feat(core): run parallel based on the number of cpu cores

[ianzone]

BREAKING CHANGE: default parallel changed from 3 to half of the cpu cores

Current Behavior

can not specify parallel based on the number of cpu cores.

Expected Behavior

--parallel 0.5 means half of the cpu cores.
--parallel 3 means exact tasks to run in parallel.

Related Issue(s)

#30238

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☁️ Nx Cloud last updated this comment at 2025-04-02 15:07:54 UTC

[MaxKless]

Hey @ianzone thanks for the PR!
Some points:

• instead of a fractional number, I think it would make more sense to go with a percentage, like jest & vitest do it. It makes sense to align with other tools in order to be more intuitive. Then it's also clear that number specifies the cores directly while a string is percentage-based
• Is there a reason that the default changed from 3 to 50%? I think it would be better to leave the default alone for now as it will affect everyone.

Here are some links to jest & vitest:

• vitest/packages/vitest/src/utils/workers.ts at a9d36c719f8ce5551f61da20181490d3673bdf99 · vitest-dev/vitest
• https://jestjs.io/docs/cli#--maxworkersnumstring

[ianzone]

Hey @ianzone thanks for the PR! Some points:

• instead of a fractional number, I think it would make more sense to go with a percentage, like jest & vitest do it. It makes sense to align with other tools in order to be more intuitive. Then it's also clear that number specifies the cores directly while a string is percentage-based
• Is there a reason that the default changed from 3 to 50%? I think it would be better to leave the default alone for now as it will affect everyone.

Here are some links to jest & vitest:

• vitest/packages/vitest/src/utils/workers.ts at a9d36c719f8ce5551f61da20181490d3673bdf99 · vitest-dev/vitest
• https://jestjs.io/docs/cli#--maxworkersnumstring

1. agree
2. sometimes i'm kinda lazy and don't want to text extra words, and i guess 50% is a decent workload.

[MaxKless]

sure, I get it. But it's still a guess that will affect everyone and if the price is a couple of extra characters.... let's stick with the same default for now

[ianzone]

sure, I get it. But it's still a guess that will affect everyone and if the price is a couple of extra characters.... let's stick with the same default for now

ok

[ianzone]

updated

[MaxKless]

Looks good! Can you add a test to shared-options.spec.ts to verify this is and will keep behaving as it should? :) Thanks!

[ianzone]

tests added

[ianzone]

Hi, could you merge this?