3 // Copyright (C) 2007, 2008 Free Software Foundation, Inc.
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the terms
7 // of the GNU General Public License as published by the Free Software
8 // Foundation; either version 2, or (at your option) any later
11 // This library is distributed in the hope that it will be useful, but
12 // WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 // General Public License for more details.
16 // You should have received a copy of the GNU General Public License
17 // along with this library; see the file COPYING. If not, write to
18 // the Free Software Foundation, 59 Temple Place - Suite 330, Boston,
19 // MA 02111-1307, USA.
21 // As a special exception, you may use this file as part of a free
22 // software library without restriction. Specifically, if other files
23 // instantiate templates or use macros or inline functions from this
24 // file, or you compile this file and link it with other files to
25 // produce an executable, this file does not by itself cause the
26 // resulting executable to be covered by the GNU General Public
27 // License. This exception does not however invalidate any other
28 // reasons why the executable file might be covered by the GNU General
31 /** @file parallel/omp_loop.h
32 * @brief Parallelization of embarrassingly parallel execution by
33 * means of an OpenMP for loop.
34 * This file is a GNU parallel extension to the Standard C++ Library.
37 // Written by Felix Putze.
39 #ifndef _GLIBCXX_PARALLEL_OMP_LOOP_H
40 #define _GLIBCXX_PARALLEL_OMP_LOOP_H 1
44 #include <parallel/settings.h>
45 #include <parallel/basic_iterator.h>
46 #include <parallel/base.h>
48 namespace __gnu_parallel
50 /** @brief Embarrassingly parallel algorithm for random access
51 * iterators, using an OpenMP for loop.
53 * @param begin Begin iterator of element sequence.
54 * @param end End iterator of element sequence.
55 * @param o User-supplied functor (comparator, predicate, adding
57 * @param f Functor to "process" an element with op (depends on
58 * desired functionality, e. g. for std::for_each(), ...).
59 * @param r Functor to "add" a single result to the already
60 * processed elements (depends on functionality).
61 * @param base Base value for reduction.
62 * @param output Pointer to position where final result is written to
63 * @param bound Maximum number of elements processed (e. g. for
65 * @return User-supplied functor (that may contain a part of the result).
67 template<typename RandomAccessIterator
,
73 for_each_template_random_access_omp_loop(RandomAccessIterator begin
,
74 RandomAccessIterator end
,
75 Op o
, Fu
& f
, Red r
, Result base
,
77 typename
std::iterator_traits
78 <RandomAccessIterator
>::
79 difference_type bound
)
82 std::iterator_traits
<RandomAccessIterator
>::difference_type
85 difference_type length
= end
- begin
;
86 thread_index_t num_threads
=
87 __gnu_parallel::min
<difference_type
>(get_max_threads(), length
);
89 Result
*thread_results
;
91 # pragma omp parallel num_threads(num_threads)
95 num_threads
= omp_get_num_threads();
96 thread_results
= new Result
[num_threads
];
98 for (thread_index_t i
= 0; i
< num_threads
; ++i
)
99 thread_results
[i
] = Result();
102 thread_index_t iam
= omp_get_thread_num();
104 # pragma omp for schedule(dynamic, _Settings::get().workstealing_chunk_size)
105 for (difference_type pos
= 0; pos
< length
; ++pos
)
106 thread_results
[iam
] =
107 r(thread_results
[iam
], f(o
, begin
+pos
));
110 for (thread_index_t i
= 0; i
< num_threads
; ++i
)
111 output
= r(output
, thread_results
[i
]);
113 delete [] thread_results
;
115 // Points to last element processed (needed as return value for
116 // some algorithms like transform).
117 f
.finish_iterator
= begin
+ length
;