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Not sure if this is possible in one Makefile alone, but I was hoping to write a Makefile in a way such that trying to build any target in the file auto-magically detects the number of processors on the current system and builds the target in parallel for the number of processors.
Something like the below "pseudo-code" examples, but much cleaner?
all: @make -j$(NUM_PROCESSORS) all Or:
all: .inparallel ... build all here ... .inparallel: @make -j$(NUM_PROCESSORS) $(ORIGINAL_TARGET) In both cases, all you would have to type is:
% make all Hopefully that makes sense.
UPDATE: Still hoping for an example Makefile for the above. Not really interested in finding the number of processes, but interested in how to write a makefile to build in parallel without the -j command line option.
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To start GNU Make in parallel mode it's enough to specify either the -j or --jobs option on the command-line. The argument to the option is the maximum number of processes that GNU Make will run in parallel. For example, typing make --jobs=4 will allow GNU Make to run up to four subprocesses in parallel.
The $@ and $< are called automatic variables. The variable $@ represents the name of the target and $< represents the first prerequisite required to create the output file. For example: hello.o: hello.c hello.h gcc -c $< -o $@ Here, hello.o is the output file.
And in your scenario, $MAKE is used in commands part (recipe) of makefile. It means whenever there is a change in dependency, make executes the command make --no-print-directory post-build in whichever directory you are on.
Q is defined somewhere after those line. Since makefile have peculiar concept of variable (which is expandable), it can be implement in anywhere. Q is used to whether show message or not (Q maybe for Quiet).
The detection part is going to be OS dependent. Here's a fragment that will work on Linux and Mac OS X:
NPROCS:=1 OS:=$(shell uname -s) ifeq($(OS),Linux) NPROCS:=$(shell grep -c ^processor /proc/cpuinfo) endif ifeq($(OS),Darwin) # Assume Mac OS X NPROCS:=$(shell system_profiler | awk '/Number Of CPUs/{print $4}{next;}') endif To get it working you are probably going to have to re-invoke make. Then your problem is preventing infinite recursion. You could manage that by having two makefiles (the first only resetting the -j value), but it is probably possible to finesse it.
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