nodelets

Nodelets are a component of the Robot Operating System (ROS) that enable multiple processing units to run within a single operating system process. In this architecture, a nodelet is a plugin that can be loaded into a dedicated process called a nodelet manager. This design allows several nodelets to share the same address space, reducing inter-process communication overhead and enabling faster data transfers between components.

A nodelet is typically implemented as a subclass of the ROS Nodelet base class and is loaded at runtime through the pluginlib framework. The nodelet manager hosts one or more nodelets, each handling a specific task such as sensor data acquisition, image processing, or data fusion. Communication between nodelets can use the same ROS topics and services as standalone nodes, but the framework supports intra-process communication that avoids serialization and deserialization, providing a potential performance advantage for high-throughput data like images and point clouds.

Management of nodelets is dynamic: a nodelet can be loaded or unloaded into a running nodelet manager, allowing the construction of flexible processing pipelines that can be reconfigured without restarting the entire system. This is commonly used in vision pipelines and real-time perception workflows where latency and throughput are important.

Limitations include reduced fault isolation, since all nodelets share a single process; debugging can be more challenging; and proper synchronization and thread safety become critical. Nodelets are primarily associated with ROS 1, and while they remain a useful pattern for lightweight, modular processing, newer ROS 2 approaches emphasize different architecture and security considerations.