@VisibleForTesting
  Map<String, AtomicInteger> getHostRequestCounts() {
    return Collections.unmodifiableMap(hostRequestCounts);
  }
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