axmol/thirdparty/yasio/cxx17/shared_mutex.hpp

//////////////////////////////////////////////////////////////////////////////////////////
// A multi-platform support c++11 library with focus on asynchronous socket I/O for any
// client application.
//////////////////////////////////////////////////////////////////////////////////////////
/*
The MIT License (MIT)

Copyright (c) 2012-2021 HALX99
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

#ifndef YASIO__SHARED_MUTEX_HPP
#define YASIO__SHARED_MUTEX_HPP

#include "yasio/compiler/feature_test.hpp"

/// The shared_mutex workaround on c++11
#if YASIO__HAS_CXX17 && !defined(__APPLE__)
#  include <shared_mutex>
#else
#  include <system_error>
#  include <mutex>
#  include <condition_variable>
#  define yaso__throw_error(e) YASIO__THROW0(std::system_error(std::make_error_code(e), ""))
namespace cxx17
{
// CLASS TEMPLATE shared_mutex, copy from: https://github.com/boostorg/thread/blob/develop/include/boost/thread/v2/shared_mutex.hpp
class shared_mutex {
  typedef std::mutex mutex_t;
  typedef std::condition_variable cond_t;
  typedef unsigned count_t;

  mutex_t mut_;
  cond_t gate1_;
  // the gate2_ condition variable is only used by functions that
  // have taken write_entered_ but are waiting for no_readers()
  cond_t gate2_;
  count_t state_;

  static const count_t write_entered_ = 1U << (sizeof(count_t) * CHAR_BIT - 1);
  static const count_t n_readers_     = ~write_entered_;

  bool no_writer() const { return (state_ & write_entered_) == 0; }

  bool one_writer() const { return (state_ & write_entered_) != 0; }

  bool no_writer_no_readers() const
  {
    // return (state_ & write_entered_) == 0 &&
    //       (state_ & n_readers_) == 0;
    return state_ == 0;
  }

  bool no_writer_no_max_readers() const { return (state_ & write_entered_) == 0 && (state_ & n_readers_) != n_readers_; }

  bool no_readers() const { return (state_ & n_readers_) == 0; }

  bool one_or_more_readers() const { return (state_ & n_readers_) > 0; }

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

public:
  shared_mutex() : state_(0) {}
  ~shared_mutex() { std::lock_guard<mutex_t> _(mut_); }

  // Exclusive ownership

  void lock()
  {
    std::unique_lock<mutex_t> lk(mut_);
    gate1_.wait(lk, std::bind(&shared_mutex::no_writer, std::ref(*this)));
    state_ |= write_entered_;
    gate2_.wait(lk, std::bind(&shared_mutex::no_readers, std::ref(*this)));
  }
  bool try_lock()
  {
    std::unique_lock<mutex_t> lk(mut_);
    if (!no_writer_no_readers())
    {
      return false;
    }
    state_ = write_entered_;
    return true;
  }
  void unlock()
  {
    std::lock_guard<mutex_t> _(mut_);
    assert(one_writer());
    assert(no_readers());
    state_ = 0;
    // notify all since multiple *lock_shared*() calls may be able
    // to proceed in response to this notification
    gate1_.notify_all();
  }

  // Shared ownership

  void lock_shared()
  {
    std::unique_lock<mutex_t> lk(mut_);
    gate1_.wait(lk, std::bind(&shared_mutex::no_writer_no_max_readers, std::ref(*this)));
    count_t num_readers = (state_ & n_readers_) + 1;
    state_ &= ~n_readers_;
    state_ |= num_readers;
  }
  bool try_lock_shared()
  {
    std::unique_lock<mutex_t> lk(mut_);
    if (!no_writer_no_max_readers())
    {
      return false;
    }
    count_t num_readers = (state_ & n_readers_) + 1;
    state_ &= ~n_readers_;
    state_ |= num_readers;
    return true;
  }
  void unlock_shared()
  {
    std::lock_guard<mutex_t> _(mut_);
    assert(one_or_more_readers());
    count_t num_readers = (state_ & n_readers_) - 1;
    state_ &= ~n_readers_;
    state_ |= num_readers;
    if (no_writer())
    {
      if (num_readers == n_readers_ - 1)
        gate1_.notify_one();
    }
    else
    {
      if (num_readers == 0)
        gate2_.notify_one();
    }
  }
};

// CLASS TEMPLATE shared_lock
template <class _Mutex>
class shared_lock {
public:
  using mutex_type = _Mutex;

  shared_lock() : _Pmtx(nullptr), _Owns(false) {}

  explicit shared_lock(mutex_type& _Mtx) : _Pmtx(YASIO__STD addressof(_Mtx)), _Owns(true)
  { // construct with mutex and lock shared
    _Mtx.lock_shared();
  }

  explicit shared_lock(mutex_type& _Mtx, YASIO__STD defer_lock_t) : _Pmtx(YASIO__STD addressof(_Mtx)), _Owns(false) {} // // construct with unlocked mutex

  explicit shared_lock(mutex_type& _Mtx, YASIO__STD try_to_lock_t)
      : _Pmtx(YASIO__STD addressof(_Mtx)), _Owns(_Mtx.try_lock_shared()) {} // construct with mutex and try to lock shared

  explicit shared_lock(mutex_type& _Mtx, YASIO__STD adopt_lock_t) : _Pmtx(YASIO__STD addressof(_Mtx)), _Owns(true) {} // construct with mutex and adopt owership

  ~shared_lock()
  {
    if (_Owns)
      _Pmtx->unlock_shared();
  }

  shared_lock(shared_lock&& _Other) : _Pmtx(_Other._Pmtx), _Owns(_Other._Owns)
  {
    _Other._Pmtx = nullptr;
    _Other._Owns = false;
  }

  shared_lock& operator=(shared_lock&& _Right)
  {
    if (_Owns)
      _Pmtx->unlock_shared();

    _Pmtx        = _Right._Pmtx;
    _Owns        = _Right._Owns;
    _Right._Pmtx = nullptr;
    _Right._Owns = false;
    return *this;
  }

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

  void lock()
  { // lock the mutex
    _Validate();
    _Pmtx->lock_shared();
    _Owns = true;
  }

  bool try_lock()
  { // try to lock the mutex
    _Validate();
    _Owns = _Pmtx->try_lock_shared();
    return _Owns;
  }

  void unlock()
  { // try to unlock the mutex
    if (!_Pmtx || !_Owns)
      yaso__throw_error(std::errc::operation_not_permitted);

    _Pmtx->unlock_shared();
    _Owns = false;
  }

  // MUTATE
  void swap(shared_lock& _Right)
  {
    YASIO__STD swap(_Pmtx, _Right._Pmtx);
    YASIO__STD swap(_Owns, _Right._Owns);
  }

  mutex_type* release()
  {
    _Mutex* _Res = _Pmtx;
    _Pmtx        = nullptr;
    _Owns        = false;
    return _Res;
  }

  // OBSERVE
  bool owns_lock() const { return _Owns; }

  explicit operator bool() const { return _Owns; }

  mutex_type* mutex() const { return _Pmtx; }

private:
  _Mutex* _Pmtx;
  bool _Owns;

  void _Validate() const
  { // check if the mutex can be locked
    if (!_Pmtx)
      yaso__throw_error(std::errc::operation_not_permitted);

    if (_Owns)
      yaso__throw_error(std::errc::resource_deadlock_would_occur);
  }
};
} // namespace cxx17
#endif

#endif