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 4.5. Gather
Chris@16: #ifndef BOOST_MPI_GATHER_HPP
Chris@16: #define BOOST_MPI_GATHER_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 gathering at the root for a type that has an associated MPI
Chris@16:   // datatype, so we'll use MPI_Gather to do all of the work.
Chris@16:   template<typename T>
Chris@16:   void
Chris@16:   gather_impl(const communicator& comm, const T* in_values, int n, 
Chris@16:               T* out_values, int root, mpl::true_)
Chris@16:   {
Chris@16:     MPI_Datatype type = get_mpi_datatype<T>(*in_values);
Chris@16:     BOOST_MPI_CHECK_RESULT(MPI_Gather,
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 gathering from a non-root for a type that has an associated MPI
Chris@16:   // datatype, so we'll use MPI_Gather to do all of the work.
Chris@16:   template<typename T>
Chris@16:   void
Chris@16:   gather_impl(const communicator& comm, const T* in_values, int n, int root, 
Chris@16:               mpl::true_)
Chris@16:   {
Chris@16:     MPI_Datatype type = get_mpi_datatype<T>(*in_values);
Chris@16:     BOOST_MPI_CHECK_RESULT(MPI_Gather,
Chris@16:                            (const_cast<T*>(in_values), n, type,
Chris@16:                             0, n, type, root, comm));
Chris@16:   }
Chris@16: 
Chris@16:   // We're gathering at 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_Gather, 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:   gather_impl(const communicator& comm, const T* in_values, int n, 
Chris@16:               T* out_values, 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 src = 0; src < size; ++src) {
Chris@16:       if (src == root)
Chris@16:         std::copy(in_values, in_values + n, out_values + n * src);
Chris@16:       else
Chris@16:         comm.recv(src, tag, out_values + n * src, n);
Chris@16:     }
Chris@16:   }
Chris@16: 
Chris@16:   // We're gathering at a non-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_Gather, 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:   gather_impl(const communicator& comm, const T* in_values, int n, int root, 
Chris@16:               mpl::false_)
Chris@16:   {
Chris@16:     int tag = environment::collectives_tag();
Chris@16:     comm.send(root, tag, in_values, n);
Chris@16:   }
Chris@16: } // end namespace detail
Chris@16: 
Chris@16: template<typename T>
Chris@16: void
Chris@16: gather(const communicator& comm, const T& in_value, T* out_values, int root)
Chris@16: {
Chris@16:   if (comm.rank() == root)
Chris@16:     detail::gather_impl(comm, &in_value, 1, out_values, root, 
Chris@16:                         is_mpi_datatype<T>());
Chris@16:   else
Chris@16:     detail::gather_impl(comm, &in_value, 1, root, is_mpi_datatype<T>());
Chris@16: }
Chris@16: 
Chris@16: template<typename T>
Chris@16: void gather(const communicator& comm, const T& in_value, int root)
Chris@16: {
Chris@16:   BOOST_ASSERT(comm.rank() != root);
Chris@16:   detail::gather_impl(comm, &in_value, 1, root, is_mpi_datatype<T>());
Chris@16: }
Chris@16: 
Chris@16: template<typename T>
Chris@16: void
Chris@16: gather(const communicator& comm, const T& in_value, std::vector<T>& out_values,
Chris@16:        int root)
Chris@16: {
Chris@16:   if (comm.rank() == root) {
Chris@16:     out_values.resize(comm.size());
Chris@16:     ::boost::mpi::gather(comm, in_value, &out_values[0], root);
Chris@16:   } else {
Chris@16:     ::boost::mpi::gather(comm, in_value, root);
Chris@16:   }
Chris@16: }
Chris@16: 
Chris@16: template<typename T>
Chris@16: void
Chris@16: gather(const communicator& comm, const T* in_values, int n, T* out_values, 
Chris@16:        int root)
Chris@16: {
Chris@16:   if (comm.rank() == root)
Chris@16:     detail::gather_impl(comm, in_values, n, out_values, root, 
Chris@16:                         is_mpi_datatype<T>());
Chris@16:   else
Chris@16:     detail::gather_impl(comm, in_values, n, root, is_mpi_datatype<T>());
Chris@16: }
Chris@16: 
Chris@16: template<typename T>
Chris@16: void
Chris@16: gather(const communicator& comm, const T* in_values, int n, 
Chris@16:        std::vector<T>& out_values, int root)
Chris@16: {
Chris@16:   if (comm.rank() == root) {
Chris@16:     out_values.resize(comm.size() * n);
Chris@16:     ::boost::mpi::gather(comm, in_values, n, &out_values[0], root);
Chris@16:   } 
Chris@16:   else
Chris@16:     ::boost::mpi::gather(comm, in_values, n, root);
Chris@16: }
Chris@16: 
Chris@16: template<typename T>
Chris@16: void gather(const communicator& comm, const T* in_values, int n, int root)
Chris@16: {
Chris@16:   BOOST_ASSERT(comm.rank() != root);
Chris@16:   detail::gather_impl(comm, in_values, n, root, is_mpi_datatype<T>());
Chris@16: }
Chris@16: 
Chris@16: 
Chris@16: } } // end namespace boost::mpi
Chris@16: 
Chris@16: #endif // BOOST_MPI_GATHER_HPP