text: //
  // basic_waitable_timer.hpp
  // ~~~~~~~~~~~~~~~~~~~~~~~~
  //
  // Copyright (c) 2003-2020 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 ASIO_BASIC_WAITABLE_TIMER_HPP
  #define ASIO_BASIC_WAITABLE_TIMER_HPP
  
  #if defined(_MSC_VER) && (_MSC_VER >= 1200)
  # pragma once
  #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
  
  #include "asio/detail/config.hpp"
  #include <cstddef>
  #include "asio/detail/chrono_time_traits.hpp"
  #include "asio/detail/deadline_timer_service.hpp"
  #include "asio/detail/handler_type_requirements.hpp"
  #include "asio/detail/io_object_impl.hpp"
  #include "asio/detail/non_const_lvalue.hpp"
  #include "asio/detail/throw_error.hpp"
  #include "asio/error.hpp"
  #include "asio/executor.hpp"
  #include "asio/wait_traits.hpp"
  
  #if defined(ASIO_HAS_MOVE)
  # include <utility>
  #endif // defined(ASIO_HAS_MOVE)
  
  #include "asio/detail/push_options.hpp"
  
  namespace asio {
  
  #if !defined(ASIO_BASIC_WAITABLE_TIMER_FWD_DECL)
  #define ASIO_BASIC_WAITABLE_TIMER_FWD_DECL
  
  // Forward declaration with defaulted arguments.
  template <typename Clock,
      typename WaitTraits = asio::wait_traits<Clock>,
      typename Executor = executor>
  class basic_waitable_timer;
  
  #endif // !defined(ASIO_BASIC_WAITABLE_TIMER_FWD_DECL)
  
  /// Provides waitable timer functionality.
  /**
   * The basic_waitable_timer class template provides the ability to perform a
   * blocking or asynchronous wait for a timer to expire.
   *
   * A waitable timer is always in one of two states: "expired" or "not expired".
   * If the wait() or async_wait() function is called on an expired timer, the
   * wait operation will complete immediately.
   *
   * Most applications will use one of the asio::steady_timer,
   * asio::system_timer or asio::high_resolution_timer typedefs.
   *
   * @note This waitable timer functionality is for use with the C++11 standard
   * library's @c &lt;chrono&gt; facility, or with the Boost.Chrono library.
   *
   * @par Thread Safety
   * @e Distinct @e objects: Safe.@n
   * @e Shared @e objects: Unsafe.
   *
   * @par Examples
   * Performing a blocking wait (C++11):
   * @code
   * // Construct a timer without setting an expiry time.
   * asio::steady_timer timer(my_context);
   *
   * // Set an expiry time relative to now.
   * timer.expires_after(std::chrono::seconds(5));
   *
   * // Wait for the timer to expire.
   * timer.wait();
   * @endcode
   *
   * @par 
   * Performing an asynchronous wait (C++11):
   * @code
   * void handler(const asio::error_code& error)
   * {
   *   if (!error)
   *   {
   *     // Timer expired.
   *   }
   * }
   *
   * ...
   *
   * // Construct a timer with an absolute expiry time.
   * asio::steady_timer timer(my_context,
   *     std::chrono::steady_clock::now() + std::chrono::seconds(60));
   *
   * // Start an asynchronous wait.
   * timer.async_wait(handler);
   * @endcode
   *
   * @par Changing an active waitable timer's expiry time
   *
   * Changing the expiry time of a timer while there are pending asynchronous
   * waits causes those wait operations to be cancelled. To ensure that the action
   * associated with the timer is performed only once, use something like this:
   * used:
   *
   * @code
   * void on_some_event()
   * {
   *   if (my_timer.expires_after(seconds(5)) > 0)
   *   {
   *     // We managed to cancel the timer. Start new asynchronous wait.
   *     my_timer.async_wait(on_timeout);
   *   }
   *   else
   *   {
   *     // Too late, timer has already expired!
   *   }
   * }
   *
   * void on_timeout(const asio::error_code& e)
   * {
   *   if (e != asio::error::operation_aborted)
   *   {
   *     // Timer was not cancelled, take necessary action.
   *   }
   * }
   * @endcode
   *
   * @li The asio::basic_waitable_timer::expires_after() function
   * cancels any pending asynchronous waits, and returns the number of
   * asynchronous waits that were cancelled. If it returns 0 then you were too
   * late and the wait handler has already been executed, or will soon be
   * executed. If it returns 1 then the wait handler was successfully cancelled.
   *
   * @li If a wait handler is cancelled, the asio::error_code passed to
   * it contains the value asio::error::operation_aborted.
   */
  template <typename Clock, typename WaitTraits, typename Executor>
  class basic_waitable_timer
  {
  public:
    /// The type of the executor associated with the object.
    typedef Executor executor_type;
  
    /// Rebinds the timer type to another executor.
    template <typename Executor1>
    struct rebind_executor
    {
      /// The timer type when rebound to the specified executor.
      typedef basic_waitable_timer<Clock, WaitTraits, Executor1> other;
    };
  
    /// The clock type.
    typedef Clock clock_type;
  
    /// The duration type of the clock.
    typedef typename clock_type::duration duration;
  
    /// The time point type of the clock.
    typedef typename clock_type::time_point time_point;
  
    /// The wait traits type.
    typedef WaitTraits traits_type;
  
    /// Constructor.
    /**
     * This constructor creates a timer without setting an expiry time. The
     * expires_at() or expires_after() functions must be called to set an expiry
     * time before the timer can be waited on.
     *
     * @param ex The I/O executor that the timer will use, by default, to
     * dispatch handlers for any asynchronous operations performed on the timer.
     */
    explicit basic_waitable_timer(const executor_type& ex)
      : impl_(ex)
    {
    }
  
    /// Constructor.
    /**
     * This constructor creates a timer without setting an expiry time. The
     * expires_at() or expires_after() functions must be called to set an expiry
     * time before the timer can be waited on.
     *
     * @param context An execution context which provides the I/O executor that
     * the timer will use, by default, to dispatch handlers for any asynchronous
     * operations performed on the timer.
     */
    template <typename ExecutionContext>
    explicit basic_waitable_timer(ExecutionContext& context,
        typename enable_if<
          is_convertible<ExecutionContext&, execution_context&>::value
        >::type* = 0)
      : impl_(context)
    {
    }
  
    /// Constructor to set a particular expiry time as an absolute time.
    /**
     * This constructor creates a timer and sets the expiry time.
     *
     * @param ex The I/O executor object that the timer will use, by default, to
     * dispatch handlers for any asynchronous operations performed on the timer.
     *
     * @param expiry_time The expiry time to be used for the timer, expressed
     * as an absolute time.
     */
    basic_waitable_timer(const executor_type& ex, const time_point& expiry_time)
      : impl_(ex)
    {
      asio::error_code ec;
      impl_.get_service().expires_at(impl_.get_implementation(), expiry_time, ec);
      asio::detail::throw_error(ec, "expires_at");
    }
  
    /// Constructor to set a particular expiry time as an absolute time.
    /**
     * This constructor creates a timer and sets the expiry time.
     *
     * @param context An execution context which provides the I/O executor that
     * the timer will use, by default, to dispatch handlers for any asynchronous
     * operations performed on the timer.
     *
     * @param expiry_time The expiry time to be used for the timer, expressed
     * as an absolute time.
     */
    template <typename ExecutionContext>
    explicit basic_waitable_timer(ExecutionContext& context,
        const time_point& expiry_time,
        typename enable_if<
          is_convertible<ExecutionContext&, execution_context&>::value
        >::type* = 0)
      : impl_(context)
    {
      asio::error_code ec;
      impl_.get_service().expires_at(impl_.get_implementation(), expiry_time, ec);
      asio::detail::throw_error(ec, "expires_at");
    }
  
    /// Constructor to set a particular expiry time relative to now.
    /**
     * This constructor creates a timer and sets the expiry time.
     *
     * @param ex The I/O executor that the timer will use, by default, to
     * dispatch handlers for any asynchronous operations performed on the timer.
     *
     * @param expiry_time The expiry time to be used for the timer, relative to
     * now.
     */
    basic_waitable_timer(const executor_type& ex, const duration& expiry_time)
      : impl_(ex)
    {
      asio::error_code ec;
      impl_.get_service().expires_after(
          impl_.get_implementation(), expiry_time, ec);
      asio::detail::throw_error(ec, "expires_after");
    }
  
    /// Constructor to set a particular expiry time relative to now.
    /**
     * This constructor creates a timer and sets the expiry time.
     *
     * @param context An execution context which provides the I/O executor that
     * the timer will use, by default, to dispatch handlers for any asynchronous
     * operations performed on the timer.
     *
     * @param expiry_time The expiry time to be used for the timer, relative to
     * now.
     */
    template <typename ExecutionContext>
    explicit basic_waitable_timer(ExecutionContext& context,
        const duration& expiry_time,
        typename enable_if<
          is_convertible<ExecutionContext&, execution_context&>::value
        >::type* = 0)
      : impl_(context)
    {
      asio::error_code ec;
      impl_.get_service().expires_after(
          impl_.get_implementation(), expiry_time, ec);
      asio::detail::throw_error(ec, "expires_after");
    }
  
  #if defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
    /// Move-construct a basic_waitable_timer from another.
    /**
     * This constructor moves a timer from one object to another.
     *
     * @param other The other basic_waitable_timer object from which the move will
     * occur.
     *
     * @note Following the move, the moved-from object is in the same state as if
     * constructed using the @c basic_waitable_timer(const executor_type&)
     * constructor.
     */
    basic_waitable_timer(basic_waitable_timer&& other)
      : impl_(std::move(other.impl_))
    {
    }
  
    /// Move-assign a basic_waitable_timer from another.
    /**
     * This assignment operator moves a timer from one object to another. Cancels
     * any outstanding asynchronous operations associated with the target object.
     *
     * @param other The other basic_waitable_timer object from which the move will
     * occur.
     *
     * @note Following the move, the moved-from object is in the same state as if
     * constructed using the @c basic_waitable_timer(const executor_type&)
     * constructor.
     */
    basic_waitable_timer& operator=(basic_waitable_timer&& other)
    {
      impl_ = std::move(other.impl_);
      return *this;
    }
  
    // All timers have access to each other's implementations.
    template <typename Clock1, typename WaitTraits1, typename Executor1>
    friend class basic_waitable_timer;
  
    /// Move-construct a basic_waitable_timer from another.
    /**
     * This constructor moves a timer from one object to another.
     *
     * @param other The other basic_waitable_timer object from which the move will
     * occur.
     *
     * @note Following the move, the moved-from object is in the same state as if
     * constructed using the @c basic_waitable_timer(const executor_type&)
     * constructor.
     */
    template <typename Executor1>
    basic_waitable_timer(
        basic_waitable_timer<Clock, WaitTraits, Executor1>&& other,
        typename enable_if<
            is_convertible<Executor1, Executor>::value
        >::type* = 0)
      : impl_(std::move(other.impl_))
    {
    }
  
    /// Move-assign a basic_waitable_timer from another.
    /**
     * This assignment operator moves a timer from one object to another. Cancels
     * any outstanding asynchronous operations associated with the target object.
     *
     * @param other The other basic_waitable_timer object from which the move will
     * occur.
     *
     * @note Following the move, the moved-from object is in the same state as if
     * constructed using the @c basic_waitable_timer(const executor_type&)
     * constructor.
     */
    template <typename Executor1>
    typename enable_if<
      is_convertible<Executor1, Executor>::value,
      basic_waitable_timer&
    >::type operator=(basic_waitable_timer<Clock, WaitTraits, Executor1>&& other)
    {
      basic_waitable_timer tmp(std::move(other));
      impl_ = std::move(tmp.impl_);
      return *this;
    }
  #endif // defined(ASIO_HAS_MOVE) || defined(GENERATING_DOCUMENTATION)
  
    /// Destroys the timer.
    /**
     * This function destroys the timer, cancelling any outstanding asynchronous
     * wait operations associated with the timer as if by calling @c cancel.
     */
    ~basic_waitable_timer()
    {
    }
  
    /// Get the executor associated with the object.
    executor_type get_executor() ASIO_NOEXCEPT
    {
      return impl_.get_executor();
    }
  
    /// Cancel any asynchronous operations that are waiting on the timer.
    /**
     * This function forces the completion of any pending asynchronous wait
     * operations against the timer. The handler for each cancelled operation will
     * be invoked with the asio::error::operation_aborted error code.
     *
     * Cancelling the timer does not change the expiry time.
     *
     * @return The number of asynchronous operations that were cancelled.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @note If the timer has already expired when cancel() is called, then the
     * handlers for asynchronous wait operations will:
     *
     * @li have already been invoked; or
     *
     * @li have been queued for invocation in the near future.
     *
     * These handlers can no longer be cancelled, and therefore are passed an
     * error code that indicates the successful completion of the wait operation.
     */
    std::size_t cancel()
    {
      asio::error_code ec;
      std::size_t s = impl_.get_service().cancel(impl_.get_implementation(), ec);
      asio::detail::throw_error(ec, "cancel");
      return s;
    }
  
  #if !defined(ASIO_NO_DEPRECATED)
    /// (Deprecated: Use non-error_code overload.) Cancel any asynchronous
    /// operations that are waiting on the timer.
    /**
     * This function forces the completion of any pending asynchronous wait
     * operations against the timer. The handler for each cancelled operation will
     * be invoked with the asio::error::operation_aborted error code.
     *
     * Cancelling the timer does not change the expiry time.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @return The number of asynchronous operations that were cancelled.
     *
     * @note If the timer has already expired when cancel() is called, then the
     * handlers for asynchronous wait operations will:
     *
     * @li have already been invoked; or
     *
     * @li have been queued for invocation in the near future.
     *
     * These handlers can no longer be cancelled, and therefore are passed an
     * error code that indicates the successful completion of the wait operation.
     */
    std::size_t cancel(asio::error_code& ec)
    {
      return impl_.get_service().cancel(impl_.get_implementation(), ec);
    }
  #endif // !defined(ASIO_NO_DEPRECATED)
  
    /// Cancels one asynchronous operation that is waiting on the timer.
    /**
     * This function forces the completion of one pending asynchronous wait
     * operation against the timer. Handlers are cancelled in FIFO order. The
     * handler for the cancelled operation will be invoked with the
     * asio::error::operation_aborted error code.
     *
     * Cancelling the timer does not change the expiry time.
     *
     * @return The number of asynchronous operations that were cancelled. That is,
     * either 0 or 1.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @note If the timer has already expired when cancel_one() is called, then
     * the handlers for asynchronous wait operations will:
     *
     * @li have already been invoked; or
     *
     * @li have been queued for invocation in the near future.
     *
     * These handlers can no longer be cancelled, and therefore are passed an
     * error code that indicates the successful completion of the wait operation.
     */
    std::size_t cancel_one()
    {
      asio::error_code ec;
      std::size_t s = impl_.get_service().cancel_one(
          impl_.get_implementation(), ec);
      asio::detail::throw_error(ec, "cancel_one");
      return s;
    }
  
  #if !defined(ASIO_NO_DEPRECATED)
    /// (Deprecated: Use non-error_code overload.) Cancels one asynchronous
    /// operation that is waiting on the timer.
    /**
     * This function forces the completion of one pending asynchronous wait
     * operation against the timer. Handlers are cancelled in FIFO order. The
     * handler for the cancelled operation will be invoked with the
     * asio::error::operation_aborted error code.
     *
     * Cancelling the timer does not change the expiry time.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @return The number of asynchronous operations that were cancelled. That is,
     * either 0 or 1.
     *
     * @note If the timer has already expired when cancel_one() is called, then
     * the handlers for asynchronous wait operations will:
     *
     * @li have already been invoked; or
     *
     * @li have been queued for invocation in the near future.
     *
     * These handlers can no longer be cancelled, and therefore are passed an
     * error code that indicates the successful completion of the wait operation.
     */
    std::size_t cancel_one(asio::error_code& ec)
    {
      return impl_.get_service().cancel_one(impl_.get_implementation(), ec);
    }
  
    /// (Deprecated: Use expiry().) Get the timer's expiry time as an absolute
    /// time.
    /**
     * This function may be used to obtain the timer's current expiry time.
     * Whether the timer has expired or not does not affect this value.
     */
    time_point expires_at() const
    {
      return impl_.get_service().expires_at(impl_.get_implementation());
    }
  #endif // !defined(ASIO_NO_DEPRECATED)
  
    /// Get the timer's expiry time as an absolute time.
    /**
     * This function may be used to obtain the timer's current expiry time.
     * Whether the timer has expired or not does not affect this value.
     */
    time_point expiry() const
    {
      return impl_.get_service().expiry(impl_.get_implementation());
    }
  
    /// Set the timer's expiry time as an absolute time.
    /**
     * This function sets the expiry time. Any pending asynchronous wait
     * operations will be cancelled. The handler for each cancelled operation will
     * be invoked with the asio::error::operation_aborted error code.
     *
     * @param expiry_time The expiry time to be used for the timer.
     *
     * @return The number of asynchronous operations that were cancelled.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @note If the timer has already expired when expires_at() is called, then
     * the handlers for asynchronous wait operations will:
     *
     * @li have already been invoked; or
     *
     * @li have been queued for invocation in the near future.
     *
     * These handlers can no longer be cancelled, and therefore are passed an
     * error code that indicates the successful completion of the wait operation.
     */
    std::size_t expires_at(const time_point& expiry_time)
    {
      asio::error_code ec;
      std::size_t s = impl_.get_service().expires_at(
          impl_.get_implementation(), expiry_time, ec);
      asio::detail::throw_error(ec, "expires_at");
      return s;
    }
  
  #if !defined(ASIO_NO_DEPRECATED)
    /// (Deprecated: Use non-error_code overload.) Set the timer's expiry time as
    /// an absolute time.
    /**
     * This function sets the expiry time. Any pending asynchronous wait
     * operations will be cancelled. The handler for each cancelled operation will
     * be invoked with the asio::error::operation_aborted error code.
     *
     * @param expiry_time The expiry time to be used for the timer.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @return The number of asynchronous operations that were cancelled.
     *
     * @note If the timer has already expired when expires_at() is called, then
     * the handlers for asynchronous wait operations will:
     *
     * @li have already been invoked; or
     *
     * @li have been queued for invocation in the near future.
     *
     * These handlers can no longer be cancelled, and therefore are passed an
     * error code that indicates the successful completion of the wait operation.
     */
    std::size_t expires_at(const time_point& expiry_time,
        asio::error_code& ec)
    {
      return impl_.get_service().expires_at(
          impl_.get_implementation(), expiry_time, ec);
    }
  #endif // !defined(ASIO_NO_DEPRECATED)
  
    /// Set the timer's expiry time relative to now.
    /**
     * This function sets the expiry time. Any pending asynchronous wait
     * operations will be cancelled. The handler for each cancelled operation will
     * be invoked with the asio::error::operation_aborted error code.
     *
     * @param expiry_time The expiry time to be used for the timer.
     *
     * @return The number of asynchronous operations that were cancelled.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @note If the timer has already expired when expires_after() is called,
     * then the handlers for asynchronous wait operations will:
     *
     * @li have already been invoked; or
     *
     * @li have been queued for invocation in the near future.
     *
     * These handlers can no longer be cancelled, and therefore are passed an
     * error code that indicates the successful completion of the wait operation.
     */
    std::size_t expires_after(const duration& expiry_time)
    {
      asio::error_code ec;
      std::size_t s = impl_.get_service().expires_after(
          impl_.get_implementation(), expiry_time, ec);
      asio::detail::throw_error(ec, "expires_after");
      return s;
    }
  
  #if !defined(ASIO_NO_DEPRECATED)
    /// (Deprecated: Use expiry().) Get the timer's expiry time relative to now.
    /**
     * This function may be used to obtain the timer's current expiry time.
     * Whether the timer has expired or not does not affect this value.
     */
    duration expires_from_now() const
    {
      return impl_.get_service().expires_from_now(impl_.get_implementation());
    }
  
    /// (Deprecated: Use expires_after().) Set the timer's expiry time relative
    /// to now.
    /**
     * This function sets the expiry time. Any pending asynchronous wait
     * operations will be cancelled. The handler for each cancelled operation will
     * be invoked with the asio::error::operation_aborted error code.
     *
     * @param expiry_time The expiry time to be used for the timer.
     *
     * @return The number of asynchronous operations that were cancelled.
     *
     * @throws asio::system_error Thrown on failure.
     *
     * @note If the timer has already expired when expires_from_now() is called,
     * then the handlers for asynchronous wait operations will:
     *
     * @li have already been invoked; or
     *
     * @li have been queued for invocation in the near future.
     *
     * These handlers can no longer be cancelled, and therefore are passed an
     * error code that indicates the successful completion of the wait operation.
     */
    std::size_t expires_from_now(const duration& expiry_time)
    {
      asio::error_code ec;
      std::size_t s = impl_.get_service().expires_from_now(
          impl_.get_implementation(), expiry_time, ec);
      asio::detail::throw_error(ec, "expires_from_now");
      return s;
    }
  
    /// (Deprecated: Use expires_after().) Set the timer's expiry time relative
    /// to now.
    /**
     * This function sets the expiry time. Any pending asynchronous wait
     * operations will be cancelled. The handler for each cancelled operation will
     * be invoked with the asio::error::operation_aborted error code.
     *
     * @param expiry_time The expiry time to be used for the timer.
     *
     * @param ec Set to indicate what error occurred, if any.
     *
     * @return The number of asynchronous operations that were cancelled.
     *
     * @note If the timer has already expired when expires_from_now() is called,
     * then the handlers for asynchronous wait operations will:
     *
     * @li have already been invoked; or
     *
     * @li have been queued for invocation in the near future.
     *
     * These handlers can no longer be cancelled, and therefore are passed an
     * error code that indicates the successful completion of the wait operation.
     */
    std::size_t expires_from_now(const duration& expiry_time,
        asio::error_code& ec)
    {
      return impl_.get_service().expires_from_now(
          impl_.get_implementation(), expiry_time, ec);
    }
  #endif // !defined(ASIO_NO_DEPRECATED)
  
    /// Perform a blocking wait on the timer.
    /**
     * This function is used to wait for the timer to expire. This function
     * blocks and does not return until the timer has expired.
     *
     * @throws asio::system_error Thrown on failure.
     */
    void wait()
    {
      asio::error_code ec;
      impl_.get_service().wait(impl_.get_implementation(), ec);
      asio::detail::throw_error(ec, "wait");
    }
  
    /// Perform a blocking wait on the timer.
    /**
     * This function is used to wait for the timer to expire. This function
     * blocks and does not return until the timer has expired.
     *
     * @param ec Set to indicate what error occurred, if any.
     */
    void wait(asio::error_code& ec)
    {
      impl_.get_service().wait(impl_.get_implementation(), ec);
    }
  
    /// Start an asynchronous wait on the timer.
    /**
     * This function may be used to initiate an asynchronous wait against the
     * timer. It always returns immediately.
     *
     * For each call to async_wait(), the supplied handler will be called exactly
     * once. The handler will be called when:
     *
     * @li The timer has expired.
     *
     * @li The timer was cancelled, in which case the handler is passed the error
     * code asio::error::operation_aborted.
     *
     * @param handler The handler to be called when the timer expires. Copies
     * will be made of the handler as required. The function signature of the
     * handler must be:
     * @code void handler(
     *   const asio::error_code& error // Result of operation.
     * ); @endcode
     * Regardless of whether the asynchronous operation completes immediately or
     * not, the handler will not be invoked from within this function. On
     * immediate completion, invocation of the handler will be performed in a
     * manner equivalent to using asio::post().
     */
    template <
        ASIO_COMPLETION_TOKEN_FOR(void (asio::error_code))
          WaitHandler ASIO_DEFAULT_COMPLETION_TOKEN_TYPE(executor_type)>
    ASIO_INITFN_AUTO_RESULT_TYPE(WaitHandler,
        void (asio::error_code))
    async_wait(
        ASIO_MOVE_ARG(WaitHandler) handler
          ASIO_DEFAULT_COMPLETION_TOKEN(executor_type))
    {
      return async_initiate<WaitHandler, void (asio::error_code)>(
          initiate_async_wait(this), handler);
    }
  
  private:
    // Disallow copying and assignment.
    basic_waitable_timer(const basic_waitable_timer&) ASIO_DELETED;
    basic_waitable_timer& operator=(
        const basic_waitable_timer&) ASIO_DELETED;
  
    class initiate_async_wait
    {
    public:
      typedef Executor executor_type;
  
      explicit initiate_async_wait(basic_waitable_timer* self)
        : self_(self)
      {
      }
  
      executor_type get_executor() const ASIO_NOEXCEPT
      {
        return self_->get_executor();
      }
  
      template <typename WaitHandler>
      void operator()(ASIO_MOVE_ARG(WaitHandler) handler) const
      {
        // If you get an error on the following line it means that your handler
        // does not meet the documented type requirements for a WaitHandler.
        ASIO_WAIT_HANDLER_CHECK(WaitHandler, handler) type_check;
  
        detail::non_const_lvalue<WaitHandler> handler2(handler);
        self_->impl_.get_service().async_wait(
            self_->impl_.get_implementation(), handler2.value,
            self_->impl_.get_implementation_executor());
      }
  
    private:
      basic_waitable_timer* self_;
    };
  
    detail::io_object_impl<
      detail::deadline_timer_service<
        detail::chrono_time_traits<Clock, WaitTraits> >,
      executor_type > impl_;
  };
  
  } // namespace asio
  
  #include "asio/detail/pop_options.hpp"
  
  #endif // ASIO_BASIC_WAITABLE_TIMER_HPP
  