154 lines
5.0 KiB
Plaintext
154 lines
5.0 KiB
Plaintext
// Copyright (C) 2005, 2006 Douglas Gregor.
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// Use, modification and distribution is subject to the Boost Software
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// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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// Message Passing Interface 1.1 -- Section 4.8. All-to-all
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#ifndef BOOST_MPI_ALL_TO_ALL_HPP
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#define BOOST_MPI_ALL_TO_ALL_HPP
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#include <boost/mpi/exception.hpp>
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#include <boost/mpi/datatype.hpp>
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#include <vector>
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#include <boost/mpi/packed_oarchive.hpp>
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#include <boost/mpi/packed_iarchive.hpp>
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#include <boost/mpi/communicator.hpp>
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#include <boost/mpi/environment.hpp>
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#include <boost/assert.hpp>
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#include <boost/mpi/collectives_fwd.hpp>
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#include <boost/mpi/allocator.hpp>
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namespace boost { namespace mpi {
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namespace detail {
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// We're performaing an all-to-all with a type that has an
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// associated MPI datatype, so we'll use MPI_Alltoall to do all of
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// the work.
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template<typename T>
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void
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all_to_all_impl(const communicator& comm, const T* in_values, int n,
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T* out_values, mpl::true_)
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{
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MPI_Datatype type = get_mpi_datatype<T>(*in_values);
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BOOST_MPI_CHECK_RESULT(MPI_Alltoall,
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(const_cast<T*>(in_values), n, type,
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out_values, n, type, comm));
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}
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// We're performing an all-to-all with a type that does not have an
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// associated MPI datatype, so we'll need to serialize
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// it. Unfortunately, this means that we cannot use MPI_Alltoall, so
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// we'll just have to send individual messages to the other
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// processes.
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template<typename T>
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void
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all_to_all_impl(const communicator& comm, const T* in_values, int n,
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T* out_values, mpl::false_)
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{
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int size = comm.size();
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int rank = comm.rank();
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// The amount of data to be sent to each process
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std::vector<int> send_sizes(size);
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// The displacements for each outgoing value.
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std::vector<int> send_disps(size);
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// The buffer that will store all of the outgoing values
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std::vector<char, allocator<char> > outgoing;
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// Pack the buffer with all of the outgoing values.
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for (int dest = 0; dest < size; ++dest) {
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// Keep track of the displacements
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send_disps[dest] = outgoing.size();
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// Our own value will never be transmitted, so don't pack it.
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if (dest != rank) {
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packed_oarchive oa(comm, outgoing);
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for (int i = 0; i < n; ++i)
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oa << in_values[dest * n + i];
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}
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// Keep track of the sizes
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send_sizes[dest] = outgoing.size() - send_disps[dest];
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}
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// Determine how much data each process will receive.
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std::vector<int> recv_sizes(size);
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all_to_all(comm, send_sizes, recv_sizes);
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// Prepare a buffer to receive the incoming data.
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std::vector<int> recv_disps(size);
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int sum = 0;
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for (int src = 0; src < size; ++src) {
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recv_disps[src] = sum;
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sum += recv_sizes[src];
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}
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std::vector<char, allocator<char> > incoming(sum > 0? sum : 1);
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// Make sure we don't try to reference an empty vector
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if (outgoing.empty())
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outgoing.push_back(0);
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// Transmit the actual data
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BOOST_MPI_CHECK_RESULT(MPI_Alltoallv,
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(&outgoing[0], &send_sizes[0],
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&send_disps[0], MPI_PACKED,
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&incoming[0], &recv_sizes[0],
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&recv_disps[0], MPI_PACKED,
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comm));
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// Deserialize data from the iarchive
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for (int src = 0; src < size; ++src) {
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if (src == rank)
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std::copy(in_values + src * n, in_values + (src + 1) * n,
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out_values + src * n);
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else {
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packed_iarchive ia(comm, incoming, boost::archive::no_header,
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recv_disps[src]);
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for (int i = 0; i < n; ++i)
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ia >> out_values[src * n + i];
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}
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}
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}
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} // end namespace detail
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template<typename T>
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inline void
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all_to_all(const communicator& comm, const T* in_values, T* out_values)
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{
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detail::all_to_all_impl(comm, in_values, 1, out_values, is_mpi_datatype<T>());
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}
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template<typename T>
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void
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all_to_all(const communicator& comm, const std::vector<T>& in_values,
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std::vector<T>& out_values)
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{
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BOOST_ASSERT((int)in_values.size() == comm.size());
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out_values.resize(comm.size());
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::boost::mpi::all_to_all(comm, &in_values[0], &out_values[0]);
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}
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template<typename T>
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inline void
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all_to_all(const communicator& comm, const T* in_values, int n, T* out_values)
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{
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detail::all_to_all_impl(comm, in_values, n, out_values, is_mpi_datatype<T>());
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}
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template<typename T>
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void
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all_to_all(const communicator& comm, const std::vector<T>& in_values, int n,
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std::vector<T>& out_values)
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{
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BOOST_ASSERT((int)in_values.size() == comm.size() * n);
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out_values.resize(comm.size() * n);
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::boost::mpi::all_to_all(comm, &in_values[0], n, &out_values[0]);
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}
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} } // end namespace boost::mpi
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#endif // BOOST_MPI_ALL_TO_ALL_HPP
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