demos/demo_nodes_cpp_native

• What Is This?
• Build
• Run
• Verify
• FAQ
• References

What Is This?

This demo provides an example of further Quality-Of-Service (QoS) configurability as well as Publication Modes in a ROS 2 node via the use of rmw_fastrtps_cpp Application Programming Interface (API).

The example utilitises eprosima::fastdds::statistics::dds::DomainParticipant as well as eprosima::fastdds::dds::DataWriter.

A DomainParticipant defines a singular working unit which groups a set of Publishers and Subscribers together. See References - DomainParticipant for more details.

A DataWriter is created by a Publisher and writes data to a topic with configurable behaviors. See References - DataWriter for more details.

Build

colcon build --packages-up-to demo_nodes_cpp_native

Run

ros2 run demo_nodes_cpp_native talker

Verify

When executed correctly, the following strings should be printed to the terminal similar to what is shown below:

[INFO] [1674525877.083735645] [talker_native]: eprosima::fastdds::dds::DomainParticipant * 94193367466752
[INFO] [1674525877.084105822] [talker_native]: eprosima::fastdds::dds::DataWriter * 94193370040688
[INFO] [1674525877.584006930] [talker_native]: Publishing: 'Hello World: 1'
[INFO] [1674525878.083967966] [talker_native]: Publishing: 'Hello World: 2'
[INFO] [1674525878.583917242] [talker_native]: Publishing: 'Hello World: 3'
[INFO] [1674525879.083963276] [talker_native]: Publishing: 'Hello World: 4'
[INFO] [1674525879.583918839] [talker_native]: Publishing: 'Hello World: 5'
#...

FAQ

Q: Why use rmw_fastrtps_cpp API directly?

A: ROS 2 only allows for the configuration of certain middleware QoS (see ROS 2 QoS policies). In addition to ROS 2 QoS policies, rmw_fastrtps sets two more Fast DDS configurable parameters:

History memory policy: PREALLOCATED_WITH_REALLOC_MEMORY_MODE

Publication mode: ASYNCHRONOUS_PUBLISH_MODE

In addition, rmw_fastrtps offers the possibility to further configure Fast DDS:

Change publication mode

Full QoS configuration

Q: Is it still called Fast RTPS?

A: No. Fast RTPS has been renamed to Fast DDS since ROS 2 Foxy.

References

1. Fast DDS
2. What Is RTPS?
3. Fast RTPS Becomes Fast DDS in Foxy
4. Advanced Usage
5. DomainParticipant
6. DataWriter