Cmake parallel build

You are right as already given here: Cmake parallel build
however @ProTur1 is seeking a CMake variable to be set in CMakeLists.txt not an environment variable.

I don’t personally know why this feature does not exist, may be you can try to implement it and see by yourself.
My very personal opinion is that I don’t want the provider of a project to enforce a level of parallelism on my build, if want to build with full parallelism I use ninja generator. If I want to chose a constrained parallelism I build with cmake --build --parallel <myChoice>.
The level of parallelism I want depends on various thing the developer of the project cannot know:

  • Am I building on my dev machine or in CI ?
  • Is my dev machine equipped with 4, 8 or 32 cores?
  • Is the build machine dedicated to that build or shall this build be a background activity which leaves enough computing power/RAM/disk activities etc… to other processes ?

So I don’t know why this feature does not exist but my personal opinion is AFAIK I won’t need it anytime soon.

May be you could explain why, in your point of view this is a desirable/useful feature?

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From all the unknowns you mentioned, the cores can also be identified easily. From them, I would like to use only a part of it (although even if fully parallel, the OS scheduler should do its jobs well done as well).

Why it is useful?

  • for people who want to compile foreign projects, and don’t have time or don’t want to configure and type manually
  • for pushing to a build server, without command arguments for the build
  • for convenience
  • because it is easily possible to be realized (cmake offers anyhow a whole universe of functionality already)
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why not use cmake presets, there a jobs preset in cmake build presets here:cmake build-presets