Solution 13

C

#include <stdio.h>
#include <mpi.h>
#define DIM_BUF 10

int main(int argc, char **argv){
int myrank, nproc;
int buf[DIM_BUF];
int i, offset, intsize;
MPI_File fh;
MPI_Status status;

MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD, &nproc);
MPI_Comm_rank(MPI_COMM_WORLD, &myrank);

for(i=0;i<DIM_BUF;i++) buf[i] = myrank*DIM_BUF+i;

/* Open the file and write by using individual file pointers */
MPI_File_open(MPI_COMM_WORLD, "output.dat", MPI_MODE_CREATE|MPI_MODE_WRONLY, MPI_INFO_NULL,&fh);
MPI_Type_size(MPI_INT, &intsize);
offset = myrank*DIM_BUF*(intsize);
MPI_File_seek(fh,offset,MPI_SEEK_SET);
MPI_File_write(fh,buf,DIM_BUF,MPI_INT,&status);
MPI_File_close(&fh);

/* Re-open the file and read by using explicit offset */
MPI_File_open(MPI_COMM_WORLD,"output.dat",MPI_MODE_RDONLY,MPI_INFO_NULL,&fh);
MPI_Offset file_size;
MPI_File_get_size(fh,&file_size);
offset = file_size/nproc*myrank;
printf("myid %d, filesize %lld, offset %d\n", myrank,file_size,offset);
MPI_File_read_at(fh,offset,&buf,DIM_BUF,MPI_INT,&status);

printf("myid %d, buffer after read:",myrank);
for(i=0;i<DIM_BUF; i++)printf("%d ",buf[i]);
printf("\n\n");
MPI_File_close(&fh);

/* Write the new file using the mpi_type_create_vector. Use the fileview */
MPI_Datatype filetype;
MPI_File_open(MPI_COMM_WORLD, "output_mod.dat", MPI_MODE_CREATE|MPI_MODE_WRONLY, MPI_INFO_NULL,&fh);
MPI_Type_vector(DIM_BUF/2,2,2*nproc,MPI_INT,&filetype);
MPI_Type_commit(&filetype);

MPI_Type_size(MPI_INT, &intsize);
offset = 2*intsize*myrank;
MPI_File_set_view(fh,offset,MPI_INT,filetype,"native",MPI_INFO_NULL);
MPI_File_write_all(fh,buf,DIM_BUF,MPI_INT,&status);
MPI_File_get_size(fh,&file_size);
printf("myid %d, filesize of the second file written %lld, offset %d\n", myrank,file_size,offset);

MPI_Type_free(&filetype);
MPI_File_close(&fh);
MPI_Finalize();
return 0;
}

FORTRAN

PROGRAM mpi2io

     USE MPI
     IMPLICIT none

     INTEGER :: myrank, nproc,ierr;
     INTEGER, PARAMETER :: dim_buf = 10
     INTEGER :: buf(dim_buf)
     INTEGER :: i, intsize;
     INTEGER(KIND=MPI_OFFSET_KIND) :: offset, file_size
     INTEGER :: fh
     INTEGER :: status(MPI_STATUS_SIZE)
     INTEGER :: filetype

     CALL MPI_Init(ierr);
     CALL MPI_Comm_size(MPI_COMM_WORLD,nproc,ierr)
     CALL MPI_Comm_rank(MPI_COMM_WORLD,myrank,ierr)

     DO i=1,dim_buf
        buf(i) = myrank*dim_buf+i-1;
     END DO

     ! Open the file and write by using individual file pointers 
     CALL MPI_File_open(MPI_COMM_WORLD, "output.dat", MPI_MODE_CREATE+MPI_MODE_WRONLY, MPI_INFO_NULL,fh,ierr)

     CALL MPI_Type_size(MPI_INTEGER,intsize,ierr)
     offset = myrank*dim_buf*(intsize)
     CALL MPI_File_seek(fh,offset,MPI_SEEK_SET,ierr)
     CALL MPI_File_write(fh,buf,dim_buf,MPI_INTEGER,status,ierr)

     CALL MPI_File_close(fh,ierr)

     ! Re-open the file and read by using explicit offset
     CALL MPI_File_open(MPI_COMM_WORLD,"output.dat",MPI_MODE_RDONLY,MPI_INFO_NULL,fh,ierr)

     CALL MPI_File_get_size(fh,file_size,ierr)
     offset = file_size/nproc*myrank
     write(6,*) "myid ",myrank,"filesize ", file_size, "offset ", offset

     CALL MPI_File_read_at(fh,offset,buf,dim_buf,MPI_INTEGER,status,ierr)
     CALL MPI_File_close(fh,ierr)

     ! Write the new file using the mpi_type_create_vector. Use the fileview 
     CALL MPI_File_open(MPI_COMM_WORLD, "output_mod.dat", MPI_MODE_CREATE+MPI_MODE_WRONLY, MPI_INFO_NULL,fh,ierr)
     CALL MPI_Type_vector(dim_buf/2,2,2*nproc,MPI_INTEGER,filetype,ierr)
     CALL MPI_Type_commit(filetype,ierr)

     CALL MPI_Type_size(MPI_INTEGER, intsize, ierr)
     offset = 2*intsize*myrank
     CALL MPI_File_set_view(fh,offset,MPI_INTEGER,filetype,"native",MPI_INFO_NULL,ierr)
     CALL MPI_File_write_all(fh,buf,DIM_BUF,MPI_INTEGER,status,ierr)

     CALL MPI_File_get_size(fh,file_size,ierr)
     write(6,*) "myid ", myrank, "filesize of the second file written", file_size, "offset", offset

     CALL MPI_Type_free(filetype,ierr)
     CALL MPI_File_close(fh,ierr) 
     CALL MPI_Finalize(ierr)

END PROGRAM mpi2io