presto-main/src/main/java/io/prestosql/operator/LookupJoinOperator.java/JoinProcessor/isFinished
class JoinProcessor:        private boolean isFinished()
        {
            boolean finished = this.finished && probe == null && pageBuilder.isEmpty() && outputPage == null;

            // if finished drop references so memory is freed early
            if (finished) {
                close();
            }
            return finished;
        }