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// Copyright (C) 2011 Júlio Hoffimann.
// Use, modification and distribution is subject to the Boost Software
// License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
// Message Passing Interface 1.1 -- Section 4.6. Scatterv
#ifndef BOOST_MPI_SCATTERV_HPP
#define BOOST_MPI_SCATTERV_HPP
#include <boost/mpi/exception.hpp>
#include <boost/mpi/datatype.hpp>
#include <vector>
#include <boost/mpi/packed_oarchive.hpp>
#include <boost/mpi/packed_iarchive.hpp>
#include <boost/mpi/detail/point_to_point.hpp>
#include <boost/mpi/communicator.hpp>
#include <boost/mpi/environment.hpp>
#include <boost/assert.hpp>
namespace boost { namespace mpi {
namespace detail {
// We're scattering from the root for a type that has an associated MPI
// datatype, so we'll use MPI_Scatterv to do all of the work.
template<typename T>
void
scatterv_impl(const communicator& comm, const T* in_values, const int* sizes,
const int* displs, T* out_values, int out_size, int root, mpl::true_)
{
MPI_Datatype type = get_mpi_datatype<T>(*in_values);
BOOST_MPI_CHECK_RESULT(MPI_Scatterv,
(const_cast<T*>(in_values), const_cast<int*>(sizes),
const_cast<int*>(displs), type,
out_values, out_size, type, root, comm));
}
// We're scattering from a non-root for a type that has an associated MPI
// datatype, so we'll use MPI_Scatterv to do all of the work.
template<typename T>
void
scatterv_impl(const communicator& comm, T* out_values, int out_size, int root,
mpl::true_)
{
MPI_Datatype type = get_mpi_datatype<T>(*out_values);
BOOST_MPI_CHECK_RESULT(MPI_Scatterv,
(0, 0, 0, type,
out_values, out_size, type,
root, comm));
}
// We're scattering from the root for a type that does not have an
// associated MPI datatype, so we'll need to serialize
// it. Unfortunately, this means that we cannot use MPI_Scatterv, so
// we'll just have the root send individual messages to the other
// processes.
template<typename T>
void
scatterv_impl(const communicator& comm, const T* in_values, const int* sizes,
const int* displs, T* out_values, int out_size, int root, mpl::false_)
{
int tag = environment::collectives_tag();
int nprocs = comm.size();
for (int dest = 0; dest < nprocs; ++dest) {
if (dest == root) {
// Our own values will never be transmitted: just copy them.
std::copy(in_values + displs[dest],
in_values + displs[dest] + out_size, out_values);
} else {
// Send archive
packed_oarchive oa(comm);
for (int i = 0; i < sizes[dest]; ++i)
oa << in_values[ displs[dest] + i ];
detail::packed_archive_send(comm, dest, tag, oa);
}
}
}
// We're scattering to a non-root for a type that does not have an
// associated MPI datatype, so we'll need to de-serialize
// it. Unfortunately, this means that we cannot use MPI_Scatterv, so
// we'll just have all of the non-root nodes send individual
// messages to the root.
template<typename T>
void
scatterv_impl(const communicator& comm, T* out_values, int out_size, int root,
mpl::false_)
{
int tag = environment::collectives_tag();
packed_iarchive ia(comm);
MPI_Status status;
detail::packed_archive_recv(comm, root, tag, ia, status);
for (int i = 0; i < out_size; ++i)
ia >> out_values[i];
}
} // end namespace detail
template<typename T>
void
scatterv(const communicator& comm, const T* in_values,
const std::vector<int>& sizes, const std::vector<int>& displs,
T* out_values, int out_size, int root)
{
int rank = comm.rank();
if (rank == root)
detail::scatterv_impl(comm, in_values, &sizes[0], &displs[0],
out_values, out_size, root, is_mpi_datatype<T>());
else
detail::scatterv_impl(comm, out_values, out_size, root,
is_mpi_datatype<T>());
}
template<typename T>
void
scatterv(const communicator& comm, const std::vector<T>& in_values,
const std::vector<int>& sizes, const std::vector<int>& displs,
T* out_values, int out_size, int root)
{
if (comm.rank() == root)
::boost::mpi::scatterv(comm, &in_values[0], sizes, displs,
out_values, out_size, root);
else
::boost::mpi::scatterv(comm, static_cast<const T*>(0), sizes, displs,
out_values, out_size, root);
}
template<typename T>
void scatterv(const communicator& comm, T* out_values, int out_size, int root)
{
BOOST_ASSERT(comm.rank() != root);
detail::scatterv_impl(comm, out_values, out_size, root, is_mpi_datatype<T>());
}
///////////////////////
// common use versions
///////////////////////
template<typename T>
void
scatterv(const communicator& comm, const T* in_values,
const std::vector<int>& sizes, T* out_values, int root)
{
int nprocs = comm.size();
int myrank = comm.rank();
std::vector<int> displs(nprocs);
for (int rank = 0, aux = 0; rank < nprocs; ++rank) {
displs[rank] = aux;
aux += sizes[rank];
}
::boost::mpi::scatterv(comm, in_values, sizes, displs, out_values,
sizes[myrank], root);
}
template<typename T>
void
scatterv(const communicator& comm, const std::vector<T>& in_values,
const std::vector<int>& sizes, T* out_values, int root)
{
::boost::mpi::scatterv(comm, &in_values[0], sizes, out_values, root);
}
} } // end namespace boost::mpi
#endif // BOOST_MPI_SCATTERV_HPP
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