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par_loop.h
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24
25/** @file parallel/par_loop.h
26 * @brief Parallelization of embarrassingly parallel execution by
27 * means of equal splitting.
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_PAR_LOOP_H
34#define _GLIBCXX_PARALLEL_PAR_LOOP_H 1
35
36#include <omp.h>
37#include <parallel/settings.h>
38#include <parallel/base.h>
39#include <parallel/equally_split.h>
40
41namespace __gnu_parallel
42{
43 /** @brief Embarrassingly parallel algorithm for random access
44 * iterators, using hand-crafted parallelization by equal splitting
45 * the work.
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, ...)
51 * @param __f Functor to "process" an element with __op (depends on
52 * desired functionality, e. g. for std::for_each(), ...).
53 * @param __r Functor to "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_ed(_RAIter __begin, _RAIter __end,
68 _Op __o, _Fu& __f, _Red __r,
69 _Result __base, _Result& __output,
70 typename std::iterator_traits<_RAIter>::difference_type __bound)
71 {
72 typedef std::iterator_traits<_RAIter> _TraitsType;
73 typedef typename _TraitsType::difference_type _DifferenceType;
74 const _DifferenceType __length = __end - __begin;
75 _Result *__thread_results;
76 bool* __constructed;
77
78 _ThreadIndex __num_threads = __gnu_parallel::min<_DifferenceType>
79 (__get_max_threads(), __length);
80
81# pragma omp parallel num_threads(__num_threads)
82 {
83# pragma omp single
84 {
85 __num_threads = omp_get_num_threads();
86 __thread_results = static_cast<_Result*>
87 (::operator new(__num_threads * sizeof(_Result)));
88 __constructed = new bool[__num_threads];
89 }
90
91 _ThreadIndex __iam = omp_get_thread_num();
92
93 // Neutral element.
94 _Result* __reduct;
95
96 _DifferenceType
97 __start = __equally_split_point(__length, __num_threads, __iam),
98 __stop = __equally_split_point(__length, __num_threads, __iam + 1);
99
100 if (__start < __stop)
101 {
102 __reduct = new _Result(__f(__o, __begin + __start));
103 ++__start;
104 __constructed[__iam] = true;
105 }
106 else
107 __constructed[__iam] = false;
108
109 for (; __start < __stop; ++__start)
110 *__reduct = __r(*__reduct, __f(__o, __begin + __start));
111
112 if (__constructed[__iam])
113 {
114 ::new(&__thread_results[__iam]) _Result(*__reduct);
115 delete __reduct;
116 }
117 } //parallel
118
119 for (_ThreadIndex __i = 0; __i < __num_threads; ++__i)
120 if (__constructed[__i])
121 {
122 __output = __r(__output, __thread_results[__i]);
123 __thread_results[__i].~_Result();
124 }
125
126 // Points to last element processed (needed as return value for
127 // some algorithms like transform).
128 __f._M_finish_iterator = __begin + __length;
129
130 ::operator delete(__thread_results);
131
132 delete[] __constructed;
133
134 return __o;
135 }
136
137} // end namespace
138
139#endif /* _GLIBCXX_PARALLEL_PAR_LOOP_H */
base.h
Sequential helper functions. This file is a GNU parallel extension to the Standard C++ Library.
equally_split.h
settings.h
Runtime settings and tuning parameters, heuristics to decide whether to use parallelized algorithms.
__gnu_parallel
GNU parallel code for public use.
Definition balanced_quicksort.h:62
__gnu_parallel::_ThreadIndex
uint16_t _ThreadIndex
Unsigned integer to index a thread number. The maximum thread number (for each processor) must fit in...
Definition types.h:123
__gnu_parallel::__for_each_template_random_access_ed
_Op __for_each_template_random_access_ed(_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 hand-crafted parallelization by ...
Definition par_loop.h:67
__gnu_parallel::min
const _Tp & min(const _Tp &__a, const _Tp &__b)
Equivalent to std::min.
Definition base.h:144
__gnu_parallel::__equally_split_point
_DifferenceType __equally_split_point(_DifferenceType __n, _ThreadIndex __num_threads, _ThreadIndex __thread_no)
function to split a sequence into parts of almost equal size.
Definition equally_split.h:75
std::iterator_traits
Traits class for iterators.
Definition stl_iterator_base_types.h:185