libstdc++: semaphore Source File

libstdc++

semaphore
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1// <semaphore> -*- C++ -*-
2
3// Copyright (C) 2020-2026 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/semaphore
26 * This is a Standard C++ Library header.
27 */
28
29#ifndef _GLIBCXX_SEMAPHORE
30#define _GLIBCXX_SEMAPHORE 1
31
32#ifdef _GLIBCXX_SYSHDR
33#pragma GCC system_header
34#endif
35
36#include <bits/requires_hosted.h> // concurrency
37
38#define __glibcxx_want_semaphore
39#include <bits/version.h>
40
41#ifdef __cpp_lib_semaphore // C++ >= 20 && hosted && atomic_wait
42#include <bits/semaphore_base.h>
43
44namespace std _GLIBCXX_VISIBILITY(default)
45{
46_GLIBCXX_BEGIN_NAMESPACE_VERSION
47
48 template<ptrdiff_t __least_max_value = _Semaphore_impl<2>::_S_max>
49 class counting_semaphore
50 {
51 static_assert(__least_max_value >= 0);
52
53 _Semaphore_impl<__least_max_value> _M_sem;
54
55 public:
56 constexpr explicit
57 counting_semaphore(ptrdiff_t __desired) noexcept
58 : _M_sem(__desired)
59 { __glibcxx_assert(__desired >= 0 && __desired <= max()); }
60
61 ~counting_semaphore() = default;
62
63 counting_semaphore(const counting_semaphore&) = delete;
64 counting_semaphore& operator=(const counting_semaphore&) = delete;
65
66 static constexpr ptrdiff_t
67 max() noexcept
68 { return __least_max_value; }
69
70 void
71 release(ptrdiff_t __update = 1) noexcept
72 {
73 [[maybe_unused]] ptrdiff_t __old = _M_sem._M_release(__update);
74 __glibcxx_assert(__update >= 0 && __update <= max() - __old);
75 }
76
77 void
78 acquire() noexcept(noexcept(_M_sem._M_acquire()))
79 { _M_sem._M_acquire(); }
80
81 bool
82 try_acquire() noexcept(noexcept(_M_sem._M_try_acquire()))
83 { return _M_sem._M_try_acquire(); }
84
85 template<typename _Rep, typename _Period>
86 bool
87 try_acquire_for(const std::chrono::duration<_Rep, _Period>& __rtime)
88 { return _M_sem._M_try_acquire_for(__rtime); }
89
90 template<typename _Clock, typename _Dur>
91 bool
92 try_acquire_until(const std::chrono::time_point<_Clock, _Dur>& __atime)
93 { return _M_sem._M_try_acquire_until(__atime); }
94 };
95
96 /** @brief A binary semaphore
97 *
98 * @since C++20
99 */
100 using binary_semaphore = std::counting_semaphore<1>;
101
102_GLIBCXX_END_NAMESPACE_VERSION
103} // namespace
104#endif // __cpp_lib_semaphore
105#endif // _GLIBCXX_SEMAPHORE
version.h
requires_hosted.h
semaphore_base.h
std
ISO C++ entities toplevel namespace is std.