1 | // <latch> -*- C++ -*- |
2 | |
3 | // Copyright (C) 2020-2021 Free Software Foundation, Inc. |
4 | // |
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 |
7 | // terms of the GNU General Public License as published by the |
8 | // Free Software Foundation; either version 3, or (at your option) |
9 | // any later version. |
10 | |
11 | // This library is distributed in the hope that it will be useful, |
12 | // but WITHOUT ANY WARRANTY; without even the implied warranty of |
13 | // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
14 | // GNU General Public License for more details. |
15 | |
16 | // Under Section 7 of GPL version 3, you are granted additional |
17 | // permissions described in the GCC Runtime Library Exception, version |
18 | // 3.1, as published by the Free Software Foundation. |
19 | |
20 | // You should have received a copy of the GNU General Public License and |
21 | // a copy of the GCC Runtime Library Exception along with this program; |
22 | // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see |
23 | // <http://www.gnu.org/licenses/>. |
24 | |
25 | /** @file include/latch |
26 | * This is a Standard C++ Library header. |
27 | */ |
28 | |
29 | #ifndef _GLIBCXX_LATCH |
30 | #define _GLIBCXX_LATCH 1 |
31 | |
32 | #pragma GCC system_header |
33 | |
34 | #if __cplusplus > 201703L |
35 | |
36 | #include <bits/atomic_base.h> |
37 | #include <ext/numeric_traits.h> |
38 | |
39 | #if __cpp_lib_atomic_wait |
40 | namespace std _GLIBCXX_VISIBILITY(default) |
41 | { |
42 | _GLIBCXX_BEGIN_NAMESPACE_VERSION |
43 | |
44 | #define __cpp_lib_latch 201907L |
45 | |
46 | class latch |
47 | { |
48 | public: |
49 | static constexpr ptrdiff_t |
50 | max() noexcept |
51 | { return __gnu_cxx::__int_traits<__detail::__platform_wait_t>::__max; } |
52 | |
53 | constexpr explicit latch(ptrdiff_t __expected) noexcept |
54 | : _M_a(__expected) { } |
55 | |
56 | ~latch() = default; |
57 | latch(const latch&) = delete; |
58 | latch& operator=(const latch&) = delete; |
59 | |
60 | _GLIBCXX_ALWAYS_INLINE void |
61 | count_down(ptrdiff_t __update = 1) |
62 | { |
63 | auto const __old = __atomic_impl::fetch_sub(&_M_a, |
64 | __update, memory_order::release); |
65 | if (__old == __update) |
66 | __atomic_impl::notify_all(&_M_a); |
67 | } |
68 | |
69 | _GLIBCXX_ALWAYS_INLINE bool |
70 | try_wait() const noexcept |
71 | { return __atomic_impl::load(&_M_a, memory_order::acquire) == 0; } |
72 | |
73 | _GLIBCXX_ALWAYS_INLINE void |
74 | wait() const noexcept |
75 | { |
76 | auto const __pred = [this] { return this->try_wait(); }; |
77 | std::__atomic_wait_address(&_M_a, __pred); |
78 | } |
79 | |
80 | _GLIBCXX_ALWAYS_INLINE void |
81 | arrive_and_wait(ptrdiff_t __update = 1) noexcept |
82 | { |
83 | count_down(__update); |
84 | wait(); |
85 | } |
86 | |
87 | private: |
88 | alignas(__alignof__(__detail::__platform_wait_t)) __detail::__platform_wait_t _M_a; |
89 | }; |
90 | _GLIBCXX_END_NAMESPACE_VERSION |
91 | } // namespace |
92 | #endif // __cpp_lib_atomic_wait |
93 | #endif // __cplusplus > 201703L |
94 | #endif // _GLIBCXX_LATCH |
95 | |