ROS 2 zero copy intraprocess communication

asked 2021-06-09 13:13:20 -0500

mschickler
95 ●5 ●10 ●11

I've written a program to measure the latency of communication between separate ROS 2 foxy publisher and a subscriber nodes running in a single process. I'm dynamically allocating memory for the message using make_unique() and passing to publish(). My understanding was that this would result in zero-copy communication to the subscriber. However, the latency seems high and the memory address of the underlying message at the subscriber is different than the address of the originally allocated message. A similar test using shared pointer publish with nodelets in ROS 1 shows the memory address is unchanged at the receiver (i.e. zero-copy occurred).

My code is at: https://github.com/mschickler/simple_...

Any help or insight appreciated.

answered 2021-06-10 06:07:31 -0500

sgvandijk

flag of United Kingdom of Great Britain and Northern Ireland

649 ●2 ●24 ●19

You have to enable intraprocess communication explicitly to have it kick in. You do this with the NodeOptions passed to the nodes. Try the following in combined_node.cpp:

int main(int argc, char** argv)
{
  rclcpp::init(argc, argv);
  rclcpp::executors::MultiThreadedExecutor executor;
  auto intra_comms_options = rclcpp::NodeOptions{}.use_intra_process_comms(true);
  auto probe = std::make_shared<simple_perf_test::ProbeComponent>(intra_comms_options);
  auto target = std::make_shared<simple_perf_test::TargetComponent>(intra_comms_options);
  executor.add_node(probe);
  executor.add_node(target);
  executor.spin();
  rclcpp::shutdown();
  return 0;
}

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Thanks! It worked. I am a little surprised that it still looks like there is about 100-200 microseconds of latency while running in my environment, but at least the addresses now match!

mschickler ( 2021-06-10 06:41:16 -0500 )edit

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