C++ async streaming with multiple clients and wait for data

[shashank shekhar]

Hi,

We have a use-case where there is one async streaming server sending messages to multiple clients in round-robin fashion. The data is not always available and need to wait for the producer to generate data before it can be sent out. 

We followed the suggestions provided in the below article to overcome the behavior of task being added to the front of the completion queue and using alarms to wait for the producer -

https://www.gresearch.co.uk/article/lessons-learnt-from-writing-asynchronous-streaming-grpc-services-in-c/

However, the approach is not elegant and adds the overhead of alarm tasks. Is this the suggested approach for async streaming or is there an alternative that we are missing?

Thanks in advance for your response.

[Jeff Steger]

Great question. I too encountered the same limitation and solved it using the same article. But the fact that grpc doesnt natively support this is def a shortcoming imo. thanks for posting this. 

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[Christopher Pisz]

Wait wait...you implemented a GRPC asynch bidirectional streaming server in C++?
I've been looking for 6 months for one that actually works and doesn't block. Can I see? Can I see?

[Jeff Steger]

I implemented a grpc async streaming server that processes single requests (ie the streaming is not bidirectional). But you should be able to modify it so that it can process streaming requests. Here she is:

https://github.com/lbj137/repo1

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[Jeff Steger]

its been a while since i looked at that code but it seems like a good place for you to tinker with is in the section that defines async writers:

// write for single request, streaming response
	template <class Reply>
	using AsyncStreamingWriter = grpc::ServerAsyncWriter<Reply>;
	// Writer for request/response one-shots
	template <class Reply>
	using AsyncStandardWriter = grpc::ServerAsyncResponseWriter<Reply>;