boost/mpi/collectives/gather.hpp
// Copyright (C) 2005, 2006 Douglas Gregor.
// 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 4.5. Gather
#ifndef BOOST_MPI_GATHER_HPP
#define BOOST_MPI_GATHER_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 gathering at the root for a type that has an associated MPI
// datatype, so we'll use MPI_Gather to do all of the work.
template<typename T>
void
gather_impl(const communicator& comm, const T* in_values, int n,
T* out_values, int root, mpl::true_)
{
MPI_Datatype type = get_mpi_datatype<T>(*in_values);
BOOST_MPI_CHECK_RESULT(MPI_Gather,
(const_cast<T*>(in_values), n, type,
out_values, n, type, root, comm));
}
// We're gathering from a non-root for a type that has an associated MPI
// datatype, so we'll use MPI_Gather to do all of the work.
template<typename T>
void
gather_impl(const communicator& comm, const T* in_values, int n, int root,
mpl::true_)
{
MPI_Datatype type = get_mpi_datatype<T>(*in_values);
BOOST_MPI_CHECK_RESULT(MPI_Gather,
(const_cast<T*>(in_values), n, type,
0, n, type, root, comm));
}
// We're gathering at 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_Gather, so
// we'll just have all of the non-root nodes send individual
// messages to the root.
template<typename T>
void
gather_impl(const communicator& comm, const T* in_values, int n,
T* out_values, int root, mpl::false_)
{
int tag = environment::collectives_tag();
int size = comm.size();
for (int src = 0; src < size; ++src) {
if (src == root)
std::copy(in_values, in_values + n, out_values + n * src);
else
comm.recv(src, tag, out_values + n * src, n);
}
}
// We're gathering at a non-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_Gather, so
// we'll just have all of the non-root nodes send individual
// messages to the root.
template<typename T>
void
gather_impl(const communicator& comm, const T* in_values, int n, int root,
mpl::false_)
{
int tag = environment::collectives_tag();
comm.send(root, tag, in_values, n);
}
} // end namespace detail
template<typename T>
void
gather(const communicator& comm, const T& in_value, T* out_values, int root)
{
if (comm.rank() == root)
detail::gather_impl(comm, &in_value, 1, out_values, root,
is_mpi_datatype<T>());
else
detail::gather_impl(comm, &in_value, 1, root, is_mpi_datatype<T>());
}
template<typename T>
void gather(const communicator& comm, const T& in_value, int root)
{
BOOST_ASSERT(comm.rank() != root);
detail::gather_impl(comm, &in_value, 1, root, is_mpi_datatype<T>());
}
template<typename T>
void
gather(const communicator& comm, const T& in_value, std::vector<T>& out_values,
int root)
{
if (comm.rank() == root) {
out_values.resize(comm.size());
::boost::mpi::gather(comm, in_value, &out_values[0], root);
} else {
::boost::mpi::gather(comm, in_value, root);
}
}
template<typename T>
void
gather(const communicator& comm, const T* in_values, int n, T* out_values,
int root)
{
if (comm.rank() == root)
detail::gather_impl(comm, in_values, n, out_values, root,
is_mpi_datatype<T>());
else
detail::gather_impl(comm, in_values, n, root, is_mpi_datatype<T>());
}
template<typename T>
void
gather(const communicator& comm, const T* in_values, int n,
std::vector<T>& out_values, int root)
{
if (comm.rank() == root) {
out_values.resize(comm.size() * n);
::boost::mpi::gather(comm, in_values, n, &out_values[0], root);
}
else
::boost::mpi::gather(comm, in_values, n, root);
}
template<typename T>
void gather(const communicator& comm, const T* in_values, int n, int root)
{
BOOST_ASSERT(comm.rank() != root);
detail::gather_impl(comm, in_values, n, root, is_mpi_datatype<T>());
}
} } // end namespace boost::mpi
#endif // BOOST_MPI_GATHER_HPP