gcc/libstdc++-v3/include/parallel/find.h - native_client/nacl-toolchain - Git at Google

 // -*- 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
 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 // 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
 // <http://www.gnu.org/licenses/>.

 /** @file parallel/find.h
  *  @brief Parallel implementation base for std::find(), std::equal()
  *  and related functions.
  *  This file is a GNU parallel extension to the Standard C++ Library.
  */

 // Written by Felix Putze and Johannes Singler.

 #ifndef _GLIBCXX_PARALLEL_FIND_H
 #define _GLIBCXX_PARALLEL_FIND_H 1

 #include <bits/stl_algobase.h>

 #include <parallel/features.h>
 #include <parallel/parallel.h>
 #include <parallel/compatibility.h>
 #include <parallel/equally_split.h>

 namespace __gnu_parallel
 {
 /**
  *  @brief Parallel std::find, switch for different algorithms.
  *  @param begin1 Begin iterator of first sequence.
  *  @param end1 End iterator of first sequence.
  *  @param begin2 Begin iterator of second sequence. Must have same
  *  length as first sequence.
  *  @param pred Find predicate.
  *  @param selector Functionality (e. g. std::find_if (), std::equal(),...)
  *  @return Place of finding in both sequences.
  */
 template<typename RandomAccessIterator1,
 	 typename RandomAccessIterator2,
 	 typename Pred,
 	 typename Selector>
   inline std::pair<RandomAccessIterator1, RandomAccessIterator2>
   find_template(RandomAccessIterator1 begin1, RandomAccessIterator1 end1,
                 RandomAccessIterator2 begin2, Pred pred, Selector selector)
   {
     switch (_Settings::get().find_algorithm)
       {
       case GROWING_BLOCKS:
         return find_template(begin1, end1, begin2, pred, selector,
 			     growing_blocks_tag());
       case CONSTANT_SIZE_BLOCKS:
         return find_template(begin1, end1, begin2, pred, selector,
 			     constant_size_blocks_tag());
       case EQUAL_SPLIT:
         return find_template(begin1, end1, begin2, pred, selector,
 			     equal_split_tag());
       default:
         _GLIBCXX_PARALLEL_ASSERT(false);
         return std::make_pair(begin1, begin2);
       }
   }

 #if _GLIBCXX_FIND_EQUAL_SPLIT

 /**
  *  @brief Parallel std::find, equal splitting variant.
  *  @param begin1 Begin iterator of first sequence.
  *  @param end1 End iterator of first sequence.
  *  @param begin2 Begin iterator of second sequence. Second sequence
  *  must have same length as first sequence.
  *  @param pred Find predicate.
  *  @param selector Functionality (e. g. std::find_if (), std::equal(),...)
  *  @return Place of finding in both sequences.
  */
 template<typename RandomAccessIterator1,
 	 typename RandomAccessIterator2,
 	 typename Pred,
 	 typename Selector>
   std::pair<RandomAccessIterator1, RandomAccessIterator2>
   find_template(RandomAccessIterator1 begin1,
                 RandomAccessIterator1 end1,
                 RandomAccessIterator2 begin2,
                 Pred pred,
                 Selector selector,
                 equal_split_tag)
   {
     _GLIBCXX_CALL(end1 - begin1)

     typedef std::iterator_traits<RandomAccessIterator1> traits_type;
     typedef typename traits_type::difference_type difference_type;
     typedef typename traits_type::value_type value_type;

     difference_type length = end1 - begin1;
     difference_type result = length;
     difference_type* borders;

     omp_lock_t result_lock;
     omp_init_lock(&result_lock);

     thread_index_t num_threads = get_max_threads();
 #   pragma omp parallel num_threads(num_threads)
       {
 #       pragma omp single
           {
             num_threads = omp_get_num_threads();
             borders = new difference_type[num_threads + 1];
             equally_split(length, num_threads, borders);
           } //single

         thread_index_t iam = omp_get_thread_num();
         difference_type start = borders[iam], stop = borders[iam + 1];

         RandomAccessIterator1 i1 = begin1 + start;
         RandomAccessIterator2 i2 = begin2 + start;
         for (difference_type pos = start; pos < stop; ++pos)
           {
             #pragma omp flush(result)
             // Result has been set to something lower.
             if (result < pos)
               break;

             if (selector(i1, i2, pred))
               {
                 omp_set_lock(&result_lock);
                 if (pos < result)
                   result = pos;
                 omp_unset_lock(&result_lock);
                 break;
               }
             ++i1;
             ++i2;
           }
       } //parallel

     omp_destroy_lock(&result_lock);
     delete[] borders;

     return
       std::pair<RandomAccessIterator1, RandomAccessIterator2>(begin1 + result,
 							      begin2 + result);
   }

 #endif

 #if _GLIBCXX_FIND_GROWING_BLOCKS

 /**
  *  @brief Parallel std::find, growing block size variant.
  *  @param begin1 Begin iterator of first sequence.
  *  @param end1 End iterator of first sequence.
  *  @param begin2 Begin iterator of second sequence. Second sequence
  *  must have same length as first sequence.
  *  @param pred Find predicate.
  *  @param selector Functionality (e. g. std::find_if (), std::equal(),...)
  *  @return Place of finding in both sequences.
  *  @see __gnu_parallel::_Settings::find_sequential_search_size
  *  @see __gnu_parallel::_Settings::find_initial_block_size
  *  @see __gnu_parallel::_Settings::find_maximum_block_size
  *  @see __gnu_parallel::_Settings::find_increasing_factor
  *
  *  There are two main differences between the growing blocks and
  *  the constant-size blocks variants.
  *  1. For GB, the block size grows; for CSB, the block size is fixed.

  *  2. For GB, the blocks are allocated dynamically;
  *     for CSB, the blocks are allocated in a predetermined manner,
  *     namely spacial round-robin.
  */
 template<typename RandomAccessIterator1,
 	 typename RandomAccessIterator2,
 	 typename Pred,
 	 typename Selector>
   std::pair<RandomAccessIterator1, RandomAccessIterator2>
   find_template(RandomAccessIterator1 begin1, RandomAccessIterator1 end1,
                 RandomAccessIterator2 begin2, Pred pred, Selector selector,
                 growing_blocks_tag)
   {
     _GLIBCXX_CALL(end1 - begin1)

     typedef std::iterator_traits<RandomAccessIterator1> traits_type;
     typedef typename traits_type::difference_type difference_type;
     typedef typename traits_type::value_type value_type;

     const _Settings& __s = _Settings::get();

     difference_type length = end1 - begin1;

     difference_type sequential_search_size =
       std::min<difference_type>(length, __s.find_sequential_search_size);

     // Try it sequentially first.
     std::pair<RandomAccessIterator1, RandomAccessIterator2> find_seq_result =
       selector.sequential_algorithm(
           begin1, begin1 + sequential_search_size, begin2, pred);

     if (find_seq_result.first != (begin1 + sequential_search_size))
       return find_seq_result;

     // Index of beginning of next free block (after sequential find).
     difference_type next_block_start = sequential_search_size;
     difference_type result = length;

     omp_lock_t result_lock;
     omp_init_lock(&result_lock);

     thread_index_t num_threads = get_max_threads();
 #   pragma omp parallel shared(result) num_threads(num_threads)
       {
 #       pragma omp single
           num_threads = omp_get_num_threads();

         // Not within first k elements -> start parallel.
         thread_index_t iam = omp_get_thread_num();

         difference_type block_size = __s.find_initial_block_size;
         difference_type start =
             fetch_and_add<difference_type>(&next_block_start, block_size);

         // Get new block, update pointer to next block.
         difference_type stop =
             std::min<difference_type>(length, start + block_size);

         std::pair<RandomAccessIterator1, RandomAccessIterator2> local_result;

         while (start < length)
           {
 #           pragma omp flush(result)
             // Get new value of result.
             if (result < start)
               {
                 // No chance to find first element.
                 break;
               }

             local_result = selector.sequential_algorithm(
                 begin1 + start, begin1 + stop, begin2 + start, pred);
             if (local_result.first != (begin1 + stop))
               {
                 omp_set_lock(&result_lock);
                 if ((local_result.first - begin1) < result)
                   {
                     result = local_result.first - begin1;

                     // Result cannot be in future blocks, stop algorithm.
                     fetch_and_add<difference_type>(&next_block_start, length);
                   }
                   omp_unset_lock(&result_lock);
               }

             block_size =
 	      std::min<difference_type>(block_size * __s.find_increasing_factor,
 					__s.find_maximum_block_size);

             // Get new block, update pointer to next block.
             start =
 	      fetch_and_add<difference_type>(&next_block_start, block_size);
             stop = ((length < (start + block_size))
 		    ? length : (start + block_size));
           }
       } //parallel

     omp_destroy_lock(&result_lock);

     // Return iterator on found element.
     return
       std::pair<RandomAccessIterator1, RandomAccessIterator2>(begin1 + result,
 							      begin2 + result);
   }

 #endif

 #if _GLIBCXX_FIND_CONSTANT_SIZE_BLOCKS

 /**
  *   @brief Parallel std::find, constant block size variant.
  *  @param begin1 Begin iterator of first sequence.
  *  @param end1 End iterator of first sequence.
  *  @param begin2 Begin iterator of second sequence. Second sequence
  *  must have same length as first sequence.
  *  @param pred Find predicate.
  *  @param selector Functionality (e. g. std::find_if (), std::equal(),...)
  *  @return Place of finding in both sequences.
  *  @see __gnu_parallel::_Settings::find_sequential_search_size
  *  @see __gnu_parallel::_Settings::find_block_size
  *  There are two main differences between the growing blocks and the
  *  constant-size blocks variants.
  *  1. For GB, the block size grows; for CSB, the block size is fixed.
  *  2. For GB, the blocks are allocated dynamically; for CSB, the
  *  blocks are allocated in a predetermined manner, namely spacial
  *  round-robin.
  */
 template<typename RandomAccessIterator1,
 	 typename RandomAccessIterator2,
 	 typename Pred,
 	 typename Selector>
   std::pair<RandomAccessIterator1, RandomAccessIterator2>
   find_template(RandomAccessIterator1 begin1, RandomAccessIterator1 end1,
                 RandomAccessIterator2 begin2, Pred pred, Selector selector,
                 constant_size_blocks_tag)
   {
     _GLIBCXX_CALL(end1 - begin1)
     typedef std::iterator_traits<RandomAccessIterator1> traits_type;
     typedef typename traits_type::difference_type difference_type;
     typedef typename traits_type::value_type value_type;

     const _Settings& __s = _Settings::get();

     difference_type length = end1 - begin1;

     difference_type sequential_search_size = std::min<difference_type>(
         length, __s.find_sequential_search_size);

     // Try it sequentially first.
     std::pair<RandomAccessIterator1, RandomAccessIterator2> find_seq_result =
       selector.sequential_algorithm(begin1, begin1 + sequential_search_size,
                                     begin2, pred);

     if (find_seq_result.first != (begin1 + sequential_search_size))
       return find_seq_result;

     difference_type result = length;
     omp_lock_t result_lock;
     omp_init_lock(&result_lock);

     // Not within first sequential_search_size elements -> start parallel.

     thread_index_t num_threads = get_max_threads();
 #   pragma omp parallel shared(result) num_threads(num_threads)
       {
 #       pragma omp single
           num_threads = omp_get_num_threads();

         thread_index_t iam = omp_get_thread_num();
         difference_type block_size = __s.find_initial_block_size;

         // First element of thread's current iteration.
         difference_type iteration_start = sequential_search_size;

         // Where to work (initialization).
         difference_type start = iteration_start + iam * block_size;
         difference_type stop =
             std::min<difference_type>(length, start + block_size);

         std::pair<RandomAccessIterator1, RandomAccessIterator2> local_result;

         while (start < length)
           {
             // Get new value of result.
 #           pragma omp flush(result)
             // No chance to find first element.
             if (result < start)
               break;
             local_result = selector.sequential_algorithm(
                 begin1 + start, begin1 + stop,
                 begin2 + start, pred);
             if (local_result.first != (begin1 + stop))
               {
                 omp_set_lock(&result_lock);
                 if ((local_result.first - begin1) < result)
                   result = local_result.first - begin1;
                 omp_unset_lock(&result_lock);
                 // Will not find better value in its interval.
                 break;
               }

             iteration_start += num_threads * block_size;

             // Where to work.
             start = iteration_start + iam * block_size;
             stop = std::min<difference_type>(length, start + block_size);
           }
       } //parallel

     omp_destroy_lock(&result_lock);

     // Return iterator on found element.
     return
       std::pair<RandomAccessIterator1, RandomAccessIterator2>(begin1 + result,
 							      begin2 + result);
   }
 #endif
 } // end namespace

 #endif /* _GLIBCXX_PARALLEL_FIND_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.

	// This library is distributed in the hope that it will be useful, but
	// WITHOUT ANY WARRANTY; without even the implied warranty of
	// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	// 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
	// <http://www.gnu.org/licenses/>.

	/** @file parallel/find.h
	* @brief Parallel implementation base for std::find(), std::equal()
	* and related functions.
	* This file is a GNU parallel extension to the Standard C++ Library.
	*/

	// Written by Felix Putze and Johannes Singler.

	#ifndef _GLIBCXX_PARALLEL_FIND_H
	#define _GLIBCXX_PARALLEL_FIND_H 1

	#include <bits/stl_algobase.h>

	#include <parallel/features.h>
	#include <parallel/parallel.h>
	#include <parallel/compatibility.h>
	#include <parallel/equally_split.h>

	namespace __gnu_parallel
	{
	/**
	* @brief Parallel std::find, switch for different algorithms.
	* @param begin1 Begin iterator of first sequence.
	* @param end1 End iterator of first sequence.
	* @param begin2 Begin iterator of second sequence. Must have same
	* length as first sequence.
	* @param pred Find predicate.
	* @param selector Functionality (e. g. std::find_if (), std::equal(),...)
	* @return Place of finding in both sequences.
	*/
	template<typename RandomAccessIterator1,
	typename RandomAccessIterator2,
	typename Pred,
	typename Selector>
	inline std::pair<RandomAccessIterator1, RandomAccessIterator2>
	find_template(RandomAccessIterator1 begin1, RandomAccessIterator1 end1,
	RandomAccessIterator2 begin2, Pred pred, Selector selector)
	{
	switch (_Settings::get().find_algorithm)
	{
	case GROWING_BLOCKS:
	return find_template(begin1, end1, begin2, pred, selector,
	growing_blocks_tag());
	case CONSTANT_SIZE_BLOCKS:
	return find_template(begin1, end1, begin2, pred, selector,
	constant_size_blocks_tag());
	case EQUAL_SPLIT:
	return find_template(begin1, end1, begin2, pred, selector,
	equal_split_tag());
	default:
	_GLIBCXX_PARALLEL_ASSERT(false);
	return std::make_pair(begin1, begin2);
	}
	}

	#if _GLIBCXX_FIND_EQUAL_SPLIT

	/**
	* @brief Parallel std::find, equal splitting variant.
	* @param begin1 Begin iterator of first sequence.
	* @param end1 End iterator of first sequence.
	* @param begin2 Begin iterator of second sequence. Second sequence
	* must have same length as first sequence.
	* @param pred Find predicate.
	* @param selector Functionality (e. g. std::find_if (), std::equal(),...)
	* @return Place of finding in both sequences.
	*/
	template<typename RandomAccessIterator1,
	typename RandomAccessIterator2,
	typename Pred,
	typename Selector>
	std::pair<RandomAccessIterator1, RandomAccessIterator2>
	find_template(RandomAccessIterator1 begin1,
	RandomAccessIterator1 end1,
	RandomAccessIterator2 begin2,
	Pred pred,
	Selector selector,
	equal_split_tag)
	{
	_GLIBCXX_CALL(end1 - begin1)

	typedef std::iterator_traits<RandomAccessIterator1> traits_type;
	typedef typename traits_type::difference_type difference_type;
	typedef typename traits_type::value_type value_type;

	difference_type length = end1 - begin1;
	difference_type result = length;
	difference_type* borders;

	omp_lock_t result_lock;
	omp_init_lock(&result_lock);

	thread_index_t num_threads = get_max_threads();
	# pragma omp parallel num_threads(num_threads)
	{
	# pragma omp single
	{
	num_threads = omp_get_num_threads();
	borders = new difference_type[num_threads + 1];
	equally_split(length, num_threads, borders);
	} //single

	thread_index_t iam = omp_get_thread_num();
	difference_type start = borders[iam], stop = borders[iam + 1];

	RandomAccessIterator1 i1 = begin1 + start;
	RandomAccessIterator2 i2 = begin2 + start;
	for (difference_type pos = start; pos < stop; ++pos)
	{
	#pragma omp flush(result)
	// Result has been set to something lower.
	if (result < pos)
	break;

	if (selector(i1, i2, pred))
	{
	omp_set_lock(&result_lock);
	if (pos < result)
	result = pos;
	omp_unset_lock(&result_lock);
	break;
	}
	++i1;
	++i2;
	}
	} //parallel

	omp_destroy_lock(&result_lock);
	delete[] borders;

	return
	std::pair<RandomAccessIterator1, RandomAccessIterator2>(begin1 + result,
	begin2 + result);
	}

	#endif

	#if _GLIBCXX_FIND_GROWING_BLOCKS

	/**
	* @brief Parallel std::find, growing block size variant.
	* @param begin1 Begin iterator of first sequence.
	* @param end1 End iterator of first sequence.
	* @param begin2 Begin iterator of second sequence. Second sequence
	* must have same length as first sequence.
	* @param pred Find predicate.
	* @param selector Functionality (e. g. std::find_if (), std::equal(),...)
	* @return Place of finding in both sequences.
	* @see __gnu_parallel::_Settings::find_sequential_search_size
	* @see __gnu_parallel::_Settings::find_initial_block_size
	* @see __gnu_parallel::_Settings::find_maximum_block_size
	* @see __gnu_parallel::_Settings::find_increasing_factor
	*
	* There are two main differences between the growing blocks and
	* the constant-size blocks variants.
	* 1. For GB, the block size grows; for CSB, the block size is fixed.

	* 2. For GB, the blocks are allocated dynamically;
	* for CSB, the blocks are allocated in a predetermined manner,
	* namely spacial round-robin.
	*/
	template<typename RandomAccessIterator1,
	typename RandomAccessIterator2,
	typename Pred,
	typename Selector>
	std::pair<RandomAccessIterator1, RandomAccessIterator2>
	find_template(RandomAccessIterator1 begin1, RandomAccessIterator1 end1,
	RandomAccessIterator2 begin2, Pred pred, Selector selector,
	growing_blocks_tag)
	{
	_GLIBCXX_CALL(end1 - begin1)

	typedef std::iterator_traits<RandomAccessIterator1> traits_type;
	typedef typename traits_type::difference_type difference_type;
	typedef typename traits_type::value_type value_type;

	const _Settings& __s = _Settings::get();

	difference_type length = end1 - begin1;

	difference_type sequential_search_size =
	std::min<difference_type>(length, __s.find_sequential_search_size);

	// Try it sequentially first.
	std::pair<RandomAccessIterator1, RandomAccessIterator2> find_seq_result =
	selector.sequential_algorithm(
	begin1, begin1 + sequential_search_size, begin2, pred);

	if (find_seq_result.first != (begin1 + sequential_search_size))
	return find_seq_result;

	// Index of beginning of next free block (after sequential find).
	difference_type next_block_start = sequential_search_size;
	difference_type result = length;

	omp_lock_t result_lock;
	omp_init_lock(&result_lock);

	thread_index_t num_threads = get_max_threads();
	# pragma omp parallel shared(result) num_threads(num_threads)
	{
	# pragma omp single
	num_threads = omp_get_num_threads();

	// Not within first k elements -> start parallel.
	thread_index_t iam = omp_get_thread_num();

	difference_type block_size = __s.find_initial_block_size;
	difference_type start =
	fetch_and_add<difference_type>(&next_block_start, block_size);

	// Get new block, update pointer to next block.
	difference_type stop =
	std::min<difference_type>(length, start + block_size);

	std::pair<RandomAccessIterator1, RandomAccessIterator2> local_result;

	while (start < length)
	{
	# pragma omp flush(result)
	// Get new value of result.
	if (result < start)
	{
	// No chance to find first element.
	break;
	}

	local_result = selector.sequential_algorithm(
	begin1 + start, begin1 + stop, begin2 + start, pred);
	if (local_result.first != (begin1 + stop))
	{
	omp_set_lock(&result_lock);
	if ((local_result.first - begin1) < result)
	{
	result = local_result.first - begin1;

	// Result cannot be in future blocks, stop algorithm.
	fetch_and_add<difference_type>(&next_block_start, length);
	}
	omp_unset_lock(&result_lock);
	}

	block_size =
	std::min<difference_type>(block_size * __s.find_increasing_factor,
	__s.find_maximum_block_size);

	// Get new block, update pointer to next block.
	start =
	fetch_and_add<difference_type>(&next_block_start, block_size);
	stop = ((length < (start + block_size))
	? length : (start + block_size));
	}
	} //parallel

	omp_destroy_lock(&result_lock);

	// Return iterator on found element.
	return
	std::pair<RandomAccessIterator1, RandomAccessIterator2>(begin1 + result,
	begin2 + result);
	}

	#endif

	#if _GLIBCXX_FIND_CONSTANT_SIZE_BLOCKS

	/**
	* @brief Parallel std::find, constant block size variant.
	* @param begin1 Begin iterator of first sequence.
	* @param end1 End iterator of first sequence.
	* @param begin2 Begin iterator of second sequence. Second sequence
	* must have same length as first sequence.
	* @param pred Find predicate.
	* @param selector Functionality (e. g. std::find_if (), std::equal(),...)
	* @return Place of finding in both sequences.
	* @see __gnu_parallel::_Settings::find_sequential_search_size
	* @see __gnu_parallel::_Settings::find_block_size
	* There are two main differences between the growing blocks and the
	* constant-size blocks variants.
	* 1. For GB, the block size grows; for CSB, the block size is fixed.
	* 2. For GB, the blocks are allocated dynamically; for CSB, the
	* blocks are allocated in a predetermined manner, namely spacial
	* round-robin.
	*/
	template<typename RandomAccessIterator1,
	typename RandomAccessIterator2,
	typename Pred,
	typename Selector>
	std::pair<RandomAccessIterator1, RandomAccessIterator2>
	find_template(RandomAccessIterator1 begin1, RandomAccessIterator1 end1,
	RandomAccessIterator2 begin2, Pred pred, Selector selector,
	constant_size_blocks_tag)
	{
	_GLIBCXX_CALL(end1 - begin1)
	typedef std::iterator_traits<RandomAccessIterator1> traits_type;
	typedef typename traits_type::difference_type difference_type;
	typedef typename traits_type::value_type value_type;

	const _Settings& __s = _Settings::get();

	difference_type length = end1 - begin1;

	difference_type sequential_search_size = std::min<difference_type>(
	length, __s.find_sequential_search_size);

	// Try it sequentially first.
	std::pair<RandomAccessIterator1, RandomAccessIterator2> find_seq_result =
	selector.sequential_algorithm(begin1, begin1 + sequential_search_size,
	begin2, pred);

	if (find_seq_result.first != (begin1 + sequential_search_size))
	return find_seq_result;

	difference_type result = length;
	omp_lock_t result_lock;
	omp_init_lock(&result_lock);

	// Not within first sequential_search_size elements -> start parallel.

	thread_index_t num_threads = get_max_threads();
	# pragma omp parallel shared(result) num_threads(num_threads)
	{
	# pragma omp single
	num_threads = omp_get_num_threads();

	thread_index_t iam = omp_get_thread_num();
	difference_type block_size = __s.find_initial_block_size;

	// First element of thread's current iteration.
	difference_type iteration_start = sequential_search_size;

	// Where to work (initialization).
	difference_type start = iteration_start + iam * block_size;
	difference_type stop =
	std::min<difference_type>(length, start + block_size);

	std::pair<RandomAccessIterator1, RandomAccessIterator2> local_result;

	while (start < length)
	{
	// Get new value of result.
	# pragma omp flush(result)
	// No chance to find first element.
	if (result < start)
	break;
	local_result = selector.sequential_algorithm(
	begin1 + start, begin1 + stop,
	begin2 + start, pred);
	if (local_result.first != (begin1 + stop))
	{
	omp_set_lock(&result_lock);
	if ((local_result.first - begin1) < result)
	result = local_result.first - begin1;
	omp_unset_lock(&result_lock);
	// Will not find better value in its interval.
	break;
	}

	iteration_start += num_threads * block_size;

	// Where to work.
	start = iteration_start + iam * block_size;
	stop = std::min<difference_type>(length, start + block_size);
	}
	} //parallel

	omp_destroy_lock(&result_lock);

	// Return iterator on found element.
	return
	std::pair<RandomAccessIterator1, RandomAccessIterator2>(begin1 + result,
	begin2 + result);
	}
	#endif
	} // end namespace

	#endif /* _GLIBCXX_PARALLEL_FIND_H */