void PSMarkSweepDecorator::advance_destination_decorator() {

  {- -------------------------------------------
  (1) (コンパクション先として使用する領域を, 次の領域に切り替える.

       具体的には, 現在の領域に応じて, 以下のように切り替わっていく.
            Old -> Eden -> From -> To                       
      )
      ---------------------------------------- -}

      ParallelScavengeHeap* heap = (ParallelScavengeHeap*)Universe::heap();
      assert(heap->kind() == CollectedHeap::ParallelScavengeHeap, "Sanity");

      assert(_destination_decorator != NULL, "Sanity");
      guarantee(_destination_decorator != heap->perm_gen()->object_mark_sweep(), "Cannot advance perm gen decorator");

      PSMarkSweepDecorator* first = heap->old_gen()->object_mark_sweep();
      PSMarkSweepDecorator* second = heap->young_gen()->eden_mark_sweep();
      PSMarkSweepDecorator* third = heap->young_gen()->from_mark_sweep();
      PSMarkSweepDecorator* fourth = heap->young_gen()->to_mark_sweep();

      if ( _destination_decorator == first ) {
        _destination_decorator = second;
      } else if ( _destination_decorator == second ) {
        _destination_decorator = third;
      } else if ( _destination_decorator == third ) {
        _destination_decorator = fourth;
      } else {
        fatal("PSMarkSweep attempting to advance past last compaction area");
      }
    }