1// -*- C++ -*- 2 3// Copyright (C) 2007-2015 Free Software Foundation, Inc. 4// 5// This file is part of the GNU ISO C++ Library. This library is free 6// software; you can redistribute it and/or modify it under the terms 7// of the GNU General Public License as published by the Free Software 8// Foundation; either version 3, or (at your option) any later 9// version. 10 11// This library is distributed in the hope that it will be useful, but 12// WITHOUT ANY WARRANTY; without even the implied warranty of 13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14// General Public License for more details. 15 16// Under Section 7 of GPL version 3, you are granted additional 17// permissions described in the GCC Runtime Library Exception, version 18// 3.1, as published by the Free Software Foundation. 19 20// You should have received a copy of the GNU General Public License and 21// a copy of the GCC Runtime Library Exception along with this program; 22// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 23// <http://www.gnu.org/licenses/>. 24 25/** @file parallel/random_shuffle.h 26 * @brief Parallel implementation of std::random_shuffle(). 27 * This file is a GNU parallel extension to the Standard C++ Library. 28 */ 29 30// Written by Johannes Singler. 31 32#ifndef _GLIBCXX_PARALLEL_RANDOM_SHUFFLE_H 33#define _GLIBCXX_PARALLEL_RANDOM_SHUFFLE_H 1 34 35#include <limits> 36#include <bits/stl_numeric.h> 37#include <parallel/parallel.h> 38#include <parallel/random_number.h> 39 40namespace __gnu_parallel 41{ 42 /** @brief Type to hold the index of a bin. 43 * 44 * Since many variables of this type are allocated, it should be 45 * chosen as small as possible. 46 */ 47 typedef unsigned short _BinIndex; 48 49 /** @brief Data known to every thread participating in 50 __gnu_parallel::__parallel_random_shuffle(). */ 51 template<typename _RAIter> 52 struct _DRandomShufflingGlobalData 53 { 54 typedef std::iterator_traits<_RAIter> _TraitsType; 55 typedef typename _TraitsType::value_type _ValueType; 56 typedef typename _TraitsType::difference_type _DifferenceType; 57 58 /** @brief Begin iterator of the __source. */ 59 _RAIter& _M_source; 60 61 /** @brief Temporary arrays for each thread. */ 62 _ValueType** _M_temporaries; 63 64 /** @brief Two-dimensional array to hold the thread-bin distribution. 65 * 66 * Dimensions (_M_num_threads + 1) __x (_M_num_bins + 1). */ 67 _DifferenceType** _M_dist; 68 69 /** @brief Start indexes of the threads' __chunks. */ 70 _DifferenceType* _M_starts; 71 72 /** @brief Number of the thread that will further process the 73 corresponding bin. */ 74 _ThreadIndex* _M_bin_proc; 75 76 /** @brief Number of bins to distribute to. */ 77 int _M_num_bins; 78 79 /** @brief Number of bits needed to address the bins. */ 80 int _M_num_bits; 81 82 /** @brief Constructor. */ 83 _DRandomShufflingGlobalData(_RAIter& __source) 84 : _M_source(__source) { } 85 }; 86 87 /** @brief Local data for a thread participating in 88 __gnu_parallel::__parallel_random_shuffle(). 89 */ 90 template<typename _RAIter, typename _RandomNumberGenerator> 91 struct _DRSSorterPU 92 { 93 /** @brief Number of threads participating in total. */ 94 int _M_num_threads; 95 96 /** @brief Begin index for bins taken care of by this thread. */ 97 _BinIndex _M_bins_begin; 98 99 /** @brief End index for bins taken care of by this thread. */ 100 _BinIndex __bins_end; 101 102 /** @brief Random _M_seed for this thread. */ 103 uint32_t _M_seed; 104 105 /** @brief Pointer to global data. */ 106 _DRandomShufflingGlobalData<_RAIter>* _M_sd; 107 }; 108 109 /** @brief Generate a random number in @c [0,2^__logp). 110 * @param __logp Logarithm (basis 2) of the upper range __bound. 111 * @param __rng Random number generator to use. 112 */ 113 template<typename _RandomNumberGenerator> 114 inline int 115 __random_number_pow2(int __logp, _RandomNumberGenerator& __rng) 116 { return __rng.__genrand_bits(__logp); } 117 118 /** @brief Random shuffle code executed by each thread. 119 * @param __pus Array of thread-local data records. */ 120 template<typename _RAIter, typename _RandomNumberGenerator> 121 void 122 __parallel_random_shuffle_drs_pu(_DRSSorterPU<_RAIter, 123 _RandomNumberGenerator>* __pus) 124 { 125 typedef std::iterator_traits<_RAIter> _TraitsType; 126 typedef typename _TraitsType::value_type _ValueType; 127 typedef typename _TraitsType::difference_type _DifferenceType; 128 129 _ThreadIndex __iam = omp_get_thread_num(); 130 _DRSSorterPU<_RAIter, _RandomNumberGenerator>* __d = &__pus[__iam]; 131 _DRandomShufflingGlobalData<_RAIter>* __sd = __d->_M_sd; 132 133 // Indexing: _M_dist[bin][processor] 134 _DifferenceType __length = (__sd->_M_starts[__iam + 1] 135 - __sd->_M_starts[__iam]); 136 _BinIndex* __oracles = new _BinIndex[__length]; 137 _DifferenceType* __dist = new _DifferenceType[__sd->_M_num_bins + 1]; 138 _BinIndex* __bin_proc = new _BinIndex[__sd->_M_num_bins]; 139 _ValueType** __temporaries = new _ValueType*[__d->_M_num_threads]; 140 141 // Compute oracles and count appearances. 142 for (_BinIndex __b = 0; __b < __sd->_M_num_bins + 1; ++__b) 143 __dist[__b] = 0; 144 int __num_bits = __sd->_M_num_bits; 145 146 _RandomNumber __rng(__d->_M_seed); 147 148 // First main loop. 149 for (_DifferenceType __i = 0; __i < __length; ++__i) 150 { 151 _BinIndex __oracle = __random_number_pow2(__num_bits, __rng); 152 __oracles[__i] = __oracle; 153 154 // To allow prefix (partial) sum. 155 ++(__dist[__oracle + 1]); 156 } 157 158 for (_BinIndex __b = 0; __b < __sd->_M_num_bins + 1; ++__b) 159 __sd->_M_dist[__b][__iam + 1] = __dist[__b]; 160 161# pragma omp barrier 162 163# pragma omp single 164 { 165 // Sum up bins, __sd->_M_dist[__s + 1][__d->_M_num_threads] now 166 // contains the total number of items in bin __s 167 for (_BinIndex __s = 0; __s < __sd->_M_num_bins; ++__s) 168 __gnu_sequential::partial_sum(__sd->_M_dist[__s + 1], 169 __sd->_M_dist[__s + 1] 170 + __d->_M_num_threads + 1, 171 __sd->_M_dist[__s + 1]); 172 } 173 174# pragma omp barrier 175 176 _SequenceIndex __offset = 0, __global_offset = 0; 177 for (_BinIndex __s = 0; __s < __d->_M_bins_begin; ++__s) 178 __global_offset += __sd->_M_dist[__s + 1][__d->_M_num_threads]; 179 180# pragma omp barrier 181 182 for (_BinIndex __s = __d->_M_bins_begin; __s < __d->__bins_end; ++__s) 183 { 184 for (int __t = 0; __t < __d->_M_num_threads + 1; ++__t) 185 __sd->_M_dist[__s + 1][__t] += __offset; 186 __offset = __sd->_M_dist[__s + 1][__d->_M_num_threads]; 187 } 188 189 __sd->_M_temporaries[__iam] = static_cast<_ValueType*> 190 (::operator new(sizeof(_ValueType) * __offset)); 191 192# pragma omp barrier 193 194 // Draw local copies to avoid false sharing. 195 for (_BinIndex __b = 0; __b < __sd->_M_num_bins + 1; ++__b) 196 __dist[__b] = __sd->_M_dist[__b][__iam]; 197 for (_BinIndex __b = 0; __b < __sd->_M_num_bins; ++__b) 198 __bin_proc[__b] = __sd->_M_bin_proc[__b]; 199 for (_ThreadIndex __t = 0; __t < __d->_M_num_threads; ++__t) 200 __temporaries[__t] = __sd->_M_temporaries[__t]; 201 202 _RAIter __source = __sd->_M_source; 203 _DifferenceType __start = __sd->_M_starts[__iam]; 204 205 // Distribute according to oracles, second main loop. 206 for (_DifferenceType __i = 0; __i < __length; ++__i) 207 { 208 _BinIndex __target_bin = __oracles[__i]; 209 _ThreadIndex __target_p = __bin_proc[__target_bin]; 210 211 // Last column [__d->_M_num_threads] stays unchanged. 212 ::new(&(__temporaries[__target_p][__dist[__target_bin + 1]++])) 213 _ValueType(*(__source + __i + __start)); 214 } 215 216 delete[] __oracles; 217 delete[] __dist; 218 delete[] __bin_proc; 219 delete[] __temporaries; 220 221# pragma omp barrier 222 223 // Shuffle bins internally. 224 for (_BinIndex __b = __d->_M_bins_begin; __b < __d->__bins_end; ++__b) 225 { 226 _ValueType* __begin = 227 (__sd->_M_temporaries[__iam] 228 + (__b == __d->_M_bins_begin 229 ? 0 : __sd->_M_dist[__b][__d->_M_num_threads])), 230 *__end = (__sd->_M_temporaries[__iam] 231 + __sd->_M_dist[__b + 1][__d->_M_num_threads]); 232 233 __sequential_random_shuffle(__begin, __end, __rng); 234 std::copy(__begin, __end, __sd->_M_source + __global_offset 235 + (__b == __d->_M_bins_begin 236 ? 0 : __sd->_M_dist[__b][__d->_M_num_threads])); 237 } 238 239 for (_SequenceIndex __i = 0; __i < __offset; ++__i) 240 __sd->_M_temporaries[__iam][__i].~_ValueType(); 241 ::operator delete(__sd->_M_temporaries[__iam]); 242 } 243 244 /** @brief Round up to the next greater power of 2. 245 * @param __x _Integer to round up */ 246 template<typename _Tp> 247 _Tp 248 __round_up_to_pow2(_Tp __x) 249 { 250 if (__x <= 1) 251 return 1; 252 else 253 return (_Tp)1 << (__rd_log2(__x - 1) + 1); 254 } 255 256 /** @brief Main parallel random shuffle step. 257 * @param __begin Begin iterator of sequence. 258 * @param __end End iterator of sequence. 259 * @param __n Length of sequence. 260 * @param __num_threads Number of threads to use. 261 * @param __rng Random number generator to use. 262 */ 263 template<typename _RAIter, typename _RandomNumberGenerator> 264 void 265 __parallel_random_shuffle_drs(_RAIter __begin, _RAIter __end, 266 typename std::iterator_traits 267 <_RAIter>::difference_type __n, 268 _ThreadIndex __num_threads, 269 _RandomNumberGenerator& __rng) 270 { 271 typedef std::iterator_traits<_RAIter> _TraitsType; 272 typedef typename _TraitsType::value_type _ValueType; 273 typedef typename _TraitsType::difference_type _DifferenceType; 274 275 _GLIBCXX_CALL(__n) 276 277 const _Settings& __s = _Settings::get(); 278 279 if (__num_threads > __n) 280 __num_threads = static_cast<_ThreadIndex>(__n); 281 282 _BinIndex __num_bins, __num_bins_cache; 283 284#if _GLIBCXX_RANDOM_SHUFFLE_CONSIDER_L1 285 // Try the L1 cache first. 286 287 // Must fit into L1. 288 __num_bins_cache = 289 std::max<_DifferenceType>(1, __n / (__s.L1_cache_size_lb 290 / sizeof(_ValueType))); 291 __num_bins_cache = __round_up_to_pow2(__num_bins_cache); 292 293 // No more buckets than TLB entries, power of 2 294 // Power of 2 and at least one element per bin, at most the TLB size. 295 __num_bins = std::min<_DifferenceType>(__n, __num_bins_cache); 296 297#if _GLIBCXX_RANDOM_SHUFFLE_CONSIDER_TLB 298 // 2 TLB entries needed per bin. 299 __num_bins = std::min<_DifferenceType>(__s.TLB_size / 2, __num_bins); 300#endif 301 __num_bins = __round_up_to_pow2(__num_bins); 302 303 if (__num_bins < __num_bins_cache) 304 { 305#endif 306 // Now try the L2 cache 307 // Must fit into L2 308 __num_bins_cache = static_cast<_BinIndex> 309 (std::max<_DifferenceType>(1, __n / (__s.L2_cache_size 310 / sizeof(_ValueType)))); 311 __num_bins_cache = __round_up_to_pow2(__num_bins_cache); 312 313 // No more buckets than TLB entries, power of 2. 314 __num_bins = static_cast<_BinIndex> 315 (std::min(__n, static_cast<_DifferenceType>(__num_bins_cache))); 316 // Power of 2 and at least one element per bin, at most the TLB size. 317#if _GLIBCXX_RANDOM_SHUFFLE_CONSIDER_TLB 318 // 2 TLB entries needed per bin. 319 __num_bins = std::min(static_cast<_DifferenceType>(__s.TLB_size / 2), 320 __num_bins); 321#endif 322 __num_bins = __round_up_to_pow2(__num_bins); 323#if _GLIBCXX_RANDOM_SHUFFLE_CONSIDER_L1 324 } 325#endif 326 327 __num_bins = __round_up_to_pow2( 328 std::max<_BinIndex>(__num_threads, __num_bins)); 329 330 if (__num_threads <= 1) 331 { 332 _RandomNumber __derived_rng( 333 __rng(std::numeric_limits<uint32_t>::max())); 334 __sequential_random_shuffle(__begin, __end, __derived_rng); 335 return; 336 } 337 338 _DRandomShufflingGlobalData<_RAIter> __sd(__begin); 339 _DRSSorterPU<_RAIter, _RandomNumber >* __pus; 340 _DifferenceType* __starts; 341 342# pragma omp parallel num_threads(__num_threads) 343 { 344 _ThreadIndex __num_threads = omp_get_num_threads(); 345# pragma omp single 346 { 347 __pus = new _DRSSorterPU<_RAIter, _RandomNumber>[__num_threads]; 348 349 __sd._M_temporaries = new _ValueType*[__num_threads]; 350 __sd._M_dist = new _DifferenceType*[__num_bins + 1]; 351 __sd._M_bin_proc = new _ThreadIndex[__num_bins]; 352 for (_BinIndex __b = 0; __b < __num_bins + 1; ++__b) 353 __sd._M_dist[__b] = new _DifferenceType[__num_threads + 1]; 354 for (_BinIndex __b = 0; __b < (__num_bins + 1); ++__b) 355 { 356 __sd._M_dist[0][0] = 0; 357 __sd._M_dist[__b][0] = 0; 358 } 359 __starts = __sd._M_starts = new _DifferenceType[__num_threads + 1]; 360 int __bin_cursor = 0; 361 __sd._M_num_bins = __num_bins; 362 __sd._M_num_bits = __rd_log2(__num_bins); 363 364 _DifferenceType __chunk_length = __n / __num_threads, 365 __split = __n % __num_threads, 366 __start = 0; 367 _DifferenceType __bin_chunk_length = __num_bins / __num_threads, 368 __bin_split = __num_bins % __num_threads; 369 for (_ThreadIndex __i = 0; __i < __num_threads; ++__i) 370 { 371 __starts[__i] = __start; 372 __start += (__i < __split 373 ? (__chunk_length + 1) : __chunk_length); 374 int __j = __pus[__i]._M_bins_begin = __bin_cursor; 375 376 // Range of bins for this processor. 377 __bin_cursor += (__i < __bin_split 378 ? (__bin_chunk_length + 1) 379 : __bin_chunk_length); 380 __pus[__i].__bins_end = __bin_cursor; 381 for (; __j < __bin_cursor; ++__j) 382 __sd._M_bin_proc[__j] = __i; 383 __pus[__i]._M_num_threads = __num_threads; 384 __pus[__i]._M_seed = __rng(std::numeric_limits<uint32_t>::max()); 385 __pus[__i]._M_sd = &__sd; 386 } 387 __starts[__num_threads] = __start; 388 } //single 389 // Now shuffle in parallel. 390 __parallel_random_shuffle_drs_pu(__pus); 391 } // parallel 392 393 delete[] __starts; 394 delete[] __sd._M_bin_proc; 395 for (int __s = 0; __s < (__num_bins + 1); ++__s) 396 delete[] __sd._M_dist[__s]; 397 delete[] __sd._M_dist; 398 delete[] __sd._M_temporaries; 399 400 delete[] __pus; 401 } 402 403 /** @brief Sequential cache-efficient random shuffle. 404 * @param __begin Begin iterator of sequence. 405 * @param __end End iterator of sequence. 406 * @param __rng Random number generator to use. 407 */ 408 template<typename _RAIter, typename _RandomNumberGenerator> 409 void 410 __sequential_random_shuffle(_RAIter __begin, _RAIter __end, 411 _RandomNumberGenerator& __rng) 412 { 413 typedef std::iterator_traits<_RAIter> _TraitsType; 414 typedef typename _TraitsType::value_type _ValueType; 415 typedef typename _TraitsType::difference_type _DifferenceType; 416 417 _DifferenceType __n = __end - __begin; 418 const _Settings& __s = _Settings::get(); 419 420 _BinIndex __num_bins, __num_bins_cache; 421 422#if _GLIBCXX_RANDOM_SHUFFLE_CONSIDER_L1 423 // Try the L1 cache first, must fit into L1. 424 __num_bins_cache = std::max<_DifferenceType> 425 (1, __n / (__s.L1_cache_size_lb / sizeof(_ValueType))); 426 __num_bins_cache = __round_up_to_pow2(__num_bins_cache); 427 428 // No more buckets than TLB entries, power of 2 429 // Power of 2 and at least one element per bin, at most the TLB size 430 __num_bins = std::min(__n, (_DifferenceType)__num_bins_cache); 431#if _GLIBCXX_RANDOM_SHUFFLE_CONSIDER_TLB 432 // 2 TLB entries needed per bin 433 __num_bins = std::min((_DifferenceType)__s.TLB_size / 2, __num_bins); 434#endif 435 __num_bins = __round_up_to_pow2(__num_bins); 436 437 if (__num_bins < __num_bins_cache) 438 { 439#endif 440 // Now try the L2 cache, must fit into L2. 441 __num_bins_cache = static_cast<_BinIndex> 442 (std::max<_DifferenceType>(1, __n / (__s.L2_cache_size 443 / sizeof(_ValueType)))); 444 __num_bins_cache = __round_up_to_pow2(__num_bins_cache); 445 446 // No more buckets than TLB entries, power of 2 447 // Power of 2 and at least one element per bin, at most the TLB size. 448 __num_bins = static_cast<_BinIndex> 449 (std::min(__n, static_cast<_DifferenceType>(__num_bins_cache))); 450 451#if _GLIBCXX_RANDOM_SHUFFLE_CONSIDER_TLB 452 // 2 TLB entries needed per bin 453 __num_bins = std::min<_DifferenceType>(__s.TLB_size / 2, __num_bins); 454#endif 455 __num_bins = __round_up_to_pow2(__num_bins); 456#if _GLIBCXX_RANDOM_SHUFFLE_CONSIDER_L1 457 } 458#endif 459 460 int __num_bits = __rd_log2(__num_bins); 461 462 if (__num_bins > 1) 463 { 464 _ValueType* __target = 465 static_cast<_ValueType*>(::operator new(sizeof(_ValueType) * __n)); 466 _BinIndex* __oracles = new _BinIndex[__n]; 467 _DifferenceType* __dist0 = new _DifferenceType[__num_bins + 1], 468 * __dist1 = new _DifferenceType[__num_bins + 1]; 469 470 for (int __b = 0; __b < __num_bins + 1; ++__b) 471 __dist0[__b] = 0; 472 473 _RandomNumber __bitrng(__rng(0xFFFFFFFF)); 474 475 for (_DifferenceType __i = 0; __i < __n; ++__i) 476 { 477 _BinIndex __oracle = __random_number_pow2(__num_bits, __bitrng); 478 __oracles[__i] = __oracle; 479 480 // To allow prefix (partial) sum. 481 ++(__dist0[__oracle + 1]); 482 } 483 484 // Sum up bins. 485 __gnu_sequential::partial_sum(__dist0, __dist0 + __num_bins + 1, 486 __dist0); 487 488 for (int __b = 0; __b < __num_bins + 1; ++__b) 489 __dist1[__b] = __dist0[__b]; 490 491 // Distribute according to oracles. 492 for (_DifferenceType __i = 0; __i < __n; ++__i) 493 ::new(&(__target[(__dist0[__oracles[__i]])++])) 494 _ValueType(*(__begin + __i)); 495 496 for (int __b = 0; __b < __num_bins; ++__b) 497 __sequential_random_shuffle(__target + __dist1[__b], 498 __target + __dist1[__b + 1], __rng); 499 500 // Copy elements back. 501 std::copy(__target, __target + __n, __begin); 502 503 delete[] __dist0; 504 delete[] __dist1; 505 delete[] __oracles; 506 507 for (_DifferenceType __i = 0; __i < __n; ++__i) 508 __target[__i].~_ValueType(); 509 ::operator delete(__target); 510 } 511 else 512 __gnu_sequential::random_shuffle(__begin, __end, __rng); 513 } 514 515 /** @brief Parallel random public call. 516 * @param __begin Begin iterator of sequence. 517 * @param __end End iterator of sequence. 518 * @param __rng Random number generator to use. 519 */ 520 template<typename _RAIter, typename _RandomNumberGenerator> 521 inline void 522 __parallel_random_shuffle(_RAIter __begin, _RAIter __end, 523 _RandomNumberGenerator __rng = _RandomNumber()) 524 { 525 typedef std::iterator_traits<_RAIter> _TraitsType; 526 typedef typename _TraitsType::difference_type _DifferenceType; 527 _DifferenceType __n = __end - __begin; 528 __parallel_random_shuffle_drs(__begin, __end, __n, 529 __get_max_threads(), __rng); 530 } 531} 532 533#endif /* _GLIBCXX_PARALLEL_RANDOM_SHUFFLE_H */ 534