class RequestStatsCollector implements RequestProgressListener {

    @Override
    public void onRequest(Object requestId) {
        Long previous = this.ongoingRequests.putIfAbsent(requestId, nanoClock.nanoTime());
        if (previous == null) {
            this.outstandingRequests.inc();
            this.requestsIncoming.mark();
        }
    }

    public  RequestStatsCollector(MetricRegistry metrics);
      RequestStatsCollector(MetricRegistry metrics, NanoClock nanoClock);

}