boost/mpi/collectives/scatter.hpp

   1 // Copyright (C) 2005, 2006 Douglas Gregor.
   2
   3 // Use, modification and distribution is subject to the Boost Software
   4 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
   5 // http://www.boost.org/LICENSE_1_0.txt)
   6
   7 // Message Passing Interface 1.1 -- Section 4.6. Scatter
   8 #ifndef BOOST_MPI_SCATTER_HPP
   9 #define BOOST_MPI_SCATTER_HPP
  10
  11 #include <boost/mpi/exception.hpp>
  12 #include <boost/mpi/datatype.hpp>
  13 #include <vector>
  14 #include <boost/mpi/packed_oarchive.hpp>
  15 #include <boost/mpi/packed_iarchive.hpp>
  16 #include <boost/mpi/detail/point_to_point.hpp>
  17 #include <boost/mpi/communicator.hpp>
  18 #include <boost/mpi/environment.hpp>
  19 #include <boost/assert.hpp>
  20
  21 namespace boost { namespace mpi {
  22
  23 namespace detail {
  24   // We're scattering from the root for a type that has an associated MPI
  25   // datatype, so we'll use MPI_Scatter to do all of the work.
  26   template<typename T>
  27   void
  28   scatter_impl(const communicator& comm, const T* in_values, T* out_values,
  29                int n, int root, mpl::true_)
  30   {
  31     MPI_Datatype type = get_mpi_datatype<T>(*in_values);
  32     BOOST_MPI_CHECK_RESULT(MPI_Scatter,
  33                            (const_cast<T*>(in_values), n, type,
  34                             out_values, n, type, root, comm));
  35   }
  36
  37   // We're scattering from a non-root for a type that has an associated MPI
  38   // datatype, so we'll use MPI_Scatter to do all of the work.
  39   template<typename T>
  40   void
  41   scatter_impl(const communicator& comm, T* out_values, int n, int root,
  42                mpl::true_)
  43   {
  44     MPI_Datatype type = get_mpi_datatype<T>(*out_values);
  45     BOOST_MPI_CHECK_RESULT(MPI_Scatter,
  46                            (0, n, type,
  47                             out_values, n, type,
  48                             root, comm));
  49   }
  50
  51   // We're scattering from the root for a type that does not have an
  52   // associated MPI datatype, so we'll need to serialize
  53   // it. Unfortunately, this means that we cannot use MPI_Scatter, so
  54   // we'll just have the root send individual messages to the other
  55   // processes.
  56   template<typename T>
  57   void
  58   scatter_impl(const communicator& comm, const T* in_values, T* out_values,
  59                int n, int root, mpl::false_)
  60   {
  61     int tag = environment::collectives_tag();
  62     int size = comm.size();
  63
  64     for (int dest = 0; dest < size; ++dest) {
  65       if (dest == root) {
  66         // Our own values will never be transmitted: just copy them.
  67         std::copy(in_values + dest * n, in_values + (dest + 1) * n, out_values);
  68       } else {
  69         // Send archive
  70         packed_oarchive oa(comm);
  71         for (int i = 0; i < n; ++i)
  72           oa << in_values[dest * n + i];
  73         detail::packed_archive_send(comm, dest, tag, oa);
  74       }
  75     }
  76   }
  77
  78   // We're scattering to a non-root for a type that does not have an
  79   // associated MPI datatype, so we'll need to de-serialize
  80   // it. Unfortunately, this means that we cannot use MPI_Scatter, so
  81   // we'll just have all of the non-root nodes send individual
  82   // messages to the root.
  83   template<typename T>
  84   void
  85   scatter_impl(const communicator& comm, T* out_values, int n, int root,
  86                mpl::false_)
  87   {
  88     int tag = environment::collectives_tag();
  89
  90     packed_iarchive ia(comm);
  91     MPI_Status status;
  92     detail::packed_archive_recv(comm, root, tag, ia, status);
  93     for (int i = 0; i < n; ++i)
  94       ia >> out_values[i];
  95   }
  96 } // end namespace detail
  97
  98 template<typename T>
  99 void
 100 scatter(const communicator& comm, const T* in_values, T& out_value, int root)
 101 {
 102   if (comm.rank() == root)
 103     detail::scatter_impl(comm, in_values, &out_value, 1, root,
 104                          is_mpi_datatype<T>());
 105   else
 106     detail::scatter_impl(comm, &out_value, 1, root, is_mpi_datatype<T>());
 107 }
 108
 109 template<typename T>
 110 void
 111 scatter(const communicator& comm, const std::vector<T>& in_values, T& out_value,
 112         int root)
 113 {
 114   if (comm.rank() == root)
 115     ::boost::mpi::scatter<T>(comm, &in_values[0], out_value, root);
 116   else
 117     ::boost::mpi::scatter<T>(comm, static_cast<const T*>(0), out_value,
 118                              root);
 119 }
 120
 121 template<typename T>
 122 void scatter(const communicator& comm, T& out_value, int root)
 123 {
 124   BOOST_ASSERT(comm.rank() != root);
 125   detail::scatter_impl(comm, &out_value, 1, root, is_mpi_datatype<T>());
 126 }
 127
 128 template<typename T>
 129 void
 130 scatter(const communicator& comm, const T* in_values, T* out_values, int n,
 131         int root)
 132 {
 133   if (comm.rank() == root)
 134     detail::scatter_impl(comm, in_values, out_values, n, root,
 135                          is_mpi_datatype<T>());
 136   else
 137     detail::scatter_impl(comm, out_values, n, root, is_mpi_datatype<T>());
 138 }
 139
 140 template<typename T>
 141 void
 142 scatter(const communicator& comm, const std::vector<T>& in_values,
 143         T* out_values, int n, int root)
 144 {
 145   if (comm.rank() == root)
 146     ::boost::mpi::scatter(comm, &in_values[0], out_values, n, root);
 147   else
 148     ::boost::mpi::scatter(comm, static_cast<const T*>(0), out_values,
 149                                     n, root);
 150 }
 151
 152 template<typename T>
 153 void scatter(const communicator& comm, T* out_values, int n, int root)
 154 {
 155   BOOST_ASSERT(comm.rank() != root);
 156   detail::scatter_impl(comm, out_values, n, root, is_mpi_datatype<T>());
 157 }
 158
 159 } } // end namespace boost::mpi
 160
 161 #endif // BOOST_MPI_SCATTER_HPP