@Subscribe
  @AllowConcurrentEvents
  public void onEvent(ServiceComponentUninstalledEvent event) {
    LOG.debug("Received event {}", event);

    long clusterId = event.getClusterId();
    String hostName = event.getHostName();

    if (null == hostName) {
      return;
    }

    // invalidate hash and enqueue commands
    m_alertDefinitionHash.get().invalidate(hostName);
    m_alertDefinitionHash.get().enqueueAgentCommands(clusterId,
        Collections.singletonList(hostName));
  }
Handles {@link AlertHashInvalidationEvent} by performing the following
tasks:
<ul>
<li>Alert has invalidation</li>
<li>Enqueuing {@link AlertDefinitionCommand}</li>
</ul>
ambari-server/src/main/java/org/apache/ambari/server/events/listeners/alerts/AlertHashInvalidationListener.java