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// -*- 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.
// This library is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// 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.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <>.
/** @file parallel/omp_loop.h
* @brief Parallelization of embarrassingly parallel execution by
* means of an OpenMP for loop.
* This file is a GNU parallel extension to the Standard C++ Library.
// Written by Felix Putze.
#include <omp.h>
#include <parallel/settings.h>
#include <parallel/basic_iterator.h>
#include <parallel/base.h>
namespace __gnu_parallel
/** @brief Embarrassingly parallel algorithm for random access
* iterators, using an OpenMP for loop.
* @param begin Begin iterator of element sequence.
* @param end End iterator of element sequence.
* @param o User-supplied functor (comparator, predicate, adding
* functor, etc.).
* @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 RandomAccessIterator,
typename Op,
typename Fu,
typename Red,
typename Result>
for_each_template_random_access_omp_loop(RandomAccessIterator begin,
RandomAccessIterator end,
Op o, Fu& f, Red r, Result base,
Result& output,
typename std::iterator_traits
difference_type bound)
typedef typename
difference_type length = end - begin;
thread_index_t num_threads =
__gnu_parallel::min<difference_type>(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 (thread_index_t i = 0; i < num_threads; ++i)
thread_results[i] = Result();
thread_index_t iam = omp_get_thread_num();
# pragma omp for schedule(dynamic, _Settings::get().workstealing_chunk_size)
for (difference_type pos = 0; pos < length; ++pos)
thread_results[iam] =
r(thread_results[iam], f(o, begin+pos));
} //parallel
for (thread_index_t 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