Liveliness demos with Fast-RTPS don't seem to work

[clalancette]

Bug report

I'm following the Quality of Service demos at https://github.com/ros2/demos/blob/master/quality_of_service_demo/README.md , and none of the liveliness demos seem to work for me.

Required Info:

• Operating System:
  • Ubuntu 18.04
• Installation type:
  • Source
• Version or commit hash:
  • cee4332
• DDS implementation:
  • Fast-RTPS
• Client library (if applicable):
  • rclcpp/rclpy

Steps to reproduce issue

ros2 run quality_of_service_demo_cpp liveliness 1000 --kill-publisher-after 2000

Expected behavior

After 2 seconds, the publisher is killed and the subscriber gets a callback which prints out some information about liveliness.

Actual behavior

After 2 seconds, the publisher seems to be killed (at least, it stops printing), but we get no information about liveliness.

Additional information

This is failing for both quality_of_service_demo_cpp and quality_of_service_demo_py. Further, trying to run ros2 run quality_of_service_demo_cpp liveliness 250 --node-assert-period 0 --policy MANUAL_BY_NODE throws an exception on startup saying "Manual liveliness unsupported for fastrtps", but that is not mentioned in the README. @emersonknapp FYI.

[emersonknapp]

I have opened this PR to disable all Liveliness for Fast-RTPS ros2/rmw_fastrtps#282 - we thought Liveliness would be supported in the 1.8 release but it ended up not being the case.

Do you think we should also update the demo README to mention this limitation?

[jacobperron]

I would update the README since it might be perceived as a bug to users (#365).