boost/mpi/collectives/gather.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 4.5. Gather
   8 #ifndef BOOST_MPI_GATHER_HPP
   9 #define BOOST_MPI_GATHER_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 gathering at the root for a type that has an associated MPI
  25   // datatype, so we'll use MPI_Gather to do all of the work.
  26   template<typename T>
  27   void
  28   gather_impl(const communicator& comm, const T* in_values, int n,
  29               T* out_values, int root, mpl::true_)
  30   {
  31     MPI_Datatype type = get_mpi_datatype<T>(*in_values);
  32     BOOST_MPI_CHECK_RESULT(MPI_Gather,
  33                            (const_cast<T*>(in_values), n, type,
  34                             out_values, n, type, root, comm));
  35   }
  36
  37   // We're gathering from a non-root for a type that has an associated MPI
  38   // datatype, so we'll use MPI_Gather to do all of the work.
  39   template<typename T>
  40   void
  41   gather_impl(const communicator& comm, const T* in_values, int n, int root,
  42               mpl::true_)
  43   {
  44     MPI_Datatype type = get_mpi_datatype<T>(*in_values);
  45     BOOST_MPI_CHECK_RESULT(MPI_Gather,
  46                            (const_cast<T*>(in_values), n, type,
  47                             0, n, type, root, comm));
  48   }
  49
  50   // We're gathering at the root for a type that does not have an
  51   // associated MPI datatype, so we'll need to serialize
  52   // it. Unfortunately, this means that we cannot use MPI_Gather, so
  53   // we'll just have all of the non-root nodes send individual
  54   // messages to the root.
  55   template<typename T>
  56   void
  57   gather_impl(const communicator& comm, const T* in_values, int n,
  58               T* out_values, int root, mpl::false_)
  59   {
  60     int tag = environment::collectives_tag();
  61     int size = comm.size();
  62
  63     for (int src = 0; src < size; ++src) {
  64       if (src == root)
  65         std::copy(in_values, in_values + n, out_values + n * src);
  66       else
  67         comm.recv(src, tag, out_values + n * src, n);
  68     }
  69   }
  70
  71   // We're gathering at a non-root for a type that does not have an
  72   // associated MPI datatype, so we'll need to serialize
  73   // it. Unfortunately, this means that we cannot use MPI_Gather, so
  74   // we'll just have all of the non-root nodes send individual
  75   // messages to the root.
  76   template<typename T>
  77   void
  78   gather_impl(const communicator& comm, const T* in_values, int n, int root,
  79               mpl::false_)
  80   {
  81     int tag = environment::collectives_tag();
  82     comm.send(root, tag, in_values, n);
  83   }
  84 } // end namespace detail
  85
  86 template<typename T>
  87 void
  88 gather(const communicator& comm, const T& in_value, T* out_values, int root)
  89 {
  90   if (comm.rank() == root)
  91     detail::gather_impl(comm, &in_value, 1, out_values, root,
  92                         is_mpi_datatype<T>());
  93   else
  94     detail::gather_impl(comm, &in_value, 1, root, is_mpi_datatype<T>());
  95 }
  96
  97 template<typename T>
  98 void gather(const communicator& comm, const T& in_value, int root)
  99 {
 100   BOOST_ASSERT(comm.rank() != root);
 101   detail::gather_impl(comm, &in_value, 1, root, is_mpi_datatype<T>());
 102 }
 103
 104 template<typename T>
 105 void
 106 gather(const communicator& comm, const T& in_value, std::vector<T>& out_values,
 107        int root)
 108 {
 109   if (comm.rank() == root) {
 110     out_values.resize(comm.size());
 111     ::boost::mpi::gather(comm, in_value, &out_values[0], root);
 112   } else {
 113     ::boost::mpi::gather(comm, in_value, root);
 114   }
 115 }
 116
 117 template<typename T>
 118 void
 119 gather(const communicator& comm, const T* in_values, int n, T* out_values,
 120        int root)
 121 {
 122   if (comm.rank() == root)
 123     detail::gather_impl(comm, in_values, n, out_values, root,
 124                         is_mpi_datatype<T>());
 125   else
 126     detail::gather_impl(comm, in_values, n, root, is_mpi_datatype<T>());
 127 }
 128
 129 template<typename T>
 130 void
 131 gather(const communicator& comm, const T* in_values, int n,
 132        std::vector<T>& out_values, int root)
 133 {
 134   ::boost::mpi::gather(comm, in_values, n, &out_values[0], root);
 135 }
 136
 137 template<typename T>
 138 void gather(const communicator& comm, const T* in_values, int n, int root)
 139 {
 140   BOOST_ASSERT(comm.rank() != root);
 141   detail::gather_impl(comm, in_values, n, root, is_mpi_datatype<T>());
 142 }
 143
 144
 145 } } // end namespace boost::mpi
 146
 147 #endif // BOOST_MPI_GATHER_HPP