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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 |