libstdc++
latch
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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
40 namespace 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
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
constexpr const _Tp & max(const _Tp &, const _Tp &)
This does what you think it does.
Definition: stl_algobase.h:254
ISO C++ entities toplevel namespace is std.
__numeric_traits_integer< _Tp > __int_traits
Convenience alias for __numeric_traits<integer-type>.