void StealRegionCompactionTask::do_it(GCTaskManager* manager, uint which) {

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

      assert(Universe::heap()->is_gc_active(), "called outside gc");

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

      NOT_PRODUCT(TraceTime tm("StealRegionCompactionTask",
        PrintGCDetails && TraceParallelOldGCTasks, true, gclog_or_tty));

  {- -------------------------------------------
  (1) ParCompactionManager::gc_thread_compaction_manager() で, 
      これを実行している GCTaskThread 用の ParCompactionManager オブジェクトを取得する.
      ---------------------------------------- -}

      ParCompactionManager* cm =
        ParCompactionManager::gc_thread_compaction_manager(which);

  {- -------------------------------------------
  (1) ParCompactionManager::drain_region_stacks() を呼んで, 
      ParCompactionManager 内のスタックに残っている全ての region に対して
      オブジェクトの移動処理を行う.
      ---------------------------------------- -}

      // Has to drain stacks first because there may be regions on
      // preloaded onto the stack and this thread may never have
      // done a draining task.  Are the draining tasks needed?

      cm->drain_region_stacks();

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

      size_t region_index = 0;
      int random_seed = 17;

      // If we're the termination task, try 10 rounds of stealing before
      // setting the termination flag

      while(true) {
        if (ParCompactionManager::steal(which, &random_seed, region_index)) {
          PSParallelCompact::fill_and_update_region(cm, region_index);
          cm->drain_region_stacks();
        } else {
          if (terminator()->offer_termination()) {
            break;
          }
          // Go around again.
        }
      }
      return;
    }