[CMake] How would I use parallel make on ExternalProjects?

[kent williams]

On Thu, Oct 7, 2010 at 11:05 AM, Bill Hoffman <bill.hoffman at kitware.com> wrote:
>
> What you want is for make to treat the external projects just like any other
> library or executable in a build.
>
> so, if you run this at the top of the build:
>
> make -j4
>
> It should run at most 4 concurrent things at once for the whole thing. By
> using $(MAKE) in the makefiles make will do that.
>

There is one problem with that, which is what I'm trying to address:
load balancing.  If your project builds ITK, VTK, and sundry other
prerequisite libraries, it will spawn 4 sequential builds.  In
practice this means everything except ITK (which we build with
wrapping on) finishes, and then ITK chugs along doing its sequential
build.

If I do what I'm talking about, I'd sequentially conduct parallel
builds of ITK VTK etc.  In which case the big hairy libraries, like
ITK with wrapping, get built in parallel.


> That said, CMake will do this by default for make based builds and external
> projects now.
>
> From ExternalProject.cmake:
>
>  get_target_property(cmake_generator ${name} _EP_CMAKE_GENERATOR)
>      if("${CMAKE_GENERATOR}" MATCHES "Make" AND
>          ("${cmake_generator}" STREQUAL "${CMAKE_GENERATOR}" OR
>          NOT cmake_generator))
>        # The project uses the same Makefile generator.  Use recursive make.
>        set(cmd "$(MAKE)")
>        if(step STREQUAL "INSTALL")
>          set(args install)
>        endif()
>
>
> -Bill
>