mpi parallel program to find prime numbers. Please help me dubug - parallel-processing

Question

I wrote the following program to find prime number with the #defined value. It is parallel program using mpi. Can anyone help me find a error in it. It compile well but crashes while executing.
#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
#define N 65
int rank, size;
double start_time;
double end_time;
int y, x, i, port1, port2, port3;
int check =0; // prime number checker, if a number is prime it always remains 0 through out calculation. for a number which is not prime it is turns to value 1 at some point
int signal =0; // has no important use. just to check if slave process work is done.
MPI_Status status;
MPI_Request request;
int main(int argc, char *argv[]){
MPI_Init(&argc, &argv); //initialize MPI operations
MPI_Comm_rank(MPI_COMM_WORLD, &rank); //get the rank
MPI_Comm_size(MPI_COMM_WORLD, &size); //get number of processes
if(rank == 0){ // master process divides work and also does initial work itself
start_time = MPI_Wtime();
printf("2\n"); //print prime number 2 first because the algorithm for finding the prime number in this program is just for odd number
port1 = (N/(size-1)); // calculating the suitable amount of work per process
for(i=1;i<size-1;i++){ // master sending the portion of work to each slave
port2 = port1 * i; // lower bound of work for i th process
port3 = ((i+1)*port1)-1; // upper bound of work for i th process
MPI_Isend(&port2, 1, MPI_INT, i, 100, MPI_COMM_WORLD, &request);
MPI_Isend(&port3, 1, MPI_INT, i, 101, MPI_COMM_WORLD, &request);
}
port2 = (size-1)*port1; port3= N; // the last process takes the remaining work
MPI_Isend(&port2, 1, MPI_INT, (size-1), 100, MPI_COMM_WORLD, &request);
MPI_Isend(&port3, 1, MPI_INT, (size-1), 101, MPI_COMM_WORLD, &request);
for(x = 3; x < port1; x=x+2){ // master doing initial work by itself
check = 0;
for(y = 3; y <= x/2; y=y+2){
if(x%y == 0) {check =1; break;}
}
if(check==0) printf("%d\n", x);
}
}
if (rank > 0){ // slave working part
MPI_Recv(&port2,1,MPI_INT, 0, 100, MPI_COMM_WORLD, &status);
MPI_Recv(&port3,1,MPI_INT, 0, 101, MPI_COMM_WORLD, &status);
if (port2%2 == 0) port2++; // changing the even argument to odd to make the calculation fast because even number is never a prime except 2.
for(x=port2; x<=port3; x=x+2){
check = 0;
for(y = 3; y <= x/2; y=y+2){
if(x%y == 0) {check =1; break;}
}
if (check==0) printf("%d\n",x);
}
signal= rank;
MPI_Isend(&signal, 1, MPI_INT, 0, 103, MPI_COMM_WORLD, &request); // just informing master that the work is finished
}
if (rank == 0){ // master concluding the work and printing the time taken to do the work
for(i== 1; i < size; i++){
MPI_Recv(&signal,1,MPI_INT, i, 103, MPI_COMM_WORLD, &status); // master confirming that all slaves finished their work
}
end_time = MPI_Wtime();
printf("\nRunning Time = %f \n\n", end_time - start_time);
}
MPI_Finalize();
return 0;
}
I got following error
mpirun -np 2 ./a.exe
Exception: STATUS_ACCESS_VIOLATION at eip=0051401C
End of stack trace

Answer 1

I found what was wrong with my program.
It was the use of the restricted variable signal. change the name of that variable (in all places it is used) to any other viable name and it works.