ros::spin() 和 ros::spinOnce()函数的区别及详解

#include "ros/ros.h"
#include "std_msgs/String.h"
#include <sstream>
int main(int argc, char **argv)
{
  ros::init(argc, argv, "talker");
  ros::NodeHandle n;
  ros::Publisher chatter_pub = n.advertise<std_msgs::String>("chatter", 1000);
  ros::Rate loop_rate(10);
  int count = 0;
  while (ros::ok())
  {
    std_msgs::String msg;
    std::stringstream ss;
    ss << "hello world " << count;
    msg.data = ss.str();
    ROS_INFO("%s", msg.data.c_str());
    /**
     * 向 Topic: chatter 发送消息, 发送频率为10Hz（1秒发10次）；消息池最大容量1000。
     */
    chatter_pub.publish(msg);
    loop_rate.sleep();
    ++count;
  }
  return 0;
}

#include "ros/ros.h"
#include "std_msgs/String.h"
void chatterCallback(const std_msgs::String::ConstPtr& msg)
{
  ROS_INFO("I heard: [%s]", msg->data.c_str());
}
int main(int argc, char **argv)
{
  ros::init(argc, argv, "listener");
  ros::NodeHandle n;
  ros::Subscriber sub = n.subscribe("chatter", 1000, chatterCallback);
  /**
   * ros::spin() 将会进入循环， 一直调用回调函数chatterCallback(),每次调用1000个数据。
   * 当用户输入Ctrl+C或者ROS主进程关闭时退出，
   */
  ros::spin();
  return 0;
}

/**接收端**/<br>#include "ros/ros.h"
#include "std_msgs/String.h"
void chatterCallback(const std_msgs::String::ConstPtr& msg)
{
  /*...TODO...*/ 
}
int main(int argc, char **argv)
{
  ros::init(argc, argv, "listener");
  ros::NodeHandle n;
  ros::Subscriber sub = n.subscribe("chatter", 2, chatterCallback);
  ros::Rate loop_rate(5);
  while (ros::ok())
  {
    /*...TODO...*/ 
    ros::spinOnce();
    loop_rate.sleep();
  }
  return 0;
}

/*...TODO...*/
ros::Rate loop_rate(100);
while (ros::ok())
{
  /*...TODO...*/
  user_handle_events_timeout(...);
  ros::spinOnce();         
  loop_rate.sleep();
}