Do/Should all packages "by default" support HOMEBREW_MAKE_JOBS?

[mathomp4]

Output of brew config

❯ brew config
HOMEBREW_VERSION: 6.0.4-2-g134f795
ORIGIN: https://github.com/Homebrew/brew
HEAD: 134f795204c20533ba78496da2fa67ee23d08a65
Last commit: 2 hours ago
Branch: main
Core tap HEAD: 399268110dbc4c31bbdf293afee6638fbd1e1e4c
Core tap last commit: 3 days ago
Core tap branch: feature/backport-266996
Core cask tap: N/A
HOMEBREW_PREFIX: /Users/mathomp4/.homebrew/brew
HOMEBREW_REPOSITORY: /Users/mathomp4/.homebrew/brew
HOMEBREW_CELLAR: /Users/mathomp4/.homebrew/brew/Cellar
HOMEBREW_CASK_OPTS: ["--appdir=/Users/mathomp4/Applications"]
HOMEBREW_DISPLAY: /var/run/com.apple.launchd.qcSptTFECU/org.xquartz:0
HOMEBREW_DOWNLOAD_CONCURRENCY: 24
HOMEBREW_EDITOR: /Users/mathomp4/.homebrew/brew/bin/vim
HOMEBREW_FORBID_PACKAGES_FROM_PATHS: set
HOMEBREW_GITHUB_API_TOKEN: set
HOMEBREW_MAKE_JOBS: 6
HOMEBREW_NO_ENV_HINTS: set
HOMEBREW_REQUIRE_TAP_TRUST: set
Homebrew Ruby: 4.0.5 => /Users/mathomp4/.homebrew/brew/Library/Homebrew/vendor/portable-ruby/4.0.5_1/bin/ruby
CPU: dodeca-core 64-bit arm_blizzard_avalanche
Clang: 21.0.0 build 2100
Git: 2.54.0 => /Users/mathomp4/.homebrew/brew/bin/git
Curl: 8.7.1 => /usr/bin/curl
macOS: 26.5-arm64
CLT: 26.5.0.0.1777544298
Xcode: 26.5
Metal Toolchain: N/A
Rosetta 2: false

Output of brew doctor

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Description of issue

So, much like https://github.com/orgs/Homebrew/discussions/6841, I have to build-from-source on my laptop (no admin access) and I have in my environment:

❯ echo $HOMEBREW_MAKE_JOBS
6

and my laptop is a 12-core (nominally) M2 Pro.

But today when brew decided to do brew upgrade it wanted to update llvm. when it did, it took all my processors. 100%.

So that made me wonder: Does a package "automatically" grab HOMEBREW_MAKE_JOBS or does the formula have to explicitly support it?

I'm guessing the latter given my experience with llvm? I tried looking around and I see llvm.rb has:

    # Now, we can build.
    mkdir llvmpath/"build" do
      system "cmake", "-G", "Ninja", "..", *(std_cmake_args + args)
      system "cmake", "--build", "."
      system "cmake", "--build", ".", "--target", "install"
    end

while v8.rb has:

    # Build with gn + ninja
    system "gn", "gen", "--args=#{gn_args_string}", "out.gn"
    system "ninja", "-j", ENV.make_jobs, "-C", "out.gn", "-v", "d8"

I see a lot of refs to ENV.make_jobs in the formulary, so I suppose that is an explicit way.

But then I see in https://github.com/Homebrew/brew/blob/main/Library/Homebrew/shims/super/ninja:

parallel_args=()
# Defer to a POSIX FIFO jobserver if MAKEFLAGS advertises one; -j would
# disable ninja's jobserver client. Other modes aren't usable on POSIX.
if [[ -n "${HOMEBREW_MAKE_JOBS}" && "${MAKEFLAGS}" != *"--jobserver-auth=fifo:"* ]]
then
  parallel_args+=(-j "${HOMEBREW_MAKE_JOBS}")
fi

(and @carlocab recently changed things around there). I don't know if that "shim" is something that "if a formula builds with ninja, it should get auto support"?

In the end, I'm wondering: If it should be automatic, why doesn't my system see it. Or does this mean I (or someone) should make a PR so that llvm supports it?

[ipatch]

i remember posting a question about this in this discussion forum a while back. and from what i remember the env var HOMEBREW_MAKE_JOBS was being passed to the formula that were configured with cmake from the formula i tested it with. i run homebrew on several different boxes, and i primarily run homebrew in a non standard prefix ie. $HOME/homebrew so i end up building most if not all formula from source when i decide to upgrade my installed formula from time to time. and from that discussion i mentioned above something i did mention in it was that when formula are configured using gnu autotools ie. the ./configure make make install process for building and installing the formula the HOMEBREW_MAKE_JOBS had no affect ie. it appeared the build / install process did not honor the env var when it was set. so sometimes when upgrading large packages ie. qtwebengine node (comes to mind) on my *nix boxes i limit the number of jobs using taskset not sure what the equivalent is for macos.

[cho-m]

CMake is tricky as they don't only search PATH but also multiple other directories - https://cmake.org/cmake/help/v4.4/command/find_program.html. Particularly the CMAKE_PREFIX_PATH environment variable will take precedence over PATH, which includes HOMEBREW_PREFIX thus picking up $HOMEBREW_PREFIX/bin/ninja

One idea that was previously proposed but never completed was to use CMAKE_BUILD_PARALLEL_LEVEL. If anyone wants to explore this again, you can see following PR:

• Set CMAKE_BUILD_PARALLEL_LEVEL environment variable. brew#18558

---

There are other ways to reorder the search path but they are more complicated, e.g.

• Restructure the Homebrew shims directory so it looks like shims/mac/super/bin and then shims/mac/super can be added to beginning of CMAKE_PREFIX_PATH so shims will always be found before other executables
• Add -DCMAKE_PROGRAM_PATH=#{ENV["PATH"]} to std_cmake_args as cache variables have priority over environment variables.
• For Ninja specifically, could consider adding parameter to std_cmake_args that sets -GNinja -DNinja_EXECUTABLE=#{which("ninja")}. I've done this as a workaround in some formulae that are close to CI limits like qtwebengine.
• Remove HOMEBREW_PREFIX from CMAKE_PREFIX_PATH. Will note that this will break some formulae so probably less ideal option.

[cho-m]

• Restructure the Homebrew shims directory so it looks like shims/mac/super/bin and then shims/mac/super can be added to beginning of CMAKE_PREFIX_PATH so shims will always be found before other executables

Added this in:

• Force CMake to find shims before $HOMEBREW_PREFIX/bin brew#22916

[mathomp4]

@cho-m So do you think this means it might now honor HOMEBREW_MAKE_JOBS? (I don't really know ruby or the internals of homebrew that well, so your PR is, well, like magic to me :D

[cho-m]

Builds using CMake + Ninja will now pick up HOMEBREW_MAKE_JOBS. Note that the change is only in brew main branch so most users may need to wait for next release, e.g. brew 6.0.7, or use developer mode version, e.g. 6.0.6-16-g8d94d5c