text: //
  // basic_deadline_timer.hpp
  // ~~~~~~~~~~~~~~~~~~~~~~~~
  //
  // Copyright (c) 2003-2017 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_BASIC_DEADLINE_TIMER_HPP
  #define BOOST_ASIO_BASIC_DEADLINE_TIMER_HPP
  
  #if defined(_MSC_VER) && (_MSC_VER >= 1200)
  # pragma once
  #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
  
  #include <boost/asio/detail/config.hpp>
  
  #if defined(BOOST_ASIO_HAS_BOOST_DATE_TIME) \
    || defined(GENERATING_DOCUMENTATION)
  
  #include <cstddef>
  #include <boost/asio/basic_io_object.hpp>
  #include <boost/asio/deadline_timer_service.hpp>
  #include <boost/asio/detail/handler_type_requirements.hpp>
  #include <boost/asio/detail/throw_error.hpp>
  #include <boost/asio/error.hpp>
  
  #include <boost/asio/detail/push_options.hpp>
  
  namespace boost {
  namespace asio {
  
  /// Provides waitable timer functionality.
  /**
   * The basic_deadline_timer class template provides the ability to perform a
   * blocking or asynchronous wait for a timer to expire.
   *
   * A deadline 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 the boost::asio::deadline_timer typedef.
   *
   * @par Thread Safety
   * @e Distinct @e objects: Safe.@n
   * @e Shared @e objects: Unsafe.
   *
   * @par Examples
   * Performing a blocking wait:
   * @code
   * // Construct a timer without setting an expiry time.
   * boost::asio::deadline_timer timer(io_service);
   *
   * // Set an expiry time relative to now.
   * timer.expires_from_now(boost::posix_time::seconds(5));
   *
   * // Wait for the timer to expire.
   * timer.wait();
   * @endcode
   *
   * @par 
   * Performing an asynchronous wait:
   * @code
   * void handler(const boost::system::error_code& error)
   * {
   *   if (!error)
   *   {
   *     // Timer expired.
   *   }
   * }
   *
   * ...
   *
   * // Construct a timer with an absolute expiry time.
   * boost::asio::deadline_timer timer(io_service,
   *     boost::posix_time::time_from_string("2005-12-07 23:59:59.000"));
   *
   * // Start an asynchronous wait.
   * timer.async_wait(handler);
   * @endcode
   *
   * @par Changing an active deadline_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_from_now(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 boost::system::error_code& e)
   * {
   *   if (e != boost::asio::error::operation_aborted)
   *   {
   *     // Timer was not cancelled, take necessary action.
   *   }
   * }
   * @endcode
   *
   * @li The boost::asio::basic_deadline_timer::expires_from_now() 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 boost::system::error_code passed to
   * it contains the value boost::asio::error::operation_aborted.
   */
  template <typename Time,
      typename TimeTraits = boost::asio::time_traits<Time>,
      typename TimerService = deadline_timer_service<Time, TimeTraits> >
  class basic_deadline_timer
    : public basic_io_object<TimerService>
  {
  public:
    /// The time traits type.
    typedef TimeTraits traits_type;
  
    /// The time type.
    typedef typename traits_type::time_type time_type;
  
    /// The duration type.
    typedef typename traits_type::duration_type duration_type;
  
    /// Constructor.
    /**
     * This constructor creates a timer without setting an expiry time. The
     * expires_at() or expires_from_now() functions must be called to set an
     * expiry time before the timer can be waited on.
     *
     * @param io_service The io_service object that the timer will use to dispatch
     * handlers for any asynchronous operations performed on the timer.
     */
    explicit basic_deadline_timer(boost::asio::io_service& io_service)
      : basic_io_object<TimerService>(io_service)
    {
    }
  
    /// Constructor to set a particular expiry time as an absolute time.
    /**
     * This constructor creates a timer and sets the expiry time.
     *
     * @param io_service The io_service object that the timer will use 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_deadline_timer(boost::asio::io_service& io_service,
        const time_type& expiry_time)
      : basic_io_object<TimerService>(io_service)
    {
      boost::system::error_code ec;
      this->service.expires_at(this->implementation, expiry_time, ec);
      boost::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 io_service The io_service object that the timer will use 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_deadline_timer(boost::asio::io_service& io_service,
        const duration_type& expiry_time)
      : basic_io_object<TimerService>(io_service)
    {
      boost::system::error_code ec;
      this->service.expires_from_now(this->implementation, expiry_time, ec);
      boost::asio::detail::throw_error(ec, "expires_from_now");
    }
  
    /// 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 boost::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 boost::system::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()
    {
      boost::system::error_code ec;
      std::size_t s = this->service.cancel(this->implementation, ec);
      boost::asio::detail::throw_error(ec, "cancel");
      return s;
    }
  
    /// 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 boost::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(boost::system::error_code& ec)
    {
      return this->service.cancel(this->implementation, ec);
    }
  
    /// 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
     * boost::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 boost::system::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()
    {
      boost::system::error_code ec;
      std::size_t s = this->service.cancel_one(this->implementation, ec);
      boost::asio::detail::throw_error(ec, "cancel_one");
      return s;
    }
  
    /// 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
     * boost::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(boost::system::error_code& ec)
    {
      return this->service.cancel_one(this->implementation, ec);
    }
  
    /// 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_type expires_at() const
    {
      return this->service.expires_at(this->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 boost::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 boost::system::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_type& expiry_time)
    {
      boost::system::error_code ec;
      std::size_t s = this->service.expires_at(
          this->implementation, expiry_time, ec);
      boost::asio::detail::throw_error(ec, "expires_at");
      return s;
    }
  
    /// 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 boost::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_type& expiry_time,
        boost::system::error_code& ec)
    {
      return this->service.expires_at(this->implementation, expiry_time, ec);
    }
  
    /// 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_type expires_from_now() const
    {
      return this->service.expires_from_now(this->implementation);
    }
  
    /// 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 boost::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 boost::system::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_type& expiry_time)
    {
      boost::system::error_code ec;
      std::size_t s = this->service.expires_from_now(
          this->implementation, expiry_time, ec);
      boost::asio::detail::throw_error(ec, "expires_from_now");
      return s;
    }
  
    /// 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 boost::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_type& expiry_time,
        boost::system::error_code& ec)
    {
      return this->service.expires_from_now(
          this->implementation, expiry_time, ec);
    }
  
    /// 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 boost::system::system_error Thrown on failure.
     */
    void wait()
    {
      boost::system::error_code ec;
      this->service.wait(this->implementation, ec);
      boost::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(boost::system::error_code& ec)
    {
      this->service.wait(this->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 boost::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 boost::system::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. Invocation
     * of the handler will be performed in a manner equivalent to using
     * boost::asio::io_service::post().
     */
    template <typename WaitHandler>
    BOOST_ASIO_INITFN_RESULT_TYPE(WaitHandler,
        void (boost::system::error_code))
    async_wait(BOOST_ASIO_MOVE_ARG(WaitHandler) handler)
    {
      // If you get an error on the following line it means that your handler does
      // not meet the documented type requirements for a WaitHandler.
      BOOST_ASIO_WAIT_HANDLER_CHECK(WaitHandler, handler) type_check;
  
      return this->service.async_wait(this->implementation,
          BOOST_ASIO_MOVE_CAST(WaitHandler)(handler));
    }
  };
  
  } // namespace asio
  } // namespace boost
  
  #include <boost/asio/detail/pop_options.hpp>
  
  #endif // defined(BOOST_ASIO_HAS_BOOST_DATE_TIME)
         // || defined(GENERATING_DOCUMENTATION)
  
  #endif // BOOST_ASIO_BASIC_DEADLINE_TIMER_HPP
  