public List<SamzaResource> getResourcesOnAHost(String host) {
    synchronized (lock) {
      List<SamzaResource> samzaResourceList = allocatedResources.get(host);
      if (samzaResourceList == null)
        return null;

      return new ArrayList<>(samzaResourceList);
    }
  }
Returns the list of resources allocated on a given host. If no resources were ever allocated on
the given host, it returns null. This method makes a defensive shallow copy. A shallow copy is
sufficient because the SamzaResource class does not expose setters.

@param host hostname
@return list of resources allocated on the given host, or null
samza-core/src/main/java/org/apache/samza/clustermanager/ResourceRequestState.java