3 // Copyright (C) 2007 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/multiway_mergesort.h
32 * @brief Parallel multiway merge sort.
33 * This file is a GNU parallel extension to the Standard C++ Library.
36 // Written by Johannes Singler.
38 #ifndef _GLIBCXX_PARALLEL_MERGESORT_H
39 #define _GLIBCXX_PARALLEL_MERGESORT_H 1
43 #include <parallel/basic_iterator.h>
44 #include <bits/stl_algo.h>
45 #include <parallel/parallel.h>
46 #include <parallel/multiway_merge.h>
48 namespace __gnu_parallel
51 /** @brief Subsequence description. */
52 template<typename _DifferenceTp
>
55 typedef _DifferenceTp difference_type
;
57 /** @brief Begin of subsequence. */
58 difference_type begin
;
60 /** @brief End of subsequence. */
64 /** @brief Data accessed by all threads.
66 * PMWMS = parallel multiway mergesort */
67 template<typename RandomAccessIterator
>
68 struct PMWMSSortingData
70 typedef std::iterator_traits
<RandomAccessIterator
> traits_type
;
71 typedef typename
traits_type::value_type value_type
;
72 typedef typename
traits_type::difference_type difference_type
;
74 /** @brief Number of threads involved. */
75 thread_index_t num_threads
;
77 /** @brief Input begin. */
78 RandomAccessIterator source
;
80 /** @brief Start indices, per thread. */
81 difference_type
* starts
;
83 /** @brief Temporary arrays for each thread.
85 * Indirection Allows using the temporary storage in different
86 * ways, without code duplication.
87 * @see _GLIBCXX_MULTIWAY_MERGESORT_COPY_LAST */
88 value_type
** temporaries
;
90 #if _GLIBCXX_MULTIWAY_MERGESORT_COPY_LAST
91 /** @brief Storage in which to sort. */
92 RandomAccessIterator
* sorting_places
;
94 /** @brief Storage into which to merge. */
95 value_type
** merging_places
;
97 /** @brief Storage in which to sort. */
98 value_type
** sorting_places
;
100 /** @brief Storage into which to merge. */
101 RandomAccessIterator
* merging_places
;
103 /** @brief Samples. */
106 /** @brief Offsets to add to the found positions. */
107 difference_type
* offsets
;
109 /** @brief Pieces of data to merge @c [thread][sequence] */
110 std::vector
<Piece
<difference_type
> >* pieces
;
112 /** @brief Stable sorting desired. */
117 * @brief Select samples from a sequence.
118 * @param sd Pointer to algorithm data. Result will be placed in
120 * @param num_samples Number of samples to select.
122 template<typename RandomAccessIterator
, typename _DifferenceTp
>
124 determine_samples(PMWMSSortingData
<RandomAccessIterator
>* sd
,
125 _DifferenceTp
& num_samples
)
127 typedef std::iterator_traits
<RandomAccessIterator
> traits_type
;
128 typedef typename
traits_type::value_type value_type
;
129 typedef _DifferenceTp difference_type
;
131 thread_index_t iam
= omp_get_thread_num();
134 Settings::sort_mwms_oversampling
* sd
->num_threads
- 1;
136 difference_type
* es
= new difference_type
[num_samples
+ 2];
138 equally_split(sd
->starts
[iam
+ 1] - sd
->starts
[iam
],
139 num_samples
+ 1, es
);
141 for (difference_type i
= 0; i
< num_samples
; i
++)
142 ::new(&(sd
->samples
[iam
* num_samples
+ i
])) value_type(
143 sd
->source
[sd
->starts
[iam
] + es
[i
+ 1]]);
148 /** @brief PMWMS code executed by each thread.
149 * @param sd Pointer to algorithm data.
150 * @param comp Comparator.
152 template<typename RandomAccessIterator
, typename Comparator
>
154 parallel_sort_mwms_pu(PMWMSSortingData
<RandomAccessIterator
>* sd
,
157 typedef std::iterator_traits
<RandomAccessIterator
> traits_type
;
158 typedef typename
traits_type::value_type value_type
;
159 typedef typename
traits_type::difference_type difference_type
;
161 thread_index_t iam
= omp_get_thread_num();
163 // Length of this thread's chunk, before merging.
164 difference_type length_local
= sd
->starts
[iam
+ 1] - sd
->starts
[iam
];
166 #if _GLIBCXX_MULTIWAY_MERGESORT_COPY_LAST
167 typedef RandomAccessIterator SortingPlacesIterator
;
169 // Sort in input storage.
170 sd
->sorting_places
[iam
] = sd
->source
+ sd
->starts
[iam
];
172 typedef value_type
* SortingPlacesIterator
;
174 // Sort in temporary storage, leave space for sentinel.
175 sd
->sorting_places
[iam
] = sd
->temporaries
[iam
] =
176 static_cast<value_type
*>(
177 ::operator new(sizeof(value_type
) * (length_local
+ 1)));
180 std::uninitialized_copy(sd
->source
+ sd
->starts
[iam
],
181 sd
->source
+ sd
->starts
[iam
] + length_local
,
182 sd
->sorting_places
[iam
]);
187 __gnu_sequential::stable_sort(sd
->sorting_places
[iam
],
188 sd
->sorting_places
[iam
] + length_local
,
191 __gnu_sequential::sort(sd
->sorting_places
[iam
],
192 sd
->sorting_places
[iam
] + length_local
,
195 // Invariant: locally sorted subsequence in sd->sorting_places[iam],
196 // sd->sorting_places[iam] + length_local.
198 if (Settings::sort_splitting
== Settings::SAMPLING
)
200 difference_type num_samples
;
201 determine_samples(sd
, num_samples
);
206 __gnu_sequential::sort(sd
->samples
,
207 sd
->samples
+ (num_samples
* sd
->num_threads
),
212 for (int s
= 0; s
< sd
->num_threads
; s
++)
214 // For each sequence.
215 if (num_samples
* iam
> 0)
216 sd
->pieces
[iam
][s
].begin
=
217 std::lower_bound(sd
->sorting_places
[s
],
218 sd
->sorting_places
[s
]
219 + (sd
->starts
[s
+ 1] - sd
->starts
[s
]),
220 sd
->samples
[num_samples
* iam
],
222 - sd
->sorting_places
[s
];
224 // Absolute beginning.
225 sd
->pieces
[iam
][s
].begin
= 0;
227 if ((num_samples
* (iam
+ 1)) < (num_samples
* sd
->num_threads
))
228 sd
->pieces
[iam
][s
].end
=
229 std::lower_bound(sd
->sorting_places
[s
],
230 sd
->sorting_places
[s
]
231 + (sd
->starts
[s
+ 1] - sd
->starts
[s
]),
232 sd
->samples
[num_samples
* (iam
+ 1)],
234 - sd
->sorting_places
[s
];
237 sd
->pieces
[iam
][s
].end
= sd
->starts
[s
+ 1] - sd
->starts
[s
];
240 else if (Settings::sort_splitting
== Settings::EXACT
)
244 std::vector
<std::pair
<SortingPlacesIterator
, SortingPlacesIterator
> >
245 seqs(sd
->num_threads
);
246 for (int s
= 0; s
< sd
->num_threads
; s
++)
247 seqs
[s
] = std::make_pair(sd
->sorting_places
[s
],
248 sd
->sorting_places
[s
]
249 + (sd
->starts
[s
+ 1] - sd
->starts
[s
]));
251 std::vector
<SortingPlacesIterator
> offsets(sd
->num_threads
);
253 // if not last thread
254 if (iam
< sd
->num_threads
- 1)
255 multiseq_partition(seqs
.begin(), seqs
.end(),
256 sd
->starts
[iam
+ 1], offsets
.begin(), comp
);
258 for (int seq
= 0; seq
< sd
->num_threads
; seq
++)
261 if (iam
< (sd
->num_threads
- 1))
262 sd
->pieces
[iam
][seq
].end
= offsets
[seq
] - seqs
[seq
].first
;
264 // very end of this sequence
265 sd
->pieces
[iam
][seq
].end
=
266 sd
->starts
[seq
+ 1] - sd
->starts
[seq
];
271 for (int seq
= 0; seq
< sd
->num_threads
; seq
++)
273 // For each sequence.
275 sd
->pieces
[iam
][seq
].begin
= sd
->pieces
[iam
- 1][seq
].end
;
277 // Absolute beginning.
278 sd
->pieces
[iam
][seq
].begin
= 0;
282 // Offset from target begin, length after merging.
283 difference_type offset
= 0, length_am
= 0;
284 for (int s
= 0; s
< sd
->num_threads
; s
++)
286 length_am
+= sd
->pieces
[iam
][s
].end
- sd
->pieces
[iam
][s
].begin
;
287 offset
+= sd
->pieces
[iam
][s
].begin
;
290 #if _GLIBCXX_MULTIWAY_MERGESORT_COPY_LAST
291 // Merge to temporary storage, uninitialized creation not possible
292 // since there is no multiway_merge calling the placement new
293 // instead of the assignment operator.
294 // XXX incorrect (de)construction
295 sd
->merging_places
[iam
] = sd
->temporaries
[iam
] =
296 static_cast<value_type
*>(
297 ::operator new(sizeof(value_type
) * length_am
));
299 // Merge directly to target.
300 sd
->merging_places
[iam
] = sd
->source
+ offset
;
302 std::vector
<std::pair
<SortingPlacesIterator
, SortingPlacesIterator
> >
303 seqs(sd
->num_threads
);
305 for (int s
= 0; s
< sd
->num_threads
; s
++)
308 std::make_pair(sd
->sorting_places
[s
] + sd
->pieces
[iam
][s
].begin
,
309 sd
->sorting_places
[s
] + sd
->pieces
[iam
][s
].end
);
312 multiway_merge(seqs
.begin(), seqs
.end(), sd
->merging_places
[iam
], comp
,
313 length_am
, sd
->stable
, false, sequential_tag());
317 #if _GLIBCXX_MULTIWAY_MERGESORT_COPY_LAST
319 std::copy(sd
->merging_places
[iam
],
320 sd
->merging_places
[iam
] + length_am
,
321 sd
->source
+ offset
);
324 delete[] sd
->temporaries
[iam
];
327 /** @brief PMWMS main call.
328 * @param begin Begin iterator of sequence.
329 * @param end End iterator of sequence.
330 * @param comp Comparator.
331 * @param n Length of sequence.
332 * @param num_threads Number of threads to use.
333 * @param stable Stable sorting.
335 template<typename RandomAccessIterator
, typename Comparator
>
337 parallel_sort_mwms(RandomAccessIterator begin
, RandomAccessIterator end
,
339 typename
std::iterator_traits
<RandomAccessIterator
>
346 typedef std::iterator_traits
<RandomAccessIterator
> traits_type
;
347 typedef typename
traits_type::value_type value_type
;
348 typedef typename
traits_type::difference_type difference_type
;
353 // at least one element per thread
355 num_threads
= static_cast<thread_index_t
>(n
);
358 PMWMSSortingData
<RandomAccessIterator
> sd
;
359 difference_type
* starts
;
361 # pragma omp parallel num_threads(num_threads)
363 num_threads
= omp_get_num_threads(); //no more threads than requested
367 sd
.num_threads
= num_threads
;
369 sd
.temporaries
= new value_type
*[num_threads
];
371 #if _GLIBCXX_MULTIWAY_MERGESORT_COPY_LAST
372 sd
.sorting_places
= new RandomAccessIterator
[num_threads
];
373 sd
.merging_places
= new value_type
*[num_threads
];
375 sd
.sorting_places
= new value_type
*[num_threads
];
376 sd
.merging_places
= new RandomAccessIterator
[num_threads
];
379 if (Settings::sort_splitting
== Settings::SAMPLING
)
382 (Settings::sort_mwms_oversampling
* num_threads
- 1)
384 sd
.samples
= static_cast<value_type
*>(
385 ::operator new(size
* sizeof(value_type
)));
390 sd
.offsets
= new difference_type
[num_threads
- 1];
391 sd
.pieces
= new std::vector
<Piece
<difference_type
> >[num_threads
];
392 for (int s
= 0; s
< num_threads
; s
++)
393 sd
.pieces
[s
].resize(num_threads
);
394 starts
= sd
.starts
= new difference_type
[num_threads
+ 1];
397 difference_type chunk_length
= n
/ num_threads
;
398 difference_type split
= n
% num_threads
;
399 difference_type pos
= 0;
400 for (int i
= 0; i
< num_threads
; i
++)
403 pos
+= (i
< split
) ? (chunk_length
+ 1) : chunk_length
;
405 starts
[num_threads
] = pos
;
408 // Now sort in parallel.
409 parallel_sort_mwms_pu(&sd
, comp
);
413 delete[] sd
.temporaries
;
414 delete[] sd
.sorting_places
;
415 delete[] sd
.merging_places
;
417 if (Settings::sort_splitting
== Settings::SAMPLING
)
423 } //namespace __gnu_parallel