libstdc++
semaphore
Go to the documentation of this file.
1 // <semaphore> -*- C++ -*-
2 
3 // Copyright (C) 2020-2024 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 #pragma GCC system_header
33 
34 #include <bits/requires_hosted.h> // concurrency
35 
36 #if __cplusplus > 201703L
37 #include <bits/semaphore_base.h>
38 
39 #define __glibcxx_want_semaphore
40 #include <bits/version.h>
41 
42 #ifdef __cpp_lib_semaphore // C++ >= 20 && hosted && (atomic_wait || posix_sem)
43 namespace std _GLIBCXX_VISIBILITY(default)
44 {
45 _GLIBCXX_BEGIN_NAMESPACE_VERSION
46 
47  template<ptrdiff_t __least_max_value = __semaphore_impl::_S_max>
48  class counting_semaphore
49  {
50  static_assert(__least_max_value >= 0);
51  static_assert(__least_max_value <= __semaphore_impl::_S_max);
52 
53  __semaphore_impl _M_sem;
54 
55  public:
56  explicit counting_semaphore(ptrdiff_t __desired) noexcept
57  : _M_sem(__desired)
58  { }
59 
60  ~counting_semaphore() = default;
61 
62  counting_semaphore(const counting_semaphore&) = delete;
63  counting_semaphore& operator=(const counting_semaphore&) = delete;
64 
65  static constexpr ptrdiff_t
66  max() noexcept
67  { return __least_max_value; }
68 
69  void
70  release(ptrdiff_t __update = 1) noexcept(noexcept(_M_sem._M_release(1)))
71  { _M_sem._M_release(__update); }
72 
73  void
74  acquire() noexcept(noexcept(_M_sem._M_acquire()))
75  { _M_sem._M_acquire(); }
76 
77  bool
78  try_acquire() noexcept(noexcept(_M_sem._M_try_acquire()))
79  { return _M_sem._M_try_acquire(); }
80 
81  template<typename _Rep, typename _Period>
82  bool
83  try_acquire_for(const std::chrono::duration<_Rep, _Period>& __rtime)
84  { return _M_sem._M_try_acquire_for(__rtime); }
85 
86  template<typename _Clock, typename _Dur>
87  bool
88  try_acquire_until(const std::chrono::time_point<_Clock, _Dur>& __atime)
89  { return _M_sem._M_try_acquire_until(__atime); }
90  };
91 
92  using binary_semaphore = std::counting_semaphore<1>;
93 
94 _GLIBCXX_END_NAMESPACE_VERSION
95 } // namespace
96 #endif // cpp_lib_atomic_wait || _GLIBCXX_HAVE_POSIX_SEMAPHORE
97 #endif // __cpp_lib_semaphore
98 #endif // _GLIBCXX_SEMAPHORE