Message Passing

• Tasks, in Unix generally separate processes, are complete programs with their own local data.

  • Each task has its own ID.
  • Tasks communicate by sending and receiving messages.

• Widely available message passing libraries:

  • PVM
    • good for clusters.
  • MPI
    • emerging standard.

#include <stdio.h>

#include "mpi.h"

main(int argc,char **argv)

{

int rank,size,sdata=100155,rdata=0;

MPI_Status status;

MPI_Init(&argc,&argv);

MPI_Comm_rank( MPI_COMM_WORLD, &rank);

MPI_Comm_size( MPI_COMM_WORLD, &size);

if(rank==0) {

MPI_Send(&sdata,1,MPI_INT,1,0,

MPI_COMM_WORLD);

MPI_Recv(&rdata,1,MPI_INT,1,1,

MPI_COMM_WORLD,&status);

if(rdata==sdata)

printf("test succeeds\n");

else printf("test fails\n");

}

else {

MPI_Recv(&rdata,1,MPI_INT,0,0,

MPI_COMM_WORLD,&status);

MPI_Send(&rdata,1,MPI_INT,0,1,

MPI_COMM_WORLD);

}

MPI_Finalize(); exit(0);

}

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