// Serializes memory and blows flags

  void membar(Membar_mask_bits order_constraint) {

  {- -------------------------------------------
  (1) MP 環境でなければ, メモリバリアは必要ないので何もしない.
      ---------------------------------------- -}

        if (os::is_MP()) {

  {- -------------------------------------------
  (1) 要求されているのが StoreLoad でなければ, バリアは不要なので何もしない.
      ---------------------------------------- -}

          // We only have to handle StoreLoad
          if (order_constraint & StoreLoad) {

  {- -------------------------------------------
  (1) lock 付きの nop (より正確には addl [rsp],0) を出すことでメモリバリアコードとする.
      ---------------------------------------- -}

            // All usable chips support "locked" instructions which suffice
            // as barriers, and are much faster than the alternative of
            // using cpuid instruction. We use here a locked add [esp],0.
            // This is conveniently otherwise a no-op except for blowing
            // flags.
            // Any change to this code may need to revisit other places in
            // the code where this idiom is used, in particular the
            // orderAccess code.
            lock();
            addl(Address(rsp, 0), 0);// Assert the lock# signal here
          }
        }
      }