DeinoMPI

The Great and Terrible implementation of MPI-2

MPI_File_get_position

Returns the current position of the individual file pointer in etype units relative to the current view

int MPI_File_get_position(
  MPI_File mpi_fh,
  MPI_Offset *offset
);

Parameters

mpi_fh: [in] file handle (handle)
offset: [out] offset of individual file pointer (nonnegative integer)

Remarks

MPI_FILE_GET_POSITION returns, in offset, the current position of the individual file pointer in etype units relative to the current view.

Advice to users.

The offset can be used in a future call to MPI_FILE_SEEK using whence = MPI_SEEK_SET to return to the current position. To set the displacement to the current file pointer position, first convert offset into an absolute byte position using MPI_FILE_GET_BYTE_OFFSET, then call MPI_FILE_SET_VIEW with the resulting displacement.

Example Code

The following sample code illustrates MPI_File_get_position.

#include "mpi.h"
#include <stdio.h>
#include <stdlib.h>

/* Test set_view with DISPLACEMENT_CURRENT */
int main( int argc, char *argv[] )
{
    int errs = 0, err;
    int size, rank, *buf;
    MPI_Offset offset;
    MPI_File fh;
    MPI_Comm comm;
    MPI_Status status;

    MPI_Init( &argc, &argv );

    /* This test reads a header then sets the view to every "size" int,
        using set view and current displacement. The file is first written
        using a combination of collective and ordered writes */

    comm = MPI_COMM_WORLD;
    err = MPI_File_open( comm, "test.ord", MPI_MODE_WRONLY | MPI_MODE_CREATE, MPI_INFO_NULL, &fh );
    if (err)
    {
        MPI_Abort(MPI_COMM_WORLD, 911);
    }
    MPI_Comm_size( comm, &size );
    MPI_Comm_rank( comm, &rank );
    buf = (int *)malloc( size * sizeof(int) );
    buf[0] = size;
    err = MPI_File_write_all( fh, buf, 1, MPI_INT, &status );
    if (err) { errs++; }
    err = MPI_File_get_position( fh, &offset );
    if (err) { errs++; }
    err = MPI_File_seek_shared( fh, offset, MPI_SEEK_SET );
    if (err) { errs++; }
    buf[0] = rank;
    err = MPI_File_write_ordered( fh, buf, 1, MPI_INT, &status );
    if (err) { errs++; }
    err = MPI_File_close( &fh );
    if (err) { errs++; }

    /* Reopen the file as sequential */
    err = MPI_File_open( comm, "test.ord", MPI_MODE_RDONLY | MPI_MODE_SEQUENTIAL | MPI_MODE_DELETE_ON_CLOSE, MPI_INFO_NULL, &fh );
    if (err)
    {
        MPI_Abort(MPI_COMM_WORLD, 911);
    }

    if (rank == 0) {
        err = MPI_File_read_shared( fh, buf, 1, MPI_INT, &status );
        if (err) { errs++; }
        if (buf[0] != size) {
            errs++;
            fprintf(stderr, "Unexpected value for the header = %d, should be %d\n", buf[0], size ); fflush(stderr);
        }
    }

    MPI_Barrier( comm );

    /* All processes must provide the same file view for MODE_SEQUENTIAL */
    err = MPI_File_set_view( fh, MPI_DISPLACEMENT_CURRENT, MPI_INT, MPI_INT, "native", MPI_INFO_NULL );
    if (err) { errs++; }
    buf[0] = -1;
    err = MPI_File_read_ordered( fh, buf, 1, MPI_INT, &status );
    if (err) { errs++; }
    if (buf[0] != rank) {
        errs++;
        fprintf( stderr, "%d: buf[0] = %d\n", rank, buf[0] ); fflush(stderr);
    }
    free( buf );
    err = MPI_File_close( &fh );
    if (err) { errs++; }
    MPI_Finalize();
    return errs;
}

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