libstdc++
omp_loop.h
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24 
25 /** @file parallel/omp_loop.h
26  * @brief Parallelization of embarrassingly parallel execution by
27  * means of an OpenMP for loop.
28  * This file is a GNU parallel extension to the Standard C++ Library.
29  */
30 
31 // Written by Felix Putze.
32 
33 #ifndef _GLIBCXX_PARALLEL_OMP_LOOP_H
34 #define _GLIBCXX_PARALLEL_OMP_LOOP_H 1
35 
36 #include <omp.h>
37 
38 #include <parallel/settings.h>
40 #include <parallel/base.h>
41 
42 namespace __gnu_parallel
43 {
44  /** @brief Embarrassingly parallel algorithm for random access
45  * iterators, using an OpenMP for loop.
46  *
47  * @param __begin Begin iterator of element sequence.
48  * @param __end End iterator of element sequence.
49  * @param __o User-supplied functor (comparator, predicate, adding
50  * functor, etc.).
51  * @param __f Functor to @a process an element with __op (depends on
52  * desired functionality, e. g. for std::for_each(), ...).
53  * @param __r Functor to @a add a single __result to the already
54  * processed elements (depends on functionality).
55  * @param __base Base value for reduction.
56  * @param __output Pointer to position where final result is written to
57  * @param __bound Maximum number of elements processed (e. g. for
58  * std::count_n()).
59  * @return User-supplied functor (that may contain a part of the result).
60  */
61  template<typename _RAIter,
62  typename _Op,
63  typename _Fu,
64  typename _Red,
65  typename _Result>
66  _Op
67  __for_each_template_random_access_omp_loop(_RAIter __begin, _RAIter __end,
68  _Op __o, _Fu& __f, _Red __r,
69  _Result __base,
70  _Result& __output,
71  typename std::iterator_traits<_RAIter>::difference_type __bound)
72  {
73  typedef typename std::iterator_traits<_RAIter>::difference_type
74  _DifferenceType;
75 
76  _DifferenceType __length = __end - __begin;
77  _ThreadIndex __num_threads = __gnu_parallel::min<_DifferenceType>
78  (__get_max_threads(), __length);
79 
80  _Result *__thread_results;
81 
82 # pragma omp parallel num_threads(__num_threads)
83  {
84 # pragma omp single
85  {
86  __num_threads = omp_get_num_threads();
87  __thread_results = new _Result[__num_threads];
88 
89  for (_ThreadIndex __i = 0; __i < __num_threads; ++__i)
90  __thread_results[__i] = _Result();
91  }
92 
93  _ThreadIndex __iam = omp_get_thread_num();
94 
95 #pragma omp for schedule(dynamic, _Settings::get().workstealing_chunk_size)
96  for (_DifferenceType __pos = 0; __pos < __length; ++__pos)
97  __thread_results[__iam] = __r(__thread_results[__iam],
98  __f(__o, __begin+__pos));
99  } //parallel
100 
101  for (_ThreadIndex __i = 0; __i < __num_threads; ++__i)
102  __output = __r(__output, __thread_results[__i]);
103 
104  delete [] __thread_results;
105 
106  // Points to last element processed (needed as return value for
107  // some algorithms like transform).
108  __f._M_finish_iterator = __begin + __length;
109 
110  return __o;
111  }
112 
113 } // end namespace
114 
115 #endif /* _GLIBCXX_PARALLEL_OMP_LOOP_H */
uint16_t _ThreadIndex
Unsigned integer to index a thread number. The maximum thread number (for each processor) must fit in...
Definition: types.h:123
_Op __for_each_template_random_access_omp_loop(_RAIter __begin, _RAIter __end, _Op __o, _Fu &__f, _Red __r, _Result __base, _Result &__output, typename std::iterator_traits< _RAIter >::difference_type __bound)
Embarrassingly parallel algorithm for random access iterators, using an OpenMP for loop...
Definition: omp_loop.h:67
Runtime settings and tuning parameters, heuristics to decide whether to use parallelized algorithms...
Includes the original header files concerned with iterators except for stream iterators. This file is a GNU parallel extension to the Standard C++ Library.
_Siter_base< _Iterator >::iterator_type __base(_Iterator __it)
Sequential helper functions. This file is a GNU parallel extension to the Standard C++ Library...