C - MPI - Bsend no work with buffer attach - c

Question

I want the buffer to be full before I start receiving. It gives me the feeling that the buffer size is less than necessary
I followed the documentation to the letter but I can't see the error
https://www.mpich.org/static/docs/v3.1/www3/MPI_Buffer_attach.html
In some cases it gives me the feeling that with a specific buffer size I can perform more bsend than theoretically allowed
#include <stdio.h>
#include <mpi.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char *argv[])
{
int rank, size, tag=0;
MPI_Status status;
MPI_Request request;
int flag;
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &size);
int bsends_totales=1000000;
if (rank!=0) //Nodos esclavos
{
int size_bsend;
MPI_Pack_size( 1, MPI_INT, MPI_COMM_WORLD, &size_bsend );
int size_buffer=bsends_totales*(size_bsend+MPI_BSEND_OVERHEAD);
int * buffer = malloc(size_buffer);
memset(buffer,0,size_buffer);
MPI_Buffer_attach(buffer,size_buffer); //Buffer saliente
int enviar=4;
int sends_realizados=0;
for (int i=0;i<bsends_totales;i++)
{
printf("BSENDS realizados... %d\n",sends_realizados);
MPI_Bsend(&enviar,1,MPI_INT,0,tag,MPI_COMM_WORLD);
sends_realizados=sends_realizados+1;
}
printf("BSENDS TOTALES REALIZADOS: %d\n",sends_realizados);
MPI_Barrier(MPI_COMM_WORLD);
MPI_Buffer_detach(&buffer,&size_buffer);
free(buffer);
printf("TERMINE\n");
}
else //Master
{
int recibido;
MPI_Barrier(MPI_COMM_WORLD);
for (int i=0;i<bsends_totales;i++)
{
MPI_Recv(&recibido,1,MPI_INT,MPI_ANY_SOURCE,MPI_ANY_TAG,MPI_COMM_WORLD,&status);
}
}
MPI_Finalize();
return 0;
}
Before being able to fill the buffer an error appears
OUTPUT:
BSENDS realizados... 119696
BSENDS realizados... 119697
BSENDS realizados... 119698
BSENDS realizados... 119699
BSENDS realizados... 119700
code exit 11