Native Windows (without WSL2)¶

Status: native Windows works for the CPU – Serial, OpenMP, the pops Python module (import pops, System, AmrSystem), DSL production (.dll, bit-identical results) and compilation of custom C++ (adc_cases.common.native). The GPU stays on WSL2 (Kokkos CUDA is not supported natively on Windows).

This page complements the WSL2 guide. WSL2 remains the simplest path and the only one that covers the GPU. The native path is useful if you want to avoid WSL2 for CPU work.

Toolchain¶

Visual Studio 2022 (MSVC, cl.exe, C++23 via /std:c++20//std:c++latest) + CMake.
LLVM/clang-cl (winget install LLVM.LLVM) only for OpenMP: MSVC keeps _OPENMP=2.0 even with /openmp:llvm, so Kokkos OpenMP (>=3.0) requires clang-cl (which reports 5.1).
Python (Miniforge recommended) + numpy, pybind11.
Any compilation at runtime (DSL production, adc_cases.common.native) launches cl/clang-cl: launch Python from an “x64 Native Tools” prompt (vcvars) to have INCLUDE/LIB.

Kokkos as a shared DLL (key to the native path)¶

The DSL and adc_cases.common.native generate a .dll that shares the Kokkos runtime of the _pops module: you therefore need Kokkos as a shared library (a single runtime, otherwise double-singleton -> crash). MSVC does not export the Kokkos symbols by default -> use WINDOWS_EXPORT_ALL_SYMBOLS:

:: Serial (CPU sequentiel) -- compilateur cl
cmake -S kokkos -B build-kokkos -G "Visual Studio 17 2022" -A x64 ^
  -DKokkos_ENABLE_SERIAL=ON -DBUILD_SHARED_LIBS=ON -DCMAKE_WINDOWS_EXPORT_ALL_SYMBOLS=ON ^
  -DCMAKE_INSTALL_PREFIX=kokkos-shared
cmake --build build-kokkos --config Release --target install

:: + OpenMP (CPU parallele) -- compilateur clang-cl (dans un invite vcvars), generateur Ninja
cmake -S kokkos -B build-omp -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_CXX_COMPILER=clang-cl ^
  -DKokkos_ENABLE_SERIAL=ON -DKokkos_ENABLE_OPENMP=ON ^
  -DBUILD_SHARED_LIBS=ON -DCMAKE_WINDOWS_EXPORT_ALL_SYMBOLS=ON -DCMAKE_INSTALL_PREFIX=kokkos-omp
cmake --build build-omp --target install

kokkos*.dll must be loadable at runtime: place it next to the .pyd (Python 3.8+ no longer uses the PATH for extension dependencies) or via os.add_dll_directory(...).

Python module `_pops`¶

cmake -S adc_cpp -B build-pywin -G "Visual Studio 17 2022" -A x64 ^
  -DPOPS_BUILD_PYTHON=ON -DPOPS_USE_KOKKOS=ON -DKokkos_ROOT=...\kokkos-shared ^
  -DPython_EXECUTABLE=...\python.exe -DCMAKE_CXX_FLAGS="/DPOPS_EXPORT_BUILDING_MODULE /DNOMINMAX /bigobj"
cmake --build build-pywin --config Release --target _pops

/DPOPS_EXPORT_BUILDING_MODULE exports the System methods (__declspec(dllexport), see export.hpp) -> produces the import library _pops.lib against which the DSL .dll links. Copy _pops.cp3XX-win_amd64.pyd, _pops.lib and kokkos*.dll next to python/pops/.

import pops
pops.doctor()
print(pops.parallel_info())

DSL production (`.dll`) and `adc_cases`¶

pops.compile(case, backend=Production()) compiles a .dll (cl/clang-cl, /LD, linked to kokkoscore.lib + _pops.lib) that the bound runtime loads (LoadLibraryW) – no Unix RTLD_GLOBAL, the _pops symbols are resolved at link time via _pops.lib. Validated bit-identical to the brick path. adc_cases.common.native.build_shared produces standalone .dll files (ctypes) in the same way.

Warning: The custom .cpp files of the cases must export their entry points as __declspec(dllexport) on Windows (extern "C" alone does not export under /LD).

Notable differences vs Linux¶

Topic	Linux/WSL2	Native Windows
Dynamic loading	`dlopen`/`RTLD_GLOBAL`	`LoadLibraryW` + import library (`_pops.lib`)
Kokkos cross-`.dll`	symbols via `RTLD_GLOBAL`	Kokkos as a shared DLL (`WINDOWS_EXPORT_ALL_SYMBOLS`)
OpenMP	gcc/clang `-fopenmp`	clang-cl (MSVC `_OPENMP` capped at 2.0)
DSL compilation at runtime	g++/clang on the `PATH`	`cl`/`clang-cl` -> vcvars env required
GPU CUDA	yes (WSL2, sm_86)	no (Kokkos CUDA not supported natively) -> use WSL2

Limitations¶

Native CUDA GPU: not available (Kokkos has no native CUDA support on Windows – neither VS+CUDA, nor nvcc-as-CXX for lack of a Windows nvcc_wrapper). The GPU goes through WSL2. CMake refuses this combination early: configuring with Kokkos_ENABLE_CUDA=ON on Windows stops at a fatal error pointing to WSL2 (no broken half-build deep in the Kokkos configure). Refs ADC-168.
CMake industrialization (shared Kokkos option, install of the import libs, clang-cl presets) to finalize so that these builds are reproducible from a single command.