// -*- 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