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Diffstat (limited to 'libstdc++-v3/include/parallel/balanced_quicksort.h')
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diff --git a/libstdc++-v3/include/parallel/balanced_quicksort.h b/libstdc++-v3/include/parallel/balanced_quicksort.h new file mode 100644 index 000000000..441e7b44a --- /dev/null +++ b/libstdc++-v3/include/parallel/balanced_quicksort.h @@ -0,0 +1,492 @@ +// -*- C++ -*- + +// Copyright (C) 2007, 2008, 2009, 2010 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/balanced_quicksort.h + * @brief Implementation of a dynamically load-balanced parallel quicksort. + * + * It works in-place and needs only logarithmic extra memory. + * The algorithm is similar to the one proposed in + * + * P. Tsigas and Y. Zhang. + * A simple, fast parallel implementation of quicksort and + * its performance evaluation on SUN enterprise 10000. + * In 11th Euromicro Conference on Parallel, Distributed and + * Network-Based Processing, page 372, 2003. + * + * This file is a GNU parallel extension to the Standard C++ Library. + */ + +// Written by Johannes Singler. + +#ifndef _GLIBCXX_PARALLEL_BALANCED_QUICKSORT_H +#define _GLIBCXX_PARALLEL_BALANCED_QUICKSORT_H 1 + +#include <parallel/basic_iterator.h> +#include <bits/stl_algo.h> +#include <bits/stl_function.h> + +#include <parallel/settings.h> +#include <parallel/partition.h> +#include <parallel/random_number.h> +#include <parallel/queue.h> + +#if _GLIBCXX_ASSERTIONS +#include <parallel/checkers.h> +#endif + +namespace __gnu_parallel +{ + /** @brief Information local to one thread in the parallel quicksort run. */ + template<typename _RAIter> + struct _QSBThreadLocal + { + typedef std::iterator_traits<_RAIter> _TraitsType; + typedef typename _TraitsType::difference_type _DifferenceType; + + /** @brief Continuous part of the sequence, described by an + iterator pair. */ + typedef std::pair<_RAIter, _RAIter> _Piece; + + /** @brief Initial piece to work on. */ + _Piece _M_initial; + + /** @brief Work-stealing queue. */ + _RestrictedBoundedConcurrentQueue<_Piece> _M_leftover_parts; + + /** @brief Number of threads involved in this algorithm. */ + _ThreadIndex _M_num_threads; + + /** @brief Pointer to a counter of elements left over to sort. */ + volatile _DifferenceType* _M_elements_leftover; + + /** @brief The complete sequence to sort. */ + _Piece _M_global; + + /** @brief Constructor. + * @param __queue_size size of the work-stealing queue. */ + _QSBThreadLocal(int __queue_size) : _M_leftover_parts(__queue_size) { } + }; + + /** @brief Balanced quicksort divide step. + * @param __begin Begin iterator of subsequence. + * @param __end End iterator of subsequence. + * @param __comp Comparator. + * @param __num_threads Number of threads that are allowed to work on + * this part. + * @pre @c (__end-__begin)>=1 */ + template<typename _RAIter, typename _Compare> + typename std::iterator_traits<_RAIter>::difference_type + __qsb_divide(_RAIter __begin, _RAIter __end, + _Compare __comp, _ThreadIndex __num_threads) + { + _GLIBCXX_PARALLEL_ASSERT(__num_threads > 0); + + typedef std::iterator_traits<_RAIter> _TraitsType; + typedef typename _TraitsType::value_type _ValueType; + typedef typename _TraitsType::difference_type _DifferenceType; + + _RAIter __pivot_pos = + __median_of_three_iterators(__begin, __begin + (__end - __begin) / 2, + __end - 1, __comp); + +#if defined(_GLIBCXX_ASSERTIONS) + // Must be in between somewhere. + _DifferenceType __n = __end - __begin; + + _GLIBCXX_PARALLEL_ASSERT((!__comp(*__pivot_pos, *__begin) + && !__comp(*(__begin + __n / 2), + *__pivot_pos)) + || (!__comp(*__pivot_pos, *__begin) + && !__comp(*(__end - 1), *__pivot_pos)) + || (!__comp(*__pivot_pos, *(__begin + __n / 2)) + && !__comp(*__begin, *__pivot_pos)) + || (!__comp(*__pivot_pos, *(__begin + __n / 2)) + && !__comp(*(__end - 1), *__pivot_pos)) + || (!__comp(*__pivot_pos, *(__end - 1)) + && !__comp(*__begin, *__pivot_pos)) + || (!__comp(*__pivot_pos, *(__end - 1)) + && !__comp(*(__begin + __n / 2), + *__pivot_pos))); +#endif + + // Swap pivot value to end. + if (__pivot_pos != (__end - 1)) + std::iter_swap(__pivot_pos, __end - 1); + __pivot_pos = __end - 1; + + __gnu_parallel::__binder2nd<_Compare, _ValueType, _ValueType, bool> + __pred(__comp, *__pivot_pos); + + // Divide, returning __end - __begin - 1 in the worst case. + _DifferenceType __split_pos = __parallel_partition(__begin, __end - 1, + __pred, + __num_threads); + + // Swap back pivot to middle. + std::iter_swap(__begin + __split_pos, __pivot_pos); + __pivot_pos = __begin + __split_pos; + +#if _GLIBCXX_ASSERTIONS + _RAIter __r; + for (__r = __begin; __r != __pivot_pos; ++__r) + _GLIBCXX_PARALLEL_ASSERT(__comp(*__r, *__pivot_pos)); + for (; __r != __end; ++__r) + _GLIBCXX_PARALLEL_ASSERT(!__comp(*__r, *__pivot_pos)); +#endif + + return __split_pos; + } + + /** @brief Quicksort conquer step. + * @param __tls Array of thread-local storages. + * @param __begin Begin iterator of subsequence. + * @param __end End iterator of subsequence. + * @param __comp Comparator. + * @param __iam Number of the thread processing this function. + * @param __num_threads + * Number of threads that are allowed to work on this part. */ + template<typename _RAIter, typename _Compare> + void + __qsb_conquer(_QSBThreadLocal<_RAIter>** __tls, + _RAIter __begin, _RAIter __end, + _Compare __comp, + _ThreadIndex __iam, _ThreadIndex __num_threads, + bool __parent_wait) + { + typedef std::iterator_traits<_RAIter> _TraitsType; + typedef typename _TraitsType::value_type _ValueType; + typedef typename _TraitsType::difference_type _DifferenceType; + + _DifferenceType __n = __end - __begin; + + if (__num_threads <= 1 || __n <= 1) + { + __tls[__iam]->_M_initial.first = __begin; + __tls[__iam]->_M_initial.second = __end; + + __qsb_local_sort_with_helping(__tls, __comp, __iam, __parent_wait); + + return; + } + + // Divide step. + _DifferenceType __split_pos = + __qsb_divide(__begin, __end, __comp, __num_threads); + +#if _GLIBCXX_ASSERTIONS + _GLIBCXX_PARALLEL_ASSERT(0 <= __split_pos && + __split_pos < (__end - __begin)); +#endif + + _ThreadIndex + __num_threads_leftside = std::max<_ThreadIndex> + (1, std::min<_ThreadIndex>(__num_threads - 1, __split_pos + * __num_threads / __n)); + +# pragma omp atomic + *__tls[__iam]->_M_elements_leftover -= (_DifferenceType)1; + + // Conquer step. +# pragma omp parallel num_threads(2) + { + bool __wait; + if(omp_get_num_threads() < 2) + __wait = false; + else + __wait = __parent_wait; + +# pragma omp sections + { +# pragma omp section + { + __qsb_conquer(__tls, __begin, __begin + __split_pos, __comp, + __iam, __num_threads_leftside, __wait); + __wait = __parent_wait; + } + // The pivot_pos is left in place, to ensure termination. +# pragma omp section + { + __qsb_conquer(__tls, __begin + __split_pos + 1, __end, __comp, + __iam + __num_threads_leftside, + __num_threads - __num_threads_leftside, __wait); + __wait = __parent_wait; + } + } + } + } + + /** + * @brief Quicksort step doing load-balanced local sort. + * @param __tls Array of thread-local storages. + * @param __comp Comparator. + * @param __iam Number of the thread processing this function. + */ + template<typename _RAIter, typename _Compare> + void + __qsb_local_sort_with_helping(_QSBThreadLocal<_RAIter>** __tls, + _Compare& __comp, _ThreadIndex __iam, + bool __wait) + { + typedef std::iterator_traits<_RAIter> _TraitsType; + typedef typename _TraitsType::value_type _ValueType; + typedef typename _TraitsType::difference_type _DifferenceType; + typedef std::pair<_RAIter, _RAIter> _Piece; + + _QSBThreadLocal<_RAIter>& __tl = *__tls[__iam]; + + _DifferenceType + __base_case_n = _Settings::get().sort_qsb_base_case_maximal_n; + if (__base_case_n < 2) + __base_case_n = 2; + _ThreadIndex __num_threads = __tl._M_num_threads; + + // Every thread has its own random number generator. + _RandomNumber __rng(__iam + 1); + + _Piece __current = __tl._M_initial; + + _DifferenceType __elements_done = 0; +#if _GLIBCXX_ASSERTIONS + _DifferenceType __total_elements_done = 0; +#endif + + for (;;) + { + // Invariant: __current must be a valid (maybe empty) range. + _RAIter __begin = __current.first, __end = __current.second; + _DifferenceType __n = __end - __begin; + + if (__n > __base_case_n) + { + // Divide. + _RAIter __pivot_pos = __begin + __rng(__n); + + // Swap __pivot_pos value to end. + if (__pivot_pos != (__end - 1)) + std::iter_swap(__pivot_pos, __end - 1); + __pivot_pos = __end - 1; + + __gnu_parallel::__binder2nd + <_Compare, _ValueType, _ValueType, bool> + __pred(__comp, *__pivot_pos); + + // Divide, leave pivot unchanged in last place. + _RAIter __split_pos1, __split_pos2; + __split_pos1 = __gnu_sequential::partition(__begin, __end - 1, + __pred); + + // Left side: < __pivot_pos; __right side: >= __pivot_pos. +#if _GLIBCXX_ASSERTIONS + _GLIBCXX_PARALLEL_ASSERT(__begin <= __split_pos1 + && __split_pos1 < __end); +#endif + // Swap pivot back to middle. + if (__split_pos1 != __pivot_pos) + std::iter_swap(__split_pos1, __pivot_pos); + __pivot_pos = __split_pos1; + + // In case all elements are equal, __split_pos1 == 0. + if ((__split_pos1 + 1 - __begin) < (__n >> 7) + || (__end - __split_pos1) < (__n >> 7)) + { + // Very unequal split, one part smaller than one 128th + // elements not strictly larger than the pivot. + __gnu_parallel::__unary_negate<__gnu_parallel::__binder1st + <_Compare, _ValueType, _ValueType, bool>, _ValueType> + __pred(__gnu_parallel::__binder1st + <_Compare, _ValueType, _ValueType, bool> + (__comp, *__pivot_pos)); + + // Find other end of pivot-equal range. + __split_pos2 = __gnu_sequential::partition(__split_pos1 + 1, + __end, __pred); + } + else + // Only skip the pivot. + __split_pos2 = __split_pos1 + 1; + + // Elements equal to pivot are done. + __elements_done += (__split_pos2 - __split_pos1); +#if _GLIBCXX_ASSERTIONS + __total_elements_done += (__split_pos2 - __split_pos1); +#endif + // Always push larger part onto stack. + if (((__split_pos1 + 1) - __begin) < (__end - (__split_pos2))) + { + // Right side larger. + if ((__split_pos2) != __end) + __tl._M_leftover_parts.push_front + (std::make_pair(__split_pos2, __end)); + + //__current.first = __begin; //already set anyway + __current.second = __split_pos1; + continue; + } + else + { + // Left side larger. + if (__begin != __split_pos1) + __tl._M_leftover_parts.push_front(std::make_pair + (__begin, __split_pos1)); + + __current.first = __split_pos2; + //__current.second = __end; //already set anyway + continue; + } + } + else + { + __gnu_sequential::sort(__begin, __end, __comp); + __elements_done += __n; +#if _GLIBCXX_ASSERTIONS + __total_elements_done += __n; +#endif + + // Prefer own stack, small pieces. + if (__tl._M_leftover_parts.pop_front(__current)) + continue; + +# pragma omp atomic + *__tl._M_elements_leftover -= __elements_done; + + __elements_done = 0; + +#if _GLIBCXX_ASSERTIONS + double __search_start = omp_get_wtime(); +#endif + + // Look for new work. + bool __successfully_stolen = false; + while (__wait && *__tl._M_elements_leftover > 0 + && !__successfully_stolen +#if _GLIBCXX_ASSERTIONS + // Possible dead-lock. + && (omp_get_wtime() < (__search_start + 1.0)) +#endif + ) + { + _ThreadIndex __victim; + __victim = __rng(__num_threads); + + // Large pieces. + __successfully_stolen = (__victim != __iam) + && __tls[__victim]->_M_leftover_parts.pop_back(__current); + if (!__successfully_stolen) + __yield(); +#if !defined(__ICC) && !defined(__ECC) +# pragma omp flush +#endif + } + +#if _GLIBCXX_ASSERTIONS + if (omp_get_wtime() >= (__search_start + 1.0)) + { + sleep(1); + _GLIBCXX_PARALLEL_ASSERT(omp_get_wtime() + < (__search_start + 1.0)); + } +#endif + if (!__successfully_stolen) + { +#if _GLIBCXX_ASSERTIONS + _GLIBCXX_PARALLEL_ASSERT(*__tl._M_elements_leftover == 0); +#endif + return; + } + } + } + } + + /** @brief Top-level quicksort routine. + * @param __begin Begin iterator of sequence. + * @param __end End iterator of sequence. + * @param __comp Comparator. + * @param __num_threads Number of threads that are allowed to work on + * this part. + */ + template<typename _RAIter, typename _Compare> + void + __parallel_sort_qsb(_RAIter __begin, _RAIter __end, + _Compare __comp, _ThreadIndex __num_threads) + { + _GLIBCXX_CALL(__end - __begin) + + typedef std::iterator_traits<_RAIter> _TraitsType; + typedef typename _TraitsType::value_type _ValueType; + typedef typename _TraitsType::difference_type _DifferenceType; + typedef std::pair<_RAIter, _RAIter> _Piece; + + typedef _QSBThreadLocal<_RAIter> _TLSType; + + _DifferenceType __n = __end - __begin; + + if (__n <= 1) + return; + + // At least one element per processor. + if (__num_threads > __n) + __num_threads = static_cast<_ThreadIndex>(__n); + + // Initialize thread local storage + _TLSType** __tls = new _TLSType*[__num_threads]; + _DifferenceType __queue_size = (__num_threads + * (_ThreadIndex)(__rd_log2(__n) + 1)); + for (_ThreadIndex __t = 0; __t < __num_threads; ++__t) + __tls[__t] = new _QSBThreadLocal<_RAIter>(__queue_size); + + // There can never be more than ceil(__rd_log2(__n)) ranges on the + // stack, because + // 1. Only one processor pushes onto the stack + // 2. The largest range has at most length __n + // 3. Each range is larger than half of the range remaining + volatile _DifferenceType __elements_leftover = __n; + for (_ThreadIndex __i = 0; __i < __num_threads; ++__i) + { + __tls[__i]->_M_elements_leftover = &__elements_leftover; + __tls[__i]->_M_num_threads = __num_threads; + __tls[__i]->_M_global = std::make_pair(__begin, __end); + + // Just in case nothing is left to assign. + __tls[__i]->_M_initial = std::make_pair(__end, __end); + } + + // Main recursion call. + __qsb_conquer(__tls, __begin, __begin + __n, __comp, 0, + __num_threads, true); + +#if _GLIBCXX_ASSERTIONS + // All stack must be empty. + _Piece __dummy; + for (_ThreadIndex __i = 1; __i < __num_threads; ++__i) + _GLIBCXX_PARALLEL_ASSERT( + !__tls[__i]->_M_leftover_parts.pop_back(__dummy)); +#endif + + for (_ThreadIndex __i = 0; __i < __num_threads; ++__i) + delete __tls[__i]; + delete[] __tls; + } +} // namespace __gnu_parallel + +#endif /* _GLIBCXX_PARALLEL_BALANCED_QUICKSORT_H */ |