awaitable.hpp
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//
// awaitable.hpp
// ~~~~~~~~~~~~~
//
// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#ifndef ASIO_AWAITABLE_HPP
#define ASIO_AWAITABLE_HPP
#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
#include "asio/detail/config.hpp"
#if defined(ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
#if defined(ASIO_HAS_STD_COROUTINE)
# include <coroutine>
#else // defined(ASIO_HAS_STD_COROUTINE)
# include <experimental/coroutine>
#endif // defined(ASIO_HAS_STD_COROUTINE)
#include "asio/any_io_executor.hpp"
#include "asio/detail/push_options.hpp"
namespace asio {
namespace detail {
#if defined(ASIO_HAS_STD_COROUTINE)
using std::coroutine_handle;
using std::suspend_always;
#else // defined(ASIO_HAS_STD_COROUTINE)
using std::experimental::coroutine_handle;
using std::experimental::suspend_always;
#endif // defined(ASIO_HAS_STD_COROUTINE)
template <typename> class awaitable_thread;
template <typename, typename> class awaitable_frame;
} // namespace detail
/// The return type of a coroutine or asynchronous operation.
template <typename T, typename Executor = any_io_executor>
class awaitable
{
public:
/// The type of the awaited value.
typedef T value_type;
/// The executor type that will be used for the coroutine.
typedef Executor executor_type;
/// Default constructor.
constexpr awaitable() noexcept
: frame_(nullptr)
{
}
/// Move constructor.
awaitable(awaitable&& other) noexcept
: frame_(std::exchange(other.frame_, nullptr))
{
}
/// Destructor
~awaitable()
{
if (frame_)
frame_->destroy();
}
/// Checks if the awaitable refers to a future result.
bool valid() const noexcept
{
return !!frame_;
}
#if !defined(GENERATING_DOCUMENTATION)
// Support for co_await keyword.
bool await_ready() const noexcept
{
return false;
}
// Support for co_await keyword.
template <class U>
void await_suspend(
detail::coroutine_handle<detail::awaitable_frame<U, Executor>> h)
{
frame_->push_frame(&h.promise());
}
// Support for co_await keyword.
T await_resume()
{
return awaitable(static_cast<awaitable&&>(*this)).frame_->get();
}
#endif // !defined(GENERATING_DOCUMENTATION)
private:
template <typename> friend class detail::awaitable_thread;
template <typename, typename> friend class detail::awaitable_frame;
// Not copy constructible or copy assignable.
awaitable(const awaitable&) = delete;
awaitable& operator=(const awaitable&) = delete;
// Construct the awaitable from a coroutine's frame object.
explicit awaitable(detail::awaitable_frame<T, Executor>* a)
: frame_(a)
{
}
detail::awaitable_frame<T, Executor>* frame_;
};
} // namespace asio
#include "asio/detail/pop_options.hpp"
#include "asio/impl/awaitable.hpp"
#endif // defined(ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
#endif // ASIO_AWAITABLE_HPP