libstdc++
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00001 // -*- C++ -*- 00002 00003 // Copyright (C) 2007-2019 Free Software Foundation, Inc. 00004 // 00005 // This file is part of the GNU ISO C++ Library. This library is free 00006 // software; you can redistribute it and/or modify it under the terms 00007 // of the GNU General Public License as published by the Free Software 00008 // Foundation; either version 3, or (at your option) any later 00009 // version. 00010 00011 // This library is distributed in the hope that it will be useful, but 00012 // WITHOUT ANY WARRANTY; without even the implied warranty of 00013 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 00014 // General Public License for more details. 00015 00016 // Under Section 7 of GPL version 3, you are granted additional 00017 // permissions described in the GCC Runtime Library Exception, version 00018 // 3.1, as published by the Free Software Foundation. 00019 00020 // You should have received a copy of the GNU General Public License and 00021 // a copy of the GCC Runtime Library Exception along with this program; 00022 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 00023 // <http://www.gnu.org/licenses/>. 00024 00025 /** @file parallel/balanced_quicksort.h 00026 * @brief Implementation of a dynamically load-balanced parallel quicksort. 00027 * 00028 * It works in-place and needs only logarithmic extra memory. 00029 * The algorithm is similar to the one proposed in 00030 * 00031 * P. Tsigas and Y. Zhang. 00032 * A simple, fast parallel implementation of quicksort and 00033 * its performance evaluation on SUN enterprise 10000. 00034 * In 11th Euromicro Conference on Parallel, Distributed and 00035 * Network-Based Processing, page 372, 2003. 00036 * 00037 * This file is a GNU parallel extension to the Standard C++ Library. 00038 */ 00039 00040 // Written by Johannes Singler. 00041 00042 #ifndef _GLIBCXX_PARALLEL_BALANCED_QUICKSORT_H 00043 #define _GLIBCXX_PARALLEL_BALANCED_QUICKSORT_H 1 00044 00045 #include <parallel/basic_iterator.h> 00046 #include <bits/stl_algo.h> 00047 #include <bits/stl_function.h> 00048 00049 #include <parallel/settings.h> 00050 #include <parallel/partition.h> 00051 #include <parallel/random_number.h> 00052 #include <parallel/queue.h> 00053 00054 #if _GLIBCXX_PARALLEL_ASSERTIONS 00055 #include <parallel/checkers.h> 00056 #ifdef _GLIBCXX_HAVE_UNISTD_H 00057 #include <unistd.h> 00058 #endif 00059 #endif 00060 00061 namespace __gnu_parallel 00062 { 00063 /** @brief Information local to one thread in the parallel quicksort run. */ 00064 template<typename _RAIter> 00065 struct _QSBThreadLocal 00066 { 00067 typedef std::iterator_traits<_RAIter> _TraitsType; 00068 typedef typename _TraitsType::difference_type _DifferenceType; 00069 00070 /** @brief Continuous part of the sequence, described by an 00071 iterator pair. */ 00072 typedef std::pair<_RAIter, _RAIter> _Piece; 00073 00074 /** @brief Initial piece to work on. */ 00075 _Piece _M_initial; 00076 00077 /** @brief Work-stealing queue. */ 00078 _RestrictedBoundedConcurrentQueue<_Piece> _M_leftover_parts; 00079 00080 /** @brief Number of threads involved in this algorithm. */ 00081 _ThreadIndex _M_num_threads; 00082 00083 /** @brief Pointer to a counter of elements left over to sort. */ 00084 volatile _DifferenceType* _M_elements_leftover; 00085 00086 /** @brief The complete sequence to sort. */ 00087 _Piece _M_global; 00088 00089 /** @brief Constructor. 00090 * @param __queue_size size of the work-stealing queue. */ 00091 _QSBThreadLocal(int __queue_size) : _M_leftover_parts(__queue_size) { } 00092 }; 00093 00094 /** @brief Balanced quicksort divide step. 00095 * @param __begin Begin iterator of subsequence. 00096 * @param __end End iterator of subsequence. 00097 * @param __comp Comparator. 00098 * @param __num_threads Number of threads that are allowed to work on 00099 * this part. 00100 * @pre @c (__end-__begin)>=1 */ 00101 template<typename _RAIter, typename _Compare> 00102 typename std::iterator_traits<_RAIter>::difference_type 00103 __qsb_divide(_RAIter __begin, _RAIter __end, 00104 _Compare __comp, _ThreadIndex __num_threads) 00105 { 00106 _GLIBCXX_PARALLEL_ASSERT(__num_threads > 0); 00107 00108 typedef std::iterator_traits<_RAIter> _TraitsType; 00109 typedef typename _TraitsType::value_type _ValueType; 00110 typedef typename _TraitsType::difference_type _DifferenceType; 00111 00112 _RAIter __pivot_pos = 00113 __median_of_three_iterators(__begin, __begin + (__end - __begin) / 2, 00114 __end - 1, __comp); 00115 00116 #if defined(_GLIBCXX_PARALLEL_ASSERTIONS) 00117 // Must be in between somewhere. 00118 _DifferenceType __n = __end - __begin; 00119 00120 _GLIBCXX_PARALLEL_ASSERT((!__comp(*__pivot_pos, *__begin) 00121 && !__comp(*(__begin + __n / 2), 00122 *__pivot_pos)) 00123 || (!__comp(*__pivot_pos, *__begin) 00124 && !__comp(*(__end - 1), *__pivot_pos)) 00125 || (!__comp(*__pivot_pos, *(__begin + __n / 2)) 00126 && !__comp(*__begin, *__pivot_pos)) 00127 || (!__comp(*__pivot_pos, *(__begin + __n / 2)) 00128 && !__comp(*(__end - 1), *__pivot_pos)) 00129 || (!__comp(*__pivot_pos, *(__end - 1)) 00130 && !__comp(*__begin, *__pivot_pos)) 00131 || (!__comp(*__pivot_pos, *(__end - 1)) 00132 && !__comp(*(__begin + __n / 2), 00133 *__pivot_pos))); 00134 #endif 00135 00136 // Swap pivot value to end. 00137 if (__pivot_pos != (__end - 1)) 00138 std::iter_swap(__pivot_pos, __end - 1); 00139 __pivot_pos = __end - 1; 00140 00141 __gnu_parallel::__binder2nd<_Compare, _ValueType, _ValueType, bool> 00142 __pred(__comp, *__pivot_pos); 00143 00144 // Divide, returning __end - __begin - 1 in the worst case. 00145 _DifferenceType __split_pos = __parallel_partition(__begin, __end - 1, 00146 __pred, 00147 __num_threads); 00148 00149 // Swap back pivot to middle. 00150 std::iter_swap(__begin + __split_pos, __pivot_pos); 00151 __pivot_pos = __begin + __split_pos; 00152 00153 #if _GLIBCXX_PARALLEL_ASSERTIONS 00154 _RAIter __r; 00155 for (__r = __begin; __r != __pivot_pos; ++__r) 00156 _GLIBCXX_PARALLEL_ASSERT(__comp(*__r, *__pivot_pos)); 00157 for (; __r != __end; ++__r) 00158 _GLIBCXX_PARALLEL_ASSERT(!__comp(*__r, *__pivot_pos)); 00159 #endif 00160 00161 return __split_pos; 00162 } 00163 00164 /** @brief Quicksort conquer step. 00165 * @param __tls Array of thread-local storages. 00166 * @param __begin Begin iterator of subsequence. 00167 * @param __end End iterator of subsequence. 00168 * @param __comp Comparator. 00169 * @param __iam Number of the thread processing this function. 00170 * @param __num_threads 00171 * Number of threads that are allowed to work on this part. */ 00172 template<typename _RAIter, typename _Compare> 00173 void 00174 __qsb_conquer(_QSBThreadLocal<_RAIter>** __tls, 00175 _RAIter __begin, _RAIter __end, 00176 _Compare __comp, 00177 _ThreadIndex __iam, _ThreadIndex __num_threads, 00178 bool __parent_wait) 00179 { 00180 typedef std::iterator_traits<_RAIter> _TraitsType; 00181 typedef typename _TraitsType::value_type _ValueType; 00182 typedef typename _TraitsType::difference_type _DifferenceType; 00183 00184 _DifferenceType __n = __end - __begin; 00185 00186 if (__num_threads <= 1 || __n <= 1) 00187 { 00188 __tls[__iam]->_M_initial.first = __begin; 00189 __tls[__iam]->_M_initial.second = __end; 00190 00191 __qsb_local_sort_with_helping(__tls, __comp, __iam, __parent_wait); 00192 00193 return; 00194 } 00195 00196 // Divide step. 00197 _DifferenceType __split_pos = 00198 __qsb_divide(__begin, __end, __comp, __num_threads); 00199 00200 #if _GLIBCXX_PARALLEL_ASSERTIONS 00201 _GLIBCXX_PARALLEL_ASSERT(0 <= __split_pos && 00202 __split_pos < (__end - __begin)); 00203 #endif 00204 00205 _ThreadIndex 00206 __num_threads_leftside = std::max<_ThreadIndex> 00207 (1, std::min<_ThreadIndex>(__num_threads - 1, __split_pos 00208 * __num_threads / __n)); 00209 00210 # pragma omp atomic 00211 *__tls[__iam]->_M_elements_leftover -= (_DifferenceType)1; 00212 00213 // Conquer step. 00214 # pragma omp parallel num_threads(2) 00215 { 00216 bool __wait; 00217 if(omp_get_num_threads() < 2) 00218 __wait = false; 00219 else 00220 __wait = __parent_wait; 00221 00222 # pragma omp sections 00223 { 00224 # pragma omp section 00225 { 00226 __qsb_conquer(__tls, __begin, __begin + __split_pos, __comp, 00227 __iam, __num_threads_leftside, __wait); 00228 __wait = __parent_wait; 00229 } 00230 // The pivot_pos is left in place, to ensure termination. 00231 # pragma omp section 00232 { 00233 __qsb_conquer(__tls, __begin + __split_pos + 1, __end, __comp, 00234 __iam + __num_threads_leftside, 00235 __num_threads - __num_threads_leftside, __wait); 00236 __wait = __parent_wait; 00237 } 00238 } 00239 } 00240 } 00241 00242 /** 00243 * @brief Quicksort step doing load-balanced local sort. 00244 * @param __tls Array of thread-local storages. 00245 * @param __comp Comparator. 00246 * @param __iam Number of the thread processing this function. 00247 */ 00248 template<typename _RAIter, typename _Compare> 00249 void 00250 __qsb_local_sort_with_helping(_QSBThreadLocal<_RAIter>** __tls, 00251 _Compare& __comp, _ThreadIndex __iam, 00252 bool __wait) 00253 { 00254 typedef std::iterator_traits<_RAIter> _TraitsType; 00255 typedef typename _TraitsType::value_type _ValueType; 00256 typedef typename _TraitsType::difference_type _DifferenceType; 00257 typedef std::pair<_RAIter, _RAIter> _Piece; 00258 00259 _QSBThreadLocal<_RAIter>& __tl = *__tls[__iam]; 00260 00261 _DifferenceType 00262 __base_case_n = _Settings::get().sort_qsb_base_case_maximal_n; 00263 if (__base_case_n < 2) 00264 __base_case_n = 2; 00265 _ThreadIndex __num_threads = __tl._M_num_threads; 00266 00267 // Every thread has its own random number generator. 00268 _RandomNumber __rng(__iam + 1); 00269 00270 _Piece __current = __tl._M_initial; 00271 00272 _DifferenceType __elements_done = 0; 00273 #if _GLIBCXX_PARALLEL_ASSERTIONS 00274 _DifferenceType __total_elements_done = 0; 00275 #endif 00276 00277 for (;;) 00278 { 00279 // Invariant: __current must be a valid (maybe empty) range. 00280 _RAIter __begin = __current.first, __end = __current.second; 00281 _DifferenceType __n = __end - __begin; 00282 00283 if (__n > __base_case_n) 00284 { 00285 // Divide. 00286 _RAIter __pivot_pos = __begin + __rng(__n); 00287 00288 // Swap __pivot_pos value to end. 00289 if (__pivot_pos != (__end - 1)) 00290 std::iter_swap(__pivot_pos, __end - 1); 00291 __pivot_pos = __end - 1; 00292 00293 __gnu_parallel::__binder2nd 00294 <_Compare, _ValueType, _ValueType, bool> 00295 __pred(__comp, *__pivot_pos); 00296 00297 // Divide, leave pivot unchanged in last place. 00298 _RAIter __split_pos1, __split_pos2; 00299 __split_pos1 = __gnu_sequential::partition(__begin, __end - 1, 00300 __pred); 00301 00302 // Left side: < __pivot_pos; __right side: >= __pivot_pos. 00303 #if _GLIBCXX_PARALLEL_ASSERTIONS 00304 _GLIBCXX_PARALLEL_ASSERT(__begin <= __split_pos1 00305 && __split_pos1 < __end); 00306 #endif 00307 // Swap pivot back to middle. 00308 if (__split_pos1 != __pivot_pos) 00309 std::iter_swap(__split_pos1, __pivot_pos); 00310 __pivot_pos = __split_pos1; 00311 00312 // In case all elements are equal, __split_pos1 == 0. 00313 if ((__split_pos1 + 1 - __begin) < (__n >> 7) 00314 || (__end - __split_pos1) < (__n >> 7)) 00315 { 00316 // Very unequal split, one part smaller than one 128th 00317 // elements not strictly larger than the pivot. 00318 __gnu_parallel::__unary_negate<__gnu_parallel::__binder1st 00319 <_Compare, _ValueType, _ValueType, bool>, _ValueType> 00320 __pred(__gnu_parallel::__binder1st 00321 <_Compare, _ValueType, _ValueType, bool> 00322 (__comp, *__pivot_pos)); 00323 00324 // Find other end of pivot-equal range. 00325 __split_pos2 = __gnu_sequential::partition(__split_pos1 + 1, 00326 __end, __pred); 00327 } 00328 else 00329 // Only skip the pivot. 00330 __split_pos2 = __split_pos1 + 1; 00331 00332 // Elements equal to pivot are done. 00333 __elements_done += (__split_pos2 - __split_pos1); 00334 #if _GLIBCXX_PARALLEL_ASSERTIONS 00335 __total_elements_done += (__split_pos2 - __split_pos1); 00336 #endif 00337 // Always push larger part onto stack. 00338 if (((__split_pos1 + 1) - __begin) < (__end - (__split_pos2))) 00339 { 00340 // Right side larger. 00341 if ((__split_pos2) != __end) 00342 __tl._M_leftover_parts.push_front 00343 (std::make_pair(__split_pos2, __end)); 00344 00345 //__current.first = __begin; //already set anyway 00346 __current.second = __split_pos1; 00347 continue; 00348 } 00349 else 00350 { 00351 // Left side larger. 00352 if (__begin != __split_pos1) 00353 __tl._M_leftover_parts.push_front(std::make_pair 00354 (__begin, __split_pos1)); 00355 00356 __current.first = __split_pos2; 00357 //__current.second = __end; //already set anyway 00358 continue; 00359 } 00360 } 00361 else 00362 { 00363 __gnu_sequential::sort(__begin, __end, __comp); 00364 __elements_done += __n; 00365 #if _GLIBCXX_PARALLEL_ASSERTIONS 00366 __total_elements_done += __n; 00367 #endif 00368 00369 // Prefer own stack, small pieces. 00370 if (__tl._M_leftover_parts.pop_front(__current)) 00371 continue; 00372 00373 # pragma omp atomic 00374 *__tl._M_elements_leftover -= __elements_done; 00375 00376 __elements_done = 0; 00377 00378 #if _GLIBCXX_PARALLEL_ASSERTIONS 00379 double __search_start = omp_get_wtime(); 00380 #endif 00381 00382 // Look for new work. 00383 bool __successfully_stolen = false; 00384 while (__wait && *__tl._M_elements_leftover > 0 00385 && !__successfully_stolen 00386 #if _GLIBCXX_PARALLEL_ASSERTIONS 00387 // Possible dead-lock. 00388 && (omp_get_wtime() < (__search_start + 1.0)) 00389 #endif 00390 ) 00391 { 00392 _ThreadIndex __victim; 00393 __victim = __rng(__num_threads); 00394 00395 // Large pieces. 00396 __successfully_stolen = (__victim != __iam) 00397 && __tls[__victim]->_M_leftover_parts.pop_back(__current); 00398 if (!__successfully_stolen) 00399 __yield(); 00400 #if !defined(__ICC) && !defined(__ECC) 00401 # pragma omp flush 00402 #endif 00403 } 00404 00405 #if _GLIBCXX_PARALLEL_ASSERTIONS 00406 if (omp_get_wtime() >= (__search_start + 1.0)) 00407 { 00408 sleep(1); 00409 _GLIBCXX_PARALLEL_ASSERT(omp_get_wtime() 00410 < (__search_start + 1.0)); 00411 } 00412 #endif 00413 if (!__successfully_stolen) 00414 { 00415 #if _GLIBCXX_PARALLEL_ASSERTIONS 00416 _GLIBCXX_PARALLEL_ASSERT(*__tl._M_elements_leftover == 0); 00417 #endif 00418 return; 00419 } 00420 } 00421 } 00422 } 00423 00424 /** @brief Top-level quicksort routine. 00425 * @param __begin Begin iterator of sequence. 00426 * @param __end End iterator of sequence. 00427 * @param __comp Comparator. 00428 * @param __num_threads Number of threads that are allowed to work on 00429 * this part. 00430 */ 00431 template<typename _RAIter, typename _Compare> 00432 void 00433 __parallel_sort_qsb(_RAIter __begin, _RAIter __end, 00434 _Compare __comp, _ThreadIndex __num_threads) 00435 { 00436 _GLIBCXX_CALL(__end - __begin) 00437 00438 typedef std::iterator_traits<_RAIter> _TraitsType; 00439 typedef typename _TraitsType::value_type _ValueType; 00440 typedef typename _TraitsType::difference_type _DifferenceType; 00441 typedef std::pair<_RAIter, _RAIter> _Piece; 00442 00443 typedef _QSBThreadLocal<_RAIter> _TLSType; 00444 00445 _DifferenceType __n = __end - __begin; 00446 00447 if (__n <= 1) 00448 return; 00449 00450 // At least one element per processor. 00451 if (__num_threads > __n) 00452 __num_threads = static_cast<_ThreadIndex>(__n); 00453 00454 // Initialize thread local storage 00455 _TLSType** __tls = new _TLSType*[__num_threads]; 00456 _DifferenceType __queue_size = (__num_threads 00457 * (_ThreadIndex)(__rd_log2(__n) + 1)); 00458 for (_ThreadIndex __t = 0; __t < __num_threads; ++__t) 00459 __tls[__t] = new _QSBThreadLocal<_RAIter>(__queue_size); 00460 00461 // There can never be more than ceil(__rd_log2(__n)) ranges on the 00462 // stack, because 00463 // 1. Only one processor pushes onto the stack 00464 // 2. The largest range has at most length __n 00465 // 3. Each range is larger than half of the range remaining 00466 volatile _DifferenceType __elements_leftover = __n; 00467 for (_ThreadIndex __i = 0; __i < __num_threads; ++__i) 00468 { 00469 __tls[__i]->_M_elements_leftover = &__elements_leftover; 00470 __tls[__i]->_M_num_threads = __num_threads; 00471 __tls[__i]->_M_global = std::make_pair(__begin, __end); 00472 00473 // Just in case nothing is left to assign. 00474 __tls[__i]->_M_initial = std::make_pair(__end, __end); 00475 } 00476 00477 // Main recursion call. 00478 __qsb_conquer(__tls, __begin, __begin + __n, __comp, 0, 00479 __num_threads, true); 00480 00481 #if _GLIBCXX_PARALLEL_ASSERTIONS 00482 // All stack must be empty. 00483 _Piece __dummy; 00484 for (_ThreadIndex __i = 1; __i < __num_threads; ++__i) 00485 _GLIBCXX_PARALLEL_ASSERT( 00486 !__tls[__i]->_M_leftover_parts.pop_back(__dummy)); 00487 #endif 00488 00489 for (_ThreadIndex __i = 0; __i < __num_threads; ++__i) 00490 delete __tls[__i]; 00491 delete[] __tls; 00492 } 00493 } // namespace __gnu_parallel 00494 00495 #endif /* _GLIBCXX_PARALLEL_BALANCED_QUICKSORT_H */