Example 1: SPMD Program

Note: The group functions in the PVM version of the program are not necessary in the MPI counterpart, since the basic group corresponding to MPI_COMM_WORLD containing all the tasks already exists in MPI.

SPMD Program in PVM Version

/*
*    SPMD example using PVM 3
*    also illustrating group functions
*/
#define NPROC 4
#include <stdio.h>
#include <sys/types.h>
#include "pvm3.h"
void dowork(int me, int nproc);
main()
{
    int mytid;                  /* my task id */
    int tids[NPROC];            /* array of task id */
    int me;                     /* my process number */
    int i;
    /* enroll in pvm */
    mytid = pvm_mytid();
    /* Join a group and if I am the first instance */
    /* i.e. me=0 spawn more copies of myself       */
    me = pvm_joingroup("foo");
    printf("me = %d mytid = %d\n",me,mytid);
    if( me == 0 )
       pvm_spawn("spmd", (char**)0, 0, "", NPROC-1,&tids[1]);
    /* Wait for everyone to startup before proceeding. */
    pvm_barrier("foo", NPROC);
/*------------------------------------------------------*/
     dowork(me, NPROC);
     /* Program finished. Leave group and exit pvm */
     pvm_lvgroup("foo");
     pvm_exit();
     exit(1);
}
/* Simple example passes a token around a ring */
void dowork(int me, int nproc)
{
     int token;
     int src, dest;
     int count  = 1;
     int stride = 1;
     int msgtag = 4;
     /* Determine neighbors in the ring */
     src = pvm_gettid("foo", me-1);
     dest= pvm_gettid("foo", me+1);
     if(me == 0)
        src = pvm_gettid("foo", NPROC-1);
     if(me == NPROC-1)
        dest = pvm_gettid("foo", 0);
     if(me == 0)
     {
        token = dest;
        pvm_initsend(PvmDataDefault);
        pvm_pkint(&token, count, stride);
        pvm_send(dest, msgtag);
        printf("token ring begun: value sent = %d\n", token);
        pvm_recv(src, msgtag);
        pvm_upkint(&token, count, stride);
        printf("token ring done: value recvd = %d\n", token);
     }
     else
     {
        pvm_recv(src, msgtag);
        pvm_upkint(&token, count, stride);
        pvm_initsend(PvmDataDefault);
        pvm_pkint(&token, count, stride);
        pvm_send(dest, msgtag);
    }
}

SPMD Program in MPI Version

/*
*    SPMD example using MPI,
*    illustrating porting from PVM to MPI.
*/
#include <stdio.h>
#include <sys/types.h>
#include <mpi.h>
void dowork(int me, int nproc);
main(int argc, char *argv[])
{
    int mytid;                  /* my task id */
    int ntasks;                 /* total number of tasks */
    int i;
    /* Initialize MPI */
    MPI_Init(&argc, &argv);
    /* Get our task id (our rank in the basic group) */
    MPI_Comm_rank(MPI_COMM_WORLD, &mytid);
    /* Get the number of MPI tasks */
    MPI_Comm_size(MPI_COMM_WORLD, &ntasks);
    if(mytid == 0)
       printf("mytid = %d, ntasks = %d\n", mytid, ntasks);
    /* Wait for everyone to startup before proceeding. */
    MPI_Barrier(MPI_COMM_WORLD);
/*-------------------------------------------------*/
     dowork(mytid, ntasks);
     MPI_Finalize();
     exit(0);
}
/* Simple example passes a token around a ring */
void dowork(int me, int nproc)
{
     int token;
     int src, dest;
     MPI_Status status;
     int count = 1;
     int msgtag = 4;
     /* Determine neighbors in the ring */
     src = me-1;
     dest= me+1;
     if(me == 0) src = nproc-1;
     if(me == nproc-1) dest = 0;
     if(me == 0)
     {
        token = dest;
        MPI_Send(&token, count, MPI_INT, dest, msgtag,
                                          MPI_COMM_WORLD);
        printf("token ring begun: value sent = %d\n", token);
        MPI_Recv(&token, count, MPI_INT, src, msgtag,
                                    MPI_COMM_WORLD, &status);
        printf("token ring done: value rcvd = %d\n", token);
     }
     else
     {
        MPI_Recv(&token, count, MPI_INT, src, msgtag,
                                    MPI_COMM_WORLD, &status);
        MPI_Send(&token, count, MPI_INT, dest, msgtag,
                                       MPI_COMM_WORLD);
     }
}