private void shutdownListenerExecutor() {
    synchronized (listenerObjectLock) {
      if (executor != null) {
        executor.shutdown();
        executor = null;
      }
    }
  }
Initialize the Executor that handles listener events. Only used by non-primary gateway senders
geode-core/src/main/java/org/apache/geode/internal/cache/wan/serial/SerialGatewaySenderEventProcessor.java