1 /* 2 Copyright (c) 2005-2021 Intel Corporation 3 4 Licensed under the Apache License, Version 2.0 (the "License"); 5 you may not use this file except in compliance with the License. 6 You may obtain a copy of the License at 7 8 http://www.apache.org/licenses/LICENSE-2.0 9 10 Unless required by applicable law or agreed to in writing, software 11 distributed under the License is distributed on an "AS IS" BASIS, 12 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 See the License for the specific language governing permissions and 14 limitations under the License. 15 */ 16 17 #ifndef __TBB_parallel_sort_H 18 #define __TBB_parallel_sort_H 19 20 #include "detail/_namespace_injection.h" 21 #include "parallel_for.h" 22 #include "blocked_range.h" 23 #include "profiling.h" 24 25 #include <algorithm> 26 #include <iterator> 27 #include <functional> 28 #include <cstddef> 29 30 namespace tbb { 31 namespace detail { 32 #if __TBB_CPP20_CONCEPTS_PRESENT 33 inline namespace d0 { 34 35 // TODO: consider using std::strict_weak_order concept 36 template <typename Compare, typename Iterator> 37 concept compare = requires( const std::remove_reference_t<Compare>& comp, typename std::iterator_traits<Iterator>::reference value ) { 38 // Forward via iterator_traits::reference 39 { comp(typename std::iterator_traits<Iterator>::reference(value), 40 typename std::iterator_traits<Iterator>::reference(value)) } -> std::convertible_to<bool>; 41 }; 42 43 // Inspired by std::__PartiallyOrderedWith exposition only concept 44 template <typename T> 45 concept less_than_comparable = requires( const std::remove_reference_t<T>& lhs, 46 const std::remove_reference_t<T>& rhs ) { 47 { lhs < rhs } -> boolean_testable; 48 }; 49 50 } // namespace d0 51 #endif // __TBB_CPP20_CONCEPTS_PRESENT 52 namespace d1 { 53 54 //! Range used in quicksort to split elements into subranges based on a value. 55 /** The split operation selects a splitter and places all elements less than or equal 56 to the value in the first range and the remaining elements in the second range. 57 @ingroup algorithms */ 58 template<typename RandomAccessIterator, typename Compare> 59 class quick_sort_range { 60 std::size_t median_of_three( const RandomAccessIterator& array, std::size_t l, std::size_t m, std::size_t r ) const { 61 return comp(array[l], array[m]) ? ( comp(array[m], array[r]) ? m : ( comp(array[l], array[r]) ? r : l ) ) 62 : ( comp(array[r], array[m]) ? m : ( comp(array[r], array[l]) ? r : l ) ); 63 } 64 65 std::size_t pseudo_median_of_nine( const RandomAccessIterator& array, const quick_sort_range& range ) const { 66 std::size_t offset = range.size / 8u; 67 return median_of_three(array, 68 median_of_three(array, 0 , offset, offset * 2), 69 median_of_three(array, offset * 3, offset * 4, offset * 5), 70 median_of_three(array, offset * 6, offset * 7, range.size - 1)); 71 72 } 73 74 std::size_t split_range( quick_sort_range& range ) { 75 RandomAccessIterator array = range.begin; 76 RandomAccessIterator first_element = range.begin; 77 std::size_t m = pseudo_median_of_nine(array, range); 78 if( m != 0 ) std::iter_swap(array, array + m); 79 80 std::size_t i = 0; 81 std::size_t j = range.size; 82 // Partition interval [i + 1,j - 1] with key *first_element. 83 for(;;) { 84 __TBB_ASSERT( i < j, nullptr ); 85 // Loop must terminate since array[l] == *first_element. 86 do { 87 --j; 88 __TBB_ASSERT( i <= j, "bad ordering relation?" ); 89 } while( comp(*first_element, array[j]) ); 90 do { 91 __TBB_ASSERT( i <= j, nullptr ); 92 if( i == j ) goto partition; 93 ++i; 94 } while( comp(array[i], *first_element) ); 95 if( i == j ) goto partition; 96 std::iter_swap(array + i, array + j); 97 } 98 partition: 99 // Put the partition key were it belongs 100 std::iter_swap(array + j, first_element); 101 // array[l..j) is less or equal to key. 102 // array(j..r) is greater or equal to key. 103 // array[j] is equal to key 104 i = j + 1; 105 std::size_t new_range_size = range.size - i; 106 range.size = j; 107 return new_range_size; 108 } 109 110 public: 111 quick_sort_range() = default; 112 quick_sort_range( const quick_sort_range& ) = default; 113 void operator=( const quick_sort_range& ) = delete; 114 115 static constexpr std::size_t grainsize = 500; 116 const Compare& comp; 117 std::size_t size; 118 RandomAccessIterator begin; 119 120 quick_sort_range( RandomAccessIterator begin_, std::size_t size_, const Compare& comp_ ) : 121 comp(comp_), size(size_), begin(begin_) {} 122 123 bool empty() const { return size == 0; } 124 bool is_divisible() const { return size >= grainsize; } 125 126 quick_sort_range( quick_sort_range& range, split ) 127 : comp(range.comp) 128 , size(split_range(range)) 129 // +1 accounts for the pivot element, which is at its correct place 130 // already and, therefore, is not included into subranges. 131 , begin(range.begin + range.size + 1) {} 132 }; 133 134 //! Body class used to test if elements in a range are presorted 135 /** @ingroup algorithms */ 136 template<typename RandomAccessIterator, typename Compare> 137 class quick_sort_pretest_body { 138 const Compare& comp; 139 task_group_context& context; 140 141 public: 142 quick_sort_pretest_body() = default; 143 quick_sort_pretest_body( const quick_sort_pretest_body& ) = default; 144 void operator=( const quick_sort_pretest_body& ) = delete; 145 146 quick_sort_pretest_body( const Compare& _comp, task_group_context& _context ) : comp(_comp), context(_context) {} 147 148 void operator()( const blocked_range<RandomAccessIterator>& range ) const { 149 RandomAccessIterator my_end = range.end(); 150 151 int i = 0; 152 //TODO: consider using std::is_sorted() for each 64 iterations (requires performance measurements) 153 for( RandomAccessIterator k = range.begin(); k != my_end; ++k, ++i ) { 154 if( i % 64 == 0 && context.is_group_execution_cancelled() ) break; 155 156 // The k - 1 is never out-of-range because the first chunk starts at begin+serial_cutoff+1 157 if( comp(*(k), *(k - 1)) ) { 158 context.cancel_group_execution(); 159 break; 160 } 161 } 162 } 163 }; 164 165 //! Body class used to sort elements in a range that is smaller than the grainsize. 166 /** @ingroup algorithms */ 167 template<typename RandomAccessIterator, typename Compare> 168 struct quick_sort_body { 169 void operator()( const quick_sort_range<RandomAccessIterator,Compare>& range ) const { 170 std::sort(range.begin, range.begin + range.size, range.comp); 171 } 172 }; 173 174 //! Method to perform parallel_for based quick sort. 175 /** @ingroup algorithms */ 176 template<typename RandomAccessIterator, typename Compare> 177 void do_parallel_quick_sort( RandomAccessIterator begin, RandomAccessIterator end, const Compare& comp ) { 178 parallel_for(quick_sort_range<RandomAccessIterator,Compare>(begin, end - begin, comp), 179 quick_sort_body<RandomAccessIterator,Compare>(), 180 auto_partitioner()); 181 } 182 183 //! Wrapper method to initiate the sort by calling parallel_for. 184 /** @ingroup algorithms */ 185 template<typename RandomAccessIterator, typename Compare> 186 void parallel_quick_sort( RandomAccessIterator begin, RandomAccessIterator end, const Compare& comp ) { 187 task_group_context my_context(PARALLEL_SORT); 188 constexpr int serial_cutoff = 9; 189 190 __TBB_ASSERT( begin + serial_cutoff < end, "min_parallel_size is smaller than serial cutoff?" ); 191 RandomAccessIterator k = begin; 192 for( ; k != begin + serial_cutoff; ++k ) { 193 if( comp(*(k + 1), *k) ) { 194 do_parallel_quick_sort(begin, end, comp); 195 return; 196 } 197 } 198 199 // Check is input range already sorted 200 parallel_for(blocked_range<RandomAccessIterator>(k + 1, end), 201 quick_sort_pretest_body<RandomAccessIterator, Compare>(comp, my_context), 202 auto_partitioner(), 203 my_context); 204 205 if( my_context.is_group_execution_cancelled() ) 206 do_parallel_quick_sort(begin, end, comp); 207 } 208 209 /** \page parallel_sort_iter_req Requirements on iterators for parallel_sort 210 Requirements on the iterator type \c It and its value type \c T for \c parallel_sort: 211 212 - \code void iter_swap( It a, It b ) \endcode Swaps the values of the elements the given 213 iterators \c a and \c b are pointing to. \c It should be a random access iterator. 214 215 - \code bool Compare::operator()( const T& x, const T& y ) \endcode True if x comes before y; 216 **/ 217 218 /** \name parallel_sort 219 See also requirements on \ref parallel_sort_iter_req "iterators for parallel_sort". **/ 220 //@{ 221 222 #if __TBB_CPP20_CONCEPTS_PRESENT 223 template<typename It> 224 using iter_value_type = typename std::iterator_traits<It>::value_type; 225 226 template<typename Range> 227 using range_value_type = typename std::iterator_traits<range_iterator_type<Range>>::value_type; 228 #endif 229 230 //! Sorts the data in [begin,end) using the given comparator 231 /** The compare function object is used for all comparisons between elements during sorting. 232 The compare object must define a bool operator() function. 233 @ingroup algorithms **/ 234 template<typename RandomAccessIterator, typename Compare> 235 __TBB_requires(std::random_access_iterator<RandomAccessIterator> && 236 compare<Compare, RandomAccessIterator> && 237 std::movable<iter_value_type<RandomAccessIterator>>) 238 void parallel_sort( RandomAccessIterator begin, RandomAccessIterator end, const Compare& comp ) { 239 constexpr int min_parallel_size = 500; 240 if( end > begin ) { 241 if( end - begin < min_parallel_size ) { 242 std::sort(begin, end, comp); 243 } else { 244 parallel_quick_sort(begin, end, comp); 245 } 246 } 247 } 248 249 //! Sorts the data in [begin,end) with a default comparator \c std::less 250 /** @ingroup algorithms **/ 251 template<typename RandomAccessIterator> 252 __TBB_requires(std::random_access_iterator<RandomAccessIterator> && 253 less_than_comparable<iter_value_type<RandomAccessIterator>> && 254 std::movable<iter_value_type<RandomAccessIterator>>) 255 void parallel_sort( RandomAccessIterator begin, RandomAccessIterator end ) { 256 parallel_sort(begin, end, std::less<typename std::iterator_traits<RandomAccessIterator>::value_type>()); 257 } 258 259 //! Sorts the data in rng using the given comparator 260 /** @ingroup algorithms **/ 261 template<typename Range, typename Compare> 262 __TBB_requires(container_based_sequence<Range, std::random_access_iterator_tag> && 263 compare<Compare, range_iterator_type<Range>> && 264 std::movable<range_value_type<Range>>) 265 void parallel_sort( Range&& rng, const Compare& comp ) { 266 parallel_sort(std::begin(rng), std::end(rng), comp); 267 } 268 269 //! Sorts the data in rng with a default comparator \c std::less 270 /** @ingroup algorithms **/ 271 template<typename Range> 272 __TBB_requires(container_based_sequence<Range, std::random_access_iterator_tag> && 273 less_than_comparable<range_value_type<Range>> && 274 std::movable<range_value_type<Range>>) 275 void parallel_sort( Range&& rng ) { 276 parallel_sort(std::begin(rng), std::end(rng)); 277 } 278 //@} 279 280 } // namespace d1 281 } // namespace detail 282 283 inline namespace v1 { 284 using detail::d1::parallel_sort; 285 } // namespace v1 286 } // namespace tbb 287 288 #endif /*__TBB_parallel_sort_H*/ 289