See ros2/rmw_cyclonedds#89 for most of the details, but the basics are:

As discussed elsewhere (ros2/rmw_fastrtps#343 (review)), the current best practice is to use the closest equivalent to the asynchronous publishing mode that some DDS implementations have for implementing rmw_publish(). Right now, this repository does not change the QoS for this when creating a publisher and therefore I assume it uses something like the synchronous publishing mode.

So a few questions:

• does OpenSplice have an "asynchronous publishing mode"-like setting?
• if not, what is the blocking behavior of publishing in OpenSplice, or more generally what happens when you call publish?

If there is an equivalent mode then it would be best to switch to it by default, even if it has a negative performance impact for some cases.

We can/should separately decide if the best practice should be adjusted, but until that time we should try to keep our rmw implementations as consistent as possible.

We can also chose to not do anything about this, given that we're doing away with OpenSplice support in ROS.