par_loop.h

Go to the documentation of this file.
00001 // -*- C++ -*-
00002 
00003 // Copyright (C) 2007, 2008, 2009 Free Software Foundation, Inc.
00004 //
00005 // This file is part of the GNU ISO C++ Library.  This library is free
00006 // software; you can redistribute it and/or modify it under the terms
00007 // of the GNU General Public License as published by the Free Software
00008 // Foundation; either version 3, or (at your option) any later
00009 // version.
00010 
00011 // This library is distributed in the hope that it will be useful, but
00012 // WITHOUT ANY WARRANTY; without even the implied warranty of
00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00014 // General Public License for more details.
00015 
00016 // Under Section 7 of GPL version 3, you are granted additional
00017 // permissions described in the GCC Runtime Library Exception, version
00018 // 3.1, as published by the Free Software Foundation.
00019 
00020 // You should have received a copy of the GNU General Public License and
00021 // a copy of the GCC Runtime Library Exception along with this program;
00022 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
00023 // <http://www.gnu.org/licenses/>.
00024 
00025 /** @file parallel/par_loop.h
00026  *  @brief Parallelization of embarrassingly parallel execution by
00027  *  means of equal splitting.
00028  *  This file is a GNU parallel extension to the Standard C++ Library.
00029  */
00030 
00031 // Written by Felix Putze.
00032 
00033 #ifndef _GLIBCXX_PARALLEL_PAR_LOOP_H
00034 #define _GLIBCXX_PARALLEL_PAR_LOOP_H 1
00035 
00036 #include <omp.h>
00037 #include <parallel/settings.h>
00038 #include <parallel/base.h>
00039 #include <parallel/equally_split.h>
00040 
00041 namespace __gnu_parallel
00042 {
00043 
00044 /** @brief Embarrassingly parallel algorithm for random access
00045   * iterators, using hand-crafted parallelization by equal splitting
00046   * the work.
00047   *
00048   *  @param begin Begin iterator of element sequence.
00049   *  @param end End iterator of element sequence.
00050   *  @param o User-supplied functor (comparator, predicate, adding
00051   *  functor, ...)
00052   *  @param f Functor to "process" an element with op (depends on
00053   *  desired functionality, e. g. for std::for_each(), ...).
00054   *  @param r Functor to "add" a single result to the already
00055   *  processed elements (depends on functionality).
00056   *  @param base Base value for reduction.
00057   *  @param output Pointer to position where final result is written to
00058   *  @param bound Maximum number of elements processed (e. g. for
00059   *  std::count_n()).
00060   *  @return User-supplied functor (that may contain a part of the result).
00061   */
00062 template<typename RandomAccessIterator,
00063      typename Op,
00064      typename Fu,
00065      typename Red,
00066      typename Result>
00067   Op
00068   for_each_template_random_access_ed(RandomAccessIterator begin,
00069                      RandomAccessIterator end,
00070                      Op o, Fu& f, Red r, Result base,
00071                      Result& output,
00072                      typename std::iterator_traits
00073                      <RandomAccessIterator>::
00074                      difference_type bound)
00075   {
00076     typedef std::iterator_traits<RandomAccessIterator> traits_type;
00077     typedef typename traits_type::difference_type difference_type;
00078     const difference_type length = end - begin;
00079     Result *thread_results;
00080     bool* constructed;
00081 
00082     thread_index_t num_threads =
00083       __gnu_parallel::min<difference_type>(get_max_threads(), length);
00084 
00085 #   pragma omp parallel num_threads(num_threads)
00086       {
00087 #       pragma omp single
00088           {
00089             num_threads = omp_get_num_threads();
00090             thread_results = static_cast<Result*>(
00091                                 ::operator new(num_threads * sizeof(Result)));
00092             constructed = new bool[num_threads];
00093           }
00094 
00095         thread_index_t iam = omp_get_thread_num();
00096 
00097         // Neutral element.
00098         Result* reduct = static_cast<Result*>(::operator new(sizeof(Result)));
00099 
00100         difference_type
00101             start = equally_split_point(length, num_threads, iam),
00102             stop = equally_split_point(length, num_threads, iam + 1);
00103 
00104         if (start < stop)
00105           {
00106             new(reduct) Result(f(o, begin + start));
00107             ++start;
00108             constructed[iam] = true;
00109           }
00110         else
00111           constructed[iam] = false;
00112 
00113         for (; start < stop; ++start)
00114           *reduct = r(*reduct, f(o, begin + start));
00115 
00116         thread_results[iam] = *reduct;
00117       } //parallel
00118 
00119     for (thread_index_t i = 0; i < num_threads; ++i)
00120         if (constructed[i])
00121             output = r(output, thread_results[i]);
00122 
00123     // Points to last element processed (needed as return value for
00124     // some algorithms like transform).
00125     f.finish_iterator = begin + length;
00126 
00127     delete[] thread_results;
00128     delete[] constructed;
00129 
00130     return o;
00131   }
00132 
00133 } // end namespace
00134 
00135 #endif /* _GLIBCXX_PARALLEL_PAR_LOOP_H */

Generated on 19 Jun 2018 for libstdc++ by  doxygen 1.6.1