| // -*- C++ -*- |
| |
| // Copyright (C) 2007-2013 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 */ |
