void VM_CGC_Operation::doit() {

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

      gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
      TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
      TraceTime t(_printGCMessage, PrintGC, true, gclog_or_tty);

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

      SharedHeap* sh = SharedHeap::heap();

  {- -------------------------------------------
  (1) コンストラクタで指定された VoidClosure (_cl) に対して
      VoidClosure::do_void() を呼び出す.
      ---------------------------------------- -}

      // This could go away if CollectedHeap gave access to _gc_is_active...
      if (sh != NULL) {
        IsGCActiveMark x;
        _cl->do_void();
      } else {
        _cl->do_void();
      }
    }