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// -*- C++ -*-
//===--------------------------- latch -----------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef _LIBCPP_LATCH
#define _LIBCPP_LATCH
/*
latch synopsis
namespace std
{
class latch
{
public:
static constexpr ptrdiff_t max() noexcept;
constexpr explicit latch(ptrdiff_t __expected);
~latch();
latch(const latch&) = delete;
latch& operator=(const latch&) = delete;
void count_down(ptrdiff_t __update = 1);
bool try_wait() const noexcept;
void wait() const;
void arrive_and_wait(ptrdiff_t __update = 1);
private:
ptrdiff_t __counter; // exposition only
};
}
*/
#include <__availability>
#include <__config>
#include <atomic>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#pragma GCC system_header
#endif
#ifdef _LIBCPP_HAS_NO_THREADS
# error <latch> is not supported on this single threaded system
#endif
_LIBCPP_PUSH_MACROS
#include <__undef_macros>
#if _LIBCPP_STD_VER >= 14
_LIBCPP_BEGIN_NAMESPACE_STD
class latch
{
__atomic_base<ptrdiff_t> __a;
public:
static constexpr ptrdiff_t max() noexcept {
return numeric_limits<ptrdiff_t>::max();
}
inline _LIBCPP_INLINE_VISIBILITY
constexpr explicit latch(ptrdiff_t __expected) : __a(__expected) { }
~latch() = default;
latch(const latch&) = delete;
latch& operator=(const latch&) = delete;
inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
void count_down(ptrdiff_t __update = 1)
{
auto const __old = __a.fetch_sub(__update, memory_order_release);
if(__old == __update)
__a.notify_all();
}
inline _LIBCPP_INLINE_VISIBILITY
bool try_wait() const noexcept
{
return 0 == __a.load(memory_order_acquire);
}
inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
void wait() const
{
auto const __test_fn = [=]() -> bool {
return try_wait();
};
__cxx_atomic_wait(&__a.__a_, __test_fn);
}
inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
void arrive_and_wait(ptrdiff_t __update = 1)
{
count_down(__update);
wait();
}
};
_LIBCPP_END_NAMESPACE_STD
#endif // _LIBCPP_STD_VER >= 14
_LIBCPP_POP_MACROS
#endif //_LIBCPP_LATCH
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