public Host add(final InetSocketAddress address) {
            final Host newHost = new Host(address, Cluster.this);
            final Host previous = hosts.putIfAbsent(address, newHost);
            return previous == null ? newHost : null;
        }
Thread pool for background work related to the {@link Connection} and {@link ConnectionPool}.
gremlin-driver/src/main/java/org/apache/tinkerpop/gremlin/driver/Cluster.java