ROS2零拷贝

REF

实际情况

工作站在使用ros2时计算量很大,不同节点之间存在大量的数据传输拷贝问题
下面的例子演示了如何在两个节点直接实施零拷贝通讯

Code_example

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#include <chrono>
#include <cinttypes>
#include <cstdio>
#include <memory>
#include <string>
#include <utility>

#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/int32.hpp"

using namespace std::chrono_literals;

// Node that produces messages.
struct Producer : public rclcpp::Node
{
  Producer(const std::string & name, const std::string & output)
  : Node(name, rclcpp::NodeOptions().use_intra_process_comms(true))
  {
    // Create a publisher on the output topic.
    pub_ = this->create_publisher<std_msgs::msg::Int32>(output, 10);
    std::weak_ptr<std::remove_pointer<decltype(pub_.get())>::type> captured_pub = pub_;
    // Create a timer which publishes on the output topic at ~1Hz.
    auto callback = [captured_pub]() -> void {
        auto pub_ptr = captured_pub.lock();
        if (!pub_ptr) {
          return;
        }
        static int32_t count = 0;
        std_msgs::msg::Int32::UniquePtr msg(new std_msgs::msg::Int32());
        msg->data = count++;
        printf(
          "Published message with value: %d, and address: 0x%" PRIXPTR "\n", msg->data,
          reinterpret_cast<std::uintptr_t>(msg.get()));
        pub_ptr->publish(std::move(msg));
      };
    timer_ = this->create_wall_timer(1s, callback);
  }

  rclcpp::Publisher<std_msgs::msg::Int32>::SharedPtr pub_;
  rclcpp::TimerBase::SharedPtr timer_;
};

// Node that consumes messages.
struct Consumer : public rclcpp::Node
{
  Consumer(const std::string & name, const std::string & input)
  : Node(name, rclcpp::NodeOptions().use_intra_process_comms(true))
  {
    // Create a subscription on the input topic which prints on receipt of new messages.
    sub_ = this->create_subscription<std_msgs::msg::Int32>(
      input,
      10,
      [](std_msgs::msg::Int32::UniquePtr msg) {
        printf(
          " Received message with value: %d, and address: 0x%" PRIXPTR "\n", msg->data,
          reinterpret_cast<std::uintptr_t>(msg.get()));
      });
  }

  rclcpp::Subscription<std_msgs::msg::Int32>::SharedPtr sub_;
};

int main(int argc, char * argv[])
{
  setvbuf(stdout, NULL, _IONBF, BUFSIZ);
  rclcpp::init(argc, argv);
  rclcpp::executors::SingleThreadedExecutor executor;

  auto producer = std::make_shared<Producer>("producer", "number");
  auto consumer = std::make_shared<Consumer>("consumer", "number");

  executor.add_node(producer);
  executor.add_node(consumer);
  executor.spin();

  rclcpp::shutdown();

  return 0;
}

例子中节点的建立有几点需要注意：

  1. 使能intra_process

    Node(name, rclcpp::NodeOptions().use_intra_process_comms(true))

配置节点时要开启intra_process。
2. 发布消息时使用UniquePtr和std::move(msg)
除了上面例子中的写法，还可以采用下面的写法：

auto dis = std::make_unique<std_msgs::msg::Float32>();dis->data = 10.0;pub_->publish(std::move(dis));

  1. 将需通信的节点加入到同一个进程中

    rclcpp::executors::SingleThreadedExecutor executor; auto producer = std::make_shared<Producer>(“producer”, “number”); auto consumer = std::make_shared<Consumer>(“consumer”, “number”); executor.add_node(producer); executor.add_node(consumer);

    1
    Published message with value: 0, and address: 0x5625E3159130 Received message with value: 0, and address: 0x5625E3159130Published message with value: 1, and address: 0x5625E3159130 Received message with value: 1, and address: 0x5625E3159130Published message with value: 2, and address: 0x5625E3159130 Received message with value: 2, and address: 0x5625E3159130Published message with value: 3, and address: 0x5625E3159130 Received message with value: 3, and address: 0x5625E3159130Published message with value: 4, and address: 0x5625E3159130 Received message with value: 4, and address: 0x5625E3159130Published message with value: 5, and address: 0x5625E3159130 Received message with value: 5, and address: 0x5625E3159130Published message with value: 6, and address: 0x5625E3159130 Received message with value: 6, and address: 0x5625E3159130Published message with value: 7, and address: 0x5625E3159130 Received message with value: 7, and address: 0x5625E3159130Published message with value: 8, and address: 0x5625E3159130 Received message with value: 8, and address: 0x5625E3159130Published message with value: 9, and address: 0x5625E3159130 Received message with value: 9, and address: 0x5625E3159130
    可以发现，发送端数据的地址和接收端数据地址是一致的。所以发送端只是把数据存放的地址发送给了接收端并没有发生数据拷贝