see more from https://github.com/openzipkin/brave/issues/867, also see https://github.com/apache/incubator-dubbo/issues/3576
private Invoker<?> invoker;
    @Deprecated
    private Invocation invocation;
    
    
    private Object request;
    private Object response;
    private AsyncContext asyncContext;
    protected RpcContext() {
    }
    /**
     * get server side context.
     *
     * @return server context
     */
    public static RpcContext getServerContext() {
        return SERVER_LOCAL.get();
    }
    public static void restoreServerContext(RpcContext oldServerContext) {
        SERVER_LOCAL.set(oldServerContext);
    }
    /**
     * remove server side context.
     *
     * @see org.apache.dubbo.rpc.filter.ContextFilter
     */
    public static void removeServerContext() {
        SERVER_LOCAL.remove();
    }
    /**