C++ gRPC双向流异步客户端处理

参考：C++ GRPC ClientAsyncReaderWriter: how to check if data is available for read? - Stack Overflow

cpp-samples/streaming_transcribe_singlethread.cc at main · GoogleCloudPlatform/cpp-samples · GitHub

如何同时从gRPC中读取和写入：

https://stackoverflow.com/questions/54481404/how-can-i-read-and-write-from-a-grpc-stream-simultaneously