public void subscribe(URILoadingRegistry registry, IAsyncResultHandler<Void> handler) {
            synchronized (URILoadingRegistry.class) {
                Objects.requireNonNull(registry, "registry must be non-null.");
                Objects.requireNonNull(handler, "handler must be non-null.");
                handlers.put(registry, handler);
                allRegistries.add(registry);
                awaiting.add(registry);
                vertx.runOnContext(action -> checkQueue());
            }
        }
URI loading registry that pulls configuration from a specified JSON file.
<ul>
  <li>configUri: apiman policy config to load from JSON via file
  ({@link FileResourceFetcher}) or HTTP/S ({@link HttpResourceFetcher}).
  See the corresponding fetcher for additional options.</li>
</ul>

@author Marc Savy {@literal <marc@rhymewithgravy.com>}
@see FileResourceFetcher
@see HttpResourceFetcher
gateway/engine/vertx-polling/src/main/java/io/apiman/gateway/engine/vertx/polling/URILoadingRegistry.java