feat: update structure

cs2106/labs/lab3/progs/part1/lab3p1-sem.c

@@ -0,0 +1,47 @@
+#include <semaphore.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/ipc.h>
+#include <sys/shm.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#define NUM_PROCESSES 5
+
+int main() {
+  int shmid;
+  int i, j, pid;
+  sem_t* sems[NUM_PROCESSES];
+
+  for (int i = 0; i < NUM_PROCESSES; i++) {
+    shmid = shmget(IPC_PRIVATE, sizeof(sem_t), IPC_CREAT | 0600);
+    sems[i] = (sem_t*)shmat(shmid, NULL, 0);
+  }
+
+  sem_post(sems[0]);
+
+  for (int i = 0; i < NUM_PROCESSES; i++) sem_init(sems[i], 1, 0);
+  // allow the first process to run
+  sem_post(sems[0]);
+
+  for (i = 0; i < NUM_PROCESSES; i++) {
+    if ((pid = fork()) == 0) {
+      break;
+    }
+  }
+
+  if (pid == 0) {
+    sem_wait(sems[i]);
+    printf("I am child %d\n", i);
+
+    for (j = i * 10; j < i * 10 + 10; j++) {
+      printf("%d ", j);
+      fflush(stdout);
+      usleep(250000);
+    }
+    printf("\n\n");
+    sem_post(sems[i + 1]);
+  } else {
+    for (i = 0; i < NUM_PROCESSES; i++) wait(NULL);
+  }
+}