 -> void
{
printf("Requested deadline missed - total %d delta %d",
event.total_count, event.total_count_change);
};](https://image.slidesharecdn.com/2ndrosbythebaypresentation-qos-190619171732/85/QoS-Policies-in-ROS-2-Dashing-9-320.jpg)
QoS Policies in ROS 2 Dashing
- 1. Miaofei Mei QoS Policies in ROS2 Dashing June 2019
- 2. What are QoS Policies and Why Have Them • Stands for quality of service • Settings that control characteristics of the middleware • Affects performance, fault tolerance, determinism, etc. of the middleware’s communications
- 3. Originally Supported QoS Policies • History • Should publishers keep a history of sent messages • Depth is a settable option • Reliability • Whether or not all messages in history must be delivered • Durability • Do messages in history need to outlive their publisher for late coming subscriptions
- 4. Newly Supported QoS Policies • Lifespan • Deadline • Liveliness
- 5. Lifespan QoS Policy • The purpose is to avoid delivering “stale” data to the client application • Messages have a lifespan. Messages past their lifespan will not be delivered to the application • (There is no notification to the application that messages were dropped)
- 6. Deadline QoS Policy • Messages are expected to be sent and received within a period • If the publisher’s offered deadline period is greater than the subscription’s requested deadline period, then they are considered incompatible • The publisher/subscription will notify the client application if it is not sending/receiving messages within the deadline
- 7. Liveliness QoS Policy • When the publisher is not sending messages, it needs to assert its liveliness to its subscriptions within some lease duration, either automatically or manually • Also subject to incompatibility between publisher and subscription • The publisher will notify the client application if it has not asserted its liveliness in time • The subscription will notify the client application if its publisher did not assert its liveliness in time
- 8. Publisher / Subscription API • How to specify QoS policy settings and how will the client application be notified of QoS events? • create_publisher(topic_name, qos_settings, publisher_options); • create_subscription(topic_name, qos_settings, msg_callback, subscription_options, mem_strat);
- 9. Event Callback Functions • Like the message callback function • Specified in the publisher_options / subscription_options arguments • Providing these callback functions are optional • For example: subscription_options.event_callbacks.deadline_callback = [](rclcpp::QOSDeadlineRequestedInfo & event) -> void { printf("Requested deadline missed - total %d delta %d", event.total_count, event.total_count_change); };
- 10. Thank You!
- 11. Q&A • Questions? • Additional information can also be found at: • DDS Specification • Design Document