ROS 2 Humble Hawksbill将于2022年5月发布

Posted 2021-09-09 zhangrelay

ROS 2 Humble Hawksbill应该是第一款走向成熟的ROS2长期支持版本（LTS）。

ROS 2目前各模块功能还在不断完善和修订，ROS 2 Humble Hawksbill是ROS2的第八个发行版。

March 21, 2022	Alpha + RMW freeze
April 4, 2022	Freeze
April 18, 2022	Branch
April 25, 2022	Beta
May 16, 2022	Release Candidate
May 19, 2022	Distro Freeze
May 23, 2022	General Availability

Rolling Ridley

rclcpp

标准格式转换案例：

std_msgs::msg::String 与 std::string 转换。

template<>
struct rclcpp::TypeAdapter<
   std::string,
   std_msgs::msg::String
>
{
  using is_specialized = std::true_type;
  using custom_type = std::string;
  using ros_message_type = std_msgs::msg::String;

  static
  void
  convert_to_ros_message(
    const custom_type & source,
    ros_message_type & destination)
  {
    destination.data = source;
  }

  static
  void
  convert_to_custom(
    const ros_message_type & source,
    custom_type & destination)
  {
    destination = source.data;
  }
};

使用案例：

using MyAdaptedType = TypeAdapter<std::string, std_msgs::msg::String>;

// Publish a std::string
auto pub = node->create_publisher<MyAdaptedType>(...);
std::string custom_msg = "My std::string"
pub->publish(custom_msg);

// Pass a std::string to a subscription's callback
auto sub = node->create_subscription<MyAdaptedType>(
  "topic",
  10,
  [](const std::string & msg) {...});

在目前较新版本的ROS2（b83b18598b）仅pub或sub的实现方式cpp代码就有5种。以上面改进为例，pub代码如下（使用 `std::string` 代替 `std_msgs::msg::String`）：

#include <chrono>
#include <functional>
#include <memory>
#include <string>

#include "rclcpp/type_adapter.hpp"
#include "rclcpp/rclcpp.hpp"

#include "std_msgs/msg/string.hpp"

using namespace std::chrono_literals;

template<>
struct rclcpp::TypeAdapter<std::string, std_msgs::msg::String>
{
  using is_specialized = std::true_type;
  using custom_type = std::string;
  using ros_message_type = std_msgs::msg::String;

  static
  void
  convert_to_ros_message(
    const custom_type & source,
    ros_message_type & destination)
  {
    destination.data = source;
  }

  static
  void
  convert_to_custom(
    const ros_message_type & source,
    custom_type & destination)
  {
    destination = source.data;
  }
};

class MinimalPublisher : public rclcpp::Node
{
  using MyAdaptedType = rclcpp::TypeAdapter<std::string, std_msgs::msg::String>;

public:
  MinimalPublisher()
  : Node("minimal_publisher"), count_(0)
  {
    publisher_ = this->create_publisher<MyAdaptedType>("topic", 10);
    timer_ = this->create_wall_timer(
      500ms, std::bind(&MinimalPublisher::timer_callback, this));
  }

private:
  void timer_callback()
  {
    std::string message = "Hello, world! " + std::to_string(count_++);
    RCLCPP_INFO(this->get_logger(), "Publishing: '%s'", message.c_str());
    publisher_->publish(message);
  }
  rclcpp::TimerBase::SharedPtr timer_;
  rclcpp::Publisher<MyAdaptedType>::SharedPtr publisher_;
  size_t count_;
};

int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);
  rclcpp::spin(std::make_shared<MinimalPublisher>());
  rclcpp::shutdown();
  return 0;
}

sub代码如下：

#include <functional>
#include <memory>
#include <string>

#include "rclcpp/type_adapter.hpp"
#include "rclcpp/rclcpp.hpp"

#include "std_msgs/msg/string.hpp"

using std::placeholders::_1;


template<>
struct rclcpp::TypeAdapter<std::string, std_msgs::msg::String>
{
  using is_specialized = std::true_type;
  using custom_type = std::string;
  using ros_message_type = std_msgs::msg::String;

  static
  void
  convert_to_ros_message(
    const custom_type & source,
    ros_message_type & destination)
  {
    destination.data = source;
  }

  static
  void
  convert_to_custom(
    const ros_message_type & source,
    custom_type & destination)
  {
    destination = source.data;
  }
};

class MinimalSubscriber : public rclcpp::Node
{
  using MyAdaptedType = rclcpp::TypeAdapter<std::string, std_msgs::msg::String>;

public:
  MinimalSubscriber()
  : Node("minimal_subscriber")
  {
    subscription_ = this->create_subscription<MyAdaptedType>(
      "topic", 10, std::bind(&MinimalSubscriber::topic_callback, this, _1));
  }

private:
  void topic_callback(const std::string & msg) const
  {
    RCLCPP_INFO(this->get_logger(), "I heard: '%s'", msg.c_str());
  }
  rclcpp::Subscription<MyAdaptedType>::SharedPtr subscription_;
};

int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);
  rclcpp::spin(std::make_shared<MinimalSubscriber>());
  rclcpp::shutdown();
  return 0;
}

这样的细节变化非常多，在dashing到foxy中，更多的是功能完善，而非bug补丁，这从侧面体现了ROS2的版本离稳定成熟还需一段时间。

ros2cli

这是命令行接口，pub和sub其实都非常常用，但是

使用标志时，将在开始发布之前等待找到一个匹配的订阅。 这避免了 ros2cli 节点在发现匹配订阅之前开始发布的问题，这会导致一些第一条消息丢失。

ros2 topic pub -1 -w 1 /chatter std_msgs/msg/String "{data: 'foo'}"

更多细节查阅官方文档。

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