class Thread2 {

   // swap instruction apprach to mutual exclusion

   public static void main(String args[]) {

      // lock shared by all threads
      HardwareData shared_lock = new HardwareData (false);

      // local lock in each thread
      HardwareData key = new HardwareData (true);

      while (true) {
         key.set (true);

         do {
            shared_lock.swap (key);
         } while (key.get() == true);

         // critical section
         shared_lock.set (false);
         // remainder section
      }
   }
}