[CMake] How to get custom commands to build in parallel ?

[Robert Maynard]

If you are using VS2013 you should look at the /maxcpucount flag which
allows msbuild to build multiple projects at the same time. You will
have to manually balance /MP and /maxcpucount as they cause a P*C
number of processes to execute.

On Tue, Sep 23, 2014 at 11:05 AM, Glenn Coombs <glenn.coombs at gmail.com> wrote:
> I have the following code in one of my CMakeLists.txt files:
>
> set(feature_files_h)
> set(feature_files_cpp)
>
> macro(create_feature_files NAME)
>     add_custom_command(
>         OUTPUT ${FEATURES_OUTPUT_DIR}/${NAME}.cpp
> ${FEATURES_OUTPUT_DIR}/${NAME}.h
>         DEPENDS ${FEATURES_INPUT_DIR}/${NAME}.txt
>         WORKING_DIRECTORY ${SIM_ROOT}/tools/features
>         COMMAND perl ${FEATURES_PERL_PATH} "-s${FEATURES_INPUT_DIR}"
> "-d${FEATURES_OUTPUT_DIR}" "-f${NAME}"
>         )
>     list(APPEND feature_files_h   ${FEATURES_OUTPUT_DIR}/${NAME}.h)
>     list(APPEND feature_files_cpp ${FEATURES_OUTPUT_DIR}/${NAME}.cpp)
> endmacro()
>
> create_feature_files(example_features)
> create_feature_files(fme_core_features)
> create_feature_files(fme_features)
> create_feature_files(front_end_features)
> create_feature_files(inloop_filter_features)
>
> add_library(${PROJECT_NAME} STATIC ${feature_files_cpp} ${feature_files_h}
> ${SIM_ROOT}/tools/features/cpp-code/cfeatures.cpp)
>
> which creates a library from an existing source file called cfeatures.cpp
> and from a bunch of auto-generated .cpp and .h files.  The whole thing works
> fine and runs the perl script to create each of the auto-generated files
> before creating the library.  The only problem I have with it is that it is
> quite slow and I would like to speed it up by having it run the perl
> commands to create the auto-generated files in parallel.  Currently, each of
> the auto-generated cpp files is generated sequentially, then they are all
> compiled in parallel and the library created in the final step.
>
> I'm using cmake 3.0.0 with Visual Studio 2013 Express Edition.  And I've
> added the /MP option so that Visual Studio will do parallel builds.  I've
> also set the "Projects and Solutions=>Build and Run=>maximum number of
> parallel project builds" option to 4.  This works well with all the normal
> cpp files in other projects and I easily see all 4 cpu cores maxxed out.
> But when building this project only 1 cpu core is used.
>
> Can anybody tell me how to change it so that the auto-geneated files are
> created in parallel as well ?
>
> --
> Glenn
>
>
> --
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