[CMake] Adding a custom line to CMake's makefiles?

Mike Wittman michael.wittman at headwave.com
Fri Sep 9 17:24:35 EDT 2011 

Yes, but only when setting MAKEFLAGS from within a Makefile.  It appears 
the rules do not apply when MAKEFLAGS is set by the invoking shell.  
(And actually, current GNU make handles parallel execution differently 
on Linux, using a job server that all make subprocesses use to 
coordinate execution -- the documentation below is from 1998.)

If you still don't believe :)  try putting the following in a Makefile 
and running MAKEFLAGS=j3 make

all: r1 r2 r3
r1 r2 r3:
         echo rule $@; sleep 5

-Mike

On 09/09/2011 02:55 PM, Jean-Christophe Fillion-Robin wrote:
> Reading through make documentation, seems setting -jx to MAKEFLAGS is 
> a no-op.
>
> /"The `-j' option is a special case (see section Parallel Execution 
> <http://theory.uwinnipeg.ca/localfiles/infofiles/make/make_47.html#SEC46>). 
> If you set it to some numeric value, `-j 1' is always put into 
> |MAKEFLAGS| instead of the value you specified. This is because if the 
> `-j' option were passed down to sub-|make|s, you would get many more 
> jobs running in parallel than you asked for. If you give `-j' with no 
> numeric argument, meaning to run as many jobs as possible in parallel, 
> this is passed down, since multiple infinities are no more than one. "/
>
> Source: http://theory.uwinnipeg.ca/localfiles/infofiles/make/make_53.html
>
> Jc
>
> On Fri, Sep 9, 2011 at 3:37 PM, Mike Wittman 
> <michael.wittman at headwave.com <mailto:michael.wittman at headwave.com>> 
> wrote:
>
>     If you are building on Linux, try
>         MAKEFLAGS=j8 make distcheck
>
>     I have successfully used the MAKEFLAGS environment variable to
>     propagate parallel build invocations through scripts that invoke
>     make with fixed options.
>
>     -Mike
>
>
>     On 09/09/2011 09:21 AM, Clifford Yapp wrote:
>>     I can finally give a good concrete case where I might need to do
>>     this (or need some other very clever solution).
>>
>>     I have created a distcheck command for BRL-CAD that has a lot of
>>     responsibilities, including doing a complete configure and build
>>     of BRL-CAD from a source archive expanded from a CPack tarball. 
>>     The distcheck rule uses cmake to fire off the build (this is to
>>     try and be future proof against using other tools than Make to do
>>     a distcheck) but I need to pass the parallel build setting -j
>>     from Make down to the ${CMAKE_COMMAND} build launched by the
>>     distcheck rule, and there doesn't seem to be any way to do it.
>>
>>     This is the subset of the distcheck rule (somewhat edited for
>>     clarity):
>>
>>        ADD_CUSTOM_TARGET(distcheck
>>           COMMAND ${CMAKE_COMMAND} -E echo "Stage 1:  Create source
>>     tgz, tbz2 and zip archives from toplevel archive."
>>           COMMAND cpack --config
>>     ${CMAKE_CURRENT_BINARY_DIR}/CPackSourceConfig.cmake
>>           COMMAND ${CMAKE_COMMAND} -E echo "Stage 2:  Expand tgz
>>     archive and prepare to build from archive sources."
>>           COMMAND ${CMAKE_COMMAND} -E tar xvzf
>>     ${CPACK_SOURCE_PACKAGE_FILE_NAME}.tar.gz
>>           COMMAND ${CMAKE_COMMAND} -E make_directory
>>     _${CPACK_SOURCE_PACKAGE_FILE_NAME}-build
>>           COMMAND ${CMAKE_COMMAND} -E make_directory
>>     _${CPACK_SOURCE_PACKAGE_FILE_NAME}-install
>>           COMMAND ${CMAKE_COMMAND} -E chdir
>>     _${CPACK_SOURCE_PACKAGE_FILE_NAME}-build ${CMAKE_COMMAND}
>>     ../${CPACK_SOURCE_PACKAGE_FILE_NAME}
>>     -DCMAKE_INSTALL_PREFIX=${CMAKE_CURRENT_BINARY_DIR}/_${CPACK_SOURCE_PACKAGE_FILE_NAME}-install
>>           COMMAND ${CMAKE_COMMAND} -E echo "Stage 3:  Compile using
>>     source from tgz archive."
>>           COMMAND ${CMAKE_COMMAND} --build
>>     _${CPACK_SOURCE_PACKAGE_FILE_NAME}-build
>>           )
>>
>>     This can be successfully fired off by "make distcheck", which is
>>     the desired behavior.  However, the --build option doesn't
>>     respect (naturally) any -jN options fed to make, since they
>>     aren't specified at CMake time when the distcheck Makefile target
>>     is being generated.
>>
>>     Perversely enough, if I'm understanding the issue correctly I
>>     won't be able to use the -jN value itself in any case, even if
>>     the Makefile can be taught to do something smart:
>>     http://old.nabble.com/MAKEFLAGS-var-does-not-show-%22-j%22-param-----td15983337.html
>>
>>     The best idea I can come up with so far is for the CMake
>>     generated Makefile to write out a variable containing some CPU
>>     related variable (e.g. make CPUS=8 and write the value of $(CPUS)
>>     to CMakeFiles/make_cpu_flag or some such) and then convert the
>>     distcheck commands above into a series of EXECUTE_PROCESS lines
>>     in a rundistcheck.cmake file that is launched by the distcheck
>>     rule with a ${CMAKE_COMMAND}.  In rundistcheck.cmake, I can check
>>     for the presence of the make_cpu_flag file and if found add the
>>     -j parallel flag to the --build line before running it.  That
>>     will mean a parallel distcheck will have to use a different make
>>     syntax than the standard make -j, but at least it would be
>>     something.  Unfortunately, that means I still need the Makefile
>>     to let me know what was passed in up front, which means tweaking
>>     the CMake generated output somehow (not really sure how yet).
>>
>>     Does anybody else have a mechanism for passing parallel build
>>     instructions from make down to child ${CMAKE_COMMAND} --build
>>     instances?
>>
>>     Cheers,
>>     CY
>>
>>
>>     On Wed, Feb 2, 2011 at 4:32 PM, Michael Hertling
>>     <mhertling at online.de <mailto:mhertling at online.de>> wrote:
>>
>>         On 02/02/2011 03:34 PM, Clifford Yapp wrote:
>>         > Is there any way to customize the Makefile output from CMake to
>>         > include user-defined lines (say, something like "#include
>>         > Makefile.inc") at the end of each Make file?
>>
>>
>>      [snip]
>>
>>         However, this approach is neither portable nor clean
>>         nor <your-expectation-here>, so I would ask Eric's questions,
>>         too. ;)
>>
>>         Regards,
>>
>>         Michael
>>
>>
>>
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