presto-main/src/main/java/io/prestosql/operator/SetBuilderOperator.java/SetBuilderOperator/addInput
class SetBuilderOperator:    @Override
    public void addInput(Page page)
    {
        requireNonNull(page, "page is null");
        checkState(!isFinished(), "Operator is already finished");

        Block sourceBlock = page.getBlock(setChannel);
        Page sourcePage = hashChannel.isPresent() ? new Page(sourceBlock, page.getBlock(hashChannel.get())) : new Page(sourceBlock);

        unfinishedWork = channelSetBuilder.addPage(sourcePage);
        processUnfinishedWork();
    }