presto-main/src/main/java/io/prestosql/operator/RowNumberOperator.java/RowNumberOperator/processUnfinishedWork
class RowNumberOperator:    private boolean processUnfinishedWork()
    {
        verifyNotNull(unfinishedWork);
        if (!unfinishedWork.process()) {
            return false;
        }
        partitionIds = unfinishedWork.getResult();
        partitionRowCount.ensureCapacity(partitionIds.getGroupCount());
        unfinishedWork = null;
        return true;
    }