contract ReferenceConsideration is ConsiderationInterface, ReferenceOrderCombiner {
    ...
    function fulfillBasicOrder(BasicOrderParameters calldata parameters) ... notEntered nonReentrant ... {
        ...
    }
    ...
}
contract Consideration is ConsiderationInterface, OrderCombiner {
    ...
    function fulfillBasicOrder(BasicOrderParameters calldata parameters) ... {
        fulfilled = _validateAndFulfillBasicOrder(parameters);
    }

   function _validateAndFulfillBasicOrder( ... ) ... {
        ...
        _prepareBasicFulfillmentFromCalldata( ... ); // sets reentrancy guard
        ...    
        _transferEthAndFinalize(... ) --or-- _transferERC20AndFinalize(...) // clears reentrancy guard
        ... 
        _triggerIfArmed(accumulator);  // not protected by reentrancy guard
        ...   
    }

    function _prepareBasicFulfillmentFromCalldata(...) ... {
        // Ensure this function cannot be triggered during a reentrant call.
        _setReentrancyGuard();
        ...
    }
     function _transferEthAndFinalize(...) ... {
        ...
        // Clear the reentrancy guard.
        _clearReentrancyGuard();
    }
  function _transferERC20AndFinalize(...) ... {
        ...  
        // Clear the reentrancy guard.
        _clearReentrancyGuard();
   }
}
