ceph/src/boost/libs/mpi/include/boost/mpi/collectives/all_reduce.hpp

   1 // Copyright (C) 2005-2006 Douglas Gregor <doug.gregor -at- gmail.com>
   2 // Copyright (C) 2004 The Trustees of Indiana University
   3
   4 // Use, modification and distribution is subject to the Boost Software
   5 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
   6 // http://www.boost.org/LICENSE_1_0.txt)
   7
   8 //   Authors: Douglas Gregor
   9 //            Andrew Lumsdaine
  10
  11 // Message Passing Interface 1.1 -- Section 4.9.1. Reduce
  12 #ifndef BOOST_MPI_ALL_REDUCE_HPP
  13 #define BOOST_MPI_ALL_REDUCE_HPP
  14
  15 #include <vector>
  16
  17 #include <boost/mpi/inplace.hpp>
  18
  19 // All-reduce falls back to reduce() + broadcast() in some cases.
  20 #include <boost/mpi/collectives/broadcast.hpp>
  21 #include <boost/mpi/collectives/reduce.hpp>
  22
  23 namespace boost { namespace mpi {
  24 namespace detail {
  25   /**********************************************************************
  26    * Simple reduction with MPI_Allreduce                                *
  27    **********************************************************************/
  28   // We are reducing for a type that has an associated MPI
  29   // datatype and operation, so we'll use MPI_Allreduce directly.
  30   template<typename T, typename Op>
  31   void
  32   all_reduce_impl(const communicator& comm, const T* in_values, int n,
  33                   T* out_values, Op /*op*/, mpl::true_ /*is_mpi_op*/,
  34                   mpl::true_ /*is_mpi_datatype*/)
  35   {
  36     BOOST_MPI_CHECK_RESULT(MPI_Allreduce,
  37                            (const_cast<T*>(in_values), out_values, n,
  38                             boost::mpi::get_mpi_datatype<T>(*in_values),
  39                             (is_mpi_op<Op, T>::op()), comm));
  40   }
  41
  42   /**********************************************************************
  43    * User-defined reduction with MPI_Allreduce                          *
  44    **********************************************************************/
  45   // We are reducing at the root for a type that has an associated MPI
  46   // datatype but with a custom operation. We'll use MPI_Reduce
  47   // directly, but we'll need to create an MPI_Op manually.
  48   template<typename T, typename Op>
  49   void
  50   all_reduce_impl(const communicator& comm, const T* in_values, int n,
  51                   T* out_values, Op op, mpl::false_ /*is_mpi_op*/,
  52                   mpl::true_ /*is_mpi_datatype*/)
  53   {
  54     user_op<Op, T> mpi_op(op);
  55     BOOST_MPI_CHECK_RESULT(MPI_Allreduce,
  56                            (const_cast<T*>(in_values), out_values, n,
  57                             boost::mpi::get_mpi_datatype<T>(*in_values),
  58                             mpi_op.get_mpi_op(), comm));
  59   }
  60
  61   /**********************************************************************
  62    * User-defined, tree-based reduction for non-MPI data types          *
  63    **********************************************************************/
  64   // We are reducing at the root for a type that has no associated MPI
  65   // datatype and operation, so we'll use a simple tree-based
  66   // algorithm.
  67   template<typename T, typename Op>
  68   void
  69   all_reduce_impl(const communicator& comm, const T* in_values, int n,
  70                   T* out_values, Op op, mpl::false_ /*is_mpi_op*/,
  71                   mpl::false_ /*is_mpi_datatype*/)
  72   {
  73     if (in_values == MPI_IN_PLACE) {
  74       // if in_values matches the in place tag, then the output
  75       // buffer actually contains the input data.
  76       // But we can just go back to the out of place
  77       // implementation in this case.
  78       // it's not clear how/if we can avoid the copy.
  79       std::vector<T> tmp_in( out_values, out_values + n);
  80       reduce(comm, &(tmp_in[0]), n, out_values, op, 0);
  81     } else {
  82       reduce(comm, in_values, n, out_values, op, 0);
  83     }
  84     broadcast(comm, out_values, n, 0);
  85   }
  86 } // end namespace detail
  87
  88 template<typename T, typename Op>
  89 inline void
  90 all_reduce(const communicator& comm, const T* in_values, int n, T* out_values,
  91            Op op)
  92 {
  93   detail::all_reduce_impl(comm, in_values, n, out_values, op,
  94                           is_mpi_op<Op, T>(), is_mpi_datatype<T>());
  95 }
  96
  97 template<typename T, typename Op>
  98 inline void
  99 all_reduce(const communicator& comm, inplace_t<T*> inout_values, int n, Op op)
 100 {
 101   all_reduce(comm, static_cast<const T*>(MPI_IN_PLACE), n, inout_values.buffer, op);
 102 }
 103
 104 template<typename T, typename Op>
 105 inline void
 106 all_reduce(const communicator& comm, inplace_t<T> inout_values, Op op)
 107 {
 108   all_reduce(comm, static_cast<const T*>(MPI_IN_PLACE), 1, &(inout_values.buffer), op);
 109 }
 110
 111 template<typename T, typename Op>
 112 inline void
 113 all_reduce(const communicator& comm, const T& in_value, T& out_value, Op op)
 114 {
 115   detail::all_reduce_impl(comm, &in_value, 1, &out_value, op,
 116                           is_mpi_op<Op, T>(), is_mpi_datatype<T>());
 117 }
 118
 119 template<typename T, typename Op>
 120 T all_reduce(const communicator& comm, const T& in_value, Op op)
 121 {
 122   T result;
 123   ::boost::mpi::all_reduce(comm, in_value, result, op);
 124   return result;
 125 }
 126
 127 } } // end namespace boost::mpi
 128
 129 #endif // BOOST_MPI_ALL_REDUCE_HPP