atomic

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// -*- C++ -*- header.
 
// Copyright (C) 2008-2023 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
 
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
 
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
 
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.
 
/** @file include/atomic
 *  This is a Standard C++ Library header.
 */
 
// Based on "C++ Atomic Types and Operations" by Hans Boehm and Lawrence Crowl.
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2427.html
 
#ifndef _GLIBCXX_ATOMIC
#define _GLIBCXX_ATOMIC 1
 
#pragma GCC system_header
 
#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else
 
#include <bits/atomic_base.h>
 
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
 
  /**
   * @addtogroup atomics
   * @{
   */
 
#if __cplusplus >= 201703L
# define __cpp_lib_atomic_is_always_lock_free 201603L
#endif
 
  template<typename _Tp>
    struct atomic;
 
  /// atomic<bool>
  // NB: No operators or fetch-operations for this type.
  template<>
  struct atomic<bool>
  {
    using value_type = bool;
 
  private:
    __atomic_base<bool> _M_base;
 
  public:
    atomic() noexcept = default;
    ~atomic() noexcept = default;
    atomic(const atomic&) = delete;
    atomic& operator=(const atomic&) = delete;
    atomic& operator=(const atomic&) volatile = delete;
 
    constexpr atomic(bool __i) noexcept : _M_base(__i) { }
 
    bool
    operator=(bool __i) noexcept
    { return _M_base.operator=(__i); }
 
    bool
    operator=(bool __i) volatile noexcept
    { return _M_base.operator=(__i); }
 
    operator bool() const noexcept
    { return _M_base.load(); }
 
    operator bool() const volatile noexcept
    { return _M_base.load(); }
 
    bool
    is_lock_free() const noexcept { return _M_base.is_lock_free(); }
 
    bool
    is_lock_free() const volatile noexcept { return _M_base.is_lock_free(); }
 
#if __cplusplus >= 201703L
    static constexpr bool is_always_lock_free = ATOMIC_BOOL_LOCK_FREE == 2;
#endif
 
    void
    store(bool __i, memory_order __m = memory_order_seq_cst) noexcept
    { _M_base.store(__i, __m); }
 
    void
    store(bool __i, memory_order __m = memory_order_seq_cst) volatile noexcept
    { _M_base.store(__i, __m); }
 
    bool
    load(memory_order __m = memory_order_seq_cst) const noexcept
    { return _M_base.load(__m); }
 
    bool
    load(memory_order __m = memory_order_seq_cst) const volatile noexcept
    { return _M_base.load(__m); }
 
    bool
    exchange(bool __i, memory_order __m = memory_order_seq_cst) noexcept
    { return _M_base.exchange(__i, __m); }
 
    bool
    exchange(bool __i,
             memory_order __m = memory_order_seq_cst) volatile noexcept
    { return _M_base.exchange(__i, __m); }
 
    bool
    compare_exchange_weak(bool& __i1, bool __i2, memory_order __m1,
                          memory_order __m2) noexcept
    { return _M_base.compare_exchange_weak(__i1, __i2, __m1, __m2); }
 
    bool
    compare_exchange_weak(bool& __i1, bool __i2, memory_order __m1,
                          memory_order __m2) volatile noexcept
    { return _M_base.compare_exchange_weak(__i1, __i2, __m1, __m2); }
 
    bool
    compare_exchange_weak(bool& __i1, bool __i2,
                          memory_order __m = memory_order_seq_cst) noexcept
    { return _M_base.compare_exchange_weak(__i1, __i2, __m); }
 
    bool
    compare_exchange_weak(bool& __i1, bool __i2,
                     memory_order __m = memory_order_seq_cst) volatile noexcept
    { return _M_base.compare_exchange_weak(__i1, __i2, __m); }
 
    bool
    compare_exchange_strong(bool& __i1, bool __i2, memory_order __m1,
                            memory_order __m2) noexcept
    { return _M_base.compare_exchange_strong(__i1, __i2, __m1, __m2); }
 
    bool
    compare_exchange_strong(bool& __i1, bool __i2, memory_order __m1,
                            memory_order __m2) volatile noexcept
    { return _M_base.compare_exchange_strong(__i1, __i2, __m1, __m2); }
 
    bool
    compare_exchange_strong(bool& __i1, bool __i2,
                            memory_order __m = memory_order_seq_cst) noexcept
    { return _M_base.compare_exchange_strong(__i1, __i2, __m); }
 
    bool
    compare_exchange_strong(bool& __i1, bool __i2,
                    memory_order __m = memory_order_seq_cst) volatile noexcept
    { return _M_base.compare_exchange_strong(__i1, __i2, __m); }
 
#if __cpp_lib_atomic_wait
    void
    wait(bool __old, memory_order __m = memory_order_seq_cst) const noexcept
    { _M_base.wait(__old, __m); }
 
    // TODO add const volatile overload
 
    void
    notify_one() noexcept
    { _M_base.notify_one(); }
 
    void
    notify_all() noexcept
    { _M_base.notify_all(); }
#endif // __cpp_lib_atomic_wait
  };
 
/// @cond undocumented
#if __cpp_lib_atomic_value_initialization
# define _GLIBCXX20_INIT(I) = I
#else
# define _GLIBCXX20_INIT(I)
#endif
/// @endcond
 
  /**
   *  @brief Generic atomic type, primary class template.
   *
   *  @tparam _Tp  Type to be made atomic, must be trivially copyable.
   */
  template<typename _Tp>
    struct atomic
    {
      using value_type = _Tp;
 
    private:
      // Align 1/2/4/8/16-byte types to at least their size.
      static constexpr int _S_min_alignment
        = (sizeof(_Tp) & (sizeof(_Tp) - 1)) || sizeof(_Tp) > 16
        ? 0 : sizeof(_Tp);
 
      static constexpr int _S_alignment
        = _S_min_alignment > alignof(_Tp) ? _S_min_alignment : alignof(_Tp);
 
      alignas(_S_alignment) _Tp _M_i _GLIBCXX20_INIT(_Tp());
 
      static_assert(__is_trivially_copyable(_Tp),
                    "std::atomic requires a trivially copyable type");
 
      static_assert(sizeof(_Tp) > 0,
                    "Incomplete or zero-sized types are not supported");
 
#if __cplusplus > 201703L
      static_assert(is_copy_constructible_v<_Tp>);
      static_assert(is_move_constructible_v<_Tp>);
      static_assert(is_copy_assignable_v<_Tp>);
      static_assert(is_move_assignable_v<_Tp>);
#endif
 
    public:
      atomic() = default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(_Tp __i) noexcept : _M_i(__i)
      {
#if __cplusplus >= 201402L && __has_builtin(__builtin_clear_padding)
        if _GLIBCXX17_CONSTEXPR (__atomic_impl::__maybe_has_padding<_Tp>())
          __builtin_clear_padding(std::__addressof(_M_i));
#endif
      }
 
      operator _Tp() const noexcept
      { return load(); }
 
      operator _Tp() const volatile noexcept
      { return load(); }
 
      _Tp
      operator=(_Tp __i) noexcept
      { store(__i); return __i; }
 
      _Tp
      operator=(_Tp __i) volatile noexcept
      { store(__i); return __i; }
 
      bool
      is_lock_free() const noexcept
      {
        // Produce a fake, minimally aligned pointer.
        return __atomic_is_lock_free(sizeof(_M_i),
            reinterpret_cast<void *>(-_S_alignment));
      }
 
      bool
      is_lock_free() const volatile noexcept
      {
        // Produce a fake, minimally aligned pointer.
        return __atomic_is_lock_free(sizeof(_M_i),
            reinterpret_cast<void *>(-_S_alignment));
      }
 
#if __cplusplus >= 201703L
      static constexpr bool is_always_lock_free
        = __atomic_always_lock_free(sizeof(_M_i), 0);
#endif
 
      void
      store(_Tp __i, memory_order __m = memory_order_seq_cst) noexcept
      {
        __atomic_store(std::__addressof(_M_i),
                       __atomic_impl::__clear_padding(__i),
                       int(__m));
      }
 
      void
      store(_Tp __i, memory_order __m = memory_order_seq_cst) volatile noexcept
      {
        __atomic_store(std::__addressof(_M_i),
                       __atomic_impl::__clear_padding(__i),
                       int(__m));
      }
 
      _Tp
      load(memory_order __m = memory_order_seq_cst) const noexcept
      {
        alignas(_Tp) unsigned char __buf[sizeof(_Tp)];
        _Tp* __ptr = reinterpret_cast<_Tp*>(__buf);
        __atomic_load(std::__addressof(_M_i), __ptr, int(__m));
        return *__ptr;
      }
 
      _Tp
      load(memory_order __m = memory_order_seq_cst) const volatile noexcept
      {
        alignas(_Tp) unsigned char __buf[sizeof(_Tp)];
        _Tp* __ptr = reinterpret_cast<_Tp*>(__buf);
        __atomic_load(std::__addressof(_M_i), __ptr, int(__m));
        return *__ptr;
      }
 
      _Tp
      exchange(_Tp __i, memory_order __m = memory_order_seq_cst) noexcept
      {
        alignas(_Tp) unsigned char __buf[sizeof(_Tp)];
        _Tp* __ptr = reinterpret_cast<_Tp*>(__buf);
        __atomic_exchange(std::__addressof(_M_i),
                          __atomic_impl::__clear_padding(__i),
                          __ptr, int(__m));
        return *__ptr;
      }
 
      _Tp
      exchange(_Tp __i,
               memory_order __m = memory_order_seq_cst) volatile noexcept
      {
        alignas(_Tp) unsigned char __buf[sizeof(_Tp)];
        _Tp* __ptr = reinterpret_cast<_Tp*>(__buf);
        __atomic_exchange(std::__addressof(_M_i),
                          __atomic_impl::__clear_padding(__i),
                          __ptr, int(__m));
        return *__ptr;
      }
 
      bool
      compare_exchange_weak(_Tp& __e, _Tp __i, memory_order __s,
                            memory_order __f) noexcept
      {
        return __atomic_impl::__compare_exchange(_M_i, __e, __i, true,
                                                 __s, __f);
      }
 
      bool
      compare_exchange_weak(_Tp& __e, _Tp __i, memory_order __s,
                            memory_order __f) volatile noexcept
      {
        return __atomic_impl::__compare_exchange(_M_i, __e, __i, true,
                                                 __s, __f);
      }
 
      bool
      compare_exchange_weak(_Tp& __e, _Tp __i,
                            memory_order __m = memory_order_seq_cst) noexcept
      { return compare_exchange_weak(__e, __i, __m,
                                     __cmpexch_failure_order(__m)); }
 
      bool
      compare_exchange_weak(_Tp& __e, _Tp __i,
                     memory_order __m = memory_order_seq_cst) volatile noexcept
      { return compare_exchange_weak(__e, __i, __m,
                                     __cmpexch_failure_order(__m)); }
 
      bool
      compare_exchange_strong(_Tp& __e, _Tp __i, memory_order __s,
                              memory_order __f) noexcept
      {
        return __atomic_impl::__compare_exchange(_M_i, __e, __i, false,
                                                 __s, __f);
      }
 
      bool
      compare_exchange_strong(_Tp& __e, _Tp __i, memory_order __s,
                              memory_order __f) volatile noexcept
      {
        return __atomic_impl::__compare_exchange(_M_i, __e, __i, false,
                                                 __s, __f);
      }
 
      bool
      compare_exchange_strong(_Tp& __e, _Tp __i,
                               memory_order __m = memory_order_seq_cst) noexcept
      { return compare_exchange_strong(__e, __i, __m,
                                       __cmpexch_failure_order(__m)); }
 
      bool
      compare_exchange_strong(_Tp& __e, _Tp __i,
                     memory_order __m = memory_order_seq_cst) volatile noexcept
      { return compare_exchange_strong(__e, __i, __m,
                                       __cmpexch_failure_order(__m)); }
 
#if __cpp_lib_atomic_wait
      void
      wait(_Tp __old, memory_order __m = memory_order_seq_cst) const noexcept
      {
        std::__atomic_wait_address_v(std::addressof(_M_i), __old,
                                     [__m, this] { return this->load(__m); });
      }
 
      // TODO add const volatile overload
 
      void
      notify_one() noexcept
      { std::__atomic_notify_address(std::addressof(_M_i), false); }
 
      void
      notify_all() noexcept
      { std::__atomic_notify_address(std::addressof(_M_i), true); }
#endif // __cpp_lib_atomic_wait
    };
#undef _GLIBCXX20_INIT
 
  /// Partial specialization for pointer types.
  template<typename _Tp>
    struct atomic<_Tp*>
    {
      using value_type = _Tp*;
      using difference_type = ptrdiff_t;
 
      typedef _Tp*                      __pointer_type;
      typedef __atomic_base<_Tp*>       __base_type;
      __base_type                       _M_b;
 
      atomic() noexcept = default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(__pointer_type __p) noexcept : _M_b(__p) { }
 
      operator __pointer_type() const noexcept
      { return __pointer_type(_M_b); }
 
      operator __pointer_type() const volatile noexcept
      { return __pointer_type(_M_b); }
 
      __pointer_type
      operator=(__pointer_type __p) noexcept
      { return _M_b.operator=(__p); }
 
      __pointer_type
      operator=(__pointer_type __p) volatile noexcept
      { return _M_b.operator=(__p); }
 
      __pointer_type
      operator++(int) noexcept
      {
#if __cplusplus >= 201703L
        static_assert( is_object<_Tp>::value, "pointer to object type" );
#endif
        return _M_b++;
      }
 
      __pointer_type
      operator++(int) volatile noexcept
      {
#if __cplusplus >= 201703L
        static_assert( is_object<_Tp>::value, "pointer to object type" );
#endif
        return _M_b++;
      }
 
      __pointer_type
      operator--(int) noexcept
      {
#if __cplusplus >= 201703L
        static_assert( is_object<_Tp>::value, "pointer to object type" );
#endif
        return _M_b--;
      }
 
      __pointer_type
      operator--(int) volatile noexcept
      {
#if __cplusplus >= 201703L
        static_assert( is_object<_Tp>::value, "pointer to object type" );
#endif
        return _M_b--;
      }
 
      __pointer_type
      operator++() noexcept
      {
#if __cplusplus >= 201703L
        static_assert( is_object<_Tp>::value, "pointer to object type" );
#endif
        return ++_M_b;
      }
 
      __pointer_type
      operator++() volatile noexcept
      {
#if __cplusplus >= 201703L
        static_assert( is_object<_Tp>::value, "pointer to object type" );
#endif
        return ++_M_b;
      }
 
      __pointer_type
      operator--() noexcept
      {
#if __cplusplus >= 201703L
        static_assert( is_object<_Tp>::value, "pointer to object type" );
#endif
        return --_M_b;
      }
 
      __pointer_type
      operator--() volatile noexcept
      {
#if __cplusplus >= 201703L
        static_assert( is_object<_Tp>::value, "pointer to object type" );
#endif
        return --_M_b;
      }
 
      __pointer_type
      operator+=(ptrdiff_t __d) noexcept
      {
#if __cplusplus >= 201703L
        static_assert( is_object<_Tp>::value, "pointer to object type" );
#endif
        return _M_b.operator+=(__d);
      }
 
      __pointer_type
      operator+=(ptrdiff_t __d) volatile noexcept
      {
#if __cplusplus >= 201703L
        static_assert( is_object<_Tp>::value, "pointer to object type" );
#endif
        return _M_b.operator+=(__d);
      }
 
      __pointer_type
      operator-=(ptrdiff_t __d) noexcept
      {
#if __cplusplus >= 201703L
        static_assert( is_object<_Tp>::value, "pointer to object type" );
#endif
        return _M_b.operator-=(__d);
      }
 
      __pointer_type
      operator-=(ptrdiff_t __d) volatile noexcept
      {
#if __cplusplus >= 201703L
        static_assert( is_object<_Tp>::value, "pointer to object type" );
#endif
        return _M_b.operator-=(__d);
      }
 
      bool
      is_lock_free() const noexcept
      { return _M_b.is_lock_free(); }
 
      bool
      is_lock_free() const volatile noexcept
      { return _M_b.is_lock_free(); }
 
#if __cplusplus >= 201703L
      static constexpr bool is_always_lock_free
        = ATOMIC_POINTER_LOCK_FREE == 2;
#endif
 
      void
      store(__pointer_type __p,
            memory_order __m = memory_order_seq_cst) noexcept
      { return _M_b.store(__p, __m); }
 
      void
      store(__pointer_type __p,
            memory_order __m = memory_order_seq_cst) volatile noexcept
      { return _M_b.store(__p, __m); }
 
      __pointer_type
      load(memory_order __m = memory_order_seq_cst) const noexcept
      { return _M_b.load(__m); }
 
      __pointer_type
      load(memory_order __m = memory_order_seq_cst) const volatile noexcept
      { return _M_b.load(__m); }
 
      __pointer_type
      exchange(__pointer_type __p,
               memory_order __m = memory_order_seq_cst) noexcept
      { return _M_b.exchange(__p, __m); }
 
      __pointer_type
      exchange(__pointer_type __p,
               memory_order __m = memory_order_seq_cst) volatile noexcept
      { return _M_b.exchange(__p, __m); }
 
      bool
      compare_exchange_weak(__pointer_type& __p1, __pointer_type __p2,
                            memory_order __m1, memory_order __m2) noexcept
      { return _M_b.compare_exchange_weak(__p1, __p2, __m1, __m2); }
 
      bool
      compare_exchange_weak(__pointer_type& __p1, __pointer_type __p2,
                            memory_order __m1,
                            memory_order __m2) volatile noexcept
      { return _M_b.compare_exchange_weak(__p1, __p2, __m1, __m2); }
 
      bool
      compare_exchange_weak(__pointer_type& __p1, __pointer_type __p2,
                            memory_order __m = memory_order_seq_cst) noexcept
      {
        return compare_exchange_weak(__p1, __p2, __m,
                                     __cmpexch_failure_order(__m));
      }
 
      bool
      compare_exchange_weak(__pointer_type& __p1, __pointer_type __p2,
                    memory_order __m = memory_order_seq_cst) volatile noexcept
      {
        return compare_exchange_weak(__p1, __p2, __m,
                                     __cmpexch_failure_order(__m));
      }
 
      bool
      compare_exchange_strong(__pointer_type& __p1, __pointer_type __p2,
                              memory_order __m1, memory_order __m2) noexcept
      { return _M_b.compare_exchange_strong(__p1, __p2, __m1, __m2); }
 
      bool
      compare_exchange_strong(__pointer_type& __p1, __pointer_type __p2,
                              memory_order __m1,
                              memory_order __m2) volatile noexcept
      { return _M_b.compare_exchange_strong(__p1, __p2, __m1, __m2); }
 
      bool
      compare_exchange_strong(__pointer_type& __p1, __pointer_type __p2,
                              memory_order __m = memory_order_seq_cst) noexcept
      {
        return _M_b.compare_exchange_strong(__p1, __p2, __m,
                                            __cmpexch_failure_order(__m));
      }
 
      bool
      compare_exchange_strong(__pointer_type& __p1, __pointer_type __p2,
                    memory_order __m = memory_order_seq_cst) volatile noexcept
      {
        return _M_b.compare_exchange_strong(__p1, __p2, __m,
                                            __cmpexch_failure_order(__m));
      }
 
#if __cpp_lib_atomic_wait
    void
    wait(__pointer_type __old, memory_order __m = memory_order_seq_cst) const noexcept
    { _M_b.wait(__old, __m); }
 
    // TODO add const volatile overload
 
    void
    notify_one() noexcept
    { _M_b.notify_one(); }
 
    void
    notify_all() noexcept
    { _M_b.notify_all(); }
#endif // __cpp_lib_atomic_wait
 
      __pointer_type
      fetch_add(ptrdiff_t __d,
                memory_order __m = memory_order_seq_cst) noexcept
      {
#if __cplusplus >= 201703L
        static_assert( is_object<_Tp>::value, "pointer to object type" );
#endif
        return _M_b.fetch_add(__d, __m);
      }
 
      __pointer_type
      fetch_add(ptrdiff_t __d,
                memory_order __m = memory_order_seq_cst) volatile noexcept
      {
#if __cplusplus >= 201703L
        static_assert( is_object<_Tp>::value, "pointer to object type" );
#endif
        return _M_b.fetch_add(__d, __m);
      }
 
      __pointer_type
      fetch_sub(ptrdiff_t __d,
                memory_order __m = memory_order_seq_cst) noexcept
      {
#if __cplusplus >= 201703L
        static_assert( is_object<_Tp>::value, "pointer to object type" );
#endif
        return _M_b.fetch_sub(__d, __m);
      }
 
      __pointer_type
      fetch_sub(ptrdiff_t __d,
                memory_order __m = memory_order_seq_cst) volatile noexcept
      {
#if __cplusplus >= 201703L
        static_assert( is_object<_Tp>::value, "pointer to object type" );
#endif
        return _M_b.fetch_sub(__d, __m);
      }
    };
 
 
  /// Explicit specialization for char.
  template<>
    struct atomic<char> : __atomic_base<char>
    {
      typedef char                      __integral_type;
      typedef __atomic_base<char>       __base_type;
 
      atomic() noexcept = default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(__integral_type __i) noexcept : __base_type(__i) { }
 
      using __base_type::operator __integral_type;
      using __base_type::operator=;
 
#if __cplusplus >= 201703L
      static constexpr bool is_always_lock_free = ATOMIC_CHAR_LOCK_FREE == 2;
#endif
    };
 
  /// Explicit specialization for signed char.
  template<>
    struct atomic<signed char> : __atomic_base<signed char>
    {
      typedef signed char               __integral_type;
      typedef __atomic_base<signed char>        __base_type;
 
      atomic() noexcept= default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(__integral_type __i) noexcept : __base_type(__i) { }
 
      using __base_type::operator __integral_type;
      using __base_type::operator=;
 
#if __cplusplus >= 201703L
      static constexpr bool is_always_lock_free = ATOMIC_CHAR_LOCK_FREE == 2;
#endif
    };
 
  /// Explicit specialization for unsigned char.
  template<>
    struct atomic<unsigned char> : __atomic_base<unsigned char>
    {
      typedef unsigned char             __integral_type;
      typedef __atomic_base<unsigned char>      __base_type;
 
      atomic() noexcept= default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(__integral_type __i) noexcept : __base_type(__i) { }
 
      using __base_type::operator __integral_type;
      using __base_type::operator=;
 
#if __cplusplus >= 201703L
      static constexpr bool is_always_lock_free = ATOMIC_CHAR_LOCK_FREE == 2;
#endif
    };
 
  /// Explicit specialization for short.
  template<>
    struct atomic<short> : __atomic_base<short>
    {
      typedef short                     __integral_type;
      typedef __atomic_base<short>              __base_type;
 
      atomic() noexcept = default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(__integral_type __i) noexcept : __base_type(__i) { }
 
      using __base_type::operator __integral_type;
      using __base_type::operator=;
 
#if __cplusplus >= 201703L
      static constexpr bool is_always_lock_free = ATOMIC_SHORT_LOCK_FREE == 2;
#endif
    };
 
  /// Explicit specialization for unsigned short.
  template<>
    struct atomic<unsigned short> : __atomic_base<unsigned short>
    {
      typedef unsigned short            __integral_type;
      typedef __atomic_base<unsigned short>             __base_type;
 
      atomic() noexcept = default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(__integral_type __i) noexcept : __base_type(__i) { }
 
      using __base_type::operator __integral_type;
      using __base_type::operator=;
 
#if __cplusplus >= 201703L
      static constexpr bool is_always_lock_free = ATOMIC_SHORT_LOCK_FREE == 2;
#endif
    };
 
  /// Explicit specialization for int.
  template<>
    struct atomic<int> : __atomic_base<int>
    {
      typedef int                       __integral_type;
      typedef __atomic_base<int>                __base_type;
 
      atomic() noexcept = default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(__integral_type __i) noexcept : __base_type(__i) { }
 
      using __base_type::operator __integral_type;
      using __base_type::operator=;
 
#if __cplusplus >= 201703L
      static constexpr bool is_always_lock_free = ATOMIC_INT_LOCK_FREE == 2;
#endif
    };
 
  /// Explicit specialization for unsigned int.
  template<>
    struct atomic<unsigned int> : __atomic_base<unsigned int>
    {
      typedef unsigned int              __integral_type;
      typedef __atomic_base<unsigned int>       __base_type;
 
      atomic() noexcept = default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(__integral_type __i) noexcept : __base_type(__i) { }
 
      using __base_type::operator __integral_type;
      using __base_type::operator=;
 
#if __cplusplus >= 201703L
      static constexpr bool is_always_lock_free = ATOMIC_INT_LOCK_FREE == 2;
#endif
    };
 
  /// Explicit specialization for long.
  template<>
    struct atomic<long> : __atomic_base<long>
    {
      typedef long                      __integral_type;
      typedef __atomic_base<long>       __base_type;
 
      atomic() noexcept = default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(__integral_type __i) noexcept : __base_type(__i) { }
 
      using __base_type::operator __integral_type;
      using __base_type::operator=;
 
#if __cplusplus >= 201703L
      static constexpr bool is_always_lock_free = ATOMIC_LONG_LOCK_FREE == 2;
#endif
    };
 
  /// Explicit specialization for unsigned long.
  template<>
    struct atomic<unsigned long> : __atomic_base<unsigned long>
    {
      typedef unsigned long             __integral_type;
      typedef __atomic_base<unsigned long>      __base_type;
 
      atomic() noexcept = default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(__integral_type __i) noexcept : __base_type(__i) { }
 
      using __base_type::operator __integral_type;
      using __base_type::operator=;
 
#if __cplusplus >= 201703L
      static constexpr bool is_always_lock_free = ATOMIC_LONG_LOCK_FREE == 2;
#endif
    };
 
  /// Explicit specialization for long long.
  template<>
    struct atomic<long long> : __atomic_base<long long>
    {
      typedef long long                 __integral_type;
      typedef __atomic_base<long long>          __base_type;
 
      atomic() noexcept = default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(__integral_type __i) noexcept : __base_type(__i) { }
 
      using __base_type::operator __integral_type;
      using __base_type::operator=;
 
#if __cplusplus >= 201703L
      static constexpr bool is_always_lock_free = ATOMIC_LLONG_LOCK_FREE == 2;
#endif
    };
 
  /// Explicit specialization for unsigned long long.
  template<>
    struct atomic<unsigned long long> : __atomic_base<unsigned long long>
    {
      typedef unsigned long long        __integral_type;
      typedef __atomic_base<unsigned long long>         __base_type;
 
      atomic() noexcept = default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(__integral_type __i) noexcept : __base_type(__i) { }
 
      using __base_type::operator __integral_type;
      using __base_type::operator=;
 
#if __cplusplus >= 201703L
      static constexpr bool is_always_lock_free = ATOMIC_LLONG_LOCK_FREE == 2;
#endif
    };
 
  /// Explicit specialization for wchar_t.
  template<>
    struct atomic<wchar_t> : __atomic_base<wchar_t>
    {
      typedef wchar_t                   __integral_type;
      typedef __atomic_base<wchar_t>    __base_type;
 
      atomic() noexcept = default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(__integral_type __i) noexcept : __base_type(__i) { }
 
      using __base_type::operator __integral_type;
      using __base_type::operator=;
 
#if __cplusplus >= 201703L
      static constexpr bool is_always_lock_free = ATOMIC_WCHAR_T_LOCK_FREE == 2;
#endif
    };
 
#ifdef _GLIBCXX_USE_CHAR8_T
  /// Explicit specialization for char8_t.
  template<>
    struct atomic<char8_t> : __atomic_base<char8_t>
    {
      typedef char8_t                   __integral_type;
      typedef __atomic_base<char8_t>    __base_type;
 
      atomic() noexcept = default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(__integral_type __i) noexcept : __base_type(__i) { }
 
      using __base_type::operator __integral_type;
      using __base_type::operator=;
 
#if __cplusplus > 201402L
      static constexpr bool is_always_lock_free
        = ATOMIC_CHAR8_T_LOCK_FREE == 2;
#endif
    };
#endif
 
  /// Explicit specialization for char16_t.
  template<>
    struct atomic<char16_t> : __atomic_base<char16_t>
    {
      typedef char16_t                  __integral_type;
      typedef __atomic_base<char16_t>   __base_type;
 
      atomic() noexcept = default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(__integral_type __i) noexcept : __base_type(__i) { }
 
      using __base_type::operator __integral_type;
      using __base_type::operator=;
 
#if __cplusplus >= 201703L
      static constexpr bool is_always_lock_free
        = ATOMIC_CHAR16_T_LOCK_FREE == 2;
#endif
    };
 
  /// Explicit specialization for char32_t.
  template<>
    struct atomic<char32_t> : __atomic_base<char32_t>
    {
      typedef char32_t                  __integral_type;
      typedef __atomic_base<char32_t>   __base_type;
 
      atomic() noexcept = default;
      ~atomic() noexcept = default;
      atomic(const atomic&) = delete;
      atomic& operator=(const atomic&) = delete;
      atomic& operator=(const atomic&) volatile = delete;
 
      constexpr atomic(__integral_type __i) noexcept : __base_type(__i) { }
 
      using __base_type::operator __integral_type;
      using __base_type::operator=;
 
#if __cplusplus >= 201703L
      static constexpr bool is_always_lock_free
        = ATOMIC_CHAR32_T_LOCK_FREE == 2;
#endif
    };
 
 
  /// atomic_bool
  typedef atomic<bool>                  atomic_bool;
 
  /// atomic_char
  typedef atomic<char>                  atomic_char;
 
  /// atomic_schar
  typedef atomic<signed char>           atomic_schar;
 
  /// atomic_uchar
  typedef atomic<unsigned char>         atomic_uchar;
 
  /// atomic_short
  typedef atomic<short>                 atomic_short;
 
  /// atomic_ushort
  typedef atomic<unsigned short>        atomic_ushort;
 
  /// atomic_int
  typedef atomic<int>                   atomic_int;
 
  /// atomic_uint
  typedef atomic<unsigned int>          atomic_uint;
 
  /// atomic_long
  typedef atomic<long>                  atomic_long;
 
  /// atomic_ulong
  typedef atomic<unsigned long>         atomic_ulong;
 
  /// atomic_llong
  typedef atomic<long long>             atomic_llong;
 
  /// atomic_ullong
  typedef atomic<unsigned long long>    atomic_ullong;
 
  /// atomic_wchar_t
  typedef atomic<wchar_t>               atomic_wchar_t;
 
#ifdef _GLIBCXX_USE_CHAR8_T
  /// atomic_char8_t
  typedef atomic<char8_t>               atomic_char8_t;
#endif
 
  /// atomic_char16_t
  typedef atomic<char16_t>              atomic_char16_t;
 
  /// atomic_char32_t
  typedef atomic<char32_t>              atomic_char32_t;
 
#ifdef _GLIBCXX_USE_C99_STDINT_TR1
  // _GLIBCXX_RESOLVE_LIB_DEFECTS
  // 2441. Exact-width atomic typedefs should be provided
 
  /// atomic_int8_t
  typedef atomic<int8_t>                atomic_int8_t;
 
  /// atomic_uint8_t
  typedef atomic<uint8_t>               atomic_uint8_t;
 
  /// atomic_int16_t
  typedef atomic<int16_t>               atomic_int16_t;
 
  /// atomic_uint16_t
  typedef atomic<uint16_t>              atomic_uint16_t;
 
  /// atomic_int32_t
  typedef atomic<int32_t>               atomic_int32_t;
 
  /// atomic_uint32_t
  typedef atomic<uint32_t>              atomic_uint32_t;
 
  /// atomic_int64_t
  typedef atomic<int64_t>               atomic_int64_t;
 
  /// atomic_uint64_t
  typedef atomic<uint64_t>              atomic_uint64_t;
 
 
  /// atomic_int_least8_t
  typedef atomic<int_least8_t>          atomic_int_least8_t;
 
  /// atomic_uint_least8_t
  typedef atomic<uint_least8_t>         atomic_uint_least8_t;
 
  /// atomic_int_least16_t
  typedef atomic<int_least16_t>         atomic_int_least16_t;
 
  /// atomic_uint_least16_t
  typedef atomic<uint_least16_t>        atomic_uint_least16_t;
 
  /// atomic_int_least32_t
  typedef atomic<int_least32_t>         atomic_int_least32_t;
 
  /// atomic_uint_least32_t
  typedef atomic<uint_least32_t>        atomic_uint_least32_t;
 
  /// atomic_int_least64_t
  typedef atomic<int_least64_t>         atomic_int_least64_t;
 
  /// atomic_uint_least64_t
  typedef atomic<uint_least64_t>        atomic_uint_least64_t;
 
 
  /// atomic_int_fast8_t
  typedef atomic<int_fast8_t>           atomic_int_fast8_t;
 
  /// atomic_uint_fast8_t
  typedef atomic<uint_fast8_t>          atomic_uint_fast8_t;
 
  /// atomic_int_fast16_t
  typedef atomic<int_fast16_t>          atomic_int_fast16_t;
 
  /// atomic_uint_fast16_t
  typedef atomic<uint_fast16_t>         atomic_uint_fast16_t;
 
  /// atomic_int_fast32_t
  typedef atomic<int_fast32_t>          atomic_int_fast32_t;
 
  /// atomic_uint_fast32_t
  typedef atomic<uint_fast32_t>         atomic_uint_fast32_t;
 
  /// atomic_int_fast64_t
  typedef atomic<int_fast64_t>          atomic_int_fast64_t;
 
  /// atomic_uint_fast64_t
  typedef atomic<uint_fast64_t>         atomic_uint_fast64_t;
#endif
 
 
  /// atomic_intptr_t
  typedef atomic<intptr_t>              atomic_intptr_t;
 
  /// atomic_uintptr_t
  typedef atomic<uintptr_t>             atomic_uintptr_t;
 
  /// atomic_size_t
  typedef atomic<size_t>                atomic_size_t;
 
  /// atomic_ptrdiff_t
  typedef atomic<ptrdiff_t>             atomic_ptrdiff_t;
 
#ifdef _GLIBCXX_USE_C99_STDINT_TR1
  /// atomic_intmax_t
  typedef atomic<intmax_t>              atomic_intmax_t;
 
  /// atomic_uintmax_t
  typedef atomic<uintmax_t>             atomic_uintmax_t;
#endif
 
  // Function definitions, atomic_flag operations.
  inline bool
  atomic_flag_test_and_set_explicit(atomic_flag* __a,
                                    memory_order __m) noexcept
  { return __a->test_and_set(__m); }
 
  inline bool
  atomic_flag_test_and_set_explicit(volatile atomic_flag* __a,
                                    memory_order __m) noexcept
  { return __a->test_and_set(__m); }
 
#if __cpp_lib_atomic_flag_test
  inline bool
  atomic_flag_test(const atomic_flag* __a) noexcept
  { return __a->test(); }
 
  inline bool
  atomic_flag_test(const volatile atomic_flag* __a) noexcept
  { return __a->test(); }
 
  inline bool
  atomic_flag_test_explicit(const atomic_flag* __a,
                            memory_order __m) noexcept
  { return __a->test(__m); }
 
  inline bool
  atomic_flag_test_explicit(const volatile atomic_flag* __a,
                            memory_order __m) noexcept
  { return __a->test(__m); }
#endif
 
  inline void
  atomic_flag_clear_explicit(atomic_flag* __a, memory_order __m) noexcept
  { __a->clear(__m); }
 
  inline void
  atomic_flag_clear_explicit(volatile atomic_flag* __a,
                             memory_order __m) noexcept
  { __a->clear(__m); }
 
  inline bool
  atomic_flag_test_and_set(atomic_flag* __a) noexcept
  { return atomic_flag_test_and_set_explicit(__a, memory_order_seq_cst); }
 
  inline bool
  atomic_flag_test_and_set(volatile atomic_flag* __a) noexcept
  { return atomic_flag_test_and_set_explicit(__a, memory_order_seq_cst); }
 
  inline void
  atomic_flag_clear(atomic_flag* __a) noexcept
  { atomic_flag_clear_explicit(__a, memory_order_seq_cst); }
 
  inline void
  atomic_flag_clear(volatile atomic_flag* __a) noexcept
  { atomic_flag_clear_explicit(__a, memory_order_seq_cst); }
 
#if __cpp_lib_atomic_wait
  inline void
  atomic_flag_wait(atomic_flag* __a, bool __old) noexcept
  { __a->wait(__old); }
 
  inline void
  atomic_flag_wait_explicit(atomic_flag* __a, bool __old,
                                memory_order __m) noexcept
  { __a->wait(__old, __m); }
 
  inline void
  atomic_flag_notify_one(atomic_flag* __a) noexcept
  { __a->notify_one(); }
 
  inline void
  atomic_flag_notify_all(atomic_flag* __a) noexcept
  { __a->notify_all(); }
#endif // __cpp_lib_atomic_wait
 
  /// @cond undocumented
  // _GLIBCXX_RESOLVE_LIB_DEFECTS
  // 3220. P0558 broke conforming C++14 uses of atomic shared_ptr
  template<typename _Tp>
    using __atomic_val_t = __type_identity_t<_Tp>;
  template<typename _Tp>
    using __atomic_diff_t = typename atomic<_Tp>::difference_type;
  /// @endcond
 
  // [atomics.nonmembers] Non-member functions.
  // Function templates generally applicable to atomic types.
  template<typename _ITp>
    inline bool
    atomic_is_lock_free(const atomic<_ITp>* __a) noexcept
    { return __a->is_lock_free(); }
 
  template<typename _ITp>
    inline bool
    atomic_is_lock_free(const volatile atomic<_ITp>* __a) noexcept
    { return __a->is_lock_free(); }
 
  template<typename _ITp>
    inline void
    atomic_init(atomic<_ITp>* __a, __atomic_val_t<_ITp> __i) noexcept
    { __a->store(__i, memory_order_relaxed); }
 
  template<typename _ITp>
    inline void
    atomic_init(volatile atomic<_ITp>* __a, __atomic_val_t<_ITp> __i) noexcept
    { __a->store(__i, memory_order_relaxed); }
 
  template<typename _ITp>
    inline void
    atomic_store_explicit(atomic<_ITp>* __a, __atomic_val_t<_ITp> __i,
                          memory_order __m) noexcept
    { __a->store(__i, __m); }
 
  template<typename _ITp>
    inline void
    atomic_store_explicit(volatile atomic<_ITp>* __a, __atomic_val_t<_ITp> __i,
                          memory_order __m) noexcept
    { __a->store(__i, __m); }
 
  template<typename _ITp>
    inline _ITp
    atomic_load_explicit(const atomic<_ITp>* __a, memory_order __m) noexcept
    { return __a->load(__m); }
 
  template<typename _ITp>
    inline _ITp
    atomic_load_explicit(const volatile atomic<_ITp>* __a,
                         memory_order __m) noexcept
    { return __a->load(__m); }
 
  template<typename _ITp>
    inline _ITp
    atomic_exchange_explicit(atomic<_ITp>* __a, __atomic_val_t<_ITp> __i,
                             memory_order __m) noexcept
    { return __a->exchange(__i, __m); }
 
  template<typename _ITp>
    inline _ITp
    atomic_exchange_explicit(volatile atomic<_ITp>* __a,
                             __atomic_val_t<_ITp> __i,
                             memory_order __m) noexcept
    { return __a->exchange(__i, __m); }
 
  template<typename _ITp>
    inline bool
    atomic_compare_exchange_weak_explicit(atomic<_ITp>* __a,
                                          __atomic_val_t<_ITp>* __i1,
                                          __atomic_val_t<_ITp> __i2,
                                          memory_order __m1,
                                          memory_order __m2) noexcept
    { return __a->compare_exchange_weak(*__i1, __i2, __m1, __m2); }
 
  template<typename _ITp>
    inline bool
    atomic_compare_exchange_weak_explicit(volatile atomic<_ITp>* __a,
                                          __atomic_val_t<_ITp>* __i1,
                                          __atomic_val_t<_ITp> __i2,
                                          memory_order __m1,
                                          memory_order __m2) noexcept
    { return __a->compare_exchange_weak(*__i1, __i2, __m1, __m2); }
 
  template<typename _ITp>
    inline bool
    atomic_compare_exchange_strong_explicit(atomic<_ITp>* __a,
                                            __atomic_val_t<_ITp>* __i1,
                                            __atomic_val_t<_ITp> __i2,
                                            memory_order __m1,
                                            memory_order __m2) noexcept
    { return __a->compare_exchange_strong(*__i1, __i2, __m1, __m2); }
 
  template<typename _ITp>
    inline bool
    atomic_compare_exchange_strong_explicit(volatile atomic<_ITp>* __a,
                                            __atomic_val_t<_ITp>* __i1,
                                            __atomic_val_t<_ITp> __i2,
                                            memory_order __m1,
                                            memory_order __m2) noexcept
    { return __a->compare_exchange_strong(*__i1, __i2, __m1, __m2); }
 
 
  template<typename _ITp>
    inline void
    atomic_store(atomic<_ITp>* __a, __atomic_val_t<_ITp> __i) noexcept
    { atomic_store_explicit(__a, __i, memory_order_seq_cst); }
 
  template<typename _ITp>
    inline void
    atomic_store(volatile atomic<_ITp>* __a, __atomic_val_t<_ITp> __i) noexcept
    { atomic_store_explicit(__a, __i, memory_order_seq_cst); }
 
  template<typename _ITp>
    inline _ITp
    atomic_load(const atomic<_ITp>* __a) noexcept
    { return atomic_load_explicit(__a, memory_order_seq_cst); }
 
  template<typename _ITp>
    inline _ITp
    atomic_load(const volatile atomic<_ITp>* __a) noexcept
    { return atomic_load_explicit(__a, memory_order_seq_cst); }
 
  template<typename _ITp>
    inline _ITp
    atomic_exchange(atomic<_ITp>* __a, __atomic_val_t<_ITp> __i) noexcept
    { return atomic_exchange_explicit(__a, __i, memory_order_seq_cst); }
 
  template<typename _ITp>
    inline _ITp
    atomic_exchange(volatile atomic<_ITp>* __a,
                    __atomic_val_t<_ITp> __i) noexcept
    { return atomic_exchange_explicit(__a, __i, memory_order_seq_cst); }
 
  template<typename _ITp>
    inline bool
    atomic_compare_exchange_weak(atomic<_ITp>* __a,
                                 __atomic_val_t<_ITp>* __i1,
                                 __atomic_val_t<_ITp> __i2) noexcept
    {
      return atomic_compare_exchange_weak_explicit(__a, __i1, __i2,
                                                   memory_order_seq_cst,
                                                   memory_order_seq_cst);
    }
 
  template<typename _ITp>
    inline bool
    atomic_compare_exchange_weak(volatile atomic<_ITp>* __a,
                                 __atomic_val_t<_ITp>* __i1,
                                 __atomic_val_t<_ITp> __i2) noexcept
    {
      return atomic_compare_exchange_weak_explicit(__a, __i1, __i2,
                                                   memory_order_seq_cst,
                                                   memory_order_seq_cst);
    }
 
  template<typename _ITp>
    inline bool
    atomic_compare_exchange_strong(atomic<_ITp>* __a,
                                   __atomic_val_t<_ITp>* __i1,
                                   __atomic_val_t<_ITp> __i2) noexcept
    {
      return atomic_compare_exchange_strong_explicit(__a, __i1, __i2,
                                                     memory_order_seq_cst,
                                                     memory_order_seq_cst);
    }
 
  template<typename _ITp>
    inline bool
    atomic_compare_exchange_strong(volatile atomic<_ITp>* __a,
                                   __atomic_val_t<_ITp>* __i1,
                                   __atomic_val_t<_ITp> __i2) noexcept
    {
      return atomic_compare_exchange_strong_explicit(__a, __i1, __i2,
                                                     memory_order_seq_cst,
                                                     memory_order_seq_cst);
    }
 
 
#if __cpp_lib_atomic_wait
  template<typename _Tp>
    inline void
    atomic_wait(const atomic<_Tp>* __a,
                typename std::atomic<_Tp>::value_type __old) noexcept
    { __a->wait(__old); }
 
  template<typename _Tp>
    inline void
    atomic_wait_explicit(const atomic<_Tp>* __a,
                         typename std::atomic<_Tp>::value_type __old,
                         std::memory_order __m) noexcept
    { __a->wait(__old, __m); }
 
  template<typename _Tp>
    inline void
    atomic_notify_one(atomic<_Tp>* __a) noexcept
    { __a->notify_one(); }
 
  template<typename _Tp>
    inline void
    atomic_notify_all(atomic<_Tp>* __a) noexcept
    { __a->notify_all(); }
#endif // __cpp_lib_atomic_wait
 
  // Function templates for atomic_integral and atomic_pointer operations only.
  // Some operations (and, or, xor) are only available for atomic integrals,
  // which is implemented by taking a parameter of type __atomic_base<_ITp>*.
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_add_explicit(atomic<_ITp>* __a,
                              __atomic_diff_t<_ITp> __i,
                              memory_order __m) noexcept
    { return __a->fetch_add(__i, __m); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_add_explicit(volatile atomic<_ITp>* __a,
                              __atomic_diff_t<_ITp> __i,
                              memory_order __m) noexcept
    { return __a->fetch_add(__i, __m); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_sub_explicit(atomic<_ITp>* __a,
                              __atomic_diff_t<_ITp> __i,
                              memory_order __m) noexcept
    { return __a->fetch_sub(__i, __m); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_sub_explicit(volatile atomic<_ITp>* __a,
                              __atomic_diff_t<_ITp> __i,
                              memory_order __m) noexcept
    { return __a->fetch_sub(__i, __m); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_and_explicit(__atomic_base<_ITp>* __a,
                              __atomic_val_t<_ITp> __i,
                              memory_order __m) noexcept
    { return __a->fetch_and(__i, __m); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_and_explicit(volatile __atomic_base<_ITp>* __a,
                              __atomic_val_t<_ITp> __i,
                              memory_order __m) noexcept
    { return __a->fetch_and(__i, __m); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_or_explicit(__atomic_base<_ITp>* __a,
                             __atomic_val_t<_ITp> __i,
                             memory_order __m) noexcept
    { return __a->fetch_or(__i, __m); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_or_explicit(volatile __atomic_base<_ITp>* __a,
                             __atomic_val_t<_ITp> __i,
                             memory_order __m) noexcept
    { return __a->fetch_or(__i, __m); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_xor_explicit(__atomic_base<_ITp>* __a,
                              __atomic_val_t<_ITp> __i,
                              memory_order __m) noexcept
    { return __a->fetch_xor(__i, __m); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_xor_explicit(volatile __atomic_base<_ITp>* __a,
                              __atomic_val_t<_ITp> __i,
                              memory_order __m) noexcept
    { return __a->fetch_xor(__i, __m); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_add(atomic<_ITp>* __a,
                     __atomic_diff_t<_ITp> __i) noexcept
    { return atomic_fetch_add_explicit(__a, __i, memory_order_seq_cst); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_add(volatile atomic<_ITp>* __a,
                     __atomic_diff_t<_ITp> __i) noexcept
    { return atomic_fetch_add_explicit(__a, __i, memory_order_seq_cst); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_sub(atomic<_ITp>* __a,
                     __atomic_diff_t<_ITp> __i) noexcept
    { return atomic_fetch_sub_explicit(__a, __i, memory_order_seq_cst); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_sub(volatile atomic<_ITp>* __a,
                     __atomic_diff_t<_ITp> __i) noexcept
    { return atomic_fetch_sub_explicit(__a, __i, memory_order_seq_cst); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_and(__atomic_base<_ITp>* __a,
                     __atomic_val_t<_ITp> __i) noexcept
    { return atomic_fetch_and_explicit(__a, __i, memory_order_seq_cst); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_and(volatile __atomic_base<_ITp>* __a,
                     __atomic_val_t<_ITp> __i) noexcept
    { return atomic_fetch_and_explicit(__a, __i, memory_order_seq_cst); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_or(__atomic_base<_ITp>* __a,
                    __atomic_val_t<_ITp> __i) noexcept
    { return atomic_fetch_or_explicit(__a, __i, memory_order_seq_cst); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_or(volatile __atomic_base<_ITp>* __a,
                    __atomic_val_t<_ITp> __i) noexcept
    { return atomic_fetch_or_explicit(__a, __i, memory_order_seq_cst); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_xor(__atomic_base<_ITp>* __a,
                     __atomic_val_t<_ITp> __i) noexcept
    { return atomic_fetch_xor_explicit(__a, __i, memory_order_seq_cst); }
 
  template<typename _ITp>
    inline _ITp
    atomic_fetch_xor(volatile __atomic_base<_ITp>* __a,
                     __atomic_val_t<_ITp> __i) noexcept
    { return atomic_fetch_xor_explicit(__a, __i, memory_order_seq_cst); }
 
#if __cplusplus > 201703L
#define __cpp_lib_atomic_float 201711L
  template<>
    struct atomic<float> : __atomic_float<float>
    {
      atomic() noexcept = default;
 
      constexpr
      atomic(float __fp) noexcept : __atomic_float<float>(__fp)
      { }
 
      atomic& operator=(const atomic&) volatile = delete;
      atomic& operator=(const atomic&) = delete;
 
      using __atomic_float<float>::operator=;
    };
 
  template<>
    struct atomic<double> : __atomic_float<double>
    {
      atomic() noexcept = default;
 
      constexpr
      atomic(double __fp) noexcept : __atomic_float<double>(__fp)
      { }
 
      atomic& operator=(const atomic&) volatile = delete;
      atomic& operator=(const atomic&) = delete;
 
      using __atomic_float<double>::operator=;
    };
 
  template<>
    struct atomic<long double> : __atomic_float<long double>
    {
      atomic() noexcept = default;
 
      constexpr
      atomic(long double __fp) noexcept : __atomic_float<long double>(__fp)
      { }
 
      atomic& operator=(const atomic&) volatile = delete;
      atomic& operator=(const atomic&) = delete;
 
      using __atomic_float<long double>::operator=;
    };
 
#ifdef __STDCPP_FLOAT16_T__
  template<>
    struct atomic<_Float16> : __atomic_float<_Float16>
    {
      atomic() noexcept = default;
 
      constexpr
      atomic(_Float16 __fp) noexcept : __atomic_float<_Float16>(__fp)
      { }
 
      atomic& operator=(const atomic&) volatile = delete;
      atomic& operator=(const atomic&) = delete;
 
      using __atomic_float<_Float16>::operator=;
    };
#endif
 
#ifdef __STDCPP_FLOAT32_T__
  template<>
    struct atomic<_Float32> : __atomic_float<_Float32>
    {
      atomic() noexcept = default;
 
      constexpr
      atomic(_Float32 __fp) noexcept : __atomic_float<_Float32>(__fp)
      { }
 
      atomic& operator=(const atomic&) volatile = delete;
      atomic& operator=(const atomic&) = delete;
 
      using __atomic_float<_Float32>::operator=;
    };
#endif
 
#ifdef __STDCPP_FLOAT64_T__
  template<>
    struct atomic<_Float64> : __atomic_float<_Float64>
    {
      atomic() noexcept = default;
 
      constexpr
      atomic(_Float64 __fp) noexcept : __atomic_float<_Float64>(__fp)
      { }
 
      atomic& operator=(const atomic&) volatile = delete;
      atomic& operator=(const atomic&) = delete;
 
      using __atomic_float<_Float64>::operator=;
    };
#endif
 
#ifdef __STDCPP_FLOAT128_T__
  template<>
    struct atomic<_Float128> : __atomic_float<_Float128>
    {
      atomic() noexcept = default;
 
      constexpr
      atomic(_Float128 __fp) noexcept : __atomic_float<_Float128>(__fp)
      { }
 
      atomic& operator=(const atomic&) volatile = delete;
      atomic& operator=(const atomic&) = delete;
 
      using __atomic_float<_Float128>::operator=;
    };
#endif
 
#ifdef __STDCPP_BFLOAT16_T__
  template<>
    struct atomic<__gnu_cxx::__bfloat16_t> : __atomic_float<__gnu_cxx::__bfloat16_t>
    {
      atomic() noexcept = default;
 
      constexpr
      atomic(__gnu_cxx::__bfloat16_t __fp) noexcept : __atomic_float<__gnu_cxx::__bfloat16_t>(__fp)
      { }
 
      atomic& operator=(const atomic&) volatile = delete;
      atomic& operator=(const atomic&) = delete;
 
      using __atomic_float<__gnu_cxx::__bfloat16_t>::operator=;
    };
#endif
 
#define __cpp_lib_atomic_ref 201806L
 
  /// Class template to provide atomic operations on a non-atomic variable.
  template<typename _Tp>
    struct atomic_ref : __atomic_ref<_Tp>
    {
      explicit
      atomic_ref(_Tp& __t) noexcept : __atomic_ref<_Tp>(__t)
      { }
 
      atomic_ref& operator=(const atomic_ref&) = delete;
 
      atomic_ref(const atomic_ref&) = default;
 
      using __atomic_ref<_Tp>::operator=;
    };
 
#define __cpp_lib_atomic_lock_free_type_aliases 201907L
#ifdef _GLIBCXX_HAVE_PLATFORM_WAIT
  using atomic_signed_lock_free
    = atomic<make_signed_t<__detail::__platform_wait_t>>;
  using atomic_unsigned_lock_free
    = atomic<make_unsigned_t<__detail::__platform_wait_t>>;
#elif ATOMIC_INT_LOCK_FREE || !(ATOMIC_LONG_LOCK_FREE || ATOMIC_CHAR_LOCK_FREE)
  using atomic_signed_lock_free = atomic<signed int>;
  using atomic_unsigned_lock_free = atomic<unsigned int>;
#elif ATOMIC_LONG_LOCK_FREE
  using atomic_signed_lock_free = atomic<signed long>;
  using atomic_unsigned_lock_free = atomic<unsigned long>;
#elif ATOMIC_CHAR_LOCK_FREE
  using atomic_signed_lock_free = atomic<signed char>;
  using atomic_unsigned_lock_free = atomic<unsigned char>;
#endif
 
#endif // C++2a
 
  /// @} group atomics
 
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
 
#endif // C++11
 
#endif // _GLIBCXX_ATOMIC