Refactor process_wait to add more comments and improve readability

src/userprog/process.c

@@ -210,7 +210,8 @@ process_init_stack (char *cmd_saveptr, void **esp, char *file_name)
            so we can safely use strlen here. Filename has already been
            split from the command line arguments. */
         push_to_stack (esp, arg, strlen (arg) + 1);
-        
+
+        /* Try to allocate memory for the argument pointer. */
         struct arg_elem *arg_elem = malloc (sizeof (struct arg_elem));
         if (arg_elem == NULL)
           {
@@ -219,9 +220,11 @@ process_init_stack (char *cmd_saveptr, void **esp, char *file_name)
             return false;
           }
 
+        /* Store the argument pointer in the linked list. */
         arg_elem->arg = *esp;
         list_push_front (&arg_list, &arg_elem->elem);
 
+        /* Increment the argument count and get the next argument. */
         arg_count++;
         arg = strtok_r (NULL, " ", &cmd_saveptr);
       }
@@ -242,7 +245,10 @@ process_init_stack (char *cmd_saveptr, void **esp, char *file_name)
     int overflow_bytes = (PHYS_BASE - *esp) + remaining_size - PGSIZE;
     if (overflow_bytes > 0)
       {
+        /* Calculate the number of pages needed to allocate. */
         int pages_needed = DIV_CEIL (overflow_bytes, PGSIZE);
+
+        /* Allocate the pages and map them to the user process. */
         for (int i = 1; i < pages_needed + 1; i++)
           {
             uint8_t *kpage = palloc_get_page (PAL_USER | PAL_ZERO);
@@ -307,11 +313,12 @@ push_to_stack (void **esp, void *data, size_t data_size)
  * This function will be implemented in task 2.
  * For now, it does nothing. */
 int
-process_wait (tid_t child_tid UNUSED) 
+process_wait (tid_t child_tid)
 {
   struct process_result *child_result = NULL;
   struct list_elem *e;
   struct thread *cur = thread_current ();
+
   for (e = list_begin (&cur->child_results);
        e != list_end (&cur->child_results); e = list_next (e))
     {
@@ -319,27 +326,40 @@ process_wait (tid_t child_tid UNUSED)
           = list_entry (e, struct process_result, elem);
       if (result->tid == child_tid)
         {
+          /* Found the child process. */
           child_result = result;
           break;
         }
-      /* List is ordered, allowing us to break early. */
+
+      /* List is ordered, allowing us to break early if the child_tid is
+         greater than the current result's tid. */
       else if (result->tid > child_tid)
         break;
     }
+
+  /* If the child process was not found, return -1. */
   if (child_result == NULL)
     return -1;
+
   /* Wait for child to die. */
   sema_down (&child_result->sema);
+
   /* We need lock release in process_exit, so we need to acquire (and possibly
      wait) for it here to ensure we don't free the lock memory before it is
      released in process_exit. */
   lock_acquire (&child_result->lock);
+
   /* To prevent waiting for child twice, remove it from the list.
      No need to use lock since this is the only thread with access to
      the struct process_result now. */
   list_remove (&child_result->elem);
+
+  /* Get the exit status of the child */
   int exit_status = child_result->exit_status;
+
+  /* Release the lock */
   lock_release (&child_result->lock);
+
   free (child_result);
   return exit_status;
 }