[MPICH] MPI-IO, vector dataype

[Russell L. Carter]

Hi folks,
I'm having some cognition problems understanding
how vector datatype works with readall/writeall.
(I.e, I'm likely being stupid).  At any rate,
I've appended a short program derived from
the UsingMPI2/moreio/read_all.c example that
generates the following output.  I expected
that there would be no lines output beginning
with 'myrank, i, obuf[i]...'.  Any clues on
where I'm being clueless?

Many thanks,
Russell


  mpiexec -n 2 /home/rcarter/mpibin/rwall
Starting rwall.
Starting rwall.
process 0 wrote 128process  ints1
  wrote 128 ints
process process 1 read 0128 read  ints128
  ints
myrank, i, obuf[i], ibuf[i]: 0 8 8 0
myrank, i, obuf[i], ibuf[i]: 0 9 9 2
myrank, i, obuf[i], ibuf[i]: 0 10 10 4
myrank, i, obuf[i], ibuf[i]: 0 11 11 6
myrank, i, obuf[i], ibuf[i]: 0 12 12 8
myrank, i, obuf[i], ibuf[i]: 0 13 13 10
myrank, i, obuf[i], ibuf[i]: 0 14 14 12
myrank, i, obuf[i], ibuf[i]: 0 15 15 14
myrank, i, obuf[i], ibuf[i]: 0 17 17 18
myrank, i, obuf[i], ibuf[i]: 0 18 18 20
myrank, i, obuf[i], ibuf[i]: 0 19 19 22
myrank, i, obuf[i], ibuf[i]: 0 20 20 24
myrank, i, obuf[i], ibuf[i]: 0 21 21 26
myrank, i, obuf[i], ibuf[i]: 0 22 22 28
myrank, i, obuf[i], ibuf[i]: 0 23 23 30
myrank, i, obuf[i], ibuf[i]: 0 24 24 32
myrank, i, obuf[i], ibuf[i]: 0 25 25 34
myrank, i, obuf[i], ibuf[i]: 0 26 26 36
myrank, i, obuf[i], ibuf[i]: 0 27 27 38
myrank, i, obuf[i], ibuf[i]: 0 28 28 40
myrank, i, obuf[i], ibuf[i]: 0 29 29 42
myrank, i, obuf[i], ibuf[i]: 0 30 30 44
myrank, i, obuf[i], ibuf[i]: 0 31 31 46
rwall end.
rwall end.

Here's the program:

#include "mpi.h"
#include <iostream>
using namespace std;

struct tester
{
     tester()
         : myrank(MPI::COMM_WORLD.Get_rank()),
           nprocs(MPI::COMM_WORLD.Get_size()),
           bufsize(FILESIZE/nprocs), nints(bufsize/sizeof(int)),
           filetype(MPI::INT),
           fname("pvfs2:/mnt/pvfs/tst/testfile")
     {
         std::ios::sync_with_stdio(false);
         filetype.Create_vector(nints/INTS_PER_BLK, INTS_PER_BLK,
                                INTS_PER_BLK * nprocs);
         filetype.Commit();
         obuf = new int[bufsize];
         ibuf = new int[bufsize];
     }

     ~tester()
     {
         delete[] obuf;
         delete[] ibuf;
     }

     void write()
     {
         for (int i = 0; i < nints; ++i) {
             obuf[i] = (myrank + 1) * i;
         }
         MPI::File f = MPI::File::Open(MPI::COMM_WORLD, fname.c_str(),
                                       MPI_MODE_CREATE | MPI_MODE_WRONLY,
                                       MPI::INFO_NULL);
         f.Set_view(INTS_PER_BLK*sizeof(int)*myrank, MPI_INT,
                    filetype, "native", MPI_INFO_NULL);
         f.Write(obuf, bufsize, MPI_INT, status);
         cerr << "process " << myrank << " wrote "
              << status.Get_count(MPI_INT) << " ints" << endl;
         f.Close();
     }

     void read()
     {
         MPI::File f = MPI::File::Open(MPI::COMM_WORLD, fname.c_str(),
                                       MPI_MODE_RDONLY, MPI::INFO_NULL);
         f.Set_view(INTS_PER_BLK*sizeof(int)*myrank, MPI_INT,
                    filetype, "native", MPI_INFO_NULL);
         f.Read(ibuf, bufsize, MPI_INT, status);
         f.Close();
         cerr << "process " << myrank << " read "
              << status.Get_count(MPI_INT) << " ints" << endl;
         for (int i = 0; i < nints; ++i) {
             if (obuf[i] != ibuf[i]) {
                 cerr << "myrank, i, obuf[i], ibuf[i]: " << myrank << " "
                      << i << " " << obuf[i] << " " << ibuf[i] << endl;
             }
         }
     }

private:
     static const int FILESIZE = 256,  INTS_PER_BLK = 8;
     int myrank, nprocs, bufsize, nints, *obuf, *ibuf;
     MPI::Datatype filetype;
     string fname;
     MPI::Status status;
};


int main()
{
     cerr << "Starting rwall.\n";
     try {
         MPI::Init();
         tester t;
         t.write();
         t.read();
         MPI::Finalize();
     } catch (exception &e) {
         cerr << "\nCaught exception: " << e.what() << endl;
         return -1;
     } catch (MPI::Exception& e) {
         cerr << "\nError:\n" << e.Get_error_string();
         return -2;
     }
     cerr << "rwall end.\n";
     return 0;
}