send_recv_ord.cpp

/*
 * Copyright 2021 Jeisson Hidalgo-Cespedes - Universidad de Costa Rica
 * Creates a secondary thread that greets in the standard output
 */

#include <mpi.h>
#include <cstdint>
#include <iostream>
#include <string>
#include <sstream>
#include <vector>

const size_t MESSAGE_CAPACITY = 256;

int main(int argc, char* argv[]) {
  if (MPI_Init(&argc, &argv) == MPI_SUCCESS) {
    int my_rank = -1;
    MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);

    int process_count = -1;
    MPI_Comm_size(MPI_COMM_WORLD, &process_count);

    char hostname[MPI_MAX_PROCESSOR_NAME];
    int hostname_len = -1;
    MPI_Get_processor_name(hostname, &hostname_len);

    std::ostringstream buffer;
    buffer << "Hello from main thread of process " << my_rank
      << " of " << process_count << " on " << hostname;

    if (my_rank != 0) {
      const std::string& message = buffer.str();
      MPI_Send(message.data(), /*count*/ message.length() + 1, MPI_SIGNED_CHAR
        , /*dest*/ 0, /*tag*/ 0, MPI_COMM_WORLD);
    } else {
      std::cout << 0 << " says: " << buffer.str() << std::endl;
      std::vector<char> message(256, '\0');
      for (int sender = 1; sender < process_count; ++sender) {
        MPI_Recv(&message[0], /*capacity*/ message.size(), MPI_SIGNED_CHAR
          , sender, /*tag*/ 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
        std::cout << sender << " says: " << &message[0] << std::endl;
      }
    }

    MPI_Finalize();
  } else {
    std::cout << "Error: could not init MPI environment" << std::endl;
  }
  return 0;
}