Is a gRPC client/stub usage across goroutines

user_8807932 0
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I'm experimenting with Protobuf and gRPC and was going through the Go basics tutorial: https://www.grpc.io/docs/languages/go/basics/

From what I could see in the documentation about the ClientConn it seems that it is safe to use the same ClientConn concurrently. But I can't anything about the stub/client that one creates...

Say I was receiving data via HTTP POST requests and I wanted to forward that data via gRPC as protobuf and then respond to the HTTP request. Should I create a client/stub every time I process a HTTP request, or can I create the client/stub when setting up the HTTP server and pass in the client/stub when setting up HTTP Handlers?

Example: I assume this is okay

var opts []grpc.DialOption
conn, err := grpc.Dial("127.0.0.1:1234", opts...)
if err != nil {
    log.Panic(err)
}
defer conn.Close()
grpcService := service.Service{GRPC: conn}
http.HandleFunc("/", util.ValidateRequest(grpcService.HandleRoot))

// listen to port
http.ListenAndServe(fmt.Sprintf("%s:%d", viper.GetString("server.address"), viper.GetInt32("server.port")), nil)

but what about this

var opts []grpc.DialOption
conn, err := grpc.Dial("127.0.0.1:1234", opts...)
if err != nil {
    log.Panic(err)
}
defer conn.Close()
client := pb.NewEventShipperClient(conn)
grpcService := service.Service{GRPC: conn, Client: client}
http.HandleFunc("/", util.ValidateRequest(grpcService.HandleRoot))

// listen to port
http.ListenAndServe(fmt.Sprintf("%s:%d", viper.GetString("server.address"), viper.GetInt32("server.port")), nil)
grpc-go grpc go
1 Answers

Thread safety ("is it safe to run this concurrently") is covered in the Generated-code reference:

Thread-safety: note that client-side RPC invocations and server-side RPC handlers are thread-safe and are meant to be run on concurrent goroutines. But also note that for individual streams, incoming and outgoing data is bi-directional but serial; so e.g. individual streams do not support concurrent reads or concurrent writes (but reads are safely concurrent with writes).

So, yes, methods on the struct returned by pb.NewEventShipperClient(conn) can be called concurrently.

You can also check this yourself by looking at the implementation of pb.NewEventShipperClient. Currently (I guess this may change) the only member variable will be an interface (cc grpc.ClientConnInterface - implemented by *ClientConn) with each method using the connection to Invoke a gRPC call.

Please note, however, that you need to be careful in your implementation of service.Service to ensure it is also threadsafe and note the caveat regarding streams.

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