lab4.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <unistd.h>

void printLab4(int n, int a, int *fibo)
{
    int i;
    for (i = 0; i < n; i++)
        printf("%d -> %d\n", i, fibo[i]);
}

void computeLab4(int n, int a, int *fibo)
{
    int i;

    for (i = 0; i < n; i++)
    {
        int sleepSec = rand() % 10;
        printf("sleeping for %d : ", sleepSec);
        sleep(sleepSec);
        fibo[i] = i * a;
        // randomly sleeping for 0-10 secs
        printf("Generated new element %d after %d seconds \n", fibo[i], sleepSec);
    }
}

int main(int argc, char *argv[])
{
    pid_t childPID;
    int status;
    int shm_fd;
    int *shared_memory;
    int msize; // the size (in bytes) of the shared memory segment
    const char *name = "Lab_4";
    int n, a;

    if (argc != 3)
    {
        fprintf(stderr, "usage: %s <Lab4 Seq to be generated>\n", argv[0]);
        return -1;
    }

    n = atoi(argv[1]);
    a = atoi(argv[2]);

    printf("%d \n", n);
    printf("%d \n", a);

    if (n < 0 || a < 0)
    {
        fprintf(stderr, "Illegal number: %s\n", argv[1]);
        return -2;
    }

    // calculating the array size based on the number of terms being passed from child to parent
    msize = (n + 2) * sizeof(int);

    // open the memory
    shm_fd = shm_open(name, O_CREAT | O_EXCL | O_RDWR, S_IRWXU | S_IRWXG);
    if (shm_fd < 0)
    {
        fprintf(stderr, "Error in shm_open()");
        return -3;
    }

    printf("Created shared memory object %s\n", name);

    // attach the shared memory segment
    ftruncate(shm_fd, msize);
    printf("shmat returned\n");

    // allocating the shared memory
    shared_memory = (int *)mmap(NULL, msize, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
    if (shared_memory == NULL)
    {
        fprintf(stderr, "Error in mmap()");
        return -3;
    }

    printf("Shared memory segment allocated correctly (%d bytes).\n", msize);

    shared_memory[0] = n;
    shared_memory[1] = a;

    childPID = fork();
    if (childPID == -1)
    {
        fprintf(stderr, "Cannot proceed. fork() error");
        return -4;
    }
    if (childPID == 0)
    {
        // then we're the child process
        computeLab4(shared_memory[0], shared_memory[1], shared_memory + 1);
        exit(0);
    }
    else
    {
        // parent will wait until the child finished
        wait(&status);

        // print the final results in the
        printLab4(shared_memory[0], shared_memory[1], shared_memory + 1);

        // now detach the shared memory segment
        shm_unlink(name);
    }
    return 0;
}