mingw/lib/gcc/mingw32/4.4.0/include/c++/parallel/omp_loop_static.h

   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/omp_loop_static.h
  26  *  @brief Parallelization of embarrassingly parallel execution by
  27  *  means of an OpenMP for loop with static scheduling.
  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_STATIC_H
  34 #define _GLIBCXX_PARALLEL_OMP_LOOP_STATIC_H 1
  35
  36 #include <omp.h>
  37
  38 #include <parallel/settings.h>
  39 #include <parallel/basic_iterator.h>
  40
  41 namespace __gnu_parallel
  42 {
  43
  44   /** @brief Embarrassingly parallel algorithm for random access
  45    * iterators, using an OpenMP for loop with static scheduling.
  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 processed
  54    *  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 RandomAccessIterator,
  62          typename Op,
  63          typename Fu,
  64          typename Red,
  65          typename Result>
  66   Op
  67   for_each_template_random_access_omp_loop_static(RandomAccessIterator begin,
  68                                                   RandomAccessIterator end,
  69                                                   Op o, Fu& f, Red r,
  70                                                   Result base, Result& output,
  71                                                   typename std::iterator_traits
  72                                                   <RandomAccessIterator>::
  73                                                   difference_type bound)
  74   {
  75     typedef typename
  76       std::iterator_traits<RandomAccessIterator>::difference_type
  77       difference_type;
  78
  79     difference_type length = end - begin;
  80     thread_index_t num_threads =
  81       std::min<difference_type>(get_max_threads(), length);
  82
  83     Result *thread_results;
  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 = new Result[num_threads];
  91
  92             for (thread_index_t i = 0; i < num_threads; ++i)
  93               thread_results[i] = Result();
  94           }
  95
  96         thread_index_t iam = omp_get_thread_num();
  97
  98 #       pragma omp for schedule(static, _Settings::get().workstealing_chunk_size)
  99         for (difference_type pos = 0; pos < length; ++pos)
 100           thread_results[iam] = r(thread_results[iam], f(o, begin+pos));
 101       } //parallel
 102
 103     for (thread_index_t i = 0; i < num_threads; ++i)
 104       output = r(output, thread_results[i]);
 105
 106     delete [] thread_results;
 107
 108     // Points to last element processed (needed as return value for
 109     // some algorithms like transform).
 110     f.finish_iterator = begin + length;
 111
 112     return o;
 113   }
 114
 115 } // end namespace
 116
 117 #endif /* _GLIBCXX_PARALLEL_OMP_LOOP_STATIC_H */