From CMake setup 'make' to use '-j' option by default

I want my CMake project to be built by make -j N, whenever I call make from the terminal. I don't want to set -j option manually every time.

For that, I set CMAKE_MAKE_PROGRAM variable to the specific command line. I use the ProcessorCount() function, which gives the number of procesors to perform build in parallel.

When I do make, I do not see any speed up. However if I do make -j N, then it is built definitely faster.

Would you please help me on this issue? (I am developing this on Linux.)

Here is the snippet of the code that I use in CMakeList.txt:

include(ProcessorCount)
ProcessorCount(N)
message("number of processors: "  ${N})
if(NOT N EQUAL 0)
  set(CTEST_BUILD_FLAGS -j${N})
  set(ctest_test_args ${ctest_test_args} PARALLEL_LEVEL ${N})
  set(CMAKE_MAKE_PROGRAM "${CMAKE_MAKE_PROGRAM} -j ${N}")      
endif()
message("cmake make program" ${CMAKE_MAKE_PROGRAM})

Thank you very much.

Solution

Via setting the CMAKE_MAKE_PROGRAM variable you want to affect the build process. But:

This variable affects only the build via cmake --build, not on native tool (make) call:

The CMAKE_MAKE_PROGRAM variable is set for use by project code. The value is also used by the cmake(1) --build and ctest(1) --build-and-test tools to launch the native build process.
This variable should be a CACHEd one. It is used in such way by make-like generators:

These generators store CMAKE_MAKE_PROGRAM in the CMake cache so that it may be edited by the user.

That is, you need to set this variable with
```
set(CMAKE_MAKE_PROGRAM <program> CACHE PATH "Path to build tool" FORCE)
```
This variable should refer to the executable itself, not to a program with arguments:

The value may be the full path to an executable or just the tool name if it is expected to be in the PATH.

That is, value "make -j 2" cannot be used for that variable (splitting arguments as list
```
set(CMAKE_MAKE_PROGRAM make -j 2 CACHE PATH "Path to build tool" FORCE)
```
wouldn't help either).

In summary, you may redefine the behavior of cmake --build calls with setting the CMAKE_MAKE_PROGRAM variable to the script, which calls make with parallel options. But you may not affect the behavior of direct make calls.