void G1MarkSweep::mark_sweep_phase1(bool& marked_for_unloading,
                                    bool clear_all_softrefs) {

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

      // Recursively traverse all live objects and mark them
      EventMark m("1 mark object");
      TraceTime tm("phase 1", PrintGC && Verbose, true, gclog_or_tty);
      GenMarkSweep::trace(" 1");

  {- -------------------------------------------
  (1) (変数宣言など)
      ---------------------------------------- -}

      SharedHeap* sh = SharedHeap::heap();

  {- -------------------------------------------
  (1) まず, SharedHeap::process_strong_roots() を呼び出して root から参照されているオブジェクトを全て処理する.
      ---------------------------------------- -}

      sh->process_strong_roots(true,  // activeate StrongRootsScope
                               true,  // Collecting permanent generation.
                               SharedHeap::SO_SystemClasses,
                               &GenMarkSweep::follow_root_closure,
                               &GenMarkSweep::follow_code_root_closure,
                               &GenMarkSweep::follow_root_closure);

  {- -------------------------------------------
  (1) 次に, ReferenceProcessor::process_discovered_references() を呼び出して, 
      上の処理中に発見された参照オブジェクト(java.lang.ref オブジェクト) の処理を行う.
      ---------------------------------------- -}

      // Process reference objects found during marking
      ReferenceProcessor* rp = GenMarkSweep::ref_processor();
      rp->setup_policy(clear_all_softrefs);
      rp->process_discovered_references(&GenMarkSweep::is_alive,
                                        &GenMarkSweep::keep_alive,
                                        &GenMarkSweep::follow_stack_closure,
                                        NULL);

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

      // Follow system dictionary roots and unload classes
      bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
      assert(GenMarkSweep::_marking_stack.is_empty(),
             "stack should be empty by now");

      // Follow code cache roots (has to be done after system dictionary,
      // assumes all live klasses are marked)
      CodeCache::do_unloading(&GenMarkSweep::is_alive,
                                       &GenMarkSweep::keep_alive,
                                       purged_class);
      GenMarkSweep::follow_stack();

      // Update subklass/sibling/implementor links of live klasses
      GenMarkSweep::follow_weak_klass_links();
      assert(GenMarkSweep::_marking_stack.is_empty(),
             "stack should be empty by now");

      // Visit memoized MDO's and clear any unmarked weak refs
      GenMarkSweep::follow_mdo_weak_refs();
      assert(GenMarkSweep::_marking_stack.is_empty(), "just drained");


      // Visit interned string tables and delete unmarked oops
      StringTable::unlink(&GenMarkSweep::is_alive);
      // Clean up unreferenced symbols in symbol table.
      SymbolTable::unlink();

      assert(GenMarkSweep::_marking_stack.is_empty(),
             "stack should be empty by now");
    }