  #include <iostream>
  #include <time.h>


  using namespace std;

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

      MPI_Init(NULL, NULL);

      int rank;
      MPI_Comm_rank(MPI_COMM_WORLD, &rank);

      srand (time(NULL)+rank);
      int wt = rand() % 5 + 1;
      cout <<"rank: "<< rank<< " sleep: "<< wt<<endl;



      //here is the magic...

      int * flag;
      MPI_Win window;
      int master;
      MPI_Win_allocate(sizeof(int), sizeof(int),MPI_INFO_NULL, MPI_COMM_WORLD, &flag, &window );


      *flag = -1;
      this_thread::sleep_for(chrono::seconds(wt));


      MPI_Win_lock (MPI_LOCK_EXCLUSIVE, 0, 0, window);
      if(rank==0)
      {
        master = *flag;
      }
      else
      {
        MPI_Get(&master, 1, MPI_INT, 0, 0, 1, MPI_INT, window);
      }

      if(master == -1)
      {
        master = rank;
        MPI_Put(&rank,1,MPI_INT,0,0,1,MPI_INT,window);
      }
      MPI_Win_unlock (0, window);


      if(master == rank)
      {
        cout<< "rank: "<<rank<<". I am the master"<<endl;
      }
      else
      {
        cout<< "rank: "<<rank<<". I am the slave of "<<master<<endl;
      }


      MPI_Win_free( &window );
      MPI_Finalize();
  }