Where Online Learning is simpler!

The C and C++ Include Header Files

/usr/include/c++/13/latch


$ cat -n /usr/include/c++/13/latch

     1	// <latch> -*- C++ -*-
     2	
     3	// Copyright (C) 2020-2023 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	#include <bits/requires_hosted.h> // concurrency
    35	
    36	#if __cplusplus > 201703L
    37	
    38	#include <bits/atomic_base.h>
    39	#include <ext/numeric_traits.h>
    40	
    41	#if __cpp_lib_atomic_wait
    42	namespace std _GLIBCXX_VISIBILITY(default)
    43	{
    44	_GLIBCXX_BEGIN_NAMESPACE_VERSION
    45	
    46	#define __cpp_lib_latch 201907L
    47	
    48	  class latch
    49	  {
    50	  public:
    51	    static constexpr ptrdiff_t
    52	    max() noexcept
    53	    { return __gnu_cxx::__int_traits<__detail::__platform_wait_t>::__max; }
    54	
    55	    constexpr explicit latch(ptrdiff_t __expected) noexcept
    56	      : _M_a(__expected) { }
    57	
    58	    ~latch() = default;
    59	    latch(const latch&) = delete;
    60	    latch& operator=(const latch&) = delete;
    61	
    62	    _GLIBCXX_ALWAYS_INLINE void
    63	    count_down(ptrdiff_t __update = 1)
    64	    {
    65	      auto const __old = __atomic_impl::fetch_sub(&_M_a,
    66					    __update, memory_order::release);
    67	      if (__old == __update)
    68		__atomic_impl::notify_all(&_M_a);
    69	    }
    70	
    71	    _GLIBCXX_ALWAYS_INLINE bool
    72	    try_wait() const noexcept
    73	    { return __atomic_impl::load(&_M_a, memory_order::acquire) == 0; }
    74	
    75	    _GLIBCXX_ALWAYS_INLINE void
    76	    wait() const noexcept
    77	    {
    78	      auto const __pred = [this] { return this->try_wait(); };
    79	      std::__atomic_wait_address(&_M_a, __pred);
    80	    }
    81	
    82	    _GLIBCXX_ALWAYS_INLINE void
    83	    arrive_and_wait(ptrdiff_t __update = 1) noexcept
    84	    {
    85	      count_down(__update);
    86	      wait();
    87	    }
    88	
    89	  private:
    90	    alignas(__alignof__(__detail::__platform_wait_t)) __detail::__platform_wait_t _M_a;
    91	  };
    92	_GLIBCXX_END_NAMESPACE_VERSION
    93	} // namespace
    94	#endif // __cpp_lib_atomic_wait
    95	#endif // __cplusplus > 201703L
    96	#endif // _GLIBCXX_LATCH