A question about CompletionQueue under the use of async c++ client.

[Arthur Wang]

Hi all:

   I know that the CompletionQueue is application threads driven, which means that the requests entrusted on the CQ will be sent out  on the wire only after there are some application threads polling on it. Before that, none of the  requests will be sent, here is a github question to consult to. 

   But I found that if I entrust enough requests to a CQ ( ~50k),  before any threads start polling on it, the CQ has already sent some of them out to the server!  It seems that the #request has reached some threshold, and CQ just can't hold the them so having to just let them go.

   Am I understanding this correctly?  There is no problems with this behavior for me except that bring troubles on benchmark : I don't know the exact start point when the server start processing , and can't get an accurate throughput data.

   language : c++ (for both client & server)

   grpc version : v1.21.x 

   OS : win10 pro

   compiler : vs2015 Microsoft (R) C/C++ Optimizing Compiler Version 19.00.24215.1 for x86

   

- Regards

- Arthur

[Yang Gao]

Other than Cq, grpc creates some internal threads to handle some background work. I guess it is possible that what you observed is that some work is offloaded to the background executor.