gcc/libstdc++-v3/include/std/stop_token

// <stop_token> -*- C++ -*-

// Copyright (C) 2019-2020 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/stop_token
 *  This is a Standard C++ Library header.
 */

#ifndef _GLIBCXX_STOP_TOKEN
#define _GLIBCXX_STOP_TOKEN

#if __cplusplus > 201703L

#include <atomic>
#include <bits/std_mutex.h>
#include <ext/concurrence.h>
#include <bits/unique_ptr.h>
#include <bits/shared_ptr.h>

#ifdef _GLIBCXX_HAS_GTHREADS
# define __cpp_lib_jthread 201907L
#endif

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  /// Tag type indicating a stop_source should have no shared-stop-state.
  struct nostopstate_t { explicit nostopstate_t() = default; };
  inline constexpr nostopstate_t nostopstate{};

  /// Allow testing whether a stop request has been made on a `stop_source`.
  class stop_token
  {
  public:
    stop_token() noexcept = default;

    stop_token(const stop_token& __other) noexcept = default;
    stop_token(stop_token&& __other) noexcept = default;

    ~stop_token() = default;

    stop_token&
    operator=(const stop_token& __rhs) noexcept = default;

    stop_token&
    operator=(stop_token&& __rhs) noexcept = default;

    [[nodiscard]]
    bool
    stop_possible() const noexcept
    {
      return static_cast<bool>(_M_state);
    }

    [[nodiscard]]
    bool
    stop_requested() const noexcept
    {
      return stop_possible() && _M_state->_M_stop_requested();
    }

    void
    swap(stop_token& __rhs) noexcept
    { _M_state.swap(__rhs._M_state); }

    [[nodiscard]]
    friend bool
    operator==(const stop_token& __a, const stop_token& __b)
    { return __a._M_state == __b._M_state; }

    friend void
    swap(stop_token& __lhs, stop_token& __rhs) noexcept
    { __lhs.swap(__rhs); }

  private:
    friend class stop_source;
    template<typename _Callback>
      friend class stop_callback;

    struct _Stop_cb
    {
      void(*_M_callback)(_Stop_cb*);
      _Stop_cb* _M_prev = nullptr;
      _Stop_cb* _M_next = nullptr;

      template<typename _Cb>
	_Stop_cb(_Cb&& __cb)
	: _M_callback(std::forward<_Cb>(__cb))
	{ }

      bool
      _M_linked() const noexcept
      {
        return (_M_prev != nullptr)
          || (_M_next != nullptr);
      }

      static void
      _S_execute(_Stop_cb* __cb) noexcept
      {
        __cb->_M_callback(__cb);
        __cb->_M_prev = __cb->_M_next = nullptr;
      }
    };

    struct _Stop_state_t
    {
      std::atomic<bool> _M_stopped{false};
      _Stop_cb* _M_head = nullptr;
#ifdef _GLIBCXX_HAS_GTHREADS
      std::mutex _M_mtx;
#endif

      _Stop_state_t() = default;

      bool
      _M_stop_requested() noexcept
      {
        return _M_stopped;
      }

      bool
      _M_request_stop()
      {
        bool __stopped = false;
        if (_M_stopped.compare_exchange_strong(__stopped, true))
          {
#ifdef _GLIBCXX_HAS_GTHREADS
            std::lock_guard<std::mutex> __lck{_M_mtx};
#endif
            while (_M_head)
              {
                auto __p = _M_head;
                _M_head = _M_head->_M_next;
                _Stop_cb::_S_execute(__p);
              }
            return true;
          }
        return false;
      }

      bool
      _M_register_callback(_Stop_cb* __cb)
      {
#ifdef _GLIBCXX_HAS_GTHREADS
        std::lock_guard<std::mutex> __lck{_M_mtx};
#endif
        if (_M_stopped)
          return false;

        __cb->_M_next = _M_head;
        if (_M_head)
          {
            _M_head->_M_prev = __cb;
          }
        _M_head = __cb;
        return true;
      }

      void
      _M_remove_callback(_Stop_cb* __cb)
      {
#ifdef _GLIBCXX_HAS_GTHREADS
        std::lock_guard<std::mutex> __lck{_M_mtx};
#endif
        if (__cb == _M_head)
          {
            _M_head = _M_head->_M_next;
            if (_M_head)
              {
                _M_head->_M_prev = nullptr;
              }
          }
        else if (!__cb->_M_linked())
          {
            return;
          }
        else
          {
            __cb->_M_prev->_M_next = __cb->_M_next;
            if (__cb->_M_next)
              {
                __cb->_M_next->_M_prev = __cb->_M_prev;
              }
          }
      }
    };

    using _Stop_state = std::shared_ptr<_Stop_state_t>;
    _Stop_state _M_state;

    explicit
    stop_token(const _Stop_state& __state) noexcept
    : _M_state{__state}
    { }
  };

  /// A type that allows a stop request to be made.
  class stop_source
  {
  public:
    stop_source()
      : _M_state(std::make_shared<stop_token::_Stop_state_t>())
    { }

    explicit stop_source(std::nostopstate_t) noexcept
    { }

    stop_source(const stop_source& __other) noexcept
      : _M_state(__other._M_state)
    { }

    stop_source(stop_source&& __other) noexcept
      : _M_state(std::move(__other._M_state))
    { }

    stop_source&
    operator=(const stop_source& __rhs) noexcept
    {
      if (_M_state != __rhs._M_state)
        _M_state = __rhs._M_state;
      return *this;
    }

    stop_source&
    operator=(stop_source&& __rhs) noexcept
    {
      std::swap(_M_state, __rhs._M_state);
      return *this;
    }

    [[nodiscard]]
    bool
    stop_possible() const noexcept
    {
      return static_cast<bool>(_M_state);
    }

    [[nodiscard]]
    bool
    stop_requested() const noexcept
    {
      return stop_possible() && _M_state->_M_stop_requested();
    }

    bool
    request_stop() const noexcept
    {
      if (stop_possible())
        return _M_state->_M_request_stop();
      return false;
    }

    [[nodiscard]]
    stop_token
    get_token() const noexcept
    {
      return stop_token{_M_state};
    }

    void
    swap(stop_source& __other) noexcept
    {
      _M_state.swap(__other._M_state);
    }

    [[nodiscard]]
    friend bool
    operator==(const stop_source& __a, const stop_source& __b) noexcept
    {
      return __a._M_state == __b._M_state;
    }

    friend void
    swap(stop_source& __lhs, stop_source& __rhs) noexcept
    {
      __lhs.swap(__rhs);
    }

  private:
    stop_token::_Stop_state _M_state;
  };

  /// A wrapper for callbacks to be run when a stop request is made.
  template<typename _Callback>
    class [[nodiscard]] stop_callback
      : private stop_token::_Stop_cb
    {
    public:
      using callback_type = _Callback;

      template<typename _Cb,
               enable_if_t<is_constructible_v<_Callback, _Cb>, int> = 0>
        explicit
	stop_callback(const stop_token& __token, _Cb&& __cb)
        noexcept(is_nothrow_constructible_v<_Callback, _Cb>)
        : _Stop_cb(&_S_execute), _M_cb(std::forward<_Cb>(__cb))
        {
	  if (auto __state = __token._M_state)
	    {
	      if (__state->_M_stop_requested())
		_S_execute(this); // ensures std::terminate on throw
	      else if (__state->_M_register_callback(this))
		_M_state.swap(__state);
	    }
        }

      template<typename _Cb,
               enable_if_t<is_constructible_v<_Callback, _Cb>, int> = 0>
        explicit
	stop_callback(stop_token&& __token, _Cb&& __cb)
        noexcept(is_nothrow_constructible_v<_Callback, _Cb>)
        : _Stop_cb(&_S_execute), _M_cb(std::forward<_Cb>(__cb))
	{
	  if (auto& __state = __token._M_state)
	    {
	      if (__state->_M_stop_requested())
		_S_execute(this); // ensures std::terminate on throw
	      else if (__state->_M_register_callback(this))
		_M_state.swap(__state);
	    }
	}

      ~stop_callback()
      {
	if (_M_state)
	  {
	    _M_state->_M_remove_callback(this);
	  }
      }

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

    private:
      _Callback _M_cb;
      stop_token::_Stop_state _M_state = nullptr;

      static void
      _S_execute(_Stop_cb* __that) noexcept
      {
	static_cast<stop_callback*>(__that)->_M_cb();
      }
    };

  template<typename _Callback>
    stop_callback(stop_token, _Callback) -> stop_callback<_Callback>;

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
#endif // __cplusplus > 201703L
#endif // _GLIBCXX_STOP_TOKEN