475 lines
15 KiB
C++
475 lines
15 KiB
C++
// -*- C++ -*-
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// Copyright (C) 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the terms
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// of the GNU General Public License as published by the Free Software
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// Foundation; either version 3, or (at your option) any later
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// version.
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// This library is distributed in the hope that it will be useful, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// General Public License for more details.
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// Under Section 7 of GPL version 3, you are granted additional
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// permissions described in the GCC Runtime Library Exception, version
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// 3.1, as published by the Free Software Foundation.
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// You should have received a copy of the GNU General Public License and
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// a copy of the GCC Runtime Library Exception along with this program;
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// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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// <http://www.gnu.org/licenses/>.
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/** @file parallel/multiway_mergesort.h
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* @brief Parallel multiway merge sort.
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* This file is a GNU parallel extension to the Standard C++ Library.
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*/
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// Written by Johannes Singler.
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#ifndef _GLIBCXX_PARALLEL_MULTIWAY_MERGESORT_H
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#define _GLIBCXX_PARALLEL_MULTIWAY_MERGESORT_H 1
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#include <vector>
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#include <parallel/basic_iterator.h>
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#include <bits/stl_algo.h>
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#include <parallel/parallel.h>
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#include <parallel/multiway_merge.h>
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namespace __gnu_parallel
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{
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/** @brief Subsequence description. */
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template<typename _DifferenceTp>
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struct _Piece
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{
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typedef _DifferenceTp _DifferenceType;
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/** @brief Begin of subsequence. */
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_DifferenceType _M_begin;
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/** @brief End of subsequence. */
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_DifferenceType _M_end;
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};
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/** @brief Data accessed by all threads.
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*
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* PMWMS = parallel multiway mergesort */
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template<typename _RAIter>
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struct _PMWMSSortingData
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{
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typedef std::iterator_traits<_RAIter> _TraitsType;
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typedef typename _TraitsType::value_type _ValueType;
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typedef typename _TraitsType::difference_type _DifferenceType;
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/** @brief Number of threads involved. */
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_ThreadIndex _M_num_threads;
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/** @brief Input __begin. */
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_RAIter _M_source;
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/** @brief Start indices, per thread. */
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_DifferenceType* _M_starts;
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/** @brief Storage in which to sort. */
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_ValueType** _M_temporary;
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/** @brief Samples. */
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_ValueType* _M_samples;
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/** @brief Offsets to add to the found positions. */
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_DifferenceType* _M_offsets;
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/** @brief Pieces of data to merge @c [thread][__sequence] */
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std::vector<_Piece<_DifferenceType> >* _M_pieces;
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};
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/**
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* @brief Select _M_samples from a sequence.
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* @param __sd Pointer to algorithm data. _Result will be placed in
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* @c __sd->_M_samples.
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* @param __num_samples Number of _M_samples to select.
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*/
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template<typename _RAIter, typename _DifferenceTp>
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void
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__determine_samples(_PMWMSSortingData<_RAIter>* __sd,
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_DifferenceTp __num_samples)
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{
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typedef std::iterator_traits<_RAIter> _TraitsType;
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typedef typename _TraitsType::value_type _ValueType;
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typedef _DifferenceTp _DifferenceType;
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_ThreadIndex __iam = omp_get_thread_num();
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_DifferenceType* __es = new _DifferenceType[__num_samples + 2];
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equally_split(__sd->_M_starts[__iam + 1] - __sd->_M_starts[__iam],
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__num_samples + 1, __es);
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for (_DifferenceType __i = 0; __i < __num_samples; ++__i)
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::new(&(__sd->_M_samples[__iam * __num_samples + __i]))
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_ValueType(__sd->_M_source[__sd->_M_starts[__iam]
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+ __es[__i + 1]]);
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delete[] __es;
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}
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/** @brief Split consistently. */
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template<bool __exact, typename _RAIter,
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typename _Compare, typename _SortingPlacesIterator>
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struct _SplitConsistently
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{ };
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/** @brief Split by exact splitting. */
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template<typename _RAIter, typename _Compare,
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typename _SortingPlacesIterator>
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struct _SplitConsistently<true, _RAIter, _Compare, _SortingPlacesIterator>
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{
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void
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operator()(const _ThreadIndex __iam,
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_PMWMSSortingData<_RAIter>* __sd,
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_Compare& __comp,
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const typename
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std::iterator_traits<_RAIter>::difference_type
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__num_samples) const
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{
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# pragma omp barrier
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std::vector<std::pair<_SortingPlacesIterator,
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_SortingPlacesIterator> >
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__seqs(__sd->_M_num_threads);
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for (_ThreadIndex __s = 0; __s < __sd->_M_num_threads; __s++)
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__seqs[__s] = std::make_pair(__sd->_M_temporary[__s],
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__sd->_M_temporary[__s]
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+ (__sd->_M_starts[__s + 1]
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- __sd->_M_starts[__s]));
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std::vector<_SortingPlacesIterator> __offsets(__sd->_M_num_threads);
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// if not last thread
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if (__iam < __sd->_M_num_threads - 1)
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multiseq_partition(__seqs.begin(), __seqs.end(),
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__sd->_M_starts[__iam + 1], __offsets.begin(),
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__comp);
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for (_ThreadIndex __seq = 0; __seq < __sd->_M_num_threads; __seq++)
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{
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// for each sequence
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if (__iam < (__sd->_M_num_threads - 1))
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__sd->_M_pieces[__iam][__seq]._M_end
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= __offsets[__seq] - __seqs[__seq].first;
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else
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// very end of this sequence
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__sd->_M_pieces[__iam][__seq]._M_end =
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__sd->_M_starts[__seq + 1] - __sd->_M_starts[__seq];
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}
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# pragma omp barrier
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for (_ThreadIndex __seq = 0; __seq < __sd->_M_num_threads; __seq++)
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{
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// For each sequence.
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if (__iam > 0)
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__sd->_M_pieces[__iam][__seq]._M_begin =
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__sd->_M_pieces[__iam - 1][__seq]._M_end;
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else
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// Absolute beginning.
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__sd->_M_pieces[__iam][__seq]._M_begin = 0;
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}
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}
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};
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/** @brief Split by sampling. */
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template<typename _RAIter, typename _Compare,
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typename _SortingPlacesIterator>
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struct _SplitConsistently<false, _RAIter, _Compare, _SortingPlacesIterator>
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{
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void
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operator()(const _ThreadIndex __iam,
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_PMWMSSortingData<_RAIter>* __sd,
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_Compare& __comp,
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const typename
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std::iterator_traits<_RAIter>::difference_type
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__num_samples) const
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{
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typedef std::iterator_traits<_RAIter> _TraitsType;
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typedef typename _TraitsType::value_type _ValueType;
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typedef typename _TraitsType::difference_type _DifferenceType;
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__determine_samples(__sd, __num_samples);
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# pragma omp barrier
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# pragma omp single
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__gnu_sequential::sort(__sd->_M_samples,
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__sd->_M_samples
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+ (__num_samples * __sd->_M_num_threads),
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__comp);
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# pragma omp barrier
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for (_ThreadIndex __s = 0; __s < __sd->_M_num_threads; ++__s)
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{
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// For each sequence.
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if (__num_samples * __iam > 0)
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__sd->_M_pieces[__iam][__s]._M_begin =
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std::lower_bound(__sd->_M_temporary[__s],
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__sd->_M_temporary[__s]
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+ (__sd->_M_starts[__s + 1]
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- __sd->_M_starts[__s]),
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__sd->_M_samples[__num_samples * __iam],
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__comp)
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- __sd->_M_temporary[__s];
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else
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// Absolute beginning.
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__sd->_M_pieces[__iam][__s]._M_begin = 0;
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if ((__num_samples * (__iam + 1)) <
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(__num_samples * __sd->_M_num_threads))
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__sd->_M_pieces[__iam][__s]._M_end =
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std::lower_bound(__sd->_M_temporary[__s],
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__sd->_M_temporary[__s]
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+ (__sd->_M_starts[__s + 1]
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- __sd->_M_starts[__s]),
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__sd->_M_samples[__num_samples * (__iam + 1)],
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__comp)
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- __sd->_M_temporary[__s];
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else
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// Absolute end.
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__sd->_M_pieces[__iam][__s]._M_end = (__sd->_M_starts[__s + 1]
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- __sd->_M_starts[__s]);
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}
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}
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};
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template<bool __stable, typename _RAIter, typename _Compare>
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struct __possibly_stable_sort
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{ };
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template<typename _RAIter, typename _Compare>
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struct __possibly_stable_sort<true, _RAIter, _Compare>
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{
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void operator()(const _RAIter& __begin,
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const _RAIter& __end, _Compare& __comp) const
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{ __gnu_sequential::stable_sort(__begin, __end, __comp); }
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};
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template<typename _RAIter, typename _Compare>
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struct __possibly_stable_sort<false, _RAIter, _Compare>
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{
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void operator()(const _RAIter __begin,
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const _RAIter __end, _Compare& __comp) const
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{ __gnu_sequential::sort(__begin, __end, __comp); }
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};
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template<bool __stable, typename Seq_RAIter,
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typename _RAIter, typename _Compare,
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typename DiffType>
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struct __possibly_stable_multiway_merge
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{ };
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template<typename Seq_RAIter, typename _RAIter,
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typename _Compare, typename _DiffType>
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struct __possibly_stable_multiway_merge<true, Seq_RAIter,
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_RAIter, _Compare, _DiffType>
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{
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void operator()(const Seq_RAIter& __seqs_begin,
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const Seq_RAIter& __seqs_end,
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const _RAIter& __target,
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_Compare& __comp,
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_DiffType __length_am) const
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{ stable_multiway_merge(__seqs_begin, __seqs_end, __target,
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__length_am, __comp, sequential_tag()); }
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};
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template<typename Seq_RAIter, typename _RAIter,
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typename _Compare, typename _DiffType>
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struct __possibly_stable_multiway_merge<false, Seq_RAIter,
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_RAIter, _Compare, _DiffType>
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{
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void operator()(const Seq_RAIter& __seqs_begin,
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const Seq_RAIter& __seqs_end,
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const _RAIter& __target,
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_Compare& __comp,
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_DiffType __length_am) const
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{ multiway_merge(__seqs_begin, __seqs_end, __target, __length_am,
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__comp, sequential_tag()); }
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};
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/** @brief PMWMS code executed by each thread.
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* @param __sd Pointer to algorithm data.
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* @param __comp Comparator.
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*/
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template<bool __stable, bool __exact, typename _RAIter,
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typename _Compare>
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void
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parallel_sort_mwms_pu(_PMWMSSortingData<_RAIter>* __sd,
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_Compare& __comp)
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{
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typedef std::iterator_traits<_RAIter> _TraitsType;
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typedef typename _TraitsType::value_type _ValueType;
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typedef typename _TraitsType::difference_type _DifferenceType;
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_ThreadIndex __iam = omp_get_thread_num();
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// Length of this thread's chunk, before merging.
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_DifferenceType __length_local =
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__sd->_M_starts[__iam + 1] - __sd->_M_starts[__iam];
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// Sort in temporary storage, leave space for sentinel.
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typedef _ValueType* _SortingPlacesIterator;
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__sd->_M_temporary[__iam] =
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static_cast<_ValueType*>(::operator new(sizeof(_ValueType)
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* (__length_local + 1)));
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// Copy there.
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std::uninitialized_copy(__sd->_M_source + __sd->_M_starts[__iam],
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__sd->_M_source + __sd->_M_starts[__iam]
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+ __length_local,
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__sd->_M_temporary[__iam]);
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__possibly_stable_sort<__stable, _SortingPlacesIterator, _Compare>()
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(__sd->_M_temporary[__iam],
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__sd->_M_temporary[__iam] + __length_local,
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__comp);
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// Invariant: locally sorted subsequence in sd->_M_temporary[__iam],
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// __sd->_M_temporary[__iam] + __length_local.
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// No barrier here: Synchronization is done by the splitting routine.
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_DifferenceType __num_samples =
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_Settings::get().sort_mwms_oversampling * __sd->_M_num_threads - 1;
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_SplitConsistently<__exact, _RAIter, _Compare, _SortingPlacesIterator>()
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(__iam, __sd, __comp, __num_samples);
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// Offset from __target __begin, __length after merging.
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_DifferenceType __offset = 0, __length_am = 0;
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for (_ThreadIndex __s = 0; __s < __sd->_M_num_threads; __s++)
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{
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__length_am += (__sd->_M_pieces[__iam][__s]._M_end
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- __sd->_M_pieces[__iam][__s]._M_begin);
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__offset += __sd->_M_pieces[__iam][__s]._M_begin;
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}
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typedef std::vector<
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std::pair<_SortingPlacesIterator, _SortingPlacesIterator> >
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_SeqVector;
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_SeqVector __seqs(__sd->_M_num_threads);
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for (_ThreadIndex __s = 0; __s < __sd->_M_num_threads; ++__s)
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{
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__seqs[__s] =
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std::make_pair(__sd->_M_temporary[__s]
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+ __sd->_M_pieces[__iam][__s]._M_begin,
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__sd->_M_temporary[__s]
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+ __sd->_M_pieces[__iam][__s]._M_end);
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}
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__possibly_stable_multiway_merge<
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__stable, typename _SeqVector::iterator,
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_RAIter, _Compare, _DifferenceType>()(__seqs.begin(), __seqs.end(),
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__sd->_M_source + __offset, __comp,
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__length_am);
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# pragma omp barrier
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::operator delete(__sd->_M_temporary[__iam]);
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}
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/** @brief PMWMS main call.
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* @param __begin Begin iterator of sequence.
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* @param __end End iterator of sequence.
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* @param __comp Comparator.
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* @param __n Length of sequence.
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* @param __num_threads Number of threads to use.
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*/
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template<bool __stable, bool __exact, typename _RAIter,
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typename _Compare>
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void
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parallel_sort_mwms(_RAIter __begin, _RAIter __end,
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_Compare __comp,
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_ThreadIndex __num_threads)
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{
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_GLIBCXX_CALL(__end - __begin)
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typedef std::iterator_traits<_RAIter> _TraitsType;
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typedef typename _TraitsType::value_type _ValueType;
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typedef typename _TraitsType::difference_type _DifferenceType;
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_DifferenceType __n = __end - __begin;
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if (__n <= 1)
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return;
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// at least one element per thread
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if (__num_threads > __n)
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__num_threads = static_cast<_ThreadIndex>(__n);
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// shared variables
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_PMWMSSortingData<_RAIter> __sd;
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_DifferenceType* __starts;
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# pragma omp parallel num_threads(__num_threads)
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{
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__num_threads = omp_get_num_threads(); //no more threads than requested
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# pragma omp single
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{
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__sd._M_num_threads = __num_threads;
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__sd._M_source = __begin;
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__sd._M_temporary = new _ValueType*[__num_threads];
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if (!__exact)
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{
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_DifferenceType __size =
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(_Settings::get().sort_mwms_oversampling * __num_threads - 1)
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* __num_threads;
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__sd._M_samples = static_cast<_ValueType*>
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(::operator new(__size * sizeof(_ValueType)));
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}
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else
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__sd._M_samples = 0;
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__sd._M_offsets = new _DifferenceType[__num_threads - 1];
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__sd._M_pieces
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= new std::vector<_Piece<_DifferenceType> >[__num_threads];
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for (_ThreadIndex __s = 0; __s < __num_threads; ++__s)
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__sd._M_pieces[__s].resize(__num_threads);
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__starts = __sd._M_starts = new _DifferenceType[__num_threads + 1];
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_DifferenceType __chunk_length = __n / __num_threads;
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_DifferenceType __split = __n % __num_threads;
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_DifferenceType __pos = 0;
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for (_ThreadIndex __i = 0; __i < __num_threads; ++__i)
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{
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__starts[__i] = __pos;
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__pos += ((__i < __split)
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? (__chunk_length + 1) : __chunk_length);
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}
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__starts[__num_threads] = __pos;
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} //single
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// Now sort in parallel.
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parallel_sort_mwms_pu<__stable, __exact>(&__sd, __comp);
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} //parallel
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delete[] __starts;
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delete[] __sd._M_temporary;
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if (!__exact)
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::operator delete(__sd._M_samples);
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delete[] __sd._M_offsets;
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delete[] __sd._M_pieces;
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}
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} //namespace __gnu_parallel
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#endif /* _GLIBCXX_PARALLEL_MULTIWAY_MERGESORT_H */
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