/*************************************************
 * this is a mpi demo program for course 4f03
 * what it does is to add 1000 random numbers
 * in parallel on several machines and return
 * the results to the root process
 *
 * how to compile:
 * mpicc mpidemo.c -o mpidemo
 *
 * how to run:
 *mpirun -np 4 -machinefile machines mpidemo
 *
 *4 number of processes(machines)
 *machines is a text file for machine name list
 * on which to run the program, looks like:
 *    wolf35
 *    wolf36
 *    wolf37
 *    wolf38
 *
 * root process gather all results and and add them up
 * printf total sum
 * when slaves start, they send a message to master
 * master displays their name
 * after calculation finishes, master sends a message to
 * slaves to exit
 */


#include "mpi.h"
#include <stdio.h>
#include <math.h>
#include <sys/utsname.h>

#define MAXSIZE 1000
#define FILE_NAME  "rand_data.txt"


int main(int argc, char *argv[])
{
    int myid, numprocs;
    int data[MAXSIZE], i, x, low, high, myresult=0, result=0;
    FILE *fp;
    struct utsname my_name;
    char name[SYS_NMLN];
    MPI_Status  status;

    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
    MPI_Comm_rank(MPI_COMM_WORLD,&myid);

    /*get my name*/
    uname(&my_name);


    if(myid == 0)
    {
        printf("\n\nMaster (rank %d): %s started\n\n\n", myid,
	my_name.nodename); 

    for(i=1; i<numprocs; i++)
    {
       MPI_Recv(name, SYS_NMLN, MPI_CHAR, i, 0, MPI_COMM_WORLD, &status);
       printf("Slave (rank %d): %s started\n\n",  status.MPI_SOURCE, name);
    }
    }
    else
        MPI_Send(my_name.nodename, SYS_NMLN, MPI_CHAR, 0, 0, MPI_COMM_WORLD);


    if (myid == 0)
    {
        printf("\n\nPreparing data...\n\n");

        /* Open Input File and Initialize Data */
        if ((fp = fopen(FILE_NAME,"r")) == NULL)
        {
            printf("Can't open the input file: %s\n\n", FILE_NAME);
            exit(1);
        }

    /*read data from file*/
        for(i=0; i<MAXSIZE; i++)
            fscanf(fp,"%d", &data[i]);

    }

    /*broadcast data to everyone*/
    MPI_Bcast(data, MAXSIZE, MPI_INT, 0, MPI_COMM_WORLD);


    /*job partitioning*/
    x = MAXSIZE/numprocs;
    low = myid * x;
    high = low + x;

    if (myid == (numprocs -1)) 
        high = MAXSIZE;

    for(i=low; i<high; i++)
        myresult += data[i];


    MPI_Reduce(&myresult, &result, 1, MPI_INT, MPI_SUM, 0, MPI_COMM_WORLD);


    if (myid == 0)
       printf("The sum is %d, calculation is done!\n\n\n\n", result);


    if(myid == 0)
        for(i=1; i<numprocs; i++)
       MPI_Send(name, SYS_NMLN, MPI_CHAR, i, 0, MPI_COMM_WORLD);
    else
    {
        MPI_Recv(name, SYS_NMLN, MPI_CHAR, 0, 0, MPI_COMM_WORLD, NULL);
        printf("Slave %s is leaving.\n\n",my_name.nodename);

    }

    MPI_Finalize();

    if(myid == 0)
        printf("Master %s is leaving.\n\n",my_name.nodename);


    return 0;
}



/*******************************************************************/