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  1. // -*- C++ -*-
  2.  
  3. // Copyright (C) 2007-2015 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/omp_loop.h
  26.  *  @brief Parallelization of embarrassingly parallel execution by
  27.  *  means of an OpenMP for loop.
  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_OMP_LOOP_H
  34. #define _GLIBCXX_PARALLEL_OMP_LOOP_H 1
  35.  
  36. #include <omp.h>
  37.  
  38. #include <parallel/settings.h>
  39. #include <parallel/basic_iterator.h>
  40. #include <parallel/base.h>
  41.  
  42. namespace __gnu_parallel
  43. {
  44.   /** @brief Embarrassingly parallel algorithm for random access
  45.    * iterators, using an OpenMP for loop.
  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, etc.).
  51.    *  @param __f Functor to @a process an element with __op (depends on
  52.    *  desired functionality, e. g. for std::for_each(), ...).
  53.    *  @param __r Functor to @a 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_omp_loop(_RAIter __begin, _RAIter __end,
  68.                                                _Op __o, _Fu& __f, _Red __r,
  69.                                                _Result __base,
  70.                                                _Result& __output,
  71.       typename std::iterator_traits<_RAIter>::difference_type __bound)
  72.     {
  73.       typedef typename std::iterator_traits<_RAIter>::difference_type
  74.         _DifferenceType;
  75.  
  76.       _DifferenceType __length = __end - __begin;
  77.       _ThreadIndex __num_threads = __gnu_parallel::min<_DifferenceType>
  78.         (__get_max_threads(), __length);
  79.  
  80.       _Result *__thread_results;
  81.  
  82. #     pragma omp parallel num_threads(__num_threads)
  83.       {
  84. #       pragma omp single
  85.         {
  86.           __num_threads = omp_get_num_threads();
  87.           __thread_results = new _Result[__num_threads];
  88.  
  89.           for (_ThreadIndex __i = 0; __i < __num_threads; ++__i)
  90.             __thread_results[__i] = _Result();
  91.         }
  92.  
  93.         _ThreadIndex __iam = omp_get_thread_num();
  94.  
  95. #pragma omp for schedule(dynamic, _Settings::get().workstealing_chunk_size)
  96.         for (_DifferenceType __pos = 0; __pos < __length; ++__pos)
  97.           __thread_results[__iam] = __r(__thread_results[__iam],
  98.                                         __f(__o, __begin+__pos));
  99.       } //parallel
  100.  
  101.       for (_ThreadIndex __i = 0; __i < __num_threads; ++__i)
  102.         __output = __r(__output, __thread_results[__i]);
  103.  
  104.       delete [] __thread_results;
  105.  
  106.       // Points to last element processed (needed as return value for
  107.       // some algorithms like transform).
  108.       __f._M_finish_iterator = __begin + __length;
  109.  
  110.       return __o;
  111.     }
  112.  
  113. } // end namespace
  114.  
  115. #endif /* _GLIBCXX_PARALLEL_OMP_LOOP_H */
  116.