Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for a snapshot of the develop branch, built from commit 43d231b32d.

boost/asio/execution/allocator.hpp

//
// execution/allocator.hpp
// ~~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2021 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_EXECUTION_ALLOCATOR_HPP
#define BOOST_ASIO_EXECUTION_ALLOCATOR_HPP

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

#include <boost/asio/detail/config.hpp>
#include <boost/asio/detail/type_traits.hpp>
#include <boost/asio/execution/executor.hpp>
#include <boost/asio/execution/scheduler.hpp>
#include <boost/asio/execution/sender.hpp>
#include <boost/asio/is_applicable_property.hpp>
#include <boost/asio/traits/query_static_constexpr_member.hpp>
#include <boost/asio/traits/static_query.hpp>

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

namespace boost {
namespace asio {

#if defined(GENERATING_DOCUMENTATION)

namespace execution {

/// A property to describe which allocator an executor will use to allocate the
/// memory required to store a submitted function object.
template <typename ProtoAllocator>
struct allocator_t
{
  /// The allocator_t property applies to executors, senders, and schedulers.
  template <typename T>
  static constexpr bool is_applicable_property_v =
    is_executor_v<T> || is_sender_v<T> || is_scheduler_v<T>;

  /// The allocator_t property can be required.
  static constexpr bool is_requirable = true;

  /// The allocator_t property can be preferred.
  static constexpr bool is_preferable = true;

  /// Default constructor.
  constexpr allocator_t();

  /// Obtain the allocator stored in the allocator_t property object.
  /**
   * Present only if @c ProtoAllocator is non-void.
   */
  constexpr ProtoAllocator value() const;

  /// Create an allocator_t object with a different allocator.
  /**
   * Present only if @c ProtoAllocator is void.
   */
  template <typename OtherAllocator>
  allocator_t<OtherAllocator operator()(const OtherAllocator& a);
};

/// A special value used for accessing the allocator_t property.
constexpr allocator_t<void> allocator;

} // namespace execution

#else // defined(GENERATING_DOCUMENTATION)

namespace execution {

template <typename ProtoAllocator>
struct allocator_t
{
#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
  template <typename T>
  BOOST_ASIO_STATIC_CONSTEXPR(bool,
    is_applicable_property_v = (
      is_executor<T>::value
        || conditional<
            is_executor<T>::value,
            false_type,
            is_sender<T>
          >::type::value
        || conditional<
            is_executor<T>::value,
            false_type,
            is_scheduler<T>
          >::type::value));
#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)

  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);

  template <typename T>
  struct static_proxy
  {
#if defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
    struct type
    {
      template <typename P>
      static constexpr auto query(BOOST_ASIO_MOVE_ARG(P) p)
        noexcept(
          noexcept(
            conditional<true, T, P>::type::query(BOOST_ASIO_MOVE_CAST(P)(p))
          )
        )
        -> decltype(
          conditional<true, T, P>::type::query(BOOST_ASIO_MOVE_CAST(P)(p))
        )
      {
        return T::query(BOOST_ASIO_MOVE_CAST(P)(p));
      }
    };
#else // defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
    typedef T type;
#endif // defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
  };

  template <typename T>
  struct query_static_constexpr_member :
    traits::query_static_constexpr_member<
      typename static_proxy<T>::type, allocator_t> {};

#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
  template <typename T>
  static BOOST_ASIO_CONSTEXPR
  typename query_static_constexpr_member<T>::result_type
  static_query()
    BOOST_ASIO_NOEXCEPT_IF((
      query_static_constexpr_member<T>::is_noexcept))
  {
    return query_static_constexpr_member<T>::value();
  }

  template <typename E, typename T = decltype(allocator_t::static_query<E>())>
  static BOOST_ASIO_CONSTEXPR const T static_query_v
    = allocator_t::static_query<E>();
#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)

  BOOST_ASIO_CONSTEXPR ProtoAllocator value() const
  {
    return a_;
  }

private:
  friend struct allocator_t<void>;

  explicit BOOST_ASIO_CONSTEXPR allocator_t(const ProtoAllocator& a)
    : a_(a)
  {
  }

  ProtoAllocator a_;
};

#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
template <typename ProtoAllocator> template <typename E, typename T>
const T allocator_t<ProtoAllocator>::static_query_v;
#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)

template <>
struct allocator_t<void>
{
#if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
  template <typename T>
  BOOST_ASIO_STATIC_CONSTEXPR(bool,
    is_applicable_property_v = (
      is_executor<T>::value
        || conditional<
            is_executor<T>::value,
            false_type,
            is_sender<T>
          >::type::value
        || conditional<
            is_executor<T>::value,
            false_type,
            is_scheduler<T>
          >::type::value));
#endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)

  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_requirable = true);
  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_preferable = true);

  BOOST_ASIO_CONSTEXPR allocator_t()
  {
  }

  template <typename T>
  struct static_proxy
  {
#if defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
    struct type
    {
      template <typename P>
      static constexpr auto query(BOOST_ASIO_MOVE_ARG(P) p)
        noexcept(
          noexcept(
            conditional<true, T, P>::type::query(BOOST_ASIO_MOVE_CAST(P)(p))
          )
        )
        -> decltype(
          conditional<true, T, P>::type::query(BOOST_ASIO_MOVE_CAST(P)(p))
        )
      {
        return T::query(BOOST_ASIO_MOVE_CAST(P)(p));
      }
    };
#else // defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
    typedef T type;
#endif // defined(BOOST_ASIO_HAS_DEDUCED_QUERY_STATIC_CONSTEXPR_MEMBER_TRAIT)
  };

  template <typename T>
  struct query_static_constexpr_member :
    traits::query_static_constexpr_member<
      typename static_proxy<T>::type, allocator_t> {};

#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
  template <typename T>
  static BOOST_ASIO_CONSTEXPR
  typename query_static_constexpr_member<T>::result_type
  static_query()
    BOOST_ASIO_NOEXCEPT_IF((
      query_static_constexpr_member<T>::is_noexcept))
  {
    return query_static_constexpr_member<T>::value();
  }

  template <typename E, typename T = decltype(allocator_t::static_query<E>())>
  static BOOST_ASIO_CONSTEXPR const T static_query_v
    = allocator_t::static_query<E>();
#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)

  template <typename OtherProtoAllocator>
  BOOST_ASIO_CONSTEXPR allocator_t<OtherProtoAllocator> operator()(
      const OtherProtoAllocator& a) const
  {
    return allocator_t<OtherProtoAllocator>(a);
  }
};

#if defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
  && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)
template <typename E, typename T>
const T allocator_t<void>::static_query_v;
#endif // defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
       //   && defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)

#if defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
constexpr allocator_t<void> allocator;
#else // defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
template <typename T>
struct allocator_instance
{
  static allocator_t<T> instance;
};

template <typename T>
allocator_t<T> allocator_instance<T>::instance;

namespace {
static const allocator_t<void>& allocator = allocator_instance<void>::instance;
} // namespace
#endif

} // namespace execution

#if !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)

template <typename T, typename ProtoAllocator>
struct is_applicable_property<T, execution::allocator_t<ProtoAllocator> >
  : integral_constant<bool,
      execution::is_executor<T>::value
        || conditional<
            execution::is_executor<T>::value,
            false_type,
            execution::is_sender<T>
          >::type::value
        || conditional<
            execution::is_executor<T>::value,
            false_type,
            execution::is_scheduler<T>
          >::type::value>
{
};

#endif // !defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)

namespace traits {

#if !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT) \
  || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)

template <typename T, typename ProtoAllocator>
struct static_query<T, execution::allocator_t<ProtoAllocator>,
  typename enable_if<
    execution::allocator_t<ProtoAllocator>::template
      query_static_constexpr_member<T>::is_valid
  >::type>
{
  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
  BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = true);

  typedef typename execution::allocator_t<ProtoAllocator>::template
    query_static_constexpr_member<T>::result_type result_type;

  static BOOST_ASIO_CONSTEXPR result_type value()
  {
    return execution::allocator_t<ProtoAllocator>::template
      query_static_constexpr_member<T>::value();
  }
};

#endif // !defined(BOOST_ASIO_HAS_DEDUCED_STATIC_QUERY_TRAIT)
       //   || !defined(BOOST_ASIO_HAS_SFINAE_VARIABLE_TEMPLATES)

} // namespace traits

#endif // defined(GENERATING_DOCUMENTATION)

} // namespace asio
} // namespace boost

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

#endif // BOOST_ASIO_EXECUTION_ALLOCATOR_HPP