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/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 */