ros之callback函式
callback() 和spin()函式
#include <ros/ros.h> #include <iostream> void callback() { std::cout << "enter callback function!" << std::endl; } int main(int argc, char** argv) { ros::init(argc, argv, "test_node"); ros::NodeHandle nh; ros::NodeHandle nh_pri("~"); ros::Subscriber sub = nh.subscribe(topic, 10, callback); ros::spin(); return 0; }
下面是ros wiki的解釋。
- Initialize the ROS system
- Subscribe to the chatter topic
- Spin, waiting for messages to arrive
4.When a message arrives, the chatterCallback() function is called
意思大概是,subscribe一個topic之後,並不會直接進入callback函式, 而是往下執行,直到遇見了ros::spin()。這也就是說, ros::spin()後面的內容不會執行,除非ros::ok() return false(使用者按下ctrl+c,或者呼叫了ros::shutdown()函式)。還有就是,如果程式中沒有ros::spin(), 那麼就永遠不會進入callback函數了。
ros::spin() will exit once ros::ok() returns false, which means ros::shutdown() has been called, either by the default Ctrl-C handler, the master telling us to shutdown, or it being called manually.
- 關於變數的作用域問題
#include <ros/ros.h> #include <iostream> void callback1() { std::cout << "enter callback1 function!" << std::endl; } void callback2() { std::cout << "enter callback2 function!" << std::endl; } int main(int argc, char** argv) { ros::init(argc, argv, "test_node"); ros::NodeHandle nh; ros::NodeHandle nh_pri("~"); ros::Subscriber sub1 = nh.subscribe(topic1, 10, callback1); if(1) { ros::Subscriber sub2 = nh.subscribe(topic2, 10, callback2); } ros::spin(); return 0; }
問題:執行程式後可以直到, 並沒有進入callback2函式,並且檢視rosnode info,發現並沒有subscribe topic2。
解答:sub2是區域性變數,也就是說作用域只能在if語句裡面, 出了if語句該區域性變數就會登出掉,因此執行程式不會subscribe topic2。解決方法就是在if語句外面定義,在if語句裡面宣告。
#include <ros/ros.h>
#include <iostream>
void callback1()
{
std::cout << "enter callback1 function!" << std::endl;
}
void callback2()
{
std::cout << "enter callback2 function!" << std::endl;
}
int main(int argc, char** argv)
{
ros::init(argc, argv, "test_node");
ros::NodeHandle nh;
ros::NodeHandle nh_pri("~");
ros::Subscriber sub1 = nh.subscribe(topic1, 10, callback1);
ros::Subscriber sub2;
if(1)
{
sub2 = nh.subscribe(topic2, 10, callback2);
}
ros::spin();
return 0;
}
謹記謹記!
單執行緒callback模式
簡介
方法一:
ros::init(argc, argv, "my_node");
ros::NodeHandle nh;
ros::Subscriber sub = nh.subscribe(...);
...
ros::spin();
方法二:
ros::Rate r(10); // 10 hz
while (should_continue)
{
... do some work, publish some messages, etc. ...
ros::spinOnce();
r.sleep();
}
示例
點雲callback
#include <ros/ros.h>
#include <sensor_msgs/PointCloud2.h>
#include <pcl/point_cloud.h>
#include <pcl/point_types.h>
#include <pcl_conversions/pcl_conversions.h>
#include <pcl/filters/filter.h>
ros::Publisher g_cloud_pub;
int g_frame_num = 0;
void callback(const sensor_msgs::PointCloud2ConstPtr input_msg)
{
std::cout << "enter into callback fuction!" << std::endl;
pcl::PointCloud<pcl::PointXYZI>::Ptr input_cloud(new pcl::PointCloud<pcl::PointXYZI>);
pcl::fromROSMsg(*input_msg, *input_cloud);
pcl::PointCloud<pcl::PointXYZI>::Ptr output_cloud(new pcl::PointCloud<pcl::PointXYZI>);
std::vector<int> indice;
pcl::removeNaNFromPointCloud(*input_cloud, *output_cloud, indice);
sensor_msgs::PointCloud2 output_msg;
pcl::toROSMsg(*output_cloud, output_msg);
output_msg.header = input_msg->header;
g_cloud_pub.publish(output_msg);
}
int main(int argc, char** argv)
{
ros::init(argc, argv, "callback");
ros::NodeHandle nh;
ros::NodeHandle priv_nh("~");
std::string cloud_topic;
priv_nh.param<std::string>("cloud_topic", cloud_topic, "input_points");
ros::Subscriber cloud_sub = nh.subscribe(cloud_topic, 10, callback);
g_cloud_pub = nh.advertise<sensor_msgs::PointCloud2>("/output_points", 10);
ros::spin();
return 0;
}
多執行緒callback模式
簡介
方法一:ros::MultiThreadedSpinner
ros::MultiThreadedSpinner spinner(4); // Use 4 threads
spinner.spin(); // spin() will not return until the node has been shutdown
MultiThreadedSpinner
is a blocking spinner, similar toros::spin()
. You can specify a number of threads in its constructor, but if unspecified (or set to 0), it will use a thread for each CPU core.
方法二: ros::AsyncSpinner
(since 0.10)
ros::AsyncSpinner spinner(4); // Use 4 threads
spinner.start();
ros::waitForShutdown();
A more useful threaded spinner is the
AsyncSpinner
. Instead of a blockingspin()
call, it hasstart()
andstop()
calls, and will automatically stop when it is destroyed. An equivalent use ofAsyncSpinner
to theMultiThreadedSpinner
示例
影象點雲多執行緒
#include <ros/ros.h>
#include <sensor_msgs/PointCloud2.h>
#include <sensor_msgs/CompressedImage.h>
#include <message_filters/subscriber.h>
#include <message_filters/synchronizer.h>
#include <message_filters/sync_policies/approximate_time.h>
#include <pcl/point_cloud.h>
#include <pcl/point_types.h>
#include <iostream>
#include <string>
void cloudCallback(const sensor_msgs::PointCloud2ConstPtr input_msg)
{
std::cout << "Enter into cloud callback function!" << std::endl;
}
void image0Callback(const sensor_msgs::CompressedImageConstPtr &input_msg)
{
std::cout << "Enter into image0 callback function!" << std::endl;
}
void image1Callback(const sensor_msgs::CompressedImageConstPtr &input_msg)
{
std::cout << "Enter into image1 callback function!" << std::endl;
}
void image2Callback(const sensor_msgs::CompressedImageConstPtr &input_msg)
{
std::cout << "Enter into image2 callback function!" << std::endl;
}
void image3Callback(const sensor_msgs::CompressedImageConstPtr &input_msg)
{
std::cout << "Enter into image3 callback function!" << std::endl;
}
void image4Callback(const sensor_msgs::CompressedImageConstPtr &input_msg)
{
std::cout << "Enter into image4 callback function!" << std::endl;
}
int main(int argc, char** argv)
{
ros::init(argc, argv, "multi callback");
ros::NodeHandle nh;
ros::NodeHandle priv_nh("~");
std::string cloud_topic;
priv_nh.param<std::string>("cloud_topic", cloud_topic, " ");
int camera_num = 0;
priv_nh.param<int>("camera_num", camera_num, 1);
std::vector<std::string> camera_topic_v(camera_num);
for (size_t i = 0; i < camera_num; ++i)
{
std::string camera_topic = "camera"+ std::to_string(i) + "_topic";
priv_nh.param<std::string>(camera_topic, camera_topic_v[i], "/image_color/compressed");
}
ros::Subscriber cloud_sub = nh.subscribe(cloud_topic, 10, cloudCallback);
ros::Subscriber image0_sub = nh.subscribe(camera_topic_v[0], 10, image0Callback);
ros::Subscriber image1_sub = nh.subscribe(camera_topic_v[1], 10, image1Callback);
ros::Subscriber image2_sub = nh.subscribe(camera_topic_v[2], 10, image2Callback);
ros::Subscriber image3_sub = nh.subscribe(camera_topic_v[3], 10, image3Callback);
ros::Subscriber image4_sub = nh.subscribe(camera_topic_v[4], 10, image4Callback);
ros::MultiThreadedSpinner spinner(camera_num + 1);
spinner.spin();
return 0;
}
注:本程式通過設計一個死迴圈來判斷是不是呼叫了多執行緒, 對於單執行緒來說會堵塞,但是對於多執行緒來說只有一個執行緒堵塞。