### 10. 发布者 Publisher 的编程实现 主讲人：古月 ## 话题模型  话题模型（发布/订阅） ## • 创建功能包 $ cd ~/catkin_ws/src $ catkin_create_pkg learning_topic ros::init(argc, argv, "velocity_publisher"); // 创建节点句柄 ros::NodeHandle n; // 创建一个Publisher，发布名为/turtle1/cmd_vel的topic，消息类型为geometry_msgs::Twist，队列长度 ros::Publisher turtle_vel_pub = n.adve vel_msg.angular.z); // 按照循环频率延时 loop_rate.sleep(); } return 0; } velocity_publisher.cpp ## 如何实现一个发布者 • 初始化ROS节点； - 向ROS Master注册节点信息，包括发布的话题名和话题中的消息类型； • 创建消息数据； - 按照一定频率循环发布

interface{}) bool type Publisher struct { m sync.RWMutex buffer int timeout time.Duration subscribers map[subscriber]topicFunc // chan中是数据，函数判断数据是否包含 } func (p *Publisher) SubscribeTopic(topic (p *Publisher) Publish(v interface{}) { // 发布时，轮询所有注册上来的对象 for sub, topic := range p.subscribers { go p.sendTopic(sub, topic, v, wg) // 消息推送到订阅者的chan } func (p *Publisher) sendTopic(sub Warningf("stop server") grpcServer.GracefulStop() 1 type Service struct { 2 bus *pubsub.Publisher 3 proto.UnimplementedPubSubServiceServer 4 } 实现 protoBuf 定义 RPC 的接口 func (s *Service)

createNode('example'); const publisher = node.createPublisher( 'std_msg/msg/String', 'topic'); setInterval(() => { publisher.publish('Hello World'); 72746f79e1/p8_1.jpg) ## List of Features ## rclnodejs ROS node -- create/destroy ROS nodes Publisher/Subscription -- send/receive ROS message • Client/Service -- write client/service of ROS request Validation utilities -- check if it meets rules Logging -- easier debugging ## ros2-web-bridge Publisher/Subscription -- send/receive msg in browser • Client/Service -- write client/service of ROS request

ros::ServiceServer command_service = n.advertiseService("/turtle_command", commandCallback); // 创建一个Publisher，发布名为/turtle1/cmd_vel的topic，消息类型为geometry_msgs::Twist，队列长度：turtle_vel_pub = n.advertise #include #include ros::Publisher turtle_vel_pub; bool pubCommand = false; // service回调函数，输入参数 req，输出参数 res bool commandCallback command state!" ## - 创建服务器代码（Python） pubCommand = False; turtle_vel_pub = rospy.Publisher('/turtle1/cmd_vel', Twist, queue_size=10) def command_thread(): while True:

Author(models.Model): name = models.CharField(max_length=100) age = models.IntegerField() class Publisher(models.Model): name = models.CharField(max_length=300) class Book(models.Model): name rating = models.FloatField() authors = models.ManyToManyField(Author) publisher = models.ForeignKey(Publisher, on_delete=models.CASCADE) pubdate = models.DateField() class Store(models >>> Book.objects.count() 2452 # Total number of books with publisher=BaloneyPress >>> Book.objects.filter(publisher__name="BaloneyPress").count() 73 ``` ```python # Average

Author(models.Model): name = models.CharField(max_length=100) age = models.IntegerField() class Publisher(models.Model): name = models.CharField(max_length=300) class Book(models.Model): name rating = models.FloatField() authors = models.ManyToManyField(Author) publisher = models.ForeignKey(Publisher, on_delete=models.CASCADE) pubdate = models.DateField() class Store(models >>> Book.objects.count() 2452 # Total number of books with publisher=BaloneyPress >>> Book.objects.filter(publisher__name="BaloneyPress").count() 73 ``` ```python # Average

Author(models.Model): name = models.CharField(max_length=100) age = models.IntegerField() class Publisher(models.Model): name = models.CharField(max_length=300) class Book(models.Model): name rating = models.FloatField() authors = models.ManyToManyField(Author) publisher = models.ForeignKey(Publisher, on_delete=models.CASCADE) pubdate = models.DateField() class Store(models >>> Book.objects.count() 2452 # Total number of books with publisher=BaloneyPress >>> Book.objects.filter(publisher__name='BaloneyPress').count() 73 # Average price across all

Author(models.Model): name = models.CharField(max_length=100) age = models.IntegerField() class Publisher(models.Model): name = models.CharField(max_length=300) class Book(models.Model): name rating = models.FloatField() authors = models.ManyToManyField(Author) publisher = models.ForeignKey(Publisher, on_delete=models.CASCADE) pubdate = models.DateField() class Store(models >>> Book.objects.count() 2452 # Total number of books with publisher=BaloneyPress >>> Book.objects.filter(publisher__name='BaloneyPress').count() 73 # Average price across all

creating a publisher: numbers = [(2, 2), (4, 4), (8, 8), (16, 16)] results = [] publisher = add.get_publisher() try: for args in numbers: res = add.apply_async(args=args, publisher=publisher) results.append(res) finally: publisher.close() publisher.connection.close() print([res.get() for res in results]) Note: This particular example is better expressed as a task apply_async([10, 10], connect_timeout=3) Or if you handle the connection manually: publisher = add.get_publisher(connect_timeout=3) #### 2.3.6 Routing options Celery uses the AMQP routing mechanisms

ros::init(argc, argv, "person_publisher"); // 创建节点句柄 ros::NodeHandle n; } // 创建一个Publisher，发布名为/person_info的topic，消息类型为learning_topic::Person，队列长度10 ros::Publisher person_info_pub = n.advert 设置需要编译的代码和生成的可执行文件； add_executable(person_publisher src/person_publisher.cpp) target_link_libraries(person_publisher ${catkin_LIBRARYES}) add_dependencies(person_publisher ${PROJECT_NAME}_generate_messages_cpp) rosrun learning_topic person_subscriber $ rosrun learning_topic person_publisher ## - 创建发布者和订阅者代码（Python） ### person_publisher.py #!/usr/bin/env python # -*- coding: utf-8 -*- # 该例程将发布/person_info