include/boost/corosio/delay.hpp

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delay.hpp

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1			//
2			// Copyright (c) 2026 Steve Gerbino
3			// Copyright (c) 2026 Michael Vandeberg
4			//
5			// Distributed under the Boost Software License, Version 1.0. (See accompanying
6			// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
7			//
8			// Official repository: https://github.com/cppalliance/corosio
9			//
10
11			#ifndef BOOST_COROSIO_DELAY_HPP
12			#define BOOST_COROSIO_DELAY_HPP
13
14			#include <boost/corosio/detail/config.hpp>
15			#include <boost/corosio/detail/except.hpp>
16			#include <boost/corosio/detail/timer.hpp>
17			#include <boost/corosio/wait_traits.hpp>
18			#include <boost/capy/error.hpp>
19			#include <boost/capy/ex/io_env.hpp>
20			#include <boost/capy/io_result.hpp>
21
22			#include <chrono>
23			#include <concepts>
24			#include <coroutine>
25			#include <exception>
26			#include <optional>
27			#include <stdexcept>
28			#include <system_error>
29			#include <type_traits>
30
31			namespace boost::corosio {
32
33			namespace detail {
34
35			// Narrow reps wrap if nanoseconds::max() is converted into them;
36			// a double comparison clamps safely in both directions.
37			template<typename Rep, typename Period>
38			std::chrono::nanoseconds
39		4454x	clamp_to_ns(std::chrono::duration<Rep, Period> dur) noexcept
40			{
41			using namespace std::chrono;
42			using dsec = duration<double>;
43			if constexpr (std::is_floating_point_v<Rep>)
44			{
45			// NaN fails both clamp comparisons and would reach the
46			// cast; treat it as no wait rather than undefined behavior.
47	1/2 ✓ Branch 3 → 4 taken 1 time. ✗ Branch 3 → 5 not taken.	1x	if (dur != dur)
48		1x	return nanoseconds::zero();
49			}
50	2/4 ✓ Branch 7 → 8 taken 1 time. ✓ Branch 7 → 9 taken 4452 times. ✗ Branch 9 → 10 not taken. ✗ Branch 9 → 11 not taken.	4453x	return dsec(dur) >= dsec((nanoseconds::max)()) ? (nanoseconds::max)()
51		8905x	: dsec(dur) <= dsec((nanoseconds::min)())
52	2/4 ✓ Branch 14 → 15 taken 1 time. ✓ Branch 14 → 16 taken 4451 times. ✗ Branch 15 → 16 not taken. ✗ Branch 15 → 17 not taken.	4452x	? (nanoseconds::min)()
53		4453x	: duration_cast<nanoseconds>(dur);
54			}
55
56			// A non-io_context executor cannot supply a timer service, and
57			// await_suspend is driven through a noexcept wrapper, so translate
58			// the service-lookup failure into a clear terminate.
59			inline void
60		2447x	emplace_delay_timer(std::optional<timer>& t, capy::execution_context& ctx)
61			{
62			try
63			{
64	1/1 ✓ Branch 2 → 3 taken 2446 times.	2447x	t.emplace(ctx);
65			}
66	1/3 ✗ Branch 4 → 5 not taken. ✓ Branch 4 → 6 taken 1 time. ✗ Branch 4 → 8 not taken.	1x	catch (std::logic_error const&)
67			{
68		1x	throw_logic_error("delay requires an io_context-backed executor");
69		1x	}
70		✗	catch (std::exception const& e)
71			{
72		✗	throw_logic_error(e.what());
73		✗	}
74		2446x	}
75
76			} // namespace detail
77
78			/** Suspends the calling coroutine until the deadline elapses or
79			the environment's stop token is activated, whichever comes
80			first. A deadline already elapsed at suspension, or a stop
81			token already active, resumes the coroutine inline, without
82			starting a timer (see Cancellation below). Otherwise the
83			coroutine resumes through the executor once the timer fires
84			or a mid-wait cancellation arrives.
85
86			Not intended to be named directly. Use the @ref delay factory
87			overloads instead.
88
89			@pre The awaiting coroutine's executor must belong to an
90			`io_context`. Any other execution context terminates with a
91			diagnostic, because silently running without a timer would
92			drop the requested delay.
93
94			@par Cancellation
95			If stop is already requested before suspension, the coroutine
96			resumes immediately with `error::canceled`. If stop is
97			requested while suspended, the pending wait is cancelled and
98			the coroutine resumes with `error::canceled`. Requesting stop from
99			another thread while the `io_context` runs in `single_threaded` mode is
100			not permitted by `io_context`'s threading rules. That mode is
101			auto-enabled at `concurrency_hint` == 1. Cross-thread cancellation
102			requires a multi-threaded-capable context.
103
104			@see delay
105			*/
106			class delay_awaitable
107			{
108			// wait() names timer's private awaitable type; decltype is
109			// the only way to store it here.
110			using wait_type = decltype(std::declval<detail::timer&>().wait());
111
112			std::chrono::steady_clock::time_point deadline_{};
113			std::chrono::nanoseconds dur_{};
114			bool has_deadline_ = false;
115			bool canceled_ = false;
116			std::optional<detail::timer> timer_;
117			std::optional<wait_type> wait_;
118
119			public:
120			/// Construct an awaitable that waits for `dur` nanoseconds.
121		4444x	explicit delay_awaitable(std::chrono::nanoseconds dur) noexcept : dur_(dur)
122			{
123		4444x	}
124
125			/// Construct an awaitable that waits until `tp`.
126		13x	explicit delay_awaitable(std::chrono::steady_clock::time_point tp) noexcept
127		13x	: deadline_(tp)
128		13x	, has_deadline_(true)
129			{
130		13x	}
131
132			// Only moved before await_suspend; wait_ is engaged after.
133			/// Construct by transferring state from `other`.
134		5471x	delay_awaitable(delay_awaitable&&) = default;
135
136			/// Copy construction is disabled; an awaitable owns its timer.
137			delay_awaitable(delay_awaitable const&) = delete;
138			/// Copy assignment is disabled; an awaitable owns its timer.
139			delay_awaitable& operator=(delay_awaitable const&) = delete;
140			/// Move assignment is disabled; an awaitable is moved only before it is awaited.
141			delay_awaitable& operator=(delay_awaitable&&) = delete;
142
143			/// Return false unconditionally; see await_suspend.
144			// The elapsed-deadline fast path must run after the stop-token
145			// check, and only await_suspend receives the env carrying it.
146		4456x	bool await_ready() const noexcept
147			{
148		4456x	return false;
149			}
150
151			/** Resume inline if stopped or elapsed; else wait on a timer.
152
153			@param h Coroutine handle to resume on completion.
154			@param env The I/O environment, carrying the executor, stop token
155			and frame allocator.
156
157			@return The handle to resume immediately, or `noop_coroutine()` when
158			the wait was published to the timer service.
159			*/
160			std::coroutine_handle<>
161		4457x	await_suspend(std::coroutine_handle<> h, capy::io_env const* env)
162			{
163	2/2 ✓ Branch 3 → 4 taken 2011 times. ✓ Branch 3 → 5 taken 2446 times.	4457x	if (env->stop_token.stop_requested())
164			{
165		2011x	canceled_ = true;
166		2011x	return h;
167			}
168
169			// Elapsed deadlines complete synchronously, but only once a
170			// pending stop request has already been ruled out above.
171	5/5 ✓ Branch 5 → 6 taken 12 times. ✓ Branch 5 → 10 taken 2434 times. ✓ Branch 7 → 8 taken 12 times. ✓ Branch 12 → 13 taken 4 times. ✓ Branch 12 → 14 taken 2442 times.	4880x	if (has_deadline_ ? deadline_ <= std::chrono::steady_clock::now()
172		2434x	: dur_.count() <= 0)
173		4x	return h;
174
175		2442x	detail::emplace_delay_timer(timer_, env->executor.context());
176
177	2/2 ✓ Branch 16 → 17 taken 11 times. ✓ Branch 16 → 19 taken 2430 times.	2441x	if (has_deadline_)
178		11x	timer_->expires_at(deadline_);
179			else
180		2430x	timer_->expires_after(dur_);
181
182		2441x	wait_.emplace(timer_->wait());
183		2441x	return wait_->await_suspend(h, env);
184			}
185
186			/// Return empty on expiry, `error::canceled` if stop won.
187		4424x	[[nodiscard]] capy::io_result<> await_resume() noexcept
188			{
189	2/2 ✓ Branch 2 → 3 taken 2011 times. ✓ Branch 2 → 5 taken 2413 times.	4424x	if (canceled_)
190		2011x	return {capy::error::canceled};
191	2/2 ✓ Branch 6 → 7 taken 2409 times. ✓ Branch 6 → 9 taken 4 times.	2413x	if (wait_)
192		2409x	return wait_->await_resume();
193		4x	return {};
194			}
195			};
196
197			/** Suspends the calling coroutine until `Clock::now()` reaches the
198			deadline or the environment's stop token is activated. The wait is a
199			sequence of steady-clock timer waits. After each expiry the clock is
200			re-read. If the deadline is unreached, the same frame-embedded
201			waiter is re-published for the next `Traits::to_wait_duration` cap.
202			That re-publish neither resumes the coroutine nor allocates.
203
204			Not intended to be named directly. Use the @ref delay factory
205			overloads instead.
206
207			@tparam Clock The clock the deadline is expressed in.
208			@tparam Traits The wait-traits policy bounding each steady-clock wait.
209
210			@pre The awaiting coroutine's executor must belong to an
211			`io_context`. Any other execution context terminates with a
212			diagnostic, because silently running without a timer would
213			drop the requested delay.
214
215			@par Cancellation
216			Identical to @ref delay_awaitable: stop already requested
217			resumes inline with `error::canceled`; stop while suspended
218			cancels the pending wait, including between re-arms.
219
220			@see delay, wait_traits
221			*/
222			template<class Clock, class Traits>
223			class clock_delay_awaitable
224			{
225			typename Clock::time_point deadline_{};
226			bool canceled_ = false;
227			std::optional<detail::timer> timer_;
228			detail::waiter_node w_;
229
230			std::chrono::nanoseconds
231		11x	next_wait(typename Clock::time_point now) const noexcept
232			{
233		11x	return detail::clamp_to_ns(Traits::to_wait_duration(deadline_ - now));
234			}
235
236			// Runs on the scheduler thread executing the completion op,
237			// before the continuation is posted, so the frame cannot die
238			// concurrently.
239		10x	static bool on_fire(void* ctx) noexcept
240			{
241		10x	auto* self = static_cast<clock_delay_awaitable*>(ctx);
242			// Canceled: resume and surface the error
243	2/2 ✓ Branch 3 → 4 taken 1 time. ✓ Branch 3 → 5 taken 9 times.	10x	if (self->w_.ec_)
244		1x	return false;
245		9x	auto now = Clock::now();
246	2/2 ✓ Branch 8 → 9 taken 3 times. ✓ Branch 8 → 10 taken 6 times.	9x	if (now >= self->deadline_)
247		3x	return false;
248			// Re-publish and return without touching the node again:
249			// the wait may complete on another thread immediately after.
250	1/2 ✓ Branch 13 → 14 taken 6 times. ✗ Branch 13 → 15 not taken.	6x	if (self->timer_->rearm_wait(self->w_, self->next_wait(now)))
251		6x	return true;
252			// Heap growth failed; finish the wait with an error rather
253			// than strand the frame with an unbalanced work count.
254		✗	self->w_.ec_ = std::make_error_code(std::errc::not_enough_memory);
255		✗	return false;
256			}
257
258			public:
259			/// Construct an awaitable that waits until `tp` on `Clock`.
260		508x	explicit clock_delay_awaitable(typename Clock::time_point tp) noexcept
261		508x	: deadline_(tp)
262			{
263		508x	}
264
265			// Only moved before await_suspend; w_ is quiescent until then.
266			/// Construct by transferring the deadline from `other`.
267		508x	clock_delay_awaitable(clock_delay_awaitable&& other) noexcept
268		508x	: deadline_(other.deadline_)
269			{
270		508x	}
271
272			/// Copy construction is disabled; an awaitable owns its timer.
273			clock_delay_awaitable(clock_delay_awaitable const&) = delete;
274			/// Copy assignment is disabled; an awaitable owns its timer.
275			clock_delay_awaitable& operator=(clock_delay_awaitable const&) = delete;
276			/// Move assignment is disabled; an awaitable is moved only before it is awaited.
277			clock_delay_awaitable& operator=(clock_delay_awaitable&&) = delete;
278
279			/// Return false unconditionally; see await_suspend.
280			// The elapsed-deadline fast path must run after the stop-token
281			// check, and only await_suspend receives the env carrying it.
282		508x	bool await_ready() const noexcept
283			{
284		508x	return false;
285			}
286
287			/** Resume inline if stopped or reached; else wait on a timer.
288
289			@param h Coroutine handle to resume on completion.
290			@param env The I/O environment, carrying the executor, stop token
291			and frame allocator.
292
293			@return The handle to resume immediately, or `noop_coroutine()` when
294			the wait was published to the timer service.
295			*/
296			std::coroutine_handle<>
297		508x	await_suspend(std::coroutine_handle<> h, capy::io_env const* env)
298			{
299	2/2 ✓ Branch 3 → 4 taken 502 times. ✓ Branch 3 → 5 taken 6 times.	508x	if (env->stop_token.stop_requested())
300			{
301		502x	canceled_ = true;
302		502x	return h;
303			}
304
305		6x	auto now = Clock::now();
306	3/3 ✓ Branch 6 → 7 taken 6 times. ✓ Branch 8 → 9 taken 1 time. ✓ Branch 8 → 10 taken 5 times.	6x	if (now >= deadline_)
307		1x	return h;
308
309	1/1 ✓ Branch 11 → 12 taken 5 times.	5x	detail::emplace_delay_timer(timer_, env->executor.context());
310
311	1/1 ✓ Branch 14 → 15 taken 5 times.	5x	timer_->expires_after(next_wait(now));
312
313		5x	w_.bind(h, *env);
314		5x	w_.on_fire_ = &on_fire;
315		5x	w_.on_fire_ctx_ = this;
316			// Never the elapsed fast path: a capped expiry that elapses
317			// before publication must still reach on_fire, not complete
318			// the clock wait early.
319	1/1 ✓ Branch 17 → 18 taken 5 times.	5x	return timer_->publish_wait(w_);
320			}
321
322			/// Return empty on deadline, `error::canceled` if stop won.
323		507x	[[nodiscard]] capy::io_result<> await_resume() noexcept
324			{
325	2/2 ✓ Branch 2 → 3 taken 502 times. ✓ Branch 2 → 5 taken 5 times.	507x	if (canceled_)
326		502x	return {capy::error::canceled};
327	2/2 ✓ Branch 6 → 7 taken 4 times. ✓ Branch 6 → 8 taken 1 time.	5x	if (timer_)
328		4x	return {w_.ec_};
329		1x	return {};
330			}
331			};
332
333			/** Suspend the current coroutine for a duration.
334
335			Returns an IoAwaitable that completes at or after the
336			specified duration, or earlier if the environment's stop
337			token is activated. Zero or negative durations complete
338			synchronously.
339
340			@par Example
341			@par !example duration
342
343			@param dur The duration to wait.
344
345			@return A @ref delay_awaitable yielding `io_result<>`.
346			*/
347			template<typename Rep, typename Period>
348			[[nodiscard]] delay_awaitable
349		4443x	delay(std::chrono::duration<Rep, Period> dur) noexcept
350			{
351		4443x	return delay_awaitable(detail::clamp_to_ns(dur));
352			}
353
354			/** Suspend the current coroutine until a time point.
355
356			Returns an IoAwaitable that completes at or after `tp`, or
357			earlier if the environment's stop token is activated. Time
358			points already reached complete synchronously.
359
360			@param tp The steady-clock time point to wait until.
361
362			@return A @ref delay_awaitable yielding `io_result<>`.
363			*/
364			[[nodiscard]] inline delay_awaitable
365		13x	delay(std::chrono::steady_clock::time_point tp) noexcept
366			{
367		13x	return delay_awaitable(tp);
368			}
369
370			/** Suspend the current coroutine until a time point on `Clock`.
371
372			Returns an IoAwaitable that completes at or after the first
373			observation of `Clock::now() >= tp`, or earlier if the
374			environment's stop token is activated. The wait is one or more
375			bounded steady-clock waits, re-reading `Clock::now()` after
376			each. `Traits::to_wait_duration` bounds each one. With the default
377			@ref wait_traits a single full-length wait is used. An adjustment of
378			`Clock` mid-wait is therefore observed only at natural wakeup.
379			Supply capping traits to bound that latency. Time
380			points already reached complete synchronously.
381
382			@note `Clock::now()` and `Traits::to_wait_duration` are invoked
383			on the `io_context`'s run thread and must not throw or block.
384
385			@par Example
386			@par !example system_clock_deadline
387
388			@tparam Traits The wait-traits policy; `void` selects
389			@ref wait_traits.
390
391			@tparam Clock The clock type. This overload does not participate
392			when `Clock` is `std::chrono::steady_clock`. The dedicated
393			@ref delay overload taking a `steady_clock::time_point` handles
394			that case.
395
396			@param tp The time point to wait until.
397
398			@return A @ref clock_delay_awaitable yielding `io_result<>`.
399			*/
400			template<class Traits = void, class Clock, class Duration>
401			requires(!std::same_as<Clock, std::chrono::steady_clock>) &&
402			(std::is_void_v<Traits> \|\| WaitTraits<Traits, Clock>)
403			[[nodiscard]] auto
404		508x	delay(std::chrono::time_point<Clock, Duration> tp) noexcept
405			{
406			using traits_type =
407			std::conditional_t<std::is_void_v<Traits>, wait_traits<Clock>, Traits>;
408			// ceil preserves completes-at-or-after when Duration is coarser
409			// than the clock's native duration
410			return clock_delay_awaitable<Clock, traits_type>(
411		508x	std::chrono::ceil<typename Clock::duration>(tp));
412			}
413
414			} // namespace boost::corosio
415
416			#endif
417