mpi/collectives/all_reduce.hpp

0001 // Copyright (C) 2005-2006 Douglas Gregor <doug.gregor -at- gmail.com>
0002 // Copyright (C) 2004 The Trustees of Indiana University
0003
0004 // Use, modification and distribution is subject to the Boost Software
0005 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
0006 // http://www.boost.org/LICENSE_1_0.txt)
0007
0008 //   Authors: Douglas Gregor
0009 //            Andrew Lumsdaine
0010
0011 // Message Passing Interface 1.1 -- Section 4.9.1. Reduce
0012 #ifndef BOOST_MPI_ALL_REDUCE_HPP
0013 #define BOOST_MPI_ALL_REDUCE_HPP
0014
0015 #include <vector>
0016
0017 #include <boost/mpi/inplace.hpp>
0018
0019 // All-reduce falls back to reduce() + broadcast() in some cases.
0020 #include <boost/mpi/collectives/broadcast.hpp>
0021 #include <boost/mpi/collectives/reduce.hpp>
0022
0023 namespace boost { namespace mpi {
0024 namespace detail {
0025   /**********************************************************************
0026    * Simple reduction with MPI_Allreduce                                *
0027    **********************************************************************/
0028   // We are reducing for a type that has an associated MPI
0029   // datatype and operation, so we'll use MPI_Allreduce directly.
0030   template<typename T, typename Op>
0031   void
0032   all_reduce_impl(const communicator& comm, const T* in_values, int n,
0033                   T* out_values, Op /*op*/, mpl::true_ /*is_mpi_op*/,
0034                   mpl::true_ /*is_mpi_datatype*/)
0035   {
0036     BOOST_MPI_CHECK_RESULT(MPI_Allreduce,
0037                            (const_cast<T*>(in_values), out_values, n,
0038                             boost::mpi::get_mpi_datatype<T>(*in_values),
0039                             (is_mpi_op<Op, T>::op()), comm));
0040   }
0041
0042   /**********************************************************************
0043    * User-defined reduction with MPI_Allreduce                          *
0044    **********************************************************************/
0045   // We are reducing at the root for a type that has an associated MPI
0046   // datatype but with a custom operation. We'll use MPI_Reduce
0047   // directly, but we'll need to create an MPI_Op manually.
0048   template<typename T, typename Op>
0049   void
0050   all_reduce_impl(const communicator& comm, const T* in_values, int n,
0051                   T* out_values, Op /* op */, mpl::false_ /*is_mpi_op*/,
0052                   mpl::true_ /*is_mpi_datatype*/)
0053   {
0054     user_op<Op, T> mpi_op;
0055     BOOST_MPI_CHECK_RESULT(MPI_Allreduce,
0056                            (const_cast<T*>(in_values), out_values, n,
0057                             boost::mpi::get_mpi_datatype<T>(*in_values),
0058                             mpi_op.get_mpi_op(), comm));
0059   }
0060
0061   /**********************************************************************
0062    * User-defined, tree-based reduction for non-MPI data types          *
0063    **********************************************************************/
0064   // We are reducing at the root for a type that has no associated MPI
0065   // datatype and operation, so we'll use a simple tree-based
0066   // algorithm.
0067   template<typename T, typename Op>
0068   void
0069   all_reduce_impl(const communicator& comm, const T* in_values, int n,
0070                   T* out_values, Op op, mpl::false_ /*is_mpi_op*/,
0071                   mpl::false_ /*is_mpi_datatype*/)
0072   {
0073     if (in_values == MPI_IN_PLACE) {
0074       // if in_values matches the in place tag, then the output
0075       // buffer actually contains the input data.
0076       // But we can just go back to the out of place
0077       // implementation in this case.
0078       // it's not clear how/if we can avoid the copy.
0079       std::vector<T> tmp_in( out_values, out_values + n);
0080       reduce(comm, detail::c_data(tmp_in), n, out_values, op, 0);
0081     } else {
0082       reduce(comm, in_values, n, out_values, op, 0);
0083     }
0084     broadcast(comm, out_values, n, 0);
0085   }
0086 } // end namespace detail
0087
0088 template<typename T, typename Op>
0089 inline void
0090 all_reduce(const communicator& comm, const T* in_values, int n, T* out_values,
0091            Op op)
0092 {
0093   detail::all_reduce_impl(comm, in_values, n, out_values, op,
0094                           is_mpi_op<Op, T>(), is_mpi_datatype<T>());
0095 }
0096
0097 template<typename T, typename Op>
0098 inline void
0099 all_reduce(const communicator& comm, inplace_t<T*> inout_values, int n, Op op)
0100 {
0101   all_reduce(comm, static_cast<const T*>(MPI_IN_PLACE), n, inout_values.buffer, op);
0102 }
0103
0104 template<typename T, typename Op>
0105 inline void
0106 all_reduce(const communicator& comm, inplace_t<T> inout_values, Op op)
0107 {
0108   all_reduce(comm, static_cast<const T*>(MPI_IN_PLACE), 1, &(inout_values.buffer), op);
0109 }
0110
0111 template<typename T, typename Op>
0112 inline void
0113 all_reduce(const communicator& comm, const T& in_value, T& out_value, Op op)
0114 {
0115   detail::all_reduce_impl(comm, &in_value, 1, &out_value, op,
0116                           is_mpi_op<Op, T>(), is_mpi_datatype<T>());
0117 }
0118
0119 template<typename T, typename Op>
0120 T all_reduce(const communicator& comm, const T& in_value, Op op)
0121 {
0122   T result;
0123   ::boost::mpi::all_reduce(comm, in_value, result, op);
0124   return result;
0125 }
0126
0127 } } // end namespace boost::mpi
0128
0129 #endif // BOOST_MPI_ALL_REDUCE_HPP