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

/* This program illustrates the simplest of MPI programs.  The program 
 * leverages   the 'six essential' MPI calls, and one additional call 
 * that determines the name of the host where the program is running.  
 * To compile this program, issue:
 *     mpicc -o hello_world_mpi hello_world_mpi.c
 * In order to run the program on the bccd:
 *    i. Make sure that each of the hosts have run "bccd-allowall"
 *   ii. Check that all of the hosts are available with 
 *             bccd-checkem <machine-file>
 *  iii. Make the binary available on all hosts in the collective with
 *             bccd-syncdir <directory where hello_world_mpi is> <machinefile>
 *   iv. Change directories to where your files were sync'd to.
 *    v. Run the program with:
 *  mpirun -np <number of tasks> -machinefile <machinefile> ./hello_world_mpi
 */
 
/* Typically process 0 in the ranking is the server process */
#define SERVER_NODE 0

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

    int my_rank, world_size, destination, tag, source, length;
    char message[256], name[80];
    MPI_Status status;

    MPI_Init(&argc, &argv); /* note that argc and argv are passed by address */

    MPI_Comm_rank(MPI_COMM_WORLD,&my_rank);
    MPI_Comm_size(MPI_COMM_WORLD,&world_size);

    if ( my_rank!=SERVER_NODE) {
        printf("I am the client, with rank %d of %d\n", my_rank, world_size);
	MPI_Get_processor_name(name,&length);
        sprintf(message,"Greetings from process %d, %s!",my_rank,name);
        destination = 0; tag = 2;
        MPI_Send(message,strlen(message)+1,MPI_CHAR,destination,tag,MPI_COMM_WORLD);
    }
    else { /* I am the server */
        printf("I am the server, with rank %d of %d\n", my_rank, world_size);
        tag = 2;
        for (source = 1; source < world_size ; source ++) {
            MPI_Recv(message,256,MPI_CHAR,source,tag,MPI_COMM_WORLD, &status);
            fprintf(stderr, "%s\n", message);
        }
    }

    printf("Calling Finalize %d\n",my_rank);

    MPI_Finalize();
}