[/
/ Copyright (c) 2003-2025 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:WaitTraits Wait traits requirements]
The `basic_waitable_timer` template uses wait traits to allow programs to
customize `wait` and `async_wait` behavior.
[inline_note Possible uses of wait traits include:[br]
[mdash] To enable timers based on non-realtime clocks.[br]
[mdash] Determining how quickly wallclock-based timers respond to system time
changes.[br]
[mdash] Correcting for errors or rounding timeouts to boundaries.[br]
[mdash] Preventing duration overflow. That is, a program may set a timer's
expiry `e` to be `Clock::max()` (meaning never reached) or `Clock::min()`
(meaning always in the past). As a result, computing the duration until timer
expiry as `e - Clock::now()` may cause overflow.]
For a type `Clock` meeting the `Clock` requirements (C++Std
[time.clock.req]), a type `X` meets the `WaitTraits` requirements if it
satisfies the requirements listed below.
In the table below, `t` denotes a (possibly const) value of type
`Clock::time_point`; and `d` denotes a (possibly const) value of type
`Clock::duration`.
[table WaitTraits requirements
[[expression] [return type] [assertion/note[br]pre/post-condition]]
[
[`X::to_wait_duration(d)`]
[`Clock::duration`]
[
Returns a `Clock::duration` value to be used in a `wait` or `async_wait`
operation. [inline_note The return value is typically representative of
the duration `d`.]
]
]
[
[`X::to_wait_duration(t)`]
[`Clock::duration`]
[
Returns a `Clock::duration` value to be used in a `wait` or `async_wait`
operation. [inline_note The return value is typically representative of
the duration from `Clock::now()` until the time point `t`.]
]
]
]
[endsect]