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
40namespace 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
51    { return __gnu_cxx::__int_traits<__detail::__platform_wait_t>::__max; }
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
95