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The C and C++ Include Header Files

/usr/include/c++/11/latch


$ cat -n /usr/include/c++/11/latch

     1	// <latch> -*- C++ -*-
     2	
     3	// Copyright (C) 2020-2021 Free Software Foundation, Inc.
     4	//
     5	// This file is part of the GNU ISO C++ Library.  This library is free
     6	// software; you can redistribute it and/or modify it under the
     7	// terms of the GNU General Public License as published by the
     8	// Free Software Foundation; either version 3, or (at your option)
     9	// any later version.
    10	
    11	// This library is distributed in the hope that it will be useful,
    12	// but WITHOUT ANY WARRANTY; without even the implied warranty of
    13	// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    14	// GNU General Public License for more details.
    15	
    16	// Under Section 7 of GPL version 3, you are granted additional
    17	// permissions described in the GCC Runtime Library Exception, version
    18	// 3.1, as published by the Free Software Foundation.
    19	
    20	// You should have received a copy of the GNU General Public License and
    21	// a copy of the GCC Runtime Library Exception along with this program;
    22	// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
    23	// <http://www.gnu.org/licenses/>.
    24	
    25	/** @file include/latch
    26	 *  This is a Standard C++ Library header.
    27	 */
    28	
    29	#ifndef _GLIBCXX_LATCH
    30	#define _GLIBCXX_LATCH 1
    31	
    32	#pragma GCC system_header
    33	
    34	#if __cplusplus > 201703L
    35	
    36	#include <bits/atomic_base.h>
    37	#include <ext/numeric_traits.h>
    38	
    39	#if __cpp_lib_atomic_wait
    40	namespace std _GLIBCXX_VISIBILITY(default)
    41	{
    42	_GLIBCXX_BEGIN_NAMESPACE_VERSION
    43	
    44	#define __cpp_lib_latch 201907L
    45	
    46	  class latch
    47	  {
    48	  public:
    49	    static constexpr ptrdiff_t
    50	    max() noexcept
    51	    { return __gnu_cxx::__int_traits<__detail::__platform_wait_t>::__max; }
    52	
    53	    constexpr explicit latch(ptrdiff_t __expected) noexcept
    54	      : _M_a(__expected) { }
    55	
    56	    ~latch() = default;
    57	    latch(const latch&) = delete;
    58	    latch& operator=(const latch&) = delete;
    59	
    60	    _GLIBCXX_ALWAYS_INLINE void
    61	    count_down(ptrdiff_t __update = 1)
    62	    {
    63	      auto const __old = __atomic_impl::fetch_sub(&_M_a,
    64					    __update, memory_order::release);
    65	      if (__old == __update)
    66		__atomic_impl::notify_all(&_M_a);
    67	    }
    68	
    69	    _GLIBCXX_ALWAYS_INLINE bool
    70	    try_wait() const noexcept
    71	    { return __atomic_impl::load(&_M_a, memory_order::acquire) == 0; }
    72	
    73	    _GLIBCXX_ALWAYS_INLINE void
    74	    wait() const noexcept
    75	    {
    76	      auto const __pred = [this] { return this->try_wait(); };
    77	      std::__atomic_wait_address(&_M_a, __pred);
    78	    }
    79	
    80	    _GLIBCXX_ALWAYS_INLINE void
    81	    arrive_and_wait(ptrdiff_t __update = 1) noexcept
    82	    {
    83	      count_down(__update);
    84	      wait();
    85	    }
    86	
    87	  private:
    88	    alignas(__alignof__(__detail::__platform_wait_t)) __detail::__platform_wait_t _M_a;
    89	  };
    90	_GLIBCXX_END_NAMESPACE_VERSION
    91	} // namespace
    92	#endif // __cpp_lib_atomic_wait
    93	#endif // __cplusplus > 201703L
    94	#endif // _GLIBCXX_LATCH