[CMake] Parallel build setup question

[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/qtcreator/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 bockemuehl.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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