//
	// executor.hpp
	// ~~~~~~~~~~~~
	//
	// Copyright (c) 2003-2018 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_EXECUTOR_HPP
	#define BOOST_ASIO_EXECUTOR_HPP
	
	#if defined(_MSC_VER) && (_MSC_VER >= 1200)
	# pragma once
	#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
	
	#include <boost/asio/detail/config.hpp>
	#include <typeinfo>
	#include <boost/asio/detail/cstddef.hpp>
	#include <boost/asio/detail/memory.hpp>
	#include <boost/asio/detail/throw_exception.hpp>
	#include <boost/asio/execution_context.hpp>
	
	#include <boost/asio/detail/push_options.hpp>
	
	namespace boost {
	namespace asio {
	
	/// Exception thrown when trying to access an empty polymorphic executor.
	class bad_executor
	  : public std::exception
	{
	public:
	  /// Constructor.
	  BOOST_ASIO_DECL bad_executor() BOOST_ASIO_NOEXCEPT;
	
	  /// Obtain message associated with exception.
	  BOOST_ASIO_DECL virtual const char* what() const
	    BOOST_ASIO_NOEXCEPT_OR_NOTHROW;
	};
	
	/// Polymorphic wrapper for executors.
	class executor
	{
	public:
	  /// Default constructor.
	  executor() BOOST_ASIO_NOEXCEPT
	    : impl_(0)
	  {
	  }
	
	  /// Construct from nullptr.
	  executor(nullptr_t) BOOST_ASIO_NOEXCEPT
	    : impl_(0)
	  {
	  }
	
	  /// Copy constructor.
	  executor(const executor& other) BOOST_ASIO_NOEXCEPT
	    : impl_(other.clone())
	  {
	  }
	
	#if defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
	  /// Move constructor.
	  executor(executor&& other) BOOST_ASIO_NOEXCEPT
	    : impl_(other.impl_)
	  {
	    other.impl_ = 0;
	  }
	#endif // defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
	
	  /// Construct a polymorphic wrapper for the specified executor.
	  template <typename Executor>
	  executor(Executor e);
	
	  /// Allocator-aware constructor to create a polymorphic wrapper for the
	  /// specified executor.
	  template <typename Executor, typename Allocator>
	  executor(allocator_arg_t, const Allocator& a, Executor e);
	
	  /// Destructor.
	  ~executor()
	  {
	    destroy();
	  }
	
	  /// Assignment operator.
	  executor& operator=(const executor& other) BOOST_ASIO_NOEXCEPT
	  {
	    destroy();
	    impl_ = other.clone();
	    return *this;
	  }
	
	#if defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
	  // Move assignment operator.
	  executor& operator=(executor&& other) BOOST_ASIO_NOEXCEPT
	  {
	    destroy();
	    impl_ = other.impl_;
	    other.impl_ = 0;
	    return *this;
	  }
	#endif // defined(BOOST_ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
	
	  /// Assignment operator for nullptr_t.
	  executor& operator=(nullptr_t) BOOST_ASIO_NOEXCEPT
	  {
	    destroy();
	    impl_ = 0;
	    return *this;
	  }
	
	  /// Assignment operator to create a polymorphic wrapper for the specified
	  /// executor.
	  template <typename Executor>
	  executor& operator=(BOOST_ASIO_MOVE_ARG(Executor) e) BOOST_ASIO_NOEXCEPT
	  {
	    executor tmp(BOOST_ASIO_MOVE_CAST(Executor)(e));
	    destroy();
	    impl_ = tmp.impl_;
	    tmp.impl_ = 0;
	    return *this;
	  }
	
	  /// Obtain the underlying execution context.
	  execution_context& context() const BOOST_ASIO_NOEXCEPT
	  {
	    return get_impl()->context();
	  }
	
	  /// Inform the executor that it has some outstanding work to do.
	  void on_work_started() const BOOST_ASIO_NOEXCEPT
	  {
	    get_impl()->on_work_started();
	  }
	
	  /// Inform the executor that some work is no longer outstanding.

	  void on_work_finished() const BOOST_ASIO_NOEXCEPT
	  {

	    get_impl()->on_work_finished();
	  }
	
	  /// Request the executor to invoke the given function object.
	  /**
	   * This function is used to ask the executor to execute the given function
	   * object. The function object is executed according to the rules of the
	   * target executor object.
	   *
	   * @param f The function object to be called. The executor will make a copy
	   * of the handler object as required. The function signature of the function
	   * object must be: @code void function(); @endcode
	   *
	   * @param a An allocator that may be used by the executor to allocate the
	   * internal storage needed for function invocation.
	   */
	  template <typename Function, typename Allocator>
	  void dispatch(BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const;
	
	  /// Request the executor to invoke the given function object.
	  /**
	   * This function is used to ask the executor to execute the given function
	   * object. The function object is executed according to the rules of the
	   * target executor object.
	   *
	   * @param f The function object to be called. The executor will make
	   * a copy of the handler object as required. The function signature of the
	   * function object must be: @code void function(); @endcode
	   *
	   * @param a An allocator that may be used by the executor to allocate the
	   * internal storage needed for function invocation.
	   */
	  template <typename Function, typename Allocator>
	  void post(BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const;
	
	  /// Request the executor to invoke the given function object.
	  /**
	   * This function is used to ask the executor to execute the given function
	   * object. The function object is executed according to the rules of the
	   * target executor object.
	   *
	   * @param f The function object to be called. The executor will make
	   * a copy of the handler object as required. The function signature of the
	   * function object must be: @code void function(); @endcode
	   *
	   * @param a An allocator that may be used by the executor to allocate the
	   * internal storage needed for function invocation.
	   */
	  template <typename Function, typename Allocator>
	  void defer(BOOST_ASIO_MOVE_ARG(Function) f, const Allocator& a) const;
	
	  struct unspecified_bool_type_t {};
	  typedef void (*unspecified_bool_type)(unspecified_bool_type_t);
	  static void unspecified_bool_true(unspecified_bool_type_t) {}
	
	  /// Operator to test if the executor contains a valid target.
	  operator unspecified_bool_type() const BOOST_ASIO_NOEXCEPT
	  {
	    return impl_ ? &executor::unspecified_bool_true : 0;
	  }
	
	  /// Obtain type information for the target executor object.
	  /**
	   * @returns If @c *this has a target type of type @c T, <tt>typeid(T)</tt>;
	   * otherwise, <tt>typeid(void)</tt>.
	   */
	#if !defined(BOOST_ASIO_NO_TYPEID) || defined(GENERATING_DOCUMENTATION)
	  const std::type_info& target_type() const BOOST_ASIO_NOEXCEPT
	  {
	    return impl_ ? impl_->target_type() : typeid(void);
	  }
	#else // !defined(BOOST_ASIO_NO_TYPEID) || defined(GENERATING_DOCUMENTATION)
	  const void* target_type() const BOOST_ASIO_NOEXCEPT
	  {
	    return impl_ ? impl_->target_type() : 0;
	  }
	#endif // !defined(BOOST_ASIO_NO_TYPEID) || defined(GENERATING_DOCUMENTATION)
	
	  /// Obtain a pointer to the target executor object.
	  /**
	   * @returns If <tt>target_type() == typeid(T)</tt>, a pointer to the stored
	   * executor target; otherwise, a null pointer.
	   */
	  template <typename Executor>
	  Executor* target() BOOST_ASIO_NOEXCEPT;
	
	  /// Obtain a pointer to the target executor object.
	  /**
	   * @returns If <tt>target_type() == typeid(T)</tt>, a pointer to the stored
	   * executor target; otherwise, a null pointer.
	   */
	  template <typename Executor>
	  const Executor* target() const BOOST_ASIO_NOEXCEPT;
	
	  /// Compare two executors for equality.
	  friend bool operator==(const executor& a,
	      const executor& b) BOOST_ASIO_NOEXCEPT
	  {
	    if (a.impl_ == b.impl_)
	      return true;
	    if (!a.impl_ || !b.impl_)
	      return false;
	    return a.impl_->equals(b.impl_);
	  }
	
	  /// Compare two executors for inequality.
	  friend bool operator!=(const executor& a,
	      const executor& b) BOOST_ASIO_NOEXCEPT
	  {
	    return !(a == b);
	  }
	
	private:
	#if !defined(GENERATING_DOCUMENTATION)
	  class function;
	  template <typename, typename> class impl;
	
	#if !defined(BOOST_ASIO_NO_TYPEID)
	  typedef const std::type_info& type_id_result_type;
	#else // !defined(BOOST_ASIO_NO_TYPEID)
	  typedef const void* type_id_result_type;
	#endif // !defined(BOOST_ASIO_NO_TYPEID)
	
	  template <typename T>
	  static type_id_result_type type_id()
	  {
	#if !defined(BOOST_ASIO_NO_TYPEID)
	    return typeid(T);
	#else // !defined(BOOST_ASIO_NO_TYPEID)
	    static int unique_id;
	    return &unique_id;
	#endif // !defined(BOOST_ASIO_NO_TYPEID)
	  }
	
	  // Base class for all polymorphic executor implementations.
	  class impl_base
	  {
	  public:
	    virtual impl_base* clone() const BOOST_ASIO_NOEXCEPT = 0;
	    virtual void destroy() BOOST_ASIO_NOEXCEPT = 0;
	    virtual execution_context& context() BOOST_ASIO_NOEXCEPT = 0;
	    virtual void on_work_started() BOOST_ASIO_NOEXCEPT = 0;
	    virtual void on_work_finished() BOOST_ASIO_NOEXCEPT = 0;
	    virtual void dispatch(BOOST_ASIO_MOVE_ARG(function)) = 0;
	    virtual void post(BOOST_ASIO_MOVE_ARG(function)) = 0;
	    virtual void defer(BOOST_ASIO_MOVE_ARG(function)) = 0;
	    virtual type_id_result_type target_type() const BOOST_ASIO_NOEXCEPT = 0;
	    virtual void* target() BOOST_ASIO_NOEXCEPT = 0;
	    virtual const void* target() const BOOST_ASIO_NOEXCEPT = 0;
	    virtual bool equals(const impl_base* e) const BOOST_ASIO_NOEXCEPT = 0;
	
	  protected:
	    impl_base(bool fast_dispatch) : fast_dispatch_(fast_dispatch) {}
	    virtual ~impl_base() {}
	
	  private:
	    friend class executor;
	    const bool fast_dispatch_;
	  };
	
	  // Helper function to check and return the implementation pointer.
	  impl_base* get_impl() const
	  {
	    if (!impl_)
	    {
	      bad_executor ex;

	      boost::asio::detail::throw_exception(ex);
	    }
	    return impl_;
	  }
	
	  // Helper function to clone another implementation.
	  impl_base* clone() const BOOST_ASIO_NOEXCEPT
	  {
	    return impl_ ? impl_->clone() : 0;
	  }
	
	  // Helper function to destroy an implementation.
	  void destroy() BOOST_ASIO_NOEXCEPT
	  {
	    if (impl_)
	      impl_->destroy();
	  }
	
	  impl_base* impl_;
	#endif // !defined(GENERATING_DOCUMENTATION)
	};
	
	} // namespace asio
	} // namespace boost
	
	BOOST_ASIO_USES_ALLOCATOR(boost::asio::executor)
	
	#include <boost/asio/detail/pop_options.hpp>
	
	#include <boost/asio/impl/executor.hpp>
	#if defined(BOOST_ASIO_HEADER_ONLY)
	# include <boost/asio/impl/executor.ipp>
	#endif // defined(BOOST_ASIO_HEADER_ONLY)
	
	#endif // BOOST_ASIO_EXECUTOR_HPP