Refactor cond_signal to add comment clarifying the logic w/ S

src/threads/synch.c

@@ -436,11 +436,12 @@ cond_signal (struct condition *cond, struct lock *lock UNUSED)
 
   if (!list_empty (&cond->waiters))
     {
+      /* Enforce wake-up of highest priority thread within the singleton 
+         semaphores waiting for condvar. */
       struct list_elem *e = list_min (&cond->waiters, sema_priority_more, NULL);
       list_remove (e);
       sema_up (&list_entry (e, struct semaphore_elem, elem)->semaphore);
     }
-
 }
 
 /* Wakes up all threads, if any, waiting on COND (protected by