gRPC

Google Remote Procedure Call.

• Built on HTTP/2: one channel = one connection, and a connection multiplexes many streams.
• Similar idea to DCOM (Distributed COM): binary interface + RPC.
• Used by e.g. hashicorp/go-plugin.

Thread Model

Sync

• gRPC holds a thread pool and uses one thread per incoming stream.
• Max thread count is limited by ResourceQuota.

Async

• An RPC call pushes a request item into a completion queue; you fetch and handle it yourself.
• You need to provide your own thread pool for multithreaded RPC processing (grpc-io: GRPC Server Threading). Example: thread_stress_test.cc.
• Ref: grpc async model 的用途

Thread Safety

• Completion queues are thread-safe (grpc-io).
• Suggested: one completion queue per thread, numcpu threads (C++ Performance Notes).

Life Cycle

Ref: gRPC Core Concepts

Unary RPC

1. Client calls the stub method.
2. Server waits for the client's request message.
3. Server returns the response.
4. Client gets the response.

Bidirectional Streaming RPC

1. Client calls the stub method.
2. Server waits for the client to start streaming messages.
3. The two streams are independent: read and write can be in any order. For example:
   • Server waits until the client has sent all its messages.
   • Server and client play ping-pong.

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0f3e120-Add gRPC note migrated from note-of-code (#68)