rmw_stats_shim

RMW Stats Shim

Depends on a modified version of rmw_implementation to provide topic statistics calculation within the RMW layer of each node, without having to instrument application code.

This component

• Wraps & intercepts some RMW API calls
• Calculates "published period" statistics for every Publisher
• Calculates "received period" statistics for every Subscription
• Calculates "take age" statistics for every Subscription
  • This is the different between publish system timestamp and the time at which rmw_take is called, so is the sum of network latency plus executor latency
• Creates a /topic_statistics Publisher for every Node and publishes to it periodically about the statistics from within the node

Key points:

• Requires no subscriptions, no extra copies, to do statistics on all topics
• Requires no modification to application code to use

Configuration

Set the following environment variables before launching a node to configure topic statistics

• Required: RMW_IMPLEMENTATION_WRAPPER=rmw_stats_shim
• ROS_TOPIC_STATISTICS_WINDOW_SIZE - how many messages to use in rolling buffer for stats (stores only timestamp information, not contents data)
  • Default: 50
• ROS_TOPIC_STATISTICS_TOPIC_NAME - name of the topic to publish statistics on
  • Default: /topic_statistics
• ROS_TOPIC_STATISTICS_PUBLISH_PERIOD - Interval in seconds at which to periodically publish stats
  • Default: 1.0

Usage

colcon build --packages-select rmw_implementation rmw_stats_shim
source install/setup.bash
export RMW_IMPLEMENTATION_WRAPPER=rmw_stats_shim
# run any ROS 2 node/launch/etc