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// -*- C++ -*- |
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|
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// Copyright (C) 2007-2021 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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|
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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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|
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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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|
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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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|
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/** @file parallel/partition.h |
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* @brief Parallel implementation of std::partition(), |
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* std::nth_element(), and std::partial_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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|
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// Written by Johannes Singler and Felix Putze. |
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|
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#ifndef _GLIBCXX_PARALLEL_PARTITION_H |
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#define _GLIBCXX_PARALLEL_PARTITION_H 1 |
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|
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#include <parallel/basic_iterator.h> |
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#include <parallel/sort.h> |
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#include <parallel/random_number.h> |
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#include <bits/stl_algo.h> |
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#include <parallel/parallel.h> |
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|
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/** @brief Decide whether to declare certain variables volatile. */ |
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#define _GLIBCXX_VOLATILE volatile |
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|
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namespace __gnu_parallel |
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{ |
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/** @brief Parallel implementation of std::partition. |
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* @param __begin Begin iterator of input sequence to split. |
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* @param __end End iterator of input sequence to split. |
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* @param __pred Partition predicate, possibly including some kind |
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* of pivot. |
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* @param __num_threads Maximum number of threads to use for this task. |
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* @return Number of elements not fulfilling the predicate. */ |
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template<typename _RAIter, typename _Predicate> |
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typename std::iterator_traits<_RAIter>::difference_type |
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__parallel_partition(_RAIter __begin, _RAIter __end, |
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_Predicate __pred, _ThreadIndex __num_threads) |
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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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|
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_DifferenceType __n = __end - __begin; |
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|
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_GLIBCXX_CALL(__n) |
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|
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const _Settings& __s = _Settings::get(); |
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|
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// shared |
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_GLIBCXX_VOLATILE _DifferenceType __left = 0, __right = __n - 1, |
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__dist = __n, |
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__leftover_left, __leftover_right, |
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__leftnew, __rightnew; |
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|
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// just 0 or 1, but int to allow atomic operations |
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int* __reserved_left = 0, * __reserved_right = 0; |
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|
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_DifferenceType __chunk_size = __s.partition_chunk_size; |
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|
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//at least two chunks per thread |
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if (__dist >= 2 * __num_threads * __chunk_size) |
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# pragma omp parallel num_threads(__num_threads) |
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{ |
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# pragma omp single |
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{ |
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__num_threads = omp_get_num_threads(); |
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__reserved_left = new int[__num_threads]; |
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__reserved_right = new int[__num_threads]; |
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|
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if (__s.partition_chunk_share > 0.0) |
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__chunk_size = std::max<_DifferenceType> |
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(__s.partition_chunk_size, (double)__n |
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* __s.partition_chunk_share / (double)__num_threads); |
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else |
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__chunk_size = __s.partition_chunk_size; |
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} |
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|
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while (__dist >= 2 * __num_threads * __chunk_size) |
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{ |
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# pragma omp single |
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{ |
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_DifferenceType __num_chunks = __dist / __chunk_size; |
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|
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for (_ThreadIndex __r = 0; __r < __num_threads; ++__r) |
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{ |
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__reserved_left [__r] = 0; // false |
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__reserved_right[__r] = 0; // false |
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} |
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__leftover_left = 0; |
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__leftover_right = 0; |
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} //implicit barrier |
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|
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// Private. |
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_DifferenceType __thread_left, __thread_left_border, |
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__thread_right, __thread_right_border; |
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|
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__thread_left = __left + 1; |
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// Just to satisfy the condition below. |
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__thread_left_border = __thread_left - 1; |
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|
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__thread_right = __n - 1; |
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// Just to satisfy the condition below. |
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__thread_right_border = __thread_right + 1; |
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|
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bool __iam_finished = false; |
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while (!__iam_finished) |
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{ |
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if (__thread_left > __thread_left_border) |
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{ |
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_DifferenceType __former_dist = |
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__fetch_and_add(&__dist, -__chunk_size); |
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if (__former_dist < __chunk_size) |
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{ |
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__fetch_and_add(&__dist, __chunk_size); |
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__iam_finished = true; |
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break; |
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} |
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else |
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{ |
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__thread_left = |
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__fetch_and_add(&__left, __chunk_size); |
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__thread_left_border = |
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__thread_left + (__chunk_size - 1); |
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} |
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} |
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|
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if (__thread_right < __thread_right_border) |
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{ |
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_DifferenceType __former_dist = |
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__fetch_and_add(&__dist, -__chunk_size); |
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if (__former_dist < __chunk_size) |
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{ |
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__fetch_and_add(&__dist, __chunk_size); |
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__iam_finished = true; |
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break; |
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} |
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else |
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{ |
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__thread_right = |
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__fetch_and_add(&__right, -__chunk_size); |
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__thread_right_border = |
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__thread_right - (__chunk_size - 1); |
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} |
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} |
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|
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// Swap as usual. |
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while (__thread_left < __thread_right) |
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{ |
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while (__pred(__begin[__thread_left]) |
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&& __thread_left <= __thread_left_border) |
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++__thread_left; |
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while (!__pred(__begin[__thread_right]) |
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&& __thread_right >= __thread_right_border) |
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--__thread_right; |
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|
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if (__thread_left > __thread_left_border |
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|| __thread_right < __thread_right_border) |
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// Fetch new chunk(__s). |
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break; |
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|
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std::iter_swap(__begin + __thread_left, |
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__begin + __thread_right); |
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++__thread_left; |
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--__thread_right; |
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} |
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} |
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|
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// Now swap the leftover chunks to the right places. |
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if (__thread_left <= __thread_left_border) |
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# pragma omp atomic |
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++__leftover_left; |
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if (__thread_right >= __thread_right_border) |
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# pragma omp atomic |
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++__leftover_right; |
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|
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# pragma omp barrier |
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|
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_DifferenceType |
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__leftold = __left, |
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__leftnew = __left - __leftover_left * __chunk_size, |
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__rightold = __right, |
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__rightnew = __right + __leftover_right * __chunk_size; |
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|
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// <=> __thread_left_border + (__chunk_size - 1) >= __leftnew |
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if (__thread_left <= __thread_left_border |
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&& __thread_left_border >= __leftnew) |
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{ |
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// Chunk already in place, reserve spot. |
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__reserved_left[(__left - (__thread_left_border + 1)) |
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/ __chunk_size] = 1; |
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} |
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|
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// <=> __thread_right_border - (__chunk_size - 1) <= __rightnew |
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if (__thread_right >= __thread_right_border |
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&& __thread_right_border <= __rightnew) |
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{ |
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// Chunk already in place, reserve spot. |
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__reserved_right[((__thread_right_border - 1) - __right) |
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/ __chunk_size] = 1; |
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} |
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|
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# pragma omp barrier |
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|
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if (__thread_left <= __thread_left_border |
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&& __thread_left_border < __leftnew) |
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{ |
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// Find spot and swap. |
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_DifferenceType __swapstart = -1; |
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for (int __r = 0; __r < __leftover_left; ++__r) |
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if (__reserved_left[__r] == 0 |
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&& __compare_and_swap(&(__reserved_left[__r]), 0, 1)) |
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{ |
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__swapstart = __leftold - (__r + 1) * __chunk_size; |
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break; |
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} |
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|
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#if _GLIBCXX_PARALLEL_ASSERTIONS |
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_GLIBCXX_PARALLEL_ASSERT(__swapstart != -1); |
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#endif |
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|
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std::swap_ranges(__begin + __thread_left_border |
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- (__chunk_size - 1), |
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__begin + __thread_left_border + 1, |
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__begin + __swapstart); |
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} |
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|
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if (__thread_right >= __thread_right_border |
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&& __thread_right_border > __rightnew) |
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{ |
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// Find spot and swap |
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_DifferenceType __swapstart = -1; |
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for (int __r = 0; __r < __leftover_right; ++__r) |
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if (__reserved_right[__r] == 0 |
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&& __compare_and_swap(&(__reserved_right[__r]), 0, 1)) |
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{ |
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__swapstart = __rightold + __r * __chunk_size + 1; |
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break; |
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} |
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|
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#if _GLIBCXX_PARALLEL_ASSERTIONS |
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_GLIBCXX_PARALLEL_ASSERT(__swapstart != -1); |
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#endif |
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|
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std::swap_ranges(__begin + __thread_right_border, |
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__begin + __thread_right_border |
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+ __chunk_size, __begin + __swapstart); |
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} |
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#if _GLIBCXX_PARALLEL_ASSERTIONS |
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# pragma omp barrier |
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|
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# pragma omp single |
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{ |
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for (_DifferenceType __r = 0; __r < __leftover_left; ++__r) |
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_GLIBCXX_PARALLEL_ASSERT(__reserved_left[__r] == 1); |
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for (_DifferenceType __r = 0; __r < __leftover_right; ++__r) |
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_GLIBCXX_PARALLEL_ASSERT(__reserved_right[__r] == 1); |
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} |
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#endif |
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|
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__left = __leftnew; |
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__right = __rightnew; |
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__dist = __right - __left + 1; |
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} |
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|
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# pragma omp flush(__left, __right) |
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} // end "recursion" //parallel |
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|
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_DifferenceType __final_left = __left, __final_right = __right; |
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|
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while (__final_left < __final_right) |
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{ |
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// Go right until key is geq than pivot. |
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while (__pred(__begin[__final_left]) |
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&& __final_left < __final_right) |
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++__final_left; |
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|
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// Go left until key is less than pivot. |
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while (!__pred(__begin[__final_right]) |
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&& __final_left < __final_right) |
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--__final_right; |
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|
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if (__final_left == __final_right) |
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break; |
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std::iter_swap(__begin + __final_left, __begin + __final_right); |
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++__final_left; |
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--__final_right; |
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} |
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|
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// All elements on the left side are < piv, all elements on the |
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// right are >= piv |
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delete[] __reserved_left; |
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delete[] __reserved_right; |
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|
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// Element "between" __final_left and __final_right might not have |
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// been regarded yet |
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if (__final_left < __n && !__pred(__begin[__final_left])) |
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// Really swapped. |
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return __final_left; |
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else |
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return __final_left + 1; |
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} |
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|
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/** |
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* @brief Parallel implementation of std::nth_element(). |
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* @param __begin Begin iterator of input sequence. |
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* @param __nth _Iterator of element that must be in position afterwards. |
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* @param __end End iterator of input sequence. |
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* @param __comp Comparator. |
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*/ |
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template<typename _RAIter, typename _Compare> |
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void |
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__parallel_nth_element(_RAIter __begin, _RAIter __nth, |
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_RAIter __end, _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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|
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_GLIBCXX_CALL(__end - __begin) |
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|
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_RAIter __split; |
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_RandomNumber __rng; |
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|
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const _Settings& __s = _Settings::get(); |
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_DifferenceType __minimum_length = std::max<_DifferenceType>(2, |
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std::max(__s.nth_element_minimal_n, __s.partition_minimal_n)); |
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|
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// Break if input range to small. |
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while (static_cast<_SequenceIndex>(__end - __begin) >= __minimum_length) |
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{ |
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_DifferenceType __n = __end - __begin; |
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|
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_RAIter __pivot_pos = __begin + __rng(__n); |
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|
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// Swap __pivot_pos value to end. |
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if (__pivot_pos != (__end - 1)) |
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std::iter_swap(__pivot_pos, __end - 1); |
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__pivot_pos = __end - 1; |
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|
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// _Compare must have first_value_type, second_value_type, |
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// result_type |
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// _Compare == |
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// __gnu_parallel::_Lexicographic<S, int, |
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// __gnu_parallel::_Less<S, S> > |
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// __pivot_pos == std::pair<S, int>* |
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__gnu_parallel::__binder2nd<_Compare, _ValueType, _ValueType, bool> |
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__pred(__comp, *__pivot_pos); |
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|
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// Divide, leave pivot unchanged in last place. |
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_RAIter __split_pos1, __split_pos2; |
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__split_pos1 = __begin + __parallel_partition(__begin, __end - 1, |
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__pred, |
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__get_max_threads()); |
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|
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// Left side: < __pivot_pos; __right side: >= __pivot_pos |
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|
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// Swap pivot back to middle. |
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if (__split_pos1 != __pivot_pos) |
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std::iter_swap(__split_pos1, __pivot_pos); |
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__pivot_pos = __split_pos1; |
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|
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// In case all elements are equal, __split_pos1 == 0 |
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if ((__split_pos1 + 1 - __begin) < (__n >> 7) |
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|| (__end - __split_pos1) < (__n >> 7)) |
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{ |
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// Very unequal split, one part smaller than one 128th |
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// elements not strictly larger than the pivot. |
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__gnu_parallel::__unary_negate<__gnu_parallel:: |
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__binder1st<_Compare, _ValueType, |
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_ValueType, bool>, _ValueType> |
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__pred(__gnu_parallel::__binder1st<_Compare, _ValueType, |
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_ValueType, bool>(__comp, *__pivot_pos)); |
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|
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// Find other end of pivot-equal range. |
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__split_pos2 = __gnu_sequential::partition(__split_pos1 + 1, |
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__end, __pred); |
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} |
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else |
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// Only skip the pivot. |
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__split_pos2 = __split_pos1 + 1; |
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|
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// Compare iterators. |
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if (__split_pos2 <= __nth) |
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__begin = __split_pos2; |
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else if (__nth < __split_pos1) |
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__end = __split_pos1; |
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else |
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break; |
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} |
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|
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// Only at most _Settings::partition_minimal_n __elements __left. |
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__gnu_sequential::nth_element(__begin, __nth, __end, __comp); |
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} |
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|
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/** @brief Parallel implementation of std::partial_sort(). |
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* @param __begin Begin iterator of input sequence. |
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* @param __middle Sort until this position. |
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* @param __end End iterator of input sequence. |
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* @param __comp Comparator. */ |
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template<typename _RAIter, typename _Compare> |
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void |
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__parallel_partial_sort(_RAIter __begin, |
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_RAIter __middle, |
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_RAIter __end, _Compare __comp) |
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{ |
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__parallel_nth_element(__begin, __middle, __end, __comp); |
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std::sort(__begin, __middle, __comp); |
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} |
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|
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} //namespace __gnu_parallel |
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|
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#undef _GLIBCXX_VOLATILE |
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|
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#endif /* _GLIBCXX_PARALLEL_PARTITION_H */ |
