ROS2 Galactic中使用Message Filters时回调函数未触发求助

问题描述 #

代码编译正常，但运行时topic_callback从未被调用。已确认两个话题的QoS匹配，运行环境为Ubuntu 20.04 + ROS2 Galactic。

问题代码 #

#include "rclcpp/rclcpp.hpp"
#include "sensor_msgs/msg/image.hpp"
#include "sensor_msgs/msg/point_cloud2.hpp"
#include <message_filters/subscriber.h>
#include <message_filters/time_synchronizer.h>
#include <message_filters/sync_policies/approximate_time.h>

//using std::placeholders::_1;

class MinimalSubscriber : public rclcpp::Node
{
public:

message_filters::Subscriber<sensor_msgs::msg::Image> image_sub_;
message_filters::Subscriber<sensor_msgs::msg::PointCloud2> cloud_sub_;

MinimalSubscriber()
: Node("minimal_subscriber_left")
{
  
  image_sub_.subscribe(this, "/left/image_raw");
  cloud_sub_.subscribe(this, "/model/prius_hybrid/laserscan/points");
  
  typedef message_filters::sync_policies::ApproximateTime<sensor_msgs::msg::Image, sensor_msgs::msg::PointCloud2> approximate_policy;
  message_filters::Synchronizer<approximate_policy> syncApproximate(approximate_policy(10), image_sub_, cloud_sub_);
  syncApproximate.registerCallback(&MinimalSubscriber::topic_callback, this); 
  
};

public:
    void topic_callback(const sensor_msgs::msg::Image::SharedPtr image, const 
    sensor_msgs::msg::PointCloud2::SharedPtr cloud2)
    { 
      std::cout<<"Hello messages are being received";
      RCLCPP_INFO(this->get_logger(), "Publishing");    
    }; 
};

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

问题原因及解决方案 #

核心问题 #

Synchronizer对象是构造函数中的局部变量，构造函数执行完毕后会被立即销毁，导致无法持续监听话题消息、匹配时间戳并触发回调。

修复步骤 #

1. 将Synchronizer声明为类的成员变量，确保其生命周期与节点一致。
2. 使用智能指针管理Synchronizer对象，避免手动内存管理问题。
3. 用std::bind正确绑定回调函数与类实例，确保回调能被正确触发。

修复后的代码 #

#include "rclcpp/rclcpp.hpp"
#include "sensor_msgs/msg/image.hpp"
#include "sensor_msgs/msg/point_cloud2.hpp"
#include <message_filters/subscriber.h>
#include <message_filters/time_synchronizer.h>
#include <message_filters/sync_policies/approximate_time.h>
#include <functional>

class MinimalSubscriber : public rclcpp::Node
{
public:
    message_filters::Subscriber<sensor_msgs::msg::Image> image_sub_;
    message_filters::Subscriber<sensor_msgs::msg::PointCloud2> cloud_sub_;
    
    // 声明同步器为类成员智能指针
    typedef message_filters::sync_policies::ApproximateTime<sensor_msgs::msg::Image, sensor_msgs::msg::PointCloud2> approximate_policy;
    std::shared_ptr<message_filters::Synchronizer<approximate_policy>> sync_approximate_;

    MinimalSubscriber()
    : Node("minimal_subscriber_left")
    {
        image_sub_.subscribe(this, "/left/image_raw");
        cloud_sub_.subscribe(this, "/model/prius_hybrid/laserscan/points");
        
        // 初始化同步器并绑定回调
        sync_approximate_ = std::make_shared<message_filters::Synchronizer<approximate_policy>>(
            approximate_policy(10), image_sub_, cloud_sub_);
        sync_approximate_->registerCallback(
            std::bind(&MinimalSubscriber::topic_callback, this, std::placeholders::_1, std::placeholders::_2)
        ); 
    };

    void topic_callback(const sensor_msgs::msg::Image::SharedPtr image, const 
    sensor_msgs::msg::PointCloud2::SharedPtr cloud2)
    { 
        std::cout<<"Hello messages are being received"<<std::endl;
        RCLCPP_INFO(this->get_logger(), "Received synchronized messages");    
    }; 
};

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

额外调试建议 #

• 运行前用ros2 topic echo确认两个话题确实有消息发布。
• 检查话题名称是否完全匹配，避免拼写错误。
• 若仍有问题，可尝试降低ApproximateTime策略的队列大小，或调整时间匹配阈值。

内容的提问来源于stack exchange，提问作者Marcelo Mafalda