Boost C++ Libraries

boost/asio/impl/use_future.hpp

//
// impl/use_future.hpp
// ~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2024 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 BOOST_ASIO_IMPL_USE_FUTURE_HPP
#define BOOST_ASIO_IMPL_USE_FUTURE_HPP

#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)

#include <boost/asio/detail/config.hpp>
#include <tuple>
#include <boost/asio/async_result.hpp>
#include <boost/asio/detail/memory.hpp>
#include <boost/asio/detail/type_traits.hpp>
#include <boost/asio/dispatch.hpp>
#include <boost/asio/disposition.hpp>
#include <boost/asio/execution.hpp>
#include <boost/asio/packaged_task.hpp>
#include <boost/system/system_error.hpp>
#include <boost/asio/system_executor.hpp>

#include <boost/asio/detail/push_options.hpp>

namespace boost {
namespace asio {
namespace detail {

template <typename T, typename F, typename... Args>
inline void promise_invoke_and_set(std::promise<T>& p,
    F& f, Args&&... args)
{
#if !defined(BOOST_ASIO_NO_EXCEPTIONS)
  try
#endif // !defined(BOOST_ASIO_NO_EXCEPTIONS)
  {
    p.set_value(f(static_cast<Args&&>(args)...));
  }
#if !defined(BOOST_ASIO_NO_EXCEPTIONS)
  catch (...)
  {
    p.set_exception(std::current_exception());
  }
#endif // !defined(BOOST_ASIO_NO_EXCEPTIONS)
}

template <typename F, typename... Args>
inline void promise_invoke_and_set(std::promise<void>& p,
    F& f, Args&&... args)
{
#if !defined(BOOST_ASIO_NO_EXCEPTIONS)
  try
#endif // !defined(BOOST_ASIO_NO_EXCEPTIONS)
  {
    f(static_cast<Args&&>(args)...);
    p.set_value();
  }
#if !defined(BOOST_ASIO_NO_EXCEPTIONS)
  catch (...)
  {
    p.set_exception(std::current_exception());
  }
#endif // !defined(BOOST_ASIO_NO_EXCEPTIONS)
}

// A function object adapter to invoke a nullary function object and capture
// any exception thrown into a promise.
template <typename T, typename F>
class promise_invoker
{
public:
  promise_invoker(const shared_ptr<std::promise<T>>& p,
      F&& f)
    : p_(p), f_(static_cast<F&&>(f))
  {
  }

  void operator()()
  {
#if !defined(BOOST_ASIO_NO_EXCEPTIONS)
    try
#endif // !defined(BOOST_ASIO_NO_EXCEPTIONS)
    {
      f_();
    }
#if !defined(BOOST_ASIO_NO_EXCEPTIONS)
    catch (...)
    {
      p_->set_exception(std::current_exception());
    }
#endif // !defined(BOOST_ASIO_NO_EXCEPTIONS)
  }

private:
  shared_ptr<std::promise<T>> p_;
  decay_t<F> f_;
};

// An executor that adapts the system_executor to capture any exception thrown
// by a submitted function object and save it into a promise.
template <typename T, typename Blocking = execution::blocking_t::possibly_t>
class promise_executor
{
public:
  explicit promise_executor(const shared_ptr<std::promise<T>>& p)
    : p_(p)
  {
  }

  execution_context& query(execution::context_t) const noexcept
  {
    return boost::asio::query(system_executor(), execution::context);
  }

  static constexpr Blocking query(execution::blocking_t)
  {
    return Blocking();
  }

  promise_executor<T, execution::blocking_t::possibly_t>
  require(execution::blocking_t::possibly_t) const
  {
    return promise_executor<T, execution::blocking_t::possibly_t>(p_);
  }

  promise_executor<T, execution::blocking_t::never_t>
  require(execution::blocking_t::never_t) const
  {
    return promise_executor<T, execution::blocking_t::never_t>(p_);
  }

  template <typename F>
  void execute(F&& f) const
  {
    boost::asio::require(system_executor(), Blocking()).execute(
        promise_invoker<T, F>(p_, static_cast<F&&>(f)));
  }

#if !defined(BOOST_ASIO_NO_TS_EXECUTORS)
  execution_context& context() const noexcept
  {
    return system_executor().context();
  }

  void on_work_started() const noexcept {}
  void on_work_finished() const noexcept {}

  template <typename F, typename A>
  void dispatch(F&& f, const A&) const
  {
    promise_invoker<T, F>(p_, static_cast<F&&>(f))();
  }

  template <typename F, typename A>
  void post(F&& f, const A& a) const
  {
    system_executor().post(
        promise_invoker<T, F>(p_, static_cast<F&&>(f)), a);
  }

  template <typename F, typename A>
  void defer(F&& f, const A& a) const
  {
    system_executor().defer(
        promise_invoker<T, F>(p_, static_cast<F&&>(f)), a);
  }
#endif // !defined(BOOST_ASIO_NO_TS_EXECUTORS)

  friend bool operator==(const promise_executor& a,
      const promise_executor& b) noexcept
  {
    return a.p_ == b.p_;
  }

  friend bool operator!=(const promise_executor& a,
      const promise_executor& b) noexcept
  {
    return a.p_ != b.p_;
  }

private:
  shared_ptr<std::promise<T>> p_;
};

// The base class for all completion handlers that create promises.
template <typename T>
class promise_creator
{
public:
  typedef promise_executor<T> executor_type;

  executor_type get_executor() const noexcept
  {
    return executor_type(p_);
  }

  typedef std::future<T> future_type;

  future_type get_future()
  {
    return p_->get_future();
  }

protected:
  template <typename Allocator>
  void create_promise(const Allocator& a)
  {
    BOOST_ASIO_REBIND_ALLOC(Allocator, char) b(a);
    p_ = std::allocate_shared<std::promise<T>>(b, std::allocator_arg, b);
  }

  shared_ptr<std::promise<T>> p_;
};

// For completion signature void().
class promise_handler_0
  : public promise_creator<void>
{
public:
  void operator()()
  {
    this->p_->set_value();
  }
};

// For completion signature void(disposition auto).
template <typename Disposition>
class promise_handler_d_0
  : public promise_creator<void>
{
public:
  void operator()(Disposition d)
  {
    if (d != no_error)
    {
      this->p_->set_exception(
          (to_exception_ptr)(static_cast<Disposition&&>(d)));
    }
    else
    {
      this->p_->set_value();
    }
  }
};

// For completion signature void(T).
template <typename T>
class promise_handler_1
  : public promise_creator<T>
{
public:
  template <typename Arg>
  void operator()(Arg&& arg)
  {
    this->p_->set_value(static_cast<Arg&&>(arg));
  }
};

// For completion signature void(disposition auto, T).
template <typename Disposition, typename T>
class promise_handler_d_1
  : public promise_creator<T>
{
public:
  template <typename Arg>
  void operator()(Disposition d, Arg&& arg)
  {
    if (d != no_error)
    {
      this->p_->set_exception(
          (to_exception_ptr)(static_cast<Disposition&&>(d)));
    }
    else
      this->p_->set_value(static_cast<Arg&&>(arg));
  }
};

// For completion signature void(T1, ..., Tn);
template <typename T>
class promise_handler_n
  : public promise_creator<T>
{
public:
  template <typename... Args>
  void operator()(Args&&... args)
  {
    this->p_->set_value(
        std::forward_as_tuple(
          static_cast<Args&&>(args)...));
  }
};

// For completion signature void(error_code, T1, ..., Tn);
template <typename Disposition, typename T>
class promise_handler_d_n
  : public promise_creator<T>
{
public:
  template <typename... Args>
  void operator()(Disposition d, Args&&... args)
  {
    if (d != no_error)
    {
      this->p_->set_exception(
          (to_exception_ptr)(static_cast<Disposition&&>(d)));
    }
    else
    {
      this->p_->set_value(
          std::forward_as_tuple(
            static_cast<Args&&>(args)...));
    }
  }
};

// Helper template to choose the appropriate concrete promise handler
// implementation based on the supplied completion signature.
template <typename, typename = void> class promise_handler_selector;

template <>
class promise_handler_selector<void()>
  : public promise_handler_0 {};

template <typename Arg>
class promise_handler_selector<void(Arg),
  enable_if_t<is_disposition<Arg>::value>>
    : public promise_handler_d_0<Arg> {};

template <typename Arg>
class promise_handler_selector<void(Arg),
  enable_if_t<!is_disposition<Arg>::value>>
    : public promise_handler_1<Arg> {};

template <typename Arg0, typename Arg1>
class promise_handler_selector<void(Arg0, Arg1),
  enable_if_t<is_disposition<Arg0>::value>>
    : public promise_handler_d_1<Arg0, Arg1> {};

template <typename Arg0, typename... ArgN>
class promise_handler_selector<void(Arg0, ArgN...),
  enable_if_t<!is_disposition<Arg0>::value>>
    : public promise_handler_n<std::tuple<Arg0, ArgN...>> {};

template <typename Arg0, typename... ArgN>
class promise_handler_selector<void(Arg0, ArgN...),
  enable_if_t<is_disposition<Arg0>::value>>
    : public promise_handler_d_n<Arg0, std::tuple<ArgN...>> {};

// Completion handlers produced from the use_future completion token, when not
// using use_future::operator().
template <typename Signature, typename Allocator>
class promise_handler
  : public promise_handler_selector<Signature>
{
public:
  typedef Allocator allocator_type;
  typedef void result_type;

  promise_handler(use_future_t<Allocator> u)
    : allocator_(u.get_allocator())
  {
    this->create_promise(allocator_);
  }

  allocator_type get_allocator() const noexcept
  {
    return allocator_;
  }

private:
  Allocator allocator_;
};

template <typename Function>
struct promise_function_wrapper
{
  explicit promise_function_wrapper(Function& f)
    : function_(static_cast<Function&&>(f))
  {
  }

  explicit promise_function_wrapper(const Function& f)
    : function_(f)
  {
  }

  void operator()()
  {
    function_();
  }

  Function function_;
};

// Helper base class for async_result specialisation.
template <typename Signature, typename Allocator>
class promise_async_result
{
public:
  typedef promise_handler<Signature, Allocator> completion_handler_type;
  typedef typename completion_handler_type::future_type return_type;

  explicit promise_async_result(completion_handler_type& h)
    : future_(h.get_future())
  {
  }

  return_type get()
  {
    return static_cast<return_type&&>(future_);
  }

private:
  return_type future_;
};

// Return value from use_future::operator().
template <typename Function, typename Allocator>
class packaged_token
{
public:
  packaged_token(Function f, const Allocator& a)
    : function_(static_cast<Function&&>(f)),
      allocator_(a)
  {
  }

//private:
  Function function_;
  Allocator allocator_;
};

// Completion handlers produced from the use_future completion token, when
// using use_future::operator().
template <typename Function, typename Allocator, typename Result>
class packaged_handler
  : public promise_creator<Result>
{
public:
  typedef Allocator allocator_type;
  typedef void result_type;

  packaged_handler(packaged_token<Function, Allocator> t)
    : function_(static_cast<Function&&>(t.function_)),
      allocator_(t.allocator_)
  {
    this->create_promise(allocator_);
  }

  allocator_type get_allocator() const noexcept
  {
    return allocator_;
  }

  template <typename... Args>
  void operator()(Args&&... args)
  {
    (promise_invoke_and_set)(*this->p_,
        function_, static_cast<Args&&>(args)...);
  }

private:
  Function function_;
  Allocator allocator_;
};

// Helper base class for async_result specialisation.
template <typename Function, typename Allocator, typename Result>
class packaged_async_result
{
public:
  typedef packaged_handler<Function, Allocator, Result> completion_handler_type;
  typedef typename completion_handler_type::future_type return_type;

  explicit packaged_async_result(completion_handler_type& h)
    : future_(h.get_future())
  {
  }

  return_type get()
  {
    return static_cast<return_type&&>(future_);
  }

private:
  return_type future_;
};

} // namespace detail

template <typename Allocator> template <typename Function>
inline detail::packaged_token<decay_t<Function>, Allocator>
use_future_t<Allocator>::operator()(Function&& f) const
{
  return detail::packaged_token<decay_t<Function>, Allocator>(
      static_cast<Function&&>(f), allocator_);
}

#if !defined(GENERATING_DOCUMENTATION)

template <typename Allocator, typename Result, typename... Args>
class async_result<use_future_t<Allocator>, Result(Args...)>
  : public detail::promise_async_result<
      void(decay_t<Args>...), Allocator>
{
public:
  explicit async_result(
    typename detail::promise_async_result<void(decay_t<Args>...),
      Allocator>::completion_handler_type& h)
    : detail::promise_async_result<
        void(decay_t<Args>...), Allocator>(h)
  {
  }
};

template <typename Function, typename Allocator,
    typename Result, typename... Args>
class async_result<detail::packaged_token<Function, Allocator>, Result(Args...)>
  : public detail::packaged_async_result<Function, Allocator,
      result_of_t<Function(Args...)>>
{
public:
  explicit async_result(
    typename detail::packaged_async_result<Function, Allocator,
      result_of_t<Function(Args...)>>::completion_handler_type& h)
    : detail::packaged_async_result<Function, Allocator,
        result_of_t<Function(Args...)>>(h)
  {
  }
};

namespace traits {

#if !defined(BOOST_ASIO_HAS_DEDUCED_EQUALITY_COMPARABLE_TRAIT)

template <typename T, typename Blocking>
struct equality_comparable<
    boost::asio::detail::promise_executor<T, Blocking>>
{
  static constexpr bool is_valid = true;
  static constexpr bool is_noexcept = true;
};

#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EQUALITY_COMPARABLE_TRAIT)

#if !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)

template <typename T, typename Blocking, typename Function>
struct execute_member<
    boost::asio::detail::promise_executor<T, Blocking>, Function>
{
  static constexpr bool is_valid = true;
  static constexpr bool is_noexcept = false;
  typedef void result_type;
};

#endif // !defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)

#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)

template <typename T, typename Blocking, typename Property>
struct query_static_constexpr_member<
    boost::asio::detail::promise_executor<T, Blocking>,
    Property,
    typename boost::asio::enable_if<
      boost::asio::is_convertible<
        Property,
        boost::asio::execution::blocking_t
      >::value
    >::type
  >
{
  static constexpr bool is_valid = true;
  static constexpr bool is_noexcept = true;
  typedef Blocking result_type;

  static constexpr result_type value() noexcept
  {
    return Blocking();
  }
};

#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)

#if !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)

template <typename T, typename Blocking>
struct query_member<
    boost::asio::detail::promise_executor<T, Blocking>,
    execution::context_t
  >
{
  static constexpr bool is_valid = true;
  static constexpr bool is_noexcept = true;
  typedef boost::asio::system_context& result_type;
};

#endif // !defined(BOOST_ASIO_HAS_DEDUCED_QUERY_MEMBER_TRAIT)

#if !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)

template <typename T, typename Blocking>
struct require_member<
    boost::asio::detail::promise_executor<T, Blocking>,
    execution::blocking_t::possibly_t
  >
{
  static constexpr bool is_valid = true;
  static constexpr bool is_noexcept = true;
  typedef boost::asio::detail::promise_executor<T,
      execution::blocking_t::possibly_t> result_type;
};

template <typename T, typename Blocking>
struct require_member<
    boost::asio::detail::promise_executor<T, Blocking>,
    execution::blocking_t::never_t
  >
{
  static constexpr bool is_valid = true;
  static constexpr bool is_noexcept = true;
  typedef boost::asio::detail::promise_executor<T,
      execution::blocking_t::never_t> result_type;
};

#endif // !defined(BOOST_ASIO_HAS_DEDUCED_REQUIRE_MEMBER_TRAIT)

} // namespace traits

#endif // !defined(GENERATING_DOCUMENTATION)

} // namespace asio
} // namespace boost

#include <boost/asio/detail/pop_options.hpp>

#endif // BOOST_ASIO_IMPL_USE_FUTURE_HPP