void initializeResources() {
        applicationEventProcessor = applicationEventProcessorSupplier.get();
        networkClientDelegate = networkClientDelegateSupplier.get();
        requestManagers = requestManagersSupplier.get();
    }
Background thread runnable that consumes {@link ApplicationEvent} and produces {@link BackgroundEvent}. It
uses an event loop to consume and produce events, and poll the network client to handle network IO.
clients/src/main/java/org/apache/kafka/clients/consumer/internals/ConsumerNetworkThread.java