feat: initial version without signaling

Makefile

@@ -0,0 +1,18 @@
+CC = gcc-13
+CFLAGS = -Wall -Wextra
+BIN = ./out
+
+TARGETS = init scheduler
+
+all: $(TARGETS)
+
+init: init.c
+	$(CC) $(CFLAGS) -o $(BIN)/init init.c
+
+scheduler: scheduler.c
+	$(CC) $(CFLAGS) -o $(BIN)/scheduler scheduler.c
+
+clean:
+	rm -f $(TARGETS)
+
+.PHONY: all clean

init.c

@@ -0,0 +1,109 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/shm.h>
+#include <time.h>
+#include <unistd.h>
+
+#define NUM_PROCS 4
+#define SHM_SIZE 1024
+#define PATHNAME "."
+#define PROJ_ID 65
+
+void write_pipes(int pipefds[][2], pid_t pids[]) {
+  for (int i = 0; i < NUM_PROCS; i++) {
+    // Creation of a pipe (child -> parent)
+    if (pipe(pipefds[i]) == -1) {
+      perror("[!] Pipe failed");
+      exit(EXIT_FAILURE);
+    }
+
+    // Creation of a fork
+    pids[i] = fork();
+
+    if (pids[i] == -1) {
+      perror("[!] Fork failed");
+      exit(EXIT_FAILURE);
+    }
+
+    // If the fork is successfully created
+    if (pids[i] == 0) {
+      // Read end of the pipe is closed before writing (sync)
+      close(pipefds[i][0]);
+
+      // Random priority in the range 0-19
+      srand(time(NULL) ^ getpid());
+      int priority = rand() % 20;
+
+      // Writing to the pipe and closing it afterwards (sync)
+      write(pipefds[i][1], &priority, sizeof(priority));
+      close(pipefds[i][1]);
+
+      printf("[P%d] Wrote %d into pipe\n", i + 1, priority);
+
+      exit(0);
+    }
+  }
+}
+
+void read_pipes(int pipefds[][2], int priorities[]) {
+  for (int i = 0; i < NUM_PROCS; i++) {
+    // Write end of the pipe is closed before reading (sync)
+    close(pipefds[i][1]);
+
+    // Reading from the pipe and closing it afterwards (sync)
+    read(pipefds[i][0], &priorities[i], sizeof(priorities[i]));
+    close(pipefds[i][0]);
+
+    printf("[INIT] Read %d from P%d\n", priorities[i], i + 1);
+  }
+}
+
+void write_mem_segment(int priorities[]) {
+  int *shm_array;
+  int shmid;
+
+  key_t key = ftok(PATHNAME, PROJ_ID);
+
+  // Get the segment identifier
+  if ((shmid = shmget(key, SHM_SIZE, 0666)) < 0) {
+    perror("[!] Shmget failed");
+    exit(EXIT_FAILURE);
+  }
+
+  // Attach (system chooses a suitable address)
+  if ((shm_array = (int *)shmat(shmid, NULL, 0)) == (int *)-1) {
+    perror("[!] Shmat failed");
+    exit(EXIT_FAILURE);
+  }
+
+  printf("[INIT] Connected to shared segment at %p (%d)\n", (void *)&shm_array,
+         shmid);
+
+  // Write
+  for (int i = 0; i < NUM_PROCS; i++) {
+    shm_array[i] = priorities[i];
+  }
+
+  // Detach
+  shmdt(shm_array);
+
+  printf("[INIT] Wrote priorities to shared memory\n");
+}
+
+int main() {
+  int pipefds[NUM_PROCS][2];
+  pid_t pids[NUM_PROCS];
+
+  // Creation of forks, their respective pipes, and random priorities
+  write_pipes(pipefds, pids);
+
+  int priorities[NUM_PROCS];
+
+  // Reading priorities from the pipes
+  read_pipes(pipefds, priorities);
+
+  // Attaching and writing priorities to a shared memory segment
+  write_mem_segment(priorities);
+
+  return 0;
+}

scheduler.c

@@ -0,0 +1,73 @@
+#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
+
+int create_mem_segment(int **shm_array) {
+  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_array = (int *)shmat(shmid, NULL, 0)) == (int *)-1) {
+    perror("[!] Shmat failed");
+    exit(EXIT_FAILURE);
+  }
+
+  return shmid;
+}
+
+int compare(const void *a, const void *b) { return (*(int *)a - *(int *)b); }
+
+int main() {
+  int *shm_array;
+
+  int delay = 5;
+
+  // Creation and attaching into a new shared segment
+  int shmid = create_mem_segment(&shm_array);
+  printf("[SCHEDULER] Shared segment created at %p (%d)\n", (void *)shm_array,
+         shmid);
+
+  // 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];
+  }
+
+  // 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
+
+  // Detaching and deleting the segment
+  shmdt(shm_array);
+  shmctl(shmid, IPC_RMID, NULL);
+
+  // Sorting and printing 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;
+}