include/boost/corosio/timeout.hpp

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timeout.hpp

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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_TIMEOUT_HPP
11			#define BOOST_COROSIO_TIMEOUT_HPP
12
13			#include <boost/corosio/detail/config.hpp>
14			#include <boost/corosio/detail/timeout_awaitable.hpp>
15			#include <boost/capy/concept/io_awaitable.hpp>
16
17			#include <chrono>
18			#include <type_traits>
19			#include <utility>
20
21			namespace boost::corosio {
22
23			/** Race an io_result-returning awaitable against a deadline.
24
25			Starts the awaitable with an interposed stop token and arms a
26			timer. If the awaitable finishes first, its result is returned
27			as-is (success, error, or exception). If the deadline passes
28			first, the awaitable is cancelled and an `io_result` whose
29			`ec` compares equal to `capy::cond::timeout` (with a
30			default-initialized payload) is produced.
31
32			Exceptions from the inner awaitable always propagate; they are
33			never swallowed by the timer.
34
35			@par Preconditions
36			The awaiting coroutine's executor must belong to an
37			`io_context`; any other execution context terminates with a
38			diagnostic.
39
40			@par Cancellation
41			If the parent's stop token is activated, the inner awaitable
42			is cancelled and its cancellation result is returned. Requesting
43			stop from another thread requires a multi-threaded-capable
44			io_context; a context running in single_threaded mode
45			(auto-enabled at concurrency_hint == 1) does not permit
46			cross-thread cancellation.
47
48			@par Example
49			@code
50			auto [ec, n] = co_await timeout(sock.read_some(buf), 50ms);
51			if (ec == capy::cond::timeout) {
52			// handle timeout
53			}
54			@endcode
55
56			@param a The awaitable to race against the deadline.
57			@param dur The maximum duration to wait, measured from
58			suspension.
59
60			@return An awaitable yielding `io_result` matching the inner
61			awaitable's result type.
62
63			@see delay
64			*/
65			template<capy::IoAwaitable A, typename Rep, typename Period>
66			requires detail::is_io_result_v<
67			std::remove_cvref_t<capy::awaitable_result_t<A>>> &&
68			std::is_default_constructible_v<
69			std::remove_cvref_t<capy::awaitable_result_t<A>>>
70		2037x	[[nodiscard]] auto timeout(A a, std::chrono::duration<Rep, Period> dur)
71			{
72			using namespace std::chrono;
73			// Narrow reps wrap if nanoseconds::max() is converted into them;
74			// a double comparison clamps safely in both directions.
75			using dsec = duration<double>;
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77		2x	? (nanoseconds::max)()
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79		2x	? (nanoseconds::min)()
80		2033x	: duration_cast<nanoseconds>(dur);
81		2037x	return detail::timeout_awaitable<A>(std::move(a), ns);
82			}
83
84			/** Race an io_result-returning awaitable against an absolute deadline.
85
86			Behaves as the duration overload with the deadline fixed at
87			`tp` instead of measured from suspension.
88
89			@param a The awaitable to race against the deadline.
90			@param tp The steady-clock time point at which the awaitable
91			is cancelled.
92
93			@return An awaitable yielding `io_result` matching the inner
94			awaitable's result type.
95
96			@see delay
97			*/
98			template<capy::IoAwaitable A>
99			requires detail::is_io_result_v<
100			std::remove_cvref_t<capy::awaitable_result_t<A>>> &&
101			std::is_default_constructible_v<
102			std::remove_cvref_t<capy::awaitable_result_t<A>>>
103		4x	[[nodiscard]] auto timeout(A a, std::chrono::steady_clock::time_point tp)
104			{
105		4x	return detail::timeout_awaitable<A>(std::move(a), tp);
106			}
107
108			} // namespace boost::corosio
109
110			#endif
111