ROS2 talker listener using difffernt DDS

Next Generation ROS
1

Hi all,

I am currently trying to use an alternative DDS rather than fastrtps. However I have noticed that the talker and listener demo which used to just run “talker” after sourcing the setup file is now changed to “ros2 run demo_nodes_cpp talker”. The old “talker__rmw_connext_cpp” that ued to let you use an alternative DDS is no longer working. My question is what is the new command for using an alternative DDS?

Thankyou

2

You can use the RMW_IMPLEMENTATION environment variable: see https://github.com/ros2/ros2/wiki/Working-with-multiple-RMW-implementations

Note, however, that this will only take effect if you have built the node in a workspace that supports multiple RMW implementations. The pre-built binaries only provide support for the default, rmw_fastrtps_cpp.

3

Hi dhood,
I have ran the RMW_IMPLEMENTATION as you mentioned earlier. However, I just wanted to know if there is a way that I could know if I am using my targeted dds or if it is just going back to the default fastrtps.

4

You can set the RCL_ASSERT_RMW_ID_MATCHES environment variable to be sure. If it doesn’t match you’ll get an error like:

$ RCL_ASSERT_RMW_ID_MATCHES=rmw_connext_cpp RMW_IMPLEMENTATION=rmw_fastrtps_cpp ros2 run demo_nodes_cpp talker
Expected RMW implementation identifier of 'rmw_connext_cpp' but instead found 'rmw_fastrtps_cpp', exiting with 102.

We have ideas for how to make this introspection easier for users in the future, but for the meantime I’ve added this info to the wiki page.