Add recorder stop() API

[MichaelOrlov]

• Relates Add BagSplitInfo on bag close #1213

• Replaces Add BagSplitInfo service call on bag close #1216

• Expose Writer::close() as public API and add Recorder::stop() API to be able to use in future for gracefully handle SIGINT and SIGTERM and send bagsplit() or bagclose() event from Recorder::stop() API.

[james-rms]

• What happens to discovery state between stop() and record()? do the full set of topics from before closing get written to the new bag file?
• I also wonder if we need pause at all. What if instead of adding stop() we just changed pause to close the bag?
• We should also update rosbag2_py to wrap these methods.

[MichaelOrlov]

@james-rms I will try to answer on your questions:

• What happens to discovery state between stop() and record()? do the full set of topics from before closing get written to the new bag file?

Discovery will be stopped and recreated with all subscriptions. If topics currently discoverable it will be added to the new bag if not it is not. Consider stop() operation as opposite to the record() operation. stop() will wrap everything up and ready for one more call for record().

• I also wonder if we need pause at all. What if instead of adding stop() we just changed pause to close the bag?

In current design we need stop(), pause() and resume(). Pause mode just dropping messages from subscriptions. The stop() really stop recording and wrapping everything up. There are lot more above pause() and resume() API and it would be a major redesign in recorder by remapping them to the stop() and record() calls.

• We should also update rosbag2_py to wrap these methods.

Sorry I missed it. I will add.
Update: Apparently there are nothing to wrap in rosbag2_py. We are not exposing rosbag2_cpp::writer class in python since it is cpp version nor exposing rosbag2_transport::recorder where relevant stop() API was added. Because we have rosbag2_py::Recorder with it's own business logic above rosbag2_transport::recorder and stop() API doesn't fit to it.

[MichaelOrlov]

Gist: https://gist.githubusercontent.com/MichaelOrlov/52b8a6060eacf2b928a2eca23185c85d/raw/d2ec5fdbe4478354c04fabd5d70ccaee677623a9/ros2.repos
BUILD args: --packages-above-and-dependencies rosbag2_transport rosbag2_cpp
TEST args: --packages-above rosbag2_transport rosbag2_cpp
ROS Distro: rolling
Job: ci_launcher
ci_launcher ran: https://ci.ros2.org/job/ci_launcher/11981

• Linux
• Linux-aarch64
• Windows

[MichaelOrlov]

@ros-pull-request-builder retest this please

[MichaelOrlov]

https://github.com/Mergifyio backport iron

[mergify]

backport iron

✅ Backports have been created

• #1334 Add recorder stop() API (backport #1300) has been created for branch iron

[ros-discourse]

This pull request has been mentioned on ROS Discourse. There might be relevant details there:

https://discourse.ros.org/t/ros-2-tsc-meeting-minutes-2023-05-18/31587/1