MPI_Gatherv memory problems (MPI+C) - c

Question

As a continuation to my previous question, I have modified the code for variable number of kernels. However, the way Gatherv is implemented in my code seems to be unreliable. Once in 3-4 runs the end sequence in the collecting buffer ends up being corrupted, it seems like, due to the memory leakage. Sample code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <mpi.h>
int main (int argc, char *argv[]) {
MPI_Init(&argc, &argv);
int world_size,*sendarray;
int rank, *rbuf=NULL, count,total_counts=0;
int *displs=NULL,i,*rcounts=NULL;
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &world_size);
if(rank==0){
displs = malloc((world_size+1)*sizeof(int));
for(int i=1;i<=world_size; i++)displs[i]=0;
rcounts=malloc(world_size*sizeof(int));
sendarray=malloc(1*sizeof(int));
for(int i=0;i<1;i++)sendarray[i]=1111;
count=1;
}
if(rank!=0){
int size=rank*2;
sendarray=malloc(size*sizeof(int));
for(int i=0;i<size;i++)sendarray[i]=rank;
count=size;
}
MPI_Barrier(MPI_COMM_WORLD);
MPI_Gather(&count,1,MPI_INT,rcounts,1,MPI_INT,0,MPI_COMM_WORLD);
MPI_Barrier(MPI_COMM_WORLD);
if(rank==0){
displs[0]=0;
for(int i=1;i<=world_size; i++){
for(int j=0; j<i; j++)displs[i]+=rcounts[j];
}
total_counts=0;
for(int i=0;i<world_size;i++)total_counts+=rcounts[i];
rbuf = malloc(10*sizeof(int));
}
MPI_Gatherv(sendarray, count, MPI_INT, rbuf, rcounts,
displs, MPI_INT, 0, MPI_COMM_WORLD);
if(rank==0){
int SIZE=total_counts;
for(int i=0;i<SIZE;i++)printf("(%d) %d ",i, rbuf[i]);
free(rbuf);
free(displs);
free(rcounts);
}
if(rank!=0)free(sendarray);
MPI_Finalize();
}
Why is this happening and is there a way to fix it?
This becomes much worse in my actual project. Each sending buffer contains 150 doubles. The receiving buffer gets very dirty and sometimes I get an error of bed termination with exit code 6 or 11.
Can anyone at least reproduce my errors?
My guess: I am allocating memory for sendarray on each thread separately. If my virtual machine was 1-to-1 to the hardware, then, probably, there would be no such problem. But I have only 2 cores and run a process for 4 or more. Could it be the reason?

Answer 1

Change this line:
rbuf = malloc(10*sizeof(int));
to:
rbuf = malloc(total_counts*sizeof(int));
As a side note: each MPI process exists in its own process address space and they cannot stomp on eachothers data except through erroneous data explicitly passed through the MPI_XXX functions, which results in undefined behavior.