TLA Line data Source code
1 : //
2 : // Copyright (c) 2026 Michael Vandeberg
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/capy
8 : //
9 :
10 : #ifndef BOOST_CAPY_DELAY_HPP
11 : #define BOOST_CAPY_DELAY_HPP
12 :
13 : #include <boost/capy/detail/config.hpp>
14 : #include <boost/capy/continuation.hpp>
15 : #include <boost/capy/error.hpp>
16 : #include <boost/capy/ex/executor_ref.hpp>
17 : #include <boost/capy/ex/io_env.hpp>
18 : #include <boost/capy/ex/detail/timer_service.hpp>
19 : #include <boost/capy/io_result.hpp>
20 :
21 : #include <atomic>
22 : #include <chrono>
23 : #include <coroutine>
24 : #include <new>
25 : #include <stop_token>
26 : #include <utility>
27 :
28 : namespace boost {
29 : namespace capy {
30 :
31 : /** IoAwaitable returned by @ref delay.
32 :
33 : Suspends the calling coroutine until the deadline elapses
34 : or the environment's stop token is activated, whichever
35 : comes first. Resumption is always posted through the
36 : executor, never inline on the timer thread.
37 :
38 : Not intended to be named directly; use the @ref delay
39 : factory function instead.
40 :
41 : @par Return Value
42 :
43 : Returns `io_result<>{}` (no error) when the timer fires
44 : normally, or `io_result<>{error::canceled}` when
45 : cancellation claims the resume before the deadline.
46 :
47 : @par Cancellation
48 :
49 : If `stop_requested()` is true before suspension, the
50 : coroutine resumes immediately without scheduling a timer
51 : and returns `io_result<>{error::canceled}`. If stop is
52 : requested while suspended, the stop callback claims the
53 : resume and posts it through the executor; the pending
54 : timer is cancelled on the next `await_resume` or
55 : destructor call.
56 :
57 : @par Thread Safety
58 :
59 : A single `delay_awaitable` must not be awaited concurrently.
60 : Multiple independent `delay()` calls on the same
61 : execution_context are safe and share one timer thread.
62 :
63 : @see delay, timeout
64 : */
65 : class delay_awaitable
66 : {
67 : std::chrono::nanoseconds dur_;
68 :
69 : detail::timer_service* ts_ = nullptr;
70 : detail::timer_service::timer_id tid_ = 0;
71 :
72 : // Declared before stop_cb_buf_: the callback
73 : // accesses these members, so they must still be
74 : // alive if the stop_cb_ destructor blocks.
75 : continuation cont_;
76 : std::atomic<bool> claimed_{false};
77 : bool canceled_ = false;
78 : bool stop_cb_active_ = false;
79 :
80 : struct cancel_fn
81 : {
82 : delay_awaitable* self_;
83 : executor_ref ex_;
84 :
85 HIT 2 : void operator()() const noexcept
86 : {
87 2 : if(!self_->claimed_.exchange(
88 : true, std::memory_order_acq_rel))
89 : {
90 2 : self_->canceled_ = true;
91 2 : ex_.post(self_->cont_);
92 : }
93 2 : }
94 : };
95 :
96 : using stop_cb_t = std::stop_callback<cancel_fn>;
97 :
98 : // Aligned storage for the stop callback.
99 : // Declared last: its destructor may block while
100 : // the callback accesses the members above.
101 : BOOST_CAPY_MSVC_WARNING_PUSH
102 : BOOST_CAPY_MSVC_WARNING_DISABLE(4324)
103 : alignas(stop_cb_t)
104 : unsigned char stop_cb_buf_[sizeof(stop_cb_t)];
105 : BOOST_CAPY_MSVC_WARNING_POP
106 :
107 20 : stop_cb_t& stop_cb_() noexcept
108 : {
109 20 : return *reinterpret_cast<stop_cb_t*>(stop_cb_buf_);
110 : }
111 :
112 : public:
113 28 : explicit delay_awaitable(std::chrono::nanoseconds dur) noexcept
114 28 : : dur_(dur)
115 : {
116 28 : }
117 :
118 : /// @pre The stop callback must not be active
119 : /// (i.e. the object has not yet been awaited).
120 43 : delay_awaitable(delay_awaitable&& o) noexcept
121 43 : : dur_(o.dur_)
122 43 : , ts_(o.ts_)
123 43 : , tid_(o.tid_)
124 43 : , cont_(o.cont_)
125 43 : , claimed_(o.claimed_.load(std::memory_order_relaxed))
126 43 : , canceled_(o.canceled_)
127 43 : , stop_cb_active_(std::exchange(o.stop_cb_active_, false))
128 : {
129 43 : }
130 :
131 71 : ~delay_awaitable()
132 : {
133 71 : if(stop_cb_active_)
134 2 : stop_cb_().~stop_cb_t();
135 71 : if(ts_)
136 20 : ts_->cancel(tid_);
137 71 : }
138 :
139 : delay_awaitable(delay_awaitable const&) = delete;
140 : delay_awaitable& operator=(delay_awaitable const&) = delete;
141 : delay_awaitable& operator=(delay_awaitable&&) = delete;
142 :
143 27 : bool await_ready() const noexcept
144 : {
145 27 : return dur_.count() <= 0;
146 : }
147 :
148 : std::coroutine_handle<>
149 25 : await_suspend(
150 : std::coroutine_handle<> h,
151 : io_env const* env) noexcept
152 : {
153 : // Already stopped: resume immediately
154 25 : if(env->stop_token.stop_requested())
155 : {
156 5 : canceled_ = true;
157 5 : return h;
158 : }
159 :
160 20 : cont_.h = h;
161 20 : ts_ = &env->executor.context().use_service<detail::timer_service>();
162 :
163 : // Schedule timer (won't fire inline since deadline is in the future)
164 20 : tid_ = ts_->schedule_after(dur_,
165 20 : [this, ex = env->executor]()
166 : {
167 17 : if(!claimed_.exchange(
168 : true, std::memory_order_acq_rel))
169 : {
170 17 : ex.post(cont_);
171 : }
172 17 : });
173 :
174 : // Register stop callback (may fire inline)
175 60 : ::new(stop_cb_buf_) stop_cb_t(
176 20 : env->stop_token,
177 20 : cancel_fn{this, env->executor});
178 20 : stop_cb_active_ = true;
179 :
180 20 : return std::noop_coroutine();
181 : }
182 :
183 26 : io_result<> await_resume() noexcept
184 : {
185 26 : if(stop_cb_active_)
186 : {
187 18 : stop_cb_().~stop_cb_t();
188 18 : stop_cb_active_ = false;
189 : }
190 26 : if(ts_)
191 18 : ts_->cancel(tid_);
192 26 : if(canceled_)
193 6 : return io_result<>{make_error_code(error::canceled)};
194 20 : return io_result<>{};
195 : }
196 : };
197 :
198 : /** Suspend the current coroutine for a duration.
199 :
200 : Returns an IoAwaitable that completes at or after the
201 : specified duration, or earlier if the environment's stop
202 : token is activated.
203 :
204 : Zero or negative durations complete synchronously without
205 : scheduling a timer.
206 :
207 : @par Example
208 : @code
209 : auto [ec] = co_await delay(std::chrono::milliseconds(100));
210 : @endcode
211 :
212 : @param dur The duration to wait.
213 :
214 : @return A @ref delay_awaitable whose `await_resume`
215 : returns `io_result<>`. On normal completion, `ec`
216 : is clear. On cancellation, `ec == error::canceled`.
217 :
218 : @throws Nothing.
219 :
220 : @see timeout, delay_awaitable
221 : */
222 : template<typename Rep, typename Period>
223 : delay_awaitable
224 27 : delay(std::chrono::duration<Rep, Period> dur) noexcept
225 : {
226 : return delay_awaitable{
227 27 : std::chrono::duration_cast<std::chrono::nanoseconds>(dur)};
228 : }
229 :
230 : } // capy
231 : } // boost
232 :
233 : #endif
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