Makefile max load on remote server - makefile

Question

we have a huge project with very time consuming sub-tasks running on Unix. The whole make process runs multiple hours. So building in parallel is essential for us. The expensive jobs are preformed on a remote server via ssh. Everything works fine. But I'm afraid that accidentally a team member could forget to specify the number for the -j flag. The --load-average flag uses the load on the local server so no matter how busy the remote server is it would generate hundreds of sub-tasks on the remote server which would slow down the entire company. Please note that I don't have admin rights on either server. We could also live with limiting the number of jobs (hardcoded).
Thanks a lot in Advance
Karl

Answer 1

If you have GNU make 4.2 or better, you can check that the user didn't give a raw -j by looking at MAKEFLAGS:
ifeq (-j,$(filter -j,$(MAKEFLAGS)))
$(error You cannot use -j without specifying a number of jobs)
endif
If you have an earlier version of GNU make you can do this by checking if both -j was given AND the jobserver is active:
ifneq (,$(filter -j,$(MAKEFLAGS)))
ifneq (,$(filter --jobserver-%,$(MAKEFLAGS)))
$(error You cannot use -j without specifying a number of jobs)
endif
endif
(this version will work for newer versions as well).
It's possible this won't work with versions of GNU make <4.0; I didn't test it.

Answer 2

For older make versions you can consider the following. That is not pure makefile way, but works.
Solution
ifneq (0,$(shell ps --pid $$PPID -o args= | grep --perl-regexp -c '^make.*-j(?!\s*[0-9]+\b)'))
$(error You cannot use -j without specifying a number of jobs)
endif
# Or oneliner:
#$(if $(shell ps --pid $$PPID -o args= | grep --perl-regexp -c '^make.*-j(?!\s*[0-9]+\b)' | grep -v '^0$$'),$(error You cannot use -j without specifying a number of jobs))
# Below part just for testing
all a 1: ; #exit 0
Testing
$ make
$ make a
$ make 1
$ make -j1
$ make -j1 a
$ make -j1 1
$ make -j 1
$ make -j 1a
Makefile:6: *** You cannot use -j without specifying a number of jobs. Stop.
$ make -j a
Makefile:6: *** You cannot use -j without specifying a number of jobs. Stop.
$ make a -j
Makefile:6: *** You cannot use -j without specifying a number of jobs. Stop.
$ make 1 -j a
Makefile:2: *** You cannot use -j without specifying a number of jobs. Stop.
How it works
It is taking information from parent process (that is make process) using ps utility, and later filter out arguments using grep (regular expression is more or less: find make command with -j parameter that is not followed by a number).

Answer 3

Based on to the answer from Kuchara above I needed the following enhancement, since I call some subsystems with:
$(MAKE) $(MFLAGS) ...
and this will add the jobserver and remove the number from the -j flag in the subsystem:
yy:
#echo yy mflags: $(MFLAGS)
#echo yy ps: $(shell ps --pid $$PPID -o args=)
$(MAKE) $(MFLAGS) zz
zz:
#echo zz mflags: $(MFLAGS)
#echo zz ps: $(shell ps --pid $$PPID -o args=)
Testing:
make -j 3 yy
yy mflags: - --jobserver-fds=3,4 -j
yy ps: make -j 3 yy
zz mflags: -w --jobserver-fds=3,4 - --jobserver-fds=3,4 -j
zz ps: make - --jobserver-fds=3,4 -j zz
I needed to combine the answers from MadScientist and Kuchara:
ifneq (0,$(shell ps --pid $$PPID -o args= | grep --perl-regexp -c '^make.*-j(?!\s*[0-9]+\b)'))
ifeq (0,$(shell ps --pid $$PPID -o args= | grep --perl-regexp -c '^make.*--jobserver'))
$(error You cannot use -j without specifying a number of jobs)
endif
endif
Thanks a lot again at both for your great ideas.