std_mutex.h

Go to the documentation of this file.

// std::mutex implementation -*- C++ -*-

// Copyright (C) 2003-2017 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/std_mutex.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{mutex}
 */

#ifndef _GLIBCXX_MUTEX_H
#define _GLIBCXX_MUTEX_H 1

#pragma GCC system_header

#if __cplusplus < 201103L
# include <bits/c++0x_warning.h>
#else

#include <system_error>
#include <bits/functexcept.h>
#include <bits/gthr.h>
#include <bits/move.h> // for std::swap

#ifdef _GLIBCXX_USE_C99_STDINT_TR1

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  /**
   * @defgroup mutexes Mutexes
   * @ingroup concurrency
   *
   * Classes for mutex support.
   * @{
   */

#ifdef _GLIBCXX_HAS_GTHREADS
  // Common base class for std::mutex and std::timed_mutex
  class __mutex_base
  {
  protected:
    typedef __gthread_mutex_t                   __native_type;

#ifdef __GTHREAD_MUTEX_INIT
    __native_type  _M_mutex = __GTHREAD_MUTEX_INIT;

    constexpr __mutex_base() noexcept = default;
#else
    __native_type  _M_mutex;

    __mutex_base() noexcept
    {
      // XXX EAGAIN, ENOMEM, EPERM, EBUSY(may), EINVAL(may)
      __GTHREAD_MUTEX_INIT_FUNCTION(&_M_mutex);
    }

    ~__mutex_base() noexcept { __gthread_mutex_destroy(&_M_mutex); }
#endif

    __mutex_base(const __mutex_base&) = delete;
    __mutex_base& operator=(const __mutex_base&) = delete;
  };

  /// The standard mutex type.
  class mutex : private __mutex_base
  {
  public:
    typedef __native_type*                      native_handle_type;

#ifdef __GTHREAD_MUTEX_INIT
    constexpr
#endif
    mutex() noexcept = default;
    ~mutex() = default;

    mutex(const mutex&) = delete;
    mutex& operator=(const mutex&) = delete;

    void
    lock()
    {
      int __e = __gthread_mutex_lock(&_M_mutex);

      // EINVAL, EAGAIN, EBUSY, EINVAL, EDEADLK(may)
      if (__e)
        __throw_system_error(__e);
    }

    bool
    try_lock() noexcept
    {
      // XXX EINVAL, EAGAIN, EBUSY
      return !__gthread_mutex_trylock(&_M_mutex);
    }

    void
    unlock()
    {
      // XXX EINVAL, EAGAIN, EPERM
      __gthread_mutex_unlock(&_M_mutex);
    }

    native_handle_type
    native_handle() noexcept
    { return &_M_mutex; }
  };

#endif // _GLIBCXX_HAS_GTHREADS

  /// Do not acquire ownership of the mutex.
  struct defer_lock_t { explicit defer_lock_t() = default; };

  /// Try to acquire ownership of the mutex without blocking.
  struct try_to_lock_t { explicit try_to_lock_t() = default; };

  /// Assume the calling thread has already obtained mutex ownership
  /// and manage it.
  struct adopt_lock_t { explicit adopt_lock_t() = default; };

  /// Tag used to prevent a scoped lock from acquiring ownership of a mutex.
  _GLIBCXX17_INLINE constexpr defer_lock_t      defer_lock { };

  /// Tag used to prevent a scoped lock from blocking if a mutex is locked.
  _GLIBCXX17_INLINE constexpr try_to_lock_t     try_to_lock { };

  /// Tag used to make a scoped lock take ownership of a locked mutex.
  _GLIBCXX17_INLINE constexpr adopt_lock_t      adopt_lock { };

  /** @brief A simple scoped lock type.
   *
   * A lock_guard controls mutex ownership within a scope, releasing
   * ownership in the destructor.
   */
  template<typename _Mutex>
    class lock_guard
    {
    public:
      typedef _Mutex mutex_type;

      explicit lock_guard(mutex_type& __m) : _M_device(__m)
      { _M_device.lock(); }

      lock_guard(mutex_type& __m, adopt_lock_t) noexcept : _M_device(__m)
      { } // calling thread owns mutex

      ~lock_guard()
      { _M_device.unlock(); }

      lock_guard(const lock_guard&) = delete;
      lock_guard& operator=(const lock_guard&) = delete;

    private:
      mutex_type&  _M_device;
    };

  /** @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.
   */
  template<typename _Mutex>
    class unique_lock
    {
    public:
      typedef _Mutex mutex_type;

      unique_lock() noexcept
      : _M_device(0), _M_owns(false)
      { }

      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)
      { }

      unique_lock(mutex_type& __m, try_to_lock_t)
      : _M_device(std::__addressof(__m)), _M_owns(_M_device->try_lock())
      { }

      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>
        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>
        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
      {
        if(_M_owns)
          unlock();

        unique_lock(std::move(__u)).swap(*this);

        __u._M_device = 0;
        __u._M_owns = false;

        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;
          }
      }

      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>
        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>
        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;
      }

      bool
      owns_lock() const noexcept
      { return _M_owns; }

      explicit operator bool() const noexcept
      { return owns_lock(); }

      mutex_type*
      mutex() const noexcept
      { return _M_device; }

    private:
      mutex_type*       _M_device;
      bool              _M_owns; // XXX use atomic_bool
    };

  /// Swap overload for unique_lock objects.
  template<typename _Mutex>
    inline void
    swap(unique_lock<_Mutex>& __x, unique_lock<_Mutex>& __y) noexcept
    { __x.swap(__y); }

  // @} group mutexes
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif // _GLIBCXX_USE_C99_STDINT_TR1

#endif // C++11

#endif // _GLIBCXX_MUTEX_H