BAD TERMINATION in MPI Bsend - c

Question

i'm trying send packed structure by MPI_Bsend(). Something i'm doing wrong and i cannot find solution.
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include "mpi.h"
#define SIZE 10
struct car {
int id;
int vmax;
char marka[SIZE];
char model[SIZE];
};
int main(int argc, char **argv) {
int i;
int rank, size;
double t1, t2;
struct car BMW, BMW2;
BMW.id = 1;
strcpy(BMW.marka, "BMW");
strcpy(BMW.model, "szybki");
BMW.vmax = 199;
MPI_Status status;
MPI_Init(&argc,&argv);
MPI_Comm_rank(MPI_COMM_WORLD,&rank);
MPI_Comm_size(MPI_COMM_WORLD,&size);
int rozmiar, packet_size, msg_size, position = 0,tag;
void *bufor;
MPI_Pack_size(2, MPI_INT, MPI_COMM_WORLD, &rozmiar);
packet_size = rozmiar;
MPI_Pack_size(2 * SIZE, MPI_CHAR, MPI_COMM_WORLD, &rozmiar);
packet_size += rozmiar;
msg_size = 2 * packet_size + MPI_BSEND_OVERHEAD;
bufor = (void *)malloc(msg_size);
MPI_Buffer_attach(bufor, msg_size);
t1 = MPI_Wtime();
if (rank == 0) {
tag = 0;
for(i=1;i<size;i++){
MPI_Pack(&BMW.id,1, MPI_INT, bufor, msg_size, &position, MPI_COMM_WORLD);
MPI_Pack(&BMW.vmax,1, MPI_INT, bufor, msg_size, &position, MPI_COMM_WORLD);
MPI_Pack(&BMW.model,SIZE, MPI_CHAR, bufor, msg_size, &position, MPI_COMM_WORLD);
MPI_Pack(&BMW.marka,SIZE, MPI_CHAR, bufor, msg_size, &position, MPI_COMM_WORLD);
MPI_Bsend(bufor,position,MPI_PACKED,i,tag,MPI_COMM_WORLD);
}
} else {
MPI_Recv(bufor,msg_size,MPI_PACKED,0,MPI_ANY_TAG,MPI_COMM_WORLD,&status);
position = 0;
MPI_Unpack(bufor, msg_size, &position, &BMW2.id, 1, MPI_INT, MPI_COMM_WORLD);
MPI_Unpack(bufor, msg_size, &position, &BMW2.vmax, 1, MPI_INT, MPI_COMM_WORLD);
MPI_Unpack(bufor, msg_size, &position, &BMW2.model, SIZE, MPI_CHAR, MPI_COMM_WORLD);
MPI_Unpack(bufor, msg_size, &position, &BMW2.marka, SIZE, MPI_CHAR, MPI_COMM_WORLD);
printf("rank = %d | BMW id: %d, marka: %s, model: %s, vmax: %d \n",rank, BMW2.id, BMW2.marka, BMW2.model, BMW2.vmax);
}
t2 = MPI_Wtime();
MPI_Buffer_detach(&bufor, &msg_size);
MPI_Finalize();
if (i == size)
printf("Elapsed time is %.15f\n", t2 - t1 );
return(0);
}
Error:
====================================================================
BAD TERMINATION OF ONE OF YOUR APPLICATION PROCESSES
PID 25637 RUNNING AT debian
EXIT CODE: 11
================================================================
YOUR APPLICATION TERMINATED WITH THE EXIT STRING: Segmentation fault
(signal 11)

Answer 1

You are using the buffered mode of MPI incorrectly. The buffer you give to MPI via MPI_Buffer_attach is supposed to be used by MPI internally. Do not use the buffered MPI interface, it is very rarely useful and very difficult to get right.
Just remove the MPI_Buffer_ and use MPI_Send instead of MPI_Bsend and you are on the right track. MPI_Pack can be a bit clumsy, you may want to look insto custom datatypes (MPI_Type_create_struct) instead. If you have a homogeneous system, you can also send the raw bytes of the struct car.