Re: Detecting parallel builds

[Philip Prindeville]

On 4/9/11 5:48 PM, David Boyce wrote:
> On Sat, Apr 9, 2011 at 2:32 PM, Philip Prindeville
> <address@hidden> wrote:
>> address@hidden ~/openwrt2]$ make -j5 -f /tmp/Makefile
>> MAKEFLAGS=
>> MFLAGS=
>> MAKE=make
>> PBUILD=
>> MAKEFLAGS=w
>> MFLAGS=-w
>> MAKE=make
>> make[1]: Entering directory `/home/philipp/openwrt2'
>> make[1]: Nothing to be done for `stop'.
>> make[1]: Leaving directory `/home/philipp/openwrt2'
>> address@hidden ~/openwrt2]$
>>
>> Not sure what I'm missing...
> 
> Unfortunately it appears that MAKEFLAGS is composed on the fly when
> forking a command (aka job). See the following makefile:
> 
> % cat /tmp/Makefile
> $(info MAKEFLAGS='$(MAKEFLAGS)')
> 
> .PHONY: all
> all:
>         @echo "MAKEFLAGS='$(MAKEFLAGS)' (recipe)"
> 
> % make -f /tmp/Makefile -j2
> MAKEFLAGS=''
> MAKEFLAGS=' --jobserver-fds=3,4 -j' (recipe)
> 
> So it's not available to $(info) and other functions outside of a
> recipe. There's probably a way to trick make into doing a simple
> recursion to harvest the data. Or if you're dealing with an
> automated/nightly build you could set MAKEFLAGS yourself to turn on
> parallelism:
> 
>     MAKEFLAGS=-j8 make ...
> 
> but at that point you might as well just take control yourself
> 
> PARALLEL=YES make -j8 ...
> 
> Here's a hack which will work by calling make recursively once, but
> note that it will only work when no explicit target is mentioned:
> 
> % cat Makefile
> .PHONY: all
> all:
> 
> ifndef PARALLEL
> .PHONY: _is_parallel
> .DEFAULT_GOAL := _is_parallel
> _is_parallel:
>         address@hidden $(MAKE) -s -f $(MAKEFILE_LIST)
> _is_parallel2` &&\
>         PARALLEL=$$PARALLEL $(MAKE) --no-print-directory -f
> $(MAKEFILE_LIST) $(MAKECMDGOALS)
> else
> .PHONY: _is_parallel2
> _is_parallel2: ; @echo "$(if $(findstring -j,$(MAKEFLAGS)),YES,NO)"
> endif
> 
> all:
>         @echo "We $(if $(findstring YES,$(PARALLEL)),ARE,ARE NOT)
> building in parallel"
> 
> 
> David Boyce

Can we come up with a patch so that the -j argument is visible at all levels of 
make?

It would seem to be a trivial and fairly harmless change.

Thanks,

-Philip