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How Can I define the number of threads for a colcon building process in ROS2?

In previous ros building tools we used "-j {number_of_threads}", but that does not work anymore.

Originally posted by Pablo Iñigo Blasco on ROS Answers with karma: 2982 on 2020-12-22

Post score: 5


3 Answers 3


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There are two independent dimensions of parallelization:

  • The maximum number of packages processed in parallel when using the parallel executor. This dimension can be limited with the option --parallel-workers NUMBER. It can also be limited to 1 by selecting the sequential executor with --executor sequential.

  • The maximum number of threads used for a specific package using make. This can be controlled using the environment variable MAKEFLAGS. By setting e.g. export MAKEFLAGS="-j 4" only four threads are used to build a single package. By default colcon-cmake uses the number of available CPU cores (including hyper threading) to limit the number of threads (-j) as well as the system load (-l).

As a result the overall number of threads is the product of packages processed in parallel and maximum number of threads per package.

Originally posted by Dirk Thomas with karma: 16276 on 2020-12-31

This answer was ACCEPTED on the original site

Post score: 7

Original comments

Comment by brianlmerritt on 2021-11-10:
For anyone finding this, I found that colcon build on a Raspberry Pi 4 can crash, but adding --executor sequential sorted this out without a massive time penalty.


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--parallel-workers NUMBER is the syntax you're looking for. "-j N" is a make specific argument.

There's documentation of the parallel executor command line options here: https://colcon.readthedocs.io/en/released/reference/executor-arguments.html

Originally posted by tfoote with karma: 58457 on 2020-12-22

This answer was NOT ACCEPTED on the original site

Post score: 3


yes, export MAKEFLAGS="-j 1" can fix this error:

c++: fatal error: Killed signal terminated program cc1plus

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