ceph/src/boost/boost/asio/awaitable.hpp

   1 //
   2 // awaitable.hpp
   3 // ~~~~~~~~~~~~~
   4 //
   5 // Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff dot com)
   6 //
   7 // Distributed under the Boost Software License, Version 1.0. (See accompanying
   8 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   9 //
  10
  11 #ifndef BOOST_ASIO_AWAITABLE_HPP
  12 #define BOOST_ASIO_AWAITABLE_HPP
  13
  14 #if defined(_MSC_VER) && (_MSC_VER >= 1200)
  15 # pragma once
  16 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
  17
  18 #include <boost/asio/detail/config.hpp>
  19
  20 #if defined(BOOST_ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
  21
  22 #include <experimental/coroutine>
  23 #include <boost/asio/executor.hpp>
  24
  25 #include <boost/asio/detail/push_options.hpp>
  26
  27 namespace boost {
  28 namespace asio {
  29 namespace detail {
  30
  31 using std::experimental::coroutine_handle;
  32 using std::experimental::suspend_always;
  33
  34 template <typename> class awaitable_thread;
  35 template <typename, typename> class awaitable_frame;
  36
  37 } // namespace detail
  38
  39 /// The return type of a coroutine or asynchronous operation.
  40 template <typename T, typename Executor = executor>
  41 class awaitable
  42 {
  43 public:
  44   /// The type of the awaited value.
  45   typedef T value_type;
  46
  47   /// The executor type that will be used for the coroutine.
  48   typedef Executor executor_type;
  49
  50   /// Default constructor.
  51   constexpr awaitable() noexcept
  52     : frame_(nullptr)
  53   {
  54   }
  55
  56   /// Move constructor.
  57   awaitable(awaitable&& other) noexcept
  58     : frame_(std::exchange(other.frame_, nullptr))
  59   {
  60   }
  61
  62   /// Destructor
  63   ~awaitable()
  64   {
  65     if (frame_)
  66       frame_->destroy();
  67   }
  68
  69   /// Checks if the awaitable refers to a future result.
  70   bool valid() const noexcept
  71   {
  72     return !!frame_;
  73   }
  74
  75 #if !defined(GENERATING_DOCUMENTATION)
  76
  77   // Support for co_await keyword.
  78   bool await_ready() const noexcept
  79   {
  80     return false;
  81   }
  82
  83   // Support for co_await keyword.
  84   template <class U>
  85   void await_suspend(
  86       detail::coroutine_handle<detail::awaitable_frame<U, Executor>> h)
  87   {
  88     frame_->push_frame(&h.promise());
  89   }
  90
  91   // Support for co_await keyword.
  92   T await_resume()
  93   {
  94     return frame_->get();
  95   }
  96
  97 #endif // !defined(GENERATING_DOCUMENTATION)
  98
  99 private:
 100   template <typename> friend class detail::awaitable_thread;
 101   template <typename, typename> friend class detail::awaitable_frame;
 102
 103   // Not copy constructible or copy assignable.
 104   awaitable(const awaitable&) = delete;
 105   awaitable& operator=(const awaitable&) = delete;
 106
 107   // Construct the awaitable from a coroutine's frame object.
 108   explicit awaitable(detail::awaitable_frame<T, Executor>* a)
 109     : frame_(a)
 110   {
 111   }
 112
 113   detail::awaitable_frame<T, Executor>* frame_;
 114 };
 115
 116 } // namespace asio
 117 } // namespace boost
 118
 119 #include <boost/asio/detail/pop_options.hpp>
 120
 121 #include <boost/asio/impl/awaitable.hpp>
 122
 123 #endif // defined(BOOST_ASIO_HAS_CO_AWAIT) || defined(GENERATING_DOCUMENTATION)
 124
 125 #endif // BOOST_ASIO_AWAITABLE_HPP