libstdc++
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 
41 namespace __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 */