mpi.hpp

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#pragma once
#include <iostream>
#include <mpi.h>
 
namespace terra::mpi {
 
using MPIRank = int;
 
inline MPIRank rank()
{
    MPIRank rank;
    MPI_Comm_rank( MPI_COMM_WORLD, &rank );
    return rank;
}
 
inline int num_processes()
{
    int num_processes;
    MPI_Comm_size( MPI_COMM_WORLD, &num_processes );
    return num_processes;
}
 
inline void barrier()
{  
    MPI_Barrier(MPI_COMM_WORLD);
}
 
namespace detail {
class MPIContext
{
  public:
    MPIContext( const MPIContext& )            = delete;
    MPIContext& operator=( const MPIContext& ) = delete;
    MPIContext( MPIContext&& )                 = delete;
    MPIContext& operator=( MPIContext&& )      = delete;
 
    /// Initialize MPI once. Safe to call only once.
    static void initialize( int* argc, char*** argv ) { instance( argc, argv ); }
 
    /// Query whether MPI is initialized
    static bool is_initialized()
    {
        int flag = 0;
        MPI_Initialized( &flag );
        return flag != 0;
    }
 
    /// Query whether MPI is finalized
    static bool is_finalized()
    {
        int flag = 0;
        MPI_Finalized( &flag );
        return flag != 0;
    }
 
  private:
    bool mpi_initialized_ = false;
 
    // private constructor
    MPIContext( int* argc, char*** argv )
    {
        if ( is_initialized() )
        {
            throw std::runtime_error( "MPI already initialized!" );
        }
 
        int err = MPI_Init( argc, argv );
        if ( err != MPI_SUCCESS )
        {
            char errstr[MPI_MAX_ERROR_STRING];
            int  len = 0;
            MPI_Error_string( err, errstr, &len );
            throw std::runtime_error( std::string( "MPI_Init failed: " ) + std::string( errstr, len ) );
        }
 
        mpi_initialized_ = true;
 
        MPI_Comm_set_errhandler( MPI_COMM_WORLD, MPI_ERRORS_RETURN );
    }
 
    // private destructor
    ~MPIContext()
    {
        if ( mpi_initialized_ && !is_finalized() )
        {
            int err = MPI_Finalize();
            if ( err != MPI_SUCCESS )
            {
                char errstr[MPI_MAX_ERROR_STRING];
                int  len = 0;
                MPI_Error_string( err, errstr, &len );
                std::cerr << "[MPI] MPI_Finalize failed: " << std::string( errstr, len ) << std::endl;
            }
        }
    }
 
    // singleton instance accessor
    static MPIContext& instance( int* argc = nullptr, char*** argv = nullptr )
    {
        static MPIContext guard( argc, argv );
        return guard;
    }
};
 
} // namespace detail
 
inline std::string mpi_error_string( int err )
{
    char errstr[MPI_MAX_ERROR_STRING];
    int  len = 0;
    MPI_Error_string( err, errstr, &len );
    return { errstr, static_cast< size_t >( len ) };
}
 
template < typename T >
MPI_Datatype mpi_datatype()
{
    static_assert( sizeof( T ) == 0, "No MPI datatype mapping for this type." );
    return MPI_DATATYPE_NULL;
}
 
template <>
inline MPI_Datatype mpi_datatype< char >()
{
    return MPI_CHAR;
}
 
template <>
inline MPI_Datatype mpi_datatype< signed char >()
{
    return MPI_SIGNED_CHAR;
}
 
template <>
inline MPI_Datatype mpi_datatype< unsigned char >()
{
    return MPI_UNSIGNED_CHAR;
}
 
template <>
inline MPI_Datatype mpi_datatype< int >()
{
    return MPI_INT;
}
 
template <>
inline MPI_Datatype mpi_datatype< unsigned int >()
{
    return MPI_UNSIGNED;
}
 
template <>
inline MPI_Datatype mpi_datatype< short >()
{
    return MPI_SHORT;
}
 
template <>
inline MPI_Datatype mpi_datatype< unsigned short >()
{
    return MPI_UNSIGNED_SHORT;
}
 
template <>
inline MPI_Datatype mpi_datatype< long >()
{
    return MPI_LONG;
}
 
template <>
inline MPI_Datatype mpi_datatype< unsigned long >()
{
    return MPI_UNSIGNED_LONG;
}
 
template <>
inline MPI_Datatype mpi_datatype< long long >()
{
    return MPI_LONG_LONG;
}
 
template <>
inline MPI_Datatype mpi_datatype< unsigned long long >()
{
    return MPI_UNSIGNED_LONG_LONG;
}
 
template <>
inline MPI_Datatype mpi_datatype< float >()
{
    return MPI_FLOAT;
}
 
template <>
inline MPI_Datatype mpi_datatype< double >()
{
    return MPI_DOUBLE;
}
 
template <>
inline MPI_Datatype mpi_datatype< long double >()
{
    return MPI_LONG_DOUBLE;
}
 
template <>
inline MPI_Datatype mpi_datatype< bool >()
{
    return MPI_CXX_BOOL;
}
 
} // namespace terra::mpi