grpc-go: rpc error: code = Unavailable desc = transport is closing error happened when launching multiple goroutines to send request by grpc client

Please answer these questions before submitting your issue.

What version of gRPC are you using?

libprotoc 3.5.1

What version of Go are you using (go version)?

go version go1.9 darwin/amd64

What operating system (Linux, Windows, …) and version?

Mac 10.11.6

What did you do?

We had one use case that: sending the requests through goroutines by grpc clients to a same endpoint simultaneously, but there is a grpc error happened “rpc error: code = Unavailable desc = transport is closing error happened”, this error is not shown every time,but frequently. And if sending requests through goroutines but to different endpoints, it can work well

What did you expect to see?

I expected that the grpc is able to support handling the client requests concurrently.

What did you see instead?