GitHub - VRGroupRWTH/mpi: Header-only C++20 wrapper for MPI 4.0.

MPI

Modern C++20 message passing interface wrapper.

Examples

Initialization:

  mpi::environment environment;
  const auto& communicator = mpi::world_communicator;

Transmitting basic types:

  std::int32_t data = 0;
  if (communicator.rank() == 0)
  {
    data = 42;
    communicator.send(data, 1);
  }
  if (communicator.rank() == 1)
  {
    communicator.receive(data, 0);
  }

Transmitting a container of basic types:

  std::vector<std::int32_t> data_container(3);
  if (communicator.rank() == 0)
  {
    data_container = {1, 2, 3};
    communicator.send(data_container, 1);
  }
  if (communicator.rank() == 1)
  {
    communicator.receive(data_container, 0);
  }

Transmitting user-defined aggregates:

  struct user_type
  {
    std::int32_t         id      ;
    std::array<float, 3> position;
  };

  user_type user_object;
  if (communicator.rank() == 0)
  {
    user_object = {42, {0.0f, 1.0f, 2.0f}};
    communicator.send(user_object, 1);
  }
  if (communicator.rank() == 1)
  {
    communicator.receive(user_object, 0);
  }

Transmitting a container of user-defined aggregates:

  std::vector<user_type> user_object_container(2);
  if (communicator.rank() == 0)
  {
    user_object_container[0] = {42, {0.0f, 1.0f, 2.0f}};
    user_object_container[1] = {84, {3.0f, 4.0f, 5.0f}};
    communicator.send(user_object_container, 1);
  }
  if (communicator.rank() == 1)
  {
    communicator.receive(user_object_container, 0);
  }

See the tests for more.

Usage Notes

Define MPI_USE_EXCEPTIONS to check the return values of all viable functions against MPI_SUCCESS and throw an exception otherwise.
Define MPI_USE_RELAXED_TRAITS to prevent the library from checking the types of aggregate elements and triggering static asserts for non-aggregates (useful for e.g. testing).
Define MPI_USE_UNSUPPORTED to enable features that are within the standard but currently not supported by major implementations (e.g. MPI_T_BIND_MPI_SESSION).
Compliant types (satisfying mpi::is_compliant) are types whose corresponding mpi::data_type can be automatically generated:
- Arithmetic types (satisfying std::is_arithmetic), enumerations (satisfying std::is_enum), specializations of std::complex are compliant types.
- C-style arrays, std::array, std::pair, std::tuple, and aggregate types (satisfying std::is_aggregate) consisting of other compliant types are also compliant types.
- If your type is none of the above, you can specialize template <> struct mpi::type_traits<TYPE> { static data_type get_data_type() { return DATA_TYPE; } }; manually.
The MPI functions accepting buffers may be used with:
- Compliant types.
- Contiguous sequential containers (i.e. std::string, std::span, std::valarray, std::vector<!bool>) of compliant types.
Extension functions (starting with MPIX) are not included as they are often implementation-specific. You can nevertheless use them with the wrapper via the native handle getters.

Design Notes

Constructors:
- Copy constructors are deleted unless MPI provides duplication functions (ending with _dup) for the object.
- Move constructors are available whenever possible.
- The object wrappers have two types of constructors:
  - Managed constructors: Construct a new MPI object, and be responsible for its destruction.
  - Unmanaged constructors: Accept an existing MPI object, and not be responsible for its destruction.
Structures:
- Structs are for POD data types. They may only contain member variables, constructors, destructors and assignment operators.
Statics:
- Namespace functions are preferred over static member functions whenever possible.

Reflection:

The data type for aggregates are created automatically through reflection.

Survey of reflection libraries:

Library	Built	Extra step	Manual	Dependencies
https://github.com/rttrorg/rttr	True	False	True	False
https://github.com/boostorg/pfr	False	False	False	False
https://github.com/apolukhin/pfr_non_boost	False	False	False	False
https://github.com/felixguendling/cista	False	False	False	False
https://github.com/veselink1/refl-cpp	False	False	True	False
https://github.com/AustinBrunkhorst/CPP-Reflection	True	True	True	True
https://github.com/billyquith/ponder	True	False	True	False
https://github.com/skypjack/meta	False	False	True	False
https://github.com/Ubpa/USRefl	False	False	True	False
https://github.com/Ubpa/UDRefl	True	False	True	False
https://github.com/garbageslam/visit_struct	False	False	True	False
https://github.com/chakaz/reflang	True	True	False	True
https://github.com/Manu343726/tinyrefl	False	True	False	False
https://github.com/Manu343726/siplasplas	True	True	False	False
https://github.com/preshing/FlexibleReflection	False	False	True	False
https://github.com/Celtoys/clReflect	True	True	True	False
https://github.com/Leandros/metareflect	False	True	True	True
https://github.com/Cylix/Reflex	False	False	True	True
https://github.com/boostorg/describe	False	False	True	True

Decided on PFR after watching https://www.youtube.com/watch?v=abdeAew3gmQ, specifically https://github.com/apolukhin/pfr_non_boost without the boost namespace.
Limitations:
- The type must be an aggregate (satisfy std::is_aggregate<type>):
  - No user-declared or inherited constructors.
  - No private or protected direct non-static data members.
  - No virtual functions.
  - No virtual, private or protected base classes.
- Additionally:
  - No const fields.
  - No references.
  - Static data members are ignored.
- See https://www.boost.org/doc/libs/1_76_0/doc/html/boost_pfr/limitations_and_configuration.html for further detail.

Constants:
- Several MPI constants are unused:
  - MPI_STATUS_IGNORE : Stati are return values and this would require void overloads for every function.
  - MPI_STATUSES_IGNORE: Stati are return values and this would require void overloads for every function.
  - MPI_ARGVS_NULL : This would require a scan over std::vector<spawn_info>::arguments() to see if they all are empty.
  - MPI_WEIGHTS_EMPTY : Prefer an empty container instead.
  - MPI_BOTTOM : Prefer nullptr instead.
  - MPI_ROOT : Unused in default arguments as intercommunicators are rarer than intracommunicators. Can nevertheless be passed to functions.
  - MPI_PROC_NULL : Unused in default arguments as intercommunicators are rarer than intracommunicators. Can nevertheless be passed to functions.
Versioning:
- The major and minor version numbers correspond to the supported MPI version, whereas the patch number is specific to the wrapper.

Coverage (list from https://www.open-mpi.org/doc/v4.1/)

Future Work

See https://github.com/acdemiralp/mpi/projects/1

Name		Name	Last commit message	Last commit date
Latest commit History 238 Commits
cmake		cmake
include/mpi		include/mpi
scripts		scripts
tests		tests
.gitignore		.gitignore
CMakeLists.txt		CMakeLists.txt
license.txt		license.txt
readme.md		readme.md

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