[CMake] Parallel build setup question

[Cornelis Bockemühl]

Thanks for your hints! And you are right: it is still interesting to
know how QtCreator is actually invoking and using cmake.

This is the beginning of a log that the QtCreator was generating during
a build. Actually with two modules where nothing had to be done, but
still showing how cmake and gmake are being invoked - and all a bit
above my understanding of the two tools:

===================================
/usr/bin/cmake -H/Sources/GitLinux/RMT -B/BinariesLinux/RMT/Debug --
check-build-system CMakeFiles/Makefile.cmake 0
/usr/bin/cmake -E cmake_progress_start
/BinariesLinux/RMT/Debug/CMakeFiles
/BinariesLinux/RMT/Debug/CMakeFiles/progress.marks
/usr/bin/gmake -f CMakeFiles/Makefile2 all
gmake[1]: Entering directory '/BinariesLinux/RMT/Debug'
/usr/bin/gmake -f CMakeFiles/FirstModule.dir/build.make
CMakeFiles/FirstModule.dir/depend
gmake[2]: Entering directory '/BinariesLinux/RMT/Debug'
cd /BinariesLinux/RMT/Debug && /usr/bin/cmake -E cmake_depends "Unix
Makefiles" /Sources/GitLinux/RMT /Sources/GitLinux/RMT
/BinariesLinux/RMT/Debug /BinariesLinux/RMT/Debug
/BinariesLinux/RMT/Debug/CMakeFiles/FirstModule.dir/DependInfo.cmake --
color=
gmake[2]: Leaving directory '/BinariesLinux/RMT/Debug'
/usr/bin/gmake -f CMakeFiles/FirstModule.dir/build.make
CMakeFiles/FirstModule.dir/build
gmake[2]: Entering directory '/BinariesLinux/RMT/Debug'
gmake[2]: Nothing to be done for 'CMakeFiles/FirstModule.dir/build'.
gmake[2]: Leaving directory '/BinariesLinux/RMT/Debug'
[  3%] Built target FirstModule
/usr/bin/gmake -f CMakeFiles/SecondModule.dir/build.make
CMakeFiles/SecondModule.dir/depend
gmake[2]: Entering directory '/BinariesLinux/RMT/Debug'
cd /BinariesLinux/RMT/Debug && /usr/bin/cmake -E cmake_depends "Unix
Makefiles" /Sources/GitLinux/RMT /Sources/GitLinux/RMT
/BinariesLinux/RMT/Debug /BinariesLinux/RMT/Debug
/BinariesLinux/RMT/Debug/CMakeFiles/SecondModule.dir/DependInfo.cmake
--color=
gmake[2]: Leaving directory '/BinariesLinux/RMT/Debug'
/usr/bin/gmake -f CMakeFiles/SecondModule.dir/build.make
CMakeFiles/SecondModule.dir/build
gmake[2]: Entering directory '/BinariesLinux/RMT/Debug'
gmake[2]: Nothing to be done for 'CMakeFiles/SecondModule.dir/build'.
gmake[2]: Leaving directory '/BinariesLinux/RMT/Debug'
[  6%] Built target SecondModule
...
===========================================

For example I do not really understand all the parameters that are
passed to cmake - and I do not find them in the documentation either
(like -H, -B or --check-build-system...

Regards,
Cornelis

Am Freitag, den 16.02.2018, 08:59 -0800 schrieb Michael Ellery:
> > > > > > > > > > > > > > I don’t know anything about QTCreator, but the question really boils
down to how to get your IDE to pass extra args to the build tool -
it’s not really a cmake issue except to the extent that CMake can be
used to invoke the build step (after it has been used to generate the
build).  It sounds like QT uses “cmake --build” to do the build phase
(which makes sense), so you just need to add your “-j N” argument to
the build step invocation. If you believe this:  https://doc.qt.io/qt
creator/creator-build-settings.html, then it sounds like maybe “Tool
Arguments” is what you want (see “CMake Build Steps”) ?  BTW, the way
I do this myself (since I don’t use an IDE) is something like “cmake
--build . -- -j 8”  where the double dash stops shell argument
processing and effectively passes everything else on to the build
tool that cmake ultimately invokes (e.g. make or ninja or msbuild,
etc.)
> 
> HTH,
> Mike
> 
> > > > On Feb 16, 2018, at 8:31 AM, Cornelis Bockemühl <cornelis at bockemueh
l.ch> wrote:
> > 
> > Hello,
> > 
> > > > > > Somehow I seem to miss some crucial point regarding setup for
parallel build with CMake, so I would be happy if somebody can push
me the last few millimeters to hit my target!
> > 
> > > > My configuration is on OpenSuse Linux (Leap - 64-bit), working with
QtCreator and CMake, using the "make" configuration.
> > 
> > > > > > > > I learned from "the internet" that actually I would have to pass a
-jN option to make or gmake (with N being the max number of
processors I want to use). Or even more elegant: go for a -lN
option to somehow balance the load. Sounds good!
> > 
> > > > > > > > > > > > But what I do not see is how to pass these nice options to make
through CMake and QtCreator! One attempt was to specify
CMAKE_CXX_FLAGS=-j4 or the like because some comment "in the
internet" seemed to suggest this. However, like I already feared:
this passes the option to the compiler call - and that is the wrong
address for it, so I get an error message.
> > 
> > > > Basically I think that it is 99% a CMake question and maximum 1% a
QtCreator problem, so I am asking this question here.
> > 
> > > > And now I am stuck - if not some friendly and knowing person can
help me out of this!
> > 
> > Thanks for any helpful hint!
> > Cornelis
> > -- 
> > 
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