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
40namespace 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

source code of include/c++/11/latch