long track(final PoolEntry<T, C> entry) {
            lock.lock();
            try {
                final AtomicLong counter = getCounter(entry);
                return counter.incrementAndGet();
            } finally {
                lock.unlock();
            }
        }
Experimental connections pool implementation that acts as a caching facade in front of
a standard {@link ManagedConnPool} and shares already leased connections to multiplex
message exchanges over active HTTP/2 connections.
@param <T> route
@param <C> connection object

@since 5.5
httpclient5/src/main/java/org/apache/hc/client5/http/impl/nio/H2SharingConnPool.java