[mpich-discuss] beginner for remote mem access

[Sufeng Niu]

Hi,

I am a beginner and just try to use remote memory access, and I wrote a
simple program to test it:

#include "mpi.h"
#include <stdio.h>
#define SIZE 8

int main(int argc, char *argv[])
{
        int numtasks, rank, source=0, dest, tag=1, i;
        float a[64] =
        {
                1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0,
12.0, 13.0, 14.0, 15.0, 16.0,
                1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0,
12.0, 13.0, 14.0, 15.0, 16.0,
                1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0,
12.0, 13.0, 14.0, 15.0, 16.0,
                1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0,
12.0, 13.0, 14.0, 15.0, 16.0,
        };
        float b[SIZE];

        MPI_Status stat;

        MPI_Init(&argc,&argv);
        MPI_Comm_rank(MPI_COMM_WORLD, &rank);
        MPI_Comm_size(MPI_COMM_WORLD, &numtasks);

        MPI_Win win;

        // check processor rank
        char processor_name[MPI_MAX_PROCESSOR_NAME];
        int name_len;
        MPI_Get_processor_name(processor_name, &name_len);
        printf("-- processor %s, rank %d out of %d processors\n",
processor_name, rank, numtasks);

        MPI_Barrier(MPI_COMM_WORLD);

        if (numtasks == 4) {
                if (rank == 0) {
                        printf("create window \n");
                        MPI_Win_create(a, 8*sizeof(float), sizeof(float),
MPI_INFO_NULL, MPI_COMM_WORLD, &win);

                }
                else {
                        MPI_Win_create(MPI_BOTTOM, 0, sizeof(float),
MPI_INFO_NULL, MPI_COMM_WORLD, &win);
                }

                MPI_Win_fence(0, win);

                if (rank == 1){
                        MPI_Get(b, SIZE, MPI_FLOAT, 0, 8, SIZE, MPI_FLOAT,
win);

                        MPI_Win_fence(0, win);
                }

                printf("rank= %d  b= %3.1f %3.1f %3.1f %3.1f %3.1f %3.1f
%3.1f %3.1f\n", rank,b[0],b[1],b[2],b[3],b[4],b[5],b[6],b[7]);
        }
        else
                printf("Must specify %d processors. Terminating.\n",SIZE);

        MPI_Win_free(&win);
        MPI_Finalize();
}

However the terminal gives some odd results:
rank= 0  b= 0.0 0.0 0.0 0.0 0.0 0.0 -71847793475452928.0 0.0
rank= 2  b= 0.0 0.0 0.0 0.0 0.0 0.0 222086852849451401216.0 0.0
rank= 3  b= 0.0 0.0 0.0 0.0 0.0 0.0 -74882.4 0.0
rank= 1  b= 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0
the rank 1 is correct results, but others should be all zero.
terminal also give some comments: "Assertion failed in file
src/mpid/ch3/src/ch3u_rma_sync.c at line 5061: win_ptr->my_counter >= 0
internal ABORT - process 0"

another question is if I use remote memory access. all process which does
not create window for share must add additional line:
MPI_Win_create(MPI_BOTTOM, 0, data_type, MPI_INFO_NULL, MPI_COMM_WORLD,
&win); correct?

Thanks a lot!

-- 
Best Regards,
Sufeng Niu
ECASP lab, ECE department, Illinois Institute of Technology
Tel: 312-731-7219
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