@Override
    public PoolEntryRequest requestPoolEntry(HttpRoute route, Object state) {
        requestCounter.increment();
        return super.requestPoolEntry(route, state);
    }
A connection pool that provides Servo counters to monitor the efficiency. 
Three counters are provided: counter for getting free entries (or reusing entries),
counter for creating new entries, and counter for every connection request.

@author awang
ribbon-httpclient/src/main/java/com/netflix/http4/NamedConnectionPool.java