Reconciling {ROS} 2 with Classical Real-Time Scheduling of Periodic Tasks

The Robot Operating System 2 ({ROS} 2) is a widely used middleware that provides software libraries and tools for developing robotic systems. In these systems, tasks are scheduled by {ROS} 2 executors. Since the scheduling behavior of the default {ROS} 2 executor is inherently different from classical real-time scheduling theory, dedicated analyses or alternative executors requiring substantial changes to {ROS} 2 have been developed. In 2023, the events executor was introduced into {ROS} 2. It features an events queue and allows the possibility to make scheduling decisions immediately after a job is completed. In this paper, we show that with minor modifications of the events executor, a large body of research results from classical real-time scheduling theory becomes directly applicable to {ROS} 2. This enables analytical bounds on the worst-case response time and the end-to-end latency, outperforming bounds for the default {ROS} 2 executor in many scenarios. Our solution is easy to integrate into existing {ROS} 2 systems since it requires only minor modifications of the events executor, which is natively included in {ROS} 2. The evaluation results show that our {ROS} 2 events executor with minor modifications can have significant improvement in terms of dropped jobs, worst-case response time, end-to-end latency, and performance compared to the default {ROS} 2 executor.