public void registerRequestWorker(final AsyncRequestWorker asyncRequestWorker) {
    int pos = asyncRequestWorkerIndex.getAndIncrement();
    Gauge<Integer> gauge = asyncRequestWorker::getRequestQueueSize;
    metricRegistry.register(MetricRegistry.name(AsyncRequestWorker.class, pos + "-RequestQueueSize"), gauge);
  }
Registers the {@code asyncRequestWorker} so that its metrics (request queue size) can be tracked.
@param asyncRequestWorker the {@link AsyncRequestWorker} whose metrics need to be tracked.
ambry-rest/src/main/java/com/github/ambry/rest/AsyncRequestResponseHandlerFactory.java