libstdc++
find.h
Go to the documentation of this file.
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/find.h
00026  *  @brief Parallel implementation base for std::find(), std::equal()
00027  *  and related functions.
00028  *  This file is a GNU parallel extension to the Standard C++ Library.
00029  */
00030 
00031 // Written by Felix Putze and Johannes Singler.
00032 
00033 #ifndef _GLIBCXX_PARALLEL_FIND_H
00034 #define _GLIBCXX_PARALLEL_FIND_H 1
00035 
00036 #include <bits/stl_algobase.h>
00037 
00038 #include <parallel/features.h>
00039 #include <parallel/parallel.h>
00040 #include <parallel/compatibility.h>
00041 #include <parallel/equally_split.h>
00042 
00043 namespace __gnu_parallel
00044 {
00045   /**
00046    *  @brief Parallel std::find, switch for different algorithms.
00047    *  @param __begin1 Begin iterator of first sequence.
00048    *  @param __end1 End iterator of first sequence.
00049    *  @param __begin2 Begin iterator of second sequence. Must have same
00050    *  length as first sequence.
00051    *  @param __pred Find predicate.
00052    *  @param __selector _Functionality (e. g. std::find_if(), std::equal(),...)
00053    *  @return Place of finding in both sequences.
00054    */
00055   template<typename _RAIter1,
00056        typename _RAIter2,
00057        typename _Pred,
00058            typename _Selector>
00059     inline std::pair<_RAIter1, _RAIter2>
00060     __find_template(_RAIter1 __begin1, _RAIter1 __end1,
00061             _RAIter2 __begin2, _Pred __pred, _Selector __selector)
00062     {
00063       switch (_Settings::get().find_algorithm)
00064     {
00065     case GROWING_BLOCKS:
00066           return __find_template(__begin1, __end1, __begin2, __pred,
00067                  __selector, growing_blocks_tag());
00068     case CONSTANT_SIZE_BLOCKS:
00069           return __find_template(__begin1, __end1, __begin2, __pred,
00070                  __selector, constant_size_blocks_tag());
00071     case EQUAL_SPLIT:
00072           return __find_template(__begin1, __end1, __begin2, __pred,
00073                  __selector, equal_split_tag());
00074     default:
00075           _GLIBCXX_PARALLEL_ASSERT(false);
00076           return std::make_pair(__begin1, __begin2);
00077     }
00078     }
00079 
00080 #if _GLIBCXX_FIND_EQUAL_SPLIT
00081 
00082   /**
00083    *  @brief Parallel std::find, equal splitting variant.
00084    *  @param __begin1 Begin iterator of first sequence.
00085    *  @param __end1 End iterator of first sequence.
00086    *  @param __begin2 Begin iterator of second sequence. Second __sequence
00087    *  must have same length as first sequence.
00088    *  @param __pred Find predicate.
00089    *  @param __selector _Functionality (e. g. std::find_if(), std::equal(),...)
00090    *  @return Place of finding in both sequences.
00091    */
00092   template<typename _RAIter1,
00093            typename _RAIter2,
00094            typename _Pred,
00095            typename _Selector>
00096     std::pair<_RAIter1, _RAIter2>
00097     __find_template(_RAIter1 __begin1, _RAIter1 __end1,
00098             _RAIter2 __begin2, _Pred __pred,
00099             _Selector __selector, equal_split_tag)
00100     {
00101       _GLIBCXX_CALL(__end1 - __begin1)
00102 
00103       typedef std::iterator_traits<_RAIter1> _TraitsType;
00104       typedef typename _TraitsType::difference_type _DifferenceType;
00105       typedef typename _TraitsType::value_type _ValueType;
00106 
00107       _DifferenceType __length = __end1 - __begin1;
00108       _DifferenceType __result = __length;
00109       _DifferenceType* __borders;
00110 
00111       omp_lock_t __result_lock;
00112       omp_init_lock(&__result_lock);
00113 
00114       _ThreadIndex __num_threads = __get_max_threads();
00115 #     pragma omp parallel num_threads(__num_threads)
00116       {
00117 #     pragma omp single
00118     {
00119       __num_threads = omp_get_num_threads();
00120       __borders = new _DifferenceType[__num_threads + 1];
00121       equally_split(__length, __num_threads, __borders);
00122     } //single
00123 
00124     _ThreadIndex __iam = omp_get_thread_num();
00125     _DifferenceType __start = __borders[__iam],
00126                      __stop = __borders[__iam + 1];
00127 
00128     _RAIter1 __i1 = __begin1 + __start;
00129     _RAIter2 __i2 = __begin2 + __start;
00130     for (_DifferenceType __pos = __start; __pos < __stop; ++__pos)
00131       {
00132 #           pragma omp flush(__result)
00133         // Result has been set to something lower.
00134         if (__result < __pos)
00135           break;
00136 
00137         if (__selector(__i1, __i2, __pred))
00138           {
00139         omp_set_lock(&__result_lock);
00140         if (__pos < __result)
00141           __result = __pos;
00142         omp_unset_lock(&__result_lock);
00143         break;
00144           }
00145         ++__i1;
00146         ++__i2;
00147       }
00148       } //parallel
00149 
00150       omp_destroy_lock(&__result_lock);
00151       delete[] __borders;
00152 
00153       return std::pair<_RAIter1, _RAIter2>(__begin1 + __result,
00154                        __begin2 + __result);
00155     }
00156 
00157 #endif
00158 
00159 #if _GLIBCXX_FIND_GROWING_BLOCKS
00160 
00161   /**
00162    *  @brief Parallel std::find, growing block size variant.
00163    *  @param __begin1 Begin iterator of first sequence.
00164    *  @param __end1 End iterator of first sequence.
00165    *  @param __begin2 Begin iterator of second sequence. Second __sequence
00166    *  must have same length as first sequence.
00167    *  @param __pred Find predicate.
00168    *  @param __selector _Functionality (e. g. std::find_if(), std::equal(),...)
00169    *  @return Place of finding in both sequences.
00170    *  @see __gnu_parallel::_Settings::find_sequential_search_size
00171    *  @see __gnu_parallel::_Settings::find_scale_factor
00172    *
00173    *  There are two main differences between the growing blocks and
00174    *  the constant-size blocks variants.
00175    *  1. For GB, the block size grows; for CSB, the block size is fixed.
00176    *  2. For GB, the blocks are allocated dynamically;
00177    *     for CSB, the blocks are allocated in a predetermined manner,
00178    *     namely spacial round-robin.
00179    */
00180   template<typename _RAIter1,
00181            typename _RAIter2,
00182            typename _Pred,
00183            typename _Selector>
00184     std::pair<_RAIter1, _RAIter2>
00185     __find_template(_RAIter1 __begin1, _RAIter1 __end1,
00186             _RAIter2 __begin2, _Pred __pred, _Selector __selector,
00187             growing_blocks_tag)
00188     {
00189       _GLIBCXX_CALL(__end1 - __begin1)
00190 
00191       typedef std::iterator_traits<_RAIter1> _TraitsType;
00192       typedef typename _TraitsType::difference_type _DifferenceType;
00193       typedef typename _TraitsType::value_type _ValueType;
00194 
00195       const _Settings& __s = _Settings::get();
00196 
00197       _DifferenceType __length = __end1 - __begin1;
00198 
00199       _DifferenceType
00200     __sequential_search_size = std::min<_DifferenceType>
00201     (__length, __s.find_sequential_search_size);
00202 
00203       // Try it sequentially first.
00204       std::pair<_RAIter1, _RAIter2>
00205     __find_seq_result = __selector._M_sequential_algorithm
00206     (__begin1, __begin1 + __sequential_search_size,
00207      __begin2, __pred);
00208 
00209       if (__find_seq_result.first != (__begin1 + __sequential_search_size))
00210     return __find_seq_result;
00211 
00212       // Index of beginning of next free block (after sequential find).
00213       _DifferenceType __next_block_start = __sequential_search_size;
00214       _DifferenceType __result = __length;
00215 
00216       omp_lock_t __result_lock;
00217       omp_init_lock(&__result_lock);
00218 
00219       const float __scale_factor = __s.find_scale_factor;
00220 
00221       _ThreadIndex __num_threads = __get_max_threads();
00222 #     pragma omp parallel shared(__result) num_threads(__num_threads)
00223       {
00224 #       pragma omp single
00225     __num_threads = omp_get_num_threads();
00226 
00227     // Not within first __k elements -> start parallel.
00228     _ThreadIndex __iam = omp_get_thread_num();
00229 
00230     _DifferenceType __block_size =
00231       std::max<_DifferenceType>(1, __scale_factor * __next_block_start);
00232     _DifferenceType __start = __fetch_and_add<_DifferenceType>
00233       (&__next_block_start, __block_size);
00234 
00235     // Get new block, update pointer to next block.
00236     _DifferenceType __stop =
00237       std::min<_DifferenceType>(__length, __start + __block_size);
00238 
00239     std::pair<_RAIter1, _RAIter2> __local_result;
00240 
00241     while (__start < __length)
00242       {
00243 #           pragma omp flush(__result)
00244         // Get new value of result.
00245         if (__result < __start)
00246           {
00247         // No chance to find first element.
00248         break;
00249           }
00250 
00251         __local_result = __selector._M_sequential_algorithm
00252           (__begin1 + __start, __begin1 + __stop,
00253            __begin2 + __start, __pred);
00254 
00255         if (__local_result.first != (__begin1 + __stop))
00256           {
00257         omp_set_lock(&__result_lock);
00258         if ((__local_result.first - __begin1) < __result)
00259           {
00260             __result = __local_result.first - __begin1;
00261 
00262             // Result cannot be in future blocks, stop algorithm.
00263             __fetch_and_add<_DifferenceType>(&__next_block_start,
00264                              __length);
00265           }
00266         omp_unset_lock(&__result_lock);
00267           }
00268 
00269         _DifferenceType __block_size =
00270          std::max<_DifferenceType>(1, __scale_factor * __next_block_start);
00271 
00272         // Get new block, update pointer to next block.
00273         __start = __fetch_and_add<_DifferenceType>(&__next_block_start,
00274                                __block_size);
00275         __stop =
00276           std::min<_DifferenceType>(__length, __start + __block_size);
00277       }
00278       } //parallel
00279 
00280       omp_destroy_lock(&__result_lock);
00281 
00282       // Return iterator on found element.
00283       return
00284     std::pair<_RAIter1, _RAIter2>(__begin1 + __result,
00285                       __begin2 + __result);
00286     }
00287 
00288 #endif
00289 
00290 #if _GLIBCXX_FIND_CONSTANT_SIZE_BLOCKS
00291 
00292   /**
00293    *   @brief Parallel std::find, constant block size variant.
00294    *  @param __begin1 Begin iterator of first sequence.
00295    *  @param __end1 End iterator of first sequence.
00296    *  @param __begin2 Begin iterator of second sequence. Second __sequence
00297    *  must have same length as first sequence.
00298    *  @param __pred Find predicate.
00299    *  @param __selector _Functionality (e. g. std::find_if(), std::equal(),...)
00300    *  @return Place of finding in both sequences.
00301    *  @see __gnu_parallel::_Settings::find_sequential_search_size
00302    *  @see __gnu_parallel::_Settings::find_block_size
00303    *  There are two main differences between the growing blocks and the
00304    *  constant-size blocks variants.
00305    *  1. For GB, the block size grows; for CSB, the block size is fixed.
00306    *  2. For GB, the blocks are allocated dynamically; for CSB, the
00307    *  blocks are allocated in a predetermined manner, namely spacial
00308    *  round-robin.
00309    */
00310   template<typename _RAIter1,
00311            typename _RAIter2,
00312            typename _Pred,
00313            typename _Selector>
00314     std::pair<_RAIter1, _RAIter2>
00315     __find_template(_RAIter1 __begin1, _RAIter1 __end1,
00316                   _RAIter2 __begin2, _Pred __pred, _Selector __selector,
00317                   constant_size_blocks_tag)
00318     {
00319       _GLIBCXX_CALL(__end1 - __begin1)
00320       typedef std::iterator_traits<_RAIter1> _TraitsType;
00321       typedef typename _TraitsType::difference_type _DifferenceType;
00322       typedef typename _TraitsType::value_type _ValueType;
00323 
00324       const _Settings& __s = _Settings::get();
00325 
00326       _DifferenceType __length = __end1 - __begin1;
00327 
00328       _DifferenceType __sequential_search_size = std::min<_DifferenceType>
00329     (__length, __s.find_sequential_search_size);
00330 
00331       // Try it sequentially first.
00332       std::pair<_RAIter1, _RAIter2>
00333     __find_seq_result = __selector._M_sequential_algorithm
00334     (__begin1, __begin1 + __sequential_search_size, __begin2, __pred);
00335 
00336       if (__find_seq_result.first != (__begin1 + __sequential_search_size))
00337     return __find_seq_result;
00338 
00339       _DifferenceType __result = __length;
00340       omp_lock_t __result_lock;
00341       omp_init_lock(&__result_lock);
00342 
00343       // Not within first __sequential_search_size elements -> start parallel.
00344 
00345       _ThreadIndex __num_threads = __get_max_threads();
00346 #     pragma omp parallel shared(__result) num_threads(__num_threads)
00347       {
00348 #       pragma omp single
00349     __num_threads = omp_get_num_threads();
00350 
00351     _ThreadIndex __iam = omp_get_thread_num();
00352     _DifferenceType __block_size = __s.find_initial_block_size;
00353 
00354     // First element of thread's current iteration.
00355     _DifferenceType __iteration_start = __sequential_search_size;
00356 
00357     // Where to work (initialization).
00358     _DifferenceType __start = __iteration_start + __iam * __block_size;
00359     _DifferenceType __stop = std::min<_DifferenceType>(__length,
00360                                __start
00361                                + __block_size);
00362 
00363     std::pair<_RAIter1, _RAIter2> __local_result;
00364 
00365     while (__start < __length)
00366       {
00367         // Get new value of result.
00368 #           pragma omp flush(__result)
00369         // No chance to find first element.
00370         if (__result < __start)
00371           break;
00372 
00373         __local_result = __selector._M_sequential_algorithm
00374           (__begin1 + __start, __begin1 + __stop,
00375            __begin2 + __start, __pred);
00376 
00377         if (__local_result.first != (__begin1 + __stop))
00378           {
00379         omp_set_lock(&__result_lock);
00380         if ((__local_result.first - __begin1) < __result)
00381           __result = __local_result.first - __begin1;
00382         omp_unset_lock(&__result_lock);
00383         // Will not find better value in its interval.
00384         break;
00385           }
00386 
00387         __iteration_start += __num_threads * __block_size;
00388 
00389         // Where to work.
00390         __start = __iteration_start + __iam * __block_size;
00391         __stop = std::min<_DifferenceType>(__length,
00392                            __start + __block_size);
00393       }
00394       } //parallel
00395 
00396       omp_destroy_lock(&__result_lock);
00397 
00398       // Return iterator on found element.
00399       return std::pair<_RAIter1, _RAIter2>(__begin1 + __result,
00400                        __begin2 + __result);
00401     }
00402 #endif
00403 } // end namespace
00404 
00405 #endif /* _GLIBCXX_PARALLEL_FIND_H */