gcc/libstdc++-v3/include/parallel/omp_loop_static.h

// -*- C++ -*-

// Copyright (C) 2007, 2008, 2009 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the terms
// of the GNU General Public License as published by the Free Software
// Foundation; either version 3, or (at your option) any later
// version.

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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

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// a copy of the GCC Runtime Library Exception along with this program;
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/** @file parallel/omp_loop_static.h
 *  @brief Parallelization of embarrassingly parallel execution by
 *  means of an OpenMP for loop with static scheduling.
 *  This file is a GNU parallel extension to the Standard C++ Library.
 */

// Written by Felix Putze.

#ifndef _GLIBCXX_PARALLEL_OMP_LOOP_STATIC_H
#define _GLIBCXX_PARALLEL_OMP_LOOP_STATIC_H 1

#include <omp.h>

#include <parallel/settings.h>
#include <parallel/basic_iterator.h>

namespace __gnu_parallel
{

  /** @brief Embarrassingly parallel algorithm for random access
   * iterators, using an OpenMP for loop with static scheduling.
   *
   *  @param __begin Begin iterator of element __sequence.
   *  @param __end End iterator of element __sequence.
   *  @param __o User-supplied functor (comparator, predicate, adding
   *  functor, ...).
   *  @param __f Functor to "process" an element with __op (depends on
   *  desired functionality, e. g. for std::for_each(), ...).
   *  @param __r Functor to "add" a single __result to the already processed
   *  __elements (depends on functionality).
   *  @param __base Base value for reduction.
   *  @param __output Pointer to position where final result is written to
   *  @param __bound Maximum number of elements processed (e. g. for
   *  std::count_n()).
   *  @return User-supplied functor (that may contain a part of the result).
   */
template<typename _RAIter,
	 typename _Op,
	 typename _Fu,
	 typename _Red,
	 typename _Result>
  _Op
  for_each_template_random_access_omp_loop_static(_RAIter __begin,
						  _RAIter __end,
						  _Op __o, _Fu& __f, _Red __r,
						  _Result __base, _Result& __output,
						  typename std::iterator_traits
						  <_RAIter>::
						  difference_type __bound)
  {
    typedef typename
      std::iterator_traits<_RAIter>::difference_type
      _DifferenceType;

    _DifferenceType __length = __end - __begin;
    _ThreadIndex __num_threads =
      std::min<_DifferenceType>(__get_max_threads(), __length);

    _Result *__thread_results;

#   pragma omp parallel num_threads(__num_threads)
      {
#       pragma omp single
          {
            __num_threads = omp_get_num_threads();
            __thread_results = new _Result[__num_threads];

            for (_ThreadIndex __i = 0; __i < __num_threads; ++__i)
              __thread_results[__i] = _Result();
          }

        _ThreadIndex __iam = omp_get_thread_num();

#       pragma omp for schedule(static, _Settings::get().workstealing_chunk_size)
        for (_DifferenceType __pos = 0; __pos < __length; ++__pos)
          __thread_results[__iam] = __r(__thread_results[__iam], __f(__o, __begin+__pos));
      } //parallel

    for (_ThreadIndex __i = 0; __i < __num_threads; ++__i)
      __output = __r(__output, __thread_results[__i]);

    delete [] __thread_results;

    // Points to last element processed (needed as return value for
    // some algorithms like transform).
    __f.finish_iterator = __begin + __length;

    return __o;
  }

} // end namespace

#endif /* _GLIBCXX_PARALLEL_OMP_LOOP_STATIC_H */