In gRPC, a client application can directly call a method on a server application on a different machine as if it were a local object, making it easier for you to create distributed applications and services. As in many RPC systems, gRPC is based around the idea of defining a service, specifying the methods that can be called remotely with their parameters and return types. On the server side, the server implements this interface and runs a gRPC server to handle client calls. On the client side, the client has a stub (referred to as just a client in some languages) that provides the same methods as the server.
gRPC 是基于 HTTP/2 协议的，所以即使他能做到双向通信也会是类似websocket通信。而且grpc本身就是强区分客户端服务端，不为双向通信设计。
和socket相比：
gRPC 最大优势是编码使用protobuf，具备语言兼容性。使用 protocol buffers 的好处，包括高效的序列号，简单的 IDL 以及容易进行接口更新。 --不过反过来讲实际只使用protorbuf编码或者json编码同样可具备语言兼容性。
但是它和socket通信本身就是不同的东西，要解决的问题完全就是不同的。