void reset_to_mark() {

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

        if (UseMallocOnly) free_malloced_objects();

  {- -------------------------------------------
  (1) ResourceArea の値 (Chunk 等) を記録していた値に戻す.
      ---------------------------------------- -}

        if( _chunk->next() )        // Delete later chunks
          _chunk->next_chop();
        _area->_chunk = _chunk;     // Roll back arena to saved chunk
        _area->_hwm = _hwm;
        _area->_max = _max;

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

        // clear out this chunk (to detect allocation bugs)
        if (ZapResourceArea) memset(_hwm, badResourceValue, _max - _hwm);
        _area->set_size_in_bytes(size_in_bytes());
      }