boost/asio/awaitable.hpp

0001 //
0002 // awaitable.hpp
0003 // ~~~~~~~~~~~~~
0004 //
0005 // Copyright (c) 2003-2023 Christopher M. Kohlhoff (chris at kohlhoff dot com)
0006 //
0007 // Distributed under the Boost Software License, Version 1.0. (See accompanying
0008 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
0009 //
0010
0011 #ifndef BOOST_ASIO_AWAITABLE_HPP
0012 #define BOOST_ASIO_AWAITABLE_HPP
0013
0014 #if defined(_MSC_VER) && (_MSC_VER >= 1200)
0015 # pragma once
0016 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
0017
0018 #include <boost/asio/detail/config.hpp>
0019
0020 #if defined(BOOST_ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
0021
0022 #if defined(BOOST_ASIO_HAS_STD_COROUTINE)
0023 # include <coroutine>
0024 #else // defined(BOOST_ASIO_HAS_STD_COROUTINE)
0025 # include <experimental/coroutine>
0026 #endif // defined(BOOST_ASIO_HAS_STD_COROUTINE)
0027
0028 #include <utility>
0029 #include <boost/asio/any_io_executor.hpp>
0030
0031 #include <boost/asio/detail/push_options.hpp>
0032
0033 namespace boost {
0034 namespace asio {
0035 namespace detail {
0036
0037 #if defined(BOOST_ASIO_HAS_STD_COROUTINE)
0038 using std::coroutine_handle;
0039 using std::suspend_always;
0040 #else // defined(BOOST_ASIO_HAS_STD_COROUTINE)
0041 using std::experimental::coroutine_handle;
0042 using std::experimental::suspend_always;
0043 #endif // defined(BOOST_ASIO_HAS_STD_COROUTINE)
0044
0045 template <typename> class awaitable_thread;
0046 template <typename, typename> class awaitable_frame;
0047
0048 } // namespace detail
0049
0050 /// The return type of a coroutine or asynchronous operation.
0051 template <typename T, typename Executor = any_io_executor>
0052 class BOOST_ASIO_NODISCARD awaitable
0053 {
0054 public:
0055   /// The type of the awaited value.
0056   typedef T value_type;
0057
0058   /// The executor type that will be used for the coroutine.
0059   typedef Executor executor_type;
0060
0061   /// Default constructor.
0062   constexpr awaitable() noexcept
0063     : frame_(nullptr)
0064   {
0065   }
0066
0067   /// Move constructor.
0068   awaitable(awaitable&& other) noexcept
0069     : frame_(std::exchange(other.frame_, nullptr))
0070   {
0071   }
0072
0073   /// Destructor
0074   ~awaitable()
0075   {
0076     if (frame_)
0077       frame_->destroy();
0078   }
0079
0080   /// Move assignment.
0081   awaitable& operator=(awaitable&& other) noexcept
0082   {
0083     if (this != &other)
0084       frame_ = std::exchange(other.frame_, nullptr);
0085     return *this;
0086   }
0087
0088   /// Checks if the awaitable refers to a future result.
0089   bool valid() const noexcept
0090   {
0091     return !!frame_;
0092   }
0093
0094 #if !defined(GENERATING_DOCUMENTATION)
0095
0096   // Support for co_await keyword.
0097   bool await_ready() const noexcept
0098   {
0099     return false;
0100   }
0101
0102   // Support for co_await keyword.
0103   template <class U>
0104   void await_suspend(
0105       detail::coroutine_handle<detail::awaitable_frame<U, Executor>> h)
0106   {
0107     frame_->push_frame(&h.promise());
0108   }
0109
0110   // Support for co_await keyword.
0111   T await_resume()
0112   {
0113     return awaitable(static_cast<awaitable&&>(*this)).frame_->get();
0114   }
0115
0116 #endif // !defined(GENERATING_DOCUMENTATION)
0117
0118 private:
0119   template <typename> friend class detail::awaitable_thread;
0120   template <typename, typename> friend class detail::awaitable_frame;
0121
0122   // Not copy constructible or copy assignable.
0123   awaitable(const awaitable&) = delete;
0124   awaitable& operator=(const awaitable&) = delete;
0125
0126   // Construct the awaitable from a coroutine's frame object.
0127   explicit awaitable(detail::awaitable_frame<T, Executor>* a)
0128     : frame_(a)
0129   {
0130   }
0131
0132   detail::awaitable_frame<T, Executor>* frame_;
0133 };
0134
0135 } // namespace asio
0136 } // namespace boost
0137
0138 #include <boost/asio/detail/pop_options.hpp>
0139
0140 #include <boost/asio/impl/awaitable.hpp>
0141
0142 #endif // defined(BOOST_ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
0143
0144 #endif // BOOST_ASIO_AWAITABLE_HPP