1 // -*- C++ -*- 2 3 // Copyright (C) 2007, 2008, 2009 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 44 /** @brief Embarrassingly parallel algorithm for random access 45 * iterators, using hand-crafted parallelization by equal splitting 46 * the work. 47 * 48 * @param begin Begin iterator of element sequence. 49 * @param end End iterator of element sequence. 50 * @param o User-supplied functor (comparator, predicate, adding 51 * functor, ...) 52 * @param f Functor to "process" an element with op (depends on 53 * desired functionality, e. g. for std::for_each(), ...). 54 * @param r Functor to "add" a single result to the already 55 * processed elements (depends on functionality). 56 * @param base Base value for reduction. 57 * @param output Pointer to position where final result is written to 58 * @param bound Maximum number of elements processed (e. g. for 59 * std::count_n()). 60 * @return User-supplied functor (that may contain a part of the result). 61 */ 62 template<typename RandomAccessIterator, 63 typename Op, 64 typename Fu, 65 typename Red, 66 typename Result> 67 Op 68 for_each_template_random_access_ed(RandomAccessIterator begin, 69 RandomAccessIterator end, 70 Op o, Fu& f, Red r, Result base, 71 Result& output, 72 typename std::iterator_traits 73 <RandomAccessIterator>:: 74 difference_type bound) 75 { 76 typedef std::iterator_traits<RandomAccessIterator> traits_type; 77 typedef typename traits_type::difference_type difference_type; 78 const difference_type length = end - begin; 79 Result *thread_results; 80 bool* constructed; 81 82 thread_index_t num_threads = 83 __gnu_parallel::min<difference_type>(get_max_threads(), length); 84 85 # pragma omp parallel num_threads(num_threads) 86 { 87 # pragma omp single 88 { 89 num_threads = omp_get_num_threads(); 90 thread_results = static_cast<Result*>( 91 ::operator new(num_threads * sizeof(Result))); 92 constructed = new bool[num_threads]; 93 } 94 95 thread_index_t iam = omp_get_thread_num(); 96 97 // Neutral element. 98 Result* reduct = static_cast<Result*>(::operator new(sizeof(Result))); 99 100 difference_type 101 start = equally_split_point(length, num_threads, iam), 102 stop = equally_split_point(length, num_threads, iam + 1); 103 104 if (start < stop) 105 { 106 new(reduct) Result(f(o, begin + start)); 107 ++start; 108 constructed[iam] = true; 109 } 110 else 111 constructed[iam] = false; 112 113 for (; start < stop; ++start) 114 *reduct = r(*reduct, f(o, begin + start)); 115 116 thread_results[iam] = *reduct; 117 } //parallel 118 119 for (thread_index_t i = 0; i < num_threads; ++i) 120 if (constructed[i]) 121 output = r(output, thread_results[i]); 122 123 // Points to last element processed (needed as return value for 124 // some algorithms like transform). 125 f.finish_iterator = begin + length; 126 127 delete[] thread_results; 128 delete[] constructed; 129 130 return o; 131 } 132 133 } // end namespace 134 135 #endif /* _GLIBCXX_PARALLEL_PAR_LOOP_H */ 136
