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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 _LIBCUDACXX_LATCH
#define _LIBCUDACXX_LATCH
/*
latch synopsis
namespace std
{
class latch
{
public:
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
};
}
*/
#ifndef __cuda_std__
#include <__config>
#include <__threading_support>
#include <atomic>
#include <cassert>
#include <__pragma_push>
#endif
#if defined(_LIBCUDACXX_USE_PRAGMA_GCC_SYSTEM_HEADER)
#pragma GCC system_header
#endif
#ifdef _LIBCUDACXX_HAS_NO_THREADS
# error <latch> is not supported on this single threaded system
#endif
#if _LIBCUDACXX_STD_VER < 11
# error <latch> is requires C++11 or later
#endif
_LIBCUDACXX_BEGIN_NAMESPACE_STD
# if _LIBCUDACXX_CUDA_ABI_VERSION < 3
# define _LIBCUDACXX_LATCH_ALIGNMENT alignas(64)
# else
# define _LIBCUDACXX_LATCH_ALIGNMENT
# endif
template<int _Sco = 0>
class __latch_base
{
_LIBCUDACXX_LATCH_ALIGNMENT __atomic_base<ptrdiff_t, _Sco> __counter;
public:
inline _LIBCUDACXX_INLINE_VISIBILITY _LIBCUDACXX_CONSTEXPR
explicit __latch_base(ptrdiff_t __expected)
: __counter(__expected) { }
~__latch_base() = default;
__latch_base(const __latch_base&) = delete;
__latch_base& operator=(const __latch_base&) = delete;
inline _LIBCUDACXX_INLINE_VISIBILITY
void count_down(ptrdiff_t __update = 1)
{
assert(__update > 0);
auto const __old = __counter.fetch_sub(__update, memory_order_release);
assert(__old >= __update);
if(__old == __update)
__counter.notify_all();
}
inline _LIBCUDACXX_INLINE_VISIBILITY
bool try_wait() const noexcept
{
return __counter.load(memory_order_acquire) == 0;
}
inline _LIBCUDACXX_INLINE_VISIBILITY
void wait() const
{
while(1) {
auto const __current = __counter.load(memory_order_acquire);
if(__current == 0)
return;
__counter.wait(__current, memory_order_relaxed)
;
}
}
inline _LIBCUDACXX_INLINE_VISIBILITY
void arrive_and_wait(ptrdiff_t __update = 1)
{
count_down(__update);
wait();
}
_LIBCUDACXX_INLINE_VISIBILITY
static constexpr ptrdiff_t max() noexcept
{
return numeric_limits<ptrdiff_t>::max();
}
};
using latch = __latch_base<>;
_LIBCUDACXX_END_NAMESPACE_STD
#ifndef __cuda_std__
#include <__pragma_pop>
#endif //__cuda_std__
#endif //_LIBCUDACXX_LATCH
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