[CMake] Parallel builds and Eclipse CDT4 generator

[Alexander Neundorf]

On Thursday 12 March 2009, Adolfo Rodríguez wrote:
> We currently use three of CMake's generators: "Unix Makefiles",
> "KDevelop3", and "Eclipse CDT4 - Unix Makefiles", and we're interested in
> doing parallel builds. Doing so with makefiles is trivial (make -j#), as
> well as with KDevelop3 (only _one_ parameter must be edited in the build
> options of the project). However Eclipse is still eluding me (I must
> confess that I'm quite new to it).
> My current hack is to edit individual targets and change the name of the
> target from, say 'all' to '-j# all', and it works. However, I haven't found
> a project-wide policy that if edited once, will affect all targets. I
> cannot set the default build command, because apparently CMake generates
> each target with a custom build command.
>
> Any clues from the CMake-Eclipse experts?
>
> I'm using CMake 2.6.2 and Eclipse CDT5 (not CDT4, could this be an issue?)

I don't think so.
We could add some special variable, like
CMAKE_MAKEFILE_PROJECT_FLAGS or CMAKE_MAKEFILE_PARALLELITY, and use this in 
the makefile-based generators to set the "-jx" parameter for make.
But then again, this shouldn't be hardcoded in the CMakeLists.txt, so it could 
only be a cache variable.
Or should cmake try to determine automatically how many cores there are and 
add "-jx" automatically ? E.g. using sysconf(_SC_NPROCESSORS_ONLN) ?
This could also be disabled by default and enabled e.g. via an option like 
CMAKE_AUTOMATIC_PARALLEL_MAKE_INVOCATION or something like this.

Alex