Check roundtrip message latency

This example shows how to check roundtrip message latency on your system.

import logging
import time

import roslibpy

# Configure logging
fmt = '%(asctime)s %(levelname)8s: %(message)s'
logging.basicConfig(format=fmt, level=logging.INFO)
log = logging.getLogger(__name__)

client = roslibpy.Ros(host='127.0.0.1', port=9090)

def receive_message(msg):
    age = int(time.time() * 1000) - msg['data']
    log.info('Age of message: %6dms', age)

publisher = roslibpy.Topic(client, '/check_latency', 'std_msgs/UInt64')
publisher.advertise()

subscriber = roslibpy.Topic(client, '/check_latency', 'std_msgs/UInt64')
subscriber.subscribe(receive_message)

def publish_message():
    publisher.publish(dict(data=int(time.time() * 1000)))
    client.call_later(.5, publish_message)

client.on_ready(publish_message)
client.run_forever()

The output on the console should look similar to the following:

$ python 02_check_latency.py
2020-04-09 07:45:49,909     INFO: Connection to ROS ready.
2020-04-09 07:45:50,431     INFO: Age of message:      2ms
2020-04-09 07:45:50,932     INFO: Age of message:      2ms
2020-04-09 07:45:51,431     INFO: Age of message:      1ms
2020-04-09 07:45:51,932     INFO: Age of message:      2ms
2020-04-09 07:45:52,434     INFO: Age of message:      3ms
2020-04-09 07:45:52,934     INFO: Age of message:      2ms
2020-04-09 07:45:53,435     INFO: Age of message:      3ms
2020-04-09 07:45:53,934     INFO: Age of message:      1ms
2020-04-09 07:45:54,436     INFO: Age of message:      2ms