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// -*- C++ -*- |
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// Copyright (C) 2007-2015 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. |
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// 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. |
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// 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/>. |
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/** @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. |
*/ |
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// Written by Johannes Singler. |
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#ifndef _GLIBCXX_PARALLEL_BALANCED_QUICKSORT_H |
#define _GLIBCXX_PARALLEL_BALANCED_QUICKSORT_H 1 |
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#include <parallel/basic_iterator.h> |
#include <bits/stl_algo.h> |
#include <bits/stl_function.h> |
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#include <parallel/settings.h> |
#include <parallel/partition.h> |
#include <parallel/random_number.h> |
#include <parallel/queue.h> |
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#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; |
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#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; |
} |
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// 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; |
} |
} |
} |
} |
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/** @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 |
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#endif /* _GLIBCXX_PARALLEL_BALANCED_QUICKSORT_H */ |