// 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 4.5. Gather
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#ifndef BOOST_MPI_GATHER_HPP
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#define BOOST_MPI_GATHER_HPP
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#include <cassert>
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#include <cstddef>
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#include <numeric>
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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/detail/point_to_point.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/mpi/detail/offsets.hpp>
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#include <boost/mpi/detail/antiques.hpp>
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#include <boost/assert.hpp>
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namespace boost { namespace mpi {
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namespace detail {
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// We're gathering at the root for a type that has an associated MPI
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// datatype, so we'll use MPI_Gather to do all of the work.
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template<typename T>
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void
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gather_impl(const communicator& comm, const T* in_values, int n,
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T* out_values, int root, 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_Gather,
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(const_cast<T*>(in_values), n, type,
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out_values, n, type, root, comm));
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}
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// We're gathering from a non-root for a type that has an associated MPI
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// datatype, so we'll use MPI_Gather to do all of the work.
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template<typename T>
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void
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gather_impl(const communicator& comm, const T* in_values, int n, int root,
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mpl::true_ is_mpi_type)
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{
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assert(comm.rank() != root);
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gather_impl(comm, in_values, n, (T*)0, root, is_mpi_type);
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}
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// We're gathering at the root for 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.
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template<typename T>
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void
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gather_impl(const communicator& comm, const T* in_values, int n, T* out_values,
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int const* nslot, int const* nskip, int root, mpl::false_)
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{
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int nproc = comm.size();
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// first, gather all size, these size can be different for
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// each process
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packed_oarchive oa(comm);
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for (int i = 0; i < n; ++i) {
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oa << in_values[i];
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}
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bool is_root = comm.rank() == root;
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std::vector<int> oasizes(is_root ? nproc : 0);
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int oasize = oa.size();
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BOOST_MPI_CHECK_RESULT(MPI_Gather,
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(&oasize, 1, MPI_INT,
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c_data(oasizes), 1, MPI_INT,
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root, MPI_Comm(comm)));
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// Gather the archives, which can be of different sizes, so
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// we need to use gatherv.
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// Everything is contiguous (in the transmitted archive), so
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// the offsets can be deduced from the collected sizes.
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std::vector<int> offsets;
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if (is_root) sizes2offsets(oasizes, offsets);
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packed_iarchive::buffer_type recv_buffer(is_root ? std::accumulate(oasizes.begin(), oasizes.end(), 0) : 0);
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BOOST_MPI_CHECK_RESULT(MPI_Gatherv,
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(const_cast<void*>(oa.address()), int(oa.size()), MPI_BYTE,
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c_data(recv_buffer), c_data(oasizes), c_data(offsets), MPI_BYTE,
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root, MPI_Comm(comm)));
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if (is_root) {
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for (int src = 0; src < nproc; ++src) {
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// handle variadic case
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int nb = nslot ? nslot[src] : n;
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int skip = nskip ? nskip[src] : 0;
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std::advance(out_values, skip);
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if (src == root) {
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BOOST_ASSERT(nb == n);
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for (int i = 0; i < nb; ++i) {
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*out_values++ = *in_values++;
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}
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} else {
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packed_iarchive ia(comm, recv_buffer, boost::archive::no_header, offsets[src]);
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for (int i = 0; i < nb; ++i) {
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ia >> *out_values++;
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}
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}
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}
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}
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}
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// We're gathering at a non-root for 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.
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template<typename T>
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void
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gather_impl(const communicator& comm, const T* in_values, int n, T* out_values,int root,
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mpl::false_ is_mpi_type)
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{
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gather_impl(comm, in_values, n, out_values, (int const*)0, (int const*)0, root, is_mpi_type);
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}
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} // end namespace detail
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template<typename T>
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void
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gather(const communicator& comm, const T& in_value, T* out_values, int root)
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{
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BOOST_ASSERT(out_values || (comm.rank() != root));
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detail::gather_impl(comm, &in_value, 1, out_values, root, is_mpi_datatype<T>());
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}
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template<typename T>
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void gather(const communicator& comm, const T& in_value, int root)
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{
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BOOST_ASSERT(comm.rank() != root);
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detail::gather_impl(comm, &in_value, 1, (T*)0, root, is_mpi_datatype<T>());
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}
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template<typename T>
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void
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gather(const communicator& comm, const T& in_value, std::vector<T>& out_values,
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int root)
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{
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using detail::c_data;
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if (comm.rank() == root) {
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out_values.resize(comm.size());
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}
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::boost::mpi::gather(comm, in_value, c_data(out_values), root);
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}
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template<typename T>
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void
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gather(const communicator& comm, const T* in_values, int n, T* out_values,
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int root)
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{
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detail::gather_impl(comm, in_values, n, out_values, root,
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is_mpi_datatype<T>());
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}
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template<typename T>
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void
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gather(const communicator& comm, const T* in_values, int n,
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std::vector<T>& out_values, int root)
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{
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if (comm.rank() == root) {
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out_values.resize(comm.size() * n);
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}
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::boost::mpi::gather(comm, in_values, n, out_values.data(), root);
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}
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template<typename T>
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void gather(const communicator& comm, const T* in_values, int n, int root)
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{
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BOOST_ASSERT(comm.rank() != root);
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detail::gather_impl(comm, in_values, n, root, is_mpi_datatype<T>());
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}
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} } // end namespace boost::mpi
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#endif // BOOST_MPI_GATHER_HPP
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