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
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