xref: /freebsd/contrib/llvm-project/libcxx/include/semaphore (revision 0fca6ea1d4eea4c934cfff25ac9ee8ad6fe95583) 
1// -*- C++ -*-
2//===----------------------------------------------------------------------===//
3//
4// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
5// See https://llvm.org/LICENSE.txt for license information.
6// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7//
8//===----------------------------------------------------------------------===//
9
10#ifndef _LIBCPP_SEMAPHORE
11#define _LIBCPP_SEMAPHORE
12
13/*
14    semaphore synopsis
15
16namespace std {
17
18template<ptrdiff_t least_max_value = implementation-defined>
19class counting_semaphore
20{
21public:
22static constexpr ptrdiff_t max() noexcept;
23
24constexpr explicit counting_semaphore(ptrdiff_t desired);
25~counting_semaphore();
26
27counting_semaphore(const counting_semaphore&) = delete;
28counting_semaphore& operator=(const counting_semaphore&) = delete;
29
30void release(ptrdiff_t update = 1);
31void acquire();
32bool try_acquire() noexcept;
33template<class Rep, class Period>
34    bool try_acquire_for(const chrono::duration<Rep, Period>& rel_time);
35template<class Clock, class Duration>
36    bool try_acquire_until(const chrono::time_point<Clock, Duration>& abs_time);
37
38private:
39ptrdiff_t counter; // exposition only
40};
41
42using binary_semaphore = counting_semaphore<1>;
43
44}
45
46*/
47
48#include <__config>
49
50#if !defined(_LIBCPP_HAS_NO_THREADS)
51
52#  include <__assert>
53#  include <__atomic/atomic_base.h>
54#  include <__atomic/atomic_sync.h>
55#  include <__atomic/memory_order.h>
56#  include <__chrono/time_point.h>
57#  include <__thread/poll_with_backoff.h>
58#  include <__thread/support.h>
59#  include <__thread/timed_backoff_policy.h>
60#  include <cstddef>
61#  include <limits>
62#  include <version>
63
64#  if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
65#    pragma GCC system_header
66#  endif
67
68_LIBCPP_PUSH_MACROS
69#  include <__undef_macros>
70
71#  if _LIBCPP_STD_VER >= 14
72
73_LIBCPP_BEGIN_NAMESPACE_STD
74
75/*
76
77__atomic_semaphore_base is the general-case implementation.
78It is a typical Dijkstra semaphore algorithm over atomics, wait and notify
79functions. It avoids contention against users' own use of those facilities.
80
81*/
82
83#    define _LIBCPP_SEMAPHORE_MAX (numeric_limits<ptrdiff_t>::max())
84
85class __atomic_semaphore_base {
86  __atomic_base<ptrdiff_t> __a_;
87
88public:
89  _LIBCPP_HIDE_FROM_ABI constexpr explicit __atomic_semaphore_base(ptrdiff_t __count) : __a_(__count) {}
90  _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void release(ptrdiff_t __update = 1) {
91    auto __old = __a_.fetch_add(__update, memory_order_release);
92    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
93        __update <= _LIBCPP_SEMAPHORE_MAX - __old, "update is greater than the expected value");
94    if (__old == 0) {
95      __a_.notify_all();
96    }
97  }
98  _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void acquire() {
99    std::__atomic_wait_unless(
100        __a_, [this](ptrdiff_t& __old) { return __try_acquire_impl(__old); }, memory_order_relaxed);
101  }
102  template <class _Rep, class _Period>
103  _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI bool
104  try_acquire_for(chrono::duration<_Rep, _Period> const& __rel_time) {
105    if (__rel_time == chrono::duration<_Rep, _Period>::zero())
106      return try_acquire();
107    auto const __poll_fn = [this]() { return try_acquire(); };
108    return std::__libcpp_thread_poll_with_backoff(__poll_fn, __libcpp_timed_backoff_policy(), __rel_time);
109  }
110  _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI bool try_acquire() {
111    auto __old = __a_.load(memory_order_relaxed);
112    return __try_acquire_impl(__old);
113  }
114
115private:
116  _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI bool __try_acquire_impl(ptrdiff_t& __old) {
117    while (true) {
118      if (__old == 0)
119        return false;
120      if (__a_.compare_exchange_weak(__old, __old - 1, memory_order_acquire, memory_order_relaxed))
121        return true;
122    }
123  }
124};
125
126template <ptrdiff_t __least_max_value = _LIBCPP_SEMAPHORE_MAX>
127class _LIBCPP_DEPRECATED_ATOMIC_SYNC counting_semaphore {
128  __atomic_semaphore_base __semaphore_;
129
130public:
131  static_assert(__least_max_value >= 0, "The least maximum value must be a positive number");
132
133  static constexpr ptrdiff_t max() noexcept { return __least_max_value; }
134
135  _LIBCPP_HIDE_FROM_ABI constexpr explicit counting_semaphore(ptrdiff_t __count) : __semaphore_(__count) {
136    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
137        __count >= 0,
138        "counting_semaphore::counting_semaphore(ptrdiff_t): counting_semaphore cannot be "
139        "initialized with a negative value");
140    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
141        __count <= max(),
142        "counting_semaphore::counting_semaphore(ptrdiff_t): counting_semaphore cannot be "
143        "initialized with a value greater than max()");
144  }
145  ~counting_semaphore() = default;
146
147  counting_semaphore(const counting_semaphore&)            = delete;
148  counting_semaphore& operator=(const counting_semaphore&) = delete;
149
150  _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void release(ptrdiff_t __update = 1) {
151    _LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(__update >= 0, "counting_semaphore:release called with a negative value");
152    __semaphore_.release(__update);
153  }
154  _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void acquire() { __semaphore_.acquire(); }
155  template <class _Rep, class _Period>
156  _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI bool
157  try_acquire_for(chrono::duration<_Rep, _Period> const& __rel_time) {
158    return __semaphore_.try_acquire_for(chrono::duration_cast<chrono::nanoseconds>(__rel_time));
159  }
160  _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI bool try_acquire() { return __semaphore_.try_acquire(); }
161  template <class _Clock, class _Duration>
162  _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI bool
163  try_acquire_until(chrono::time_point<_Clock, _Duration> const& __abs_time) {
164    auto const __current = _Clock::now();
165    if (__current >= __abs_time)
166      return try_acquire();
167    else
168      return try_acquire_for(__abs_time - __current);
169  }
170};
171
172_LIBCPP_SUPPRESS_DEPRECATED_PUSH
173using binary_semaphore _LIBCPP_DEPRECATED_ATOMIC_SYNC = counting_semaphore<1>;
174_LIBCPP_SUPPRESS_DEPRECATED_POP
175
176_LIBCPP_END_NAMESPACE_STD
177
178#  endif // _LIBCPP_STD_VER >= 14
179
180_LIBCPP_POP_MACROS
181
182#endif // !defined(_LIBCPP_HAS_NO_THREADS)
183
184#if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
185#  include <atomic>
186#endif
187
188#endif //_LIBCPP_SEMAPHORE
189