115 lines
2.6 KiB
C++
115 lines
2.6 KiB
C++
// -*- C++ -*-
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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP_LATCH
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#define _LIBCPP_LATCH
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/*
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latch synopsis
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namespace std
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{
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class latch
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{
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public:
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static constexpr ptrdiff_t max() noexcept;
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constexpr explicit latch(ptrdiff_t __expected);
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~latch();
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latch(const latch&) = delete;
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latch& operator=(const latch&) = delete;
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void count_down(ptrdiff_t __update = 1);
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bool try_wait() const noexcept;
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void wait() const;
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void arrive_and_wait(ptrdiff_t __update = 1);
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private:
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ptrdiff_t __counter; // exposition only
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};
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}
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*/
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#include <__assert> // all public C++ headers provide the assertion handler
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#include <__availability>
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#include <__config>
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#include <atomic>
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#include <limits>
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#include <version>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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#endif
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#ifdef _LIBCPP_HAS_NO_THREADS
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# error "<latch> is not supported since libc++ has been configured without support for threads."
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#endif
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_LIBCPP_PUSH_MACROS
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#include <__undef_macros>
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#if _LIBCPP_STD_VER >= 14
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_LIBCPP_BEGIN_NAMESPACE_STD
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class latch
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{
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__atomic_base<ptrdiff_t> __a;
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public:
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static constexpr ptrdiff_t max() noexcept {
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return numeric_limits<ptrdiff_t>::max();
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}
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inline _LIBCPP_INLINE_VISIBILITY
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constexpr explicit latch(ptrdiff_t __expected) : __a(__expected) { }
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~latch() = default;
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latch(const latch&) = delete;
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latch& operator=(const latch&) = delete;
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inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
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void count_down(ptrdiff_t __update = 1)
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{
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auto const __old = __a.fetch_sub(__update, memory_order_release);
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if(__old == __update)
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__a.notify_all();
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}
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inline _LIBCPP_INLINE_VISIBILITY
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bool try_wait() const noexcept
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{
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return 0 == __a.load(memory_order_acquire);
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}
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inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
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void wait() const
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{
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__cxx_atomic_wait(&__a.__a_, [&]() -> bool {
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return try_wait();
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});
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}
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inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
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void arrive_and_wait(ptrdiff_t __update = 1)
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{
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count_down(__update);
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wait();
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}
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};
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP_STD_VER >= 14
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_LIBCPP_POP_MACROS
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#endif //_LIBCPP_LATCH
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