int MPI_File_iwrite(
  MPI_File mpi_fh,
  void *buf,
  int count,
  MPI_Datatype datatype,
  MPI_Request *request
);

Parameters

mpi_fh

[in] file handle (handle)

buf

[in] initial address of buffer (choice)

count

[in] number of elements in buffer (nonnegative integer)

datatype

[in] datatype of each buffer element (handle)

request

[out] request object (handle)

Remarks

MPI_FILE_IWRITE is a nonblocking version of the MPI_FILE_WRITE interface. MPI_FILE_WRITE writes a file using the individual file pointer.

Example Code

The following sample code illustrates MPI_File_iwrite.

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

#define SIZE (65536)
/* Uses asynchronous I/O. Each process writes to separate files and
reads them back. The file name is taken as a command-line argument,
and the process rank is appended to it.*/

int main(int argc, char **argv)
{
    int *buf, i, rank, nints, len;
    char *filename, *tmp;
    int errs=0;
    MPI_File fh;
    MPI_Status status;
    MPI_Request request;

    MPI_Init(&argc,&argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    /* process 0 takes the file name as a command-line argument and broadcasts it to other processes */
    if (rank == 0)
    {
        i = 1;
        while ((i < argc) && strcmp("-fname", *argv)) {
            i++;
            argv++;
        }
        if (i >= argc) {
            /* Use a default filename of testfile */
            len = 8;
            filename = (char *)malloc(len + 10);
            strcpy( filename, "testfile" );
        }
        else {
            argv++;
            len = (int)strlen(*argv);
            filename = (char *) malloc(len+10);
            strcpy(filename, *argv);
        }
        MPI_Bcast(&len, 1, MPI_INT, 0, MPI_COMM_WORLD);
        MPI_Bcast(filename, len+10, MPI_CHAR, 0, MPI_COMM_WORLD);
    }
    else {
        MPI_Bcast(&len, 1, MPI_INT, 0, MPI_COMM_WORLD);
        filename = (char *) malloc(len+10);
        MPI_Bcast(filename, len+10, MPI_CHAR, 0, MPI_COMM_WORLD);
    }

    buf = (int *) malloc(SIZE);
    nints = SIZE/sizeof(int);
    for (i=0; i<nints; i++) buf[i] = rank*100000 + i;

    /* each process opens a separate file called filename.'myrank' */
    tmp = (char *) malloc(len+10);
    strcpy(tmp, filename);
    sprintf(filename, "%s.%d", tmp, rank);
    MPI_File_open(MPI_COMM_SELF, filename, MPI_MODE_CREATE | MPI_MODE_RDWR, MPI_INFO_NULL, &fh);
    MPI_File_set_view(fh, 0, MPI_INT, MPI_INT, "native", MPI_INFO_NULL);
    MPI_File_iwrite(fh, buf, nints, MPI_INT, &request);
    MPI_Wait( &request, &status );
    MPI_File_close(&fh);

    /* reopen the file and read the data back */
    for (i=0; i<nints; i++) buf[i] = 0;
    MPI_File_open(MPI_COMM_SELF, filename, MPI_MODE_CREATE | MPI_MODE_RDWR, MPI_INFO_NULL, &fh);
    MPI_File_set_view(fh, 0, MPI_INT, MPI_INT, "native", MPI_INFO_NULL);
    MPI_File_iread(fh, buf, nints, MPI_INT, &request);
    MPI_Wait( &request, &status );
    MPI_File_close(&fh);

    /* check if the data read is correct */
    for (i=0; i<nints; i++) {
        if (buf[i] != (rank*100000 + i)) {
            errs++;
            fprintf(stderr, "Process %d: error, read %d, should be %d\n", rank, buf[i], rank*100000+i);fflush(stderr);
        }
    }
    free(buf);
    free(filename);
    free(tmp);
    MPI_Finalize();
    return errs;
}