These files are used to generate C++ code and data structures which are used for publishing and when receiving from a subscription. Don't be shy! Specifically, this exercise calls the Descartes motion planner as seen in Exercise 4.1. Keep building! lambda(.cpp23lambda)bind, serviceclientclnt_test, Register as a new user and use Qiita more conveniently. #include "my_clnt_with_lambda.hpp", WHI7Value Qiita Advent Calendar 2022, ROS2 publisher/subscriber: -class style-, ROS2service/client with request header: -class style-, #include "my_messages/srv/calc_two_floats.msg", 32Timer1servicecallback_timer_, 20ROSasync_send_requestservice(request)servicecallback(callback_response_), callback_response_rclcpp::Client<>::SharedFuture(future), callbackSharedFuture, You can efficiently read back useful information. The main function accomplishes the following, line by line: Creates a node named add_two_ints_server: Creates a service named add_two_ints for that node and automatically advertises it over the networks with the &add method: Spins the node, making the service available. Fork 300. The add function adds two integers from the request and gives the sum to the response, while notifying the console of its status using logs. ros2 run cpp_srvcli server Open a new terminal, and run the client node. The ros::ServiceClient object is used to call the service later on. Messages are defined using the ROS IDL within .msg files. Just go one line at a time and read the comments to understand what each line does. Before publishing, a message must be created and filled with information. If the node object goes out of scope or is explicitly shutdown then any objects created using the node are also invalid. It's time to use the ros2 service call command to call the service. Also follow my LinkedIn page where I post cool robotics-related content. The following is an example of a service_client node, taken from here: https://github.com/ros2/examples/tree/foxy/rclcpp/services/minimal_client. Your email address will not be published. Uusimaa (Finnish: [usim]; Swedish: Nyland, Finland Swedish: [nylnd]; both lit. This program will be built from single file named hello_world_node.cpp with the following contents: Create a Basic Publisher and Subscriber (Python) | ROS2 Foxy, How to Create a Service and Client (Python) | ROS2 Foxy, ROS 2 Foxy Fitzroy installed on Ubuntu Linux 20.04, How to Install Ubuntu and VirtualBox on a Windows PC, How to Display the Path to a ROS 2 Package, How To Display Launch Arguments for a Launch File in ROS2, Getting Started With OpenCV in ROS 2 Galactic (Python), Connect Your Built-in Webcam to Ubuntu 20.04 on a VirtualBox. The while loop gives the client 1 second to search for service nodes in the network. My goal is to meet everyone in the world who loves robotics. Open a new terminal, and run the client node. Calling the service was still not possible using a minmal service client, nor ros2 service call. Step 1: Create the service (.srv) file, namely ServiceName.srv, inside an srv folder. Exiting. #include "my_clnt.hpp", #include #include Toggle line numbers 16 beginner_tutorials::AddTwoInts srv; 17 srv.request.a = atoll(argv[1]); 18 srv.request.b = atoll(argv[2]); Here we instantiate an autogenerated service class, and assign values into its request member. This is a bit complex, because we are turning the asynchronous ROS2 service call into a synchronous blocking call. It consists of these main components: Node rclcpp::Node rclcpp/node.hpp Publisher rclcpp::Node::create_publisher () rclcpp::Publisher rclcpp::Publisher::publish () rclcpp/publisher.hpp Subscription rclcpp::Node::create_subscription () Following the ROS2 tutorials: Writing A Simple Cpp Publisher And Subscriber Writing A Simple Cpp Service And Client You will see that using std::bind is the intended way of giving the create_service or create_subscription call a function to run. serviceclient service/client request headerROS2 ROS2service/client with request header: -class style- "request header" :service :my_messages :srv That's it. ros::ServiceClient also has a number of other useful methods suchs as exists () and waitForExistence (). where turtlesim is the package containing the service type. Make sure you are in the root of your workspace: cd ~/dev_ws/. One of the middleware communication primitives provided by rclcpp is the publish-subscribe pattern using topics. Pull requests 51. Therefore nodes are scoped and must be kept around to keep the node valid. #include "my_messages/srv/calc_two_floats.hpp", #include Writing a simple service and client (C++) Goal: Create and run service and client nodes using C++. Install and run your ROS2 Cpp node If you don't already have a ROS2 Cpp package, create one and create a Cpp file in its src/ directory. Creating an rclcpp::Publisher is done using the node and by providing a topic name, topic type, and, at a minimum, the publishing queue depth. Some things that are implemented are not documented here and other things documented here are the desired state but are not implemented in the actual code yet. Inside the ros2_ws/src/cpp_srvcli/src directory, create a new file called add_two_ints_server.cpp and paste the following code within: The first two #include statements are your package dependencies. Introduction to Programming with ROS2-Services | by Daniel Jeswin | Medium 500 Apologies, but something went wrong on our end. method chaining: Generated Messages also have some common smart pointer definitions built in, for example: link to exhaustive list of aliases provided. Although only covering three percent (9,440 km 2) of our national land area, our Region is home to around 1.7 million inhabitants, which is about a third of the country's total population. Step 2 Creating action service-client package for generating a Fibonacci series Actions have the exact same concept in ROS2 as ROS1, except they are a part of ROS2 core library. In this pattern Messages, that are defined by the user in an interface description file, are passed between Publishers and Subscribers which are on the same Topic. Nodes can have publishers and subscribers on topics, provide or call services, have parameters, and many other things. Id love to hear from you! Go back to the service node terminal. Recall that packages should be created in the src directory, not the root of the workspace. It also destroys any global resources created when the initialization function was originally called. ros2 / rclcpp Public. I just want to confirm my understanding of the changes you want. @wjwwood Thanks very much for the feedback. Your email address will not be published. Goal: Create and run service and client nodes using C++. Edit vision_node.cpp; remember that the ros documentation is a resource. The request is input from the client side and contains a value. link to complete API docs for Publishers. There are several ways you could write a service and client in C++; check out the minimal_service and minimal_client packages in the ros2/examples repo. Save my name, email, and website in this browser for the next time I comment. #include "my_messages/srv/calc_two_floats.hpp", "Client interrupted while waiting for service", #include You will note that we added the dependencies command after the package creation command. service_type: The type message received by of the service. Creating a node is done by calling the constructor of the rclcpp::Node class and providing a name for the node (after calling rclcpp::init()): It is recommended that nodes be created within a smart pointer for automatic object lifetime management, e.g. You're reading the documentation for a version of ROS 2 that has reached its EOL (end-of-life), and is no longer officially supported. The service node then sends a reply to the client node. 'new land') is a region of Finland.It borders the regions of Southwest Finland, Tavastia Proper (Kanta-Hme), Pijnne Tavastia (Pijt-Hme), and Kymenlaakso.Finland's capital and largest city, Helsinki, along with the surrounding Greater Helsinki area, are both contained in the region, and . values: The actual message sent to the service. At the end of the command, put the two integers you would like to add. Required fields are marked *. Apache License 2.0). Start the client node, followed by any two integers separated by a space: If you chose 2 and 3, for example, the client would receive a response like this: Return to the terminal where your service node is running. All it does is prepare to announce itself as a ros2 node called hello_world_node, then broadcast a Hello-world message over the standard /rosout topic, and then wait for a SIGINT or ctrl-c.. Add the following code block to CMakeLists.txt to create an executable named server: So ros2 run can find the executable, add the following lines to the end of the file, right before ament_package(): You could build your package now, source the local setup files, and run it, but lets create the client node first so you can see the full system at work. Open a new terminal, navigate to ros2_ws, and source the setup files: The terminal should return the following message, and then wait: Open another terminal, source the setup files from inside ros2_ws again. Navigate into the ros2_ws directory created in a previous tutorial. Dont be intimidated. I like to use gedit. define a ROS Service Client as a private member variable of the class. Help us understand the problem. Setup your ROS2 Cpp and Python package Create a standard Cpp package Add a Cpp node + header Add a Python node + module to import ROS2 Package architecture with both Python and Cpp nodes - final Configure your ROS2 package for both Cpp and Python package.xml CMakeLists.txt Compile and run your ROS2 Cpp and Python nodes Going further Note that if you intend to call rclcpp::init() multiple times, be sure to use the do_not_prune_arguments initialization option, as is done above, in order to preserve the original arguments for future invocations. For example, a C++ header file is generated for each message: And that header would contain a C++ data structure with a similar namespace: In addition to defining custom Messages, there are many predefined Messages that are defined in the common Message packages that come with ROS, for example: There are many others, but throughout this document some of the standard messages will be used. If the client is canceled (e.g. This command takes three arguments: service_name: The name of the service. Because you used the --dependencies option during package creation, you dont have to manually add dependencies to package.xml or CMakeLists.txt. Tutorial level: Beginner Time: 20 minutes Contents Background Prerequisites Tasks 1 Create a package 2 Write the service node 3 Write the client node 4 Build and run Summary Next steps Related content Background Next, youll learn how to create custom interfaces. The official tutorial is located in the ROS 2 Foxy documentation, but well run through the entire process step-by-step below. Write the following code. Step 2: Modify CMakeLists.txt. Add the following lines above the # find dependencies block: Right before the ament_package() line, add the following lines. The Code Explained. document.getElementById( "ak_js" ).setAttribute( "value", ( new Date() ).getTime() ); #include "example_interfaces/srv/add_two_ints.hpp", "client interrupted while waiting for service to appear.". The first step is writing the simplest C++ program that can interact with ros2 in a meaningful way. 1.2.3. Actions. 1 [ROS2] service failure feedback to client ros2 foxy design asked May 5 '21 LanceChen 11 1 1 3 In ROS1, a service client would receive a false value when it either failed to call the service server, or there was some error such as invalid input. At the end of the command, put the two integers you would like to add. example_interfaces is the package that includes the .srv file you will need to structure your requests and responses: The first two lines are the parameters of the request, and below the dashes is the response. Before using rclcpp it must be initialized exactly once per process. Fill in the description of the cpp_srvcli package, your email address and name on the maintainer line, and the license you desire (e.g. Just a few notes on mechanical engineering and robotics. Add processing to this and assign it to response and return it. Navigate into ros2_ws/src and create a new package: Your terminal will return a message verifying the creation of your package cpp_srvcli and all its necessary files and folders. Add section about namespaces within nodes, e.g. 322. The topic type is conveyed as a template argument to the rclcpp::Node::advertise method, for example: An rclcpp::Publisher can also be created by passing one of the built-in QoS policies: Or with a programmatically created QoS profile based on an existing one: Consider moving alternative signatures to a separate section and link to it. Create a new C++ file named add_two_ints_client.cpp. If you want up-to-date information, please have a look at Humble . What are the problem? . #include "my_srv.hpp", #include Inside the ros2_ws/src/cpp_srvcli/src directory, create a new file called add_two_ints_client.cpp and paste the following code within: Similar to the service node, the following lines of code create the node and then create the client for that node: Next, the request is created. http://wiki.ros.org/roscpp/Overview/NodeHandles#Namespaces. You could use the Message with a custom allocator by using the template version of the Message structure that ends with a _: In rclcpp publishing is achieved by creating an rclcpp::Publisher object and calling rclcpp::Publisher::publish with a Message as the first parameter. In this tutorial, we will learn how to create a service and a client in ROS 2 Foxy Fitzroy using C++. This service node adds two integers together. Refresh the page, check Medium 's site status, or find something. In the last few tutorials youve been utilizing interfaces to pass data across topics and services. You added their dependencies and executables to the package configuration files so that you could build and run them, and see a service/client system at work. However, it can be created on the stack as well: Since the rclcpp::Node class operates on an RAII-style pattern, the node is initialized and exposed to the ROS graph on construction and is shutdown and removed from the graph on destruction. ROS2: -class style-, :ROS2 publisher/subscriber: -class style- Add the following: 1 2 3 4 5 6 7 8 find_package(builtin_interfaces REQUIRED) find_package(rosidl_default_generators REQUIRED) # and put below before ament_package (): Open a new terminal and source your ROS 2 installation so that ros2 commands will work. When the service is created in main, then the service is both discoverable and callable. Background . Here is what I see: When youre done, press CTRL + C in all terminal windows to shut everything down. The structure of the request and response is determined by a .srv file. A client node sends a request for data to the service node. Make sure you are in the root of your workspace: Open a new terminal, and run the client node. Doing this automatically adds the dependencies to your package.xml and CMakeLists.txt files. For example, the nav_msgs/msg/Path.msg Message has a list of time stamped poses which are stored in a std::vector. ROS 2 introduces the concept of managed nodes, also called LifecycleNode s. In the following tutorial, we explain the purpose of these nodes, what makes them different from regular nodes and how they comply to a lifecycle management. A C# .NET library for ROS2, including C# implementation of rcl APIs, message generation, tests and examples. In order to complete this tutorial, you will need: Open a new terminal window, and navigate to the src directory of your workspace: Now lets create a package named cpp_srvcli. Managed nodes contain a state machine with a set of predefined states. With a persistent connection, a client stays connected to a service. At the end of the command, put the two integers you would like to add. In the case of the callback function from line 6 to the callback function.service, there are two arguments to the callback function, and the request and response variables are assigned. Persistent Connections ROS also allows for persistent connections to services. To run the nodes, open a new terminal window. In this exercise, the ROS1 ARMarker message, which is the goal destination for the robot, must be communicated to the ROS2 application. Then the client sends its request, and the node spins until it receives its response, or fails. The ros::ServiceClient object is used to call the service later on. Initialization can be done again, after a call to rclcpp::shutdown() has been completed successfully: The shutdown function causes all nodes and their constituent parts to become invalid and shutdown. Generated Messages are also template-able based on an Allocator. lambda(src/my_clnt_with_lambda.cpp2022) If a node with a colliding name is created, then the conflicting node already running will be shutdown. See docs.ros.org for information on supported releases. We will create a client node that requests the sum of two integers. rclcpp provides the standard C++ API for interacting with ROS 2. A unique name will be created and returned if this is empty --- string name ros2 . Step 4: Write your service_server node in the src folder inside the package. After removing some unnecessary boilerplate from the automatically generated file, your CMakeLists.txt should look like this: Its good practice to run rosdep in the root of your workspace (ros2_ws) to check for missing dependencies before building: rosdep only runs on Linux, so you can skip ahead to next step. As always, though, make sure to add the description, maintainer email and name, and license information to package.xml. Run the service node. 15 ros::ServiceClient client = n.serviceClient<beginner_tutorials::AddTwoInts> ("add_two_ints"); 16. This document is for a very old and outdated version of ROS 2. $ cd ~/ros2_ws/src/ $ ros2 pkg create my_robot_tutorials --build-type ament_cmake $ cd my_robot_tutorials/src/ $ touch my_cpp_node.cpp Write the previous code into "my_cpp_node.cpp". Toggle line numbers. a shared pointer or a unique pointer, as demonstrated above for the former with the make_shared alias:: Connect with me onLinkedIn if you found my information useful to you. #include "my_clnt.hpp" Follow instructions there instead if you are intending to use ros2cs with Unity3D. More than 1 year has passed since last update. The following is an example of a service_server node, taken from here: https://github.com/ros2/examples/tree/foxy/rclcpp/services/minimal_service, Step 5: Write your service_client node in the src folder inside the package. Writing an action server and client (C++) ROS 2 Documentation: Dashing documentation You're reading the documentation for a version of ROS 2 that has reached its EOL (end-of-life), and is no longer officially supported. requestresponseresponse or return, std::bindusing namespace std::placeholdersstd::bind_1std::placeholders::_1, clientserviceTimer(client)callbackcallback_timer_(), ROSspinspin_until_future_completenodespin(mainnodemy_clnt_main.cpp6)spin_until_future_complete spinservice(future)callbackasync_send_request, servicecallbackserviceservicefuturefutureasync_send_requestfutureservicecallbackfuturecallbackfuturerclcpp::Client<>::SharedFuture, callback_response_lambda Is it something about creating the service in the constructor that I am doing incorrectly? ros2 service find <type_name> ros2 service find std_srvs/srv/Empty /clear /reset ros2 interface show <type_name>.srv ros2 interface show std_srvs/srv/Empty.srv --- ros2 interface show turtlesim/srv/Spawn float32 x float32 y float32 theta string name # Optional. #include "my_messages/srv/calc_two_floats.hpp", #include Creating C++ Service in ROS2 July 8, 2021 by Abdur Rosyid Step 1: Create the service (.srv) file, namely ServiceName.srv, inside an "srv" folder. ROS2 :srv The example used here is a simple integer addition system; one node requests the sum of two integers, and the other responds with the result. ", "service not available, waiting again", find_package(example_interfaces REQUIRED), add_executable(client src/add_two_ints_client.cpp), rosdep install -i --from-path src --rosdistro galactic -y, colcon build --packages-select cpp_srvcli, [INFO] [rclcpp]: sending back response: [5], ROS 2 Iron Irwini (codename iron; May, 2023), Writing a simple publisher and subscriber (C++), Writing a simple publisher and subscriber (Python), Writing a simple service and client (C++), Writing a simple service and client (Python), Writing an action server and client (C++), Writing an action server and client (Python), Composing multiple nodes in a single process, Integrating launch files into ROS 2 packages, Running Tests in ROS 2 from the Command Line, Building a visual robot model from scratch, Using Fast DDS Discovery Server as discovery protocol [community-contributed], Unlocking the potential of Fast DDS middleware [community-contributed], Setting up a robot simulation (Ignition Gazebo), Using quality-of-service settings for lossy networks, Setting up efficient intra-process communication, Deploying on IBM Cloud Kubernetes [community-contributed], Building a real-time Linux kernel [community-contributed], Migrating launch files from ROS 1 to ROS 2, Using Python, XML, and YAML for ROS 2 Launch Files, Using ROS 2 launch to launch composable nodes, Migrating YAML parameter files from ROS 1 to ROS 2, Passing ROS arguments to nodes via the command-line, Synchronous vs. asynchronous service clients, Working with multiple ROS 2 middleware implementations, Running ROS 2 nodes in Docker [community-contributed], Visualizing ROS 2 data with Foxglove Studio, Building ROS 2 with tracing instrumentation, On the mixing of ament and catkin (catment), ROS 2 Technical Steering Committee Charter. The command line arguments can be mutated by this function, as it will remove any client library specific arguments so that later argument parsing does not have to deal with client library specific arguments. ROS 2 Service Server. You will see that it published log messages when it received the request and the data it received, and the response it sent back: Enter Ctrl+C in the server terminal to stop the node from spinning. Type this command (this is a single command): Your package named cpp_srvcli has now been created. The message values need are sent in YAML format. Create a new C++ file named add_two_ints_server.cpp. The RAII-style pattern is also used with the rclcpp::Publisher, so once created it has been advertised to the ROS graph and other nodes are aware of it. Generated Messages provide attribute access to the Fields so they can be accessed directly for setting and getting: The fields can also be accessed using methods and the named parameter idiom, a.k.a. ros2 pkg create --build-type ament_cmake cpp_srvcli --dependencies rclcpp example_interfaces, "example_interfaces/srv/add_two_ints.hpp", add_executable(server src/add_two_ints_server.cpp), "Interrupted while waiting for the service. The ROS 2 core software stack breaks down into a few discrete but related parts: This document is under construction. Code. This client object will allow us to connect to the vision node's Service Server. Messages are namespaced by the package in which they are defined and are converted into C++ code in a conventional way. by you entering Ctrl+C into the terminal), it will return an error log message stating it was interrupted. Make sure you have a text editor installed. bool callback (MReq& request, MRes& response); Usage #include "rclcpp/rclcpp.hpp" allows use of the most common elements of the ROS 2 system. :CalcTwoFloats.msg, create_servicecallbackmainspinnode, privatehandleService_callbackservicecallback, request, response When nodes communicate using services, the node that sends a request for data is called the client node, and the one that responds to the request is the service node.The structure of the request and response is determined by a .srv file.. Notifications. ros2 run cpp_srvcli client 5 3 Go back to the service node terminal. The main entry point to the rclcpp API is the rclcpp::Node class. To run the nodes, open a new terminal window. GitHub. ros2 run py_srvcli service. Return to CMakeLists.txt to add the executable and target for the new node. Now, let's break the code down. :ROS2parameter: -class type-, serviceclient, service/client, request headerROS2ROS2service/client with request header: -class style-"request header", :my_messages The rclcpp::Node class represents a single element in the ROS graph. A real-world example of this is a client node requesting sensor data from a service node. . Since the fixed and dynamic sized arrays within a generated C++ Message use STL containers like std::vector, the generated Messages also expose an Allocator. If it cant find any, it will continue waiting. This example tackles the task of bridging a ROS 2 server with one or more client applications, implemented using a wide variety of protocols.. Here is what I see: When you're done, press CTRL + C in all terminal windows to shut everything down. The --dependencies argument will automatically add the necessary dependency lines to package.xml and CMakeLists.txt. The add_executable macro generates an executable you can run using ros2 run. When nodes communicate using services, the node that sends a request for data is called the client node, and the one that responds to the request is the service node. Writing an action server and client (C++) The ROS 2 core software stack breaks down into a few discrete but related parts: Initialization and Shutdown Shutdown and Reinitialization Testing for Shutdown and Reinitialization Nodes Publish and Subscribe with Topics Working with Messages Publishing with a Publisher Warning This document is under construction. Navigate back to the root of your workspace, ros2_ws, and build your new package: colcon build merge-install packages-select cpp_srvcli. A Topic is a name with an associated Message type, which determines whether or not Publishers and Subscribers should exchange messages. The client object: To carry out a service call, an object of class ros::ServiceClient is created: ros::ServiceClient client = node_handle.serviceClient<service_type> (service_name); The node_handle is an object of class ros::NodeHandle, nh in the example. #include "my_srv.hpp" You created two nodes to request and respond to data over a service. rclcpp: ROS Client Library for C++ rclcpp provides the canonical C++ API for interacting with ROS. These states can be changed by invoking a . Add the following lines after the servers add_executable block: Here is what your CMakeLists.txt file should look like: We need to double check that all the dependencies needed are already installed. Step 6: Build the package using colcon build command. Conversely, when the rclcpp::Publisher is allowed to go out of scope, or is explicitly deleted, it is unadvertised from the ROS graph. Toggle line numbers. Welcome to AutomaticAddison.com, the largest robotics education blog online (~50,000 unique visitors per month)! See the ros::ServiceClient API docs for more information. Copyright 2014, Open Source Robotics Foundation, Inc. // Reinitialization happened since the last rclcpp::ok check std::shared_ptr, geometry_msgs::msg::Point::ConstSharedPtr, std::unique_ptr. Update 2 Switching to cycloneDDS only helped solve service discovery. Issues 154. The service node then responds to the client node with the requested sensor data. https://github.com/ros2/examples/tree/foxy/rclcpp/services/minimal_service, https://github.com/ros2/examples/tree/foxy/rclcpp/services/minimal_client, Developing Teleoperation Node for 1-DOF On-Off Gripper, Autonomous SLAM Using Explore_Lite in ROS, Autonomous SLAM Using Frontier Exploration in ROS. Ros2cs is also an independent part of Ros2 For Unity, which enables high-performance communication between simulation and ROS2 robot packages. #include "my_messages/srv/calc_two_floats.hpp", #include Testing for Shutdown and Reinitialization, Common Packages for DDS Middleware Packages, Structure of ROS Middleware Implementations, http://wiki.ros.org/roscpp/Overview/NodeHandles#Namespaces. We will then create a service node that will respond to the client node with the sum of those two integers. The example used here is a simple integer addition system; one node requests the sum of two integers, and the other responds with the result. This repository contains the source code for the ROS Client Library for C++ package, included with a standard install of any ROS 2 distro. Then, the ROS2 application needs to use service clients to call a planner that only exists as a ROS1 package. Publishers publish new Messages onto the Topic and any Subscribers that have subscribed to the same Topic (and with the same Message type) will receive those messages asynchronously. ros2 run py_srvcli client 5 3. This creates a client for the add_two_ints service. Its structure is defined by the .srv file mentioned earlier. Initializing rclcpp is done using the rclcpp::init() function: This function initializes any global resources needed by the middleware and the client library, as well as doing client library related command line argument parsing. If you want up-to-date information, please have a look at Humble. In previous tutorials, you learned how to create a workspace and create a package. The PR in its current state artificially delays the destruction of the ROS2 subscriber to ensure that the 'finalized' pointer doesn't become invalidated until we're done with it, which somewhat violates the idea that the user is the owner and is managing the lifecycle of that subscriber. #include "my_clnt_with_lambda.hpp" Therefore, it is generally a good idea to call this function before doing application specific command line argument parsing. The Helsinki-Uusimaa Region is at the heart of Northern Europe, more precisely in the very south of Finland and it has some 230 km of Baltic Sea coastline. For example, the cpp api was specified like this. A file called a .srv file defines the structure of the service-client node interaction. The example we will use here is an addition system. In order to test whether or not rclcpp::shutdown() has been called, the rclcpp::ok() function can be used: In order to test if the system has been reinitialized, an rclcpp::init::InitInstance can be retrieved using the rclcpp::init::get_instance() function and tested against the current instance using rclcpp::ok(): The instance can be compared to check that the reinitialization was not missed: The initialization instance is just a handle used for comparison and can be copied, moved, or destroyed without consequence. Specifically, we discuss how to forward petitions coming from Fast DDS, ROS 1 and a WebSocket service client applications to a ROS 2 add_two_ints_server server application, from the built-in ROS 2 package demo_nodes_cpp . The client-service relationship in ROS 2 is a request-reply relationship. Move to the dev_ws/src/cpp_srvcli/src folder. The name of the node must be unique across all nodes in the ROS graph. 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