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// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// 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 <__assert> // all public C++ headers provide the assertion handler
#include <__atomic/atomic_base.h>
#include <__atomic/atomic_sync.h>
#include <__atomic/memory_order.h>
#include <__availability>
#include <__config>
#include <cstddef>
#include <limits>
#include <version>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
#endif
#ifdef _LIBCPP_HAS_NO_THREADS
# error "<latch> is not supported since libc++ has been configured without support for threads."
#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 _LIBCPP_HIDE_FROM_ABI constexpr ptrdiff_t max() noexcept {
return numeric_limits<ptrdiff_t>::max();
}
inline _LIBCPP_INLINE_VISIBILITY
constexpr explicit latch(ptrdiff_t __expected) : __a_(__expected)
{
_LIBCPP_ASSERT_UNCATEGORIZED(__expected >= 0,
"latch::latch(ptrdiff_t): latch cannot be "
"initialized with a negative value");
_LIBCPP_ASSERT_UNCATEGORIZED(__expected <= max(),
"latch::latch(ptrdiff_t): latch cannot be "
"initialized with a value greater than max()");
}
_LIBCPP_HIDE_FROM_ABI ~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)
{
_LIBCPP_ASSERT_UNCATEGORIZED(
__update >= 0, "latch::count_down called with a negative value");
auto const __old = __a_.fetch_sub(__update, memory_order_release);
_LIBCPP_ASSERT_UNCATEGORIZED(
__update <= __old, "latch::count_down called with a value greater "
"than the internal counter");
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
{
__cxx_atomic_wait(&__a_.__a_, [this]() -> bool {
return try_wait();
});
}
inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_INLINE_VISIBILITY
void arrive_and_wait(ptrdiff_t __update = 1)
{
_LIBCPP_ASSERT_UNCATEGORIZED(
__update >= 0, "latch::arrive_and_wait called with a negative value");
// other preconditions on __update are checked in count_down()
count_down(__update);
wait();
}
};
_LIBCPP_END_NAMESPACE_STD
#endif // _LIBCPP_STD_VER >= 14
_LIBCPP_POP_MACROS
#if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
# include <atomic>
#endif
#endif //_LIBCPP_LATCH
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