Topics, services, and actionlib are used in different scenarios. We know topics are a unidirectional communication method, services are a bidirectional request/reply kind of communication, and actionlib is a modified form of ROS services in which we can cancel the executing process running on the server whenever required.

Here are some of the areas where we use these methods:

• Topics: Streaming continuous data flow, such as sensor data. For example, stream joypad data to teleoperate a robot, publish robot odometry, publish video stream from a camera.
• Services: Executing procedures that terminate quickly. For example, save calibration parameter of sensors, save a map generated by the robot during its navigation, or load a parameter file.
• Actionlib: Execute long and complex actions managing their feedback. For example, navigate towards a target or plan a motion path.

$ git clone https://github.com/jocacace/mastering_ros_demo_pkg.git