public void put(Node node, ClientRequest request) {
            // the lock protects the put from a concurrent removal of the queue for the node
            synchronized (unsent) {
                ConcurrentLinkedQueue<ClientRequest> requests = unsent.computeIfAbsent(node, key -> new ConcurrentLinkedQueue<>());
                requests.add(request);
            }
        }
Return whether the caller is still awaiting an IO event.
@return true if so, false otherwise.
clients/src/main/java/org/apache/kafka/clients/consumer/internals/ConsumerNetworkClient.java