mw::com: Support for methods

[LittleHuba]

mw::com currently lacks support for methods.

This epic is about introducing this support.

Relevant Feature: https://eclipse-score.github.io/score/main/features/communication/index.html

[lak9999]

Status: The high level architecture concept changes are pushed. Detailed design is being worked out. Target to have design ready until the end of CW33

[HartmannNico]

While designing the Rust API I already did an RPC interface design here:

qor-com/src/concepts/rpc.rs.

Brief procedural logic: An RPC (method) (Rpc) consists of a Clientand a Server role. Server is the callee side and Client is the caller side. Invocation flow is like this:

Client:

• Client::loan_uninit --> RequestMaybeUninit.
• Fill the parameter tuple -> RequestMut
• Request::Send --> PendingRequest

Server:

• Server::Receive --> Request
• Request::loan_response_uninit --> ResponseMaybeUninit
• Execute invokation untilizing parameters and put the result into the response --> ResponseMut
• ResponseMut::Send

Client:

• PendingRequest::receive --> Response
• Process the response data

In essence, the Request and Response are each following the Topic or Event logic of an IPC communication. This allows to reuse the zero-copy IPC mechanisms already in place for Events. On the other hand, it introduces an individual communication pattern for RPC, so other than e.g. ROS RPC is not simply mapped to Topic communication.

[lak9999]

Status: The design is ready, and also in review with some early users who have showed interest in using the method support in mw::com (e.g. ConfigDeamon)

Target is have a finalized design with user feedback until end of CW37. primarily driven by @hoe-jo @SebSparrowHawk

[JochenSatETAS]

I also would like to take a look into the design, is this possible? @hoe-jo