Tiny updates from experience building on Mac (#2894)

Co-authored-by: Paul Romano <paul.k.romano@gmail.com>

CMakeLists.txt

@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.10 FATAL_ERROR)
-project(openmc C CXX)
+project(openmc CXX)
 
 # Set version numbers
 set(OPENMC_VERSION_MAJOR 0)
@@ -80,6 +80,14 @@ if(NOT CMAKE_BUILD_TYPE)
     set(CMAKE_BUILD_TYPE RelWithDebInfo CACHE STRING "Choose the type of build" FORCE)
 endif()
 
+#===============================================================================
+# OpenMP for shared-memory parallelism (and GPU support some day!)
+#===============================================================================
+
+if(OPENMC_USE_OPENMP)
+  find_package(OpenMP REQUIRED)
+endif()
+
 #===============================================================================
 # MPI for distributed-memory parallelism
 #===============================================================================
@@ -192,13 +200,6 @@ endif()
 # Skip for Visual Studio which has its own configurations through GUI
 if(NOT MSVC)
 
-if(OPENMC_USE_OPENMP)
-  find_package(OpenMP REQUIRED)
-  # In CMake 3.9+, can use the OpenMP::OpenMP_CXX imported target
-  list(APPEND cxxflags ${OpenMP_CXX_FLAGS})
-  list(APPEND ldflags ${OpenMP_CXX_FLAGS})
-endif()
-
 set(CMAKE_POSITION_INDEPENDENT_CODE ON)
 
 if(OPENMC_ENABLE_PROFILE)
@@ -522,6 +523,10 @@ if (PNG_FOUND)
   target_link_libraries(libopenmc PNG::PNG)
 endif()
 
+if (OPENMC_USE_OPENMP)
+  target_link_libraries(libopenmc OpenMP::OpenMP_CXX)
+endif()
+
 if (OPENMC_USE_MPI)
   target_link_libraries(libopenmc MPI::MPI_CXX)
 endif()

cmake/OpenMCConfig.cmake.in

@@ -31,6 +31,10 @@ if(@OPENMC_USE_MPI@)
   find_package(MPI REQUIRED)
 endif()
 
+if(@OPENMC_USE_OPENMP@)
+  find_package(OpenMP REQUIRED)
+endif()
+
 if(@OPENMC_USE_MCPL@)
   find_package(MCPL REQUIRED)
 endif()

docs/source/quickinstall.rst

@@ -107,31 +107,54 @@ can be used to access the installed packages.
 .. _Spack: https://spack.readthedocs.io/en/latest/
 .. _setup guide: https://spack.readthedocs.io/en/latest/getting_started.html
 
---------------------------------
-Installing from Source on Ubuntu
---------------------------------
+-------------------------------
+Manually Installing from Source
+-------------------------------
 
-To build OpenMC from source, several :ref:`prerequisites <prerequisites>` are
-needed. If you are using Ubuntu or higher, all prerequisites can be installed
-directly from the package manager:
+Obtaining prerequisites on Ubuntu
+---------------------------------
+
+When building OpenMC from source, all :ref:`prerequisites <prerequisites>` can
+be installed using the package manager:
 
 .. code-block:: sh
 
     sudo apt install g++ cmake libhdf5-dev libpng-dev
 
-After the packages have been installed, follow the instructions below for
-building and installing OpenMC from source.
+After the packages have been installed, follow the instructions to build from
+source below.
 
--------------------------------------------
-Installing from Source on Linux or Mac OS X
--------------------------------------------
+Obtaining prerequisites on macOS
+--------------------------------
+
+For an OpenMC build with multithreading enabled, a package manager like
+`Homebrew <https://brew.sh>`_ should first be installed. Then, the following
+packages should be installed, for example in Homebrew via:
+
+.. code-block:: sh
+
+   brew install llvm cmake xtensor hdf5 python libomp libpng
+
+The compiler provided by the above LLVM package should be used in place of the
+one provisioned by XCode, which does not support the multithreading library used
+by OpenMC. Consequently, the C++ compiler should explicitly be set before
+proceeding:
+
+.. code-block:: sh
+
+   export CXX=/opt/homebrew/opt/llvm/bin/clang++
+
+After the packages have been installed, follow the instructions to build from
+source below.
+
+Building Source on Linux or macOS
+---------------------------------
 
 All OpenMC source code is hosted on `GitHub
 <https://github.com/openmc-dev/openmc>`_. If you have `git
-<https://git-scm.com>`_, the `gcc <https://gcc.gnu.org/>`_ compiler suite,
-`CMake <https://cmake.org>`_, and `HDF5
-<https://www.hdfgroup.org/solutions/hdf5/>`_ installed, you can download and
-install OpenMC be entering the following commands in a terminal:
+<https://git-scm.com>`_, a modern C++ compiler, `CMake <https://cmake.org>`_,
+and `HDF5 <https://www.hdfgroup.org/solutions/hdf5/>`_ installed, you can
+download and install OpenMC by entering the following commands in a terminal:
 
 .. code-block:: sh
 
@@ -151,14 +174,14 @@ should specify an installation directory where you have write access, e.g.
     cmake -DCMAKE_INSTALL_PREFIX=$HOME/.local ..
 
 The :mod:`openmc` Python package must be installed separately. The easiest way
-to install it is using `pip <https://pip.pypa.io/en/stable/>`_, which is
-included by default in Python 3.4+. From the root directory of the OpenMC
-distribution/repository, run:
+to install it is using `pip <https://pip.pypa.io/en/stable/>`_.
+From the root directory of the OpenMC repository, run:
 
 .. code-block:: sh
 
     python -m pip install .
 
-If you want to build a parallel version of OpenMC (using OpenMP or MPI),
-directions can be found in the :ref:`detailed installation instructions
+By default, OpenMC will be built with multithreading support. To build
+distributed-memory parallel versions of OpenMC using MPI or to configure other
+options, directions can be found in the :ref:`detailed installation instructions
 <usersguide_build>`.

docs/source/usersguide/install.rst

@@ -464,11 +464,11 @@ can typically be set for a single command, i.e.
 
 .. _compile_linux:
 
-Compiling on Linux and Mac OS X
--------------------------------
+Compiling on Linux and macOS
+----------------------------
 
-To compile OpenMC on Linux or Max OS X, run the following commands from within
-the root directory of the source code:
+To compile OpenMC on Linux or macOS, run the following commands from within the
+root directory of the source code:
 
 .. code-block:: sh
 

examples/custom_source/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.3 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.10 FATAL_ERROR)
 project(openmc_sources CXX)
 add_library(source SHARED source_ring.cpp)
 find_package(OpenMC REQUIRED)

examples/parameterized_custom_source/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.3 FATAL_ERROR)
+cmake_minimum_required(VERSION 3.10 FATAL_ERROR)
 project(openmc_sources CXX)
 add_library(parameterized_source SHARED parameterized_source_ring.cpp)
 find_package(OpenMC REQUIRED)

openmc/data/multipole.py

@@ -1169,10 +1169,11 @@ def _evaluate(self, E, T):
         sqrtE = sqrt(E)
         invE = 1.0 / E
 
-        # Locate us.  The i_window calc omits a + 1 present in F90 because of
-        # the 1-based vs. 0-based indexing.  Similarly startw needs to be
-        # decreased by 1.  endw does not need to be decreased because
-        # range(startw, endw) does not include endw.
+        # Locate us.  The i_window calc omits a + 1 present from the legacy
+        # Fortran version of OpenMC because of the 1-based vs. 0-based
+        # indexing.  Similarly startw needs to be decreased by 1.  endw does
+        # not need to be decreased because range(startw, endw) does not include
+        # endw.
         i_window = min(self.n_windows - 1,
                        int(np.floor((sqrtE - sqrt(self.E_min)) / self.spacing)))
         startw = self.windows[i_window, 0] - 1

openmc/mgxs/mdgxs.py

@@ -20,7 +20,7 @@
     'delayed-nu-fission matrix'
 )
 
-# Maximum number of delayed groups, from src/constants.F90
+# Maximum number of delayed groups, from include/openmc/constants.h
 MAX_DELAYED_GROUPS = 8
 
 

src/nuclide.cpp

@@ -634,16 +634,23 @@ void Nuclide::calculate_xs(
       }
     }
 
-    // Ensure these values are set
-    // Note, the only time either is used is in one of 4 places:
-    // 1. physics.cpp - scatter - For inelastic scatter.
-    // 2. physics.cpp - sample_fission - For partial fissions.
-    // 3. tally.F90 - score_general - For tallying on MTxxx reactions.
-    // 4. nuclide.cpp - calculate_urr_xs - For unresolved purposes.
-    // It is worth noting that none of these occur in the resolved
-    // resonance range, so the value here does not matter.  index_temp is
-    // set to -1 to force a segfault in case a developer messes up and tries
-    // to use it with multipole.
+    /*
+     * index_temp, index_grid, and interp_factor are used only in the
+     * following places:
+     *   1. physics.cpp - scatter - For inelastic scatter.
+     *   2. physics.cpp - sample_fission - For partial fissions.
+     *   3. tallies/tally_scoring.cpp - score_general -
+     *        For tallying on MTxxx reactions.
+     *   4. nuclide.cpp - calculate_urr_xs - For unresolved purposes.
+     * It is worth noting that none of these occur in the resolved resonance
+     * range, so the value here does not matter.  index_temp is set to -1 to
+     * force a segfault in case a developer messes up and tries to use it with
+     * multipole.
+     *
+     * However, a segfault is not necessarily guaranteed with an out-of-bounds
+     * access, so this technique should be replaced by something more robust
+     * in the future.
+     */
     micro.index_temp = -1;
     micro.index_grid = -1;
     micro.interp_factor = 0.0;

src/tallies/filter_energy.cpp

@@ -3,7 +3,7 @@
 #include <fmt/core.h>
 
 #include "openmc/capi.h"
-#include "openmc/constants.h" // For F90_NONE
+#include "openmc/constants.h" // For C_NONE
 #include "openmc/mgxs_interface.h"
 #include "openmc/search.h"
 #include "openmc/settings.h"

tests/regression_tests/cpp_driver/test.py

@@ -20,7 +20,7 @@ def cpp_driver(request):
     openmc_dir = Path(str(request.config.rootdir)) / 'build'
     with open('CMakeLists.txt', 'w') as f:
         f.write(textwrap.dedent("""
-            cmake_minimum_required(VERSION 3.3 FATAL_ERROR)
+            cmake_minimum_required(VERSION 3.10 FATAL_ERROR)
             project(openmc_cpp_driver CXX)
             add_executable(cpp_driver driver.cpp)
             find_package(OpenMC REQUIRED HINTS {})

tests/regression_tests/dagmc/external/test.py

@@ -25,7 +25,7 @@ def cpp_driver(request):
     openmc_dir = Path(str(request.config.rootdir)) / 'build'
     with open('CMakeLists.txt', 'w') as f:
         f.write(textwrap.dedent("""
-            cmake_minimum_required(VERSION 3.3 FATAL_ERROR)
+            cmake_minimum_required(VERSION 3.10 FATAL_ERROR)
             project(openmc_cpp_driver CXX)
             add_executable(main main.cpp)
             find_package(OpenMC REQUIRED HINTS {})

tests/regression_tests/external_moab/test.py

@@ -32,7 +32,7 @@ def cpp_driver(request):
     openmc_dir = Path(str(request.config.rootdir)) / 'build'
     with open('CMakeLists.txt', 'w') as f:
         f.write(textwrap.dedent("""
-            cmake_minimum_required(VERSION 3.3 FATAL_ERROR)
+            cmake_minimum_required(VERSION 3.10 FATAL_ERROR)
             project(openmc_cpp_driver CXX)
             add_executable(main main.cpp)
             find_package(OpenMC REQUIRED HINTS {})

tests/regression_tests/source_dlopen/test.py

@@ -18,7 +18,7 @@ def compile_source(request):
     openmc_dir = Path(str(request.config.rootdir)) / 'build'
     with open('CMakeLists.txt', 'w') as f:
         f.write(textwrap.dedent("""
-            cmake_minimum_required(VERSION 3.3 FATAL_ERROR)
+            cmake_minimum_required(VERSION 3.10 FATAL_ERROR)
             project(openmc_sources CXX)
             add_library(source SHARED source_sampling.cpp)
             find_package(OpenMC REQUIRED HINTS {})

tests/regression_tests/source_parameterized_dlopen/test.py

@@ -18,7 +18,7 @@ def compile_source(request):
     openmc_dir = Path(str(request.config.rootdir)) / 'build'
     with open('CMakeLists.txt', 'w') as f:
         f.write(textwrap.dedent("""
-            cmake_minimum_required(VERSION 3.3 FATAL_ERROR)
+            cmake_minimum_required(VERSION 3.10 FATAL_ERROR)
             project(openmc_sources CXX)
             add_library(source SHARED parameterized_source_sampling.cpp)
             find_package(OpenMC REQUIRED HINTS {})