Suspend master CMake when using ExternalProject - cmake

Question

I use ExternalProject in my CMakeLists.txt as follows:
include(ExternalProject)
ExternalProject_Add(eigen_build
SOURCE_DIR ${PROJECT_SOURCE_DIR}/${EIGEN_DIR}
# CONFIGURE_COMMAND cmake
CMAKE_ARGS
-DCMAKE_INSTALL_PREFIX=${CATKIN_DEVEL_PREFIX}
-DCMAKE_BUILD_TYPE:STRING=Release
)
This works fine when building on a PC, but when building on a resource-limited target with cmake -j8, having two active make instances with 8 tasks each causes the build to often fail with out of memory conditions.
One workaround I have tried is:
# Find out host architecture
execute_process(COMMAND
dpkg-architecture
-qDEB_HOST_ARCH
OUTPUT_VARIABLE
CMAKE_DEB_HOST_ARCH
OUTPUT_STRIP_TRAILING_WHITESPACE
)
# If we are building on arm64 then limit subprocesses to 2
if(${CMAKE_DEB_HOST_ARCH} MATCHES "arm64")
set(NUM_SUB_PROCESSES 2)
else()
set(NUM_SUB_PROCESSES 8)
endif()
message("Building library with ${NUM_SUB_PROCESSES} subprocess(es)")
include(ExternalProject)
ExternalProject_Add(eigen_build
SOURCE_DIR ${PROJECT_SOURCE_DIR}/${EIGEN_DIR}
# CONFIGURE_COMMAND cmake
CMAKE_ARGS
-DCMAKE_INSTALL_PREFIX=${CATKIN_DEVEL_PREFIX}
-DCMAKE_BUILD_TYPE:STRING=Release
BUILD_COMMAND make -j${NUM_SUB_PROCESSES}
INSTALL_COMMAND make install -j${NUM_SUB_PROCESSES}
)
This appears to work, but there is still perhaps a risk of occasional failure, plus it makes the sub-build really slow resulting in other tasks wait on completion; building the target separately is of course a manual workaround. However, ideally I would like some option to suspend all parent tasks while this ExternalProject is building; is there some way to do this? (Note, I cannot easily fiddle with dependencies as this is just one small part of a 100+ module build system)

Answer 1

When using a Makefile generator you should try to use the load option -l to limit the number of jobs instead of using the jobs number -j (RTFM ;) )
ref: https://www.gnu.org/software/make/manual/make.html#Parallel