void G1CollectedHeap::do_full_collection(bool clear_all_soft_refs) {

  {- -------------------------------------------
  (1) G1CollectedHeap::do_collection() を呼び出すだけ.
      ---------------------------------------- -}

      // do_collection() will return whether it succeeded in performing
      // the GC. Currently, there is no facility on the
      // do_full_collection() API to notify the caller than the collection
      // did not succeed (e.g., because it was locked out by the GC
      // locker). So, right now, we'll ignore the return value.
      bool dummy = do_collection(true,                /* explicit_gc */
                                 clear_all_soft_refs,
                                 0                    /* word_size */);
    }