DeinoMPI

The Great and Terrible implementation of MPI-2

MPI_File_iread_at

Nonblocking read using explict offset

int MPI_File_read_at(
  MPI_File mpi_fh,
  MPI_Offset offset,
  void *buf,
  int count,
  MPI_Datatype datatype,
  MPI_Request *request
);

Parameters

mpi_fh: [in] file handle (handle)
offset: [in] file offset (nonnegative integer)
buf: [out] 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_READ_AT starts a non-blocking read of a file beginning at the position specified by offset.

If MPI_MODE_SEQUENTIAL mode was specified when the file was opened, it is erroneous to call this routine.

Example Code

The following sample code illustrates MPI_File_iread_at.

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

/* tests noncontiguous reads/writes using nonblocking I/O */
#define SIZE 5000

int main(int argc, char **argv)
{
    int *buf, i, mynod, nprocs, len, b[3];
    int errs=0;
    MPI_Aint d[3];
    MPI_File fh;
    MPI_Status status;
    char *filename;
    MPI_Datatype typevec, newtype, t[3];
    MPI_Request req;

    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD, &nprocs);
    MPI_Comm_rank(MPI_COMM_WORLD, &mynod);
    if (nprocs != 2) {
        fprintf(stderr, "Run this program on two processes\n");
        MPI_Abort(MPI_COMM_WORLD, 1);
    }

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

    buf = (int *) malloc(SIZE*sizeof(int));
    MPI_Type_vector(SIZE/2, 1, 2, MPI_INT, &typevec);
    b[0] = b[1] = b[2] = 1;
    d[0] = 0;
    d[1] = mynod*sizeof(int);
    d[2] = SIZE*sizeof(int);
    t[0] = MPI_LB;
    t[1] = typevec;
    t[2] = MPI_UB;
    MPI_Type_struct(3, b, d, t, &newtype);
    MPI_Type_commit(&newtype);
    MPI_Type_free(&typevec);

    if (mynod == 0) {
        fprintf(stderr, "\ntesting noncontiguous in memory, noncontiguous in file using nonblocking I/O\n");fflush(stderr);
        MPI_File_delete(filename, MPI_INFO_NULL);
    }
    MPI_Barrier(MPI_COMM_WORLD);
    MPI_File_open(MPI_COMM_WORLD, filename, MPI_MODE_CREATE | MPI_MODE_RDWR, MPI_INFO_NULL, &fh);
    MPI_File_set_view(fh, 0, MPI_INT, newtype, "native", MPI_INFO_NULL);
    for (i=0; i<SIZE; i++) buf[i] = i + mynod*SIZE;
    MPI_File_iwrite(fh, buf, 1, newtype, &req);
    MPI_Wait(&req, &status);

    MPI_Barrier(MPI_COMM_WORLD);

    for (i=0; i<SIZE; i++) buf[i] = -1;
    MPI_File_iread_at(fh, 0, buf, 1, newtype, &req);
    MPI_Wait(&req, &status);
    for (i=0; i<SIZE; i++) {
        if (!mynod) {
            if ((i%2) && (buf[i] != -1)) {
                errs++;
                fprintf(stderr, "Process %d: buf %d is %d, should be -1\n", mynod, i, buf[i]);fflush(stderr);
            }
            if (!(i%2) && (buf[i] != i)) {
                errs++;
                fprintf(stderr, "Process %d: buf %d is %d, should be %d\n", mynod, i, buf[i], i);fflush(stderr);
            }
        }
        else {
            if ((i%2) && (buf[i] != i + mynod*SIZE)) {
                errs++;
                fprintf(stderr, "Process %d: buf %d is %d, should be %d\n", mynod, i, buf[i], i + mynod*SIZE);fflush(stderr);
            }
            if (!(i%2) && (buf[i] != -1)) {
                errs++;
                fprintf(stderr, "Process %d: buf %d is %d, should be -1\n", mynod, i, buf[i]);fflush(stderr);
            }
        }
    }
    MPI_File_close(&fh);

    MPI_Barrier(MPI_COMM_WORLD);

    if (!mynod) {
        fprintf(stderr, "\ntesting noncontiguous in memory, contiguous in file using nonblocking I/O\n");fflush(stderr);
        MPI_File_delete(filename, MPI_INFO_NULL);
    }
    MPI_Barrier(MPI_COMM_WORLD);
    MPI_File_open(MPI_COMM_WORLD, filename, MPI_MODE_CREATE | MPI_MODE_RDWR, MPI_INFO_NULL, &fh);
    for (i=0; i<SIZE; i++) buf[i] = i + mynod*SIZE;
    MPI_File_iwrite_at(fh, mynod*(SIZE/2)*sizeof(int), buf, 1, newtype, &req);
    MPI_Wait(&req, &status);

    MPI_Barrier(MPI_COMM_WORLD);

    for (i=0; i<SIZE; i++) buf[i] = -1;
    MPI_File_iread_at(fh, mynod*(SIZE/2)*sizeof(int), buf, 1, newtype, &req);
    MPI_Wait(&req, &status);
    for (i=0; i<SIZE; i++) {
        if (!mynod) {
            if ((i%2) && (buf[i] != -1)) {
                errs++;
                fprintf(stderr, "Process %d: buf %d is %d, should be -1\n", mynod, i, buf[i]);fflush(stderr);
            }
            if (!(i%2) && (buf[i] != i)) {
                errs++;
                fprintf(stderr, "Process %d: buf %d is %d, should be %d\n", mynod, i, buf[i], i);fflush(stderr);
            }
        }
        else {
            if ((i%2) && (buf[i] != i + mynod*SIZE)) {
                errs++;
                fprintf(stderr, "Process %d: buf %d is %d, should be %d\n", mynod, i, buf[i], i + mynod*SIZE);fflush(stderr);
            }
            if (!(i%2) && (buf[i] != -1)) {
                errs++;
                fprintf(stderr, "Process %d: buf %d is %d, should be -1\n", mynod, i, buf[i]);fflush(stderr);
            }
        }
    }
    MPI_File_close(&fh);

    MPI_Barrier(MPI_COMM_WORLD);

    if (!mynod) {
        fprintf(stderr, "\ntesting contiguous in memory, noncontiguous in file using nonblocking I/O\n");fflush(stderr);
        MPI_File_delete(filename, MPI_INFO_NULL);
    }
    MPI_Barrier(MPI_COMM_WORLD);
    MPI_File_open(MPI_COMM_WORLD, filename, MPI_MODE_CREATE | MPI_MODE_RDWR, MPI_INFO_NULL, &fh);
    MPI_File_set_view(fh, 0, MPI_INT, newtype, "native", MPI_INFO_NULL);
    for (i=0; i<SIZE; i++) buf[i] = i + mynod*SIZE;
    MPI_File_iwrite(fh, buf, SIZE, MPI_INT, &req);
    MPI_Wait(&req, &status);

    MPI_Barrier(MPI_COMM_WORLD);

    for (i=0; i<SIZE; i++) buf[i] = -1;
    MPI_File_iread_at(fh, 0, buf, SIZE, MPI_INT, &req);
    MPI_Wait(&req, &status);
    for (i=0; i<SIZE; i++) {
        if (!mynod) {
            if (buf[i] != i) {
                errs++;
                fprintf(stderr, "Process %d: buf %d is %d, should be %d\n", mynod, i, buf[i], i);
            }
        }
        else {
            if (buf[i] != i + mynod*SIZE) {
                errs++;
                fprintf(stderr, "Process %d: buf %d is %d, should be %d\n", mynod, i, buf[i], i + mynod*SIZE);
            }
        }
    }
    MPI_File_close(&fh);

    MPI_Type_free(&newtype);
    free(buf);
    free(filename);

    MPI_Finalize();
    return errs;
}

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