presto-main/src/main/java/io/prestosql/operator/TableFinishOperator.java/TableFinishOperator/isFinished
class TableFinishOperator:    @Override
    public boolean isFinished()
    {
        if (state == State.FINISHED) {
            verify(statisticsAggregationOperator.isFinished());
            return true;
        }
        return false;
    }