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include/boost/corosio/wait_traits.hpp

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wait_traits.hpp
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boost::corosio::wait_traits<boost::corosio::wait_traits_test::minute_clock>::to_wait_duration(std::chrono::duration<int, std::ratio<60ll, 1ll> >) :69 2x 100.0% 100.0% boost::corosio::wait_traits<boost::corosio::wall_clock>::to_wait_duration(std::chrono::duration<long long, std::ratio<1ll, 1000000000ll> >) :69 1x 100.0% 100.0% boost::corosio::wait_traits<std::chrono::_V2::system_clock>::to_wait_duration(std::chrono::duration<long long, std::ratio<1ll, 1000000000ll> >) :69 1x 100.0% 100.0%
Line TLA Hits Source Code
1 //
2 // Copyright (c) 2026 Steve Gerbino
3 //
4 // Distributed under the Boost Software License, Version 1.0. (See accompanying
5 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
6 //
7 // Official repository: https://github.com/cppalliance/corosio
8 //
9
10 #ifndef BOOST_COROSIO_WAIT_TRAITS_HPP
11 #define BOOST_COROSIO_WAIT_TRAITS_HPP
12
13 #include <boost/corosio/detail/config.hpp>
14
15 #include <concepts>
16
17 namespace boost::corosio {
18
19 /** Default wait traits for clock-based delays.
20
21 Controls how much of the remaining time a single underlying
22 steady-clock wait may cover before `Clock::now()` is re-read.
23 A larger value costs fewer wakeups; a smaller value bounds how
24 late an adjustment of `Clock` ( e.g. a stepped time-of-day
25 clock ) is observed. The default covers the full remaining
26 duration, which is exact for clocks that advance in lockstep
27 with the machine's monotonic clock.
28
29 @par Example
30 @code
31 // Observe wall-clock steps within one second
32 struct capped_traits
33 {
34 static std::chrono::system_clock::duration
35 to_wait_duration(std::chrono::system_clock::duration d)
36 {
37 return (std::min)(d,
38 std::chrono::system_clock::duration(
39 std::chrono::seconds(1)));
40 }
41 };
42
43 auto [ec] = co_await delay<capped_traits>(
44 std::chrono::system_clock::now() + std::chrono::hours(1));
45 @endcode
46
47 @tparam Clock The clock type whose durations are converted.
48
49 @see delay
50 */
51 template<class Clock>
52 struct wait_traits
53 {
54 /** Convert a remaining duration into a wait duration.
55
56 Should return a positive duration when @p d is positive; a
57 non-positive result degrades to reactor-rate re-checking.
58
59 @par Preconditions
60 Must not throw and must not block — invoked on the
61 io_context's run thread, including from the timer
62 completion path.
63
64 @param d The remaining time until the deadline.
65
66 @return The duration the next underlying wait may cover.
67 */
68 static typename Clock::duration
69 4x to_wait_duration(typename Clock::duration d)
70 {
71 4x return d;
72 }
73 };
74
75 /** Concept for wait-traits policies usable with `Clock`.
76
77 Satisfied when `Traits::to_wait_duration` accepts a
78 `Clock::duration` and returns something convertible back to it.
79 `Traits::to_wait_duration` must not throw.
80 */
81 template<class Traits, class Clock>
82 concept WaitTraits = requires(typename Clock::duration d)
83 {
84 { Traits::to_wait_duration(d) }
85 -> std::convertible_to<typename Clock::duration>;
86 };
87
88 } // namespace boost::corosio
89
90 #endif
91