feat: signal flag (data readiness)

init.c

@@ -9,6 +9,11 @@
 #define PATHNAME "."
 #define PROJ_ID 65
 
+struct shared_data {
+  int ready;
+  int priorities[NUM_PROCS];
+};
+
 void write_pipes(int pipefds[][2], pid_t pids[]) {
   for (int i = 0; i < NUM_PROCS; i++) {
     // Creation of a pipe (child -> parent)
@@ -34,7 +39,7 @@ void write_pipes(int pipefds[][2], pid_t pids[]) {
       srand(time(NULL) ^ getpid());
       int priority = rand() % 20;
 
-      // Writing to the pipe and closing it afterwards (sync)
+      // Write to the pipe and close it afterwards (sync)
       write(pipefds[i][1], &priority, sizeof(priority));
       close(pipefds[i][1]);
 
@@ -50,7 +55,7 @@ void read_pipes(int pipefds[][2], int priorities[]) {
     // Write end of the pipe is closed before reading (sync)
     close(pipefds[i][1]);
 
-    // Reading from the pipe and closing it afterwards (sync)
+    // Read from the pipe and close it afterwards (sync)
     read(pipefds[i][0], &priorities[i], sizeof(priorities[i]));
     close(pipefds[i][0]);
 
@@ -59,7 +64,7 @@ void read_pipes(int pipefds[][2], int priorities[]) {
 }
 
 void write_mem_segment(int priorities[]) {
-  int *shm_array;
+  struct shared_data *shm_ptr;
   int shmid;
 
   key_t key = ftok(PATHNAME, PROJ_ID);
@@ -71,38 +76,47 @@ void write_mem_segment(int priorities[]) {
   }
 
   // Attach (system chooses a suitable address)
-  if ((shm_array = (int *)shmat(shmid, NULL, 0)) == (int *)-1) {
+  if ((shm_ptr = (struct shared_data *)shmat(shmid, NULL, 0)) ==
+      (struct shared_data *)-1) {
     perror("[!] Shmat failed");
     exit(EXIT_FAILURE);
   }
 
   printf("[INIT] Connected to shared segment %d (%p)\n", shmid,
-         (void *)&shm_array);
+         (void *)&shm_ptr);
 
   // Write
   for (int i = 0; i < NUM_PROCS; i++) {
-    shm_array[i] = priorities[i];
+    shm_ptr->priorities[i] = priorities[i];
   }
 
-  // Detach
-  shmdt(shm_array);
+  // Signal that data is ready
+  shm_ptr->ready = 1;
 
   printf("[INIT] Wrote priorities to shared memory\n");
+
+  // Detach
+  if (shmdt(shm_ptr) == -1) {
+    perror("[!] Shmdt failed");
+    exit(EXIT_FAILURE);
+  }
+
+  printf("[INIT] Deteached from shared memory\n");
 }
 
 int main() {
   int pipefds[NUM_PROCS][2];
   pid_t pids[NUM_PROCS];
 
-  // Creation of forks, their respective pipes, and random priorities
+  // Create forks, their respective pipes, and random priorities
   write_pipes(pipefds, pids);
 
   int priorities[NUM_PROCS];
 
-  // Reading priorities from the pipes
+  // Read priorities from the pipes
   read_pipes(pipefds, priorities);
 
-  // Attaching and writing priorities to a shared memory segment
+  // Attach and write priorities to a shared memory segment
   write_mem_segment(priorities);
 
   return 0;

scheduler.c

@@ -8,7 +8,12 @@
 #define PATHNAME "."
 #define PROJ_ID 65
 
-int create_mem_segment(int **shm_array) {
+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);
 
@@ -19,7 +24,8 @@ int create_mem_segment(int **shm_array) {
   }
 
   // Attach (system chooses a suitable address)
-  if ((*shm_array = (int *)shmat(shmid, NULL, 0)) == (int *)-1) {
+  if ((*shm_ptr = (struct shared_data *)shmat(shmid, NULL, 0)) ==
+      (struct shared_data *)-1) {
     perror("[!] Shmat failed");
     exit(EXIT_FAILURE);
   }
@@ -30,35 +36,45 @@ int create_mem_segment(int **shm_array) {
 int compare(const void *a, const void *b) { return (*(int *)a - *(int *)b); }
 
 int main() {
-  int *shm_array;
+  struct shared_data *shm_ptr;
 
-  int delay = 5;
-
-  // Creation and attaching into a new shared segment
-  int shmid = create_mem_segment(&shm_array);
+  // 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_array);
+         (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
-  printf("[SCHEDULER] Sleeping for %d seconds before reading\n", delay);
-  sleep(delay);
-
-  // Copying array to a local variable
-  int priorities[NUM_PROCS];
-
-  for (int i = 0; i < NUM_PROCS; i++) {
-    priorities[i] = shm_array[i];
+  while (shm_ptr->ready == 0) {
+    usleep(100000); // 100 ms (to reduce CPU usage)
   }
 
-  // TODO: "After scheduler prints the data, init should detach from shared
-  // memory" -> Some mechanism to indicate when init has detached must be put in
-  // place
+  int priorities[NUM_PROCS];
 
-  // Detaching and deleting the segment
-  shmdt(shm_array);
-  shmctl(shmid, IPC_RMID, NULL);
+  // Copy array to a local variable
+  for (int i = 0; i < NUM_PROCS; i++) {
+    priorities[i] = shm_ptr->priorities[i];
+  }
 
-  // Sorting and printing the priorities
+  // 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: ");