libstdc++
omp_loop_static.h
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24 
25 /** @file parallel/omp_loop_static.h
26  * @brief Parallelization of embarrassingly parallel execution by
27  * means of an OpenMP for loop with static scheduling.
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_STATIC_H
34 #define _GLIBCXX_PARALLEL_OMP_LOOP_STATIC_H 1
35 
36 #include <omp.h>
37 
38 #include <parallel/settings.h>
40 
41 namespace __gnu_parallel
42 {
43  /** @brief Embarrassingly parallel algorithm for random access
44  * iterators, using an OpenMP for loop with static scheduling.
45  *
46  * @param __begin Begin iterator of element sequence.
47  * @param __end End iterator of element sequence.
48  * @param __o User-supplied functor (comparator, predicate, adding
49  * functor, ...).
50  * @param __f Functor to @a process an element with __op (depends on
51  * desired functionality, e. g. for std::for_each(), ...).
52  * @param __r Functor to @a add a single __result to the already processed
53  * __elements (depends on functionality).
54  * @param __base Base value for reduction.
55  * @param __output Pointer to position where final result is written to
56  * @param __bound Maximum number of elements processed (e. g. for
57  * std::count_n()).
58  * @return User-supplied functor (that may contain a part of the result).
59  */
60  template<typename _RAIter,
61  typename _Op,
62  typename _Fu,
63  typename _Red,
64  typename _Result>
65  _Op
67  _RAIter __end, _Op __o,
68  _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 = std::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(static, _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.finish_iterator = __begin + __length;
109 
110  return __o;
111  }
112 
113 } // end namespace
114 
115 #endif /* _GLIBCXX_PARALLEL_OMP_LOOP_STATIC_H */
Runtime settings and tuning parameters, heuristics to decide whether to use parallelized algorithms....
_Op __for_each_template_random_access_omp_loop_static(_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 with static s...
Includes the original header files concerned with iterators except for stream iterators....
GNU parallel code for public use.
uint16_t _ThreadIndex
Unsigned integer to index a thread number. The maximum thread number (for each processor) must fit in...
Definition: types.h:123