EFFICIENCY.md

Tips for efficent use of rclnodejs

While our benchmarks place rclnodejs performance at or above that of rclpy we recommend applying efficient coding and configuration practices where applicable.

Tip-1: Disable Parameter Services

The typical ROS 2 node creation process includes creating an internal parameter service who's job is to fulfill requests for parameter meta-data and to set and update node parameters. If your ROS 2 node does not support public parameters then you can save the resources consumed by the parameter service. Disable the node parameter service by setting the NodeOption.startParameterServices property to false as shown below:

let options = new NodeOptions(false);
// or
options.startParameterServices = false;

let node = new Node(nodeName, namespace, Context.defaultContext(), options);

Tip-2: Disable LifecycleNode Lifecycle Services

The LifecycleNode constructor creates 5 life-cycle services to support the ROS 2 lifecycle specification. If your LifecycleNode instance will not be operating in a managed-node context consider disabling the lifecycle services via the LifecycleNode constructor as shown:

let enableLifecycleCommInterface = false;

let node = new LifecycleNode(
  nodeName,
  namespace,
  Context.defaultContext,
  NodeOptions.defaultOptions,
  enableLifecycleCommInterface
);

Tip-3: Use Content-filtering Subscriptions

The ROS Humble release introduced content-filtering topics which enable a subscription to limit the messages it receives to a subset of interest. While the application of the a content-filter is specific to the DDS/RMW vendor, the general approach is to apply filtering on the publisher side. This can reduce network bandwidth for pub-sub communications and message processing and memory overhead of rclnodejs nodes.

Note: Be sure to confirm that your RMW implementation supports content-filter before attempting to use it. In cases where content-filtering is not supported your Subscription will simply ignore your filter and continue operating with no filtering.

Example:

  // create a content-filter to limit incoming messages to
  // only those with temperature > 75C.
  const options = rclnodejs.Node.getDefaultOptions();
  options.contentFilter = {
    expression: 'temperature > %0',
    parameters: [75],
  };

  node.createSubscription(
    'sensor_msgs/msg/Temperature',
    'temperature',
    options,
    (temperatureMsg) => {
      console.log(`EMERGENCY temperature detected: ${temperatureMsg.temperature}`);
    }
  );