ceph/src/boost/boost/mpi/collectives/all_to_all.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 4.8. All-to-all
   8 #ifndef BOOST_MPI_ALL_TO_ALL_HPP
   9 #define BOOST_MPI_ALL_TO_ALL_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/communicator.hpp>
  17 #include <boost/mpi/environment.hpp>
  18 #include <boost/assert.hpp>
  19 #include <boost/mpi/collectives_fwd.hpp>
  20 #include <boost/mpi/allocator.hpp>
  21
  22 namespace boost { namespace mpi {
  23
  24 namespace detail {
  25   // We're performing an all-to-all with a type that has an
  26   // associated MPI datatype, so we'll use MPI_Alltoall to do all of
  27   // the work.
  28   template<typename T>
  29   void
  30   all_to_all_impl(const communicator& comm, const T* in_values, int n,
  31                   T* out_values, mpl::true_)
  32   {
  33     MPI_Datatype type = get_mpi_datatype<T>(*in_values);
  34     BOOST_MPI_CHECK_RESULT(MPI_Alltoall,
  35                            (const_cast<T*>(in_values), n, type,
  36                             out_values, n, type, comm));
  37   }
  38
  39   // We're performing an all-to-all with a type that does not have an
  40   // associated MPI datatype, so we'll need to serialize
  41   // it.
  42   template<typename T>
  43   void
  44   all_to_all_impl(const communicator& comm, const T* in_values, int n,
  45                   T* out_values, mpl::false_)
  46   {
  47     int size = comm.size();
  48     int rank = comm.rank();
  49
  50     // The amount of data to be sent to each process
  51     std::vector<int> send_sizes(size);
  52
  53     // The displacements for each outgoing value.
  54     std::vector<int> send_disps(size);
  55
  56     // The buffer that will store all of the outgoing values
  57     std::vector<char, allocator<char> > outgoing;
  58
  59     // Pack the buffer with all of the outgoing values.
  60     for (int dest = 0; dest < size; ++dest) {
  61       // Keep track of the displacements
  62       send_disps[dest] = outgoing.size();
  63
  64       // Our own value will never be transmitted, so don't pack it.
  65       if (dest != rank) {
  66         packed_oarchive oa(comm, outgoing);
  67         for (int i = 0; i < n; ++i)
  68           oa << in_values[dest * n + i];
  69       }
  70
  71       // Keep track of the sizes
  72       send_sizes[dest] = outgoing.size() - send_disps[dest];
  73     }
  74
  75     // Determine how much data each process will receive.
  76     std::vector<int> recv_sizes(size);
  77     all_to_all(comm, send_sizes, recv_sizes);
  78
  79     // Prepare a buffer to receive the incoming data.
  80     std::vector<int> recv_disps(size);
  81     int sum = 0;
  82     for (int src = 0; src < size; ++src) {
  83       recv_disps[src] = sum;
  84       sum += recv_sizes[src];
  85     }
  86     std::vector<char, allocator<char> > incoming(sum > 0? sum : 1);
  87
  88     // Make sure we don't try to reference an empty vector
  89     if (outgoing.empty())
  90       outgoing.push_back(0);
  91
  92     // Transmit the actual data
  93     BOOST_MPI_CHECK_RESULT(MPI_Alltoallv,
  94                            (&outgoing[0], &send_sizes[0],
  95                             &send_disps[0], MPI_PACKED,
  96                             &incoming[0], &recv_sizes[0],
  97                             &recv_disps[0], MPI_PACKED,
  98                             comm));
  99
 100     // Deserialize data from the iarchive
 101     for (int src = 0; src < size; ++src) {
 102       if (src == rank)
 103         std::copy(in_values + src * n, in_values + (src + 1) * n,
 104                   out_values + src * n);
 105       else {
 106         packed_iarchive ia(comm, incoming, boost::archive::no_header,
 107                            recv_disps[src]);
 108         for (int i = 0; i < n; ++i)
 109           ia >> out_values[src * n + i];
 110       }
 111     }
 112   }
 113 } // end namespace detail
 114
 115 template<typename T>
 116 inline void
 117 all_to_all(const communicator& comm, const T* in_values, T* out_values)
 118 {
 119   detail::all_to_all_impl(comm, in_values, 1, out_values, is_mpi_datatype<T>());
 120 }
 121
 122 template<typename T>
 123 void
 124 all_to_all(const communicator& comm, const std::vector<T>& in_values,
 125            std::vector<T>& out_values)
 126 {
 127   BOOST_ASSERT((int)in_values.size() == comm.size());
 128   out_values.resize(comm.size());
 129   ::boost::mpi::all_to_all(comm, &in_values[0], &out_values[0]);
 130 }
 131
 132 template<typename T>
 133 inline void
 134 all_to_all(const communicator& comm, const T* in_values, int n, T* out_values)
 135 {
 136   detail::all_to_all_impl(comm, in_values, n, out_values, is_mpi_datatype<T>());
 137 }
 138
 139 template<typename T>
 140 void
 141 all_to_all(const communicator& comm, const std::vector<T>& in_values, int n,
 142            std::vector<T>& out_values)
 143 {
 144   BOOST_ASSERT((int)in_values.size() == comm.size() * n);
 145   out_values.resize(comm.size() * n);
 146   ::boost::mpi::all_to_all(comm, &in_values[0], n, &out_values[0]);
 147 }
 148
 149 } } // end namespace boost::mpi
 150
 151 #endif // BOOST_MPI_ALL_TO_ALL_HPP