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ROS2: Preferred method of making worker threads

asked 2018-11-12 06:35:07 -0500

uthinu gravatar image

Hi, what is a preferred method of making worker threads in ROS2? If I would want real-time, should I use independently made rea- time threads, or is there an API for that?

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answered 2018-11-12 11:45:23 -0500

William gravatar image

updated 2018-11-12 11:45:42 -0500

There's no API for creating threads in ROS 2. The Executor class calls callbacks (if that's what you mean), and if you want a different threading model from SingleThreadedExecutor and MultiThreadedExecutor then you should make you're own executor, using one of those two as an example. They are fairly simple:

https://github.com/ros2/rclcpp/blob/3...

https://github.com/ros2/rclcpp/blob/3...

Then you can create an instance of your custom executor, add nodes to it, and then call spin on it.

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Any help on the code? It is somewhat cryptic for me, I can not see where the thread is created... I would like a fixed node:thread mapping which does not seem unusual to me, think nodes real-time and nodes non real-time. Any plans of adding such an executor?

uthinu gravatar image uthinu  ( 2018-11-14 09:43:00 -0500 )edit
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gvdhoorn gravatar image gvdhoorn  ( 2018-11-14 09:44:25 -0500 )edit
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Just add each node to it's own SingleThreadedExecutor, and call spin on each of those executors in their own thread, and you can setup each thread to be a real-time priority thread or not.

William gravatar image William  ( 2018-11-14 11:31:45 -0500 )edit
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The only built-in executor that creates a thread is the MultiThreadedExecutor , see: https://github.com/ros2/rclcpp/blob/3...

William gravatar image William  ( 2018-11-14 11:31:54 -0500 )edit

And if I would want this thread:node mapping and also reentrant callbacks? Could I spin each MultiThreaderExecutor in its own thread, and the threads created by that executor in its pool would inherit the parent thread's properties?

uthinu gravatar image uthinu  ( 2018-11-14 11:38:49 -0500 )edit

I don't know, it depends on what priority your operating system gives to new threads. If they are not inherited, then you'd need to make a new MultiThreadedExecutor which modifies the priorities of the threads it creates before using them. But as I said the MultiThreadedExecutor is trivial.

William gravatar image William  ( 2018-11-14 11:47:07 -0500 )edit

I do not know C++ well... Could you point me to an exact line in MultiThreaderExecutor.cpp where the threads are created?

uthinu gravatar image uthinu  ( 2018-11-14 12:09:36 -0500 )edit

I do not know C++ well...

That won't mix well with writing real-time safe code...

I already linked to it, the emplace_back : https://github.com/ros2/rclcpp/blob/3...

William gravatar image William  ( 2018-11-14 12:21:07 -0500 )edit

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Asked: 2018-11-12 06:35:07 -0500

Seen: 1,956 times

Last updated: Nov 12 '18