C / C++ multi-node workspaces

This page now holds only the contract sections of the C and C++ workspace walkthrough. The workspace layout, the node and bringup packages, the image and the entry it generates moved to Organize a larger workspace and Mix languages.

The reference C++ workspace is examples/workspaces/cpp/.

Contracts for a C or C++ workspace

Telling the build what the component creates

NROS_EXECUTOR_MAX_CBS, the subscriber slots and the arena are const sizes compiled into nros-node before a component TU is compiled, while a typed component wires itself in its CONSTRUCTOR, at runtime. Nothing the macros emit can supply those sizes — it exists only after linking. So somebody has to state what the image creates, ahead of the build.

That statement is a contract sidecar beside the launch file, not something in this CMakeLists. <stem>.contract.yaml next to <stem>.launch.xml in the bringup package:

# src/demo_bringup/launch/system.contract.yaml
version: 1

nodes:
  talker:
    paths:
      on_timer:                                  # a path with a timer trigger
        trigger: { timer: { rate_hz: 1 } }       # IS the periodic callback
        output: [chatter]
    pub:
      chatter: {}
  listener:
    sub:
      chatter: {}

topics:
  /chatter:
    type: std_msgs/msg/Int32
    pub: [talker/chatter]
    sub: [listener/chatter]

nodes: keys are LOCAL endpoint names — an absolute path there is concatenated onto the node’s FQN and matches no topic. topics:, services: and actions: wire those endpoints to absolute names and carry the type. paths: is where timers live: the model records a path with no input as the periodic callback.

The build folds it into the resolved SystemModel and sizes the image’s pools from it; nothing in the CMakeLists takes an argument for it. The tasks that build on this sidecar have their own pages, for every language:

• Declare QoS in a contract
• Size an image from its contract
• Contracts for a bringup with no launch file
• Fix a contract refusal

Design background

• RFC-0122: behaviour bringups, single-node witnesses, and cadence-backed CI. The paired examples as image rows of behaviour bringups in the language workspaces.