fork.c

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/wait.h>
       
#define N 6
#define K 2

int main(int argc, char* argv[])
{
    int i, n = 1, p[N][2];
    
    printf("Creating pipes\n");
    
    for (i = 0; i < N; i++)
    {        
        if (pipe(p[i]) == -1)
        {
            perror("Cannot open pipe\n");
            exit(1);            
        }
    }
    
    write(p[0][1], &n, sizeof(int));
    
    printf("Compute in each child process\n");
    
    for (i = 0; i < N; i++)
    {
        switch(fork())
        {
            case -1: /* Handle error */
            {
                perror("Cannot fork");
                exit(-1);
                break;
            }

            case 0:  /* Child */
            {
                //printf("Child %d\n", i+1);
                read(p[i][0], &n, sizeof(int));
                n++;
                printf("Child %d, n=%d\n", i+1, n);
                
                // K = 1
                // (0 + 1) % 6 = 1
                // (1 + 1) % 6 = 2
                // (2 + 1) % 6 = 3
                // (3 + 1) % 6 = 4
                // (4 + 1) % 6 = 5
                // (5 + 1) % 6 = 0
                
                // K = 2
                // (0 + 2) % 6 = 2
                // (1 + 2) % 6 = 3
                // (2 + 2) % 6 = 4
                // (3 + 2) % 6 = 5
                // (4 + 2) % 6 = 0
                // (5 + 2) % 6 = 1
                printf("n=%d, i=%d, K=%d, N=%d, (i + K) \% N = %d\n", n, i, K, N, (i + K) % N);
                write(p[(i + K) % N][1], &n, sizeof(int));
                exit(0);
            }
            
            default:  /* Parent */
                break;
        }
    }
    
    printf("Waiting for all child processes to finish\n");
    for (i = 0; i < N; i++)
    {
        wait(0);
    }
    
    read(p[0][0], &n, sizeof(int));
    printf("%d\n", n);
    
    for (i = 0; i < N; i++)
    {
        close(p[i][0]);
        close(p[i][1]);
    }
    
    return 0;
}