偶然发现chromium代码中有NSApplicationMain函数的使用，发现是个demo。想编译看看，就有了对grpc和protoc的研究。

  1. ./third_party/grpc/src/examples/objective-c/helloworld_macos/main.m:  return NSApplicationMain(argc, argv);

protobuf

https://github.com/protocolbuffers/protobuf
grpc需要依赖protobuf, 去官网下载protobuf，其包含两部分，编译器protoc和语言运行时。
https://github.com/protocolbuffers/protobuf/releases

grpc

https://grpc.io/docs/quickstart/objective-c/
https://grpc.io/docs/quickstart/objective-c/