gfa99 / events-executor

ROS 2 C++ executor bringing low CPU usage, low latency and deterministic ordering

events-executor

The events-executor is now merged in rclcpp: ros2/rclcpp#2155 and this repository is now deprecated

This repository contains a C++ implementation of the EventsExecutor designed by iRobot. It is a new type of executor compatible with the ROS 2 rclcpp library.

The EventsExecutor design is based on the following principles:

1. You don't pay for what you don't use.
2. The abstractions between the application and the RMW should have minimal overhead.
3. Extensibility.

The following data have been measured using the iRobot ros2-performance framework and show how, for a 10 nodes system, the EventsExecutor reduces both CPU and latency by 75% with respect to the default SingleThreadedExecutor and by 50% with respect to the StaticSingleThreadedExecutor.

These results have been obtained using the default implementation of the EventsExecutor events queue, i.e. an std::queue. The extensibility of the EventsExecutor comes from the fact that this core components can be re-implemented by the users. For example in this repository we also include an extension that uses a lock-free queue, based on this great concurrent queue implementation. Other extensions would allow to bound the queue or enforce deterministic execution constraints.

To know more about the design of the Events Executor, refer to ros2/design#305.

Known bugs and limitations

The executor has some known bugs and limitations when used together with standard ROS 2 core libraries. These are described here, together with how to fix them.

• The executor is not notified when a ROS 2 timer is reset. This means that the timer may not be triggered anymore. To fix this bug:
  1. Use the humble-future branch of this repository
  2. Cherry-pick ros2/rclcpp#1979
  3. Cherry-pick ros2/rcl#995
• Enabling Intra-Process Optimization in rclcpp may result in a runtime exception. To fix this bug:
  1. Cherry-pick ros2/rclcpp#2061.
• Segmentation fault if using compiler optimizations (e.g. -DCMAKE_BUILD_TYPE=Release). To fix this bug:
  1. Cherry-pick ros2/rclcpp#2059

Instructions

This repository provides libraries that can be built and installed alongside a standard ROS 2 installation and give access to the EventsExecutor class and its related components.

To use the EventsExecutor you just need to build the irobot_events_executor project and add it as a dependency in your application.

The irobot_lock_free_events_queue is an optional package that provides access to a more performant implementation of the EventsExecutor events queue. It also serves as an example of how the EventsExecutor can be customized and extended.

Examples

The repository contains some example applications showing how to use the EventsExecutor in your application.

To build and run the examples you can do the following:

docker run -it osrf/ros:humble-desktop bash
sudo apt-get update && sudo apt-get upgrade && sudo apt-get install ros-humble-test-msgs
mkdir -p /root/ws/src
cd /root/ws/src
git clone https://github.com/irobot-ros/events-executor.git
cd /root/ws
colcon build
source install/setup.sh
ros2 run events_executor_examples hello_events_executor

Branches

• main: this is the default branch and it is compatible with standard humble and rolling ROS 2 systems.
• humble-future: this is an experimental branch that requires to apply some changes to core ROS 2 libraries before being able to compile it.
• humble-future-gcc8: this branch builds on top of humble-future, and in addition it is compatible with gcc8 compilers.