ROS 2 message flow test cases

This repo contains simple test cases for different message link types needed to extract the flow of messages in ROS 2. See the ROS 2 message flow analysis repository.

This is part of the ROS 2 message flow paper. If you use or refer to this method or this repository, please cite:

• C. Bédard, P.-Y. Lajoie, G. Beltrame, and M. Dagenais, "Message Flow Analysis with Complex Causal Links for Distributed ROS 2 Systems," Robotics and Autonomous Systems, vol. 161, p. 104361, 2023.

BibTeX:

@article{bedard2023messageflow,
  title={Message flow analysis with complex causal links for distributed {ROS} 2 systems},
  author={B{\'e}dard, Christophe and Lajoie, Pierre-Yves and Beltrame, Giovanni and Dagenais, Michel},
  journal={Robotics and Autonomous Systems},
  year={2023},
  volume={161},
  pages={104361},
  doi={10.1016/j.robot.2022.104361}
}

Message link types

1. Synchronous 1-to-N
   • New messages are published on N topics directly in the subscription callback for a received message
   • No instrumentation or annotation necessary
2. Periodic asynchronous N-to-M
   • Messages are received from N topics and are cached
   • A timer periodically uses the last messages from each topic to compute a result and publish messages on M topics
     • In case the timer callback is executed when at least one topic has not received a message yet (i.e., empty cache), no new message(s) are published
     • This behaviour is defined for the sake of simplicity and could be adapted or changed
   • Message link annotation is required
   • Equivalent to the cyclic node, but with M output topics instead of 1
3. Partially synchronous N-to-M
   • Messages are received from N topics and are cached
   • Every time a new message is received and put into the corresponding cache, all topic caches are checked in the callback itself
     • If (at least) one new message for each input topic has been received, a result is computed and messages are published on M topics in the subscription callback itself
     • Then all the cache is reset and at least one new message for each topic needs to be received for the new message(s) to be published
   • Message link annotation is required
   • Equivalent to the fusion node, but with N input topics and M output topics instead of 2 and 1, respectively

Base nodes

1. Source
   • Publishes messages on N topics periodically using a timer
2. Sink
   • Receives messages from N topics