semaphore

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// <semaphore> -*- C++ -*-
 
// Copyright (C) 2020-2026 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/semaphore
 *  This is a Standard C++ Library header.
 */
 
#ifndef _GLIBCXX_SEMAPHORE
#define _GLIBCXX_SEMAPHORE 1
 
#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif
 
#include <bits/requires_hosted.h> // concurrency
 
#define __glibcxx_want_semaphore
#include <bits/version.h>
 
#ifdef __cpp_lib_semaphore // C++ >= 20 && hosted && atomic_wait
#include <bits/semaphore_base.h>
 
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
 
  template<ptrdiff_t __least_max_value = _Semaphore_impl<2>::_S_max>
    class counting_semaphore
    {
      static_assert(__least_max_value >= 0);
 
      _Semaphore_impl<__least_max_value> _M_sem;
 
    public:
      constexpr explicit
      counting_semaphore(ptrdiff_t __desired) noexcept
      : _M_sem(__desired)
      { __glibcxx_assert(__desired >= 0 && __desired <= max()); }
 
      ~counting_semaphore() = default;
 
      counting_semaphore(const counting_semaphore&) = delete;
      counting_semaphore& operator=(const counting_semaphore&) = delete;
 
      static constexpr ptrdiff_t
      max() noexcept
      { return __least_max_value; }
 
      void
      release(ptrdiff_t __update = 1) noexcept
      {
        [[maybe_unused]] ptrdiff_t __old = _M_sem._M_release(__update);
        __glibcxx_assert(__update >= 0 && __update <= max() - __old);
      }
 
      void
      acquire() noexcept(noexcept(_M_sem._M_acquire()))
      { _M_sem._M_acquire(); }
 
      bool
      try_acquire() noexcept(noexcept(_M_sem._M_try_acquire()))
      { return _M_sem._M_try_acquire(); }
 
      template<typename _Rep, typename _Period>
        bool
        try_acquire_for(const std::chrono::duration<_Rep, _Period>& __rtime)
        { return _M_sem._M_try_acquire_for(__rtime); }
 
      template<typename _Clock, typename _Dur>
        bool
        try_acquire_until(const std::chrono::time_point<_Clock, _Dur>& __atime)
        { return _M_sem._M_try_acquire_until(__atime); }
    };
 
  /** @brief A binary semaphore
   *
   * @since C++20
   */
  using binary_semaphore = std::counting_semaphore<1>;
 
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif // __cpp_lib_semaphore
#endif // _GLIBCXX_SEMAPHORE