private static Object getLock(Id id) {
        return locks[id.hashCode() & LOCK_MASK];
    }
An array of locks to guard the gauges.   This is the same as Guava's Striped, but avoids the dep.
<p>
This can be removed after https://github.com/Netflix/spectator/issues/862 is fixed.
zuul-core/src/main/java/com/netflix/zuul/monitoring/ConnCounter.java