default CloseableIterator<R> execute(final ServiceCallContext ctx, final TraverserSet<I> in, final Map params)  {
        throw new UnsupportedOperationException(Exceptions.doesNotSupportBarrier);
    }
Execute a Barrier service call with all upstream input.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/service/Service.java