Reservations

[arjo129]

Implemented feature

This PR implements reservations.

⚠️ The quality of the code in this feature is pretty low. There are many unnecessary copies of objects made along the way and the PR can definitely be subject to a lot of clean ups. As this is a pretty big feature, I'm using the PR as an Minimal Viable Product.

Implementation description

The overall idea of this is to have an intelligent reservation protocol. This would allow robots to reserve items like parking spots, chargers and lifts intelligently. The initial discussion for this PR can be seen at osrf/rmf_core#297. Essentially, robots make reservations with a set of given constraints that can be defined by the ReservationRequest class. A robot may place a Request consisting of multiple alternatives of ReservationRequest. When the Reservation System (ResSys (for short)) receives the request it sets out to optimize the given constraints. Once it finds a satisfactory set of constraints it then asks the participants for approvals. If one of the robots disagrees, then the optimizer will find the next best solution. If all the participants agree, then we rollout the reservation.

The key files of interest if you wish to review the API are the following:

• rmf_traffic/include/rmf_traffic/reservations/ReservationRequest.hpp - The class through which you specify your constraints.
• rmf_traffic/include/rmf_traffic/reservations/Participant.hpp - Abstract class through which you receive callbacks.
• rmf_traffic/include/rmf_traffic/reservations/Writer.hpp - Abstract class, which is implemented by Database. This is how you place reservations on the system. These are the main API which a user will be likely to call.

An example of how the reservation may be used can be found in rmf_traffic/test/unit/reservations/test_Database.cpp

Internally, the planner performs a best-first-search. Honestly, theres a lot of work to do here but the critical files for this are all stored here:

• src/rmf_traffic/reservations/internal/State.hpp - Keeps track of the State. Is used to explore the search space.
• src/rmf_traffic/reservations/internal/StateDiff.hpp - Calculates patches between the states.
• src/rmf_traffic/reservations/internal/Heuristic.hpp - Abstract class and naive implementation of a greedy heuristic.
• src/rmf_traffic/reservations/internal/Optimizer.hpp - Actual implementation of Greedy Best-First-Search. Short and simple not much to see...

There are also some classes to help with synchronization and general book keeping.

• ParticipantStore - stores the participants and provides general book-keeping for participants.
• RequestStore - stores the requests.
• Protocol - The actual implementation of the protocol.