1 // -*- C++ -*-
2
3 // Copyright (C) 2007-2023 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the terms
7 // of the GNU General Public License as published by the Free Software
8 // Foundation; either version 3, or (at your option) any later
9 // version.
10
11 // This library is distributed in the hope that it will be useful, but
12 // WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 // General Public License for more details.
15
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24
25 /** @file parallel/par_loop.h
26 * @brief Parallelization of embarrassingly parallel execution by
27 * means of equal splitting.
28 * This file is a GNU parallel extension to the Standard C++ Library.
29 */
30
31 // Written by Felix Putze.
32
33 #ifndef _GLIBCXX_PARALLEL_PAR_LOOP_H
34 #define _GLIBCXX_PARALLEL_PAR_LOOP_H 1
35
36 #include <omp.h>
37 #include <parallel/settings.h>
38 #include <parallel/base.h>
39 #include <parallel/equally_split.h>
40
41 namespace __gnu_parallel
42 {
43 /** @brief Embarrassingly parallel algorithm for random access
44 * iterators, using hand-crafted parallelization by equal splitting
45 * the work.
46 *
47 * @param __begin Begin iterator of element sequence.
48 * @param __end End iterator of element sequence.
49 * @param __o User-supplied functor (comparator, predicate, adding
50 * functor, ...)
51 * @param __f Functor to "process" an element with __op (depends on
52 * desired functionality, e. g. for std::for_each(), ...).
53 * @param __r Functor to "add" a single __result to the already
54 * processed elements (depends on functionality).
55 * @param __base Base value for reduction.
56 * @param __output Pointer to position where final result is written to
57 * @param __bound Maximum number of elements processed (e. g. for
58 * std::count_n()).
59 * @return User-supplied functor (that may contain a part of the result).
60 */
61 template<typename _RAIter,
62 typename _Op,
63 typename _Fu,
64 typename _Red,
65 typename _Result>
66 _Op
67 __for_each_template_random_access_ed(_RAIter __begin, _RAIter __end,
68 _Op __o, _Fu& __f, _Red __r,
69 _Result __base, _Result& __output,
70 typename std::iterator_traits<_RAIter>::difference_type __bound)
71 {
72 typedef std::iterator_traits<_RAIter> _TraitsType;
73 typedef typename _TraitsType::difference_type _DifferenceType;
74 const _DifferenceType __length = __end - __begin;
75 _Result *__thread_results;
76 bool* __constructed;
77
78 _ThreadIndex __num_threads = __gnu_parallel::min<_DifferenceType>
79 (__get_max_threads(), __length);
80
81 # pragma omp parallel num_threads(__num_threads)
82 {
83 # pragma omp single
84 {
85 __num_threads = omp_get_num_threads();
86 __thread_results = static_cast<_Result*>
87 (::operator new(__num_threads * sizeof(_Result)));
88 __constructed = new bool[__num_threads];
89 }
90
91 _ThreadIndex __iam = omp_get_thread_num();
92
93 // Neutral element.
94 _Result* __reduct;
95
96 _DifferenceType
97 __start = __equally_split_point(__length, __num_threads, __iam),
98 __stop = __equally_split_point(__length, __num_threads, __iam + 1);
99
100 if (__start < __stop)
101 {
102 __reduct = new _Result(__f(__o, __begin + __start));
103 ++__start;
104 __constructed[__iam] = true;
105 }
106 else
107 __constructed[__iam] = false;
108
109 for (; __start < __stop; ++__start)
110 *__reduct = __r(*__reduct, __f(__o, __begin + __start));
111
112 if (__constructed[__iam])
113 {
114 ::new(&__thread_results[__iam]) _Result(*__reduct);
115 delete __reduct;
116 }
117 } //parallel
118
119 for (_ThreadIndex __i = 0; __i < __num_threads; ++__i)
120 if (__constructed[__i])
121 {
122 __output = __r(__output, __thread_results[__i]);
123 __thread_results[__i].~_Result();
124 }
125
126 // Points to last element processed (needed as return value for
127 // some algorithms like transform).
128 __f._M_finish_iterator = __begin + __length;
129
130 ::operator delete(__thread_results);
131
132 delete[] __constructed;
133
134 return __o;
135 }
136
137 } // end namespace
138
139 #endif /* _GLIBCXX_PARALLEL_PAR_LOOP_H */