presto-main/src/main/java/io/prestosql/operator/TableScanOperator.java/TableScanOperator/addSplit
class TableScanOperator:    @Override
    public Supplier<Optional<UpdatablePageSource>> addSplit(Split split)
    {
        requireNonNull(split, "split is null");
        checkState(this.split == null, "Table scan split already set");

        if (finished) {
            return Optional::empty;
        }

        this.split = split;

        Object splitInfo = split.getInfo();
        if (splitInfo != null) {
            operatorContext.setInfoSupplier(() -> new SplitOperatorInfo(splitInfo));
        }

        blocked.set(null);

        if (split.getConnectorSplit() instanceof EmptySplit) {
            source = new EmptySplitPageSource();
        }

        return () -> {
            if (source instanceof UpdatablePageSource) {
                return Optional.of((UpdatablePageSource) source);
            }
            return Optional.empty();
        };
    }