Section 10.7 Glossary

Synchronous Communication

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A communication style where a process sends a request and blocks, waiting for a response before continuing its own execution.

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Asynchronous Communication

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A communication style where a process broadcasts data or registers a listener, then immediately continues its own execution without waiting for a response.

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Publisher

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A node component that sends messages onto a topic.

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Subscriber

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A node component that receives messages from a topic and processes them through a callback.

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Callback Function

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Code that runs automatically in response to an event, such as a timer firing or a message arriving, rather than being called directly by the main program.

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Timer Callback

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A callback function invoked repeatedly at a fixed interval, commonly used to trigger periodic publishing.

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Quality of Service (QoS)

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Settings, such as a publisher’s queue size, that control how message delivery is handled between a publisher and its subscribers.

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spin

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The ROS2 call that keeps a node running and processing callbacks until it is shut down.

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cmd_vel

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A conventional topic name used to send velocity commands, typically as a Twist message, to a mobile robot.

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Twist Message

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A standard ROS2 message type describing linear and angular velocity.

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sensor_msgs/LaserScan

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A standard ROS2 message type describing a set of distance readings from a range sensor such as a LiDAR.

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Decoupling

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A design property where publishers and subscribers can be added, removed, or replaced without requiring changes to one another.

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TurtleSim

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A lightweight ROS2 simulator used to practice publishing and subscribing without physical robot hardware.

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turtlesim/msg/Pose

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The standard ROS2 message type published by TurtleSim on /turtle1/pose, describing the turtle’s current position \((x, y)\) and heading (\(\theta\)).

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