macOS OpenMP build failure

[mdmeeker]

• On macOS on Apple Silicon
• Homebrew OpenMP
• Built PyKokkos from source, main branch

When @pk.workunit is invoked, the JIT compiler calls find_package(Kokkos) which loads KokkosConfig.cmake which then calls

FIND_DEPENDENCY(OpenMP REQUIRED COMPONENTS CXX)

Apple Clang/CMake cannot find OpenMP though and so fails with

Could NOT find OpenMP_CXX (missing: OpenMP_CXX_FLAGS OpenMP_CXX_LIB_NAMES)

User must therefore set CPATH and LIBRARY_PATH. My current hack is to activate my uv venv with

SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"

if [ ! -d "$SCRIPT_DIR/.venv" ]; then
    echo "Error: .venv not found. Run 'make setup' first."
    return 1 2>/dev/null || exit 1
fi

source "$SCRIPT_DIR/.venv/bin/activate"

if [ "$(uname)" = "Darwin" ]; then
    OMP_PREFIX="$(brew --prefix libomp 2>/dev/null)"
    if [ -n "$OMP_PREFIX" ]; then
        export CPATH="${OMP_PREFIX}/include${CPATH:+:$CPATH}"
        export LIBRARY_PATH="${OMP_PREFIX}/lib${LIBRARY_PATH:+:$LIBRARY_PATH}"
    fi
fi

[JBludau]

yeah, this is a general problem with Apple and comes from homebrew not adding openmp to the standard paths. Thus I would say this is on whoever maintains the system this is running on.
What we could do however, is put a note into our docs saying that we know this can be an issue and this is where it comes from

[mdmeeker]

pykokkos/pykokkos/core/cpp_setup.py

Lines 239 to 248 in 58fe485

	cmake_args = [
	f"-DMODULE_NAME={module_name}",
	f"-DKokkos_ROOT={lib_path.parent.resolve()}",
	f"-DPK_EXEC_SPACE={space_value}",
	f"-DPK_ARG_MEMSPACE={view_space}",
	f"-DPK_ARG_LAYOUT={view_layout}",
	f"-DPK_REAL={precision}",
	f"-DLIB_SUFFIX={lib_suffix}",
	f"-DPython3_EXECUTABLE={sys.executable}",
	]

Maybe there would be a sort of combinatorial explosion, but would it be sensible to eg. have this branch on platform-specific info?

[JBludau]

Hmm I don't think we would want that. Even though homebrew is pretty widespread, I don't tink we should assume something about the configuration of a particular system.