@Override
    protected BasicPoolEntry getFreeEntry(RouteSpecificPool rospl, Object state) {
        BasicPoolEntry entry = super.getFreeEntry(rospl, state);
        if (entry != null) {
            freeEntryCounter.increment();
        }
        return entry;
    }
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