using zero-copy transport in ROS2 with ros2_shm_msgs
motivation
zero-copy transport has been available in iceoryx, cyclonedds, FastDDS and eCAL, and the loaned_api can be used to get minimum copy to get better performance suce as lower cpu usage and transport latency.
Due to the unbounded nature of the point cloud and image message types being used in ROS2, these messages will not be supported by zero-copy in Galactic. To utilize zero-copy for point cloud and image data, message types will need to be revised.
ros2_shm_msgs
ros2_shm_msgs provides ROS2 image and pointcloud2 message definitions that support zero copy transportation, demos and tools also included.
api usage
there is a code snip in shm_image1m_talker, the usage is much like cv_bridge and pcl_conversions.
class Talker : public rclcpp::Node {
private:
using Topic = shm_msgs::msg::Image1m;
public:
explicit Talker(const rclcpp::NodeOptions &options)
: Node("shm_image1m_talker", options) {
m_input_cvimage->image = cv::imread("./res/img/205_182.png");
m_input_cvimage->header.frame_id = "camera_link";
m_input_cvimage->encoding = "bgr8";
// cv::imshow("input image", m_input_cvimage->image);
// cv::waitKey(0);
auto publishMessage = [this]() -> void {
auto loanedMsg = m_publisher->borrow_loaned_message();
populateLoanedMessage(loanedMsg);
m_publisher->publish(std::move(loanedMsg));
// We gave up ownership and loanedMsg is not supposed to be accessed
// anymore
m_count++;
};
rclcpp::QoS qos(rclcpp::KeepLast(10));
m_publisher = this->create_publisher<Topic>("shm_image_1m", qos);
// Use a timer to schedule periodic message publishing.
m_timer = this->create_wall_timer(0.1s, publishMessage);
}
private:
uint64_t m_count = 1;
rclcpp::Publisher<Topic>::SharedPtr m_publisher;
rclcpp::TimerBase::SharedPtr m_timer;
std::shared_ptr<shm_msgs::CvImage> m_input_cvimage{std::make_shared<shm_msgs::CvImage>()};
void populateLoanedMessage(rclcpp::LoanedMessage<Topic> &loanedMsg) {
Topic &msg = loanedMsg.get();
m_input_cvimage->header.stamp = now();
m_input_cvimage->toImageMsg(msg);
RCLCPP_INFO(this->get_logger(), "Publishing ");
}
};
rviz bridge
as discussied in publish each image to its own topic for use in rqt_image or rviz2 · Issue #11 · MatthiasKillat/ros2_shm_vision_demo · GitHub
there is need for visualization of the custom ros2_shm_msgs types, so the rviz bridge is developed for this.
see this as an example
performance in benchmarks
see zero-copy performance of rmw_cyclonedds and rmw_fastrtps in GitHub - ZhenshengLee/ros2_jetson_benchmarks: The ros2 benchmarks for jetson xavier and pc.
which is tested within GitHub - ZhenshengLee/performance_test: Github repo for apex.ai performance_test for more middlewares.
performance in ros_shm_msgs demo
there are demos in the repo to show the performance like transport time and fps.
see this as an example
cd install/v4l2_camera/lib/v4l2_camera
./v4l2_camera_image1m_subscriber
[INFO] [1654154565.559710174] [shm_image1m_subscriber]: Received...
[INFO] [1654154565.559730953] [shm_image1m_subscriber]: get-image1m-transport-time: 0.253
performance in device driver
this lib has been used in the custom version of ros2_v4l2_camera
and rslidar_sdk, and the performance improvement is awesome!
For example, in my pc of dell 3630, the zero-copy transport of a shm_msgs::msg::Image1m can save about 80% of transport time, from 1.4ms to 0.3ms
issues
- the memcopy cannot avoid in the construction phase of loaned_msg.
from [ROS2] IPC support in CameraPublisher · Issue #212 · ros-perception/image_common · GitHub - these are zero-copy capable but breaks the current idea of ROS where the community can reuse on message type for a lot of nodes.
from 2021 08 05 Eclipse iceoryx developer meetup · eclipse-iceoryx/iceoryx Wiki · GitHub
Feedback from community is welcomed!
status of usage of device drivers
to be added.
future work
the type adaptation and type negotiation in Humble ROS2 shall be applied in the repo.
