Utilities

Detailed Description

Miscellaneous helpers used throughout the mpi library.

The most user-facing entries are:

• mpi::check_mpi_call: thin wrapper that turns a non-MPI_SUCCESS return code into a std::runtime_error. Used internally by every direct MPI C-API call in the library.
• mpi::chunk and mpi::chunk_length: split a range across the processes of a communicator as evenly as possible. mpi::chunk returns the slice assigned to the calling rank; mpi::chunk_length is the integer-range variant with an optional min_size granularity.
• mpi::MPICompatibleRange: concept that holds for contiguous, sized ranges whose value type satisfies mpi::has_mpi_type. This is what enables the fast paths in the generic range communication functions.

Concepts
concept	mpi::MPICompatibleRange
	A concept that checks if a range type is contiguous and sized and has an MPI compatible value type.

Functions
void	mpi::check_mpi_call (int errcode, const std::string &mpi_routine)
	Check the success of an MPI call.
template<typename R>
auto	mpi::chunk (R &&rg, communicator c={})
	Divide a given range as evenly as possible across the MPI processes in a communicator.
long	mpi::chunk_length (long end, int n, int i, long min_size=1)
	Get the length of the ith subrange after splitting the integer range [0, end) as evenly as possible across n subranges.

Function Documentation

check_mpi_call()

void mpi::check_mpi_call ( int errcode, const std::string & mpi_routine )

inline

#include <mpi/utils.hpp>

Check the success of an MPI call.

It checks if the given error code returned by an MPI routine is equal to MPI_SUCCESS. If it isn't, it throws an exception.

Note

MPI routines only return an error code if the error handler is set to MPI_ERRORS_RETURN. By default, it uses MPI_ERRORS_ARE_FATAL, which aborts the program in case of an error.

Parameters

errcode	Error code returned by an MPI routine.
mpi_routine	Name of the MPI routine used in the error message.

Definition at line 48 of file utils.hpp.

chunk()

template<typename R>

auto mpi::chunk ( R && rg, communicator c = {} )

nodiscard

#include <mpi/chunk.hpp>

Divide a given range as evenly as possible across the MPI processes in a communicator.

It calculates the subrange assigned to the calling process based on its rank in the given communicator and returns it as a slice of the original range.

Template Parameters

R	Range type.

Parameters

rg	Range to divide.
c	mpi::communicator.

Returns

An itertools::sliced range assigned to the calling process.

Definition at line 71 of file chunk.hpp.

chunk_length()

long mpi::chunk_length ( long end, int n, int i, long min_size = 1 )

inlinenodiscard

#include <mpi/chunk.hpp>

Get the length of the i^th subrange after splitting the integer range [0, end) as evenly as possible across n subranges.

The optional parameter min_size can be used to first divide the range into equal parts of size min_size before distributing them as evenly as possible across the number of specified subranges.

It is expected that min_size > 0 and that min_size is a divisor of end.

Parameters

end	End of the integer range [0, end).
n	Number of subranges.
i	Index of the subrange of interest.
min_size	Minimum size of the subranges.

Returns

Length of the i^th subrange.

Definition at line 54 of file chunk.hpp.