void MarkSweepPolicy::initialize_generations() {

  {- -------------------------------------------
  (1) initialize_perm_generation() で, Perm Generation 用の GenerationSpec を作成する.
      (See: initialize_perm_generation())
      ---------------------------------------- -}

      initialize_perm_generation(PermGen::MarkSweepCompact);

  {- -------------------------------------------
  (1) GenerationSpec を格納する配列を確保する.
      (確保に失敗したら, ここで異常終了)
      ---------------------------------------- -}

      _generations = new GenerationSpecPtr[number_of_generations()];
      if (_generations == NULL)
        vm_exit_during_initialization("Unable to allocate gen spec");

  {- -------------------------------------------
  (1) Young Generation と Old Generation 用の GenerationSpec を作成する.
      (もし GenerationSpec の作成に失敗したら, ここで異常終了)
      ---------------------------------------- -}

      if (UseParNewGC && ParallelGCThreads > 0) {
        _generations[0] = new GenerationSpec(Generation::ParNew, _initial_gen0_size, _max_gen0_size);
      } else {
        _generations[0] = new GenerationSpec(Generation::DefNew, _initial_gen0_size, _max_gen0_size);
      }
      _generations[1] = new GenerationSpec(Generation::MarkSweepCompact, _initial_gen1_size, _max_gen1_size);

      if (_generations[0] == NULL || _generations[1] == NULL)
        vm_exit_during_initialization("Unable to allocate gen spec");
    }