inter/scheduler.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/shm.h>
#include <unistd.h>

#define NUM_PROCS 4
#define SHM_SIZE 1024
#define PATHNAME "."
#define PROJ_ID 65

struct shared_data {
  int ready;
  int priorities[NUM_PROCS];
};

int create_mem_segment(struct shared_data **shm_ptr) {
  int shmid;
  key_t key = ftok(PATHNAME, PROJ_ID);

  // Create a new shared segment
  if ((shmid = shmget(key, SHM_SIZE, IPC_CREAT | 0666)) < 0) {
    perror("[!] Shmget failed");
    exit(EXIT_FAILURE);
  }

  // Attach (system chooses a suitable address)
  if ((*shm_ptr = (struct shared_data *)shmat(shmid, NULL, 0)) ==
      (struct shared_data *)-1) {
    perror("[!] Shmat failed");
    exit(EXIT_FAILURE);
  }

  return shmid;
}

int compare(const void *a, const void *b) { return (*(int *)a - *(int *)b); }

int main() {
  struct shared_data *shm_ptr;

  // Create and attach into a new shared segment
  int shmid = create_mem_segment(&shm_ptr);
  printf("[SCHEDULER] Shared segment %d created (%p)\n", shmid,
         (void *)shm_ptr);

  // Initialize signal flag to 0 (not ready)
  shm_ptr->ready = 0;
  printf("[SCHEDULER] Signal flag initialized to 0\n");
  printf("[SCHEDULER] Waiting for init to write data...\n");

  // Wait until init has finished writing into the segment
  while (shm_ptr->ready == 0) {
    usleep(100000); // 100 ms (to reduce CPU usage)
  }

  int priorities[NUM_PROCS];

  // Copy array to a local variable
  for (int i = 0; i < NUM_PROCS; i++) {
    priorities[i] = shm_ptr->priorities[i];
  }

  // Detach
  if (shmdt(shm_ptr) == -1) {
    perror("[!] Shmdt failed");
    exit(EXIT_FAILURE);
  }

  // Delete
  if (shmctl(shmid, IPC_RMID, NULL) == -1) {
    perror("[!] Shmctl failed");
    exit(EXIT_FAILURE);
  }

  printf("[SCHEDULER] Shared memory segment %d detached and deleted\n", shmid);

  // Sort and print the priorities
  qsort(&priorities, NUM_PROCS, sizeof(int), compare);

  printf("[SCHEDULER] Priorities: ");

  for (int i = 0; i < NUM_PROCS; i++) {
    printf("%d ", priorities[i]);
  }

  printf("\n");

  return 0;
}