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d55c9a68 TT |
1 | /* Parallel for loops |
2 | ||
b811d2c2 | 3 | Copyright (C) 2019-2020 Free Software Foundation, Inc. |
d55c9a68 TT |
4 | |
5 | This file is part of GDB. | |
6 | ||
7 | This program is free software; you can redistribute it and/or modify | |
8 | it under the terms of the GNU General Public License as published by | |
9 | the Free Software Foundation; either version 3 of the License, or | |
10 | (at your option) any later version. | |
11 | ||
12 | This program is distributed in the hope that it will be useful, | |
13 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
15 | GNU General Public License for more details. | |
16 | ||
17 | You should have received a copy of the GNU General Public License | |
18 | along with this program. If not, see <http://www.gnu.org/licenses/>. */ | |
19 | ||
20 | #ifndef GDBSUPPORT_PARALLEL_FOR_H | |
21 | #define GDBSUPPORT_PARALLEL_FOR_H | |
22 | ||
23 | #include <algorithm> | |
24 | #if CXX_STD_THREAD | |
25 | #include <thread> | |
26 | #include "gdbsupport/thread-pool.h" | |
27 | #endif | |
28 | ||
29 | namespace gdb | |
30 | { | |
31 | ||
32 | /* A very simple "parallel for". This splits the range of iterators | |
33 | into subranges, and then passes each subrange to the callback. The | |
34 | work may or may not be done in separate threads. | |
35 | ||
36 | This approach was chosen over having the callback work on single | |
37 | items because it makes it simple for the caller to do | |
38 | once-per-subrange initialization and destruction. */ | |
39 | ||
40 | template<class RandomIt, class RangeFunction> | |
41 | void | |
42 | parallel_for_each (RandomIt first, RandomIt last, RangeFunction callback) | |
43 | { | |
44 | #if CXX_STD_THREAD | |
45 | /* So we can use a local array below. */ | |
46 | const size_t local_max = 16; | |
47 | size_t n_threads = std::min (thread_pool::g_thread_pool->thread_count (), | |
48 | local_max); | |
49 | size_t n_actual_threads = 0; | |
50 | std::future<void> futures[local_max]; | |
51 | ||
52 | size_t n_elements = last - first; | |
53 | if (n_threads > 1) | |
54 | { | |
55 | /* Arbitrarily require that there should be at least 10 elements | |
56 | in a thread. */ | |
57 | if (n_elements / n_threads < 10) | |
58 | n_threads = std::max (n_elements / 10, (size_t) 1); | |
59 | size_t elts_per_thread = n_elements / n_threads; | |
60 | n_actual_threads = n_threads - 1; | |
61 | for (int i = 0; i < n_actual_threads; ++i) | |
62 | { | |
63 | RandomIt end = first + elts_per_thread; | |
64 | auto task = [=] () | |
65 | { | |
66 | callback (first, end); | |
67 | }; | |
68 | ||
69 | futures[i] = gdb::thread_pool::g_thread_pool->post_task (task); | |
70 | first = end; | |
71 | } | |
72 | } | |
73 | #endif /* CXX_STD_THREAD */ | |
74 | ||
75 | /* Process all the remaining elements in the main thread. */ | |
76 | callback (first, last); | |
77 | ||
78 | #if CXX_STD_THREAD | |
79 | for (int i = 0; i < n_actual_threads; ++i) | |
80 | futures[i].wait (); | |
81 | #endif /* CXX_STD_THREAD */ | |
82 | } | |
83 | ||
84 | } | |
85 | ||
86 | #endif /* GDBSUPPORT_PARALLEL_FOR_H */ |