libstdc++
semaphore
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1 // <semaphore> -*- C++ -*-
2 
3 // Copyright (C) 2020-2025 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 #if __cplusplus > 201703L
39 #include <bits/semaphore_base.h>
40 
41 #define __glibcxx_want_semaphore
42 #include <bits/version.h>
43 
44 #ifdef __cpp_lib_semaphore // C++ >= 20 && hosted && (atomic_wait || posix_sem)
45 namespace std _GLIBCXX_VISIBILITY(default)
46 {
47 _GLIBCXX_BEGIN_NAMESPACE_VERSION
48 
49  template<ptrdiff_t __least_max_value = __semaphore_impl::_S_max>
50  class counting_semaphore
51  {
52  static_assert(__least_max_value >= 0);
53  static_assert(__least_max_value <= __semaphore_impl::_S_max);
54 
55  __semaphore_impl _M_sem;
56 
57  public:
58  explicit counting_semaphore(ptrdiff_t __desired) noexcept
59  : _M_sem(__desired)
60  { }
61 
62  ~counting_semaphore() = default;
63 
64  counting_semaphore(const counting_semaphore&) = delete;
65  counting_semaphore& operator=(const counting_semaphore&) = delete;
66 
67  static constexpr ptrdiff_t
68  max() noexcept
69  { return __least_max_value; }
70 
71  void
72  release(ptrdiff_t __update = 1) noexcept(noexcept(_M_sem._M_release(1)))
73  { _M_sem._M_release(__update); }
74 
75  void
76  acquire() noexcept(noexcept(_M_sem._M_acquire()))
77  { _M_sem._M_acquire(); }
78 
79  bool
80  try_acquire() noexcept(noexcept(_M_sem._M_try_acquire()))
81  { return _M_sem._M_try_acquire(); }
82 
83  template<typename _Rep, typename _Period>
84  bool
85  try_acquire_for(const std::chrono::duration<_Rep, _Period>& __rtime)
86  { return _M_sem._M_try_acquire_for(__rtime); }
87 
88  template<typename _Clock, typename _Dur>
89  bool
90  try_acquire_until(const std::chrono::time_point<_Clock, _Dur>& __atime)
91  { return _M_sem._M_try_acquire_until(__atime); }
92  };
93 
94  using binary_semaphore = std::counting_semaphore<1>;
95 
96 _GLIBCXX_END_NAMESPACE_VERSION
97 } // namespace
98 #endif // cpp_lib_atomic_wait || _GLIBCXX_HAVE_POSIX_SEMAPHORE
99 #endif // __cpp_lib_semaphore
100 #endif // _GLIBCXX_SEMAPHORE