MPI_File_set_info

int MPI_File_set_info(
  MPI_File mpi_fh,
  MPI_Info info
);

Parameters

mpi_fh

[in] file handle (handle)

info

[in] info object (handle)

Remarks

MPI_FILE_SET_INFO sets new values for the hints of the file associated with mpi_fh. MPI_FILE_SET_INFO is a collective routine. The info object may be different on each process, but any info entries that an implementation requires to be the same on all processes must appear with the same value in each process's info object.

Advice to users.

Many info items that an implementation can use when it creates or opens a file cannot easily be changed once the file has been created or opened. Thus, an implementation may ignore hints issued in this call that it would have accepted in an open call.

Example Code

The following sample code illustrates MPI_File_set_info.

#include "mpi.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/*
* access style is explicitly described as modifiable. values include
* read_once, read_mostly, write_once, write_mostlye, random
*/
int main( int argc, char *argv[] )
{
    int errs = 0, err;
    int buf[10];
    int rank;
    MPI_Comm comm;
    MPI_Status status;
    MPI_File fh;
    MPI_Info infoin, infoout;
    char value[1024];
    int flag, count;

    MPI_Init( &argc, &argv );
    comm = MPI_COMM_WORLD;
    MPI_Comm_rank( comm, &rank );
    MPI_Info_create( &infoin );
    MPI_Info_set( infoin, "access_style", "write_once,random" );

    err = MPI_File_open( comm, "testfile", MPI_MODE_RDWR | MPI_MODE_CREATE, infoin, &fh );
    if (err) {
        errs ++;
        MPI_Abort( MPI_COMM_WORLD, 911 );
    }

    buf[0] = rank;
    err = MPI_File_write_ordered( fh, buf, 1, MPI_INT, &status );
    if (err) { errs ++; }

    MPI_Info_set( infoin, "access_style", "read_once" );
    err = MPI_File_seek_shared( fh, 0, MPI_SEEK_SET );
    if (err) { errs ++; }

    err = MPI_File_set_info( fh, infoin );
    if (err) { errs ++; }
    MPI_Info_free( &infoin );
    buf[0] = -1;

    err = MPI_File_read_ordered( fh, buf, 1, MPI_INT, &status );
    if (err) { errs ++; }
    MPI_Get_count( &status, MPI_INT, &count );
    if (count != 1) {
        errs++;
        printf( "Expected to read one int, read %d\n", count );fflush(stdout);
    }
    if (buf[0] != rank) {
        errs++;
        printf( "Did not read expected value (%d)\n", buf[0] );fflush(stdout);
    }
    err = MPI_File_get_info( fh, &infoout );
    if (err) { errs ++; }
    MPI_Info_get( infoout, "access_style", 1024, value, &flag );
    /* Note that an implementation is allowed to ignore the set_info, so we'll accept either the original or the updated version */
    if (!flag) {
    }
    else {
        if (strcmp( value, "read_once" ) != 0 && strcmp( value, "write_once,random" ) != 0) {
            errs++;
            printf( "value for access_style unexpected; is %s\n", value );fflush(stdout);
        }
    }
    MPI_Info_free( &infoout );

    err = MPI_File_close( &fh );
    if (err) { errs ++; }

    MPI_Barrier( comm );

    if (rank == 0) {
        err = MPI_File_delete( "testfile", MPI_INFO_NULL );
        if (err) { errs ++; }
    }
    MPI_Finalize( );
    return errs;
}