High CPU load if there are no registered handles

[meyerj]

From https://github.com/RobotWebTools/rclnodejs/pull/751:

Originally posted by @renehoelbling in Intermodalics#1:

Add sleep to avoid busy waiting

Without the patch we observed situations where the ros2-web-bridge process consumed 100% of CPU while looping in Executor::Run(), if there is actually nothing to do (no clients connected). But I am not familiar with rclnodejs internals to check whether it is still an issue with the latest version, and in which cases handle_manager->is_empty() can return true.

This patch was based on version 0.10.3 (for ROS dashing). In the meantime the is_empty() check has been moved to https://github.com/RobotWebTools/rclnodejs/blob/45d7bd0a5cbc7b9d5bd6b397b33abc770845771b/src/executor.cpp#L166-L167

in #563, but nothing fundamentally changed and the loop in Executor::Run() could still busy-wait. What do you think? Is this a real issue, and if yes, would you solve it in a different way?

Thanks for giving the feedback and submitting the PR. Indeed, if there are no subscriptions/clients created, the CPU load will be high (although we usually created a node with clients added).

Some thoughts: Waiting for a certain period, .e.g 1ms, could solve the high CPU load issue, but using a semaphore is a perfect way to do this because there will be no extra looping, and totally event-driven.

Originally posted by @minggangw in https://github.com/RobotWebTools/rclnodejs/issues/751#issuecomment-743775623

[minggangw]

Because currently the node will create parameter services by default, it's small chance that no handle is added at the beginning. I'd like to put this issue to be low-priority. Meanwhile, #763 has been submitted to solve it. https://github.com/RobotWebTools/rclnodejs/blob/6f8a1a156780b131823e48650a35d9ff4760e462/lib/node_options.js#L22-L31

[meyerj]

Cool, thanks!