Node Spinning and Execution Model

Why Spinning Matters

Spinning is how a ROS 2 node processes incoming data and scheduled callbacks. Without spinning, subscriptions, timers, and services will never be triggered.

Single-Threaded Spinner

The simplest pattern uses the single-threaded spinner:

rclcpp::spin(node);

  • Processes callbacks one at a time.

  • Easy to reason about and debug.

  • Suitable for many small nodes.

Multi-Threaded Spinner

For nodes that must handle many callbacks in parallel (for example, high-rate sensors and multiple services), ROS 2 also offers multi-threaded spinning:

rclcpp::executors::MultiThreadedExecutor executor;
executor.add_node(node);
executor.spin();

  • Uses multiple threads internally.

  • Allows callbacks to run concurrently.

  • Requires careful consideration of shared data and thread safety.

Node Lifecycle and Best Practices

  • Always call rclcpp::shutdown() before exiting main.

  • Use RAII and smart pointers for node ownership.

  • Keep callbacks small and focused; offload heavy work to helper classes or worker threads when needed.

  • Prefer composition: encapsulate functionality inside classes that are used by your node, instead of writing one very large node class.