public T initializeDataIfNeeded(Long hostId, boolean regenerateHash) throws AmbariRuntimeException {
    return data.computeIfAbsent(hostId, id -> initializeData(hostId, regenerateHash));
  }
Is used to saving and updating last version of event in host scope
@param <T> event with hash to control version
ambari-server/src/main/java/org/apache/ambari/server/agent/stomp/AgentHostDataHolder.java