presto-main/src/main/java/io/prestosql/operator/WorkProcessorPipelineSourceOperator.java/WorkProcessorPipelineSourceOperator/finish
class WorkProcessorPipelineSourceOperator:    @Override
    public void finish()
    {
        // operator is finished early without waiting for all pages to process
        operatorFinishing = true;
        noMoreSplits();
        closeOperators(workProcessorOperatorContexts.size() - 1);
    }