void CMTask::drain_global_stack(bool partially) {

  {- -------------------------------------------
  (1) 何らかの理由でこの CMTask が中断されていたら, ここでリターン
      ---------------------------------------- -}

      if (has_aborted())
        return;

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

      // We have a policy to drain the local queue before we attempt to
      // drain the global stack.
      assert(partially || _task_queue->size() == 0, "invariant");

  {- -------------------------------------------
  (1) (変数宣言など)
      (target_size は, 今回の処理で _task_queue 内の要素をどこまで減らすかを表す.
      partially 引数が true なら partial_mark_stack_size_target() で計算する.
      partially 引数が false なら, すべて処理し終える.)
      ---------------------------------------- -}

      // Decide what the target size is, depending whether we're going to
      // drain it partially (so that other tasks can steal if they run out
      // of things to do) or totally (at the very end).  Notice that,
      // because we move entries from the global stack in chunks or
      // because another task might be doing the same, we might in fact
      // drop below the target. But, this is not a problem.
      size_t target_size;
      if (partially)
        target_size = _cm->partial_mark_stack_size_target();
      else
        target_size = 0;

  {- -------------------------------------------
  (1) (以降の処理で,
      _cm->mark_stack_size() 内の要素数が目標数(target_size)以下になるまで処理を続ける)
      ---------------------------------------- -}

      if (_cm->mark_stack_size() > target_size) {

    {- -------------------------------------------
  (1.1) (トレース出力)
        ---------------------------------------- -}

        if (_cm->verbose_low())
          gclog_or_tty->print_cr("[%d] draining global_stack, target size %d",
                                 _task_id, target_size);

    {- -------------------------------------------
  (1.1) ... するまで,
        CMTask::get_entries_from_global_stack() で取ってきて
        CMTask::drain_local_queue() で処理する,
        という作業を続ける.
        ---------------------------------------- -}

        while (!has_aborted() && _cm->mark_stack_size() > target_size) {
          get_entries_from_global_stack();
          drain_local_queue(partially);
        }

    {- -------------------------------------------
  (1.1) (トレース出力)
        ---------------------------------------- -}

        if (_cm->verbose_low())
          gclog_or_tty->print_cr("[%d] drained global stack, size = %d",
                                 _task_id, _cm->mark_stack_size());
      }
    }