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- // <latch> -*- C++ -*-
- // Copyright (C) 2020-2022 Free Software Foundation, Inc.
- //
- // This file is part of the GNU ISO C++ Library. This library is free
- // software; you can redistribute it and/or modify it under the
- // terms of the GNU General Public License as published by the
- // Free Software Foundation; either version 3, or (at your option)
- // any later version.
- // This library is distributed in the hope that it will be useful,
- // but WITHOUT ANY WARRANTY; without even the implied warranty of
- // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- // GNU General Public License for more details.
- // Under Section 7 of GPL version 3, you are granted additional
- // permissions described in the GCC Runtime Library Exception, version
- // 3.1, as published by the Free Software Foundation.
- // You should have received a copy of the GNU General Public License and
- // a copy of the GCC Runtime Library Exception along with this program;
- // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
- // <http://www.gnu.org/licenses/>.
- /** @file include/latch
- * This is a Standard C++ Library header.
- */
- #ifndef _GLIBCXX_LATCH
- #define _GLIBCXX_LATCH 1
- #pragma GCC system_header
- #if __cplusplus > 201703L
- #include <bits/atomic_base.h>
- #include <ext/numeric_traits.h>
- #if __cpp_lib_atomic_wait
- namespace std _GLIBCXX_VISIBILITY(default)
- {
- _GLIBCXX_BEGIN_NAMESPACE_VERSION
- #define __cpp_lib_latch 201907L
- class latch
- {
- public:
- static constexpr ptrdiff_t
- max() noexcept
- { return __gnu_cxx::__int_traits<__detail::__platform_wait_t>::__max; }
- constexpr explicit latch(ptrdiff_t __expected) noexcept
- : _M_a(__expected) { }
- ~latch() = default;
- latch(const latch&) = delete;
- latch& operator=(const latch&) = delete;
- _GLIBCXX_ALWAYS_INLINE void
- count_down(ptrdiff_t __update = 1)
- {
- auto const __old = __atomic_impl::fetch_sub(&_M_a,
- __update, memory_order::release);
- if (__old == __update)
- __atomic_impl::notify_all(&_M_a);
- }
- _GLIBCXX_ALWAYS_INLINE bool
- try_wait() const noexcept
- { return __atomic_impl::load(&_M_a, memory_order::acquire) == 0; }
- _GLIBCXX_ALWAYS_INLINE void
- wait() const noexcept
- {
- auto const __pred = [this] { return this->try_wait(); };
- std::__atomic_wait_address(&_M_a, __pred);
- }
- _GLIBCXX_ALWAYS_INLINE void
- arrive_and_wait(ptrdiff_t __update = 1) noexcept
- {
- count_down(__update);
- wait();
- }
- private:
- alignas(__alignof__(__detail::__platform_wait_t)) __detail::__platform_wait_t _M_a;
- };
- _GLIBCXX_END_NAMESPACE_VERSION
- } // namespace
- #endif // __cpp_lib_atomic_wait
- #endif // __cplusplus > 201703L
- #endif // _GLIBCXX_LATCH
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