presto-main/src/main/java/io/prestosql/operator/WindowOperator.java/WindowOperator/createOperator
class WindowOperator:        @Override
        public Operator createOperator(DriverContext driverContext)
        {
            checkState(!closed, "Factory is already closed");

            OperatorContext operatorContext = driverContext.addOperatorContext(operatorId, planNodeId, WindowOperator.class.getSimpleName());
            return new WindowOperator(
                    operatorContext,
                    sourceTypes,
                    outputChannels,
                    windowFunctionDefinitions,
                    partitionChannels,
                    preGroupedChannels,
                    sortChannels,
                    sortOrder,
                    preSortedChannelPrefix,
                    expectedPositions,
                    pagesIndexFactory,
                    spillEnabled,
                    spillerFactory,
                    orderingCompiler);
        }