CODEWITHSUNDEEP
cmpi
Sparker0i
Sparker0i

Reputation: 1851

MPI - Error sending random int to root process

Here is my piece of code:

int world_size;
MPI_Comm_size(MPI_COMM_WORLD , &world_size);

int world_rank;
MPI_Comm_rank(MPI_COMM_WORLD , &world_rank);

int *rbuf , arr[world_size];
if (world_rank == 0)
{
    rbuf = (int *) malloc(world_size * 1 * sizeof(int));
}
else
{
    rbuf[0] = rand() % 100;
    MPI_Send(rbuf , 1 , MPI_INT , 0 , 0 , MPI_COMM_WORLD);
}
if (world_rank == 0)
{
    MPI_Gather(arr , world_size , MPI_INT , rbuf , 1 , MPI_INT , 0 , MPI_COMM_WORLD);
    for (int i = 0; i < world_size; ++i)
    {
        printf("%d " , arr[i]);
    }
    printf("\n");
}

I want to generate a random number at every process which is not the root process. Then I want each such process to send the number generated to the root process, ie. the root process should gather all the numbers generated at each process.

When I am trying to run this code, I get the error:

Fatal error in PMPI_Gather: Message truncated, error stack:
PMPI_Gather(896)......: MPI_Gather(sbuf=0x7ffc3b23c180, scount=10, MPI_INT, rbuf=0x564a753dc790, rcount=1, MPI_INT, root=0, MPI_COMM_WORLD) failed
MPIR_Gather_impl(718).: 
MPIR_Gather(678)......: 
MPIR_Gather_intra(184): 
MPIR_Localcopy(74)....: Message truncated; 40 bytes received but buffer size is 4

(PS. I run this program using mpirun -n 10 ./helloworld)

Upvotes: 1

Views: 178

Answers (1)

SRhm
SRhm

Reputation: 459

MPI_Gather send messages from all ranks to root and receive itself it does not need MPI_Send.

I changed your example:

#include<stdio.h>
#include<mpi.h>
#include<stdlib.h>
#include<time.h>
int main(int argc, char **argv){

  MPI_Init(&argc, &argv);
  int world_size;
  MPI_Comm_size(MPI_COMM_WORLD , &world_size);
  int world_rank;
  MPI_Comm_rank(MPI_COMM_WORLD , &world_rank);

  srand(time(NULL)+world_rank);
  int *rbuf,*sender;
  if (world_rank == 0)
  {
    rbuf = (int *) malloc(world_size * 1 * sizeof(int));
  }
  sender = (int *) malloc( 1 * sizeof(int));
  sender[0] = rand() % 100;

  MPI_Gather(sender , 1 , MPI_INT , rbuf , 1 , MPI_INT , 0 , MPI_COMM_WORLD);
  if (world_rank == 0)
  {
    for (int i = 0; i < world_size; ++i)
    {
        printf("%d " , rbuf[i]);
    }
    printf("\n");
  }
  MPI_Finalize();
}

Upvotes: 3

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