coroutine

// <coroutine> -*- 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/coroutine
 *  This is a Standard C++ Library header.
 */

#ifndef _GLIBCXX_COROUTINE
#define _GLIBCXX_COROUTINE 1

#pragma GCC system_header

// It is very likely that earlier versions would work, but they are untested.
#if __cplusplus >= 201402L

#include <bits/c++config.h>

/**
 * @defgroup coroutines Coroutines
 *
 * Components for supporting coroutine implementations.
 */

#if __cplusplus > 201703L && __cpp_impl_three_way_comparison >= 201907L
#  include <compare>
#  define _COROUTINES_USE_SPACESHIP 1
#else
#  include <bits/stl_function.h> // for std::less
#  define _COROUTINES_USE_SPACESHIP 0
#endif

namespace std _GLIBCXX_VISIBILITY (default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

#if __cpp_impl_coroutine

#define __cpp_lib_coroutine 201902L

  inline namespace __n4861 {

  // 17.12.2 coroutine traits
  /// [coroutine.traits]
  /// [coroutine.traits.primary]
  /// If _Result::promise_type is valid and denotes a type then the traits
  /// have a single publicly accessible member, otherwise they are empty.
  template <typename _Result, typename = void>
   struct __coroutine_traits_impl {};

  template <typename _Result>
    struct __coroutine_traits_impl<_Result,
				    __void_t<typename _Result::promise_type>>
    {
      using promise_type = typename _Result::promise_type;
    };

  template <typename _Result, typename...>
    struct coroutine_traits : __coroutine_traits_impl<_Result> {};

  // 17.12.3 Class template coroutine_handle
  /// [coroutine.handle]
  template <typename _Promise = void>
    struct coroutine_handle;

  template <> struct
    coroutine_handle<void>
    {
    public:
      // 17.12.3.1, construct/reset
      constexpr coroutine_handle() noexcept : _M_fr_ptr(0) {}

      constexpr coroutine_handle(std::nullptr_t __h) noexcept
	: _M_fr_ptr(__h)
      {}

      coroutine_handle& operator=(std::nullptr_t) noexcept
      {
	_M_fr_ptr = nullptr;
	return *this;
      }

    public:
      // 17.12.3.2, export/import
      constexpr void* address() const noexcept { return _M_fr_ptr; }

      constexpr static coroutine_handle from_address(void* __a) noexcept
      {
	coroutine_handle __self;
	__self._M_fr_ptr = __a;
	return __self;
      }

    public:
      // 17.12.3.3, observers
      constexpr explicit operator bool() const noexcept
      {
	return bool(_M_fr_ptr);
      }

      bool done() const noexcept { return __builtin_coro_done(_M_fr_ptr); }

      // 17.12.3.4, resumption
      void operator()() const { resume(); }

      void resume() const { __builtin_coro_resume(_M_fr_ptr); }

      void destroy() const { __builtin_coro_destroy(_M_fr_ptr); }

    protected:
      void* _M_fr_ptr;
  };

  // 17.12.3.6 Comparison operators
  /// [coroutine.handle.compare]
  constexpr bool operator==(coroutine_handle<> __a,
			    coroutine_handle<> __b) noexcept
  {
    return __a.address() == __b.address();
  }

#if _COROUTINES_USE_SPACESHIP
  constexpr strong_ordering
  operator<=>(coroutine_handle<> __a, coroutine_handle<> __b) noexcept
  { return std::compare_three_way()(__a.address(), __b.address()); }
#else
  // These are to enable operation with std=c++14,17.
  constexpr bool operator!=(coroutine_handle<> __a,
			    coroutine_handle<> __b) noexcept
  {
    return !(__a == __b);
  }

  constexpr bool operator<(coroutine_handle<> __a,
			   coroutine_handle<> __b) noexcept
  {
    return less<void*>()(__a.address(), __b.address());
  }

  constexpr bool operator>(coroutine_handle<> __a,
			   coroutine_handle<> __b) noexcept
  {
    return __b < __a;
  }

  constexpr bool operator<=(coroutine_handle<> __a,
			    coroutine_handle<> __b) noexcept
  {
    return !(__a > __b);
  }

  constexpr bool operator>=(coroutine_handle<> __a,
			    coroutine_handle<> __b) noexcept
  {
    return !(__a < __b);
  }
#endif

  template <typename _Promise>
    struct coroutine_handle : coroutine_handle<>
    {
      // 17.12.3.1, construct/reset
      using coroutine_handle<>::coroutine_handle;

      static coroutine_handle from_promise(_Promise& p)
      {
	coroutine_handle __self;
	__self._M_fr_ptr
	  = __builtin_coro_promise((char*) &p, __alignof(_Promise), true);
	return __self;
      }

      coroutine_handle& operator=(std::nullptr_t) noexcept
      {
	coroutine_handle<>::operator=(nullptr);
	return *this;
      }

    // 17.12.3.2, export/import
    constexpr static coroutine_handle from_address(void* __a)
    {
      coroutine_handle __self;
      __self._M_fr_ptr = __a;
      return __self;
    }

    // 17.12.3.5, promise accesss
    _Promise& promise() const
    {
      void* __t
	= __builtin_coro_promise (this->_M_fr_ptr, __alignof(_Promise), false);
      return *static_cast<_Promise*>(__t);
    }
  };

  /// [coroutine.noop]
  struct noop_coroutine_promise
  {
  };

  void __dummy_resume_destroy() __attribute__((__weak__));
  void __dummy_resume_destroy() {}

  struct __noop_coro_frame
  {
    void (*__r)() = __dummy_resume_destroy;
    void (*__d)() = __dummy_resume_destroy;
    struct noop_coroutine_promise __p;
  } __noop_coro_fr __attribute__((__weak__));

  // 17.12.4.1 Class noop_coroutine_promise
  /// [coroutine.promise.noop]
  template <>
    struct coroutine_handle<noop_coroutine_promise> : public coroutine_handle<>
    {
      using _Promise = noop_coroutine_promise;

    public:
      // 17.12.4.2.1, observers
      constexpr explicit operator bool() const noexcept { return true; }

      constexpr bool done() const noexcept { return false; }

      // 17.12.4.2.2, resumption
      void operator()() const noexcept {}

      void resume() const noexcept {}

      void destroy() const noexcept {}

      // 17.12.4.2.3, promise access
      _Promise& promise() const
      {
	return *static_cast<_Promise*>(
	  __builtin_coro_promise(this->_M_fr_ptr, __alignof(_Promise), false));
      }

      // 17.12.4.2.4, address
    private:
      friend coroutine_handle<noop_coroutine_promise> noop_coroutine() noexcept;

      coroutine_handle() noexcept { this->_M_fr_ptr = (void*) &__noop_coro_fr; }
    };

  using noop_coroutine_handle = coroutine_handle<noop_coroutine_promise>;

  inline noop_coroutine_handle noop_coroutine() noexcept
  {
    return noop_coroutine_handle();
  }

  // 17.12.5 Trivial awaitables
  /// [coroutine.trivial.awaitables]
  struct suspend_always
  {
    bool await_ready() { return false; }

    void await_suspend(coroutine_handle<>) {}

    void await_resume() {}
  };

  struct suspend_never
  {
    bool await_ready() { return true; }

    void await_suspend(coroutine_handle<>) {}

    void await_resume() {}
  };

  } // namespace __n4861

#else
#error "the coroutine header requires -fcoroutines"
#endif

  _GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

#endif // C++14 (we are allowing use from at least this)

#endif // _GLIBCXX_COROUTINE