[/
 / Copyright (c) 2003-2014 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)
 /]

[section:TimerService Timer service requirements]

A timer service must meet the requirements for an [link
boost_asio.reference.IoObjectService I/O object service], as well as the
additional requirements listed below.

In the table below, `X` denotes a timer service class for time type `Time` and
traits type `TimeTraits`, `a` denotes a value of type `X`, `b` denotes a value
of type `X::implementation_type`, `t` denotes a value of type `Time`, `d`
denotes a value of type `TimeTraits::duration_type`, `e` denotes a value of
type `error_code`, and `h` denotes a value meeting [link
boost_asio.reference.WaitHandler `WaitHandler`] requirements.

[table TimerService requirements
  [[expression] [return type] [assertion/note\npre/post-condition]]
  [
    [`a.destroy(b);`]
    []
    [
      From [link boost_asio.reference.IoObjectService IoObjectService]
      requirements. Implicitly cancels asynchronous wait operations, as if by
      calling `a.cancel(b, e)`.
    ]
  ]
  [
    [``
      a.cancel(b, e);
    ``]
    [`size_t`]
    [
      Causes any outstanding asynchronous wait operations to complete as soon
      as possible. Handlers for cancelled operations shall be passed the error
      code `error::operation_aborted`. Sets `e` to indicate success or failure.
      Returns the number of operations that were cancelled.
    ]
  ]
  [
    [`a.expires_at(b);`]
    [`Time`]
    []
  ]
  [
    [``
      a.expires_at(b, t, e);
    ``]
    [`size_t`]
    [
      Implicitly cancels asynchronous wait operations, as if by calling
      `a.cancel(b, e)`. Returns the number of operations that were cancelled.\n
      post: `a.expires_at(b) == t`.
    ]
  ]
  [
    [`a.expires_from_now(b);`]
    [`TimeTraits::duration_type`]
    [
      Returns a value equivalent to `TimeTraits::subtract(a.expires_at(b),
      TimeTraits::now())`.
    ]
  ]
  [
    [``
      a.expires_from_now(b, d, e);
    ``]
    [`size_t`]
    [
      Equivalent to `a.expires_at(b, TimeTraits::add(TimeTraits::now(), d), e)`.
    ]
  ]
  [
    [``
      a.wait(b, e);
    ``]
    [`error_code`]
    [
      Sets `e` to indicate success or failure. Returns `e`.\n
      post: `!!e || !TimeTraits::lt(TimeTraits::now(), a.expires_at(b))`.
    ]
  ]
  [
    [``
      a.async_wait(b, h);
    ``]
    []
    [
      Initiates an asynchronous wait operation that is performed via the
      `io_service` object `a.get_io_service()` and behaves according to [link
      boost_asio.reference.asynchronous_operations asynchronous operation]
      requirements.\n
      \n
      The handler shall be posted for execution only if the condition
      `!!ec || !TimeTraits::lt(TimeTraits::now(), a.expires_at(b))`
      holds, where `ec` is the error code to be passed to the handler.
    ]
  ]
]

[endsect]