libstdc++
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00001 // -*- C++ -*- 00002 00003 // Copyright (C) 2007, 2008, 2009, 2010 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_ASSERTIONS 00055 #include <parallel/checkers.h> 00056 #endif 00057 00058 namespace __gnu_parallel 00059 { 00060 /** @brief Information local to one thread in the parallel quicksort run. */ 00061 template<typename _RAIter> 00062 struct _QSBThreadLocal 00063 { 00064 typedef std::iterator_traits<_RAIter> _TraitsType; 00065 typedef typename _TraitsType::difference_type _DifferenceType; 00066 00067 /** @brief Continuous part of the sequence, described by an 00068 iterator pair. */ 00069 typedef std::pair<_RAIter, _RAIter> _Piece; 00070 00071 /** @brief Initial piece to work on. */ 00072 _Piece _M_initial; 00073 00074 /** @brief Work-stealing queue. */ 00075 _RestrictedBoundedConcurrentQueue<_Piece> _M_leftover_parts; 00076 00077 /** @brief Number of threads involved in this algorithm. */ 00078 _ThreadIndex _M_num_threads; 00079 00080 /** @brief Pointer to a counter of elements left over to sort. */ 00081 volatile _DifferenceType* _M_elements_leftover; 00082 00083 /** @brief The complete sequence to sort. */ 00084 _Piece _M_global; 00085 00086 /** @brief Constructor. 00087 * @param __queue_size size of the work-stealing queue. */ 00088 _QSBThreadLocal(int __queue_size) : _M_leftover_parts(__queue_size) { } 00089 }; 00090 00091 /** @brief Balanced quicksort divide step. 00092 * @param __begin Begin iterator of subsequence. 00093 * @param __end End iterator of subsequence. 00094 * @param __comp Comparator. 00095 * @param __num_threads Number of threads that are allowed to work on 00096 * this part. 00097 * @pre @c (__end-__begin)>=1 */ 00098 template<typename _RAIter, typename _Compare> 00099 typename std::iterator_traits<_RAIter>::difference_type 00100 __qsb_divide(_RAIter __begin, _RAIter __end, 00101 _Compare __comp, _ThreadIndex __num_threads) 00102 { 00103 _GLIBCXX_PARALLEL_ASSERT(__num_threads > 0); 00104 00105 typedef std::iterator_traits<_RAIter> _TraitsType; 00106 typedef typename _TraitsType::value_type _ValueType; 00107 typedef typename _TraitsType::difference_type _DifferenceType; 00108 00109 _RAIter __pivot_pos = 00110 __median_of_three_iterators(__begin, __begin + (__end - __begin) / 2, 00111 __end - 1, __comp); 00112 00113 #if defined(_GLIBCXX_ASSERTIONS) 00114 // Must be in between somewhere. 00115 _DifferenceType __n = __end - __begin; 00116 00117 _GLIBCXX_PARALLEL_ASSERT((!__comp(*__pivot_pos, *__begin) 00118 && !__comp(*(__begin + __n / 2), 00119 *__pivot_pos)) 00120 || (!__comp(*__pivot_pos, *__begin) 00121 && !__comp(*(__end - 1), *__pivot_pos)) 00122 || (!__comp(*__pivot_pos, *(__begin + __n / 2)) 00123 && !__comp(*__begin, *__pivot_pos)) 00124 || (!__comp(*__pivot_pos, *(__begin + __n / 2)) 00125 && !__comp(*(__end - 1), *__pivot_pos)) 00126 || (!__comp(*__pivot_pos, *(__end - 1)) 00127 && !__comp(*__begin, *__pivot_pos)) 00128 || (!__comp(*__pivot_pos, *(__end - 1)) 00129 && !__comp(*(__begin + __n / 2), 00130 *__pivot_pos))); 00131 #endif 00132 00133 // Swap pivot value to end. 00134 if (__pivot_pos != (__end - 1)) 00135 std::iter_swap(__pivot_pos, __end - 1); 00136 __pivot_pos = __end - 1; 00137 00138 __gnu_parallel::__binder2nd<_Compare, _ValueType, _ValueType, bool> 00139 __pred(__comp, *__pivot_pos); 00140 00141 // Divide, returning __end - __begin - 1 in the worst case. 00142 _DifferenceType __split_pos = __parallel_partition(__begin, __end - 1, 00143 __pred, 00144 __num_threads); 00145 00146 // Swap back pivot to middle. 00147 std::iter_swap(__begin + __split_pos, __pivot_pos); 00148 __pivot_pos = __begin + __split_pos; 00149 00150 #if _GLIBCXX_ASSERTIONS 00151 _RAIter __r; 00152 for (__r = __begin; __r != __pivot_pos; ++__r) 00153 _GLIBCXX_PARALLEL_ASSERT(__comp(*__r, *__pivot_pos)); 00154 for (; __r != __end; ++__r) 00155 _GLIBCXX_PARALLEL_ASSERT(!__comp(*__r, *__pivot_pos)); 00156 #endif 00157 00158 return __split_pos; 00159 } 00160 00161 /** @brief Quicksort conquer step. 00162 * @param __tls Array of thread-local storages. 00163 * @param __begin Begin iterator of subsequence. 00164 * @param __end End iterator of subsequence. 00165 * @param __comp Comparator. 00166 * @param __iam Number of the thread processing this function. 00167 * @param __num_threads 00168 * Number of threads that are allowed to work on this part. */ 00169 template<typename _RAIter, typename _Compare> 00170 void 00171 __qsb_conquer(_QSBThreadLocal<_RAIter>** __tls, 00172 _RAIter __begin, _RAIter __end, 00173 _Compare __comp, 00174 _ThreadIndex __iam, _ThreadIndex __num_threads, 00175 bool __parent_wait) 00176 { 00177 typedef std::iterator_traits<_RAIter> _TraitsType; 00178 typedef typename _TraitsType::value_type _ValueType; 00179 typedef typename _TraitsType::difference_type _DifferenceType; 00180 00181 _DifferenceType __n = __end - __begin; 00182 00183 if (__num_threads <= 1 || __n <= 1) 00184 { 00185 __tls[__iam]->_M_initial.first = __begin; 00186 __tls[__iam]->_M_initial.second = __end; 00187 00188 __qsb_local_sort_with_helping(__tls, __comp, __iam, __parent_wait); 00189 00190 return; 00191 } 00192 00193 // Divide step. 00194 _DifferenceType __split_pos = 00195 __qsb_divide(__begin, __end, __comp, __num_threads); 00196 00197 #if _GLIBCXX_ASSERTIONS 00198 _GLIBCXX_PARALLEL_ASSERT(0 <= __split_pos && 00199 __split_pos < (__end - __begin)); 00200 #endif 00201 00202 _ThreadIndex 00203 __num_threads_leftside = std::max<_ThreadIndex> 00204 (1, std::min<_ThreadIndex>(__num_threads - 1, __split_pos 00205 * __num_threads / __n)); 00206 00207 # pragma omp atomic 00208 *__tls[__iam]->_M_elements_leftover -= (_DifferenceType)1; 00209 00210 // Conquer step. 00211 # pragma omp parallel num_threads(2) 00212 { 00213 bool __wait; 00214 if(omp_get_num_threads() < 2) 00215 __wait = false; 00216 else 00217 __wait = __parent_wait; 00218 00219 # pragma omp sections 00220 { 00221 # pragma omp section 00222 { 00223 __qsb_conquer(__tls, __begin, __begin + __split_pos, __comp, 00224 __iam, __num_threads_leftside, __wait); 00225 __wait = __parent_wait; 00226 } 00227 // The pivot_pos is left in place, to ensure termination. 00228 # pragma omp section 00229 { 00230 __qsb_conquer(__tls, __begin + __split_pos + 1, __end, __comp, 00231 __iam + __num_threads_leftside, 00232 __num_threads - __num_threads_leftside, __wait); 00233 __wait = __parent_wait; 00234 } 00235 } 00236 } 00237 } 00238 00239 /** 00240 * @brief Quicksort step doing load-balanced local sort. 00241 * @param __tls Array of thread-local storages. 00242 * @param __comp Comparator. 00243 * @param __iam Number of the thread processing this function. 00244 */ 00245 template<typename _RAIter, typename _Compare> 00246 void 00247 __qsb_local_sort_with_helping(_QSBThreadLocal<_RAIter>** __tls, 00248 _Compare& __comp, _ThreadIndex __iam, 00249 bool __wait) 00250 { 00251 typedef std::iterator_traits<_RAIter> _TraitsType; 00252 typedef typename _TraitsType::value_type _ValueType; 00253 typedef typename _TraitsType::difference_type _DifferenceType; 00254 typedef std::pair<_RAIter, _RAIter> _Piece; 00255 00256 _QSBThreadLocal<_RAIter>& __tl = *__tls[__iam]; 00257 00258 _DifferenceType 00259 __base_case_n = _Settings::get().sort_qsb_base_case_maximal_n; 00260 if (__base_case_n < 2) 00261 __base_case_n = 2; 00262 _ThreadIndex __num_threads = __tl._M_num_threads; 00263 00264 // Every thread has its own random number generator. 00265 _RandomNumber __rng(__iam + 1); 00266 00267 _Piece __current = __tl._M_initial; 00268 00269 _DifferenceType __elements_done = 0; 00270 #if _GLIBCXX_ASSERTIONS 00271 _DifferenceType __total_elements_done = 0; 00272 #endif 00273 00274 for (;;) 00275 { 00276 // Invariant: __current must be a valid (maybe empty) range. 00277 _RAIter __begin = __current.first, __end = __current.second; 00278 _DifferenceType __n = __end - __begin; 00279 00280 if (__n > __base_case_n) 00281 { 00282 // Divide. 00283 _RAIter __pivot_pos = __begin + __rng(__n); 00284 00285 // Swap __pivot_pos value to end. 00286 if (__pivot_pos != (__end - 1)) 00287 std::iter_swap(__pivot_pos, __end - 1); 00288 __pivot_pos = __end - 1; 00289 00290 __gnu_parallel::__binder2nd 00291 <_Compare, _ValueType, _ValueType, bool> 00292 __pred(__comp, *__pivot_pos); 00293 00294 // Divide, leave pivot unchanged in last place. 00295 _RAIter __split_pos1, __split_pos2; 00296 __split_pos1 = __gnu_sequential::partition(__begin, __end - 1, 00297 __pred); 00298 00299 // Left side: < __pivot_pos; __right side: >= __pivot_pos. 00300 #if _GLIBCXX_ASSERTIONS 00301 _GLIBCXX_PARALLEL_ASSERT(__begin <= __split_pos1 00302 && __split_pos1 < __end); 00303 #endif 00304 // Swap pivot back to middle. 00305 if (__split_pos1 != __pivot_pos) 00306 std::iter_swap(__split_pos1, __pivot_pos); 00307 __pivot_pos = __split_pos1; 00308 00309 // In case all elements are equal, __split_pos1 == 0. 00310 if ((__split_pos1 + 1 - __begin) < (__n >> 7) 00311 || (__end - __split_pos1) < (__n >> 7)) 00312 { 00313 // Very unequal split, one part smaller than one 128th 00314 // elements not strictly larger than the pivot. 00315 __gnu_parallel::__unary_negate<__gnu_parallel::__binder1st 00316 <_Compare, _ValueType, _ValueType, bool>, _ValueType> 00317 __pred(__gnu_parallel::__binder1st 00318 <_Compare, _ValueType, _ValueType, bool> 00319 (__comp, *__pivot_pos)); 00320 00321 // Find other end of pivot-equal range. 00322 __split_pos2 = __gnu_sequential::partition(__split_pos1 + 1, 00323 __end, __pred); 00324 } 00325 else 00326 // Only skip the pivot. 00327 __split_pos2 = __split_pos1 + 1; 00328 00329 // Elements equal to pivot are done. 00330 __elements_done += (__split_pos2 - __split_pos1); 00331 #if _GLIBCXX_ASSERTIONS 00332 __total_elements_done += (__split_pos2 - __split_pos1); 00333 #endif 00334 // Always push larger part onto stack. 00335 if (((__split_pos1 + 1) - __begin) < (__end - (__split_pos2))) 00336 { 00337 // Right side larger. 00338 if ((__split_pos2) != __end) 00339 __tl._M_leftover_parts.push_front 00340 (std::make_pair(__split_pos2, __end)); 00341 00342 //__current.first = __begin; //already set anyway 00343 __current.second = __split_pos1; 00344 continue; 00345 } 00346 else 00347 { 00348 // Left side larger. 00349 if (__begin != __split_pos1) 00350 __tl._M_leftover_parts.push_front(std::make_pair 00351 (__begin, __split_pos1)); 00352 00353 __current.first = __split_pos2; 00354 //__current.second = __end; //already set anyway 00355 continue; 00356 } 00357 } 00358 else 00359 { 00360 __gnu_sequential::sort(__begin, __end, __comp); 00361 __elements_done += __n; 00362 #if _GLIBCXX_ASSERTIONS 00363 __total_elements_done += __n; 00364 #endif 00365 00366 // Prefer own stack, small pieces. 00367 if (__tl._M_leftover_parts.pop_front(__current)) 00368 continue; 00369 00370 # pragma omp atomic 00371 *__tl._M_elements_leftover -= __elements_done; 00372 00373 __elements_done = 0; 00374 00375 #if _GLIBCXX_ASSERTIONS 00376 double __search_start = omp_get_wtime(); 00377 #endif 00378 00379 // Look for new work. 00380 bool __successfully_stolen = false; 00381 while (__wait && *__tl._M_elements_leftover > 0 00382 && !__successfully_stolen 00383 #if _GLIBCXX_ASSERTIONS 00384 // Possible dead-lock. 00385 && (omp_get_wtime() < (__search_start + 1.0)) 00386 #endif 00387 ) 00388 { 00389 _ThreadIndex __victim; 00390 __victim = __rng(__num_threads); 00391 00392 // Large pieces. 00393 __successfully_stolen = (__victim != __iam) 00394 && __tls[__victim]->_M_leftover_parts.pop_back(__current); 00395 if (!__successfully_stolen) 00396 __yield(); 00397 #if !defined(__ICC) && !defined(__ECC) 00398 # pragma omp flush 00399 #endif 00400 } 00401 00402 #if _GLIBCXX_ASSERTIONS 00403 if (omp_get_wtime() >= (__search_start + 1.0)) 00404 { 00405 sleep(1); 00406 _GLIBCXX_PARALLEL_ASSERT(omp_get_wtime() 00407 < (__search_start + 1.0)); 00408 } 00409 #endif 00410 if (!__successfully_stolen) 00411 { 00412 #if _GLIBCXX_ASSERTIONS 00413 _GLIBCXX_PARALLEL_ASSERT(*__tl._M_elements_leftover == 0); 00414 #endif 00415 return; 00416 } 00417 } 00418 } 00419 } 00420 00421 /** @brief Top-level quicksort routine. 00422 * @param __begin Begin iterator of sequence. 00423 * @param __end End iterator of sequence. 00424 * @param __comp Comparator. 00425 * @param __num_threads Number of threads that are allowed to work on 00426 * this part. 00427 */ 00428 template<typename _RAIter, typename _Compare> 00429 void 00430 __parallel_sort_qsb(_RAIter __begin, _RAIter __end, 00431 _Compare __comp, _ThreadIndex __num_threads) 00432 { 00433 _GLIBCXX_CALL(__end - __begin) 00434 00435 typedef std::iterator_traits<_RAIter> _TraitsType; 00436 typedef typename _TraitsType::value_type _ValueType; 00437 typedef typename _TraitsType::difference_type _DifferenceType; 00438 typedef std::pair<_RAIter, _RAIter> _Piece; 00439 00440 typedef _QSBThreadLocal<_RAIter> _TLSType; 00441 00442 _DifferenceType __n = __end - __begin; 00443 00444 if (__n <= 1) 00445 return; 00446 00447 // At least one element per processor. 00448 if (__num_threads > __n) 00449 __num_threads = static_cast<_ThreadIndex>(__n); 00450 00451 // Initialize thread local storage 00452 _TLSType** __tls = new _TLSType*[__num_threads]; 00453 _DifferenceType __queue_size = (__num_threads 00454 * (_ThreadIndex)(__rd_log2(__n) + 1)); 00455 for (_ThreadIndex __t = 0; __t < __num_threads; ++__t) 00456 __tls[__t] = new _QSBThreadLocal<_RAIter>(__queue_size); 00457 00458 // There can never be more than ceil(__rd_log2(__n)) ranges on the 00459 // stack, because 00460 // 1. Only one processor pushes onto the stack 00461 // 2. The largest range has at most length __n 00462 // 3. Each range is larger than half of the range remaining 00463 volatile _DifferenceType __elements_leftover = __n; 00464 for (_ThreadIndex __i = 0; __i < __num_threads; ++__i) 00465 { 00466 __tls[__i]->_M_elements_leftover = &__elements_leftover; 00467 __tls[__i]->_M_num_threads = __num_threads; 00468 __tls[__i]->_M_global = std::make_pair(__begin, __end); 00469 00470 // Just in case nothing is left to assign. 00471 __tls[__i]->_M_initial = std::make_pair(__end, __end); 00472 } 00473 00474 // Main recursion call. 00475 __qsb_conquer(__tls, __begin, __begin + __n, __comp, 0, 00476 __num_threads, true); 00477 00478 #if _GLIBCXX_ASSERTIONS 00479 // All stack must be empty. 00480 _Piece __dummy; 00481 for (_ThreadIndex __i = 1; __i < __num_threads; ++__i) 00482 _GLIBCXX_PARALLEL_ASSERT( 00483 !__tls[__i]->_M_leftover_parts.pop_back(__dummy)); 00484 #endif 00485 00486 for (_ThreadIndex __i = 0; __i < __num_threads; ++__i) 00487 delete __tls[__i]; 00488 delete[] __tls; 00489 } 00490 } // namespace __gnu_parallel 00491 00492 #endif /* _GLIBCXX_PARALLEL_BALANCED_QUICKSORT_H */