You're using ``ConcurrentHashMap`` above, and I am unfamiliar with how if at all any of Hysterix core will call into this class.

No matter what, the semantics you are using for the map coherency and static registration are incorrect:

``
final Gauge g = gauges.putIfAbsent(k, v);
if (g == null) {
  // No k in map.
  g.build();
}
``