Automatically setting jobs (-j) flag for a multicore machine?

Question

I have a Makefile on a machine that has a ton of cores in it, but I always seem to forget to write -jX when compiling my project and it takes way longer than it

Answer 1

Until sometime in 2016, you could put this in your makefile: (GNU make tested)

MAKEFLAGS += "-j$(NUM_CORES) -l$(NUM_CORES)

(where NUM_PPROCS is calculated or set according to one of many of the other answers here) And, bam! you have multi-process building going on.

Given that this has stopped working, the best thing that I could come up with is this, where the makefile calls itself, but with -jX and -lX.

ifeq ($(PARALELL_WRAPPER_ABXCOEOEKCOEBMQJKHTOEUB),done)

all: ...
   ...

other_target: ...
    ...

else
# add parallelism equal to number of cores every time.
# "random" strings are to ensure uniqueness
NUM_CORES ?= $(shell grep -c "vendor_id" /proc/cpuinfo)
MAKEFLAGS +=" -j$(NUM_CORES) -l$(NUM_CORES) "

# for the default target case
parallel_wrapper_default_target_anthsqjkshbeohcbmeuthnoethoaeou:
    $(MAKE) PARALELL_WRAPPER_ABXCOEOEKCOEBMQJKHTOEUB=done

# catches everything else
% :
    $(MAKE) $@ PARALELL_WRAPPER_ABXCOEOEKCOEBMQJKHTOEUB=done

endif