feat: update structure

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

@@ -0,0 +1,56 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/shm.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#define NUM_PROCESSES 5
+
+int main() {
+
+  int i, j, pid;
+
+  // We create a new shared variable for our lock
+  int *lock;
+  int shmid;
+
+  shmid = shmget(IPC_PRIVATE, sizeof(int), IPC_CREAT | 0600);
+  lock = shmat(shmid, NULL, 0);
+
+  // If lock is 1, we get to run our code.
+  lock[0] = 1;
+
+  for (i = 0; i < NUM_PROCESSES; i++) {
+    if ((pid = fork()) == 0) {
+      break;
+    }
+  }
+
+  if (pid == 0) {
+
+    // Spin lock until lock is 1
+    while (lock[0] == 0)
+      ;
+
+    // Claim to lock
+    lock[0] = 0;
+    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");
+
+    // Release the lock
+    lock[0] = 1;
+  } else {
+    for (i = 0; i < NUM_PROCESSES; i++)
+      wait(NULL);
+
+    shmdt(lock);
+    shmctl(shmid, IPC_RMID, 0);
+  }
+}