CODEWITHSUNDEEP
makefilegnu-makeparallel-builds
Ludwig Schulze
Ludwig Schulze

Reputation: 2315

Restrict concurrency in sub-make

For a project spread over several sub-directories we use GNU make for the builds. Developers can use the -j <number> flag to parallelize the build tasks, and choose a number that suits the hardware of their machines.

However, the Makefiles of a third-party library that we use are not safe to parallelize - they apparently rely on implicit order of targets instead of explicit dependency rules between all dependent targets.

Since I have no desire to fix third-party Makefiles, we currently invoke their Makefiles with an explicit -j 1 parameter to restrict the number of jobs to 1 for building that library. The rule looks like this:

third_party_lib:
    $(MAKE) -j 1 -C $@

This works as desired, however, make emits a warning for this:

make[1]: warning: -jN forced in submake: disabling jobserver mode.

which leads me to ask here if there is a better way to restrict the number of parallel jobs in one sub-make.

Upvotes: 2

Views: 1759

Answers (1)

MadScientist
MadScientist

Reputation: 100856

You can add the .NOTPARALLEL: special target to the makefiles which should not be parallelized.

If you don't want to modify those makefiles you can use the --eval option on the command line (note --eval was added in GNU make 3.82):

third_party_lib:
        $(MAKE) --eval .NOTPARALLEL: -C $@

Upvotes: 4

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