unique_lock.h

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// std::unique_lock implementation -*- C++ -*-
 
// Copyright (C) 2008-2025 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 bits/unique_lock.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{mutex}
 */
 
#ifndef _GLIBCXX_UNIQUE_LOCK_H
#define _GLIBCXX_UNIQUE_LOCK_H 1
 
#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif
 
#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else
 
#include <bits/chrono.h>
#include <bits/error_constants.h> // for std::errc
#include <bits/move.h> // for std::swap
#include <bits/std_mutex.h> // for std::defer_lock_t
 
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
 
  /** @brief A movable scoped lock type.
   *
   * A unique_lock controls mutex ownership within a scope. Ownership of the
   * mutex can be delayed until after construction and can be transferred
   * to another unique_lock by move construction or move assignment. If a
   * mutex lock is owned when the destructor runs ownership will be released.
   *
   * @headerfile mutex
   * @ingroup mutexes
   * @since C++11
   */
  template<typename _Mutex>
    class unique_lock
    {
    public:
      typedef _Mutex mutex_type;
 
      unique_lock() noexcept
      : _M_device(0), _M_owns(false)
      { }
 
      [[__nodiscard__]]
      explicit unique_lock(mutex_type& __m)
      : _M_device(std::__addressof(__m)), _M_owns(false)
      {
        lock();
        _M_owns = true;
      }
 
      unique_lock(mutex_type& __m, defer_lock_t) noexcept
      : _M_device(std::__addressof(__m)), _M_owns(false)
      { }
 
      [[__nodiscard__]]
      unique_lock(mutex_type& __m, try_to_lock_t)
      : _M_device(std::__addressof(__m)), _M_owns(_M_device->try_lock())
      { }
 
      [[__nodiscard__]]
      unique_lock(mutex_type& __m, adopt_lock_t) noexcept
      : _M_device(std::__addressof(__m)), _M_owns(true)
      {
        // XXX calling thread owns mutex
      }
 
      template<typename _Clock, typename _Duration>
        [[__nodiscard__]]
        unique_lock(mutex_type& __m,
                    const chrono::time_point<_Clock, _Duration>& __atime)
        : _M_device(std::__addressof(__m)),
          _M_owns(_M_device->try_lock_until(__atime))
        { }
 
      template<typename _Rep, typename _Period>
        [[__nodiscard__]]
        unique_lock(mutex_type& __m,
                    const chrono::duration<_Rep, _Period>& __rtime)
        : _M_device(std::__addressof(__m)),
          _M_owns(_M_device->try_lock_for(__rtime))
        { }
 
      ~unique_lock()
      {
        if (_M_owns)
          unlock();
      }
 
      unique_lock(const unique_lock&) = delete;
      unique_lock& operator=(const unique_lock&) = delete;
 
      unique_lock(unique_lock&& __u) noexcept
      : _M_device(__u._M_device), _M_owns(__u._M_owns)
      {
        __u._M_device = 0;
        __u._M_owns = false;
      }
 
      unique_lock& operator=(unique_lock&& __u) noexcept
      {
        // _GLIBCXX_RESOLVE_LIB_DEFECTS
        // 4172. unique_lock self-move-assignment is broken
        unique_lock(std::move(__u)).swap(*this);
        return *this;
      }
 
      void
      lock()
      {
        if (!_M_device)
          __throw_system_error(int(errc::operation_not_permitted));
        else if (_M_owns)
          __throw_system_error(int(errc::resource_deadlock_would_occur));
        else
          {
            _M_device->lock();
            _M_owns = true;
          }
      }
 
      _GLIBCXX_NODISCARD
      bool
      try_lock()
      {
        if (!_M_device)
          __throw_system_error(int(errc::operation_not_permitted));
        else if (_M_owns)
          __throw_system_error(int(errc::resource_deadlock_would_occur));
        else
          {
            _M_owns = _M_device->try_lock();
            return _M_owns;
          }
      }
 
      template<typename _Clock, typename _Duration>
        _GLIBCXX_NODISCARD
        bool
        try_lock_until(const chrono::time_point<_Clock, _Duration>& __atime)
        {
          if (!_M_device)
            __throw_system_error(int(errc::operation_not_permitted));
          else if (_M_owns)
            __throw_system_error(int(errc::resource_deadlock_would_occur));
          else
            {
              _M_owns = _M_device->try_lock_until(__atime);
              return _M_owns;
            }
        }
 
      template<typename _Rep, typename _Period>
        _GLIBCXX_NODISCARD
        bool
        try_lock_for(const chrono::duration<_Rep, _Period>& __rtime)
        {
          if (!_M_device)
            __throw_system_error(int(errc::operation_not_permitted));
          else if (_M_owns)
            __throw_system_error(int(errc::resource_deadlock_would_occur));
          else
            {
              _M_owns = _M_device->try_lock_for(__rtime);
              return _M_owns;
            }
         }
 
      void
      unlock()
      {
        if (!_M_owns)
          __throw_system_error(int(errc::operation_not_permitted));
        else if (_M_device)
          {
            _M_device->unlock();
            _M_owns = false;
          }
      }
 
      void
      swap(unique_lock& __u) noexcept
      {
        std::swap(_M_device, __u._M_device);
        std::swap(_M_owns, __u._M_owns);
      }
 
      mutex_type*
      release() noexcept
      {
        mutex_type* __ret = _M_device;
        _M_device = 0;
        _M_owns = false;
        return __ret;
      }
 
      _GLIBCXX_NODISCARD
      bool
      owns_lock() const noexcept
      { return _M_owns; }
 
      explicit operator bool() const noexcept
      { return owns_lock(); }
 
      _GLIBCXX_NODISCARD
      mutex_type*
      mutex() const noexcept
      { return _M_device; }
 
    private:
      mutex_type*       _M_device;
      bool              _M_owns;
    };
 
  /// Swap overload for unique_lock objects.
  /// @relates unique_lock
  template<typename _Mutex>
    inline void
    swap(unique_lock<_Mutex>& __x, unique_lock<_Mutex>& __y) noexcept
    { __x.swap(__y); }
 
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
 
#endif // C++11
#endif // _GLIBCXX_UNIQUE_LOCK_H