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Comparison of Real-Time Performance with Other ROS 2 Executors

This document compares the real-time performance of the ROS 2 Default Executor and Executors proposed in academic literature from the following perspectives:

Immediate Enqueue of Ready Callbacks

In the ROS 2 Default Executor, a callback instance that becomes ready is enqueued only when the queue becomes empty. If the callback is enqueued immediately at the moment it becomes ready, ✔ is marked.

Per-Callback Priority Assignment

The ROS 2 Default Executor does not provide an API to assign priorities on a per-callback basis. If an Executor provides such an API, or allows users to assign priorities per callback through another mechanism, ✔ is marked.

Non-Nested Scheduling

In many Executors, the Executor maintains its own scheduling layer (e.g., a ready queue with priority ordering), and the OS independently schedules the threads that run callbacks. This two-level structure is referred to as nested scheduling. If the Executor's scheduling and the OS scheduling do not form such a nested structure, ✔ is marked.

Fully Preemptive

If a lower-priority callback can be preempted by any higher-priority callback during execution, ✔ is marked.

Support for Reentrant Callbacks

If, when a callback becomes ready while it is executing, it can be properly enqueued and executed, ✔ is marked.

ROS 2 Mainline

If the Executor has been merged into the ROS 2 mainline, or can be used by simply installing a standalone package without requiring changes to rcl or rclcpp, ✔ is marked.

Comparison Table

Executor Immediate Enqueue Per-Callback Priority Non-Nested Scheduling Fully Preemptive Support for Reentrant Callbacks ROS 2 Mainline
SingleThreadedExecutor / MultiThreadedExecutor ✔
EventExecutor ✔ ✔ ✔
PiCAS Single [1] ✔
PiCAS Multi [2] ✔*1 ✔
Dynamic-Priority-based Executor [3,4] ✔*1 ✔
Extended EventExecutor [5] ✔ ✔ ✔
RTeX [6] ✔ ✔ ✔
Budget-based Real-Time Executor [7] ✔*1 ✔ ✔ ✔
Preemptive EDF Executor [8] ✔*1 ✔ ✔ ✔
Ros-RT [9] ✔ ✔ ✔ ✔ ✔
CallbackIsolatedExecutor [10] ✔*1 ✔ ✔ ✔ ✔ ✔

*1: The ready queue is updated each time a thread selects a callback to execute.

References

  1. H. Choi, Y. Xiang and H. Kim, “PiCAS: New Design of Priority-Driven Chain-Aware Scheduling for ROS2,” 2021 IEEE 27th Real-Time and Embedded Technology and Applications Symposium (RTAS), Nashville, TN, USA, 2021, pp. 251–263. doi: 10.1109/RTAS52030.2021.00028

  2. H. Sobhani, H. Choi and H. Kim, “Timing Analysis and Priority-driven Enhancements of ROS 2 Multi-threaded Executors,” 2023 IEEE 29th RTAS, San Antonio, TX, USA, 2023, pp. 106–118. doi: 10.1109/RTAS58335.2023.00016

  3. A. Al Arafat et al., “Response time analysis for dynamic priority scheduling in ROS2,” DAC ’22, ACM, 2022, pp. 301–306. doi: 10.1145/3489517.3530447

  4. A. Al Arafat et al., “Dynamic Priority Scheduling of Multithreaded ROS 2 Executor With Shared Resources,” IEEE Transactions on CAD, vol. 43, no. 11, pp. 3732–3743, Nov. 2024. doi: 10.1109/TCAD.2024.3445259

  5. H. Teper et al., “Reconciling ROS 2 with Classical Real-Time Scheduling of Periodic Tasks,” 2025 IEEE 31st RTAS, Irvine, CA, USA, 2025, pp. 177–189. doi: 10.1109/RTAS65571.2025.00027

  6. S. Liu et al., “RTeX: An Efficient and Timing-Predictable Multithreaded Executor for ROS 2,” IEEE Transactions on CAD, vol. 43, no. 9, pp. 2578–2591, Sept. 2024. doi: 10.1109/TCAD.2024.3380551

  7. J. Staschulat et al., “Budget-based real-time Executor for Micro-ROS,” arXiv:2105.05590, 2021.

  8. K. Wilson et al., “Physics-Informed Mixed-Criticality Scheduling for F1Tenth Cars with Preemptable ROS 2 Executors,” 2025 IEEE 31st RTAS, Irvine, CA, USA, 2025, pp. 215–227. doi: 10.1109/RTAS65571.2025.00030

  9. S. Liu et al., “Ros-RT: Enabling Flexible Scheduling in ROS 2,” 2025 IEEE Real-Time Systems Symposium (RTSS), Dec. 2025, pp. 42–54. doi: 10.1109/RTSS66672.2025.00013

  10. T. Ishikawa-Aso et al., “Middleware-Transparent Callback Enforcement in Commoditized Component-Oriented Real-Time Systems,” 2025 IEEE 31st RTAS, Irvine, CA, USA, 2025, pp. 426–429. doi: 10.1109/RTAS65571.2025.00017