broadcast.hpp

#include <boost/mpi.hpp>

/*
 * Example how boost::mpi::broadcast could be implemented efficiently for types
 * that need to be serialized, without falling back to Point-to-Point communication
 *
 * Lorenz Hübschle-Schneider, 2015
 * Distributed under the Boost Software License, Version 1.0
 */

template <typename T>    
void broadcast(const boost::mpi::communicator &comm, std::vector<T> &data, int root) {
    if (comm.size() < 2) return;
    if (boost::mpi::is_mpi_datatype<T>()) {
        // Use existing behaviour
        boost::mpi::broadcast(comm, data, root);
    } else {
        // Boost.MPI doesn't use MPI_Bcast for types it doesn't know.
        // Therefore, we need to do the archive broadcast ourselves.
        if (comm.rank() == root) {
            // Serialize data
            boost:mpi::packed_oarchive oa(comm);
            oa << data;
            // Broadcast archive size
            size_t archive_size = oa.size();
            boost:mpi::broadcast<size_t>(comm, archive_size, root);
            // Broadcast archive data
            auto sendptr = const_cast<void*>(oa.address());
            MPI_Bcast(sendptr, archive_size, MPI_PACKED, root, comm);
        } else {
            // Receive archive size and allocate space
            size_t archive_size;
            boost::mpi::broadcast<size_t>(comm, archive_size, root);
            boost::mpi::packed_iarchive ia(comm);
            ia.resize(archive_size);
            // Receive broadcast archive data
            auto recvptr = ia.address();
            MPI_Bcast(recvptr, archive_size, MPI_PACKED, root, comm);
            // Unpack received data
            ia >> data;
        }
    }
}