void ThreadLocalStorage::set_thread(Thread* thread) {

  {- -------------------------------------------
  (1) ThreadLocalStorage::pd_set_thread() で TLS への登録処理を行う.
      ---------------------------------------- -}

      pd_set_thread(thread);

  {- -------------------------------------------
  (1) (assert)
      ---------------------------------------- -}

      // The following ensure that any optimization tricks we have tried
      // did not backfire on us:
      guarantee(get_thread()      == thread, "must be the same thread, quickly");
      guarantee(get_thread_slow() == thread, "must be the same thread, slowly");
    }