private void failExpiredRequests(long now) {
        // clear all expired unsent requests
        final Collection<ClientRequest> timedOutRequests = unsentRequests.removeAllTimedOut(now);
        for (ClientRequest request : timedOutRequests) {
            log.debug("Failed to send the following request after {} ms: {}", request.requestTimeoutMs(), request);
            completeWithDisconnect(request, now, null);
        }
    }
An inter-broker send thread that utilizes a non-blocking network client.
server-common/src/main/java/org/apache/kafka/server/util/InterBrokerSendThread.java