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204 lines
6.6 KiB
204 lines
6.6 KiB
5 years ago
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// 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 4.6. Scatter
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#ifndef BOOST_MPI_SCATTER_HPP
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#define BOOST_MPI_SCATTER_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/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 scattering from the root for a type that has an associated MPI
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// datatype, so we'll use MPI_Scatter to do all of the work.
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template<typename T>
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void
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scatter_impl(const communicator& comm, const T* in_values, T* out_values,
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int n, 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_Scatter,
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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 scattering from a non-root for a type that has an associated MPI
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// datatype, so we'll use MPI_Scatter to do all of the work.
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template<typename T>
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void
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scatter_impl(const communicator& comm, T* out_values, int n, int root,
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mpl::true_)
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{
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MPI_Datatype type = get_mpi_datatype<T>(*out_values);
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BOOST_MPI_CHECK_RESULT(MPI_Scatter,
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(0, n, type,
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out_values, n, type,
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root, comm));
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}
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// Fill the sendbuf while keeping trac of the slot's footprints
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// Used in the first steps of both scatter and scatterv
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// Nslots contains the number of slots being sent
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// to each process (identical values for scatter).
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// skiped_slots, if present, is deduced from the
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// displacement array authorised be the MPI API,
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// for some yet to be determined reason.
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template<typename T>
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void
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fill_scatter_sendbuf(const communicator& comm, T const* values,
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int const* nslots, int const* skipped_slots,
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packed_oarchive::buffer_type& sendbuf, std::vector<int>& archsizes) {
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int nproc = comm.size();
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archsizes.resize(nproc);
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for (int dest = 0; dest < nproc; ++dest) {
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if (skipped_slots) { // wee need to keep this for backward compatibility
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for(int k= 0; k < skipped_slots[dest]; ++k) ++values;
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}
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packed_oarchive procarchive(comm);
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for (int i = 0; i < nslots[dest]; ++i) {
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procarchive << *values++;
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}
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int archsize = procarchive.size();
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sendbuf.resize(sendbuf.size() + archsize);
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archsizes[dest] = archsize;
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char const* aptr = static_cast<char const*>(procarchive.address());
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std::copy(aptr, aptr+archsize, sendbuf.end()-archsize);
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}
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}
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template<typename T, class A>
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T*
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non_const_data(std::vector<T,A> const& v) {
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using detail::c_data;
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return const_cast<T*>(c_data(v));
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}
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// Dispatch the sendbuf among proc.
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// Used in the second steps of both scatter and scatterv
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// in_value is only provide in the non variadic case.
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template<typename T>
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void
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dispatch_scatter_sendbuf(const communicator& comm,
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packed_oarchive::buffer_type const& sendbuf, std::vector<int> const& archsizes,
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T const* in_values,
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T* out_values, int n, int root) {
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// Distribute the sizes
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int myarchsize;
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BOOST_MPI_CHECK_RESULT(MPI_Scatter,
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(non_const_data(archsizes), 1, MPI_INT,
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&myarchsize, 1, MPI_INT, root, comm));
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std::vector<int> offsets;
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if (root == comm.rank()) {
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sizes2offsets(archsizes, offsets);
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}
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// Get my proc archive
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packed_iarchive::buffer_type recvbuf;
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recvbuf.resize(myarchsize);
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BOOST_MPI_CHECK_RESULT(MPI_Scatterv,
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(non_const_data(sendbuf), non_const_data(archsizes), c_data(offsets), MPI_BYTE,
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c_data(recvbuf), recvbuf.size(), MPI_BYTE,
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root, MPI_Comm(comm)));
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// Unserialize
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if ( in_values != 0 && root == comm.rank()) {
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// Our own local values are already here: just copy them.
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std::copy(in_values + root * n, in_values + (root + 1) * n, out_values);
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} else {
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// Otherwise deserialize:
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packed_iarchive iarchv(comm, recvbuf);
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for (int i = 0; i < n; ++i) {
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iarchv >> out_values[i];
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}
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}
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}
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// We're scattering from the root for a type that does not have an
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// associated MPI datatype, so we'll need to serialize it.
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template<typename T>
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void
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scatter_impl(const communicator& comm, const T* in_values, T* out_values,
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int n, int root, mpl::false_)
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{
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packed_oarchive::buffer_type sendbuf;
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std::vector<int> archsizes;
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if (root == comm.rank()) {
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std::vector<int> nslots(comm.size(), n);
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fill_scatter_sendbuf(comm, in_values, c_data(nslots), (int const*)0, sendbuf, archsizes);
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}
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dispatch_scatter_sendbuf(comm, sendbuf, archsizes, in_values, out_values, n, root);
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}
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template<typename T>
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void
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scatter_impl(const communicator& comm, T* out_values, int n, int root,
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mpl::false_ is_mpi_type)
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{
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scatter_impl(comm, (T const*)0, out_values, n, 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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scatter(const communicator& comm, const T* in_values, T& out_value, int root)
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{
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detail::scatter_impl(comm, in_values, &out_value, 1, 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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scatter(const communicator& comm, const std::vector<T>& in_values, T& out_value,
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int root)
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{
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using detail::c_data;
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::boost::mpi::scatter<T>(comm, c_data(in_values), out_value, root);
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}
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template<typename T>
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void scatter(const communicator& comm, T& out_value, int root)
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{
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BOOST_ASSERT(comm.rank() != root);
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detail::scatter_impl(comm, &out_value, 1, 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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scatter(const communicator& comm, const T* in_values, T* out_values, int n,
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int root)
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{
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detail::scatter_impl(comm, in_values, out_values, n, 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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scatter(const communicator& comm, const std::vector<T>& in_values,
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T* out_values, int n, int root)
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{
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::boost::mpi::scatter(comm, &in_values[0], out_values, n, root);
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}
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template<typename T>
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void scatter(const communicator& comm, T* out_values, int n, int root)
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{
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BOOST_ASSERT(comm.rank() != root);
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detail::scatter_impl(comm, out_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_SCATTER_HPP
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