1# Concurrency 2 3In general, gRPC-go provides a concurrency-friendly API. What follows are some 4guidelines. 5 6## Clients 7 8A [ClientConn][client-conn] can safely be accessed concurrently. Using 9[helloworld][helloworld] as an example, one could share the `ClientConn` across 10multiple goroutines to create multiple `GreeterClient` types. In this case, 11RPCs would be sent in parallel. `GreeterClient`, generated from the proto 12definitions and wrapping `ClientConn`, is also concurrency safe, and may be 13directly shared in the same way. Note that, as illustrated in 14[the multiplex example][multiplex-example], other `Client` types may share a 15single `ClientConn` as well. 16 17## Streams 18 19When using streams, one must take care to avoid calling either `SendMsg` or 20`RecvMsg` multiple times against the same [Stream][stream] from different 21goroutines. In other words, it's safe to have a goroutine calling `SendMsg` and 22another goroutine calling `RecvMsg` on the same stream at the same time. But it 23is not safe to call `SendMsg` on the same stream in different goroutines, or to 24call `RecvMsg` on the same stream in different goroutines. 25 26## Servers 27 28Each RPC handler attached to a registered server will be invoked in its own 29goroutine. For example, [SayHello][say-hello] will be invoked in its own 30goroutine. The same is true for service handlers for streaming RPCs, as seen 31in the route guide example [here][route-guide-stream]. Similar to clients, 32multiple services can be registered to the same server. 33 34[helloworld]: https://github.com/grpc/grpc-go/blob/master/examples/helloworld/greeter_client/main.go#L43 35[client-conn]: https://godoc.org/google.golang.org/grpc#ClientConn 36[stream]: https://godoc.org/google.golang.org/grpc#Stream 37[say-hello]: https://github.com/grpc/grpc-go/blob/master/examples/helloworld/greeter_server/main.go#L41 38[route-guide-stream]: https://github.com/grpc/grpc-go/blob/master/examples/route_guide/server/server.go#L126 39[multiplex-example]: https://github.com/grpc/grpc-go/tree/master/examples/features/multiplex 40