Process creation and management

Spawn

Master process spawns two worker processes and scatters sendbuf to workers.

master.c

#include "mpi.h"

int main(int argc, char *argv[])
{ 
   int n_spawns = 2;
   MPI_Comm intercomm;

   MPI_Init(&argc, &argv);

   MPI_Comm_spawn("worker_program", MPI_ARGV_NULL, n_spawns, MPI_INFO_NULL, 0, MPI_COMM_SELF, &intercomm, MPI_ERRCODES_IGNORE); 

   int sendbuf[2] = {3, 5};
   int recvbuf; // redundant for master.

   MPI_Scatter(sendbuf, 1, MPI_INT, &recvbuf, 1, MPI_INT, MPI_ROOT, intercomm);

   MPI_Finalize();
   return 0;
}

worker.c

#include "mpi.h"
#include <stdio.h>

int main(int argc, char *argv[])
{  
   MPI_Init(&argc, &argv);

   MPI_Comm intercomm; 
   MPI_Comm_get_parent(&intercomm);

   int sendbuf[2]; // redundant for worker.
   int recvbuf;

   MPI_Scatter(sendbuf, 1, MPI_INT, &recvbuf, 1, MPI_INT, 0, intercomm);
   printf("recvbuf = %d\n", recvbuf);

   MPI_Finalize();
   return 0;
}

Execution

mpicc master.c -o master_program
mpicc worker.c -o worker_program
mpirun -n 1 master_program

Establishing connection between two independent applications

Master process spawns server and client applications with a single process for each application. Server opens a port and client connects to that port. Then client sends data to server with MPI_Send to verify that the connection is established.

master.c

#include "mpi.h"

int main(int argc, char *argv[])
{   
   MPI_Init(&argc, &argv);

   MPI_Comm intercomm;
   // Spawn two applications with a single process for each application.
   // Server must be spawned before client otherwise the client will complain at MPI_Lookup_name().
   MPI_Comm_spawn("server", MPI_ARGV_NULL, 1, MPI_INFO_NULL, 0, MPI_COMM_SELF, &intercomm, MPI_ERRCODES_IGNORE);
   MPI_Comm_spawn("client", MPI_ARGV_NULL, 1, MPI_INFO_NULL, 0, MPI_COMM_SELF, &intercomm, MPI_ERRCODES_IGNORE);
   
   MPI_Finalize();
   return 0;
}

server.c

#include "mpi.h"
#include <stdio.h>

int main(int argc, char *argv[])
{  
   MPI_Init(&argc, &argv);

   // Open port.
   char port_name[MPI_MAX_PORT_NAME];
   MPI_Open_port(MPI_INFO_NULL, port_name);

   // Publish port name and accept client.
   MPI_Comm client;
   MPI_Publish_name("name", MPI_INFO_NULL, port_name);
   MPI_Comm_accept(port_name, MPI_INFO_NULL, 0, MPI_COMM_WORLD, &client);
   
   // Receive data from client.
   int recvbuf;
   MPI_Recv(&recvbuf, 1, MPI_INT, 0, 0, client, MPI_STATUS_IGNORE);
   printf("recvbuf = %d\n", recvbuf);

   MPI_Unpublish_name("name", MPI_INFO_NULL, port_name);

   MPI_Finalize();
   return 0;
}

client.c

#include "mpi.h"

int main(int argc, char *argv[])
{   
   MPI_Init(&argc, &argv);

   // Look up for server's port name.
   char port_name[MPI_MAX_PORT_NAME];
   MPI_Lookup_name("name", MPI_INFO_NULL, port_name);
   
   // Connect to server.
   MPI_Comm server;
   MPI_Comm_connect(port_name, MPI_INFO_NULL, 0, MPI_COMM_SELF, &server);

   // Send data to server.
   int sendbuf = 3;
   MPI_Send(&sendbuf, 1, MPI_INT, 0, 0, server);
   
   MPI_Finalize();
   return 0;
}

Command line

mpicc master.c -o master_program
mpicc server.c -o server
mpicc client.c -o client
mpirun -n 1 master_program