ROS 2 Real-Time Support

Overview

This repository provides experimental real-time extensions for ROS 2.
It extends the ROS 2 Client Libraries with real-time–oriented capabilities, such as configurable thread attributes and scheduling behavior, while abstracting RTOS-specific thread APIs behind a common interface.

Background

The work in this repository is based on the concept proposed in REP-2017.

Originally, real-time–related functionality was planned as an extension to core ROS 2 packages (e.g., rcl, rclcpp). Community discussions, including feedback from the PTC, concluded that such functionality would be difficult to maintain within the core. As a result, these capabilities are provided as a separate package set, allowing independent evolution while keeping the ROS 2 core lightweight.

Features

The repository provides experimental real-time extensions for ROS 2, with a focus on thread configuration, scheduling control, and RTOS portability. Basic usage is written in examples_rclcpp_realtime.

Current Status

• External YAML-based real-time configuration is supported.
• Thread attributes can be applied to Executors at runtime.
• POSIX is used as the initial reference backend.

RCL

• rcl_realtime based on rcl/rcl
  • Introcudes a dedicated context for real-time configuration.
  • Provides APIs for loading and accessing real-time settings (e.g., thread attributes).
• rcl_realtime_yaml_param_parser based on rcl/rcl_yaml_param_parser
  • Implements a YAML-based configuration parser for real-time settings.
  • Designed to decouple configuration formats from core logic.
• rcutils_realtime based on rcutils
  • Introduces common data structures for representing thread attributes (priority, affinity, scheduling policy, etc.).

RCLCPP

• rclcpp_realtime based on rclcpp/rclcpp (reference implementation)
  • Provides a thread-based Executor capable of applying real-time configuration.
  • Extends execution behavior based on the real-time context added to rcl.
  • Only additional executors SchedParamSingleThreadedExecutor and SchedParamMultiThreadedExecutor capable of reading thread attributes
• rcpputils_realtime based on rcpputils
  • Implements an abstraction layer over OS-specific thread APIs.
  • Currently supports POSIX-based APIs only.

TODO

• Improve documentation
  • Add API documentation (Doxygen)
  • Document configuration usage (See README of examples_rclcpp_realtime_executor)
    • Executor-option-based configuration
    • YAML-based configuration
    • rosparam-based configuration
  • Provide sample programs and usage examples
• Expand test coverage
  • Add additional API tests
  • Verify interoperability between rcl and rclcpp APIs
• Add git history for copied files and improve traceability

Future Work

• Revise implementation to extend --ros-args
• Separate rclcpp compatible test workflow
• Extend backend support to additional platforms and RTOS environments (e.g., Windows, macOS, QNX, VxWorks, eMCOS POSIX, Zephyr)
• Replace std::thread, std::mutex, and std::condition_variable with implementations that expose and utilize native_handle
• Apply and validate real-time configurations for ROS message communication mechanisms
• Compare implementation details and performance with existing publicly available executors

Change Log

(2026 July) 0.1.0

• Features
  • Add example package exmaple_rclcpp_realtime
  • Remove unnecessary class rclcpp_realtime::Node
  • Implement scheduling-parameter based executors (SchedParamSingleThreadedExecutor, SchedParamMultiThreadedExecutor)
  • Restructure API (e.g., add context_register)
• Bug Fixes
  • Handle --ros-args argument removal in rcl_realtime::init()
  • Initialize rcl_realtime_context upon adding new entries
  • Improve compatibility and revise the executor in rclcpp_realtime
  • Migrate git history from original ROS core packages
• Test
  • Add Python tools for testing and implement BUILD_COMP_TESTING CMake option
  • Add rclcpp_preload_wrapper.h to compatibirity check for rclcpp
• Documentation
  • Add Doxygen API comments to headers
  • Improve README and package documentation
  • Update "Getting Started" guide in examples

(2026 Mar) prototype

• Features
  • Migrate implementation of REP-2017 & sched_param examples
  • Implement realtime context, arguments and functions
• Documentation
  • Add project documentation (README, TODOs, and YAML notes)
  • Add package.xml and other package metadata

Acknowlegement

This work was supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan, under commissioned research project JPNP25016.