presto-main/src/main/java/io/prestosql/execution/SqlTaskExecution.java/Status/getAndAcknowledgeLifespansWithNoMoreDrivers
class Status:        public synchronized List<Lifespan> getAndAcknowledgeLifespansWithNoMoreDrivers(int pipelineId)
        {
            List<Lifespan> result = ImmutableList.copyOf(per(pipelineId).unacknowledgedLifespansWithNoMoreDrivers);
            per(pipelineId).unacknowledgedLifespansWithNoMoreDrivers.clear();
            return result;
        }