libstdc++
find.h
Go to the documentation of this file.
1 // -*- C++ -*-
2 
3 // Copyright (C) 2007, 2008, 2009, 2010, 2011 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/find.h
26  * @brief Parallel implementation base for std::find(), std::equal()
27  * and related functions.
28  * This file is a GNU parallel extension to the Standard C++ Library.
29  */
30 
31 // Written by Felix Putze and Johannes Singler.
32 
33 #ifndef _GLIBCXX_PARALLEL_FIND_H
34 #define _GLIBCXX_PARALLEL_FIND_H 1
35 
36 #include <bits/stl_algobase.h>
37 
38 #include <parallel/features.h>
39 #include <parallel/parallel.h>
40 #include <parallel/compatibility.h>
41 #include <parallel/equally_split.h>
42 
43 namespace __gnu_parallel
44 {
45  /**
46  * @brief Parallel std::find, switch for different algorithms.
47  * @param __begin1 Begin iterator of first sequence.
48  * @param __end1 End iterator of first sequence.
49  * @param __begin2 Begin iterator of second sequence. Must have same
50  * length as first sequence.
51  * @param __pred Find predicate.
52  * @param __selector _Functionality (e. g. std::find_if(), std::equal(),...)
53  * @return Place of finding in both sequences.
54  */
55  template<typename _RAIter1,
56  typename _RAIter2,
57  typename _Pred,
58  typename _Selector>
60  __find_template(_RAIter1 __begin1, _RAIter1 __end1,
61  _RAIter2 __begin2, _Pred __pred, _Selector __selector)
62  {
63  switch (_Settings::get().find_algorithm)
64  {
65  case GROWING_BLOCKS:
66  return __find_template(__begin1, __end1, __begin2, __pred,
67  __selector, growing_blocks_tag());
68  case CONSTANT_SIZE_BLOCKS:
69  return __find_template(__begin1, __end1, __begin2, __pred,
70  __selector, constant_size_blocks_tag());
71  case EQUAL_SPLIT:
72  return __find_template(__begin1, __end1, __begin2, __pred,
73  __selector, equal_split_tag());
74  default:
75  _GLIBCXX_PARALLEL_ASSERT(false);
76  return std::make_pair(__begin1, __begin2);
77  }
78  }
79 
80 #if _GLIBCXX_FIND_EQUAL_SPLIT
81 
82  /**
83  * @brief Parallel std::find, equal splitting variant.
84  * @param __begin1 Begin iterator of first sequence.
85  * @param __end1 End iterator of first sequence.
86  * @param __begin2 Begin iterator of second sequence. Second __sequence
87  * must have same length as first sequence.
88  * @param __pred Find predicate.
89  * @param __selector _Functionality (e. g. std::find_if(), std::equal(),...)
90  * @return Place of finding in both sequences.
91  */
92  template<typename _RAIter1,
93  typename _RAIter2,
94  typename _Pred,
95  typename _Selector>
97  __find_template(_RAIter1 __begin1, _RAIter1 __end1,
98  _RAIter2 __begin2, _Pred __pred,
99  _Selector __selector, equal_split_tag)
100  {
101  _GLIBCXX_CALL(__end1 - __begin1)
102 
103  typedef std::iterator_traits<_RAIter1> _TraitsType;
104  typedef typename _TraitsType::difference_type _DifferenceType;
105  typedef typename _TraitsType::value_type _ValueType;
106 
107  _DifferenceType __length = __end1 - __begin1;
108  _DifferenceType __result = __length;
109  _DifferenceType* __borders;
110 
111  omp_lock_t __result_lock;
112  omp_init_lock(&__result_lock);
113 
114  _ThreadIndex __num_threads = __get_max_threads();
115 # pragma omp parallel num_threads(__num_threads)
116  {
117 # pragma omp single
118  {
119  __num_threads = omp_get_num_threads();
120  __borders = new _DifferenceType[__num_threads + 1];
121  __equally_split(__length, __num_threads, __borders);
122  } //single
123 
124  _ThreadIndex __iam = omp_get_thread_num();
125  _DifferenceType __start = __borders[__iam],
126  __stop = __borders[__iam + 1];
127 
128  _RAIter1 __i1 = __begin1 + __start;
129  _RAIter2 __i2 = __begin2 + __start;
130  for (_DifferenceType __pos = __start; __pos < __stop; ++__pos)
131  {
132 # pragma omp flush(__result)
133  // Result has been set to something lower.
134  if (__result < __pos)
135  break;
136 
137  if (__selector(__i1, __i2, __pred))
138  {
139  omp_set_lock(&__result_lock);
140  if (__pos < __result)
141  __result = __pos;
142  omp_unset_lock(&__result_lock);
143  break;
144  }
145  ++__i1;
146  ++__i2;
147  }
148  } //parallel
149 
150  omp_destroy_lock(&__result_lock);
151  delete[] __borders;
152 
153  return std::pair<_RAIter1, _RAIter2>(__begin1 + __result,
154  __begin2 + __result);
155  }
156 
157 #endif
158 
159 #if _GLIBCXX_FIND_GROWING_BLOCKS
160 
161  /**
162  * @brief Parallel std::find, growing block size variant.
163  * @param __begin1 Begin iterator of first sequence.
164  * @param __end1 End iterator of first sequence.
165  * @param __begin2 Begin iterator of second sequence. Second __sequence
166  * must have same length as first sequence.
167  * @param __pred Find predicate.
168  * @param __selector _Functionality (e. g. std::find_if(), std::equal(),...)
169  * @return Place of finding in both sequences.
170  * @see __gnu_parallel::_Settings::find_sequential_search_size
171  * @see __gnu_parallel::_Settings::find_scale_factor
172  *
173  * There are two main differences between the growing blocks and
174  * the constant-size blocks variants.
175  * 1. For GB, the block size grows; for CSB, the block size is fixed.
176  * 2. For GB, the blocks are allocated dynamically;
177  * for CSB, the blocks are allocated in a predetermined manner,
178  * namely spacial round-robin.
179  */
180  template<typename _RAIter1,
181  typename _RAIter2,
182  typename _Pred,
183  typename _Selector>
185  __find_template(_RAIter1 __begin1, _RAIter1 __end1,
186  _RAIter2 __begin2, _Pred __pred, _Selector __selector,
188  {
189  _GLIBCXX_CALL(__end1 - __begin1)
190 
191  typedef std::iterator_traits<_RAIter1> _TraitsType;
192  typedef typename _TraitsType::difference_type _DifferenceType;
193  typedef typename _TraitsType::value_type _ValueType;
194 
195  const _Settings& __s = _Settings::get();
196 
197  _DifferenceType __length = __end1 - __begin1;
198 
199  _DifferenceType
200  __sequential_search_size = std::min<_DifferenceType>
201  (__length, __s.find_sequential_search_size);
202 
203  // Try it sequentially first.
205  __find_seq_result = __selector._M_sequential_algorithm
206  (__begin1, __begin1 + __sequential_search_size,
207  __begin2, __pred);
208 
209  if (__find_seq_result.first != (__begin1 + __sequential_search_size))
210  return __find_seq_result;
211 
212  // Index of beginning of next free block (after sequential find).
213  _DifferenceType __next_block_start = __sequential_search_size;
214  _DifferenceType __result = __length;
215 
216  omp_lock_t __result_lock;
217  omp_init_lock(&__result_lock);
218 
219  const float __scale_factor = __s.find_scale_factor;
220 
221  _ThreadIndex __num_threads = __get_max_threads();
222 # pragma omp parallel shared(__result) num_threads(__num_threads)
223  {
224 # pragma omp single
225  __num_threads = omp_get_num_threads();
226 
227  // Not within first __k elements -> start parallel.
228  _ThreadIndex __iam = omp_get_thread_num();
229 
230  _DifferenceType __block_size =
231  std::max<_DifferenceType>(1, __scale_factor * __next_block_start);
232  _DifferenceType __start = __fetch_and_add<_DifferenceType>
233  (&__next_block_start, __block_size);
234 
235  // Get new block, update pointer to next block.
236  _DifferenceType __stop =
237  std::min<_DifferenceType>(__length, __start + __block_size);
238 
239  std::pair<_RAIter1, _RAIter2> __local_result;
240 
241  while (__start < __length)
242  {
243 # pragma omp flush(__result)
244  // Get new value of result.
245  if (__result < __start)
246  {
247  // No chance to find first element.
248  break;
249  }
250 
251  __local_result = __selector._M_sequential_algorithm
252  (__begin1 + __start, __begin1 + __stop,
253  __begin2 + __start, __pred);
254 
255  if (__local_result.first != (__begin1 + __stop))
256  {
257  omp_set_lock(&__result_lock);
258  if ((__local_result.first - __begin1) < __result)
259  {
260  __result = __local_result.first - __begin1;
261 
262  // Result cannot be in future blocks, stop algorithm.
263  __fetch_and_add<_DifferenceType>(&__next_block_start,
264  __length);
265  }
266  omp_unset_lock(&__result_lock);
267  }
268 
269  _DifferenceType __block_size =
270  std::max<_DifferenceType>(1, __scale_factor * __next_block_start);
271 
272  // Get new block, update pointer to next block.
273  __start = __fetch_and_add<_DifferenceType>(&__next_block_start,
274  __block_size);
275  __stop =
276  std::min<_DifferenceType>(__length, __start + __block_size);
277  }
278  } //parallel
279 
280  omp_destroy_lock(&__result_lock);
281 
282  // Return iterator on found element.
283  return
284  std::pair<_RAIter1, _RAIter2>(__begin1 + __result,
285  __begin2 + __result);
286  }
287 
288 #endif
289 
290 #if _GLIBCXX_FIND_CONSTANT_SIZE_BLOCKS
291 
292  /**
293  * @brief Parallel std::find, constant block size variant.
294  * @param __begin1 Begin iterator of first sequence.
295  * @param __end1 End iterator of first sequence.
296  * @param __begin2 Begin iterator of second sequence. Second __sequence
297  * must have same length as first sequence.
298  * @param __pred Find predicate.
299  * @param __selector _Functionality (e. g. std::find_if(), std::equal(),...)
300  * @return Place of finding in both sequences.
301  * @see __gnu_parallel::_Settings::find_sequential_search_size
302  * @see __gnu_parallel::_Settings::find_block_size
303  * There are two main differences between the growing blocks and the
304  * constant-size blocks variants.
305  * 1. For GB, the block size grows; for CSB, the block size is fixed.
306  * 2. For GB, the blocks are allocated dynamically; for CSB, the
307  * blocks are allocated in a predetermined manner, namely spacial
308  * round-robin.
309  */
310  template<typename _RAIter1,
311  typename _RAIter2,
312  typename _Pred,
313  typename _Selector>
315  __find_template(_RAIter1 __begin1, _RAIter1 __end1,
316  _RAIter2 __begin2, _Pred __pred, _Selector __selector,
318  {
319  _GLIBCXX_CALL(__end1 - __begin1)
320  typedef std::iterator_traits<_RAIter1> _TraitsType;
321  typedef typename _TraitsType::difference_type _DifferenceType;
322  typedef typename _TraitsType::value_type _ValueType;
323 
324  const _Settings& __s = _Settings::get();
325 
326  _DifferenceType __length = __end1 - __begin1;
327 
328  _DifferenceType __sequential_search_size = std::min<_DifferenceType>
329  (__length, __s.find_sequential_search_size);
330 
331  // Try it sequentially first.
333  __find_seq_result = __selector._M_sequential_algorithm
334  (__begin1, __begin1 + __sequential_search_size, __begin2, __pred);
335 
336  if (__find_seq_result.first != (__begin1 + __sequential_search_size))
337  return __find_seq_result;
338 
339  _DifferenceType __result = __length;
340  omp_lock_t __result_lock;
341  omp_init_lock(&__result_lock);
342 
343  // Not within first __sequential_search_size elements -> start parallel.
344 
345  _ThreadIndex __num_threads = __get_max_threads();
346 # pragma omp parallel shared(__result) num_threads(__num_threads)
347  {
348 # pragma omp single
349  __num_threads = omp_get_num_threads();
350 
351  _ThreadIndex __iam = omp_get_thread_num();
352  _DifferenceType __block_size = __s.find_initial_block_size;
353 
354  // First element of thread's current iteration.
355  _DifferenceType __iteration_start = __sequential_search_size;
356 
357  // Where to work (initialization).
358  _DifferenceType __start = __iteration_start + __iam * __block_size;
359  _DifferenceType __stop = std::min<_DifferenceType>(__length,
360  __start
361  + __block_size);
362 
363  std::pair<_RAIter1, _RAIter2> __local_result;
364 
365  while (__start < __length)
366  {
367  // Get new value of result.
368 # pragma omp flush(__result)
369  // No chance to find first element.
370  if (__result < __start)
371  break;
372 
373  __local_result = __selector._M_sequential_algorithm
374  (__begin1 + __start, __begin1 + __stop,
375  __begin2 + __start, __pred);
376 
377  if (__local_result.first != (__begin1 + __stop))
378  {
379  omp_set_lock(&__result_lock);
380  if ((__local_result.first - __begin1) < __result)
381  __result = __local_result.first - __begin1;
382  omp_unset_lock(&__result_lock);
383  // Will not find better value in its interval.
384  break;
385  }
386 
387  __iteration_start += __num_threads * __block_size;
388 
389  // Where to work.
390  __start = __iteration_start + __iam * __block_size;
391  __stop = std::min<_DifferenceType>(__length,
392  __start + __block_size);
393  }
394  } //parallel
395 
396  omp_destroy_lock(&__result_lock);
397 
398  // Return iterator on found element.
399  return std::pair<_RAIter1, _RAIter2>(__begin1 + __result,
400  __begin2 + __result);
401  }
402 #endif
403 } // end namespace
404 
405 #endif /* _GLIBCXX_PARALLEL_FIND_H */