Chris@16: // Copyright (C) 2005, 2006 Douglas Gregor.
Chris@16: 
Chris@16: // Use, modification and distribution is subject to the Boost Software
Chris@16: // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
Chris@16: // http://www.boost.org/LICENSE_1_0.txt)
Chris@16: 
Chris@16: // Message Passing Interface 1.1 -- Section 4.6. Scatter
Chris@16: #ifndef BOOST_MPI_SCATTER_HPP
Chris@16: #define BOOST_MPI_SCATTER_HPP
Chris@16: 
Chris@16: #include <boost/mpi/exception.hpp>
Chris@16: #include <boost/mpi/datatype.hpp>
Chris@16: #include <vector>
Chris@16: #include <boost/mpi/packed_oarchive.hpp>
Chris@16: #include <boost/mpi/packed_iarchive.hpp>
Chris@16: #include <boost/mpi/detail/point_to_point.hpp>
Chris@16: #include <boost/mpi/communicator.hpp>
Chris@16: #include <boost/mpi/environment.hpp>
Chris@16: #include <boost/assert.hpp>
Chris@16: 
Chris@16: namespace boost { namespace mpi {
Chris@16: 
Chris@16: namespace detail {
Chris@16:   // We're scattering from the root for a type that has an associated MPI
Chris@16:   // datatype, so we'll use MPI_Scatter to do all of the work.
Chris@16:   template<typename T>
Chris@16:   void
Chris@16:   scatter_impl(const communicator& comm, const T* in_values, T* out_values, 
Chris@16:                int n, int root, mpl::true_)
Chris@16:   {
Chris@16:     MPI_Datatype type = get_mpi_datatype<T>(*in_values);
Chris@16:     BOOST_MPI_CHECK_RESULT(MPI_Scatter,
Chris@16:                            (const_cast<T*>(in_values), n, type,
Chris@16:                             out_values, n, type, root, comm));
Chris@16:   }
Chris@16: 
Chris@16:   // We're scattering from a non-root for a type that has an associated MPI
Chris@16:   // datatype, so we'll use MPI_Scatter to do all of the work.
Chris@16:   template<typename T>
Chris@16:   void
Chris@16:   scatter_impl(const communicator& comm, T* out_values, int n, int root, 
Chris@16:                mpl::true_)
Chris@16:   {
Chris@16:     MPI_Datatype type = get_mpi_datatype<T>(*out_values);
Chris@16:     BOOST_MPI_CHECK_RESULT(MPI_Scatter,
Chris@16:                            (0, n, type,
Chris@16:                             out_values, n, type,
Chris@16:                             root, comm));
Chris@16:   }
Chris@16: 
Chris@16:   // We're scattering from the root for a type that does not have an
Chris@16:   // associated MPI datatype, so we'll need to serialize
Chris@16:   // it. Unfortunately, this means that we cannot use MPI_Scatter, so
Chris@16:   // we'll just have the root send individual messages to the other
Chris@16:   // processes.
Chris@16:   template<typename T>
Chris@16:   void
Chris@16:   scatter_impl(const communicator& comm, const T* in_values, T* out_values, 
Chris@16:                int n, int root, mpl::false_)
Chris@16:   {
Chris@16:     int tag = environment::collectives_tag();
Chris@16:     int size = comm.size();
Chris@16: 
Chris@16:     for (int dest = 0; dest < size; ++dest) {
Chris@16:       if (dest == root) {
Chris@16:         // Our own values will never be transmitted: just copy them.
Chris@16:         std::copy(in_values + dest * n, in_values + (dest + 1) * n, out_values);
Chris@16:       } else {
Chris@16:         // Send archive
Chris@16:         packed_oarchive oa(comm);
Chris@16:         for (int i = 0; i < n; ++i)
Chris@16:           oa << in_values[dest * n + i];
Chris@16:         detail::packed_archive_send(comm, dest, tag, oa);
Chris@16:       }
Chris@16:     }
Chris@16:   }
Chris@16: 
Chris@16:   // We're scattering to a non-root for a type that does not have an
Chris@16:   // associated MPI datatype, so we'll need to de-serialize
Chris@16:   // it. Unfortunately, this means that we cannot use MPI_Scatter, so
Chris@16:   // we'll just have all of the non-root nodes send individual
Chris@16:   // messages to the root.
Chris@16:   template<typename T>
Chris@16:   void
Chris@16:   scatter_impl(const communicator& comm, T* out_values, int n, int root, 
Chris@16:                mpl::false_)
Chris@16:   {
Chris@16:     int tag = environment::collectives_tag();
Chris@16: 
Chris@16:     packed_iarchive ia(comm);
Chris@16:     MPI_Status status;
Chris@16:     detail::packed_archive_recv(comm, root, tag, ia, status);
Chris@16:     for (int i = 0; i < n; ++i)
Chris@16:       ia >> out_values[i];
Chris@16:   }
Chris@16: } // end namespace detail
Chris@16: 
Chris@16: template<typename T>
Chris@16: void
Chris@16: scatter(const communicator& comm, const T* in_values, T& out_value, int root)
Chris@16: {
Chris@16:   if (comm.rank() == root)
Chris@16:     detail::scatter_impl(comm, in_values, &out_value, 1, root, 
Chris@16:                          is_mpi_datatype<T>());
Chris@16:   else
Chris@16:     detail::scatter_impl(comm, &out_value, 1, root, is_mpi_datatype<T>());
Chris@16: }
Chris@16: 
Chris@16: template<typename T>
Chris@16: void
Chris@16: scatter(const communicator& comm, const std::vector<T>& in_values, T& out_value,
Chris@16:         int root)
Chris@16: {
Chris@16:   if (comm.rank() == root)
Chris@16:     ::boost::mpi::scatter<T>(comm, &in_values[0], out_value, root);
Chris@16:   else
Chris@16:     ::boost::mpi::scatter<T>(comm, static_cast<const T*>(0), out_value, 
Chris@16:                              root);
Chris@16: }
Chris@16: 
Chris@16: template<typename T>
Chris@16: void scatter(const communicator& comm, T& out_value, int root)
Chris@16: {
Chris@16:   BOOST_ASSERT(comm.rank() != root);
Chris@16:   detail::scatter_impl(comm, &out_value, 1, root, is_mpi_datatype<T>());
Chris@16: }
Chris@16: 
Chris@16: template<typename T>
Chris@16: void
Chris@16: scatter(const communicator& comm, const T* in_values, T* out_values, int n,
Chris@16:         int root)
Chris@16: {
Chris@16:   if (comm.rank() == root)
Chris@16:     detail::scatter_impl(comm, in_values, out_values, n, root,
Chris@16:                          is_mpi_datatype<T>());
Chris@16:   else
Chris@16:     detail::scatter_impl(comm, out_values, n, root, is_mpi_datatype<T>());
Chris@16: }
Chris@16: 
Chris@16: template<typename T>
Chris@16: void
Chris@16: scatter(const communicator& comm, const std::vector<T>& in_values, 
Chris@16:         T* out_values, int n, int root)
Chris@16: {
Chris@16:   if (comm.rank() == root)
Chris@16:     ::boost::mpi::scatter(comm, &in_values[0], out_values, n, root);
Chris@16:   else
Chris@16:     ::boost::mpi::scatter(comm, static_cast<const T*>(0), out_values, 
Chris@16:                                     n, root);
Chris@16: }
Chris@16: 
Chris@16: template<typename T>
Chris@16: void scatter(const communicator& comm, T* out_values, int n, int root)
Chris@16: {
Chris@16:   BOOST_ASSERT(comm.rank() != root);
Chris@16:   detail::scatter_impl(comm, out_values, n, root, is_mpi_datatype<T>());
Chris@16: }
Chris@16: 
Chris@16: } } // end namespace boost::mpi
Chris@16: 
Chris@16: #endif // BOOST_MPI_SCATTER_HPP